LXRalpha Research Articles

P0433 : Selective LXR alpha intestinal activation reduces hepatic inflammation and fibrosis during the development of chronic liver injury

P0433 : Selective LXR alpha intestinal activation reduces hepatic inflammation and fibrosis during the development of chronic liver injury

Fungal natural products-the mushroom perspective.

Among the first documented studies on the chemistry of fungal natural products were descriptions of quinoid pigments, i.e., the L-tyrosine- and L-phenylalanine-derived terphenylquinones atromentin and polyporic acid, respectively. The isolation of these compounds from mushroom fruiting bodies (basidiomes) was published around 1877 by Stahlschmidt and Thorner. Ever since, organic chemists embraced basidiomycetes as a prolific source of bioactive compounds and investigated these fungi with regard to compound isolation, structure elucidation, and synthesis (Gill and Steglich, 1987; Zhou and Liu, 2010; De Silva et al., 2013 and previous reviews referenced therein, Lorenzen and Anke, 1998; Richter et al., in press). Mushrooms seem to be particularly talented in producing unique terpenoids, and the molecular background behind the biosynthesis of some of those compounds has only recently been elucidated (Quin et al., 2014). Prominent examples of basidiomycete metabolites for lead structures in agrochemistry and drug research are, among others, the strobilurins, i.e., agriculturally used s-methoxyacrylate fungicides from cultures of Mycena, Oudemansiella, Strobilurus, Xerula and several other basidiomycete genera (Sauter et al., 1999, Figure 1). Other examples are the pleuromutilins, the illudins, and the omphalotins (Figure ​(Figure1).1). The pleuromutilins from cultures of species that are now placed in the genera Clitopilus and Omphalina served as scaffold for the development of the semisynthetic antibacterial antibiotic retapamulin (Kirst, 2013) which is clinically used for topical treatment of infections with Staphylococcus aureus. The illudins from Lampteromyces and Omphalotus species (Omphalotaceae) are sesquiterpenes featuring an unusual cyclopropane ring and are currently developed as anticancer drugs (Tanasova and Sturla, 2012). The omphalotins are cyclopeptides with pronounced nematicidal activites against root knot nematodes (Buchel et al., 1998), which are also exclusively found in the Omphalotaceae. Recently, the blazeispirols from Agaricus subrufescens were discovered as strong and selective agonists of the Liver X receptor (LXR alpha). Concurrently, relevant in vivo effects of blazeispirols in a mouse model were observed which might give rise to the development of a new anti-hypercholesterolemic agent from cultures of a medicinal mushroom (Grothe et al., 2011).

Abstract 2448: Meiosis activating sterols counteract KRas-driven epithelial carcinogenesis via an LXR-dependent mechanism

