Beneficial effects of N-acetylcysteine and cysteine in stunned myocardium in perfused rat heart

Glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system in old rats

Introduction: Aging is accompanied by cardiovascular disorders which is associated with an imbalance of pro- and antioxidant systems, the mitochondrial dysfunction, etc. Glutathione (GSH) plays a critical role in protecting cells from oxidative damage. The aim of the work was to study the effect of exogenous glutathione on the redox status of mitochondria, the content of H₂S and the function of the cardiovascular system in old rats. Methods: Experiments were performed on adult (6 months) and old (24 months) Wistar rats divided into three groups: adult, old and glutathionetreated old rats. Glutathione was injected intraperitoneally at a dose of 52 mg/kg. We investigated glutathione redox balance, H₂S levels, oxidative stress, the opening of the mitochondrial permeability transition pore (mPTP), the resistance of isolated heart to ischemia/reperfusion in Langendorff model, endothelium-dependent vasorelaxation of isolated aortic rings, and cardiac levels of 3-MST, CSE, and UCP3 mRNA were determined using real-time PCR analysis. Results: Our data shows that in old rats treated with glutathione, the balance of its oxidized and reduced form changes in the direction of a significant increase (by 53.6%) of the reduced form. Glutathione pretreatment significantly increased the H₂S levels, mtNOS activity, and UCP3 expression which considered as protective protein, and conversely, significantly decreased oxidative stress markers (the rate of O₂•^- generation, the levels of H₂O₂, diene conjugates and malone dialdehyde, in 2.5, 2.3, 2, and 1.6 times, respectively) in heart mitochondria. This was associated with the inhibition mitochondrial permeability transition pore opening and increased resistance of the isolated heart to ischemia/reperfusion in these animals. At the same time, in glutathione-treated old rats, we also observed restoration of endothelium-dependent vasorelaxation responses to acetylcholine, which were almost completely abolished by the NO-synthase inhibitor L-NAME. Conclusion: Thus, the pretreatment of old rats with glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system.

The effects of N-acetylcysteine on cisplatin-induced changes of cardiodynamic parameters within coronary autoregulation range in isolated rat hearts

The aim of this study was to evaluate the effects of chronic NAC administration along with cisplatin on cisplatin-induced cardiotoxicity by means of coronary flow (CF), cardiodynamic parameters, oxidative stress markers and morphological changes in isolated rat heart. Isolated hearts of Wistar albino rats (divided into four groups: control, cisplatin, NAC and cisplatin+NAC group) were perfused according to Langendorff technique at constant coronary perfusion pressure starting at 50 and gradually increased to 65, 80, 95 and 110 cm H2O to evaluate cardiodynamic parameters within autoregulation range. Samples of coronary venous effluent (CVE) were collected for determination of CF and biochemical assays, and heart tissue samples for biochemical assays and histopathological examination. Cisplatin treatment decreased CF and heart rate, and increased left ventricular systolic pressure and maximum left ventricular pressure development rate. Cisplatin increased H2O2 and TBARS, but decreased NO2(-) levels in CVE. In tissue samples, cisplatin reduced pathological alterations in myocardium and coronary vessels, with no changes in the amount of total glutathione, as well as in activity of glutathione peroxidase and glutathione reductase. NAC coadministration, by reducing oxidative damage, attenuated cisplatin-induced changes of cardiodynamic and oxidative stress parameters, as well as morphological changes in myocardium and coronary vasculature.

The effects of N-acetylcysteine on cisplatin-induced cardiotoxicity on isolated rat hearts after short-term global ischemia

The aim of this study was to estimate the protective effect of N-acetyl-l-cysteine (NAC) against cisplatin-induced cardiotoxicity under conditions of ischemic-reperfusion injury.

Wistar albino rats were randomly divided into three groups (n = 8): control, cisplatin (5 mg/kg/w, i.p., 5 weeks) and cisplatin + NAC group (cisplatin – 5 mg/kg/w, i.p. and NAC – 500 mg/kg/w, i.p., 5 weeks). Isolated hearts were perfused according to the modified Langendorff technique at constant pressure (70 cmH₂O). Following cardiodynamic parameters were measured: maximum rate of left ventricular pressure development, minimum rate of left ventricular pressure development, left ventricular systolic pressure (SLVP), left ventricular diastolic pressure and heart rate. The ischemic vasodilation episodes were induced by the complete interruption of coronary inflow for 30, 60 and 120 s. The samples of the coronary venous effluent (CVE) were continuously collected during the reperfusion period for determination of coronary flow (CF) rate and oxidative stress markers (H₂O₂, O₂⁻, NO₂⁻ and thiobarbituric acid reactive substances – TBARS).

Cisplatin reduced CF, heart rate and overflow (total, maximal and duration of overflow) during reperfusion, and increased SLVP (under basal conditions and after global ischemias). Cisplatin increased levels of H₂O₂ (under basal conditions), O₂⁻ and TBARS (under basal conditions and after ischemia), but decreased NO₂⁻ levels (during reperfusion) in CVE, and decreased superoxide dismutase and reduced glutathione in serum. NAC attenuated cisplatin-induced changes of cardiodynamic parameters (except CF under basal conditions) and oxidative stress parameters.

Those results suggest that NAC, by decreasing oxidative stress, may be useful in cardioprotection during cisplatin therapy.

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.

