The role of nitric oxide in cardiac ischemia-reperfusion injury

pH-sensitive release of nitric oxide gas using peptide-graphene co-assembled hybrid nanosheets

Nitric oxide (NO) donating drugs such as organic nitrates have been used to treat cardiovascular diseases for more than a century. These donors primarily produce NO systemically. It is however sometimes desirable to control the amount, location, and time of NO delivery. We present the design of a novel pH-sensitive NO release system that is achieved by the synthesis of dipeptide diphenylalanine (FF) and graphene oxide (GO) co-assembled hybrid nanosheets (termed as FF@GO) through weak molecular interactions. These hybrid nanosheets were characterised by using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, zeta potential measurements, X-ray photoelectron spectroscopy, scanning and transmission electron microscopies. The weak molecular interactions, which include electrostatic, hydrogen bonding and π-π stacking, are pH sensitive due to the presence of carboxylic acid and amine functionalities on GO and the dipeptide building blocks. Herein, we demonstrate that this formulation can be loaded with NO gas with the dipeptide acting as an arresting agent to inhibit NO burst release at neutral pH; however, at acidic pH it is capable of releasing NO at the rate of up to 0.6 μM per minute, comparable to the amount of NO produced by healthy endothelium. In conclusion, the innovative conjugation of dipeptide with graphene can store and release NO gas under physiologically relevant concentrations in a pH-responsive manner. pH responsive NO-releasing organic-inorganic nanohybrids may prove useful for the treatment of cardiovascular diseases and other pathologies.

Effects of Ischemic and Proton Pump Inhibitors Preconditioning on Oxidative Stress of Isolated Rat Heart

Aim of present study was to determine the participation of various biomarkers of oxidative damage: nitrite (NO2 −), superoxide anion radicals (O2 −), index of lipid peroxidation (TBARS) and hydrogen peroxide (H2O2) in coronary circulation after application of the different models of preconditioning such as ischemic and preconditioning with proton pump inhibitors.

Examining a biochemical markers of oxidative damage we did not notice any increased production values of any parameter, according to that we can hypothesize that possible occurrence of reperfusion injury after ischemia and PPIs preconditioning is not mediated by this mechanism.

Due to the very difficult and controversial application of ischemic preconditioning in clinical practice, the results of this study suggest that in the future proton pump inhibitors can contribute to the prevention of myocardial damage following ischemia

The peroxynitrite evoked contractile depression can be partially reversed by antioxidants in human cardiomyocytes

In this study, we aimed to determine the contribution of peroxynitrite-dependent sulfhydryl group (SH) oxidation to the contractile dysfunction in permeabilized left ventricular human cardiomyocytes using a comparative approach with the SH-oxidant 2,2'-dithiodipyridine (DTDP). Additionally, different antioxidants: dithiothreitol (DTT), reduced glutathione (GSH) or N-acetyl-L-cysteine (NAC) were employed to test reversibility. Maximal isometric active force production (F(o)) and the maximal turnover rate of the cross-bridge cycle (k(tr,max)) illustrated cardiomyocyte mechanics. SH oxidation was monitored by a semi-quantitative Ellman's assay and by SH-specific protein biotinylation. Both peroxynitrite and DTDP diminished F(o) in a concentration-dependent manner (EC(50,peroxynitrite) = 49 microM; EC(50,DTDP) = 2.75 mM). However, k(tr,max) was decreased only by 2.5-mM DTDP, but not by 50 microM peroxynitrite. The diminution of F(o) to zero by DTDP was paralleled by the complete elimination of the free SH groups, while the peroxynitrite-induced maximal reduction in free SH groups was only to 58 +/- 6% of the control (100%). The diminutions in F(o) and free SH groups evoked by 2.5-mM DTDP were completely reverted by DTT. In contrast, DTT induced only a partial restoration in F(o) (DeltaF(o,): approximately 13%; P < 0.05) despite full reversion in protein SH content after 50 microM peroxynitrite. Although, NAC or DTT were equally effective on F(o) after peroxynitrite exposures, NAC or GSH did not restore F(o) or k(tr,max) after DTDP treatments. Our results revealed that the peroxynitrite-evoked cardiomyocyte dysfunction has a small, but significant component resulting from reversible SH oxidation, and thereby illustrated the potential benefit of antioxidants during cardiac pathologies with excess peroxynitrite production.

