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Effect of Crocin during In Vitro Maturation on Cytoplasmic Maturation and Embryonic Development of Pig Oocytes after Parthenogenesis
Crocin is a carotenoid that may protect cells against oxidative stress by scavenging free radicals particularly superoxide anions. It has been reported that oocyte maturation is influenced by the free radicals generated during in vitro culture (IVC) process. The objective of study was to examine the effect of crocin in in vitro maturation (IVM) medium as an antioxidant on oocyte maturation and embryonic development after parthenogenesis (PA). Cumulus-oocyte complexes (COCs) were collected from ovaries of prepubertal gilts. The basic medium for IVM was medium-199 containing 10% pig follicular fluid, cysteine, pyruvate, epidermal growth factor, kanamycin, insulin, and hormones. Oocytes were treated for 44 hours with crocin at 0, 25, 50, and 100 μg/ml during IVM. Oocytes reached the metaphase II stage were induced for PA and cultured for 7 days in porcine zygote medium-3. Nuclear maturation of oocytes was not influenced by various concentrations of crocin (89.0, 87.3, 84.3, and 94.1% for control, 25, 50, and 100 μg/ml crocin, respectively). IVM oocytes treated with 50 μg/ml crocin showed a higher (P<0.05) intraoocyte glutathione (GSH) contents than untreated oocytes (1.00 vs. 1.29 pixels/oocyte). Blastocyst formation of PA embryos treated with 50 (42.9%) and 100 μg/ml crocin (43.8%) was significantly higher (P<0.05) than oocytes treated with 25 μg/ml crocin (30.5%) but not different from that (35.2%) of untreated oocytes. In summary, crocin increases cytoplasmic maturation in terms of intraoocyte GSH content which may be beneficial for later embryonic development by protecting from harmful effect of reactive oxygen species. Further studies are needed to determine whether the beneficial effect of crocin treatment during IVC would be shown in embryonic development after in vitro fertilization and somatic cell nuclear transfer.
