Reduction of lipid peroxidation in reperfused isolated rabbit hearts by diltiazem

Therapeutic Potential of Heterocyclic Compounds Targeting Mitochondrial Calcium Homeostasis and Signaling in Alzheimer's Disease and Parkinson's Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases in the elderly. The key histopathological features of these diseases are the presence of abnormal protein aggregates and the progressive and irreversible loss of neurons in specific brain regions. The exact mechanisms underlying the etiopathogenesis of AD or PD remain unknown, but there is extensive evidence indicating that excessive generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), along with a depleted antioxidant system, mitochondrial dysfunction, and intracellular Ca²⁺ dyshomeostasis, plays a vital role in the pathophysiology of these neurological disorders. Due to an improvement in life expectancy, the incidence of age-related neurodegenerative diseases has significantly increased. However, there is no effective protective treatment or therapy available but rather only very limited palliative treatment. Therefore, there is an urgent need for the development of preventive strategies and disease-modifying therapies to treat AD/PD. Because dysregulated Ca²⁺ metabolism drives oxidative damage and neuropathology in these diseases, the identification or development of compounds capable of restoring Ca²⁺ homeostasis and signaling may provide a neuroprotective avenue for the treatment of neurodegenerative diseases. In addition, a set of strategies to control mitochondrial Ca²⁺ homeostasis and signaling has been reported, including decreased Ca²⁺ uptake through voltage-operated Ca²⁺ channels (VOCCs). In this article, we review the modulatory effects of several heterocyclic compounds on Ca²⁺ homeostasis and trafficking, as well as their ability to regulate compromised mitochondrial function and associated free-radical production during the onset and progression of AD or PD. This comprehensive review also describes the chemical synthesis of the heterocycles and summarizes the clinical trial outcomes.

Mitochondrial Effects of Common Cardiovascular Medications: The Good, the Bad and the Mixed

Mitochondria are central organelles in the homeostasis of the cardiovascular system via the integration of several physiological processes, such as ATP generation via oxidative phosphorylation, synthesis/exchange of metabolites, calcium sequestration, reactive oxygen species (ROS) production/buffering and control of cellular survival/death. Mitochondrial impairment has been widely recognized as a central pathomechanism of almost all cardiovascular diseases, rendering these organelles important therapeutic targets. Mitochondrial dysfunction has been reported to occur in the setting of drug-induced toxicity in several tissues and organs, including the heart. Members of the drug classes currently used in the therapeutics of cardiovascular pathologies have been reported to both support and undermine mitochondrial function. For the latter case, mitochondrial toxicity is the consequence of drug interference (direct or off-target effects) with mitochondrial respiration/energy conversion, DNA replication, ROS production and detoxification, cell death signaling and mitochondrial dynamics. The present narrative review aims to summarize the beneficial and deleterious mitochondrial effects of common cardiovascular medications as described in various experimental models and identify those for which evidence for both types of effects is available in the literature.

The Neuroprotective and Anti-inflammatory Effects of Diltiazem in Spinal Cord Ischaemia–Reperfusion Injury

The protective effects of diltiazem were examined in a rabbit model of spinal cord ischaemia–reperfusion induced by infrarenal aortic occlusion for 30 min. In the diltiazem group ( n = 6), an intravenous infusion (2 μg/kg per min) was started 10 min before ischaemia induction; normal saline solution was infused in the control group ( n = 6). Neurological function was assessed using modified Tarlov criteria 24 h after surgery. Plasma samples were analysed for interleukin (IL)-6 and IL-10. Spinal tissue was analysed for malondialdehyde, nitric oxide and reduced glutathione activities. Tarlov scores of the diltiazem-treated rabbits indicated significantly improved hind-limb motor function compared with the control group. The diltiazem group also had better quantitative and qualitative histopathological findings. Diltiazem infusion significantly reduced IL-6 levels 3 and 24 h after reperfusion compared with the control group. The mean IL-10 level in the diltiazem group was significantly higher than in the control group 24 h after reperfusion. It is concluded that diltiazem has cytoprotective and anti-inflammatory properties, leading to reduced spinal cord injury.

Myocardial protection in man--from research concept to clinical practice

Myocardial protection aims at preventing myocardial tissue loss: (a) In the acute stage, i.e., during primary angioplasty in acute myocardial infarction. In this setup, the attenuation of reperfusion injury is the main target. As a "mechanical" means, post-conditioning has already been tried in man with encouraging results. Pharmacologic interventions that could be of promise are statins, insulin, peptide hormones, including erythropoietin, fibroblast growth factor, and many others. (b) The patient with chronic coronary artery disease offers another paradigm, with the target of avoidance of further myocyte loss through apoptosis and inflammation. Various pharmacologic agents may prove useful in this context, together with exercise and "mechanical" improvement of cardiac function with attenuation of myocardial stretch, which by itself is a noxious influence. A continuous effort toward acute and chronically preserving myocardial integrity is a concept concerning both the researcher and the clinician.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

The vascular endothelium of the coronary arteries has been identified as the important organ that locally regulates coronary perfusion and cardiac function by paracrine secretion of nitric oxide (NO) and vasoactive peptides. NO is constitutively produced in endothelial cells by endothelial nitric oxide synthase (eNOS). NO derived from this enzyme exerts important biological functions including vasodilatation, scavenging of superoxide and inhibition of platelet aggregation. Routine cardiac surgery or cardiologic interventions lead to a serious temporary or persistent disturbance in NO homeostasis. The clinical consequences are "endothelial dysfunction", leading to "myocardial dysfunction": no- or low-reflow phenomenon and temporary reduction of myocardial pump function. Uncoupling of eNOS (one electron transfer to molecular oxygen, the second substrate of eNOS) during ischemia-reperfusion due to diminished availability of L-arginine and/or tetrahydrobiopterin is even discussed as one major source of superoxide formation. Therefore maintenance of normal NO homeostasis seems to be an important factor protecting from ischemia/reperfusion (I/R) injury. Both, the clinical situations of cardioplegic arrest as well as hypothermic cardioplegic storage are followed by reperfusion. However, the presently used cardioplegic solutions to arrest and/or store the heart, thereby reducing myocardial oxygen consumption and metabolism, are designed to preserve myocytes mainly and not endothelial cells. This review will focus on possible drug additives to cardioplegia, which may help to maintain normal NO homeostasis after I/R.

