Melatonin Protects Intact Rat Ovarian Transplantation via the MT1/Nrf2/ARE Pathway

Cryopreservation and transplantation of intact ovaries offer a promising approach to fertility restoration in cancer patients. However, ischemia-reperfusion injury following transplantation significantly impairs graft function. This study aimed to evaluate the protective effects of melatonin and elucidate its underlying mechanisms of action, including antioxidant and anti-inflammatory properties. Intact ovaries from 8 to 12-week-old LEWIS rats were cryopreserved and subsequently transplanted. Melatonin (25 mg/kg and 50 mg/kg) was administered daily from day 1 to day 4 postoperatively. Estrous cycle recovery and ovarian histology were examined, along with measurements of hormone concentrations, antioxidant activity, and inflammatory mediators. The oxidative stress response, particularly the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response elements (ARE) signaling pathway-including Nrf2, Kelch-like ECH-associated protein 1 (Keap1), and sMafg-was investigated to elucidate melatonin's protective mechanisms. The roles of melatonin receptors and Nrf2 were investigated using specific receptor antagonists (Luzindole, 4P-PDOT) and an inhibitor (ML385) to confirm the involvement of the MT1/Nrf2/ARE pathway. As a result, rats treated with high-dose melatonin (50 mg/kg) exhibited accelerated estrous cycle recovery, reduced follicular loss, improved serum hormone levels, enhanced antioxidant capacity in serum and ovarian tissue, and decreased levels of inflammatory cytokines. Furthermore, melatonin exerted its antioxidant and anti-inflammatory effects through activation of the Nrf2/ARE signaling pathway via the MT1 receptor. These protective effects were abolished by the inhibition of either Nrf2 or MT1 receptor. In conclusion, these findings demonstrate that melatonin mitigates oxidative stress and inflammatory damage in intact transplanted ovaries through the MT1/Nrf2/ARE signaling axis, thereby preserving ovarian function post-transplantation.