Abstract Sterols are structural components of lipid membranes which can exert potent biological activities by regulating cell surface receptor trafficking and stability. Arrest of the sterol pathway at the level of SC4MOL (sterol C4-methyl oxydase-like) or NSDHL (NADPH-dependent steroid dehydrogenase-like) specifically antagonizes signaling and trafficking of the epidermal growth factor receptor (EGFR) (Sukhanova, 2013). SC4MOL and NSDHL catalyze two sequential steps of oxidative decarboxylation of the C4-methyl groups of meiosis activating sterols (MAS). The protein binding MAS has not been identified. We investigated whether the anti-EGFR activities of MAS metabolites are mediated via their interaction with the Liver X Receptor (LXR) so that LXR and its transcriptional targets induce subsequent deregulation of intracellular cholesterol homeostasis. In EGFR-positive carcinoma cell, inhibition of SC4MOL or NSDHL induces upregulation of two canonical LXR targets: the ATP-binding cassette transporter A1 and G1 (ABCA1 and ABCG1). In keeping with the LXR activation, expression of low density lipoprotein receptor (LDLR) is markedly reduced in SC4MOL or NSDHL-deficient cells. These effects were completely reversible with inactivation of LXR alpha, or via inactivation of an upstream enzyme, CYP51A1, which eliminated MAS. Inactivation of SC4MOL and NSDHL sterol pathway enzymes and upregulation of cholesterol efflux via ABCA1 depleted cholesterol from cellular membranes as evidenced by marked increase of nuclear form of SREBP2. Direct manipulation of SREBP, LXR or LDLR produced concordant synergistic effects with anti-EGFR drugs in carcinoma cell lines suggesting novel combinatorial strategies to treat EGFR-positive carcinomas. In in vivo experiments, SC4MOL or NSDHL-depleted A431 carcinoma xenografts showed exquisite sensitivity to cetuximab. This phenotype was associated with upregulation of LXR target ABCA1 and loss of LDLR. Conditional inactivation of a “floxed” Nsdhl allele via K14-Cre transgene triggered ABCA1 expression in the skin, arrested keratinocytes proliferation and caused lethality in newborn male pups. The anti-proliferative effect of NSDHL deficiency was tested in vivo against KRAS-driven tumors. Skin tumors induced by KRAS in transgenic LSL-KRasG12D mice are EGFR-dependent. Tamoxifen-inducible Tg(K5-CreERTam) mice were crossed with LSL-KRasG12D;NsdhlloxP/loxP and tumors induced by oral tamoxifen administration. Both, NsdhlloxP/Y (NSDHL-null) males carrying only the “floxed” allele and NsdhlloxP/+ heterozygous mosaic females formed skin tumors at similar rate. However, the growth of tumors in NSDHL-null males was completely abrogated. In sum, specific sterol metabolites play a fundamental role in regulating activity of oncogenic EGFR. Inhibition of SC4MOL or NSDHL is a highly effective strategy to counteract oncogenic signaling in carcinomas with activated EGFR-KRAS axis. Citation Format: Linara Gabitova, Andrey Gorin, Diana Restifo, Dong-Hua Yang, David Cunningham, Gail E. Herman, Igor A. Astsaturov. Meiosis activating sterols counteract KRas-driven epithelial carcinogenesis via an LXR-dependent mechanism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2448. doi:10.1158/1538-7445.AM2014-2448

Effect of garlic on lipid profile and expression of LXR alpha in intestine and liver of hypercholesterolemic mice

BackgroundGarlic is one of the medicinal plants which has showed beneficial effects on atherosclerosis risk factors. The liver X receptor α (LXRα) is an important regulator of cholesterol, triglyceride and glucose homeostasis that belongs to the nuclear receptor superfamily. In this study we investigated the effect of garlic on lipid profile, glucose as well as LXRα expression in intestine and liver of mice.MethodsForty male N-Mary mice were randomly divided into 3 groups (n = 8): group1 received chow + 2% cholesterol + 0.5% cholic acid, group 2: chow + 4% (w/w) garlic extract + 2% cholesterol + 0.5% cholic acid, and group 3: chow only. After one month of treatment, mice were anesthetized, blood was collected from their heart, and the first 10 cm of the small intestine and liver were removed. Glucose was measured by a glucometer; other biochemical factors were measured by enzymatic methods. LXR expression was checked by RT-PCR and western blotting.ResultsCompared with hypercholesterolemic mice, treatment with garlic extract significantly decreased total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides, very low density lipoprotein-cholesterol (VLDL-C), atherogenic index, alanine aminotranferease (ALT) and aspartate aminotransferase (AST) (all of them P < 0.05). Change in HDL-C levels was not significant in garlic-extract treated animals compared with hypercholesterolemic group. LXR protein and mRNA in the intestine were increased in garlic-extract treated group compared with chow group (P < 0.05), while in the liver, only mRNA of LXR was increased in hypercholesterolemic control mice (P < 0.05).ConclusionsThe present study demonstrated that garlic extract reduced LXRα expression in the liver and increased its expression in the intestine. These effects probably have an important role in reducing serum triglyceride and cholesterol.

Effect of simvastatin on the expression of farnesoid X receptor in diabetic animal models of altered glucose homeostasis.

