Short-term treatment with ranolazine improves mechanical efficiency in dogs with chronic heart failure

Metabolic modulation and cellular therapy of cardiac dysfunction and failure

At present the prevalence of heart failure rises along with aging of the population. Current heart failure therapeutic options are directed towards disease prevention via neurohormonal antagonism (β-blockers, angiotensin converting enzyme inhibitors and/or angiotensin receptor blockers and aldosterone antagonists), symptomatic treatment with diuretics and digitalis and use of biventricular pacing and defibrillators in a special subset of patients. Despite these therapies and device interventions heart failure remains a progressive disease with high mortality and morbidity rates. The number of patients who survive to develop advanced heart failure is increasing. These patients require new therapeutic strategies. In this review two of emerging therapies in the treatment of heart failure are discussed: metabolic modulation and cellular therapy. Metabolic modulation aims to optimize the myocardial energy utilization via shifting the substrate utilization from free fatty acids to glucose. Cellular therapy on the other hand has the goal to achieve true cardiac regeneration. We review the experimental data that support these strategies as well as the available pharmacological agents for metabolic modulation and clinical application of cellular therapy.

Ranolazine: new paradigm for management of myocardial ischemia, myocardial dysfunction, and arrhythmias

Ranolazine, which was approved by the US Food and Drug Administration in January 2006, provides a mechanism of action to treat ischemia that has not hitherto been available. Ranolazine is effective in reducing manifestations of ischemia and angina, and it also holds potential promise to be effective in the management of left ventricular dysfunction, particularly diastolic dysfunction, and arrhythmias. This article provides an update on the available studies concerning the value of ranolazine across the spectrum of cardiovascular disease.

In vivo cardioprotection by S-nitroso-2-mercaptopropionyl glycine

The reversible S-nitrosation and inhibition of mitochondrial complex I is a potential mechanism of cardioprotection, recruited by ischemic preconditioning (IPC), S-nitrosothiols, and nitrite. Previously, to exploit this mechanism, the mitochondrial S-nitrosating agent S-nitroso-2-mercaptopropionyl glycine (SNO-MPG) was developed, and protected perfused hearts and isolated cardiomyocytes against ischemia-reperfusion (IR) injury. In the present study, the murine left anterior descending coronary artery (LAD) occlusion model of IR injury was employed, to determine the protective efficacy of SNO-MPG in vivo. Intraperitoneal administration of 1 mg/kg SNO-MPG, 30 min prior to occlusion, significantly reduced myocardial infarction and improved EKG parameters, following 30 min occlusion plus 2 or 24 h reperfusion. SNO-MPG protected to the same degree as IPC, and notably was also protective when administered at reperfusion. Cardioprotection was accompanied by increased mitochondrial protein S-nitrosothiol content, and inhibition of complex I, both of which were reversed after 2 h reperfusion. Finally, hearts from mice harboring a heterozygous mutation in the complex I NDUSF4 subunit were refractory to protection by either SNO-MPG or IPC, suggesting that a fully functional complex I, capable of reversible inhibition is critical for cardioprotection. Overall, these results are consistent with a role for mitochondrial S-nitrosation and complex I inhibition in the cardioprotective mechanism of IPC and SNO-MPG in vivo.

Effects of trimetazidine on myocardial perfusion and left ventricular systolic function in type 2 diabetic patients with ischemic cardiomyopathy

AIMS

To determine whether short-term treatment with trimetazidine (TMZ), an antiischemic agent that directly inhibits fatty acid oxidation and results in stimulation of glucose oxidation, may improve myocardial perfusion and left ventricular systolic function in diabetic patients with ischemic cardiomyopathy.

METHODS AND RESULTS

We studied 34 clinically stable patients with type 2 diabetes mellitus (DM) and documented multivessel coronary artery disease (29 men and 5 women, mean age 54 +/- 9 years) with depressed systolic function (left ventricular ejection fraction 38 +/- 6%). Patients were randomized into two groups. One group received TMZ (20 mg tid) for 3 months (n = 19), while another group received a placebo during the same period (n = 15). On study entry and at 3 months, all patients underwent a gated Single Photon Emission Computed Tomography (SPECT) myocardial scintigraphy with a 2-day stress(Bruce)-rest protocol (500 MBq tetrofosmin). At 3 months, TMZ-treated patients had a significant improvement in systolic wall thickening (P < 0.05) and ejection fraction (P = 0.007) as compared with control patients. These effects were more marked in patients with more severe reversible perfusion defects on initial evaluation and were not associated with changes in myocardial defects (P = 0.38). Total exercise time was also improved in TMZ-treated patients (20.5%, P < 0.05 vs. controls).

CONCLUSIONS

In diabetic cardiomyopathy, short-term TMZ improved left ventricular systolic function and functional capacity despite no change in myocardial perfusion. These benefits were more evident in patients with more severe perfusion defects on initial evaluation, suggesting that chronic myocardial ischemia is a requirement for the effects of TMZ on left ventricular systolic performance.

Ranolazine combined with enalapril or metoprolol prevents progressive LV dysfunction and remodeling in dogs with moderate heart failure

Acute intravenous infusion of ranolazine (Ran), an anti-ischemic/antiangina drug, was previously shown to improve left ventricular (LV) ejection fraction (EF) without a concomitant increase in myocardial oxygen consumption in dogs with chronic heart failure (HF). This study examined the effects of treatment with Ran alone and in combination with metoprolol (Met) or enalapril (Ena) on LV function and remodeling in dogs with HF. Dogs (n = 28) with microembolization-induced HF were randomized to 3 mo oral treatment with Ran alone [375 mg twice daily (bid); n = 7], Ran (375 mg bid) in combination with Met tartrate (25 mg bid; n = 7), Ran (375 mg bid) in combination with Ena (10 mg bid; n = 7), or placebo (PL; Ran vehicle bid; n = 7). Ventriculographic measurements of LV end-diastolic volume (EDV) and end-systolic volume (ESV) and LV EF were obtained before treatment and after 3 mo of treatment. In PL-treated dogs, EDV and ESV increased significantly. Ran alone prevented the increase in EDV and ESV seen in the PL group and significantly increased EF, albeit modestly, from 35 +/- 1% to 37 +/- 2%. When combined with either Ena or Met, Ran prevented the increase in EDV, significantly decreased ESV, and markedly increased EF compared with those of PL. EF increased from 35 +/- 1% to 40 +/- 1% with Ran + Ena and from 34 +/- 1% to 41 +/- 1% with Ran + Met. Ran alone or in combination with Ena or Met was also associated with beneficial effects at the cellular level on histomorphometric parameters such as hypertrophy, fibrosis, and capillary density as well as the expression for pathological hypertrophy and Ca2+ cycling genes. In conclusion, Ran prevented progressive LV dysfunction and global and cellular myocardial remodeling, and Ran in combination with Ena or Met improved LV function beyond that observed with Ran alone.

