G.J. van der Vusse

Skeletal muscle fibre-type shifting and metabolic profile in patients with chronic obstructive pulmonary disease

The aim of this study was to examine the nature of fibre-type redistribution in relation to fibre metabolic profile in the vastus lateralis in chronic obstructive pulmonary disease (COPD) and COPD subtypes. Fifteen COPD patients (eight with emphysema stratified by high-resolution computed tomography) and 15 healthy control subjects were studied. A combination of myofibrillar adenosine triphosphatase staining and immunohistochemistry was used to identify pure, as well as hybrid fibre types. For oxidative capacity, fibres were stained for cytochrome c oxidase and succinate dehydrogenase activities, and glycogen phosphorylase for glycolytic capacity. The proportion of type‐I fibres in COPD patients was markedly lower (16% versus 42%), especially in emphysema, and the proportion of hybrid fibres was higher (29% versus 16%) compared to controls. The proportion of fibres staining positive for oxidative enzymes was lower in COPD patients, which correlated with the proportion of type‐I fibres. In COPD oxidative capacity was lower within IIA fibres. The authors conclude that fibre-type transitions are involved in the fibre-type redistribution in chronic obstructive pulmonary disease. Low oxidative capacity is closely related to the proportion of type‐I fibres, but an additional reduction of oxidative enzyme activity is present within IIA fibres. Fibre-type abnormalities may be aggravated in emphysema.

Palmitate transport and fatty acid transporters in red and white muscles

We performed studies 1) to investigate the kinetics of palmitate transport into giant sarcolemmal vesicles, 2) to determine whether the transport capacity is greater in red muscles than in white muscles, and 3) to determine whether putative long-chain fatty acid (LCFA) transporters are more abundant in red than in white muscles. For these studies we used giant sarcolemmal vesicles, which contained cytoplasmic fatty acid binding protein (FABPc), an intravesicular fatty acid sink. Intravesicular FABPcconcentrations were sufficiently high so as not to limit the uptake of palmitate under conditions of maximal palmitate uptake (i.e., 4.5-fold excess in white and 31.3-fold excess in red muscle vesicles). All of the palmitate taken up was recovered as unesterified palmitate. Palmitate uptake was reduced by phloretin (-50%), sulfo- N-succinimidyl oleate (-43%), anti-plasma membrane-bound FABP (FABPpm, -30%), trypsin (-45%), and when incubation temperature was lowered to 0°C (-70%). Palmitate uptake was also reduced by excess oleate (-65%), but not by excess octanoate or by glucose. Kinetic studies showed that maximal transport was 1.8-fold greater in red vesicles than in white vesicles. The Michaelis-Menten constant in both types of vesicles was ∼6 nM. Fatty acid transport protein mRNA and fatty acid translocase (FAT) mRNA were about fivefold greater in red muscles than in white muscles. FAT/CD36 and FABPpm proteins in red vesicles or in homogenates were greater than in white vesicles or homogenates ( P < 0.05). These studies provide the first evidence of a protein-mediated LCFA transport system in skeletal muscle. In this tissue, palmitate transport rates are greater in red than in white muscles because more LCFA transporters are available.We performed studies 1) to investigate the kinetics of palmitate transport into giant sarcolemmal vesicles, 2) to determine whether the transport capacity is greater in red muscles than in white muscles, and 3) to determine whether putative long-chain fatty acid (LCFA) transporters are more abundant in red than in white muscles. For these studies we used giant sarcolemmal vesicles, which contained cytoplasmic fatty acid binding protein (FABPc), an intravesicular fatty acid sink. Intravesicular FABPc concentrations were sufficiently high so as not to limit the uptake of palmitate under conditions of maximal palmitate uptake (i.e., 4.5-fold excess in white and 31.3-fold excess in red muscle vesicles). All of the palmitate taken up was recovered as unesterified palmitate. Palmitate uptake was reduced by phloretin (-50%), sulfo-N-succinimidyl oleate (-43%), anti-plasma membrane-bound FABP (FABPpm, -30%), trypsin (-45%), and when incubation temperature was lowered to 0 degrees C (-70%). Palmitate uptake was also reduced by excess oleate (-65%), but not by excess octanoate or by glucose. Kinetic studies showed that maximal transport was 1.8-fold greater in red vesicles than in white vesicles. The Michaelis-Menten constant in both types of vesicles was approximately 6 nM. Fatty acid transport protein mRNA and fatty acid translocase (FAT) mRNA were about fivefold greater in red muscles than in white muscles. FAT/CD36 and FABPpm proteins in red vesicles or in homogenates were greater than in white vesicles or homogenates (P < 0.05). These studies provide the first evidence of a protein-mediated LCFA transport system in skeletal muscle. In this tissue, palmitate transport rates are greater in red than in white muscles because more LCFA transporters are available.