Statin therapy has affected glucose homoeostasis of type 2 diabetes patients, which could be related with bile acids metabolism. Whether bile acid metabolism and the expression of farnesoid X receptor (FXR), liver X receptor-α (LXR-α) and sterol regulatory element-binding protein (Srebp)-1c is regulated by hyperglycemia, or whether simvastatin therapy led to higher glucose is related with down-regulated expression of FXR in diabetic rats remained unclear. Forty male Wistar rats were randomly divided into four groups: normal control rats, insulin resistance rats, diabetic model rats, and the late simvastatin induced diabetic rats. Normal control rats were fed with standard diet, others were fed with high-fat diet. Diabetic model rats were induced by a single intraperitoneal injection of streptozotocin (STZ). The late simvastatin induced diabetic rats started simvastatin administration after STZ induced diabetic model rats. Characteristics of fasting blood glucose (FPG), lipid files and total bile acids (TBAs) were measured and the oral glucose tolerance test (OGTT) was performed after overnight fasting at the eighth weekend. RNA and protein levels of FXR, LXR-α and Srebp-1c were tested by Western blotting and reverse transcription polymerase chain reaction (RT-PCR). The insulin resistance rats showed higher glucose, lipid files and lower expression of FXR compared with normal control rats (P > 0.05). The diabetic model rats showed significantly higher glucose, lipid files, TBA and lower expression of FXR compared with insulin resistance rats (P < 0.05). The late simvastatin induced diabetic rats displayed higher glucose and TBA and lower expression of FXR compared with diabetic model rats (P < 0.05). Changes in bile acid homeostasis, including the alterations of bile acid levels and bile acid receptors, are either a cause or a consequence of the metabolic disturbances observed during diabetic models. Statin therapy induced hyperglycemia may be related with FXR, SHP, LXR-α and Srebp-1 pathways.

Liver X receptors alpha gene (NR1H3) promoter polymorphisms are associated with systemic lupus erythematosus in Koreans.

IntroductionLiver X receptors are established sensors of lipid and cholesterol homeostasis. Recent studies have reported that these receptors are involved in the regulation of inflammation and immune responses. We attempted to identify single nucleotide polymorphisms (SNPs) of the NR1H3 gene associated with the susceptibility to systemic lupus erythematosus (SLE).MethodsSNPs were genotyped using SNaPSHOT assay in 300 Korean patients with SLE and 217 normal controls (NC), and in replication samples (160 SLE patients and 143 NC). Also, the functional effects of NR1H3 gene promoter polymorphisms were analyzed using a luciferase assay, real-time polymerase chain reaction, B cell proliferation assay and an electrophoretic mobility shift assay.ResultsWe identified five polymorphisms: -1851 T > C (rs3758673), -1830 T > C (rs3758674), -1003 G > A (new), -840 C > A (rs61896015) and -115 G > A (rs12221497). There was a significant and reproducible difference in the -1830 T > C, -1003 G > A and -115 G > A polymorphisms between the SLE and the NC. Luciferase activity of the structure containing -1830 C was less enhanced compared to the structure containing -1830 T in basal, GW3965 and T0901317 treated Hep3B cells (P = 0.009, P = 0.034 and P <0.001, respectively). Proliferation of the -1830 TC type was increased compared to the -1830 TT type in basal, GW3965 and T0901317 treated B cells from SLE patients (P = 0.011, P = 0.040 and P = 0.017, respectively). Transcription factor GATA-3 preferentially bound the -1830 T allele in the promoter.ConclusionsNR1H3 genetic polymorphisms may be associated with disease susceptibility and clinical manifestations of SLE. Specifically, -1830 T > C polymorphism within NR1H3 promoter region may be involved in regulation of NR1H3 expression.

Effects of NR1H3 Genetic Variation on the Expression of Liver X Receptor α and the Progression of Alzheimer's Disease

