New anti-ischaemic drugs: cytoprotective action with no primary haemodynamic effects

Trimetazidine-induced enhancement of myocardial recovery during reperfusion: a comparative study in diabetic and non-diabetic rat hearts

BACKGROUND

Diabetes mellitus (DM) is a major predisposing factor for ischemic heart disease. Metabolic disturbances in diabetic heart including impaired myocardial glucose uptake and elevated plasma free fatty acids and increased rate of fatty acid beta-oxidation are probably important contributing factors to greater mortality. Trimetazidine (TMZ), a well-studied anti-ischemic agent, has been demonstrated to be beneficial in treatment of coronary artery disease as well as in treatment of diabetic patients. However, studies reporting the effects of the drug against global myocardial ischemia/reperfusion injury, particularly in diabetic hearts, are rare. This study was mainly aimed to investigate the cardioprotective action of TMZ against global ischemia in diabetic hearts and to compare its protective efficiency level with non-diabetics.

METHODS

Twenty streptozotocin-induced diabetic and 20 non-diabetic rats were divided into two groups each. Group I (diabetic, n = 10) and group III (non-diabetic, n = 10) rats were given saline in both pretreatment and acute treatment protocols and reserved as control groups. Group II (diabetic, n = 10) and group IV (non-diabetic, n = 10) rats were both pretreated orally with 3 mg/kg TMZ twice daily for 5 days and treated with TMZ infusion at a concentration of 10(-6) M for 30 min during the experiment. Isolated hearts from each rat were submitted to Langendorff perfusion and a period of 60 min of global ischemia following 60 min of reperfusion. Myocardial post-ischemic recovery was compared in each group using hemodynamic data (peak systolic pressure, end diastolic pressure, +dP/dt(max)), coronary flow, biochemical parameters (CK-MB, cTnT) from coronary effluent, and obtained data were statistically analyzed by both MANOVA and two-sample Hotelling's T2 tests.

RESULTS

Both hemodynamic and biochemical findings signaled a significantly enhanced myocardial recovery provided by TMZ treatment in diabetic and non-diabetic hearts as compared to non-treated hearts. Although efficiency level of TMZ on mechanical recovery was not different between diabetics and non-diabetics, the protective action of TMZ on myocardial damage measured by biochemical parameters was more evident in diabetic hearts than in non-diabetics.

CONCLUSIONS

Shifting myocardial energy metabolism away from fatty acids toward glucose oxidation and regulating transmembrane ion disturbances by TMZ can be considered as an appropriate adjunctive treatment in diabetics, especially in patients undergoing open-heart surgery who will be exposed to global myocardial ischemia.

Novel inhibitors of fatty acid oxidation as potential metabolic modulators

We describe the synthesis of novel inhibitors of fatty acid oxidation as potential metabolic modulators for the treatment of stable angina. Replacement of the 2H-benzo[d]1,3-dioxolene ring system in our initial lead 3 with different benzthiazoles, benzoxazoles and introducing small alkyl substituents into the piperazine ring resulted in analogues with enhanced inhibitory activity against 1-(14)[C]-palmitoyl-CoA oxidation in isolated rat heart mitochondria (6, IC(50)=70 nM; 25, IC(50)=23 nM).

Metabolic modulation and optimization of energy consumption in heart failure

Chronic heart failure (CHF) is a common and disabling syndrome with a poor prognosis. It is a major and increasing public health problem. Angiotensin-converting enzyme inhibitors, diuretics, and digitalis are the standards treatments for CHF. Other drugs, such as beta-blockers, spironolactone, calcium antagonists, vasodilators, and antiarrhythmic agents are used to counteract the progression of the syndrome or to improve the hemodynamic profile. Despite optimum treatment with neurohumoral antagonists, prognosis of CHF remains poor; the patients complain of persistent reductions in their exercise capacity and quality of life. Fatigue and shortness of breath, two common and disabling symptoms in patient with CHF, are relatively independent from hemodynamic and neuroendocrine changes, although they seem to be related to the impairment of peripheral muscle metabolism and energetic phosphate production. Therefore, CHF is a complex metabolic syndrome in which the metabolism of cardiac and peripheral muscles is impaired and novel therapeutic strategies have been aimed at positive modulation with compounds such as carnitine, trimetazidine, and ranolazine.