Mechanism of reduced myocardial glucose utilization during acute hypertriglyceridemia in rats

PURPOSE

The purpose of the research is to study the effect of acute inhibition of intravascular lipolysis on myocardial substrate selection during hypertriglyceridemia using in vivo radiotracer analysis and positron emission tomography.

PROCEDURES

We induced acute hypertriglyceridemia in vivo using an intravenous infusion of Intralipid 20% (IL) without and with acute inhibition of fatty acid delivery from circulating triglycerides with injection of Triton WR-1339 (TRI) during a euglycemic-hyperinsulinemic clamp in Wistar rats. We determined the effect of TRI on myocardial uptake of circulating triglycerides and free fatty acids using intravenous injection of [(3)H]-triolein and [(14)C]-bromopalmitate, respectively. Myocardial blood flow, oxidative metabolism, and metabolic rate of glucose (MMRG) were determined using micro-positron emission tomography (microPET) with [(13)N]-ammonia, [(11)C]-acetate, and 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG).

RESULTS

TRI reduced myocardial incorporation of [(3)H]-triolein but not [(14)C]-bromopalmitate showing that it selectively reduces myocardial fatty acid delivery from circulating triglycerides but not from free fatty acids. IL reduced myocardial blood flow and MMRG by 37% and 56%, respectively, but did not affect myocardial oxidative metabolism. TRI did not abolish the effect of IL on myocardial blood flow and MMRG.

CONCLUSIONS

Hypertriglyceridemia acutely reduces myocardial blood flow and MMRG in rats, but this effect is not explained by increased myocardial fatty acid delivery through intravascular triglyceride lipolysis.

Myocardial fatty acid metabolism and cardiac performance in heart failure

It is well established that cardiac metabolism is abnormal in heart failure (HF). Experimental studies suggest that in severe HF, cardiac metabolism reverts to a more fetal-like substrate use characterized by enhanced glucose and downregulated free fatty acid (FFA) metabolism. Correspondingly, in humans, when FFA levels are similar, myocardial glucose metabolism is increased, and FFA metabolism is decreased. However, depression of left ventricular function and insulin resistance induces a shift back to greater FFA uptake and oxidation by increasing circulating FFA availability. Myocardial insulin resistance may further impair myocardial glucose uptake and lead to an energy depletion state. Experimental and preliminary clinical studies suggest that metabolic modulators enhancing myocardial glucose oxidation may improve cardiac function in patients with chronic HF. However, it has been found that acute FFA deprivation is harmful to the cardiac performance. Optimizing myocardial energy metabolism may serve as an additional approach for managing HF, but further studies are warranted.

Late sodium current inhibition as a new cardioprotective approach

There is increasing evidence that the late sodium current of the sodium channel in myocytes plays a critical role in the pathophysiology of myocardial ischemia and thus is a potential therapeutic target in patients with ischemic heart disease. Ranolazine, an inhibitor of the late sodium current, reduces the frequency and severity of anginal attacks and ST-segment depression in humans, and unlike other antianginal drugs, ranolazine does not alter heart rate or blood pressure. In experimental animal models, ranolazine has been shown to reduce myocardial infarct size and to improve left ventricular function after acute ischemia and chronic heart failure. This article reviews published data describing the role of late sodium current and its inhibition by ranolazine in clinical and experimental studies of myocardial ischemia.

Chronic inhibition of the Na+/H+ - exchanger causes regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling

BACKGROUND AND PURPOSE

Increased activity of the Na+/H+ -exchanger (NHE-1) in heart failure underlies raised [Na+]i causing disturbances of calcium handling. Inhibition of NHE-1, initiated at the onset of pressure/volume overload, prevents development of hypertrophy, heart failure and remodelling. We hypothesized that chronic inhibition of NHE-1, initiated at a later stage, would induce regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling.

EXPERIMENTAL APPROACH

Development of heart failure in rabbits was monitored electrocardiographically and echocardiographically, after one or three months. Cardiac myocytes were also isolated. One group of animals were treated with cariporide (inhibitor of NHE-1) in the diet after one month. Cytoplasmic calcium, sodium and action potentials were measured with fluorescent markers and sarcoplasmic reticulum calcium content by rapid cooling. Calcium after-transients were elicited after rapid pacing. Sodium channel current (INa) was measured using patch-clamp techniques.

KEY RESULTS

Hypertrophy and heart failure developed after one month and progressed during the next two months. After one month, dietary treatment with cariporide was initiated. Two months of treatment reduced hypertrophy and heart failure, duration of action potential QT-interval and QRS, and restored sodium and calcium handling and the incidence of calcium after-transients. In cardiac myocytes, parameters of INa were not changed by cariporide.

CONCLUSION AND IMPLICATIONS

In rabbit hearts with hypertrophy and signs of heart failure one month after induction of pressure/volume overload, two months of dietary treatment with the NHE-1 inhibitor cariporide caused regression of hypertrophy, heart failure and ionic and electrophysiological remodelling.

Metabolic response to an acute jump in cardiac workload: effects on malonyl-CoA, mechanical efficiency, and fatty acid oxidation

Inhibition of myocardial fatty acid oxidation can improve left ventricular (LV) mechanical efficiency by increasing LV power for a given rate of myocardial energy expenditure. This phenomenon has not been assessed at high workloads in nonischemic myocardium; therefore, we subjected in vivo pig hearts to a high workload for 5 min and assessed whether blocking mitochondrial fatty acid oxidation with the carnitine palmitoyltransferase-I inhibitor oxfenicine would improve LV mechanical efficiency. In addition, the cardiac content of malonyl-CoA (an endogenous inhibitor of carnitine palmitoyltransferase-I) and activity of acetyl-CoA carboxylase (which synthesizes malonyl-CoA) were assessed. Increased workload was induced by aortic constriction and dobutamine infusion, and LV efficiency was calculated from the LV pressure-volume loop and LV energy expenditure. In untreated pigs, the increase in LV power resulted in a 2.5-fold increase in fatty acid oxidation and cardiac malonyl-CoA content but did not affect the activation state of acetyl-CoA carboxylase. The activation state of the acetyl-CoA carboxylase inhibitory kinase AMP-activated protein kinase decreased by 40% with increased cardiac workload. Pretreatment with oxfenicine inhibited fatty acid oxidation by 75% and had no effect on cardiac energy expenditure but significantly increased LV power and LV efficiency (37 +/- 5% vs. 26 +/- 5%, P < 0.05) at high workload. In conclusion, 1) myocardial fatty acid oxidation increases with a short-term increase in cardiac workload, despite an increase in malonyl-CoA concentration, and 2) inhibition of fatty acid oxidation improves LV mechanical efficiency by increasing LV power without affecting cardiac energy expenditure.

