The aim of this study was to assess the stability of nuclear and mitochondrial DNA (n-DNA and mt-DNA) of spermatozoa under freeze-thawing and to find out the correlation between them and their association with standard sperm parameters. Forty-three semen samples were collected from fertile (G.1; n = 29) and sub-fertile (G.2; n = 14). N-DNA fragmentation was determined by TUNEL assay and mt-DNA using caspase 3 staining. Each semen sample was frozen at -196°C by the programmed freezer. Freeze-thawing decrease vitality, total motility and membrane integrity from (43.02 ± 22.74%; 31.63 ± 18.15%; 51.5 ± 24.82%) to (22.71 ± 17.3%; 9.21 ± 6.61%; 34.64 ± 19.92% respectively [p < .001]). G.1 native spermatozoa stained positive with TUNEL and caspase 3 were (14.85 ± 17.6% and 5.8 ± 11.59%) and increased after freeze-thawing to 27.54 ± 19.74% (p = .004) and 7.3 ± 6.13% (p = .01) respectively. In G.2, TUNEL and caspase 3 were (19.84 ± 17.52% and 7.53 ± 8.56%) and increased to (29.48 ± 16.97% [p = .03] and 10.21 ± 11.73%). In conclusion, freeze-thawing process affects not only semen parameters but also n-DNA and mt-DNA. Therefore, n-DNA and mt-DNA could be used as sensitive parameters for assessment of the cryodamage of human spermatozoa.
Keywords: freeze-thawing; human spermatozoa; mitochondrial DNA damage; nuclear DNA fragmentation.
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