Processing of semen by density gradient centrifugation selects spermatozoa with longer telomeres for assisted reproduction techniques

The ends of eukaryotic chromosomes contain specialized chromatin structures called telomeres, the length of which plays a key role in early human embryonic development. Although the effect of sperm preparation techniques on major sperm characteristics, such as concentration, motility and morphology have been previously documented, the possible status of telomere length and its relation with sperm preparation techniques is not well-known for humans. The aim of this study was to investigate the role of density gradient centrifugation in the selection of spermatozoa with longer telomeres for use in assisted reproduction techniques in 105 samples before and after sperm processing. After density gradient centrifugation, the average telomere length of the sperm was significantly longer (6.51 ± 2.54 versus 5.16 ± 2.29, P < 0.01), the average motile sperm rate was significantly higher (77.9 ± 11.8 versus 44.6 ± 11.2, P < 0.01), but average DNA fragmentation rate was significantly lower (11.1 ± 5.9 versus 25.9 ± 12.9, P < 0.01) compared with raw semen. Additionally, telomere length was positively correlated with semen sperm count (rs = 0.58; P < 0.01). In conclusion, density gradient centrifugation is a useful technique for selection of sperm with longer telomeres.