Reproductive toxicity and preliminary mechanism of polystyrene nanoplastics in male mice

To analyze the effect of subchronic exposure of polystyrene nanoplastics（PS-NPs）on reproductive function in adult male mice, and to explore the preliminary molecular mechanism of its impact on testosterone synthesis.

Sixty 8-week-old C57BL/6 male mice were fully randomly divided into control group（deionized water）and PS-NPs low（10 mg/kg, 10 PS）and high exposure group（40 mg/kg, 40 PS）, with 20 mice in each group. The mice were treated once per day for 60 d by gavage. The weights and organ coefficient of the testes, epididymis, brain, liver, spleen, lung and kidney of each group of mice were weighed and calculated at 24 h after the last exposure. HE staining was used to analyze the histopathological differences of testicular tissue, and transmission electron microscopy was used to observe the ultrastructural changes of testicular cells. The computer assisted sperm assay system was used to analyze semen parameters, the contents of serum testosterone（T）, luteinizing hormone（LH）and follicle-stimulating hormone（FSH）were detected by enzyme-linked immunosorbent assay（ELISA）, and the expression levels of key genes for T synthesis, which had been screened by transcriptome sequencing, were determined in testicular tissues by real-time PCR.

Compared with the control group, the weight of the epididymis in the 40 PS group was increased significantly（P<0.05）, the testicular organ coefficients of mice in the 10 PS group and the epididymis organs coefficients of mice in the 40 PS group were increased obviously（P<0.05）, and the weight and organ coefficients of the liver and spleen of the mice in the 10 PS and 40 PS groups were decreased remarkably（P<0.05）. The pathological results showed that compared with the testis of the control group, the lumen of the semininogenic tubule in the 10 PS and 40 PS groups were enlarged, the semimatogenic cells were loose, and the vacuoleization was increased. Transmission electron microscopy displayed that mitochondrial swelling and endoplasmic reticulum expansion were observed in the cytoplasm of Leydig cells in 10 PS and 40 PS groups. The sperm motility of mice in the 10 PS group was decreased significantly compared with the control group（P<0.05）. The serum T level of mice in the 10 PS and 40 PS groups was decreased, with that of the 40 PS group more significant（P<0.05）. The serum LH and FSH levels of mice in the 10 PS and 40 PS groups were increased notably. Compared with the control group, the mRNA levels of CYP11A1 in the testes of mice were significantly down-regulated in both 10 PS and 40 PS groups（P<0.05）.

PS-NPs can cause damage to the testes pathologically and functionally in mice, and may reduce T synthesis by inducing structural abnormalities of Leydig cells and down-regulating CYP11A1 expression.