Soy Isoflavones Ameliorate Fatty Acid Metabolism of Visceral Adipose Tissue by Increasing the AMPK Activity in Male Rats with Diet-Induced Obesity (DIO)

Abstract

Soy isoflavones are natural active ingredients of soy plants that are beneficial to many metabolic diseases, especially obesity. Many studies have reported that obesity is closely related to visceral fatty acid metabolism, but the effect has not been well defined. In this study, we show that soy isoflavones improve visceral fatty acid metabolism in diet-induced obese male rats, which was indicated by reduced body weight and visceral fat cell area, as well as suppressed visceral fat synthesis and accelerated fat hydrolysis. We also found that common components of soy isoflavones, daidzein and genistein, were able to inhibit the lipid accumulation process in 3T3-L1 cells. Moreover, we showed that soy isoflavones can promote on AMP-activated protein kinase (AMPK) activity both in vivo and in vitro, which may be implicated in lipid metabolism regulation of soy isoflavones. Our study demonstrates the potential of soy isoflavones as a mechanism for regulating lipid homeostasis in visceral adipose tissue, proven to be beneficial for obesity treatment.

Keywords: AMPK; lipid homeostasis; soy isoflavones.

Figure 1

Soy isoflavones reduce body weight and the serum triglycerides (TG), total cholesterol (TC), and low-density lipoprotein (LDL) concentrations. (A) The body weight of rats fed a basal diet and the high-fat diet for nine weeks; (B) the plasma TG, TC, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) concentrations of rats fed a basal diet and high-fat diet; (C) the body weight trend of rats in the control, obesity control group (OB), low dose of isoflavones (LSI), middle dose of isoflavones (MSI), and high dose of isoflavones (HSI) groups. a**: b vs. a, p < 0.01; d*: b vs. d, p < 0.05; e*: b vs. e, p < 0.05; e**: b vs. e, p < 0.01; (D) the plasma TG, TC, HDL, and LDL concentration of rats in each group at the thirteenth week; and (E) feed intake of rats in each group during the intervention of soy isoflavones. Error bars indicate SEM. * p < 0.05, ** p < 0.01. ns, no statistical significance. ^a control group, ^b obesity group, ^c low-dose soy isoflavones group, ^d middle-dose soy isoflavones group, ^e high-dose soy isoflavones group.

Figure 2

Soy isoflavones reduce the average area of a single visceral lipocyte and lipid accumulation. (A) Representative images of H and E staining in visceral adipose tissues, bar: mesenteric fat 50 µM, epididymal fat 100 µM, and perirenal fat 100 µM; (B) the average area of a single visceral lipocyte in each group rats; (C) the weight of visceral adipose tissues; (D) representative images of Oil red O staining in visceral adipose tissues, bar: 200 µM; (E) the effect of daidzein and genistein on cell viability; and (F) representative images of Oil red O staining in each group 3T3-L1 cells, bar: 100 µM.

Figure 3

Soy isoflavones promote fatty acid hydrolysis and inhibit fatty acid synthesis. (A) Relative mRNA expression of visceral fat synthesis-related genes in each group of rats, the dotted lines in the graphs represent the control group; (B) the western blot results of sterol regulatory element-binding transcription factor 1c (SREBP-1c) in visceral fat of each group of rats; (C) relative mRNA expression of visceral fat hydrolysis-related genes in each group of rats, the dotted lines in the graphs represent the control group; (D) the western blot results of adipose triglyceride lipase (ATGL) in visceral fat of each group of rats; and (E) effects of daidzein and genistein on the mRNA levels and the protein levels of ATGL and SREBP-1c in differentiated 3T3-L1 cells.

Figure 4

Soy isoflavones increase AMP-activated protein kinase (AMPK) activity in visceral fat and 3T3-L1 cells. (A) The western blot results of AMPKα and phosphor-AMPKα in visceral fat of each group of rats; (B) the western blot results of AMPKα and phosphor-AMPKα in differentiated 3T3-L1 cells after treatment with daidzein and genistein; and (C) the western blot results of AMPKα, phosphor-AMPKα, and SREBP-1c in differentiated 3T3-L1 cells after treatment with Compound C, daidzein, and genistein.