Protection of Swiss albino mice against whole-body gamma irradiation by diltiazem

The aim of the present study was to evaluate the radioprotective effect of diltiazem (DTZ) on Swiss albino mice exposed to gamma radiation. In the present study, radioprotective efficacy of DTZ (a calcium channel blocker) was studied against radiation induced haematological and biochemical alterations. Swiss albino mice of 6-8 weeks old were administered diltiazem (100 mg kg(-1) by weight) intraperitoneally prior to whole body gamma-irradiation (7.5 Gy). Radiation exposure resulted in a significant decline in different bone marrow cells (pro- and normoblasts) and blood constituents (erythrocytes, leukocytes, differential leukocyte count, haematocrit, haemoglobin and erythrocyte sedimentation rate). Pro- and normoblasts, erythrocytes, leukocytes, haematocrit and haemoglobin values showed a significant (p<0.0051) decline until day 3, following a gradual recovery from day 7, but normal values were not recorded until 28 days post-exposure. In contrast, erythropoietin levels increased significantly and reached a maximum on day 3. In DTZ pre-treated irradiated animals, a significant increase in pro- and normoblasts, erythrocytes, leukocytes, differential leukocyte count, haematocrit and haemoglobin values, and a significant decrease in erythropoietin values, were observed compared with control. A significant elevation above normal in lipid peroxidation level was recorded in gamma irradiated mice, whereas this increase was considerably less in DTZ pre-treated animals. Similarly, pre-treatment of DTZ caused a significant increase in erythropoietin and glutathione levels in serum in comparison with irradiated animals. From our study it is clear that DTZ provides protection against radiation-induced haematological and biochemical alterations in Swiss albino mice.

Diltiazem during reperfusion preserves high energy phosphates by protection of mitochondrial integrity

OBJECTIVE

This study evaluates the effects of diltiazem administered during reperfusion on hemodynamic, metabolic, and ultrastructural postischemic outcome.

METHODS

Hearts of 38 adult White New Zealand rabbits underwent 60 min of global cold ischemia followed by 40 min of reperfusion in an erythrocyte perfused isolated working heart model. Hearts were randomly assigned to four groups and received diltiazem (0.1, 0.25, and 0.5 micromol/l) during reperfusion only, or served as control.

RESULTS

The postischemic time courses of heart rate, aortic flow, and external stroke work clearly reflected the dose-dependent negative chronotropic and inotropic efficacy of diltiazem in the two higher concentrations. High energy phosphates (HEP) determined from myocardial biopsies taken after 40 min of reperfusion were significantly better preserved in all treatment groups compared to control hearts. Similarly ultrastructural grading of mitochondria and myofilaments revealed a significant reduction of reperfusion injury in hearts that received diltiazem compared to control.

CONCLUSIONS

Diltiazem protects mitochondrial integrity and function, thereby preserving myocardial HEP levels. Only low dose diltiazem (0.1 micromol/l) during reperfusion combines both, optimal mitochondrial preservation with minimal changes in hemodynamics.

Role of oxidative stress in cardiovascular diseases

OBJECTIVES

In view of the critical role of intracellular Ca2 overload in the genesis of myocyte dysfunction and the ability of reactive oxygen species (ROS) to induce the intracellular Ca2+-overload, this article is concerned with analysis of the existing literature with respect to the role of oxidative stress in different types of cardiovascular diseases.

OBSERVATIONS

Oxidative stress in cardiac and vascular myocytes describes the injury caused to cells resulting from increased formation of ROS and/or decreased antioxidant reserve. The increase in the generation of ROS seems to be due to impaired mitochondrial reduction of molecular oxygen, secretion of ROS by white blood cells, endothelial dysfunction, auto-oxidation of catecholamines, as well as exposure to radiation or air pollution. On the other hand, depression in the antioxidant reserve, which serves as a defense mechanism in cardiac and vascular myocytes, appears to be due to the exhaustion and/or changes in gene expression. The deleterious effects of ROS are mainly due to abilities of ROS to produce changes in subcellular organelles, and induce intracellular Ca2+-overload. Although the cause-effect relationship of oxidative stress with any of the cardiovascular diseases still remains to be established, increased formation of ROS indicating the presence of oxidative stress has been observed in a wide variety of experimental and clinical conditions. Furthermore, antioxidant therapy has been shown to exert beneficial effects in hypertension, atherosclerosis, ischemic heart disease, cardiomyopathies and congestive heart failure.

CONCLUSIONS

The existing evidence support the view that oxidative stress may play a crucial role in cardiac and vascular abnormalities in different types of cardiovascular diseases and that the antioxidant therapy may prove beneficial in combating these problems.

