ANGPTL3 Inhibition With Evinacumab Results in Faster Clearance of IDL and LDL apoB in Patients With Homozygous Familial Hypercholesterolemia-Brief Report.

[Figure: see text].

ILRUN, a Human Plasma Lipid GWAS Locus, Regulates Lipoprotein Metabolism in Mice.

RATIONALE: Single-nucleotide polymorphisms near the ILRUN (inflammation and lipid regulator with ubiquitin-associated-like and NBR1 [next to BRCA1 gene 1 protein]-like domains) gene are genome-wide significantly associated with plasma lipid traits and coronary artery disease (CAD), but the biological basis of this association is unknown. OBJECTIVE: To investigate the role of ILRUN in plasma lipid and lipoprotein metabolism. METHODS AND RESULTS: ILRUN encodes a protein that contains a ubiquitin-associated-like domain, suggesting that it may interact with ubiquitinylated proteins. We generated mice globally deficient for Ilrun and found they had significantly lower plasma cholesterol levels resulting from reduced liver lipoprotein production. Liver transcriptome analysis uncovered altered transcription of genes downstream of lipid-related transcription factors, particularly PPARα (peroxisome proliferator-activated receptor alpha), and livers from Ilrun-deficient mice had increased PPARα protein. Human ILRUN was shown to bind to ubiquitinylated proteins including PPARα, and the ubiquitin-associated-like domain of ILRUN was found to be required for its interaction with PPARα. CONCLUSIONS: These findings establish ILRUN as a novel regulator of lipid metabolism that promotes hepatic lipoprotein production. Our results also provide functional evidence that ILRUN may be the casual gene underlying the observed genetic associations with plasma lipids at 6p21 in human.

Differential Effects of Roux-en-Y Gastric Bypass Surgery and Laparoscopic Sleeve Gastrectomy on Fatty Acid Levels.

BACKGROUND: Bariatric surgery is associated with improved cardiovascular outcomes and also affects lipid levels, but few studies have compared the effects of Roux-en-Y gastric bypass (RYGB) surgery with those of laparoscopic sleeve gastrectomy (LSG) on serum fatty acid levels. The present study compares the effects of RYGB and LSG surgeries on serum fatty acid levels. METHODS: The study participants were women who were undergoing either RYGB or LSG and body mass index (BMI)-matched controls. Fasting blood samples to measure glucose, insulin, and fatty acids were drawn at baseline and at 6 and 18 months from baseline. RESULTS: Serum fatty acid data were available for 57 participants at baseline, of whom 56 had data at 6 months and 41 had data at 18 months from baseline. Compared with baseline, serum non-esterified fatty acids (NEFAs) levels were significantly higher at 6 and 18 months in the LSG group compared with the RYGB group. In the RYGB group, 2 saturated fatty acids (SFAs), 2 monounsaturated fatty acids (MUFAs), and 1 polyunsaturated fatty acid (PUFA) were significantly decreased after surgery, compared with those of the LSG group. CONCLUSIONS: A significant increase in NEFAs was seen after LSG, compared with RYGB. Compared with the LSG group, several serum fatty acids were significantly reduced after RYGB. TRIAL REGISTRATION: NCT01228097.

CETP (Cholesteryl Ester Transfer Protein) Inhibition With Anacetrapib Decreases Production of Lipoprotein(a) in Mildly Hypercholesterolemic Subjects.

