The role of nitric oxide and NO-donor agents in myocardial protection from surgical ischemic-reperfusion injury

Post-Cardiac Arrest: Mechanisms, Management, and Future Perspectives

Cardiac arrest is an important public health issue, with a survival rate of approximately 15 to 22%. A great proportion of these deaths occur after resuscitation due to post-cardiac arrest syndrome, which is characterized by the ischemia-reperfusion injury that affects the role body. Understanding physiopathology is mandatory to discover new treatment strategies and obtain better results. Besides improvements in cardiopulmonary resuscitation maneuvers, the great increase in survival rates observed in recent decades is due to new approaches to post-cardiac arrest care. In this review, we will discuss physiopathology, etiologies, and post-resuscitation care, emphasizing targeted temperature management, early coronary angiography, and rehabilitation.

Improvement of Left Ventricular Graft Function Using an Iron-Chelator-Supplemented Bretschneider Solution in a Canine Model of Orthotopic Heart Transplantation

Demand for organs is increasing while the number of donors remains constant. Nevertheless, not all organs are utilized due to the limited time window for heart transplantation (HTX). Therefore, we aimed to evaluate whether an iron-chelator-supplemented Bretschneider solution could protect the graft in a clinically relevant canine model of HTX with prolonged ischemic storage. HTX was performed in foxhounds. The ischemic time was standardized to 4 h, 8 h, 12 h or 16 h, depending on the experimental group. Left ventricular (LV) and vascular function were measured. Additionally, the myocardial high energy phosphate and iron content and the in-vitro myocyte force were evaluated. Iron chelator supplementation proved superior at a routine preservation time of 4 h, as well as for prolonged times of 8 h and longer. The supplementation groups recovered quickly compared to their controls. The LV function was preserved and coronary blood flow increased. This was also confirmed by in vitro myocyte force and vasorelaxation experiments. Additionally, the biochemical results showed significantly higher adenosine triphosphate content in the supplementation groups. The iron chelator LK614 played an important role in this mechanism by reducing the chelatable iron content. This study shows that an iron-chelator-supplemented Bretschneider solution effectively prevents myocardial/endothelial damage during short- as well as long-term conservation.

Efficacy of Nitric Oxide Administration in Attenuating Ischemia/Reperfusion Injury During Neonatal Cardiopulmonary Bypass

OBJECTIVE

Nitric oxide (NO) plays several protective roles in ischemia/reperfusion (I/R) injury. Neonates undergoing the Norwood procedure are subject to develop I/R injury due to the immaturity of their organs and the potential need to interrupt or decrease systemic flow during surgery. We hypothesized that NO administration during cardiopulmonary bypass (CPB) ameliorates the I/R and could help the postoperative recovery after the Norwood procedure.

METHODS

Twenty-four neonates who underwent a Norwood procedure were enrolled in a prospective randomized blinded controlled trial to receive NO (12 patients) or placebo (12 patients) into the oxygenator of the CPB circuit during the Norwood procedure. Markers of I/R injury were collected at baseline (T0), after weaning from CPB before modified ultrafiltration (T1), after modified ultrafiltration (T2), and at 12 hours (T3) and 24 hours (T4) after surgery, and they were compared between both groups, as well as other postoperative clinical variables.

RESULTS

There was no difference in age, weight, anatomical diagnosis, CPB, and aortic cross-clamp time between both groups. Troponin levels were lower in the study group at T1 (0.62 ± 58 ng/mL vs 0.87 ± 0.58 ng/mL, P = .31) and became significantly lower at T2 (0.36 ± 0.32 ng/mL vs 0.97 ± 0.48 ng/mL, P = .009).There were no significant differences between both groups for all other markers. Despite a lower troponin level, there was no difference in inotropic scores or ventricular function between both groups. Time to start diuresis, time to sternal closure and extubation, and intensive care unit and hospital stay were not different between both groups.

CONCLUSION

Systemic administration of NO during the Norwood procedure has myocardial protective effects (lower Troponin levels) but we observed no effect on postoperative recovery. Larger sample size may be needed to show clinical differences.

