Ginsenoside Rb2 Alleviates Obesity by Activation of Brown Fat and Induction of Browning of White Fat

Abstract

Ginsenoside Rb2 (Rb2), the most abundant saponin contained in Panax ginseng, has been used to treat variety of metabolic diseases. However, its effects in obesity and potential mechanisms are not well-understood. In the present study, we investigated metabolic performance with a Rb2 supplement in diet-induced obese (DIO) mice, focusing on the effects and mechanisms of Rb2 on brown and beige fat functions. Our results demonstrated that Rb2 effectively reduced body weight, improved insulin sensitivity, as well as induced energy expenditure in DIO mice. Histological and gene analysis revealed that Rb2 induced activation of brown fat and browning of white fat by reducing lipid droplets, stimulating uncoupling protein 1 (UCP1) staining, and increasing expression of thermogenic and mitochondrial genes, which could be recapitulated in 3T3-L1, C3H10T1/2, and primary adipocytes. In addition, Rb2 induced phosphorylation of AMP-activated protein kinase (AMPK) both in vitro and in vivo. These effects were shown to be dependent on AMPK since its inhibitor blocked Rb2 from inducing expressions of Pgc1α and Ucp1. Overall, the present study revealed that Rb2 activated brown fat and induced browning of white fat, which increased energy expenditure and thermogenesis, and consequently ameliorated obesity and metabolic disorders. These suggest that Rb2 holds promise in treating obesity.

Keywords: AMPK; Ginsenoside Rb2; UCP1; browning; obesity.

Figure 1

Rb2 treatment reduced body weight and improved insulin sensitivity in DIO mice. (A) Representative photograph of DIO mice after intraperitoneal injection of PBS or Rb2 for 10 days. (B) Body weight of DIO mice treated with or without Rb2 for 10 days (n = 6). (C–F) Performances of GTT (C) and ITT (E) of DIO mice treated with or without Rb2. Area under the curve (AUC) of GTT and ITT was also shown as D and F. N = 6 per group. Data are presented as mean ± SEM and ^*P < 0.05, ^**P < 0.01 compared to HFD group.

Figure 2

Rb2 treatment increased energy expenditure in DIO mice. (A–F) Energy expenditure was evaluated by measurement of oxygen consumption (V_O2) (A) carbon dioxide release (V_CO2) (C) heat production (E) over a 24 h period in DIO mice after 10 days of PBS or Rb2 treatment. The average numbers calculated as day and night were shown in (B,D,F). N = 6 per group. Data are presented as mean ± SEM and ^*P < 0.05, ^**P < 0.01 compared to HFD group.

Figure 3

Rb2 treatment reduced adiposity and induced brown fat gene programs in adipose tissues. (A–C) Representive photographs, fat mass and tissue weight of iWAT, eWAT, and BAT of DIO mice treated with Rb2 and PBS for 10 days. (D–F) Representative hematoxylin and eosin staining from iWAT, eWAT, and BAT sections and quantifications of adipocytes sizes of white fat. (G,H) gene expression analysis of thermogenic and mitochondrial genes in iWAT and BAT. N = 6 per group. Data are presented as mean ± SEM, ^*P < 0.05, ^**P < 0.01 compared to chow group and ^#P < 0.05, ^##P < 0.01 compared to HFD group.

Figure 4

Rb2 treatment increased adaptive thermogenesis. (A,B) Rectal body temperature and related AUC of DIO mice treated with or without Rb2 during cold tolerance test. (C–F) Immunohistochemistry for UCP1 staining and gene expression of Pgc1α and Ucp1 in iWAT and BAT of DIO mice treated with or without Rb2 under cold stimuli for 24 h. N = 6 per group. Data are presented as mean ± SEM and ^#P < 0.05 compared to HFD group in (A,B), ^*P < 0.05, ^**P < 0.01 compared to HFD 22°C group and ^#P < 0.05, ^##P < 0.01 compared to HFD 4°C group in (D,F).

Figure 5

Rb2 treatment induced brown gene programs in white adipocytes. (A,B) mRNA levels of Ucp1 in 3T3-L1 cells treated with or without Rb2 in dose and time dependent manner. (C,D) mRNA levels of thermogenic and mitochondrial genes in 3T3-L1 adipocytes and differentiated adipocytes from primary iWAT SVF. N = 6 per group. Data are presented as mean ± SEM and ^*P < 0.05, ^**P < 0.01 compared to control group.

Figure 6

AMPK signaling pathway was dispensable for the beneficial effects of Rb2 in browning. (A,B) Phosphorylation and total protein levels of AMPK in response to Rb2 treatment in the iWAT and BAT of DIO mice. (C) Phosphorylation and total AMPK levels in 3T3-L1 adipocytes treated with or without Rb2 in the absence or presence of compound C (10 μM). mRNA levels of Pgc1α and Ucp1 in 3T3-L1 adipocytes (D,E) and differentiated adipocytes from primary iWAT SVF (F,G) treated with or without Rb2 in the absence or presence of compound C. Data are presented as mean ± SEM, ^*P < 0.05, ^**P < 0.01 compared to control group and ^#P < 0.05, ^##P < 0.01 compared to Rb2 group.