Myopathological features in skeletal muscle of patients with chronic obstructive pulmonary disease

Despite the fact that muscle weakness is a major problem in chronic obstructive pulmonary disease (COPD), detailed information on myopathological changes at the microscopic level in these patients is scarce, if indeed available at all. Vastus lateralis biopsies of 15 COPD weight-stable patients (body mass index (BMI) 23.9±1.0 kg·m−2; fat-free mass index (FFMI) 17.2±1.7 kg·m−2) and 16 healthy age-matched controls (BMI 26.3±0.8 kg·m−2; FFMI 19.6±2.2 kg·m−2) were evaluated. Histochemistry was used to evaluate myopathological features. Immunohistochemistry was used for the detection of macrophages and leukocytes, and active caspase 3 and terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL) as markers of apoptosis. Fatty cell replacement and fibrosis were observed in both groups, the latter being slightly, but significantly, more pronounced in COPD. No differences between COPD and controls were found with respect to central nuclei, necrosis, regeneration, or fibre splitting. Signs of mitochondrial abnormalities were absent and normal numbers of inflammatory cells were found. Active caspase 3 positive myocytes were not observed and no difference was found in the number of TUNEL-positive myonuclei between controls and COPD patients (1.1% versus 1.0%, respectively). The cross-sectional area of type-IIX muscle fibres was smaller in COPD than in controls (2,566 versus 4,248 µm2). Except for the I to IIX shift in fibre types, the selective type-IIX atrophy and a slight accompanying increase in fibrosis and fat cell replacement in chronic obstructive pulmonary disease relative to age-matched controls, no other morphological abnormalities were observed in the muscle biopsies of chronic obstructive pulmonary disease patients. Also, in this group of clinically and weight stable chronic obstructive pulmonary disease patients, apoptosis appeared not to be involved in muscle pathology.

Fatty-acid-binding protein as a plasma marker for the estimation of myocardial infarct size in humans.

BACKGROUND--There are substantial amounts of cytoplasmic heart-type fatty-acid-binding protein (FABP) (15 kDa) in myocardial tissue. The rapid release of FABP into plasma during ischaemia indicates the possibility of using this protein as a biochemical marker for ischaemic myocardial injury. OBJECTIVE--To study the completeness of the release of FABP from damaged tissue in patients with acute myocardial infarction (AMI) and the suitability of serial plasma FABP concentrations for estimation of myocardial infarct size. METHODS--Immunochemically assayed FABP and enzymatically assayed creatine kinase isoenzyme MB (CK-MB) and alpha-hydroxybutyrate dehydrogenase (HBDH) were determined serially in plasma samples from 49 patients with AMI who had been treated with thrombolytic agents within six hours after the onset of AMI. Previously validated circulatory models and a value of 2.6 h-1 for the fractional clearance rate of FABP from plasma were used to calculate cumulative protein release into plasma. RESULTS--Release of FABP was completed earlier (24-36 h) after AMI than that of CK-MB (50-70 h) and that of HBDH (> 70 h). However, infarct size estimated from the cumulative release of the proteins and expressed as gram equivalents of healthy myocardium per litre of plasma yielded a comparable value of 4-6 for both FABP and the two enzymes. CONCLUSION--The data indicate that FABP released from the heart after AMI is quantitatively recovered in plasma and that FABP is a useful biochemical plasma marker for the estimation of myocardial infarct size in humans.

Release of fatty acid-binding protein from isolated rat heart subjected to ischemia and reperfusion or to the calcium paradox

The release of cardiac fatty acid-binding protein (cFABP) and of fatty acids from isolated rat hearts was measured during both reperfusion following 60 min of ischemia and the calcium paradox (readmission of Ca2+ after a period of Ca2+-free perfusion). Total cFABP release was much more pronounced after Ca2+ readmission (over 50% of tissue content) than during post-ischemic reperfusion (on average, 3% of tissue content), but in both cases, it closely paralleled the release of lactate dehydrogenase. Only minor amounts of long-chain fatty acids, if any, were released from the heart. These observations are challenging the idea that cFABP plays a fatty acid-buffering role under the pathophysiological conditions studied.

Cellular fatty acid transport in heart and skeletal muscle as facilitated by proteins.

Despite the importance of long-chain fatty acids (FA) as fuels for heart and skeletal muscles, the mechanism of their cellular uptake has not yet been clarified. There is dispute as to whether FA are taken up by the muscle cellsvia passive diffusion and/or carrier-mediated transport. Kinetic studies of FA uptake by cardiac myocytes and the use of membrane protein-modifying agents have suggested the bulk of FA uptake is due to a protein component. Three membrane-associated FA-binding proteins were proposed to play a role in FA uptake, a 40-kDa plasma membrane FA-binding protein (FABPpm), an 88-kDa FA translocase (FAT/CD36), and a 60-kDa FA transport protein (FATP). In cardiac and skeletal myocytes the intracellular carrier for FA is cytoplasmic heart-type FA-binding protein (H-FABP), which likely transports FA from the sarcolemma to their intracellular sites of metabolism. A scenario is discussed in which FABPpm, FAT/CD36, and H-FABP, probably assisted by an albumin-binding protein, cooperate in the translocation of FA across the sarcolemma.

Lipid alterations in isolated, working rat hearts during ischemia and reperfusion: its relation to myocardial damage.

