Efficiency of L-arginine enriched cardioplegia and non-cardioplegic reperfusion in ischemic hearts

Pharmacological Cardioprotection against Ischemia Reperfusion Injury-The Search for a Clinical Effective Therapy

Pharmacological conditioning aims to protect the heart from myocardial ischemia-reperfusion injury (IRI). Despite extensive research in this area, today, a significant gap remains between experimental findings and clinical practice. This review provides an update on recent developments in pharmacological conditioning in the experimental setting and summarizes the clinical evidence of these cardioprotective strategies in the perioperative setting. We start describing the crucial cellular processes during ischemia and reperfusion that drive acute IRI through changes in critical compounds (∆G_ATP, Na⁺, Ca²⁺, pH, glycogen, succinate, glucose-6-phosphate, mitoHKII, acylcarnitines, BH₄, and NAD⁺). These compounds all precipitate common end-effector mechanisms of IRI, such as reactive oxygen species (ROS) generation, Ca²⁺ overload, and mitochondrial permeability transition pore opening (mPTP). We further discuss novel promising interventions targeting these processes, with emphasis on cardiomyocytes and the endothelium. The limited translatability from basic research to clinical practice is likely due to the lack of comorbidities, comedications, and peri-operative treatments in preclinical animal models, employing only monotherapy/monointervention, and the use of no-flow (always in preclinical models) versus low-flow ischemia (often in humans). Future research should focus on improved matching between preclinical models and clinical reality, and on aligning multitarget therapy with optimized dosing and timing towards the human condition.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Oxidative Stress after Surgery on the Immature Heart

Paediatric heart surgery is associated with increased inflammation and the production of reactive oxygen species. Use of the extracorporeal cardiopulmonary bypass during correction of congenital heart defects generates reactive oxygen species by various mechanisms: haemolysis, neutrophil activation, ischaemia reperfusion injury, reoxygenation injury, or depletion of the endogenous antioxidants. The immature myocardium is more vulnerable to reactive oxygen species because of developmental differences compared to the adult heart but also because of associated congenital heart diseases that can deplete its antioxidant reserve. Oxidative stress can be manipulated by various interventions: exogenous antioxidants, use of steroids, cardioplegia, blood prime strategies, or miniaturisation of the cardiopulmonary bypass circuit. However, it is unclear if modulation of the redox pathways can alter clinical outcomes. Further studies powered to look at clinical outcomes are needed to define the role of oxidative stress in paediatric patients.

Cardiopulmonary bypass and oxidative stress

The development of the cardiopulmonary bypass (CPB) revolutionized cardiac surgery and contributed immensely to improved patients outcomes. CPB is associated with the activation of different coagulation, proinflammatory, survival cascades and altered redox state. Haemolysis, ischaemia, and perfusion injury and neutrophils activation during CPB play a pivotal role in oxidative stress and the associated activation of proinflammatory and proapoptotic signalling pathways which can affect the function and recovery of multiple organs such as the myocardium, lungs, and kidneys and influence clinical outcomes. The administration of agents with antioxidant properties during surgery either intravenously or in the cardioplegia solution may reduce ROS burst and oxidative stress during CPB. Alternatively, the use of modified circuits such as minibypass can modify both proinflammatory responses and oxidative stress.

Antioxidant therapies for the management of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, representing a major public health problem. Recent evidence suggests oxidative stress may play an important role in the pathogenesis and perpetuation of AF. In the past few years, experimental data and clinical evidence have tested the concept of antioxidant therapies to prevent AF. Besides statins, ACE-inhibitors (ACEIs) and/or angiotensin-receptor blockers (ARBs), and omega-3 polyunsaturated fatty acids, several other interventions with antioxidant properties, such as Vitamin C and E, thiazolidinediones, N-acetylcysteine, probucol, nitric oxide donors or precursors, NADPH oxidase inhibitors, Xanthine oxidase inhibitors have emerged as novel strategies for the management of AF. We aim to review recent evidence regarding antioxidant therapies in the prevention and treatment of atrial fibrillation.

