Anti-obesity Activity of Ethanol Extract from Bitter Melon in Mice Fed High-Fat Diet

Abstract

In many cases, obesity is associated with metabolic disorders. Recently, natural compounds that may be beneficial for improving obesity have received increasing attention. Bitter melon has received attention as a diabetes treatment. NAD⁺-dependent deacetylase (Sirtuin 1, SIRT1) has emerged as a novel therapeutic target for metabolic diseases. In this study, ethanol extract of bitter melon (BME) suppressed adipocyte differentiation and significantly increased the expression of SIRT1 in fully differentiated 3T3-L1 cells. Moreover, it enhanced the activation of AMP-activated protein kinase (AMPK). In high-fat diet (HFD)-fed induced-obesity mice, BME suppressed HFD-induced increases in body weight and white adipose tissue (WAT) weight. BME also increased the expression of SIRT1 and suppressed peroxisome proliferator-activated receptor and sterol regulatory element binding protein 1 expressions of WAT from HFD-fed mice. These findings suggest that BME prevents obesity by activating the SIRT1 and AMPK pathway and that it may be a useful dietary supplement for preventing obesity.

Keywords: 3T3-L1; Bitter melon; High-fat diet; Obesity; Sirtuin 1.

Fig. 1.. Effects of BME on 3T3-L1 cells. The effect of BME on 3T3-L1 cell proliferation was measured by the MTS assay. 3T3-L1 cells were treated with the indicated concentrations of BME (500 μg/ml) for 24, 48, and 72 h. The bar graphs show the mean± SEM of 3 independent experiments (n.s. compared with the DMSO-treated control). BME, ethanol extract of bitter melon.

Fig. 2.. Inhibitory effect of BME on lipid accumulation in 3T3-L1 adipocytes. (A) The effect of BME on lipid droplet formation was measured by oil-red O staining. 3T3-L1 pre-adipocytes were differentiated into adipocytes in the presence of BME (500 μg/ml) for 6 days. (B) Quantification of triglyceride content. The bar graphs show the mean±SEM of 3 independent experiments ^a p<0.001 vs. DM- & BME-, ^b p<0.001 vs. DM+ & BME–. Scale bar represents 200 μm. BME, ethanol extract of bitter melon.

Fig. 3.. BME activated SIRT1 and AMPK in differentiated 3T3-L1 cells. 3T3-L1 pre-adipocytes were differentiated into adipocytes in the presence of BME for 6 days. The protein expressions of (A) SIRT1, PPARγ, SREBP1 and (B) p-AMPK were evaluated by western blotting. HFD was used as the control, and β–actin was used as the loading control. The bar graphs show the mean±SEM of 3 independent experiments ^a p<0.01 vs. DM– & BME–, ^b p<0.01 vs. DM+ & BME–. BME, ethanol extract of bitter melon; SIRT1, Sirtuin 1; AMPK, AMP-activated protein kinase; PPARγ, peroxisome proliferator-activated receptor γ; HFD, high-fat diet.

Fig. 4.. Effect of BME on anti-obesity activity in HFD-induced obese mice. HFD-induced obese mice were supplemented with BME for 12 weeks. (A) Body weight was measured with 2 weeks interval for 24 weeks. (B) WATs (epididymal fat, perirenal fat, mesentery fat) weights, (C) Images of WATs, (D) H&E-stained images of WATs samples from the ND, HFD, BME 500 groups. The bar graphs show the mean±SEM of 4–8 individual animals. ^a p<0.001 vs. ND, ^b p<0.001 vs. HFD. Scale bar represents 100 μm. HFD, high-fat diet. BME, ethanol extract of bitter melon; WAT, white adipose tissue.

Fig. 5.. BME activated SIRT1 in epididymal adipose tissue. The protein expressions of SIRT1, PPARγ and SREBP1 were evaluated by western blotting. Upper panel shows the representative photos of 4 individual animals. HFD was used as the control, and β–actin was used as the loading control. Lower bar graph shows quantification of western bands normalized with β-actin. ^a p<0.05 vs. HFD only group, ^b p<0.05 vs. HFD + BME 250 group. HFD, high-fat diet. BME, ethanol extract of bitter melon; SIRT1, Sirtuin 1; PPARγ, peroxisome proliferator-activated receptor γ; SREBP1, sterol regulatory element binding protein 1.