Aim: To investigate whether early apoptotic changes in spermatozoa can be significant markers for sperm quality.

Methods: Two early apoptotic changes in the semen of 56 men were assessed using Annexin V (AN)/propidium iodide (PI) staining for phosphatidylserine externalization and JC-1 staining for mitochondrial membrane potential (MMP). The results were compared with conventional semen parameters and DNA fragmentation identified using the TUNEL assay.

Results: The different labeling patterns in the bivariate Annexin V/PI analysis identified four distinctive spermatozoa populations. The percentage of AN^-/PI^- spermatozoa positively correlated with conventional semen parameters and MMP, but negatively correlated with TUNEL (+) spermatozoa. As for the AN^-/PI⁺ fraction, we found an opposite result in comparison to AN^-/PI^- spermatozoa. The level of early apoptotic AN⁺/PI^- spermatozoa negatively correlated with MMP and sperm motility. The level of late apoptotic AN⁺/PI⁺ spermatozoa negatively correlated with conventional semen parameters and MMP, and positively correlated with TUNEL (+) spermatozoa. MMP positively correlated with conventional semen parameters, but negatively correlated with TUNEL (+) spermatozoa.

Conclusion: Although early apoptotic AN⁺/PI^- spermatozoa only negatively correlates with sperm motility, the differences in proportion of each subpopulation of spermatozoa (especially, the percentage of AN^-/PI^- spermatozoa), and decreased MMP might be significant markers for diagnosing male infertility. They possibly bring additional information to predict the outcome of in vitro fertilization.

Keywords: Annexin V, apoptosis, DNA fragmentation, infertility, mitochondria, sperm

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