A liver-selective LXR inverse agonist that suppresses hepatic steatosis

Liver X receptor inverse agonist SR9243 attenuates rheumatoid arthritis via modulating glycolytic metabolism of macrophages

Liver X receptors (LXRs) which link lipid metabolism and inflammation, were overexpressed in experimental rheumatoid arthritis (RA) rats as observed in our previous studies, while suppression of LXRα by silybin ameliorates arthritis and abnormal lipid metabolism. However, the role of LXRs in RA remains undefined. In this study, we investigated the inhibition role of LXRs in the polarization and activation of M1 macrophage by using a special LXRs inverse agonist SR9243, which led to ameliorating the progression of adjuvant-induced arthritis (AIA) in rats. Mechanistically, SR9243 disrupted the LPS/IFN-γ-induced Warburg effect in M1 macrophages, while glycolysis inhibitor 2-DG attenuated the inhibition effect of SR9243 on M1 polarization and the cytokines expression of M1 macrophages including iNOS, TNF-α, and IL-6 in vitro. Furthermore, SR9243 downregulated key glycolytic enzymes, including LDH-A, HK2, G6PD, GLUT1, and HIF-1α in M1 macrophages, which is mediated by increased phosphorylation of AMPK (Thr172) and reduced downstream phosphorylation of mTOR (Ser2448). Importantly, gene silencing of LXRs compromises the inhibition effect of SR9243 on M1 macrophage polarization and activation. Collectively, for the first time, our findings suggest that the LXR inverse agonist SR9243 mitigates adjuvant-induced rheumatoid arthritis and protects against bone erosion by inhibiting M1 macrophage polarization and activation through modulation of glycolytic metabolism via the AMPK/mTOR/HIF-1α pathway.

Discovery of N-Aryl-N'-[4-(aryloxy)cyclohexyl]squaramide-Based Inhibitors of LXR/SREBP-1c Signaling Pathway Ameliorating Steatotic Liver Disease: Navigating the Role of SIRT6 Activation

Metabolic dysfunction-associated steatotic liver disease (MASLD) is primarily attributed to the abnormal upregulation of hepatic lipogenesis, which is especially caused by the overactivation of the liver X receptor/sterol regulatory element-binding protein-1c (LXR/SREBP-1c) pathway in hepatocytes. In this study, we report the rational design and synthesis of a novel series of squaramides via bioisosteric replacement, which was evaluated for its inhibitory activity on the LXR/SREBP-1c pathway using dual cell-based assays. Compound 31 was found to significantly downregulate LXR, SREBP-1c, and their target genes associated with lipogenesis. Further investigation revealed that compound 31 may indirectly inhibit the LXR/SREBP-1c pathway by activating the upstream regulator sirtuin 6 (SIRT6). Encouragingly, compound 31 substantially attenuated lipid accumulation in HepG2 cells and in the liver of high-fat-diet-fed mice. These findings suggest that compound 31 holds promise as a candidate for the development of treatments for MASLD and other lipid metabolism-related diseases.

Damaging mutations in liver X receptor-α are hepatotoxic and implicate cholesterol sensing in liver health

Liver X receptor-α (LXRα) regulates cellular cholesterol abundance and potently activates hepatic lipogenesis. Here we show that at least 1 in 450 people in the UK Biobank carry functionally impaired mutations in LXRα, which is associated with biochemical evidence of hepatic dysfunction. On a western diet, male and female mice homozygous for a dominant negative mutation in LXRα have elevated liver cholesterol, diffuse cholesterol crystal accumulation and develop severe hepatitis and fibrosis, despite reduced liver triglyceride and no steatosis. This phenotype does not occur on low-cholesterol diets and can be prevented by hepatocyte-specific overexpression of LXRα. LXRα knockout mice exhibit a milder phenotype with regional variation in cholesterol crystal deposition and inflammation inversely correlating with steatosis. In summary, LXRα is necessary for the maintenance of hepatocyte health, likely due to regulation of cellular cholesterol content. The inverse association between steatosis and both inflammation and cholesterol crystallization may represent a protective action of hepatic lipogenesis in the context of excess hepatic cholesterol.

A Novel Mutation in LXRα Uncovers a Role for Cholesterol Sensing in Limiting Metabolic Dysfunction-Associated Steatohepatitis (MASH)

Liver x receptor alpha (LXRα, Nr1h3) functions as an important intracellular cholesterol sensor that regulates fat and cholesterol metabolism at the transcriptional level in response to the direct binding of cholesterol derivatives. We have generated mice with a mutation in LXRα that reduces activity in response to endogenous cholesterol derived LXR ligands while still allowing transcriptional activation by synthetic agonists. The mutant LXRα functions as a dominant negative that shuts down cholesterol sensing. When fed a high fat, high cholesterol diet LXRα mutant mice rapidly develop pathologies associated with Metabolic Dysfunction-Associated Steatohepatitis (MASH) including ballooning hepatocytes, liver inflammation, and fibrosis. Strikingly LXRα mutant mice have decreased liver triglycerides but increased liver cholesterol. Therefore, MASH-like phenotypes can arise in the absence of large increases in triglycerides. Reengaging LXR signaling by treatment with synthetic agonist reverses MASH suggesting that LXRα normally functions to impede the development of liver disease.

Association of Di(2-ethylhexyl) Terephthalate and Its Metabolites with Nonalcoholic Fatty Liver Disease: An Epidemiology and Toxicology Study

As an alternative plasticizer to conventional phthalates, di(2-ethylhexyl) terephthalate (DEHTP) has attracted considerable concerns, given its widespread detection in the environment and humans. However, the potential toxicity, especially liver toxicity, posed by DEHTP remains unclear. In this study, based on the 2017-2018 National Health and Nutrition Examination Survey, two metabolites of DEHTP, i.e., mono(2-ethyl-5-hydroxyhexyl) terephthalate (MEHHTP) and mono(2-ethyl-5-carboxypentyl) terephthalate (MECPTP), were found to be present in the urine samples of nearly all representative U.S. adults. Moreover, a positive linear correlation was observed between the concentrations of the two metabolites and the risk of nonalcoholic fatty liver disease (NAFLD) in the population. Results of weighted quantile sum and Bayesian kernel machine regression indicated that MEHHTP contributed a greater weight to the risk of NAFLD in comparison with 12 conventional phthalate metabolites. In vitro experiments with hepatocyte HepG2 revealed that MEHHTP exposure could increase lipogenic gene programs, thereby promoting a dose-dependent hepatic lipid accumulation. Activation of liver X receptor α may be an important regulator of MEHHTP-induced hepatic lipid disorders. These findings provide new insights into the liver lipid metabolism toxicity potential of DEHTP exposure in the population.

