335 EFFECT OF VITAMIN E ON THE DEVELOPMENT OF BOVINE OOCYTES AFTER CHEMICAL ACTIVATION

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Oxidative stress is known to induce apoptotic cell death by reactive oxygen species (ROS) generated from in vitro culture systems. This study was conducted to evaluate the effect of Vitamin E (VitE), as antioxidant, on development of bovine embryos activated in vitro. Bovine ovaries were collected from slaughtered cows at a local abattoir. Oocytes were aspirated from follicles 3-8 mm in diameter and transferred to maturation medium: tissue culture medium (TCM)-199 supplemented with 10% (v/v) fetal calf serum, 100 mg/mL-1 l-cysteine, 20 mg/mL-1 sodium pyruvate, gonadotropins (250 IU each of eCG and hCG/mL), 10 mg/mL-1 epidermal growth factor, and 100 �M VitE. Oocytes were cultured at 38.9�C in 5% CO2 in humidified air. After 22 hours of culture, oocytes with polar bodies were selected and subjected to activation treatments. Oocytes were exposed to calcium ionomycin (5 �M for 5 min), followed by incubation with 6-DMAP (2 mM) for 3.5 hours in medium supplemented with or without VitE (100 �M). After activation, oocytes were cultured in mSOF medium containing 0.8% BSA at 38.9�C in 5% CO2, 5% O2 in humidified air for 7–8 days. Cell numbers were counted by the number of nuclei of blastocysts stained with Hoechst 33342, and apoptosis was detected by TUNEL assay using a MK500 kit (Takara Bio, Inc., Otsu, Shiga, Japan). Total cell and apoptotic cell number were determined under a fluorescence microscope. Data were analyzed using Student's t-test and chi-square test. The cleavage and blastocyst rates were significantly higher (P < 0.05) after activation with VitE (78.1% and 16.3%, n = 80) than without VitE (66.7% and 11.0%, n = 60). Total cell numbers were also significantly higher (P < 0.05) in blastocysts after activation with VitE (143.0 ± 34.02, n = 21) than in those without VitE (127.63 ± 40.25, n = 20). However, the percentage of TUNEL-positive (apoptotic) cells was similar between blastocysts activated with VitE (5.38 ± 2.22) and those without VitE (6.76 ± 1.98). The results of the present study demonstrate that vitamin E added to activation medium promoted further development of activated embryos, although its role in the alleviation of apoptosis remains unclear.