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1 March 2002 Promoting Effect of β-Mercaptoethanol on In Vitro Development under Oxidative Stress and Cystine Uptake of Bovine Embryos
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The effects of β-mercaptoethanol (β-ME) on in vitro development under oxidative stress and cystine uptake of bovine embryos were investigated. Bovine 1-cell embryos obtained by in vitro fertilization were cultured in TCM-199 or synthetic oviductal fluid (SOF) in 20% O2 supplemented with β-ME. Addition of β-ME significantly (P < 0.01) promoted embryo development when cultured in both TCM-199 and SOF under high levels of O2, to almost the same rates when they were cultured in 5% O2. To investigate whether the growth-promoting effect of β-ME was related to cystine uptake, which is an important amino acid for intracellular glutathione (GSH) synthesis, 1-cell, 8-cell, morula, and blastocyst stage embryos were incubated in cystine, cysteine-free TCM-199 containing radioisotope-labeled cystine supplemented with or without β-ME. It was found that cystine uptake was consistently low in each embryo stage incubated without β-ME. In contrast, addition of β-ME significantly (P < 0.05 to 0.0001) promoted cystine uptake in each stage of embryo development. This increase of cystine uptake by β-ME was significantly inhibited by supplementation of buthionine sulfoximine, a specific inhibitor of GSH biosynthesis (P < 0.0001). High-performance liquid chromatography (HPLC) analysis clearly revealed a decrease of cystine in culture medium after supplementation by β-ME, thereby forming another peak. HPLC analysis also showed the incorporated cystine by supplementation of β-ME was possibly metabolized for GSH synthesis in the embryos. These results indicate that β-ME has a protective effect in embryo development against oxidative stress and that the effect of β-ME is associated with the promotion of cystine uptake of low availability in embryos.

M. Takahashi, T. Nagai, N. Okamura, H. Takahashi, and A. Okano "Promoting Effect of β-Mercaptoethanol on In Vitro Development under Oxidative Stress and Cystine Uptake of Bovine Embryos," Biology of Reproduction 66(3), 562-567, (1 March 2002).
Received: 14 May 2001; Accepted: 1 October 2001; Published: 1 March 2002

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