Targeting ABCG1 and SREBP-2 mediated cholesterol homeostasis ameliorates Zika virus-induced ocular pathology

Zika virus (ZIKV) infection during pregnancy causes severe neurological and ocular abnormalities in infants, yet no vaccine or antivirals are available. Our transcriptomic analysis of ZIKV-infected retinal pigment epithelial (RPE) cells revealed alterations in the cholesterol pathway. Thus, we investigated the functional roles of ATP binding cassette transporter G1 (ABCG1) and sterol response element binding protein 2 (SREPB-2), two key players in cholesterol metabolism, during ocular ZIKV infection. Our in vitro data showed that increased ABCG1 activity via liver X receptors (LXRs), reduced ZIKV replication, while ABCG1 knockdown increased replication with elevated intracellular cholesterol. Conversely, inhibiting SREBP-2 or its knockdown reduced ZIKV replication by lowering cholesterol levels. In vivo, LXR agonist or SREBP-2 inhibitor treatment mitigated ZIKV-induced chorioretinal lesions in mice, concomitant with decreased expression of inflammatory mediators and increased activation of antiviral response genes. In summary, our study identifies ABCG1's antiviral role and SREBP-2's proviral effects in ocular ZIKV infection, offering cholesterol metabolism as a potential target to develop antiviral therapies.

The roles of nuclear receptors in cholesterol metabolism and reverse cholesterol transport in nonalcoholic fatty liver disease

As the most prevalent chronic liver disease globally, NAFLD encompasses a pathological process that ranges from simple steatosis to NASH, fibrosis, cirrhosis, and HCC, closely associated with numerous extrahepatic diseases. While the initial etiology was believed to be hepatocyte injury caused by lipid toxicity from accumulated triglycerides, recent studies suggest that an imbalance of cholesterol homeostasis is of greater significance. The role of nuclear receptors in regulating liver cholesterol homeostasis has been demonstrated to be crucial. This review summarizes the roles and regulatory mechanisms of nuclear receptors in the 3 main aspects of cholesterol production, excretion, and storage in the liver, as well as their cross talk in reverse cholesterol transport. It is hoped that this review will offer new insights and theoretical foundations for the study of the pathogenesis and progression of NAFLD and provide new research directions for extrahepatic diseases associated with NAFLD.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Characterization of an in vitro steatosis model simulating activated de novo lipogenesis in MAFLD patients

Activated de novo lipogenesis (DNL) is the critical pathway involved in the progression of metabolic-associated fatty liver disease (MAFLD). We present an in vitro steatosis model for MAFLD that induces steatosis through activated DNL. This model utilizes insulin and LXR receptor ligand T0901317, eliminating the need for fatty acid treatment. Significant increases in triglycerides (TAGs) and expression of DNL-related transcription factors were observed. Transcriptomic analysis revealed distinct gene expression profiles between the DNL and conventional oleic acid (OA)-induced steatosis model. DNL steatosis model exhibited elevated pathways related to glycolysis, cholesterol homeostasis, and bile acid metabolism, reflecting its clinical relevance to MAFLD. Moreover, C75 and JNK-IN-5A compounds effectively reduced TAG accumulation and steatosis-related protein expression in the DNL model, whereas they had no significant impact on TAG accumulation in the OA model. In conclusion, we introduce an ideal model for steatosis study, which could help in understanding the MAFLD mechanisms.

Development and pharmacological evaluation of a new chemical series of potent pan-ERR agonists, identification of SLU-PP-915

Estrogen-related receptors (ERR) are an orphan nuclear receptor sub-family that play a critical role in regulating gene transcription for several physiological processes including mitochondrial function, cellular energy utilization and homeostasis. They have also been implicated to play a role in several pathological conditions. Herein, we report the identification, synthesis, structure-activity relationships and pharmacological evaluation of a new chemical series of potent pan-ERR agonists. This template was designed for ERRγ starting from the known acyl hydrazide template and compounds such as agonist GSK-4716 employing a structure-based drug design approach. This led to the preparation of a series of 2,5-disubstituted thiophenes from which several were found to be potent agonists of ERRγ in cell-based co-transfection assays. Additionally, direct binding to ERRγ was established through 1H NMR protein-ligand binding experiments. Compound optimization revealed that the phenolic or aniline groups could be replaced with a boronic acid moiety, which was able to maintain activity and demonstrated improved metabolic stability in microsomal in vitro assays. Further pharmacological evaluation of these compounds showed that they had roughly equivalent agonist activity on ERR isoforms α and β representing an ERR pan-agonist profile. One potent agonist, SLU-PP-915 (10s), which contained a boronic acid moiety was profiled in gene expression assays and found to significantly upregulate the expression of ERR target genes such as peroxisome-proliferator activated receptor γ co-activators-1α, lactate dehydrogenase A, DNA damage inducible transcript 4 and pyruvate dehydrogenase kinase 4 both in vitro and in vivo.

Genetic perturbation of AMP biosynthesis extends lifespan and restores metabolic health in a naturally short-lived vertebrate

During aging, the loss of metabolic homeostasis drives a myriad of pathologies. A central regulator of cellular energy, the AMP-activated protein kinase (AMPK), orchestrates organismal metabolism. However, direct genetic manipulations of the AMPK complex in mice have, so far, produced detrimental phenotypes. Here, as an alternative approach, we alter energy homeostasis by manipulating the upstream nucleotide pool. Using the turquoise killifish, we mutate APRT, a key enzyme in AMP biosynthesis, and extend the lifespan of heterozygous males. Next, we apply an integrated omics approach to show that metabolic functions are rejuvenated in old mutants, which also display a fasting-like metabolic profile and resistance to high-fat diet. At the cellular level, heterozygous cells exhibit enhanced nutrient sensitivity, reduced ATP levels, and AMPK activation. Finally, lifelong intermittent fasting abolishes the longevity benefits. Our findings suggest that perturbing AMP biosynthesis may modulate vertebrate lifespan and propose APRT as a promising target for promoting metabolic health.