Synthesis and biological evaluation of new 4-arylpiperidines and 4-aryl-4-piperidinols: dual Na(+) and Ca(2+) channel blockers with reduced affinity for dopamine D(2) receptors

A series of novel 4-arylpiperidines and 4-aryl-4-piperidinols (2a-f, 3a-f and 4a-f) was synthesized and evaluated for blocking effects on both neuronal Na(+) and T-type Ca(2+) channels and binding affinity for dopamine D(2) receptors. Most of the compounds blockaded both ion channels with potency greater than or equal to flunarizine 1a which was adopted as a reference standard. In addition, these compounds had significantly reduced affinity for dopamine D(2) receptors which is common in this class of structure. Compounds 2a-f, 3a-f and 4a-f exhibited potent anticonvulsant effects following systemic (ip) administration on audiogenic seizures in DBA/2 mice, indicating their excellent brain permeability. The neuroprotective activity of 2a, 3a and 4a was also assessed in a transient middle cerebral artery occlusion (MCAO) model. These compounds significantly reduced neuronal damage without affecting ischemic hyperthemia, while flunarizine 1a produced only minor reductions. In particular, 4a had 1.7-fold the potency in this MCAO model but only 1/20 the affinity for dopamine D(2) receptors of 1a. The superposition of 2a, 3a and 4a on the basis of analyses of systematic conformation and similar structure has revealed that the cinnamyl, phenacyl and phenoxypropanol groups are likely to be structurally and biologically equivalent. Moreover, the superposition of 2a and 2f shows that diphenyl ether and biphenyl groups occupy a similar space, suggesting that both groups act as a bioisostere for the blockade of ion channels; however, this is not the case for dopamine D(2) receptors since only biphenyl compounds such as 2f had high affinity similar to flunarizine 1a. Compound 4a (SUN N5030) has a good pharmacological profile and may be useful in the alleviation and treatment of ischemic diseases.

A novel class of Na+ and Ca2+ channel dual blockers with highly potent anti-ischemic effects

A series of novel arylpiperidines (4a-d) which have highly potent blocking effects for both neuronal Na+ and T-type Ca2+ channels with extremely low affinity for dopamine D2 receptors were synthesized. Among these compounds, 1-(2-hydroxy-3-phenoxy)propyl-4-(4-phenoxyphenyl)-piperidine hydrochloride (4c; SUN N5030) exhibited remarkable neuroprotective activity in a transient middle cerebral artery occlusion (MCAO) model.

Ranolazine: a novel metabolic modulator for the treatment of angina

1. Ranolazine shifts ATP production away from fatty acid oxidation toward glucose oxidation. 2. Because more oxygen is required to phosphorylate a given amount of ATP during fatty acid oxidation than during carbohydrate oxidation, the ranolazine-induced shift in substrate selection reduces the cell's demand for oxygen without decreasing its ability to do work. The shift also maintains coupling of glycolysis to glucose oxidation during ischemia, thus reducing tissue acidosis. 3. This unique, non-hemodynamic mechanism offers the potential to treat angina without reducing blood pressure, heart rate or myocardial contractility. 4. At least three double-blind, randomized, placebo-controlled clinical trials have yielded data consistent with this hypothesis.

Focal cerebral ischemia in the mouse: hypothermia and rapid screening of drugs

1. We have investigated the ability of several compounds to diminish both infarct area and volume induced by middle cerebral artery occlusion in the mouse. 2. Lifarizine, ipsapirone and N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl (DPPE) all reduced both infarct area and volume. Ifenprodil diminished the infarct area, but the effect on total infarct volume was much less pronounced. 3. In addition, we tested the protective effects of some other drugs on infarct area only. Nimodipine, verapamil, diltiazem, N-[1-[4-(4-fluorophenoxy)butyl]-4-piperidinyl]-N-methyl-2-benzothiazo lamine (R56865) and sabeluzole had no effect on infarct area. (S)-Emopamil significantly diminished infarct area. 2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) also diminished infarct area significantly. 4. In some brain ischemia models hypothermia protects against ischemic damage. Mild hypothermia had no effect on infarct area in the present mouse model of focal ischemia.