Inhibition of Na+ channel or Na+/H+ exchanger attenuates the hydrogen peroxide-induced derangements in isolated perfused rat heart

The effect of tetrodotoxin, a specific inhibitor of the Na+ channel, and 5-(N,N-dimethyl)-amiloride, a specific inhibitor of the Na+/H+ exchanger, on the mechanical and metabolic derangements induced by hydrogen peroxide (H2O2) was studied in the isolated perfused rat heart. The isolated rat heart was perfused aerobically at a constant flow rate and driven electrically. H2O2 (600 microM) decreased the left ventricular developed pressure and increased the left ventricular end-diastolic pressure (i.e. mechanical dysfunction), decreased the tissue levels of adenosine triphosphate and adenosine diphosphate (i.e. metabolic derangement), and increased the tissue level of malondialdehyde (i.e. lipid peroxidation). These mechanical and metabolic derangements induced by H2O2 were significantly attenuated by tetrodotoxin (3 microM) or 5-(N,N-dimethyl)-amiloride (15 microM). Neither tetrodotoxin nor 5-(N,N-dimethyl)-amiloride modified the tissue malondialdehyde level, which was increased by H2O2. In the normal (H2O2-untreated) heart, neither tetrodotoxin nor 5-(N,N-dimethyl)-amiloride affected the mechanical function and energy metabolism. These results suggested that inhibition of the Na+ channel or Na+/H+ exchanger was effective in attenuating the H2O2-induced mechanical dysfunction and metabolic derangements in the isolated perfused rat heart.

Lipid peroxidation and alterations to oxidative metabolism in mitochondria isolated from rat heart subjected to ischemia and reperfusion

Ischemia-reperfusion injury to cardiac myocytes involves membrane damage mediated by oxygen free radicals. Lipid peroxidation is considered a major mechanism of oxygen free radical toxicity in reperfused heart. Mitochondrial respiration is an important source of these reactive oxygen species and hence a potential contributor to reperfusion injury. We have examined the effects of ischemia (30 min) and ischemia followed by reperfusion (15 min) of rat hearts, on the kinetic parameters of cytochrome c oxidase, on the respiratory activities and on the phospholipid composition in isolated mitochondria. Mitochondrial content of malonyldialdheyde (MDA), an index of lipid peroxidation, was also measured. Reperfusion was accompanied by a significant increase in MDA production. Mitochondrial preparations from control, ischemic and reperfused rat heart had equivalent Km values for cytochrome c, although the maximal activity of the oxidase was 25 and 51% less in ischemic and reperfused mitochondria than that of controls. These changes in the cytochrome c oxidase activity were associated to parallel changes in state 3 mitochondrial respiration. The cytochrome aa3 content was practically the same in these three types of mitochondria. Alterations were found in the mitochondrial content of the major phospholipid classes, the most pronounced change occurring in the cardiolipin, the level that decreased by 28 and by 50% as function of ischemia and reperfusion, respectively. The lower cytochrome c oxidase activity in mitochondria from reperfused rat hearts could be almost completely restored to the level of control hearts by exogenously added cardiolipin, but not by other phospholipids nor by peroxidized cardiolipin. It is proposed that the reperfusion-induced decline in the mitochondrial cytochrome c oxidase activity can be ascribed, at least in part, to a loss of cardiolipin content, due to peroxidative attack of its unsaturated fatty acids by oxygen free radicals. These findings may provide an explanation for some of the factors that lead to myocardial reperfusion injury.

Protective effect of prazosin on the hydrogen peroxide-induced derangements in the isolated perfused rat heart

The effect of prazosin, an alpha1-selective adrenoceptor antagonist, on the hydrogen peroxide (H2O2)-induced mechanical and metabolic derangements was studied in the isolated rat heart, which was perfused aerobically by the Langendorffs technique at a constant flow rate and driven electrically. H2O2 (600 microM) produced both mechanical dysfunction (e.g., increase in the left ventricular end-diastolic pressure) and metabolic damage (e.g., decrease in the level of adenosine triphosphate) associated with lipid peroxidation (e.g., increase in the level of malondialdehyde). The H2O2-induced mechanical and metabolic derangements were attenuated by 2.5, 5, or 10 microM prazosin, and the increase in the level of malondialdehyde was attenuated by 5 or 10 microM prazosin. Nevertheless, prazosin had practically no effects on the mechanical function and energy metabolism of the H2O2-untreated normal heart at 2.5 or 5 microM, although it reduced the mechanical function at 10 microM. Prazosin was shown to have a hydroxyl radical scavenging effect. These results suggest that prazosin attenuates the H2O2-induced mechanical and metabolic derangements probably because of attenuation of the H2O2-induced lipid peroxidation in the heart.

Protective effects of ranolazine, a novel anti-ischemic drug, on the hydrogen peroxide-induced derangements in isolated, perfused rat heart: comparison with dichloroacetate

The effect of ranolazine, a novel anti-ischemic drug that stimulates the activity of pyruvate dehydrogenase, on hydrogen peroxide (H2O2)-induced mechanical and metabolic derangements was studied in isolated rat heart and compared with that of dichloroacetate (DCA), an activator of pyruvate dehydrogenase. The heart was perfused aerobically by the Langendorff's technique at a constant flow and driven electrically. H2O2 (600 microM) decreased the left ventricular developed pressure and increased the left ventricular end-diastolic pressure (i.e., mechanical dysfunction), decreased the tissue level of adenosine triphosphate (i.e., metabolic derangement), and increased the tissue level of malondialdehyde (MDA) (i.e., lipid peroxidation). These mechanical and metabolic derangements induced by H2O2 were significantly attenuated by ranolazine (10 or 20 microM). On the other hand, DCA (1 mM) was ineffective in attenuating the H2O2-induced mechanical and metabolic derangements. Ranolazine, however, did not modify the tissue MDA level, which was increased by H2O2. In the normal (H2O2-untreated) heart, ranolazine did not alter the mechanical function and energy metabolism. These results demonstrate that ranolazine attenuates mechanical and metabolic derangements induced by H2O2. It is suggested that the protective action of ranolazine against the H2O2-induced derangements is due to neither the energy-sparing, DCA-like, nor anti-oxidant effects.

