Mechanisms of reproductive toxicity and ferroptosis induced by polystyrene microplastics in male mice

Background Polystyrene microplastics (PS-MPs) attract widespread public attention due to their adverse effects on mammalian reproductive systems. However, it is currently unclear whether ferroptosis is related to testicular damage and decreased sperm quality in mice exposed to PS-MPs.

Objective To clarify the reproductive damage in male mice exposed to PS-MPs and investigate the mechanism of ferroptotic effects.

Methods Five-week-old male BALB/c mice were randomly divided into four experimental groups, including one control group and three PS-MPs groups at low dose (0.5 mg·kg⁻¹), medium dose (5 mg·kg⁻¹), and high dose (50 mg·kg⁻¹), respectively, with 6 mice in each group. The treatment was delivered by gavage for 35 consecutive days (one time per day). After the mice were neutralized, the wet weights of testis and epididymis were measured, and organ coefficients were then calculated. Sperm was counted by hematimetry, and sperm motility and adenosine triphosphate (ATP) level were evaluated using CCK-8 and CellTiter Glo ® Kit 2.0 Assay respectively. In addition, serum testosterone, follicle-stimulating hormone, and luteinizing hormone were determined using ELISA kit, total testicular iron content was measured using tissue iron kit, and pathological changes in testicular tissue were observed after hematoxylin-eosin (HE) staining. We also used glutathione (GSH), malondialdehyde (MDA), and superoxide dismutase (SOD) assays to examine their changes to better understand the physiological status of testicular tissue. Finally, the expression levels of ferroptosis-associated proteins glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) were detected by Western blotting.

Results Compared with the control group, the testicular index in the high dose group decreased, and the epididymal index decreased in all dose groups (P<0.05). The results of sperm quality analysis showed that the sperm count in each dose group was lower than that of the control group; the sperm motility decreased, sperm malformation rate increased, and ATP level in sperm decreased in the medium and high dose groups. The results of HE staining showed that the spermatogenic epithelium was disordered and the arrangement of spermatogenic cells were loose in the low dose group, the spermatogenic gap was enlarged in the middle dose group, and the cells in the high dose group were vacuolated and even azoospermic. The results of serum sex hormone levels showed that the serum testosterone levels decreased in each dose group, the serum follicle-stimulating hormone levels decreased in the medium and high dose groups, and the serum luteinizing hormone levels decreased in the high dose group (P<0.05). The iron content in the testicular tissue homogenate of the high dose group increased (P<0.05). The levels of GSH and SOD in the homogenate of testicular tissue decreased in the medium and high dose groups, while the levels of MDA increased (P<0.05). The results of Western blotting showed that the protein expression level of GPX4 in the testis in the high dose group was lower than that in the control group. The protein expression levels of SLC7A11 in the medium and high dose groups were lower than that in the control group. The results of correlation analysis showed that the expression level of GPX4 was positively correlated with sperm count, and negatively correlated with MDA level (P<0.05). SLC7A11 expression level was positively correlated with sperm count, and negatively correlated with sperm malformation rate and MDA level (P<0.05).

Conclusion PS-MPs exposure leads to decreased sperm quality, testicular damage, and decreased serum sex hormone levels in male mice, and its mechanism of action may involve ferroptosis.