Angiotensin subtype 1 rReceptor (AT1) blockade improves vasorelaxation in heart failure by up-regulation of endothelial nitric-oxide synthase via activation of the AT2 receptor

To determine whether angiotensin receptor blockade decreases vascular tone in heart failure by improving endothelial-dependent vasorelaxation and increasing nitric oxide (NO) bioavailability, we treated infarcted adult male Sprague-Dawley rats with candesartan for 7 days or 8 weeks (10 mg/kg/day in drinking water). Candesartan, at both time points, lowered left ventricular (LV) systolic pressure (P < 0.05) (122 +/- 22 versus 74 +/- 16 and 73 +/- 10 mm Hg) and LV dP/dt (5914 +/- 1294 versus 2857 +/- 1672 versus 3175 +/- 769 mm Hg/s), but lowered LV end-diastolic pressure only at 8 weeks (16.9 +/- 9.7 versus 11.2 +/- 5.7 versus 6.9 +/- 5.3 mm Hg). The vasorelaxation response to acetylcholine (ACh) in thoracic aortic segments was decreased with infarction (P < 0.05), remained unchanged with 1 week of candesartan, but increased 84 and 86% at 10-4 and 10-5 M ACh (P < 0.05) at 8 weeks. The enhanced candesartan-induced vasorelaxation at 8 weeks was abolished with NG-nitro-l-arginine methyl ester (200 microM). In bovine pulmonary endothelial cells, 20 microM candesartan increased endothelial nitric-oxide synthase (eNOS) protein levels (P < 0.05) (28.9 +/- 2.6 versus 16.1 +/- 3.7 intensity units/microg of protein); the increased eNOS was abolished by a specific angiotensin subtype 2 (AT2) receptor antagonist, PD 123319. These data suggest that AT1 receptor blockade enhances vasorelaxation in heart failure by increasing NO bioavailability, in part via an AT2 receptor-mediated up-regulation of eNOS protein.

Deficiency of PDK1 in cardiac muscle results in heart failure and increased sensitivity to hypoxia

We employed Cre/loxP technology to generate mPDK1(-/-) mice, which lack PDK1 in cardiac muscle. Insulin did not activate PKB and S6K, nor did it stimulate 6-phosphofructo-2-kinase and production of fructose 2,6-bisphosphate, in the hearts of mPDK1(-/-) mice, consistent with PDK1 mediating these processes. All mPDK1(-/-) mice died suddenly between 5 and 11 weeks of age. The mPDK1(-/-) animals had thinner ventricular walls, enlarged atria and right ventricles. Moreover, mPDK1(-/-) muscle mass was markedly reduced due to a reduction in cardiomyocyte volume rather than cardiomyocyte cell number, and markers of heart failure were elevated. These results suggested mPDK1(-/-) mice died of heart failure, a conclusion supported by echocardiographic analysis. By employing a single-cell assay we found that cardiomyocytes from mPDK1(-/-) mice are markedly more sensitive to hypoxia. These results establish that the PDK1 signalling network plays an important role in regulating cardiac viability and preventing heart failure. They also suggest that a deficiency of the PDK1 pathway might contribute to development of cardiac disease in humans.

Using a gene-switch transgenic approach to dissect distinct roles of MAP kinases in heart failure

We have demonstrated that Cre-loxP-mediated gene-switch transgenesis is an effective approach to achieve targeted and temporally regulated gene manipulation in the heart. Using this approach, we have established animal models with targeted activation of different MAPK pathways. From these animal models, we identified distinct features of cardiac pathology associated with individual MAPK branches (summarized in Fig. 8). Specifically, Ras activation appears to promote cardiac hypertrophy, whereas p38 and JNK activation does not. Whereas Ras activation leads to depressed diastolic function associated with suppressed calcium transients and SR calcium uptake, p38 activity seems to modulate cellular contractility without affecting intracellular calcium cycling. Although all three models displayed extensive remodeling in the myocardium, the extent and the composition of interstitial fibrosis are different among them, with Ras- and p38-activated hearts promoting collagen-based fibrosis, and JNK activation leading to induction in fibronectin-based reticular fiber. In addition, JNK activation leads to loss of Cx43 expression and abnormal cell-cell communication. Therefore, ERK, p38, and JNK are three distinct intracellular signaling pathways that contribute to different aspects of cardiac pathology during heart failure. Combining sophisticated genetic manipulation with comprehensive analysis at physiological, molecular, and genomic levels, the transgenic animals established in these studies should serve as valuable model systems to identify and dissect the underlying mechanisms for different aspects of cardiac pathology such as hypertrophy, contractile dysfunction, and abnormal cell-cell communication. The insights learned from these investigations may help to develop novel therapeutic approaches to confront this devastating disease.

