Involvement of oxidative stress in tri-ortho-cresyl phosphate-induced autophagy of mouse Leydig TM3 cells in vitro

Background: As a plasticizer, plastic softener, and flame-retardant, tri-ortho-cresyl phosphate (TOCP) is and has been widely used in industry and reported to have a toxic effect on the male reproductive system in animals besides neurotoxicity and immunotoxicity. We have reported that TOCP inhibits spermatogenesis and induces autophagy of rat spermatogonial stem cells, but it is still unknown whether TOCP induces autophagy of mouse Leydig cells and its potential mechanism. Methods: Cell viability was observed by MTT assay. Level of testosterone was measured by radioimmunoassay. Apoptosis was observed by AnnexinV-FITC/PI assay. The contents of LC3, Atg5-Atg12, and Beclin 1 were detected by Western blotting analysis. Autophagosomes were investigated by transmission electron microscopy. The contents of MDA and GSH and the activities of SOD, GSH-PX, total antioxidant status (TAS) and total oxidant status (TOS) were measured by oxidative stress kits. Results: The present study shows that TOCP markedly inhibited viability and testosterone output of mouse Leydig TM3 cells but had no effect on apoptosis. However, TOCP significantly increased both LC3-II and the ratio of LC3-II to LC3-I and the contents of autophagy proteins Atg5 and Beclin 1. Transmission electron microscopy (TEM) showed that TOCP increased autophagic vacuoles of the cytoplasm, indicating that TOCP could induce autophagy of the cells. TOCP significantly induced oxidative stress of mouse Leydig TM3 cells. H2O2 also inhibited viability and induced autophagy of the cells; however, inhibition of oxidative stress by N-acetyl-L-cysteine (NAC) could rescue the inhibition of cell viability and induction of autophagy by TOCP. Conclusions: The results show oxidative stress might be involved in TOCP-induced autophagy of mouse Leydig TM3 cells.