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Binding studies at 37 °C showed that lipoprotein lipase-treated very low density lipoproteins (LPL-VLDL) and very low density lipoproteins (VLDL), once taken up via the low density lipoprotein (LDL) receptor, are poorly degraded by HepG2 cells as compared with LDL. Determination of the initial endocytotic rate for LPL-VLDL and VLDL as compared to LDL shows that LPL- VLDL and VLDL are internalized at a similar rate as LDL. Incubation of cells with labeled LDL, LPL-VLDL, and VLDL at 18 °C for 4.5 h resulted in the accumulation of these particles in the early endosomes, without subsequent transport to the lysosomes and degradation. After washing the cells and a temperature shift to 37 °C, the labeled LDL present in the early endosomes is transported to the lysosomal compartment almost completely within 15 min. Strikingly, for LPL-VLDL and for VLDL, only about 50% or less of the label was moved to the lysosomal compartment within 45 min. However, once present in the lysosomes, VLDL and LPL-VLDL are degraded about 1.6-fold more rapidly than LDL. Retroendocytosis accounts for less than 10% of the internalized LDL, whereas a higher rate of retroendocytosis, up to 20 and 40%, respectively, was observed for LPL-VLDL and VLDL. To evaluate the effect of the inefficient transport of VLDL and LPL-VLDL to the lysosomal compartment on cellular cholesterol homeostasis, acyl-CoA:cholesterol acyltransferase (ACAT) activity was measured. Incubation with 30 μg/ml of LDL induced a 2.5- fold increase in ACAT activity, whereas the incubation with similar amounts of both VLDL and LPL-VLDL failed to stimulate this enzyme. We conclude that both a slower transport to the lysosomal compartment and a higher rate of retroendocytosis, possibly as the consequence of the longer residence time in the early endosomes, are responsible for the poor degradation of VLDL and LPL-VLDL by HepG2 cells. Chemicals/CAS: cholesterol acyltransferase, 9027-63-8; Cholesterol, 57-88-5; Lipoprotein Lipase, EC 3.1.1.34; Lipoproteins, LDL; Lipoproteins, VLDL; Sterol O-Acyltransferase, EC 2.3.1.26; Triglycerides

Accumulation of lipid-laden macrophages is a hallmark of atherosclerosis. The relevance of the key transcription factor nuclear factor κB (NF-κB) for macrophage-derived foam-cell formation has not been unequivocally resolved. Transgenic mice lines were generated in which NF-κB activation is specifically inhibited in macrophages by overexpressing a trans-dominant, non-degradable form of IκBα (IκBα (32A/36A)) under control of the macrophage-specific SR-A promoter. Alanine substitution of serines 32 and 36 prevents degradation and retains the inactive NF-κB/IκBα (32A/36A) complex in the cytoplasm. Similarly, stable human THP1 monocytic cell lines were generated with integrated copies of IκBα (32A/36A) cDNA. Upon treatment with oxidized low-density lipoprotein (ox-LDL), murine peritoneal macrophages from transgenic IκBα (32A/36A) mice, as well as THP1/IκBα (32A/36A) clones, display decreased lipid loading after differentiation into macrophages. This is accompanied by increased expression of the transcription factors PPARγ and LXRα as well as of the major cholesterol-efflux transporter ABCA1. Paradoxically, mRNA expression of the 'lipid-uptake' receptor CD36 is also increased. Since the net result of these changes is reduction of foam-cell formation, it is proposed that under specific inhibition of NF-κB activation, ABCA1-mediated cholesterol efflux prevails over CD36-mediated lipid influx. © 2006 Elsevier Ireland Ltd. All rights reserved.