Toxicokinetic and toxicodynamic mixture effects of plant protection products: A case study

Authorisation of ready to use plant protection products (PPPs) usually relies on the testing of acute and local toxicity only. This is in stark contrast to the situation for active substances where the mandatory data set comprises a most comprehensive set of studies. While the combination of certain active ingredients and co-formulants may nevertheless result in increased toxicity of the final product such combinations have never been evaluated systematically for complex and long-term toxicological endpoints. We therefore investigated the effect of three frequently used co-formulants on the toxicokinetic and toxicodynamic of the representative active substance combination of tebuconazol (Teb) and prothioconazol (Pro) or of cypermethrin (Cpm) and piperonyl butoxide (Pip), respectively. With all four active substances being potential liver steatogens, cytotoxicity and triglyceride accumulation in HepaRG were used as primary endpoints. Concomitantly transcriptomics and biochemical studies were applied to interrogate for effects on gene expression or inhibition of CYP3A4 as key enzyme for functionalization. Some of the tested combinations clearly showed more than additive effects, partly due to CYP3A4 enzyme inhibition. Other effects comprised the modulation of the expression and activity of steatosis-related nuclear key receptors. Altogether, the findings highlight the need for a more systematic consideration of toxicodynamic and toxicokinetic mixture effects during assessment of PPPs.

The diverse roles of macrophages in metabolic inflammation and its resolution

Macrophages are one of the most functionally diverse immune cells, indispensable to maintain tissue integrity and metabolic health. Macrophages perform a myriad of functions ranging from promoting inflammation, through inflammation resolution to restoring and maintaining tissue homeostasis. Metabolic diseases encompass a growing list of diseases which develop from a mix of genetics and environmental cues leading to metabolic dysregulation and subsequent inflammation. In this review, we summarize the contributions of macrophages to four metabolic conditions-insulin resistance and adipose tissue inflammation, atherosclerosis, non-alcoholic fatty liver disease and neurodegeneration. The role of macrophages is complex, yet they hold great promise as potential therapies to address these growing health concerns.

Trust Your Gut: Strategies and Tactics for Intestinally Restricted Drugs

Non-absorbable small-molecule drugs targeted to the gut represent an alternative approach to safe, non-systemic therapeutics. Such drugs remain confined to the gastrointestinal tract upon oral dosing by virtue of their limited passive permeability, increasing the local concentration at the site of action while minimizing exposure elsewhere in the body. Herein we review the latest advances in the field of gut-restricted therapeutics, highlighting the different strategies and tactics that medicinal chemists have employed in pursuit of drugs with minimal intestinal absorption.

Microsomal Prostaglandin E Synthase-1 and -2: Emerging Targets in Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) affects a substantial proportion of the general population and is even more prevalent in obese and diabetic patients. NAFLD, and particularly the more advanced manifestation of the disease, nonalcoholic steatohepatitis (NASH), increases the risk for both liver-related and cardiovascular morbidity. The pathogenesis of NAFLD is complex and multifactorial, with many molecular pathways implicated. Emerging data suggest that microsomal prostaglandin E synthase-1 and -2 might participate in the development and progression of NAFLD. It also appears that targeting these enzymes might represent a novel therapeutic approach for NAFLD. In the present review, we discuss the association between microsomal prostaglandin E synthase-1 and -2 and NAFLD.

Development of LXR inverse agonists to treat MAFLD, NASH, and other metabolic diseases

Activation of LXR activity by synthetic agonists has been the focus of many drug discovery efforts with a focus on treatment of dyslipidemia and atherosclerosis. Many agonists have been developed, but all have been hindered due to their ability to efficaciously stimulate de novo lipogenesis. Here, we review the development of LXR inverse agonists that were originally optimized for their ability to enable recruitment of corepressors leading to silencing of genes that drive de novo lipogenesis. Such compounds have efficacy in animal models of MAFLD, dyslipidemia, and cancer. Several classes of LXR inverse agonists have been identified and one is now in clinical trials for treatment of severe dyslipidemia.

Cyclic Phthalate Esters as Liver X Receptor Antagonists with Anti-hepatitis C Virus and Anti-severe Acute Respiratory Syndrome Coronavirus 2 Properties

The liver X receptor is a nuclear hormone receptor that regulates lipid metabolism. Previously, we had demonstrated the antiviral properties of a liver X receptor antagonist associated with the hepatitis C virus and severe acute respiratory syndrome coronavirus 2. In this study, we screened a chemical library and identified two potential liver X receptor antagonists. Spectroscopic analysis revealed that the structures of both antagonists (compounds 1 and 2) were cyclic dimer and trimer of esters, respectively, that consisted of phthalate and 1,6-hexane diol. This study is the first to report the structure of the cyclic trimer of phthalate ester. Further experiments revealed that the compounds were impurities of solvents used for purification, although their source could not be traced. Both phthalate esters exhibited anti-hepatitis C virus activity, whereas the cyclic dimer showed anti-severe acute respiratory syndrome coronavirus 2 activity. Cyclic phthalate derivatives may constitute a novel class of liver X receptor antagonists and broad-spectrum antivirals.

Antihyperlipidemic Activity of Gut-Restricted LXR Inverse Agonists

Hyperlipidemia and increased circulating cholesterol levels are associated with increased cardiovascular disease risk. The liver X receptors (LXRs) are regulators of de novo lipogenesis and cholesterol transport and have been validated as potential therapeutic targets for the treatment of atherosclerosis. However, efforts to develop LXR agonists to reduce cardiovascular diseases have failed due to poor clinical outcomes-associated increased hepatic lipogenesis and elevated low-density lipoprotein (LDL) cholesterol (C). Here, we report that LXR inverse agonists are effective in lowering plasma LDL cholesterol and triglycerides in several models of hyperlipidemia, including the Ldlr null mouse model of atherosclerosis. Mechanistic studies demonstrate that LXR directly regulates the expression of Soat2 enzyme in the intestine, which is directly responsible for the re-uptake or excretion of circulating lipids. Oral administration of a gut-specific LXR inverse agonist leads to reduction of Soat2 expression in the intestine and effectively lowers circulating LDL cholesterol and triglyceride levels without modulating LXR target genes in the periphery. In summary, our studies highlight the therapeutic potential of the gut-restricted molecules to treat hyperlipidemia and atherosclerosis through the intestinal LXR-Soat2 axis.