Depressed mitochondrial transcription factors and oxidative capacity in rat failing cardiac and skeletal muscles

Congestive heart failure (CHF) induces alterations in energy metabolism and mitochondrial function that span cardiac as well as skeletal muscles. Whether these defects originate from altered mitochondrial DNA copy number and/or mitochondrial gene transcription is not known at present, nor are the factors that control mitochondrial capacity in different muscle types completely understood. We used an experimental model of CHF induced by aortic banding in the rat and investigated mitochondrial respiration and enzyme activity of biochemical mitochondrial markers in cardiac, slow and fast skeletal muscles. We quantified mitochondrial DNA (mtDNA), expression of nuclear (COX IV) and mitochondrial (COX I) encoded cytochrome c oxidase subunits as well as nuclear factors involved in mitochondrial biogenesis and in the necessary coordinated interplay between nuclear and mitochondrial genomes in health and CHF. CHF induced a decrease in oxidative capacity and mitochondrial enzyme activities with a parallel decrease in the mRNA level of COX I and IV, but no change in mtDNA content. The expression of the peroxisome proliferator activated receptor gamma co-activator 1 alpha (PGC-1 alpha) gene was downregulated in CHF, as well as nuclear respiratory factor 2 and mitochondrial transcription factor A, which act downstream from PGC-1 alpha. Most interestingly, only the level of PGC-1 alpha expression was strongly correlated with muscle oxidative capacity in cardiac and skeletal muscles, both in healthy and CHF rats. Mitochondrial gene transcription is reduced in CHF, and PGC-1 alpha appears as a potential modulator of muscle oxidative capacity under these experimental conditions.

Decreased cardiac activity of AMP deaminase in subjects with the AMPD1 mutation—A potential mechanism of protection in heart failure

OBJECTIVES

Possession of the C34T (Glu12Stop) nonsense mutation in the AMP-deaminase 1 (AMPD1) gene has been shown to be associated with improved prognosis in heart failure and ischemic heart disease. The most likely event leading to these clinical effects is a reduced capacity of the AMP deamination pathway and increased production of cardio-protective adenosine. However, since AMPD1 is predominantly expressed in skeletal muscle, the protective effects could be related not only to local cardiac changes, but also to a systemic mechanism. In the present study we evaluated the effect of the C34T mutation on cardiac AMP-deaminase activity and on the systemic changes in adenosine production.

METHODS

The presence of the C34T mutation was assayed by single-stranded conformational polymorphism (SSCP). Analysis of the AMPD1 genotype and measurement of enzyme activities was performed on 27 patients with heart failure (HF). In addition, blood adenosine concentration was measured by liquid chromatography/mass spectrometry (LC/MS) in 21 healthy subjects with established AMPD1 genotype at rest and following exhaustive exercise.

RESULTS

Cardiac AMP-deaminase activity in heterozygotes (C/T) was 0.59+/-0.02 nmol/min/g wet wt-about half of the activity found in normal wild-type (C/C) individuals (1.06+/-0.09 nmol/min/g wet wt, P=0.003). There were no significant differences in the activities of any other enzymes between subjects with the C/T or C/C genotype. Resting venous blood adenosine concentration was similar in subjects with C/C, C/T and homozygous for the mutated allele (T/T) genotype. Following exercise, a significant increase in adenosine was observed in T/T subjects (by 0.013+/-0.009 micromol/l, P=0.035) but not in C/C (0.003+/-0.009 micromol/l) or C/T (-0.002+/-0.011 micromol/l).