Aims/hypothesis. Insulin resistance for glucose metabolism is associated with hyperlipidaemia and high blood pressure. In this study we investigated the effect of primary hyperlipidaemia on basal and insulin-mediated glucose and on non-esterified fatty acid (NEFA) metabolism and mean arterial pressure in hyperlipidaemic transgenic mice overexpressing apolipoprotein C1 (APOC1). Previous studies have shown that APOC1 transgenic mice develop hyperlipidaemia primarily because of an impaired hepatic uptake of very low density lipoprotein (VLDL). Methods. Basal and hyperinsulinaemic (6 mU · kg-1 · min-1), euglycaemic (7 mmol/l) clamps with 3-3H-glucose or 9,10-3H-palmitic acid infusions and in situ freeze clamped tissue collection were carried out. Results. The APOC1 mice showed increased basal plasma cholesterol, triglyceride, NEFA and decreased glucose concentrations compared with wild-type mice (7.0 ± 1.2 vs 1.6 ± 0.1, 9.1 ± 2.3 vs 0.6 ± 0.1, 1.9 ± 0.2 vs 0.9 ± 0.1 and 7.0 ± 1.0 vs 10.0 ± 1.1 mmol/l, respectively, p < 0.05). Basal whole body glucose clearance was increased twofold in APOC1 mice compared with wild-type mice (18 ± 2 vs 10 ± 1 ml · kg-1 · min-1, p < 0.05). Insulin-mediated whole body glucose uptake, glycolysis (generation of 3H2O) and glucose storage increased in APOC1 mice compared with wild-type mice (339 ± 28 vs 200 ± 11; 183 ± 39 vs 128 ± 17 and 156 ± 44 vs 72 ± 17 μmol · kg-1 · min-1, p < 0.05, respectively), corresponding with a twofold to three-fold increase in skeletal muscle glycogenesis and de novo lipogenesis from 3-3H-glucose in skeletal muscle and adipose tissue (p < 0.05). Basal whole body NEFA clearance was decreased threefold in APOC1 mice compared with wild-type mice (98 ± 21 vs 314 ± 88 ml · kg-1 · min-1, p < 0.05). Insulin-mediated whole body NEFA uptake, NEFA oxidation (generation of 3H2O) and NEFA storage were lower in APOC1 mice than in wild-type mice (15 ± 3 vs 33 ± 6; 3 ± 2 vs 11 ± 4 and 12 ± 2 vs 22 ± 4 μmol · kg-1· min-1, p < 0.05) in the face of higher plasma NEFA concentrations (1.3 ± 0.3 vs 0.5 ± 0.1 mmol/l, p < 0.05), respectively. Mean arterial pressure and heart rate were similar in APOC1 vs wild-type mice (82 ±4 vs 85 ± 3 mm Hg and 459 ± 14 vs 484 ± 11 beats, min-1). Conclusions/interpretation. 1) Hyperlipidaemic APOC1 mice show reduced NEFA and increased glucose metabolism under both basal and insulin-mediated conditions, suggesting an intrinsic defect in NEFA metabolism. Primary hyperlipidaemia alone in APOC1 mice does not lead to insulin resistance for glucose metabolism and high blood pressure. Chemicals/CAS: Apolipoprotein C-I; Apolipoproteins C; Blood Glucose; Cholesterol, 57-88-5; Fatty Acids, Nonesterified; Glucose, 50-99-7; Glycogen, 9005-79-2; Insulin, 11061-68-0; Palmitic Acid, 57-10-3; Triglycerides; Tritium, 10028-17-8

Purpose: Osteoarthritis (OA) is associated with obesity in which altered fatty acid levels have been observed. We investigated whether the most common fatty acids in synovial fluid influence cartilage deterioration in OA. Design: Cartilage was obtained from OA patients undergoing total knee arthroplasty. Chondrocytes or cartilage explants were cultured with linoleic (n-6 polyunsaturated), oleic (monounsaturated), or palmitic (saturated) acid. After preculture, media were renewed and inflammation was simulated in half of the samples by addition of 10 ng/mL tumor necrosis factor-α (TNFα) with or without the fatty acids. Effects on lipid uptake (Oil-Red-O), cell toxicity (lactate dehydrogenase), prostaglandin-E2 (PGE2) release and gene expression for prostaglandin-endoperoxide synthase-2 (PTGS2), matrix metalloproteinase-1 (MMP1), and MMP13, and a disintegrin and metalloproteinase with thrombospondin motifs 4 were determined on chondrocytes in monolayer. Effects on glycosaminoglycan (GAG) release were evaluated on cartilage explants. Results: None of the fatty acids were cytotoxic and all were taken up by the cells, resulting in a higher amount of intracellular lipid in chondrocytes. Linoleic acid increased PGE2 production in the presence of TNFα. Oleic acid and palmitic acid inhibited MMP1 gene expression in chondrocytes stimulated with TNFα. In cartilage explants, GAG release was also inhibited by oleic acid and palmitic acid, and oleic acid decreased PTGS2 gene expression in stimulated chondrocytes. Conclusions: Linoleic acid has a pro-inflammatory effect on cartilage whereas oleic acid and palmitic acid seem to inhibit cartilage destruction. These results indicate that altered fatty acid levels may influence loss of cartilage structure in OA. © The Author(s) 2013.Chemicals/CAS: collagenase 3, 175449-82-8; glyceraldehyde 3 phosphate dehydrogenase, 9001-50-7; interstitial collagenase, 9001-12-1; lactate dehydrogenase, 9001-60-9; linoleic acid, 1509-85-9, 2197-37-7, 60-33-3, 822-17-3; oleic acid, 112-80-1, 115-06-0; palmitic acid, 57-10-3; prostaglandin E2, 363-24-6; prostaglandin synthase, 39391-18-9, 59763-19-8, 9055-65-6