N-acetylcysteine instead of theophylline in patients with COPD who are candidates for elective off-pump CABG surgery: Is it possible in cardiovascular surgery unit?

Background:

Forced expiratory volume in one second (FEV1) is a good predictor of chronic obstructive pulmonary disease (COPD). COPD is characterized by a chronic limitation of airflow. This study was designed to compare the effects and complications of theophylline alone, N-acetylcysteine (NAC) alone, and a combination of the two drugs on the rates of FEV1 in patients with COPD who were candidates for off-pump coronary artery bypass graft (CABG) surgery.

Methods:

This clinical trial was performed on 100 patients who had a smoking history of 27 pack years with a range of 20 to 40 pack years but were not heavy smokers and were candidates for elective off-pump CABG surgery in Afshar Cardiovascular Hospital, Yazd, Iran. The patients with a history of asthma and bronchospasm and non-COPD respiratory disorders were excluded. There were three groups, that is, the theophylline group (n=33) that received theophylline 10 mg/kg TDS after consumption of food, NAC group (n=33) who received NAC 10-15 mg/kg BD after consumption of food, and the combined group (n=32) who received theophylline and NAC together. Data were analyzed by analysis of variance (ANOVA), Chi-square, and exact test for quantitative and qualitative variables.

Results:

One hundred patients with COPD enrolled in this study as possible candidates for CABG surgery. Average age of the patients was 60.36±10.21 years. Of the participants, 83 (83.3%) were male and 17 (17%) were female. Rate of postoperative FEV1 to basal FEV1 was 0.76±0.32, 0.66±0.22, and 0.69±0.24 in the treatments with theophylline, NAC, and the combination, respectively. Theophylline, NAC, and a combination of these drugs can decrease the rate of postoperative FEV1 compared to basal FEV1 significantly. (P=0.0001)

Conclusion:

Theophylline alone, NAC alone, and a combination of these drugs improve pulmonary function, and there are no significant differences between these protocols. Stomach discomfort and cardiac complications in treatment with theophylline alone is significantly higher than NAC alone and the combination.

Cardioprotective Effects of Cysteine Alone or in Combination With Taurine in Diabetes

This study was undertaken to examine the effects of dietary supplementation of cysteine and taurine in rats with diabetes induced with streptozotocin (STZ, 65 mg/kg body weight). Experimental animals were treated orally (by gavage) with cysteine (200 mg/kg) and taurine (400 mg/kg), alone or in combination, daily for 8 weeks. In one group, rats were also pretreated 3 weeks before the induction of diabetes (prevention arm) whereas in the other, the treatment was started 3 days after the induction of diabetes (reversal arm). Diabetes increased heart weight/body weight (HW/BW) ratio, plasma glucose, triglyceride and cholesterol levels as well as depressed heart rate (HR), blood pressure, left ventricular systolic pressure (LVSP), rate of contraction (+dP/dt), rate of relaxation (-dP/dt), fractional shortening (FS) and cardiac output (CO). The left ventricular internal diameter in systole (LViDs) was increased whereas that in diastole (LViDd) was decreased. In the prevention arm, treatment of the diabetic animals with cysteine or taurine decreased HW/BW ratio and improved HR, FS, +dP/dt and -dP/dt, as well as normalized LViDs, without altering the increase in glucose level. Cysteine decreased plasma triglyceride and cholesterol levels and improved LVSP whereas CO was improved by taurine. In the reversal arm, cysteine alone or with taurine did not correct the changes in hemodynamic parameters, FS and plasma triglycerides. Diabetes-induced cardiac dysfunction and increases in plasma triglycerides can be prevented, but not reversed, by dietary cysteine alone or in combination with taurine.

Oxidative stress increases SNAT1 expression and stimulates cysteine uptake in freshly isolated rat cardiomyocytes

Intracellular cysteine availability is an important rate-limiting factor governing glutathione synthesis in the heart. This is also dependent on the magnitude and rate of cysteine uptake into cardiomyocytes, which has been little studied. This study investigated the hypothesis that changes to cysteine transporter expression and activity during oxidative stress influence cardiomyocyte glutathione levels. The uptake of 0-3 mM L-[(35)S]cysteine into ventricular cardiomyocytes isolated from adult male Wistar rats was measured using oil filtration. Cysteine transporter expression was investigated by conventional and real-time quantitative reverse-transcription polymerase chain reaction and Western blotting. Glutathione levels were measured enzymatically. Oxidative stress was induced via 0-6 h incubation with 0.05 mM H(2)O(2). Cysteine uptake was greatest in sodium-containing media and was inhibited by glutamine, 2-(methylamino)-isobutyric acid (αMeAIB), serine or alanine. The K(m) and V(max) of the αMeAIB insensitive and sensitive portions were 0.133 ± 0.01 mM and 468.11 ± 9.04 pmol/μl cell vol/min, and 0.557 ± 0.096 mM and 279.87 ± 16.06 pmol/μl cell vol/min, respectively. Cardiomyocytes expressed ASCT2, SNAT1 and SNAT2 but not ASCT1. Oxidative stress significantly enhanced cysteine uptake, which was attenuated by αMeAIB. This was accompanied by significantly enhanced SNAT1 expression, whilst SNAT2 and ASCT2 were unaffected. Incubation with cysteine significantly reduced the oxidative-stress-induced decline in cardiomyocyte glutathione as compared to cells incubated without cysteine or cells incubated with cysteine and αMeAIB. In conclusion, under control conditions SNAT transporters aid in the delivery of cysteine for cardiomyocyte GSH synthesis, whilst oxidative stress increases cardiomyocyte cysteine uptake and stimulates cardiomyocyte SNAT1 expression.

