L-arginine reduces endothelial inflammation and myocardial stunning during ischemia/reperfusion

Mobility Coupled with Motivation Promotes Survival: The Evolution of Cognition as an Adaptive Strategy

Morphine plays a critical regulatory role in both simple and complex plant species. Dopamine is a critical chemical intermediate in the morphine biosynthetic pathway and may have served as a primordial agonist in developing catecholamine signaling pathways. While dopamine remains the preeminent catecholamine in invertebrate neural systems, epinephrine is the major product of catecholamine synthetic pathways in vertebrate species. Given that the enzymatic steps leading to the generation of morphine are similar to those constraining the evolutionary adaptation of the biosynthesis of catecholamines, we hypothesize that the emergence of these more advanced signaling pathways was based on conservation and selective "retrofitting" of pre-existing enzyme activities. This is consistent with observations that support the recruitment of enzymatically synthesized tetrahydrobiopterin (BH4), which is a cofactor for tyrosine hydroxylase, the enzyme responsible for dopamine production. BH4 is also an electron donor involved in the production of nitric oxide (NO). The links that coordinate BH4-mediated NO and catecholaminergic-mediated processes provide these systems with the capacity to regulate numerous downstream signaling pathways. We hypothesize that the evolution of catecholamine signaling pathways in animal species depends on the acquisition of a mobile lifestyle and motivationally driven feeding, sexual, and self-protective responses.

Low albumin levels are independently associated with neonatal acute kidney injury: a report from AWAKEN Study Group

BACKGROUND

Data from adult and pediatric literature have shown an association between albumin levels and AKI. Whether hypoalbuminemia and neonatal AKI are associated has not been studied.

METHODS

We evaluated the association of albumin with early (during the first postnatal week) and late (after the first postnatal week) AKI for 531 neonates from the Assessment of Worldwide AKI Epidemiology in Neonates (AWAKEN) database and for 3 gestational age (GA) subgroups: < 29, 29 to < 36, and ≥ 36 weeks GA.

RESULTS

Low albumin levels were associated with increased odds of neonatal AKI; for every 0.1 g/dL decrease in albumin, the odds of late AKI increased by 12% on continuous analysis. After adjustment for potential confounders, neonates with albumin values in the lowest quartiles (< 2.2 g/dL) had an increased odds of early [Adjusted Odd Ratio (AdjOR) 2.5, 95% CI = 1.1-5.3, p < 0.03] and late AKI [AdjOR 13.4, 95% CI = 3.6-49.9, p < 0.0001] compared to those with albumin in the highest quartile (> 3.1 g/dL). This held true for albumin levels 2.3 to 2.6 g/dL for early [AdjOR 2.5, 95% CI = 1.2-5.5, p < 0.02] and late AKI [AdjOR 6.4, 95% CI = 1.9-21.6, p < 0.01]. Albumin quartiles of (2.7 to 3.0 g/dL) were associated with increased odds of late AKI. Albumin levels of 2.6 g/dL and 2.4 g/dL best predicted early (AUC = 0.59) and late AKI (AUC = 0.64), respectively. Analysis of albumin association with AKI by GA is described.

CONCLUSIONS

Low albumin levels are independently associated with early and late neonatal AKI. Albumin could be a potential modifiable risk factor for neonatal AKI.

Daily watermelon consumption decreases plasma sVCAM-1 levels in overweight and obese postmenopausal women

Postmenopausal status is associated with an increase in total and abdominal body fat as well as increased incidence of insulin resistance and cardiovascular disease. The purpose of this study was to determine if watermelon supplementation affects select systemic markers of atherosclerosis and measures of insulin resistance in overweight and obese postmenopausal women. We hypothesized that overweight and obese postmenopausal women consuming 100% watermelon puree daily for 6 weeks would have improved levels of select systemic markers connected with cardiovascular disease without changing markers of insulin resistance. To test this hypothesis, overweight and obese postmenopausal women were recruited to participate in this study. Participants were randomly assigned to either the control group (no intervention) or the watermelon puree group (WM) for 6 weeks. Plasma concentration of markers connected with atherosclerosis and glycemic control were measured pre- and poststudy. A significant 6% decrease in soluble vascular cell adhesion molecule-1 occurred pre- to poststudy in WM, P = .003. The pattern of change in fasting blood glucose (P = .633), insulin (P = .158), and homeostatic model assessment-estimated insulin resistance (P = .174) did not differ between groups. Pre- to poststudy increases were measured in the fasting plasma concentration of l-arginine (8%, P = .005), cis-lycopene (32%, P = .003), and trans-lycopene (42%, P = .003) in WM. We conclude that 6 weeks of watermelon supplementation improved soluble vascular cell adhesion molecule-1 levels, a marker connected to atherogenesis, independent of changes in body composition or glycemic control.

The effect of intracoronary sodium nitrite on the burden of ventricular arrhythmias following primary percutaneous coronary intervention for acute myocardial infarction

OBJECTIVE

Pre-clinical evidence suggests delivery of nitric oxide (NO) through administration of inorganic nitrite suppresses arrhythmias resulting from acute ischaemia and reperfusion (I/R). To date no assessment of whether inorganic nitrite might limit reperfusion arrhythmia has occurred in man, therefore we explored the effects on I/R-induced ventricular arrhythmias in the NITRITE-AMI cohort.

METHODS

In the NITRITE-AMI cohort, Holter analysis was performed prior to and for 24 h after primary PCI in 80 patients who received either intra-coronary sodium nitrite (N = 40) or placebo (N = 40) during primary PCI for AMI.

RESULTS

Ventricular rhythm disturbance was experienced by 100% patients; however, there was no difference in the number between the groups, p = .2196. Non-sustained ventricular tachycardia (NSVT) occurred in 67.5% (27/40) of nitrite-treated patients compared to 89% (35/39) of those treated with placebo (p = .027). There was a significant reduction in both the number of runs (63%, p ≤.0001) and total beats of NSVT (64%, p = .0019) in the nitrite-treated patients compared to placebo. Post-hoc analyses demonstrate a direct correlation of occurrence of NSVT with infarct size, with the correlation stronger in the placebo versus the nitrite group initiating an independent nitrite effect (Nitrite: r = 0.110, p = .499, placebo: r = 0.527, p = .001, p for comparison: 0.004).

CONCLUSION

Overall no difference in ventricular rhythm disturbance was seen with intra-coronary nitrite treatment during primary PCI in STEMI patients, however nitrite treatment was associated with an important reduction in the incidence and severity of NSVT. In view of the sustained reduction of MACE seen, this effect warrants further study in a large-scale trial.

Glycine Does Not Add to the Beneficial Effects of Perioperative Oral Immune-Enhancing Nutrition Supplements in High-Risk Cardiac Surgery Patients

BACKGROUND

Elderly patients and patients with a poor cardiac function have increased morbidity rates when undergoing cardiac surgery. The aim of this study was to determine whether addition of glycine to a standard preoperative oral immune-enhancing nutrition supplement (OIENS) improves outcome. Glycine-enriched OIENS was compared with 2 formulas: standard OIENS and control.

METHODS

In this double-blind, 3-armed study, patients scheduled to undergo cardiac surgery with the use of extracorporeal circulation received either the glycine-enriched OIENS (OIENS + glyc, n = 24), standard OIENS (OIENS, n = 25), or control formula (Control, n = 25) for minimally 5 preoperative days. Patients were included if they were aged 70 years or older, had a compromised left ventricular function, or were planned for mitral valve surgery. Main outcome measures were postoperative infectious morbidity, organ function, and postoperative recovery.

RESULTS

Infectious morbidity was significantly lower in both treatment groups compared with the control group (p = .02). An infection was diagnosed in 5 and 4 patients in the OIENS + glyc and OIENS groups, respectively, and in 12 control patients. Less supportive therapy was necessary to stabilize circulation in both treatment groups compared with the control group. Median length of hospital stay was 7.0, 6.5, and 8.0 days in the OIENS + glyc, OIENS, and control groups, respectively. Inflammatory responses, as measured by systemic levels of proinflammatory cytokines and surface markers on polymorphonuclear cells, were comparable for all groups.

CONCLUSIONS

Preoperative OIENS reduces postoperative infectious morbidity and results in a more stable circulation; the addition of glycine does not result in any beneficial effect over standard OIENS.

Early postoperative albumin level following total knee arthroplasty is associated with acute kidney injury: A retrospective analysis of 1309 consecutive patients based on kidney disease improving global outcomes criteria

Hypoalbuminemia has been reported to be an independent risk factor for acute kidney injury (AKI). However, little is known about the relationship between the albumin level and the incidence of AKI in patients undergoing total knee arthroplasty (TKA). The aim of our study was to assess incidence and risk factors for AKI and to evaluate the relationship between albumin level and AKI following TKA.The study included a retrospective review of medical records of 1309 consecutive patients who underwent TKA between January 2008 and December 2014. The patients were divided into 2 groups according to the lowest serum albumin level within 2 postoperative days (POD2_alb level < 3.0 g/dL vs ≥3.0 g/dL). Multivariate logistic regression analysis was used to assess risk factors for AKI. A comparison of incidence of AKI, hospital stay, and overall mortality in the 2 groups was performed using propensity score analysis.Of 1309 patients, 57 (4.4%) developed AKI based on Kidney Disease Improving Global Outcomes criteria. Factors associated with AKI included age (odds ratio [OR] 1.05; 95% confidence interval [CI] 1.01-1.09; P = 0.030), diabetes (OR 3.12; 95% CI 1.65-5.89; P < 0.001), uric acid (OR 1.51; 95% CI 1.26-1.82; P < 0.001), beta blocker use (OR 2.65; 95% CI 1.48-4.73; P = 0.001), diuretics (OR 16.42; 95% CI 3.08-87.68; P = 0.001), and POD2_alb level < 3.0 g/dL (OR 1.92; 95% CI 1.09-3.37; P = 0.023). After propensity score analysis, POD2_alb level<3.0 g/dL was associated with AKI occurrence (OR 1.82; 95% CI 1.03-3.24, P = 0.041) and longer hospital stay (P = 0.001).In this study, we demonstrated that POD2_alb level<3.0 g/dL was an independent risk factor for AKI and lengthened hospital stay in patients undergoing TKA.