Propofol improves functional and metabolic recovery in ischemic reperfused isolated rat hearts

Propofol attenuates mechanical dysfunction, metabolic derangement, and lipid peroxidation by exogenous administration of H2O2 in the Langendorff rat heart. In this study, we examined the effects of propofol on mechanical and metabolic changes, as well as on lipid peroxidation induced by ischemia-reperfusion, in isolated, working rat hearts. Rat hearts (in control-modified Krebs-Henseleit bicarbonate buffer) were treated with two doses (25 microM and 50 microM) of propofol in an intralipid vehicle. In the first protocol, propofol was administered during the preischemic and reperfusion period, whereas in the second, it was only administered during the reperfusion period. Ischemia (15 min) decreased peak aortic pressure (PAOP), heart rate (HR), rate-pressure product (RPP), coronary flow (CF), and tissue concentrations of adenosine triphosphate (ATP) and creatine phosphate. After postischemic reperfusion (20 min), the CF and tissue concentration of ATP recovered incompletely; however, PAOP, HR, and RPP did not. Ischemia-reperfusion also increased the tissue concentration of malondialdehyde (MDA). In both protocols, both doses of propofol enhanced recovery of PAOP, HR, RPP, CF, and tissue concentration of ATP during reperfusion, and inhibited the tissue accumulation of MDA. These results indicate that propofol improves recovery of mechanical function and the energy state in ischemic reperfused isolated rat hearts, and the mechanism may involve the reduction of lipid peroxidation during postischemic reperfusion.

IMPLICATIONS

We evaluated the possible cardioprotective effects of propofol in isolated, working rat hearts subjected to 15-min ischemia, followed by 20-min reperfusion. We observed that propofol attenuated mechanical dysfunction, metabolic derangement, and lipid peroxidation during reperfusion. This latter finding seems to be one mechanism for cardioprotective effects of propofol.

Cardiac reperfusion injury: aging, lipid peroxidation, and mitochondrial dysfunction

Cardiac reperfusion and aging are associated with increased rates of mitochondrial free radical production. Mitochondria are therefore a likely site of reperfusion-induced oxidative damage, the severity of which may increase with age. 4-Hydroxy-2-nonenal (HNE), a major product of lipid peroxidation, increases in concentration upon reperfusion of ischemic cardiac tissue, can react with and inactivate enzymes, and inhibits mitochondrial respiration in vitro. HNE modification of mitochondrial protein(s) might, therefore, be expected to occur during reperfusion and result in loss in mitochondrial function. In addition, this process may be more prevalent in aged animals. To begin to test this hypothesis, hearts from 8- and 24-month-old rats were perfused in Langendorff fashion and subjected to periods of ischemia and/or reperfusion. The rate of state 3 respiration of mitochondria isolated from hearts exposed to ischemia (25 min) was approximately 25% less than that of controls, independent of age. Reperfusion (40 min) caused a further decline in the rate of state 3 respiration in hearts isolated from 24- but not 8-month-old rats. Furthermore, HNE modification of mitochondrial protein (approximately 30 and 44 kDa) occurred only during reperfusion of hearts from 24-month-old rats. Thus, HNE-modified protein was present in only those mitochondria exhibiting reperfusion-induced declines in function. These studies therefore identify mitochondria as a subcellular target of reperfusion damage and a site of age-related increases in susceptibility to injury.

Sarcoplasmic reticulum Ca(2+)-pump dysfunction in rat cardiomyocytes briefly exposed to hydroxyl radicals

The effects of hydroxyl radical exposure of intact cardiomyocytes on sarcoplasmic reticulum (SR) function were investigated. For this purpose, isolated rat heart myocytes were exposed briefly (1 min) to the hydroxyl radical generating system (H2O2/FeCl2 or FeSO4) or 5-5'-dithiobis-nitrobenzoic acid (DTNB), a sulfhydryl oxidizing reagent, and following this a SR-enriched fraction was isolated. Marked decreases in the SR calcium uptake activities were seen in the myocytes exposed to either the hydroxyl radical-generating system or DTNB. The exposure of myocytes to the hydroxyl radical, but not DTNB, markedly increased the amount of malonyldialdehyde (MDA) in the subsequently isolated SR. Total sulfhydryl group content in SR was decreased by exposure of myocytes to DTNB. Further, there was a significant decrease in [3H]-NEM binding to SR isolated from the hydoxyl radical-treated myocytes indicating that sulfhydryl groups are affected (oxidized). Both mannitol and catalase were found to offer complete protection against the inhibitory effect of peroxide +/- iron on calcium uptake. Also the above-mentioned alterations in both MDA and sulfhydryl group content were prevented by mannitol and catalase. Exogenously added cyclic AMP-dependent protein kinase (A-PK) or calmodulin (CAM) increased SR calcium uptake activity. In the SR isolated from the treated myocytes, the stimulatory effects of A-PK and CAM were also seen, although under all assay conditions calcium uptakes were of lower magnitude. The findings are consistent with the view that the damaging effect of the hydroxyl radical and DTNB on the functioning of SR occurs rapidly in the intact cardiomyocytes. The hydroxyl radical-provoked damage involves both protein sulfhydryl and lipid oxidation.

