Reactive oxygen-induced reactive oxygen formation during human sperm capacitation

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.