Alzheimer's disease (AD) has been postulated to involve defects in the clearance of amyloid-β (Aβ). Activation of liver X receptor α (LXRα) increases the expression of apolipoprotein E (ApoE) as well as cholesterol transporters ABCA1 and ABCG1, leading to augmented clearance of Aβ. We have previously shown that the C allele of rs7120118 in the NR1H3 gene encoding LXRα reduces the risk of AD. Here, we wanted to assess whether the rs7120118 variation affects the progression of AD and modulates the expression of NR1H3 and its downstream targets APOE, ABCA1 and ABCG1.We utilized tissue samples from the inferior temporal cortex of 87 subjects, which were subdivided according to Braak staging into mild, moderate and severe AD groups on the basis of AD-related neurofibrillary pathology. APOE ε4 allele increased soluble Aβ42 levels in the tissue samples in a dose-dependent manner, but did not affect the expression status of APOE. In contrast, the CC genotype of rs7120118 was underrepresented in the severe group, although this result did not reach statistical significance. Also, patients with the CC genotype of rs7120118 showed significantly decreased soluble Aβ42 levels as compared to the patients with TT genotype. Although the severity of AD did not affect NR1H3 expression, the mRNA levels of NR1H3 among the patients with CT genotype of rs7120118 were significantly increased as compared to the patients with TT genotype. These results suggest that genetic variation in NR1H3 modulates the expression of LXRα and the levels of soluble Aβ42.

Stimulation of murine biliary cholesterol secretion by thyroid hormone is dependent on a functional ABCG5/G8 complex

Secretion of cholesterol into bile is important for the elimination of cholesterol from the body. Thyroid hormone (TH) increases biliary cholesterol secretion and hepatic gene expression of adenosine triphosphate (ATP)-binding cassette, subfamily G (WHITE), member 5 (ABCG5) and ATP-binding cassette, subfamily G (WHITE), member 8 (ABCG8), two half-transporters that act as a heterodimeric complex promoting sterol secretion. In addition, nuclear liver x receptor-alpha (LXRa), also regulated by TH, induces gene expression of ABCG5/G8. We here investigated if the TH-induced stimulation of biliary cholesterol secretion is mediated by the ABCG5/G8 complex in vivo, and if so, whether LXRa is involved. Mice homozygous for disruption of Abcg5 (Abcg5−/−) or Lxra (Lxra−/−) and their wild-type counterparts were treated with triiodothyronine (T3) for 14 days and compared to untreated mice of corresponding genetic backgrounds. Bile was collected by gallbladder cannulation, and liver samples were analyzed for gene expression levels. Basal biliary cholesterol secretion in Abcg5−/− mice was 72% lower than in Abcg5+/+ mice. T3 treatment increased cholesterol secretion 3.1-fold in Abcg5+/+ mice, whereas this response was severely blunted in Abcg5−/− mice. In contrast, biliary cholesterol secretion in T3-treated Lxra+/+ and Lxra−/− mice was increased 3.5- and 2.6-fold, respectively, and did not differ significantly. Conclusions: TH-induced secretion of cholesterol into bile is largely dependent on an intact ABCG5/G8 transporter complex, whereas LXRa is not critical for this effect. (HEPATOLOGY 2012;56:1828–1837)

Abstract 9782: Genetic Variation at the SLCO1B1 Gene Locus and Low Density Lipoprotein Cholesterol Lowering Response to Pravastatin in the Elderly

Background: Statins have been shown to significantly lower the risk of coronary heart disease morbidity and mortality, and these benefits have been related t lowering of low density lipoprotein (LDL) cholesterol lowering. Statin metabolism is affected by the liver X receptor alpha ( LXRA ) and the solute carrier organic anion transporter ( SLCO1B1 ). The SLCO1B1 rs4149056 variant has been linked to an increased risk of statin induced myositis due to decreased liver uptake of the statin, increased blood levels, and presumably greater statin uptake in muscle tissue. Our goal was to determine whether genetic variation at these gene loci would influence low density lipoprotein (LDL) cholesterol lowering with pravastatin, baseline heart disease, or cardiac endpoints on trial. Methods: We examined associations of single nucleotide polymorphisms (SNPs) at the LXRA (rs12221497) and SLCO1B1 (rs4149056 and rs2306283) gene loci with these variables in 5411 participants in PROSPER (Prospective Study of Pravastatin in the Elderly at Risk) (mean age 75.3 years), who had been randomized to pravastatin 40 mg/day or placebo and were followed for a mean of 3.2 years. Results: No relationships between genetic variation at the LXRA gene locus with statin induced LDL lowering response or other parameters were noted. Both the SLCO1B1 rs4149056 (valine for alanine at 174) and the rs2306283 (asparagine for aspartic acid at 130) SNPs affect the amino acid of the SLCO1B1 gene product. No effects of the rs2306283 SNP on any of the variables was noted. However the presence of the rs4149056 SNP was associated with significantly less LDL cholesterol lowering response to pravastatin (wildtype, 71.5% of the population, -37.0%, heterozygotes, 25.8% of the population, -36.0%, and homozygotes, 2.7% of the population, -31.8%, p=0.003. Conclusions: Our data indicate that the presence of the rs4149056 non-synonymous SNP at the SLCO1B1 gene locus, especially in the approximately 3% of the population that are homozygous for this variant, can significantly decrease the pravastatin induced LDL cholesterol lowering response. Therefore the presence of this variant not only predicts statin induced myositis, but also statin induced LDL lowering response.

