Comparison of N-methyl hexanoylhydroxamic acid, a novel antioxidant, with desferrioxamine and N-acetyl cysteine against reperfusion-induced dysfunctions in isolated rat heart

Effect of intravenous administration of antioxidants alone and in combination on myocardial reperfusion injury in an experimental pig model

BACKGROUND

Several antioxidants have been found to have conflicting results in attenuating myocardial reperfusion injury. These studies were done primarily in experimental protocols that did not approximate clinical situations.

OBJECTIVE

The aim of this study was to test the efficacy of 3 different antioxidants (ascorbic acid [AA], desferrioxamine, and N-acetylcysteine [NAC]) administered IV alone and in combination in a closed-chest pig model.

METHODS

Farm-raised domestic male pigs (aged 3-5 months, weight of 30-35 kg) were assigned to 1 of 5 groups to receive treatment as follows: group A, AA 100 mg/kg; group B, desferrioxamine 60 mg/kg; group C, a loading dose of NAC 100 mg/kg for 20 minutes and a 20-mg/kg maintenance dose; group D, all 3 drugs in combination; and group E, normal saline (control group). The infusion of all drugs was started 15 minutes before and completed 5 minutes after reperfusion, except for the administration of NAC, which was terminated 60 minutes postreperfusion. Myocardial ischemia (45 minutes) and reperfusion (210 minutes) were achieved percutaneously by circumflex artery balloon occlusion. Ejection fraction, left ventricular end-diastolic pressure (LVEDP), flow in the infarcted artery, and all ventricular arrhythmias were recorded. Oxidative stress was estimated by serial measurements of thiobarbituric acid reactive substance (TBARS) concentration in coronary sinus blood. Infarct size was assessed as a percentage of the area at risk (I/R ratio) using the tetrazolium red staining method.

RESULTS

The 25 pigs were divided into 5 groups of 5 pigs each. No significant between-group differences were found in I/R ratio or in oxidative stress (as measured by TBARS concentration). Group C developed significantly more ventricular atrhythmias than the control group (80% vs 0%, P = 0.02). No other differences among groups were found. LVEDP was significantly elevated in all treatment groups (mean LVEDP difference [SD] for group A, 6.0 [1.6] mm Hg; group B, 17.6 [1.9] mm Hg; group C, 3.6 [1.7] mm Hg; group D, 6.8 [3.2] and group E, 5.4 [3.4] mm Hg). LVEDP elevation was found to be significantly higher in group B compared with all the other groups (all, P < 0.001). No significant between-group differences were found in the other parameters measured.

CONCLUSION

In this experimental pig model, the antioxidants AA, desferrioxamine, and NAC administered alone or in combination did not reduce the deleterious effects of reperfusion injury and specifically the extent of myocardial necrosis.

Myocardial protection with the use of L-arginine and N-alpha-acetyl-histidine

OBJECTIVE

Effective myocardial preservation is an important condition for cardiac surgery, especially in heart transplantation with long ischemia times. During ischemia and reperfusion, myocardial function is altered by cold-induced ischemic injury. Cold-induced ischemic injury is triggered by cold storage and the amino acid histidine, a main component of the storage solution histidine-tryptophan-ketoglutarate (HTK). Cold-induced ischemic injury generates free oxygen radicals in an iron-dependent way. We investigated the efficacy of new modifications with the addition of L-arginine and N-alpha-acetyl-histidine to the well-established HTK solution (Custodiol) using a rat heart transplant model.

MATERIALS AND METHODS

Heterotopic transplantation was performed in Lewis rats (n = 20). After 1 hour of ischemic preservation and 1 hour of reperfusion, we assessed myocardial function and energy charge potential. The modifications of HTK solution included the addition of L-arginine, partial replacement of histidine with acetyl-histidine, and reduction of chloride concentration (HTK-1). In a second group, Custodiol served as the control.

RESULTS

After 1 hour of reperfusion, left ventricular systolic pressure (106 +/- 33 vs 69 +/- 9 mm Hg; P < .05) and minimum rate of pressure development (dP/dt) (-1388 +/- 627 vs -735 +/- 219 mm Hg/s; P < .05) were significantly higher among the HTK-1 group compared with the control group. Energy charge potential did not differ significantly between the groups.

CONCLUSION

This study showed that the novel modified HTK-1 solution improved myocardial contractility and relaxation after heart transplantation.