Role of nitric oxide in kidney and liver (as distance organ) function in bilateral renal ischemia-reperfusion: Effect of L-Arginine and NG-nitro-L-Arginine methyl ester

Background:

Renal ischemia-reperfusion (RIR) is a major cause of renal dysfunction that acts through different mechanisms. We investigated the role of L-Arginine as an endogenous nitric oxide (NO) precursor and NG-nitro-L-Arginine methyl ester (L-NAME) as an NO inhibitor on kidney and liver function in RIR model.

Materials and Methods:

Fifty-eight Wistar rats were randomly assigned to four groups. Groups 1 (sham-operated, n = 13) received a single dose of saline (4 ml/kg, i.p.) and 2 (Ischemia [Isch], n = 14) received a single dose of saline (4 ml/kg, i.p.). Groups 3 (Isch + L-NAME, n = 15) received a single dose of L-NAME (20 mg/kg, i.p.) and 4 (Isch + L-Arginine n = 16) received a single dose of L-Arginine (300 mg/kg, i.p.), After 2 h, renal failure was induced by clamping both renal pedicles for 45 min, followed by 24-h reperfusion in Groups 2–4. Finally, blood samples were obtained, and kidney tissue samples were subjected for pathology investigations.

Results:

The body weight decreased, and the serum levels of blood urea nitrogen (BUN) and creatinine (Cr), and kidney tissue damage score (KTDS) increased significantly in the Isch and Isch + L-NAME groups compared with the sham group while L-Arginine improved weight reduction (P < 0.05), and it reduced the serum levels of BUN and Cr, and KTDS when compared with the Isch and Isch + L-NAME groups. Kidney weight increased significantly in all groups compared with the sham group. L-Arginine reduced the liver tissue level of malondialdehyde and increased alkaline phosphatase.

Conclusion:

L-Arginine as an NO precursor can improve kidney function against RIR. It also improves oxidative stress in liver tissue.

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Competitive metabolism of L-arginine: arginase as a therapeutic target in asthma

Exhaled breath nitric oxide (NO) is an accepted asthma biomarker. Lung concentrations of NO and its amino acid precursor, L-arginine, are regulated by the relative expressions of the NO synthase (NOS) and arginase isoforms. Increased expression of arginase I and NOS2 occurs in murine models of allergic asthma and in biopsies of asthmatic airways. Although clinical trials involving the inhibition of NO-producing enzymes have shown mixed results, small molecule arginase inhibitors have shown potential as a therapeutic intervention in animal and cell culture models. Their transition to clinical trials is hampered by concerns regarding their safety and potential toxicity. In this review, we discuss the paradigm of arginase and NOS competition for their substrate L-arginine in the asthmatic airway. We address the functional role of L-arginine in inflammation and the potential role of arginase inhibitors as therapeutics.

Role of l-Arginine on Dyslipidemic Conditions of Acute Myocardial Infarction Patients

Oxidative stress conditions associated with atherosclerosis leads to oxidative modification of low-density lipoprotein (LDL). The body's capabilities to inhibit LDL oxidation and to remove or neutralize the atherogenic oxidized LDL (ox-LDL) are limited. When the LDL cholesterol level increases in the blood, it leads to dangerous consequences like atherosclerosis, leading to myocardial infarction. The major effect of an antioxidant in the LDL environment is to prevent the formation of ox-LDL (during atherogenesis. Strategies to reduce LDL oxidation and prevent atherogenesis can involve the enrichment of arterial cells with potent antioxidants that can prevent oxidative damage to the arterial wall. The objective of this study is to evaluate the effect of l-arginine on serum lipid and cholesterol levels in the patients of acute myocardial infarction (AMI). The study consisted of 70 AMI patients and 60 healthy individuals (serving as control) age 55-65 years. Serum levels of total cholesterol, high density lipoprotein (HDL), LDL and Triglycerides were determined on day 1 and day 15 of l-arginine administration (oral dose 3 g/day). The total cholesterol/HDL and the LDL/HDL ratio were calculated and compared. As per the observations, l-arginine administration was found to improve the lipid profile of the subjects. Hence it could be used as an adjuvant therapy for AMI and as a preventive measure for the onset of the disease in the healthy elderly also.

Role of inflammation in the regulation of coronary blood flow in ischemia and reperfusion: mechanisms and therapeutic implications

A multitude of factors, including increased coronary vascular resistance and dysregulated coronary microcirculatory function, contribute to the impairment of coronary blood flow (CBF) regulation and the pathogenesis of myocardial ischemia/reperfusion (I/R) injury. CBF is primarily determined by coronary vascular resistance, which is affected by the balance between various vasodilators and vasoconstrictors. Myocardial I/R causes reduced production of endogenous vasodilators, such as nitric oxide (NO), leaving unopposed vasoconstriction that is caused mainly by continued presence of endothelin-1 (ET-1) and serotonin (5-HT); this imbalance in turn enhances vascular tone, triggers inflammatory response, decreases CBF and exacerbates reperfusion injury. Various inflammatory cytokines participate in the regulation of coronary vasomotor function by affecting the balance between vasodilators and vasoconstrictors. In addition to the enhanced coronary vasoconstriction, coronary microembolization, inflammatory cell infiltration and post-ischemic hyperpermeability contribute to the impairment of coronary microcirculatory function and myocardial perfusion during I/R. Ongoing research examining the role of inflammation in the regulation of CBF and coronary microcirculatory function in myocardial I/R is expected to yield new insights that will lead to therapies for ameliorating the vascular inflammatory response in coronary artery diseases (CADs) in the clinical setting. This article is part of a Special Issue entitled "Coronary Blood Flow".

Oral administration of L-arginine in patients with angina or following myocardial infarction may be protective by increasing plasma superoxide dismutase and total thiols with reduction in serum cholesterol and xanthine oxidase

Administration of L-arginine has been shown to control ischemic injury by producing nitric oxide which dilates the vessels and thus maintains proper blood flow to the myocardium. In the present study attempt has been made to determine whether oral administration of L-arginine has any effect on oxidant/antioxidant homeostasis in ischemic myocardial patients [represented by the patients of acute angina (AA) and acute myocardial infarction (MI)]. L-arginine has antioxidant and antiapoptotic properties, decreases endothelin-1 expression and improves endothelial function, thereby controlling oxidative injury caused during myocardial ischemic syndrome. Effect of L-arginine administration on the status of free radical scavenging enzymes, pro-oxidant enzyme and antioxidants viz. total thiols, carbonyl content and plasma ascorbic acid levels in the patients has been evaluated. We have observed that L-arginine administration (three grams per day for 15 days) resulted in increased activity of free radical scavenging enzyme superoxide dismutase (SOD) and increase in the levels of total thiols (T-SH) and ascorbic acid with concomitant decrease in lipid per-oxidation, carbonyl content, serum cholesterol and the activity of proxidant enzyme, xanthine oxidase (XO). These findings suggest that the supplementation of L-arginine along with regular therapy may be beneficial to the patients of ischemic myocardial syndromes.

The role of nitric oxide, superoxide and peroxynitrite in the anti-arrhythmic effects of preconditioning and peroxynitrite infusion in anaesthetized dogs

BACKGROUND AND PURPOSE

Both ischaemia preconditioning (PC) and the intracoronary infusion of peroxynitrite (PN) suppress ischaemia and reperfusion (I/R)-induced arrhythmias and the generation of nitrotyrosine (NT, a marker of PN). However, it is still unclear whether this latter effect is due to a reduction in nitric oxide (NO) or superoxide (O(2)(-)) production.

EXPERIMENTAL APPROACH

Dogs anaesthetized with chloralose and urethane were infused, twice for 5 min, with either saline (control) or 100 nM PN, or subjected to similar periods of occlusion (PC), 5 min prior to a 25 min occlusion and reperfusion of the left anterior descending coronary artery. Severities of ischaemia and ventricular arrhythmias, as well as changes in the coronary sinus nitrate/nitrite (NOx) levels were assessed throughout the experiment. The production of myocardial NOx, O(2)(-) and NT was determined following reperfusion.

KEY RESULTS

Both PC and PN markedly suppressed the I/R-induced ventricular arrhythmias, compared to the controls, and increased NOx levels during coronary artery occlusion. Reperfusion induced almost the same increases in NOx levels in all groups, but superoxide production and, consequently, the generation of NT were significantly less in PC- and PN-treated dogs than in controls.

