Melatonin Enhances Glutathione Peroxidase Activity and Improves Antioxidant Defense in Cryopreserved Ovarian Transplants: A Rat Model Study

Background: Although ovarian cryopreservation is an essential strategy for fertility preservation, ischemia–reperfusion injury and oxidative stress can significantly compromise graft viability after transplantation. Melatonin is a potent antioxidant capable of modulating redox homeostasis and tissue repair; however, its effects on the ovarian microenvironment after cryopreservation are not fully understood. Objective: To investigate whether melatonin supplementation during ovarian cryopreservation enhances GPx1/2-mediated antioxidant defense, preserves follicular integrity, and modulates the angiogenic balance (assessed via VEGF-A expression) after autologous ovarian transplantation in rats. Methods: Twenty-four Wistar rats were ovariectomized and divided into control (standard cryopreservation) and melatonin-treated (0.1 μM melatonin) groups. Ovaries were cryopreserved, thawed, and autotransplanted. After 30 days, the grafts were analyzed for GPx1/2 expression (immunohistochemistry), VEGF-A levels (ELISA), biochemical markers, and follicular integrity (histomorphometry) Results: The melatonin treatment significantly increased GPx1/2 expression in the corpus luteum (p = 0.002), theca interna (p = 0.007), and interstitium (p = 0.012), and reduced the number of degenerated follicles (p = 0.03). Although absolute VEGF-A levels did not differ between groups, melatonin-treated animals showed higher VEGF/FSH ratios (p = 0.0007) and VEGF/LH (p = 0.0494) ratios. Positive correlations were observed between GPx1/2 expression and VEGF-A expression. Conclusions: Melatonin increases antioxidant defenses in cryopreserved ovarian grafts through the upregulation of GPx1/2 and preservation of follicular morphology. Instead of directly increasing VEGF-A levels, melatonin appears to modulate angiogenic signaling, contributing to a more stable microenvironment for ovarian graft survival.