Effect of glutathione synthesis stimulation during in vitro maturation of ovine oocytes on embryo development and intracellular peroxide content

Cysteamine and beta-mercaptoethanol supplementation of in vitro maturation (IVM) medium has been found to increase intracellular glutathione (GSH) content in oocytes and to improve embryo development and quality in several species. The objective of this experiment was to study the effect of cysteamine and beta-mercaptoethanol added during IVM of sheep oocytes on GSH synthesis and embryo development. Furthermore, we examined if cysteamine addition (hence GSH production) had an effect on the reduction of the intracellular peroxide content. We matured oocytes obtained from ovaries collected at a slaughterhouse in vitro in the presence of 0, 50, 100, and 200 microM cysteamine (Experiment 1) or with 0, 50, 100, and 200 microM beta-mercaptoethanol (Experiment 2). Following fertilization and embryo development, there was a increasing level of morula and blastocyst development in the presence of cysteamine, reaching significance in the presence of 200 microM (P < 0.05). However, beta-mercaptoethanol did not influence on the rate of embryo development. GSH levels were measured in oocytes matured in the presence or absence of 200 microM cysteamine (Experiment 3) or 50 microM beta-mercaptoethanol (Experiment 4), with or without buthionine sulfoximide (BSO), an inhibitor of GSH synthesis. Results demonstrated that for both cysteamine and beta-mercaptoethanol, intracellular GSH levels increased against control values (P < 0.01), which was abolished in the presence of BSO. Finally, we reduced intracellular peroxide levels, as measured by the relative fluorescence of the intracellular peroxide probe, carboxy-H2DCFDA, in the presence of either 200 microM cysteamine or 50 microM beta-mercaptoethanol (Experiment 5). These results demonstrate that cysteamine, but not beta-mercaptoethanol, when present during IVM, stimulates sheep embryo development; both cysteamine and beta-mercaptoethanol stimulate GSH synthesis; the increase in intracellular GSH is associated with a decrease in peroxide levels within oocytes.