CONCLUSIONS AND IMPLICATIONS

Since both PC and the administration of PN enhanced NOx levels during I/R, the attenuation of endogenous PN formation in these dogs is primarily due to a reduction in the amount of O(2) produced. Thus, the anti-arrhythmic effect of PC and PN can almost certainly be attributed to the preservation of NO availability during myocardial ischaemia.

Cardiac electrophysiological effects of nitric oxide

Nitric oxide (NO) synthetized by essentially all cardiac cell types plays a key role in the regulation of cardiac function. Recent evidence shows that NO modulates the activity of cardiac ion channels implicated in the genesis of the cardiac action potential and exerts anti-arrhythmic properties under some circumstances. We review the effects of NO on cardiac ion channels and the signalling pathways, including cGMP-dependent (protein kinase G and cGMP-regulated phosphodiesterases) and cGMP-independent mechanisms (S-nitrosylation and direct effects on G proteins) and finally the role of NO in the genesis of cardiac arrhythmias during ischemia-reperfusion, heart failure, long QT syndrome, atrial fibrillation, and sudden cardiac death.

Dopamine, morphine, and nitric oxide: an evolutionary signaling triad

Morphine biosynthesis in relatively simple and complex integrated animal systems has been demonstrated. Key enzymes in the biosynthetic pathway have also been identified, that is, CYP2D6 and COMT. Endogenous morphine appears to exert highly selective actions via novel mu opiate receptor subtypes, that is, mu3,-4, which are coupled to constitutive nitric oxide release, exerting general yet specific down regulatory actions in various animal tissues. The pivotal role of dopamine as a chemical intermediate in the morphine biosynthetic pathway in plants establishes a functional basis for its expansion into an essential role as the progenitor catecholamine signaling molecule underlying neural and neuroendocrine transmission across diverse animal phyla. In invertebrate neural systems, dopamine serves as the preeminent catecholamine signaling molecule, with the emergence and limited utilization of norepinephrine in newly defined adaptational chemical circuits required by a rapidly expanding set of physiological demands, that is, motor and motivational networks. In vertebrates epinephrine, emerges as the major end of the catecholamine synthetic pathway consistent with a newly incorporated regulatory modification. Given the striking similarities between the enzymatic steps in the morphine biosynthetic pathway and those driving the evolutionary adaptation of catecholamine chemical species to accommodate an expansion of interactive but distinct signaling systems, it is our overall contention that the evolutionary emergence of catecholamine systems required conservation and selective "retrofit" of specific enzyme activities, that is, COMT, drawn from cellular morphine expression. Our compelling hypothesis promises to initiate the reexamination of clinical studies, adding new information and treatment modalities in biomedicine.

Recipient treatment with L-arginine attenuates donor lung injury associated with hemorrhagic shock

BACKGROUND

Organ donors are frequently trauma victims, but the impact of donor hemorrhagic shock and resuscitation (HSR) on pulmonary graft function has not been assessed. L-arginine treatment during reperfusion increases the production of endothelial nitric oxide and thus ameliorates ischemia-reperfusion injury. Objective of the present porcine study was to investigate the effect of donor hemorrhage on pulmonary graft function and potential beneficial effects of L-arginine administration.

METHODS

In the control-group (n=6), lungs were harvested from donors without hypotensive periods. In the HSR-group (n=6) and HSR-Arg-group (n=6), donors were subjected to hemorrhagic shock (40% blood shed) and resuscitation before harvest. Left lungs were transplanted after hypothermic preservation of 18 hr, and graft function was observed for 6 hr after reperfusion. Recipients in the HSR-Arg-group received a bolus of L-arginine (50 mg/kg BW) intravenously 5 min before reperfusion followed by a continuous intravenous administration of L-arginine 200 mg/kg BW for 2 hr. Tissue specimens and bronchoalveolar lavage fluid were obtained at the end of the observation period.

RESULTS

Donor lung function did not differ between study groups. Compared with the control group, pulmonary graft gas exchange was significantly impaired in the HSR-group. Graft function in the HSR-Arg-group did not differ from control organs. Neutrophil fraction, protein content, and malondialdehyde levels in the bronchoalveolar lavage fluid in the HSR-group were higher compared with control and HSR-Arg-Group.

CONCLUSION

Although fulfilling ideal donor criteria, pulmonary graft function of lungs harvested from donors subjected to HSR is impaired, but improves significantly when l-arginine is administered during reperfusion.

Inhibition of S6K1 accounts partially for the anti-inflammatory effects of the arginase inhibitor L-norvaline

Background

Pharmacological inhibition of endothelial arginase-II has been shown to improve endothelial nitric oxide synthase (eNOS) function and reduce atherogenesis in animal models. We investigated whether the endothelial arginase II is involved in inflammatory responses in endothelial cells.

Methods

Human endothelial cells were isolated from umbilical veins and stimulated with TNFα (10 ng/ml) for 4 hours. Endothelial expression of the inflammatory molecules i.e. vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin were assessed by immunoblotting.

Results

The induction of the expression of endothelial VCAM-1, ICAM-1 and E-selectin by TNFα was concentration-dependently reduced by incubation of the endothelial cells with the arginase inhibitor L-norvaline. However, inhibition of arginase by another arginase inhibitor S-(2-boronoethyl)-L-cysteine (BEC) had no effects. To confirm the role of arginase-II (the prominent isoform expressed in HUVECs) in the inflammatory responses, adenoviral mediated siRNA silencing of arginase-II knocked down the arginase II protein level, but did not inhibit the up-regulation of the adhesion molecules. Moreover, the inhibitory effect of L-norvaline was not reversed by the NOS inhibitor L-NAME and L-norvaline did not interfere with TNFα-induced activation of NF-κB, JNK, p38mapk, while it inhibited p70s6k (S6K1) activity. Silencing S6K1 prevented up-regulation of E-selectin, but not that of VCAM-1 or ICAM-1 induced by TNFα.

Conclusion

The arginase inhibitor L-norvaline exhibits anti-inflammatory effects independently of inhibition of arginase in human endothelial cells. The anti-inflammatory properties of L-norvaline are partially attributable to its ability to inhibit S6K1.

Cholinergic agonists attenuate renal ischemia-reperfusion injury in rats

Inflammation plays a significant role in the pathophysiology of renal ischemia-reperfusion injury. Local inflammation is modulated by the brain via the vagus nerve and nicotinic acetylcholine receptors such that electrical or pharmacologic stimulation of this cholinergic anti-inflammatory pathway results in suppression of proinflammatory cytokine production. We examined the effects of cholinergic stimulation using agonists, nicotine or GTS-21, given before or after bilateral renal ischemia-reperfusion injury in rats. Pretreatment of rats with either agonist significantly attenuated renal dysfunction and tubular necrosis induced by renal ischemia. Similarly, tumor necrosis factor-alpha protein expression and leukocyte infiltration of the kidney were markedly reduced following treatment with cholinergic agonists. We found functional nicotinic acetylcholine receptors were present on rat proximal tubule epithelial cells. Cholinergic stimulation significantly decreased tubular necrosis in vagotomized rats after injury, implying an intact vagus nerve is not required for this renoprotective effect.

Myocardial release of nitric oxide during ischaemia and reperfusion: effects of L-arginine and hypercholesterolaemia

AIMS

Nitric oxide (NO) may modulate myocardial ischaemia/reperfusion (I/R) injury, but effects of hypercholesterolaemia on myocardial NO release during I/R are unknown.

METHODS

A NO-specific carbon fibre electrode continuously measured coronary sinus [NO] during 60 min low-flow ischaemia (1 ml/min) and 60 min free reperfusion (I/R) in isolated rabbit hearts. Experimental groups (n=7 per group) were control, L-arginine supplement (200 microM), N-nitro-L-arginine methyl ester (L-NAME) treatment (8 microM) and hypercholesterolaemic.

RESULTS

During early I, NO release decreased markedly in control (-1356+/-286 pmol/min/g) and L-arginine (-1972+/-172) groups, but less in L-NAME (-441+/-89) and hypercholesterolaemic (-602+/-164) groups (both p<0.01 vs. controls). No increase in NO release during I was seen in any group. After R, NO release increased above baseline in control (+2333+/-591 pmol/min/g) and L-arginine (+1048+/-278) groups and hypercholesterolaemic (+1100+/-478) (p<0.05 vs. pre-ischaemia each group). There was little increase in NO release in the L-NAME group (+436+/-247 pmol/min/g, p<0.05 vs. controls). In each group, myocardial NO release declined towards pre-ischaemic levels during 60 min R. Hearts treated with L-arginine had similar NO release but better functional recovery than controls (p<0.01). Treatment with L-NAME was also associated with better functional recovery than in controls or hypercholesterolaemic hearts.

CONCLUSION

Myocardial NO release declines rapidly during ischaemia, but increases above baseline during early reperfusion. Improved function after L-arginine treatment appears to be independent of effects upon NO release. Hypercholesterolaemia is associated with reduced myocardial NO release, under both baseline conditions and during ischaemia and reperfusion.

