**Acknowledgements**

The research discussed here (published and not published from this laboratory) was conducted at Texas Tech University and was funded by the university and by Animal Biotech. Many other studies are also presented and we thank those authors for their valuable contributions.


**4. Lupus-like syndrome**

Systemic lupus erythematosus (SLE) is a common autoimmune disease, with 10% of SLE cases being drug-induced. The autoimmune drug-induced response is idiosyncratic, influenced by multiple factors, such as genetics, comorbidities, interactions with other medicinal products and external environmental factors [23]. Drug-induced lupus erythematosus (DILE) is defined as a lupus-like disease that is temporally related to drug exposure (from 1 month after the commencement of drug application but sometimes even more than 10 years) [24].

DILE may not meet all the SLE criteria. The most common manifestations are arthritis, serositis, the presence of ANA antibodies and anti-histone antibodies. The most important criterion is that the symptoms cease after discontinuing application of the suspected drug [25].

plaque psoriasis is ustekinumab. Ustekinumab is also a good alternative in the treatment of inflammatory bowel disease and in the treatment of spondylarthritis or psoriatic arthritis [31]. However, the literature contains also cases of an ustekinumab-induced DILE. Biologics with a different mechanism of action are alternative treatments, but it cannot be said whether other mechanisms of action (anti-IL13/23, anti-IL-17, anti-IL 6) will be a potential threat to DILE

**Figure 2.** Significant facial erythema, total weakness and laboratory elevated ANA antibodies were observed. After discontinuation of the treatment, gradual regression of skin manifestations and neutralisation of ANA antibodies took

Immune-Mediated Skin Reactions Induced by Recombinant Antibodies and Other TNF-Alpha…

http://dx.doi.org/10.5772/intechopen.72449

265

The manifestations of vasculitis are another disease that is associated with the anti-TNF-alpha treatment. Several case reports and patient groups have been described in the literature. In almost half of the cases, leukocytoclastic vasculitis was histologically described, while the other patients included cases of necrotising vasculitis, lymphocytic vasculitis and urticarial

An aggregate paper of 118 cases of vasculitis newly formed during the anti-TNF-alpha treatment (99 cases of rheumatoid arthritis, 8 Crohn's disease, 5 juvenile rheumatoid arthritis, 3 ankylosing spondylitis, 3 psoriasis) presented skin manifestations in 86% of patients. The anti-TNF agent administered was etanercept in 60 (51%) cases, infliximab in 51 (43%), adalimumab in 5 (4%) and other agents in 2 (2%). Purpura was manifested in 63% of the patients, whereas others had other skin manifestations of vasculitis, such as ulcerations, nodosities, maculopapular manifestations, etc. Systemic involvement was observed in 24% of patients. Immunological examinations showed that the antinuclear antibodies (ANAs) were positive in 27 patients and antineutrophil cytoplasmic antibodies (ANCAs) in 11 patients (pANCA in 5 patients and cANCA in 1 patient). Treatment in the form of anti-TNF-alpha discontinuation was used in 11 patients, 71 of whom completely recovered (41% of them had additional immunosuppressive therapy) [33]. Mohan et al. describe in an aggregate paper including 50 patients that almost 63% of patients experienced a complete recovery of the manifestations

induction in genetically predisposed individuals.

place. Manifestations were assessed as DILE after infliximab.

after discontinuation of the anti-TNF-alpha treatment [34].

**5. Vasculitis**

vasculitis [32].

DILE induced by TNF-alpha inhibitors appears to be a separate DILE group with different signs compared to classical DILE. Women are more often affected than men, with an average age between 46.2 and 50.9 years. The average time to the manifestation of symptoms is 40.6 weeks from the commencement of drug treatment. Skin manifestations occur more frequently than in classical DILE and include butterfly erythema, photosensitivity and other skin manifestations of systemic and sub-acute lupus. The exact mechanism of DILE formation during anti-TNF-alpha treatment is unknown. Post-marketing follow-ups have demonstrated that DILE induced by TNF-alpha inhibitors may occur across all anti-TNF-alpha inhibitors. However, it is more often reported with the use of infliximab (0.19–0.22%) and etanercept (0.18%) compared to adalimumab (0.10%). An increase in ANA or anti-DNA antibodies in patients treated with anti-TNF-alpha therapy is known and relatively common [26]. The frequency of elevated ANA antibodies was higher in a greater number of patients treated with infliximab compared to a group of patients treated with etanercept [27]. Anti-dsDNA antibodies as well as ENAs (extractable nuclear antibodies) and low complement levels have been described more often than in case of classical DILE. Particularly, anti-histone antibodies have been more common in DILE induced by anti-TNF-alpha treatment [28, 29] (**Figure 2**).

The basic therapeutic procedure is the discontinuation of the treatment with the drug that induced the symptoms. In more severe conditions, it is necessary to add suppressors—corticosteroids, azathioprine, cyclosporine and methotrexate. Treatment selection is also based on the status of the underlying disease and comorbidities of the patient. In psoriasis, it is recommended to avoid systemic corticosteroids for a possible rebound phenomenon after discontinuation. There is no need to discontinue the treatment of anti-TNF-alpha in the case of ANA positivity or in very mild DILE manifestations [26]. Only limited data are available in the literature describing a switch of the treatment to another anti-TNF-alpha agent. Some authors claim that a similar reaction can be caused by any of the agents from the group of anti-TNF-alpha inhibitors [30]. As stated by Lomicova et al., an alternative treatment for chronic Immune-Mediated Skin Reactions Induced by Recombinant Antibodies and Other TNF-Alpha… http://dx.doi.org/10.5772/intechopen.72449 265

**Figure 2.** Significant facial erythema, total weakness and laboratory elevated ANA antibodies were observed. After discontinuation of the treatment, gradual regression of skin manifestations and neutralisation of ANA antibodies took place. Manifestations were assessed as DILE after infliximab.

plaque psoriasis is ustekinumab. Ustekinumab is also a good alternative in the treatment of inflammatory bowel disease and in the treatment of spondylarthritis or psoriatic arthritis [31]. However, the literature contains also cases of an ustekinumab-induced DILE. Biologics with a different mechanism of action are alternative treatments, but it cannot be said whether other mechanisms of action (anti-IL13/23, anti-IL-17, anti-IL 6) will be a potential threat to DILE induction in genetically predisposed individuals.


