**1. Introduction**

The market paradigms in existence have suffered a radical change since the 1980s following the changes in the economic paradigm due to the evolution from an industrial economy to a knowledge economy [1]. Consumers have become more demanding, and that rapidly resulted in shorter and shorter product and process life cycles. Markets that were, until that point, part of more or less stable economies suffered the impact of globalisation, and 'turbulence, disorder and unstable balance became the main features of the new competitive landscapes' [2] (p. 17).

This background of fast changes and the global economy leveraged by technological evolution provided an unprecedented focus on the importance of people possessing knowledge within organisations. Attraction and retention of talent by organisations became consequently more and more strategic and vital to organisational success and sustainability. As mentioned by Michaels, Handfield-Jones, and Axelrod, [3] the biggest organisational competitive advantage is the ability of the organisation to develop and maintain (i.e., manage) talent both in turbulent and stable times. The search for tools capable of managing talent has assumed great relevance over the last decade. EB has emerged as one of the most complete tools based on the culture and reputation of each organisation.

EB provides employer value proposition (EVP) and emerges as a differentiation tool, as well as an identification and employees' commitment mechanism [4] towards each organisation: 'the employers' brand role and impact rise to a new relevance within talent and employees 'careers management' [5]. Therefore, the present research aims to show evidence of the importance of the EB concept to talent management, especially as a tool

129

**Citation:** Reis, I.; Sousa, M.J.; Dionísio, A. Employer Branding as a Talent Management Tool: A Systematic Literature Revision. *Sustainability* **2021**, *13*, 10698. https://doi.org/10.3390/su131910698

Academic Editor: Carlos Rodríguez Monroy

Received: 26 August 2021 Accepted: 21 September 2021 Published: 26 September 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

to attract and retain the best employees within the organisations. In order to do so, the research concerning the correlation of these two topics on the last 10 years was systematised, and the EB models identified throughout this revision were listed.

#### *1.1. Talent Management*

The new challenges organisations are facing force them to distinguish themselves from one another to accomplish competitive advantage in the market. This advantage is reached through new work forms and structures, more flexible and more able to achieve agility when addressing markets, human resources practices that improve internal organisational creativity [6], and particularly by investing in 'the right employees' [7]. According to Klein [8], these employees possess traits, skills, values, and experiences that match the intellectual capital, and form the organisational competitive differential, that also contributes to organisational success or failure.

In this view, talent emerges as the central key of organisational strategy—talent is considered a key factor to organisational success and sustainability, and talent management assumes the central role becoming an imperative of human resources management rather than just a best practice. Organisations must therefore design and apply specific strategies concerning the attraction, retention, and development of their talents [9].

Talent is per se a complex concept, not always consensual amongst the authors addressing it. Michaels et al. [3] (p. 12) define talent as the 'set of skills of a person— gifts, capabilities, intelligence, insight, attitude, character, and innate impulses, as well as the ability to learn and self-improvement'. The authors understand talent as something focused on knowledge, skills, innate and acquired abilities, behaviour, values, and the potential for development.

On the other hand, Câmara, Guerra, and Rodrigues [10] explain that talent consists of good interaction between three dimensions: action, passion, and vision. Action is defined by the authors as the set of competences that enable the employees to execute their tasks. Passion concerns both the enthusiasm revealed by workers when executing their functions, and the commitment and sense of respect towards the organisation. Finally, the vision matches the workers' sense of anticipation, allowing them to perceive the potential they might achieve in the projects they are involved in.

According to Tansley and Tietze [11] (p. 1802), talent management encompasses the 'attraction, identification, development, retention, and deployment strategies and protocols' of employees that reveal high levels of potential, adding value to the organisation. According to Henriques [12], however, these authors show a 'transversal functional perspective', meaning they only mention individuals with high levels of potential. Therefore, in order to include all employees, Henriques [12] defines talent management as a mechanism to assure that the workers are properly prepared to execute the functions attributed to them while maintaining their development.

A model of talent management derived from a macro-contingent approach was introduced in 2019 (see Figure 1). This model provides the macro-contingent vision of organisational talent management and is intended to illustrate the dynamic relations between talent systems at both micro and macro levels, therefore enhancing the overview of organisational talent management considering the broader landscape of the macro system(s) in which the organisation is integrated [13].

**Figure 1.** Talent management macro adaptive approach. Source: King and Vaiman (2019) [13].


Probiotics and Postbiotics from Food to Health: Antimicrobial Experimental Confirmation

*Janet Cheruiyot Kosgey, Mercy W. Mwaniki and Fengmin Zhang*

## **Abstract**

The field of probiotics is up-and-coming, especially in management of microbial pathogens. Probiotics confer nutritional benefits, reduce inflammation and infection. Probiotics have also shown to be helpful in the management of microbial pathogens, which include bacteria, fungi, and viruses. To ernes this potential maximumly, there is a need for an elaborate screening system for new isolates. This entails; rigorous screening methods and thorough confirmatory systems. There is need also to come up with standard methods used to evaluate the probiotics mechanism of action both in vivo and in vitro. In summary, there is a need for a standard screening process for probiotic microorganisms that is reproducible. The aim is to ensure that, the candidate microbial cultures are not written off without proper investigations. This will also fasten the screening process and save time and resources wasted in pre-screening experiments.

**Keywords:** probiotics, screening methods, confirmatory methods, postbiotics, animal model, coculture

## **1. Introduction**

Fermentation is one of the oldest technologies used for food preservation. It involves converting carbohydrates to alcohol, carbon dioxide, and organic acids using microorganisms under anaerobic conditions. The fermentation process improves food by developing diverse flavors, aromas, and textures in food substrates. Also, it enriches food substrates with protein, essential amino acids, essential fatty acids, and vitamins. The primary mechanism of the preservation of foods is the production of acid, which lowers the pH to a level at which most of the spoilage-causing microorganisms cannot grow, hence prolonging the shelf life of such foods [1]. At present, various fermented foods are produced worldwide at household and industrial levels, in both small-scale and large commercial enterprises. Associated with fermentation are beneficial microorganisms known as probiotics. The vast majority of the probiotics are lactic acid microorganisms [2] to produce fermented dairy products.

Among the beneficial effects of probiotics include improved intestinal health, enhancement of the immune response, reduction of serum cholesterol, and cancer prevention [3–5]. There is also substantial evidence to support probiotic use in

treating acute diarrhoeal diseases, prevention of antibiotic-associated diarrhea, and improvement of lactose metabolism [6]. The range of food products containing probiotic strains is vast and still growing. And so is the list of beneficial effects. More so, with an increasing desire for quality life, preference for minimal use of chemicals, and the rising cost of healthcare. Natural products like probiotics is a promising alternative. Related to probiotics are prebiotics. Biogenics involves the use of beneficial bioactive substances produced by probiotic bacteria whose activities are independent of the viability of probiotic bacteria.

This book chapter focuses on the use of probiotics in the management of microbial pathogens, emphasizing the need to have a reproducible standard screening process both *in vivo* and *in vitro*. This will highlight areas in the used technologies that need harmonization, technologies for investigation and confirmation of the antimicrobial activities of probiotics, and finally, the future prospects of probiotics and antimicrobial agents.

#### **1.1 Mechanism of action of probiotics**

WHO/FAO defines probiotics as **"**live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" [7, 8]. Prebiotics refer to the substrates that are selectively utilized by host microorganisms that result in conferring a health benefit to the host [8–11]. Furthermore, postbiotics entails the use of beneficial bioactive compounds produced by probiotic bacteria. The activity of postbiotics is independent of probiotic bacteria's viability [11]. The term synbiotics is where both prebiotics and probiotics are utilized simultaneously [11, 12].

The probiotics have myriad of mechanisms in which it protects against infection. These include; (1) they lower pH, (2) pathogen antagonism by producing antimicrobial compounds for example, bacteriocins and or other metabolic products, (3) competitive exclusion with the pathogen for binding sites and receptors sites, (4) competition for substrates that is, nutrients and growth factors, therefore, limiting resources, (5) stimulate immunomodulatory cells, (6) production of enzymes example, enzymes that neutralize toxins produced by pathogens (7) improve the barrier function of the intestinal mucosa, (8) modulate inflammatory responses, (9) aggregate with pathogens, (10) produce hydrogen peroxide (H2O2) a strong oxidizing agent that damage nucleic acids and proteins, (11) produce organic acids like lactic acid, acetic acid among others (12) produce CO2 thus creating anaerobic microenvironment (**Figure 1**) [3, 4, 13–16].

The probiotics are generally regarded as safe [17]. The few results obtained when probiotics are administered together with conventional drugs clinically are promising and include synergy with the drug, half dose of conventional drug needed, and faster healing [18–21]. Further research is needed in this area.

#### **1.2 Probiotics as antimicrobial agents**

Besides the health-improving benefits, the antimicrobial activity of probiotics has been well documented, with promising results against microbial pathogens. Probiotics have been deemed as the following most crucial immune defense systems according to WHO [7]. This is due to increasing antibiotic resistance to commonly prescribed antibiotics [22, 23]. There is a need, therefore, to come up with reproducible screening protocols for *in vitro*, *in vivo*, and clinical studies. Therefore, this book chapter will highlight protocols used in screening probiotics and postbiotics, cite their strengths and drawbacks, and point areas that need harmonization.

