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Articles

An Extract of Lagerstroemia speciosa L. Has Insulin-Like Glucose Uptake–Stimulatory and Adipocyte Differentiation–Inhibitory Activities in 3T3-L1 Cells¹

Fang Liu^*, Jae-kyung Kim^**, Yunsheng Li^*, Xue-qing Liu^**, Jing Li^* and Xiaozhuo Chen^*,,**2

^* Edison Biotechnology Institute, Department of Biomedical Sciences, College of Osteopathic Medicine and ^** Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701

²To whom correspondence should be addressed. E-mail: chenx{at}ohiou.edu.

The effects of extracts isolated from Lagerstroemia speciosa L. (banaba) on glucose transport and adipocyte differentiation in 3T3-L1 cells were studied. Glucose uptake–inducing activity of banaba extract (BE) was investigated in differentiated adipocytes using a radioactive assay, and the ability of BE to induce differentiation in preadipocytes was examined by Northern and Western blot analyses. The hot water BE and the banaba methanol eluent (BME) stimulated glucose uptake in 3T3-L1 adipocytes with an induction time and a dose-dependent response similar to those of insulin. Furthermore, there were no additive or synergistic effects found between BE and insulin on glucose uptake, and the glucose uptake activity of insulin could be reduced to basal levels by adding increasing amounts of BE. Unlike insulin, BE did not induce adipocyte differentiation in the presence of 3-isobutyl-1-methylxanthine (IBMX) and dexamethasone (DEX). BE inhibited the adipocyte differentiation induced by insulin plus IBMX and DEX (IS-IBMX-DEX) of 3T3-L1 preadipocytes in a dose-dependent manner. The differences in the glucose uptake and differentiation inhibitory activities between untreated cells and those treated with BE were significant (P < 0.01). The inhibitory activity was further demonstrated by drastic reductions of peroxisome proliferator-activated receptor 2 (PPAR2) mRNA and glucose transporter-4 (GLUT4) protein in cells induced from preadipocytes with IS-IBMX-DEX in the presence of BE. The unique combination of a glucose uptake stimulatory activity, the absence of adipocyte differentiation activity and effective inhibition of adipocyte differentiation induced by IS-IBMX-DEX in 3T3-L1 cells suggest that BE may be useful for prevention and treatment of hyperglycemia and obesity in type II diabetics.

KEY WORDS: • type II diabetes • banaba extract • insulin • adipocyte differentiation • glucose uptake

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