*Edited by Chaouki Ghenai and Tareq Salameh*

Air conditioning system is one of the major consumers of electrical energy in many parts of the world today. It represents between 40 and 70% of the energy consumption in commercial buildings. The demand of energy for air conditioning systems is expected to increase further in the next decades due to the population growth, the new economic boom, and the urbanization development. The rapid growth of air conditioning and electricity consumption will contribute further to climate change if fossil and nonrenewable resources are used. More energy-efficient and renewable energy-based air conditioning systems to accomplish space cooling are needed. This book intends to provide the reader with a comprehensive overview of the current state of the art in sustainable air conditioning technologies and focus on the most recent research and development on green air conditioning systems including energy-efficient and renewable energy-based air conditioning systems.

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

Sustainable Air Conditioning Systems

Sustainable

Air Conditioning Systems

*Edited by Chaouki Ghenai and Tareq Salameh*


**Abstract**

Although the use of general anesthesia in the obstetric population has decreased substantially, it remains the most appropriate choice in certain cases. While the use of general anesthesia is essential, maternal deaths associated with general anesthesia continue. Difficult airway remains the leading cause. Maternal mortality due to airway difficulty during general anesthesia is approximately four times higher than in general population. The incidence of failed tracheal intubation in obstetrics has remained unchanged over the past 40 years. The significant anatomic and physiologic changes of pregnancy, which are exacerbated during labor, explain the increased difficulty in airway management in obstetric patients. The presence of anesthesia staff with adequate knowledge of maternal airway management is vital to minimize the incidence of failed intubation in the parturient.

**Keywords:** obstetric anesthesia, difficult airway, airway management, failed intubation, general anesthesia


Animal models continue to be crucial in determining the genetic factors underlying SHS and COPD (**Table 1**). When considering mouse models for experimental use, the choice of strain is critical in studies related to both SHS and COPD as there are strain-related differences in the metabolism of TS as well as the inflammatory cell composition and magnitude. Vecchio et al. examined this issue by comparing C57BL/6J and Institute of Cancer Research (ICR) mice post-cigarette smoke extract exposure (Vecchio et al., 2010). They found that alveolar macrophages from C57BL/6J mice produced higher levels of ROS, NF-κB, and proinflammatory cytokines (Vecchio et al., 2010). They hypothesize that the higher pro-inflammatory response in C57BL/6J versus ISC mice is due to higher oxidative stress in this strain, leading to increased activation of NFκB. This may describe the differences in susceptibility of the different strains of mice (Vecchio et al., 2010). Cavarra et al. found that after acute TS exposure, DBA/2 and C57BL/6J mice had decreased antioxidant defenses, measured in bronchoalveolar lavage fluid, while ICR mice had increased antioxidants (Cavarra et al., 2001). After chronic exposure to TS for 7 months, they found that DBA/2 and C57BL/6J mice are more likely to develop emphysema and decreased lung elastin levels, while ICR mice did not develop these phenotypes (Cavarra et al., 2001). Tsuji et al. compared CS-exposure in AKR/J and C57BL/6J mice and found that C57BL/6J mice inhaled higher

#### **Table 1 | Factors that influence SHS-induced COPD development and progression.**

*(continued)*

*Listed in alphabetical order are proteins, receptors, and other factors which have been discovered in animal models that influence SHS-induced COPD. Their degree of influence in vivo could vary based on the experimental design; therefore the exposure models and mouse strains are also included in the table.*

amounts of smoke and more severe respiratory lesions, while AKR/J mice had higher inflammatory cytokine levels (Tsuji et al., 2011).

Our lab developed a mouse model to simulate the development of COPD and SHS (Birru et al., 2012). We separated mice into four treatment groups: filtered-air control, lipopolysacharide (LPS) to stimulate inflammation, CS, and LPS combined with CS. Mice were sacrificed after 6 months of weekly LPS and daily CS exposure. The inflammatory response, alveolar space enlargement, and lung tumor incidence were assessed. In the LPS only group, mice displayed increased inflammation, but no alveolar space enlargement (**Figure 1**). In the LPS and CS group, mice displayed enhanced inflammation and alveolar space enlargement compared to the CS only group (**Figure 1**). No groups developed tumors in this exposure model at the duration examined. Our results indicate that chronic inflammation enhances emphysema-like alveolar space enlargement.

We also developed an animal exposure paradigm using components of TS to determine the role of inflammation in the development and progression of tumor formation (Keohavong et al., 2011). We used LPS to incite inflammation and nicotinederived nitrosamine (NNK) for tumorigenesis (14). Mice were assigned into four different treatment groups: saline control, LPS only, NNK only, and LPS combined with NNK for 4 months. The saline and LPS only groups had no tumor development, but there was a six-fold increase in tumor numbers in the LPS and NNK group compared to the NNK only group. The LPS only and LPS with NNK groups displayed significantly elevated inflammation compared to the saline and NNK only groups. Our results indicate that repeated exposure to inflammation enhances the progression of TS carcinogen-induced lung tumorigenesis.

