Role of Nrf2 in prevention of high-fat diet-induced obesity by synthetic triterpenoid CDDO-imidazolide

Abstract

The synthetic oleanolic triterpenoid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Imidazolide or CDDO-Im) is an extremely potent activator of Nrf2 signaling. In cells undergoing adipogenesis, CDDO-Im prevents lipid accumulation in an Nrf2-dependent manner. However, in vivo evidence for effects of CDDO-Im on obesity is lacking. The goals of these studies were to determine if CDDO-Im can prevent high-fat diet-induced obesogenesis in the mouse, and to elucidate the molecular target of drug action. Wild-type and Nrf2-disrupted C57BL/6J female mice were dosed 3 times per week with 30 micromol/kg CDDO-Im or vehicle by oral gavage, during 95 days of access to a control diet or a high-fat diet. Body weights, organ weights, hepatic fat accumulation and gene expression were measured. Treatment with CDDO-Im effectively prevented high-fat diet-induced increases in body weight, adipose mass, and hepatic lipid accumulation in wild-type mice but not in Nrf2-disrupted mice. Wild-type mice on a high-fat diet and treated with CDDO-Im exhibited higher oxygen consumption and energy expenditure than vehicle-treated mice, while food intake was lower in CDDO-Im-treated than vehicle-treated mice. Levels of gene transcripts for fatty acid synthesis enzymes were downregulated after CDDO-Im treatment in the liver of wild-type mice. This inhibitory effect of CDDO-Im on lipogenic gene expression was significantly reduced in Nrf2-disrupted mice. The results indicate that CDDO-Im is an exceedingly potent agent for preventing obesity, and identify the Nrf2 pathway as a novel target for management of obesogenesis.

Fig. 1

Effects of CDDO-Im on body weight gain of (A) wild-type mice and (B) Nrf2-disrupted mice. Mice fed a control diet (Con) or a high-fat diet (HF) for 95 days were dosed with 30 μmol/kg body weight CDDO-Im or vehicle by gavage 3 times per week throughout the feeding period with both diets. Body weights were monitored before each treatment, 3 times per week. Data represent mean ± S.E.M., n = 8–15 per group.

Fig. 2

Indirect calorimetry and food intake analysis in wild-type mice fed a high-fat diet. (A) Protocol for indirect calorimetry. High-fat diet-fed mice were treated with 30 μmol/kg body weight CDDO-Im or vehicle for 82 days and indirect calorimetry was performed thereafter from days 0 to 4. Mice were dosed with CDDO-Im on days 0 and 2 (*). (B–H) All data represent mean ± S.E.M., n = 8 per group. ^* P < 0.05, CDDO-Im vs. vehicle. (B) Food intake (C) Oxygen consumption (VO₂) (D) Average oxygen consumption (E) Respiratory exchange ratio (RER) (F) Average respiratory exchange ratio (G) Energy expenditure normalized to body weight (H) Average energy expenditure normalized to body weight.

Fig. 3

Effects of CDDO-Im on hepatic lipid accumulation in wild-type mice and Nrf2-disrupted mice. Liver sections were stained with Oil Red O, and surface area of stained lipid droplets was normalized by number of hepatocyte nuclei per field. All data represent mean ± S.E.M., n = 5–8 per group. ^* P < 0.05, CDDO-Im vs. vehicle. ^{^} P < 0.05, high-fat diet vs. control diet.

Fig. 4

Effects of CDDO-Im on gene expression and fatty acid synthase activity in wild-type mice fed a control diet or a high-fat diet for 95 days (A, B, D) or 21 days (C). (A) Analysis of hepatic gene expression using quantitative real-time PCR following 95 days of treatment. Data represent mean ± S.E.M., n = 6–8 per group. ^* P ≤ 0.05, CDDO-Im vs. vehicle. ^{^} P < 0.05, high-fat diet vs. control diet. (B) Specific activity of fatty acid synthase in the liver of mice fed a high-fat diet for 95 days (nmol NADPH oxidized per min per mg protein). Data represent mean ± S.E.M., n = 4 per group. ^* P < 0.05, CDDO-Im vs. vehicle. (C) Analysis of hepatic gene expression using quantitative RT-PCR following 21 days of treatment. Data represent mean ± S.E.M., n = 6 per group. ^* P < 0.05, CDDO-Im vs. vehicle. ^{^} P < 0.05, high-fat diet vs. control diet. (D) Analysis of gene expression in white adipose tissue using quantitative RT-PCR following 95 days of treatment. Data represent mean ± S.E.M., n = 6 per group. ^* P < 0.05, CDDO-Im vs. vehicle. ^{^} P < 0.05, high-fat diet vs. control diet.

Fig. 5

Effects of CDDO-Im on hepatic gene expression in Nrf2-disrupted mice. Data represent mean ± S.E.M., n = 6 per group. ^* P < 0.05, CDDO-Im vs. vehicle. ^{^} P < 0.05, high-fat diet vs. control diet.