Antioxidant screening of medicinal herbal teas

Herbal tea consumption is deeply and widely rooted amongst South-American populations. In view of the involvement of oxygen- and nitrogen-reactive species in the ethiogenesis of several diseases, the antioxidant properties of some of the herbal teas most commonly consumed in the southern regions was assessed in vitro. Around one-third of the 13 examined herbs, displayed a substantially higher ability to scavenge ABTS(+.) radicals (TEAC assay), and to quench the pro-oxidant species, hypochlorite (HClO) and peroxynitrite (ONOO(-)). Amongst the tested herbs, teas prepared from Haplopappus baylahuen, Rosa moschata and Peumus boldus showed the highest TEAC and HClO-quenching activities. These herbs were around 5- to 7-fold more potent than the least active herbs. Based on the TEAC assay, 150 mL of tea prepared from H. baylahuen, R. moschata and P. boldus would be equivalent to around 200 mg of Trolox). Teas from H. baylahuen and P. boldus were also found to be particularly potent in quenching HClO. In the ONOO(-) assay, H. baylahuen and Buddleia globosa showed the highest activities. The results obtained suggest that the regular consumption of teas prepared from some of these herbs may be useful potentially to provide the organism with molecules capable of protecting the gastrointestinal tract against certain pathologically relevant oxidant species.

Role of melatonin in reducing hypoxia-induced oxidative stress and morphological changes in the liver of male mice

Oxygen deficiency during critical illness may cause profound changes in cellular metabolism and subsequent tissue and organ dysfunction. Thus, the present study was designed to determine the effects of hypoxia and reoxygenation on the levels of lipid peroxidation and the morphological changes in the liver of male mice as well as the protective role of melatonin as an antioxidant. Two experiments were carried out in this study. Experiment I includes three groups of mice (control, hypoxic, and hypoxic+melatonin) while the experiment II includes two groups (reoxygenated and reoxygenated+melatonin). The levels of oxidized lipids were measured and the morphological changes were investigated using light and electron microscopy. In experiment I, hypoxia strongly stimulated lipid peroxidation levels (88%) while melatonin administration inhibited this increase (69%). Severe morphological changes (necrosis, dilated congested blood vessels, collection of inflammatory cells, condensed heterochromatic with irregular outlines nuclei, and mitochondrial degeneration) were detected in the liver of hypoxic mice. In experiment II, reoxygenation inhibited the levels of oxidized lipids (42%) versus hypoxic mice and some morphological changes were detected. When melatonin was given before reoxygenation, it inhibited the levels of lipid peroxidation by 66% versus hypoxic mice. Also, melatonin enhanced the recovery profile by 41% when compared with mice that reoxygenated with room air only. All morphological alterations that detected in both hypoxic and reoxygenated mice were repaired when melatonin administered. These results indicate that hypoxia and reoxygenation induce severe alterations in the liver and that melatonin exerts beneficial role in restoring tissue alterations after subjection to hypoxia.

Role of gastric oxidative stress and nitric oxide in formation of hemorrhagic erosion in rats with ischemic brain

AIM: To investigate the role of gastric oxidative stress and nitric oxide (NO) in the formation of gastric hemorrhagic erosion and their protection by drugs in rats with ischemic brain.

METHODS: Male Wistar rats were deprived of food for 24 h. Under chloral hydrate (300 mg/kg) anesthesia, bilateral carotid artery ligation was performed. The pylorus and carotid esophagus of the rats were also ligated. The stomachs were then irrigated for 3 h with either normal saline or simulated gastric juice containing 100 mmol/L HCl plus 17.4 mmol/L pepsin and 54 mmol/L NaCl. Rats were killed and stomachs were dissected. Gastric mucosa and gastric contents were harvested. The rat brain was dissected for the examination of ischemia by triphenyltetrazolium chloride staining method. Changes in gastric ulcerogenic parameters, such as decreased mucosal glutathione level as well as enhanced gastric acid back-diffusion, mucosal lipid peroxide generation, histamine concentration, luminal hemoglobin content and mucosal erosion in gastric samples, were measured.