#### **CONCLUSIONS**

SHS exposure is detrimental to the lung, resulting in lung destruction through the introduction of toxic chemicals to the lung and oxidants, as well as the inhibiting the repair pathways of the lung. Continued SHS exposure can also lead to the development of inflammation, which worsen COPD, due to the abnormal polarization of T- and B-cell differentiation. The enhanced inflammatory environment of the lung can also promote tumor initiation and progression of malignant cells through the activation of transcription factors that

**REFERENCES**

A. G. (2008). Phenotypic characterisation of T-lymphocytes in COPD: abnormal CD4+CD25+ regulatory T-lymphocyte response to tobacco smoking. *Eur. Respir. J.* 31, 555–562.

promote cell proliferation and inhibit apoptosis. Both environmental factors and genetic components underlying COPD continue to be uncovered, and will be crucial in developing useful treatments for the disease. Animal models for SHS-driven COPD studies will continue to play an essential role for this objective.

#### **ACKNOWLEDGMENTS**

The work was supported by ES011033 and HL091938 from the National Institutes of Health.

and Reinhart, W. H. (2011). Effect of brief secondhand smoke exposure on endothelial function and circulating markers of inflammation. *Atherosclerosis* 215, 218–222.

IL-1alpha/IL-1R1 expression in chronic obstructive pulmonary disease and mechanistic relevance to smoke-induced neutrophilia in mice. *PLoS ONE* 6:e28457. doi: 10.1371/journal.pone.0028457

K., and Zheng, M. (2011). IL-17RA is required for CCL2 expression, macrophage recruitment, and emphysema in response to cigarette smoke. *PLoS ONE* 6:e20333. doi: 10.1371/journal.pone.0020333

Markovic, D., Glojnaric, I., and Erakovic Haber, V. (2012). Claudin-3 and clara cell 10 kDa protein as early signals of cigarette smokeinduced epithelial injury along alveolar ducts. *Toxicol. Pathol*. PMID: 22659244. [Epub ahead of print].

the ubiquitin-proteasome system. *J. Biol. Chem.* 286, 31932–31943.

tumor regression. *Cancer Cell* 6, 297–305.

development of emphysema. *Proc. Am. Thorac. Soc.* 3, 703–708.

(2011). Role of extracellular signalregulated kinase 1/2 in cigarette smoke-induced mucus hypersecretion in a rat model. *Chin. Med*. *J. (Engl.)* 124, 3327–3333.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

*Received: 14 June 2012; accepted: 09 August 2012; published online: 28 August 2012.*

*Citation: Birru RL and Di YP (2012) Pathogenic mechanism of second hand smoke induced inflammation and COPD. Front. Physio. 3:348. doi: 10.3389/fphys.2012.00348*

*This article was submitted to Frontiers in Respiratory Physiology, a specialty of Frontiers in Physiology.*

*Copyright © 2012 Birru and Di. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any thirdparty graphics etc.*

### Effects of second hand smoke on airway secretion and mucociliary clearance

#### *Yanyan Liu1,2 and Y. Peter Di 1 \**

*1 Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA, USA 2 Department of Physiology, Harbin Medical University, Harbin, China*

#### *Edited by:*

*Laima Taraseviciene-Stewart, University of Colorado Denver, USA*

#### *Reviewed by:*

*Deepak A. Deshpande, University of Maryland Baltimore, USA Hiroaki Iijima, Tsukuba Medical Center, Japan*

#### *\*Correspondence:*

*Y. Peter Di, Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Rm 322, Pittsburgh, PA 15260, USA. e-mail<EMAIL_ADDRESS>
The airway acts as the first defense against inhaled pathogens and particulate matter from the environment. One major way for the airway to clear inhaled foreign objects is through mucociliary clearance (MCC), an important component of the respiratory innate immune defense against lung disease. MCC is characterized by the upward movement of mucus by ciliary motion that requires a balance between the volume and composition of the mucus, adequate periciliary liquid (PCL) volume, and normal ciliary beat frequency (CBF). Airway surface fluid (ASL) is a thin layer liquid that consists of the highly viscous mucus upper "gel" layer, and the watery lubricating lower "sol" layer. Mucus production, secretion and clearance are considered to play a critical role in maintenance of airway health because it maintains hydration in the airway and traps particulates, bacteria, and viruses. Different types of epithelial cells, including secretory cells, and ciliated cells, contribute to the MCC function. Cigarette smoke (CS) contains chemicals and particulates that significantly affect airway secretion. Active and passive CS-induced chronic obstructive pulmonary disease (COPD) is frequently associated with hyperplasia of goblet cells and submucosal glands (SMGs), thus increasing the secretory capacity of the airways that impairs MCC.

 Tobacco use is a major risk factor for heart attacks, strokes, chronic obstructive pulmonary disease (COPD), and cancer. Approximately 90% of lung cancer cases in the USA are attributed to cigarette smoking. Similarly, the United States Centers for Disease Control and Prevention describes tobacco use as "the single most important preventable risk to human health in developed countries and an important cause of premature death worldwide." CS aerosols are highly concentrated mixtures of particles and gases. This "gas/particle partitioning" is the same type of physical, gas/liquid distribution process by which an atmospheric gas, such as nitrogen, dissolves in blood. When a CS aerosol is drawn into the respiratory tract (RT), a portion of each compound of interest (e.g., nicotine) will initially be in the gas phase, and a portion will be in the particle phase. Both of these phases can serve as pathways for the delivery of the compound to RT tissues include pharyngeal, bronchial, or alveolar regions (Pankow, 2001). There are an estimated 5000 different chemicals in tobacco smoke (Borgerding and Klus, 2005; Thielen et al., 2008). Many of them are the most significant source of toxic chemicals of chemically mediated disease in humans (Ezzati and Lopez, 2003; Fowles and Dybing, 2003). Most of these compounds are not present in the tobacco plant but are formed when the cigarette burns. Many studies provide evidence of the relationship between the amount of exposure to tar or CS and the risk for head and neck, lung and skin cancers. The most known CS carcinogens include polynuclear aromatic hydrocarbons (PAH), acrolein, and nitrosamines. The gas phase

of CS contains various gases including ammonia, carbon dioxide, carbon monoxide, hydrogen cyanide, and nitric oxide. The particle phase contains important constituents of CS, such as tar, nicotine, aromatic hydrocarbons, phenol, and cresol. The mean size of CS particles is 0.1–0.5μm, so they are capable of reaching small airways (Domagala-Kulawik, 2008). In addition, radioactive carcinogens such as lead-210 (210Pb) and polonium-210 (210Po) linger in second-hand smoke (SHS), which is deeper and longer than when inhaling cigarettes especially in an indoors environment.

