Micro- and nanoplastics as emerging disruptors of Leydig cell function: A systematic review of experimental evidence

Plastic particles have been detected in human testicular tissue, raising concerns about potential effects on male reproductive health. This systematic review synthesizes experimental evidence from mammalian in vitro and in vivo studies evaluating the effects of MNP exposure on Leydig cell structure and function. A systematic search of PubMed, Scopus, Embase, and Web of Science identified 19 eligible studies. Study selection, data extraction, and risk-of-bias assessment were performed independently by two reviewers using ToxRTool for in vitro studies and SYRCLE for in vivo studies. Certainty of evidence was evaluated using the GRADE framework. Across experimental models, MNP exposure was associated with particle internalization, oxidative stress, mitochondrial and endoplasmic reticulum dysfunction, reduced cell viability, activation of apoptotic pathways, and impaired testosterone synthesis. Together, the available experimental evidence supports the biological plausibility that MNP exposure may impair Leydig cell function and testosterone synthesis, although the overall certainty of evidence remains limited.