Cysteine protects freshly isolated cardiomyocytes against oxidative stress by stimulating glutathione peroxidase

Cysteine has been implicated in myocardial protection, although this is controversial and constrained by limited knowledge about the effects of cysteine at the cellular level. This study tested the hypothesis that a physiologically relevant dose of L: -cysteine could be safely loaded into isolated cardiomyocytes leading to improved protection against oxidative stress. Freshly isolated adult rat ventricular cardiomyocytes were incubated for 2 h at 37°C with (cysteine incubated) or without (control) 0.5 mM cysteine prior to washing and suspension in fresh cysteine-free media. Cysteine incubated cells had higher intracellular cysteine levels compared to controls (9.6 ± 0.78 vs. 6.5 ± 0.65 nmol/mg protein, P < 0.02, n = 6 ± SE). Cell homeostasis indicators were similar in the two groups. Cysteine incubated cells had significantly higher glutathione peroxidase (GPx) activity (1.11 ± 0.23 vs. 0.54 ± 0.1 U/mg protein, P < 0.05, n = 5 ± SE) and significantly greater expression of GPx-1 (5.01 ± 0.48 vs. 3.01 ± 0.25 OD units/mm(2), P < 0.05, n = 4 ± SE) compared to controls. Upon exposure to H(2)O(2), cysteine incubated cells generated fewer reactive oxygen species and took longer to show contractile changes and undergo hypercontracture. However, when cells were exposed to H(2)O(2) in the presence of 0.05 mM of the GPx inhibitor mercaptosuccinic acid, this increased the control cells' susceptibility to H(2)O(2) and completely abolished the cysteine mediated protection. These results suggest a new role for cysteine in myocardial protection involving stimulation of glutathione peroxidase.

L-cysteine stimulates hydrogen sulfide synthesis in myocardium associated with attenuation of ischemia-reperfusion injury

Hydrogen sulfide (H( 2)S) is a biological mediator produced by enzyme-regulated pathways from L-cysteine, which is a substrate for cystathionine-gamma-lyase (CSE). In myocardium, endogenously and exogenously administered H(2)S has been shown to protect against ischemia-reperfusion injury. We hypothesized that L-cysteine exerts its protective action through stimulation of H(2)S production. Rat isolated hearts were Langendorff-perfused and underwent 35-minute regional ischemia and 120-minute reperfusion. L-cysteine perfusion from 10 minutes before ischemia until 10 minutes after reperfusion limited infarct size in a concentration-dependent manner, maximal at 1 mmol/L (control 36.4% +/- 2.4% vs L-cysteine 24.3% +/- 3.4%, P < .05). This protective action was attenuated by the CSE inhibitor, DL-propargylglycine (PAG) 1 mmol/L (31.4 +/- 5.9%, not significant vs control) but administration of the CSE cofactor pyridoxal-5'-phosphate (PLP) 50 mumol/L did not enhance the effect of L-cysteine. Ten minutes normoxic perfusion with L-cysteine 1 mmol/L caused a 3-fold increase in myocardial H(2)S concentration (0.64 +/- 0.16 vs 2.01 +/- 0.07 mumol/g protein, P < .01), an effect that was significantly attenuated by PAG (1.17 +/- 0.15 mumol/g protein). These data provide evidence that exogenous L-cysteine administration limits ischemia-reperfusion injury through a mechanism that appears to be at least partially dependent on H(2)S synthesis.

The use of comparative quantitative RT-PCR to investigate the effect of cysteine incubation on GPx1 expression in freshly isolated cardiomyocytes

Intracellular cysteine availability is one of the major rate limiting factors that regulate the synthesis of the major antioxidant, glutathione. Little is known, however, about the effect of cysteine upon glutathione-associated enzymes in isolated heart cells. Such knowledge is important if a full understanding and exploitation of cysteine's cardioprotective potential is to be achieved. Therefore, this study describes the use of a comparative quantitative reverse transcription polymerase chain reaction (RT-PCR) assay to investigate the effect of incubation of freshly isolated rat cardiomyocytes for 2 h at 37 degrees C with or without 0.5 mM cysteine on the expression of cellular glutathione peroxidase (GPx1). The main analytical method is the conventional RT-PCR in a standard thermal cycler followed by electrophoresis and scanning densitometry using the expression of the housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), for normalising purposes. Each step of this straight-forward and relatively inexpensive method is explained in detail to facilitate its adoption by the reader for experiments investigating the effects of any compound on any gene in any cell population. The results of the current investigation show that cysteine incubation significantly increases the expression of GPx1 in freshly isolated cardiomyocytes compared to control, suggesting the possibility of a new beneficial role for cysteine in myocardial protection.

