Efficacy of zinc oxide nanoparticles in chemical castration of male Wistar rats.

This study investigated the dose-dependent effects of intratesticular zinc oxide nanoparticles (ZnO NPs) on reproductive toxicity in male Wistar rats, evaluating their potential as a chemical castration agent. Fifty rats, weighing 250-300 g and aged 12-14 weeks, were divided into five groups: control, sham (normal saline), and ZnO NPs at 5 mg/mL, 10 mg/mL, and 25 mg/mL. ZnO NPs (< 100 nm) were dissolved in saline and injected into the caudal testis. After 60 days, assessments included testicular oxidative stress markers (total antioxidant capacity [TAC], catalase [CAT], glutathione peroxidase [GPx], superoxide dismutase [SOD], malondialdehyde [MDA], nitric oxide [NO]), epididymal sperm parameters (count, motility, viability, morphology, DNA integrity, plasma membrane functionality), histopathological and morphometric evaluations (Johnsen/Cosentino scores, seminiferous tubule diameter [STsD], Sertoli cell index [SCI], repopulation index [RI], meiotic index [MI], Leydig cell nuclear diameter [LCND], tubular differentiation index [TDI], spermiogenesis index [SPI]), apoptosis-related gene expression (Caspase-3, Caspase-8, Caspase-9, Fas, Bcl-2 via quantitative real-time polymerase chain reaction [qRT-PCR]), and fertility indices post-mating. Results revealed dose-dependent impairments: reduced sperm concentration, motility, viability, and membrane integrity; increased DNA damage and morphological abnormalities; depleted antioxidants with elevated MDA/NO; severe histopathological changes including tubule atrophy and cell loss; upregulation of pro-apoptotic genes and downregulation of Bcl-2; and reduced fertility with higher implantation losses. While ZnO NPs exhibit beneficial effects, such as antioxidant and antimicrobial properties at low concentrations (typically < 5 mg/mL or 1-50 mg/kg in oral/intraperitoneal studies), they become toxic at higher doses (≥ 10 mg/mL in this intratesticular model), primarily through oxidative stress and apoptosis. These findings, despite species-specific and route-dependent variations, underscore ZnO NPs' detrimental impact on spermatogenesis, emphasizing the need for cautious application to mitigate risks to male fertility.