In vitro effect of zinc on oxidative changes in human semen

Summary The in vitro effect of zinc on superoxide anion (O₂^?) generation and on experimentally induced lipid peroxidation (LPO) in spermatozoa of infertile men was investigated. Washed spermatozoa pre-incubated for 30 min at 37°C in the presence of 1 or 3 mmol l^-1 zinc, released less superoxide anions (P<0.03 and P<0.02, respectively; n=9) than the untreated spermatozoa. Similar results were obtained using activated polymorphonuclear leukocytes (1 times 10⁶ cells ml^-1) in the presence of 1 or 3 mmol l^-1 Zn (P<0.001 and P<0.0002, respectively; n=9). The in vitro evidence of the inhibitory effect of zinc on O₂^? generation by human spermatozoa and leukocytes indicates that zinc may act in vivo as a scavenger of excessive O₂^? production by defective spermatozoa and/or leukocytes in semen after ejaculation. A significant stimulatory effect of Zn (3 mmol l^-1) on iron-induced lipid peroxidation, measured by the formation of thiobarbituric acid reactive substances (TBARS), was detected in the spermatozoa of 16 normo- and 17 asthenozoospermic males (P<0.0001 and P<0.001, respectively). In 11 samples with sperm concentration 20.3±2.1 times 10⁶ ml^-1, exhibiting initial TBARS concentration two times higher than in normo-and asthenozoospermic samples (40.5±2.4 vs. 17.1±1.1 and 28.5±4.1 nmoles TBARS 10^-8 spermatozoa), no effect of zinc on the LPO rate was found. The observed inhibitory effect of zinc on superoxide anion regardless of the initial O₂^? level and stimulatory effect of zinc depending on the initial LPO rate in human spermatozoa suggests that this metal ion participates in the oxidative changes occurring after ejaculation and thus may modulate the properties of germ cells.