Date Published: December 13, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Marlea Di Santo, Nicoletta Tarozzi, Marco Nadalini, Andrea Borini.
Cryopreservation of human spermatozoa—introduced in the 1960’s—has been recognized as an efficient procedure for management of male fertility before therapy for malignant diseases, vasectomy or surgical infertility treatments, to store donor and partner spermatozoa before assisted reproduction treatments and to ensure the recovery of a small number of spermatozoa in severe male factor infertility. Despite the usefulness of it, cryopreservation may lead to deleterious changes of sperm structure and function: while the effects of cryopreservation on cells are well documented, to date there is no agreement in the literature on whether or not cryopreservation affects sperm chromatin integrity or on the use of a unique and functional protocol for the freezing-thawing procedure. Therefore, sperm cryopreservation is an important component of fertility management and much of its successful application seems to affect the reproductive outcome of assisted reproduction technologies (ART): appropriate use of cryoprotectants before and sperm selection technologies after cryopreservation seem to have the greatest impact on preventing DNA fragmentation, thus improving sperm cryosurvival rates.
The procedure that makes it possible to stabilize the cells at cryogenic temperatures is called cryopreservation, also known as an applied aspect of cryobiology or the study of life at low temperatures. Many advances in the cryopreservation technology have led to the development of methods that allow for low-temperature maintenance of a variety of cell types including male and female gametes, small multicellular organisms, and even more complex organisms such as embryos. Cryopreservation of human spermatozoa—introduced in the 1960’s —has overcome many space and time limitations and now forms integral part of assisted reproduction technologies (ARTs).
There are two main conventional freezing techniques used in sperm cryopreservation: slow freezing and rapid freezing
Compared with other cell types, spermatozoa seem to be less sensitive to cryopreservation damage because of the high fluidity of the membrane and the low water content (about 50%). Despite this, cryopreservation may lead to deleterious changes of sperm structure and function . It was largely reported that several damaging processes could occur during freezing-thawing of human spermatozoa, such as thermal shock with formation of intracellular and extracellular ice crystals, cellular dehydration, and osmotic shock .
Cryopreservation is widely known to raise impaired sperm motility and decrease fertilization rate through detrimental effects on membranes, acrosomal structure, and acrosin activity . The freezing-thawing procedure of human spermatozoa may also be detrimental to the chromatin structure , leading to a potential risk of decondensation of the sperm nucleus after injection into the oocyte, thus, reducing fertilization rate . However, a cumulative effect of cryopreservation on sperm fertilization capacity is not definitely established. Considering the decrease in sperm fertilization power induced by cryopreservation, it can be easily understood that intrauterine insemination and conventional in vitro fertilization (IVF) with frozen-thawed spermatozoa result in lower pregnancy rates compared with insemination with fresh sperm : this is the reason why cryopreservation of semen samples before intrauterine insemination or conventional IVF is not recommended.
Today, sperm cryopreservation is widely used to store donor and partner spermatozoa before assisted reproduction treatments, to preserve spermatozoa before therapy for malignant diseases, vasectomy, or surgical infertility treatments and to ensure the recovery of a small number of spermatozoa in severe male factor infertility. Therefore, sperm cryopreservation is an important component of fertility management, and much of its successful application seems to affect the reproductive outcome of ART.