Excitation-contraction coupling and mitochondrial energetics

Cardiac excitation-contraction (EC) coupling consumes vast amounts of cellular energy, most of which is produced in mitochondria by oxidative phosphorylation. In order to adapt the constantly varying workload of the heart to energy supply, tight coupling mechanisms are essential to maintain cellular pools of ATP, phosphocreatine and NADH. To our current knowledge, the most important regulators of oxidative phosphorylation are ADP, Pi, and Ca2+. However, the kinetics of mitochondrial Ca2+-uptake during EC coupling are currently a matter of intense debate. Recent experimental findings suggest the existence of a mitochondrial Ca2+ microdomain in cardiac myocytes, justified by the close proximity of mitochondria to the sites of cellular Ca2+ release, i. e., the ryanodine receptors of the sarcoplasmic reticulum. Such a Ca2+ microdomain could explain seemingly controversial results on mitochondrial Ca2+ uptake kinetics in isolated mitochondria versus whole cardiac myocytes. Another important consideration is that rapid mitochondrial Ca2+ uptake facilitated by microdomains may shape cytosolic Ca2+ signals in cardiac myocytes and have an impact on energy supply and demand matching. Defects in EC coupling in chronic heart failure may adversely affect mitochondrial Ca2+ uptake and energetics, initiating a vicious cycle of contractile dysfunction and energy depletion. Future therapeutic approaches in the treatment of heart failure could be aimed at interrupting this vicious cycle.

Potential of metabolic agents as adjunct therapies in heart failure

Heart failure continues to have a significant morbidity and mortality rate despite several recent advances in treatment such as additional neurohumoral blockades and cardiac resynchronisation therapy. There is emerging evidence that, irrespective of etiology, heart failure is associated with an energetic disorder and that this may contribute to the pathogenesis of the syndrome. Recently, a number of studies have suggested that some metabolic agents may have potential as adjunctive therapy in patients with heart failure. These agents cause a shift of myocardial-substrate utilization away from free fatty acids toward glucose. Free fatty acid utilization consumes more oxygen to generate an equivalent amount of energy compared with glucose. Some of these agents are also effective antianginals, presumably by reducing the myocardial oxygen requirement. In this review we will discuss some of the current issues and progresses relating to metabolic manipulation in heart failure.

Therapy with cardiac contractility modulation electrical signals improves left ventricular function and remodeling in dogs with chronic heart failure

OBJECTIVES

This study examined the effects of long-term delivery of cardiac contractility modulation (CCM) electric signals on left ventricular (LV) function and global, cellular, and molecular remodeling in dogs with chronic heart failure (HF).

BACKGROUND

Acute studies in dogs with experimentally induced HF showed that CCM signals applied to the failing myocardium during the absolute refractory period improved LV function without increasing myocardial oxygen consumption.

METHODS

In one study, dogs with intracoronary microembolization-induced HF were randomized to 3 months of active CCM monotherapy or to a sham-operated control group. In another study, 19 HF dogs were randomized to 3 months chronic monotherapy with extended release metoprolol succinate (MET-ER), MET-ER with CCM, or no therapy at all (control group).

RESULTS

In CCM-only treated dogs, LV ejection fraction (EF) increased (27 +/- 1% vs. 33 +/- 1%, p < 0.0001) compared with a decrease in sham-operated control animals (27 +/- 1% vs. 23 +/- 1%, p < 0.001). The increase in EF seen with CCM-treated dogs was accompanied by reduced LV volumes, improved myocardial structure, reversal of the maladaptive fetal gene program, and an improvement in sarcoplasmic reticulum calcium cycling proteins. Dogs treated with a combination of MET-ER and CCM showed a greater increase in LV EF and a greater reversal of LV global, structural, and biochemical remodeling compared with dogs treated with MET-ER alone.

CONCLUSIONS

In dogs with HF, long-term CCM therapy improves LV systolic function. The improvements are additive to those seen with beta-blockers. These findings are further strengthened by the concomitant benefits of CCM therapy on LV global, cellular, and biochemical remodeling.

Enhanced inotropic state of the failing left ventricle by cardiac contractility modulation electrical signals is not associated with increased myocardial oxygen consumption

BACKGROUND

Previous studies in patients and in dogs with experimentally induced heart failure (HF) showed that electrical signals applied to the failing myocardium during the absolute refractory period improved left ventricular (LV) function. We examined the effects these same cardiac contractility modulating (CCM) electrical signals on myocardial oxygen consumption (MVO(2)) in both patients and dogs with chronic HF.

METHODS AND RESULTS

Six dogs with microembolizations-induced HF and 9 HF patients underwent CCM leads and generator (OPTIMIZER II) implantation. After baseline measurements, CCM signals were delivered continuously for 2 hours in dogs and for 30 minutes in patients. MVO(2) was measured before and after CCM therapy. In dogs, CCM therapy increased LV ejection fraction at 2 hours (26 +/- 1 versus 31 +/- 2 %, P = .001) without increasing MVO(2) (257 +/- 41 versus 180 +/- 34 micromol/min). In patients, CCM therapy increased LV peak +dP/dt by 10.1 +/- 1.5 %. As with dogs, the increase in LV function after 30 minutes of CCM therapy was not associated with increased MVO(2) (13.6 +/- 9.7 versus 12.5 +/- 7.2 mL O(2)/min).

CONCLUSIONS

The study results suggest that unlike cAMP-dependent positive inotropic drugs, the increase in LV function during CCM therapy is elicited without increasing MVO(2).

Ranolazine: a novel agent that improves dysfunctional sodium channels

Treatment for coronary heart disease is usually directed at either increasing myocardial oxygen supply or decreasing myocardial oxygen demand. Although combination therapy with beta-blockers, calcium-channel blockers and nitrates are effective, many patients suffer from adverse effects of hypotension and bradycardia. Ranolazine is a novel medication that reduces ischaemia by preventing sodium induced calcium overload in myocardial cells without adversely affecting haemodynamic parameters. This agent is the first in the USA to be approved to treat angina in over 10 years. The purpose of this review is to evaluate the pharmacology, pharmacokinetics, clinical trials for safety and efficacy, precautions, adverse effects, drug interactions, and dosage and administration of ranolazine in the treatment of chronic stable angina and acute coronary syndrome.

