Comparison of Sperm Telomere Length between Two Sperm Selection Procedures: Density Gradient Centrifugation and Zeta Potential

Telomeres are the sequence of DNA at the end of the eukaryotic chromosome that is essential for genome integrity. Several studies have shown that telomere length in sperm differs between individual men and individual spermatozoa. In addition, decreased telomere length in sperm from infertile men are associated with the reduction of fertility potential and embryo quality. In this regard, previous studies showed that density gradient centrifugation (DGC) and swim up are useful techniques for separation of sperm with longer telomeres. On the other hand, recent studies showed that selection of sperm based on surface negative electric charge or “Zeta potential”, can separate high percentage of sperm with intact chromatin compared to DGC alone, and also the combination of DGC-Zeta can improve clinical outcomes in infertile men candidate for intracytoplasmic sperm injection (ICSI). Therefore, we compared sperm telomere length and DNA fragmentation between two sperm preparation procedures (DGC and Zeta).

In this experimental study, we assessed sperm telomere length and DNA fragmentation by quantitative Real-time PCR and TUNEL assay, respectively in prepared spermatozoa by either DGC or Zeta method of fifteen infertile men with normozoospermia from September 2017 to December 2017. Sperm telomere length was expressed as relative, and absolute.

When the results compared to washed semen samples or control, we did not observe any significant difference in mean of relative or absolute sperm telomere length after DGC or Zeta method (P>0.05). While the mean percentage of DNA fragmentation was significantly lower in both DGC or Zeta methods compared to control (P<0.05).

This is the first study that compared the effect of DGC and Zeta sperm preparation methods on sperm telomere length and concluded that both these methods can select sperm population with high DNA integrity and same sperm telomeres length.