*Probiotics and Postbiotics from Food to Health: Antimicrobial Experimental Confirmation DOI: http://dx.doi.org/10.5772/intechopen.99675*

**Figure 1.** *Mechanisms in which probiotics protect against infection.*


Prebiotics, Probiotics and Synbiotic for Bone Health

*Bolaji Lilian Ilesanmi-Oyelere and Marlena Cathorina Kruger*

## **Abstract**

Prebiotics, probiotics and synbiotics has been shown to enhance calcium absorption, gut and bone health. Probiotics are also known to ferment prebiotics to produce the fermentative substrates such as short chain fatty acids (SCFAs), mainly acetate, butyrate and propionate with the help of beneficial micro-organisms in the gut. The expression of these SCFAs has been associated with the inhibition of osteoclast differentiation and bone resorption both *in vitro* and *in vivo.* In this review, we discuss the benefits of SCFAs and ways in which prebiotics and probiotics affect bone health by the reduction of inflammation in the gut and the bone.

**Keywords:** prebiotic, probiotic, synbiotic, gut microbiota, bone metabolism

#### **1. Introduction**

Prebiotics and probiotics have been proven to confer multiple health benefits to animals and humans alike when consumed either singly or in combination. Consumption of prebiotics and probiotics modulates the gut microbiota and the colonization of the gastrointestinal tract which is now known as the second gene pool of the human body. Evidence shows the health benefits of synbiotic intake in many aspects of human health including metabolic functions, gastrointestinal diseases, and bone health. Some of these documented evidence-based benefits include their immunomodulatory effect [1], improvement of diarrhea, lactose metabolism, digestive health and metabolic syndrome [2], antidiabetic and hypocholestrolemic [3], anticarcinogenic [4] and hypotensive attributes/features [5]. In a short review that we conducted, the importance of prebiotics, probiotics and synbiotics was expressed to be important across human lifespan from childhood to adulthood and the elderly [6].

### **2. The significance of prebiotics and probiotics**

Probiotics in the presence of prebiotics undergo different biochemical pathways/ messenger systems to inhibit pathogens and boost the immunity of the host, these includes

a.Presence of probiotics in the gut leads to competition for nutrients with pathogens which can then lead to starvation and reduction of these unwanted bacteria.

Probiotic microorganisms may also be able to produce enzymes, such as lipase, esterase, and co-enzymes A, Q, NAD, and NADP [10]. Likewise, some of the by-products of probiotics' metabolism may exhibit antibiotic properties and these include bacitracin, lactacin and acidophiline [11].

d.The bio-metabolization of prebiotics into lactate and short chain fatty acids (SCFAs) such as acetate, mainly produced by *Bifidobacteria*, *Lactobacilli* and *Akkermansia muciniphilia* through fermentation by probiotics has significant beneficial role to the health*.* Acetate is the most abundant in the human colon. Butyrate is produced by *Faecalibacterium prausnitzii*, *Eubacterium rectale* and *Roseburia* spp. and mainly by *Lachnospiraceae* and *Ruminococcaceae* and propionate which is produced by *Propionibacteria,*, *Firmicutes, Lachnospiraceae* and *Bacteroidetes* [12]. The release of these SCFAs by the prebiotic fermentation reduces the intestinal pH level and also reduces the production of putrefactive compounds such as ammonia, phenol, as well as indole and branched-chain fatty acids (BCFAs) [13]. SCFA synthesis are mainly by anaerobic saccharolytic fermentation of carbohydrates that have not been digested or absorbed in the small intestine. Acetate is metabolized in the muscles, kidney, brain and heart, butyrate acts mainly in the colon while propionate and butyrate are cleared by the liver. SCFAs may also regulate fat and glucose metabolism as reported in rat adipocytes [14]. In chronic inflammatory diseases such as IBD, it has been shown that fecal butyrate levels are significantly reduced while high levels of lactic acid are observed [15].

The production of butyrate is mainly from complex carbohydrates through the pyruvate and acetyl-coenzyme A (CoA) pathway; however, it can also be produced from amino acids via the glutarate, 4-aminobutyrate and lysine pathways in the gut [13]. Butyrate acts epigenetically as histone deacetylase (HDAC) inhibitors and the research into HDAC may be capable of providing cancer chemoprevention and therapies [16]. There are different functions of butyrate in the colon; it is the main source of energy for colonocytes. Furthermore, butyrate has been documented to inhibit proinflammatory cytokines such as tumor necrosis α (TNF-α) in monocytes [17], interferon-α (IFN-α) and IL-2 in rat mesenteric lymph nodes [18], chemokine CXCL-8 (IL-8) in Caco-2 cells [19].

*Prebiotics, Probiotics and Synbiotic for Bone Health DOI: http://dx.doi.org/10.5772/intechopen.100525*

The concept and use of prebiotics has been argued to be more important when compared to probiotics due to the vulnerability and susceptibility of probiotics to environmental stresses, manufacturing process (such as heat) and endangered conditions during storage [29].

## **3. Prebiotics and human health**

Glenn Gibson and Marcel Roberfroid launched the prebiotic concept in 1995 as 'a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health' [30]. This definition has however been modified several times, but the initial main features have been retained. Prebiotics tend to stimulate the growth of the gut bacteria endogenously. The pH of the gut environment plays a major role in determining bacterial interspecies competition outcome.

Food sources of prebiotics consist of edible plants such as fruits, vegetables, cereal component which provides the body with carbohydrate. Specific potential sources are artichokes, tomatoes, bananas, asparagus, garlic, berries, kiwi fruit, onions, chicory, green leafy vegetables, legumes as well as linseed, barley, oats, and wheat.

Even though various molecules can be prebiotics, the great majority are dietary fibers which are oligosaccharides such as inulin (mainly from chicory), GOS (obtained from lactose using β-galactosidase), Fructooligosaccharides (FOS) (from chicory by partial enzymatic hydrolysis), soybean oligosaccharides (SOS), and xylooligosaccharides (XOS). Inulin, GOS and FOS have been widely studied. The list of prebiotics also includes compounds such as resistant starches, arabinoxylan, pectin, whole grains as well as non-carbohydrate complex such as polyphenols [13]. Absence of dietary fiber in the colon causes anaerobic bacteria to obtain their energy from protein fermentation, and this metabolism leads to the production of potentially toxic and carcinogenic compounds such as ammoniac and phenolic compounds [31]. In contrast, carbohydrate fermentation (for example dietary fiber) will produce non-toxic SCFAs which can serve as fuel for the epithelial cells. The production of volatile fatty acids, including, SCFAs and BCFAs, play a role in energy homeostasis maintenance as well as in the regulation of functionality in peripheral tissues [32]. Prebiotics are also mainly active in the large intestine/colon.

Different strains of bacterial genus or species would prefer different substrates for fermentation in the colon. Generally, the strains of *Bifidobacterium* and *Lactobacillus* genera have been reported to prefer fructans as substrate, as opposed to glucose while other bacteria such as *Clostridia* and *Bacteroides* have been reported to thrive on fructans [33, 34].

The use of prebiotics has been shown to be efficient and effective against a few human health disorders such as Type 2 diabetes mellitus and inflammatory bowel diseases which has been termed the "Western" chronic diseases and colorectal cancer. This is accomplished by the modulation of the intestinal gut microbiota which confer a protective, metabolic, and trophic benefits to the host [13].

### **4. Probiotics and human health**

The history of probiotics spans back to the 20th century when Mechnicoff (1907) revealed the virtues associated with the consumption of fermented dairy products, he hypothesized that the aging process resulted from the putrefaction of the large intestine. Almost simultaneously, another scientist Tissier indicated that the main component of the gut flora of breast-fed infants were bifidobacterial [35]. Even earlier, biblical recommendations have pointed out yoghurt as important/ significant for the treatment of some ailments [36]. Furthermore, the indication has been that probiotics is more beneficial when consumed with food as opposed to supplement due to the available nutrient and energy sources. Probiotics are mainly active in the small and large intestine.

Organizations such as FAO, WHO and the European Food Safety Authority have indicated probiotic strains must meet both safety and effectiveness criteria for their selection process. The regulations require that safety and absence of risks is paramount for human and animal health. The human probiotic products usually belong to the *Lactobacillus*, *Bifidobacterium*, *Lactococus*, *Streptococcus* and *Enterococcus* genus. In addition, there are some Gram-positive bacteria of genus Bacillus and some yeast of Saccharomyces genus which are also used as probiotics.

Probiotic use has been postulated to be potent against human disorders such as inflammatory enteral diseases such as Crohn's disease, colitis, and non-specific ileitis. Intake of probiotics has also been assessed by various studies as capable of treating lactose intolerance, irritable bowel syndrome [37] and in the prevention of peptic ulcers and colorectal cancer [38]. Beneficial effects of probiotics have been observed in the process of digestion, food allergies treatment [39], dental caries [40], and candidoses [41]. The beneficial effects of probiotics observed by the host

*Prebiotics, Probiotics and Synbiotic for Bone Health DOI: http://dx.doi.org/10.5772/intechopen.100525*

through augmentation of the epithelial wall, intestinal mucosal and competitive elimination of pathogens has been reported to aid inflammatory bowel disease (determined by cytokine-induced harm to the epithelial cell walls). Probiotics is capable of repressing gut inflammation via the downregulation of Toll-like Receptors' expression, the prevention of TNF-α entrance into the mononuclear cell in blood and the suppression of enterocyte's NF-kB (Nuclear Factor kappa-lightchain-enhancer of activated B cells) signaling pathway [42].

## **5. Synbiotics and human health**

Synbiotics are a combination of prebiotics and probiotics. The consumption and intake of the combination of prebiotics and probiotics has been reported to stimulate, modulate, and alter the gut microbiota by lowering the colonic secretion of pro-inflammatory and immunoregulatory cytokines such as TNF-α, IL-1β and IL-6. Synbiotics can be used to help improve the beneficial microbes as well as increase the number of specific beneficial strains in the gastrointestinal tract [11].

Immunomodulatory effects of prebiotics and probiotics on human health.