Multi-Omics Approach Reveals Dysregulation of Protein Phosphorylation Correlated with Lipid Metabolism in Mouse Non-Alcoholic Fatty Liver

Obesity caused by overnutrition is a major risk factor for non-alcoholic fatty liver disease (NAFLD). Several lipid intermediates such as fatty acids, glycerophospholipids and sphingolipids are implicated in NAFLD, but detailed characterization of lipids and their functional links to proteome and phosphoproteome remain to be elucidated. To characterize this complex molecular relationship, we used a multi-omics approach by conducting comparative proteomic, phoshoproteomic and lipidomic analyses of high fat (HFD) and low fat (LFD) diet fed mice livers. We quantified 2447 proteins and 1339 phosphoproteins containing 1650 class I phosphosites, of which 669 phosphosites were significantly different between HFD and LFD mice livers. We detected alterations of proteins associated with cellular metabolic processes such as small molecule catabolic process, monocarboxylic acid, long- and medium-chain fatty acid, and ketone body metabolic processes, and peroxisome organization. We observed a significant downregulation of protein phosphorylation in HFD fed mice liver in general. Untargeted lipidomics identified upregulation of triacylglycerols, glycerolipids and ether glycerophosphocholines and downregulation of glycerophospholipids, such as lysoglycerophospholipids, as well as ceramides and acylcarnitines. Analysis of differentially regulated phosphosites revealed phosphorylation dependent deregulation of insulin signaling as well as lipogenic and lipolytic pathways during HFD induced obesity. Thus, this study reveals a molecular connection between decreased protein phosphorylation and lipolysis, as well as lipid-mediated signaling in diet-induced obesity.

Emerging Role of Nuclear Receptors for the Treatment of NAFLD and NASH

Non-alcoholic fatty liver (NAFLD) over the past years has become a metabolic pandemic linked to a collection of metabolic diseases. The nuclear receptors ERRs, REV-ERBs, RORs, FXR, PPARs, and LXR are master regulators of metabolism and liver physiology. The characterization of these nuclear receptors and their biology has promoted the development of synthetic ligands. The possibility of targeting these receptors to treat NAFLD is promising, as several compounds including Cilofexor, thiazolidinediones, and Saroglitazar are currently undergoing clinical trials. This review focuses on the latest development of the pharmacology of these metabolic nuclear receptors and how they may be utilized to treat NAFLD and subsequent comorbidities.

Pseudorabies Virus Inhibits Expression of Liver X Receptors to Assist Viral Infection

Pseudorabies virus (PRV) is a contagious herpesvirus that causes Aujeszky’s disease and economic losses worldwide. Liver X receptors (LXRs) belong to the nuclear receptor superfamily and are critical for the control of lipid homeostasis. However, the role of LXR in PRV infection has not been fully established. In this study, we found that PRV infection downregulated the mRNA and protein levels of LXRα and LXRβ in vitro and in vivo. Furthermore, we discovered that LXR activation suppressed PRV proliferation, while LXR inhibition promoted PRV proliferation. We demonstrated that LXR activation-mediated reduction of cellular cholesterol was critical for the dynamics of PRV entry-dependent clathrin-coated pits. Replenishment of cholesterol restored the dynamics of clathrin-coated pits and PRV entry under LXR activation conditions. Interestingly, T0901317, an LXR agonist, prevented PRV infection in mice. Our results support a model that PRV modulates LXR-regulated cholesterol metabolism to facilitate viral proliferation.

Remembering your A, B, C's: Alzheimer's disease and ABCA1

The function of ATP binding cassette protein A1 (ABCA1) is central to cholesterol mobilization. Reduced ABCA1 expression or activity is implicated in Alzheimer's disease (AD) and other disorders. Therapeutic approaches to boost ABCA1 activity have yet to be translated successfully to the clinic. The risk factors for AD development and progression, including comorbid disorders such as type 2 diabetes and cardiovascular disease, highlight the intersection of cholesterol transport and inflammation. Upregulation of ABCA1 can positively impact APOE lipidation, insulin sensitivity, peripheral vascular and blood–brain barrier integrity, and anti-inflammatory signaling. Various strategies towards ABCA1-boosting compounds have been described, with a bias toward nuclear hormone receptor (NHR) agonists. These agonists display beneficial preclinical effects; however, important side effects have limited development. In particular, ligands that bind liver X receptor (LXR), the primary NHR that controls ABCA1 expression, have shown positive effects in AD mouse models; however, lipogenesis and unwanted increases in triglyceride production are often observed. The longstanding approach, focusing on LXRβ vs. LXRα selectivity, is over-simplistic and has failed. Novel approaches such as phenotypic screening may lead to small molecule NHR modulators that elevate ABCA1 function without inducing lipogenesis and are clinically translatable.

Synthesis and structure activity relationship of the first class of LXR inverse agonists

Liver X Receptors (LXRs) are members of the nuclear receptor family, and they play significant role in lipid and cholesterol metabolism. Moreover, they are key regulators of several inflammatory pathways. Pharmacological modulation of LXRs holds great potential in treatment of metabolic diseases, neurodegenerative diseases, and cancer. We were the first group to identify LXR inverse agonists SR9238 (6) and SR9243 (7) and demonstrate their potential utility in treating liver diseases and cancer. Here, we present the results of structure-activity relationship (SAR) studies, based around SR9238 (6) and SR9243 (7). This study led to identification of 16, 17, 19, and 38, which were more potent inverse agonists than SR9238 (6) and SR9243 (7) and inhibited expression of the fatty acid synthase gene in DU145 cells. We previously demonstrated that inhibition of FASN is correlated to the anticancer activity of SR9243 (7) and this suggests that new inverse agonists have great potential as anticancer agents. We identified compounds with distinct selectivity toward both LXR isoforms, which can be excellent tools to study the pharmacology of both isoforms. We employed molecular dynamic (MD) simulations to better understand the molecular mechanism underlying inverse agonist activity and to guide our future design.

Development of Agonist-Based PROTACs Targeting Liver X Receptor

Liver X receptors (LXRs) belong to the nuclear hormone receptor superfamily and function as ligand-dependent transcription factors that regulate cholesterol homeostasis, lipid homeostasis, and immune responses. LXR antagonists are promising treatments for hypercholesterolemia and diabetes. However, effective LXR antagonists and inhibitors are yet to be developed. Thus, we aimed to develop LXR degraders (proteolysis targeting chimeras PROTACs against LXR) as a complementary strategy to provide a similar effect to LXR inhibition. In this study, we report the development of GW3965-PEG5-VH032 (3), a PROTAC capable of effectively degrading LXRβ protein. Compound 3 induced the ubiquitin-proteasome system-dependent degradation of the LXRβ protein, which requires VHL E3 ligase. We hope that PROTACs targeting LXR proteins will become novel therapeutic agents for LXR-related diseases.