Disturbances in lipid metabolism may play an important role in the onset of irreversible myocardial damage. To investigate the effect of ischemia and reperfusion on lipid homeostasis and to delineate its possible consequences for myocardial damage, Krebs-Henseleit-perfused, working rat hearts were subjected to various periods of no-flow ischemia (10 to 90 minutes) with or without 30 minutes of reperfusion. During ischemia, the rise in nonesterified fatty acids (NEFAs) was preceded by the accumulation of substantial amounts of glycerol, indicating the presence of an active triacylglycerol-NEFA cycle. The subsequent rise in NEFAs (from 0.25 to 1.64 μmol/g dry residue wt after 90 minutes [means]) coincided with the reduction of ATP to values lower than 10 μmol/g dry wt and the rise of AMP, a potent inhibitor of acyl-coenzyme A synthetase, to values exceeding 2 μmol/g dry wt, making the latter compound a good candidate to hamper the turnover of endogenous lipids during prolonged ischemia. Reperfusion resulted in an additional rise in NEFAs (up to 4.1 μmol/g dry residue wt after 60 minutes of ischemia). Neither ischemia nor reperfusion resulted in significant decreases in the tissue content of triacylglycerols and the various phospholipids. During reperfusion recovery of stroke volume was still adequate at tissue NEFA levels thought to be incompatible with normal mitochondrial function.37 A positive correlation (r=0.81) was found between NEFA content of reperfused hearts and cumulative release of lactate dehydrogenase during reperfusion. Accordingly it is concluded that 1) reperfusion results in additional changes in myocardial lipid homeostasis, 2) the accumulating NEFAs are compartmentalized, possibly at the cellular level, and 3) the accumulation of NEFAs is a sensitive marker for myocardial cell damage.

Connective tissue growth factor and cardiac fibrosis

Cardiac fibrosis is a major pathogenic factor in a variety of cardiovascular diseases and refers to an excessive deposition of extracellular matrix components in the heart, which leads to cardiac dysfunction and eventually overt heart failure. Evidence is accumulating for a crucial role of connective tissue growth factor (CTGF) in fibrotic processes in several tissues including the heart. CTGF orchestrates the actions of important local factors evoking cardiac fibrosis. The central role of CTGF as a matricellular protein modulating the fibrotic process in cardiac remodelling makes it a possible biomarker for cardiac fibrosis and a potential candidate for therapeutic intervention to mitigate fibrosis in the heart.

Cytoplasmic fatty acid binding protein: Significance for intracellular transport of fatty acids and putative role on signal transduction pathways

The cellular transport of long-chain fatty acid moieties is thought to be mediated by a plasmalemmal and a cytoplasmic fatty acid binding protein (FABPPM and FABPC, respectively) and a cytoplasmic acyl-coenzyme A binding protein (ACBP). Their putative main physiological significance is the assurance that long-chain fatty acids and derivatives, either in transit through membranes or present in intracellular compartments, are largely complexed to proteins. FABPC distinguishes from the other proteins in that distinct types of FABPC exist and that these are found in a variety of tissues in remarkable abundance, with some cells containing more than one type In addition, liver type FABPC binds not only fatty acids, but also several other hydrophobic ligands, including heme, bilirubin, prostaglandin E1 and lipoxygenase metabolites of arachidonic acid. Calculations made for rat cardiomyocytes reveal that the presence of FABPC substantially enhances the cytoplasmic solubility as well as the maximal diffusional flux of fatty acids in these cells. Apart from this putative function in the bulk transport of ligands, FABPC may also function in the fine-tuning of cellular events by modulating the metabolism of hydrophobic compounds implicated in the regulation of cell growth and differentiation.

Role of membrane-associated and cytoplasmic fatty acid-binding proteins in cellular fatty acid metabolism

A number of membrane-associated and cytoplasmic fatty acid-binding proteins (FABPs) are now being implicated in the cellular uptake and intracellular transport of long-chain fatty acids (FA). These proteins each have the capacity of non-covalent binding of FA, are present in tissues actively involved in FA metabolism, and are upregulated in conditions of increased cellular FA metabolism. To date, five distinct membrane FABPs have been described, ranging in mass from 22 to 88 kDa and each showing a characteristic tissue distribution. Evidence for involvement in cellular fatty acid uptake has been provided for several of them, because it was recently found that isolated cell lines transfected with 88-kDa putative fatty acid translocase (FAT; homologous to CD36) or with 63-kDa fatty acid-transport protein show an increased rate of FA uptake. The (at least nine) FABPs of cytoplasmic origin belong to a family of small (14-15 kDa) lipid binding proteins, all having a similar tertiairy structure but differing in binding properties and in tissue occurrence. The biological functions of the various FABPs, possibly exerted in a concerted action among them, comprise solubilization and compartmentalization of FA, facilitation of the cellular uptake and intracellular trafficking of FA, and modulation of mitosis, cell growth, and cell differentiation. In addition, the FABPs have been suggested to participate in and/or modulate FA-mediated signal transduction pathways and FA regulation of gene expression, and to prevent local high FA concentrations thereby contributing to the protection of cells against the toxic effects of FA. In conclusion, long-chain fatty acids are subject to continuous interaction with multiple proteins, which interplay influences their cellular metabolism.