L-arginine cardioplegia reduces oxidative stress and preserves diastolic function in patients with low ejection fraction undergoing coronary artery surgery

PL-arginine cardioplegia decreases biochemical markers of myocardial damage and oxidative stress in patients with normal left ventricular function. We investigated the effects of L-arginine supplemented cardioplegic arrest in patients with reduced ejection fraction. Fifty-three adult patients with left ventricular ejection fraction <35% undergoing elective coronary artery bypass surgery were randomised to receive blood cardioplegia with or without L-arginine. Following cardiopulmonary bypass, measured endpoints were cardiac troponin-I concentration at 12 and 24 hours, coronary sinus concentrations of malondialdehyde and superoxide dismutase activity at five and 15 minutes, lactic acid flux at one, five and 15 minutes and left ventricular systolic and diastolic function after protamine administration. There were no differences in cardiac troponin-I between groups. Malondialdehyde was lower in the L-arginine group, 0.28 ± 0.12 vs 0.48 ± 0.32 (5 minutes) and 0.31 ± 0.14 vs 0.38 ± 0.15 nmol.ml(-1) (15 minutes) (P=0.0004). Superoxide dismutase activity was higher in L-arginine group, 229 ± 87 vs 191.3 ± 68 (5 minutes), 229 ± 54 vs 198 ± 15 nmol.minute(-1).m(l) (15 minutes) (P=0.005). Lactic acid flux was lower in L-arginine group, 0.15 ± 0.23 vs 0.48 ± 0.32 (1 minute), 0.08 ± 0.19 vs 0.38 ± 0.31 (5 minutes) and -0.15 ± 0.13 vs 0.26 ± 0.30 mmol.l(-1) (15 minutes), (P=0.0003). There was no difference in left ventricular systolic function. The mitral annular tissue Doppler inflow (e') velocity during early diastole improved in the L-arginine group following cardiopulmonary bypass (control 4.2 ± 1.9 cm.s(-1) to 3.6 ± 1.2 cm.s(-1) vs L-arginine 3.8 ±1.2 cm.s(-1) to 4.6 ± 1.4 cm.s(-1)) (P=0.018). In patients with reduced ejection fraction, L-arginine supplemented cardioplegic arrest did not affect postoperative cardiac troponin-I levels, but attenuated cardiac cellular peroxidation and improved early left ventricular diastolic function.

Effect of N-acetylcysteine in attenuating ischemic reperfusion injury in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass

Ischemic reperfusion injury due to oxidative stress remains one of the challenging problems during cardiac surgeries. The imbalance in the production of free radicals and antioxidants in vivo determines the extent of oxidative stress. The use of antioxidants in cardioplegia has become an important strategy to salvage the myocardium from the attack of these radicals. The objective of this study was to analyze the cardioprotective effect of N-acetylcysteine (NAC) on early reperfusion injury in patients undergoing coronary artery bypass grafting using biochemical markers. Fifty-three patients with left ventricular ejection fraction >0.4 scheduled for coronary artery bypass grafting with cardiopulmonary bypass were selected and divided into two groups. The first group of patients (n=25) received isothermic cardioplegia alone, whereas the second group of patients (n=28) received cardioplegia enriched with NAC (50mg/kg body weight). The free radicals, antioxidants, cardiac troponin I, and hemodynamic and clinical properties of the patients were preoperatively and postoperatively evaluated at five different time intervals. Malondialdehyde level as a measure of free radicals was significantly lower in the NAC-enriched group during reperfusion (p<0.05) and after 12 hr (p<0.05) and 24hr (p<0.001) of surgery. All the antioxidants were elevated in the test group during the reperfusion period (p<0.01). A significant improvement (p=0.001) in the postoperative ejection fraction was noted in the test group. No significant differences were observed between the groups in the level of cardiac troponin I (p=not significant). The use of NAC in patients undergoing coronary artery bypass grafting using cardiopulmonary bypass decreased oxidative stress substantially. However, it did not lead to improvement in the level of cardiac troponin I, a marker of myocardial injury, in our study. Hence, the cardioprotective effect of NAC and the adaptation of the myocardium to oxidative stress should be extensively studied.

Limitation of myocardial and endothelial injury of the rat heart graft after preservation with Centre de Résonance Magnétique Biologique et Médicale (CRMB) solution