The Role of Lipid Sensing Nuclear Receptors (PPARs and LXR) and Metabolic Lipases in Obesity, Diabetes and NAFLD

Obesity and type 2 diabetes mellitus (T2DM) are metabolic disorders characterized by metabolic inflexibility with multiple pathological organ manifestations, including non-alcoholic fatty liver disease (NAFLD). Nuclear receptors are ligand-dependent transcription factors with a multifaceted role in controlling many metabolic activities, such as regulation of genes involved in lipid and glucose metabolism and modulation of inflammatory genes. The activity of nuclear receptors is key in maintaining metabolic flexibility. Their activity depends on the availability of endogenous ligands, like fatty acids or oxysterols, and their derivatives produced by the catabolic action of metabolic lipases, most of which are under the control of nuclear receptors. For example, adipose triglyceride lipase (ATGL) is activated by peroxisome proliferator-activated receptor γ (PPARγ) and conversely releases fatty acids as ligands for PPARα, therefore, demonstrating the interdependency of nuclear receptors and lipases. The diverse biological functions and importance of nuclear receptors in metabolic syndrome and NAFLD has led to substantial effort to target them therapeutically. This review summarizes recent findings on the roles of lipases and selected nuclear receptors, PPARs, and liver X receptor (LXR) in obesity, diabetes, and NAFLD.

The oxysterome and its receptors as pharmacological targets in inflammatory diseases

Oxysterols have gained attention over the last decades and are now considered as fully fledged bioactive lipids. The study of their levels in several conditions, including atherosclerosis, obesity and neurodegenerative diseases, led to a better understanding of their involvement in (patho)physiological processes such as inflammation and immunity. For instance, the characterization of the cholesterol-7α,25-dihydroxycholesterol/GPR183 axis and its implication in immunity represents an important step in the oxysterome study. Besides this axis, others were identified as important in several inflammatory pathologies (such as colitis, lung inflammation and atherosclerosis). However, the oxysterome is a complex system notably due to a redundancy of metabolic enzymes and a wide range of receptors. Indeed, deciphering oxysterol roles and identifying the potential receptor(s) involved in a given pathology remain challenging. Oxysterol properties are very diverse, but most of them could be connected by a common component: inflammation. Here, we review the implication of oxysterol receptors in inflammatory diseases.

Tanshinone IIA Downregulates Lipogenic Gene Expression and Attenuates Lipid Accumulation through the Modulation of LXRα/SREBP1 Pathway in HepG2 Cells

Abnormal and excessive accumulation of lipid droplets within hepatic cells is the main feature of steatosis and nonalcoholic fatty liver disease (NAFLD) or metabolic-associated fatty liver disease (MAFLD). Dysregulation of lipogenesis contributes to hepatic steatosis and plays an essential role in the pathological progress of MAFLD. Tanshinone IIA is a bioactive phytochemical isolated from Salvia miltiorrhiza Bunge and exhibits anti-inflammatory, antiatherosclerotic and antihyperlipidemic effects. In this study, we aimed to investigate the lipid-lowering effects of tanshinone IIA on the regulation of lipogenesis, lipid accumulation, and the underlying mechanisms in hepatic cells. We demonstrated that tanshinone IIA can significantly inhibit the gene expression involved in de novo lipogenesis including FASN, ACC1, and SCD1, in HepG2 and Huh 7 cells. Tanshinone IIA could increase phosphorylation of ACC1 protein in HepG2 cells. We further demonstrated that tanshinone IIA also could suppress the fatty-acid-induced lipogenesis and TG accumulation in HepG2 cells. Furthermore, tanshinone IIA markedly downregulated the mRNA and protein expression of SREBP1, an essential transcription factor regulating lipogenesis in hepatic cells. Moreover, we found that tanshinone IIA attenuated liver X receptor α (LXRα)-mediated lipogenic gene expression and lipid droplet accumulation, but did not change the levels of LXRα mRNA or protein in HepG2 cells. The molecular docking data predicted tanshinone IIA binding to the ligand-binding domain of LXRα, which may result in the attenuation of LXRα-induced transcriptional activation. Our findings support the supposition that tanshinone IIA possesses a lipid-modulating effect that suppresses lipogenesis and attenuates lipid accumulation by modulating the LXRα/SREBP1 pathway in hepatic cells. Tanshinone IIA can be potentially used as a supplement or drug for the prevention or treatment of MAFLD.

LXRα/β Antagonism Protects against Lipid Accumulation in the Liver but Increases Plasma Cholesterol in Rhesus Macaques

Nonalcoholic fatty liver disease (NAFLD) is characterized by lipid accumulation in the liver and associates with obesity, hyperlipidemia, and insulin resistance. NAFLD could lead to nonalcoholic steatohepatitis (NASH), hepatic fibrosis, cirrhosis, and even cancers. The development of therapy for NAFLD has been proven difficult. Emerging evidence suggests that liver X receptor (LXR) antagonist is a potential treatment for fatty liver disease. However, concerns about the cholesterol-increasing effects make it questionable for the development of LXR antagonists. Here, the overweight monkeys were fed with LXRβ-selective antagonist sophoricoside or LXRα/β dual-antagonist morin for 3 months. The morphology of punctured liver tissues was examined by H&E staining. The liver, heart, and kidney damage indices were analyzed using plasma. The blood index was assayed using complete blood samples. We show that LXRβ-selective antagonist sophoricoside and LXRα/β dual-antagonist morin alleviated lipid accumulation in the liver in overweight monkeys. The compounds resulted in higher plasma TC or LDL-c contents, increased white blood cell and lymphocyte count, and decreased neutrophile granulocyte count in the monkeys. The compounds did not alter plasma glucose, apolipoprotein A (ApoA), ApoB, ApoE, lipoprotein (a) (LPA), nonesterified fatty acid (NEFA), aspartate transaminases (AST), creatinine (CREA), urea nitrogen (UN), and creatine kinase (CK) levels. Our data suggest that LXRβ-selective and LXRα/β dual antagonism may lead to hypercholesterolemia in nonhuman primates, which calls into question the development of LXR antagonist as a therapy for NAFLD.

Screening for liver X receptor modulators: Where are we and for what use?

