## 4 Discussion
However, MDA, GSH, GST, GPX, and SOD in species exposed to toxic substances are regarded as reliable biomarkers and can serve as essential diagnostic tools for evaluating xenobiotic exposure and its effects. According to [PERSON] et al. (2005) [58], MDA is the most abundant aldehyde resulting from lipid peroxidation. This aldehyde can be considered a significant indicator of lipid peroxidation [59]. Malondialdehyde has been shown to induce cross-linking and polymerization of membrane components and may contribute to mutagenic and genotoxic effects. These effects result from the impairment of antioxidant defense mechanisms, including detoxification and scavenging enzymes, as well as increased lipid peroxidation following the interaction between reactive oxygen species and cell membranes [60]. Our findings supported previous studies indicating that treatment with SiNPs significantly triggered oxidative stress and induced an increase in MDA [61]. Our results demonstrated a significant increase in MDA levels in liver, kidney, and heart tissues following the injection of SiNPs. This increase may result from elevated levels of reactive oxygen species, which can attack polyunsaturated fatty acids in the cell membrane, leading to lipid peroxidation [62]. The rise in reactive oxygen species could be attributed to either an increase in their production or a reduction in their elimination, potentially due to the depletion of antioxidant scavenging systems, as previously reported [63]. Glutathione is the major non-enzymatic antioxidant in animal cells. It is the most abundant sulfur-containing reducing compound in the intracellular compartment and is involved in metabolism, transport processes, and cell protection against the toxic effects of both endogenous and exogenous compounds, including reactive oxygen species and heavy metals [64]. GSH plays a pivotal role in the detoxification of free radicals and heavy metals. Our results indicated a significant reduction in GSH levels in the studied organs (liver, kidney, and heart) following exposure to SiNPs. Several other studies conducted on these nanoparticles have also reported a decrease in this parameter in the liver and kidney cells of male rats in vivo [65]. Regarding glutathione S-transferase, an enzyme responsible for catalyzing the conjugation of glutathione (which possesses a nucleophilic -SH group) with a wide variety of compounds (carrying electrophilic groups) and also involved in the transport and removal of reactive compounds while performing other antioxidant functions, GST activity has been extensively used as a stress biomarker [66]. This enzyme plays a crucial role in the detoxification of xenobiotics, demonstrating a high capacity to reduce lipid peroxides [67, 68] and protect against harmful metabolites generated after the degradation of macromolecules following exposure to oxidative stress [69]. Our results indicate a decrease in GST activity following the injection of SiNPs. This decrease can be attributed to the significant role of GST in catalyzing the conjugation of electrophilic substrates with glutathione to protect the cell against the effects of xenobiotics [70]. Our findings are consistent with those of [PERSON] et al. (2010) [71], who conducted their research on MRC-5 cells. These authors suggested that these cells were capable of coping with oxidative stress induced by SiO\({}_{2}\) nanoparticles. Furthermore, our results unequivocally demonstrated a decrease in superoxide dismutase enzyme activity in the livers, kidneys, and hearts of SiNP-injected rats compared to the healthy control rats. The reduction in SOD activity, a key component of cellular antioxidant defenses, results from the conversion of superoxide anion into oxygen and hydrogen peroxide, which is a potentially toxic compound. Catalase represents the second stage of the enzymatic defense system. It functions to convert hydrogen peroxide, previously produced by superoxide dismutases, into water. CAT plays a crucial role in protecting the body against oxidative stress damage.