Cardioprotection by adenosine A2A agonists in a canine model of myocardial stunning produced by multiple episodes of transient ischemia

We sought to determine whether administration of a very low, nonvasodilating dose of a highly selective adenosine A(2A) receptor agonist (ATL-193 or ATL-146e) would be cardioprotective in a canine model of myocardial stunning produced by multiple episodes of transient ischemia. Twenty-four anesthetized open-chest dogs underwent either 4 (n=12) or 10 cycles (n=12) of 5-min left anterior descending coronary artery (LAD) occlusions interspersed by 5 or 10 min of reperfusion. Left ventricular thickening was measured from baseline through 180 min after the last occlusion-reperfusion cycle. Regional flow was measured with microspheres. In 12 of 24 dogs, A(2A) receptor agonist was infused intravenously beginning 2 min prior to the first occlusion and continuing throughout reperfusion at a dose below that which produces vasodilatation (0.01 microg x kg(-1) x min(-1)). Myocardial flow was similar between control and A(2A) receptor agonist-treated animals, confirming the absence of A(2) receptor agonist-induced vasodilatation. During occlusion, there was severe dyskinesis with marked LAD zone thinning in all animals. After 180 min of reperfusion following the last cycle, significantly greater recovery of LAD zone thickening was observed in A(2A) receptor agonist-treated vs. control animals in both the 4-cycle (91 +/- 7 vs. 56 +/- 12%, respectively; P<0.05) and the 10-cycle (65 +/- 9 vs. 8 +/- 16%, respectively; P<0.05) occlusion groups. The striking amount of functional recovery observed with administration of low, nonvasodilating doses of adenosine A(2A) agonist ATL-193 or ATL-146e supports their further evaluation for the attenuation of postischemic stunning in the clinical setting.

Concentration decrease of nitric oxide in the postischemic muscle is not only caused by the generation of O2−

Reperfusion of ischemic skeletal muscle is associated with an alteration of the concentrations of O(2) (-) and NO. In this study, the influence of epigallocatechin-3-gallate (EGCG), a known radical scavenger, on the balance of O(2) (-) and NO has been measured online in the skeletal muscle of Wistar rats. The hind limb of 14 male rats had been exposed to ischemic stress for 2 h. Seven rats received an infusion of 1.5 micromol EGCG/kg 5 min before reperfusion. O(2) (-), NO, and temperature were measured during reperfusion. The concentration of O(2) (-) declined under the influence of EGCG from 156.5 to 72.2 nmol/l (P = 0.01). The level of NO was found to decrease; this decrease was not significantly changed by EGCG (-175 nmol/l vs. - 227 nmol/l; P = 0.33). Thus the different superoxide concentrations did not correspond to different levels of NO, and the interaction of both radicals is not the only reason for the concentration decrease of NO in the reperfusion period. We conclude that EGCG protects skeletal muscle from I/R-injury without influencing the NO concentration profile to a large extent.

Prognostic significance of microalbuminuria in non-diabetic patients with acute myocardial infarction

BACKGROUND

The aim of this study was to examine whether the presence of microalbuminuria (20-200 microg/min) can predict in-hospital morbidity and mortality in non-diabetic patients with acute myocardial infarction.

METHODS

Two hundred twenty-three (172 men and 51 women) non-diabetic patients with acute myocardial infarction were studied prospectively. The main outcome measures of the study were based on a comparison of in-hospital mortality and major non-fatal in-hospital events (pulmonary edema, post-infarction angina, infarct extension, mechanical complications, conduction disturbances and ventricular arrhythmias) between microalbuminuric and normoalbuminuric patients.

RESULTS

A significant proportion of patients (33.6%) had microalbuminuria. Seventy-six patients (34%) developed an in-hospital event (fatal or non-fatal). Six patients (2.7%) with acute myocardial infarction died in the hospital. Patients with microalbuminuria had a higher mortality rate in comparison with normoalbuminuric patients (6.6% vs. 0.68%, p = 0.01). For non-fatal events, the incidence of pulmonary edema and ventricular arrhythmias was significantly higher in patients with microalbuminuria (14.6% vs. 3.4%, p < 0.001 and 12% vs. 3.4%, p = 0.01, respectively). The combined end-point of the total number of fatal and non-fatal events was significantly higher in patients with microalbuminuria (57.3% vs. 22.3%, p < 0.001). In multiple logistic regression analysis, microalbuminuria (p < 0.001) and ejection fraction (p = 0.01) were independently related to the occurrence of major in-hospital events.

CONCLUSIONS

Microalbuminuria is a significant predictor of in-hospital morbidity and mortality in non-diabetic patients with acute myocardial infarction.

Coordinated induction of iNOS-VEGF-KDR-eNOS after resveratrol consumption: a potential mechanism for resveratrol preconditioning of the heart

Existing evidence indicates that resveratrol, a red wine and grape-derived polyphenolic antioxidant, can pharmacologically precondition the heart in a nitric oxide (NO)-dependent manner. To further explore the role of NO in resveratrol-mediated cardioprotection, the induction for the expression of the potential molecular targets of NO including VEGF and KDR as well as iNOS and eNOS were examined by Western blot analysis and immunohistochemistry. Two groups of rats were studied, one group of animals was fed resveratrol for 7 days while the other group was given water only. After 1, 3, 5 and 7 days, the rats were sacrificed and the expression of the proteins was examined by Western blot analysis. Western blot detected an overexpression of iNOS and VEGF within 24 h of resveratrol treatment while the induction of KDR was not increased until after 3 days and eNOS expression after 5 days of resveratrol treatment. These expressions were further increased after 7 days of resveratrol treatment, when the rats were sacrificed for the isolated working heart preparation. Resveratrol provided cardioprotection as evidenced by superior post-ischemic ventricular recovery, reduced myocardial infarct size and decreased number of apoptotic cardiomyocytes. Immunohistochemistry was performed in the hearts at baseline, and at the end of 30-min ischemia/2-h reperfusion. The hearts obtained from resveratrol-treated rats revealed enhanced expression for iNOS, eNOS and VEGF and KDR compared to control hearts at the end of reperfusion. The results of this study demonstrate that resveratrol leads to a coordinated upregulation of iNOS-VEGF-KDR-eNOS, which is likely to play a role in resveratrol-mediated cardioprotection.

Nitric oxide insufficiency and atherothrombosis

Nitric oxide (NO) is a structurally simple compound that participates in a wide range of biological reactions to maintain normal endothelial function and an antithrombotic intravascular milieu. Among its principal effects are the regulation of vascular tone, vascular smooth muscle cell proliferation, endothelial-leukocyte interactions, and the antiplatelet effects of the endothelium. Impaired NO bioavailability represents the central feature of endothelial dysfunction, the earliest stage in the atherosclerotic process, and also contributes to the pathogenesis of acute vascular syndromes by predisposing to intravascular thrombosis. The causes of NO insufficiency can be grouped into two fundamental mechanisms: inadequate synthesis and increased inactivation of NO. Polymorphisms in the endothelial NO synthase gene and decreased substrate or cofactor availability for this enzyme are the main mechanisms that compromise the synthesis of NO. Inactivation of NO occurs mainly through its interaction with reactive oxygen species and can be favored by a deficiency of antioxidant enzymes such as glutathione peroxidase. In this review, we present an overview of NO synthesis and biological chemistry, discuss the mechanisms of action of NO in regulating endothelial and platelet function, and explore the causes of NO insufficiency, as well as the evidence linking these causes to the pathophysiology of endothelial dysfunction and atherothrombosis.

Potent antifibrillatory effects of intrapericardial nitroglycerin in the ischemic porcine heart

OBJECTIVES

We investigated the antiarrhythmic effects of intrapericardial nitroglycerin (NTG) during acute myocardial ischemia in the porcine heart.

BACKGROUND

Nitroglycerin is a nitric oxide donor that exerts potent effects on the cardiovascular system. Intrapericardial administration allows investigation of pharmacologic actions on cardiac tissue in an in vivo system while minimizing the confounding influences of systemic effects.

METHODS

In 29 closed-chest pigs, myocardial ischemia was induced by intraluminal balloon occlusion of the left anterior descending coronary artery. Arrhythmia incidence was monitored during 5-min balloon inflations performed without drug and at 15, 45, 75, and 105 min after NTG (4,000 microg bolus) administered by percutaneous transatrial access into the pericardial space. Electrocardiograms were monitored for ischemia-induced T-wave alternans (TWA), a marker of electrical instability. The antiadrenergic potential of NTG was investigated by examining the drug's suppression of dobutamine-induced increase in myocardial contractility.

RESULTS

Control coronary artery occlusion provoked ventricular fibrillation (VF) in all animals. Intrapericardial NTG suppressed VF at 45 min in all six pigs (p < 0.05) and reduced TWA across a parallel time course (from 459.1 +/- 144.4 microV before drug to 42.22 +/- 13.96 microV at 45 min, p = 0.047). The antifibrillatory effect occurred as early as 15 min and persisted for up to 75 min. Augmentation of maximum of the first time derivative of left ventricular pressure by dobutamine was blunted by intrapericardial NTG (from 3,999 +/- 196 mm Hg/s before NTG to 3,543 +/- 220 mm Hg/s at 15 min, p = 0.012).

CONCLUSIONS

Intrapericardial NTG exerts a robust antifibrillatory action. Potential mechanisms include reduction in electrical instability and blunting of adrenergic effects.

