the small sizes of the nanoparticles and large surface to volume ratio put the nanoparticles in a position for tremendous and wide applications essentially in biomedicine . though the small sizes of engineered nanoparticles have been linked with highly desirable properties ( mechanical , electrical , and chemical ) for specific uses , yet these same desirable properties are also likely to be associated with unwanted biological / toxicological reactivity .
although metal nanoparticles have received increasing attention due to their widespread medical , consumer , industrial , and military applications , studies have correlated particle size of some metal - based nanoparticles ( e.g. , ag , au , and cu ) with toxicity , even if the same material is relatively inert in its bulk form [ 2 , 3 ] .
indeed , there are increasing concerns about the safety of nanoparticles for human health and environment [ 46 ] , highlighting the need for further investigations on the safety of metal nanoparticles .
moreover , data on the safety / toxicity profiles of metal nanoparticles are scarce . perhaps , the fears of health risks may not be completely unfounded , if the small sizes and the large surface area to volume ratio as well as the chemical reactivity and/or biological activity of the nanoparticles are to be considered .
also there are studies revealing the potential of nanoparticles to alter normal physiology by interacting with biomolecules in living cells [ 79 ] thereby causing adverse effects at the cellular , subcellular , and protein levels .
furthermore , nanoparticles enter the human body through ingestion , inhalation , and skin contact or genitourinary tract and become deposited in vital organs such as brain , liver , or kidneys [ 10 , 11 ] .
studies have shown that nanoparticles may change or damage cellular processes by passing through cellular membranes to interact with biomolecules leading to dna and protein damage [ 12 , 13 ] or cross the blood - brain barrier to cause neurotoxicity .
these factors underscore the urgent need for investigations aimed at establishing the influence of nanoparticles on biochemical parameters .
the present study determined the effect of the oral administration of silver nanoparticle on some biochemical parameters in wistar rats .
alanine aminotransferase ( alt ) , aspartate aminotransferase ( ast ) , and alkaline phosphatase ( alp ) assay kits were supplied by randox laboratory ( crumlin , uk ) .
all other reagents were of analytical grade and were prepared in distilled water unless otherwise stated .
male rats of wistar strain weighing between 170 and 180  g were obtained from the university of ibadan , ibadan , nigeria .
animals were housed in hygienic environment and allowed to acclimatize for a week before commencement of treatments .
the preparation and characterization of silver nanoparticles were as previously reported [ 15 , 16 ] .
briefly , the agnps were made by adding 100  mm silver nitrate to a 1% ( w / v ) tannic acid solution ( ph adjusted to 8 by adding 150  mm potassium carbonate ) of polyvinylpyrrolidone ( pvp ) with stirring .
the agnps were filtered using the 0.22  m filter and characterized by uv / vis spectrophotometry ( biotek epoch , usa ) , inductively coupled plasma optical emission spectrometry ( icp - oes , cambridge , united kingdom ) , and transmission electron microscopy ( tem , brno , czech republic ) .
groups b , c , and d each were daily administered with 100 , 1000 , and 5000  mg / kg agnps , respectively , for 7 days . 
groups e , f , and g each were daily administered with 100 , 1000 , and 5000  mg / kg agnps , respectively , for 14 days . 
groups b , c , and d each were daily administered with 100 , 1000 , and 5000  mg / kg agnps , respectively , for 7 days .
groups e , f , and g each were daily administered with 100 , 1000 , and 5000  mg / kg agnps , respectively , for 14 days .
doses were fixed based on a recent report which demonstrated that the ld50 for silver nanoparticles ( agnps ) was greater than 5000  mg / kg . all treatments were orally administered with the aid of a cannula and animals sacrificed alternately 24 hours after cessation of treatments .
the study was carried out in accordance with institutional guidelines on the handling of animals as approved for scientific research .
24 hours following cessation of last treatments , rats were sacrificed under anaesthetization in slight chloroform .
blood samples were obtained by cardiac puncture into clean centrifuge bottles and spun at 4000  g for 5 minutes ( heraeus labofuge 300 , thermo scientific , hampshire , uk ) to yield the serum . the heart , liver , and kidneys from each animal were excised and weighed immediately .
excised tissues were homogenized in ice - cold 0.25  m sucrose ( 1  :  5 w / v ) using a teflon homogeniser ( sigma - aldrich chemie gmbh , munich , germany ) . the tissue homogenates were centrifuged at 4000  g for 5 minutes ( heraeus labofuge 300 , thermo scientific , hampshire , uk ) to remove unbroken particulates .
the following biochemical parameters were determined in rat serum , kidney , liver , and heart using a uv / vis spectrophotometer ( shimadzu , kyoto , japan ) where applicable ; protein concentrations in serum and tissue homogenates were estimated as described by gornall et al . .
aspartate aminotransferase ( ast ) was determined using commercial randox kit [ 19 , 20 ] .
data were subjected to statistical analysis using one - way anova with graphpad prism 3.0 ( graphpad software inc . , san diego , ca ) .
the agnps had a maximal uv absorption at 430  nm with diameter sizes ranging between 8 and 20  nm ( figure 1 ) .
treatment with agnps at the dose of 5000  mg / kg caused dullness in the rats , with one death recorded in the same group .
the relative organ - to - body weight ratios for the animals are presented in table 1 .
there are no significant differences when comparing between the agnps treatment groups and the control .
the weights of the rats treated with silver nanoparticles increased at all concentrations ( figure 2 ) .