Modification of epinephrine-induced arrhythmias by N-acetyl-L-cysteine and vitamin E

Sprague-Dawley rats were pretreated for 21 days with N-acetyl-L-cysteine (NAC) or vitamin E to investigate their influence on arrhythmias induced by a bolus injection or by cumulative doses of epinephrine. Electrocardiographic analysis revealed that both NAC and vitamin E decreased the duration and increased the time of onset of epinephrine-induced arrhythmias in a dose-dependent manner. The antiarrhythmic effects of NAC were comparable with those seen in the vitamin E-pretreated animals. The lipid peroxidation due to cumulative doses of epinephrine was reduced in both pretreated groups; however, NAC, unlike vitamin E, failed to decrease the basal level of malondialdehyde. Although the plasma concentrations of both norepinephrine and epinephrine were markedly increased, the level of aminochromes on epinephrine administration was decreased by both NAC and vitamin E pretreatments. The results support the view that antioxidants may prevent the catecholamine-induced heart rhythm disorders by reducing the formation of oxidized catecholamines.

Effects of N-acetylcysteine on myocardial ischemia-reperfusion injury in bypass surgery

Myocardial ischemia-reperfusion injury may complicate coronary artery bypass grafting (CABG) operations. N-Acetylcysteine (NAC) had antioxidant and microcirculatory effects, and inhibits neutrophil aggregation. The aim of this study was to determine the effects of NAC in limiting myocardial ischemia-reperfusion injury in CABG operations. Twenty patients undergoing elective coronary bypass operation with cardiopulmonary bypass were enrolled and randomly assigned to two groups: a control group operated with a routine CABG protocol, and one where NAC was administered intravenously during the operation (NAC group). Blood samples from coronary sinus for tumor necrosis factor-alpha assay, myocardial biopsy specimens for chemiluminescent luminol, and lucigenin measurements of reactive oxygen species were taken. The luminol (specific for (*)OH, H(2)O(2), and HOCl(-) radicals) and lucigenin (specific for O(2) (*-)) levels and the difference ratios after reperfusion were significantly lower in the NAC group. Tumor necrosis factor-alpha levels increased in the control group but, in contrast, a significant decrease was detected in the NAC group (P < 0.01). Creatine kinase-MB levels at 6 and 12 hours were significantly lower in the NAC group (P = 0.02). N-Acetylcysteine has potential effects to limit ischemia reperfusion injury during CABG operations. We believe that its effects on clinical outcome may be more apparent in patients prone to ischemia-reperfusion injury.

Do N-acetylcystein, beta-glucan, and coenzyme Q10 mollify myocardial ischemia-reperfusion injury?

BACKGROUND

N-acetylcysteine, beta-glucan, and coenzyme Q10 have been shown to have antioxidant and anti-inflammatory effects on reperfusion injury. The aim of our study was to determine and evaluate the effects of these agents on myocardial ischemia-reperfusion injury.

METHODS

Forty-four New Zealand white rabbits, all female, weighing 2.4 to 4.1 kg (mean, 3.6 kg) were used in the study. Four study groups of 11 animals were arranged by randomization. The groups were the control group (group C), a group premedicated with coenzyme Q10 (group Q), a group premedicated with beta-glucan (group betaT), and a group premedicated with N-acetylcysteine (group N). After exploration of the heart, a basal myocardial biopsy was taken from the anteroapical left ventricle, and the first blood sampling was done before ischemia. For the ischemia-reperfusion experiments, the major left anterior descending artery was occluded after baseline measurements. After a 45-minute transient ischemic period, the heart was perfused for 120 minutes. After perfusion, the second myocardial biopsy was taken from the anteroapical left ventricle, and the second blood sampling was done. Blood and tissue analysis were performed and evaluated statistically.

RESULTS

Baseline and reperfusion levels of glutathione peroxidase, superoxide dismutase, malonyldialdehyde, and nitric oxide changed significantly. While malonyldialdehyde levels increased in group C, they decreased in the other study groups (P =.001). The increases in glutathione peroxidase and superoxide dismutase levels were significant in all groups except group C (P =.0001 and P <.05, respectively). Levels of nitric oxide were found to be decreased in group C, whereas they increased in the other groups (P =.001).

CONCLUSION

Antioxidant medication may help in lowering the risk of myocardial ischemia-reperfusion injury. All the medications in our study are shown to have effective roles in preventing ischemia-reperfusion injury to some extent through their antioxidant properties.

Protective effects of antioxidant medications on limb ischemia reperfusion injury

BACKGROUND

N-acetylcysteine, beta-glucan, and coenzyme Q(10) were shown to have antioxidant and anti-inflammatory effects on reperfusion injury. The aim of our study was to determine and evaluate the effects of these agents on ischemia reperfusion injury of limb.

MATERIAL AND METHOD

Forty-four New Zealand white rabbits, all female, weighing between 2.3 to 4.2 (mean 3.8) kg, were used in the study. Four study groups were arranged of 11 animals each, by randomization. The first group was the control group (Group C), the other groups were the Group Q, which was medicated with coenzyme Q10, the Group betaG, which was medicated with beta-glucan, and the Group N, medicated with N-acetylcysteine. After baseline measurements, for the ischemia-reperfusion experiments, common iliac artery was clamped and collateral flow was occluded by a rubber arterial tourniquet wrapped around the thigh at the proximal third of the leg. After 60 min of transient ischemic period, the limb was perfused for 180 min. After perfusion, biopsy was taken from the adductor magnus muscle. Second blood sampling was done after reperfusion period. Blood and tissue analysis were done and evaluated statistically.

