Addition of zinc to human ejaculate prior to cryopreservation prevents freeze-thaw-induced DNA damage and preserves sperm function

Purpose: To study the effect of addition of zinc to human semen sample prior to cryopreservation on post-thaw sperm quality and function. Methods: Semen samples were collected from men attending university infertility clinic for semen analysis (n=109). Liquefied semen samples were cryopreserved in glycerol-egg yolk- citrate medium with or without the prior addition of zinc (100 μM) and stored in liquid nitrogen. After 10 days, the semen samples were thawed to assess the outcome. Sperm motility, DNA integrity, mitochondrial potential and the ability of spermatozoa to undergo capacitation and acrosome reaction was assessed in post-thaw samples. Results: Semen samples cryopreserved after addition of zinc had a significantly higher percentage of sperm with intact DNA (p<0.001), mitochondrial function (p<0.001) and progressive motility (p<0.01) compared to the semen samples cryopreserved without zinc supplementation. Apart from this, ability to undergo capacitation and acrosome reaction in vitro was significantly higher in semen samples cryopreserved with zinc (p<0.0001 and p<0.001 respectively). Conclusions: Addition of zinc to semen samples prior to cryopreservation helps in preventing the freeze-thaw-induced sperm DNA damage and loss of sperm function.