SHS is the inhalation of smoke, called passive smoking, or environmental tobacco smoke (ETS), by persons other than the intended "active" smoker. It occurs when CS permeates any environment, causing its inhalation by people within that environment. SHS contains largely the same components as mainstream smoke, but with varying concentrations. SHS has been shown to produce more particulate-matter (PM) pollution than an idling low-emission diesel engine and it contains not only the gas phase of exhaled smoke, but also the products of combustion of a cigarette.  Additionally, the smoke can also enter the body through the skin, adding an additional source of exposure.

#### **HEALTH EFFECT OF SHS**

Similar to active smoking, exposure to SHS is also a significant health problem concern worldwide. SHS exposure increases nonsmokers' risk of cardiovascular disease and stroke by inducing several proatherosclerotic changes, including endothelial damage related to oxidative stress and inflammation, increased platelet aggregation, and increased arterial stiffness (Venn and Britton, 2007; Jefferis et al., 2010). SHS is also linked to several diseases of the lung, including cancer (Brownson et al., 2002; Hecht, 2006), and COPD (Eisner et al., 2006, 2009), asthma (Butz et al., 2011). Furthermore, SHS is associated with an increased risk of type 2 diabetes mellitus (Houston, 2006; Kowall et al., 2010) and with neurocellular changes (Slotkin et al., 2006) in infants with prenatal SHS exposure. Several studies show that causal associations exist between SHS and sudden infant death syndrome, acute respiratory infections, middle ear disease, asthma in children, and coronary heart disease as well as lung and sinus cancers in adults. Evidence is suggestive but not conclusive regarding a causal relationship between SHS and many other diseases. SHS is a major public health problem because more than 126 million people in the United States are exposed to SHS. Comprehensive bans on smoking in public lead to a reduction in overall exposure to SHS for both adults and children (Menzies, 2011), but the incidence of SHS exposure is still worrisome. SHS also contributes to the development of COPD in non-smokers and significantly impairs their airway secretion and mucociliary clearance (MCC).

#### **MUCOCILIARY CLEARANCE**

MCC is a self-clearing mechanism of the airway to remove inhaled pathogens and particulates. The mechanisms of bronchial secretion and MCC are critical components of lung innate immunity. Bronchial secretions are mainly produced by goblet cells and submucosal glands (SMGs), but also include small amounts of surfactant from Clara cells and other fluids that are part of the airway epithelium fluid. Cilium is present on respiratory surface epithelium, bearing hair-shaped structures on its surface (cilia). Cilia beat within a PCL layer with low viscosity for which PCL is the "sol" layer with a height that approximates the length of the outstretched cilia (about 7μm) and keeps mucus at an optimal distance from the underlying epithelia, consequently affecting the clearance of mucus (Knowles and Boucher, 2002; Tarran, 2004). The airway epithelium fluid contains many antibacterial proteins and peptides including lysozyme, lactoferrin, and β-defensins. On the top of "sol" layer is a second viscous film of mucus "gel" that traps foreign particles and microorganisms. Acute inflammatory or toxic stimuli can promote hypersecretion of mucus mediated by a large variety of cytokines and chemokines. Within the thin fluid film of mucus, the cilia act out movements coordinated in a direction toward the pharynx. Therefore the viscous film of mucus that includes its freight is transported off in the direction of the mouth, where it is either swallowed or expelled via coughing. The "gel" layer of the airway epithelium fluid is formed mainly by water, mucins (MUC), and free proteins. Mucins are highly glycosylated macromolecules. To date, more than 21 different MUC-genes have been described, at least eight of which are expressed in the RT, although MUC5AC and MUC5B are the two main gel-forming mucins secreted in the airway. Also important for good MCC are the number, structure, activity, and coordinated movement of cilia. Function of ciliary cell is essential for MCC and ciliary cells may suspend their transport function after a short time under the adverse condition of insufficient temperature and humidity, which subsequently facilitate bacterial germinal colonization. Inhaled SHS contains PM and toxic chemicals that negatively impact MCC by increasing mucus secretion and decreasing ciliated cell numbers and ciliary beat frequency (CBF). Pulmonary infections and injury to the lung tissues in COPD patients may arise when the MCC function is compromised.

#### **LUNG EPITHELIAL CELLS AND MCC**

In addition to acting as a physical barrier, airway epithelium regulates fluid balance, modulates metabolism and clearance of inhaled agents, and secretes numerous mediators (Knight and Holgate, 2003). The MCC function is a coordinated action of lung epithelial cells that include a variety of cell types such as mucous, serous, goblet, ciliated, Clara, and basal cells (**Figure 1**). Secretory cells located in airway epithelium and SMGs are an important component of MCC mechanisms in the normal lung, and alterations in the phenotype of these cells are associated with the pathogenesis of several lung diseases. In human large airways, goblet cells of the surface epithelium, as well as serous and mucous cells of the glands, are the principal secretory cell types. Serous and mucous cells may control the properties of the mucus gel by regulating the ratio between secreted proteoglycans and mucins. Airway glandular epithelium forms an integrated structure with functionally appropriate proportion of ciliated cells, goblet cells, and basal cells. A proper ciliary movement improves valid host defense and is necessary in the cleansing processes of the airway epithelium. A brief description of major types of epithelial cells is provided in the following paragraph and summarized in **Table 1**. Effects of SHS on these cells and MCC will then be discussed further.

