Protective Effects and Potential Mechanisms of D-Aspartate on Testicular Damage Induced by Polystyrene Microplastics

Polystyrene Microplastics (PS-MPs) affect testicular activity, as evidenced by increased oxidative stress, apoptosis, and autophagy activation, impairing steroidogenesis and spermatogenesis. The present study investigates, for the first time in vivo, the potential protective effect of D-aspartate (D-Asp) against PS-MPs-induced damage on the testicular function of adult rats. D-Asp, well-known stimulator of testosterone biosynthesis and spermatogenesis progression, possesses pharmacological properties, including antioxidant and anti-apoptotic ones. The results showed that PS-MP's adverse effects on testicular activity were reversed by D-Asp treatment. Mechanistically, D-Asp inhibited testicular oxidative stress by modulating the protein levels of CAT, SOD1, SOD2, and 4-HNE; affecting TBARS levels; and reducing apoptosis, as suggested by CYT C analysis and a TUNEL assay. Furthermore, D-Asp administration mitigated PS-MPs-induced autophagy activation by modulating the expression of LC3BI, LC3BII, and p62 proteins. Finally, the amino acid counteracts PS-MPs damage on steroidogenesis and spermatogenesis by restoring normal levels of steroidogenic (StAR, 3 beta-HSD, and 17 beta-HSD) and spermatogenic (PCNA and SYCP3) markers. This study encourages further research to understand the potential value of the amino acid in improving human testicular health and male fertility.