DNA integrity is maintained after freeze-drying of human spermatozoa

Abstract

Objective: To evaluate the effects on human spermatozoa of freeze-drying, also known as lyophilization, and of cryopreservation in liquid nitrogen.

Design: Prospective experimental study.

Setting: Reproductive medicine unit and a private IVF center.

Patient(s): Thirty healthy male donors.

Intervention(s): Sperm samples from 30 donors divided as two aliquots, one to be lyophilized and the other to be cryopreserved in liquid nitrogen.

Main outcome measure(s): Assessment of count, motility, morphology, viability, DNA integrity, chromosomal status, and birefringence properties of lyophilized and cryopreserved human spermatozoa compared with the same parameters in the fresh sample.

Result(s): Although sperm viability and motility were totally compromised after freeze-drying, the sperm chromatin structure was not altered in comparison with fresh samples, which demonstrated that the procedure did not affect DNA integrity. The sperm-head inner protoplasmic structures were also preserved, which was estimated by assessing the corresponding birefringence characteristics. After cryopreservation with liquid nitrogen, the motility, viability, and DNA integrity of spermatozoa were statistically significantly reduced compared with the fresh samples; the proportion of sperm cells with abnormal head birefringence increased meaningfully.

Conclusion(s): The process of freeze-drying deeply damages cell membranes; however, unlike with liquid nitrogen preservation, it does not affect DNA integrity.