The production of peroxynitrite by human spermatozoa may affect sperm motility through the formation of protein nitrotyrosine

OBJECTIVE: To detect peroxynitrite and 3-nitrotyrosine production in human spermatozoa of asthenozoospermic infertile patients and normospermic donors, and evaluate any influence on kinetic sperm features. DESIGN: Basic study. SETTING: Andrology Unit, Dept of Internal Medicine and Biochemistry Institute, Polytechnic University of Marche, Italy. PATIENT(S): Sixty-nine infertile patients affected by idiopathic asthenozoospermia and 29 normal fertile donors. INTERVENTION(S): No therapeutic intervention was performed on patients. MAIN OUTCOME MEASURE(S): Production of peroxynitrite (ONOO-) and 3-nitrotyrosine by human spermatozoa; kinetic sperm cells parameters. RESULT(S): Normospermic fertile donors exhibited ONOO- concentrations significantly lower than those of asthenozoospermic infertile men (9.11 +/- 3.37 vs. 27.46 +/- 5.77 nmol/10(6) cells); confocal microscopy showed that ONOO- was more evident in spermatozoa of patients than in healthy donors. Moreover, a significant negative correlation was evident between ONOO- concentration and total sperm motility, curvilinear velocity (VCL), straight progressive velocity (VSL), and linearity coefficient. Finally, an increase was found in the nitration of the tyrosine residues in asthenozoospermic samples compared to controls. CONCLUSION(S): Spontaneous tyrosine nitration occurs in human spermatozoa. This post-translational protein modification is enhanced by an overproduction of peroxynitrite, which is more evident in asthenozoospermic infertile patients when compared with normospermic fertile donors. Motility parameters are negatively affected, suggesting that ONOO- may be involved in defective sperm function.