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are canonically activated by oxidized derivatives of cholesterol. Since the mid-90s, numerous groups have identified LXRs as endocrine receptors that are involved in the regulation of various physiological functions. As a result, when their expression is genetically modified in mice, phenotypic analyses reveal endocrine disorders ranging from infertility to diabetes and obesity, nervous system pathologies such Alzheimer's or Parkinson's disease, immunological disturbances, inflammatory response, and enhancement of tumour development. Based on such findings, it appears that LXRs could constitute good pharmacological targets to prevent and/or to treat these diseases. This review discusses the various aspects of LXR drug discovery, from the tools available for the screening of potential LXR modulators to the current situational analysis of the drugs in development. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Activation of the Liver X Receptor Pathway Inhibits HBV Replication in Primary Human Hepatocytes

BACKGROUND AND AIMS

Hepatitis B virus (HBV) infection is ranked among the top health priorities worldwide. Accumulating evidence suggests that HBV infection and replication are closely associated with liver metabolism. The liver X receptors (LXRs), which belong to the superfamily of nuclear hormone receptors, are important physiological regulators of lipid and cholesterol metabolism. However, the association between the LXR pathway and HBV infection remains largely unclear.

APPROACH AND RESULTS

In this study, the antiviral activity of LXR agonists was investigated using multiple HBV cellular models. We observed that in HBV-infected primary human hepatocytes (PHHs), synthetic LXR agonists (T0901317, GW3965, and LXR-623), but not an LXR antagonist (SR9238), potently inhibited HBV replication and gene expression, as demonstrated by substantial reductions in viral RNA, DNA, and antigen production following agonist treatment. However, covalently closed circular DNA (cccDNA) levels were not significantly reduced by the agonists. In addition, no rebound in viral replication was observed after treatment withdrawal, indicating a long-lasting inhibitory effect. These results suggest that LXR agonists decrease the transcriptional activity of cccDNA. In contrast, no significant anti-HBV effect was observed in HepG2-derived cell lines. Interestingly, LXR agonist treatment strongly reduced cholesterol 7α-hydroxylase 1 (CYP7A1) mRNA levels. Knockdown of CYP7A1 gene expression with small interfering RNA inhibited HBV activity in PHHs, suggesting CYP7A1 as a potential factor contributing to the antiviral effects of LXR agonists.

CONCLUSIONS

We found that activation of the LXR pathway with synthetic LXR agonists could elicit potent anti-HBV activity in PHHs, possibly through sustained suppression of cccDNA transcription. Our work highlights the therapeutic potential of targeting the LXR pathway for the treatment of chronic HBV infection.

Screening of Focused Compound Library Targeting Liver X Receptors in Pancreatic Cancer Identified Ligands with Inverse Agonist and Degrader Activity

Pancreatic ductal adenocarcinoma (PDAC) is the predominant form of pancreatic cancer. PDACs harbor oncogenic mutations in the KRAS gene, and ongoing efforts to directly target its mutant protein product to inhibit tumor growth are a priority not only in pancreatic cancer but in other malignancies such as lung and colorectal cancers where KRAS is also commonly mutated. An alternative strategy to directly targeting KRAS is to identify and target druggable receptors involved in dysregulated cancer hallmarks downstream of KRAS dysregulation. Liver X receptors (LXRs) are members of the nuclear receptor family of ligand-modulated transcription factors and are involved in the regulation of genes which function in key cancer-related processes, including cholesterol transport, lipid and glucose metabolism, and inflammatory and immune responses. Modulation of LXRs via small molecule ligands has emerged as a promising approach for directly targeting tumor cells or the stromal and immune cells within the tumor microenvironment. We have previously shown that only one of the two LXR subtypes (LXRβ) is expressed in pancreatic cancer cells, and targeting LXR with available synthetic ligands blocked the proliferation of PDAC cells and tumor formation. In a screen of a focused library of drug-like small molecules predicted to dock in the ligand-binding pocket of LXRβ, we identified two novel LXR ligands with more potent antitumor activity than current LXR agonists used in our published studies. Characterization of the two lead compounds (GAC0001E5 and GAC0003A4) indicates that they function as LXR inverse agonists which inhibit their transcriptional activity. Prolonged treatments with novel ligands further revealed their function as LXR "degraders" which significantly reduced LXR protein levels in all three PDAC cell lines tested. These findings support the utility of these novel inhibitors in basic research on ligand design, allosteric mechanisms, and LXR functions and their potential application as treatments for advanced pancreatic cancer and other recalcitrant malignancies.

REV-ERB agonism improves liver pathology in a mouse model of NASH

Non-alcoholic fatty liver disease (NAFLD) affects a significant number of people worldwide and currently there are no pharmacological treatments. NAFLD often presents with obesity, insulin resistance, and in some cases cardiovascular diseases. There is a clear need for treatment options to alleviate this disease since it often progresses to much more the much more severe non-alcoholic steatohepatitis (NASH). The REV-ERB nuclear receptor is a transcriptional repressor that regulates physiological processes involved in the development of NAFLD including lipogenesis and inflammation. We hypothesized that pharmacologically activating REV-ERB would suppress the progression of fatty liver in a mouse model of NASH. Using REV-ERB agonist SR9009 in a mouse NASH model, we demonstrate the beneficial effects of REV-ERB activation that led to an overall improvement of hepatic health by suppressing hepatic fibrosis and inflammatory response.

Modulation of estrogen-related receptors subtype selectivity: Conversion of an ERRβ/γ selective agonist to ERRα/β/γ pan agonists

Estrogen Related Receptors (ERRs) are key regulators of energy homeostasis and play important role in the etiology of metabolic disorders, skeletal muscle related disorders, and neurodegenerative diseases. Among the three ERR isoforms, ERRα emerged as a potential drug target for metabolic and neurodegenerative diseases. Although ERRβ/γ selective agonist chemical tools have been identified, there are no chemical tools that effectively target ERRα agonism. We successfully engineered high affinity ERRα agonism into a chemical scaffold that displays selective ERRβ/γ agonist activity (GSK4716), providing novel ERRα/β/γ pan agonists that can be used as tools to probe the physiological roles of these nuclear receptors. We identified the structural requirements to enhance selectivity toward ERRα. Molecular modeling shows that our novel modulators have favorable binding modes in the LBP of ERRα and can induce conformational changes where Phe328 that originally occupies the pocket is dislocated to accommodate the ligands in a rather small cavity. The best agonists up-regulated the expression of target genes PGC-1α and PGC-1β, which are necessary to achieve maximal mitochondrial biogenesis. Moreover, they increased the mRNA levels of PDK4, which play an important role in energy homeostasis.

