INFLUENCE OF OXIDATIVE STRESS ON OOCYTE QUALITY AND PROTECTIVE ROLE OF MELATONIN AS AN ANTIOXIDANT

Abstract

Poor oocyte quality is a critical factor of female infertility. Reactive oxygen species are produced within the follicle especially during the ovulatory process. It has been reported that oxidative stress may be a cause of poor oocyte quality. Melatonin, a pineal hormone, is detected in the human follicular fluid. Recent reports have shown that melatonin works as a potent radical scavenger. This study was undertaken to examine a relationship between oxidative stress and poor oocyte quality and whether melatonin improves oocyte quality as an antioxidant. To investigate the effect of oxidative stress and melatonin on oocyte maturation, oocytes were recovered from preovulatory follicles 48 h after injection of 10 IU of equine chorionic gonadotropin (eCG) in immature ICR mice. Oocytes were then incubated in the presence or absence of hydrogen peroxide (H2O2; 1, 10, 100, 1000 μM). After 12 h incubation, oocytes with a first polar body were defined as mature oocytes. The percentage of the mature oocytes was significantly decreased (0%) by addition of H202 (≥10 μM) compared with control (62%). When oocytes were incubated with H202 (10 μM) in the presence of melatonin (1, 10 ng/ml), the decrease in the percentage of mature oocytes caused by H202 was blocked by melatonin (10 ng/ml) addition. It is, therefore, suggested that oxidative stress inhibits oocytes maturation and melatonin showed a protective activity against oxidative stress. Follicular fluid was sampled at the oocyte retrieval in IVF-ET patients. Intrafollicular concentrations of 8-hydroxy-2′-deoxyguanosine (8-OHdG) or Hexanoyl-lysine adduct (HEL) were determined by ELISA as an oxidative stress marker. 8-OHdG concentrations in women with high rates (≥30%) of degenerate oocytes were significantly higher than those in women with <30% degenerate oocytes, suggesting a close relationship between oxidative stress and poor oocyte quality. In order to reduce oxidative stress in the follicles, melatonin (3 mg/day, at 22:00) was orally given to IVF-ET patients (n=56), who failed to achieve a fertilization rate of at least 50% in the previous IVF-ET cycle, from the fifth day of the previous menstrual cycle to the day of oocyte retrieval of the IVF-ET cycle. Fifty-nine women underwent IVF-ET without melatonin treatment. The fertilization rate was improved by melatonin treatment compared with the previous IVFET cycle (20.0±19.0 % vs. 50.0±38 %), and 11 women (19.6%) conceived. On the other hand, without melatonin treatment, the fertilization rate was not changed (20.9±16.5 % vs. 22.8±19.0 %) and 6 women (10.2%) conceived. Intrafollicular melatonin concentrations were significantly increased (112±51 vs. 432±260 pg/ml) and intrafollicular concentrations of 8-OHdG and HEL were significantly decreased by melatonin treatment (17.4±8.8 vs. 11.6±0.7 ng/ml, 25.0±7.2 vs. 19.2±2.5 nmol/L, respectively). In conclusions, oxidative stress causes toxic effect on oocyte maturation and melatonin protects oocytes from oxidative stress. Melatonin administration is likely to improve oocyte quality. (platform)