Influence of semen processing technique on human sperm DNA integrity

To compare the effects of density-gradient centrifugation and swim-up technique on sperm DNA integrity.

Semen samples (n = 22) were obtained from consecutive nonazoospermic men presenting for infertility evaluation. Individual samples were divided into three aliquots (whole semen, density-gradient centrifugation, and swim-up) for subsequent analysis of sperm motility and DNA integrity. Sperm DNA integrity was evaluated by flow cytometry analysis of acridine orange-treated spermatozoa and expressed as the percentage of spermatozoa demonstrating denatured DNA.

Mean sperm motility (+/-SEM) improved significantly after processing with two-layer density-gradient and swim-up compared with whole semen (65.6% +/- 4.0% and 73.0% +/- 3.0% versus 52.0% +/- 3.6%, respectively, P <0.005), with no significant difference in motility between Percoll-treated and swim-up-treated spermatozoa. In contrast, the percentage of spermatozoa with denatured DNA was reduced significantly in swim-up-treated but not in Percoll-treated spermatozoa compared with whole semen (4.8% +/- 1. 2% and 13.6% +/- 3.6% versus 10.1% +/- 2.3%, respectively, P <0. 0001).

Although density-gradient centrifugation is comparable to swim-up technique in recovering spermatozoa with enhanced motility, spermatozoa recovered after swim-up possess higher DNA integrity. These data urge us to reexamine our current sperm processing techniques in order to minimize sperm DNA damage.