Pathophysiology of hepatic Na+/H+ exchange (Review)

Na+/H+ exchangers (NHEs) are a family of membrane proteins that contribute to exchanging one intracellular proton for one extracellular sodium. The family of NHEs consists of nine known members, NHE1-9. Each isoform represents a different gene product that has unique tissue expression, membrane localization, physiological effects, pathological regulation and sensitivity to drug inhibitors. NHE1 was the first to be discovered and is often referred to as the 'housekeeping' isoform of the NHE family. NHEs are not only involved in a variety of physiological processes, including the control of transepithelial Na+ absorption, intracellular pH, cell volume, cell proliferation, migration and apoptosis, but also modulate complex pathological events. Currently, the vast majority of review articles have focused on the role of members of the NHE family in inflammatory bowel disease, intestinal infectious diarrhea and digestive system tumorigenesis, but only a few reviews have discussed the role of NHEs in liver disease. Therefore, the present review described the basic biology of NHEs and highlighted their physiological and pathological effects in the liver.

Assessing the Selectivity of FXR, LXRs, CAR, and RORγ Pharmaceutical Ligands With Reporter Cell Lines

To characterize human nuclear receptor (NR) specificity of synthetic pharmaceutical chemicals we established stable cell lines expressing the ligand binding domains (LBDs) of human FXR, LXRα, LXRβ, CAR, and RORγ fused to the yeast GAL4 DNA binding domain (DBD). As we have already done for human PXR, a two-step transfection procedure was used. HeLa cells stably expressing a Gal4 responsive gene (HG5LN cell line) were transfected by Gal4-NRs expressing plasmids. At first, using these cell lines as well as the HG5LN PXR cells, we demonstrated that the basal activities varied from weak (FXR and LXRs), intermediate (PXR), to strong (CAR and RORγ), reflecting the recruitment of HeLa co-regulators in absence of ligand. Secondly, we finely characterized the activities of commercially available FXR, LXRα, LXRβ, CAR, RORγ, and PXR agonists/antagonists GW4064, feraxamine, DY268, T0901317, GW3965, WAY252623, SR9238, SR9243, GSK2033, CITCO, CINPA1, PK11195, S07662, SR1078, SR0987, SR1001, SR2211, XY018, clotrimazole, dabrafenib, SR12813, and SPA70, respectively. Among these compounds we revealed both, receptor specific agonists/antagonists, as well as less selective ligands, activating or inhibiting several nuclear receptors. FXR ligands manifested high receptor selectivity. Vice versa, LXR ligands behaved in non-selective manner, all activating at least PXR. CAR was selectively influenced by their ligands, while it also responded to several LXR ligands. Finally, although PXR was quite selectively activated or antagonized by its own ligands, it responded to several NRs ligands as well. Thus, using these reporter cell lines enabled us to precisely characterize the selectivity of pharmaceutical ligands for different nuclear receptors.

Transcriptional Regulation in Non-Alcoholic Fatty Liver Disease

Obesity is the primary risk factor for the pathogenesis of non-alcoholic fatty liver disease (NAFLD), the worldwide prevalence of which continues to increase dramatically. The liver plays a pivotal role in the maintenance of whole-body lipid and glucose homeostasis. This is mainly mediated by the transcriptional activation of hepatic pathways that promote glucose and lipid production or utilization in response to the nutritional state of the body. However, in the setting of chronic excessive nutrition, the dysregulation of hepatic transcriptional machinery promotes lipid accumulation, inflammation, metabolic stress, and fibrosis, which culminate in NAFLD. In this review, we provide our current understanding of the transcription factors that have been linked to the pathogenesis and progression of NAFLD. Using publicly available transcriptomic data, we outline the altered activity of transcription factors among humans with NAFLD. By expanding this analysis to common experimental mouse models of NAFLD, we outline the relevance of mouse models to the human pathophysiology at the transcriptional level.

Emerging targets and potential therapeutic agents in non-alcoholic fatty liver disease treatment

Nonalcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in the world, which is characterized by liver fat accumulation unrelated to excessive drinking. Indeed, it attracts growing attention and becomes a global health problem. Due to the complexity of the NAFLD pathogenic mechanism, no related drugs were approved by Food and Drug Administration (FDA) till now. However, it is encouraging that a series of candidate drugs have entered the clinical trial stage with expectation to treat NAFLD. In this review, we summarized the main pathways and pathogenic mechanisms of NAFLD, as well as introduced the main potential therapeutic targets and the corresponding compounds involved in metabolism, inflammation and fibrosis. Furthermore, we also discuss the progress of these compounds, such as drug design and optimization, the choice of pharmacological properties and druglikeness, and the analysis of structure-activity relationship. This review offers a medium on future drug design and development, to be beneficial to relevant studies.

Lipidomic analysis of human primary hepatocytes following LXR activation with GW3965 identifies AGXT2L1 as a main target associated to changes in phosphatidylethanolamine

Liver X receptor (LXR) agonists have the potential to alleviate obesity related diseases, particularly atherosclerosis. However, LXRs are transcriptional regulators that induce de novo lipogenesis and lipid accumulation in hepatocytes which represents a serious adverse effect. In this work, we sought to characterize the LXR agonist GW3965 effects on fatty acid (FA) and phospholipid (PL) remodelling and the correlation with gene expression in order to better understand the underlying effects leading to hepatic pathology upon LXR activation. Human primary hepatocytes treated for 48 h with GW3965 were analysed for changes in lipid metabolism gene expression by qPCR, variations in the FA profile was evaluated by GC-FID and in PL profiles using thin layer chromatography, ESI-MS and MS/MS analysis. Changes in cell membrane biochemical properties were studied using bilayer models generated with CHARMM-GUI. ELOLV6 and SCD1 mRNA increase was consistent with higher C16:1 and C18:1n9 at the expense of C16:0 and C18:0. The reduction of C18:2n6 and increase in C20:2n6 was in agreement with ELOVL5 upregulation. Phosphatydilethanolamine (PE) levels tended to decrease and phosphatidylinositol to increase; although differences did not reach significance, they correlated with changes in AGXT2L1, CDS1 and LPIN1 mRNA levels that were increased. The overall effect of GW3965 on PEs molecular profiles was an increase of long-chain polyunsaturated FA chains and a decrease of C16/C18 saturated and monounsaturated FAs chains. Additionally, PC (32:1) and PC (34:2) were decreased, and PC (36:1) and PC (34:1) were increased. AGXT2L1 is an enzyme with strict substrate specificity for phosphoethanolamine, which is converted into ammonia in GW3965-treated hepatocytes and could explain the PE reduction. In summary, LXR activation by GW3965 targets PE biosynthesis and FA elongation/desaturation, which tends to decrease PE in relation to total PL levels, and remodelling of PC and PE molecular species. We identified the human AGXT2L1 gene as induced by LXR activation by both synthetic and endogenous agonist treatment. The increase in acetaldehyde-induced oxidative stress, and in the lipid species identified have the potential to enhance the inflammatory process and impair membrane function. Future studies should focus on inhibition of AGXT2L1 activity with the aim of reverting the steatosis induced by LXR activation.

