Endocrine PharmacologyRole of Nrf2 in prevention of high-fat diet-induced obesity by synthetic triterpenoid CDDO-Imidazolide
Introduction
There has been a striking increase in the incidence of obesity worldwide over the past several decades. In 2005–2006, a third of adults in the USA were defined as obese (Centers for Disease Control and Prevention). Interest in obesity has expanded over the past decade because obesity is associated with increased morbidity and mortality (Rosen and MacDougald, 2006). Obesity is linked with type 2 diabetes, cardiovascular disease, osteoarthritis, as well as certain type of cancers (Rosen, 2005, Ginter and Simko, 2008, Cerulli et al., 2007). A wide range of pharmacologic approaches for the management of obesity such as appetite suppressants and lipase inhibitors have been evaluated (Cerulli et al., 2007), but their efficacy is often restricted to a weight reduction of 5–10% (Cerulli et al., 2007, Weigle, 2003), necessitating development of alternative options.
The synthetic triterpenoid analog of oleanolic acid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im) is a potent inducer of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling both in vitro and in vivo (Yates et al., 2007). Nrf2 is a member of the Cap'n'Collar subfamily of basic leucine zipper transcription factors that regulate expression of antioxidant and cytoprotective genes. Nrf2-disrupted mice do not exhibit any remarkable phenotype in the absence of exogenous stress, but are more sensitive to toxic challenges such as exposure to carcinogens, allergens and other inflammatory factors (Kensler et al., 2007). Therefore, studies using Nrf2-disrupted mice and/or CDDO-Im have been focused on its protective effects against electrophilic and oxidative stresses. However, previous studies have indicated that CDDO-Im inhibits accumulation of lipid droplets in an Nrf2-dependent manner in an adipocyte differentiation model in mouse embryonic fibroblasts (Shin et al., 2007), and CDDO-Im downregulates expression of fatty acid synthase (encoded by Fasn) in a liposarcoma cell line (Hughes et al., 2008). Moreover, recent expression analyses in our lab indicate that hepatic genes involved in fat and carbohydrate metabolism are major targets of CDDO-Im and Keap1, a cytoplasmic protein that binds Nrf2, thereby preventing its nuclear translocation and nuclear accumulation (Yates et al., 2009).
Oral administrations of CDDO-Im have been shown to ameliorate chronic diseases such as carcinogenesis and emphysema in rodent models (Yates et al., 2006, Sussan et al., 2009). However, the effects of this pharmacologic agent on obesogenesis in vivo remain unknown. We evaluated the potential for CDDO-Im to function as an anti-obesity drug in mice fed a high-fat diet. In order to determine whether and how CDDO-Im regulates whole body energy balance, and to identify molecular target responsible for drug actions on obesogenesis, effects of CDDO-Im treatment were examined on multiple parameters associated with obesity in wild-type and Nrf2-disrupted mice.
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Experimental animals
All procedures were approved by the Johns Hopkins University Animal Care and Use Committee. Wild-type C57BL/6J mice were obtained from The Jackson Laboratories (Bar Harbor, ME). Nrf2-disrupted mice on a C57BL/6J background were generated as described previously (Iida et al., 2004). Female mice (6–7 week-old) were fed a control diet (10 kcal% fat, Research Diets, New Brunswick, NJ) or a high-fat diet (60 kcal% fat, Research Diets) for 21 days or 95 days. Mice were dosed by oral gavage with vehicle
CDDO-Im prevents body weight gain following a high-fat diet in an Nrf2-dependent manner
Previous studies indicated that CDDO-Im inhibits fat accumulation in cell culture models (Shin et al., 2007, Hughes et al., 2008). In order to determine the effects of CDDO-Im on body weight gain, wild-type mice fed a control diet or a high-fat diet were dosed chronically with vehicle or 30 μmol/kg CDDO-Im (Fig. 1A). Our previous study indicated that 30 μmol/kg CDDO-Im was optimal to induce the Nrf2-target gene NAD(P)H: quinone acceptor oxidoreductase 1 in mouse liver (Yates et al., 2007). A
Discussion
Prevalence of obesity has markedly increased in many parts of the world (Ginter and Simko, 2008). According to the Centers for Disease Control and Prevention, health consequences of obesity include coronary heart disease, type 2 diabetes, cancers, liver and gallbladder disease, highlighting the importance of prevention of obesity. An inhibitory effect of CDDO-Im on lipid synthesis has been demonstrated in vitro (Shin et al., 2007, Hughes et al., 2008), but its effect on obesogenesis in vivo
Acknowledgments
This work was supported by NIH grants CA094076 (TWK) and CA78814 (MBS), and by a grant from Reata Pharmaceuticals (MBS). Soona Shin is recipient of a Samsung Scholarship (Samsung Foundation of Culture). This forms part of the dissertation of S.S. at the Johns Hopkins University. We thank Brian H. Schofield, Nadine Forbes, and Patricia Egner for assistance with histology, the lipid panel, and fatty acid synthase assay, respectively.
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