Antioxidative effect of melatonin on cryopreserved ovarian tissue in mice

Abstract

Cryopreservation of ovarian tissues (OTs) has become the most effective way to preserve the fertility of female cancer patients. However, cryopreservation of OTs is still relatively at an experimental stage. The aim of study is to examine the effect of melatonin (MTL) on cryopreserved-thawed OTs. Fragments of OTs were cryopreserved in medium containing different concentrations (0 mM, 0.001 mM, 0.01 mM, 0.1 mM and 1 mM) of MLT. The endogenous enzymes (GSH-PX, GSH, SOD, CAT and T-AOC), MDA and ROS levels were all evaluated after cryopreservation. Our results showed that the 0.1 mM of MLT significantly improved the survival and diameter of follicles (P < 0.001). Meanwhile, the antioxidant enzymes activities (including GSH-PX, GSH, SOD, CAT and T-AOC) were enhanced and MDA content were significantly decreased in 0.1 mM of MLT group compared to other groups (P < 0.001). Additionally, compared to the control group, MTL of 0.1 mM resulted in a significantly lower ROS level. In conclusion, MLT protects the quality of cryopreserved OTs by decreasing oxidative stress level and the optimal concentration is 0.1 mM.

Introduction

The ovaries are important organs for female reproductive functions. Although the survival rate of cancer patients has improved with radiotherapy and chemotherapy, these cancer treatments may cause irreversible damage to the ovaries, and even cause premature ovarian insufficiency, loss of fertility and endocrine function [25]. Thus, the maintenance of long-term quality of life and fertility of cancer survivors has become a major concern. For adolescent cancer patients, cryopreservation of oocytes or embryos is not appropriate. Therefore, cryopreservation of ovarian tissues (OTs) has become an option for cancer survivors to preserve their fertility [22,25].

Cryopreservation and auto-transplantation of ovarian cortex have been widely used in the preservation and restoration of fertility in various species, including human [9]. To date, although more than 86 babies have been born worldwide through cryopreserved-thawed OTs, there are many unsolved problems [11]. For example, there is cryopreserved-thawed damage to OTs and high rates of intact follicle loss during cryopreservation [25]. In addition, reactive oxygen species (ROS) is produced during cryopreservation of OTs, which can destroy follicles and cause oxidative damage [19,28]. Studies have shown that ROS is one of the key factors affecting the cryopreservation effect of vitrification, which can induce apoptosis or dysfunction of cells, and ultimately lead to the decline of oocyte survival rate and development ability [7,16,18]. Therefore, addition of exogenous antioxidants in vitrified solution can reduce the production of ROS and the oxidative stress response [3,19,20].

Melatonin (MLT) is a neuroendocrine hormone secreted by the pineal gland. It is an effective antioxidant with a wide range of biological effects and can resist oxidative stress through a variety of mechanisms [3,19,28]. For example, MLT can be used as a scavenger of toxic oxygen derivatives and reduce the formation of ROS [19]. In addition, MLT has a variety of biological functions such as increasing gene expression or activity of other antioxidant enzymes, preventing oxidative stress damage, inhibiting lipid peroxidation and preventing DNA damage [3,19,27]. In recent years, the researches on the role of MLT in the reproductive system are increasing [3,19,27]. Our study has demonstrated interactions between NF-E2-related factor-2 (Nrf-2), heme oxygenase-1 (HO-1) and MLT, and it is suggested that MLT may have a role in the development of polycystic ovaries [28]. Recent evidence suggests that MLT has a protective effect on OTs [1,8]. However, the effect of MLT on cryopreservation of OTs is less studied.

In this study, we aim to investigate the role of MLT in protecting OTs from the negative effects of cryopreservation.