Toxic effects of sterigmatocystin on porcine oocyte maturation and subsequent embryo development

Sterigmatocystin (STE), a precursor of aflatoxin B1, is one of the mycotoxins that easily contaminates feed. Although previous studies have suggested the toxic effects of aflatoxin B1 on oocyte maturation, little attention has been given to the effects of STE. Therefore, we investigated the effects of STE on porcine oocyte maturation. In this study, porcine oocytes were subjected to in vitro maturation supplemented with various concentrations of STE (0, 5, 10, and 25 μM). The results showed that the cumulus cell expansion indexes of all STE-treated groups were significantly decreased compared to the control group, with 10 μM significantly decreasing the transcript expression of cumulus expansion-related genes. Regarding nuclear maturation, metaphase II rates in all STE-treated groups were significantly lower than in the control group, with 10 μM significantly decreasing the transcript expression of oocyte competence-, mitogen-activated protein kinase-, and maturation-promoting factor-related genes. While cleavage rates showed no significant differences, the blastocyst formation rates significantly declined in groups treated with more than 10 μM of STE. Based on these findings, the 10 μM STE group was selected for subsequent experiments. STE supplementation significantly increased reactive oxygen species levels and decreased glutathione levels in oocytes compared to the control group. Furthermore, STE significantly decreased mitochondrial quantity and membrane potential, while increasing the percentage of γ-H2AX-positive oocytes. The number of LC3-positive dots and Annexin-V-positive oocytes was also significantly higher in the STE-treated group than in the control group. In conclusion, STE impairs porcine oocyte maturation and subsequent embryo development by inducing oxidative stress, mitochondrial dysfunction, DNA damage, excessive autophagy, and early apoptosis.