Effects of brief ischemia and reperfusion on the myocardium and the role of nitric oxide

Brief myocardial ischemia/reperfusion has complex effects on the myocardium. In the short term the myocardium may be stunned with temporarily reduced contractile function, though this may also be accompanied by the modification and de novo synthesis of proteins that protect the heart against subsequent early or delayed insults. Repeated episodes of non-lethal ischemia, which are common in the clinical setting, combine all of these phenomena and may ultimately result in chronic contractile dysfunction. Nitric oxide is intimately linked to many of these alterations in cellular function and defense. This article examines data predominantly from in vivo large animal studies that relate to these ischemia-induced changes, the evidence for the proposed mechanisms behind both myocardial stunning and preconditioning while concentrating on the role of nitric oxide in these conditions.

Pharmacological preconditioning with resveratrol: role of nitric oxide

Resveratrol (trans-3,4',5-trihydroxystilbene), a recently described grape-derived polyphenolic antioxidant, has been found to protect the heart from ischemic-reperfusion injury. The present study sought to determine the mechanism of cardioprotection by investigating the ability of resveratrol to precondition the heart. Isolated perfused rat hearts were randomly divided into six groups: group I was perfused for 15 min with Kreb-Henseleit buffer (KHB) only; group II was perfused with 10 microM resveratrol; group III was perfused with 10 microM resveratrol plus 100 microM N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective nitric oxide (NO) synthase (NOS) inhibitor; group IV was perfused with 10 microM resveratrol plus 100 microM aminoguanidine (AG), an inducible NOS (iNOS) blocker; and groups V and VI consisted of hearts perfused with L-NAME and AG, respectively. The perfusion was then switched to working mode, and all hearts were made globally ischemic for 30 min followed by 2 h of reperfusion. Preconditioning of the hearts with resveratrol provided cardioprotection as evidenced by improved postischemic ventricular functional recovery (developed pressure and aortic flow) and reduced myocardial infarct size and cardiomyocyte apoptosis. Resveratrol-mediated cardioprotection was completely abolished by both L-NAME and AG. In a separate study, hearts were examined for iNOS mRNA induction. Resveratrol caused an induction of the expression of iNOS mRNA beginning at 30 min after reperfusion, increasing steadily up to 60 min of reperfusion, and then decreasing progressively up to 2 h after reperfusion. Preperfusion of the hearts with AG almost completely blocked the induction of iNOS. The results of our study demonstrate that resveratrol can pharmacologically precondition the heart in a NO-dependent manner.

Pharmacological preconditioning with resveratrol: an insight with iNOS knockout mice

Resveratrol, a natural antioxidant and polyphenol found in grapes and wine, has been found to pharmacologically precondition the heart through the upregulation of nitric oxide (NO). To gain further insight of the role of NO in resveratrol preconditioning, mouse hearts devoid of any copies of inhibitory NO synthase (iNOS) (iNOS knockout) and corresponding wild-type hearts were perfused with 10 microM resveratrol for 15 min followed by 25 min of ischemia and 2 h of reperfusion. Control experiments were performed with wild-type and iNOS knockout hearts that were not treated with resveratrol. Resveratrol-treated wild-type mouse hearts displayed significant improvement in postischemic ventricular functional recovery compared with those of nontreated hearts. Both resveratrol-treated and nontreated iNOS knockout mouse hearts resulted in relatively poor recovery in ventricular function compared with wild-type resveratrol-treated hearts. Myocardial infarct size was lower in the resveratrol-treated wild-type mouse hearts compared with other group of hearts. In concert, a number of apoptotic cardiomyocytes was lower in the wild-type mouse hearts treated with resveratrol. Cardioprotective effects of resveratrol was abolished when the wild-type mouse hearts were simultaneously perfused with aminoguanidine, an iNOS inhibitor. Resveratrol induced the expression of iNOS in the wild-type mouse hearts, but not in the iNOS knockout hearts, after only 30 min of reperfusion. Expression of iNOS remained high even after 2 h of reperfusion. Resveratrol-treated wild-type mouse hearts were subjected to a lower amount of oxidative stress as evidenced by reduced amount of malonaldehyde content in these hearts compared with iNOS knockout and untreated hearts. The results of this study demonstrated that resveratrol was unable to precondition iNOS knockout mouse hearts, whereas it could successfully precondition the wild-type mouse hearts, indicating an essential role of iNOS in resveratrol preconditioning of the heart.

Effect of treatment on ventricular function and troponin I proteolysis in reperfused myocardium

Effects of ischemia time and treatment interventions upon troponin I (TnI) proteolysis and function of reperfused myocardium were examined in isolated, perfused rabbit hearts. Hearts were randomized to 90 min aerobic perfusion, 15 min low-flow (1 ml/min) ischemia (I) and 60 min reperfusion (R) or 60 min low-flow I and 60 min R. Hearts subject to 60 min I and 60 min R received either no treatment, l -arginine treatment, or treatment with oxygen free radical (OFR) scavengers (mercapto-proponyl-glycine, catalase and superoxide dismutase). Hearts from cholesterol-fed rabbits were also studied after 60 min I and R. Isovolumic LV pressure and heart rate were recorded throughout and Western analysis of ventricular myocardium, using 3 specific antibodies, detected intact TnI (29 kDa) and TnI fragment (25 kDa). Hearts subject to 15 min I had minimal irreversible injury (TTC negative region=0.6+/-0.4% LV) but hearts subject to 60 min I had more extensive injury (TTC negative=40.7+/-5.8% LV). Recovery of rate-pressure product after 15 min I and 60 min R (56+/-9% of baseline) was better than after 60 min I and 60 min R (23+/-9%, P<0.01). Both l -arginine and OFR scavengers were associated with better recovery of function after 60 min I, (66+/-7% and 72+/-3% of baseline respectively, P<0.01 v no treatment) but cholesterol hearts had poor recovery after 60 min I (37+/-8%). The 25 kDa TnI (% total TnI immunoreactivity) was 8.7+/-0.9% in controls, 10.0+/-1.6% after 15 min I and 60 min R, and 17.4+/-2.4% after 60 min I and 60 min R (P<0.01 v controls and 15 min I). The proportion of 25 kDa TnI was increased in all hearts after 60 min I and did not change with treatment (l -arginine 16.8+/-1.8%, OFR scavengers 16.0+/-3.2%, cholesterol 14.0+/-1.9%). There was no relation between proportion of 25 kDa TnI and recovery of function. Samples from freshly excised rabbit hearts and human right atria also had 25 kDa TnI (relative intensities 8.5+/-2.3% and 5.1+/-2.6% respectively). Although TnI fragmentation increases after prolonged ischemia and reperfusion, the functional recovery of stunned myocardium is independent of degree of TnI fragmentation.

Cardioplegic arrest with L-arginine improves myocardial protection: results of a prospective randomized clinical trial

BACKGROUND

Blood cardioplegic arrest remains the method of choice for myocardial protection. L-arginine has been suggested to improve protection through an increase in nitric oxide production.

METHODS

A prospective, randomized, double-blinded clinical trial comparing standard blood cardioplegic solution to L-arginine-enriched solution (7.5 g/500 mL) enrolled 200 patients undergoing coronary artery bypass grafting. Clinical data and biochemical markers of ischemia were recorded. Warm blood cardioplegia (33 degrees C) was administered in 74% of patients and cold blood (20 degrees C) was used in 26% of patients. Both groups averaged three grafts per patient.

RESULTS

There were two (2%) deaths in both groups. There were four (4%) myocardial infarctions (MI) in the control group and six (6%) infarctions in the L-arginine group (p = 0.5). For the 190 patients without MI, serum levels of troponin T averaged 0.40+/-0.43, 0.38+/-0.42, and 0.39+/-0.50 microg/L in control patients compared with 0.28+/-0.22, 0.24+/-0.18, and 0.27+/-0.20 microg/L in L-arginine patients, respectively, 12, 24 and 48 hours after coronary artery bypass grafting (p = 0.03). The cardiac index averaged 2.7+/-0.8 L x min(-1) x m(-2) in control patients and 2.9+/-0.7 L x min(-1) x m(-2) in arginine patients immediately after surgery (p = 0.09). Intensive care unit and hospital length of stay averaged 3.5+/-5 days and 7.3+/-6 days in control patients compared with 2.5+/-3 days and 6.1+/-4 days in arginine patients (p = 0.09).

CONCLUSIONS

L-arginine-supplemented blood cardioplegic solution is associated with reduced release of biochemical markers of myocardial damage, suggesting improved myocardial protection.

