Acute and Chronic Treatment of L-Isoleucine Ameliorates Glucose Metabolism in Glucose-Intolerant and Diabetic Mice

Abstract

It is well known that amino acids, one of the three major classes of nutrients, are involved in the metabolism of carbohydrates.1,2) Among various amino acids, L-leucine (leucine) and L-isoleucine (isoleucine) show potent activity for controlling blood glucose. In normal or cirrhotic rats, acute administration of leucine or isoleucine improves the glucose tolerance curve after an oral glucose challenge, 3,4) while chronic leucine supplementation reduces obesity and improves glucose metabolism in mice on a high-fat diet (HFD).5) The glucose-lowering activity of isoleucine beyond normoglycemia seems to be relatively mild and becomes saturated as its blood level increases.6) If the glucose-lowering activity of isoleucine in diabetic animals was as strong as in normal animals, this amino acid or another agent with the same target molecule could be a promising candidate as an anti-diabetic agent. Accordingly, we determined the acute effects of isoleucine in glucose-intolerant and diabetic mice. We also investigated the chronic effect of isoleucine supplementation on glucose metabolism in mice fed a highfat/high-sucrose diet. MATERIALS AND METHODS AnimalsThe study protocol was designed to comply with the relevant institutional guidelines and was approved by the Animal Care Committee of Ajinomoto Co., Inc. Male or female C57BL/6J mice (10-16 weeks) and male BKS.Cg-mϩ/ϩLepr db /J(ϩLeprdb/ϩLeprdb) mice (db/db mice, 7-8 weeks) were purchased from Charles River Japan (Yokohama, Japan). The animals were maintained in an airconditioned room (24Ϯ1°C) with a 12 : 12-h light-dark cycle and were given free access to regular chow (CRF-1; Oriental Yeast Co., Tokyo, Japan). In the HFD study, female C57BL/6J mice were fed control chow (D12450B; 4% w/w fat, Research Diet, New Brunswick, NJ, U.S.A.) or an HFD (D12492; 35% w/w fat, Research Diet) for 8 weeks before undergoing a glucose tolerance test. In the high-fat/high-sucrose (HFHS) diet study, female C57BL/6J mice also had free access to drinking water containing 20% sucrose without or with 1 or 2% of isoleucine for 6 weeks. Mice were deprived of food and had access to isoleucine-and sucrose-free water 18 h before undergoing a glucose tolerance test. Since it was reported that female C57BL/6J mice on a HFD develop impaired glucose tolerance after a relatively short period, 7) we used female mice for our glucose-intolerance model.Oral Glucose Tolerance Test Mice fasted for 18 h were given isoleucine orally, which was immediately followed by bolus administration of glucose (1 or 2 g/kg as indicated). Distilled water or 0.5% methylcellulose was given to mice in the control group. To determine the blood glucose and plasma insulin levels, approximately 25 ml of blood was taken from the tail vein at each time indicated. Blood glucose levels were measured by the glucose oxidase method using a Fuji Dri-Chem 5500 autoanalyzer (Fuji Medical Systems, Tokyo, Japan). Plasma was separated by centrifugation and the plasma insulin level was measured by an ELISA kit (Morinaga, Tokyo, Japan). The p...

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Isoleucine or valine deprivation stimulates fat loss via increasing energy expenditure and regulating lipid metabolism in WAT

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Branched-chain amino acids in liver diseases

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