Subchronic Cadmium-Induced Xenobiotic Toxicity in Male Wistar Rats: Antioxidant and Reproductive Protection by Standardized Silymarin with Molecular Docking Insights

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Abstract
Cadmium is a widespread environmental xenobiotic that poses serious risks to hepatic, renal, and male reproductive functions. Natural compounds such as silymarin, a bioactive extract from Silybum marianum, have gained attention for their protective potential against xenobiotic-induced toxicity. This study investigated whether subchronic oral administration of silymarin (30 mg/kg) mitigates cadmium-induced toxicity (5 mg/kg) in adult rats over six weeks. Twenty-four rats were assigned to four groups: control, cadmium-exposed, silymarin-treated, and co-treated. Biochemical, hematological, oxidative stress, and reproductive parameters were assessed. Sperm quality was evaluated using CASA, and testicular tissues were examined histologically. Cadmium exposure significantly reduced body weight (−30.8%), elevated transaminases (AST, ALT; p < 0.01), increased serum creatinine and total cholesterol, and induced multi-organ oxidative stress, as reflected by elevated malondialdehyde and markedly reduced SOD, CAT, and thiol group levels in testicular, hepatic, and renal tissues (p < 0.01). Sperm concentration dropped from 75.2 to 21.8 × 106/mL, with total motility falling to 35% and progressive motility to 18%, accompanied by severe seminiferous tubule degeneration (Score III in 5 rats). Co-administration of silymarin partially restored these parameters, sperm concentration recovered to 38.5 × 106/mL, total motility improved to 50.2%, and antioxidant enzyme activities and liver/kidney biomarkers showed significant but incomplete recovery (p < 0.05). Molecular docking revealed favorable binding affinities of silybin toward GPx (−8.4 kcal/mol), CAT (−8.3 kcal/mol), and SOD (−6.4 kcal/mol), offering a preliminary computational hypothesis suggesting possible interactions between silybin and antioxidant enzymes, pending experimental validation. Silymarin alone exerted no adverse effects. These findings establish silymarin as a partial but promising multi-organ cytoprotectant against cadmium toxicity, and highlight the need for future studies optimizing dosing strategies, exploring longer treatment durations, and investigating combination approaches with metal chelators or Nrf2-activating agents to achieve complete tissue recovery.

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