t0901317 and Hypertriglyceridemia

Objective- APOA5 variants are strongly associated with hypertriglyceridemia, as well as increased risks of cardiovascular disease and acute pancreatitis. Hypertriglyceridemia in apo AV dysfunction often aggravates by environmental factors such as high-carbohydrate diets or aging. To date, the molecular mechanisms by which these environmental factors induce hypertriglyceridemia are poorly defined, leaving the high-risk hypertriglyceridemia condition undertreated. Previously, we reported that LXR (liver X receptor)-SREBP (sterol regulatory element-binding protein)-1c pathway regulates large-VLDL (very low-density lipoprotein) production induced by LXR agonist. However, the pathophysiological relevance of the finding remains unknown. Approach and Results- Here, we reconstitute the environment-induced hypertriglyceridemia phenotype of human APOA5 deficiency in Apoa5

Topics: Aging; Animal Feed; Animals; Apolipoprotein A-V; Apolipoproteins; Chylomicrons; Female; Fructose; Gene Expression Regulation; Gene-Environment Interaction; Humans; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Lipids; Lipoproteins, VLDL; Liver X Receptors; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Models, Animal; Olive Oil; Sterol Regulatory Element Binding Protein 1; Sulfonamides

Liver X receptors (LXRs) are transcription factors essential for cholesterol homeostasis and lipogenesis. LXRα has been implicated in regulating hepatic triglyceride (TG) accumulation upon both influx of adipose-derived fatty acids (FAs) during fasting and stimulation of de novo FA synthesis by chemical agonism of LXR. However, whether or not a convergent mechanism is employed to drive deposition of FAs from these 2 different sources in TGs is undetermined. Here, we report that the G0/G1 Switch Gene 2 (G0S2), a selective inhibitor of intracellular TG hydrolysis/lipolysis, is a direct target gene of LXRα. Transcriptional activation is conferred by LXRα binding to a direct repeat 4 (DR4) motif in the G0S2 promoter. While LXRα

Topics: Animals; Arabidopsis Proteins; Cell Cycle Proteins; Cholesterol, HDL; Fasting; Fatty Liver; Hydrocarbons, Fluorinated; Hydrolysis; Hypertriglyceridemia; Lipolysis; Liver; Liver X Receptors; Mice; Mice, Knockout; Repetitive Sequences, Nucleic Acid; Sulfonamides; Triglycerides

Activation of liver X receptor (LXR) inhibits atherosclerosis but induces hypertriglyceridemia. In vitro, it has been shown that mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor synergizes LXR ligand-induced macrophage ABCA1 expression and cholesterol efflux. In this study, we determined whether MEK1/2 (U0126) and LXR ligand (T0901317) can have a synergistic effect on the reduction of atherosclerosis while eliminating LXR ligand-induced fatty livers and hypertriglyceridemia. We also set out to identify the cellular mechanisms of the actions.. Wild-type mice were used to determine the effect of U0126 on a high-fat diet or high-fat diet plus T0901317-induced transient dyslipidemia and liver injury. ApoE deficient (apoE(-/-)) mice or mice with advanced lesions were used to determine the effect of the combination of T0901317 and U0126 on atherosclerosis and hypertriglyceridemia. We found that U0126 protected animals against T0901317-induced transient or long-term hepatic lipid accumulation, liver injury, and hypertriglyceridemia. Meanwhile, the combination of T0901317 and U0126 inhibited the development of atherosclerosis in a synergistic manner and reduced advanced lesions. Mechanistically, in addition to synergistic induction of macrophage ABCA1 expression, the combination of U0126 and T0901317 maintained arterial wall integrity, inhibited macrophage accumulation in aortas and formation of macrophages/foam cells, and activated reverse cholesterol transport. The inhibition of T0901317-induced lipid accumulation by the combined U0126 might be attributed to inactivation of lipogenesis and activation of lipolysis/fatty acid oxidation pathways.. Our study suggests that the combination of mitogen-activated protein kinase kinase 1/2 inhibitor and LXR ligand can function as a novel therapy to synergistically reduce atherosclerosis while eliminating LXR-induced deleterious effects.