*Mucous cells* are defined by electron-lucent acidic-mucin granules that secrete mucus into the airway to trap foreign objects such as pathogens and dust particles (Jeffery, 1983). The mucous layer present in the airway from the level of the trachea to the bronchioles consists of a mixture of highly glycosylated mucin proteins. In the normal airways, there is a fine equilibrium between mucous production and clearance. However, in chronic airway inflammatory diseases, such as chronic bronchitis and asthma, mucous cell hyperplasia and metaplasia occur, which lead to excessive sputum production.

*Goblet cells* are simple columnar epithelial cells that share multiple characteristics with mucous cells but are scattered on the surface epithelium instead of located in the secretory glands. The term goblet refers to these cells' unique "goblet-like" shape. The apical portion is shaped like a cup, as it is distended by abundant mucinogen granules; its basal portion is shaped like a stem, as it is narrow for lack of these granules. Goblet cell hyperplasia is a prominent feature in peripheral airways of smokers with both symptoms of chronic bronchitis and chronic airflow limitation (Wongsurakiat et al., 1998).

*Serous cells* are the most abundant secretory cells in human airway glands (estimated serous/mucous cell volume ratio is 60%:40%) with variable numbers of electron-dense granules that contain large quantities of enzymes. They have irregularly shaped basally oriented nuclei, a perinuclear zone containing

#### **Table 1 | Major cell types of respiratory tract epithelium.**

long

large quantities of rough endoplasmic reticulum (RER) required for protein (enzyme) manufacture. Serous cells are the primary defensive cells of the mucosa because they discharge bactericidal compounds that deal efficiently with pathogens (Basbaum and Jany, 1990; Joo et al., 2004). Serous cells secrete various antibacterial proteins including lysozyme, lactoferrin, secretory immunoglobin A, peroxidase, and protease inhibitors, many of which are cationic in nature.

*Clara cells* contain electron-dense granules and are found mostly in the small airways in humans (Knight and Holgate, 2003). To regulate bronchiolar epithelial integrity and immunity, Clara cells have been shown to produce bronchiolar surfactants and specific antiproteases, such as secretory leukocyte protease inhibitor. In addition, Clara cells can produce p450 monooxygenases (Dewater et al., 1986), which are able to metabolize xenobiotic compounds such as aromatic hydrocarbons, which are found in cigarette smoke (CS). Clara cells produce Clara cell 10-kDa protein, Clara cell 55-kDa protein, Clara cell tryptase, galactoside-binding lectin, possibly a specific phospholipase, and surfactant proteins A, B, and D.

*Basal cells* are highly abundant in both the upper and lower airways (Boers et al., 1998). Basal cells have been demonstrated to possess stem cell-like properties in that they can self-renew and give rise to secretory and ciliated epithelial cells in response to epithelial injuries (Hong et al., 2004). Thus, basal cells are thought to be the progenitor cells of lung epithelium and are potentially capable of differentiating and proliferating in many pathological circumstances.

*Ciliated epithelial cells* are columnar epithelial cells with specialized ciliary modifications and are terminally differentiated cells that originate in either basal or secretory cells (Ayers and Jeffery, 1988). Usually, there are 250–300 cilia per cell and a large number of mitochondria provide energy to the cilia for MCC via proper ciliary beating. In general, cilia are sensory organelles and motile cilia in the airway epithelium are the engine for MCC. Ciliary beats provide the required physical force to move mucus and the trapped foreign particles while the CBF determines the flow speed of the movement. SHS decreases not only ciliated cells and ciliogenesis but also CBF.

#### **EFFECT OF SHS ON MCC**

COPD is characterized by chronic obstruction of expiratory flow affecting peripheral airways, associated with chronic bronchitis (mucus hypersecretion with goblet cell and SMG hyperplasia) and emphysema (destruction of pulmonary parenchyma), together with fibrosis and tissue damage, and inflammation of the small airways (Chung, 2001; Reid and Sallenave, 2003; Hogg et al., 2004). Most COPD is caused by long-term active smoking or SHS and it has been documented that smoke significantly compromises MCC. Multiple toxins in SHS, including PM, oxidative chemicals, and organic compounds induce mucin production (Deshmukh et al., 2008) and excessive airway mucus is a hallmark feature of COPD. Airflow obstruction in COPD correlates with changes in mucin gene expression, increases in goblet-cell number and size (Innes et al., 2006), the occlusion of small airways with mucus (Sheehan et al., 1995), and expansion of the SMGs (Hogg, 2004; Hogg et al., 2004). CS-induced MCC dysfunction is complex and incompletely understood, but it involves adverse effects on the structure and function of cilia (Verra et al., 1995; Leopold et al., 2009; Tamashiro et al., 2009), activation of ErbB receptors, and proinflammatory effects that increase mucin production while decreasing mucus hydration and clearance. It is suggested that a CS-decreased MCC in COPD may lead to airway infection, which subsequently leads to inflammation and fibrosis.