Effect of MET-88, a gamma-butyrobetaine hydroxylase inhibitor, on myocardial derangements induced by hydrogen peroxide in the isolated perfused rat heart

The effect of MET-88 (3-(2,2,2-trimethylhydrazinium) propionate dihydrate), a gamma-butyrobetaine (gamma-BB) hydroxylase inhibitor, on the hydrogen peroxide (H2O2)-induced mechanical and metabolic derangements was studied in the isolated rat heart, which was perfused aerobically by the Langendorff's technique at a constant flow rate and driven electrically. In the first series of experiments, MET-88 (100 mg/kg/d) was orally administered to rats for 10 days prior to isolation of the heart. In the second series of experiments, MET-88 or gamma-BB was directly infused to the isolated perfused heart. In both series of experiments, H2O2 (600 microM) decreased the left ventricular developed pressure (mechanical dysfunction) and the tissue levels of high-energy phosphates (metabolic derangement). In the first series of experiments, oral pretreatment with MET-88 attenuated the H2O2-induced metabolic derangement with a marked increase in the myocardial level of gamma-BB, while it did not attenuate the H2O2-induced mechanical dysfunction. In the second series of experiments, MET-88 (1 mM) did not attenuate the H2O2-induced metabolic derangement, whereas gamma-BB (500 microM or 1 mM) attenuated it. Nevertheless, gamma-BB did not modify the energy metabolism of H2O2-untreated heart (normal heart). These results suggest that oral pretreatment with MET-88 protects the energy metabolism against the H2O2-induced derangement and that the beneficial effect of the oral pretreatment with MET-88 may be mediated by gamma-BB that has accumulated in the myocardium because of inhibition of gamma-BB hydroxylase.

Calcium-channel blockers inhibit human low-density lipoprotein oxidation by oxygen radicals

Previous studies have shown that calcium channel blockers may reduce the development of experimental atherosclerosis, and that nifedipine may slow the progression of coronary atherosclerosis in humans. The mechanisms responsible for this antiatherogenic effect are still unclear. It has been recently proposed that oxygen free radicals can induce the oxidation of human low-density lipoproteins (LDL) and that oxidized LDL may be an atherogenic stimulus. Previous studies in other systems have shown that calcium channel blockers may effectively inhibit oxygen radical-induced lipid peroxidation in vitro. Thus, the aim of the present study was to investigate whether calcium channel blockers may also reduce LDL modifications induced by oxygen radicals. Isolated human LDL were exposed to oxygen radicals generated by CuSO4 (10 microM for 18 hours) after a 30 minute pre-incubation with different concentrations (1-100 microM) of nifedipine, diltiazem, and verapamil. Lipid peroxidation was measured from malonyldihaldehyde (MDA) production. Oxygen radical-induced damage on apolipoprotein-B100 was evaluated by acrylamide and agarose gel electrophoresis. Calcium channel blockers dose-dependently prevented oxidation of both the lipid and protein components of LDL. MDA formation was reduced in LDL pre-incubated with calcium antagonists before exposure to oxygen radicals (% MDA inhibition was 89.8 +/- 6.9 with 30 microM nifedipine, 68.6 +/- 4.9 with 30 microM verapamil, and 65.6 +/- 7.1 with 30 microM diltiazem; p < 0.01 vs. controls). Similarly, apolipoprotein-B100 integrity was preserved against oxygen radical attack in the presence of calcium antagonists. Thus, calcium channel blockers reduce the oxidation of human LDL in vitro. These data suggest that reduced formation of atherogenic oxidized LDL may be an additional mechanism for the antiatherosclerotic effects of calcium channel blockers in vivo.

Beneficial effects of felodipine on myocardial and coronary function during low-flow ischemia and reperfusion

An acute coronary occlusion causes severe low-flow ischemia in the occluded region. Calcium antagonists have the potential to reduce the rate of ischemic injury by decreasing myocardial oxygen demand, as well as by other mechanisms, especially when given prior to the onset of ischemia. However, their clinical use may be limited by their negative inotropic effects. The purpose of this study was to assess the effects of felodipine as a potentially protective agent against myocardial ischemia and reperfusion injury, independent of any negative inotropic actions, when given after the onset of low-flow ischemia. Isolated isovolumic (balloon-in-LV), blood-perfused rabbit hearts, paced at a constant heart rate, were subjected to 90 minutes of low-flow ischemia at a coronary perfusion pressure of 10 mmHg, which reduced coronary blood flow to 22-24% of baseline. After 15 minutes of low-flow ischemia, hearts received 2 x 10(-6) M felodipine (n = 7) or no drug (controls, n = 8). Felodipine was given until 15 minutes of reperfusion. During low-flow ischemia both groups of hearts had identical coronary blood flow, heart rate, left ventricular (LV) developed pressure, lactate production, and O2 consumption. However, felodipine markedly protected against ischemic diastolic dysfunction. At the end of low-flow ischemia, LV end-diastolic pressure (LVEDP) had increased from 10 +/- 1 to 28 +/- 5 mmHg in the felodipine group, while in the controls LVEDP increased to 48 +/- 8 mmHg (p < 0.05). During 30 minutes of reperfusion, felodipine had a beneficial effect upon coronary blood flow (initial postischemic hyperemia 245 +/- 38% of baseline in the felodipine group vs. 124 +/- 18% in the controls; p < 0.01) Felodipine markedly improved the recovery of contractile function [LV developed pressure recovered from a baseline of 104 +/- 4 to 75 +/- 6 mmHg (72%) in the felodipine group vs. 34 +/- 10 mmHg (32%) in the control group; p < 0.01], as well as diastolic function (LVEDP = 25 +/- 4 mmHg in the felodipine group vs. 61 +/- 10 mmHg in the controls; p < 0.05), and ATP levels (8.5 +/- 1.4 mumoles/g d.w. in the felodipine group vs. 3.9 +/- 1.4 mumoles/g d.w. in the control group, p < 0.05). Felodipine, given after the onset of low-flow ischemia, protects the myocardium during both ischemia and reperfusion by mechanisms other than reducing myocardial oxygen demand.