One the putative ways by which prebiotics and probiotics affect the health is altering the immune system. There are two categories of the immune system: either the innate immunity or the adaptive immune system. The immune system is responsible for protecting the host against pathogens. The type of effective immune response which recognizes and mounts reactions to eliminate the pathogen is determined by the site and type of pathogen present. Prebiotics and probiotics modulate the gut immune system thereby also having effects on bone health.

Further studies are needed to investigate the benefits of synbiotics on bone health both in human and animal model.

### **6. Probiotics and bone health**

Bone loss/osteoporosis is a major health problem that is associated with the imbalance between bone formation and bone resorption; often resulting in osteoporotic fractures. In addition, the estimation is that one in two women and one in four men over the age of 50 years will break a bone due to osteoporosis in their life time [43]. Postmenopausal osteoporosis is largely attributed to estrogen deficiency in women age 50 years and above due to ablation of the ovarian function which stimulates bone resorption resulting in bone loss. Risk factors leading to bone diseases include internal (genetic and aging) and external modifiable factors (e.g., diet, exercise, environment, medication etc). In osteoporosis treatment, different approaches have been used but lately due to the safety, low adverse effect and lack of major side effects, probiotics and prebiotics have been introduced. Treatment of bone diseases including osteoporosis and fracture has been mainly through hormone replacement therapy (HRT) as well as others such as bisphosphonates and more recently low-dose parathyroid hormone. However, there are side effects reported with this such as tumorigenesis, mood swings, fluid retention and bleeding as well as low compliance of daily injections [44].

#### **7. The role probiotics in inflammatory homeostasis**

Probiotics may aid the modulation of the hosts' inflammatory status by reducing the cytokine secretion levels. The downregulation of proinflammatory cytokines

such as IL-6 [45] and TNF-α [46, 47] by probiotics has been reported on several occasions. Studies have shown that some peptides such as p40 and p75 secreted by *Lactobaccillus rhamnosus GG* (LGG) may prevent cytokine-induced apoptosis, increase heat-shock proteins, and could lead to the activation of mitogen-activated protein kinase (MAPK) [48]. Furthermore, TNF (as well as IL-1 and RANKL) has been described as the major physiological inducer of NF-kappa B, one of the transcription factors responsible for the regulation of normal cell functions and the development of inflammatory osteolysis [49].

The role of the intestinal microbiota has been implicated in influencing bone health. A way by which the intestinal tract aids bone is by the regulation of the absorption of minerals such as calcium, phosphorus, and magnesium. This can also be accomplished by endocrine and gut-derived factors such as incretins and serotonins which may influence bone remodeling. Evidence from using germ-free mice indicated the effect of the intestinal microbiome on bone physiology. These studies observed higher bone mass in germ-free mice as compared to the conventional mice. In addition, a decrease in the number of osteoclasts per bone surface and a reduction in CD4+ T cells and osteoclasts precursors were observed in the bone marrow of the mice [50].

The RANKL/RANK/OPG pathway is one of the mechanisms that influence bone turnover/remodeling. Osteoclast's formation and activities are controlled by the RANKL/RANK pathway. They are also an essential pathological process of the bone remodeling. Concomitantly, OPG (decoy receptor of RANKL) acts as a bone protector by binding to RANKL and preventing further resorption [42]. Probiotics (beneficial microbes) have been postulated to reduce inflammation [51] and increase OPG expression in bone [52].

#### **8. Studies emphasizing the importance of probiotics for bone health**

#### **8.1 Animal studies**

Studies have shown that various strains of *Lactobacillus* [52–54] and *Bifidobacterium* [55, 56] possess the ability to prevent and restore estrogen deficiency-related bone loss in animal models. However, not many studies have been conducted in humans. The study by Ohlsson et al. showed that C-terminal telopeptides (resorption markers) levels were not increased in probiotic treated mice as compared to the vehicle treated mice. Furthermore, there was a reduction in expression of two proinflammatory cytokines (TNF-α and IL-1β), and an increase in the expression of OPG in the cortical bone of ovariectomised mice [52].

*Lactobacillus reuteri* ATCC PTA 6475 has been used in two animal studies to modulate bone outcomes. Findings from the first study showed increase in femoral trabecular BV/TV, BMD, BMC, trabecular number, spacing, and thickness as well as suppression of the basal TNF-α mRNA expression in the ileum and jejunum in 14-week-old C57Bl/6 J male mice [51]. Meanwhile, the second study showed similar positive bone effects in Ovx Balb/c mice when treated with *Lactobacillus reuteri* for four weeks and changes in the gut microbiota composition was observed revealing an increase in *Clostridiales* and a decrease in *Bacteroidales* in the ileum and jejunum [57]. Furthermore, a study by Collins et al. showed that supplementation with *Lactobaccillus reuteri* 6475 could influence inflammatory status and bone formation after the inflammatory state of female mice were mildly induced. This was achieved via a dorsal surgical incision (DSI) and then administration of the probiotic. The findings indicated that the probiotic supplementation increased bone density, the DSI-treated female mice showed higher trabecular number and mineral apposition

#### *Prebiotics, Probiotics and Synbiotic for Bone Health DOI: http://dx.doi.org/10.5772/intechopen.100525*

rate when compared to the non-treated mice. Although *L. reuteri* treatment had no effect on CD4+ T cell numbers, it led to a decrease in IL-1β and TGFβ expression in the non-surgery cohort [58].

Probiotics are known to aid mineral absorption for the purpose of bone health maintenance. A study showed that supplementation of growing rats with *L. rhamnosus* HN001 enhanced calcium and magnesium absorption [59]. In addition, rats treated with yoghurt with a mix of *Lactobacillus casei*, *L. reuteri* and *L. gasseri* presented higher calcium absorption which resulted in an increased BMC in comparison to the control as well as production of SCFAs [60].

Narva et al. demonstrated the effect a bioactive peptide (valylprolyl-proline) and *Lactobacillus helveticus* LBK-16H fermented milk on bone loss in ovariectomized rats. Their findings showed that *L. helveticus* fermented milk decreased bone turnover and increased BMD in growing rats [61], ovariectomised rats [62] and increased serum calcium while reduced serum PTH was observed in postmenopausal women [63].

Studies have also shown that supplementation with *Bifidobacterium longum*-fermented broccoli suppressed TRAP-positive osteoclast differentiation on the alveolar bone surface in rats [64]. Similarly, administration of yacon flour as prebiotics with *B. longum* as probiotics resulted in significant retention of minerals (such as Ca, Mg and P) in bones of Wistar rats [56]. *B. longum* also increased the BMD of ovariectomised rats by increasing the expression of Sparc and Bmp-2 genes [55].

In a study, male senescence-accelerated mice prone to developing osteoporosis with aging were orally administered heat-killed and living (viable) *Lactococcus lactis* subsp. *cremoris* H61 (strain H61). The protective effect of the heat-killed bacterium included reduction in loss of bone density, reduction in incidence of skin ulcer and reduction in hair loss of the aged SAMP6 [65]. On the other hand, reduction of bone density loss was not observed for the administration of the viable bacterium which may suggest the role of membrane-bound protein, inactivated microbial cells or cell fractions from the cellular death, that is, paraprobiotic and/or postbiotic effect.

The growth of bone as an extra-intestinal organ is suppressed by undernutrition in children. The study by Schwarzer et al. indicated that *L. plantarum* promoted juvenile growth in a strain-dependent manner using mono-colonized mouse model [66]. Supplementation with the bacterium increased the levels of insulin growth factor (IGF-1) and IGF-1 binding protein-3 (IGFBP- 3), the endocrine determinants of somatic growth to wild type levels [66].

Furthermore, the effects of probiotics have also been reported in dysbiosisinduced bone loss observed in the periodontal model [67, 68], Type-1 diabetesinduced bone loss [69] and IBD-induced bone loss [70, 71].

#### **8.2 Human studies**

A human study conducted in Denmark evaluated the combined effects of bioavailable isoflavones and probiotics on bone health and estrogen metabolism using a randomized controlled trial in postmenopausal women. Their findings showed that administration red clover extract (isoflavones) and probiotic attenuated BMD at the lumbar spine and femoral neck, reduced plasma concentrations of C-terminal telopeptide of type I collagen (CTX-1) as well as increased the urinary 2-hydroxyestrone (2-OH) to 16α-hydroxyestrone (16α-OH) ratio (the equol producer status) [72].

The use of probiotics however needs to be administered with caution since although the potential beneficial effect in the treatment of inflammatory and auto-immune gastrointestinal diseases for the modulation of immune response is well recognized, individuals with weaker immune systems may still be at risk of

viable bacterial cells; in which case the administration the use of killed/inactivated bacteria might be more beneficial [73].

### **9. Prebiotics and bone health**

Prebiotics are non-digestible short-chain carbohydrates also known as oligosaccharides (and maybe polysaccharides) which selectively improves the function and activities of specific types of beneficial microbes. The chemical compounds are neither hydrolyzed by the human digestive system nor absorbed in the upper gastrointestinal tract. Prebiotics have been termed 'colonic foods' due to the ability of these types of foods to move through the colon serving as a substrate to endogenous bacteria while benefitting the host by providing energy and essential nutrients [74].

#### **9.1 Animal studies**

Some varieties of benefits have been attributed to the consumption of prebiotics. These include the ability of prebiotics to increase the absorption of minerals such as calcium, magnesium, and phosphorus [75–78] as well as iron [79] as reported quite recently. The absorption of these minerals has consequently been observed to improve bone mineralization and density [80], trabecular structure and increase equol production [81] which is known to reduce bone loss.