Emerging drugs for acute and chronic heart failure: current and future developments

Heart failure continues to be a major public health issue. Although angiotensin-converting enzyme inhibitors and beta-adrenergic blockers have been broadly used as evidence-based therapies in heart failure, morbidity and mortality remains high. Furthermore, treatment for acute decompensated heart failure and diastolic heart failure (or 'heart failure with preserved ejection fraction') is far from perfect. This review provides a broad overview of some of the novel compounds under investigation for the treatment of heart failure. Novel strategies include drugs that aim to alleviate congestion and improve hemodynamics, drugs that preserve renal function, drugs that reduce arterial and myocardial stiffness, drugs that module myocardial contractility, drugs that affect metabolic and hormonal balance, and drugs that act on existing and novel physiologic targets.

Inhibition of free fatty acids metabolism as a therapeutic target in patients with heart failure

Recent studies have evidenced that alterations of cardiac metabolism can be present in several cardiac syndromes. In heart failure, wasting of subcutaneous fat and skeletal muscle is relatively common and suggests an increased utilisation of non-carbohydrate substrates for energy production. In fact, fasting blood ketone bodies as well as fat oxidation during exercise have been shown to be increased in patients with heart failure. This metabolic shift determines a reduction of myocardial oxygen consumption efficiency. A direct approach to manipulate cardiac energy metabolism consists in modifying substrate utilisation by the heart. To date, the most effective metabolic treatments include several pharmacological agents that directly inhibit fatty acid oxidation. Clinical studies have shown that these agents can substantially increase the ischaemic threshold in patients with effort angina. However, the results of current research is also supporting the concept that shifting the energy substrate preference away from fatty acid metabolism and towards glucose metabolism could be an effective adjunctive treatment in patients with heart failure, in terms of left ventricular function and glucose metabolism improvement. In fact, these agents have also been shown to improve overall glucose metabolism in diabetic patients with left ventricular dysfunction. In this paper, the recent literature on the beneficial therapeutic effects of modulation of cardiac metabolic substrates utilisation in patients with heart failure is reviewed and discussed.

Hemodynamic properties of a new-generation positive luso-inotropic agent for the acute treatment of advanced heart failure

Currently available positive inotropic agents, such as dobutamine and milrinone, although needed as "rescue therapy" for patients with acute decompensated heart failure (ADHF), are not ideal drugs because of an inherent adverse side-effect profile. This study examined the hemodynamic effects of istaroxime, a novel agent with positive inotropic and lusitropic (luso-intropic) effects, under investigation for the treatment of ADHF. Studies were performed in 7 dogs with advanced heart failure (HF). Each dog received intravenous istaroxime or saline solution in random order 1 week apart in equal volume/volume escalating doses, with each dose maintained for 1 hour. Escalating istaroxime doses of 0.5, 1.0, 2.0, 3.0, and 5.0 microg/kg per min were used. Hemodynamic, ventriculographic, and 2-dimensional echocardiographic and Doppler indices of left ventricular (LV) systolic and diastolic function were made at baseline and at the end of each hour of each dose of istaroxime or saline solution used. Electrocardiographic results were monitored throughout the study for development of de novo arrhythmias. Results showed that saline solution had no effect on any hemodynamic, ventriculographic, echocardiographic, or Doppler indices of LV function. Compared with baseline, istaroxime had no effect on heart rate, with only a modest reduction of mean aortic pressure at high doses. Istaroxime decreased LV end-diastolic and end-systolic volumes and significantly increased LV ejection fraction in a dose-dependent manner from 0.25+/-0.01 to 0.42+/-0.02 at the highest dose (p<0.05), without increasing myocardial oxygen consumption (194+/-21 micromol/min at baseline to 144+/-20 micromol/min at the highest dose, p<0.05). In addition, istaroxime significantly reduced LV end-diastolic pressure and end-diastolic wall stress and increased deceleration time of early mitral inflow velocity. None of the doses administered were associated with the development of de novo arrhythmias. In dogs with advanced HF, istaroxime elicits potent positive luso-intropic effects. Unlike classic cyclic adenosine monophospate-dependent positive inotropic agents, istaroxime elicits its benefits without increasing myocardial oxygen consumption or heart rate. These results suggest that istaroxime may be a unique positive luso-inotropic agent for the treatment of patients with ADHF.

Optimizing cardiac fatty acid and glucose metabolism as an approach to treating heart failure

Despite the recent introduction of new therapeutic approaches to treat heart failure, mortality from heart failure remains high, and patients still frequently experience progression of contractile dysfunction and ongoing left ventricular enlargement. Therefore, new treatments are needed for heart failure that work independently of mechanisms already targeted. Emerging evidence suggests that the failure of the myocardium in heart failure is affected by alterations in the energy substrate metabolism. In particular, there is now evidence that in the failing heart, shifting metabolism away from a preference for fatty acids toward more carbohydrate oxidation can improve contractile function and slow the progression of pump failure.

A Comparison between Ranolazine and CVT-4325, a Novel Inhibitor of Fatty Acid Oxidation, on Cardiac Metabolism and Left Ventricular Function in Rat Isolated Perfused Heart during Ischemia and Reperfusion

Inhibition of fatty acid oxidation has been reported to be cardioprotective against myocardial ischemic injury; however, recent studies have questioned whether the cardioprotection associated with putative fatty acid oxidation inhibitors, such as ranolazine and trimetazidine, are due to changes in substrate oxidation. Therefore, the goals of this study were to compare the effects of ranolazine with a new fatty acid oxidation inhibitor, CVT-4325 [(R)-1-(2-methylbenzo[d]thiazol-5-yloxy)-3-(4-((5-(4-(trifluoromethyl)phenyl)-1,2,4-oxadiazol-3-yl)methyl)-piperazin-1-yl)propan-2-ol], on carbohydrate and fatty acid oxidation and on left ventricular (LV) function in the response to ischemia/reperfusion in rat isolated perfused hearts. Metabolic fluxes were determined in hearts perfused in an isovolumic Langendorff mode using 13C nuclear magnetic resonance isotopomer analysis or in isolated working hearts using [14C]glucose and [3H]palmitate, with and without 10 microM ranolazine or 3 microM CVT-4325. Isovolumic perfused hearts were also subjected to 30 min of low-flow ischemia (0.3 ml/min) and 60 min of reperfusion, and working hearts were subjected to 15 min of zero-flow ischemia and 60 min of reperfusion. Regardless of the experimental protocol, ranolazine had no effect on carbohydrate or fatty acid oxidation, whereas CVT-4325 significantly reduced fatty acid oxidation up to approximately 7-fold with a concomitant increase in carbohydrate oxidation. At these same concentrations, although ranolazine significantly improved LV functional recovery following ischemia/reperfusion, CVT-4325 had no significant protective effect. These results demonstrate that at pharmacologically relevant concentrations, ischemic protection by ranolazine was not mediated by inhibition of fatty acid oxidation and conversely that inhibition of fatty acid oxidation with CVT-4325 was not associated with improved LV functional recovery.

