The Adrenergic-Fatty Acid Load in Heart Failure
Lionel H. Opie, MD, DPhil, DSc*,* and
Juhani Knuuti, MD, PhD
* Hatter Cardiovascular Research Institute, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, South Africa
Turku PET Centre, University of Turku, Turku, Finland
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Figure 1 FFA Effects on Mitochondria
High circulating levels of free fatty acid (FFA), activated within the muscle cell to fatty acid-coenzyme A (CoA), enter the mitochondria by the action of carnitine palmitoyl transferase (CPT)-1, thereby inhibiting the action of pyruvate dehydrogenase (PDH), blocking protective glycolysis that supplies cytosolic adenosine triphosphate used for ion pumps, and decreasing glucose uptake by muscle. Excess activated FFA increases the formation of reactive oxygen species. For oxygen wastage, see Figure 2. FAO = free fatty acid oxidation.
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Figure 2 Mitochondrial Sources of ROS
As protons are passed along the electron transport chain, reactive oxygen species (ROS) are formed at complexes I and III. FFA-induced proton leakage passes through uncoupling proteins, which divert protons form ATP formation and, hence, waste oxygen. Modified, with permission, from Opie (16). Figure copyright of L. H. Opie. ADP = adenosine diphosphate; ATP = adenosine triphosphate; FA = fatty acid; other abbreviations as in Figure 1.
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Figure 3 Pacing-Induced DCM in Dogs
Changes in circulating norepinephrine (NE), free fatty acids (FFAs), insulin, and glucose with progressive heart failure. Note major increases in FFA and NE. Modified from Nikolaidis et al. (3) with permission of Oxford University Press. DCM = dilated cardiomyopathy.
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Figure 4 Sites of Metabolic Interventions in HF
FFAs are mobilized from adipose tissue to inhibit the uptake of glucose by muscle (including heart muscle). The result is hyperglycemia and increased insulin resistance. Elevated FFAs also act on mitochondria (mito) to cause excess oxygen wastage with formation of ROS (42). The consequences include mitochondrial and cellular dysfunction (ionic changes, increased cell calcium and sodium). Metabolic interventions decrease insulin resistance, hyperglycemia, and ROS formation to decrease the severity of heart failure. Abbreviations as in Figures 1 and 2.
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Figure 5 Site of Action of Metformin
Molecular steps leading from increased FFA to insulin resistance. Excess FFA entering the muscle cell is activated to long-chain acyl-CoA, which inhibits the insulin signaling pathway so that there is less translocation of glucose transporter vesicles (GLUT-4 and -1) to the cell surface. Glucose uptake is decreased and hyperglycemia promoted. The increased uptake of FFA promotes the accumulation of lipid metabolites in various organs, including the heart and pancreas. Metformin and exercise, by stimulating adenosine monophosphate-activated kinase (AMPK), promote the translocation of transport vesicles to the cell surface to promote glucose entry and to oppose insulin resistance. Protein kinase B (PKB), also called Akt, plays a key role. Modified, with permission, from Opie (16). Figure copyright of L. H. Opie. IRS = insulin receptor substrate; P-I-3 = phosphoinositide-3; other abbreviations as in Figure 1.
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