#### **9.2 Human studies**

FOS supplementation has been administered to both Korean [82] and Chinese [83] postmenopausal women to investigate its effect in the prevention of osteoporosis, modulation of bone biomarkers and mineral absorption. Their findings indicate that there is potential for prebiotics to play a pivotal role in the above mentioned. The study by van den Heuvel et al. reported the benefit of intake of both GOS and inulin in increasing calcium absorption in postmenopausal women [84] and oligofructose stimulating calcium absorption in adolescents [85]. Intake of oligofructoseenriched inulin resulted in improved mineral absorption and impacted the bone turnover markers in postmenopausal women [86]. Other studies also looked into the effect of prebiotics in infants as was recorded with GOS, polydextrose [87] and inulin [88]. Some of these studies have also been conducted in animal models as has been shown in a recent review [89].

#### **10. Other clinical benefits of prebiotics**

Due to the effect of the change in metabolism from protein fermentation causing the release of ammonia that leads to an increase in pH to more carbohydrate fermentation resulting in the release of acids, a reduction in the intestinal pH is observed. Low intestinal pH tends to increase bowel movement while protecting against pathogens. Diseases such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and Crohn's diseases are characterized by high pH levels [90]. Prebiotics are therefore able to reduce the symptoms and severity of these diseases. In addition, they are able to restore intestinal bacterial imbalance created by antibiotics, diarrhea, stress and sometimes medication and drugs intake [74].

Prebiotics are also known to help relief constipation. Most carbohydrates are able to increase water retention of the intestine and the acids' production thereby increasing intestinal motility [91]. Furthermore, prebiotics have been used as

*Prebiotics, Probiotics and Synbiotic for Bone Health DOI: http://dx.doi.org/10.5772/intechopen.100525*

bioactive functional foods to modulate blood lipid levels [92] and it also been effective in weight loss and metabolic syndrome [93]. The anti-carcinogenic effects of both prebiotics and probiotics have been reported in the inhibition of aberrant crypt foci (ACF) which is a biomarker of colon cancer [94–96].

Recently, prebiotic food and Bidobacterium spp. have been reported to improve bone resorption and reduce serum TRACP-5b levels of Japanese female athletes [97]. Application of the combination of probiotic and prebiotic has been reported to confer a synergistical effect on the host due to the combined benefits of the two. This has been backed with the study by Scholz-Ahrens et al. which showed that probiotics supports the growth of other habitual microbiota strains and prebiotics chain length impacts the composition colonic, caecal, and fecal microflora. The combined administration of oligofructose and *Lactobacillus acidophilus* reduced the pH in the intestinal segments including the caecum, stimulated the colonic absorption as is indicated by increase in the colon weight [98].

## **11. Conclusion**

The study of the effect of synbiotics on gut microbiota and bone health profile is now growing rapidly. Probiotic strains have differing genotype and phenotype and may therefore show different metabolic and immunological functions. The mechanisms however still need further investigation to look into the effect of synbiotics on the gut for the regulation of bone metabolism via the process of mineral absorption, the immune, endocrine system. Further studies are needed to elucidate the importance and mechanisms by which prebiotics and probiotics modulates the microbiota-gut-bone axis in order to get the full benefit of the long-term safety and efficacy of consumption of these functional bioactive products.

### **Author details**

Bolaji Lilian Ilesanmi-Oyelere1 \* and Marlena Cathorina Kruger1,2

1 School of Health Sciences, College of Health, Massey University, New Zealand

2 Riddet Institute, Massey University, New Zealand

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


**5. Regenerative medicine and EVS**

Regenerative medicine is a relatively new concept and a complex domain that involves the restoration of damaged tissues using multiple techniques (e.g., SCs, biomaterials, differentiated autologous cells, or combinations of the aforementioned techniques). Regenerative medicine is focusing on repairing, regrowing, or replacing injured, malfunctioning, or missing tissue and addresses many tissular types: skin, heart tissue, cartilage tissue, bone tissue, adipose tissue etc. [101]. Thus, SC research focuses on their properties of repairing damaged tissues, either by producing new tissues by division and differentiation or by their partial repair.

Stem cells represent a highly interesting resource and were considered the ideal choice for regenerative therapies. SCs are defined as non-specialized cells, characterized by an enormous capacity of differentiation, which varies depending on their origin (embryonic, fetal, or adult). SCs are capable of differentiation into adipocytes, osteocytes, chondrocytes, endothelial cells, cardiomyocytes, pericytes, and smooth muscle cells [102–107]. They can also differentiate into neurogenic, cardiovascular, and neovascular pathways [108–113]. Allogeneic transplantation can be used in other applications due to the immunosuppressive properties of SCs [114].

Over the last decades, in an attempt to better understand SCs to use them in the processes of tissue repair and regeneration, multiple classifications have been made, depending on many aspects: the organism of origin (embryo, fetus, infant, adult), the tissue of origin within the adult-origin cells (mesenchymal tissue, hematopoietic, nervous, gastrointestinal, cutaneous, etc.), and the ability to divide (totipotent, pluripotent, multipotent, etc.) [115–117]. The understanding, even partial, of SCs' ability to divide, especially the asymmetric division of adult SCs has opened new horizons in terms of reparative and regenerative medicine [115]. Overpassing the initial idea that considers EVs as cellular debris, nowadays they are seen as tools for intercellular communication and as possible therapeutic vehicles. However, the same cannot be said about SCs. In the last decades, the interest for their properties has gained more and more interest. However, they have been regarded as cells at the origin of many pathologies since 1933, when Sabin *et al.* emphasize the possibility of radioactive damage to lymphoid tissue by affecting SCs [115, 118].

Although at the beginning researchers, scientists, and clinical doctors considered that the success of stem cell transplantation depends on the purity of the transplanted cells, not always the purer means also the better. Over time, it has become increasingly clear that the success of SC therapy depends on EVs and the soluble secreted factors because they play important paracrine roles. Our recent work also demonstrated that some other cellular types, such as the newly discovered telocytes, can act as cellular adjutants participating in the regenerative processes possibly through the released EVs influencing the microenvironment of the stem cell niche [118, 119]. Other additional evidence suggests that EVs can have not only regenerative properties, but also immunomodulatory roles, consequently summing up the therapeutic effects of stem cells. EVs, by contrast to stem cells, are nonimmunogenic and are not able to self-replicate [120]. In addition, EVs display powerful therapeutic potential, with positive outcomes regarding regeneration in many tissues (**Table 2**).

The central point of the pathophysiological mechanisms by which SCs contribute to the tissular repair are EVs that function as carriers of many biomolecules, such as miRNA, mRNA, cytokines, growth factors, differentiating factors with a key role in the main processes involved in tissue regeneration: immunomodulation, angiogenesis, differentiation [2]. Thus, multiple preclinical studies performed *in vitro* or *in vivo* on animal subjects have tried to identify the molecules involved and their role, important advances being made in diseases with high mortality and morbidity such as myocardial infarction, neuronal degeneration, osteoarticular diseases, skin ulcers, corneal damage etc. [121, 133, 134].

The use of SCs, despite promising results, has many disadvantages that require careful control of this procedure and the formation of very specific microenvironments to induce the differentiation of these cells [135]. Among the disadvantages mentioned before, those given by the ethical considerations of embryo use, the risk of uncontrolled differentiation, and the appearance of teratomas and genetic instability (especially those of embryonic origin) are the most important. To these disadvantages, a lower capacity for division and differentiation is added, as well as a laborious procedure for adult SCs acquirement [136, 137].

Among SCs, MSCs secrete growth factors and cytokines, with autocrine and paracrine properties. These substances inhibit the local immune system, fibrosis, and apoptosis, amplifying mitosis and differentiation of tissue-intrinsic reparative cells. These phenomena are known as trophic effects and differ from the direct differentiation of MSCs for tissue repair [138].

The numerous functions of MSCs in tissue regeneration and implicitly in the possible treatment of many diseases are mainly achieved by the secretion of exosomes loaded with key molecules (cytokines, growth factors, miRNA) and by molecules secreted directly into the extracellular environment with paracrine action [138–141].

However, they cannot produce infinite numbers of exosomes, repetitive isolation of cells being needed. The advantages of MSCs exosomes are their non-immunogenic

*Extracellular Vesicles as Intercellular Communication Vehicles in Regenerative Medicine DOI: http://dx.doi.org/10.5772/intechopen.101530*

*MSCs—mesenchymal stem cells; CSCs—cardiac stem cells; BM-MSCs—bone marrow mesenchymal stem cells; ADSc—Adipose tissue stem cells; miRNA—microRNA; TCA-3—T-cell activation gene-3; SDF-1—stromal derived factor 1; VEGF—vascular endothelial growth factor; bFGF—basic fibroblast growth factor; SCF—F box containing complex; DKK 1—Dickkopf-related protein 1; TGF beta—transforming growth factor 1; MMP-13—matrix metalloproteinase; IL—interleukin; TNF—tumor necrosis factor; CCL—CC chemokine ligand; BMP—bone morphogenic protein.*

#### **Table 2.**

*The role of stem cell-derived EVs depending on their content and tissue type.*

property, the intrinsic therapeutic capacity of reducing tissue damage, large *ex vivo* expansion, conveniently reachable source, and clinically tested cell source [18].

MSCs are a source of small EVs which can favor angiogenesis and cell proliferation in infarcted myocardium, can inhibit cardiac remodeling, and improve ventricular functions [121, 142, 143].

Moreover, MSCs can repair infarcted myocardium through paracrine interactions. EVs derived from MSCs have a better therapeutic effect than simple MSCs therapy. In animal subjects, suffering from myocardial infarction, exosomes derived from MSCs

diminished inflammation, improved cardiac function, stimulated cardiomyocyte H9C2 cell proliferation, inhibited apoptosis induced by H2O2 and cardiac fibrosis, and slowed down the transformation of fibroblasts into myofibroblasts mediated by TGF-β [144].