Myocardial injury caused by prolonged storage compromises post-transplantation contractile performance and induces endothelial injury. The aim of this study was to compare a solution developed in our laboratory [Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution] with a widely used solution (Celsior, Genzyme, Saint Germain en Laye, France). Metabolic and contractile parameters as well as indexes of endothelial injury were measured in a heterotopic rat heart transplantation model with a 3-h ischaemia and a 1-h reperfusion. The two solutions were randomly used for cardioplegia and graft preservation in six experiments each. During reperfusion, developed pressure and rate pressure product were higher with CRMBM compared with Celsior (P = 0.0002 and P = 0.0135, respectively). Phosphocreatine and adenosine triphosphate (ATP) concentrations after reperfusion were significantly higher with CRMBM (P = 0.0069 and P = 0.0053, respectively). Endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) protein expression were decreased to the same extent after reperfusion compared with baseline with CRMBM (P = 0.0001 and P < 0.0001, respectively) and Celsior (P = 0.0007 and P < 0.0001, respectively). Total nitrate concentration (NOx) was significantly increased after reperfusion with CRMBM (P < 0.0001 versus baseline and P < 0.0001 versus Celsior). Na,K-ATPase activity was decreased in both groups versus baseline after reperfusion (P < 0.0001 for CRMBM and P < 0.0001 for Celsior). We showed limitation of both myocardial and endothelial damage with CRMBM compared with Celsior during heterotopic rat heart transplantation in vivo.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

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

Reperfusion injury as a therapeutic challenge in patients with acute myocardial infarction

Cardiomyocyte death secondary to transient ischemia occurs mainly during the first minutes of reperfusion, in the form of contraction band necrosis involving sarcolemmal rupture. Cardiomyocyte hypercontracture caused by re-energisation and pH recovery in the presence of impaired cytosolic Ca(2+) control as well as calpain-mediated cytoskeletal fragility play prominent roles in this type of cell death. Hypercontracture can propagate to adjacent cells through gap junctions. More recently, opening of the mitochondrial permeability transition pore has been shown to participate in reperfusion-induced necrosis, although its precise relation with hypercontracture has not been established. Experimental studies have convincingly demonstrated that infarct size can be markedly reduced by therapeutic interventions applied at the time of reperfusion, including contractile blockers, inhibitors of Na(+)/Ca(2+) exchange, gap junction blockers, or particulate guanylyl cyclase agonists. However, in most cases drugs for use in humans have not been developed and tested for these targets, while the effect of existing drugs with potential cardioprotective effect is not well established or understood. Research effort should be addressed to elucidate the unsolved issues of the molecular mechanisms of reperfusion-induced cell death, to identify and validate new targets and to develop appropriate drugs. The potential benefits of limiting infarct size in patients with acute myocardial infarction receiving reperfusion therapy are enormous.

Perioperative Amino Acid Infusion Improves Recovery and Shortens the Duration of Hospitalization After Off-Pump Coronary Artery Bypass Grafting

Perioperative amino acid infusion helps maintain core temperature and improves patient outcomes after gynecologic and orthopedic surgery. In the present study we prospectively determined the effect of amino acid infusion on esophageal core temperature and postoperative outcomes during off-pump coronary artery bypass grafting (CABG). One-hundred-eighty consecutive patients undergoing primary elective or urgent off-pump CABG were randomly divided into two groups: the i.v. amino acid infusion group (4 kJ kg(-1) h(-1) starting 2 h before surgery) and the saline infusion group (similar period and volume of saline infusion). The esophageal core temperature at the end of surgery was 35.6 (35.3-35.8) degrees C [mean (95% confidence interval)] in the saline infusion group and 36.1 degrees C (35.9-36.3) degrees C in the amino acid infusion group (P = 0.01). Kaplan-Meier analysis demonstrated that patients given amino acids required a significantly shorter duration of postoperative mechanical ventilation than patients given saline [median (95% confidence interval), 3.0 (2.5-3.9) vs 4.5 (3.8-5.8) h; P = 0.01]. Furthermore, intensive care unit stay [20 (19.5-38.4) vs 44 (21-45) h; P = 0.001] and days until fit for discharge from hospital [10 (9-11) vs 12 (11-13) days; P = 0.004] were significantly shorter in patients given amino acid. Perioperative amino acid infusion in patients undergoing off-pump CABG effectively minimizes intraoperative hypothermia and improves postoperative recovery.

Cardioprotective effect of cold-blood cardioplegia enriched with N-acetylcysteine during coronary artery bypass grafting

BACKGROUND

Cold-blood cardioplegia is a well-known method in coronary artery bypass graft surgery, and several authors have used various agents in the enrichment of cold-blood cardioplegia to decrease ischemia-reperfusion injury seen during surgery. N-acetylcysteine, which can increase glutathione levels, is one of the agents added to cardioplegic solutions to decrease myocardial injury. This study was planned to assess the efficiency of N-acetylcysteine-enriched cold-blood cardioplegia on early reperfusion injury in patients with ischemic heart disease undergoing coronary artery bypass grafting, using measurements of cardiac troponin I and malondialdehyde release.

