Arvinder Dhalla

A Novel, Potent, and Selective Inhibitor of Cardiac Late Sodium Current Suppresses Experimental Arrhythmias

Inhibition of cardiac late sodium current (late INa) is a strategy to suppress arrhythmias and sodium-dependent calcium overload associated with myocardial ischemia and heart failure. Current inhibitors of late INa are unselective and can be proarrhythmic. This study introduces GS967 (6-[4-(trifluoromethoxy)phenyl]-3-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine), a potent and selective inhibitor of late INa, and demonstrates its effectiveness to suppress ventricular arrhythmias. The effects of GS967 on rabbit ventricular myocyte ion channel currents and action potentials were determined. Anti-arrhythmic actions of GS967 were characterized in ex vivo and in vivo rabbit models of reduced repolarization reserve and ischemia. GS967 inhibited Anemonia sulcata toxin II (ATX-II)–induced late INa in ventricular myocytes and isolated hearts with IC50 values of 0.13 and 0.21 µM, respectively. Reduction of peak INa by GS967 was minimal at a holding potential of −120 mV but increased at −80 mV. GS967 did not prolong action potential duration or the QRS interval. GS967 prevented and reversed proarrhythmic effects (afterdepolarizations and torsades de pointes) of the late INa enhancer ATX-II and the IKr inhibitor E-4031 in isolated ventricular myocytes and hearts. GS967 significantly attenuated the proarrhythmic effects of methoxamine+clofilium and suppressed ischemia-induced arrhythmias. GS967 was more potent and effective to reduce late INa and arrhythmias than either flecainide or ranolazine. Results of all studies and assays of binding and activity of GS967 at numerous receptors, transporters, and enzymes indicated that GS967 selectively inhibited late INa. In summary, GS967 selectively suppressed late INa and prevented and/or reduced the incidence of experimentally induced arrhythmias in rabbit myocytes and hearts.

Ranolazine, an antianginal agent, markedly reduces ventricular arrhythmias induced by ischemia and ischemia-reperfusion.

We tested the effect of the antianginal agent ranolazine on ventricular arrhythmias in an ischemic model using two protocols. In protocol 1, anesthetized rats received either vehicle or ranolazine (10 mg/kg, iv bolus) and were subjected to 5 min of left coronary artery (LCA) occlusion and 5 min of reperfusion with electrocardiogram and blood pressure monitoring. In protocol 2, rats received either vehicle or three doses of ranolazine (iv bolus followed by infusion) and 20 min of LCA occlusion. With protocol 1, ventricular tachycardia (VT) occurred in 9/12 (75%) vehicle-treated rats and 1/11 (9%) ranolazine-treated rats during reperfusion (P = 0.003). Sustained VT occurred in 5/12 (42%) vehicle-treated but 0/11 in ranolazine-treated rats (P = 0.037). The median number of episodes of VT during reperfusion in vehicle and ranolazine groups was 5.5 and 0, respectively (P = 0.0006); median duration of VT was 22.2 and 0 s in vehicle and ranolazine rats, respectively (P = 0.0006). With protocol 2, mortality in the vehicle group was 42 vs. 17% (P = 0.371), 10% (P = 0.162) and 0% (P = 0.0373) with ranolazine at plasma concentrations of 2, 4, and 8 microM, respectively. Ranolazine significantly reduced the incidence of ventricular fibrillation [67% in controls vs. 42% (P = 0.414), 30% (P = 0.198) and 8% (P = 0.0094) in ranolazine at 2, 4, and 8 microM, respectively]. Median number (2.5 vs. 0; P = 0.0431) of sustained VT episodes, incidence of sustained VT (83 vs. 33%, P = 0.0361), and the duration of VT per animal (159 vs. 19 s; P = 0.0410) were also significantly reduced by ranolazine at 8 microM. Ranolazine markedly reduced ischemia-reperfusion induced ventricular arrhythmias. Ranolazine demonstrated promising anti-arrhythmic properties that warrant further investigation.

A1 adenosine receptor: role in diabetes and obesity.

