Resilience of porcine oocyte-cumulus complexes derived from antral follicles with various diameters to oxidative stress by BCB staining.

The present study aimed to determine the resilience of oocyte-cumulus complexes (OCCs) derived from three different follicle sizes, including medium follicles (with 3-6 mm in diameter; MF), small follicles (1-3 mm in diameter; SF), and very small follicles (with less than 1 mm in diameter; VSF) to brilliant cresyl blue (BCB) staining. BCB staining affected transcriptional levels of oxidative stress-related genes in both oocytes and cumulus cells. Regardless of the origins of OCCs, even in BCB+ oocytes, the blue dye disappeared around 1 h in an IVM culture condition. Within 1 h after BCB staining, distinct responses in the NADPH regulation were observed between MF-, SF-, and VSF-derived OCCs, and were affected by both the origins of OCCs and the BCB status. A transient increase in ROS and a decrease in GSH in BCB+ oocytes were also observed. After BCB staining, the ROS levels in both BCB+ and BCB- oocytes were increased, although the level was affected by both the origin of OCCs and BCB status until 4 h of IVM and remained at low levels during IVM. The GSH levels of MF-, SF-, and VSF-derived BCB+ oocytes were significantly lower than those of BCB- ones and non-stained controls, but the difference disappeared during IVM. These results demonstrate that, although BCB staining induces transient oxidative stress in porcine OCCs, especially those including BCB+ oocytes, OCCs rapidly restore redox balance by regulating and utilizing NADPH to produce reduced GSH, with different resilience between the origin of OCCs.