Currently, silver nanoparticles are one of the most widely used NPs in commercial products because of their strong anti-inflammatory and antimicrobial properties . The small size of nanoparticles defines their distinct target organs and bio-distribution pattern. The impact of particle size to the AgNPs toxicity on cell death and cell cycle progression has been reported [29, 30]. Particle size plays an important role on the uptake kinetics of NPs in the cells [31, 32].
In line with previous published data, the current study has demonstrated that AgNPs (25 ± 5 nm) administration to mice induced oxidative stress in their liver tissues indicated by significant elevation in MDA with concomitant increase in NO level in liver in comparison to control mice, accompanied with significant depletion in the other antioxidant parameters; GSH and SOD.
AgNPs have the ability to generate ROS/RNS that lead to oxidative stress and tissue damage. These ROS and RNS can initiate lipid peroxidation, result in DNA strand breaks, and indiscriminately oxidize all molecules in biological membranes and tissues resulting in increase in levels of MDA [33, 34].
Nitric oxide is an ambivalent agent that behaves as a mediator of inflammation and as a regulator of redox metabolism. The exposure to different AgNPs doses caused an increase of nitric oxide levels, which can be associated with either cell activation or cytochrome C release from mitochondria and apoptosis .
The antioxidants GSH and SOD can quench free radicals or serve as a substrate for other antioxidant enzymes, such as glutathione peroxidase and glutathione reductase .
The decreased levels of GSH and SOD after exposure to AgNPs and their toxic effect on the mitochondria of liver, may be due to complexing of AgNPs with thiol groups, leading to production of ROS and oxidative stress[34, 36], or to increasing use of GSH to downplay the effect of free radicals after exposure to the nanoparticles .
In this study, administration of chitosan-coated AgNPs greatly improved the level of the hepatic oxidative stress markers MDA and NO meanwhile up regulating the levels of the antioxidant markers GSH and SOD compared to their corresponding groups of AgNPs with varied significances.
This improvement may be attributed to the properties of chitosan, including its biocompatibility, bioactivity and biodegradability. In addition, the antioxidant activity of chitosan can be attributed to in vitro and in vivo free radical-scavenging activities .
In the present study, intoxication with AgNPs caused damage of liver and lead to increase in the activities of serum AST, ALT and ALP and a decrease in γ-GT enzyme level indicating a destruction of hepatocytes architecture because of oxidative stress relative to size and composition of these particles in agreement with .
The increase in AST and ALT after nanosilver exposure was in accordance with the histological findings. Hence, the increase of these enzymes is an indicator of liver damage and thus otherwise alterations in the hepatic function .
The decline observed in γ-GT enzyme is an indication of impaired GSH synthesis. In addition, γ-GT enzyme is the first enzyme in the degradation of GSH to its precursor amino acids making them available for reuptake and reutilization by the cell for GSH resynthesis .
Meanwhile, ALP enzyme elevation in serum is correlated with the presence of bone, liver, and other diseases , which may be attributed to the proliferation of bile ductules and bile canaliculi as a result of nanoparticles exposure or due to increased loss of intracellular enzyme by
diffusion through cell membranes which appears to act as a stimulus to the synthesis of more enzyme protein in agreement with [32, 43]
On the other hand, administration of chitosan-coated AgNPs to mice significantly restore AST, ALT, γ-GT and ALP activities compared to AgNPs administrated groups with varied significances. This may indicate that coating with chitosan tend to attenuate liver damage by maintaining the integrity of the plasma membranes, thereby suppressing the leakage of enzymes through membranes, exhibiting hepatoprotective activity.
The present data showed that AgNPs induced a significant elevation in α-L-fucosidase and arginase activities compared to control mice. The elevation of tumor markers and their release in the sera may result from the liver abnormalities and toxicity induced by AgNPs that leads to accumulation of glutamate or other alterations in enzymes of the glutamate-GABA (glutamate and alpha-amino butyrate) system .
The inhibitory effect of chitosan-coated silver nanoparticles on the activity of these tumor markers may indicate the significant antitumor activity of chitosan due to its non-toxic, biocompatible and bioactive properties. The antitumor mechanism of chitosan nanoparticles was related to its membrane-disrupting and apoptosis-inducing activities .
Nanoparticles are also known to up-regulate the transcription of various pro-inflammatory genes due to oxidative stress, including TNF-α, IL-1, IL-6 and IL-8, by activating nuclear factor-kappa B (NF-κB) signaling .
In this regard, the present data showed that AgNPs induced a significant elevation in TNF-α and IL-6 levels demonstrating the most inflammatory potential of AgNPs at the higher doses that can be an important sign of NP toxicity [38, 47], while chitosan-coated silver nanoparticles significantly attenuated these elevated levels, indicating that the anti-inflammatory role of this coating is associated with the oxidative damage.
Results of the current study were confirmed by studying the degree of DNA damage after AgNPs as an evidence for the stress. Comet assay showed that DNA damage, which appear like comets, increased significantly in all AgNPs administered groups compared to that of the control group. The increasing in DNA damage observed a clear induction in DNA breaks [48, 49]. However, DNA damage, appearing like comets is significantly restored in animals administered chitosan-coated silver Nano composites as a further indication of anti-apoptotic activity and significant tumor regression of chitosan coating in agreement with .
There is evidence that histological changes in liver tissue following AgNPs exposure may be associated with oxidative stress . The connection between AgNPs, behavioral changes, oxidative stress, apoptosis and histopathological modification could be ROS as the key molecules [52, 53]. Microscopic study of liver revealed that various alterations denoting the hepatotoxic effect of AgNPs including hepatocellular degeneration and focal necrobiosis in the hepatic parenchyma were the most recognized hepatic changes that were dose dependent.
Administration of chitosan-coated silver nanoparticles showed marked reduction in
histological structure of the liver compared to AgNPs administered groups. These were paralleled with the results of biochemical analysis of the present study .