RESULTS: Bilateral carotid artery ligation produced severe brain ischemia (BI) in rats. An exacerbation of various ulcerogenic parameters and mucosal hemorrhagic erosions were observed in these rats. The exacerbated ulcerogenic parameters were significantly (P < 0.05) attenuated by antioxidants, such as exogenous glutathione and allopurinol. These gastric parameters were also improved by intraperitoneal aminoguanidine (100 mg/kg) but were aggravated by N^G-nitro-L-arginine-methyl ester (L-NAME: 25 mg/kg). Intraperitoneal L-arginine (0-500 mg/kg) dose-dependently attenuated BI-induced aggravation of ulcerogenic parameters and hemorrhagic erosions that were reversed by L-NAME.

CONCLUSION: BI could produce hemorrhagic erosions through gastric oxidative stress and activation of arginine-nitric oxide pathway.

Protective effects of L-arginine on pulmonary oxidative stress and antioxidant defenses during exhaustive exercise in rats

AIM

To assess the effects of L-arginine (L-Arg) supplementation on pulmonary oxidative stress and antioxidant defenses in rats after exhaustive exercise.

METHODS

Rats were randomly divided into four groups: sedentary control (SC), sedentary control with L-Arg treatment (SC+Arg), exhaustive exercise with control diet (E) and exhaustive exercise with L-Arg treatment (E+Arg). Rats in groups SC+Arg and E+Arg received a 2% L-Arg diet. Rats in groups E and E+Arg underwent an exhaustive running test on a motorized treadmill. Pulmonary oxidative stress indices [xanthine oxidase (XO), myeloperoxidase (MPO), and malondialdehyde (MDA)] and antioxidant defense systems [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), and glutathione (GSH)] were investigated in this study.

RESULTS

L-Arg supplementation significantly reduced exercise-induced elevations of XO and MPO activities in lung. L-Arg reversed the exercise-induced increase in SOD and GR activities, but increased CAT and GPX activities. L-Arg administration also significantly increased the GSH levels in plasma.

CONCLUSION

L-Arg supplementation can prevent elevations of XO and MPO activities in the lung and favorably influence pulmonary antioxidant defense systems after exhaustive exercise.

Effect of nitric oxide synthase modulation on resuscitation success in a swine ventricular fibrillation cardiac arrest model

BACKGROUND

We have demonstrated previously that the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NNA) decreases free radical generation and nitrosative injury via peroxynitrite formation after epicardial dc shocks.

OBJECTIVE

Our purpose was to explore the effects of NOS inhibition and NOS donation on cardiopulmonary resuscitation (CPR) success after cardiac arrest of variable duration. We used the non-selective NOS inhibitor L-NNA and the selective neuronal NOS inhibitor ARR-17477, the NOS donor S-nitroso-N-acetylpenicillamine (SNAP) and the vasodilator Enalaprilat, which lowers arterial pressure via a non-NO mechanism.

METHODS

Part I: 17 pigs undergoing 4 min supported (i.e. with closed-chest compression and ventilation) ventricular fibrillation (VF) were divided into two groups: a no-L-NNA group (n=8) receiving IV saline and an L-NNA group (n=9) receiving IV L-NNA (5 mg/kg) for 8 min before VF was induced. Part II: 35 pigs undergoing 6-8 min VF were randomized to three groups: a no-L-NNA group (n=13) receiving IV saline, an L-NNA group (n=11) receiving IV L-NNA (5 mg/kg) and an ARR17477 group (n=11) receiving IV ARR17477 (5 mg/kg) before VF. All animals in Part II underwent unsupported VF (no chest compression or ventilation) for 6 min (n=13) or 8 min (n=22); closed-chest compression, ventilation and epinephrine (adrenaline) were employed after defibrillation. Part III: 12 swine were divided into two groups: control (n=6) receiving saline and an LNNA group (n=6) receiving IV LNNA (5 mg/kg). Swine underwent 6 min unsupported VF and 2 min supported VF before defibrillation. Part IV: 25 animals were studied to determine the effect of the NO donor SNAP and the angiotensin-converting enzyme inhibitor Enalaprilat on coronary perfusion pressure (CPP).