Relationship of NOR-1 with the regulation of inflammation via liver X receptor alpha in Kupffer cells

To investigate the relationship of NOR-1 with the inhibition of inflammatory reaction in mice Kupffer cells (KCs) induced by lipopolysaccharide (LPS) via liver X receptor alpha (LXR alpha). KCs from male KM mice were isolated by density gradient centrifugation, incubated and then randomly assigned to three groups: control group, LPS treated group and LPS+T0901317 treated group. The mRNA and protein expressions of LXR alpha and NOR-1 in each group were determined by RT-PCR, immunofluorescent assay and western blot, respectively. The densities of TNF alpha and IL-10 in supernatants were evaluated by enzyme linked immunosorbent assay (ELISA). The mRNA and protein expression levels of LXR alpha in LPS + T0901317 group were the highest as compared to the other two groups (0.748+/-0.072 and 1.217+/-0.133 respectively), The mRNA and protein expression levels of NOR-1 in LPS+ T0901317 group were the highest as compared to the other two groups (2.726+/-0.065 and 0.842+/-0.058 respectively). The densities of supernatant TNF alpha in LPS group and IL-10 in LPS+T0901317 group were the highest [(450.89+/-78.52) ng/L and (537.41+/-36.41) ng/L respectively]. Promoting the expression of LXR alpha in KCs can elevate the NOR-1 expression and then inhibit inflammatory reaction.

Differential effects of broccoli‐derived phytochemicals indole‐3‐carbinol and its dimer 3, 3’‐diindolylmethane on liver X receptor‐responsive genes in human prostate cancer cells

This study examined the effects of indole‐3‐carbinol (I3C) and 3, 3’‐diindolylmethane (DIM) on liver X receptor (LXR)‐dependent pathways. DIM, but not I3C, induced transcription of ABCG1 and ABCA1 mRNA, two LXR‐responsive ATP‐binding cassette transporters involved in cholesterol efflux, in the androgen responsive LNCaP cells, but not the androgen non‐responsive PC3 cells. Exposure of LNCaP cells to 5 microM DIM for 48 hrs led to a 5‐fold increase in ABCG1 and ABCA1 mRNA levels. Knockdown of LXR alpha and beta isoforms using siRNA abrogated the ability of DIM to induce ABCG1 but not ABCA1 mRNA. Furthermore, knockdown of androgen receptor (AR) expression in LNCaP cells with AR siRNA blocked DIM induction of ABCA1 and ABCG1 mRNAs. The results suggest that DIM modulates cholesterol metabolism through both androgen‐mediated and LXR‐dependent pathways in prostate cancer cells. Furthermore, these effects are unique to DIM but not I3C suggesting that these two dietary components exert cancer preventive effects through different mechanisms.

Associations between common genetic polymorphisms in the liver X receptor alpha and its target genes with the serum HDL-cholesterol concentration in adolescents of the HELENA Study

ObjectiveGenetic variability in the NR1H3 gene (encoding LXRα) and in several of its target genes is associated with serum HDL-cholesterol (HDL-C) concentrations. We sought to assess if these associations could be detected in adolescents. MethodsThirty-nine polymorphisms in NR1H3, ABCA1, APOE, CETP, PLTP and LPL were analysed in the HELENA study (n=1144 European adolescents). ResultsThe minor alleles of rs11039155 in NR1H3, rs2575879 in ABCA1, rs708272, rs17231506 and rs5882 in CETP and rs328 in LPL were associated with higher serum HDL-C concentrations (p≤0.0012). The minor alleles of rs12221497 in NR1H3, rs1800978 in ABCA1 and the APOE ɛ4 allele were associated with lower HDL-C concentrations (p≤0.01). The combined set of associated polymorphisms accounted for ∼6.6% of the variance in HDL-C. ConclusionWe report for the first time that polymorphisms in NR1H3 and its target genes ABCA1, APOE, CETP and LPL contribute to the genetic variance for HDL-C concentrations in adolescence.