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.

Stunned myocardium and the attenuation of stunning by calcium antagonists

Myocardial "stunning" is characterized by a reversible postischemic contractile dysfunction despite full restoration of blood flow. The underlying mechanisms are not clearly understood. Inadequate energy supply and impaired sympathetic neurotransmission may have been excluded. Potential mechanisms, which are not mutually exclusive, may include damage to membranes and enzymes by free radicals, an increase in free cytosolic calcium during ischemia and reperfusion, and a lower calcium sensitivity of myofibrils. The equally pronounced increases in regional contractility in normal and stunned myocardium during postextrasystolic potentiation and the infusion of calcium or the calcium-sensitizing agent AR-L-57, however, suggest an unchanged calcium sensitivity in reperfused myocardium. Pretreatment with calcium antagonists before ischemia attenuates myocardial stunning. This effect is probably related to a lessened myocardial calcium overload during early ischemia. The potential benefit of treatment with calcium antagonists after reperfusion is established remains controversial.

Lipid peroxidation in open-heart surgery

Production of oxygen free radicals and subsequent lipid peroxidation are thought to occur during cardiopulmonary bypass (CPB) and myocardial ischaemia-reperfusion injury. Malondialdehyde (MDA), a lipid peroxidation product, was measured simultaneously in arterial and coronary sinus blood before CPB and after release of the aortic crossclamp. Additional arterial samples were drawn pre-, per-, and postoperatively. Thirteen patients scheduled for coronary artery and/or valvular surgery were studied. Cold, crystalloid, cardioplegic arrest (54 [35-120] minutes, median [range]) was induced retrogradely. Preoperatively, arterial MDA was 0.78 +/- 0.4 (mean +/- SD) mumol/l, and increased during CPB (highest level 3.66 +/- 1.08 mumol/l, p < 0.002, 30 minutes after the start of reperfusion). Arterial MDA was still increased four hours after the end of CPB (3.17 +/- 0.88 mumol/l, p < 0.003), but had returned to normal the first postoperative day. No difference was found between arterial and coronary sinus samples at any time. In conclusion, MDA increased in arterial blood during CPB, indicating that lipid peroxidation occurred. There was no intracoronary release of MDA during reperfusion of the ischaemic heart.

The effect of verapamil and diltiazem on alveolar type II cells during warm and cold metabolic ischaemia

The alteration of cytosolic free calcium concentration is an important event during cellular ischaemia. Calcium channel blockers have been shown to be beneficial during experimental ischaemic organ protection. To investigate the mechanisms of this protection, the behaviour of type II pneumocyte cultures, subjected to warm and cold metabolic ischaemia (6 h), was studied. The cells were incubated in electrolytic solutions and treated with high doses of verapamil (10 mg/l) or diltiazem (100 mg/l). Alveolar type II epithelial cells were removed from adult rat lungs using the modified Dobbs' method. Cell viability was determined by analysis of the total protein content, and from the rate of protein synthesis as indicated by the [35S]methionine uptake assay. The results show that verapamil does not have a direct cytoprotective or cytotoxic effect on the incubated cells, but diltiazem seems to be toxic to the cells, especially during cold ischaemia when the toxicity is significant (P < 0.05). Thus, the protection from ischaemia previously attributed to calcium channel blockers is ascribed to action on the blood vessels resulting in vasodilatation, rather than to a direct influence on cytosolic free calcium homeostasis.

Acyloin production from aldehydes in the perfused rat heart: the potential role of pyruvate dehydrogenase

Aldehydes represent an important class of cytotoxic products derived from free radical-induced lipid peroxidation which may contribute to reperfusion injury following myocardial infarct. Metabolism of aldehydes in the heart has not been well characterized aside from conjugation of unsaturated aldehydes with glutathione. However, aliphatic aldehydes like hexanal do not form stable glutathione conjugates. We have recently demonstrated in vitro that pig heart pyruvate dehydrogenase catalyses a reaction between pyruvate and saturated aldehydes to produce acyloins (3-hydroxyalkan-2-ones). In the present study, rat hearts were perfused with various aldehydes and pyruvate. Acyloins were generated from saturated aldehydes (butanal, hexanal or nonanal), but not from 2-hexanal (an unsaturated aldehyde) or malondialdehyde. Hearts perfused with 2 mM pyruvate and 10-100 microM hexanal rapidly took up hexanal in a dose-related manner (140-850 nmol/min), and released 3-hydroxyoctan-2-one (0.7-30 nmol/min), 2,3-octanediol (0-12 nmol/min) and hexanol (10-200 nmol/min). Small quantities of hexanoic acid (about 10 nmol/min) were also released. The rate of release of acyloin metabolites rose with increased concentration of hexanal, whereas hexanol release attained a plateau when hexanal infusion concentrations rose above 50 microM. Up to 50% of hexanal uptake could be accounted for by metabolite release. Less than 0.5% of hexanal uptake was found to be bound to acid-precipitable macromolecules. When hearts perfused with 50 microM hexanal and 2 mM pyruvate were subjected to a 15 min ischaemic period, the rates of release of 2,3-octanediol, 3-hydroxyoctan-2-one, hexanol and hexanoate during the reperfusion period were not significantly different from those in the pre-ischaemic period. Our results indicate that saturated aldehydes can be metabolically converted by the heart into stable diffusible compounds.