A Review of the Benefits of Satureja Species on Metabolic Syndrome and Their Possible Mechanisms of Action

Metabolic syndrome, also known as insulin resistance disorder, is the simultaneous manifestation of multiple metabolic disorders in an individual. The present-day complementary and alternative therapies suggest several medicinal herbs that may have the potential to improve one or multiple complications of metabolic syndrome. All of them have their own limitations in efficacy and unwanted effects. Therefore, we reviewed species of Satureja as widespread medicinal herbs and potentially good remedies for metabolic syndrome. We reviewed literature found in PubMed and the ISI Web of Knowledge with the key word Satureja in the title. The influence of any species of Satureja on any disease or syndrome, enzymatic, metabolic, or physiological pathways, in human, animals, or in vitro conditions related to any characteristics of metabolic syndrome were considered. The main outcomes of treatment with Satureja species were categorized, and the possible mechanisms of action are discussed in this article.

Effects of FP15, a peroxynitrite decomposition catalyst on cardiac and pulmonary function after cardiopulmonary bypass

OBJECTIVE

Peroxynitrite, a toxic nitrogen species, has been implicated in the development of ischemia/reperfusion injury. The aim of the present study was to investigate the effects of the potent peroxynitrite decomposition catalyst, FP15, on myocardial, endothelial, and pulmonary function in an experimental model of cardioplegic arrest and extracorporal circulation.

METHODS

Twelve anesthetized dogs underwent hypothermic cardiopulmonary bypass. After 60 min of hypothermic cardiac arrest, reperfusion was started and either saline vehicle (control, n = 6) or FP15 (n = 6) was administered. Left-ventricular preload-recruitable stroke work (PRSW) was measured by a combined pressure-volume conductance catheter at baseline and after 60 min of reperfusion. Left anterior descending (LAD) coronary (CBF) and pulmonary blood flow (PBF), endothelium-dependent vasodilatation to acetylcholine (ACh), and alveolo-arterial O2 gradient were determined.

RESULTS

The administration of FP15 led to a significantly better recovery of PRSW (given as percent of baseline: 93 ± 9 vs 62 ± 6%, p < 0.05). CBF was also significantly higher in the FP15 group (44 ± 6 vs 25 ± 4 ml min(-1), p < 0.05). Injection of ACh resulted in a significantly higher increase in CBF (70 ± 6 vs 35 ± 5%, p < 0.05) in the FP15-treated animals. The alveolo-arterial O2 gradient was significantly lower after FP15 administration (83 ± 7 vs 49 ± 6 mmHg, p < 0.05). Catalytic peroxynitrite decomposition did not affect baseline cardiovascular and pulmonary functions.

CONCLUSIONS

Application of FP15 improves myocardial, endothelial, and pulmonary function after cardiopulmonary bypass with hypothermic cardiac arrest. The observed protective effects imply that catalytic peroxynitrite decomposition could be a novel therapeutic option in the treatment of ischemia/reperfusion injury.

Pre-conditioning with the soluble guanylate cyclase activator Cinaciguat reduces ischaemia-reperfusion injury after cardiopulmonary bypass

OBJECTIVE

Activation of the nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate (NO-sGC-cGMP) pathway can induce potent cardioprotection-like effects against ischaemia-reperfusion injury and nitro-oxidative stress. We investigated the effects of pharmacological pre-conditioning with Cinaciguat (BAY 58-2667), a novel sGC activator on peroxynitrite-induced endothelial dysfunction in vitro, as well as on myocardial and coronary vascular function during reperfusion in a canine model of cardioplegic arrest and extracorporeal circulation.

METHODS

Isolated coronary arterial rings exposed to peroxynitrite were investigated for vasomotor function. Vehicle- and Cinaciguat-pre-treated (8.33 μg h(-1) or 25 μg h(-1) intravenous (IV) for 30 min) anaesthetised dogs (n = 6-7 per group) underwent hypothermic cardiopulmonary bypass with 60 min of hypothermic cardioplegic arrest. Left- and right-ventricular end-systolic pressure-volume relationship (ESPVR) was measured by a pressure-volume conductance catheter at baseline and after 60 min of reperfusion. Coronary blood flow, vasodilatation to acetylcholine and myocardial level of adenosine triphosphate were determined.

RESULTS

Pre-incubation of coronary rings with Cinaciguat improved peroxynitrite-induced endothelial dysfunction. Compared with control, pharmacological pre-conditioning with Cinaciguat (25 μg h(-1)) led to higher myocardial adenosine triphosphate content, to a better recovery of left- and right-ventricular contractility (Δ slope of left ventricular ESPVR given as percent of baseline: 102.4 ± 19.1% vs 56.0 ± 7.1%) and to a higher coronary blood flow (49.6 ± 3.5 ml min(-1) vs 28.0 ± 3.9 ml min(-1)). Endothelium-dependent vasodilatation to acetylcholine was improved in the treatment groups.