Dietary calcium decreases plasma cholesterol by down‐regulation of intestinal Niemann–Pick C1 like 1 and microsomal triacylglycerol transport protein and up‐regulation of CYP7A1 and ABCG 5/8 in hamsters

It has been shown that calcium supplementation favorably modifies plasma lipoprotein profile in postmenopausal women. The present study investigated the interaction of dietary calcium with genes of transporters, receptors and enzymes involved in cholesterol metabolism. Forty-eight ovariectomized hamsters were fed one of the four diets containing 0, 2, 6 and 8 g calcium per kg. Plasma total cholesterol (TC), triacylglycerols (TG), and non-high density lipoprotein cholesterol were dose-dependently decreased, whereas high-density lipoprotein cholesterol (HDL-C) was dose-dependently increased with the increasing dietary calcium levels. Dietary calcium had no effect on protein mass of hepatic sterol regulatory element binding protein-2 (SREBP), liver X receptor-alpha (LXR), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), LDL receptor (LDLR) and cholesterol-7α-hydroxylase (CYP7A1). However, dietary calcium up-regulated the mRNA levels of hepatic CYP7A1 and intestinal ATP binding cassette transporters (ABCG5/8) whereas it down-regulated the intestinal Niemann-Pick C1 like 1 (NPC1L1) and microsomal triacylglycerol transport protein (MTP). In addition, dietary calcium increased the activity of intestinal acyl coenzyme A: cholesterol acyltransferase 2, while it decreased plasma cholesteryl ester transport protein (CETP). Beneficial modification of lipoprotein profile by dietary calcium was mediated by sequestering bile acid absorption and enhancing excretion of fecal cholesterol, via up-regulation of mRNA CYP7A1 and intestinal ABCG 5/8 with down-regulation of mRNA NPC1L1 and MTP.

The liver X-receptor gene promoter is hypermethylated in a mouse model of prenatal protein restriction

Prenatal nutrition as influenced by the nutritional status of the mother has been identified as a determinant of adult disease. Feeding low-protein diets during pregnancy in rodents is a well-established model to induce programming events in offspring. We hypothesized that protein restriction would influence fetal lipid metabolism by inducing epigenetic adaptations. Pregnant C57BL/6J mice were exposed to a protein-restriction protocol (9% vs. 18% casein). Shortly before birth, dams and fetuses were killed. To identify putative epigenetic changes, CG-dinucleotide-rich region in the promoter of a gene (CpG island) methylation microarrays were performed on DNA isolated from fetal livers. Two hundred four gene promoter regions were differentially methylated upon protein restriction. The liver X-receptor (Lxr) alpha promoter was hypermethylated in protein-restricted pups. Lxr alpha is a nuclear receptor critically involved in control of cholesterol and fatty acid metabolism. The mRNA level of Lxra was reduced by 32% in fetal liver upon maternal protein restriction, whereas expression of the Lxr target genes Abcg5/Abcg8 was reduced by 56% and 51%, respectively, measured by real-time quantitative PCR. The same effect, although less pronounced, was observed in the fetal intestine. In vitro methylation of a mouse Lxra-promoter/luciferase expression cassette resulted in a 24-fold transcriptional repression. Our study demonstrates that, in mice, protein restriction during pregnancy interferes with DNA methylation in fetal liver. Lxra is a target of differential methylation, and Lxra transcription is dependent on DNA methylation. It is tempting to speculate that perinatal nutrition may influence adult lipid metabolism by DNA methylation, which may contribute to the epidemiological relation between perinatal/neonatal nutrition and adult disease.