CONCLUSIONS

Our findings indicate that the C34T mutation of AMPD1 leads to a decrease in cardiac enzyme activity of AMP-deaminase without changes in any other adenosine-regulating enzymes, highlighting the importance of local cardiac metabolic changes. Systemic (blood) changes in adenosine concentration were apparent only in homozygous subjects and therefore may play a relatively small part in cardio-protection.

Fasidotril Eli Lilly

Lilly is developing fasidotril, a diester prodrug of the active metabolite fasidotrilat, for the potential treatment of hypertension and congestive heart failure (CHF). Phase II trials to investigate the potential of fasidotril for the treatment of hypertension and CHF had commenced by the late 1990s, and were ongoing in July 2003 in the US and Europe.

Effects of angiotensin-converting enzyme inhibition on changes in left ventricular myocardial creatine kinase system after myocardial infarction: their relation to ventricular remodeling and function

We assessed the effects of angiotensin-converting enzyme (ACE) inhibition on changes in the myocardial intracellular creatine kinase (CK) system in relation to left ventricular (LV) remodeling and function in heart failure after myocardial infarction (MI) in rats. We compared the findings at 4 weeks after MI to those at 12 weeks after MI. LV weight and chamber size were significantly increased and percent fractional shortening (%FS) was decreased in untreated MI rats compared with normal control animals both at 4 and 12 weeks after MI. Animals with MI and treated with the ACE inhibitor temocapril showed significantly reduced LV weight and chamber size and increased %FS compared with untreated MI rats at 12 weeks after MI, but not at 4 weeks after MI. At 4 weeks after MI, no significant changes were found in the total creatine and relative distribution of each CK isoenzyme in either the temocapril-treated or untreated animals with MI compared with the normal controls. In contrast, at 12 weeks after MI, untreated MI rats showed significant reductions in the total creatine and mitochondrial and MM-CK fractions and increases in the MB- and BB-CK fractions compared with the controls. The alterations in the mitochondrial and MB-CK fractions were significantly attenuated after 12 weeks of ACE inhibition. Thus, LV myocardial energy metabolism is progressively impaired and its alteration is not related to the magnitude of geometric changes and LV dysfunction after MI. Most of the beneficial effects of ACE inhibition were observed at 12 weeks after MI. Our results may provide an insight into the therapeutic strategy of ACE inhibition in chronic heart failure after MI.

Increased myocardial NADPH oxidase activity in human heart failure

OBJECTIVES

This study was designed to investigate whether nicotinamide adenine dinucleotide 3-phosphate (reduced form) (NADPH) oxidase is expressed in the human heart and whether it contributes to reactive oxygen species (ROS) production in heart failure.

BACKGROUND

A phagocyte-type NADPH oxidase complex is a major source of ROS in the vasculature and is implicated in the pathophysiology of hypertension and atherosclerosis. An increase in myocardial oxidative stress due to excessive production of ROS may be involved in the pathophysiology of congestive heart failure. Recent studies have suggested an important role for myocardial NADPH oxidase in experimental models of cardiac disease. However, it is unknown whether NADPH oxidase is expressed in the human myocardium or if it has any role in human heart failure.

METHODS

Myocardium of explanted nonfailing (n = 9) and end-stage failing (n = 13) hearts was studied for the expression of NADPH oxidase subunits and oxidase activity.

RESULTS

The NADPH oxidase subunits p22(phox), gp91(phox), p67(phox), and p47(phox) were all expressed at messenger ribonucleic acid and protein level in cardiomyocytes of both nonfailing and failing hearts. NADPH oxidase activity was significantly increased in end-stage failing versus nonfailing myocardium (5.86 +/- 0.41 vs. 3.72 +/- 0.39 arbitrary units; p < 0.01). The overall level of oxidase subunit expression was unaltered in failing compared with nonfailing hearts. However, there was increased translocation of the regulatory subunit, p47(phox), to myocyte membranes in failing myocardium.

