Reduction of heat stress-induced oxidative stress in bovine oocytes by Proanthocyanidins

<bold>Objective</bold> The objective of this study is to explore the protective mechanisms of proanthocyanidin B2（PB2）when incorporated into the maturation medium of bovine oocytes under heat stress conditions.This investigation aims to provide a scientific foundation for enhancing the quality of bovine oocytes exposed to high temperatures and improving their capacity for embryonic development in vitro. <bold>Method</bold> A total of 103 pairs of ovaries were collected from 6-8 years old Holstein cattle.The cumulus oocyte complex（COCs）in ovarian follicles were aspirated in the laboratory and randomly divided into 3 groups for in vitro maturation：control group（cultured at 38.5 ℃ for 24 h）；heat stress group（cultured at 41 ℃ for 8h and transferred to 38.5 ℃ incubator for 16 h）；proanthocyanidin group（25 µmol/L PB2，cultured at 41 ℃ for 8h and transferred to 38.5 ℃ incubator for 16 h）.After the oocytes were treated by hyaluronidase，the oocyte maturation rate of each group was measured under stereomicroscope.After parthenogenetic activation of oocytes by chemical agent，the cleavage rate and blastocyst rate were recorded at 48 h and 168 h，respectively.The ROS and GSH of oocytes and the total number of blastocysts were measured by fluorescence staining.The expression levels of antioxidant genes（<italic>SOD1</italic>，<italic>SOD2</italic>，<italic>CAT</italic>）and maturation genes（<italic>GSS</italic>，<italic>GPX1</italic>，<italic>CAS6</italic>）were detected by quantitative real-time PCR（qPCR）. <bold>Result</bold> （1）COCs matured in vitro for 24 h.Compared with the heat stress group，the proanthocyanidin group increased the oocyte maturation rate，but there was no significant difference between the two groups（<italic>P</italic>&gt;0.05）；（2）After parthenogenesis activation，compared with heat stress group，the cleavage rate of proanthocyanidin group was significantly increased（<italic>P</italic>&lt;0.05），the blastocyst rate was not significantly different（<italic>P</italic>&gt;0.05），but the total number of blastocyst cells was significantly increased（<italic>P</italic>&lt;0.05）；（3）After 24h maturation in vitro，compared with heat stress group，ROS content in proanthocyanidins group was significantly decreased（<italic>P</italic>&lt;0.01），GSH content was significantly increased（<italic>P</italic>&lt;0.05），the expression levels of maturation genes and antioxidant genes were significantly increased（<italic>P</italic>&lt;0.05）. <bold>Conclusion</bold> By adding proanthocyanidin B2 to in vitro maturation medium，oxidative stress of bovine oocytes induced by heat stress can be effectively alleviated，thus improving the maturation process of oocytes in vitro and enhancing the development potential of embryos as well as embryo quality.