This article is available online at http://www.jlr.org Cardiovascular disease (CVD) remains a leading cause of morbidity and mortality in the Western world ( 1 ). Elevated levels of LDL-cholesterol (LDL-C) have consistently shown a positive association with the development of CVD, justifying the current therapeutic strategies to prevent CVD primarily by the use of statins. Members of this drug class inhibit HMG-CoA reductase (HMGR), the rate-limiting enzyme for de novo cholesterol synthesis, thereby leading to decreased LDL-C ( 2-4 ). While the benefi ts of statins have been documented ( 2 ), many individuals on statin therapy still remain at a higher risk of developing CVD. It is possible this residual risk is a result of other metabolic syndrome (MetS) risk factors characterized by dyslipidemia and insulin resistance and is also in part due to statin intolerance ( 5-7 ) and noncompliance often related to statininduced myalgia ( 8, 9 ). Statins are effective at decreasing LDL-C and CVD; however, frequent muscle-related side effects limit dosage and impede maximal risk reduction in dyslipidemic patients ( 10 ). Furthermore, recent evidence suggests that high-dose statins may increase the risk of developing type 2 diabetes (T2D) ( 11 ), further justifying the need for alternative therapeutic interventions that have statin-like effects for lowering LDL-C and are designed to Abstract ETC-1002 (8-hydroxy-2,2,14,14-tetramethylpentadecanedioic acid) is a novel investigational drug being developed for the treatment of dyslipidemia and other cardio-metabolic risk factors. The hypolipidemic, anti-atherosclerotic, anti-obesity, and glucose-lowering properties of ETC-1002, characterized in preclinical disease models, are believed to be due to dual inhibition of sterol and fatty acid synthesis and enhanced mitochondrial long-chain fatty acid ␤ -oxidation. However, the molecular mechanism(s) mediating these activities remained undefi ned.

The glucagon-like peptides (GLP-1 and GLP-2) are processed from the proglucagon polypeptide and secreted in equimolar amounts but have opposite effects on chylomicron (CM) production, with GLP-1 significantly reducing and GLP-2 increasing postprandial chylomicronemia. In the current study, we evaluated the apparent paradoxical roles of GLP-1 and GLP-2 under physiological conditions in the Syrian golden hamster, a model with close similarity to humans in terms of lipoprotein metabolism. A short (30-min) intravenous infusion of GLP-2 resulted in a marked increase in postprandial apolipoprotein B48 (apoB48) and triglyceride (TG) levels in the TG-rich lipoprotein (TRL) fraction, whereas GLP-1 infusion decreased lipid absorption and levels of TRL-TG and apoB48. GLP-1 and GLP-2 coinfusion resulted in net increased lipid absorption and an increase in TRL-TG and apoB48. However, prolonged (120-min) coinfusion of GLP-1 and GLP-2 decreased postprandial lipemia. Blocking dipeptidyl peptidase-4 activity resulted in decreased postprandial lipemia. Interestingly, fructose-fed, insulin-resistant hamsters showed a more pronounced response, including possible hypersensitivity to GLP-2 or reduced sensitivity to GLP-1. In conclusion, under normal physiological conditions, the actions of GLP-2 predominate; however, when GLP-1 activity is sustained, the hypolipidemic action of GLP-1 predominates. Pharmacological inhibition of GLP-1 degradation tips the balance toward an inhibitory effect on intestinal production of atherogenic CM particles.

