RESUMO
BACKGROUND: Male factor infertility has increased to more than 40% during the last decade. About 30% of these couples are diagnosed with unexplained infertility. In fact, reactive oxygen species (ROS), especially superoxide anion (O2-·) and hydrogen peroxide (H2O2), play a crucial role in regulation of physiological and pathological processes in spermatozoa. Moreover, since the diagnosis of unexplained infertility just through semen analysis is a matter of much controversy; we aimed to evaluate the levels of ROS and sperm DNA fragmentation in the semen samples of unexplained infertile and fertile control couples. METHODS: The semen samples of 28 unexplained infertile couples and 30 fertile control couples were analyzed according to WHO criteria. The intracellular levels of H2O2 and O2-· were detected by flow cytometry with 2',7'-Dichlorodihydrofluorescin diacetate and Dihydroethidium, respectively, and DNA fragmentation was evaluated by sperm chromatin dispersion test. RESULTS: In unexplained infertile group, sperm motility and normal morphology were significantly lower than the control. The levels of sperm H2O2, O2-·, and DNA fragmentation were significantly higher in unexplained infertile men compared to fertile. Moreover, a positive correlation was found between the level of H2O2 and sperm DNA fragmentation in the unexplained infertile group. Besides, reduced sperm motility in the unexplained infertile group was significantly correlated with elevated levels of ROS. CONCLUSIONS: The higher levels of intracellular ROS and DNA fragmentation in the semen samples of unexplained infertile couples and their causes might be considered as an important factor related to diagnosis and treatment of the unexplained infertile couples.