Topics: Animals; Aorta; Aortic Diseases; Apolipoproteins E; Atherosclerosis; Butadienes; Chemical and Drug Induced Liver Injury; Cholesterol; Disease Models, Animal; Drug Synergism; Drug Therapy, Combination; Fatty Liver; Female; Foam Cells; Hep G2 Cells; Humans; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Liver; Liver X Receptors; Male; Mice, Inbred C57BL; Mice, Knockout; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Nitriles; Orphan Nuclear Receptors; Protein Kinase Inhibitors; Signal Transduction; Sulfonamides

Liver X receptors (LXR) have been characterized as key transcriptional regulators of hepatic lipid and carbohydrate metabolism. LXR are expressed also in skeletal muscle, however, their role in this tissue is poorly investigated and the vast majority of available data comes from studies on cultured myotubes. Therefore, we aimed to examine effects of in vivo LXR activation on muscle lipid metabolism. The experiments were performed on male Wistar rats fed on a standard rodent chow. The animals were divided into two groups (n=10) receiving either LXR activator (T0901317, 10 mg/kg/day) or vehicle for one week. Samples of the soleus as well as red and white sections of the gastrocnemius muscle were excised. T0901317 increased muscle expression of peroxisome proliferator-activated receptor-δ and its target genes involved in fatty acid uptake and oxidation. In addition, LXR agonist enhanced palmitate oxidation (by 55%) in isolated soleus muscle. However, palmitate incorporation into triacylglycerol was decreased (by 38%), which was associated with reduced diacylglycerol acyltransferase expression (by 66%). Despite markedly increased plasma lipid concentration upon T0901317 treatment, muscle triacylglycerol level was elevated only in the red section of the gastrocnemius muscle. We conclude that T0901317 enhances muscle fatty acid oxidation, which prevents overt accumulation of intramuscular lipids that could be expected considering T0901317-induced hyperlipidemia.

Topics: Animals; Anticholesteremic Agents; Diacylglycerol O-Acyltransferase; Down-Regulation; Fatty Acids, Nonesterified; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Liver X Receptors; Male; Muscle, Skeletal; Organ Specificity; Orphan Nuclear Receptors; Oxidation-Reduction; Palmitic Acid; PPAR delta; Random Allocation; Rats; Rats, Wistar; RNA, Messenger; Sulfonamides; Triglycerides; Up-Regulation

Liver X receptors (LXRs) activate triglyceride synthesis in liver directly and indirectly by inducing sterol regulatory element-binding protein-1c (SREBP-1c). When administered to wild-type mice, the LXR activator T0901317 produces a mild and transient hypertriglyceridemia. Here, we show that T0901317 produces massive hypertriglyceridemia when given to mice lacking low density lipoprotein (LDL) receptors (Ldlr(-/-) mice). Triglycerides ranged from 4000 to 6000 mg/dl, and the plasma turned milky. The median diameter of VLDL particles, measured by electron microscopy, increased from 43 to 112 nm, 87% exceeding 80 nm, the size of chylomicrons. Hypertriglyceridemia was prevented in Ldlr(-/-) recipient mice that lacked SREBP-1c (Ldlr(-/-);Srebp-1c(-/-) double knock-out mice). In Ldlr(-/-) mice, T0901317 increased mRNAs not only for enzymes of fatty acid and triglyceride synthesis, but also for phospholipid transfer protein (PLTP), which transfers phospholipids into nascent VLDL, allowing particle expansion. The PLTP increase was blunted in Ldlr(-/-);Srebp-1c(-/-) animals. When Ldlr(-/-);Srebp-1c(-/-) mice received an adenovirus encoding Pltp, the hypertriglyceridemic response to T0901317 was partially restored and the VLDL size increased. We conclude that LXR agonists activate triglyceride synthesis and Pltp transcription by activating Srebp-1c. In concert with the increase in TG synthesis, the increased PLTP permits triglyceride incorporation into abnormally large VLDL, which are removed from plasma by LDL receptors. In the absence of LDL receptors, the large VLDLs accumulate and produce massive hypertriglyceridemia.