OBJECTIVE: Lp(a) [lipoprotein (a)] is composed of apoB (apolipoprotein B) and apo(a) [apolipoprotein (a)] and is an independent risk factor for cardiovascular disease and aortic stenosis. In clinical trials, anacetrapib, a CETP (cholesteryl ester transfer protein) inhibitor, causes significant reductions in plasma Lp(a) levels. We conducted an exploratory study to examine the mechanism for Lp(a) lowering by anacetrapib. APPROACH AND RESULTS: We enrolled 39 participants in a fixed-sequence, double-blind study of the effects of anacetrapib on the metabolism of apoB and high-density lipoproteins. Twenty-nine patients were randomized to atorvastatin 20 mg/d, plus placebo for 4 weeks, and then atorvastatin plus anacetrapib (100 mg/d) for 8 weeks. The other 10 subjects were randomized to double placebo for 4 weeks followed by placebo plus anacetrapib for 8 weeks. We examined the mechanisms of Lp(a) lowering in a subset of 12 subjects having both Lp(a) levels >20 nmol/L and more than a 15% reduction in Lp(a) by the end of anacetrapib treatment. We performed stable isotope kinetic studies using 2H3-leucine at the end of each treatment to measure apo(a) fractional catabolic rate and production rate. Median baseline Lp(a) levels were 21.5 nmol/L (interquartile range, 9.9-108.1 nmol/L) in the complete cohort (39 subjects) and 52.9 nmol/L (interquartile range, 38.4-121.3 nmol/L) in the subset selected for kinetic studies. Anacetrapib treatment lowered Lp(a) by 34.1% (P≤0.001) and 39.6% in the complete and subset cohort, respectively. The decreases in Lp(a) levels were because of a 41% reduction in the apo(a) production rate, with no effects on apo(a) fractional catabolic rate. CONCLUSIONS: Anacetrapib reduces Lp(a) levels by decreasing its production. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00990808.

A novel approach to measuring macrophage-specific reverse cholesterol transport in vivo in humans.

Reverse cholesterol transport (RCT) is thought to be an atheroprotective function of HDL, and macrophage-specific RCT in mice is inversely associated with atherosclerosis. We developed a novel method using 3H-cholesterol nanoparticles to selectively trace macrophage-specific RCT in vivo in humans. Use of 3H-cholesterol nanoparticles was initially tested in mice to assess the distribution of tracer and response to interventions known to increase RCT. Thirty healthy subjects received 3H-cholesterol nanoparticles intravenously, followed by blood and stool sample collection. Tracer counts were assessed in plasma, nonHDL, HDL, and fecal fractions. Data were analyzed by using multicompartmental modeling. Administration of 3H-cholesterol nanoparticles preferentially labeled macrophages of the reticuloendothelial system in mice, and counts were increased in mice treated with a liver X receptor agonist or reconstituted HDL, as compared with controls. In humans, tracer disappeared from plasma rapidly after injection of nanoparticles, followed by reappearance in HDL and nonHDL fractions. Counts present as free cholesterol increased rapidly and linearly in the first 240 min after nadir; counts in cholesteryl ester increased steadily over time. Estimates of fractional transfer rates of key RCT steps were obtained. These results support the use of 3H-cholesterol nanoparticles as a feasible approach for the measurement of macrophage RCT in vivo in humans.

Overexpression and deletion of phospholipid transfer protein reduce HDL mass and cholesterol efflux capacity but not macrophage reverse cholesterol transport.

Phospholipid transfer protein (PLTP) may affect macrophage reverse cholesterol transport (mRCT) through its role in the metabolism of HDL. Ex vivo cholesterol efflux capacity and in vivo mRCT were assessed in PLTP deletion and PLTP overexpression mice. PLTP deletion mice had reduced HDL mass and cholesterol efflux capacity, but unchanged in vivo mRCT. To directly compare the effects of PLTP overexpression and deletion on mRCT, human PLTP was overexpressed in the liver of wild-type animals using an adeno-associated viral (AAV) vector, and control and PLTP deletion animals were injected with AAV-null. PLTP overexpression and deletion reduced plasma HDL mass and cholesterol efflux capacity. Both substantially decreased ABCA1-independent cholesterol efflux, whereas ABCA1-dependent cholesterol efflux remained the same or increased, even though preß HDL levels were lower. Neither PLTP overexpression nor deletion affected excretion of macrophage-derived radiocholesterol in the in vivo mRCT assay. The ex vivo and in vivo assays were modified to gauge the rate of cholesterol efflux from macrophages to plasma. PLTP activity did not affect this metric. Thus, deviations in PLTP activity from the wild-type level reduce HDL mass and ex vivo cholesterol efflux capacity, but not the rate of macrophage cholesterol efflux to plasma or in vivo mRCT.