Adenosine mediates its diverse effects via four subtypes (A(1), A(2A), A(2B) and A(3)) of G-protein-coupled receptors. The A(1) adenosine receptor (A(1)AR) subtype is the most extensively studied and is well characterized in various organ systems. The A(1)ARs are highly expressed in adipose tissue, and endogenous adenosine has been shown to tonically activate adipose tissue A(1)ARs. Activation of the A(1)ARs in adipocytes reduces adenylate cyclase and cAMP content and causes inhibition of lipolysis. The role of A(1)ARs in lipolysis has been well characterized by using several selective A(1)AR agonists as well as A(1)AR knockout mice. However, the contribution of A(1)ARs to the regulation of lipolysis in pathological conditions like insulin resistance, diabetes and dyslipidemia, where free fatty acids (FFA) play an important role, has not been well characterized. Pharmacological agents that reduce the release of FFA from adipose tissue and thus the availability of circulating FFA have the potential to be useful for insulin resistance and hyperlipidemia. Toward this goal, several selective and efficacious agonists of the A(1)ARs are now available, and some have entered early-phase clinical trials; however, none have received regulatory approval yet. Here we review the existing knowledge on the role of A(1)ARs in insulin resistance, diabetes and obesity, and the progress made in the development of A(1)AR agonists as antilipolytic agents, including the challenges associated with this approach.

Effect of Ranolazine on A1C and Glucose Levels in Hyperglycemic Patients With Non-ST Elevation Acute Coronary Syndrome

OBJECTIVE We determined the relationships between glycemia at randomization, concurrent antidiabetic therapy, and change in A1C and fasting plasma glucose (FPG) in patients with diabetes receiving standard treatment for diabetes and randomized to ranolazine or placebo within the MERLIN-TIMI-36 (MERLIN) study. Ranolazine is a novel first-in-class drug approved for treating angina pectoris. RESEARCH DESIGN AND METHODS Randomization and 4-month glycemic and antidiabetes drug usage data from MERLIN were analyzed using Spotfire and SAS version 9.1 software. RESULTS In patients with diabetes and A1C of ≥8–10% at randomization (n = 171), there was an absolute A1C reduction in the ranolazine group of 1.2% (95% CI −1.4 to −1.0), and the placebo-adjusted (n = 182) decrease in A1C by ranolazine was 0.59% (95% CI −0.99 to −0.20, P < 0.001). In patients with FPG of 150–400 mg/dl at randomization, ranolazine (n = 131) compared with placebo (n = 147) reduced FPG by 25.7 mg/dl (95% CI −43.3 to −8.1, P = 0.001). When changes in either A1C or FPG were correlated to A1C or FPG at randomization, the slopes were significantly steeper for ranolazine than placebo (A1C, P = 0.046; FPG, P < 0.001), indicating that lowering of A1C and FPG by ranolazine is related to hyperglycemia at randomization. Ranolazine, compared with placebo, was not associated with serious hypoglycemic events, associated with significant changes in concurrent antidiabetic therapy, or dependent on a history of angina. CONCLUSIONS Ranolazine, when added to concurrent antidiabetes treatment, lowers FPG and A1C in patients with cardiovascular disease and poorly controlled diabetes.

Antitorsadogenic effects of ({+/-})-N-(2,6-dimethyl-phenyl)-(4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1-piperazine (ranolazine) in anesthetized rabbits.

Ranolazine [Ranexa; (±)-N-(2,6-dimethyl-phenyl)-(4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1-piperazine] is novel anti-ischemic agent that has been shown to inhibit late INa and IKr and to have antiarrhythmic effects in various preclinical in vitro models. This study was undertaken to investigate the effects of ranolazine on drug-induced Torsade de Pointes (TdP) in vivo. TdP was induced by an IKr blocker, clofilium, in anesthetized, α1-agonist-sensitized rabbits. Clofilium prolonged QT interval corrected for heart rate (QTc) (52 ± 9%) and monophasic action potential duration (MAPD)90 (56 ± 9%) and caused TdP in eight of eight rabbits. Pretreatment with ranolazine (480 μg/kg/min) or lidocaine (200 μg/kg/min) reduced the clofilium-induced prolongation of QTc (15 ± 3 and 19 ± 3%, respectively, p < 0.001 versus vehicle) and MAPD90 (21 ± 4 and 20 ± 2%, respectively, p < 0.001 versus vehicle) and prevented the occurrence of TdP (zero of eight and zero of eight, respectively). Administration of ranolazine after the first episode of TdP terminated TdP and prevented its recurrence (zero of four versus vehicle, four of four). To rule out an α1-adrenoceptor antagonistic activity of ranolazine, we compared the effects of ranolazine on blood pressure with those of the α1-antagonist, prazosin. Although prazosin (10 μg/kg/min) markedly shifted the phenylephrine (α1-agonist) dose-response curve to the right, it did not have any effect on clofilium-induced prolongation of QTc and MAPD90 (43 ± 7 and 53 ± 9%, respectively) or the occurrence of TdP (seven of eight). In contrast, ranolazine completely suppressed TdP but did not cause any shift in the phenylephrine dose-response curve at the highest dose tested (480 μg/kg/min). We conclude that ranolazine antagonizes the ventricular repolarization changes caused by clofilium and suppresses clofilium-induced TdP in rabbits.