Although macrovascular reperfusion is the gold standard therapy for acute myocardial infarction, heart failure developed due to deficient cardiac remodeling is still a major issue for long-term therapeutic management. Angiogenesis is crucial for tissular regeneration, therefore, interest for therapeutic enhancement of angiogenesis has increased. Preclinical and human clinical trials showed conflicting results, the use of one growth factor not being enough to promote adequate angiogenesis [144–147]. Cell transplantation could be an alternative/another solution [148, 149]. Stem cells were utilized as sources for new cardiac cells production (endothelial progenitor cells, MSCs, cardiac progenitor cells). Paracrine factors secreted by transplanted cells seem to influence endogenous repair of damaged tissues [121].

*In vivo* studies indicate that small EVs from MSCs that overexpress Akt can amplify neovascularization, ameliorating the left ventricle ejection fraction [150]. The angiogenic involvement is supported by the treatment of renal ischemic reperfusion injury with small EVs derived from umbilical cord MSCs ameliorated capillary density through promoting VEGF up-regulation, independently from HIF-1α [151]. Small EVs can also deliver miRNAs (miR-125a) to endothelial cells, favoring angiogenesis [152]. Comparable outcomes were also obtained from the use of MSCs which overexpress hypoxia-inducible factors (HIF-1α). Injection of exosomes from MSCs, containing Jagged1, and hypoxia-inducible factor—MSCs cultures led to angiogenesis *in vivo* and *in vitro*. Exosomes derived from HIF-1α-overexpressing MSCs have a strong angiogenic function, through an expansion in the packaging of Jagged1 [153]. In addition, the immune system has a big role in the repair of the ischemic myocardium, in the inflammatory and angiogenesis phases. Chemokines, cytokines, and the release of EVs with paracrine actions sustain this restoration. EVs favor tissular regeneration and angiogenesis, therefore, research in this area is of high interest for patients suffering from acute myocardial infarction.

A study evaluating the effect of intracoronary administration of cardiac-derived SCs-secreted small EVs showed a lower number and altered polarization state of CD68+ macrophages in the infarcted myocardium, with elevated expression of antiinflammatory genes (Arg1, IL4ra, Tgfb1, Vegfa). Macrophages primed with EVs from cardiac-derived SCs displayed high levels of miR-181b, which targets protein kinase C δ. Therefore, exosomal transfer of miR-181b into macrophages lowered the levels of protein kinase C δ transcript, underlining the cardioprotective properties of stem cell infusion after reperfusion [154].

According to L. Cambier and colleagues, cardiosphere-derived cells proved to reduce myocardial infarction size through secreted EVs-Y RNA fragment, found in generous concentrations in EVs from cardiosphere-derived cells, correlated with the potency of these cells *in vivo*. This fragment can be transferred from cardiac cells to target macrophages through EVs, inducing transcription and secretion of IL-10, offering cardioprotection. *In vivo* injection of EV-Y RNA fragment after reperfusion reduced the infarct size [121, 155].

One of the major issues in diabetic patients is inadequate myocardial angiogenesis, which is responsible for an elevated risk for ischemic heart disease in these patients. Exosomes loaded with miRNAs (miR-320-3p or 320a) derived from diabetic cardiomyocytes proved, they can influence angiogenesis in endothelial cell cultures. Moreover, miR-320-3p, together with the miR-29 family and miR-7a can regulate insulin secretion and its signaling pathways [156, 157].

*Extracellular Vesicles as Intercellular Communication Vehicles in Regenerative Medicine DOI: http://dx.doi.org/10.5772/intechopen.101530*


**4. Electrical Stimulation**

#### *4.1. Promoting Axotomized Neurons to Extend Axons*

As mentioned previously, within increasing the time of axotomy, neurons lose their ability to extend axons [83]. However, these neurons can be induced to extend axons by electrical stimulation of the proximal portion of the transected nerves for as little as one hour [94,101,102] This results in a 34–50% increase in the number of neurons that extend axons [98,103,104]. Electrical stimulation also induces a 2.3-fold increase in the extent of axon sprouting from transected axons [105] while increasing the speed of axon regeneration [101,103,106]. At the same time, in animal models, electrical stimulation increases the distance axons regenerate across nerve gaps, the accuracy of sensory vs. motor axon innervation of their appropriate targets, and extent of functional recovery [107–110]. Electrical stimulation of peripheral nerve clinically also induces enhanced axon regeneration [102].

Electrical stimulation acts by inducing neurons to upregulate their level of cyclic-AMP [89,103]. This, in turn, induces motor neurons to upregulate their expression and synthesis of the neurotrophic factor BDNF and its trkB receptor mRNA, as well as the mRNA for other factors that enhance axon regeneration [99,111] These actions make neurons more receptive to regeneration-promoting factors [112].

#### *4.2. Activating Senescent Schwann Cells*

The decrease in axon regeneration across long nerve grafts, and with increasing time between nerve injury and repair, is attributed in part to Schwann cells becoming senescent when they lose contact with axons [69,75]. Thus, they stop proliferating and releasing neurotrophic factors that are required to promote axon regeneration. Electrical stimulation enhances axon regeneration by inducing the senescent Schwann cells to proliferate, migrate, and upregulate their synthesis and release of neurotrophic factors, which act to promote axon regeneration [99,113].

Schwann cells can also be induced to exit their senescent state by the application of VEGF [76,112,114] and marrow-derived mesenchymal stem cells. Thus, the Schwann cells reinitiate their ability to proliferate and to express and release neurotrophic factors [80].

#### *4.3. Vascularized Nerve Grafts and Promoting Vascularization*

The standard sensory nerve graft is cut from a donor nerve without maintaining its vasculature. As stated earlier, non-vascularized grafts become necrotic, which creates a toxic environment that inhibits axons regeneration until re-vascularization occurs. However, re-vascularized takes days

to develop, and takes more time for longer nerve grafts. This is because vascularization normally progresses from one end of the graft to the other.

The limitation of using non-vascularized grafts is avoided by using vascularized nerve grafts. In the rat sciatic nerve model, vascularized grafts induce significantly greater neurological recovery than non-vascularized nerve grafts [115]. Clinically, vascularized nerve grafts are required for axons to regenerate across gaps of longer than 6 cm [116]. Although vascularized nerve grafts are more e ffective in restoring function than non-vascularized grafts, they are not commonly used because the surgery is more complicated and time-consuming.

An alternative technique to using vascularized autografts is to induce the rapid re-vascularization of non-vascularized grafts. This can be done by pre-treating nerve grafts with VEGF before using them [117]. This treatment stimulates neovascularization of the graft, and Schwann cell invasion into the graft [117] and can reduce the time of graft ischemia by three days [118].

Axon regeneration can also be enhanced by using autografts with cells overexpressing VEGF, which leads to hyper-vascularization [119]. This enhances axon regeneration by reducing endoneurial scarring, by maintaining the viability of Schwann and other cells within the graft, and by decreasing fibroblast infiltration. This results in a good nutritional environment for supporting axonal regeneration.

The decrease in axon regeneration through nerve grafts with increasing age is also attributed to reduced graft vascularization. This is because aging is associated with a decrease in the upregulation of the expression, and release of VEGF following nerve injury [91]. Following nerve injury to aged mice, there is a significant reduction in the upregulation of VEGF synthesis and release, and thus, a failure of axons to regenerate. These findings suggest that, with increasing age, vascular abnormalities might play a role in the decreasing ability of axons to regenerate. They also suggest that clinically, inducing enhanced vascularization might enhance axon regeneration and functional recovery.

#### *4.4. Conclusion about Sensory Nerve Grafts*

The use of sensory nerve grafts leads to a permanent neurological deficit of the donor nerve. While such grafts can induce good to excellent functional recovery, such recovery is only for young patients [120,121], short gaps [65,67] (Aszmann et al., 2008b), and 3 when the repairs are performed within a short time post-trauma [77,79,81]. As any one of these values increases, the extent of recovery decreases precipitously. When the values of two or all three of these parameters increase, there is minimal to no functional recovery. However, even when nerve repair surgery is o ffered to patients who are considered good candidates for recovery function, <50% of them recover function [122]. Thus, most individuals who su ffer peripheral nerve traumas su ffer permanent neurological deficits and commonly chronic neuropathic pain. Therefore, there is a need for novel techniques that induce recovery under conditions where sensory nerve grafts are not e ffective.

The following sections examine other techniques that have been tested for their e fficacy in enhancing the extent of axon regeneration and neurological recovery across nerve gaps. They also examine methods tested for increasing their e fficacy in enhancing the extent of axon regeneration. The final section briefly discusses a novel technique that holds promise for restoring function, even when simultaneously the values of all three nerve injury parameters far exceed those when sensory nerve grafts are e ffective in promoting axon regeneration.


**2. Animal models for PD**

Cellular processes associated with PD such as oxidative stress, neurodegeneration, neuroinflammation and cell death, has been successfully evaluated in rat and mice. Till date, there exist two general types of experimental murine models: genetically manipulated and chemically induced.

#### **2.1. Genetically manipulated**

The induction of gene mutations, alterations in protein functionality and sub- or overexpression of proteins have generated models for PD. These innovative genetic engineering strategies have been developing for PARK2, alpha-synuclein, PINK1, and oxDJ-1. The results are diverse. For example, the genetic deletion of exon 3 of PARK2 in mice increases extracellular striatal dopamine contents but the DAT levels are decreased [4, 5]. These facts do not alter the nigrostriatal pathway because the number of dopaminergic neurons remains normal. A key factor for Parkinson's disease progression is the formation of Lewy bodies [6], due to which, α-synuclein has been incorporated as a gene or peptide to produce amyloid-like composed fibrils. Other strategy involves the incorporation of drugs to modify alpha synuclein aggregation in mice and in *in vitro* models [7, 8]. In mice, it causes dopaminergic neuronal death [2]. But the deleterious effect is dependent on the site of administration, type of particle (gene, peptides, and oligomers), dose, and molecular vector used.