CVT-4325 Inhibits Myocardial Fatty Acid Uptake and Improves Left Ventricular Systolic Function without Increasing Myocardial Oxygen Consumption in Dogs with Chronic Heart Failure

BACKGROUND

Inhibition of myocardial fatty acid oxidation has been suggested as a therapeutic approach for improving cardiac function in chronic heart failure (HF). The novel piperazine derivative CVT-4325 was shown to inhibit fatty acid oxidation in cardiac mitochondria and in isolated perfused rat hearts. In the present study, we tested the hemodynamic and metabolic effects of acute intravenous CVT-4325 in dogs with HF.

METHODS AND RESULTS

HF (LV ejection fraction <or=35%) was created in eight dogs by multiple sequential intracoronary microembolizations. Treatment with CVT-4325 administered intravenously as 0.5 mg/kg bolus followed by a continuous infusion of 0.8 mg/kg/h for 40 min reduced free fatty acid (FFA) uptake (4.51+/-0.96 to 1.65+/-0.32 micromols/min, p<0.04), coronary blood flow (56+/-3 to 46+/-4 ml/min, p<0.01), and myocardial oxygen consumption (MVO2) (240+/-23 to 172+/-7 micromols/min, p<0.03), and increased LV ejection fraction (30+/-2 to 37+/-1%, p<0.0001). In the same study, but on a different day, the same dogs were treated with an inactive analogue of CVT-4325 (CVT-2540), and no hemodynamic or metabolic effects were observed.

CONCLUSIONS

In dogs with HF, acute intravenous infusion of CVT-4325 reduces FFA uptake and improves LV systolic function without increasing MVO2. The improvement in LV systolic function in the absence of an increase in MVO2 and a lower FFA uptake is consistent with the concept that inhibition of myocardial fatty acid oxidation may be an effective treatment for HF.

Modification of myocardial substrate use as a therapy for heart failure

Despite advances in treatment, chronic heart failure is still associated with significant morbidity and a poor prognosis. The scope for further advances based on additional neurohumoral blockade is small. Effective adjunctive therapies acting via a different cellular mechanism would, therefore, be attractive. Energetic impairment seems to contribute to the pathogenesis of heart failure. The findings from several studies have shown that the so-called metabolic agents could have potential as adjunctive therapies in heart failure. These agents cause a shift in the substrate used by the heart away from free fatty acids, the oxidation of which normally provides around 70% of the energy needed, towards glucose. The oxygen cost of energy generation is lessened when glucose is used as the substrate. In this review we aim to draw attention to the metabolic alteration in heart failure and we present evidence supporting the use of metabolic therapy in heart failure.

Inhibition of the late sodium current as a potential cardioprotective principle: effects of the late sodium current inhibitor ranolazine

Pathological conditions linked to imbalances in oxygen supply and demand (for example, ischaemia, hypoxia and heart failure) are associated with disruptions in intracellular sodium ([Na(+)](i)) and calcium ([Ca(2+)](i)) concentration homeostasis of myocardial cells. A decreased efflux or increased influx of sodium may cause cellular sodium overload. Sodium overload is followed by an increased influx of calcium through sodium-calcium exchange. Failure to maintain the homeostasis of [Na(+)](i) and [Ca(2+)](i) leads to electrical instability (arrhythmias), mechanical dysfunction (reduced contractility and increased diastolic tension) and mitochondrial dysfunction. These events increase ATP hydrolysis and decrease ATP formation and, if left uncorrected, they cause cell injury and death. The relative contributions of various pathways (sodium channels, exchangers and transporters) to the rise in [Na(+)](i) remain a matter of debate. Nevertheless, both the sodium-hydrogen exchanger and abnormal sodium channel conductance (that is, increased late sodium current (I(Na))) are likely to contribute to the rise in [Na(+)](i). The focus of this review is on the role of the late (sustained/persistent) I(Na) in the ionic disturbances associated with ischaemia/hypoxia and heart failure, the consequences of these ionic disturbances, and the cardioprotective effects of the antianginal and anti-ischaemic drug ranolazine. Ranolazine selectively inhibits late I(Na), reduces [Na(+)](i)-dependent calcium overload and attenuates the abnormalities of ventricular repolarisation and contractility that are associated with ischaemia/reperfusion and heart failure. Thus, inhibition of late I(Na) can reduce [Na(+)](i)-dependent calcium overload and its detrimental effects on myocardial function.

Evaluation of a novel anti-ischemic agent in acute coronary syndromes: design and rationale for the Metabolic Efficiency with Ranolazine for Less Ischemia in Non-ST-elevation acute coronary syndromes (MERLIN)-TIMI 36 trial

BACKGROUND

Despite advances in antithrombotic therapies and invasive technology, the risk of recurrent ischemic complications in patients with non-ST-elevation acute coronary syndromes (NSTE-ACSs) remains substantial. Ranolazine is a novel agent that inhibits the late sodium current thereby reducing cellular sodium and calcium overload and has been shown to reduce ischemia in patients with chronic stable angina.

STUDY DESIGN

MERLIN-TIMI 36 is a phase III, randomized, double-blind, parallel-group, placebo-controlled, multinational clinical trial to evaluate the efficacy and safety of ranolazine during long-term treatment of patients with NSTE-ACS receiving standard therapy (N = 6500). Eligible patients are randomized 1:1 to ranolazine or matched placebo, initiated as 200 mg intravenously over 1 hour, followed by an 80-mg/h infusion (40 mg/h for patients with severe renal insufficiency) for up to 96 hours and oral ranolazine ER 1000 mg BID or matched placebo until the end of study. The primary end point is the time to first occurrence of any element of the composite of cardiovascular death, myocardial infarction, or recurrent ischemia. Secondary end points include ischemia on Holter monitoring, hospitalization for new or worsening heart failure, quality of life measures, and exercise performance. The evaluation of long-term safety will include death from any cause and symptomatic documented arrhythmia. Recruitment began in October 2004. The trial will continue until 730 major cardiovascular events and 310 deaths are recorded with expected completion in 24 to 28 months.

CONCLUSIONS

MERLIN-TIMI 36 will evaluate the role of ranolazine in the acute and chronic management of patients presenting with NSTE-ACS.

