t0901317 and pirinixic-acid

The fatty acid sensing nuclear receptor families retinoid X receptors (RXRs) and peroxisome proliferator-activated receptors (PPARs) hold therapeutic potential in neurodegeneration. Valuable pleiotropic activities of Wy14,643 in models of such conditions exceed its known PPAR agonistic profile. Here, we characterize the compound as an RXR agonist explaining the pleiotropic effects and report its systematic structure-activity relationship analysis with the discovery of specific molecular determinants driving activity on PPARs and RXRs. We have designed close analogues of the drug comprising selective and dual agonism on RXRs and PPARs that may serve as superior pharmacological tools to study the role and interplay of the nuclear receptors in various pathologies. A systematically optimized high potency RXR agonist revealed activity in vivo and active concentrations in brain. With its lack of RXR/liver X receptor-mediated side effects and superior profile compared to classical rexinoids, it establishes a new class of innovative RXR modulators to overcome key challenges in RXR targeting drug discovery.

Topics: Animals; HEK293 Cells; Hep G2 Cells; Humans; Male; Mice, Inbred C57BL; Microsomes, Liver; Molecular Structure; Peroxisome Proliferator-Activated Receptors; Pyrimidines; Rats; Retinoid X Receptors; Structure-Activity Relationship

Nuclear receptors are a superfamily of ligand-activated transcription factors that play key roles in many biological processes, and have become one class of the most important targets in drug discovery. Mammalian one-hybrid system has been used to develop a cell-based functional transactivation high-throughput screening (HTS) assay for detecting nuclear receptors ligands. In the present study, we proved that different promoters used in the reporter vector had significant different impacts on the performance of HTS assays. The assay using the SV40 promoter in the reporter vector showed the characteristics of much higher signal/noise ratios, acceptable Z' factors (>0.6), low coefficient variation (<12.5%) and higher hits rate, which could be more robust, reproducible, and sensitive. In contrast, utilizing a TATA box promoter in the assay resulted in higher variance and low sensitivity. In addition, it was found that the assay using SV40 had longer signal decay time and was easier to be miniaturized in 384-well format. It has been confirmed that the choice of a promoter is a critical factor in developing a reporter gene HTS assay. However, the SV40 promoter used in the present study has been shown to be more adaptable than the minimal promoter TATA box in the Mammalian one-hybrid HTS assays for detecting nuclear receptor agonists.

Topics: Animals; Bezafibrate; Cells, Cultured; Chenodeoxycholic Acid; Drug Discovery; Genetic Vectors; HeLa Cells; High-Throughput Screening Assays; Humans; Hydrocarbons, Fluorinated; Ligands; Mice; NIH 3T3 Cells; Peroxisome Proliferator-Activated Receptors; Pioglitazone; Promoter Regions, Genetic; Pyrimidines; Rosiglitazone; Sensitivity and Specificity; Structure-Activity Relationship; Sulfonamides; Thiazolidinediones; Two-Hybrid System Techniques

The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Except for LD association, a clear role for ADFP has not been found. We demonstrate that ADFP is transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha) in mouse liver and rat and human hepatoma cells through a highly conserved direct repeat-1(DR-1) element. Although the ADFP mRNA is highly increased by a synthetic PPARalpha agonist, the ADFP protein is only substantially increased in cells containing LDs, such as hepatocytes incubated with fatty acids, and in livers of fasted mice. ADFP is induced by fasting even in the absence of a functional PPARalpha, in marked contrast to the PPARalpha target gene acyl-coenzyme A oxidase-1. Activation of LXRs, which stimulates LD formation through the activation of lipogenesis, does not affect ADFP mRNA levels. TIP47, another PAT member known to be expressed in liver, was unaffected by all treatments. This constitutively expressed PAT member seems to be less transcriptionally regulated than ADFP. These observations suggest that ADFP is primarily a fasting-induced protein in liver that coats the newly synthesized triacylglycerol-containing LDs formed during fasting.

Topics: Animals; Chlorocebus aethiops; COS Cells; DNA-Binding Proteins; Eating; Fasting; Fatty Acids; Humans; Hydrocarbons, Fluorinated; Liver X Receptors; Male; Membrane Proteins; Mice; Nicotinic Acids; Oleic Acid; Orphan Nuclear Receptors; Perilipin-2; PPAR alpha; Pyrimidines; Rats; Receptors, Cytoplasmic and Nuclear; Retinoid X Receptors; Sulfonamides; Tetrahydronaphthalenes; Tumor Cells, Cultured

Fatty acid elongases and desaturases play an important role in hepatic and whole body lipid composition. We examined the role that key transcription factors played in the control of hepatic elongase and desaturase expression. Studies with peroxisome proliferator-activated receptor alpha (PPARalpha)-deficient mice establish that PPARalpha was required for WY14643-mediated induction of fatty acid elongase-5 (Elovl-5), Elovl-6, and all three desaturases [Delta(5) desaturase (Delta(5)D), Delta(6)D, and Delta(9)D]. Increased nuclear sterol-regulatory element binding protein-1 (SREBP-1) correlated with enhanced expression of Elovl-6, Delta(5)D, Delta(6)D, and Delta(9)D. Only Delta(9)D was also regulated independently by liver X receptor (LXR) agonist. Glucose induction of l-type pyruvate kinase, Delta(9)D, and Elovl-6 expression required the carbohydrate-regulatory element binding protein/MAX-like factor X (ChREBP/MLX) heterodimer. Suppression of Elovl-6 and Delta(9)D expression in livers of streptozotocin-induced diabetic rats and high fat-fed glucose-intolerant mice correlated with low levels of nuclear SREBP-1. In leptin-deficient obese mice (Lep(ob/ob)), increased SREBP-1 and MLX nuclear content correlated with the induction of Elovl-5, Elovl-6, and Delta(9)D expression and the massive accumulation of monounsaturated fatty acids (18:1,n-7 and 18:1,n-9) in neutral lipids. Diabetes- and obesity-induced changes in hepatic lipid composition correlated with changes in elongase and desaturase expression. In conclusion, these studies establish a role for PPARalpha, LXR, SREBP-1, ChREBP, and MLX in the control of hepatic fatty acid elongase and desaturase expression and lipid composition.