#### **2.2. Chemically induced**

The most commonly used neurotoxins are: (a) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) [9], which is converted to 1-methyl-4-phenylpyridinium (MPP+) by monoamine oxidase (MAO-B), (b) 6-hydroxydopamine (6-OHDA) [6, 10], (c) herbicides such as paraquat or rotenone [11] and (d) metals (manganese, iron) [12]. MPTP crosses the blood-brain barrier (BBB) [13], which in addition to cause damage to the nigrostriatal pathway, causes neuronal loss of the GABAergic neurons [14], catecholaminergic neurons (VTA, *locus coeruleus*, retrorubral nuclei) [15], reduction of serotonine receptor in the cortical and subcortical regions and reactive gliosis [16]. The toxicity of herbicides and metals is characterized by mitochondrial dysfunction due to peripheral and brain cellular stress [6, 17]. The neurotoxin 6-hydroxydopamine is more selective for the dopaminergic neurons of the SNpc [18, 19] because it causes specific degeneration of dopaminergic neurons in the SNpc [19–21] and does not cross the BBB. The advantages and limitations of 6-hydroxydopamine model are showed in **Table 1**.

**3. Vulnerability of dopaminergic neurons to 6-OHDA**

**Feature Advantages Limitations**

(uncommon)

performed in rats (most common), mice, cats, guinea pigs, dogs and monkeys

intracranial injection by stereotaxis needs precise administrations on nigrostriatal

progressive. Dose and site dependent

Selective entry into the target using Dopamine transporter (DAT), can cause selective destruction of brain

More in SNpc, nucleus specific to dopaminergic neuronal population, than in VTA, nucleus containing glutamatergic neuronal populations, representing a

of methamphetamine or apomorphine injected and severity of the lesion; correlates with the magnitude of

Survival rate [27] High survival 5 in 100 die due to lack of proper

Oxidative/nitrosative stress, apoptosis, autophagy, necrosis, neuroinflammation

dopaminergic neurons

good model for PD

nigrostriatal lesions

Circling motor behavior [12, 20] Quantifiable depending on the dosage

common) or bilateral (uncommon) injection into the nigrostriatal pathway None

Animal Model of Parkinson Disease: Neuroinflammation and Apoptosis in the…

None

equipment

neurons

neurons

None

None Causes cognitive, psychiatric and

None Absent due to acute

pathophysiology

Stereotaxis procedure needs special

http://dx.doi.org/10.5772/intechopen.71271

377

Cannot reproduce complete

Noradrenaline transporter (NAT) mediated entry causes damage and destruction of brain noradrenergic

Toxic for other catecholaminergic

neurodegenerative property of

gastrointestinal disorders

No Lewy body formation

post-surgery recovery

6-OHDA injection

Animal(s) used [6, 22] The injection of 6-OHDA can be

Usage of the model [1, 20, 23, 24] Unilateral (standardized and most

Mode of administration [20, 25] As the 6-OHDA does not cross BBB,

Type of lesion [20, 26] Reproducible; retrograde; relatively

Transporter mediated entry

Dopaminergic neuronal loss

Progressive and age-dependent

effects of PD [6, 22]

Non-motor behavioral phenotypes [3, 6]

Cellular process associated to the cytotoxicity [3, 13, 29–31]

**Table 1.** Characteristics of 6-OHDA model.

[13, 27]

[6, 28]

pathway

6-Hydroxydopamine (6-OHDA) is a highly oxidizable dopamine analog, which can be captured through the dopamine transporter (DAT) [25]. Till date, three mechanisms have been proposed to explain the cytotoxic effect of 6-OHDA: (1) intra- or extracellular auto-oxidation,

**Table 1.** Characteristics of 6-OHDA model.

progressive degeneration of the dopaminergic neurons of the nigrostriatal pathway, neuroinflammation, the presence of Lewy bodies and generalized damage of the neuronal circuits

Cellular processes associated with PD such as oxidative stress, neurodegeneration, neuroinflammation and cell death, has been successfully evaluated in rat and mice. Till date, there exist two general types of experimental murine models: genetically manipulated and chemi-

The induction of gene mutations, alterations in protein functionality and sub- or overexpression of proteins have generated models for PD. These innovative genetic engineering strategies have been developing for PARK2, alpha-synuclein, PINK1, and oxDJ-1. The results are diverse. For example, the genetic deletion of exon 3 of PARK2 in mice increases extracellular striatal dopamine contents but the DAT levels are decreased [4, 5]. These facts do not alter the nigrostriatal pathway because the number of dopaminergic neurons remains normal. A key factor for Parkinson's disease progression is the formation of Lewy bodies [6], due to which, α-synuclein has been incorporated as a gene or peptide to produce amyloid-like composed fibrils. Other strategy involves the incorporation of drugs to modify alpha synuclein aggregation in mice and in *in vitro* models [7, 8]. In mice, it causes dopaminergic neuronal death [2]. But the deleterious effect is dependent on the site of administration, type of particle (gene, peptides, and oligomers), dose, and

The most commonly used neurotoxins are: (a) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) [9], which is converted to 1-methyl-4-phenylpyridinium (MPP+) by monoamine oxidase (MAO-B), (b) 6-hydroxydopamine (6-OHDA) [6, 10], (c) herbicides such as paraquat or rotenone [11] and (d) metals (manganese, iron) [12]. MPTP crosses the blood-brain barrier (BBB) [13], which in addition to cause damage to the nigrostriatal pathway, causes neuronal loss of the GABAergic neurons [14], catecholaminergic neurons (VTA, *locus coeruleus*, retrorubral nuclei) [15], reduction of serotonine receptor in the cortical and subcortical regions and reactive gliosis [16]. The toxicity of herbicides and metals is characterized by mitochondrial dysfunction due to peripheral and brain cellular stress [6, 17]. The neurotoxin 6-hydroxydopamine is more selective for the dopaminergic neurons of the SNpc [18, 19] because it causes specific degeneration of dopaminergic neurons in the SNpc [19–21] and does not cross the BBB. The advantages and limitations of 6-hydroxydopamine model are

that control the movement [3].

376 Experimental Animal Models of Human Diseases - An Effective Therapeutic Strategy

**2. Animal models for PD**

**2.1. Genetically manipulated**

molecular vector used.

**2.2. Chemically induced**

showed in **Table 1**.

cally induced.


**5. Conservation of island ecosystem**

Since the early-2000s eradication campaigns of rodents have been conducted in islands such as Yururi-Moyururi in Hokkaido, northern Japan, and the Ogasawara Islands, southern Japan [14, 15]. These projects were supported by the Ministry of Environment to conserve island ecosystems.

*Rodents*


**3. Example of concrete crack inspection using CNN**

#### **3.1 Textbook example of crack inspection using CNN**

This chapter provides an example of how convolution, pooling, fully connected, and benchmarking can be demonstrated in real-world concrete crack inspection using CNN. The above-mentioned calculation was carried out using the Python programming language and the Pytorch package.

#### *3.1.1 Dataset*

In this example, the input images were gathered from Kaggle, the world's most well-known data science community. Kaggle allows access to thousands of public datasets covering a wide range of topics, including medical, agriculture, and construction [9]. By searching "concrete crack" in Kaggle datasets module, 12 datasets were found. The "SDNET2018" dataset was chosen from among them since it comprises sufficient and clean concrete surface images with and without cracks [10]. In "SDNET2018", 56,096 images were captured in the Utah State University Campus using a 16-megapixel Nikon digital camera, including 54 bridge decks, 72 walls, and 104 pavements. In this example, only images of walls and pavements were used to demonstrate the comparison analysis between manual inspection and CNN-based automatic inspection. Therefore, 42,472 images were used as training and testing dataset. Among them, 6459 cracked concrete surfaces are considered as positive class. The captured cracks are as narrow as 0.06 mm and as wide as 25 mm, while 36,013 uncracked concrete surfaces are considered as negative class. Images in this dataset contain a range of impediments, such as shadows, surface roughness, scaling, edges, and holes. The diverse photographing backgrounds contribute to ensuring the robustness of the designed CNN architecture. At a ratio of 80/20, the cracked and uncracked concrete photos were randomly separated into training and testing datasets. The input images' pixels were standardized to 227 227 3 for AlexNet, and 224 224 3 for VGG16. **Table 4** shows the details of the input images. **Figure 6** shows the examples of the input images.

#### *3.1.2 CNN architecture*

In this section, two pre-trained CNN networks, AlexNet and VGG16, were introduced to illustrate CNN computation process. AlexNet was designed as an eight-layer architecture. VGG16 has a depth that is two twice that of AlexNet. According to [11, 12], the depth of CNN network has a significant impact on model performance.

#### **Table 4.** *Details of prepared dataset.*

*Computer Vision-Based Techniques for Quality Inspection of Concrete Building Structures DOI: http://dx.doi.org/10.5772/intechopen.104405*

**Figure 6.** *Examples of cracked and non-cracked surface.*

Therefore, by training and testing the prepared dataset with AlexNet and VGG16, the comparison of network depth to prediction performance and computation cost can be further highlighted.