CONCLUSIONS

This is the first report of the presence of NADPH oxidase in human myocardium. The increase in NADPH oxidase activity in the failing heart may be important in the pathophysiology of cardiac dysfunction by contributing to increased oxidative stress.

Subcellular redistribution of focal adhesion kinase and its related nonkinase in hypertrophic myocardium

Focal adhesion kinase (FAK) and focal adhesion kinase-related nonkinase (FRNK) are likely involved in mechanical signaling during hypertension. We investigated expression, subcellular distribution, and phosphorylation of FAK, as well as FRNK in left ventricles of spontaneously hypertensive heart failure rats. Compared with normotensive controls, FAK and FRNK increased in left ventricles of hypertensive rats. Increased FAK and FRNK were mainly present in membrane cytoskeleton and nuclear fractions. Confocal microscopy demonstrated that FAK and FRNK translocated to nuclei and intercalated disks in cardiac myocytes from hypertensive rats. Serine and tyrosine phosphorylation of FAK increased dramatically in hypertensive rats. FAK phosphorylated at tyrosine 397 was present in membranes and intercalated disks, but not in nuclei. FAK was also phosphorylated on serine 722 but not on serine 910. In contrast, FRNK was phosphorylated on serine 217, the equivalent site of FAK serine 910, but not serine on 30, the homologous site of FAK serine 722. Serine phosphorylated FAK and FRNK accumulated in membranes and nuclei but not in intercalated disks. Nuclear translocation of FAK and FRNK may play important roles in regulating mechanical signal transduction in cardiac myocytes.

Training-induced changes in skeletal muscle Na+-K+ pump number and isoform expression in rats with chronic heart failure

The mechanisms responsible for the decrements in exercise performance in chronic heart failure (CHF) remain poorly understood, but it has been suggested that sarcolemmal alterations could contribute to the early onset of muscular fatigue. Previously, our laboratory demonstrated that the maximal number of ouabain binding sites (B(max)) is reduced in the skeletal muscle of rats with CHF (Musch TI, Wolfram S, Hageman KS, and Pickar JG. J Appl Physiol 92: 2326-2334, 2002). These reductions may coincide with changes in the Na(+)-K(+)-ATPase isoform (alpha and beta) expression. In the present study, we tested the hypothesis that reductions in B(max) would coincide with alterations in the alpha- and beta-subunit expression of the sarcolemmal Na(+)-K(+)-ATPase of rats with CHF. Moreover, we tested the hypothesis that exercise training would increase B(max) along with producing significant changes in alpha- and beta-subunit expression. Rats underwent a sham operation (sham; n = 10) or a surgically induced myocardial infarction followed by random assignment to either a control (MI; n = 16) or exercise training group (MI-T; n = 16). The MI-T rats performed exercise training (ET) for 6-8 wk. Hemodynamic indexes demonstrated that MI and MI-T rats suffered from severe left ventricular dysfunction and congestive CHF. Maximal oxygen uptake (Vo(2 max)) and endurance capacity (run time to fatigue) were reduced in MI rats compared with sham. B(max) in the soleus and plantaris muscles and the expression of the alpha(2)-isoform of the Na(+)-K(+)-ATPase in the red portion of the gastrocnemius (gastrocnemius(red)) muscle were reduced in MI rats. After ET, Vo(2 max) and run time to fatigue were increased in the MI-T group of rats. This coincided with increases in soleus and plantaris B(max) and the expression of the alpha(2)-isoform in the gastrocnemius(red) muscle. In addition, the expression of the beta(2)-isoform of the gastrocnemius(red) muscle was increased in the MI-T rats compared with their sedentary counterparts. This study demonstrates that CHF-induced alterations in skeletal muscle Na(+)-K(+)-ATPase, including B(max) and isoform expression, can be partially reversed by ET.