One major characteristics of airway remodeling in COPD is airway goblet cells metaplasia and hyperplasia, which results in airway mucus hypersecretion. Airway goblet cell hyperplasia is a prominent pathophysiological feature of COPD and is an oftenused end point in animal models of respiratory disease (Rogers, 1997). The cellular composition of the airway epithelium can be altered both by cell division and by differentiation of one cell into another (Ayers and Jeffery, 1988). In terms of goblet cell hyperplasia, differentiation is the major pathway for producing of new goblet cells, and cell division is the major carcinogenic pathway. The basal, serous and Clara cells are considered the primary progenitor cells, because they have the capacity to undergo division, followed by differentiation into "mature" ciliated or goblet cells. In specific experimental conditions such as exposure to SHS, goblet cell division contributes in part to the hyperplasia. However, differentiation of nongranulated airway epithelial cells is a major route for production of new goblet cells (Rogers, 1994; Nadel and Burgel, 2001). In experimental animals, production of goblet cells is usually at the "expense" of the progenitor cells, most notably serous and Clara cells, which decrease in number as goblet cell numbers increase. Serous-like cells and Clara cells are found in macroscopically normal bronchioles in human lung (Rogers et al., 1993). The decreased numbers of serous and Clara cell has pathophysiological importance because these cells produce a large number of anti-inflammatory, immunomodulatory, and antibacterial molecules that are vital to host defense (Basbaum et al., 1990; Singh and Katyal, 2000). Therefore, in CS-related respiratory diseases associated with airway mucus hypersecretion and impaired MCC, it seems that not only is there goblet cell hyperplasia, with associated mucus hypersecretion, but also a reduction in serous and Clara cells, with concomitant impaired potential for host defense.

It has been supported by epidemiological data that mucus hypersecretion is significantly associated with a more rapid decline in FEV1 and increased hospitalization of patients with COPD. Among all identified mucins, MUC5AC appears to be the predominant mucin in healthy human airway epithelial cells, and its expression is augmented in smokers and COPD patients (Peter Di et al., 2012). CS induces mucin expression in cultured human airway epithelial cells (Phillips et al., 2005; Cortijo et al., 2011) and MUC5AC secretion can be regulated by several inflammatory cytokines including TNF-α and IL-13. The expression level of MUC5B is approximately 20% of that seen for MUC5AC in airway epithelial cell and it is secreted mainly by mucous cells in SMGs and partially by goblet cells. Several mechanisms have been reported to be responsible for CS-induced mucus hypersecretion. First, CS could cause mucin production via epidermal growth factor receptor (EGFR) activation both *in vitro* and *in vivo* (Takeyama et al., 2001). Then, TNF-α-converting enzyme (TACE)-proligand-EGFR signal pathway could also be involved in CS-induced mucin overproduction (Shao et al., 2004). Furthermore, CS could promote goblet cell metaplasia indirectly through activation and recruitment of neutrophils and subsequent epithelial cell oxidative stress (Fischer and Voynow, 2002). *In vivo*, neutrophils and neutrophil products can cause the upregulation and release of mucin from surface epithelial cells (Takeyama et al., 1998; Voynow et al., 2004). EGF increased MUC5AC gene expression via ERK/MAP kinase but not p38/MAP kinase in NCI-H292 cells (Takeyama et al., 2000). Extracellular signal-regulated Kinase1/2 (ERK 1/2) plays an important role in airway mucus hypersecretion induced by CS in rats (Xiao et al., 2011).

In general, animal models have been essential to the development of every drug and therapeutic used to treat of COPD. One of important reasons for using animal models to tissues and cells isolated from COPD patients is that animals provide experimental settings that allow a clearer understanding of how an active immune system interacts with whole respiratory system. There are a large number of experimental researches on drugs and therapies of COPD induced by CS in laboratory animals.  However, not all of the useful treatments in animal models have been used in humans. Actually, no one animal species can accurately model all features of human disease situations and humans normally get treated when they have more severe and sophisticated COPD than used experimentally in animal models. Current COPD animal models concentrate on emphysema rather than small airway remodeling, the key cause of airflow obstruction. It should be noted that small airway remodeling and emphysema are independent symptoms of CS that could co-exist in COPD patients.

#### **CONCLUSIONS**

CS/SHS induces airway mucus hypersecretion and inflammation through various chemical components and signaling pathways. The significantly increased mucus production and secretion result in excess sputum that may promote airflow obstruction and inflammation. CS/SHS exposure also results in composition changes in airway secretion and impairment of cilia beating that are critical to a normal MCC. Increased mucin production, decreased luminal liquid, and impaired cilia beating motion in COPD have deleterious consequences for airway health, including mucus stasis and airway infection. CS/SHS-impaired MCC results in the increased infection rate and disease severity that could be associated with COPD exacerbations.

#### **ACKNOWLEDGMENTS**

The work was supported by ES011033 and HL091938 from the *National Institutes of Health*.

### **REFERENCES**

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obstructive pulmonary disease. *Lancet* 364, 709–721.

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emphysema in mice. *Am. J. Physiol. Lung Cell. Mol. Physiol.* 296, L614–L623.

N., Sakiyalak, U., and Ruengjam, C. (1998). Diagnostic value of bronchoalveolar lavage and postbronchoscopic sputum cytology in peripheral lung cancer. *Respirology* 3, 131–137.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

*Received: 14 June 2012; accepted: 08 August 2012; published online: 28 August 2012.*

*Citation: Liu Y and Di YP (2012) Effects of second hand smoke on airway secretion and mucociliary clearance. Front. Physio. 3:342. doi: 10.3389/fphys. 2012.00342*

*This article was submitted to Frontiers in Respiratory Physiology, a specialty of Frontiers in Physiology.*

*Copyright © 2012 Liu and Di. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any thirdparty graphics etc.*

#### *Mardi A. Crane-Godreau\* and Peter Payne*

*Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA \*Correspondence<EMAIL_ADDRESS>
*Edited by:*

*Laima Taraseviciene-Stewart, University of Colorado Denver, USA*

This commentary is written to accompany a special research topic, *Second Hand Smoke and COPD: lessons from animal studies*, hosted by *Frontiers in Respiratory Physiology.*

Model systems allow researchers to study disease, to tease out cause and effect and mechanisms of action, and to conduct the preliminary studies of the safety and efficacy of treatments. The underlying objective of the research is, of course, to improve healthcare outcomes. Pointing out the difficulty of studying a disease that takes decades to develop in humans, this collection of articles focuses on what has been learned from studies using models of COPD. It also presents an opportunity to circle back to the implications of the research and to ask a most basic question: do healthcare providers recognize the impact of second hand smoke (SHS) exposure on health and, if they do, are they asking the right questions?