RESULTS

In Part I, after defibrillation, with continued ventilation, chest compression and epinephrine, 8/9 L-NNA pigs achieved ROSC versus 4/8 control pigs (p=0.11). After 60 s of CPR, 7/9 pigs in the L-NNA group achieved ROSC versus 2/8 pigs in the no-L-NNA group (p<0.05). Only 2/9 pigs receiving L-NNA required epinephrine (1 mg) after defibrillation, compared to 6/8 pigs requiring at least one dose of epinephrine in the no-L-NNA group (p<0.05). In Part II, there was no significant difference between L-NNA, ARR17477 and control pigs in ROSC. However, control pigs required 6.8+/-1.4S.E. mg epinephrine; L-NNA pigs and ARR17477 pigs required less epinephrine (3.7+/-0.7 and 3.0+/-0.3 mg, both p=0.01). Shorter chest compression was required in the L-NNA group (252+/-38 s, p<0.05) and in ARR17477 group (222+/-15 s, p<0.05) compared to the control group (405+/-77 s). In Part III, L-NNA infusion caused a significant increase in mean blood pressure at baseline, but did not change CPP throughout the experiment. In Part IV, there were no significant differences in the changes of mean blood pressure and CPP between SNAP and Enalaprilat group in all animals throughout the experiment.

CONCLUSION

NOS inhibition pre-arrest did not improve survival, but did reduce requirements for epinephrine and closed-chest compression in a swine resuscitation model.

Cardioprotection afforded by ischemic preconditioning interferes with chronic beta-blocker treatment

OBJECTIVES

The efficacy of ischemic preconditioning of the heart has remained controversial. We investigated whether chronic treatment with beta-blockers affects the ischemic preconditioning in the isolated rat heart model.

DESIGN

Wistar rats were treated with propranolol (50 mg/kg/day, p.o.) (PRL), with nipradilol (10 mg/kg/day, p.o.) (NPL), or with vehicle, for 4 weeks. Isolated rat hearts were divided into global ischemia hearts (GI, PRL and NPL, each n=6) and ischemic preconditioned hearts (IP, PRL+IP and NPL+IP, each n=6).

RESULTS

Significant differences in left ventricular pressure were observed between the PRL and PRL+IP, and between the NPL and NPL+IP groups. In the NPL group, significant amelioration and preservation of left ventricular peak pressure, coronary flow, reduction of infarct size, and NOx preservation were observed. Lipid peroxidation in the NPL group was significantly reduced before and after global ischemia compared to the GI group.

CONCLUSIONS

The effect of ischemic preconditioning was abolished in the hearts of rats following oral treatment of propranolol or nipradilol. However, the administration of nipradilol protected the ischemic and reperfused myocardium, partly due to the prevention of lipid peroxide formation.

N-acetylcysteine prevents reactive oxygen species-mediated myocardial stress in patients undergoing cardiac surgery: results of a randomized, double-blind, placebo-controlled clinical trial

OBJECTIVE

Reactive oxygen species have been shown to contribute to myocardial stress in patients undergoing cardiac surgery, as demonstrated by myocardial 8-iso-prostaglandin-F(2)alpha and nitrotyrosine formation. We hypothesized that the reactive oxygen species scavenger N-acetylcysteine attenuates reactive oxygen species-mediated myocardial stress in patients undergoing cardiac surgery.

METHODS

Forty patients undergoing coronary artery surgery (mean age +/- SD, 66 +/- 9 years; 9 women and 31 men) were randomized to receive either N-acetylcysteine (100 mg/kg into cardiopulmonary bypass prime followed by infusion at 20 mg.kg(-1).h(-1), n = 20) or placebo (n = 20). Patients and clinical staff were blinded to group assignment. Transmural left ventricular biopsy specimens collected before and at the end of cardiopulmonary bypass were subjected to immunocytochemical staining against 8-iso-prostaglandin-F(2)alpha (primary measure) as an indicator for reactive oxygen species-mediated lipid peroxidation and nitrotyrosine (coprimary measure) as a marker for peroxynitrite-mediated tissue injury. Cardiomyocyte staining was quantitatively determined by using densitometry (in gray units). Global left ventricular function was measured on the basis of fractional area of contraction by using transesophageal echocardiography.