Intestinal lipid dysregulation is a common feature of insulin-resistant states. The present study investigated alterations in gene expression of key proteins involved in the active absorption of dietary fat and cholesterol in response to development of insulin resistance. Studies were conducted in two diet-induced animal models of insulin resistance: fructose-fed hamster and high-fat-fed mouse. Changes in the mRNA abundance of lipid transporters, adenosine triphosphate cassette (ABC) G5, ABCG8, FA-CoA ligase fatty acid translocase P4, Niemann-Pick C1-Like1 (NPC1L1), fatty acid transport protein 4 (FATP4), and Scavenger Receptor Class B Type I (SR-BI), were assessed in intestinal fragments (duodenum, jejunum, and ileum) using quantitative real-time PCR. Of all the transporters evaluated, SR-B1 showed the most significant changes in both animal models examined. A marked stimulation of SR-B1 expression was observed in all intestinal segments examined in both insulin-resistant animal models. The link between SR-BI expression and intestinal lipoprotein production was then examined in the Caco-2 cell model. SR-B1 overexpression in Caco-2 cells increased apolipoprotein B (apoB) 100 and apoB48 secretion, whereas RNAi knock down of SR-B1 decreased secretion of both apoB100 and apoB48. We also observed changes in subcellular distribution of SR-B1 in response to exogenous lipid and insulin. Confocal microscopy revealed marked changes in SR-BI subcellular distribution in response to both exogenous lipids (oleate) and insulin. In summary, marked stimulation of intestinal SR-BI occurs in vivo in animal models of diet-induced insulin resistance, and modulation of SR-BI in vitro regulates production of apoB-containing lipoprotein particles. We postulate that apical and/or basolateral SR-BI may play an important role in intestinal chylomicron production and may contribute to chylomicron overproduction normally observed in insulin-resistant states.

Background: Hepatic ER stress promotes insulin resistance, but the role of cholesterol in this pathway is unknown. Results: LCAT-deficient mice maintain a low ER cholesterol and are protected from cholesterol-induced ER stress. Conclusion: ER cholesterol, not tissue cholesterol, is crucial for hepatic ER stress development. Significance: Modulators of hepatic ER cholesterol may be novel targets to treat diabetes.

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Liver X receptor-␣ (LXR␣) is considered a master regulator of hepatic lipid metabolism; however, little is known about the link between LXR activation, hepatic insulin signaling, and very low-density lipoprotein (VLDL)-apolipoprotein B (apoB) assembly and secretion. Here, we examined the effect of LXR␣ activation on hepatic insulin signaling and apoB-lipoprotein production. In vivo activation of LXR␣ for 7 days using a synthetic LXR agonist, TO901317, in hamsters led to increased plasma triglyceride (TG; 3.6-fold compared with vehicle-treated controls, P ϭ 0.006), apoB (54%, P Ͻ 0.0001), and VLDL-TG (eightfold increase compared with vehicle). As expected, LXR stimulation activated maturation of sterol response element binding protein-1c (SREBP-1c) as well as the SREBP-1c target genes steroyl CoA desaturase (SCD) and fatty acid synthase (FAS). Metabolic pulse-chase labeling experiments in primary hamster hepatocytes showed increased stability and secretion of newly synthesized apoB following LXR activation. Microsomal triglyceride transfer protein (MTP) mRNA and protein were unchanged, however, likely because of the relatively short period of treatment and long half-life of MTP mRNA. Examination of hepatic insulin-signaling molecules revealed LXR-mediated reductions in insulin receptor (IR)␤ subunit mass (39%, P ϭ 0.014) and insulin receptor substrate (IRS)-1 tyrosine phosphorylation (24%, P ϭ 0.023), as well as increases in protein tyrosine phosphatase (PTP)1B (29%, P Ͻ 0.001) protein mass. In contrast to IRS-1, a twofold increase in IRS-2 mass (228%, P ϭ 0.0037) and a threefold increase in IRS-2 tyrosine phosphorylation (321%, P ϭ 0.012) were observed. In conclusion, LXR activation dysregulates hepatic insulin signaling and leads to a considerable increase in the number of circulating TG-rich VLDL-apoB particles, likely due to enhanced hepatic assembly and secretion of apoB-containing lipoproteins.liver X receptor; very low-density lipoprotein; hamster NUCLEAR LIVER X RECEPTORS (LXRs) act as intracellular sensors for sterols (22) and, in response to ligands, induce transcriptional responses to maintain cholesterol, lipid, and glucose homeostasis (23,25,51). LXR is a central player in energy homeostasis, as indicated by its putative involvement in lipogenesis, gluconeogenesis, lipoprotein metabolism, and glucose uptake (46). The initial rationale for studies of LXR and LXR agonists was based on observations of their beneficial effects on reverse cholesterol transport, a process whereby cholesterol is transported from extrahepatic tissues to the liver for eventual excretion through the bile (9). Synthetic LXR agonists have therefore been designed with the intention of treating disorders such as atherosclerosis and diabetes (8, 17).The two isoforms of LXR, ␣ and ␤, are highly homologous and form obligate heterodimers with retinoid X receptor (RXR) (11,55). LXR is part of a large family of ligand-activated nuclear transcription factors that includes the farnesoid X receptor (FXR). Hepatic lipogenic genes known to b...