Xanthine oxidase inhibitors improve energetics and function after infarction in failing mouse hearts

After myocardial infarction, ventricular geometry and function, as well as energy metabolism, change markedly. In nonischemic heart failure, inhibition of xanthine oxidase (XO) improves mechanoenergetic coupling by improving contractile performance relative to a reduced energetic demand. However, the metabolic and contractile effects of XO inhibitors (XOIs) have not been characterized in failing hearts after infarction. After undergoing permanent coronary ligation, mice received a XOI (allopurinol or oxypurinol) or matching placebo in the daily drinking water. Four weeks later, 1H MRI and 31P magnetic resonance spectroscopy (MRS) were used to quantify in vivo functional and metabolic changes in postinfarction remodeled mouse myocardium and the effects of XOIs on that process. End-systolic (ESV) and end-diastolic volumes (EDV) were increased by more than sixfold after infarction, left ventricle (LV) mass doubled ( P < 0.005), and the LV ejection fraction (EF) decreased (14 ± 9%) compared with control hearts (59 ± 8%, P < 0.005) at 1 mo. The myocardial phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) was also significantly decreased in infarct remodeled hearts (1.4 ± 0.6) compared with control animals (2.1 ± 0.5, P < 0.02), in agreement with prior studies in larger animals. The XOIs allopurinol and oxypurinol did not change LV mass but limited the increase in ESV and EDV of infarct hearts by 50%, increased EF (23 ± 9%, P = 0.01), and normalized cardiac PCr/ATP (2.0 ± 0.5, P < 0.04). We conclude that XOIs improve ventricular function after infarction and normalize high-energy phosphate ratio in heart failure. Thus XOI therapy offers a new and potentially complementary approach to limit the adverse contractile and metabolic consequences after infarction.

Ranolazine

Ranolazine (Ranexa), a piperazine derivative, is a new antianginal agent approved for the treatment of chronic stable angina pectoris for use as combination therapy when angina is not adequately controlled with other antianginal agents. While the exact mechanism of action of ranolazine is not known, its antianginal and anti-ischaemic effects do not appear to depend upon changes in blood pressure or heart rate. An extended-release (ER) oral formulation of ranolazine has been developed to facilitate twice-daily administration whilst maintaining therapeutically effective plasma concentrations. In patients with chronic stable angina, ranolazine ER monotherapy was shown to improve exercise duration at trough plasma drug concentration in a dose-dependent manner compared with placebo. The drug was effective as adjunctive therapy in patients with chronic stable angina whose condition was not controlled adequately with conventional antianginal therapy. In randomised clinical trials, ranolazine ER was well tolerated, with no overt effects on cardiovascular haemodynamics or conduction, apart from a modest increase in corrected QT (QTc) interval (but no torsades de pointes). Importantly, the efficacy and tolerability of ranolazine ER were not affected by comorbid conditions, including old age, heart failure (HF) or diabetes mellitus. Comparative trials of ranolazine ER with other antianginal agents and trials examining its effects on long-term morbidity and mortality in patients with ischaemic heart disease are required to determine with greater certainty the place of the drug in current antianginal therapy. Nevertheless, ranolazine ER may well prove to be a useful alternative and adjunct to conventional haemodynamic antianginal therapy in the treatment of chronic stable angina.

Combination pharmacologic therapies for heart failure: what next after angiotensin-converting enzyme inhibitors and beta-blockers?

Although the introduction of angiotensin-converting enzyme (ACE) inhibitors and beta-adrenergic blockers has resulted in significant improvements in the management of heart failure (HF), morbidity and mortality remain high. Therefore, additional approaches have been sought to discover newer agents that might add incremental benefit. Although not all of these approaches have been successful, there have been some notable new approaches to therapy that have shown benefit or may be promising in terms of additional benefit. Most of these agents are targeted to achieve a more global neurohormonal blockade aiming to reduce or potentially reverse the ventricular remodeling process that occurs in HF. Some of the newer approaches aim for targets other than neurohormonal systems, eg, effects on myocardial metabolism or the vasculature. This article reviews the latest advances in pharmacologic therapy in HF, looking at several trials that may have a significant impact on the treatment of HF. We also discuss several newer agents with promising potential in HF management.

Myocardial substrate metabolism in the normal and failing heart

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 that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Electrophysiologic properties and antiarrhythmic actions of a novel antianginal agent

Ranolazine is a novel antianginal agent capable of producing anti-ischemic effects at plasma concentrations of 2 to 6 microM without a significant reduction of heart rate or blood pressure. This review summarizes the electrophysiologic properties of ranolazine. Ranolazine significantly blocks I(Kr) (IC(50) = 12 microM), late I(Na), late I(Ca), peak I(Ca), I(Na-Ca) (IC(50) = 5.9, 50, 296, and 91 microM, respectively) and I(Ks) (17% at 30 microM), but causes little or no inhibition of I(to) or I(K1). In left ventricular tissue and wedge preparations, ranolazine produces a concentration-dependent prolongation of action potential duration (APD) in epicardium, but abbreviation of APD of M cells, leading to either no change or a reduction in transmural dispersion of repolarization (TDR). The result is a modest prolongation of the QT interval. Prolongation of APD and QT by ranolazine is fundamentally different from that of other drugs that block I(Kr) and induce torsade de pointes in that APD prolongation is rate-independent (ie, does not display reverse rate-dependent prolongation of APD) and is not associated with early after depolarizations, triggered activity, increased spatial dispersion of repolarization, or polymorphic ventricular tachycardia. Torsade de pointes arrhythmias were not observed spontaneously nor could they be induced with programmed electrical stimulation in the presence of ranolazine at concentrations as high as 100 microM. Indeed, ranolazine was found to possess significant antiarrhythmic activity, acting to suppress the arrhythmogenic effects of other QT-prolonging drugs. Ranolazine produces ion channel effects similar to those observed after chronic exposure to amiodarone (reduced late I(Na), I(Kr), I(Ks), and I(Ca)). Ranolazine's actions to reduce TDR and suppress early after depolarization suggest that in addition to its anti-anginal actions, the drug possesses antiarrhythmic activity.

