Impact of peroxynitrite-mediated nitrosative stress on human sperm cells

Nitrosative stress is caused by high levels of reactive nitrogen species (RNS) and among the most toxic RNS is peroxynitrite. In infertile men there is an association between high levels of peroxynitrite and decreased sperm quality; however, less is known about the specific cellular impairment caused by peroxynitrite in sperm cells. The aim here was to characterize the in vitro effect of peroxynitrite on human sperm. For this, spermatozoa were exposed to 3-morpholinosydnonimine, a compound that generates peroxynitrite, and several parameters of sperm quality and biochemical markers of cell death were assessed. Untreated sperm were included as controls. At early incubation times peroxynitrite exposure caused a decrease in mitochondrial membrane potential, ATP level and motility while thiol oxidation and tyrosine nitration increased. At prolonged incubation time viability decreased and DNA oxidation, DNA fragmentation and ultrastructural damage increased. Mitochondrial permeability transition (MPT) was induced while caspase activation and phosphatidylserine externalization were not evidenced. These results indicate that peroxynitrite exposure impairs sperm function and ultrastructure and lead to the appearance of biochemical markers of cell death compatible with MPT-driven necrosis