The 2006 Surgeon General's Report, "Health Consequences of Involuntary Exposure to Tobacco Smoke" (Surgeon General, 2006) documents the health implications of exposure to SHS, including firm evidence that SHS contributes to coronary and lung disease, lung cancer, premature death in adults, slow lung development, SIDS, asthma, and ear infections in children, as well as suggestive evidence that implicate SHS in COPD, asthma, breast cancer, and nasal sinus cancer in adults, and leukemia, lymphoma, and brain tumors in children. The report indicates that there is no risk-free level of SHS.

Despite evidence that SHS is a risk factor for disease, most healthcare organizations and many physicians fail to ask patients about their history of SHS exposure. The implications of that failure are considerable because knowledge of a patient's history of SHS exposure enables providers to make better-informed decisions about what to include in each patient's examination and lab tests, and how to conduct long-term monitoring, as well as alerting the patient to the need for measures to help them avoid further smoke exposure.

An example of a medical history of SHS exposure on health status can be seen in the development of lung disease in flight attendants, a group who historically worked in SHS filled aircraft. Recent research has revealed decreased exercise tolerance, decreased diffusing capacity with decreased pulmonary capillary recruitment as well as air trapping and airway obstruction in never-smoking flight attendants who were exposed prior to the ban on smoking in aircraft (Arjomandi et al., 2009, 2012). US aircraft became smoke-free by 1990 for flights less than 6 h, and by 2000 all US carriers were required to be smoke-free. These flight attendants, despite never smoking, have evidence of lung disease 10–20 years after their SHS exposure. For patients with a history of SHS exposure, failure of providers to include the right questions may leave risks hidden and opportunities for early intervention lost.

The American Academy of Pediatrics (AAP) has pioneered efforts to encourage physicians to ask the right questions regarding the exposure of children to SHS. Recognizing that SHS is a major contributor to childhood morbidity and mortality, the AAP has made asking about SHS exposure an essential part of regular pediatric care. This practice of asking the right questions could serve as a model for healthcare providers worldwide.

Prevention of disease progression due to SHS of course has clear implications for patients' suffering and their ability to continue to function in society. SHS exposure also has significant financial implications for healthcare payers. As the health care system in the US moves from a fee-forservice to a fee-for-results structure, prevention of disease and promotion of wellness become much more important. Early recognition of the presence of risk factors for the development of tobacco smokerelated disease enables intervention before more severe conditions arise; from the most pragmatic perspective, advanced disease is simply more costly to treat.

The importance of asking about SHS exposure is not limited to clinical care. Researchers too can improve study design and outcomes when they recognize the impact of SHS exposure. In human studies that look for risk factors for disease, the failure to ask about an individual's history of SHS exposure may lead to confusing or less significant results. For instance, when looking for the impact of smoking on cancer incidence, osteoporosis, or lung disease, placing those who have been exposed to SHS in the category "non-smoker," as many studies have done, simply makes no sense.

Additional reason for asking about a history of SHS exposure is suggested by the links between Vitamin D deficiency and the development of COPD. Our own laboratory has recently focused on the impact of Vitamin D deficiency on the development and progression of SHSrelated emphysema in a mouse model. Epidemiologic studies by Janssens and colleagues demonstrated low serum levels of 25-hydroxyvitamin D in advanced stage COPD patients, as well as an increased incidence of COPD in individuals who carry a mutation in one or more of the genes involved in vitamin D metabolism (Janssens et al., 2009a, 2011). Our model of cigarette smoke exposure with vitamin D deficiency supports the hypothesis that low levels of 25-hydroxyvitamin D may contribute to the severity of SHS-related emphysema. Given the multiple roles of vitamin D in infection, cardiovascular disease, and osteoporosis (all comorbidities of COPD), it seems prudent for health care providers to screen for vitamin D levels in at-risk patients (Holick, 2004; Lee et al., 2008; Janssens et al., 2009b). Without knowing a patient's history of SHS exposure, vitamin D screening might not be considered.

COPD is the third leading cause of death worldwide. While lung damage from COPD is irreversible, recognition of the early stages of the disease allows providers to intervene so as to slow or arrest disease progression. While smoking is widely acknowledged as a risk factor, the danger of SHS exposure is significantly underrecognized. Since the initial symptoms of COPD are hard to detect, increased awareness of SHS exposure as a risk factor should alert caregivers to screen for early signs of disease. This would give them an earlier indicator of increased disease risk and provide crucial additional time in which to mitigate the onset and progression of disease. Counseling to avoid smoke exposure, monitoring for early evidence of changes in lung function, vitamin D monitoring, and early inclusion of interventions such as exercise, respiratory training, and mind-body practices such as Qigong or Tai Chi, can all be part of a strategy to control the disease process.

There is an ongoing emphasis on improving outcomes and lowering costs of health care. The AAP has taken the lead in encouraging a simple and inexpensive approach to lowering the impact of SHS exposure: simply talking to patients about it and taking it into account when considering the patient's overall health. It's a winning strategy; asking about the history of SHS exposure as part of the course of regular care would give providers greater opportunities for early intervention and patients opportunities for improved longterm health.

#### **ACKNOWLEDGMENTS**

Research support from The Flight Attendant Medical Research Institute. FAMRI is acknowledged for its ongoing support of research in the area of SHS-associated disease.

#### **REFERENCES**

and correlates with variants in the vitamin Dbinding gene. *Thorax* 65, 215–220.

