Quantitative profiling of oxylipins in plasma and atherosclerotic plaques of hypercholesterolemic rabbits.

Oxylipins are oxidation products of polyunsaturated fatty acids (PUFAs) that affect a broad range of physiological processes, including cell proliferation, inflammation, inflammation resolution, and vascular function. Moreover, oxylipins are readily detectable in plasma, and certain subsets of oxylipins have been detected in human atherosclerotic lesions. Taken together, we set out to produce a detailed quantitative assessment of plasma and plaque oxylipins in a widely used model of atherosclerosis, to identify potential biomarkers of disease progression. We administered regular chow or regular chow supplemented with 0.5% cholesterol (HC) to male New Zealand white rabbits for 12 weeks to induce hypercholesterolemia and atherosclerosis. Our targeted lipidomic analyses of oxylipins on plaques isolated from rabbits fed the HC diet detected 34 oxylipins, 28 of which were in compliance with our previously established quality control acceptance criteria. The arachidonic acid (AA) metabolite derived from the COX pathway, 6-keto-PGF1α was the most abundant plaque oxylipin, followed by the linoleic acid (LA) metabolites 9-HODE, 13-HODE and 9,12,13-TriHOME and the arachidonic acid (AA)-derivatives 11-HETE and 12-HETE. We additionally found that the most abundant oxylipins in plasma were three of the five most abundant oxylipins in plaque, namely 11-HETE, 13-HODE, and 9-HODE. The studies reported here make the first step towards a comprehensive characterization of oxylipins as potentially translatable biomarkers of atherosclerosis.

Lipidome of atherosclerotic plaques from hypercholesterolemic rabbits.

The cellular, macromolecular and neutral lipid composition of the atherosclerotic plaque has been extensively characterized. However, a comprehensive lipidomic analysis of the major lipid classes within atherosclerotic lesions has not been reported. The objective of this study was to produce a detailed framework of the lipids that comprise the atherosclerotic lesion of a widely used pre-clinical model of plaque progression. Male New Zealand White rabbits were administered regular chow supplemented with 0.5% cholesterol (HC) for 12 weeks to induce hypercholesterolemia and atherosclerosis. Our lipidomic analyses of plaques isolated from rabbits fed the HC diet, using ultra-performance liquid chromatography (UPLC) and high-resolution mass spectrometry, detected most of the major lipid classes including: Cholesteryl esters, triacylglycerols, phosphatidylcholines, sphingomyelins, diacylglycerols, fatty acids, phosphatidylserines, lysophosphatidylcholines, ceramides, phosphatidylglycerols, phosphatidylinositols and phosphatidylethanolamines. Given that cholesteryl esters, triacylglycerols and phosphatidylcholines comprise greater than 75% of total plasma lipids, we directed particular attention towards the qualitative and quantitative assessment of the fatty acid composition of these lipids. We additionally found that sphingomyelins were relatively abundant lipid class within lesions, and compared the abundance of sphingomyelins to their precursor phosphatidylcholines. The studies presented here are the first approach to a comprehensive characterization of the atherosclerotic plaque lipidome.

PPARδ activation attenuates hepatic steatosis in Ldlr-/- mice by enhanced fat oxidation, reduced lipogenesis, and improved insulin sensitivity.

PPARδ regulates systemic lipid homeostasis and inflammation, but its role in hepatic lipid metabolism remains unclear. Here, we examine whether intervening with a selective PPARδ agonist corrects hepatic steatosis induced by a high-fat, cholesterol-containing (HFHC) diet. Ldlr(-/-) mice were fed a chow or HFHC diet (42% fat, 0.2% cholesterol) for 4 weeks. For an additional 8 weeks, the HFHC group was fed HFHC or HFHC plus GW1516 (3 mg/kg/day). GW1516-intervention significantly attenuated liver TG accumulation by induction of FA ß-oxidation and attenuation of FA synthesis. In primary mouse hepatocytes, GW1516 treatment stimulated AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylation in WT hepatocytes, but not AMPKß1(-/-) hepatocytes. However, FA oxidation was only partially reduced in AMPKß1(-/-) hepatocytes, suggesting an AMPK-independent contribution to the GW1516 effect. Similarly, PPARδ-mediated attenuation of FA synthesis was partially due to AMPK activation, as GW1516 reduced lipogenesis in WT hepatocytes but not AMPKß1(-/-) hepatocytes. HFHC-fed animals were hyperinsulinemic and exhibited selective hepatic insulin resistance, which contributed to elevated fasting FA synthesis and hyperglycemia. GW1516 intervention normalized fasting hyperinsulinemia and selective hepatic insulin resistance and attenuated fasting FA synthesis and hyperglycemia. The HFHC diet polarized the liver toward a proinflammatory M1 state, which was reversed by GW1516 intervention. Thus, PPARδ agonist treatment inhibits the progression of preestablished hepatic steatosis.

Peroxisome proliferator-activated receptor δ agonist GW1516 attenuates diet-induced aortic inflammation, insulin resistance, and atherosclerosis in low-density lipoprotein receptor knockout mice.