RESULTS

Patient characteristics in both groups were comparable. The change in left ventricular cardiomyocyte staining (end of cardiopulmonary bypass--before cardiopulmonary bypass) differed significantly between groups for both primary measures: 8-iso-prostaglandin-F(2)alpha, -1.8 +/- 7.5 gray units (mean +/- SD, N-acetylcysteine group) versus 5.0 +/- 4.1 gray units (placebo group; 95% confidence interval, 2.6-11.0, P =.003); nitrotyrosine, -6.4 +/- 10.0 gray units (N-acetylcysteine group) versus 9.2 +/- 8.4 gray units (placebo group; 95% confidence interval, 9.4-21.7, P <.001). Hemodynamics and clinical outcomes were comparable in both groups.

CONCLUSIONS

Reactive oxygen species scavenging with N-acetylcysteine attenuates myocardial oxidative stress in the hearts of patients subjected to cardiopulmonary bypass and cardioplegic arrest.

Does lidocaine provoke clinically significant vasospasm?

Two cases with peripheral vasoconstriction possibly caused by topical application of lidocaine were reported. A potential risk of vasospasm provoked by lidocaine may be a pitfall for anesthesiologists because lidocaine is commonly considered a vasodilator.

Nitrotyrosine and 8-isoprostane formation indicate free radical-mediated injury in hearts of patients subjected to cardioplegia

OBJECTIVE

Myocardial ischemia and reperfusion induced by cardioplegic arrest subjects the heart to free radical-mediated stress. The purpose of our study was to investigate the effect of cardioplegia-induced ischemia and reperfusion on myocardial formation and distribution of (1) nitrotyrosine as an indicator for peroxynitrite-mediated tissue injury resulting from increased nitric oxide release and (2) 8-isoprostane as an indicator for oxygen-derived free radical-mediated lipid peroxidation.

METHODS

In 10 patients undergoing coronary artery operations (64 +/- 6 [mean +/- SD] years, 3 women and 7 men) subjected to cardiopulmonary bypass and intermittent cold blood cardioplegia, we collected transmural left ventricular biopsy specimens before and at the end of cardiopulmonary bypass. Specimens were cut at 10 micro m and subjected to immunocytochemical staining against the nitric oxide-producing enzyme constitutive nitric oxide synthase, cyclic guanosine monophosphate (intracellular second messenger of nitric oxide), nitrotyrosine, and 8-isoprostane by using polyclonal antibodies. For global left ventricular function determination, we measured the fractional area of contraction using transesophageal echocardiography.

RESULTS

Nitric oxide synthase activity in cardiac myocytes increased from 34 +/- 10 gray units before cardiopulmonary bypass to 47 +/- 12 gray units at the end of bypass (P =.015), and all hearts showed increased cyclic guanosine monophosphate content in both myocytes and endothelial cells at the end of bypass. The number of nitrotyrosine-positive capillaries increased from 36 +/- 29/mm(2) before bypass to 82 +/- 47/mm(2) at the end of bypass (P =.012), and 8-isoprostane-positive capillaries increased from 92 +/- 72/mm(2) before bypass to 209 +/- 108/mm(2) at the end of bypass (P =.005). The fractional area of contraction was 53% +/- 12% before bypass and 56% +/- 12% after bypass (P =.47) but was slightly decreased to 45% +/- 14% at 4 hours after bypass (P =.121).

CONCLUSIONS

Our data show that cardioplegia-induced myocardial ischemia and reperfusion is associated with nitrotyrosine and 8-isoprostane formation mainly in the coronary endothelium, indicating injury mediated by both peroxynitrite and oxygen-derived free radicals. Because nitric oxide synthase activation was accompanied with increased cyclic guanosine monophosphate, these data suggest that direct effects of nitric oxide on cardiac myocytes, as well as nitric oxide-mediated coronary endothelial injury, might contribute to injury associated with cardioplegia and cardiopulmonary bypass.

Myocyte and endothelial effects of preconditioning the jeopardized heart by inhibiting Na/H exchange

OBJECTIVES

The preconditioning effects of the adjunctive, cardiac-specific sodium-hydrogen ion exchange inhibitor cariporide (cariporide mesilate, HOE 642) were studied in hearts subjected to 30 minutes of normothermic ischemia and reperfusion to assess myocardial and endothelial changes.