Impaired LXRα Phosphorylation Attenuates Progression of Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a very common indication for liver transplantation. How fat-rich diets promote progression from fatty liver to more damaging inflammatory and fibrotic stages is poorly understood. Here, we show that disrupting phosphorylation at Ser196 (S196A) in the liver X receptor alpha (LXRα, NR1H3) retards NAFLD progression in mice on a high-fat-high-cholesterol diet. Mechanistically, this is explained by key histone acetylation (H3K27) and transcriptional changes in pro-fibrotic and pro-inflammatory genes. Furthermore, S196A-LXRα expression reveals the regulation of novel diet-specific LXRα-responsive genes, including the induction of Ces1f, implicated in the breakdown of hepatic lipids. This involves induced H3K27 acetylation and altered LXR and TBLR1 cofactor occupancy at the Ces1f gene in S196A fatty livers. Overall, impaired Ser196-LXRα phosphorylation acts as a novel nutritional molecular sensor that profoundly alters the hepatic H3K27 acetylome and transcriptome during NAFLD progression placing LXRα phosphorylation as an alternative anti-inflammatory or anti-fibrotic therapeutic target.

•

LXRαS196A induces liver steatosis and prevents cholesterol accumulation

•

LXRαS196A reduces progression to hepatic inflammation and fibrosis

•

LXRαS196A modulates hepatic chromatin acetylation

•

LXRαS196A reveals unique dual LXRα phosphorylation and diet-responsive genes

Paraconiothins A-J: Sesquiterpenoids from the Endophytic Fungus Paraconiothyrium brasiliense ECN258

Paraconiothins A-J (1-10), 10 new sesquiterpenoids, as well as five known sesquiterpenoids, were isolated from the cultures of the endophytic fungus Paraconiothyrium brasiliense ECN-258. The structures of the sesquiterpenoids were elucidated by extensive spectroscopic analysis. Furthermore, the absolute structures of 7 and 8 were determined by comparing their experimental and computed electronic circular dichroism data. Paraconiothins A-G (1-7) were eremophilane sesquiterpenoids, while paraconiothins H-J (8-10) had new or rare carbon frameworks that are possibly biosynthesized by a pathway involving the rearrangement of eremophilane sesquiterpenoids. Paraconiothins C (3) and I (9) exhibited an inhibitory effect on the liver X receptor α at a concentration of 50 μM.

LXR-inverse agonism stimulates immune-mediated tumor destruction by enhancing CD8 T-cell activity in triple negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subtype that is untreatable with hormonal or HER2-targeted therapies and is also typically unresponsive to checkpoint-blockade immunotherapy. Within the tumor microenvironment dysregulated immune cell metabolism has emerged as a key mechanism of tumor immune-evasion. We have discovered that the Liver-X-Receptors (LXRα and LXRβ), nuclear receptors known to regulate lipid metabolism and tumor-immune interaction, are highly activated in TNBC tumor associated myeloid cells. We therefore theorized that inhibiting LXR would induce immune-mediated TNBC-tumor clearance. Here we show that pharmacological inhibition of LXR activity induces tumor destruction primarily through stimulation of CD8+ T-cell cytotoxic activity and mitochondrial metabolism. Our results imply that LXR inverse agonists may be a promising new class of TNBC immunotherapies.

4-cholesten-3-one decreases breast cancer cell viability and alters membrane raft-localized EGFR expression by reducing lipogenesis and enhancing LXR-dependent cholesterol transporters

Background

The alteration of lipid metabolism in cancer cells is recognized as one of the most important metabolic hallmarks of cancer. Membrane rafts defined as plasma membrane microdomains enriched in cholesterol and sphingolipids serve as platforms for signaling regulation in cancer. The main purpose of this study was to evaluate the effect of the cholesterol metabolite, 4-cholesten-3-one, on lipid metabolism and membrane raft integrity in two breast cancer cell lines, MCF-7 and MDA-MB-231. Its ability to reduce cell viability and migration has also been investigated.

Methods

RT-qPCR was performed to evaluate the expression of enzymes involved in lipogenesis and cholesterol synthesis, and ABCG1 and ABCA1 transporters involved in cholesterol efflux. Its effect on cell viability and migration was studied using the MTT assay, the wound healing assay and the Transwell migration assay, respectively. The effect of 4-cholesten-3-one on membrane rafts integrity was investigated by studying the protein expression of flotillin-2, a membrane raft marker, and raft-enriched EGFR by western blot.

Results

Interestingly, we found that 4-cholesten-3-one treatment decreased mRNA expression of different enzymes including ACC1, FASN, SCD1 and HMGCR. We further demonstrated that 4-cholesten-3-one increased the expression of ABCG1 and ABCA1. We also found that 4-cholesten-3-one decreased the viability of MCF-7 and MDA-MB-231 cells. This effect was neutralized after treatment with LXR inverse agonist or after LXRβ knockdown by siRNA. As a result, we also demonstrated that 4-cholesten-3-one disrupts membrane rafts and cell migration capacity.

Conclusion

Our results show that 4-cholesten-3-one exerts promising antitumor activity by altering LXR-dependent lipid metabolism in breast cancer cells without increasing lipogenesis.

Inhibition of Chikungunya Virus Replication in Primary Human Fibroblasts by Liver X Receptor Agonist

The mosquito-borne chikungunya virus (CHIKV) causes acute pain and joint inflammation, and in recent years the virus has caused large epidemics in previously CHIKV-free geographic areas. To advance the understanding of host factors that antagonize CHIKV, we show that synthetic agonist of liver X receptor (LXR-623) inhibits CHIKV replication by upregulating the cholesterol exporter ABCA1 and that endogenous and pharmacological activation of interferon signaling pathway partners with LXR-623 to generate a superior antiviral state.