OBJECTIVE: The peroxisome proliferator-activated receptor (PPAR) δ regulates systemic lipid homeostasis and inflammation. However, the ability of PPARδ agonists to improve the pathology of pre-established lesions and whether PPARδ activation is atheroprotective in the setting of insulin resistance have not been reported. Here, we examine whether intervention with a selective PPARδ agonist corrects metabolic dysregulation and attenuates aortic inflammation and atherosclerosis. APPROACH AND RESULTS: Low-density lipoprotein receptor knockout mice were fed a chow or a high-fat, high-cholesterol (HFHC) diet (42% fat, 0.2% cholesterol) for 4 weeks. For a further 8 weeks, the HFHC group was fed either HFHC or HFHC plus GW1516 (3 mg/kg per day). GW1516 significantly attenuated pre-established fasting hyperlipidemia, hyperglycemia, and hyperinsulinemia, as well as glucose and insulin intolerance. GW1516 intervention markedly reduced aortic sinus lesions and lesion macrophages, whereas smooth muscle α-actin was unchanged and collagen deposition enhanced. In aortae, GW1516 increased the expression of the PPARδ-specific gene Adfp but not PPARα- or γ-specific genes. GW1516 intervention decreased the expression of aortic proinflammatory M1 cytokines, increased the expression of the anti-inflammatory M2 cytokine Arg1, and attenuated the iNos/Arg1 ratio. Enhanced mitogen-activated protein kinase signaling, known to induce inflammatory cytokine expression in vitro, was enhanced in aortae of HFHC-fed mice. Furthermore, the HFHC diet impaired aortic insulin signaling through Akt and forkhead box O1, which was associated with elevated endoplasmic reticulum stress markers CCAAT-enhancer-binding protein homologous protein and 78kDa glucose regulated protein. GW1516 intervention normalized mitogen-activated protein kinase activation, insulin signaling, and endoplasmic reticulum stress. CONCLUSIONS: Intervention with a PPARδ agonist inhibits aortic inflammation and attenuates the progression of pre-established atherosclerosis.

Peroxisome proliferator-activated receptor δ: a multifaceted metabolic player.

PURPOSE OF REVIEW: Therapeutic strategies to alleviate the growing epidemic of insulin-resistant syndromes (obesity and type 2 diabetes) as well as the conferred cardiovascular disease risk remain sparse. The peroxisome proliferator-activated receptor δ (PPARδ) has emerged as a versatile regulator of lipid homeostasis and inflammatory signaling, making it an attractive therapeutic target for the treatment and prevention of type 2 diabetes and atherosclerosis. RECENT FINDINGS: PPARδ activation regulates lipid homeostasis and inflammatory signaling in a variety of cell types, conferring protection from metabolic disease and atherosclerosis. Specifically, PPARδ activation in the liver stimulates glucose utilization and inhibits gluconeogenesis, which improves insulin resistance and hyperglycemia. In macrophages, PPARδ-specific activation with synthetic agonists inhibits VLDL-induced triglyceride accumulation and inflammation. In mice, PPARδ agonists halt the progression of atherosclerosis and stabilize existing lesions by promoting an anti-inflammatory milieu within the diseased macrovasculature. In humans, PPARδ activation improves insulin sensitivity and reduces atherogenic dyslipidemia via a mechanism complementary to statin monotherapy. SUMMARY: Recent advances in the understanding of PPARδ reveal that activation of this receptor represents a multifaceted therapeutic strategy for the prevention and treatment of insulin-resistant syndromes and atherosclerosis.

Activation of peroxisome proliferator-activated receptor δ inhibits human macrophage foam cell formation and the inflammatory response induced by very low-density lipoprotein.

OBJECTIVE: Hypertriglyceridemia is an important risk factor for cardiovascular disease. Elevated plasma very low-density lipoprotein (VLDL) puts insulin-resistant patients at risk for atherosclerosis. VLDL readily induces macrophage lipid accumulation and inflammatory responses, for which targeted therapeutic strategies remain elusive. We examined the ability of VLDL to induce macrophage foam cells and the inflammatory response and sought to define the cell signaling cascades involved. We further examined the potential of peroxisome proliferator-activated receptor (PPAR) δ activation to attenuate both VLDL-stimulated lipid accumulation and cytokine expression. METHODS AND RESULTS: THP-1 macrophages exposed to VLDL displayed significant triglyceride accumulation, which was attenuated by PPARδ activation. PPARδ agonists stimulated a transcriptional program resulting in inhibition of lipoprotein lipase activity, activation of fatty acid uptake, and enhanced ß-oxidation. VLDL-treated macrophages significantly increased the expression of activator protein 1 associated cytokines interleukin-1ß, macrophage inflammatory protein 1α, and intercellular adhesion molecule-1. VLDL treatment significantly increased the phosphorylation of both extracellular signal-related kinase 1 and 2 and p38. VLDL reduced AKT phosphorylation as well as its downstream effector forkhead box protein O1, concomitant with increased nuclear forkhead box protein O1. Cells treated with PPARδ agonists were completely resistant to VLDL-induced expression of inflammatory cytokines, mediated by normalization of mitogen-activated protein kinase (MAPK)(erk) and AKT/forkhead box protein O1 signaling. CONCLUSIONS: The combined PPARδ-mediated reductions of lipid accumulation and inflammatory cytokine expression suggest a novel macrophage-targeted therapeutic option in treating atherosclerosis.