Cryopreservation of spermatozoa is becoming more important because of new clinical requirements and current clinical practice. Despite the success of sperm cryopreservation this routinely used procedure induces serious detrimental changes in sperm function. Some researchers believe that cryopreservation is associated with DNA fragmentation and DNA single strand breaks in sperm. Mechanisms of cryodamage to human spermatozoa are thought to be multifactorial including: cold shock, osmotic stress, intracellular ice crystal formation, oxidative stress, and combinations of these conditions. Additives showing antioxidative properties reported to reduce the impact of ROS-induced and cold shock damages. Many studies exist as regards the effects of antioxidants on the cryopreservation aimed at improving the quality of post-thaw semen. Hence, this review will clarify results of recent applications of various antioxidants used in numerous research efforts to improve cryopreservation of spermatozoa. This review is to increase the understanding of the roles of these antioxidants concerning mechanisms which enhance resistance to cryodamage of spermatozoa.

Biochemical and physical modifications during the freeze-thaw process adversely influence the restoration of energy-dependent sperm functions required for fertilization. Resveratrol, a phytoalexin, has been introduced to activate 5' AMP-activated protein kinase which is a cell energy sensor and a cell metabolism regulator. The cryoprotection of resveratrol on sperm cryoinjury via activation of AMP-activated protein kinase also remains to be elucidated. Our aim, thus, was to investigate: (i) the presence and intracellular localization of AMP-activated protein kinase protein; (ii) whether resveratrol may exert a protective effect on certain functional properties of fresh and post-thaw human spermatozoa through modulation of AMP-activated protein kinase. Spermatozoa from normozoospermic men were incubated with or without different concentrations of Compound C as an AMP-activated protein kinase inhibitor or resveratrol as an AMP-activated protein kinase activator for different lengths of time and were then cryopreserved. AMP-activated protein kinase is expressed essentially in the entire flagellum and the post-equatorial region. Viability of fresh spermatozoa was not significantly affected by the presence of Compound C or resveratrol. However, although Compound C caused a potent inhibition of spermatozoa motility parameters, resveratrol did not induce negative effect, except a significant reduction in motility at 25 μm for 1 h. Furthermore, resveratrol significantly increased AMP-activated protein kinase phosphorylation and mitochondrial membrane potential and decreased reactive oxygen species and apoptosis-like changes in frozen-thawed spermatozoa. Nevertheless, it was not able to compensate decreased sperm viability and motility parameters following cryopreservation. In contrast, Compound C showed opposite effects to resveratrol on AMP-activated protein kinase phosphorylation, reactive oxygen species, apoptosis-like changes, mitochondrial membrane potential, and motility parameters. These findings, although preliminary, suggest that resveratrol-induced improvement of cryopreserved sperm functions may be mediated through activation of AMP-activated protein kinase, indicating the importance of AMP-activated protein kinase activity for human spermatozoa functions. Further investigations are required to elucidate the mechanism by which resveratrol ameliorates oxidative stress-mediated damages in an AMP-activated protein kinase-dependent mechanism.

Cryopreservation of spermatogonial stem cells (SSCs) is an applicable method for young males seeking fertility preservation before starting a treatment. It increases reactive oxygen species (ROS) formation and oxidative stress, which damages cellular structures. In this study, we added two antioxidants, catalase and α-tocopherol (α-TCP), to the basic freezing medium to evaluate their effects on the efficiency of SSCs. SSCs were isolated from testes of 3- to 6-day-old male mice using enzymatic digestion. The enrichment of isolated cells was evaluated by flow cytometry and Stra8 antibody. Catalase (40 μg/mL), or α-TCP (200 μg/mL) was added to the basic freezing medium. The cell viability was evaluated by the methylthiazoltetrazolium (MTT) assay. After thawing, cells were cultured for 1 month, and the expression pattern of specific genes of SSCs and the ability of the cells to restore spermatogenesis were used to determine the efficiency of the cryopreservation method. The survival rate of the frozen cells in the presence of catalase or α-TCP was significantly higher than the control group (p < 0.05). The number of colonies and their diameter measured after 1 month were significantly higher in the antioxidant groups than in the control group (p < 0.05). Gene expression and resumption of spermatogenesis also followed the same pattern. Thus, adding antioxidants to the basic freezing medium can be helpful in increasing the quality and viability of SSCs after cryopreservation. This new approach to stem cells cryopreservation can also be a promising strategy for fertility preservation in patients who suffer from malignancy.

AMHR-II: anti-müllerian hormone receptor-II; 3β-HSD: 3β-hydroxysteroid dehydrogenase; Cyp11a1: Cytochrome P450 Family 11 Subfamily A Member 1; Cyp19a1: cytochrome P450 aromatase; DHEA: dehydroepiandrosterone; FSH: follicle stimulating hormone; FSHR: follicle stimulating hormone receptor; IVF: in vitro fertilization; 25OHD: 25-hydroxy vitamin D; OHSS: ovarian hyperstimulation syndrome; PCOS: polycystic ovarian syndrome; P450scc: P450 side-chain cleavage enzyme; StAR: steroidogenic acute regulatory protein; VDRs: vitamin D receptors.