Experimental and molecular docking evidence for the protective role of Monascus purpureus red pigments against hydroxyapatite nanoparticle-induced testicular injury in male rats

Hydroxyapatite nanoparticles (HANPs) are increasingly utilized in biomedical and technological fields due to their biocompatibility and structural similarity to bone mineral. However, accumulating evidence indicates that prolonged exposure to HANPs may adversely affect the male reproductive system through oxidative stress, inflammation, apoptosis, and dysregulated autophagy. This study investigated the protective role of Monascus purpureus red pigments (RP), naturally derived bioactive compounds with antioxidant and anti-inflammatory properties, against HANP-induced testicular damage in adult male rats. Animals were orally treated with HANPs (88.3 mg/kg), RP (10, 20, or 40 mg/kg), or their combination for 50 days. Reproductive toxicity was assessed by analyzing semen quality, serum reproductive hormones, oxidative and inflammatory markers, apoptotic activity, expression of key autophagy-related genes (Beclin-1, LC3B, ULK1, and ATG9), and testicular histopathology. HANPs exposure caused significant reproductive impairment, evidenced by deteriorated semen parameters, disrupted testosterone, follicle-stimulating hormone and luteinizing hormone levels, elevated oxidative stress, increased NF-κB and caspase-3 activity, and upregulation of autophagy-related genes, accompanied by marked histopathological damage. Co-administration of RP markedly attenuated these alterations in a dose-dependent manner, with the highest dose (40 mg/kg) restoring reproductive function, redox balance, inflammatory and apoptotic status, autophagy signaling, and testicular architecture toward near-control levels. Molecular docking analysis revealed strong binding affinities of the major RP components, monascorubramine and rubropunctamine, to the autophagy-related protein LC3B, supporting a potential mechanistic role in autophagy modulation. Collectively, these findings demonstrate that M. purpureus RPs effectively protect against HANP-induced testicular toxicity through coordinated antioxidant, anti-inflammatory, anti-apoptotic, and autophagy-regulatory mechanisms.