Oxidative state and zona-binding ability in mouse spermatozoa treated with reduced glutathione

Background and Aims: Nuclear proteins in mature mammalian spermatozoa nuclei are oxidized to form numerous disulfide bonds. Reduced glutathione (GSH) in the oocyte has been linked to spermatozoan nuclear decondensation after fertilization. In this study, we analyzed whether GSH reduced protamines in sperm nuclei in vitro, and examined the zona-binding ability of treated nuclei. Methods:  Three groups of mouse cauda epididymal spermatozoa were prepared. The first group was cultured in Chatot-Tasca-Ziomek (CZB; control group), the second in 10 mmol/L GSH (GSH group), and the third group was the GSH group re-cultured in CZB (re-cultured group). Each sperm was stained with acridine orange, and the oxidative and reductive state of nuclei was analyzed by using fluorescence microscopy. Furthermore, we examined the zona-binding ability for each group by insemination to mouse oocytes after exposure to hyaluronidase. Results:  All sperm nuclei from the control group displayed an oxidized pattern (green), and those from the GSH group displayed a reduced pattern (red), attributable to reduced protamines. Sperm nuclei from the re-cultured group displayed the oxidized pattern. Although the zona-binding ability of the GSH group was deteriorated compared with the control group sperm, no significant differences were observed between the control and re-cultured groups. Conclusion:  From these results, in vitro reduced sperm were shown to be oxidized in CZB. A reduction of mouse spermatozoa in vitro by GSH is, therefore, reversible, and the oxidative state of sperm nuclei exerts an effect on zona-binding ability. (Reprod Med Biol 2002; 1: 55-58).