Polymorphisms in the RAS and cardiac function

Since the discovery of the polymorphism in the angiotensin converting enzyme (ACE) and the consequences of this polymorphism on the activity levels of the enzyme, numerous association studies have been performed. However, these investigations do not often adhere to the most stringent criteria for such studies. The initial study reporting a positive association of the ACE polymorphism and myocardial infarction showed an increased risk of the DD genotype. This initial association was eventually refuted by a large, well conducted association study, which found a risk ratio of 1.02 after combining their own data with all published data. Although such large, well conducted association studies have not been performed in left ventricular (LV) hypertrophy, the association between DD genotype and hypertrophy is more convincing with a 192% excess risk of LV hypertrophy in untreated hypertensives. The role of ACE genotype in LV growth is well established, especially in athletes. In heart failure, large studies or meta-analyses have not been performed, because most studies have selected different end-points. This hampers a proper meta-analysis of the results obtained in associations with heart failure. As most association studies do not fulfill the criteria for good association studies and use too small sample sizes, it remains important to perform a meta-analysis to add meaning to the results of such studies. Above all, it is important to obey the rules set for association studies, large sample size, small P values, report associations that make biological sense and alleles that affect the gene product in a physiologically meaningful way.

Increased expression of protein kinase C isoforms in heart failure due to myocardial infarction

The activities of cardiac protein kinase C (PKC) were examined in hemodynamically assessed rats subsequent to myocardial infarction (MI). Both Ca(2+)-dependent and Ca(2+)-independent PKC activities increased significantly in left ventricular (LV) and right ventricular (RV) homogenates at 1, 2, 4, and 8 wk after MI was induced. PKC activities were also increased in both LV and RV cytosolic and particulate fractions from 8-wk infarcted rats. The relative protein contents of PKC-alpha, -beta, -epsilon, and -zeta isozymes were significantly increased in LV homogenate, cytosolic (except PKC-alpha), and particulate fractions from the failing rats. On the other hand, the protein contents of PKC-alpha, -beta, and -epsilon isozymes, unlike the PKC-zeta isozyme, were increased in RV homogenate and cytosolic fractions, whereas the RV particulate fraction showed an increase in the PKC-alpha isozyme only. These changes in the LV and RV PKC activities and protein contents in the 8-wk infarcted animals were partially corrected by treatment with the angiotensin-converting enzyme inhibitor imidapril. No changes in protein kinase A activity and its protein content were seen in the 8-wk infarcted hearts. The results suggest that the increased PKC activity in cardiac dysfunction due to MI may be associated with an increase in the expression of PKC-alpha, -beta, and -epsilon isozymes, and the improvement of heart function in the infarcted animals by imidapril may be due to partial prevention of changes in PKC activity and isozyme contents.

COX-2-dependent cardiac failure in Gh/tTG transgenic mice

Gh is a GTP binding protein that couples to the thromboxane receptor (TP), but also functions as tissue transglutaminase II (tTG). A transgenic mouse model was generated in which Gh was overexpressed (GhOE) in ventricular myocytes under the control of the alpha-myosin heavy chain promoter. Heart rate was elevated and both blood pressure and left ventricular ejection fraction were depressed in GhOEs. Left ventricular mass was increased, consistent with genetic and ultrastructural evidence of hypertrophy. Fibrosis and apoptosis were also augmented. Survival declined disproportionately in older GhOEs. Cardiomyocyte expression of COX-2, thromboxane synthase (TxS), and the receptors for TxA2 (the TP), PGF2alpha (the FP), and PGI2 (the IP) were upregulated and urinary 8,12-iso-iPF2alpha-VI,2,3-dinor-6-keto-PGF1alpha and 2,3-dinor-thromboxane B2 were increased in GhOEs, reflecting increased lipid peroxidation and cyclooxygenase (COX) activation. Selective COX-2 inhibition, TP antagonism, and suppression of lipid peroxidation each rescued the cardiac phenotype. Infusion of an FP agonist exacerbated the phenotype, whereas administration of an IP agonist improved cardiac function. Directed cardiac overexpression of Gh/tTG causes both TG activation and increased TP/Gh-dependent signaling. The COX-2-dependent increase in TxA2 generation augments cardiac hypertrophy, whereas formation of PGI2 by the same isozyme ameliorates the phenotype. Oxidant stress may contribute, via regulation of COX-2 expression and/or ligation of the TP and the FP by isoprostanes. Gh/tTG activation regulates expression of COX-2 and its products may differentially modulate cardiomyocyte commitment to cell death or survival.

