Melatonin protects human spermatozoa from apoptosis via melatonin receptor- and extracellular signal-regulated kinase-mediated pathways.

To evaluate whether the protective effect of melatonin on H2O2-induced caspase activation and DNA fragmentation depends on the interaction between melatonin and its surface receptors. Laboratory study. Center for assisted human reproduction at a Spanish hospital. Twenty-one healthy donors. Human spermatozoa were treated with increasing concentrations of hydrogen peroxide (H2O2; 1 μM, 10 μM, 100 μM, 1 mM) and preincubated with 1 mM melatonin. Activation of caspase-3 and -9 as well as DNA fragmentation were examined by fluorescence methods. Our findings showed that H2O2 induced a significant increase in caspase-9 and caspase-3, which was dose independent. Conversely, pretreatment with melatonin reduced H2O2-mediated caspase activation in a dose-dependent way. Moreover, the antiapoptotic effects of melatonin in ejaculated human spermatozoa may involve membrane melatonin receptor MT1. In addition, we found that the survival-promoting pathway extracellular signal-regulated kinase (ERK) is likely to have a role in the protective actions of melatonin in ejaculated human spermatozoa. Finally, we confirmed these results further by demonstrating that melatonin prevention of H2O2-induced DNA fragmentation is dependent on both MT1 receptor and ERK signaling. These results indicate that the stimulation with melatonin triggers a set of events culminating in cell death prevention in ejaculated human spermatozoa. Copyright © 2011 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.