The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest th...

/pdf/myocardial-substrate-metabolism-in-the-normal-and-failing-1cql6lgwxf.pdf

Myocardial Substrate Metabolism in the Normal and Failing Heart

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the β-oxidation of long-chain fatty acids. The control of fatty acid β-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via β-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and β-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid β-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid β-oxidation and how alterations in fatty acid β-oxidation can contribute to heart disease. The implications of inhibiting fatty acid β-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Myocardial Fatty Acid Metabolism in Health and Disease

Arterial stiffness is a growing epidemic associated with increased risk of cardiovascular events, dementia, and death. Decreased compliance of the central vasculature alters arterial pressure and flow dynamics and impacts cardiac performance and coronary perfusion. This article reviews the structural, cellular, and genetic contributors to arterial stiffness, including the roles of the scaffolding proteins, extracellular matrix, inflammatory molecules, endothelial cell function, and reactive oxidant species. Additional influences of atherosclerosis, glucose regulation, chronic renal disease, salt, and changes in neurohormonal regulation are discussed. A review of the hemodynamic impact of arterial stiffness follows. A number of lifestyle changes and therapies that reduce arterial stiffness are presented, including weight loss, exercise, salt reduction, alcohol consumption, and neuroendocrine-directed therapies, such as those targeting the renin-angiotensin aldosterone system, natriuretic peptides, insulin modulators, as well as novel therapies that target advanced glycation end products.

Mechanisms, Pathophysiology, and Therapy of Arterial Stiffness

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Physiology of local renin-angiotensin systems.

Remodeling of large and small arteries contributes to the development and complications of hypertension. The focus of this review is some of the mechanisms involved in the remodeling of small arteries in hypertension. In hypertension, changes in small artery structure are basically of 2 kinds: (1) inward eutrophic remodeling, in which outer and lumen diameters are decreased, media/lumen ratio is increased, and cross-sectional area of the media is unaltered; and (2) hypertrophic remodeling, in which the media thickens to encroach on the lumen, resulting in increased media cross-sectional area and media/lumen ratio. Growth, apoptosis, inflammation, and fibrosis contribute to vascular remodeling in hypertension. Apoptosis is gene-regulated cell death, with minimal membrane disruption and inflammation, that counters cell proliferation and fine-tunes developmental growth. Apoptosis has been reported in hypertension to be both increased and decreased in different tissues, including blood vessels. Inflammation, which may be low grade, probably plays an important role in triggering fibrosis in cardiovascular disease and hypertension. Vascular fibrosis entails accumulation of collagen, fibronectin, and other extracellular matrix components in the vessel wall and is an important aspect of extracellular matrix remodeling in hypertension. Associated with this, there may be increases in cell-matrix attachment sites (integrins) and changes in their topographical localization that may modulate arterial structure. Imbalance in matrix metalloproteinase/tissue inhibitors of metalloproteinases may contribute to alteration in collagen turnover and extracellular matrix remodeling. Chronic vasoconstriction may lead to embedding of the contracted vessel structure in a remodeled extracellular matrix, contributing to the inward remodeling of the blood vessel as smooth muscle cells are rearranged around a smaller lumen. The resulting remodeling of small arteries may initially be adaptive, but eventually it becomes maladaptive and compromises organ function, contributing to cardiovascular complications of hypertension.

Vascular Remodeling in Hypertension Roles of Apoptosis, Inflammation, and Fibrosis

The present study evaluated the effects of peroxisome proliferator-activated receptor (PPAR)-γ activators on ANG II-induced signaling pathways and cell growth. Vascular smooth muscle cells (VSMC) d...

PPAR-γ inhibits ANG II-induced cell growth via SHIP2 and 4E-BP1

Background— The nuclear receptors peroxisome proliferator-activated receptor-α (PPARα) and retinoid X receptor α (RXRα) stimulate the expression of key enzymes of free fatty acid (FFA) oxidation. We tested the hypothesis that the altered metabolic phenotype of the failing heart involves changes in the protein expression of PPARα and RXRα. Methods and Results— Cardiac substrate uptake and oxidation were measured in 8 conscious, chronically instrumented dogs with decompensated pacing-induced heart failure and in 8 normal dogs by infusing 3 isotopically labeled substrates: 3H-oleate, 14C-glucose, and 13C-lactate. Although myocardial O2 consumption was not different between the 2 groups, the rate of oxidation of FFA was lower (2.8±0.6 versus 4.7±0.3 μmol · min−1 · 100g−1) and of glucose was higher (4.6±1.0 versus 1.8±0.5 μmol · min−1 · 100g−1) in failing compared with normal hearts (P<0.05). The rates of lactate uptake and lactate output were not significantly different between the 2 groups. In left ventricul...

Impaired Myocardial Fatty Acid Oxidation and Reduced Protein Expression of Retinoid X Receptor-α in Pacing-Induced Heart Failure

Background— Pioglitazone and rosiglitazone, thiazolidinedione peroxisome proliferator–activated receptor-γ (PPARγ) activators, reduce blood pressure (BP) in some hypertensive models by unclear mechanisms. We tested the hypothesis that pioglitazone or rosiglitazone would prevent BP elevation and vascular dysfunction in angiotensin (Ang) II–infused rats by direct vascular effects. Methods and Results— Sprague-Dawley rats received Ang II (120 ng · kg−1 · min−1 SC) with or without pioglitazone (10 mg · kg−1 · d−1) or rosiglitazone (5 mg · kg−1 · d−1) for 7 days. Systolic BP, elevated in Ang II–infused rats (176±5 mm Hg) versus controls (109±2 mm Hg, P<0.01), was reduced by pioglitazone (134±2 mm Hg) or rosiglitazone (123±2 mm Hg). In mesenteric small arteries studied in a pressurized myograph, media/lumen ratio was increased (P<0.05) and acetylcholine-induced relaxation impaired in Ang II–infused rats (P<0.05); both were normalized by the thiazolidinediones. In Ang II–infused rats, vascular DNA synthesis (by ...

Structure, endothelial function, cell growth, and inflammation in blood vessels of angiotensin II-infused rats: role of peroxisome proliferator-activated receptor-gamma.

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PPAR-γ inhibits ANG II-induced cell growth via SHIP2 and 4E-BP1

Impaired Myocardial Fatty Acid Oxidation and Reduced Protein Expression of Retinoid X Receptor-α in Pacing-Induced Heart Failure

Structure, endothelial function, cell growth, and inflammation in blood vessels of angiotensin II-infused rats: role of peroxisome proliferator-activated receptor-gamma.