Cell lipid metabolism modulators 2-bromopalmitate, D609, monensin, U18666A and probucol shift discoidal HDL formation to the smaller-sized particles: implications for the mechanism of HDL assembly.

ATP-binding cassette transporter A1 (ABCA1) mediates formation of disc-shaped high-density lipoprotein (HDL) from cell lipid and lipid-free apolipoprotein A-I (apo A-I). Discoidal HDL particles are heterogeneous in physicochemical characteristics for reasons that are understood incompletely. Discoidal lipoprotein particles similar in characteristics and heterogeneity to cell-formed discoidal HDL can be reconstituted from purified lipids and apo A-I by cell-free, physicochemical methods. The heterogeneity of reconstituted HDL (rHDL) is sensitive to the lipid composition of the starting lipid/apo A-I mixture. To determine whether the heterogeneity of cell-formed HDL is similarly sensitive to changes in cell lipids, we investigated four compounds that have well-established effects on cell lipid metabolism and ABCA1-mediated cell cholesterol efflux. 2-Bromopalmitate, D609, monensin and U18666A decreased formation of the larger-sized, but dramatically increased formation of the smaller-sized HDL. 2-Bromopalmitate did not appear to affect ABCA1 activity, subcellular localization or oligomerization, but induced dissolution of the cholesterol-phospholipid complexes in the plasma membrane. Arachidonic and linoleic acids shifted HDL formation to the smaller-sized species. Tangier disease mutations and inhibitors of ABCA1 activity wheat germ agglutinin and AG 490 reduced formation of both larger-sized and smaller-sized HDL. The effect of probucol was similar to the effect of 2-bromopalmitate. Taking rHDL formation as a paradigm, we propose that ABCA1 mutations and activity inhibitors reduce the amount of cell lipid available for HDL formation, and the compounds in the 2-bromopalmitate group and the polyunsaturated fatty acids change cell lipid composition from one that favors formation of the larger-sized HDL particles to one that favors formation of the smaller-sized species.

Loss of Function of GALNT2 Lowers High-Density Lipoproteins in Humans, Nonhuman Primates, and Rodents.

Human genetics studies have implicated GALNT2, encoding GalNAc-T2, as a regulator of high-density lipoprotein cholesterol (HDL-C) metabolism, but the mechanisms relating GALNT2 to HDL-C remain unclear. We investigated the impact of homozygous GALNT2 deficiency on HDL-C in humans and mammalian models. We identified two humans homozygous for loss-of-function mutations in GALNT2 who demonstrated low HDL-C. We also found that GALNT2 loss of function in mice, rats, and nonhuman primates decreased HDL-C. O-glycoproteomics studies of a human GALNT2-deficient subject validated ANGPTL3 and ApoC-III as GalNAc-T2 targets. Additional glycoproteomics in rodents identified targets influencing HDL-C, including phospholipid transfer protein (PLTP). GALNT2 deficiency reduced plasma PLTP activity in humans and rodents, and in mice this was rescued by reconstitution of hepatic Galnt2. We also found that GALNT2 GWAS SNPs associated with reduced HDL-C also correlate with lower hepatic GALNT2 expression. These results posit GALNT2 as a direct modulator of HDL metabolism across mammals.

Functional analysis and transcriptomic profiling of iPSC-derived macrophages and their application in modeling Mendelian disease.