Topics: Animals; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Lipoproteins, VLDL; Liver X Receptors; Mice; Mice, Inbred C57BL; Mice, Knockout; Orphan Nuclear Receptors; Particle Size; Phospholipid Transfer Proteins; Receptors, LDL; Sterol Regulatory Element Binding Protein 1; Sulfonamides

Activation of liver X receptors (LXRs) has been reported to reduce atherosclerosis in mouse models. However, this can be associated with enhanced liver de novo lipogenesis and elevation of plasma triglyceride-rich VLDL, which may limit its clinical use. In this study, we administered orally the LXR agonist T0901317 to male LDLR-/- mice fed a Western diet. This induced a persistent enhanced hypertriglyceridemia by largely increasing plasma triglyceride-rich VLDL. T0901317 treatment decreased atherosclerosis with a much more pronounced response and dose dependence in the innominate artery than in the aortic sinus. Lesions in the innominate artery were less complex containing mostly macrophage foam cells in T0901317-treated mice. However, in the aortic root, a significant reduction of atherosclerosis was seen only in the right coronary-related aortic sinus (RC) of T0901317-treated mice. Increasing the dose of T0901317 did not extend atheroprotection to the other sinuses of the aortic root. Lesions in the RC were less complex both in T0901317 and vehicle-treated mice with macrophage foam cells predominating. On the other hand, in T0901317-treated mice, the left coronary-related sinus (LC) lesions while not reduced in size, were more complex with a large fibrous cap and necrotic core, more collagen-positive areas, and variable macrophage foam cell content compared to vehicle-treated mice. These data suggest that activation of LXR by T0901317 had differential anti-atherosclerotic effects in two arterial regions in mice with hypertriglyceridemia.

Topics: Animals; Atherosclerosis; Brachiocephalic Trunk; DNA-Binding Proteins; Foam Cells; Gene Expression Regulation; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Lipids; Liver X Receptors; Macrophages; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Orphan Nuclear Receptors; Receptors, Cytoplasmic and Nuclear; Sinus of Valsalva; Sulfonamides

Stearoyl-coenzyme A desaturase (SCD) is the rate-limiting enzyme necessary for the biosynthesis of monounsaturated fatty acids. In this study, we investigated the regulation of mouse SCD1 by liver X receptor (LXR) and its role in plasma lipoprotein metabolism upon LXR activation. In vivo, the SCD1 gene remained induced upon LXR activation in the absence of sterol regulatory element-binding protein 1c (SREBP-1c), a known transcriptional regulator of SCD1. Serial deletion and point mutation analyses in reporter gene assays, as well as a gel mobility shift assay, identified an LXR response element in the mouse SCD1 promoter. In addition, SCD1 deficiency prevented the hypertriglyceridemic effect and reduced hepatic triglyceride accumulation associated with LXR activation despite induced hepatic expression of SREBP-1c protein and several SREBP1c and LXR target genes involved in lipoprotein metabolism. Unlike wild-type mice, SCD1-deficient mice failed to elevate the hepatic triglyceride monounsaturated acid (MUFA)/saturated fatty acid (SFA) ratio despite induction of the SCD2 gene. Together, these findings suggest that SCD1 plays a pivotal role in the regulation of hepatic and plasma triglyceride accumulation, possibly by modulating the MUFA-to-SFA ratio. In addition, SCD1 deficiency also increased plasma high-density lipoprotein cholesterol levels induced by LXR activation.

Topics: Animals; Base Sequence; Cholesterol, HDL; DNA-Binding Proteins; Humans; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Lipid Metabolism; Lipids; Liver X Receptors; Mice; Molecular Sequence Data; Orphan Nuclear Receptors; Pregnane X Receptor; Protein Binding; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Receptors, Steroid; Response Elements; Sequence Deletion; Stearoyl-CoA Desaturase; Sterol Regulatory Element Binding Protein 1; Sulfonamides

The KK/San obese and diabetic mouse, a mutant strain from KK obese mice, exhibits significantly low plasma triglyceride levels. In KK/San mice, genetic analysis identified a mutation in the gene encoding angiopoietinlike protein 3 (Angptl3), a liver-specific secretory protein, which had suppressive effect on lipoprotein lipase activity. In the current study, LXR ligands augmented Angptl3 mRNA expression and protein production in hepatoma cells. LXR ligands and LXR.retinoid X receptor (RXR) complex increased the promoter activity of Angptl3 gene. Serial deletion and point mutation of Angptl3 promoter identified an LXR response element (LXRE). Gel mobility shift assay showed the direct binding of LXR.RXR complex to the LXRE of the Angptl3 promoter. Furthermore, treatment of mice with synthetic LXR ligand caused triglyceride accumulation in the liver and plasma, which was accompanied by induction of hepatic mRNAs of several LXR target genes, including sterol regulatory element binding protein-1c (SREBP-1c), fatty acid synthase (FAS), and Angptl3. In Angptl3-deficient C57BL/6J mice, LXR ligand did not cause hypertriglyceridemia but accumulation of triglyceride in the liver. Our results demonstrate that Angptl3 is a direct target of LXR and that induction of hepatic Angptl3 accounts for hypertriglyceridemia associated with the treatment of LXR ligand.