TGF-&amp;beta;1 Up-Regulates Expression of ABCA1, ABCG1 and SR-BI through Liver X Receptor &amp;alpha; Signaling Pathway in THP-1 Macrophage-Derived Foam Cells

High density lipoprotein (HDL) and its apolipoproteins can promote cholesterol efflux from macrophage foam cells via the ATP-binding cassette transporter A1 (ABCA1), ABCG1, and scavenger receptor class B type I (SR-BI). Liver X receptors (LXRs) operate as cholesterol sensors which may protect from cholesterol overload by stimulating cholesterol efflux from cells to HDL through ABCA1, ABCG1 and SR-BI. The regulation of ABCA1, ABCG1 and SR-BI expression by cytokines present within the microenvironment of the atheroma may play an important role in determining the impact of reverse cholesterol transport on the atherosclerotic lesion. In the current study, we examined the effect of transforming growth factor-beta1 (TGF-beta1) on expressions of ABCA1, ABCG1 and SR-BI and explored the role of LXR alpha in the regulation of ABCA1, ABCG1 and SR-BI in THP-1 macrophage-derived foam cells. TGF-beta1 significantly increased expressions of ABCA1, ABCG1 and SR-BI at both transcriptional and translational levels in a dose-dependent and time-dependent manner. Cellular cholesterol content was decreased while cholesterol efflux was increased by TGF-beta1 treatment. Moreover, LXR alpha was up-regulated by TGF-beta1 treatment. In addition, LXR alpha small interfering RNA completely abolished the promotion effect induced by TGF-beta1. These results provide evidence that TGF-beta1 up-regulates expressions of ABCA1, ABCG1 and SR-BI through the LXR alpha pathway in THP-1 macrophage-derived foam cells.

Epigenetic changes in gene expression: focus on “The liver X-receptor gene promoter is hypermethylated in a mouse model of prenatal protein restriction”

the term epigenetics was first coined in 1942 by Waddington ([20][1]) to describe the interaction of genes with their environment during development that gives rise to a phenotype. Today, the term epigenetics is used when describing a phenotype that occurs in a manner outside conventional genetic

LXR ligand lowers LDL cholesterol in primates, is lipid neutral in hamster, and reduces atherosclerosis in mouse

Liver X receptors (LXRs) are ligand-activated transcription factors that coordinate regulation of gene expression involved in several cellular functions but most notably cholesterol homeostasis encompassing cholesterol transport, catabolism, and absorption. WAY-252623 (LXR-623) is a highly selective and orally bioavailable synthetic modulator of LXR, which demonstrated efficacy for reducing lesion progression in the murine LDLR(-/-) atherosclerosis model with no associated increase in hepatic lipogenesis either in this model or Syrian hamsters. In nonhuman primates with normal lipid levels, WAY-252623 significantly reduced total (50-55%) and LDL-cholesterol (LDLc) (70-77%) in a time- and dose-dependent manner as well as increased expression of the target genes ABCA1/G1 in peripheral blood cells. Statistically significant decreases in LDLc were noted as early as day 7, reached a maximum by day 28, and exceeded reductions observed for simvastatin alone (20 mg/kg). Transient increases in circulating triglycerides and liver enzymes reverted to baseline levels over the course of the study. Complementary microarray analysis of duodenum and liver gene expression revealed differential activation of LXR target genes and suggested no direct activation of hepatic lipogenesis. WAY-252623 displays a unique and favorable pharmacological profile suggesting synthetic LXR ligands with these characteristics may be suitable for evaluation in patients with atherosclerotic dyslipidemia.

Abstract 5165: Liver-x-receptor Activation Inhibits Chemokine Induced Cd4-positive Lymphocyte Migration