RATIONALE: An efficient and reproducible source of genotype-specific human macrophages is essential for study of human macrophage biology and related diseases. OBJECTIVE: To perform integrated functional and transcriptome analyses of human induced pluripotent stem cell-derived macrophages (IPSDMs) and their isogenic human peripheral blood mononuclear cell-derived macrophage (HMDM) counterparts and assess the application of IPSDM in modeling macrophage polarization and Mendelian disease. METHODS AND RESULTS: We developed an efficient protocol for differentiation of IPSDM, which expressed macrophage-specific markers and took up modified lipoproteins in a similar manner to HMDM. Like HMDM, IPSDM revealed reduction in phagocytosis, increase in cholesterol efflux capacity and characteristic secretion of inflammatory cytokines in response to M1 (lipopolysaccharide+interferon-γ) activation. RNA-Seq revealed that nonpolarized (M0) as well as M1 or M2 (interleukin-4) polarized IPSDM shared transcriptomic profiles with their isogenic HMDM counterparts while also revealing novel markers of macrophage polarization. Relative to IPSDM and HMDM of control individuals, patterns of defective cholesterol efflux to apolipoprotein A-I and high-density lipoprotein-3 were qualitatively and quantitatively similar in IPSDM and HMDM of patients with Tangier disease, an autosomal recessive disorder because of mutations in ATP-binding cassette transporter AI. Tangier disease-IPSDM also revealed novel defects of enhanced proinflammatory response to lipopolysaccharide stimulus. CONCLUSIONS: Our protocol-derived IPSDM are comparable with HMDM at phenotypic, functional, and transcriptomic levels. Tangier disease-IPSDM recapitulated hallmark features observed in HMDM and revealed novel inflammatory phenotypes. IPSDMs provide a powerful tool for study of macrophage-specific function in human genetic disorders as well as molecular studies of human macrophage activation and polarization.

Robust passive and active efflux of cellular cholesterol to a designer functional mimic of high density lipoprotein.

The ability of HDL to support macrophage cholesterol efflux is an integral part of its atheroprotective action. Augmenting this ability, especially when HDL cholesterol efflux capacity from macrophages is poor, represents a promising therapeutic strategy. One approach to enhancing macrophage cholesterol efflux is infusing blood with HDL mimics. Previously, we reported the synthesis of a functional mimic of HDL (fmHDL) that consists of a gold nanoparticle template, a phospholipid bilayer, and apo A-I. In this work, we characterize the ability of fmHDL to support the well-established pathways of cellular cholesterol efflux from model cell lines and primary macrophages. fmHDL received cell cholesterol by unmediated (aqueous) and ABCG1- and scavenger receptor class B type I (SR-BI)-mediated diffusion. Furthermore, the fmHDL holoparticle accepted cholesterol and phospholipid by the ABCA1 pathway. These results demonstrate that fmHDL supports all the cholesterol efflux pathways available to native HDL and thus, represents a promising infusible therapeutic for enhancing macrophage cholesterol efflux. fmHDL accepts cholesterol from cells by all known pathways of cholesterol efflux: unmediated, ABCG1- and SR-BI-mediated diffusion, and through ABCA1.

RYR1-related malignant hyperthermia with marked cerebellar involvement - a paradigm of heat-induced CNS injury?

Heat-induced CNS injury has been recognized for more than 50 years but the biological basis for the marked selectivity of CNS damage is currently uncertain. We present clinical, imaging, autopsy and genetic findings of a 14-year-old male who developed fatal cerebellar swelling in the course of a malignant hyperthermia (MH) episode caused by triggering anaesthetics. Unaccustomed intense exercise in the days prior to general anaesthesia was a probable confounding factor for the MH reaction. Autopsy findings demonstrated pronounced degeneration of cerebellar Purkinje cells. Post mortem genetic analysis revealed a mutation (c.6502G>A; p.Val2168Met) in the skeletal muscle ryanodine receptor (RYR1) gene previously associated with the MH trait. RYR1 mutations appear to be associated with heat-induced CNS injury in a distribution compatible with known expression pattern of the RyR1 isoform in cerebellar Purkinje cells. Recent exercise in genetically predisposed individuals may prime abnormal muscle prior to general anaesthesia and contribute to the severity of MH reactions.

A functional, genome-wide evaluation of liposensitive yeast identifies the "ARE2 required for viability" (ARV1) gene product as a major component of eukaryotic fatty acid resistance.