The deltaC isoform of CaMKII is activated in cardiac hypertrophy and induces dilated cardiomyopathy and heart failure

Recent studies have demonstrated that transgenic (TG) expression of either Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) or CaMKIIdeltaB, both of which localize to the nucleus, induces cardiac hypertrophy. However, CaMKIV is not present in heart, and cardiomyocytes express not only the nuclear CaMKIIdeltaB but also a cytoplasmic isoform, CaMKIIdeltaC. In the present study, we demonstrate that expression of the deltaC isoform of CaMKII is selectively increased and its phosphorylation elevated as early as 2 days and continuously for up to 7 days after pressure overload. To determine whether enhanced activity of this cytoplasmic deltaC isoform of CaMKII can lead to phosphorylation of Ca2+ regulatory proteins and induce hypertrophy, we generated TG mice that expressed the deltaC isoform of CaMKII. Immunocytochemical staining demonstrated that the expressed transgene is confined to the cytoplasm of cardiomyocytes isolated from these mice. These mice develop a dilated cardiomyopathy with up to a 65% decrease in fractional shortening and die prematurely. Isolated myocytes are enlarged and exhibit reduced contractility and altered Ca2+ handling. Phosphorylation of the ryanodine receptor (RyR) at a CaMKII site is increased even before development of heart failure, and CaMKII is found associated with the RyR in immunoprecipitates from the CaMKII TG mice. Phosphorylation of phospholamban is also increased specifically at the CaMKII but not at the PKA phosphorylation site. These findings are the first to demonstrate that CaMKIIdeltaC can mediate phosphorylation of Ca2+ regulatory proteins in vivo and provide evidence for the involvement of CaMKIIdeltaC activation in the pathogenesis of dilated cardiomyopathy and heart failure.

Regulation of sarco(endo)plasmic reticulum Ca2+ adenosine triphosphatase by phospholamban and sarcolipin: implication for cardiac hypertrophy and failure

The cardiac isoform of sarco(endo)plasmic reticulum Ca(2)(+) adenosine triphosphatase (SERCA2a) plays an important role in the contraction and relaxation of cardiac muscle. Phospholamban (PLN) and its homologue sarcolipin (SLN) are the endogenous regulators of SERCA2a. Evidence is accumulating that SERCA2a is intimately involved in the pathogenesis of cardiac hypertrophy and failure. Recent studies using genetically engineered animals revealed the implication of PLN for the development of cardiomyopathic phenotypes. This review focuses on advances in the understanding of molecular regulation of SERCA2a by PLN and SLN, and their implications for cardiac hypertrophy and failure in vivo.

Calcium and the failing heart: phospholamban, good guy or bad guy?

In cardiac cells, phospholamban is a potent inhibitor of sarcoplasmic reticulum calcium (Ca(2+)) transport. Overexpression of mutant forms of phospholamban may result in beneficial or detrimental effects on intracellular Ca(2+) handling and cardiac systolic and diastolic function. Mutations in phospholamban have also been linked to human cardiomyopathies, providing important insights into the underlying disease mechanisms and the key role of phospholamban in myocardial excitation-contraction coupling. This Perspective discusses new advances in our understanding of the role of phospholamban in intracellular Ca(2+) handling and the development of human and murine cardiomyopathies.

