OBJECTIVEThe global epidemic of metabolic syndrome and its complications demands rapid evaluation of new and accessible interventions. Insulin resistance is the central biochemical disturbance in the metabolic syndrome. The citrus-derived flavonoid, naringenin, has lipid-lowering properties and inhibits VLDL secretion from cultured hepatocytes in a manner resembling insulin. We evaluated whether naringenin regulates lipoprotein production and insulin sensitivity in the context of insulin resistance in vivo.RESEARCH DESIGN AND METHODSLDL receptor–null (Ldlr−/−) mice fed a high-fat (Western) diet (42% calories from fat and 0.05% cholesterol) become dyslipidemic, insulin and glucose intolerant, and obese. Four groups of mice (standard diet, Western, and Western plus 1% or 3% wt/wt naringenin) were fed ad libitum for 4 weeks. VLDL production and parameters of insulin and glucose tolerance were determined.RESULTSWe report that naringenin treatment of Ldlr−/− mice fed a Western diet corrected VLDL overproduction, ameliorated hepatic steatosis, and attenuated dyslipidemia without affecting caloric intake or fat absorption. Naringenin 1) increased hepatic fatty acid oxidation through a peroxisome proliferator–activated receptor (PPAR) γ coactivator 1α/PPARα-mediated transcription program; 2) prevented sterol regulatory element–binding protein 1c–mediated lipogenesis in both liver and muscle by reducing fasting hyperinsulinemia; 3) decreased hepatic cholesterol and cholesterol ester synthesis; 4) reduced both VLDL-derived and endogenously synthesized fatty acids, preventing muscle triglyceride accumulation; and 5) improved overall insulin sensitivity and glucose tolerance.CONCLUSIONSThus, naringenin, through its correction of many of the metabolic disturbances linked to insulin resistance, represents a promising therapeutic approach for metabolic syndrome.

OBJECTIVEIncreased plasma concentrations of apolipoprotein B100 often present in patients with insulin resistance and confer increased risk for the development of atherosclerosis. Naturally occurring polyphenolic compounds including flavonoids have antiatherogenic properties. The aim of the current study was to evaluate the effect of the polymethoxylated flavonoid nobiletin on lipoprotein secretion in cultured human hepatoma cells (HepG2) and in a mouse model of insulin resistance and atherosclerosis.RESEARCH DESIGN AND METHODSLipoprotein secretion was determined in HepG2 cells incubated with nobiletin or insulin. mRNA abundance was evaluated by quantitative real-time PCR, and Western blotting was used to demonstrate activation of cell signaling pathways. In LDL receptor–deficient mice (Ldlr−/−) fed a Western diet supplemented with nobiletin, metabolic parameters, gene expression, fatty acid oxidation, glucose homeostasis, and energy expenditure were documented. Atherosclerosis was quantitated by histological analysis.RESULTSIn HepG2 cells, activation of mitogen-activated protein kinase-extracellular signal–related kinase signaling by nobiletin or insulin increased LDLR and decreased MTP and DGAT1/2 mRNA, resulting in marked inhibition of apoB100 secretion. Nobiletin, unlike insulin, did not induce phosphorylation of the insulin receptor or insulin receptor substrate-1 and did not stimulate lipogenesis. In fat-fed Ldlr−/− mice, nobiletin attenuated dyslipidemia through a reduction in VLDL-triglyceride (TG) secretion. Nobiletin prevented hepatic TG accumulation, increased expression of Pgc1α and Cpt1α, and enhanced fatty acid β-oxidation. Nobiletin did not activate any peroxisome proliferator–activated receptor (PPAR), indicating that the metabolic effects were PPAR independent. Nobiletin increased hepatic and peripheral insulin sensitivity and glucose tolerance and dramatically attenuated atherosclerosis in the aortic sinus.CONCLUSIONSNobiletin provides insight into treatments for dyslipidemia and atherosclerosis associated with insulin-resistant states.

Metabolic syndrome is a collection of abnormalities, including obesity, dyslipidemia, hypertension, and insulin resistance, all of which contribute to the development of type 2 diabetes and atherosclerosis. Insulin resistance, dyslipidemia, and atherosclerosis are amplifi ed by the development of a chronic low-grade infl ammatory response ( 1 ). In insulin-resistant states, monocyte-derived macrophages infi ltrate visceral adipose tissue, resulting in proinfl ammatory cytokine synthesis, either from adipocytes or resident macrophages, which impairs insulin sensitivity ( 2, 3 ). Administration of diets rich in saturated fats to Ldlr Ϫ / Ϫ mice represents a model with many characteristics of the metabolic syndrome ( 4-6 ). Recent studies in this Abstract Obesity-associated chronic infl ammation contributes to metabolic dysfunction and propagates atherosclerosis. Recent evidence suggests that increased dietary cholesterol exacerbates infl ammation in adipose tissue and liver, contributing to the proatherogenic milieu. The ability of the citrus fl avonoid naringenin to prevent these cholesterol-induced perturbations is unknown. To assess the ability of naringenin to prevent the amplifi ed infl ammatory response and atherosclerosis induced by dietary cholesterol, male Ldlr ؊ / ؊ mice were fed either a cholesterol-enriched high-fat or low-fat diet supplemented with 3% naringenin for 12 weeks. Naringenin, through induction of hepatic fatty acid (FA) oxidation and attenuation of FA synthesis, prevented hepatic steatosis, hepatic VLDL overproduction, and hyperlipidemia induced by both cholesterol-rich diets. Naringenin attenuated hepatic macrophage infi ltration and infl ammation stimulated by dietary cholesterol. Insulin resistance, adipose tissue expansion, and infl ammation were alleviated by naringenin. Naringenin attenuated the cholesterol-induced formation of both foam cells and expression of infl ammatory markers in peritoneal macrophages. Naringenin signifi cantly decreased atherosclerosis and inhibited the formation of complex lesions, which was associated with normalized aortic lipids and a reversal of aortic infl ammation. We demonstrate that in mice fed cholesterolenriched diets, naringenin attenuates peripheral and systemic infl ammation, leading to protection from atherosclerosis. These studies offer a therapeutically relevant alternative for the prevention of cholesterol-induced metabolic dysregulation. -Assini, J. M., E. E. Mulvihill, B. G. Sutherland, D. E. Telford, C. G. Sawyez, S. L. Felder, S. Chhoker, J. Y. Edwards, R. Gros, and M. W. Huff. Naringenin prevents cholesterol-induced systemic infl ammation, This work was supported by Heart and Stroke Foundation of Ontario (HSFO)Grants , Canadian Foundation for Innovation and Ontario Research Fund (to R.G.), a HSFO Masters Award (to J.M.A.), and a Canadian Institutes of Health Research-Canada Graduate Scholarship Doctoral Award (to E.E.M.). 14 December 2012. Published, JLR Papers in Press, December 19, 2012 DOI 10.1194 Abbreviations: ABCG, ATP-binding...