D-ASPARTATE ALLEVIATES THE TESTICULAR DAMAGE INDUCED BY POLYSTYRENE MICROPLASTICS

Over the last three decades, a significant decline in male reproductive health has been linked to increasing exposure to environmental contaminants. Among these, polystyrene microplastics (PS-MPs) have the ability to accumulate in testicular tissue in mice and rat models, impairing reproductive functions through oxidative stress, inflammation, and apoptosis. Therefore, the attention has focused on the potential protective agents against reprotoxicity induced by environmental pollutants. D-Aspartate (D-Asp), an endogenous amino acid present in the testes, has been shown to exert antioxidant and anti-apoptotic activities and, more importantly, it is known to play a fundamental role in male fertility by activating steroidogenesis and spermatogenesis through increase of the expression of steroidogenic enzymes and proteins of germ cell proliferation, respectively. The present study investigates, for the first time, the potential protective effect of D-Asp against PS-MPs-induced damage on the testicular function. The experimental design consisted of D-Asp oral treatment, performed contemporaneously or given at different times with PS-MPs, to adult rats. The results demonstrated that the adverse effects of PS-MPs on testicular function were reversed by D-Asp treatment, indicating that D-Asp mitigates PS-MP-induced toxicity. Specifically, D-Asp reduced testicular oxidative stress by modulating the expression of antioxidant enzymes (CAT, SOD1, SOD2) and oxidative stress markers (4-HNE, TBARS), as well as by decreasing apoptosis, as evidenced by CYT C expression and TUNEL assay results. Additionally, D-Asp administration attenuated PS-MP-induced autophagy by regulating the levels of LC3BI, LC3BII, and p62 proteins. Analysis of steroidogenic (StAR, 3β-HSD, 17β-HSD) and spermatogenic (PCNA, SYCP3) markers, along with sperm quality parameters, further supported the protective role of D-Asp in restoring normal steroidogenesis and spermatogenesis after PS-MPs testicular damage. This study is the first to provide evidence of the protective action of D-Asp against testicular dysfunction induced by PS-MPs.