Antilipolytic Activity of a Novel Partial A1 Adenosine Receptor Agonist Devoid of Cardiovascular Effects: Comparison with Nicotinic Acid

Elevated lipolysis and circulating free fatty acid (FFA) levels have been linked to the pathogenesis of insulin resistance. A1 adenosine receptor agonists are potent inhibitors of lipolysis. Several A1 agonists have been tested as potential antilipolytic agents; however, their effect on the cardiovascular system remains a potential problem for development of these agents as drugs. In the present study, we report that CVT-3619 [(2-{6-[((1R,2R)-2-hydroxycyclopentyl) amino] purin9-yl} (4S,5 S,2R,3R)5-[(2fluorophenylthio) methyl] oxolane-3,4-diol)], a novel partial A1 receptor agonist, significantly reduces circulating FFA levels without any effect on heart rate and blood pressure in awake rats. Rats were implanted with indwelling arterial and venous cannulas to obtain serial blood samples, record arterial pressure, and administer drug. CVT-3619 decreased FFA levels in a dose-dependent manner at doses from 1 up to 10 mg/kg. The FFA-lowering effect was blocked by the A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine. Triglyceride (TG) levels were also significantly reduced by CVT-3619 treatment in the absence and presence of Triton. Tachyphylaxis of the antilipolytic effect of CVT-3619 (1 mg/kg i.v. bolus) was not observed with three consecutive treatments. An acute reduction of FFA by CVT-3619 was not followed by a rebound increase of FFA as seen with nicotinic acid. The potency of insulin to decrease lipolysis was increased 4-fold (p < 0.01) in the presence of CVT-3619 (0.5 mg/kg). In summary, CVT-3619 is an orally bioavailable A1 agonist that lowers circulating FFA and TG levels by inhibiting lipolysis. CVT-3619 has antilipolytic effects at doses that do not elicit cardiovascular effects.

Ranolazine Increases β-Cell Survival and Improves Glucose Homeostasis in Low-Dose Streptozotocin-Induced Diabetes in Mice

In addition to its anti-ischemic and antianginal effects, ranolazine has been shown to lower hemoglobin A1c (HbA1c) in patients with coronary artery disease and diabetes. The present study was undertaken to test the hypothesis that ranolazine lowers HbA1c because of improved glucose homeostasis in an animal model. Diabetes in mice was induced by giving multiple low doses of streptozotocin. Ranolazine was given twice daily via an oral gavage (20 mg/kg) for 8 weeks. Fasting plasma glucose levels were significantly lower in the ranolazine-treated group (187 ± 19 mg/dl) compared with the vehicle group (273 ± 23 mg/dl) at 8 weeks. HbA1c was 5.8 ± 0.4% in the vehicle group and 4.5 ± 0.2% in the ranolazine-treated group (p < 0.05). Glucose disposal during the oral glucose tolerance test (OGTT) and insulin tolerance test were not different between the two groups; however, during OGTT, peak insulin levels were significantly (p < 0.05) higher in ranolazine-treated mice. Mice treated with ranolazine had healthier islet morphology and significantly (p < 0.01) higher β-cell mass (69 ± 2% per islet) than the vehicle group (50 ± 5% per islet) as determined from hematoxylin and eosin staining. The number of apoptotic cells was significantly (p < 0.05) less in the pancreas of the ranolazine-treated group (14 ± 2% per islet) compared with the vehicle group (24 ± 4% per islet). In addition, ranolazine increased glucose-stimulated insulin secretion in rat and human islets in a glucose-dependent manner. These data suggest that ranolazine may be a novel antidiabetic agent that causes β-cell preservation and enhances insulin secretion in a glucose-dependent manner in diabetic mice.

Ranolazine as a Cardioplegia Additive Improves Recovery of Diastolic Function in Isolated Rat Hearts

