Interstitial purine metabolites in hearts with LV remodeling

Metabolomic analysis of serum and myocardium in compensated heart failure after myocardial infarction

AIMS

To determine the metabolic adaptations to compensated heart failure using a reproducible model of myocardial infarction and an unbiased metabolic screen. To address the limitations in sample availability and model variability observed in preclinical and clinical metabolic investigations of heart failure.

MAIN METHODS

Metabolomic analysis was performed on serum and myocardial tissue from rabbits after myocardial infarction (MI) was induced by cryo-injury of the left ventricular free wall. Rabbits followed for 12 weeks after MI exhibited left ventricular dilation and depressed systolic function as determined by echocardiography. Serum and tissue from the viable left ventricular free wall, interventricular septum and right ventricle were analyzed using a gas chromatography time of flight mass spectrometry-based untargeted metabolomics assay for primary metabolites.

KEY FINDINGS

Unique results included: a two- three-fold increase in taurine levels in all three ventricular regions of MI rabbits and similarly, the three regions had increased inosine levels compared to sham controls. Reduced myocardial levels of myo-inositol in the myocardium of MI animals point to altered phospholipid metabolism and membrane receptor function in heart failure. Metabolite profiles also provide evidence for responses to oxidative stress and an impairment in TCA cycle energy production in the failing heart.

SIGNIFICANCE

Our results revealed metabolic changes during compensated cardiac dysfunction and suggest potential targets for altering the progression of heart failure.

Impact of cardiac-specific expression of CD39 on myocardial infarct size in mice

AIMS

Prior work suggests that ischemic preconditioning increases the level of CD39 in the heart and contributes to cardiac protection. Therefore, we examined if targeted cardiac expression of CD39 protects against myocardial injury.

MAIN METHODS

Mice with cardiac-specific expression of human CD39 (αMHC/hCD39-Tg) were generated, characterized and subjected to left coronary artery ischemia-reperfusion injury and infarct size at 24h following injury quantified.

KEY FINDINGS

αMHC/hCD39-Tg mice have increased in cardiac ATPase and ADPase activity compared to WT littermates. The increased activity in αMHC/hCD39-mice was inhibited by the CD39 antagonist sodium polyoxotungstate (POM-1). Measurement of basal cardiac function by echocardiography revealed that αMHC/hCD39-Tg mice have a lower resting heart rate and increased stroke volume. In response to myocardial ischemia, systolic and diastolic function was better preserved in αMHC/hCD39-Tg compared to WT mice. Comparison of Tau also revealed preserved cardiac relaxation during ischemia in αMHC/hCD39-Tg hearts. Assessment of myocardial infarct size in response to 60min of ischemia and 24h of reperfusion demonstrated a significant reduction in infarct size in αMHC/hCD39-Tg hearts. Analysis of isolated cardiomyocytes revealed no basal difference in calcium transients between WT and αMHC/hCD39-Tg cardiomyocytes. However, in response to isoproterenol stimulation, there was a trend toward lower calcium transients in αMHC/hCD39 cardiomyocytes suggesting less calcium accumulation in response to metabolic stress.

SIGNIFICANCE

Cardiac-specific expression of CD39 reduces myocardial dysfunction and infarct size following ischemia-reperfusion injury. Increasing nucleotidase expression in the heart may be a novel approach to protect the heart from ischemic injury.

Myocardial energetics in left ventricular hypertrophy

The heart carries out its pumping function by converting the chemical energy stored in fatty acids and glucose into the mechanical energy of actin-myosin interaction of myofibrils. Development of congestive heart failure is usually preceded by a period of compensated left ventricular hypertrophy (LVH) and alterations in myocardial bioenergetics have been considered to play an important role in this transition. Myocardial energetic state that is reflected by the ratio of Phosphocreatine to Adenosine Triphosphate (PCr/ATP) is significantly decreased in hearts with LVH. The severity of this abnormality is linearly related to the severity of cardiac hypertrophy as well as left ventricular (LV) dysfunction, and is independent of a persistent myocardial ischemia. The decrease in PCr/ATP is accompanied by a decrease in creatine kinase flux and alterations in substrate utilization in LVH hearts. Moreover, there is a profound heterogeneity in alterations in myocardial energy metabolism in hearts with post-infarction hypertrophy with the most severe abnormality present in the inner layers of the periscar border zone (BZ). This review will discuss various aspects of myocardial energetics in animal models of three different types of LVH (pressure-overload, volume overload and post-infarction) with a brief description of myocardial energetics in humans with LVH.

