Oxidation of intramyocellular lipids is dependent on mitochondrial function and the availability of extracellular fatty acids

Corpeleijn E, Hessvik NP, Bakke SS, Levin K, Blaak EE, Thoresen GH, Gaster M, Rustan AC. Oxidation of intramyocellular lipids is dependent on mitochondrial function and the availability of extracellular fatty acids. Am J Physiol Endocrinol Metab 299: E14-E22, 2010. First published May 4, 2010; doi:10.1152/ajpendo.00187.2010.-Obesity and insulin resistance are related to both enlarged intramyocellular triacylglycerol stores and accumulation of lipid intermediates. We investigated how lipid overflow can change the oxidation of intramyocellular lipids (ICLOX) and intramyocellular lipid storage (ICL). These experiments were extended by comparing these processes in primary cultured myotubes established from healthy lean and obese type 2 diabetic (T2D) individuals, two extremes in a range of metabolic phenotypes. ICLs were prelabeled for 2 days with 100 mu M [C-14] oleic acid (OA). ICLOX was studied using a (CO2)-C-14 trapping system and measured under various conditions of extracellular OA (5 or 100 mu M) and glucose (0.1 or 5.0 mM) and the absence or presence of mitochondrial uncoupling [carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)]. First, increased extracellular OA availability (5 vs. 100 mu M) reduced ICLOX by 37%. No differences in total lipolysis were observed between low and high OA availability. Uncoupling with FCCP restored ICLOX to basal levels during high OA availability. Mitochondrial mass was positively related to ICLOX, but only in myotubes from lean individuals. In all, a lower mitochondrial mass and lower ICLOX were related to a higher cell-associated OA accumulation. Second, myotubes established from obese T2D individuals showed reduced ICLOX. ICLOX remained lower during uncoupling (P <0.001), even with comparable mitochondrial mass, suggesting decreased mitochondrial function. Furthermore, the variation in ICLOX in vitro was significantly related to the in vivo fasting respiratory quotient of all subjects (P <0.02). In conclusion, the rate of ICLOX is dependent on the availability of extracellular fatty acids and mitochondrial function rather than mitochondrial mass

Eicosapentaenoic acid improves metabolic switching in human myotubes

Metabolically healthy skeletal muscle is characterized by the ability to switch easily between glucose and fat oxidation, whereas loss of this ability seems to be related to insulin resistance. The aim of this study was to investigate whether different fatty acids (FAs) and the LXR ligand T0901317 affected metabolic switching in human skeletal muscle cells (myotubes). Pretreatment of myotubes with eicosapentaenoic acid (EPA) increased suppressibility, the ability of glucose to suppress FA oxidation, and metabolic flexibility, the ability to increase FA oxidation when changing from “fed” to “fasted” state. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was increased after pretreatment with EPA, linoleic acid (LA) and palmitic acid (PA). T0901317 counteracted the effect of EPA on suppressibility and adaptability, but did not affect these parameters alone. EPA itself accumulated less, however, EPA, LA, OA and T0901317 increased the number of lipid droplets (LDs) in myotubes, whereas LD size and mitochondria amount were independent of pretreatment. Microarray analysis showed that EPA regulated more genes than the other FAs. Some pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggests a possible favorable effect of EPA on skeletal muscle metabolic switching and glucose utilization

Eicosapentaenoic acid improves metabolic switching in human myotubes

Metabolically healthy skeletal muscle is characterized by the ability to switch easily between glucose and fat oxidation, whereas loss of this ability seems to be related to insulin resistance. The aim of this study was to investigate whether different fatty acids (FAs) and the LXR ligand T0901317 affected metabolic switching in human skeletal muscle cells (myotubes). Pretreatment of myotubes with eicosapentaenoic acid (EPA) increased suppressibility, the ability of glucose to suppress FA oxidation, and metabolic flexibility, the ability to increase FA oxidation when changing from “fed” to “fasted” state. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was increased after pretreatment with EPA, linoleic acid (LA) and palmitic acid (PA). T0901317 counteracted the effect of EPA on suppressibility and adaptability, but did not affect these parameters alone. EPA itself accumulated less, however, EPA, LA, OA and T0901317 increased the number of lipid droplets (LDs) in myotubes, whereas LD size and mitochondria amount were independent of pretreatment. Microarray analysis showed that EPA regulated more genes than the other FAs. Some pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggests a possible favorable effect of EPA on skeletal muscle metabolic switching and glucose utilization

Cholesterol crystals use complement to increase NLRP3 signaling pathways in coronary and carotid atherosclerosis

Background: During atherogenesis, cholesterol precipitates into cholesterol crystals (CC) in the vessel wall, which trigger plaque inflammation by activating the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome. We investigated the relationship between CC, complement and NLRP3 in patients with cardiovascular disease. Methods: We analysed plasma, peripheral blood mononuclear cells (PBMC) and carotid plaques from patients with advanced atherosclerosis applying ELISAs, multiplex cytokine assay, qPCR, immunohistochemistry, and gene profiling. Findings: Transcripts of interleukin (IL)-1beta(b) and NLRP3 were increased and correlated in PBMC from patients with acute coronary syndrome (ACS). Priming of these cells with complement factor 5a (C5a) and tumour necrosis factor (TNF) before incubation with CC resulted in increased IL-1b protein when compared to healthy controls. As opposed to healthy controls, systemic complement was significantly increased in patients with stable angina pectoris or ACS. In carotid plaques, complement C1q and C5b-9 complex accumulated around CC-clefts, and complement receptors C5aR1, C5aR2 and C3aR1 were higher in carotid plaques compared to control arteries. Priming human carotid plaques with C5a followed by CC incubation resulted in pronounced release of IL-1b, IL-18 and IL-1a. Additionally, mRNA profiling demonstrated that C5a and TNF priming followed by CC incubation upregulated plaque expression of NLRP3 inflammasome components. Interpretation: We demonstrate that CC are important local- and systemic complement activators, and we reveal that the interaction between CC and complement could exert its effect by activating the NLRP3 inflammasome, thus promoting the progression of atherosclerosis