Long-term therapy with trimetazidine in cardiomyopathic Syrian hamster BIO 14:6

The cardiomyopathic Syrian hamster (CMH) of the strain BIO 14:6 is a model for both cardiac and skeletal muscle abnormalities. It has reduced longevity and noticeable hypertrophy of the heart and liver. At 220 days, CMHs display a total Ca2+ overload, 1.3-1.8-fold normal and a cytosolic Ca2+ concentration 2-4-fold higher than normal. Long-term oral treatment (18 mg/kg per day) with trimetazidine (anti-ischaemic drug), from age 30 to 350 days, was more efficient than the standard Ca2+ blocker verapamil. Trimetazidine increased the median survival time of CMH by 57% and the hypertrophy disappeared. The total Ca2+ level in CMHs reverted to that of normal Syrian hamsters (F1B). The cytosolic Ca2+ overload was limited to a factor of approximately 2. Therefore, trimetazidine possesses anti-Ca2+ properties and is effective in increasing survival and decreasing the heart and liver hypertrophy of CMH. This suggests that trimetazidine may be valuable in the prevention of congestive heart failure of similar aetiology.

Protection of rat myocardium by mitogenic and non-mitogenic fibroblast growth factor during post-ischemic reperfusion

The effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) and a non mitogenic form of FGF1 on myocardial ischemia and reperfusion were assessed. Rats underwent 10 minutes of coronary artery occlusion followed by 24 hours of reperfusion. Creatinine kinase content of the affected myocardium showed that both fibroblast growth factors 1 and 2 effectively protected against ischemia reperfusion injury (p < 0.01), and that the vasoactive but nonmitogenic form of the FGF1 was equally protective (p < 0.01 versus control + vehicle). The results were confirmed by light and electron-microscopy histological studies. Histological evaluations after treatment with the non-mitogenic fibroblast growth factor 1 showed that it did not generate the severe hyperplasia and connective tissue disorganization observed with the native mitogenic proteins. The possibility of using a non-mitogenic form of fibroblast growth factor for cardio-protection circumvents many of the potentially undesirable effects that may derive from systemically introducing broad spectrum acting fibroblast growth factors in vivo. This myocardial protection observed 24 hours after the treatment with fibroblast growth factors, and the efficacy of the non-mitogenic form of the protein, also suggest that the protective effect of fibroblast growth factors may be due to the increased blood flow rather than to angiogenesis.

Ranolazine stimulates glucose oxidation in normoxic, ischemic, and reperfused ischemic rat hearts

BACKGROUND

Ranolazine is a novel antianginal agent that may reduce symptoms without affecting hemodynamics and has shown cardiac antiischemic effects in in vivo and in vitro models. In one study it increased active pyruvate dehydrogenase (PDHa). Other agents that increase PDHa and so increase glucose and decrease fatty acid (FA) oxidation are beneficial in ischemic-reperfused hearts. Effects of ranolazine on glucose and palmitate oxidation and glycolysis were assessed in isolated rat hearts.

METHODS AND RESULTS

Working hearts were perfused with Krebs-Henseleit buffer plus 3% albumin under normoxic conditions and on reperfusion after 30-minute no-flow ischemia and under conditions designed to give either low [low (Ca) (1.25 mmol/L), high [FA] (1.2 mmol/L palmitate; with/without insulin] or high (2.5 mmol/L Ca, 0.4 mmol/L palmitate; with/without pacing) glucose oxidation rates; Langendorff-perfused hearts (high Ca, low FA) were subjected to varying degrees of low-flow ischemia. Glycolysis and glucose oxidation were measured with the use of [5-3H/U-14C]-glucose and FA oxidation with the use of [1-14C]- or [9,10-3H]-palmitate. In working hearts, 10 micromol/L ranolazine significantly increased glucose oxidation 1.5-fold to 3-fold under conditions in which the contribution of glucose to overall ATP production was low (low Ca, high FA, with insulin), high (high Ca, low Fa, with pacing), or intermediate. In some cases, reductions in FA oxidation were seen. No substantial changes in glycolysis were noted with/without ranolazine; rates were approximately 10-fold glucose oxidation rates, suggesting that pyruvate supply was not limiting. Insulin increased basal glucose oxidation and glycolysis but did not alter ranolazine responses. In normoxic Langendorff hearts (high Ca, low FA; 15 mL/min), all basal rates were lower compared with working hearts, but 10 micromol/L ranolazine similarly increased glucose oxidation; ranolazine also significantly increased it during flow reduction to 7, 3, and 0.5 mL/min. Ranolazine did not affect baseline contractile or hemodynamic parameters or O2 use. In reperfused ischemic working hearts, ranolazine significantly improved functional outcome, which was associated with significant increases in glucose oxidation, a reversal of the increased FA oxidation seen in control reperfusions (versus preischemic), and a smaller but significant increase in glycolysis.