METHODS

Sixteen Yorkshire-Duroc pigs (27-34 kg) receiving cardiopulmonary bypass underwent either cardiopulmonary bypass alone (control, n = 4) or 30 minutes of normothermic ischemia, followed by 30 minutes of blood reperfusion (n = 12). Six hearts were treated with 5 mg/kg cariporide administered intravenously 15 minutes before ischemia.

RESULTS

Cardiopulmonary bypass alone caused no changes. Conversely, 30 minutes of global normothermic ischemia caused 33% mortality and, in survivors, depression of left ventricular function to 22% +/- 6% of baseline preload recruitable stroke work and increased creatine kinase MB by 406% (88 +/- 13 U/L), conjugated dienes by 17% (161 +/- 0.2 AU/mL), and myeloperoxidase activity by 297% (0.036 +/- 0.005 U/g). Myocardial edema developed (3.5% water gain). Coronary sinus endothelin 1 increased by 111% (2.05 +/- 0.38 pg/mL), and nitric oxide production decreased by 10%. These adverse effects were limited by pretreatment with cariporide, which allowed complete survival and restored preload recruitable stroke work to 78% +/- 11%. Measurements of creatine kinase MB, conjugated dienes, myeloperoxidase, water, and endothelin 1 returned to baseline values, and nitric oxide production was accentuated 3-fold.

CONCLUSIONS

These observations show that adjunctive pretreatment with cariporide delays myocardial and endothelial injury during ischemia and reperfusion, limits oxygen-derived radical injury, restores function, reduces edema, and preserves endothelin and nitric oxide balance at normal values. The myeloperoxidase changes show that less white blood cell adherence supports reduced reperfusion endothelial damage.

Long-term treatment with nipradilol, a nitric oxide-releasing beta-adrenergic blocker, enhances postischemic recovery and limits infarct size

BACKGROUND

This study examines whether the chronic administration of nipradilol, a nitric oxide-releasing beta-adrenergic blocker, decreases ischemia-reperfusion injury.

METHODS

Rats were treated with nipradilol (10 mg/kg per day orally) or a vehicle alone for 4 weeks. Isolated rat hearts were assigned to one of five groups (each n = 6): global ischemia groups treated with the vehicle or with nipradilol were subjected to 20 minutes of ischemia; ischemic preconditioning groups treated with the vehicle or with nipradilol were subjected to 3 minutes of ischemic preconditioning; and the L-arginine group treated with the vehicle received 1 mmol/L of L-arginine before global ischemia. Hemodynamic variables and coronary flow were recorded continuously. Nitrites and nitrates levels were measured 60 minutes after reperfusion, and the infarct size was determined. In another series (each n = 6), lipid peroxidation was investigated.

RESULTS

In the nipradilol group, significant preservation of the left ventricular pressure and coronary flow, as well as the level of nitrates and nitrites, was observed, compared with the global ischemia group. The infarct size was also significantly reduced in the ischemic preconditioning (23.5%+/-5.47%), L-arginine (25.6%+/-5.59%), and especially the nipradilol (10.7%+/-1.65%) groups. However, in the nipradilol plus ischemic preconditioning group, the protective effects were eliminated. Lipid peroxidation after nipradilol treatment was significantly reduced before and after global ischemia, compared with the global ischemia group.

CONCLUSIONS

The chronic administration of nipradilol improves postischemic functional recovery and infarct size, partly by preventing the formation of lipid peroxides. These cardioprotective effects were, however, abolished by ischemic preconditioning.

Ischemia increases detectable endothelial nitric oxide synthase in rat and human myocardium

The aims of the present study were to establish if myocardial ischemia/reperfusion is associated with altered eNOS activity and if myocardial eNOS detection depends on its activity. We determined detectable eNOS in (1) myocardium of isolated perfused rat hearts subjected to either global or regional ischemia and (2) in left ventricular biopsies from patients undergoing two different methods of myocardial protection (i.e., intermittent cold blood cardioplegia and continuous coronary perfusion with warm, beta-blocker-enriched blood) during coronary artery surgery. NOS detection was performed by NADPH-d staining and three eNOS-antibodies against different eNOS epitopes. In addition, activity dependent alteration of detectable eNOS was proofed by bradykinin treatment for 2 to 10 min. Ischemic and receptor mediated eNOS activation increased NADPH-d reactivity and eNOS immunoreaction as measured by antibodies against either amino acids of a central bovine eNOS domain or the human eNOS N-terminal end. In contrast, the antibody against the human eNOS C-terminal end exhibited no alteration of eNOS immunoreaction. The transient eNOS activation was associated with increased cGMP content. In human myocardium subjected to ischemia during cardiac surgery we found that early reperfusion increases eNOS activity. These data demonstrate a strong association between myocardial ischemia/reperfusion and increased eNOS activity as measured by immunocytochemical staining against specific eNOS epitopes. It appears that eNOS activation and subsequent NO release may act as a regulatory system to counter balance the potentially deleterious effects of myocardial ischemia/reperfusion.