Mechanisms whereby rapid RV pacing causes LV dysfunction: perfusion-contraction matching and NO

Incessant tachycardia induces dilated cardiomyopathy in humans and experimental models; mechanisms are incompletely understood. We hypothesized that excessive chronotropic demands require compensatory contractility reductions to balance metabolic requirements. We studied 24 conscious dogs during rapid right ventricular (RV) pacing over 4 wk. We measured hemodynamic, coronary blood flow (CBF), myocardial O(2) consumption (MVO(2)) responses, myocardial nitric oxide (NO) production, and substrate utilization. Early pacing (6 h) resulted in decreased heart rate (HR)-adjusted coronary blood flow (CBF), MVO(2) (CBF/beat: 0.33 +/- 0.02 to 0.19 +/- 0.01 ml, P < 0.001, MVO(2)/beat: 0.031 +/- 0.002 to 0.016 +/- 0.001 ml O(2), P < 0.001), and contractility [left ventricular (LV) first derivative pressure (dP/dt)/LV end-diastolic diameter (EDD): 65 +/- 4 to 44 +/- 3 mmHg x s(-1) x mm(-1), P < 0.01], consistent with flow-metabolism-function coupling, which persisted over the first 72 h of pacing (CBF/beat: 0.15 +/- 0.01 ml, MVO(2)/beat: 0.013 +/- 0.001 ml O(2), P < 0.001). Thereafter, CBF per beat and MVO(2) per beat increased (CBF/beat: 0.25 +/- 0.01 ml, MVO(2)/beat: 0.021 +/- 0.001 ml O(2) at 28 days, P < 0.01 vs. 72 h). Contractility declined [(LV dP/dt)/LVEDD: 19 +/- 2 mmHg x s(-1) x mm(-1), P < 0.0001], signifying flow-function mismatch. Cardiac NO production, endothelial NO synthase expression, and fatty acid utilization decreased in late phase, whereas glycogen content and lactate uptake increased. Incessant tachycardia induces contractile, metabolic, and flow abnormalities reflecting flow-function matching early, but progresses to LV dysfunction late, despite restoration of flow and metabolism. The shift to flow-function mismatch is associated with impaired myocardial NO production.

Effects of L-arginine administration before cardioplegic arrest on ischemia-reperfusion injury

BACKGROUND

Administration of L-arginine during reperfusion or its addition to cardioplegic solution has been shown to protect myocardium against ischemia-reperfusion injury. This study aimed at evaluating the role of L-arginine in ischemia-reperfusion injury when administered intraperitoneally 24 hours before cardioplegic arrest.

METHODS

Two groups of Sprague-Dawley rats (control, n = 10; and L-arginine, n = 10) were studied in an isolated buffer-perfused heart model. Both groups were injected intraperitoneally 24 hours before ischemia. Before experimentation blood samples were collected for cardiac troponin I and cGMP analysis. In the coronary effluents, cardiac troponin I, adenosine, cyclic guanosine monophosphate, and nitric oxide metabolites were assayed.

RESULTS

Before heart excision, serum cardiac troponin I concentrations were higher in the L-arginine than in the control group (0.037 +/- 0.01 versus 0.02 +/- 0.05 microg x L(-1); p < 0.05). During reperfusion, cardiac troponin I release was lower in the L-arginine than in the control group (0.04 +/- 0.01 versus 0.19 +/- 0.03 ng x min(-1); p < 0.05). The coronary flow as well as the left ventricular developed pressure were higher in the L-arginine than in the control group before ischemia and remained so throughout the experimentation.

CONCLUSIONS

These results indicate that L-arginine administered intraperitoneally 24 hours before cardioplegic arrest reduced myocardial cell injury and seems to protect myocardium against ischemia-reperfusion injury.

Cardioprotective function of inducible nitric oxide synthase and role of nitric oxide in myocardial ischemia and preconditioning: an overview of a decade of research

Over the past decade, an enormous number of studies (>100) have focused on the role of nitric oxide (NO) in myocardial ischemia. It is important to distinguish the function of NO in unstressed (non-preconditioned) myocardium from its function in preconditioned myocardium (i.e. myocardium that has shifted to a defensive phenotype in response to stress). Of the 92 studies that have examined the role of NO in modulating the severity of ischemia/reperfusion injury in non-preconditioned myocardium, the vast majority [67 (73%)] have concluded that NO (either endogenous or exogenous) has a protective effect and only 11 (12%) found a detrimental effect. The proportion of studies supporting a cytoprotective role of NO is similar in vivo[35 (71%) out of 49] and in vitro[32 (74%) out of 43]. With regard to the delayed acquisition of tolerance to ischemia [late preconditioning (PC)], overwhelming evidence indicates a critical role of NO in this phenomenon. Specifically, enhanced biosynthesis of NO by eNOS is essential to trigger the late phase of ischemia-induced and exercise-induced PC, and enhanced NO production by iNOS is obligatorily required to mediate the anti-stunning and anti-infarct actions of late PC elicited by five different stimuli (ischemia, adenosine A1 agonists, opioid delta1 agonists, endotoxin derivatives and exercise). Thus, NO plays a dual role in the pathophysiology of the late phase of PC, acting initially as the trigger and subsequently as the mediator of this adaptive response ("NO hypothesis of late PC"). The diversity of the PC stimuli that converge on iNOS implies that the upregulation of this enzyme is a central mechanism whereby the myocardium protects itself from ischemia. The NO hypothesis of late PC has thus revealed a cytoprotective function of iNOS in the heart, a novel paradigm which has recently been extended to other tissues, including kidney and intestine. Other corollaries of this hypothesis are that the heart responds to stress in a biphasic manner, utilizing eNOS as an immediate but short-term response and iNOS as a delayed but long-term defense, and that the fundamental difference between non-preconditioned and late preconditioned myocardium is the tissue level of iNOS-derived NO, which is tonically higher in the latter compared with the former. Hence, late PC can be viewed as a state of enhanced NO synthesis. The NO hypothesis of late PC has important therapeutic implications. In experimental animals, administration of NO donors in lieu of ischemia can faithfully reproduce the molecular and functional aspects of ischemia-induced late PC, indicating that NO is not only necessary but also sufficient to induce late PC. The recent demonstration that nitroglycerin also induces late PC in patients provides proof-of-principle for the concept that nitrates could be used as a PC-mimetic therapy for the prophylaxis of ischemic injury in the clinical arena. This novel application of nitrates could be as important as, or perhaps even more important than, their current use as antianginal and preload-reducing agents. In addition, gene transfer of either eNOS or iNOS has been shown to replicate the infarct-sparing actions of ischemic PC, suggesting that NOS gene therapy could be an effective strategy for alleviating ischemia/reperfusion injury. Ten years of research have demonstrated that NO plays a fundamental biological role in protecting the heart against ischemia/reperfusion injury. The time has come to translate this enormous body of experimental evidence into clinically useful therapies by harnessing the cytoprotective properties of NO.

Changes in coronary vessel resistance during postischemic reperfusion and effectiveness of nitroglycerin

OBJECTIVE

Microvascular incompetence after ischemia and reperfusion may compromise the normal postischemic coronary perfusion and additionally jeopardize the recovery of the myocytes. We investigated whether such a form of acute endothelial dysfunction occurs in the routine operative setting despite the use of protective measures. For this purpose, we measured pressure-flow relations in the coronary vasculature during heart operations before and after ischemia and after reperfusion and their reaction to the nitric oxide donor nitroglycerin.

METHODS

Forty-eight patients with a low risk profile scheduled for routine coronary artery bypass surgery were included. During normothermic extracorporeal circulation, the fibrillating heart was completely excluded from bypass by clamping of the ascending aorta and snaring of the caval veins. It was relieved of blood by opening the right atrium and venting the left atrium and ventricle to avoid distention. The coronary vessels were perfused under controlled flow, and the perfusion pressures were monitored. This protocol was performed in 24 patients before and immediately after ischemia and after a reperfusion period.

RESULTS

Compared with the preischemic control, vascular resistance was decreased by 17% (P <.003) immediately after ischemia but increased again by 46% (P <.0001) during an average of 25 minutes of reperfusion and, even more important, by 23% (P <.028) in comparison with the preischemic values. In two groups of 12 patients, nitroglycerin was added to the perfusate either in a dosage of 3 microg. kg. min(-1) or as a bolus injection of 2 mg. Low-dose nitroglycerin did not reduce the elevated postreperfusion resistances significantly, but bolus injection did (P <.0002). Coronary vessel resistance increased during reperfusion in particular in patients with a history of hypertension.

CONCLUSION

Coronary vasoconstriction during postischemic reperfusion is regularly present in the routine operative setting in cardiac surgery, despite myocardial protection measures. The amount of vasoconstriction varies considerably and is particularly increased in patients with hypertension. The nitric oxide donor nitroglycerin can normalize the elevated resistances, but only in high dosages. This demonstrates a preserved ability of vascular smooth muscle to relax. The phenomenon had no sequelae in our low-risk patients having elective operations. However, it may gain significance in the case of severe left heart hypertrophy and in patients at risk with both a postoperative low-output syndrome and reduced mean arterial pressures during reperfusion.

Peroxynitrite formation from human myocardium after ischemia-reperfusion during open heart operation

BACKGROUND

Current experimental studies have demonstrated that peroxynitrite (ONOO-) has both cytotoxic and cytoprotective effects on myocardial ischemia-reperfusion injury. However, even myocardial ONOO- formation has not yet been investigated in humans undergoing open heart operation. We measured plasma nitrotyrosine as an indicator of ONOO- formation during open heart operation and examined its association with myocardial ischemia-reperfusion injury.

METHODS

Twenty adult patients undergoing mitral valve replacement under cardiopulmonary bypass between 1997 and 1998 were enrolled in this study (6 men and 14 women). Arterial blood (Ao) and coronary sinus effluent (CS) were obtained: (1) before the initiation of cardiopulmonary bypass, (2) just after aortic unclamping, (3) at 5 minutes, (4) at 10 minutes, (5) at 15 minutes, and (6) at 20 minutes after aortic unclamping.

