Hepatitis B Virus S Protein Enhances Sperm Apoptosis and Reduces Sperm Fertilizing Capacity In Vitro

OBJECTIVE: Studying the impact of Hepatitis B virus S protein (HBs) on early apoptotic events in human spermatozoa and sperm fertilizing capacity. METHODOLOGY/PRINCIPAL FINDINGS: Spermatozoa were exposed to HBs (0, 25, 50, 100 µg/ml) for 3 h, and then fluo-4 AM calcium assay, Calcein/Co(2+) assay, protein extraction and ELISA, ADP/ATP ratio assay, sperm motility and hyperactivation and sperm-zona pellucida (ZP) binding and ZP-induced acrosome reaction (ZPIAR) tests were performed. The results showed that in the spermatozoa, with increasing concentration of HBs, (1) average cytosolic free Ca(2+) concentration ([Ca(2+)](i)) rose; (2) fluorescence intensity of Cal-AM declined; (3) average levels of cytochrome c decreased in mitochondrial fraction and increased in cytosolic fraction; (4) ADP/ATP ratios rose; (5) average rates of total motility and mean hyperactivation declined; (6) average rate of ZPIAR declined. In the above groups the effects of HBs exhibited dose dependency. However, there was no significant difference in the number of sperms bound to ZP between the control and all test groups. CONCLUSION: HBs could induce early events in the apoptotic cascade in human spermatozoa, such as elevation of [Ca(2+)](i), opening of mitochondrial permeability transition pore (MPTP), release of cytochrome c (cyt c) and increase of ADP/ATP ratio, but exerted a negative impact on sperm fertilizing capacity.