Captopril and its time of administration in myocardial ischaemic-reperfusion injury

The present study was designed to investigate the role of captopril in an in vivo model of myocardial ischaemic-reperfusion injury with respect to its time of administration. In open-chest pentobarbitone anaesthetized cats, the left anterior descending coronary artery was occluded for 15 min followed by 60 min of reperfusion. Vehicle (saline) or captopril (4 mg kg(-1)) was administered 10 min before instituting ischaemia (pre-treatment) or 5 min before reperfusion (post-treatment). In the vehicle-treated group, ischaemic-reperfusion injury (IRI) was evidenced by enhanced plasma renin activity, depression of global haemodynamic function (mean arterial pressure, left ventricular-end-diastolic-pressure, peak positive and negative dP/dt) along with depletion of myocardial high energy phosphate (HEP) compounds. Oxidant stress in IRI was evidenced by raised levels of myocardial thiobarbituric acid reactive substances (TBARS) and depletion of endogenous myocardial antioxidants (glutathione, superoxide dismutase and catalase). Pre-treatment with captopril prevented (i) loss of myocardial haemodynamic function, (ii) rise in TBARS and (iii) depletion of myocardial HEP compounds. However, in the post-treatment group, only partial recovery of myocardial haemodynamic function, with no significant reduction in TBARS, was observed. Glutathione, superoxide dismutase and catalase were unaffected by either treatment schedules. The results of the present study suggest that captopril is more effective in attenuating ischaemic-reperfusion injury when administered before ischaemia rather than before reperfusion.

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts

OBJECTIVE

Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined.

METHODS

Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined.

RESULTS

In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group.

CONCLUSIONS

Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.

Amrinone reduces ischaemia-reperfusion injury in rat heart

We investigated the effects of amrinone on ischaemia-induced changes in myocardial function in isolated rat hearts. Isolated hearts from male Sprague-Dawley rats (150-275 g) were perfused with physiological salt solution at a constant flow rate. The effects of amrinone (30 microM) on left ventricular end diastolic pressure, positive and negative dP/dt, heart rate and coronary perfusion pressure were observed following global ischaemia and reperfusion. In normal hearts, amrinone had no effect on myocardial contractility, heart rate, coronary perfusion pressure or left ventricular end diastolic pressure. Ischaemia-reperfusion caused an increase in coronary perfusion pressure, left ventricular end diastolic pressure and creatine kinase outflow and amrinone (present from before ischaemia) decreased the rise in all of these parameters. However, when amrinone was added only after the ischaemia, it had no effect on coronary perfusion pressure or left ventricular end diastolic pressure. Thus, the effect on coronary perfusion pressure must be due to actions during the ischaemia phase. We suggest that amrinone has pharmacological properties which may be useful in reducing ischaemia-reperfusion injury. We speculate that this involves altering ischaemia-induced changes in intracellular Ca(2+) in the myocytes.

Activation of myocardial constitutive nitric oxide synthase during coronary artery surgery

OBJECTIVE

The role of nitric oxide (NO) in myocardial ischemia/reperfusion is controversial. While some studies have shown cardioprotective effects of NO, others suggested that increased myocardial NO release secondary to ischemia may contribute to reperfusion injury. However, the impact of cardioplegia-induced myocardial ischemia/reperfusion on the activity of the NO-producing enzyme constitutive NO-synthase (cNOS or NOS-III) has not been investigated.

