New permeable cryoprotectant-free vitrification method for native human sperm

Abstract

STUDY QUESTION: Is permeable cryoprotectant-free vitrification of native sperm samples a good alternative to conventional slow freezing? SUMMARY ANSWER: The permeable cryoprotectant-free sperm vitrification protocol tested in this study renders considerably better recovery rates of good quality sperm compared to slow freezing. WHAT IS KNOWN ALREADY: Slow freezing is currently the most commonly used technique for sperm cryopreservation, though this method has been repeatedly shown to have negative effects on both structural and functional sperm features. New alternative methods such as vitrification have been established as a successful alternative in other reproductive cell types, but vitrification of spermatozoa is still a rather unexplored methodology, with limited studies showing its efficacy in male gametes. STUDY DESIGN SIZE, DURATION: This study included 18 normozoospermic sperm samples from patients seeking ART treatment between 2014 and 2015. The effects of a new vitrification protocol on functional and structural sperm quality parameters in comparison to fresh and slow-frozen samples were assessed. PARTICIPANTS/MATERIALS, SETTING, METHODS: All samples were divided into three aliquots: fresh (F), slow freezing–thawing (S) and vitrification-warming (V). Sperm concentration, motility, morphology, vitality, DNA fragmentation, cytoskeleton integrity and spontaneous acrosome reaction were assessed and compared between the groups. MAIN RESULTS AND THE ROLE OF CHANCE: Results showed improved preservation of sperm features after vitrification compared to conventional freezing. Permeable cryoprotectant-free vitrification presented a significantly higher percentage of live spermatozoa, than slow freezing, better preservation of acrosomes was achieved in vitrified samples and DNA fragmentation was reduced approximately one-third on average compared to slow freezing. Regarding tubulin assay, three different labelling patterns were observed. The frequency of these labelling patterns was similar in F and V groups but this was not the case of the S group. The multivariate analysis of all sperm quality parameters studied revealed that the V group presented features that are closer to the F group than the S group, indicating that samples are better preserved through vitrification than slow freezing. LIMITATIONS REASONS FOR CAUTION: This validation has been undertaken only on normozoospermic sperm samples. It would be necessary to compare these results in pathological samples and also to evaluate the influence of the application of this methodology on clinical outcomes. WIDER IMPLICATIONS OF THE FINDINGS: The sperm vitrification protocol here described warrants better maintenance of sperm quality parameters than traditional freezing methods and may be a good alternative to preserve sperm samples from patients seeking IVF treatment. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by IVF-Spain Foundation. The authors have no conflicts of interest to declare.