Antagonism by ranolazine of the pro-arrhythmic effects of increasing late INa in guinea pig ventricular myocytes

The new anti-anginal drug ranolazine causes a slight (<10 milliseconds) prolongation of the QT interval, raising the concern that its use may be associated with an increased incidence of torsades de pointes ventricular tachyarrhythmias. The goal of this study was to show that ranolazine inhibits the late component of INa and attenuates prolongation of action potential duration when late INa is increased, both in the absence and presence of IK-blocking drugs. Currents and action potentials of guinea pig isolated ventricular myocytes were measured by whole-cell patch clamp. Sea anemone toxin (ATX)-II was used to increase late INa and mimic the effect of an SCN5A gene mutation. ATX-II (3-5 nmol/L) increased late INa by 5-fold; ranolazine attenuated this increase of late INa by up to 61 +/- 8%. ATX-II (10-20 nmol/L) increased action potential duration (APD) by > 1 seconds, and caused early afterdepolarizations; both actions were attenuated by ranolazine (0.1-30 micromol/L). Ranolazine (10 micromol/L) reduced by 89% the 13.6-fold increase in variability of APD caused by 10 nmol/L ATX-II. The effects of ATX-II (3 nmol/L) in combinations with either the IKr blocker E-4031 or the IKs blocker chromanol 293B to increase APD were attenuated 76 +/- 5% and 71 +/- 4%, respectively, by 10 micromol/L ranolazine. The results demonstrate that ranolazine reduces late INa and has an anti-arrhythmic effect when late INa is increased.

Novel pharmacological treatments for heart failure

Pharmacological therapies remain the primary strategy for treating patients with acute and chronic heart failure. Several novel neurohormonal antagonists, inotropic agents, immune modulators, and metabolic and replacement therapies are currently in development to meet the demands of an increasing number of patients with heart failure. The success in drug development in this field will require a better understanding of the effects of heart failure on drug dosing, better integration of novel and existing drug therapies, the development of more reliable surrogate markers to effectively tailor medical therapy to individual needs and the ability to detect and treat patients at risk before the onset of heart failure.

Comparative efficacy of ranolazine versus atenolol for chronic angina pectoris

We investigated whether ranolazine therapy improves exercise-induced angina pectoris and myocardial ischemia compared with placebo or with standard doses of atenolol in patients who had chronic angina and evaluated the effects on hemodynamics at rest and during exercise. In this trial, 158 patients who had symptom-limited exercise discontinued beta-blocker therapy and were randomized into a double-blind, 3-period, crossover study of 400 mg of immediate-release ranolazine 3 times daily, 100 mg/day of atenolol, or placebo, each administered for 1 week. Exercise tests were administered at the end of each treatment period. Therapy with ranolazine or atenolol produced statistically significant improvement in all 3 exercise end points compared with placebo. Compared with atenolol therapy, ranolazine therapy resulted in significantly longer total exercise duration and was statistically indistinguishable from atenolol for time to onset of angina and ST-segment depression. Except for a modest increase in systolic blood pressure at peak exercise during ranolazine therapy, hemodynamic measurements did not differ significantly during ranolazine and placebo therapies. In contrast, atenolol significantly decreased blood pressure, heart rate, and rate-pressure product at rest and during exercise compared with placebo or ranolazine. In conclusion, ranolazine therapy prolonged exercise duration and decreased exercise-induced ischemia and angina with quantitative effects equal to or greater than those with atenolol. Unlike atenolol, the anti-ischemic and antianginal effects of ranolazine occurred without decreases in blood pressure, heart rate, or rate-pressure product.

Moderate severity heart failure does not involve a downregulation of myocardial fatty acid oxidation

Recent human and animal studies have demonstrated that in severe end-stage heart failure (HF), the cardiac muscle switches to a more fetal metabolic phenotype, characterized by downregulation of free fatty acid (FFA) oxidation and an enhancement of glucose oxidation. The goal of this study was to examine myocardial substrate metabolism in a model of moderate coronary microembolization-induced HF. We hypothesized that during well-compensated HF, FFA oxidation would predominate as opposed to a more fetal metabolic phenotype of greater glucose oxidation. Cardiac substrate uptake and oxidation were measured in normal dogs ( n = 8) and in dogs with microembolization-induced HF ( n = 18, ejection fraction = 28%) by infusing three isotopic tracers ([9,10-3H]oleate, [U-14C]glucose, and [1-13C]lactate) in anesthetized open-chest animals. There were no differences in myocardial substrate metabolism between the two groups. The total activity of pyruvate dehydrogenase, the key enzyme regulating myocardial pyruvate oxidation (and hence glucose and lactate oxidation) was not affected by HF. We did not observe any difference in the activity of carnitine palmitoyl transferase I (CPT-I) and its sensitivity to inhibition by malonyl-CoA between groups; however, malonyl-CoA content was decreased by 22% with HF, suggesting less in vivo inhibition of CPT-I activity. The differences in malonyl-CoA content cannot be explained by changes in the Michaelis-Menten constant and maximal velocity for malonyl-CoA decarboxylase because neither were affected by HF. These results support the concept that there is no decrease in fatty acid oxidation during compensated HF and that the downregulation of fatty acid oxidation enzymes and the switch to carbohydrate oxidation observed in end-stage HF is only a late-stage phenomemon.

Electrophysiological effects of ranolazine, a novel antianginal agent with antiarrhythmic properties

BACKGROUND

Ranolazine is a novel antianginal agent capable of producing antiischemic effects at plasma concentrations of 2 to 6 micromol/L without reducing heart rate or blood pressure. The present study examines its electrophysiological effects in isolated canine ventricular myocytes, tissues, and arterially perfused left ventricular wedge preparations.

METHODS AND RESULTS

Transmembrane action potentials (APs) from epicardial and midmyocardial (M) regions and a pseudo-ECG were recorded simultaneously from wedge preparations. APs were also recorded from epicardial and M tissues. Whole-cell currents were recorded from epicardial and M myocytes. Ranolazine inhibited I(Kr) (IC50=11.5 micromol/L), late I(Na), late I(Ca), peak I(Ca), and I(Na-Ca) (IC50=5.9, 50, 296, and 91 micromol/L, respectively) and I(Ks) (17% at 30 micromol/L), but caused little or no inhibition of I(to) or I(K1). In tissues and wedge preparations, ranolazine produced a concentration-dependent prolongation of AP duration of epicardial but abbreviation of that of M cells, leading to reduction or no change in transmural dispersion of repolarization (TDR). At [K+]o=4 mmol/L, 10 micromol/L ranolazine prolonged QT interval by 20 ms but did not increase TDR. Extrasystolic activity and spontaneous torsade de pointes (TdP) were never observed, and stimulation-induced TdP could not be induced at any concentration of ranolazine, either in normal or low [K+]o. Ranolazine (5 to 20 micromol/L) suppressed early afterdepolarizations (EADs) and reduced the increase in TDR induced by the selective I(Kr) blocker d-sotalol.

CONCLUSIONS

Ranolazine produces ion channel effects similar to those observed after chronic amiodarone (reduced I(Kr), I(Ks), late I(Na), and I(Ca)). The actions of ranolazine to suppress EADs and reduce TDR suggest that, in addition to its antianginal actions, the drug may possess antiarrhythmic activity.

