Segregation of sperm subpopulations in normozoospermic infertile men

Sperm function is essential for fertilization and embryogenesis yet semen contain a heterogeneous population of sperm. This study was designed to evaluate two different sperm populations separated by the density gradient method. Semen from 25 idiopathic normozoospermic infertile men was processed by double density gradient centrifugation and evaluated for sperm present in the 50% (upper) layer and the 90% (lower) layer for reactive oxygen species (ROS), sperm chromatin integrity, and morphology. The population of sperm in the 90% layer showed significantly lower ROS levels (22.90 (0.92, 85.32) vs. 382.03 (158.30, 1409.51) and lower DNA fragmentation index (DFI) (24.26 (22.54, 25.50) vs. 29.93 (28.48, 31.25) and higher number of sperm with normal morphology (55 (45.0, 60.0) vs. 32.5 (20, 40) compared to sperm in the 50% layer. However, in the original raw semen, sperm DFI (27.02 (26.19, 27.76)) and percentage high DNA stainability (% HDS) (3.1 (2.40, 3.78)) cells were significantly higher compared to the 90% layer population. Density gradient separation of the sperm subpopulation from the original semen favors the selection of sperm with genome integrity, low levels of ROS, and normal morphology. Therefore presence of pathological sperm in the semen may disrupt the function of normal spermatozoa, and hence the selection of the normal sperm subpopulation may be a better candidate for assisted conception. Further studies are required to evaluate the gradient separated sperm population in assisted reproductive techniques (ART).