CONCLUSIONS

Beneficial effects of ranolazine in cardiac ischemia/reperfusion may be due, at least in part, to a stimulation of glucose oxidation and a reduction in FA oxidation, allowing improved ATP/O2 and reduction in the buildup of H+, lactate, and harmful fatty acyl intermediates.

Alzheimer's disease: fundamental and therapeutic aspects

Alzheimer's disease is the most common type of progressive and debilitating dementia affecting aged people. In some early--as well as late--onset familial cases, a genetic linkage with chromosomes 14, 21 (early-onset) or 19 (late-onset) has been indicated. Furthermore, a direct or indirect role has been attributed to normal or structurally altered amyloid beta-protein (concentrated in senile plaques) and/or excessively phosphorylated tau protein (located in neurofibrillary tangles). Degeneration of cholinergic neurons and concomitant impairment of cortical and hippocampal neurotransmission lead to cognitive and memory deficits. Several compounds are being tested in attempts to prevent and/or cure Alzheimer's disease, including tacrine, which has very modest efficacy in a sub-group of patients, and new acetylcholinesterase inhibitors. Pilot experiments have also been launched using nerve growth factor (NGF) to prevent or stabilize the processes of cholinergic pathway degeneration. Alternatively, antioxidants, free radical scavengers and/or non steroidal anti-inflammatory agents may be screened as potential therapies for neurodegenerative diseases induced by multiple endogenous and/or exogenous factors. The recent use of transgenic mice, in parallel with other genetic, biochemical and neurobiological systems, in vivo and/or in vitro (cell cultures), should accelerate the discovery and development of specific drugs for the treatment of Alzheimer's disease.

Trimetazidine: a new concept in the treatment of angina. Comparison with propranolol in patients with stable angina. Trimetazidine European Multicenter Study Group

1. Trimetazidine has a direct anti-ischaemic effect on the myocardium without altering the rate x pressure product or coronary blood flow. 2. The effects of trimetazidine (20 mg three times daily) were compared with those of propranolol (40 mg three times daily) in a double-blind parallel group multicentre study in 149 men with stable angina. 3. Reproducibility of exercise performance was verified during a 3 week run-in placebo washout period. All patients had > 1 mm ST-depression on exercise test. 4. After 3 months, similar anti-anginal efficacy was observed between the trimetazidine (n = 71) and propranolol (n = 78) groups. No significant differences were observed between trimetazidine and propranolol as regards anginal attack rate per week (mean difference P-TMZ: 2; 95% CI: -4.4, 0.5) and exercise duration (mean difference P-TMZ: 0 s; 95% CI: -33, 34) or time to 1 mm ST segment depression (mean difference P-TMZ: 13 s; 95% CI: -24, 51). Heart rate and rate x pressure product at rest and at peak exercise remained unchanged in the trimetazidine group but significantly decreased with propranolol (P < 0.001 in all cases). With both drugs there was a trend to decreased ischaemic episodes in the 46% patients who experienced ambulatory ischaemia on Holter monitoring. Six patients stopped trimetazidine and 12 propranolol. Of these, five in each group were withdrawn because of deterioration in cardiovascular status. 5. The results suggest that trimetazidine and propranolol at the doses studied have similar efficacy in patients with stable angina pectoris.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of felbamate and other compounds on N-methyl-D-aspartic acid-induced convulsions and lethality in mice

Felbamate and selected compounds were evaluated for their ability to protect against N-methyl-D-aspartic acid (NMDA)-induced convulsions and lethality in mice. Convulsions produced by intracerebroventricular administration of NMDA (0.8 micrograms per mouse) were antagonized by felbamate, phenytoin, carbamazepine, phenobarbital, valproate, diazepam, 2-amino-5-phosphonovalergic acid (APV), dextromethorphan and ketamine. NMDA (350 mg kg-1 intraperitoneally) produced 100% lethality in mice. Felbamate, phenytoin, and phenobarbital were ineffective in preventing NMDA-induced lethalities, whereas diazepam, APV, ketamine and dextromethorphan were the most potent compounds in preventing lethalities. Any relationship between the protective effects of felbamate against NMDA-induced seizures and competitive or non-competitive antagonism of NMDA receptor sites, however, cannot be established until further experimentation is carried out.

