In vitro inhibition of superoxide anion production and superoxide dismutase activity by zinc in human spermatozoa

The in vitro effect of zinc on superoxide anion (O-2(-)) generation and on SOD-like activity in spermatozoa of infertile men was investigated. The for mation of superoxide anion was stimulated by NADPH and the level of superox ide anion was measured by the reduction of ferricytochrome c. Both Percoll- isolated (n = 14) and washed spermatozoa (n = 14) exposed to 1 mmol/L zinc (60 min, 37 degrees C), released less (p < 0.002 and p < 0.04, respectively ) superoxide anions than did zinc-untreated spermatozoa. These results impl icate a possible role for zinc as a scavenger of excessive superoxide anion s produced by defective spermatozoa in semen after ejaculation. Additionall y, zinc was found to dose-dependently inhibit superoxide dismutase (SOD)-li ke activity of spermatozoa in vitro. The inhibition of SOD-like activity by an equal concentration of zinc (1 mmol/L) was less pronounced in oligosper mic (p < 0.002; n = 16) and asthenozoospermic (p < 0.0005; n = 20) than in normozoospermic samples (p < 0.0001; n = 20). This differential ability of zinc to inhibit SOD-like activity may be relevant to the physiological func tion of spermatozoa in fertilization. The evidence that zinc may elicit an inhibition of both superoxide anion production and SOD-like activity in hum an spermatozoa, indicate the existence of novel, zinc-related mechanism(s) involved in the oxidative events occurring after ejaculation, with a possib le modulatory effect on germ cell function.