Effect of iron overload in the isolated ischemic and reperfused rat heart

It has been suggested that iron might play a pivotal role in the development of reperfusion-induced cellular injury through the activation of oxygen free radical producing reactions. The present study examined the effects of myocardial iron overload on cardiac vulnerability to ischemia and reperfusion. Moreover, the effect of the iron chelator deferoxamine in reversing ischemia-reperfusion injury was studied. Animals were treated with iron dextran solution (i.m. injection, 25 mg every third day during a 5 week period). The control group received the same treatment without iron. Isolated rat hearts were perfused at constant flow (11 ml/min) and subjected to a 15 minute period of global normothermic ischemia followed by reperfusion for 15 minutes. The effects of iron overload were investigated using functional and biochemical parameters, as well as ultrastructural characteristics of the ischemic-reperfused myocardium compared with placebo values. The results suggest that (a) a significant iron overload was obtained in plasma and hepatic and cardiac tissues (x2.5, x16, and x8, respectively) after chronic intramuscular administration of iron dextran (25 mg); (b) during normoxia, iron overload was associated with a slight reduction in cardiac function and an increase in lactate dehydrogenase (LDH) release (x1.5); (c) upon reperfusion, functional recovery was similar whether the heart had been subjected to iron overload or not. However, in the control group left ventricular end-diastolic pressure remained higher than in preischemic conditions, an effect that was not observed in the iron-overloaded group. Moreover, LDH release was markedly increased in the iron-loaded group (x4.2); (d) iron overload was associated with a significant worsening of the structural alterations observed during reperfusion, particularly at the mitochondrial and sarcomere level; (e) after 15 minutes of reperfusion, the activity of the anti-free-radical enzyme, glutathione peroxidase (GPX), was significantly reduced in iron-overloaded hearts, whereas catalase activity was increased; (e) the overall modifications observed in the presence of iron overload were prevented by deferoxamine. In conclusion, this study underlines the possible role of cardiac iron in the development of injury associated with ischemia and reperfusion, and the possible importance of the use of an iron-chelating agent in anti-ischemic therapy.

The effect of hypochlorous acid and hydrogen peroxide on coronary flow and arrhythmogenesis in myocardial ischemia and reperfusion

The purpose of this study was to investigate the effect of the oxidants hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) on the vulnerability of the myocardium to reperfusion-induced arrhythmias following global ischemia. After a 15 min equilibration period with or without experimental intervention, isolated perfused rat hearts in the Langendorff mode were made globally ischemic for 5 min by cross-clamping the aortic line. No dysrhythmias were evoked upon reperfusion at the 5 min global ischemia time period. HOCl or H2O2 were added to the perfusate 5 min into the equilibration period with a total exposure of 10 min. Global ischemia was then induced for 5 min followed by 10 min of reperfusion. A dose-response curve for HOCl (50-200 microM) indicated the development of idioventricular rhythms, in a concentration-dependent way. Furthermore, coronary flow of the hearts exposed to 100 and 200 microM HOCl, at 5 min post-reperfusion, was decreased; methionine (10 microM to 1 mM), an accepted scavenger for HOCl, prevented the responses to 200 microM HOCl, in a concentration-dependent manner. All hearts exposed to 200 microM H2O2 developed ventricular dysrhythmias during the reperfusion period. Coronary flow increased after 5 min of exposure to 200 microM H2O2 and remained elevated during reperfusion. It is concluded that toxic oxygen derived products are capable of increasing the susceptibility of the myocardium to reperfusion induced arrhythmias, and that although the electrical responses to exposure to those two oxidants were similar, the effects on the vasculature were not the same.

Calcium and stunned myocardium

Calcium administration during ischemia or at the onset of reperfusion is generally considered to be deleterious because cytosolic calcium is elevated at this time. In contrast, the administration of calcium antagonists before or during ischemia is protective. While calcium antagonists may not be beneficial when given after reperfusion, calcium administration during this period has been found to enhance the recovery of systolic and diastolic function of stunned myocardium.

Calcium antagonists protect mice against lethal doses of ionizing radiation

Currently available radioprotectors are poorly tolerated in man and the general use of aminothiol radioprotectors is compromised by their side-effects. In a search for less toxic radioprotective agents, diltiazem, a calcium antagonist with a benzothiazepine structure, was found to protect mice against a lethal (LD100) gamma radiation dose allowing survival of up to 93%. Dihydropyridine calcium antagonists such as nifedipine, nimodipine, isradipine and nitrendipine also provided radioprotection. Calcium antagonists might attenuate radiation-induced injury by inhibiting cellular calcium overload, subsequent to cell membrane damage caused by radiation-generated free radicals. In view of their good tolerance, calcium antagonists may be applied safely in situations of radiation exposure, including radiotherapy and internal radionuclide contamination. These calcium antagonists may also be viewed in other contexts where free radicals are implicated in pathological processes.