Topics: Acetyltransferases; Adult; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Diabetes Mellitus; Fatty Acid Desaturases; Fatty Acid Elongases; Female; Glucose; Humans; Hydrocarbons, Fluorinated; Insulin; Leptin; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Middle Aged; Obesity; PPAR alpha; Pyrimidines; Rats; Rats, Sprague-Dawley; Sterol Regulatory Element Binding Protein 1; Sulfonamides

Liver X receptors (LXRs) are master transcription factors regulating cholesterol and fatty acid metabolism. Treatment of C57B6 mice with a specific synthetic LXR agonist, N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1(trifluoromethyl)-ethyl]phenyl]-benzenesulfonamide (T0901317), resulted in elevated high-density lipoprotein (HDL) cholesterol as well as plasma and liver triglycerides. Peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists are known to induce peroxisomal fatty acid beta-oxidation and also mediate HDL cholesterol metabolism. We have explored the hypothesis that simultaneous activation of PPARalpha and LXR may lead to additive effects on HDL cholesterol elevation as well as attenuation of triglyceride accumulation. Coadministration of T0901317 and the specific PPARalpha agonist [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (Wy14643)] in mice led to synergistic elevation of HDL cholesterol that was primarily associated with enlarged HDL particles enriched with apoE and apoAI. Liver phospholipid transfer protein (PLTP) mRNA and plasma PLTP activity were additively elevated, suggesting a role of PLTP in the observed HDL cholesterol elevation. Moderate increases in plasma triglyceride levels induced by LXR activation was reduced, whereas the accumulation of triglyceride in the liver was not altered upon coadministration of the PPARalpha agonist. Peroxisomal fatty acid beta-oxidation in the liver was dramatically elevated upon PPARalpha activation as expected. Interestingly, activation of LXRs via T0901317 also led to a significant increase in peroxisomal fatty acid beta-oxidation. Sterol regulatory element binding protein 1c expression was dramatically up-regulated by the LXR agonist but was not changed with PPARalpha agonist treatment. Liver lipoprotein lipase expression was additively increased upon LXR agonist and PPARalpha agonist coadministration. Our studies mark the first exploration of nuclear receptor interplay on lipid homeostasis in vivo.

Topics: Animals; Anticholesteremic Agents; Carrier Proteins; DNA-Binding Proteins; Hydrocarbons, Fluorinated; Lipoproteins, HDL; Liver; Liver X Receptors; Membrane Proteins; Mice; Mice, Inbred C57BL; Orphan Nuclear Receptors; Phospholipid Transfer Proteins; Pyrimidines; Receptors, Cytoplasmic and Nuclear; Sulfonamides; Transcription Factors; Triglycerides

Liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) are members of nuclear receptors that form obligate heterodimers with retinoid X receptors (RXRs). These nuclear receptors play crucial roles in the regulation of fatty acid metabolism: LXRs activate expression of sterol regulatory element-binding protein 1c (SREBP-1c), a dominant lipogenic gene regulator, whereas PPARalpha promotes fatty acid beta-oxidation genes. In the current study, effects of PPARs on the LXR-SREBP-1c pathway were investigated. Luciferase assays in human embryonic kidney 293 cells showed that overexpression of PPARalpha and gamma dose-dependently inhibited SREBP-1c promoter activity induced by LXR. Deletion and mutation studies demonstrated that the two LXR response elements (LXREs) in the SREBP-1c promoter region are responsible for this inhibitory effect of PPARs. Gel shift assays indicated that PPARs reduce binding of LXR/RXR to LXRE. PPARalpha-selective agonist enhanced these inhibitory effects. Supplementation with RXR attenuated these inhibitions by PPARs in luciferase and gel shift assays, implicating receptor interaction among LXR, PPAR, and RXR as a plausible mechanism. Competition of PPARalpha ligand with LXR ligand was observed in LXR/RXR binding to LXRE in gel shift assay, in LXR/RXR formation in nuclear extracts by coimmunoprecipitation, and in gene expression of SREBP-1c by Northern blot analysis of rat primary hepatocytes and mouse liver RNA. These data suggest that PPARalpha activation can suppress LXR-SREBP-1c pathway through reduction of LXR/RXR formation, proposing a novel transcription factor cross-talk between LXR and PPARalpha in hepatic lipid homeostasis.

Topics: Animals; Anticholesteremic Agents; CCAAT-Enhancer-Binding Proteins; Cells, Cultured; DNA-Binding Proteins; Fatty Acids; Gene Expression Regulation; Hepatocytes; Humans; Hydrocarbons, Fluorinated; Liver; Liver X Receptors; Male; Mice; Mice, Inbred C57BL; Nutritional Physiological Phenomena; Orphan Nuclear Receptors; Promoter Regions, Genetic; Pyrimidines; Rats; Rats, Sprague-Dawley; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Response Elements; Retinoid X Receptors; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Sulfonamides; Transcription Factors