Impact of elevated uric acid on ventricular remodeling in infarcted rats with experimental hyperuricemia

Hyperuricemia is associated with cardiovascular disease, but it is usually considered a marker rather than a risk factor. Previous studies using uric acid-lowering drugs in normouricemic animals are not suitable to answer the effect of hyperuricemia on ventricular remodeling after myocardial infarction. The purpose of this study was to determine whether hyperuricemia adversely affects ventricular remodeling in infarcted rats with elevated uric acid. Male Wistar rats aged 8 wk were randomly assigned into either vehicle, oxonic acid, oxonic acid + allopurinol, oxonic acid + benzbromarone, oxonic acid + ABT-627, or oxonic acid + tempol for 4 wk starting 24 h after ligation. Postinfarction was associated with increased oxidant production, as measured by myocardial superoxide, isoprostane, xanthine oxidase activity, and dihydroethidium staining. Compared with normouricemic infarcted rats, hyperuricemic infarcted rats had a significant increase of superoxide production (1.7×) and endothelin-1 protein (1.2×) and mRNA (1.4×) expression, which was associated with increased left ventricular dysfunction and enhanced myocardial hypertrophy and fibrosis. These changes were all prevented by treatment with allopurinol. For similar levels of urate lowering, the uricosuric agent benzbromarone had no effect on ventricular remodeling. In spite of equivalent hyperuricemia, the ability of both ABT-627 and tempol to attenuate ventricular remodeling suggested involvement of endothelin-1 and redox pathways. Hyperuricemia is associated with unfavorable ventricular remodeling probably through a superoxide and endothelin-1-dependent pathway. Uric acid lowering without inhibition of superoxide and endothelin-1 may not have an effect on remodeling. Chronic administration of allopurinol, ABT-627, and tempol is associated with attenuated ventricular remodeling.

Endothelin-converting enzyme inhibition in the rat model of acute heart failure: heart function and neurohormonal activation

Endothelin-1 (ET-1) has been implicated in many cardiovascular diseases, including acute heart failure (AHF) due to myocardial ischemia. Previously we described the oral endothelin-converting enzyme (ECE) inhibitor, PP36, and in this study, we investigated its cardioprotective effect in more detail, and examined the role of PP36 in the neurohormonal activation in rats that had been subjected to acute myocardial ischemia due to the microsphere embolization of coronary microcirculation. PP36 treatment (3.5 x 10(-5) M/kg/day) led to a significant fourfold decrease in hypertensive response when big-ET-1 was administered to healthy, conscious rats. ECE inhibition did not affect mortality during the first 48 hours after ischemia initiation. Systemic hemodynamic, heart function, and neurohormonal activation were analyzed in the healthy control group, the AHF group, and the AHF+PP36 group two days after AHF induction. In conscious rats in the AHF+PP36 group, mean arterial pressure (MAP) was restored and became similar to that of the MAP of the control group. In anesthetized rats, in the AHF+PP36 group, MAP was not restored and was 22% lower than the MAP of the control group. Myocardial contractility was partially restored and cardiac relaxation significantly improved after PP36 application. Further analysis of cardiac output and peripheral resistance in anesthetized rats revealed no differences between the AHF group and the AHF+PP36 group. There were no differences in plasma ET-1 concentration, serum angiotensin converting enzyme activity, and in the adrenal glands' catecholamine content between the AHF group and the AHF+PP36 group. However, rats in the AHF+PP36 group demonstrated a 60% decrease in cardiac endothelial nitric oxide synthase (eNOS) protein expression, and a 56% reduction of myocardial norepinephrine release, when compared with the AHF group's animals. These results suggest that PP36 can preserve heart function during the recovery from acute ischemic injury, and may modulate the cardiac norepinephrine release and eNOS protein level.

Profound bioenergetic abnormalities in peri-infarct myocardial regions

Regions of myocardial infarct (MI) are surrounded by a border zone (BZ) of normally perfused but dysfunctional myocardium. Although systolic dysfunction has been attributed to elevated wall stress in this region, there is evidence that intrinsic abnormalities of contractile performance exist in BZ myocardium. This study examined whether decreases of high-energy phosphates (HEP) and mitochondrial F(1)F(0)-ATPase (mtATPase) subunits typical of failing myocardium exist in BZ myocardium of compensated postinfarct remodeled hearts. Eight pigs were studied 6 wk after MI was produced by ligation of the left anterior descending coronary artery (LAD) distal to the second diagonal. Animals developed compensated LV remodeling with a decrease of ejection fraction from 54.6 +/- 5.4% to 31 +/- 2.1% (MRI) 5 wk after LAD occlusion. The remote zone (RZ) myocardium demonstrated modest decreases of ATP and mtATPase components. In contrast, BZ myocardium demonstrated profound abnormalities with ATP levels decreased to 42% of normal, and phosphocreatine-to-ATP ratio ((31)P-magnetic resonance spectroscopy) decreased from 2.06 +/- 0.19 in normal hearts to 1.07 +/- 0.10, with decreases in alpha-, beta-, OSCP, and IF(1) subunits of mtATPase, especially in the subendocardium. The reduction of myocardial creatine kinase isoform protein expression was also more severe in the BZ relative to the RZ myocardium. These abnormalities were independent of a change in mitochondrial content because the mitochondrial citrate synthase protein level was not different between the BZ and RZ. This regional heterogeneity of ATP content and expression of key enzymes in ATP production suggests that energetic insufficiency in the peri-infarct region may contribute to the transition from compensated LV remodeling to congestive heart failure.