CONCLUSIONS

Pre-conditioning with Cinaciguat improves myocardial and endothelial function after cardiopulmonary bypass with hypothermic cardiac arrest. The observed protective effects imply that pharmacological sGC activation could be a novel therapeutic option in the protection against ischaemia-reperfusion injury in cardiac surgery.

Ranolazine as an Adjunct to Cardioplegia: A Potential New Therapeutic Application

The purpose of this study was to examine the therapeutic potential of ranolazine, a novel antianginal drug, as an adjunctive therapy to hyperkalemic cardioplegia. Rat hearts were Langendorff-perfused and exposed to 40 minutes of ischemia and 30 minutes of reperfusion without (control) or with cardioplegia or cardioplegia with 50 µmol/L ranolazine. During ischemia, cardioplegia prolonged time to contracture, defined as the time to reach an intraventricular pressure of 20 mm Hg, from 12 + 1 minute (control) to 25 + 2 minutes (P < .05). Ranolazine supplement further lengthened the time to contracture to 34 + 2 minutes (P < .05). Ischemia/reperfusion caused a dramatic elevation in left ventricular end diastolic pressure (LVEDP) during reperfusion. Cardioplegia lessened the LVEDP elevation measured at 30 minutes of reperfusion from 76 + 3 mm Hg (control) to 32 + 3 mm Hg (P < .05). The increase in LVEDP was reduced even further to 17 + 2 mm Hg in hearts receiving cardioplegia plus ranolazine (P < .05). These results suggest that addition of ranolazine during hyperkalemic ischemic cardioplegic arrest is beneficial and provides further protection against contracture.

Effects of selective phosphodiesterase-5-inhibition on myocardial contractility and reperfusion injury after heart transplantation

Recently, the infarct reducing and cardioprotective effects of phosphodiesterase-5-inhibitors were described. In this study, we investigated these effects on ischemia/reperfusion injury in a rat model of heart transplantation. Three groups were assigned for our study: a vardenafil preconditioning group, an ischemic control, and a nonischemic control. Hemodynamic parameters were significantly increased in the vardenafil group (Pmax: 82+/-4 vs. 110+/-12 vs. 127+/-13 mm Hg; dP/dtmax: 1740+/-116 vs. 3197+/-599 vs. 4397+/-602 mm Hg/sec; ischemic control vs. vardenafil vs. nonischemic control; P<0.05 vs. ischemic control). Furthermore, we recorded increased ATP levels and significantly less apoptosis in the treatment group after terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (apoptosis index: 27.23%+/-1.54% vs. 16.77%+/-1.42% vs. 18.86%+/-1.07%; ischemic control vs. vardenafil vs. nonischemic control; P<0.05 vs. ischemic control). Our current results support the concept that the cGMP-PKG-pathway plays an important role in ischemia/reperfusion injury. We could show that up-regulating this pathway has a preconditioning-like effect and can effectively reduce ischemia/reperfusion injury.

Simultaneous Electrochemical Detection of Nitric Oxide and Carbon Monoxide Generated from Mouse Kidney Organ Tissues

A planar-type amperometric dual microsensor for simultaneous detection of nitric oxide and carbon monoxide is presented. The sensor consists of a dual platinum microdisk-based working electrode (WE) and a Ag/AgCl counter/reference electrode covered with an expanded poly(tetrafluoroethylene) (Tetra-tex) gas-permeable membrane. The dual WE possesses two different platinized platinum disks (WE1 and WE2, 250 and 25 microm in diameter, respectively). The larger WE1 is further modified with electrochemical deposition of tin. Use of two sensing disks different in their size as well as in their surface modification produces apparently different sensitivity ratios of NO to CO at WE1 and at WE2 (approximately 2 and approximately 10, respectively) that are induced by favorable CO oxidation on the surface of tin versus platinum. Anodic currents independently measured at WE1 and at WE2 are successfully converted to the concentrations of NO and CO in the co-presence of these gases using the differentiated sensitivities at each electrode. The sensor is evaluated in terms of its analytical performance: respectable linear dynamic range (sub nM to microM); low detection limit (approximately 1 nM for NO and <5 nM for CO); selectivity (over nitrite up to approximately 1 mM); and sensitivity (sufficient for analyzing physiological levels of NO and CO). Using the NO/CO dual microsensor, real-time, simultaneous, direct, and quantitative measurements of NO and CO generated from living biological tissue (mouse, c57, kidney) surfaces, for the first time, are reported.