#### 1.AlexNet architecture

The AlexNet architecture, developed by Alex Krizhevsky, Ilya Sutskever, and Geoffrey E. Hinton in 2012, is considered one of the most influential CNN architectures [13]. AlexNet consists of five convolution layers and three fully-connected layers. The max-pooling layers follow the first, second, and fifth convolution layers. AlexNet was designed to predict 1000 object classifications. 1.2 million images with a pixel size of 2,242,243 were used as input images. As a result, 60 million parameters and 650,000 neurons are included in the computation process. The details of the AlexNet architecture are shown in **Figure 7**.

In the first convolution stage, 96 convolution filters with size of 11 11 were applied; they move with a stride with four pixels. The size of pooling filters is 3 3. The pooling filters move with a stride of two. It is worth noticing that the error rate can be reduced by applying overlapping pooling technique (the size of pooling filters is smaller than its stride). In the second convolution stage, the size of convolution filters becomes smaller from 11 11 to 5 5 while its number becomes larger from 96 to 256. The convolution filters in the third and the fourth convolution stage keep minimizing, from 5 5 to 3 3, while its number keeps increasing from 256 to 384. In the last convolution stage, the size of convolution filters remains same as 3 3, and its number turns back to 256. The size and stride of pooling filters also remain the same in the second and fifth convolution stage. Finally, 4096 neurons are included for both first and second fully-connected layers. The final fully-connected layer contains 1000 neurons to output the probabilities of 1000 classifications. The 1000 neurons are activated by softmax function.

The outputs of each convolution and fully-connected layer are activated by a nonlinear function, namely the Rectified Linear Units (ReLU) [14]. It is proved in

**Figure 7.** *Details of AlexNet architecture.*

AlexNet that using ReLU instead of other activation functions effectively solves the overfitting problem and improves computation efficiency. Especially for the larger architectures trained on larger datasets. The local response normalization [15] technique (LRN) is also applied following ReLUs to reduce the error rate. Moreover, to avoid overfitting, drop-out techniques [16] are also applied in the first two fullyconnected layers. The dropout criteria was set at 0.5.

AlexNet was computed using SGD. The batch size, momentum [17], and weight decay [18] were set as 128, 0.9, and 0.0005, respectively. The learning rate was set as 0.00001. AlexNet was computed for roughly 90 periods in NVIDIA GTX 580 3GB GPUs. As a result, the error rate of AlexNet on test set of top-1 and top-5 achieved 37.5% and 17.0%, which was 10% lower than the out-performed CNN architecture at that time.

### 2. VGG16 architecture

VGG16, designed by Karen Simonyan and Andrew Zisserman in 2015, was developed to investigate the influence of convolution network depth on prediction accuracy in larger datasets [19]. Therefore, VGG16 was designed as a deep architecture with 16 weight layers, including 13 convolution layers and three fully-connected layers. Convolution layers in VGG16 are presented as five convolution blocks. The details of the VGG16 architecture are shown in **Figure 8**.

*Computer Vision-Based Techniques for Quality Inspection of Concrete Building Structures DOI: http://dx.doi.org/10.5772/intechopen.104405*

**Figure 8.** *Details of VGG16 architecture.*

As seen from **Figure 8**, there are two convolution layers in the first two convolution blocks, respectively, and three convolution layers in the following three convolution blocks, respectively. The size of all convolution filters is uniformly 3 3. All the convolution filters move with a stride of one. The number of convolution filters increases gradually from 64 to 128, 256, and 512 in the five convolution blocks. To preserve information about image boundaries as completely as possible, spatial padding is applied [20]. As with AlexNet, ReLU is applied as a non-linearity function for convolution and fully-connected outputs to avoid overfitting problems. However, unlike in AlexNet, LRN is not used in VGG16 because the authors stated that LRN has no influence on model performance and increases memory consumption and computation time.

Five max-pooling layers follow the last convolution layer in each block. The maxpooling filters are uniformed with a size of 2 2, and a stride of two. As with AlexNet, the first two fully-connected layers have 4096 neurons and 1000 output neurons. The output neurons are activated by softmax. To avoid overfitting problems, drop-out technique is also applied in the first two fully-connected layers. The dropout ratio is set at 0.5. It can be concluded that the most important novelty of VGG16 compared with AlexNet are: (1) the designed deep architecture; (2) the uniformed and small size convolution filters.

In the training process, the training batch size, momentum, weight decay, and learning rate were set as 256, 0.9, and 0.0005, 0.0001, respectively. As a result, the top-1 and top-5 errors of VGG16 achieved 24.4% and 7.2%, which is 13% and 9.8% lower than AlexNet. The result proved that the deep architecture and small convolution filters have positive influences on CNN performance.

#### *3.1.3 Training and benchmarking*

Finally, the prepared dataset mentioned in Section 3.3.1 was used to train and test AlexNet and VGG16, respectively. The training and testing process was conducted in Kaggle kernels [21]. Kaggle kernel, provided by Kaggle community, is a virtual environment equipped with NVIDIA Tesla K80, a dual GPU design, and 24GB of GDDR5 memory. This high computing performance enables 5–10 times faster training and testing processes than CPU-only devices. Both AlexNet and VGG16 were trained using SGD. Batch size was and learning rate set as 64, 0.0001, respectively. To avoid overfitting problem, dropout was applied at the fully-connected stage, dropout probability was set as 0.5.

Python was used to program the computing process. Pytorch library was imported. The whole computation time of AlexNet was roughly 2 h, and 4 h for VGG16. The model's performance in the training and testing datasets is shown in **Figures 9** and **10**,

#### **Figure 9.**

*Training loss and accuracy of AlexNet and VGG16.*

**Figure 10.** *Testing loss and accuracy of AlexNet and VGG16.*

#### *Computer Vision-Based Techniques for Quality Inspection of Concrete Building Structures DOI: http://dx.doi.org/10.5772/intechopen.104405*

respectively. The training and testing loss and accuracy values are represented on the vertical axis, while the processing epochs are represented on the horizontal axis. Since the loss and accuracy variation remained consistent after the 60th epoch overtraining the model could lead to an overfitting problem [22]. The training epoch was set to 60 epochs.

As shown in **Figure 9**, both AlexNet and VGG16 converged successfully. The training loss for AlexNet reduced steadily from 0.43 to 0.05 in the 58th epoch and then remained constant in subsequent epochs. Similarly, at the 58th epoch, AlexNet's training accuracy increased from 0.85 to 0.98. At the 35th epoch, the training loss for VGG16 dropped from 0.42 to 0.01 and subsequently stayed steady at approximately 0.008–0.01 in following epochs. At the 34th epoch, the training accuracy of VGG16 increased from 0.85 to 0.99 and then remained at 0.99. The results revealed that VGG16 performed better during the training procedure. VGG16's convergence speed is roughly two times that of AlexNet. VGG16's minimum training loss is 0.04 lower than AlexNet's, while its maximum accuracy is 0.01 times higher. It is observed that deeper CNN designs assist in the faster processing of larger datasets, which contributes to producing more trustworthy weights and biased matrices. These results are in accordance with those proposed by [23].

**Figure 10** shows the loss and accuracy variations of AlexNet and VGG16 in the testing dataset. The testing loss and accuracy consist of the fluctuation tendency of training loss and accuracy. It indicated that neither AlexNet nor VGG16 had overfitting or underfitting problems. VGG16 also out-performed AlexNet in the testing process. AlexNet and VGG16 have minimum testing losses of 0.01 and 0.00003, respectively. AlexNet's maximum accuracy was 0.98, and VGG16's was 0.99. In the testing dataset, VGG16 converges at the 34th epoch, which is nearly 2 times faster than AlexNet.

The confusion matrix of AlexNet and VGG16 is shown in **Table 5**. It can be shown that the accuracy scores of AlexNet and VGG16 are nearly identical, indicating that AlexNet and VGG16 have similar prediction abilities for cracked and uncracked concrete surfaces. VGG16 has a precision and recall of 96.5% and 89.6%, respectively, which is nearly 1% and 5% greater than AlexNet. The results show that VGG16 outperforms AlexNet for predicted positive variables (cracked surfaces). Meanwhile, more cracked images from actual datasets can be correctly identified by applying VGG16. AlexNet and VGG16 have F1-scores of 89.6% and 92.9%, respectively, indicating that the VGG16 model is more robust.

#### **Table 5.**

*Confusion matrix of AlexNet and VGG16.*

In conclusion, VGG16 demonstrates better performance. Since it is important to avoid ignoring any cracked surfaces, the model with the highest recall and F1-score is more worthwhile. Meanwhile, AlexNet is also a preferable option when the number of cracked and uncracked images is balanced because it shows a similar accuracy score as VGG16 and has a lower computation cost.

#### **3.2 Comparison of CNN and manual inspection**

During on-site construction quality management process, quality control managers (QCM) or registered inspectors (RI) are responsible for personally inspecting and reporting quality problems with forms, reports, and photocopies. According to the Mandatory Building Inspection Scheme (MBIS) and related contract regulations, QCMs and RIs are obliged to examine cracks and other defects in building components visually or with non-destructive equipment [24]. For example (1) cracks on the structural components, e.g., structural beam, column, (2) cracks on the external finishes, e.g., tiling, rendering, and cladding, (3) cracks on the fins, grilles, windows, curtain walls.

When using computer-vision-based inspection techniques, differently, there is no necessity for QCMs and RIs to conduct the aforementioned inspection tasks on-site. Instead, their primary responsibilities may switch to (1) taking photos or videos of building components, and (2) inputting the images and videos into pre-trained CNN models. To highlight the differences between manual and computer-vision-based crack inspection, an experiment was set up to calculate and compare inspection time and cost.

