Development of an assay to assess the functional integrity of the human sperm membrane and its relationship to other semen characteristics

TLDR

Human spermatozoa swell under hypo‑osmotic conditions due to water influx and membrane expansion. The study aimed to develop a simple test to evaluate the functional integrity of human sperm membranes. A 150 mosmol mixture of equal parts fructose and sodium citrate (ionic strength 0.15) produced the maximum number of clearly identifiable swollen spermatozoa. The assay demonstrated high repeatability and accuracy, with a strong correlation (r = 0.94) between expected and observed swollen sperm and a good correlation (r = 0.90) with in‑vitro fertilization success, while correlations with conventional semen parameters were weak, indicating that hypo‑osmotic swelling is a reliable indicator of sperm functional integrity and fertilizing potential. Summary.

Abstract

Summary. The objective of this study was to develop a relatively simple test to evaluate the functional integrity of the membranes of human spermatozoa. As in some other species, human spermatozoa 'swell' under hypo-osmotic conditions due to the influx of water and the expansion of the membranes. A mixture of equal parts of fructose and sodium citrate (150 mosmol) with calculated ionic strength of 0·15 resulted in a maximal number of clearly identifiable swollen spermatozoa. Only small variations were seen when different aliquants of the same semen samples were separately evaluated. A high correlation (r = 0·94) was obtained between expected and observed values of swollen spermatozoa when known amounts of heat-treated spermatozoa, unable to undergo swelling, were added to untreated spermatozoa. A good correlation (r = 0·90) was also observed between the % spermatozoa in a semen sample that were capable of undergoing swelling and the % of denuded hamster oocytes that were penetrated by capacitated spermatozoa from the same semen sample. By contrast, the correlations between % sperm swelling in ejaculates and % normal sperm forms, % motile spermatozoa and % spermatozoa that do not stain with eosin-Y (supravital stain) in the same ejaculates were 0·30,0·61 and 0·52, respectively. Therefore, the hypo-osmotic swelling technique to evaluate the functional integrity of the sperm membrane appears to give high repeatability and accuracy and is closely correlated to the in-vitro fertilizing ability of spermatozoa. It may be a useful addition to the standard semen analysis.