RESULTS

Baseline and post-reperfusion levels of glutathione peroxidase (GPx), super oxide dismutase (SOD), malonyldialdehyde (MDA), and nitric oxide (NO) changed significantly. While MDA levels increased in the control group, it decreased in the other study groups. The increase in GPx and SOD levels were significant in all groups except the control group. Levels of NO were found to have decreased in the control group, whereas it had increased in the other groups.

CONCLUSION

Antioxidant medication may help lowering limb ischemia reperfusion injury. All mentioned medications in our study are shown to be able to have an effective role for preventing ischemia reperfusion injury to some extent through their antioxidant properties.

Inhibition of iNOS protects the aging heart against beta-adrenergic receptor stimulation-induced cardiac dysfunction and myocardial ischemic injury

BACKGROUND

beta-adrenergic receptor (AR) and aging are two major contributors to pathogenesis of perioperative myocardial ischemia and infarction. This study compared the response to beta-AR stimulation in the young and aging heart and examined the role of inducible nitric oxide synthase (iNOS) in aging related myocardial ischemic injury and its relation to beta-AR stimulation.

MATERIAL AND METHODS

Isolated perfused hearts from young (3-5 months) and aging (24-25 months) rats were subjected to 60 min of 50% coronary flow reduction and 30 min of isoproterenol (Iso) stimulation starting at 30 min of ischemia. The rats were randomized to receive vehicle or 1400W (a selective iNOS inhibitor) at 24 h (2 mg/kg, i.p.) and 1 h (1 mg/kg, i.p.) pre-ischemia.

RESULTS

The 30 min of myocardial ischemia resulted in cardiac dysfunction as indicated by a 13 to 45% of reduction in left ventricular developed pressure (LVDP) and +/- dp/dtmax in either young or aging rats. Infusion of Iso for 30 min caused a partial recovery of cardiac function in hearts from young animals receiving either vehicle or 1400W as evidenced by improvements in LVDP and +/- dp/dtmax. In striking contrast, Iso infusion to hearts from aging animals receiving vehicle not only failed to improve ischemia-induced cardiac depression but worsened cardiac function as indicated by a 43 to 60% further reduction in LVDP and +/- dp/dtmax at the end of 30-min Iso infusion, which was also associated with a significant increase in myocardial NO production, ONOO- formation, caspase-3 activation and creatine kinase (CK) release. However, the treatment with a selective iNOS inhibitor-1400W blocked NO production and ONOO- formation, attenuated caspase-3 activation and CK release, and improved LV function in the aging heart, demonstrating a critical link between iNOS generated NO production and aging myocardial ischemic injury. A significant increase of iNOS protein expression, activity and immunoreactivity was found in the baseline aging LV tissues versus their young counterparts.

CONCLUSIONS

Aging induces phenotypic up-regulation of iNOS in the heart, in which beta-AR stimulation interacts with ischemia and triggers a markedly increased NO production, which creates a nitrative stress, generates toxic peroxynitrite, activates apoptosis, and eventually causes cardiac dysfunction and myocardial injury. An iNOS inhibitor-1400W can markedly attenuate these adverse effects in the aging heart.

Mechanisms underlying the cardioprotective effect of l-cysteine

In many tissues the availability of L-cysteine is a rate-limiting factor in glutathione production, though this has yet to be fully tested in heart. This study aimed to test the hypothesis that supplying hearts with 0.5 mM L-cysteine would preserve glutathione levels leading to an increased resistance to ischaemia reperfusion. Left ventricular function was measured in isolated perfused rat hearts before, during and after exposure to 45 min global normothermic ischaemia. Control hearts received Krebs throughout, whilst in treated hearts 0.5 mM L-cysteine was added to the perfusate 10 min before ischaemia, and was then present throughout ischaemia and for the first 10 min of reperfusion. Reperfusion injury was assessed from the appearance of lactate dehydrogenase (LDH) in the effluent. In two separate groups of control and treated hearts, ATP and glutathione (GSH) contents were measured at the beginning and end of ischaemia. Hearts treated with 0.5 mM L-cysteine showed a significantly higher recovery of rate pressure product (16,256+/- 1288 mmHg bpm vs. 10,324+/- 2102 mmHg bpm, p < 0.05) and a significantly lower release of LDH (0.54+/- 0.16 IU/g wet weight vs. 1.44+/- 0.31 IU/g wet weight, p < 0.05) compared to controls. Also, the L-cysteine treated group showed significantly better preservation of ATP and GSH during ischaemia in comparison to control. These results suggest that the mechanisms underlying the cardioprotective effects of 0.5 mM L-cysteine may include: increased anaerobic energy production either directly or through reduced degradation of adenine nucleotides; direct scavenging of free radicals; and/or improved antioxidant capacity through glutathione preservation.

