Comparative effects of a calcium chelator (BAPTA-AM) and melatonin on cryopreservation-induced oxidative stress and damage in ovarian tissue

Prospective solutions to ovarian reserve damage during the ovarian tissue cryopreservation and transplantation procedure

Birth rates continue to decline as more women experience fertility issues. Assisted reproductive technologies are available for patients seeking fertility treatment, including cryopreservation techniques. Cryopreservation can be performed on gametes, embryos, or gonadal tissue and can be used for patients who desire to delay in vitro fertilization treatment. This review focuses on ovarian tissue cryopreservation, the freezing of ovarian cortex containing immature follicles. Ovarian tissue cryopreservation is the only available treatment for the restoration of ovarian function in patients who undergo gonadotoxic treatments, and its wide adoption has led to its recent designation as "no longer experimental" by the American Society for Reproductive Medicine. Ovarian tissue cryopreservation and subsequent transplantation can restore native endocrine function and can support the possibility of pregnancy and live birth for the patient. Importantly, there are multiple steps in the procedure that put the ovarian reserve at risk of damage. The graft is highly susceptible to ischemic reperfusion injury and mass primordial follicle growth activation, resulting in a "burnout" phenomenon. In this review, we summarize current efforts to combat the loss of primordial follicles in grafts through improvements in freeze and thaw protocols, transplantation techniques, and pharmacologic adjuvant treatments. We conducted a review of the literature, with emphasis on emergent research in the last 5 years. Regarding freeze and thaw protocols, we discuss the widely accepted slow freezing approach and newer vitrification protocols. Discussion of improved transplantation techniques includes consideration of the transplantation location of the ovarian tissue and the importance of graft sites in promoting neovascularization. Finally, we discuss pharmacologic treatments being studied to improve tissue performance postgraft. Of note, there is significant research into the efficacy of adjuvants used to reduce ischemic injury, improve neovascularization, and inhibit hyperactivation of primordial follicle growth activations. Although the "experimental" label has been removed from ovarian tissue cryopreservation and subsequent transplantation, there is a significant need for further research to better understand sources of ovarian reserve damage to improve outcomes. Future research directions are provided as we consider how to reach the most hopeful results for women globally.

Melatonin reduces oxidative stress and improves follicular morphology in feline (Felis catus) vitrified ovarian tissue

Ovarian tissue vitrification is associated with multiple events that promote accumulation of ROS (reactive oxygen species) which culminate in follicular apoptosis. Thus, this study was aimed at evaluating the role of melatonin in vitrification and culture of feline (Felis catus) ovarian tissue. In phase 1, domestic cat ovaries were fragmented into equal circular pieces of 1.5 mm diameter by 1 mm thickness and divided into four groups (fresh control and 3 treatments). The treatments were exposed to vitrification solutions supplemented with melatonin at 0 M, 10-9 M, and 10-7 M, then vitrified-warmed, histologically evaluated and assayed for ROS. Consequently, phase 2 experiment was designed wherein ovarian fragments were divided into two groups. One group was exposed to vitrification solution without melatonin and the other with 10-7 M melatonin supplementation, then vitrified-warmed and cultured for ten days with fresh ovarian fragments as control prior to assessment for histology, immunohistochemistry (Ki-67, MCM-7 and caspase-3) and ROS. Concentration of ROS was lower (p = 0.0009) in 10-7 M supplemented group in addition to higher proportion of grade 1 follicles. After culture, proportions of intact and activated follicles were higher (p < 0.05) in melatonin supplemented group evidenced by higher expression of Ki-67 and MCM-7. Follicular apoptosis was lower in melatonin supplemented group. In conclusion, melatonin at 10-7 M concentration preserved follicular morphological integrity while reducing ROS concentration in vitrified-warmed feline ovarian tissue. It has also promoted the follicular viability and activation with reduced apoptosis during in vitro culture of vitrified-warmed feline ovarian tissue.

Role of Melatonin in Ovarian Function

Melatonin is a hormone mainly produced by the pineal gland in the absence of light stimuli. The light, in fact, hits the retina, which sends a signal to the suprachiasmatic nucleus, which inhibits the synthesis of the hormone by the epiphysis. Mostly by interacting with MT1/MT2 membrane receptors, melatonin performs various physiological actions, among which are its regulation of the sleep-wake cycle and its control of the immune system. One of its best known functions is its non-enzymatic antioxidant action, which is independent from binding with receptors and occurs by electron donation. The hormone is also an indicator of the photoperiod in seasonally reproducing mammals, which are divided into long-day and short-day breeders according to the time of year in which they are sexually active and fertile. It is known that melatonin acts at the hypothalamic-pituitary-gonadal axis level in many species. In particular, it inhibits the hypothalamic release of GnRH, with a consequent alteration of FSH and LH levels. The present paper mainly aims to review the ovarian effect of melatonin.