The larvicide temephos decreases the fertilization rate of rat spermatozoa by altering different processes of the acrosome reaction and actin polymerization.

Temephos is a larvicide used in health campaigns against disease vectors, classified as slightly toxic. However, it has adverse effects on sperm function, the mechanisms of which are unknown. During fertilization, sperm are capacitated and proteins undergo tyrosine phosphorylation (p-Tyr), followed by actin cytoskeleton remodeling, which is important for the acrosome reaction (AR). Finally, IZUMO1 relocation during the AR is essential for gamete fusion. This study aimed to investigate the mechanism by which temephos decreases fertilization in male rats exposed to 10 or 100 mg/kg/day/5 days (WHO-NOAEL and LOAEL, respectively) and sacrificed 1-day after treatment. Sperm cells were collected from the cauda epididymis-vas deferens. No effects were observed with 10 mg/kg/day/5 days. However, at 100 mg/kg/day/5 days, the fertilization rate decreased (22%) and the chlortetracycline assay showed a decrease in Ca2+ ionophore-induced AR (49%), suggesting that functional AR was impaired. This was confirmed by the decrease in p-Tyr and actin polymerization, which reduced IZUMO1 relocation. Furthermore, significant increases in protein serine and threonine phosphorylation (p-Ser and p-Thr) were observed, which may contribute to these effects. These results suggest that temephos exposure reduced the fertilization rate by decreasing sperm capacitation and actin polymerization, thereby affecting AR and IZUMO1 migration.