Effects of astaxanthin-containing oil on development and stress-related gene expression of bovine embryos exposed to heat stress.

Early bovine embryos are vulnerable to heat stress during the first few days after fertilization. The inhibitory effect of heat stress on embryonic development is known to be associated with oxidative stress, which can be attenuated by antioxidants. In the present study, we focused on the use of astaxanthin as an antioxidant and examined the effects of astaxanthin-containing oil (Ax) on post-fertilization development of bovine embryos subjected to heat stress in vitro and the expression of stress-related genes. Bovine 1-cell embryos were in vitro produced by in vitro maturation and fertilization (IVF) of oocytes recovered from abattoir-derived ovaries. At 20 h post-insemination (hpi, 0 h = the start of IVF), the embryos were introduced in modified synthetic oviduct fluid supplemented with 25 ppm of Ax (concentration of astaxanthin was 0.25 ppm) or vehicle (dimethyl sulfoxide) up to 72 hpi. The embryos were basically cultured at 38.5°C, and in the heat stress group, embryos were exposed twice to 40.5°C for 10 h (at 20-30 and 44-54 hpi). Under the condition without the Ax treatment, the cleavage rate, rate of development to the 5-8 cell stage, blastocyst yield from cultured embryos and that from cleaved embryos were lower in the heat stress group than in the group not subjected to heat stress (p < 0.05). In the heat stress group, the rate of development to the 5-8 cell stage was improved (p < 0.05) by the addition of Ax. Subsequently, we performed semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) to investigate the effects of heat stress and Ax on the mRNA expression of Src homology 2 domain-containing transforming protein C1 (SHC1), an oxidative stress adaptor protein, and superoxide dismutase 2 (SOD2), a mitochondrial reactive oxygen species (ROS) scavenger. In 5-8 cell embryos at 72 hpi, the mRNA expression levels of SHC1 and SOD2 were lower in the Ax- and heat-treated group than in the other groups (p < 0.05). These results suggest that Ax added to the culture medium ameliorates the embryonic development impaired by heat stress with its altering effects on the expression of stress-related genes.