Background and aims Activation of brown adipose tissue (BAT) reduces both hyperlipidemia and atherosclerosis by increasing the uptake of triglyceride-derived fatty acids by BAT, accompanied by formation and clearance of lipoprotein remnants. We tested the hypothesis that the hepatic uptake of lipoprotein remnants generated by BAT activation would be accelerated by concomitant statin treatment, thereby further reducing hypercholesterolemia and atherosclerosis. Methods APOE*3-Leiden.CETP mice were fed a Western-type diet and treated without or with the selective β3-adrenergic receptor (AR) agonist CL316,243 that activates BAT, atorvastatin (statin) or both. Results β3-AR agonism increased energy expenditure as a result of an increased fat oxidation by activated BAT, which was not further enhanced by statin addition. Accordingly, statin treatment neither influenced the increased uptake of triglyceride-derived fatty acids from triglyceride-rich lipoprotein-like particles by BAT nor further lowered plasma triglyceride levels induced by β3-AR agonism. Statin treatment increased the hepatic uptake of the formed cholesterol-enriched remnants generated by β3-AR agonism. Consequently, statin treatment further lowered plasma cholesterol levels. Importantly, statin, in addition to β3-AR agonism, also further reduced the atherosclerotic lesion size as compared to β3-AR agonism alone, without altering lesion severity and composition. Conclusions Statin treatment accelerates the hepatic uptake of remnants generated by BAT activation, thereby increasing the lipid-lowering and anti-atherogenic effects of BAT activation in an additive fashion. We postulate that, in clinical practice, combining statin treatment with BAT activation is a promising new avenue to combat hyperlipidemia and cardiovascular disease.

Objective - Niacin potently decreases plasma triglycerides and LDL-cholesterol. In addition, niacin is the most potent HDL-cholesterol- increasing drug used in the clinic. In the present study, we aimed at elucidation of the mechanism underlying its HDL-raising effect. Methods and Results - InAPOE*3Leiden transgenic mice expressing the human CETP transgene, niacin dose-dependently decreased plasma triglycerides (up to -77%, P<0.001) and total cholesterol (up to -66%, P<0.001). Concomitantly, niacin dose-dependently increased HDL-cholesterol (up to +87%, P<0.001), plasma apoAI (up to +72%, P<0.001), as well as the HDL particle size. In contrast, in APOE*3Leiden mice, not expressing CETP, niacin also decreased total cholesterol and triglycerides but did not increase HDL-cholesterol. In fact, in APOE*3Leiden.CETP mice, niacin dose-dependently decreased the hepatic expression of CETP (up to -88%; P<0.01) as well as plasma CETP mass (up to -45%, P<0.001) and CETP activity (up to -52%, P<0.001). Additionally, niacin dose-dependently decreased the clearance of apoAI from plasma and reduced the uptake of apoAI by the kidneys (up to -90%, P<0.01). Conclusion - Niacin markedly increases HDL-cholesterol in APOE*3Leiden. CETP mice by reducing CETP activity, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool, and increases HDL-apoAI by decreasing the clearance of apoAI from plasma. © 2008 American Heart Association, Inc.

The peroxisome proliferator-activated receptor alpha (PPARα) activator fenofibrate efficiently decreases plasma triglycerides (TG), which is generally attributed to enhanced very low density lipoprotein (VLDL)-TG clearance and decreased VLDL-TG production. However, because data on the effect of fenofibrate on VLDL production are controversial, we aimed to investigate in (more) detail the mechanism underlying the TG-lowering effect by studying VLDL-TG production and clearance using APOE*3-Leiden.CETP mice, a unique mouse model for human-like lipoprotein metabolism. Male mice were fed a Western-type diet for 4 weeks, followed by the same diet without or with fenofibrate (30 mg/kg bodyweight/day) for 4 weeks. Fenofibrate strongly lowered plasma cholesterol (-38%) and TG (-60%) caused by reduction of VLDL. Fenofibrate markedly accelerated VLDL-TG clearance, as judged from a reduced plasma halflife of glycerol tri[³H]oleate-labeled VLDL-like emulsion particles (-68%). This was associated with an increased postheparin lipoprotein lipase (LPL) activity (+110%) and an increased uptake of VLDL-derived fatty acids by skeletal muscle, white adipose tissue, and liver. Concomitantly, fenofibrate markedly increased the VLDL-TG production rate (+73%) but not the VLDL-apolipoprotein B (apoB) production rate. Kinetic studies using [ ³H]palmitic acid showed that fenofibrate increased VLDL-TG production by equally increasing incorporation of re-esterified plasma fatty acids and liver TG into VLDL, which was supported by hepatic gene expression profiling data. We conclude that fenofibrate decreases plasma TG by enhancing LPL-mediated VLDL-TG clearance, which results in a compensatory increase in VLDL-TG production by the liver. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.