Antioxidant properties of myocardial fuels

Oxidative metabolism of blood-borne fuels provides myocardium the energy required to sustain its contractile performance. Recent research has revealed that, in addition to supplying energy, certain fuels are able to detoxify harmful oxidants and bolster the myocardium's endogenous antioxidant defenses. These antioxidant capabilities could potentially protect the myocardium from the ravages of reactive oxygen and nitrogen intermediates generated upon reperfusion of ischemic myocardium. This article reviews experimental evidence that two fuels, pyruvate and acetoacetate, provide such antioxidant protection. Pyruvate's antioxidant properties stem in part from its alpha-keto carboxylate structure, which enables it to directly, non-enzymatically neutralize peroxides and peroxynitrite. Also, citrate, which accumulates in pyruvate-perfused myocardium following anaplerotic pyruvate carboxylation, supports NADPH production to maintain glutathione:glutathione disulfide (GSH/GSSG) redox potential, the central component of the myocardial antioxidant system. Like pyruvate, acetoacetate restores GSH/GSSG and increases contractile function of post-ischemic stunned myocardium, although some of its antioxidant mechanisms may differ from pyruvate's. Both compounds restore beta-adrenergic signaling and inotropism, which are compromised in stunned myocardium. N-acetylcysteine, a pharmacological antioxidant that does not provide energy, duplicated the salutary effects of pyruvate and acetoacetate on post-ischemic gamma-adrenergic signaling and GSH/GSSG. These findings reveal novel, energy-independent mechanisms for enhancement of post-ischemic cardiac performance by metabolic fuels.

Effect of the antioxidant Mesna (2-mercaptoethane sulfonate) on experimental colitis

Reactive oxygen species play a key role in intestinal inflammation, although interventional studies using antioxidants have shown only weak beneficial effects both in humans and animals. Hence, our aim was to examine the possible beneficial effect of the antioxidant 2-mercaptoethane sulfonate (Mesna) on experimental colitis. Colitis was induced in rats by intrarectal instillation of trinitrobenzene sulfonic acid (TNB) followed immediately by intrarectal Mesna or saline, administered for 14 days, twice daily. A beneficial effect of Mesna was observed, resulting in a significant reduction in inflammation followed by almost full recovery. iNOS mRNA expression and myeloperoxidase (MPO) activity were significantly increased in the TNB-Mesna group. These results suggest that the induction of iNOS in the presence of Mesna reduced intestinal inflammation. Mesna probably resolved this inflammation by scavenging reactive oxygen species generated by the augmented infiltration of polymorphonuclear leukocytes.

Reactive oxygen species contribute to contractile dysfunction following rapid ventricular pacing in dogs

BACKGROUND

Ventricular tachyarrhythmias may produce subsequent myocardial dysfunction through the formation of oxygen-derived free radicals. We tested the hypothesis that the antioxidant N-acetylcysteine enhances recovery of contractile function after rapid ventricular pacing.

METHODS

Barbiturate-anesthetized dogs were instrumented for measurement of systemic and coronary hemodynamics and subendocardial segment shortening (%SS). All dogs were subjected to 3 h of rapid ventricular pacing (230 beats/min) followed by a 2 h recovery period. In three groups (n=8 each), dogs received intravenous 0.9% saline or N-acetylcysteine (50 or 150 mg/kg over 60 min) in a random manner before pacing.

RESULTS

N-acetylcysteine did not affect systemic and coronary hemodynamics or alter regional myocardial contractility. Rapid ventricular pacing significantly (P<0.05) increased rate-pressure product and left ventricular end-diastolic pressure and decreased +dP/dt(max). Rapid ventricular pacing produced equivalent degrees of contractile dysfunction in dogs receiving saline or N-acetylcysteine (e.g. %SS of 14.7+/-1.8 to -3.8+/-2.7% before and during pacing in saline-pretreated dogs). Dogs receiving the 150 mg/kg dose of N-acetylcysteine demonstrated greater recovery of contractile function than those pretreated with saline or the 50 mg/kg dose (e.g. %SS of 12.3+/-1.7% compared to 7.0+/-2.0% 2 h after pacing in dogs receiving saline). No differences in systemic and coronary hemodynamics were observed between groups during recovery from pacing.

CONCLUSIONS

The results indicate that the N-acetylcysteine enhances recovery of contractile function after rapid ventricular pacing independent of alterations in systemic and coronary hemodynamics and imply that reactive oxygen species are an important component of the contractile dysfunction following rapid pacing in vivo.

Generation of oxidative stress contributes to the development of pulmonary hypertension induced by hypoxia

Chronic hypoxia causes pulmonary hypertension and right ventricular hypertrophy associated with pulmonary vascular remodeling. Because hypoxia might promote generation of oxidative stress in vivo, we hypothesized that oxidative stress may play a role in the hypoxia-induced cardiopulmonary changes and examined the effect of treatment with the antioxidant N-acetylcysteine (NAC) in rats. NAC reduced hypoxia-induced cardiopulmonary alterations at 3 wk of hypoxia. Lung phosphatidylcholine hydroperoxide (PCOOH) increased at days 1 and 7 of the hypoxic exposure, and NAC attenuated the increase in lung PCOOH. Lung xanthine oxidase (XO) activity was elevated from day 1 through day 21, especially during the initial 3 days of the hypoxic exposure. The XO inhibitor allopurinol significantly inhibited the hypoxia-induced increase in lung PCOOH and pulmonary hypertension, and allopurinol treatment only for the initial 3 days also reduced the hypoxia-induced right ventricular hypertrophy and pulmonary vascular thickening. These results suggest that oxidative stress produced by activated XO in the induction phase of hypoxic exposure contributes to the development of chronic hypoxic pulmonary hypertension.