Endothelial dysfunction after long-term cold storage in HTK organ preservation solutions: effects of iron chelators and N-alpha-acetyl-L-histidine

BACKGROUND

To improve the rate of successful heart transplantations, organ preservation should be optimized in cardiac transplantation surgery. Iron-dependent oxidative damage and iron-independent, chloride-dependent injury of the endothelium have been described after cold ischemic storage and reperfusion, leading to an enhanced rate of complications and unfavorable outcomes. This screening study tested the effects of iron chelator supplementation in different histidine-tryptophan-ketoglutarate (HTK) organ preservation solutions on endothelial function in a long-term storage model of the isolated rat aorta.

METHODS

Isolated rat aortic rings underwent a 24-hour cold ischemic preservation in different HTK solutions supplemented with iron chelators of low (deferoxamine) and high (LK-614) membrane permeability. In vascular reactivity measurements we investigated the phenyleprine-induced contraction and both endothelium-dependent and -independent vasorelaxation by using cumulative concentrations of acetylcholine and sodium nitroprusside with and without an additional external oxidant injury during re-oxygenation.

RESULTS

Traditional HTK solution, Custodiol, failed to prevent endothelial dysfunction in our experiments. Use of chloride-poor HTK solutions containing N-alpha-acetyl-l-histidine with and without supplementation with LK-614, but not with deferoxamine, resulted in significant improvement of impaired endothelial function; moreover, complete protection of the endothelium was feasible after 24-hour cold storage. Endothelium-independent functions of vascular smooth muscle were not affected in any of the groups.

CONCLUSIONS

Our results demonstrate the important pathophysiologic role of iron-dependent oxidative injury in the development of endothelial dysfunction after cold storage, which can be prevented by cell-permeable iron chelators.

Cardioprotective effects of Ilex paraguariensis extract: evidence for a nitric oxide-dependent mechanism

AIM

To examine the effects of an Ilex paraguariensis (Ip) extract on postischemic alterations derived from 20 min of global ischemia and 30 min of reperfusion.

METHODS

Isolated rat hearts were treated 10 min before ischemia and the first 10 min of reperfusion with Ip 30 microg/ml. In other hearts, chelerythrine (1 microM), a protein kinase C blocker, or l(G)-nitro l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, were administered prior to Ip infusion. Left ventricular developed pressure (LVDP), +dP/dt(max), -dP/dt(max), and left ventricular end diastolic pressure (LVEDP) were used to assess myocardial function. Thiobarbituric acid reactive substances (TBARS) were measured.

RESULTS

Ip treatment produced an improvement of postichemic recovery (LVDP=96+/-8%; +dP/dt(max)=95+/-10%; -dP/dt(max)=90+/-12% vs. 57+/-6%, 53+/-6% and 57+/-8%, respectively, in untreated hearts) and an attenuation of the increase of LVEDP and TBARS content. Chelerythrine did not modify and l-NAME abolished the protection induced by Ip.

CONCLUSIONS

These data are the first demonstration that Ip extract attenuates the myocardial dysfunction provoked by ischemia and reperfusion and that this cardioprotection involves a diminution of oxidative damage through a nitric oxide-dependent mechanism.

Reactive oxygen species generated during myocardial ischemia enable energetic recovery during reperfusion

We studied the differences between the functional and bioenergetic effects of antioxidants (AOX) administered before or after myocardial ischemia. Sprague-Dawley rat hearts were perfused with a modified Krebs-Henseleit solution and bubbled with 95% O(2)-5% CO(2). The protocol consisted of 10 min of baseline perfusion, 20 min of global ischemia, and 30 min of reperfusion. An AOX, either 1,2-dihydroxybenzene-3,5-disulfonate (Tiron), a superoxide scavenger, or N-acetyl-L-cysteine, was infused during either baseline or reperfusion. An additional group received deferoxamine as a bolus before ischemia. Hearts were freeze-clamped at baseline, at end of ischemia, and at end of reperfusion for analysis of high-energy phosphates. All AOX, when given before ischemia, inhibited recovery of ATP compared with controls. Both Tiron and deferoxamine also inhibited recovery of phosphocreatine. AOX given before ischemia decreased the efficiency of contraction during reperfusion compared with controls. All of the changes in energetics and efficiency brought on by preischemic AOX treatment could be blocked by a preconditioning stimulus. This suggests that reactive oxygen species, which are generated during ischemia, enhance bioenergetic recovery by increasing the efficiency of contraction.