Migration of CD4-positive lymphocytes into the vessel wall is a critical step in atherogenesis. Recent data suggest that activation of the nuclear transcription factor Liver-X-Receptor (LXR) limits plaque formation in animal models by modulating macrophage function. Previous data demonstrated LXR alpha and beta mRNA and protein expression in human CD4-positive lymphocytes. In addition, activation of LXR limits TH1-cytokine release from CD4-positive cells, but the role of LXR in lymphocyte migration remains currently unexplored. Therefore, the present study investigated whether LXR activation might modulate chemokine-induced migration of these cells. Stimulation of CD4-positive lymphocytes with SDF-1 leads to a 2.5±0.8 fold increase in cell migration (p&lt;0.05; n=12). Pretreatment of cells with the LXR activator T0901317 reduces this effect in a concentration-dependent manner to a maximal 0.9±0.4 fold induction at 1 μ mol/L T0901317 (p&lt;0.05 compared to SDF-1-treated cells, n=12). Similar results were received with the LXR activator GW3965. In addition, T0901317 also reduced RANTES-induced cell migration, suggesting an effect independent of the chemotactic stimulus employed. The effect of T0901317 on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced PI-3 kinase activity as determined by PI-3 kinase activity assays. Downstream, T0901317 inhibited the activation of the small GTPase Rac and the phosphorylation of the Myosin Light Chain (MLC). Pretreatment with the LXR activator also reduces f-actin formation as well as ICAM3 translocation to the uropod, both important steps in T cell migration. Transfection of CD4-positive lymphocytes with LXR α / β siRNA abolished T0901317 inhibitory effect on MLC-phosphorylation. LXR activation by T0901317 or GW3965 inhibits chemokine-induced migration of CD4-positive lymphocytes. Given the crucial importance of chemokine-induced T-cell migration in early atherogenesis, LXR activators may be promising tools to modulate this effect.

Safety, Pharmacokinetics, and Pharmacodynamics of Single Doses of LXR‐623, a Novel Liver X‐Receptor Agonist, in Healthy Participants

Liver X-receptor (LXR) agonists have been postulated to enhance reverse cholesterol transport (RCT), a process believed to shuttle cholesterol from the periphery back to the liver. Enhancing RCT via the upregulation of cholesterol transporters such as the adenosine triphosphate-binding cassettes ABCA1 and ABCG1 could therefore inhibit the progression of atherosclerosis. LXR-623 is a synthetic ligand for LXRs alpha and beta that has shown promise in animal models of atherosclerosis. The authors present results from a single ascending-dose study of the safety, pharmacokinetics, and pharmacodynamics of LXR-623 in healthy participants. LXR-623 was absorbed rapidly with peak concentrations (C(max)) achieved at approximately 2 hours. The C(max) and area under the concentration-time curve increased in a dose-proportional manner. The mean terminal disposition half-life was between 41 and 43 hours independently of dose. LXR activation resulted in a dose-dependent increase in ABCA1 and ABCG1 expression. The effect of LXR-623 concentration on ABCA1 and ABCG1 expression was further characterized via a population pharmacokinetic-pharmacodynamic analysis, yielding EC(50) estimates of 526 ng/mL and 729 ng/mL, respectively. Central nervous system-related adverse events were observed at the 2 top doses tested. The pharmacodynamic effects described here are the first demonstration of "target engagement" by an LXR agonist in humans.

NO-1886 Up-regulates Niemann–Pick C1 Protein (NPC1) Expression Through Liver X Receptor α Signaling Pathway in THP-1 Macrophage-Derived Foam Cells

The Niemann-Pick C1 (NPC1) protein regulates the transport of cholesterol from late endosomes/lysosomes to other compartments responsible for maintaining intracellular cholesterol homeostasis. Liver X receptors (LXRs) operate as cholesterol sensors which may protect from cholesterol overload by increasing the amount of free cholesterol in the plasma membrane through inducing NPC1 expression. NO-1886 has been proven to be highly effective at increasing liver X receptor alpha expression and promoting cellular cholesterol efflux. In this study, the effects of NO-1886 on NPC1 expression were investigated in THP-1 macrophage-derived foam cells. Results showed that NO-1886 markedly increased expression of NPC1 at both mRNA level and protein level in a dose-dependent and time-dependent manner. Cellular cholesterol content was decreased while cholesterol efflux was increased by NO-1886 treatment. In addition, LXR alpha was also up-regulated by NO-1886 treatment. And LXR alpha small interfering RNA completely abolished the promotion effect which was induced by NO-1886. These results provide evidence that NO-1886 up-regulates expression of NPC1 through LXR alpha pathway in THP-1 macrophage- derived foam cells.