Ezetimibe is a cholesterol uptake inhibitor that targets the Niemann-Pick C1-like 1 cholesterol transporter. Ezetimibe treatment has been shown to cause significant decreases in plasma cholesterol levels in patients with hypercholesterolemia and familial hypercholesterolemia. A recent study in humans has shown that ezetimibe can decrease the release of atherogenic postprandial intestinal lipoproteins. In the present study, we evaluated the mechanisms by which ezetimibe treatment can lower postprandial apoB48-containing chylomicron particles, using a hyperlipidemic and insulin-resistant hamster model fed a diet rich in fructose and fat (the FF diet) and fructose, fat, and cholesterol (the FFC diet). Male Syrian Golden hamsters were fed either chow or the FF or FFC diet ± ezetimibe for 2 wk. After 2 wk, chylomicron production was assessed following intravenous triton infusion. Tissues were then collected and analyzed for protein and mRNA content. FFC-fed hamsters treated with ezetimibe showed improved glucose tolerance, decreased fasting insulin levels, and markedly reduced circulating levels of TG and cholesterol in both the LDL and VLDL fractions. Examination of triglyceride (TG)-rich lipoprotein (TRL) fractions showed that ezetimibe treatment reduced postprandial cholesterol content in TRL lipoproteins as well as reducing apoB48 content. Although ezetimibe did not decrease TRL-TG levels in FFC hamsters, ezetimibe treatment in FF hamsters resulted in decreases in TRL-TG. Jejunal apoB48 protein expression was lower in ezetimibe-treated hamsters. Reductions in jejunal protein levels of scavenger receptor type B-1 (SRB-1) and fatty acid transport protein 4 were also observed. In addition, ezetimibe-treated hamsters showed significantly lower jejunal mRNA expression of a number of genes involved in lipid synthesis and transport, including srebp-1c, sr-b1, ppar-γ, and abcg1. These data suggest that treatment with ezetimibe not only inhibits cholesterol uptake, but may also alter intestinal function to promote improved handling of dietary lipids and reduced chylomicron production. These, in turn, promote decreases in fasting and postprandial lipid levels and improvements in glucose homeostasis.

1 The vasoactive effects of the synthetic cannabinoid (CB) arachidonyl-2-chloroethylamide (ACEA) was tested in the knee joints of urethane-anaesthetised rats. Experiments were also performed to determine whether these vasomotor responses could be blocked by the selective CB 1 receptor antagonists AM251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) (10 À9 mol) and AM281 (1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide) (10 À8 mol), as well as the selective CB 2 receptor antagonistPeripheral application of ACEA (10 À14 -10 À9 mol) onto the exposed surface of the knee joint capsule caused a dose-dependent increase in synovial blood flow. The dilator action of the CB occurred within 1 min after drug administration and rapidly returned to control levels shortly thereafter. The maximal vasodilator effect of ACEA corresponded to a 30% increase in articular perfusion compared to control levels. 3 The hyperaemic action of ACEA was not significantly altered by coadministration of AM251, AM281 or AM630 (P40.05; two-way ANOVA). 4 The transient receptor potential channel vanilloid receptor 1 (TRPV 1 ) antagonist capsazepine (10 À6 mol) significantly reduced the vasodilator effect of ACEA on joint blood vessels (P ¼ 0.002). Furthermore, destruction of unmyelinated and thinly myelinated joint sensory nerves by capsaicin (8-methyl-N-vanillyl-6-nonenamide) treatment also attenuated ACEA responses (Po0.0005).5 These data clearly demonstrate a vasodilator effect of the cannabinomimetic ACEA on knee joint perfusion. Rather than a classic CB receptor pathway, ACEA exerts its vasomotor influence by acting via TRPV 1 receptors located on the terminal branches of capsaicin-sensitive afferent nerves innervating the joint.