*Received: 08 January 2013; accepted: 30 January 2013; published online: 20 February 2013.*

*Citation: Crane-Godreau MA and Payne P (2013) A history of second hand smoke exposure: are we asking the right questions? Front. Physio. 4:25. doi: 10.3389/fphys. 2013.00025*

*This article was submitted to Frontiers in Respiratory Physiology, a specialty of Frontiers in Physiology.*

*Copyright © 2013 Crane-Godreau and Payne. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.*


**2. Materials and Methods**

#### *2.1. Experimental Design*

A greenhouse experiment was conducted during the winter season of 2017/2018 at the Faculty of Science (Girls Branch), Al-Azhar University (latitude 30◦03 22.3" N longitude 31◦19 25.4" E), Nasr City, Cairo, Egypt. The study aimed to test the effects of pretreatment with γ-radiation (0, 25, and 50 Gy) and foliar application of stigmasterol (0, 100, and 200 ppm) on growth, biochemical constituents, and yield characters of wheat plants (*Triticum aestivum*, L.). Wheat grains (Cultivar Sids 12) were received from the Agriculture Research Center (latitude 30◦01 13.4" N longitude 31◦12 24.2" E), Giza, Egypt. Stigmasterol, purity ≥ 95, soluble in chloroform, 50 mg/mL, MP Biomedicals, LLC, France, was used. The seeds were irradiated by gamma 60Co at different doses including 0 (non-irradiated), 25, and 50 Gray (Gy) at the Egyptian Atomic Energy Authority (latitude 30◦02 41.8" N longitude 31◦20 41.0" E), Cairo, Egypt. Wheat grains were sown on November 21 in earthenware pots (no. 50) filled with sandy soil with six replicates for each treatment. The soil texture was sandy, field capacity 11.5%, pH 8.7, EC 0.35 dSm−1, Cl− 1.7, HCO3 − 1.10, Na+ 1.2, K+ 0.25, Ca2+ 1.27%, and Mg2+ 0.58 meq L−1. Phosphorus fertilizer was added before sowing at a rate of 6.0 g per pot of calcium superphosphate (15.5% P2O5). Nitrogen fertilizer was applied in two equal portions at a rate of 0.60 g/pot for each in the form of ammonium nitrate (33.5%N) at 30 and 60 days after planting. Potassium fertilizer was applied as a soil application at the rate of 2 g/pot in the form of potassium sulfate (48–52% K2O) 45 days after planting. The foliar spray of stigmasterol treatments was applied at the vegetative stage (45 days after sowing).

#### *2.2. Growth Parameters*

At 65 days after sowing, three representative samples were collected from each treatment for detecting the tested growth traits (shoot length (cm), root length (cm), leaves (no. per plant, flag leaf area), as well as fresh and dry weights of shoot and root per plant).

#### *2.3. Photosynthetic Pigments*

According to the procedure in [26], photosynthetic pigments—chlorophyll-a (Chl *a*), chlorophyll-b (Chl *b*)—and total carotenoids in samples of wheat fresh leaves tissues using 85% acetone with 0.1 g fresh weight (FW) of wheat leaves after grinding in the solvent was measured. The homogenized samples were centrifuged at 3000 rpm, and the filtrate was topped up to 10 mL with acetone (85%). The absorbance was recorded at 663, 644, and 452 nm using a spectrophotometer (VEB, Carl-Zeiss-Promenade, Jena, Germany) using acetone as a blank. The concentration of the pigment fractions (Chl *a*, Chl *b*, and carotenoids) was accounted for as μg/mL using the following equations:

$$\text{Chl } a = \text{[(10.3 \times E663) - (0.918 \times E644)]} = \mu\text{g } \text{mL}^{-1} \tag{1}$$

$$\text{Chl } b = \text{[(19.7 \times E644) - (3.870 \times E663)]} = \text{\textdegree{\#m mL}}^{-1} \tag{2}$$

$$\text{Caroteroides} = \left(4.2 \times \text{E452}\right) - \left[\left(0.0264 \times \text{Chl } a\right) + \left(0.426 \times \text{Chl } b\right)\right] = \mu\text{g }\text{mL}^{-1} \tag{3}$$

The concentrations of chlorophylls and carotenoids were expressed as mg g−1 fresh weight (FW) of plant material. Pigment contents are represented as mg g−1 FW.


**Abdulaziz AlHazaa 1,2,\*, Ibrahim Alhoweml 1, Muhammad Ali Shar 2, Mahmoud Hezam 2, Hany Sayed Abdo 3,4 and Hamad AlBrithen 1,2,5**

Received: 6 February 2019; Accepted: 1 March 2019; Published: 6 March 2019

**Abstract:** Ti-6Al-4V and Mg-AZ31 were bonded together using the Transient Liquid Phase Bonding Process (TLP) after coating both surfaces with zinc. The zinc coatings were applied using the screen printing process of zinc paste. Successful bonds were obtained in a vacuum furnace at 500 ◦C and under a uniaxial pressure of 1 MPa using high frequency induction heat sintering furnace (HFIHS). Various bonding times were selected and all gave solid joints. The bonds were successfully achieved at 5, 10, 15, 20, 25, and 30 min. The energy dispersive spectroscopy (EDS) line scan confirmed the diffusion of Zn in both sides but with more diffusion in the Mg side. Diffusion of Mg into the joint region was detected with significant amounts at bonds made for 20 min and above, which indicate that the isothermal solidification was achieved. In addition, Ti and Al from the base alloys were diffused into the joint region. Based on microstructural analysis, the joint mechanism was attributed to the formation of solidified mixture of Mg and Zn at the joint region with a presence of diffused Ti and Al. This conclusion was also supported by structural analysis of the fractured surfaces as well as the analysis across the joint region. The fractured surfaces were analyzed and it was concluded that the fractures occurred within the joint region where ductile fractures were observed. The strength of the joint was evaluated by shear test and found that the maximum shear strength achieved was 30.5 MPa for the bond made at 20 min.

**Keywords:** TLP Bonding; Mg alloy; Ti alloy; coatings; Zinc; shear strength