Protection against oxidative damage and cell death by the natural antioxidant ergothioneine

The natural antioxidant ergothioneine (EGT) was tested for its ability to inhibit cell death caused by hydrogen peroxide (H2O2) and to inhibit DNA oxidation by peroxynitrite (ONOO-) in human neuronal hybridoma cell line (N-18-RE-105). High concentrations of EGT (5 mM) were tolerated by the N-18-RE-105 cells. N-acetylcysteine (NAC) was not well tolerated by the cells at concentrations greater than 3 mM (cell viability averaged 50%). Increasing concentrations of EGT increases cell viability in the presence of NAC. EGT at concentrations up to 2 mM weakly improved cell viability in the presence of H2O2. NAC at concentrations up to 2 mM weakly decreased, but not significantly, the viability of the cells. At a higher concentration of 5 mM, NAC weakly protected the neuronal cells against the H2O2-induced cell death. The protection was significantly enhanced by preincubation with EGT. Ergothioneine inhibited ONOO(-)-induced oxidative damage in isolated calf thymus DNA and DNA in N-18-RE-105 cells. The concentration of EGT in human and mammalian tissue has been estimated to be 1-2 mM, which suggests that EGT may serve as a non-toxic thiol buffering antioxidant in vivo and may find applications in pharmaceutical preparations where oxidative stability is desired.

Antioxidant properties of pyruvate mediate its potentiation of beta-adrenergic inotropism in stunned myocardium

This study tested the hypothesis that pyruvate's antioxidant actions, particularly its enhancement of the endogenous glutathione system, mediate its potentiation of beta-adrenergic inotropism in stunned myocardium. Isolated working guinea pig hearts, metabolizing 10 m M glucose and stunned by 45 min of low flow ischemia, were treated with 5 m M pyruvate, 5 m M N-acetylcysteine (NAC) and/or 2 n M isoproterenol beginning 15 min after reperfusion. The antioxidant NAC alone did not increase cardiac power (mJ/min/g wet: 11 +/- 1 in untreated and 15 +/- 2 in NAC treated stunned hearts), but NAC potentiated the increase in power produced by 2 n M isoproterenol (isoproterenol alone: 50+/-10; NAC plus isoproterenol: 133 +/- 24). Addition of NAC doubled cyclic AMP content but lowered cytosolic phosphorylation potential by 32% in isoproterenol-stimulated hearts. Stunning decreased the glutathione antioxidant ratio (GSH/GSSG) by 68%. The antioxidant ratio was completely restored by pyruvate alone or in combination with isoproterenol, but only partially restored by isoproterenol alone. Combining isoproterenol and NAC increased the GSH/GSSG ratio by an additional 36%. The combined treatment of pyruvate and isoproterenol increased the NADPH/NADP(+) ratio almost three-fold, and produced the greatest accumulation of glucose-6-phosphate of any treatment.

CONCLUSIONS

like pyruvate, the antioxidant NAC potentiated beta-adrenergic inotropism of stunned myocardium. Unlike pyruvate, NAC did not increase cellular energy reserves, thus effectively limiting its potentiation of beta-adrenergic stimulation. Thus, pyruvate's potentiation of beta-adrenergic stimulation in stunned myocardium is most likely the result of the combined effects of its antioxidant and energetic properties.

Bradykinin mediates myocardial ischaemic preconditioning against free radical injury in guinea-pig isolated heart

1. Myocardial ischaemic preconditioning (IP) against free radical injury and its possible mediator(s) was investigated in a Langendorff-perfused guinea-pig heart. 2. 1,1-Diphenyl-2-picryl-hydrazyl (DPPH) was used for triggering free radical injury in cardiac tissue. It reduced left ventricular developed pressure (LVDP), +/- dp/dtmax, heart rate (HR) and coronary flow (CF) and increased thiobarbituric acid-reactive substances (TBARS) in cardiac tissue. 3. Ischaemic preconditioning (5 min global ischaemia and 5 min reperfusion) exerted cardioprotection against DPPH-induced functional impairment, with significant improvement in LVDP, +/- dp/dtmax, HR and CF. The formation of TBARS in cardiac tissue was reduced. Blockade of bradykinin (BK) B2 receptors with icatibant (HOE 140) abolished the cardio-protective effects of IP. 4. Bradykinin (10(-7) mol/L) perfusion for 10 min protected the heart against free radical injury. The cardioprotection induced by BK was reversed by HOE 140. 5. Pretreatment with IP and BK results in cardiac protection against free radical injury through the activation of B2 receptors. Endogenously generated BK may mediate IP in the guinea-pig heart.

Ramipril-induced delayed myocardial protection against free radical injury involves bradykinin B2 receptor-NO pathway and protein synthesis

1. The aim of the present study was to examine whether ramipril induces delayed myocardial protection against free radical injuries ex vivo and to determine the possible role of the bradykinin B2-nitric oxide (NO) pathway, prostaglandins(PGs) and protein synthesis in this delayed adaptive response. 2. Rats were pretreated with ramipril (10 or 50 microg kg(-1), i.v.) and hearts were isolated after 24, 48 and 72 h. Langendorff hearts were subjected to 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical-induced injury. 3. Left ventricular developed pressure (LVDP) and its maximal increase velocity (+ dP/dtmax), coronary flow (CF), heart rate (HR), lactate dehydrogenase (LDH) in coronary effluent and thiobarbituric acid reactive substances (TBARS) in the myocardium were measured. 4. The results showed that in the DPPH control group, 20 min after free radical-induced injury, LVDP, +dP/dtmax, CF, HR declined, whereas TBARS and LDH increased significantly. The above cardiac function parameters were significantly improved in RAM-pretreated rats after 24 and 48 h. 5. Pretreatment with HOE 140, the selective bradykinin B2 receptor antagonist, NG-nitro-L-arginine, the NO synthase inhibitor, and actinomycin D, the RNA transcription inhibitor, prior to ramipril injection abolished the beneficial effects of ramipril at 24 h while indomethacin, a cyclooxygenase inhibitor, pretreatment had no effect on ramipril-induced delayed protection. 6. In conclusion, ramipril induces delayed myocardial protection against free radical injury in the rat heart. This delayed protection was sustained for 48 h, is associated with the bradykinin B2 receptor-NO pathway and depends on protein but not prostaglandin synthesis.