The toxic subcellular accumulation of lipids predisposes several human metabolic syndromes, including obesity, type 2 diabetes, and some forms of neurodegeneration. To identify pathways that prevent lipid-induced cell death, we performed a genome-wide fatty acid sensitivity screen in Saccharomyces cerevisiae. We identified 167 yeast mutants as sensitive to 0.5 mm palmitoleate, 45% of which define pathways that were conserved in humans. 63 lesions also impacted the status of the lipid droplet; however, this was not correlated to the degree of fatty acid sensitivity. The most liposensitive yeast strain arose due to deletion of the "ARE2 required for viability" (ARV1) gene, encoding an evolutionarily conserved, potential lipid transporter that localizes to the endoplasmic reticulum membrane. Down-regulation of mammalian ARV1 in MIN6 pancreatic ß-cells or HEK293 cells resulted in decreased neutral lipid synthesis, increased fatty acid sensitivity, and lipoapoptosis. Conversely, elevated expression of human ARV1 in HEK293 cells or mouse liver significantly increased triglyceride mass and lipid droplet number. The ARV1-induced hepatic triglyceride accumulation was accompanied by up-regulation of DGAT1, a triglyceride synthesis gene, and the fatty acid transporter, CD36. Furthermore, ARV1 was identified as a transcriptional of the protein peroxisome proliferator-activated receptor α (PPARα), a key regulator of lipid homeostasis whose transcriptional targets include DGAT1 and CD36. These results implicate ARV1 as a protective factor in lipotoxic diseases due to modulation of fatty acid metabolism. In conclusion, a lipotoxicity-based genetic screen in a model microorganism has identified 75 human genes that may play key roles in neutral lipid metabolism and disease.

The corporate determinants of health: how big business affects our health, and the need for government action!

Corporations have a great effect on the health of Canadians.Good companies create jobs, sell valued products at market value, pay a living wage, empower employees, have progressive human resource policies (parental, mental health leaves, workplace wellness programs, day care), and pay their appropriate corporate taxes. They embrace corporate social responsibility and some have a triple bottom line - people, planet and profits. More good corporations are needed.But others are selling products that are damaging to health and the environment, at prices that do not account for these damaging effects and often target consumers that are ill-informed and susceptible (e.g., children). These include businesses involving tobacco, alcohol, drugs, junk foods and beverages, resource extraction, arms production and the electronic media.Governments have a responsibility to take action when the market mechanism fails in this way.A priority for action is the food and beverage sector. The overconsumption of sugar, fat and salt is causing a rising prevalence of all the major chronic diseases, rising health care costs and declining population health and productivity. Urgent government action is required: taxation, advertising and sales restrictions, and a salt reduction program.

Novel benefits of peroxisome proliferator-activated receptors on cardiovascular risk.

PURPOSE OF REVIEW: This review provides an overview of newly described mechanisms by which peroxisome proliferator-activated receptors (PPARs) (α, γ, and δ) regulate several factors associated with cardiovascular risk. RECENT FINDINGS: PPAR agonists have known effects on plasma lipoprotein levels, inflammation, and insulin resistance all of which influence the risk of cardiovascular disease. Recent studies provide more detail regarding the mechanisms behind these changes. PPAR-α activation in the enterocyte on HDL and chylomicron formation. PPAR-γ agonists reduce inflammation, in part, through direct effects on adipocytes and regulatory T cells within visceral adipose. PPAR-δ also has a relatively high expression in the macrophage. Incubation of macrophages with PPAR-δ agonists was shown to inhibit foam cell formation induced excessive levels of VLDL remnants. SUMMARY: Treatments that activate PPAR-α, PPAR-γ, and PPAR-δ alone or in combination have the potential to reduce cardiovascular risk although multiple independent mechanisms. Treatment with PPAR agonists can reduce the burden of atherogenic postprandial lipoproteins and improve vascular function, reduce inflammation and inhibit foam cell formation. All of these would be expected to have favorable effects on cardiovascular risk. The challenge remains to develop compounds that maximize these potential cardiovascular benefits while minimizing undesirable effects of these compounds.

Effects of Therapeutic Lifestyle Change diets high and low in dietary fish-derived FAs on lipoprotein metabolism in middle-aged and elderly subjects.

