Zinc preserves an inherent capacity for human sperm chromatin decondensation

The effect of zinc on the nuclear chromatin decondensation ability of human, ejaculated spermatozoa was studied by exposing washed spermatozoa to the detergent sodium dodecyl sulphate (SDS) before and after sperm storage. Treatment with EDTA increased the proportion of decondensing spermatozoa before storage. Zinc supplementation before storage reversibly inhibited spontaneous decondensation as well as EDTA-enhanced decondensation. Treatment with EDTA before storage decreased the proportion of spermatozoa decondensing after storage. Zinc supplementation during storage reduced the decrease in the proportion of spermatozoa decondensing after storage. Two effects of zinc were observed: one immediate effect (reversible inhibition of the decondensation) and one long-term effect (protection of the intrinsic capacity for decondensation during storage). Both effects may be explained by a zinc-thiol interaction in the chromatin. Spermatozoal zinc is suggested to protect an inherent capacity for decondensation, thereby helping to extend the functional life-span of the ejaculated spermatozoon.