INO-1001 a novel poly(ADP-ribose) polymerase (PARP) inhibitor improves cardiac and pulmonary function after crystalloid cardioplegia and extracorporal circulation

Poly(ADP-ribose) polymerase (PARP) activation plays a key role in free radical-induced injury in the context of systemic inflammation and ischemia/reperfusion. In the present preclinical study, we investigated the effects of INO-1001, a novel PARP inhibitor, on cardiac and pulmonary function during reperfusion in an experimental model of cardioplegic arrest and extracorporal circulation. Twelve anesthetized dogs underwent hypothermic cardiopulmonary bypass. After 60 min of hypothermic cardiac arrest, reperfusion was started after application of either saline vehicle (control, n = 6), or INO-1001 (1 mg/kg), a potent PARP inhibitor (n = 6). Biventricular hemodynamic variables were measured by combined pressure-volume-conductance catheters. Coronary and pulmonary blood flow and vasodilative responses to acetylcholine and sodium nitroprusside as well as pulmonary gas exchange were also determined. The administration of INO-1001 led to a significantly better recovery of left and right ventricular systolic function (P < 0.05) after 60 min of reperfusion. Coronary blood flow was also significantly higher in the INO-1001 group (P < 0.05). Although the vasodilative response to sodium nitroprusside was similar in both groups, acetylcholine resulted in a significantly greater increase in coronary and pulmonary blood flow in the INO-1001 group (P < 0.05). Pulmonary function in terms of alveolar arterial oxygen difference was better preserved in the INO-1001-treated group (P < 0.05). Thus, PARP inhibition improves the recovery of myocardial and endothelial function after hypothermic cardiac arrest and reduces pulmonary injury associated with extracorporal circulation.

Improved Planar Amperometric Nitric Oxide Sensor Based on Platinized Platinum Anode. 2. Direct Real-Time Measurement of NO Generated from Porcine Kidney Slices in the Presence ofl-Arginine,l-Arginine Polymers, and Protamine

Nitric oxide generation from porcine kidney slices is assessed using a new planar NO-selective amperometric sensor. The planar shape of the sensor allows for direct NO measurements near the surface (10 microm) of renal tissue slices in real time. Renal NO production may be modulated by the addition of L-arginine, arginine homopolymers (R2, R6, R10), and protamine, all of which can potentially transport across cellular membranes and provide a substrate for nitric oxide synthase within kidney parenchyma. Real-time amperometric measurements demonstrate that most L-arginine species can translocate across the cell membrane and rapidly increase NO production. However, no increase in NO generation is observed when the dimer of L-arginine (R2) is added to the solution bathing the tissue, suggesting that this species cannot permeate cell membranes. The degree of enhancement in NO generation observed for L-arginine and the larger peptides depends on the structure and follows the following sequence: R10 (decamer) > protamine > R6 (hexamer) > L-arginine. Protamine and the R10 decamer, especially, induce the largest increases in NO generation owing to their apparent rapid translocation into cells and subsequent cleavage by proteases to create high intracellular levels of L-arginine. The effect of sensor size (for sensor dimensions of 0.15- and 1-mm outer diameters) on the measured surface NO levels is also examined. The larger sensor traps more NO but hinders access of the L-arginine species to the tissue area between the flat distal plane of the sensor and the surface of the kidney slice. The use of such NO-generating peptides may be important in numerous biological systems that depend on NO production, such as ischemia-reperfusion injury and thrombogenesis.

Evaluation of nitric oxide release in the coronary effluent by a novel EPR technique: A study on isolated rat hearts subjected to cold cardioplegia and reperfusion