Time window of nitroxide effect on myocardial ischemic-reperfusion injury potentiated by iron

Transition metals such as iron and copper potentiate the postischemic reperfusion (I/R) injury induced by oxygen-derived radical and nonradical toxic species (ROS). Various natural and synthetic antioxidants have been previously tested to ameliorate such injury, yet the limitations of the common antioxidants are well known. An alternative strategy for combating oxidative damage is presented wherein cell-permeable, nitroxide stable radicals, which act as SOD-mimics and oxidize reduced metals thus prompting the Fenton-like chemistry, are investigated for utility in ameliorating I/R injury. Our study concentrates on the early effect of nitroxide on the myocardial I/R injury. Isolated rat hearts in the Langendorff configuration were equilibrated with Krebs-Henseleit buffer and then subjected to 18 min of normothermic global ischemia followed by 20 min reperfusion. Iron administered as Fe(III)-citrate (10 microM) did not affect the cardiac function under normoxia but did potentiate I/R injury and decreased the recovery during reperfusion. The iron-induced damage was manifested by further deterioration of the cardiac hemodynamic function and the energy status as reflected by decreased tissue level of phosphorylated nucleotides. Nitroxide at 200 microM protected against the iron-potentiated I/R injury by improving the recovery of the hemodynamic function and the cardiac energy status. Exogenously added iron requires bioreduction to form deleterious Fe(II) bound to critical cellular sites. The nitroxide, which enters the cell and oxidizes the reduced metal instantaneously, provided protection even when administered 2 or 3.5, but not 5 min, after the onset of reperfusion. Thus, its narrow therapeutic time window provides insight into the schedule of the I/R injurious process.

Dimerumic acid as an antioxidant from the mold, Monascus anka: the inhibition mechanisms against lipid peroxidation and hemeprotein-mediated oxidation

This study aimed to investigate the antioxidant mechanism of dimerumic acid isolated as the active component with a radical scavenging action from the mold Monascus anka, traditionally used for the fermentation of foods. Dimerumic acid inhibited NADPH- and iron(II)-dependent lipid peroxidation (LPO) of rat liver microsomes at 20 and 200 microM, respectively. When ferrylmyoglobin was incubated with dimerumic acid, the myoglobin was scavenged and an electron spin resonance (ESR) signal with nine peaks was observed. The spin adduct was identified as a nitroxide radical by analysis of hyperfine structure. Similar ESR signal was also detected by incubation of dimerumic acid with peroxyl radicals. Thus, it was clarified that the antioxidant action of dimerumic acid is due to one electron donation of the hydroxamic acid group in the dimerumic acid molecule toward oxidants resulting in formation of nitroxide radical.

Dimerumic acid as an antioxidant of the mold, Monascus anka

We previously reported that the mold Monascus anka, traditionally used for fermentation of food, showed antioxidant and hepatoprotective actions against chemically induced liver injuries. In the present study, the antioxidant component of M. anka was isolated and identified. The antioxidant was elucidated to be dimerumic acid. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical was significantly scavenged by the antioxidant whereas hydroxyl radical and superoxide anion were moderately scavenged. When the antioxidant (12 mg/kg) was given to mice prior to carbon tetrachloride (CCl(4), 20 microl/kg, ip) treatment, the CCl(4)-induced liver toxicity in mice seen in an elevation of serum aspartate aminotransferase and alanine aminotransferase activities was depressed, suggesting the hepatoprotective action of the antioxidant. The liver microsomal glutathione S-transferase activity, which is known to be activated by oxidative stress or active metabolites, was increased by CCl(4) treatment and the increase was also depressed by pretreatment with the mold antioxidant. Thus these data confirmed that the dimerumic acid isolated from M. anka is the potential antioxidant and protective against CCl(4)-induced liver injury.

Lack of a neuroprotective effect from N-acetylcysteine after cardiac arrest and resuscitation in a canine model

OBJECTIVE

Oxygen free radicals cause brain injury following resuscitation from cardiac arrest. In preclinical trials, some free radical scavenging drugs reduce oxidative neuronal damage after ischemia and reperfusion, but these drugs are generally not yet available for clinical testing or use. N-Acetylcysteine (NAC), a commonly used antidote in acetaminophen poisoning, is also a potent free radical scavenger that can ameliorate oxidative injury following ischemia and reperfusion in neuronal cell culture. We hypothesized that treatment with NAC would improve neurological outcome after cardiac arrest and resuscitation.