Endothelial nitric oxide synthase overexpression attenuates congestive heart failure in mice

Congestive heart failure results in cardiovascular dysfunction and diminished vascular nitric oxide (NO) production. We hypothesized that overexpression of endothelial NO synthase (eNOS) within the endothelium would reduce the extent of contractile dysfunction in a murine model of infarct-induced congestive heart failure. We generated transgenic (TG) mice overexpressing the human eNOS gene. The TG mice displayed significantly enhanced eNOS protein levels and eNOS activity levels (10- to 12-fold greater) in the aorta and the coronary vasculature. Non-TG (NTg) and eNOS TG mice were subjected to permanent left anterior descending coronary artery occlusion and then observed for 1 mo. We assessed cardiac function in vivo by using echocardiography and ultraminiature ventricular pressure catheters. Myocardial infarct size was similar between study groups (approximately 70% of the risk zone). Survival was increased by 43% in the eNOS TG mice compared with NTg (P < 0.05). Fractional shortening and cardiac output were also significantly (P < 0.05) greater in the eNOS TG than in NTg. Interestingly, pulmonary edema was evident only in NTg mice, and no evidence of pulmonary edema was observed in the eNOS TG mice. Thus, targeted overexpression of the eNOS gene within the vascular endothelium in mice attenuates both cardiac and pulmonary dysfunction and dramatically improves survival during severe congestive heart failure.

Plasma semicarbazide-sensitive amine oxidase in human (patho)physiology

Semicarbazide-sensitive amine oxidases (SSAO) are widely distributed enzymes, with as yet not fully elucidated functions and roles, present in many tissues but also circulating in plasma. The enzyme also functions as an adhesion molecule, the vascular adhesion protein-1. In healthy humans, plasma SSAO activity is constant from birth until 16 years of age, when it drops to lower values, gradually increasing again at advanced ages. When measuring SSAO activity, care should be taken to ensure proper preparation and storage conditions, and it should be realized that quite a few drugs unintentionally are good inhibitors, and sometimes even substrates, of SSAO. Under normal conditions SSAO activity is constant and inter-individual variation is small. In various pathophysiological conditions plasma SSAO activities are increased, most notably in diabetes mellitus (both type I and type II), in congestive heart failure and in cirrhotic liver inflammation. In patients with other vascular and inflammatory diseases plasma SSAO is normal, while it is low in children with congenital lung diseases. Interpretation of these changes is speculative, since source and regulation of plasma SSAO are as yet unknown. However, in two situations where the disease-causing process was ended (transplantation, delivery), plasma SSAO returned to normal. Many questions remain to be answered.

Functional consequences of endothelial nitric oxide synthase uncoupling in congestive cardiac failure

BACKGROUND

Impaired endothelium-mediated vasodilatation (EMVD) in congestive cardiac failure (CCF) has been linked to decreased nitric oxide (NO) bioavailability because of its interaction with vascular superoxide (O2*-), derived predominantly from NAD(P)H-dependent oxidases. When uncoupled from essential cofactors, endothelial nitric oxide synthase (eNOS) produces O2*-. We studied the functional consequences of eNOS uncoupling in relation to EMVD in patients with CCF.

METHODS AND RESULTS

We employed the platelet as a compartmentalized ex-vivo model to examine O2*- and NO production. When eNOS is functioning normally, incorporation of Nomega-Nitro-L-Arginine methyl ester (L-NAME, 1 mmol/L), results in increased O2*- detection, as inhibition of NO production prevents NO scavenging of O2*-. This was observed in controls and 9 of the CCF patients, in whom O2*- detection increased by 63% and 101%, respectively. In the remaining 9 CCF patients, incorporation of L-NAME reduced O2*- production by 39%, indicating O2*- production by eNOS uncoupling. Detection of platelet-derived NO was significantly greater in eNOS-coupled platelets compared with the uncoupled group (2.8+/-1.4 versus 0.9+/-0.4 pmol/108 platelets, P=0.04). Endothelium-dependent and -independent vasodilator responses to acetylcholine and sodium nitroprusside recorded using venous occlusion plethysmography were significantly impaired in patients exhibiting eNOS uncoupling.

CONCLUSIONS

This study provides first evidence that platelet eNOS can become uncoupled in human CCF. Impaired endothelium-dependent and -independent vasodilator responses and diminished platelet-derived NO production occurred in association with enzyme uncoupling.