Use of intravenous diltiazem in patients with acute coronary artery disease

The use of calcium antagonists for the treatment of patients with unstable angina and acute myocardial infarction has been a promising area of both basic and clinical research. Despite consistently beneficial effects experimentally, the clinical extrapolation of these results has been less than ideal, especially in patients with evolving myocardial infarction. Calcium antagonists have in some instances failed to manifest benefit and at times have been shown to have negative effects. One reason for this could be the use of oral or sublingual preparations, which result in variable absorption, variable volumes of distribution, and variable clearance. For this reason, an intravenous preparation of one of the calcium antagonists, diltiazem, may be more beneficial. Such a preparation has been developed and its safety confirmed in patients without cardiovascular disease and in patients with acute infarction. Substantial benefit has been documented in patients with stable angina and during noncardiac surgery. Preliminary data in patients with unstable angina suggest that the drug is effective, although studies comparing intravenous diltiazem with other agents or with the oral preparation of diltiazem have not yet been reported. Experimental data in animals with acute infarction have demonstrated that administration of intravenous diltiazem after occlusion, but prior to reperfusion, elicits a marked increase in the degree of myocardial salvage induced by thrombolysis. This appears to be due to the inhibition of lipid peroxidation rather than alterations in coronary perfusion. Thus, it appears that the intravenous preparation may permit the more effective use of diltiazem in patients with acute coronary artery disease.

Maintenance of left ventricular function (90%) after twenty-four-hour heart preservation with deferoxamine

During 24-h in vitro heart preservation and reperfusion, irreversible tissue damage occurs caused by reactive oxygen intermediates, such as superoxide radicals, singlet oxygen, hydrogen peroxide, hydroperoxyl, hydroxyl radicals, as well as the peroxynitrite radical. Reduction of the related oxidative damage of reperfused ischemic tissue by free radical scavengers and metal chelators is of primary importance in maintaining heart function. We assessed whether deferoxamine (DFR) added to a cardioplegia solution decreased free radical formation during 24-h cold (5 degrees C) heart preservation and normothermic reperfusion (37 degrees C) in the Langendorff isolated perfused rat heart. The deferoxamine treated hearts were significantly (p less than .001) better preserved than the control hearts after 24 h of preservation with regard to recovery of left ventricular diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), creatine kinase release, and lipid peroxidation. DFR preserved cell membrane integrity and maintained 93% of left ventricular contractility. The evidence suggests that DFR reduces lipid peroxidation damage by reducing free radical formation and thereby maintaining normal coronary perfusion flow and myocardial function.

Impairment by cyclosporin A of reperfusion-induced arrhythmias

This study introduces the immunosuppressor, cyclosporin A, as a cardioprotective drug. This effect was analyzed during development of reperfusion/induced arrhythmias after 5-min period of coronary ligation in hearts of rats under anesthesia. The results indicate that cyclosporin, when given before coronary occlusion, at a dose of 20 mg/kg, effectively protects against the high incidence of arrhythmias and the fall in blood pressure induced by reperfusion. In addition, in inhibits the delivery of lactic dehydrogenase and creatine kinase enzymes to the plasma. We propose that the protective effect could be related with its well documented action to restrain Ca(2+)-induced damage of mitochondrial functions.

Calcium antagonists and stunned myocardium: importance for clinicians?

Experimental evidence indicates that calcium antagonists enhance the recovery of contractile function in canine myocardium stunned by a brief, 15-minute episode of transient coronary artery occlusion. In fact, both nifedipine and verapamil have been shown to improve systolic contraction, even when treatment was delayed, that is, when the agents were administered 30 minutes after reperfusion. The beneficial effects of delayed treatment were not a consequence of myocardial high-energy phosphate preservation. Furthermore, as low-dose intracoronary nifedipine enhanced the recovery of function in the absence of systemic hemodynamic or coronary vasodilatory effects, the improved function associated with delayed administration of calcium antagonists could not be attributed solely to afterload reduction or increased coronary blood flow. These data suggest that calcium-channel blockers exert a direct effect on the previously ischemic tissue, perhaps by subtle modulation of calcium transport or flux within the stunned myocytes. Although the precise mechanism of action of these agents remain unresolved, these intriguing experimental results raise the possibility that calcium antagonists may provide a clinically useful means of attenuating postischemic dysfunction of viable myocardium salvaged by thrombolysis, angioplasty, or cardiopulmonary bypass. The potential role of calcium-channel blockers in these clinical instances of stunned myocardium awaits further evaluation.

Oxygen radicals generated at reflow induce peroxidation of membrane lipids in reperfused hearts

To test whether generation of oxygen radicals during postischemic reperfusion might promote peroxidation of cardiac membrane lipids, four groups of Langendorff-perfused rabbit hearts were processed at the end of (a) control perfusion, (b) 30 min of total global ischemia at 37 degrees C without reperfusion, (c) 30 min of ischemia followed by reperfusion with standard perfusate, (d) 30 min of ischemia followed by reperfusion with the oxygen radical scavenger human recombinant superoxide dismutase (h-SOD). The left ventricle was homogenized and tissue content of malonyldialdehyde (MDA), an end product of lipid peroxidation, was measured on the whole homogenate as well as on various subcellular fractions. Reperfusion was accompanied by a significant increase in MDA content of the whole homogenate and of the fraction enriched in mitochondria and lysosomes. This phenomenon was not observed in hearts subjected to ischemia but not reperfused, and was similarly absent in those hearts which received h-SOD at reflow. Reperfused hearts also had significantly greater levels of conjugated dienes (another marker of lipid peroxidation) in the mitochondrial-lysosomal fraction. Again, this phenomenon did not occur in ischemic hearts or in reperfused hearts treated with h-SOD. Unlike the effect on tissue MDA and conjugated dienes, reperfusion did not significantly stimulate release of MDA in the cardiac effluent. Treatment with h-SOD was also associated with significant improvement in the recovery of cardiac function. In conclusion, these data directly demonstrate that postischemic reperfusion results in enhanced lipid peroxidation of cardiac membranes, which can be blocked by h-SOD, and therefore is most likely secondary to oxygen radical generation at reflow.