Gamete Biology

Protection of Porcine Oocytes Against Cell Damage Caused by Oxidative Stress During In Vitro Maturation: Role of Superoxide Dismutase Activity in Porcine Follicular Fluid

Abstract
To elucidate the beneficial effects of porcine follicular fluid (pFF) added to maturation medium on the sustenance of cytoplasmic maturation responsible for the subsequent developmental competence after in vitro fertilization (IVF) of porcine oocytes, we focused on the antioxidative role of pFF as it functioned in the protection of oocytes from reactive oxygen species (ROS)-induced cell damage. pFF collected from small (2-6 mm) follicles had about 7.2-fold higher levels of superoxide dismutase (SOD) activity than that of fetal bovine serum (FBS), and this activity was markedly blocked by the CuZn-SOD inhibitor, diethyldithiocarbamate (DETC). The interruption of the meiotic progression and the increasing intracellular glutathione (GSH) content throughout the maturation period, as well as outbreak of DNA damage in oocytes and cumulus cells were hardly detected in oocytes cultured in a medium supplemented with 10% pFF, even in the presence of ROS generated by the hypoxanthine-xanthine oxidase system, whereas cell damage encompassed by ROS was prominently found in the oocytes cultured with 10% FBS and 10% pFF plus 100 µM DETC. Similarly, significant enhancement in the degree of transformation of the sperm nucleus into the male pronucleus (MPN) after IVF was shown by the addition of pFF to the maturation medium. The presence of DETC during in vitro maturation reduced the ability of the oocytes to promote MPN formation in the same extent as the oocytes matured with FBS. The proportion developing to the blastocyst stage was increased in oocytes which matured with pFF, but this developmental competence was significantly lowered by treatment with DETC (P<0.05). These findings suggest that pFF plays critical role in protecting oocytes from oxidative stress through a higher level of radical scavenging activity elicited from SOD isoenzymes, resulting in the enhancement of cytoplasmic maturation responsible for developmental competence post-fertilization.

Key words: Gamete Biology • Apoptosis • Early development • In vitro fertilization • Ovum

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