NDGA alleviates oxidative stress and supports early embryonic development in porcine oocytes

Nordihydroguaiaretic acid (NDGA) is a potent cell-permeable antioxidant that regulates cellular redox balance, but its role in porcine oocyte in vitro maturation (IVM) and embryonic development remains unclear. In this study, porcine oocytes were cultured in IVM medium supplemented with different concentrations of NDGA (0, 8, 10, 20, and 100 μM). The results showed that 8 μM NDGA significantly enhanced cumulus cell expansion and increased the first polar body extrusion rate, whereas a high concentration (100 μM) impaired these processes. Immunofluorescence analysis demonstrated that 8 μM NDGA upregulated the maturation-promoting factor core proteins Cyclin B1 and CDK1. NDGA treatment promoted catalase (CAT) and superoxide dismutase (SOD) activities, accompanied by reduced reactive oxygen species levels and increased glutathione content. In addition, JC-1 and TMRM staining, together with ATP assays, indicated that NDGA improved mitochondrial membrane potential and energy metabolism. Real-time PCR analysis showed that NDGA significantly downregulated KEAP1 while upregulating NRF2 and its downstream target genes HO-1, CAT, and SOD. Functionally, 8 μM NDGA improved pre-hatching blastocyst formation in low-quality oocytes; however, although a modest improvement in post-hatching survival cannot be excluded, parthenotes derived from NDGA-treated low-quality oocytes remained markedly inferior to those from untreated high-quality oocytes in the N2B27 culture system. Overall, these findings indicate that NDGA promotes porcine oocyte maturation and pre-hatching embryonic development by exerting antioxidant effects, supporting mitochondrial function, and activating the KEAP1-NRF2 signaling pathway.