Biochemical and Biophysical Research Communications
Promiscuous activity of the LXR antagonist GSK2033 in a mouse model of fatty liver disease
Introduction
The Liver X Receptor (LXR) serves as a receptor for oxysterols and regulates lipid and carbohydrate metabolism as well as immune function. Two LXRs exist, LXRα (NR1H3), which is expressed in liver, adipose tissue, and macrophages, and LXRβ (NR1H2) that is expressed ubiquitously. Both LXRs share a high degree of homology and act as cholesterol sensors, activated by cholesterol derivatives and regulate reverse cholesterol transport [1], [2], [3], [4], [5], [6], [7].
LXRs form heterodimers with the Retinoid X Receptor (RXR) and bind to LXR response elements (LXREs) and associate with coactivator or corepressor complexes to regulate the transcription of target genes. LXR agonists, including the well-characterized T0901317, are well characterized for their ability to suppress atherosclerosis in animal models and have also been shown to display anti-diabetic and anti-inflammatory activity [8], [9], [10], [11], [12], [13] Although the LXR agonists display beneficial effects in these disease models, they also increase hepatic lipogenesis resulting in elevated plasma, which precludes them from further development towards clinical therapeutics [14], [15], [16], [17], [18]. Antagonists of LXR have also been described [3], [19], [20], [21], [22], [23] and we recently described the action of a synthetic LXR inverse (SR9238) agonist that suppresses hepatic lipogenesis [24], [25]. One might expect that LXR antagonists/inverse agonists would display proinflammatory effects as well as proatherogenic effects; however, SR9238 displays liver specificity. By limiting its extrahepatic exposure (SR9238), these untoward effects were eliminated [24], [25]. SR9238 displays efficacy in reducing fatty liver in a mouse model of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis [24], [25]. In this study, we examined the activity of a LXR antagonist that displays systemic exposure, GSK2033 [21].
Section snippets
Cell lines and cotransfection assays
HEK293 cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% FBS and antibiotics (penicillin and streptomycin; Invitrogen). HepG2 cells were maintained in minimal essential medium supplemented with 10% FBS and antibiotics. Transfection assays were carried out as previously described [24].
Pharmacokinetic studies
Pharmacokinetic studies were performed as previously described [24], [26].
Animals and preparation of tissue samples
21-week old male C57BL6 DIO mice were purchased from Jackson Labs. All procedures were approved and
Results
Zuercher et al. previously identified GSK2033 (Fig. 1A) as an LXR antagonist that displayed high binding affinity for LXR while antagonizing LXR target gene expression in cell culture [21]. We confirmed this activity in cell based cotransfection assays where we assessed the ability of GSK2033 to suppress basal transcription LXRα and LXRβ as detected by luciferase reporters driven by either DR4 LXREs (Fig. 1B) or the ABCA1 promoter (Fig. 1C). As shown in Fig. 1B, GSK2033 dose-dependently
Discussion
LXR is ligand-activated nuclear receptor that plays a role in cholesterol, fatty acid, and glucose homeostasis and is also a potential drug target for the treatment of several diseases including atherosclerosis [11], [9], [12], Alzheimer's Disease [33] and NAFLD/NASH [24], [25]. Several studies have previously shown the beneficial effects on atherosclerosis when treating with LXR agonists such as T0901317 or GSK3965 [8], [12], [34], [35], [36], however the development of LXR agonists for
Conflict of interest
The authors declare that they have no conflicts of interest.
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