Aim of this study was to investigate the cardiac release of nitric oxide (NO) before and after cold cardioplegia by a novel electron paramagnetic resonance (EPR) technique. Isolated rat hearts were perfused for 20 min in a Langendorff apparatus and then subjected to 3 hours potassium-hypotermic cardioplegia, followed by 20 min reperfusion. The coronary effluent was collected in a flask containing ferrous-bis-diethyldithiocarbamate as a spin trap of NO. Since the trapping agent was not delivered to the heart with the perfusion medium, we avoided that an abnormal extraction of NO from the tissue could inhibit its biological activity. The EPR signal was well detectable after equilibration (25.6 +/- 3.0 nmol/L +/- S.E.M.) and significantly increased following perfusion with 10 micromol/L serotonin (41.1 +/- 3.2 nmol/L) or 10 micromol/L nitroprusside (43.5 +/- 2.9 nmol/L). The basal level of NO did not change after reperfusion, but serotonin administration was not able to stimulate its release. Serotonin failure to stimulate NO production was not due to a loss of endothelial NO synthase, since its protein expression was not modified after reperfusion. The perfusion pressure increased by 51% after reperfusion and was quite completely restored following serotonin or nitroprusside treatment, with respect to the non-stimulated equilibration condition. Therefore, we suggest that the coronary spasm following a cold cardioplegic arrest is not due to an impaired production of basal NO and that NO-donors can be effective in relaxing vascular smooth muscle cells.

L-arginine polymers enhance coronary flow and reduce oxidative stress following cardiac transplantation in rats

BACKGROUND

Hearts treated with l-arginine polymers have demonstrated upregulated production of nitric oxide. The current study examined whether these polymers improved coronary flow and reduced myocardial oxidative stress after rat heart transplantation.

METHODS

PVG donor hearts were incubated ex vivo with either 100 mumol/L l-arginine polymers 9 amino acids in length (R9) (n = 7) or phosphate-buffered saline (n = 7) for 30 minutes after arrest and then transplanted heterotopically into the abdomen of ACI recipient rats. Coronary flows were assessed using fluorescent microspheres both at baseline (30 minutes after reperfusion) and at 6 hours and compared using the paired Student t test. Evidence of oxidative stress was assessed in a separate cohort of similarly treated animals by enzyme-linked imunosorbent assay for rat tumor necrosis factor-alpha at 6 hours.

RESULTS

Histochemistry with biotinylated l-arginine polymers demonstrated uptake of R9 into the vascular walls of treated allografts. Although all hearts experienced deterioration in coronary flow between baseline and 6 hours, the R9-treated group had a smaller reduction (29.9%, P =.10) than the phosphate-buffered saline control group (58.0%, P =.003). Tumor necrosis factor-alpha levels were also significantly reduced in the R9 treatment group compared with the phosphate-buffered saline category (160 +/- 30 versus 205 +/- 38, P =.007).

CONCLUSION

Rat cardiac allografts treated with R9 at the time of procurement exhibited less deterioration in coronary flow and a reduction in myocardial oxidative stress than the phosphate-buffered saline control group in the perioperative period. The use of arginine polymers may thus provide important myocardial protection against ischemia-reperfusion injury in both transplant and routine cardiac surgery cases.

Cardiac surgery: myocardial energy balance, antioxidant status and endothelial function after ischemia-reperfusion

Myocardial and endothelial damage is still a widely debated problem during the ischemia-reperfusion sequence in heart surgery. We evaluated myocardial purine metabolites, antioxidant defense mechanisms, oxidative status and endothelial dysfunction markers in 14 patients undergoing coronary artery by-pass graft (CABG). Heart biopsies were taken before aortic cross-clamping (t1), before clamp removal (t2) and 30 min after reperfusion (t3); perchloric extracts of the tissue were analyzed for glutathione, NAD, nucleotide nucleoside and base content by capillary electrophoresis (CE). In plasma samples from the coronary sinus we evaluated: nitrate and nitrite concentrations by CE, plasma glutathione peroxidase (plGPx) by ELISA, endothelin-1 (ET-1) by RIA and reactive oxygen metabolites (ROM) by colorimetric assay. During the ischemic period (t2) we observed a reduction in cellular NAD and GSH levels, as well as nitrate, nitrite and plGPx. ATP and GTP levels decreased and their catabolic products AMP, GMP, IMP, adenosine, inosine and hypoxanthine accumulated. The energy charge, ATP/ADP ratio, and nucleotide/(nucleoside + base) ratios decreased. At t3, levels of plasma ET-1 increased and monophosphate nucleotides tended to return to basal values. The energy charge did not increase but the nucleotide/(nucleoside + nucleobase) ratio recovered to some extent. Levels of nitrates plus nitrites continued to decrease. No significant variation in ROM levels was observed. Our data indicate that oxidative stress and endothelial damage are major events during CABG, overwhelming the scavenging capacity of the myocyte and preventing restoration of the normal energy balance for 30 min after reperfusion. The AMP deaminase pathway leading to IMP production is active during ischemia and adenosine is not the main compound derived from ATP break-down in the human heart. The possible role of extracorporeal circulation is also discussed.