R56865 and flunarizine as Na(+)-channel blockers in isolated Purkinje neurons of rat cerebellum

Dose-related blocking effects of R56865, flunarizine and nimodipine on voltage-activated Na+ currents recorded in the whole-cell voltage clamp mode were studied in acutely isolated Purkinje neurons of rat cerebellum. The dose-dependences of blocking action were obtained for all drugs at a holding potential of -110 mV and rare stimulation. At stimulation frequencies 5 and 15 Hz the block produced by R56865 was increased showing a shift of dose-dependence to lower concentrations of antagonist. This shift was less pronounced for flunarizine, practically absent for nimodipine, and increased for all drugs with an increase in the amplitude of stimulating voltage pulse. With the change in holding potential to -80 mV the block produced by R56865 and flunarizine increased showing a dose-dependence shift to lower concentrations of antagonists. All the drugs tested induced parallel shifts of the steady-state voltage-dependence of inactivation of Na+ channels to more negative membrane potentials. R56865, and to a lesser extent flunarizine, slowed down the recovery of Na+ channels from steady-state inactivation increasing the relative number of channels which showed slow recovery. In the absence of Na+ current inactivation (treatment by intracellular pronase) R56865 at a concentration of 1 microM blocked modified channels preferentially in the open state, while the block produced by flunarizine showed no dependence on voltage pulse protocol. R56865 was shown to decrease the cell leakage while other drugs produced little or no effect. It is concluded that R56865 and flunarizine block Na+ currents predominantly by interacting with inactivated Na+ channels. The higher ability of R56865 to block open channels and to increase slow inactivation underlies its higher frequency-dependence. These characteristics suggest the use of R56865 and flunarizine in the treatment of cerebral ischemia.

Lactate accumulation in isolated hypoxic rat ventricular myocardium: effect of different modulators of the cyclic GMP system

Different agents which are known to increase tissue levels of cyclic guanosine 3':5'-monophosphate (cGMP), were found to decrease the lactate accumulation induced by hypoxia in isolated, non-beating rat myocardium from the right ventricle. One microM sodium nitroprusside increased the intracellular cGMP content 4 times during hypoxic conditions, and after 5 min. of hypoxia the intracellular lactate accumulation decreased by about 20%. 0.1 microM atrial natriuretic peptide increased cGMP 10 times during hypoxic conditions and decreased the lactate accumulation by about 40%. The reduction in lactate accumulation was mimicked by 1 mM 8-Br-cGMP and by Zaprinast (10 microM), a selective inhibitor of cGMP phosphodiesterase, which reduced lactate accumulation by 60% and 45%, respectively. Glyceryl trinitrate (1 nM and 1 microM) caused a slight increase in lactate accumulation both during normooxic and hypoxic conditions, but had no effect on tissue levels of cGMP. In conclusion, the results indicate that cyclic GMP reduces lactate accumulation in hypoxic, non-beating rat heart ventricular muscle and suggests that atrial natriuretic peptide, which is released from atrial tissue, may have beneficial metabolic effects on the heart.

Evolution of free radical formation during low-flow ischemia and reperfusion in isolated rat heart

Free radicals have been implicated in several aspects of cellular injury, both during ischemia and reperfusion of the myocardium. In this study, formation of free radicals in the isolated rat heart was measured a) directly using electron paramagnetic resonance (EPR) spectroscopy and b) indirectly using the generation of thiobarbituric acid reactants as an index of lipid peroxidation. EPR spectra of frozen heart powder recorded at 100 degrees K show several lines and consist of different components separated by temperature studies: signal C disappears after warming the sample 1 minute at 190 degrees K and is suggestive of a triplet signal g = 2.001, aN = 25 Gauss; signal B g parallel = 2.034, g perpendicular = 2.007, disappears after 1 min at 240 degrees K, and is similar to those previously reported for oxygen alkylperoxyl free radical; the remaining signal, signal A with g = 2.004 is identical to that of a carbon-centered ubiquinone free radical. The total free radical concentration in isolated rat heart perfused at a constant flow rate of 12 ml/min was increased by 44% compared with control (p less than 0.05) after 10 minutes of normothermic global ischemia with a 10% residual flow, and by only 31% compared with control after 20 seconds of reflow with oxygenated perfusate (p less than 0.05). Compared with the reperfused group, trimetazidine 10(-5) M administered 15 minutes before the ischemic period decreased the free radical concentration (-20%). However, this free radical generation in heart was not associated with a concomitant increase of lipid peroxides.