RESULTS

At every sampling point after reperfusion, plasma nitrate and nitrite was significantly lower in CS than in Ao, and the percentage ratio of nitrotyrosine to tyrosine (%NO2-Tyr; an index of ONOO- formation) was significantly higher in CS than in Ao. The CS-Ao difference in %NO2-Tyr, myocardium-derived ONOO-, reached its peak at 5 minutes after reperfusion (2.17+/-0.74%), which was significantly correlated with the peak CS-Ao difference in plasma malondialdehyde, and with postoperative maximum creatine kinase-MB.

CONCLUSIONS

These results first demonstrate that ONOO- is produced from human myocardium after ischemia-reperfusion during open heart operation, and myocardium-derived ONOO- can be determined by the CS-Ao difference in %NO2-Tyr.

L-Arginine in lung graft preservation and reperfusion

BACKGROUND

Inhaled nitric oxide has been shown to ameliorate early lung graft dysfunction. It improves oxygenation by inducing pulmonary vasodilatation in well-ventilated lung areas, and it also modulates leukocyte-endothelium interactions. We used a porcine, single lung transplantation model to evaluate whether the benefits of exogenously administered gas could be achieved easier by adding L-arginine, the substrate of endogenous nitric oxide synthesis, as an additive to the flush solution and intravenously during reperfusion.

METHODS

Six pig lungs were flushed with modified Euro-Collins solutions containing L-arginine (2 g/liter). After cold (4 degrees C) storage, the left lung was transplanted. Ischemic time was 260 minutes. The recipients received intravenous boluses of L-arginine (30 mg/kg), followed by infusion (20 mg/kg/min) during the first 30 minutes of reperfusion. Six control animals received saline as placebo. We measured the blood flow and pulmonary vascular resistance (PVR) in the transplanted and in the native lung using a right heart bypass model. We measured blood gases, leukocyte counts, plasma free-radical trapping capacity, and diene conjugates in pulmonary venous blood and myeloperoxidase activity of the lung tissue.

RESULTS

Pulmonary vascular resistance was 4 to 5-fold higher in the transplanted lung than in the native lung, which received 80% of the total blood flow. L-arginine reduced PVR by 30% in the native lung (p < 0.001), but not in the transplanted lung. L-arginine had no effect on oxygenation or carbon dioxide exchange of the transplanted lung. Nor did L-arginine treatment have any effect on leukocyte sequestration or myeloperoxidase activity in the transplanted lung. The plasma antioxidant capacity in venous blood of the transplanted lung almost doubled shortly during early reperfusion without influence of L-arginine.

CONCLUSIONS

L-arginine reduced PVR in the native lung but did not improve pulmonary hemodynamics, gas exchange, or reduce leukocyte sequestration of the transplanted lung.

Nitric oxide: a trigger for classic preconditioning?

To determine whether nitric oxide (NO) is involved in classic preconditioning (PC), the effect of NO donors as well as inhibition of the L-arginine-NO-cGMP pathway were evaluated on 1) the functional recovery during reperfusion of ischemic rat hearts and 2) cyclic nucleotides during both the PC protocol and sustained ischemia. Tissue cyclic nucleotides were manipulated with NO donors [S-nitroso-N-penicillamine (SNAP), sodium nitroprusside (SNP), or L-arginine] and inhibitors of nitric oxide synthase (N(omega)-nitro-L-arginine methyl ester or N-nitro-L-arginine) or guanylyl cyclase (1H-[1,2,4]oxadiazolol-[4,3-a]quinoxaline-1-one). Pharmacological elevation in tissue cGMP levels by SNAP or SNP before sustained ischemia elicited functional improvement during reperfusion comparable to that by PC. Administration of inhibitors before and during the PC protocol partially attenuated functional recovery, whereas they had no effect when given after the ischemic PC protocol and before sustained ischemia only, indicating a role for NO as a trigger but not as a mediator. Ischemic PC, SNAP, or SNP caused a significant increase in cGMP and a reduction in cAMP levels after 25 min of sustained ischemia that may contribute to the protection obtained. The results obtained suggest a role for NO (and cGMP) as a trigger in classic PC.

Oxidative stress developed during open heart surgery induces apoptosis: reduction of apoptotic cell death by ebselen, a glutathione peroxidase mimic

Apoptosis, a genetically controlled programmed cell death, has been found to play a role in ischemic reperfusion injury in several animal species including rats and rabbits. To examine whether this also is true for other animals, a surgically relevant model was established using an isolated in situ swine heart. Hearts were subjected to 15 min of normothermic regional ischemia by left anterior descending artery (LAD) occlusion followed by 30 min of normothermic cardioplegic arrest and 3 h of reperfusion. Oxygen free radicals have been shown to be the inducers of apoptosis and because reperfusion of ischemic myocardium is associated with the generation of free radicals, an additional group of hearts was preperfused with three different doses (5, 10, and 25 nM) ebselen, a glutathione peroxidase mimic, for 15 min before 15 min of LAD occlusion. Hearts were then subjected to 30 min of normothermic cardioplegic arrest followed by 3 h of reperfusion at normothermia. Control experiments were performed by perfusing the hearts for 4 h at normothermia. Two other groups of hearts were subjected to either 30 or 60 min of LAD occlusion followed by 30 min of cardioplegic arrest without subjecting them to reperfusion. At the end of each experiment, hearts were processed for the evaluation of apoptosis and DNA laddering. The in situ end-labeling (ISEL) technique was used to detect apoptotic cardiomyocyte nuclei while DNA laddering was evaluated by subjecting the DNA obtained from the cardiomyocytes to 1.8% agarose gel electrophoresis followed by photographing under UV illumination. The apoptotic cells appeared only after 90 min of reperfusion, as demonstrated by the intense fluorescence of the immunostained genomic DNA when observed under fluorescence microscopy. None of the ischemic hearts showed any evidence of apoptosis. These results were corroborated with the findings of DNA fragmentation showing increased ladders of DNA bands in the same reperfused hearts. The presence of apoptotic cells and DNA fragmentation in the myocardium was abolished by preperfusing the hearts in the presence of 10 nM ebselen, which also moderated the oxidative stress developed in the heart. Apoptotic cells and DNA ladders were completely absent in the hearts subjected to either 30 or 60 min of LAD occlusion. The results demonstrate that reperfusion of the ischemic heart induces apoptosis, which can be reduced with ebselen by reducing the oxidative stress associated with ischemia/reperfusion.

Neuroprotective strategies in Parkinson's disease: protection against progressive nigral damage induced by free radicals

Brain undergoes neurodegeneration when excess free radicals overwhelm antioxidative defense systems during senescence, head trauma and/or neurotoxic insults. A site-specific accumulation of ferrous citrate-iron complexes in the substantia nigra dopaminergic neurons could lead to exaggerated dopamine turnover, dopamine auto-oxidation, free radical generation, and oxidant stress. Eventually, this iron-catalyzed dopamine auto-oxidation results in the accumulation of neuromelanin, a progressive loss of nigral neurons, and the development of Parkinson's disease when brain dopamine depletion is greater than 80%. Emerging evidence indicates that free radicals such as hydroxyl radicals ((.-)OH) and nitric oxide ((.-)NO) may play opposite role in cell and animal models of parkinsonism. (.-)OH is a cytotoxic oxidant whereas oNO is an atypical neuroprotective antioxidant. (.-)NO and S-nitrosoglutathione (GSNO) protect nigral neurons against oxidative stress caused by 1-methyl-4-phenylpyridinium (MPP(+)), dopamine, ferrous citrate, hemoglobin, sodium nitroprusside and peroxynitrite. MPP(+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), increases the nigral uptake of iron complexes and dopamine overflow leading to the generation of (.-)OH, protein oxidation, lipid peroxidation, and associated retrograde degeneration. In addition to GSNO, MPP(+)-induced oxidative neurotoxicity can be prevented by antioxidants including selegiline, 7-nitroindazole, 17beta-estradiol, melatonin, alpha-phenyl-tert-butylnitrone and U78517F. Similar to selegiline, 7-nitroindazole is a MAO-B inhibitor, which blocks the bio-activation of MPTP and oxidative stress. Freshly prepared but not light exposed, (.-)NO-exhausted GSNO is about 100 times more potent than the classic antioxidant glutathione. Via S-nitrosylation, GSNO also inhibits proteolysis and cytotoxicity caused by caspases and HIV-1 protease. Furthermore, in addition to protection against serum deprivation stress, the induction of neuronal NOS1 in human cells increases tolerance to MPP(+)-induced neuro-toxicity since newly synthesized (.-)NO prevents apoptosis possibly through up-regulation of bcl-2 and down regulation of p66(shc). In conclusion, reactive oxygen species are unavoidable by-products of iron-catalyzed dopamine auto-oxidation, which can initiate lipid peroxidation, protein oxidation, DNA damage, and nigral loss, all of which can be prevented by endogenous and exogenous (.-)NO. Natural and man-made antioxidants can be employed as part of preventative or neuroprotective treatments in Parkinson's disease and perhaps dementia complexes as well. For achieving neuroprotection and neuro-rescue in early clinical parkinsonian stages, a cocktail therapy of multiple neuroprotective agents may be more effective than the current treatment with extremely high doses of a single antioxidative agent.