FK409 inhibits both local and remote organ damage after intestinal ischaemia

In addition to localized tissue injury, intestinal ischaemia-reperfusion (I/R) leads to remote organ damage, in particular to the lungs. Given that nitric oxide (NO) can attenuate I/R-induced tissue injury in many situations, this study evaluated the effects of the NO donor, FK409, on leukocyte adhesion in the microcirculation of the intestinal villus and also assessed pulmonary tissue damage after intestinal I/R injury. PVG rats were subjected to 30 min intestinal ischaemia and a sub-group of animals received the NO donor FK409 (10 mg/kg; i.v.) both 30 min prior to ischaemia and 30 min post-reperfusion. The intestinal mucosal surface was visualized via an incision made in an exteriorized ileal segment and leukocyte adhesion in the villous microcirculation was determined by in vivo microscopy. Total and differential leukocyte counts from peripheral blood were evaluated. Lungs were removed at the end for histological assessment. Six out of ten untreated I/R animals failed to survive the 2 h reperfusion period, whereas all ten FK409-treated animals survived. I/R induced a significant increase in villous leukocyte adhesion of untreated I/R animals (p<0.001) and this was significantly decreased by FK409 treatment (p<0.001). The total leukocyte count was significantly decreased in untreated I/R animals (p<0.001) and this primarily resulted from a reduction in circulating neutrophil numbers. This effect was not observed in FK409-treated animals. Collapsed alveoli, thickened interstitial walls, and a dense neutrophilic infiltrate were apparent in the lungs of untreated I/R animals, whereas lung histology was normal in FK409-treated animals. In conclusion, FK409 prevented mortality, significantly reduced villous leukocyte adhesion, maintained circulating leukocyte numbers, and prevented pulmonary tissue injury following intestinal I/R. FK409 may therefore be of value in reducing both local and remote tissue damage and improving outcome in situations where intestinal I/R injury is obligatory, such as small bowel transplantation.

The hemodynamic effects of diaspirin cross-linked hemoglobin in dopamine-resistant endotoxic shock in swine

As the blood substitute Diaspirin Cross-linked Hemoglobin (DCLHb) has potent vasopressor activity, we assessed its hemodynamic effects in a clinically relevant dopamine-resistant endotoxic shock model in swine. In a randomized and controlled study, E. coli LPS was administered to anesthetized and invasively monitored swine. Group I (n = 3) control pigs were not resuscitated. Groups II (n = 5) and III (n = 6) pigs received dopamine (DA) after MAP decreased 30%, and hetastarch and DCLHb, respectively, after dopamine-resistance occurred. Progressive hemodynamic decline occurred in Group I pigs. DA failed to restore MAP to baseline. However, 0% and 67% of pigs also treated with heta-starch and DCLHb, respectively, achieved temporary restoration of baseline MAP (p = 0.03), prompting a reduction in the dose of DA in 0% of hetastarch vs. 50% of DCLHb treated pigs. Except for increased MPAP and decreased heart in DCLHb treated pigs (p<0.001), hemodynamics and survival were not different (p>0.05). In conclusion, although DCLHb exacerbated pulmonary hypertension and did not improve O2 utilization or survival, because DCLHb restored MAP to baseline and had a dopamine sparing effect, further investigation of DCLHb's hemodynamic effects in adrenergic agent-resistant endotoxemia is warranted.

Effects of FK409 on intestinal ischemia-reperfusion injury and ischemia-induced changes in the rat mucosal villus microcirculation

BACKGROUND

The small intestine is extremely sensitive to ischemia-reperfusion (I/R) injury and a range of microcirculatory disturbances contribute to tissue damage. Nitric oxide (NO) seems to be involved in tissue protection after I/R injury. This study therefore assessed the effects of the NO donor, FK409, on intestinal I/R injury and changes induced in intestinal microcirculation.

METHODS

PVG rats were subjected to 30-min intestinal ischemia with a subgroup of animals receiving FK409 (10 mg/kg i.v.) 30 min before ischemia and 30 min postreperfusion. Controls underwent sham surgery. The mucosal surface was visualized via an incision made in an exteriorized ileal segment and FITC-BSA or acridine orange was used to quantitate macromolecular leak (MML) and leukocyte adhesion, respectively. MML from, and numbers of adherent leukocytes within, individual villi were determined every 15 min for 2 hr after removal of the vessel clamp. Heart rate and mean blood pressure (mBP) were monitored throughout the experiment.