Background— Ranolazine (Ran), an antianginal agent, inhibits late Na+ current. The purpose of this study was to determine whether there was an added benefit of adding Ran to cardioplegia (CP) in a model of global ischemia/reperfusion. Methods and Results— Isolated rat hearts were Langendorff-perfused and exposed to 40-minute normothermic, cardioplegic global ischemia and 30 minutes of reperfusion. Before ischemia and during reperfusion, hearts were treated with no drug (control) or with the late Na+ current inhibitors Ran (5 &mgr;mol/L) or tetrodotoxin (1 &mgr;mol/L). Ischemic cardioplegic arrest led to an increase of left ventricular end-diastolic pressure (LVEDP) by ≥20 mm Hg (ie, cardiac contracture). Ten out of 11 hearts treated with CP alone developed contracture, whereas 6 out of 11 hearts treated with CP plus Ran developed contracture. Ran added to CP reduced LVEDP at the end of ischemia from 41±5 mm Hg in CP alone to 26±3 mm Hg in CP plus Ran (P=0.024). Area under the curve for LVEDP during the entire ischemic period was also smaller in CP plus Ran versus CP alone. The percent increase (from baseline) of LVEDP measured at the end of 30-minute reperfusion was smaller for CP plus Ran (66±18%) versus CP alone (287±90%; P=0.035). The area under the curve for LVEDP during reperfusion was smaller in CP plus Ran versus CP alone. Tetrodotoxin (1 &mgr;mol/L) also reduced cardiac contracture during ischemia/reperfusion, compared to CP alone. Conclusions— Our results suggest that Ran may have therapeutic potential as an adjunct to CP and further support a protective role of Na+ current inhibition during ischemia/reperfusion.

A Novel Partial Agonist of the A1 -Adenosine Receptor and Evidence of Receptor Homogeneity in Adipocytes

This study characterizes the receptor binding and functional effects of CVT-3619 [2-{6-[((1R,2R)-2-hydroxycyclopentyl)-amino]purin-9-yl}(4S,5S,2R,3R)-5-[(2-fluorophenylthio)methyl]-oxolane-3,4-diol], a novel N6-5′ -substituted adenosine analog and A1 -adenosine receptor (A AdoR) agonist, on rat epididymal and inguinal adipocytes and on the isolated heart and compares these effects with those caused by the full agonist N6 -cyclopentyladenosine (CPA). In addition, the hypothesis that adipocyte A1AdoR are a heterogeneous population with regard to their affinities for ligands was tested. CVT-3619 was 10–100-fold selective for A1AdoR versus other AdoR and bound to adipocyte membranes with high (KH = 14 nM) and low (K = 5.4 μM) affinities. CVT-3619 reduced cyclic AMP content and release of nonesterified fatty acids from epididymal adipocytes with IC50 values of 6 and 44 nM, respectively. CVT-3619 was a partial agonist relative to CPA to reduce lipolysis in epididymal and inguinal adipocytes. CVT-3619 did not change atrial rate in rat heart and caused a small (6-ms) prolongation of the stimu-lus-to-His bundle interval without causing atrioventricular block in guinea pig heart (effects mediated by A1AdoR), whereas CPA caused atrioventricular block and near cessation of atrial electrical activity. CVT-3619 increased coronary conductance (effect mediated by A2AAdoR) only at concentrations ≥10 μM. Rat epididymal adipocyte A1AdoR had similar affinities for the antagonist 8-cyclopentyl-1,3-dipropylxanthine in the presence of three dissimilar A AdoR agonists (2-chloro-N6 -cyclopentyladenosine, N6 -sulfophenyladenosine, and N-5′ -ethylcarboxamidoadenosine) as determined by Schild analysis. It was concluded that rat epididymal adipocyte A1AdoR are a homogeneous receptor population with regard to affinities for ligands and that CVT-3619 is a partial agonist with selectivity for A1AdoR and inhibition of lipolysis.

Blockade of Na+ Channels in Pancreatic α-Cells Has Antidiabetic Effects

Pancreatic α-cells express voltage-gated Na+ channels (NaChs), which support the generation of electrical activity leading to an increase in intracellular calcium, and cause exocytosis of glucagon. Ranolazine, a NaCh blocker, is approved for treatment of angina. In addition to its antianginal effects, ranolazine has been shown to reduce HbA1c levels in patients with type 2 diabetes mellitus and coronary artery disease; however, the mechanism behind its antidiabetic effect has been unclear. We tested the hypothesis that ranolazine exerts its antidiabetic effects by inhibiting glucagon release via blockade of NaChs in the pancreatic α-cells. Our data show that ranolazine, via blockade of NaChs in pancreatic α-cells, inhibits their electrical activity and reduces glucagon release. We found that glucagon release in human pancreatic islets is mediated by the Nav1.3 isoform. In animal models of diabetes, ranolazine and a more selective NaCh blocker (GS-458967) lowered postprandial and basal glucagon levels, which were associated with a reduction in hyperglycemia, confirming that glucose-lowering effects of ranolazine are due to the blockade of NaChs. This mechanism of action is unique in that no other approved antidiabetic drugs act via this mechanism, and raises the prospect that selective Nav1.3 blockers may constitute a novel approach for the treatment of diabetes.