Renal interstitial fluid ATP responses to arterial pressure and tubuloglomerular feedback activation during calcium channel blockade

A close relationship between changes in renal interstitial fluid (RIF) ATP concentrations and renal autoregulatory or tubuloglomerular feedback (TGF)-dependent changes in renal vascular resistance (RVR) has been demonstrated, but it has not been determined whether the changes in RIF ATP are a consequence or the cause of the changes in RVR. The present study was performed in anesthetized dogs to assess the changes in RIF ATP following changes in renal arterial pressure (RAP) or stimulation of the TGF mechanism under conditions where changes in RVR were prevented by nifedipine, a calcium channel blocker. RIF ATP levels were measured by using microdialysis probes. Intra-arterial infusion of nifedipine (0.36 microg x kg(-1) x min(-1)) increased renal blood flow (RBF: from 4.49 +/- 0.27 to 5.34 +/- 0.39 ml x min(-1) x g(-1)) and glomerular filtration rate (GFR: from 0.84 +/- 0.07 to 1.09 +/- 0.11 ml x min(-1) x g(-1)). Under conditions of nifedipine infusion, autoregulatory adjustments in RBF, GFR, and RVR were not observed during stepwise reductions in RAP within the autoregulatory range (from 135 +/- 7 to 76 +/- 1 mmHg, n = 7). Furthermore, stimulation of the TGF mechanism with intra-arterial infusion of acetazolamide (100 microg x kg(-1) x min(-1)) did not alter RBF, GFR, and RVR (n = 7). During treatment with nifedipine, RIF ATP levels were significantly decreased in response to reductions in RAP (10.7 +/- 0.7, 5.8 +/- 0.7 and 2.8 +/- 0.3 nmol/l at 135 +/- 7, 101 +/- 4, and 76 +/- 1 mmHg, n = 7) and increased by acetazolamide infusion (from 8.8 +/- 0.8 to 17.0 +/- 1.8 nmol/l, n = 7). These results are similar to those that occurred in dogs not treated with nifedipine and thus demonstrate that the changes in RIF ATP can occur in the absence of autoregulatory or TGF-mediated changes in RVR. The data provide further support to the hypothesis that RIF ATP contributes to adjustments in RVR associated with renal autoregulation and changes in activity of the TGF mechanism.

Transient reduction in myocardial free oxygen radical levels is involved in the improved cardiac function and structure after long-term allopurinol treatment initiated in established chronic heart failure

AIMS

Oxidative stress, i.e. imbalance between reactive oxygen species (ROS) and antioxidant defences, contributes to the progression of chronic heart failure (CHF). Acute inhibition of xanthine oxidase (XO), which produces ROS, improves mechanical efficiency of the failing heart, but whether long-term XO inhibition exerts beneficial effects in CHF is unknown.

METHODS AND RESULTS

In rats with established CHF induced by left coronary ligation, we assessed the effects of a 5-day and a 10-week treatment with the XO inhibitor allopurinol (50 mg kg(-1) day(-1)) on haemodynamics and left ventricular (LV) function and structure. Both acute and chronic allopurinol treatment increase cardiac output without modification of arterial pressure, but only chronic allopurinol treatment reduces LV end-diastolic pressure and LV relaxation constant. Chronic allopurinol treatment decreases both LV systolic and diastolic diameters, but acute allopurinol treatment only decreases LV systolic diameter. Moreover, chronic allopurinol decreases LV weight and collagen density. Despite XO inhibition after acute and chronic allopurinol treatment, as both treatments reduce uric acid plasma levels, only acute allopurinol treatment reduces LV ROS determined using electron spin resonance spectroscopy. However, the CHF-enhanced myocardial thiobarbituric acid reactive substances levels were never modified.

CONCLUSION

In experimental CHF, long-term allopurinol treatment, initiated in a pathological state of overt CHF, improves LV haemodynamics and function and prevents LV remodelling. These long-term effects are, at least partially, caused by a transient reduction of myocardial ROS shortly after initiation of allopurinol treatment, but whether other mechanism(s), independent of myocardial redox 'status', such as reduced inflammation, are implicated remains to be confirmed.