RESULTS

Eleven of 12 untreated animals subjected to intestinal I/R injury failed to survive the 2 hr reperfusion period, whereas all 12 FK409-treated animals survived. MML and leukocyte adhesion were increased in untreated animals (P<0.001), and blood flow stasis eventually ensued. Although FK409 decreased mBP (P<0.001), MML and leukocyte adhesion were significantly (P<0.001) reduced, and villus blood flow was maintained throughout the observation period.

CONCLUSIONS

FK409 prevented mortality after intestinal I/R, significantly reduced leukocyte adhesion, and maintained blood flow after intestinal ischemia and may therefore be of value in reducing tissue damage and improving outcome after small bowel transplantation.

L-arginine polymers inhibit the development of vein graft neointimal hyperplasia

OBJECTIVE

We sought to determine whether L -arginine polymer treatment of vein grafts enhances vascular production of nitric oxide and inhibits the development of neointimal hyperplasia.

METHODS

External jugular veins of New Zealand White rabbits (n = 42) were harvested; treated intraluminally for 15 minutes with phosphate-buffered saline solution or L -arginine polymer 5, 7, or 9 at either 10 or 100 micromol/L; and then grafted into the contralateral carotid artery. Rabbits were killed after 28 days, and 5-microm sections of vessels were stained with hematoxylin and scored for intima/media ratio by using computerized morphometric analysis. Separate veins were treated in a similar fashion with biotinylated polymers and phosphate-buffered saline solution to assess for translocation efficiencies. Finally, vein segments pretreated with either phosphate-buffered saline solution or L -arginine polymers were cultured in Dulbecco's modified Eagle's medium containing lipopolysaccharide (100 microg/mL) and interferon gamma (200 U/mL) for 48 hours before measuring nitric oxide levels by means of the Griess reaction.

RESULTS

Biotinylated L -arginine polymers demonstrated a dose- and length-dependent uptake into intimal and medial cells of treated vessels. Nitric oxide levels were significantly higher in vein segments treated with 100 micromol/L of L -arginine polymer 9 compared with control segments. Finally, the intima/media ratio also reflected both length- and concentration-dependent inhibition of neointimal hyperplasia.intima/media ratio PBS R5 R7 R9 10 micromol/L 0.909 +/- 0.072 0.920 +/- 0.073 0.861 +/- 0.138 0.710 +/- 0.122 100 micromol/L 0.924 +/- 0.061 0.581 +/- 0.089* 0.529 +/- 0.093* PBS, Phosphate-buffered saline solution; R, L -arginine polymer. *P <.001 versus phosphate-buffered saline solution and L -arginine polymer 5 controls (Bonferroni-corrected value).

CONCLUSIONS

Arginine polymers of sufficient length and concentration were effective in increasing nitric oxide levels and reducing neointimal hyperplasia in this vein graft model.

Perfusion-assisted direct coronary artery bypass: selective graft perfusion in off-pump cases

BACKGROUND

Hemodynamic instability during multivessel off-pump coronary artery bypass grafting can lead to hypotension, progressive myocardial ischemia, further hypotension, and the need for urgent cardiopulmonary bypass.

METHODS

In 10 patients undergoing off-pump coronary artery bypass grafting, a novel technique of pressure-controlled blood delivery has been used that allows the immediate restoration of arterial blood to distal coronary beds after distal coronary anastomosis. This technique utilizes a servo-controlled pump to allow delivery of blood at systemic or suprasystemic pressures, and provides the option for infusion of supplemental additives for myocardial resuscitation, myocardial vasodilation, and enhancement of myocardial performance.

RESULTS

Myocardial perfusion was successfully enhanced via one or two grafts in all 10 patients with an average graft flow of 98+/-8 mL/min. In 3 patients, a 27% increase in perfusion pressure led to a 59% increase in perfusate flow. All patients were hemodynamically stable after initiation of selective graft perfusion.

CONCLUSIONS

Based on this preliminary patient series, the selective perfusion of grafted vessels seems to facilitate multivessel off-pump coronary artery bypass grafting by promoting rapid recovery of grafted segments, by enhanced hemodynamic stability during subsequent anastomoses, and by providing increased flexibility in the sequence of grafting.