Topics: Angiopoietin-Like Protein 3; Angiopoietin-like Proteins; Angiopoietins; Animals; Anticholesteremic Agents; Base Sequence; Cell Line; Cells, Cultured; DNA-Binding Proteins; Enzyme-Linked Immunosorbent Assay; Fatty Acid Synthases; Genes, Reporter; Humans; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Intercellular Signaling Peptides and Proteins; Ligands; Lipid Metabolism; Lipoproteins; Liver; Liver X Receptors; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Mice, Obese; Molecular Sequence Data; Mutation; Orphan Nuclear Receptors; Plasmids; Point Mutation; Promoter Regions, Genetic; Protein Binding; Protein Biosynthesis; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Retinoid X Receptors; RNA; RNA, Messenger; Sulfonamides; Time Factors; Transcription Factors; Transcription, Genetic; Transcriptional Activation; Transfection; Triglycerides; Tumor Cells, Cultured

The oxysterol-activated liver X receptor (LXR) provides a link between sterol and fatty acid metabolism; activation of LXR induces transcription of lipogenic genes. This study shows that induction of the lipogenic genes Srebp-1c, Fas, and Acc1 upon administration of the synthetic LXR agonist T0901317 to C57BL/6J mice (10 mg/kg/day, 4 days) is associated with massive hepatic steatosis along the entire liver lobule and a 2.5-fold increase in very low density lipoprotein-triglyceride (VLDL-TG) secretion. The increased VLDL-TG secretion was fully accounted for by formation of larger (129 +/- 9 nm versus 94 +/- 12 nm, a 2.5-fold increase of particle volume) TG-rich particles. Stimulation of VLDL-TG secretion did not lead to elevated plasma TG levels in C57BL/6J mice, indicating efficient particle metabolism and clearance. However, T0901317 treatment did lead to severe hypertriglyceridemia in mouse models of defective TG-rich lipoprotein clearance, i.e. APOE*3-Leiden transgenic mice (3.2-fold increase) and apoE-/- LDLr-/- double knockouts (12-fold increase). Incubation of rat hepatoma McA-RH7777 cells with T0901317 also resulted in intracellular TG accumulation and enhanced TG secretion. We conclude that, in addition to raising high density lipoprotein cholesterol concentrations, pharmacological LXR activation in mice leads to development of hepatic steatosis and secretion of atherogenic, large TG-rich VLDL particles.

Topics: Animals; Anticholesteremic Agents; Apolipoproteins E; Carrier Proteins; Cell Line; DNA-Binding Proteins; Hydrocarbons, Fluorinated; Hypertriglyceridemia; Lipids; Lipoproteins, VLDL; Liver; Liver X Receptors; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Orphan Nuclear Receptors; Phospholipid Transfer Proteins; Rats; Receptors, Cytoplasmic and Nuclear; Receptors, LDL; Receptors, Retinoic Acid; Receptors, Thyroid Hormone; Sulfonamides; Triglycerides

The discovery of oxysterols as the endogenous liver X receptor (LXR) ligands and subsequent gene targeting studies in mice provided strong evidence that LXR plays a central role in cholesterol metabolism. The identification here of a synthetic, nonsteroidal LXR-selective agonist series represented by T0314407 and T0901317 revealed a novel physiological role of LXR. Oral administration of T0901317 to mice and hamsters showed that LXR activated the coordinate expression of major fatty acid biosynthetic genes (lipogenesis) and increased plasma triglyceride and phospholipid levels in both species. Complementary studies in cell culture and animals suggested that the increase in plasma lipids occurs via LXR-mediated induction of the sterol regulatory element-binding protein 1 (SREBP-1) lipogenic program.

Topics: Animals; CCAAT-Enhancer-Binding Proteins; Cricetinae; DNA-Binding Proteins; Dose-Response Relationship, Drug; Fatty Acids; Hypertriglyceridemia; Lipids; Lipoproteins; Liver; Liver X Receptors; Mice; Mice, Mutant Strains; Orphan Nuclear Receptors; Phospholipids; Receptors, Cytoplasmic and Nuclear; Sterol Regulatory Element Binding Protein 1; Sulfonamides; Transcription Factors; Triglycerides