Reactive oxygen-induced reactive oxygen formation during human sperm capacitation

Abstract

Physiological processes are often activated by reactive oxygen species (ROS), such as the superoxide anion (O 2 –) and nitric oxide (NO ) produced by cells. We studied the interactions between NO and O 2 –, and their generators (NO synthase, NOS, and a still elusive oxidase), in human spermatozoa during capacitation (transformations needed for acquisition of fertility). Albumin, fetal cord serum ultrafiltrate, and L-arginine triggered capacitation and ROS generation (NO and O 2 –) and superoxide dismutase (SOD) and NOS inhibitors prevented all these effects. Surprisingly, capacitation due to exogenous NO (or O 2 –) was also blocked by SOD (or NOS inhibitors). Probes used were proven specific and innocuous on spermatozoa. Whereas O 2 – was needed only for 30 min, the continuous NO generation was essential for hours. Capacitation caused a time-dependent increase in protein tyrosine nitration that was prevented by SOD and NOS inhibitors, suggesting that O 2 – and NO· also act via the formation of ONOO –. Spermatozoa treated with NO (or O 2 –) initiated a dose-dependent O 2 – (or NO ) production, providing, for the first time in cells, a strong evidence for a two-sided ROS-induced ROS generation. Data presented show a close interaction between NO and O 2 – and their generators during sperm capacitation.