Apoptosis and necrosis in human ejaculated spermatozoa

Background: Features of both apoptosis and necrosis have been reported in ejaculated human spermatozoa. This study examines the relative contribution of these two modes of cell death to the demise of these terminally differentiated cells. Methods: Sperm fractions were prepared from aliquots of semen samples from young normozoospermic donors by simple washing from seminal plasma, by discontinuous density gradient centrifugation or by swim-up technique. They were subsequently incubated in vitro at 37degreesC for 24 h. Sperm motility, viability, and the presence of two apoptotic markers, phosphatidylserine externalization (annexin-V binding) and DNA fragmentation (TUNEL), were examined before incubation and again after 4 and 24 h of incubation. Results: The swim-up technique was the most efficient in terms of the recovery of viable, motile and non-apoptotic spermatozoa, followed by density gradient centrifugation and finally simple washing. No changes in the parameters tested were observed after 4 h of incubation, but a significant decrease in sperm motility and viability was detected after 24 h irrespective of the sperm preparation technique employed. However, these changes were not accompanied by any increase in the incidence of spermatozoa showing markers of an active apoptotic process. Conclusions: Healthy human ejaculated spermatozoa appear incapable of initiating apoptosis, at least under in vitro conditions.