Kazumi YAGASAKI, Masato NAGAOKA and Yutaka MIURA

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1 Kazumi YAGASAKI, Masato NAGAOKA and Yutaka MIURA Division of Agriscience and Bioscience, Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Fuchu ABSTRACT Effect of a soybean isoflavone, genistein, on (1) glucose uptake by rat-derived L6 myotubes and (2) insulin secretion from rat-derived RIN-5F pancreatic -cells was studied in vitro. Then, (3) that on blood glucose levels in type 2 diabetic KK-Ay/Ta mice was studied in vivo. Genistein dose-dependently and significantly stimulated glucose uptake by L6 myotubes and insulin secretion from RIN-5F cells in culture at M, where genistein exerted no influence on the viability of RIN-5F cells. Feeding 0.1% genistein in 20% casein diet (20C) for 5 weeks to KK-Ay/Ta mice suppressed increases in blood glucose levels and the suppressive effect was significant at 1 st and 5 th week of feeding as compared with 20C-fed diabetic control mice. Genistein also suppressed urinary glucose excretion as compared with control mice during the feeding period. These effects of genistein were not due to reduction in food intake. From these results, genistein was strongly suggested to suppress the increases in blood glucose level in type 2 diabetic mice through stimulating glucose uptake and/or insulin secretion. Soy Protein Research, Japan 11, , Key words : soybean genistein, muscle cells, pancreatic -cell, glucose uptake, insulin secretion, type 2 diabetes ,0501, , ) 121

2 Soyabean phytochemical extractspesglt1 2) SPE L6 3) 10%FBS DMEM10%FBS/DMEM11 L6 L6 4) RIN-5F 5) 10% FBS RPMI164010%FBS/RPMI1640RIN-5F 1%FBS/RPMI1640 ELISARIN-5F LDH KK-Ay/Ta C57BL/6J CE-2AIN C, Table 1 10 KK-Ay/Ta 20C0.1% 20C C57BL/6J 20C TGCh TBARS Dunnet multiple comparisons test p < 0.05 Fig M 10100MFig. 2A LDHTriton X-100 LDH LDH 100Fig. 2B 10, 100M 0MLDH LDH1%FBS LDH in vitroin vivo KK-Ay/Ta 0.1% Table 2 122

3 Fig. 3 Fig. 4 Fig. 4 TGChTBARSTG Ch Table 2 Table 1. Composition of experimental diets Ingredient (%) 20C 20C+G Casein a Corn starch b Corn starch b Corn oil c Cellulose powder a Mineral mixture b (AIN93G-MX) Vitamin mixture b (AIN-93-VX) L-Cystine d Choline bitartrate d Genistein e 0.1 a Oriental Yeast Co., Ltd., Tokyo. b Nihon Nosan Kogyo Co., Ltd., Yokohama. c Hayashi Chemicals Co., Ltd., Tokyo. d Wako Pure Chemical Industries., Ltd., Osaka. e Tyger Sci. Inc., USA. Fig. 1. Effect of genistein on glucose consumption in cultured L6 myotubes. Each value represents the mean SEM for 6 wells. Asterisks mean statistical significance at *p <0.05 or **p <0.01 by Dunnet multiple comparisons test. Fig. 2. Effect of genistein on insulin secretion and cytotoxicity in cultured RIN-5F cells. Each value represents the mean SEM for 6 wells. Asterisks mean statistical significance at **p <0.01 by Dunnet multiple comparisons test. 123

4 PPAR 6) PPAR PPAR [ 14 C]2-deoxyglucose Table 2. Effect of genistein on methabolic parameters in KK-Ay/Ta mice Measurement Nor Con Gen Initial body weight (g/mouse) Food intake (g/35 days) Body weight gain (g/35 days) Initial blood glucose (mg/100ml) Serum lipid levels Cholesterol (mmol/l) Triglyceride (mmol/l) TBARS (mol/l) Serum adiponectin (g/ml) Serum insulin (ng/ml) Liver lipid levels Cholesterol (mg/g liver) Triglyceride (mg/g liver) Each value represents the mean SEM for 6 mice. Asterisks mean statistical significance at *p <0.05 by Dunnet multiple comparisons test. Fig. 3. Effect of genistein on non-fasting blood glucose levels in KK-Ay/Ta mice. Mice were kept on diets during blood collection from tail vein. Each value represents the mean SEM for 6 mice. Asterisks mean statistical significance at *p <0.05 or **p <0.01 by Dunnet multiple comparisons test. 124

5 Fig. 4. Effect of genistein on urine glucose excretion in KK-Ay/Ta Jcl mice. Urine glucose excretion in mice was determined using urine test paper. Urine glucose concentration; (0 mg/100ml), (~50 mg/100ml), (~100 mg/100ml), (~500 mg/100ml), (~2,000 mg/100ml). L6 RIN-5F 10100M KK-Ay/Ta ) /04/h html 2) Vedavanam K, Srijayanta S, O'Reilly J, Raman A and Wiseman H (1999): Antioxidant action and potential antidiabetic properties of isoflavonoidcontaining soybean phytochemical extract (SPE). Phytother Res, 13, ) Yagasaki K, Morisaki N, Kitahara Y, Miura A and Funabiki R (2003): Involvement of protein kinase C activation in L-leucine-induced stimulation of protein synthesis in L6 myotubes. Cytotechnology, 43, ) Doi M, Yamaoka I, Fukunaga T and Nakayama M (2003): Isoleucine, a potent plasma glucoselowering amino acid, stimulates glucose uptake in C 2 C 12 myotubes. Biochem Biophys Res Commun, 312, ) Nomura E, Kashiwada A, Hosoda A, Nakamura K, Morishita H, Tsuno T and Taniguchi H (2003): Synthesis of amide compounds of ferulic acid, and their stimulatory effects on insulin secretion in vitro. Bioorg Med Chem, 11, ) Kwon DY, Jang JS, Lee JE, Kim YS, Shin DH and 125

6 Park S (2006): The isoflavonoid aglycone-rich fractions of Chungkookjang, fermented unsalted soybeans, enhance insulin signaling and peroxisome proliferator-activated receptorgamma activity in vitro. Biofactors, 26,