METHODS

In 16 adult female beagles, 10 min of ventricular fibrillation was followed by 3 min of open-chest CPR, and defibrillation. Immediately following return of spontaneous circulation, animals randomly received either 150 mg/kg NAC (3% solution) (n = 8) or an equivalent volume of normal saline (n = 8). Twenty-three hours later, neurological deficit was scored (0 = normal, 100 = brain death).

RESULTS

All animals were successfully resuscitated, and there were no apparent adverse effects to the administration of NAC in post resuscitative animals. There was, however, no significant difference in neurological deficit in the animals receiving NAC (40 +/- 12.9, mean +/- SD) compared to control animals (44 +/- 6.5, P = 0.73).

CONCLUSION

No neuroprotective effect was found from the administration of NAC at currently used clinical dosages, to dogs subjected to 10 min of global cerebral ischemia from cardiac arrest and resuscitation.

Novel monohydroxamate drugs attenuate myocardial reperfusion-induced arrhythmias

The novel monohydroxamates N-methyl hexanoylhydroxamic acid, N-methyl acetohydroxamic acid, and N-methyl butyrohydroxamic acid have antioxidant and iron chelating properties. They attenuated reperfusion-induced contractile dysfunction following long periods of ischaemia (50 min) in the isolated rat heart. Here we compare their effects and that of the trihydroxamate desferrioxamine on reperfusion-induced arrhythmias following short duration ischaemia (10 min). Isolated rat hearts were perfused by the Langendorff method, subjected to regional ischaemia and reperfusion. Arrhythmias induced during the first 5 min of reperfusion were quantified. Drugs (all at 150 microM) were introduced during the last 2 min of ischaemia and remained throughout reperfusion. Although the monohydroxamate- and desferrioxamine-treated hearts showed a reduction in the incidence of ventricular tachycardia and fibrillation, only the reduction in the incidence of sustained fibrillation ( > 3 min duration) in N-methyl acetohydroxamic acid--(27%), N-methyl hexanoylhydroxamic acid--(27%) and desferrioxamine-treated hearts (20%) was statistically significant (p < 0.05 vs control 73%; n = 15). There was a reduction in the severity of the arrhythmias, manifest as a significant increase in the duration of sinus rhythm in all the monohydroxamate-treated hearts, and a significant reduction (vs control 218 +/- 29 s; mean +/- SEM) in the duration of ventricular fibrillation in hearts treated with N-methyl acetohydroxamic acid (101 +/- 31 s) and desferrioxamine (112 +/- 30 s). This improvement was offset by an increase in the duration of ventricular tachycardia, in hearts treated with N-methyl acetohydroxamic acid, N-methyl butyrohydroxamic acid and desferrioxamine. These results suggest that these novel monohydroxamates, particularly N-methyl acetohydroxamic acid, attenuate reperfusion-induced arrhythmias in this model when introduced during the ischaemic period.

Effects of N-acetylcysteine in the rat heart reperfused after low-flow ischemia: evidence for a direct scavenging of hydroxyl radicals and a nitric oxide-dependent increase in coronary flow

The capacity of N-acetylcysteine to directly scavenge hydroxyl radical produced by rat hearts reperfused after 90 min of low-flow ischemia was assessed by the hydroxylation of 4-hydroxybenzoate into 3,4-dihydroxybenzoate using a gas chromatography-mass spectrometric assay. Reperfused hearts showed a massive release of 3,4-dihydroxybenzoate, lactate dehydrogenase, and total glutathione, contained less reduced and oxidized glutathione, but maintained spontaneous beating and coronary flow rates close to preischemic values. Compared to untreated hearts: reperfused hearts treated with N-acetylcysteine from the start of ischemia (i) released four times less 3,4-dihydroxybenzoate, but similar amounts of lactate dehydrogenase or glutathione, (ii) showed a nitric oxide-dependent increase in coronary flow rate, and (iii) contained less oxidized glutathione, but similar amounts of reduced glutathione. Reperfused hearts receiving N-acetylcysteine since the last 5 min of ischemia had also a four-times lower 3,4-dihydroxybenzoate release, but their coronary flow rate response was similar to that of untreated hearts. These results indicate that N-acetylcysteine can directly scavenge hydroxyl radicals produced by reperfused ischemic hearts, although this effect is not associated with any protective effects as indicated by the lactate dehydrogenase and glutathione release and cannot explain the nitric oxide-dependent reperfusion hyperemia.