METHODS

Thirty patients (11 women and 19 men) with left ventricular ejection fraction greater than 0.40 scheduled for coronary artery bypass grafting were randomly divided into two groups. We used cold-blood cardioplegia enriched with N-acetylcysteine (50 mg per kilogram of body weight) in the first group and cold-blood cardioplegia alone in the second group. Hemodynamic variables and clinical properties of the patients were preoperatively and postoperatively evaluated. Enzyme releases were measured in the early hours after the operation.

RESULTS

In the N-acetylcysteine-enriched group cardiac troponin I levels were lower than in the N-acetylcysteine-free group, and this difference was statistically significant. Cardiac troponin I levels increased in both groups in the 6th and 12th hours postoperatively, but there was a statistically significant difference between the two groups. Malondialdehyde levels were significantly higher in the N-acetylcysteine-free group after the 6th, 12th, 24th, and 48th hours postoperatively when compared with the N-acetylcysteine-enriched group.

CONCLUSIONS

N-acetylcysteine-supplemented cold-blood cardioplegia minimizes myocardial injury in the early hours after and during the cardiac surgery.

Reduced cytokines release and myocardial damage in coronary artery bypass patients due to L-arginine cardioplegia supplementation

BACKGROUND

Recently, L-arginine has been added to cardioplegia to limit myocardial ischemic damage. The mechanism of action is related to the production of nitric oxide, with vasodilatation and reduction of endothelial dysfunction. Our prospective randomized study on coronary artery bypass patients investigates the effect of L-arginine on myocardial stress as expressed by myocardial cytokines release and myocardial ischemia in terms of troponin T concentration.

METHODS

Coronary artery surgery patients were randomly assigned to receive 7.5 g L-arginine in 500 mL of cardioplegic solution (group A). Group B was used as control. Cold blood 4:1 anterograde and retrograde cardioplegia with warm induction was administered. Blood samples were collected from the retrograde coronary sinus catheter to determine interleukin-2 receptor, interleukin-6, and tumor necrosis factor levels. Serum samples at different time points were also analyzed to measure myocardial ischemia markers. Hemodynamic and echocardiographic evaluations were obtained perioperatively.

RESULTS

Sixty-five patients were enrolled (group A, treated with L-arginine, n = 33; group B, control, n = 32). Wedge pressure and intensive care unit stay were significantly reduced in group A (p = 0.023 and p = 0.03, respectively). Cytokines levels were lower in group A, with a significance for interleukin-6 (p = 0.026); troponin T was reduced in treated patients (0.33 versus 0.57 ng/mL at 18 hours: p = 0.009).

CONCLUSIONS

Coronary artery surgery patients benefit from L-arginine cardioplegia supplementation in terms of reduced inflammatory reaction, limitation of myocardial ischemia, and better hemodynamic performance. Moreover, a clinical advantage is evident in terms of a shorter intensive care unit stay in patients treated with L-arginine.

Elimination of cardiac arrhythmias using oral taurine with l-arginine with case histories: Hypothesis for nitric oxide stabilization of the sinus node

We searched for nutrient deficiencies that could cause cardiac arrhythmias [premature atrial contractions (PACs), premature ventricular contractions (PVCs), atrial fibrillation, and related sinus pauses], and found literature support for deficiencies of taurine and l-arginine. Case histories of people with very frequent arrhythmias are presented showing 10-20g taurine per day reduced PACs by 50% and prevented all PVCs but did not prevent pauses. Adding 4-6g of l-arginine immediately terminated essentially all remaining pauses and PACs, maintaining normal cardiac rhythm with continued treatment. Effects of taurine useful in preventing arrhythmias include regulating potassium, calcium and sodium levels in the blood and tissues, regulating excitability of the myocardium, and protecting against free radicals damage. Taurine restored energy and endurance in one of the cases from a debilitated status to normal. Arrhythmias may also respond to taurine because it dampens activity of the sympathetic nervous system and dampens epinephrine release. l-arginine may have anti-arrhythmic properties resulting from its role as a nitric oxide (NO) precursor and from its ability to restore sinus rhythm spontaneously. Endogenous production of taurine and l-arginine may decline in aging perturbing cardiac rhythm, and these "conditional" essential nutrients therefore become "essential" and require supplementation to prevent morbidity and mortality. l-arginine is hypothesized to prevent cardiac arrhythmias by NO stabilization of the sinus node. Cardiac arrhythmias having no known cause in otherwise healthy people are hypothesized to be symptoms of deficiencies of taurine and arginine.