The effects of Therapeutic Lifestyle Change (TLC) diets, low and high in dietary fish, on apolipoprotein metabolism were examined. Subjects were provided with a Western diet for 6 weeks, followed by 24 weeks of either of two TLC diets (10/group). Apolipoprotein kinetics were determined in the fed state using stable isotope methods and compartmental modeling at the end of each phase. Only the high-fish diet decreased median triglyceride-rich lipoprotein (TRL) apoB-100 concentration (-23%), production rate (PR, -9%), and direct catabolism (-53%), and increased TRL-to-LDL apoB-100 conversion (+39%) as compared with the baseline diet (all P < 0.05). This diet also decreased TRL apoB-48 concentration (-24%), fractional catabolic rate (FCR, -20%), and PR (-50%) as compared with the baseline diet (all P < 0.05). The high-fish and low-fish diets decreased LDL apoB-100 concentration (-9%, -23%), increased LDL apoB-100 FCR (+44%, +48%), and decreased HDL apoA-I concentration (-15%, -14%) and PR (-11%, -12%) as compared with the baseline diet (all P < 0.05). On the high-fish diet, changes in TRL apoB-100 PR were negatively correlated with changes in plasma eicosapentaenoic and docosahexaenoic acids. In conclusion, the high-fish diet decreased TRL apoB-100 and TRL apoB-48 concentrations chiefly by decreasing their PR. Both diets decreased LDL apoB-100 concentration by increasing LDL apoB-100 FCR and decreased HDL apoA-I concentration by decreasing HDL apoA-I PR.

Hepatic sortilin regulates both apolipoprotein B secretion and LDL catabolism.

Genome-wide association studies (GWAS) have identified a genetic variant at a locus on chromosome 1p13 that is associated with reduced risk of myocardial infarction, reduced plasma levels of LDL cholesterol (LDL-C), and markedly increased expression of the gene sortilin-1 (SORT1) in liver. Sortilin is a lysosomal sorting protein that binds ligands both in the Golgi apparatus and at the plasma membrane and traffics them to the lysosome. We previously reported that increased hepatic sortilin expression in mice reduced plasma LDL-C levels. Here we show that increased hepatic sortilin not only reduced hepatic apolipoprotein B (APOB) secretion, but also increased LDL catabolism, and that both effects were dependent on intact lysosomal targeting. Loss-of-function studies demonstrated that sortilin serves as a bona fide receptor for LDL in vivo in mice. Our data are consistent with a model in which increased hepatic sortilin binds intracellular APOB-containing particles in the Golgi apparatus as well as extracellular LDL at the plasma membrane and traffics them to the lysosome for degradation. We thus provide functional evidence that genetically increased hepatic sortilin expression both reduces hepatic APOB secretion and increases LDL catabolism, providing dual mechanisms for the very strong association between increased hepatic sortilin expression and reduced plasma LDL-C levels in humans.

Selective peroxisome proliferator-activated receptor-γ modulation to reduce cardiovascular risk in patients with insulin resistance.

The thiazolidinediones (TZDs) rosiglitazone and pioglitazone improve glucose homeostasis through activation of peroxisome proliferator-activated receptor (PPAR)-γ. Their use, however, has been limited due to adverse effects that include body weight gain and edema leading to congestive heart failure. Selective PPAR-γ modulators (SPPARMs) are second generation PPAR-γ ligands designed to improve insulin sensitivity with minimal undesirable effects associated with first generation PPAR-γ agonists. INT131 is one of the first SPPARMs to reach human trials. Early phase human studies with INT131 look promising with changes in plasma lipids and glucose being equal or better than what is seen with rosiglitazone and pioglitazone treatment but without evidence of edema. This profile of improved glucose homeostasis, improved plasma lipids, and reduced inflammation in the absence of edema would be expected to reduce cardiovascular risk in patients with Type 2 diabetes mellitus. Recent patents of novel approaches for the use of PPAR-γ related compounds with the potential for this improved risk-benefit ratio are discussed.

PPARγ activation redirects macrophage cholesterol from fecal excretion to adipose tissue uptake in mice via SR-BI.