Cyclic GMP reduces ventricular myocyte stunning after simulated ischemia-reperfusion

We tested the hypothesis that the second messenger activated by nitric oxide, cyclic GMP, would reduce the effects of myocyte stunning following simulated ischemia-reperfusion and that this was related to cyclic GMP protein kinase. Ventricular cardiac myocytes were isolated from New Zealand White rabbits (n = 8). Cell shortening was measured by a video edge detector and protein phosphorylation was determined autoradiographically after SDS gel electrophoresis. Cell shortening data were acquired at: (i) baseline followed by 8-Bromo-cGMP 10(-6) M (8-Br-cGMP) and then KT 5823 10(-6) M (cyclic GMP protein kinase inhibitor) and (ii) simulated ischemia (20 min of 95% N(2)-5% CO(2) at 37 degrees C) followed by simulated reperfusion (reoxygenation) with addition of 8-Br-cGMP 10(-6) M followed by KT 5823 10(-6) M, (iii) addition of 8-Br-cGMP prior to ischemia followed by the addition of KT 5823 10(-6) M after 30 min of reoxygenation. In the control group, 8-Br-cGMP 10(-6) M decreased percentage shortening (%short) (5.0 +/- 0.6 vs 3.8 +/- 0. 4) and the maximum velocity (V(max), microm/s) (48.6 +/- 6.9 vs 40.2 +/- 6.4). KT 5823 10(-6) M added after 8-Br-cGMP partially restored %short (4.6 +/- 0.5) and V(max) (46.6 +/- 8.0). After stunning, baseline myocytes had decreased %short (3.4 +/- 0.2) and V(max) (36. 0 +/- 4.2). After the addition of 8-Br-cGMP, the %short (2.7 +/- 0. 2) and V(max) (27.6 +/- 2.5) decreased further. The addition of KT 5823 did not change either the %short or the V(max). The myocytes with 8-Br-cGMP during ischemia had increased %short (4.2 +/- 0.2) and V(max) (37.2 +/- 3.4) when compared to the stunned group. The addition of KT 5823 did not significantly alter %short (3.3 +/- 0.4) or V(max) (29.2 +/- 5.0) in the myocytes pretreated with 8-Br-cGMP. Protein phosphorylation was increased by 8-Br-cGMP in control and stunned myocytes. KT 5823 blocked this effect in control but not stunned myocytes, suggesting some change in the cyclic GMP protein kinase. Ischemia-reperfusion produced myocyte stunning that was reduced when 8-Br-cGMP was added prior to but not after ischemia.

Nitric oxide donors attenuate myocardial stunning in conscious rabbits

Although previous studies suggested that the protection of late preconditioning (PC) against myocardial stunning is mediated by nitric oxide (NO), direct evidence that exogenous administration of NO attenuates myocardial stunning is lacking. Furthermore, although exogenous NO administration was shown to elicit a late PC phase, it is unknown whether NO donors also induce an early PC phase. Therefore, conscious rabbits underwent two experimental stages (3 days of six 4-min occlusion/4-min reperfusion cycles each) 2 wk apart. In study I, both stages were control stages (n = 7). In studies II and III, stage I was the control stage. On day 1 of stage II, seven rabbits received infusion of nitroglycerin (NTG; 2 microg. kg(-1). min(-1) iv) during the ischemia-reperfusion sequence, starting 30 min before the 1st occlusion and ending 10 min after the 6th reperfusion (study II). Another seven rabbits received infusion of NTG (2 microg. kg(-1). min(-1) iv) for 1 h followed by a 30-min washout interval and then underwent six 4-min occlusion/4-min reperfusion cycles (study III). In the control stage of all three studies, recovery of wall thickening (WTh) after occlusion/reperfusion cycles was markedly enhanced on days 2 and 3 compared with day 1, indicating late PC. In study II, infusion of NTG during the occlusion/reperfusion cycles on day 1 resulted in significant and sustained enhancement in WTh recovery. A similar attenuation of stunning was observed in study IV in six rabbits given intravenous infusion of S-nitroso-N-acetylpenicillamine (SNAP) during occlusion/reperfusion cycles. The magnitude of the protection afforded by NTG and SNAP was comparable to that afforded by the late ischemic PC phase. In contrast, in study III infusion of NTG before occlusion/reperfusion cycles did not enhance WTh recovery, indicating that NTG failed to induce an early PC effect against stunning. This study demonstrates that administration of hemodynamically inactive doses of two unrelated NO donors alleviates myocardial stunning in conscious rabbits, providing direct evidence for a protective action of NO in this setting.

Molecular targets of gene therapy

Ischemic reperfused heart represents a potential target for gene therapy because gene transfer can represent an alternate pharmacological approach to protect the heart from cellular injury. Gene therapy may be particularly useful to deal with previously unapproachable problems. For myocardial preservation, gene therapy could replace those pharmacological interventions when drugs are delivered locally by sustained release with the help of mechanical device, eg, implants. In this review, attempts are made to define the molecular targets for gene therapy primarily applicable to myocardial preservation associated with ischemia and reperfusion. It has been emphasized that for successful gene transfer, not only characterization of proper targets and elimination of undesirable side effects are necessary, but also the therapy must be proven superior compared to other pharmacological interventions including surgery.

Oxidized proteins as a marker of oxidative stress during coronary heart surgery

The measurement of the degree of oxidative stress in patients often causes problems because of the lack of useful parameters. Therefore, we used an ELISA technique to evaluate serum protein carbonyls as a parameter of oxidative stress in patients during coronary heart surgery. Protein carbonyls were detected in serum samples of 14 patients undergoing coronary surgery and cardiopulmonary artery bypass grafting. A clear 2- to 3-fold increase in protein carbonyls in serum samples taken from human venous coronary sinus could be detected in the reperfusion period of the heart. We compared these data with markers of oxidative stress previously used, such as the glutathione status and the lipid peroxidation product malondialdehyde (MDA). Strong correlations of the protein carbonyl formation with MDA (r2 = 0.86) and oxidized glutathione (r2 = 0.81) were found in the early reperfusion stage. Increased levels of oxidized glutathione and MDA were detected only in the early reperfusion period. In contrast, the serum protein carbonyl content remained elevated for several hours, indicating a considerably slower serum clearance of oxidized proteins compared with that of lipid peroxidation products and the normalization of the glutathione status. We therefore concluded that the measurement of serum carbonyls by this ELISA technique is suitable to detect oxidative stress in serum samples of patients. The relative stability of the parameter makes the protein carbonyl detection even more valuable for clinical purposes.

L-Arginine: a novel therapy for coronary artery disease?

Coronary artery disease (CAD) is a significant cause of morbidity and mortality today. The treatment of CAD is improving, but its prevalence is increasing: both primary and secondary prevention measures are of vital importance. Atherosclerosis starts at an early age; it is initiated at the vascular endothelium level, a single layer entity that modulates vascular function. Modulation of vascular function is carried out through the L-arginine/nitric oxide (NO) pathway. Normal endothelial function requires an intact L-arginine/NO pathway and endothelium. Endothelial dysfunction may be a precursor to overt CAD. CAD risk factors have been shown to influence endothelial function, and the treatment of these risk factors can restore endothelial function. L-Arginine is a safe, novel, semiessential amino acid that increases NO production, thereby improving endothelial function. L-Arginine/NO has numerous beneficial neurohormonal modulating properties. Numerous animal model and human studies have been carried out to assess L-arginine in CAD and other related disorders such as congestive heart failure (CHF), peripheral vascular disease (PVD) and acute myocardial infarction (AMI). Prospective clinical trials are required to assess the promising role of L-arginine in CAD and related disorders

The reported clinical utility of taurine in ischemic disorders may reflect a down-regulation of neutrophil activation and adhesion

The first publications regarding clinical use of taurine were Italian reports claiming therapeutic efficacy in angina, intermittent claudication and symptomatic cerebral arteriosclerosis. A down-regulation of neutrophil activation and endothelial adhesion might plausibly account for these observations. Endothelial platelet-activating factor (PAF) is a crucial stimulus to neutrophil adhesion and activation, whereas endothelial nitric oxide (NO) suppresses PAF production and acts in various other ways to antagonize binding and activation of neutrophils. Hypochlorous acid (HOCl), a neutrophil product which avidly oxidizes many sulfhydryl-dependent proteins, can be expected to inhibit NO synthase while up-regulating PAF generation; thus, a vicious circle can be postulated whereby HOCl released by marginating neutrophils acts on capillary or venular endothelium to promote further neutrophil adhesion and activation. Taurine is the natural detoxicant of HOCl, and thus has the potential to intervene in this vicious circle, promoting a less adhesive endothelium and restraining excessive neutrophil activation. Agents which inhibit the action of PAF on neutrophils, such as ginkgolides and pentoxifylline, have documented utility in ischemic disorders and presumably would complement the efficacy of taurine in this regard. Fish oil, which inhibits endothelial expression of various adhesion factors and probably PAF as well, and which suppresses neutrophil leukotriene production, may likewise be useful in ischemia. These agents may additionally constitute a non-toxic strategy for treating inflammatory disorders in which activated neutrophils play a prominent pathogenic role. Double-blind studies to confirm the efficacy of taurine in symptomatic chronic ischemia are needed.