CLARIFICATION OF THE MECHANISM OF ANIT-DIABETIC EFFET BY THE ADMINISTRATION OF BIOTIN

生物素是一种水溶性维生素，在哺乳动物体内作为四种羧化酶的辅因子，参与脂质、碳水化合物和氨基酸的代谢。我们的研究小组已经表明，生物素具有改善糖尿病患者碳水化合物代谢的新功能。本研究旨在阐明生物素这种新作用的机制，首先，我们试图确定生物素刺激胰腺B细胞分泌胰岛素的作用位点。从大鼠胰腺中分离培养胰岛。在有或没有生物素的葡萄糖刺激后，测量培养基中分泌的胰岛素。生物素给药以剂量依赖性方式（高达50μM）增加胰岛素分泌。当使用丙酮酸代替葡萄糖作为刺激物时观察到这种现象，因此推测生物素参与了糖酵解途径上线粒体内的反应。然后，氧化磷酸盐的能力， ...更多信息 通过使用具有不同标记位点的葡萄糖的放射性同位素来测量TCA循环中的球化。结果表明，当<14>以[U-^ C]葡萄糖为刺激物时，生物素使^ CO_2生成量增加两倍<14>，而以[6-^ C]葡萄糖为刺激物时，生物素对^ CO_2生成量无影响<14>。这些结果表明，生物素可以通过显著增加葡萄糖的氧化而刺激ATP的合成，而不改变TCA循环中的旋转能力。接下来，我们分析了生物素对肝脏磷酸烯醇式丙酮酸羧激酶（PEPCK）基因表达的调控。链脲佐菌素诱导的糖尿病大鼠给予生物素后，PEPCK mRNA表达较对照组下降40%。因此，生物素具有胰岛素样作用，可以改善糖尿病动物的病情。本研究以胰岛素敏感的大鼠肝癌细胞H4 IIE为实验材料，试图确定PEPCK基因的生物素调控位点。当细胞与胰岛素培养基一起孵育时，在生物素处理后3小时，H4 IIE细胞中PEPCK mRNA增加。这一结果表明，生物素可抑制该细胞系中的胰岛素作用。少

Biotin is one of water-soluble vitamin that functions as a cofactor of four types of carboxylase involved in lipid, carbohydrate and amino acids metabolism in mammalian. Our group has shown that biotin has a novel function that improves carbohydrate metabolism in diabetes mellitus. This research aimed clarification of mechanism of this novel action of biotin.First of all, we tried to identify site to action of biotin in the stimulation of insulin secretion from the B cells of pancreas. The Langerhan's islet was isolated from rat pancreas, and cultured. Secreted insulin in cultured medium was measured after stimulation of glucose with or without biotin. The secretion of insulin has been increased by biotin administration dose-dependent manner (up to 50μM). This phenomenon was observed when pyruvate was used as a stimulant instead of glucose, therefore biotin was presumed to be participation in the reaction within mitochondria on the glycolytic pathway. Then, the ability of oxidative pho … More sphorylation at the TCA cycle was measured by using radioisotope of glucose with a different labeling site. As a result, the amount of ^<14>CO_2 formations was increased twice by biotin administration when [U-^<14>C] glucose was used as a stimulant, while it was not changed in case of [6-^<14>C] glucose administration. These results indicate that biotin could stimulate ATP synthesis through significant increase of glucose oxidation without the change of rotation ability in TCA cycle.Next, we analyzed the involvement of biotin in the regulation of liver phosphoenolpyruvate carboxykinase (PEPCK) gene expression. PEPCK mRNA was decreased by 40% compared with the control when the biotin was administered to the streptozotocin induced diabetic rat. Therefore biotin has insulin-like action and could improve the condition of diabetic animal. We tried to identify the site of biotin regulation of PEPCK gene using rat hepatoma cell H4IIE that has the insulin susceptibility. PEPCK mRNA increased in H4IIE cells 3 hours after treatment of biotin when cells were incubated with insulin medium. This result indicated that biotin could suppress the insulin action in this cell line. Less