Effects of cryopreservation on phosphatidylserine translocation, intracellular hydrogen peroxide, and DNA integrity in canine sperm

Evaluating cryoinjury of canine spermatozoa is crucial to improving the probability of fertilization. Recently, studies on sperm ROS production, phospholipid scrambling, and DNA damage induced by cryopreservation have been reported. However, the consequences of cryopreservation on these crucial factors are lacking with respect to canine semen. Therefore, the current study was designed to investigate the effects of the freezing-thawing procedure on these factors in canine semen. Ejaculates from five dogs were cryopreserved and thawed. Spermatozoa before and after a freezing-thawing process were assessed for phosphatidylserine (PS) translocation (Annexin V AN]/propidium iodide PI] assay), intracellular H₂O₂ level (dichlorofluorescein DCF]/PI assay), DNA integrity (sperm chromatin structure assay), and conventional sperm parameters. The freezing-thawing process decreased motility, viability, normal morphology, and membrane integrity in canine sperm (P < 0.05). The frozen-thawed semen also showed a decrease in AN−/PI− sperm (%) and an increase in the PS translocation index, the intracellular H₂O₂ level in the viable sperm fraction, and the DNA fragmentation compared with that of fresh semen (P < 0.05). In conclusion, the freezing-thawing procedure significantly affects PS translocation, the intracellular H₂O₂ level, and DNA integrity in canine semen, which may explain the lower fertilization rate and in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) outcome when frozen-thawed spermatozoa are used. It is therefore recommended that these parameters be used as an additional parameter for the assessment of sperm quality after freeze-thawing in canine semen.