METHODS

Twenty elective CABG patients were randomized to receive myocardial protection using either intermittent cold blood cardioplegia with 'hot-shot' (CBC; n=10) or continuous warm blood enriched with the ultra-fast-acting beta-blocker esmolol (WBE; n=10). We collected transmural LV biopsies prior to cardiopulmonary bypass (CPB), at the end of the cross-clamp period, and at the end of CPB. Specimen were subjected to immunocytochemical staining against myocardial NOS-III and cGMP using polyclonal antibodies. NOS-III activity was determined using TV-densitometry (gray units) and cGMP content using a semiquantitative score. Global myocardial metabolism was assessed by arterio-coronary sinus lactate concentration difference (a-csD(LAC)). For LV function determination we measured the fractional area of contraction (FAC) using TEE.

RESULTS

In CBC hearts a-csD(LAC) was significantly decreased following cross-clamp removal as compared to pre-CPB indicating global ischemia during cross-clamp. In contrast, a-csD(LAC) was unchanged in WBE hearts indicating absence of relevant ischemia in this group. In CBC hearts NOS-III activity did not change from pre-CPB (35.6+/-11.1 U) to the end of the cross-clamp period (38. 0+/-8.1 U; P=0.2), but increased significantly to 48.5+/-12.1 U at the end of CPB following initial warm blood reperfusion (P=0.026). In WBE hearts NOS-III activity remained unchanged throughout (29. 2+/-10.8, 35.1+/-11.8, and 32.2+/-14.7 U, respectively; 0.3). At the end of CPB, nine CBC hearts, but only one WBE heart showed increased cGMP content (P=0.002). Compared to pre-CPB, FAC in the CBC group was 109+/-25% following weaning off CPB (P=0.26), but was slightly decreased to 87+/-22% at 4 h post-CPB (P=0.03). In the WBE group FAC remained unchanged compared to pre-CPB throughout (103+/-21 and 96+/-37%, respectively; 0.5).

CONCLUSIONS

Our data show that global myocardial ischemia and reperfusion induced by CBC is associated with myocardial NOS-III activation and increased cGMP content suggesting increased NO release. In contrast, avoidance of ischemia by use of WBE prevented NOS-III and c-GMP increase. As LV function was decreased at 4 h post-CPB in the CBC group, these data suggest that increased NO release secondary to NOS-III activation may have contributed to ischemia-reperfusion injury as has been shown experimentally.

Nitric oxide mediates protein kinase C isoform translocation in rat heart during postischemic reperfusion

It is controversial whether nitric oxide (NO) is protective or deleterious against ischemia-reperfusion injury. We examined the effect of NO on PKC isoform translocation and protection against ischemia-reperfusion injury in perfused heart. An NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester, 3.0 microM), administered only during reperfusion but not during ischemia, inhibited the translocation of PKC-alpha, -delta and -epsilon isoforms to the nucleus-myofibril fraction and the translocation of PKC-alpha to the membrane fraction after ischemia (20 min) and reperfusion (10 min) in the perfused rat heart. NO donors, 3-morpholinosydnonimine (SIN-1) or S-nitroso-N-acetylpenicillamine (SNAP) activated purified PKC in vitro. SIN-1 also induced PKC isoform translocation in perfused heart. On the other hand, PKC selective inhibitor, calphostin C (0.2 microM) or chelerythrine (1.0 microM), aggravated the contractile dysfunction of ischemic heart during reperfusion, when they were perfused during reperfusion. These data suggest that NO generated during reperfusion following ischemia activates PKC isoforms and may protect the heart against contractile dysfunction in the perfused rat heart.

Transfer and expression of recombinant nitric oxide synthase genes in the cardiovascular system

Gene therapy involves the transfer of a functional gene into host cells to correct the malfunction of a specific gene or to alleviate the symptoms of a disease. For gene transfer to the cardiovascular system, adenoviral vectors are the most efficient means of transfer. Recently, transfer and functional expression of recombinant nitrio oxide synthase (NOS) genes to cerebral and cardiovascular beds have been demonstrated both ex vivo and in vivo. Here, Alex Chen and colleagues review current progress in the field of vascular NOS gene transfer and the potential use of NOS gene therapy for a number of cardiovascular diseases. Although the feasibility of the NOS gene transfer approach has been demonstrated in animal models, currently available vectors have a number of technical and safety limitations that have to be solved before human NOS gene therapy for cardiovascular disease can be attempted.