A simple colorimetric method for the simultaneous determination of N-acetylcysteine and cysteine

The widespread use of N-acetylcysteine as an antioxidant and a precursor for tissue cysteine creates a need for a simple method that measures both and distinguishes them from one another. We describe a procedure based on the use of the enzyme acylase, which hydrolyzes N-acetylcysteine to cysteine. Cysteine is subsequently measured with a specific colorimetric procedure. Unhydrolyzed N-acetylcysteine gives only a weak colorimetric response (11.5% that for cysteine); after hydrolysis, however, the two are equivalent. Hence, N-acetylcysteine can be distinguished by the enhanced response after hydrolysis.

N-acetylcysteine: pharmacological considerations and experimental and clinical applications

The diversity of application of the thiol drug NAC in both the experimental setting, as a tool for the study of the mechanisms and consequences of oxidative stress, and the clinical setting, as a therapeutic agent, clearly reflects the central role played by the redox chemistries of the group XVI elements, oxygen and sulfur, in biology. As our understanding of such redox processes increases, particularly their roles in specific pathophysiological processes, new avenues will open for the use of NAC in the clinical setting. As a drug, NAC represents perhaps the ideal xenobiotic, capable of directly entering endogenous biochemical processes as a result of its own metabolism. Thus, it is hoped that the experience gained with this unique agent will help in future efforts to design antioxidants and chemoprotective principles which are able to more accurately utilize endogenous biochemical processes for cell- or tissue-specific therapy.

Photodynamic action of aluminium phthalocyanine tetrasulphonate (A1PcS4) on smooth muscle: effects of thiols and a cyclic GMP analogue

1. The smooth muscle system of the guinea-pig taenia caeci has been used in vitro to characterize the photodynamic action of aluminium phthalocyanine tetrasulphonate (A1PcS4) in the presence or absence of the thiol reductants L-cysteine (Cys), N-acetyl-L-cysteine (NAC), DL-dithiothreitol (DTT) or reduced glutathione (GSH). 2. In all photodynamic experiments the muscle was exposed to A1PcS4 (10(-5) M) for 30 min, followed by a 30 min washout period before photon irradiation at 32,000 lux (lambda > 570 nm) for 30 min. Photodynamic contractions were measured relative to the contractile response to carbachol (5 x 10(-5) M) and relaxation responses were determined in muscle precontracted with either carbachol 5 x 10(-5) M or KCl 23.5 mM. 3. Photon-activation of A1PcS4-sensitized smooth muscle evoked a triphasic response: an initial transient contraction and subsequent relaxation followed by a secondary sustained contraction. Cys 10 mM, NAC 10 mM and DTT 5 mM had no effect on the initial photodynamic contraction but significantly decreased the magnitude of the sustained contraction from mean values of 98% to 18%, 95% to 72% and 93% to 6% of the standard carbachol contraction (5 x 10(-5) M), respectively; GSH 10 mM was without significant effect on either the initial or sustained contraction. 4. In the absence of extracellular calcium the A1PcS4-sensitized smooth muscle did not respond to photon activation but re-introduction of calcium after cessation of illumination produced a sustained contraction which was markedly inhibited by Cys 10 mM. 5. In precontracted AlPcS4-treated muscle preparations photon activation produced a triphasic relaxation response, i.e. a rapid relaxation followed by a transient contraction and a secondary more sustained relaxation. The sustained phase of photodynamic relaxation was potentiated significantly by Cys 10 mM,NAC 10 mM, DTT 5 mM and GSH 10 mM, the relaxation being approximately doubled in magnitude from mean values of 34% to 68%, 30% to 73%, 34% to 68%, and 48% to 77%, respectively, relative to the standard carbachol (5 x l0-5 M) response.6. The cyclic GMP analogue, 8-(4-chlorophenylthio)-guanosine-3':5'-cyclic monophosphate (8-PCPTcGMP)(2 x 10-4 M) alone caused a triphasic relaxation response similar to that produced by photon activation of an AIPcS4-sensitized precontracted preparation in the presence of thiol reductants. The pattern of 8-PCPT-cGMP-induced relaxation was similar in muscle precontracted with carbachol 5 x 10-5M or KCI 23.5 mM.7. It is concluded that the rapid generation of reactive intermediates by photon-activation of boundAlPcS4 leads to membrane permeabilization, calcium entry and muscle contraction. These effects may be opposed by a direct stimulatory action of singlet oxygen on guanylate cyclase which is enhanced by the action of thiol reagents and mimicked by the cyclic GMP analogue, 8-PCPT-cGMP.