Mitochondrial membrane potential integrity and plasma membrane translocation of phosphatidylserine as early apoptotic markers: a comparison of two different sperm subpopulations.

Objective: To examine whether a relationship exists between loss of mitochondrial transmembrane potential and plasma membrane translocation of phosphatidylserine (PS) in subpopulations of human spermatozoa of men consulting for infertility.

Setting: A tertiary institutional research center.

Design: Prospective observational study.

Patient(s): Twelve infertile men and five fertile controls were compared.

Intervention(s): Sperm subpopulations were compared after density gradient separation.

Main Outcome Measure(s): Mitochondrial membrane potential was measured with a cationic dye, translocation of PS was evaluated with Annexin-V binding, and motion parameters were assessed manually.

Result(s): In both the study and control groups and compared with the high-motility fraction, the low-motility fraction had significantly lower sperm motility and normal morphology, and significantly higher percentage of cells with disrupted mitochondrial membrane potential and plasma membrane PS translocation. There was a positive and significant correlation in both subfertile and control groups between the percentages of Annexin-V+ live cells and cells with mitochondrial membrane potential disruption (r = 0.82 and r = 0.85, respectively).

Conclusion(s): The correlation of plasma membrane PS translocation and loss of mitochondrial membrane potential is suggestive of an early apoptosis phenotype, as is typically observed in somatic cells identified in sperm subpopulations with percentage of low-motile cells. We speculate that such changes might be used as diagnostic markers of sperm dysfunction(s) and that increased levels found in subfertile men might be indicators of reduced fertility potential.