Ranolazine: ion-channel-blocking actions and in vivo electrophysiological effects

Ranolazine is a novel anti-ischemic drug that prolongs the QT interval. To evaluate the potential mechanisms and consequences, we studied: (i) Ranolazine's effects on HERG and IsK currents in Xenopus oocytes with two-electrode voltage clamp; (ii) effects of ranolazine, compared to d-sotalol, on effective refractory period (ERP), QT interval and ventricular rhythm in a dog model of acquired long QT syndrome; and (iii) effects on selected native currents in canine atrial myocytes with whole-cell patch-clamp technique. Ranolazine inhibited HERG and IsK currents with different potencies. HERG was inhibited with an IC(50) of 106 micromol l(-1), whereas the IC(50) for IsK was 1.7 mmol l(-1). d-Sotalol caused reverse use-dependent ERP and QT interval prolongation, whereas ranolazine produced modest, nonsignificant increases that plateaued at submaximal doses. Neither drug affected QRS duration. d-Sotalol had clear proarrhythmic effects, with all d-sotalol-treated dogs developing torsades de pointes (TdP) ventricular tachyarrhythmias, of which they ultimately died. In contrast, ranolazine did not generate TdP. Effects on I(Kr) and I(Ks) were similar to those on HERG and IsK. Ranolazine blocked I(Ca) with an IC(50) of approximately 300 micromol l(-1). I(Na) was unaffected. We conclude that ranolazine inhibits I(Kr) by blocking HERG currents, inhibits I(Ca) at slightly larger concentrations, and has modest and self-limited effects on the QT interval. Unlike d-sotalol, ranolazine does not cause TdP in a dog model. The greater safety of ranolazine may be due to its ability to inhibit I(Ca) at concentrations only slightly larger than those that inhibit I(Kr), thus producing offsetting effects on repolarization.

Peroxisome Proliferator Activator Receptors (PPAR), Insulin Resistance, and Cardiomyopathy

Diabetes is a risk factor for coronary atherosclerosis, myocardial infarction, and ischemic cardiomyopathy. Insulin resistance is associated with left ventricular (LV) hypertrophy and hypertensive cardiomyopathy. Even in the absence of coronary artery disease or hypertension, "diabetic cardiomyopathy" can develop because of myocardial autonomic dysfunction or impaired coronary flow reserve. The relationship between insulin resistance and cardiomyopathy is bidirectional. Systemic and myocardial glucose uptake is compromised in heart failure independent of etiology. These abnormalities are associated with cellular deficits of insulin signaling. Insulin resistance in heart failure can be detrimental, because transcriptional shifts in metabolic gene expression favor glucose over fat as a substrate for high-energy phosphate production. Although preexisting diabetes accelerates this process of "metabolic death," insulin resistance can also develop secondary to cardiomyopathy-associated overabundance of neurohormones and cytokines. Insulin resistance and fatty acid excess are potential therapeutic targets in heart failure, striving for efficient myocardial substrate utilization. Peroxisome proliferator activator receptor gamma (PPARgamma) agonists are antidiabetic agents with antilipemic and insulin-sensitizing activity. Experimental studies suggest salutary effects in limiting infarct size, attenuating myocardial reperfusion injury, inhibiting hypertrophic signaling and vascular antiinflammatory actions through cytokine inhibition. However, clinical applicability in diabetic patients experiencing heart failure has been hampered because of increased edema and even fewer reports of exacerbation associated with these compounds. Evidence to date argues for peripheral mechanisms of edema unrelated to central hemodynamics. Nevertheless, they are currently contraindicated in New York Heart Association (NYHA) III-IV patients, particularly in combination with insulin. Investigations are underway to decipher mechanisms, risks, and benefits of PPARgamma agonists, as well as the role of the structurally related PPARalpha receptor on cardiovascular metabolism and function.

Ranolazine, a partial fatty acid oxidation (pFOX) inhibitor, improves left ventricular function in dogs with chronic heart failure

BACKGROUND

Abnormalities of energy metabolism are often cited as key elements in the progressive worsening of left ventricular (LV) dysfunction that characterizes the heart failure (HF) state. The present study tested the hypothesis that partial inhibition of fatty acids will ameliorate the hemodynamic abnormalities associated with HF.

METHODS AND RESULTS

Chronic HF (LV ejection fraction 27 +/- 1%) was produced in 13 dogs by intracoronary microembolizations. Hemodynamic and angiographic measurements were made before and 40 minutes after intravenous administration of ranolazine, a partial fatty acid oxidation (pFOX) inhibitor. Ranolazine was administered as an intravenous bolus dose of 0.5 mg/kg followed by a continuous infusion for 40 minutes at a constant rate of 1.0 mg / kg / hr. Ranolazine significantly increased LV ejection fraction (27 +/- 1 versus 36 +/- 2, P =.0001), peak LV +dP/dt (1712 +/- 122 versus 1900 +/- 112 mm Hg/sec, P =.001), and stroke volume (20 +/- 1 versus 26 +/- 1 mL). These improvements occurred in the absence of any effects on heart rate or systemic pressure. In 8 normal healthy dogs, ranolazine had no effect on LV ejection fraction or any other index of LV function.

CONCLUSIONS

In dogs with HF, acute intravenous administration of the pFOX inhibitor ranolazine improves LV systolic function. The absence of any hemodynamic effects of ranolazine in normal dogs suggests that the drug is devoid of any positive inotropic effects and acts primarily by optimizing cardiac metabolism in the setting of chronic HF.

Functional alpha 1 protease inhibitor produced by a human hepatoma cell line

Alpha 1 protease inhibitor antigen was identified in the culture medium of the human ascites hepatoma cell line SK-HEP-1. Trypsin inhibitory activity and alpha 1 Pl antigen accumulated in serum-free medium concomitantly over a period of several days. Radioactive alpha 1 Pl antigen was detected in conditioned medium from cultures supplemented with 35S-L-methionine, indicating a synthesis and release of the protein. Alpha 1 Pl antigen in conditioned medium appeared to be antigenically identical to that in human plasma, and the newly synthesized (radiolabeled) antigen co-migrated with plasma, alpha 1 Pl after immunoelectrophoresis or SDS-polyacrylamide gel electrophoresis. Moreover, evidence is presented that the synthesized inhibitor exhibits functional activity, since the 35S-labeled alpha 1 Pl in conditioned medium complexes with trypsin. We conclude that SK-HEP-1 cells in culture produce functionally active alpha 1 Pl which may be identical to that in plasma.