The layout of the experiment is shown in **Figure 11**. Suppose this experiment case is a 15 m 15 m 2 m residential building that is located in San Bernardino. The inspection items include cracks on slab, internal walls, and external walls. According to Dohm, John Carl [25], the total manual inspection time for 1600–2600ft2 home in San Bernardino is around 13.65 h, including inspection items of building slab, shear walls, etc. The manual inspection service cost is around \$85.9 per hour.

Referring to the computer-vision-based inspection process described above, the total inspection time includes the time of taking images or videos and CNN processing. Assume that the input videos are obtained with handheld camera devices while QCMs or RIs are by means of walking. Then, the time of taking videos can be considered as the time of walking.

**Figure 11.** *Layout of the experiment case.*

*Computer Vision-Based Techniques for Quality Inspection of Concrete Building Structures DOI: http://dx.doi.org/10.5772/intechopen.104405*

#### **Figure 12.** *Walking path of the inspectors.*

#### **Table 6.**

*Time and cost of manual and computer-vision based crack inspection.*

Normally, the average walking speed between the age of 20–49 is around 1.42 m/s [26]. Considering the time delays of taking videos, the walking speed can be considered as 0.1 m/s. Suppose the walking path follows an S-curve, shown in **Figure 12**.

According to [27], the universally accepted frame rate is 24 FPS per second. Suppose the inspector begins to record video while taking the first step. Then the time of captured video equals the time of walking. The number of the input images that converted from the captured video can be calculated as 2390 s 24FPS = 57,360. According to the testing time of the textbook examples mentioned in Section 3.1, and the study outcomes of [28], the time of CNN processing is around 100 images per second. Then, the time of CNN processing can be calculated as 57,360/100 = 573.6 s. Therefore, the cost of computer-vision based crack inspection can be calculated as (2390 s + 573.6 s) (85.9/3600) = \$70.7.

**Table 6** summarizes the calculation process of time and cost of manual and computer-vision-based crack inspection. It can be seen that using CNN-based technique can effectively reduce inspection time and cost. The inspection time decreases from 13.65 to 0.8 h in total, the inspection cost decreases from \$1172.5 to \$70.7.

### **4. Conclusion**

To facilitate automatic building quality inspection and management, this study introduced a computer-vision-based automated concrete crack inspection technique. In order to demonstrate the computing and benchmarking process, the mathematical understanding of one of the most essential computer vision algorithms, convolution neural network, was first detailed.

The theoretical foundation was then explained using a textbook example. In this case, the input dataset "SDNET2018" was obtained from the Kaggle community. A digital camera was used to acquire the 56,096 photos from the Utah State University campus. To train the input images, the two most basic CNN architectures, AlexNet and VGG16, were chosen. The Pytorch library was used to carry out the training process in the Kaggle kernel. The model's performance was evaluated using a confusion matrix. The results revealed that the prediction accuracy of AlexNet and VGG16 is nearly identical. However, VGG16's precision and recall are higher than AlexNet's, indicating that VGG16 has a stronger capacity to identify cracked surfaces. VGG16's F1 score is also greater than AlexNet's, signifying that VGG16 is more robust. VGG16 is deemed to have a better significance since it has higher precision, recall, and F1 score, which is crucial when distinguishing cracked and uncracked surfaces. When the ratio of cracked and uncracked images is almost the same, however, AlexNet is a feasible alternative because of its high accuracy score and low computation cost. It's worth noting that, when compared to shallow CNN architectures, deeper and broader CNN architectures outperform shallow CNN architectures for larger datasets.

Next, an experimental case was designed to compare manual and computer-visionbased crack inspection in terms of time and cost. The results showed that the efficiency and cost-effectiveness can be effectively improved when adopting computer-vision-based techniques. The inspection time and cost or the designed case can nearly decrease from 13.65 to 0.8 h, and from \$1172.5 to \$70.7, respectively.

The findings help to demonstrate the computer-vision-based quality inspection technique in both theory and practice. Although the recently developed computervision-based technology improves the efficiency, cost-effectiveness, and safety of human quality inspection, it still relies primarily on the collected image quality. Some concrete surface images are difficult to capture in real-life situations, including among others high-rise buildings, component corners, and buildings in extremely harsh environments. To address this issue, robotics techniques are growing rapidly as a means of upgrading computer-vision-based quality inspection [29]. Previous research has begun to use mobile robots, such as UAVs in order to gather surface images [30–32]. Some studies have focused on exploring robotic inspection systems to raise the automatic level of quality inspection [33, 34]. Therefore, merging robotics and computer vision approaches may be considered as a worthwhile future research direction to improve the efficiency and accuracy of manual quality control and management.

### **Acknowledgements**

The authors highly appreciate the full support funding of the full-time PhD research studentship under the auspice of the Department of Building and Real Estate, The Hong Kong Polytechnic University, Hong Kong. The authors would like to express their deepest gratitude to Prof. Heng Li for his guidance. Finally, the authors would like to acknowledge the research team members (Mr. King Chi Lo, Mr. Qi Kai) and anyone who provided help and comments to improve the content of this article.

#### **Conflict of interest**

All authors declare that they have no conflicts of interest.

*Computer Vision-Based Techniques for Quality Inspection of Concrete Building Structures DOI: http://dx.doi.org/10.5772/intechopen.104405*


**7. Conclusion**

On the basis of an imperative tradeoff between equality and efficiency assumption, optimal taxation literature which claims that egalitarian redistribution policies of the state will create negative results oppose redistribution policies of the state because of equality-efficiency dilemma. The main starting point on this topic is not being able to enable a certain budget revenue goal via lump-sum taxes because of the asymmetrical information between state and individual and the need for distortionary taxes. In this context, one of the propositions for resolution in the literature is optimal commodity tax application.

In optimal tax application with the aim of efficiency, discussion of single rate or differential tax application is in question.

Ramsey's study on optimal commodity taxes, which suggest goods to be taxed inversely proportional with price elasticity of demand, is one of the primary studies in the literature. While Ramsey rule basically proposes goods with low price elasticity of demand to be taxed at higher rates, its purpose is to preserve individuals' decisions about the consumption of goods with increasing prices unchanged as part of low elasticity, or in other words, a deadweight loss or wealth loss not to be formed in the economy. This rule, in which economic efficiency concern dominates, faces the biggest criticism because of the unjust distribution emerging as a result of the assumption that all individuals resemble each other.

With the inverse elasticity rule, Ramsey suggests necessity goods, which occupy a large share in the consumption basket of lower income groups, to be taxed at higher rates and goods, which appeal to higher income groups, to be taxed at lower rates due to demand elasticity. What is important in this context is whether price elasticity of demand for goods change or not as part of macrovariables and microvariables.

Price elasticity of demand for luxury and necessity goods rises depending on short and long term effect, commercial liberalization, and increased competition and innovation, which are all macroeconomic variables. On the other hand, since brand loyalty, which is the leading microeconomic variable, is high especially for luxury goods, it affects price elasticity of demand for the aforementioned goods.

Additionally, luxury goods to be taxed at higher rates under the assumption that they are leisure complementaries may affect the decisions of individuals on behalf of working. In this context, the criticisms brought about by Ramsey's rule in terms of economic efficiency at the differential taxation, it can be seen that the rule of inverse elasticity on equality can be reconsidered.


*Drug Delivery Applications of Metal-Organic Frameworks (MOFs) DOI: http://dx.doi.org/10.5772/intechopen.103684*

anti-cancer drugs, based on both *in vitro* and *in vivo* experiments. In 2006, Horcajada et al. were the first ones to report the ability of MOFs to act as efficient drug delivery agents. They prepared two mesoporous cubic MOFs, namely MIL-100 and MIL-101. They employed them to adsorb ibuprofen, a commonly used anti-inflammatory drug and found that MIL-101 with a larger cage size was able to adsorb more amount of drug (1.4 g/g of MOF) [30]. Nasrabadi et al. reported the use of UiO-66 NMOF with surface area 1196 m2 /g to post-synthetically load ciprofloxacin (CIP), an antibiotic. The resulting CIP-UiO-66 NMOF showed a very high drug loading percentage of about 84%, with significant antibacterial activity against *Escherichia coli* (Gramnegative) and *Staphylococcus aureus* (Gram-positive) bacteria in comparison to free CIP [52]. ZIF-8 is a pH-responsive MOF, which disintegrates in an acidic environment, and thus is a promising drug carrier especially for anti-cancer applications because of acidic nature of tumor micro-environment. Sun et al. for the first time reported the use of ZIF-8 for the controlled and pH-triggered release of 5-fluorouracil (5-FU), an anticancer drug with high loading capacity (660 mg/g of MOF) [53]. **Table 1** summarizes some of the NMOFs and MOFs reported for the delivery of therapeutic agents.


*Edited by Ahmed R. G.*

The World Health Organization estimated that each year there are more than 13 million deaths caused by environmental causes. Exposure to endocrine disrupting chemicals (EDCs) during development may cause long-term health outcomes. This book, Endocrine Disruptors, includes eight chapters that illustrate potential endocrinedisrupting activities in water, sediments, crops, animals, and humans. This book assesses the relationship between the EDCs and development, reproduction, or obesity. Finally, detection of the levels of EDCs by autobioluminescent cellular bioreporters is discussed. Scientists, physicians, neuroendocrinologists, neurotoxicologists, and lay readers who have engaged in EDC studies or practice will discover that this book offers insight into all areas of EDC research.

Published in London, UK © 2018 IntechOpen © digicomphoto / iStock

Endocrine Disruptors

Endocrine Disruptors


**Non-Invasive Diagnosis of Acute Renal Allograft Rejection − Special Focus on Gamma Scintigraphy and Positron Emission Tomography**

Alexander Grabner, Dominik Kentrup, Uta Schnöckel, Michael Schäfers and Stefan Reuter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54737