Thymoquinone's Impact on Mercury-Induced Reproductive Derangement in Rats: An In Vivo and In Silico Study

Mercury exposure has been linked to male infertility. Given that mercury chloride (HgCl2) may promote an oxido-inflammatory milieu associated with pathophysiological derangements, it is hypothesised that thymoquinone (TQ), an anti oxido-inflammatory agent, may mitigate the gradual harmful effects of mercury exposure on rat testes, epididymis, and hypothalamus, as these organs are vital to reproductive function. To test this hypothesis, 40 male Wistar rats were randomised into five groups (n=8). After a 7-day acclimation, treatments were dispensed for 28 days as follows: Group I: control (distilled water only); Group II: HgCl2 only (20 µg/mL); Group III: TQ only (2.5 mg/kg); Group IV: HgCl2 + TQ (20 µg/mL + 2.5 mg/kg); and Group V: HgCl2 + TQ (20 µg/mL + 5 mg/kg). Co-treatment with TQ preserved the body and organ weight of the HgCl2­-exposed animals. However, TQ did not reduce HgCl2-induced dysfunction in sperm function and morphology. Co-treatment with TQ significantly (p< 0.05) increased the serum levels of follicle-stimulating hormone (FSH), luteinising hormone (LH), and testosterone while decreasing the prolactin level. TQ administration also increased (p< 0.05) the activity of testicular enzymes alkaline phosphatase (ALP), acid phosphatase (ACP), lactate dehydrogenase (LDH), and glucose-6-phosphate dehydrogenase (G6PD), decreased by HgCl2. TQ administration significantly (p< 0.05) restored HgCl2-induced decreases in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-s-transferase (GST), glutathione (GSH), and total sulfhydryl groups (TSH) levels in the testes, epididymis, and hypothalamus of experimental rats. Further, TQ reduced HgCl2-mediated increases in reactive oxygen and nitrogen species (RONS), lipid peroxidation (LPO), protein carbonyl (PC), and xanthine oxidase (XO) activity. Furthermore, levels of inflammatory biomarkers including nitric oxide (NO), tumor necrotic factor alpha (TNF-), interleukin-1 beta (IL-1), and myeloperoxidase (MPO) were significantly (p< 0.05) decreased in the co-treated groups, with a higher dose of TQ (5.0 mg/kg) showing a more pronounced protective effect. Additionally, TQ co-administration increased Bax and decreased Bcl-2 and P53 protein levels (p< 0.05), protecting rats' testes, epididymis, and hypothalamus from HgCl2-induced apoptosis. Molecular docking simulation studies showed that TQ may interact with PPAR-α and PPAR- to suppress NF-kB-mediated pro-inflammatory sequela as well as activate Nrf-2-mediated antioxidant defence system. These predicted biological effects of TQ resonate with the findings from the in vivo studies. Therefore, supplementation with TQ may help reduce chemical-induced toxicities, including HgCl2‘s reproductive toxicity.