Effects of Vitamin C, Rosmarinic Acid, or Quercetin on Fertilisation-Related Gene Expression in Porcine Cumulus–Oocyte Complexes During In Vitro Maturation

Antioxidant supplementation during in vitro maturation (IVM) has been proposed as a strategy to influence transcriptional responses in oocytes and cumulus–oocyte complexes. In this study, we investigated whether vitamin C, rosmarinic acid, or quercetin influence the expression of key fertilisation-associated genes (CD9, ITGA6, MFGE8, ZP2, and ZP3) in porcine cumulus–oocyte complexes (COCs). COCs were classified into three intrinsic quality groups (I–III) and matured in the presence or absence of antioxidants. Gene expression was quantified by RT-qPCR and analysed using a two-way ANOVA model to assess the effects of COC quality and treatment. ZP2 and ZP3 transcript levels were consistently lower in class II and III COCs than in class I controls (p < 0.001). Antioxidant supplementation was associated with treatment- and quality-dependent differences in gene expression. Quercetin was associated with the most pronounced upregulation, with Q I increasing ZP2 expression to 2.95-fold and ZP3 to 2.43-fold relative to class I controls (p < 0.001). Vitamin C was also associated with increased transcript abundance across several treatment groups, including class II and class III COCs, whereas rosmarinic acid exhibited more moderate and gene-specific effects. In contrast, MFGE8 expression, which was elevated in lower-quality COCs, was reduced in antioxidant-treated class II and III complexes. These findings provide transcript-level evidence that antioxidant exposure during IVM is associated with treatment- and quality-dependent changes in fertilisation-related gene expression in porcine COCs.