PPARγ agonists, used in the treatment of Type 2 diabetes, can raise HDL-cholesterol, therefore could potentially stimulate macrophage-to-feces reverse cholesterol transport (RCT). We aimed to test whether PPARγ activation promotes macrophage RCT in vivo. Macrophage RCT was assessed in mice using cholesterol loaded/(3)H-cholesterol labeled macrophages. PPARγ agonist GW7845 (20 mg/kg/day) did not change (3)H-tracer plasma appearance, but surprisingly decreased fecal (3)H-free sterol excretion by 43% (P<0.01) over 48h. Total free cholesterol efflux from macrophages to serum (collected from control and GW7845 groups) was not different, although ABCA1-mediated efflux was significantly higher with GW7845. To determine the effect of PPARγ activation on HDL cholesterol uptake by different tissues, the metabolic fate of HDL labeled with (3)H-cholesteryl ether (CE) was also measured. We observed two-fold increase in HDL derived (3)H-CE uptake by adipose tissue (P<0.005) with concomitant 22% decrease in HDL derived (3)H-CE uptake by the liver (P<0.05) in GW7845 treated wild type mice. This was associated with a significant increase in SR-BI protein expression in adipose tissue, but not liver. The same experiment in SR-BI knockout mice, showed no difference in HDL derived (3)H-CE uptake by adipose tissue or liver. In conclusion, PPARγ activation decreases the fecal excretion of macrophage derived cholesterol in mice. This is not due to inhibition of cholesterol efflux from macrophages, but rather involves redirection of effluxed cholesterol from liver towards adipose tissue uptake via SR-BI. This represents a novel mechanism for regulation of RCT and may extend the therapeutic implications of these ligands.

Short-term treatment with high-dose atorvastatin reduces LDL cholesterol but shows no anti-inflammatory effects in normolipidemic subjects with normal CRP levels.

The benefit in reducing cardiovascular risk with statins has been attributed both to cholesterol lowering and pleiotropic effects. These pleiotropic effects are thought to include attenuation of the inflammatory response due to reduced prenylation of proteins in the inflammatory cascade. We conducted studies in normolipidemic subjects to determine if treatment with high-dose (80 mg) atorvastatin could reduce circulating levels of inflammatory markers. We also determined whether high-dose atorvastatin affected the inflammatory response of monocytes stimulated with lipopolysaccharide (LPS) ex vivo. We found that treatment with atorvastatin rapidly and significantly reduced plasma low-density lipoprotein (LDL) cholesterol levels in subjects treated for 2 weeks. However, statin treatment had no discernible effect on plasma levels of the inflammatory markers high-sensitivity C-reactive protein (hsCRP), tumor necrosis factor (TNF)-alpha, or interleukin (IL-6) and no effect on the cytokine response of monocytes following ex vivo stimulation with LPS. High-dose atorvastatin treatment of normolipidemic subjects with normal C-reactive protein levels has no effect on the inflammatory response assessed by monocyte stimulation with LPS ex vivo despite significant reductions in LDL cholesterol levels.

Modulation of HDL metabolism by the niacin receptor GPR109A in mouse hepatocytes.

The niacin receptor GPR109A is a G(i)-protein-coupled receptor which mediates the effects of niacin on inhibiting intracellular triglyceride lipolysis in adipocytes. However, the role of GPR109A in mediating the effects of niacin on high density lipoprotein (HDL) metabolism is unclear. We found niacin has no effect on HDL-C in GPR109A knockout mice. Furthermore, niacin lowered intracellular cAMP in primary hepatocytes mediated by GPR109A. We used an adeno-associated viral (AAV) serotype 8 vector encoding GPR109A under the control of the hepatic-specific thyroxine-binding globulin promoter to specifically overexpress GPR109A in mouse liver. Plasma HDL-C, hepatic ABCA1 and the HDL cholesterol production rate were significantly reduced in mice overexpressing GPR109A. Overexpression of GPR109A reduced primary hepatocyte free cholesterol efflux to apoA-I; conversely, GPR109A deficient hepatocytes had increased ABCA1-mediated cholesterol efflux. These data support the concept that the HDL-C lowering effect of niacin in wild-type mice is mediated through stimulation of GPR109A in hepatocytes; such an effect then leads to reduced hepatocyte ABCA1 expression and activity, decreased cholesterol efflux to nascent apoA-I, and reduced HDL-C levels. These results indicate that niacin-mediated activation of GP109A in liver lowers ABCA1 expression leading to reduced hepatic cholesterol efflux to HDL.