however , the weight increments were only significant in the 1000  mg / kg for 14 days as well as the 5000  mg / kg for 21 days .
treatment of rats with agnps caused elevation ( p < 0.05 ) in total protein levels in rat liver ( figure 3 ) .
in contrast , the levels of total protein were reduced in rat serum , kidney , and heart for groups treated with agnps . oral exposure of rats to agnps at various concentrations inconsistently altered the serum and tissue levels of alp relative to the control ( figure 4 ) . in the serum , level of alp increased with increasing length of treatment administration .
in contrast , nonsignificant reductions were recorded for tissue levels of alp caused by agnps treatments .
for all the agnps treatment groups , the rat serum and tissue levels of ast were inconsistently affected relative to the control ( figure 5 ) .
conversely , there was significant ( p < 0.001 ) reduction in the levels of alt in rat serum which was dose and duration dependent ( figure 6 ) . on the other hand ,
the rat kidney and heart levels of alt were not significantly altered by agnps treatment relative to control .
humans can be exposed to these nanomaterials via a number of routes with the nanoparticles tending to accumulate in vital organs . according to gatti , nanoparticle deposition in vital organs or tissues
the death could have been accidental . however , treatment at 5000  mg / kg agnps caused dullness in rats .
the physical observation supports previous report   which reported no death and no effect on the percentage weight gain between the control and treatment groups of mice orally given 5,000  mg / kg of colloidal agnps .
, enzyme assays play a crucial role in toxicological evaluation . in the past several years
, serum aminotransferases analyses have become a standard measure of hepatotoxicity because of the significance of these enzymes .
normally , these enzymes are present in the liver and other tissues where they function in energy metabolism involving the transamination of amino acids . however , in cases of cellular damage , the ast and alt could leak out into the general circulation leading to elevated activity [ 2426 ] . in the present study ,
the treatment of rats with 100  mg / kg agnps decreased ( p < 0.001 ) levels of ast and alt enzyme significantly , whereas there were increases ( p < 0.001 ) in ast levels in serum , kidney , and heart for the 14- and 21-day treatment groups .
treatment of rats with 1000  mg / kg and 5000  mg / kg agnps led to a significant decrease in alt levels and a significant increase in ast levels for the 14- and 21-day treatment groups .
in contrast , ast levels significantly decreased while alt levels increased in rat serum treated with colloidal agnps for 7 days when compared with those treated for 21 days .
this study also caused elevated ( p < 0.05 ) levels of rat serum alp levels .
the effect of the oral administration of agnps to rats on alp , ast , and alt did not follow a definite pattern but may suggest partial inactivation of enzyme activity or depression of enzyme synthesis . although the liver has been reported as one of the recurrent target organs and a dominant site of accumulation of nanoparticles , the alterations to the levels of enzymes may represent adaptive mechanisms by the animals trying to offset stress imposed by exposure to the agnps .
the dosages at 100  mg / kg produced more significant alterations to the biochemical parameters than did the higher dosages at 1000 and 5000  mg / kg , respectively .
however , a previous study has demonstrated that administration of agnps to rats caused significant alterations to the alp levels .
furthermore , alterations to the levels of ast , alt , or alp may not be unconnected with the affinity of agnps for thiol groups in protein molecules . moreover , a separate study by srivastava et al .  
has also demonstrated the potential of agnps to affect the activity of transaminase enzymes . in separate studies , the potential of silver nanoparticles to modulate enzyme activity was attributable to their affinity for thiol groups [ 15 , 16 ] .
it is probable that thiol groups in the enzymes made them attractive to the agnps leading to formation of complexes and consequent modulation of enzyme activity .
furthermore , the pronounced biochemical alterations noticed with the 100  mg / kg agnps in the present study may not be completely consistent with earlier report   in which agnps had an ld50 of > 5000  mg / kg in mice .
the administration of agnps in rats did not induce major changes in body weight and feed intake . however , this study is evidence indicating that rat tissue biochemical indices were altered following oral exposure to agnps .
future studies are ongoing and target the determination of whether the alterations to the biochemical parameters were signs of agnps toxicity or not .
 
 background . 
 silver nanoparticles have found wider and increasing biomedical applications due to their broad antimicrobial characteristics 
 . however , toxicity of nanoparticles is a subject of continued controversy , thus necessitating further studies in this direction . objectives . 
 this study investigated the biochemical effects of silver nanoparticles in wistar rats . 
 materials and methods . 
 forty male rats were randomly distributed into eight experimental groups of five . 
 group a served as the control and received distilled water . 
 groups b to h were orally exposed to varying concentrations of silver nanoparticles ( agnps ) at 100 , 1000 , and 5000  mg / kg daily for 7 , 14 , and 21 days alternately . following cessation of treatments , 
 rats were sacrificed and the blood and other vital organs were collected and prepared as specimens for biochemical analysis . results . 
 administration of agnps to rats did not produce significant loss in feed intake and body weight . 
 however , rat exposure to agnps caused significant alterations to levels of serum and tissue ast , alt , and alp . at the 100  mg / kg agnps exposure , rat serum and tissue ast and alt levels were significantly decreased ( p < 0.05 ) . 
 in contrast , agnps administration elevated ( p < 0.05 ) alp levels in rat serum and tissues . 
 conclusion . 
 we show evidence that agnps administration to wistar rats altered some biochemical parameters . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion
5. Conclusion