Opposite effects of nitric oxide and nitroxyl on postischemic myocardial injury

Recent experimental evidence suggests that reactive nitrogen oxide species can contribute significantly to postischemic myocardial injury. The aim of the present study was to evaluate the role of two reactive nitrogen oxide species, nitroxyl (NO(-)) and nitric oxide (NO(.)), in myocardial ischemia and reperfusion injury. Rabbits were subjected to 45 min of regional myocardial ischemia followed by 180 min of reperfusion. Vehicle (0.9% NaCl), 1 micromol/kg S-nitrosoglutathione (GSNO) (an NO(.) donor), or 3 micromol/kg Angeli's salt (AS) (a source of NO(-)) were given i.v. 5 min before reperfusion. Treatment with GSNO markedly attenuated reperfusion injury, as evidenced by improved cardiac function, decreased plasma creatine kinase activity, reduced necrotic size, and decreased myocardial myeloperoxidase activity. In contrast, the administration of AS at a hemodynamically equieffective dose not only failed to attenuate but, rather, aggravated reperfusion injury, indicated by an increased left ventricular end diastolic pressure, myocardial creatine kinase release and necrotic size. Decomposed AS was without effect. Co-administration of AS with ferricyanide, a one-electron oxidant that converts NO(-) to NO(.), completely blocked the injurious effects of AS and exerted significant cardioprotective effects similar to those of GSNO. These results demonstrate that, although NO(.) is protective, NO(-) increases the tissue damage that occurs during ischemia/reperfusion and suggest that formation of nitroxyl may contribute to postischemic myocardial injury.

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

Myocardial protection during cardiac surgery from the viewpoint of coronary endothelial function

1. During cardiac surgery, the heart is arrested and subject to ischaemia-reperfusion injury. 2. To protect the heart, cardioplegia is usually used to initially stop and then maintain the still condition of the heart, which not only facilitates the precise operation but, more importantly, minimizes the energy consumption of the heart during this period. 3. The ischaemia-reperfusion injury may involve both myocytes and coronary endothelium-smooth muscle and, therefore, the protection of the heart should also involve these two aspects. 4. Injury to the heart involves: (i) ischaemia-reperfusion injury to the myocytes and coronary circulation; and (ii) possible injury to the coronary circulation by cardioplegia due to its hyperkalaemic components. 5. Injury to the coronary circulation may involve both endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) mechanisms. The EDNO mechanism is susceptible to ischaemia-reperfusion, whereas the EDHF mechanism may be altered by hyperkalaemic cardioplegia. 6. To further protect the heart, supplemental therapy for EDNO and optimizing the components of cardioplegia to restore the EDHF mechanism may be important.

Inhibition of inducible nitric oxide synthase after myocardial ischemia increases coronary flow

BACKGROUND

The role of nitric oxide synthase in myocardial ischemia-reperfusion injury is complex. Our hypothesis was that inducible nitric oxide synthase has a role in the regulation of coronary flow after ischemia.

METHODS

Four groups of isolated blood-perfused rabbit hearts underwent sequential periods of perfusion, ischemia, and reperfusion (20, 30, and 20 minutes). Two groups underwent 40 minutes of perfusion. Ischemic groups received saline vehicle, N omega-nitro-L-arginine methyl ester (L-NAME) or the highly specific inducible nitric oxide synthase inhibitor 1400W in low or high doses during reperfusion. Two nonischemic groups were treated with saline vehicle or 1400W during the last 20 minutes of perfusion. Left ventricular developed pressure and coronary flow were measured after each perfusion period. Ventricular levels of myeloperoxidase and cyclic guanosine monophosphate were measured at the end of the second perfusion period.

RESULTS

Coronary flow was significantly increased in both 1400W groups versus L-NAME (p < 0.001) and in high-dose 1400W versus control (p < 0.001). Coronary flow was not significantly different between the nonischemic groups. Left ventricular developed pressure was not significantly different among the ischemic groups or between the two nonischemic groups. There were no differences in cyclic guanosine monophosphate levels in any of the ischemic hearts. Myeloperoxidase levels were significantly elevated in L-NAME versus high-dose 1400W, nonischemic 1400W, and nonischemic saline groups (p < 0.02).

CONCLUSIONS

Highly selective inhibition of inducible nitric oxide synthase results in increased coronary flow after ischemia but not after continuous perfusion. This occurs with decreased neutrophil accumulation and a trend toward increased contractility without elevation of cyclic guanosine monophosphate levels.