Prostacyclin protects ischemic reperfused myocardium in the dog by inhibition of neutrophil activation

"Endothelial Dysfunction in Resuscitated Cardiac Arrest (ENDO-RCA): Safety and efficacy of low-dose Iloprost, a prostacyclin analogue, in addition to standard therapy, as compared to standard therapy alone, in post-cardiac-arrest-syndrome patients."

OBJECTIVE

An increasingly recognized prognostic factor for out-of-hospital-cardiac-arrest (OHCA) patients is the ischemia-reperfusion injury after restored blood circulation. Endothelial injury is common in patients resuscitated from cardiac arrest and is associated with poor outcome. This study was designed to investigate if iloprost infusion, a prostacyclin analogue, reduces endothelial damage in OHCA patients.

METHODS

50 patients were randomized in a placebo controlled double-blinded trial and allocated 1:2 to 48-hours iloprost infusion, (1 ng/kg/min) or placebo (saline infusion). Endothelial biomarkers (soluble thrombomodulin (sTM), sE-selectin, syndecan-1, soluble vascular endothelial growth factor (sVEGF), vascular endothelial cadherine (VEcad), nucleosomes) and sympathoadrenal activation (epinephrine/norepinephrine) from baseline to 48 and 96-hours were evaluated.

RESULTS

Iloprost infusion did not influence endothelial biomarkers by the 48-hour endpoint. A rebound effect was observed with higher biomarker plasma values in the iloprost group (sTM p=0.02; Syndecan p=0.004; nucleosomes p<0.001; VEcad p<0.03) after 96-hours. There was a significant difference in 180-day mortality in favor of placebo. There was no difference regarding total adverse events between groups (p=0.73). Two patients were withdrawn in the iloprost group due to hypotension.

CONCLUSIONS

The administration of low-dose iloprost (1ng/kg/min) to OHCA patients did not significantly influence endothelial biomarkers as measured by the 48- hour endpoint. A rebound effect was however observed in the 96-hour statistical model, with increasing endothelial biomarker levels after cessation of the iloprost-infusion.

Evaluation of Free Radical Injury in Myocardium

Abundant evidence now is available that free radicals are produced in excess when myocardium is reperfused following an episode of ischemia and that free radicals can injure myocytes and endothelial cells. Free radicals may contribute to either reversible or irreversible manifestations of cell injury from ischemia and reperfusion. Several investigators have observed that postischemic contractile dysfunction (myocardial stunning) can be attenuated by a variety of anti-free radical therapies, and there seems to be general agreement that free radical injury contributes to stunning. Whether free radicals are an important cause of lethal myocyte injury (“lethal reperfusion injury”) remains controversial. Using similar interventions and animal models, both positive and negative results have been reported from a growing number of studies done to test the effect of anti-free radical therapies on infarct size. Proposed explanations include differences in: 1) dose of drug and onset or duration of treatment, 2) duration of occlusion or reperfusion, 3) methods of measuring infarct size or area at risk, and 4) failure of some studies to control for baseline variation in the major determinants of infarct size, e.g., collateral blood flow. At present, none of these explanations seems sufficient to resolve the question.

Effects of Prostacyclin on Heparin Reversal with Protamine

This study was planned to show the beneficial effects of prostacyclin (PGI2) utilization on adverse effects of protamine. PGI2 was administered at a rate of 5 ng/kg/min. Twenty patients entered this study. Half of them received PGI2 whereas the others did not.

Right ventricular end-diastolic volume index and right ventricular stroke work index were 72 mL/m2 and 2.2 g.m/m2, respectively, after patients were weaned off the bypass and 79 and 1.5, respectively, at five minutes after pro tamine administration in the control group; these values were 88 and 3.2, re spectively, and 86 and 3, respectively, in the PGI2 group. Left ventricular stroke work index (g.m/m2) was 27.9 in the control group and 36.7 in the PGI2 group (p < 0.05) after protamine administration.

Thromboxane B2 levels (pmoL/mL) in coronary sinus (CS) blood were 251 in the control group and 90 in the PGI2 group at five minutes after protamine administration (p < 0.05). Myocardial blood flow was 174 mL in the control group and 245 mL in the PGI2 group at five minutes after protamine adminis tration (p < 0.05). Cyclic adenosine monophosphate (cAMP) and cyclic guano- sine monophosphate (cGMP) levels in CS blood were 17 pmoL/mL and 2.1 pmoL/mL, respectively, in the control group and 36 and 0.3, respectively, in the PGI2 group at five minutes after protamine administration. Leukotriene B4 level was 129 and 57 pmoL/mL in the control and PGI2 groups, respectively (at the same time as the cAMP measurement) (p < 0.05).

From the results of this study the authors conclude that adverse effects of heparin reversal with protamine can be reduced with the use of PGI2.

Captopril Induces Iron Release From Ferritin and Oxidative Stress

Captopril has been reported to possess reducing and iron-binding properties, which could favour iron delocalization from ferritin and oxidative stress.

In the present paper, we have found that the drug was effectively capable of inducing a significant mobilization of ferritin iron, which was apparently superoxide anion-independent. Once released from ferritin as a result of captopril action, iron became free in the reduced form and could induce oxidant damage, as evaluated by deoxyribose-oxidative degradation. This phenomenon was not antagonized by the reported oxygen radical-scavenging properties of the drug.

These data indicate that captopril is not always an antioxidant drug, and suggest that it may act as a pro-oxidant in the presence of ferritin in-vivo.

Pleiotropic effects of neutrophils on myocyte apoptosis and left ventricular remodeling during early volume overload

Most of the available evidence on the role of neutrophils on pathological cardiac remodeling has been pertained after acute myocardial infarction. However, whether neutrophils directly contribute to the pathogenesis of cardiac remodeling after events other than acute myocardial infarction remains unknown. Here we show that acute eccentric hypertrophy induced by aorto-caval fistula (ACF) in the rats induced an increase in the inflammatory response characterized by activation of the STAT pathway and increased infiltration of neutrophils in the myocardium. This early inflammation was associated with a decrease in interstitial collagen accumulation and an increase in myocyte apoptosis. Neutrophil infiltration blockade attenuated MMP activation, ECM degradation, and myocyte apoptosis induced by ACF at 24 hours and attenuated the development of eccentric hypertrophy induced by ACF at 2 and 3 weeks, suggesting a causal relationship between neutrophils and the ACF-induced cardiac remodeling. In contrast, sustained neutrophil depletion over 4 weeks resulted in adverse cardiac remodeling with further increase in cardiac dilatation and macrophage infiltration, but with no change in myocyte apoptosis level. These data support a functional role for neutrophils in MMP activation, ECM degradation, and myocyte apoptosis during eccentric cardiac hypertrophy and underscore the adverse effects of chronic anti-neutrophil therapy on cardiac remodeling induced by early volume overload.

The influence of controlled limb reperfusion with PGE1 on reperfusion injury after prolonged ischemia

BACKGROUND

Controlled reperfusion of ischemic limbs has been found to be protective in limiting ischemia-reperfusion injury. We aimed to analyze local hemodynamic effects of prostaglandin E1 (PGE1) administrated during controlled reperfusion in an in vivo setting.

MATERIAL AND METHODS

Twenty-four pigs underwent exposure of the infrarenal aorta and iliac vessels. Pigs were observed for 7.5 h without limb ischemia (group I). In the others, limb ischemia was produced by clamping the aorta for 6 h. Reperfusion was conducted in uncontrolled (group II), controlled (group III), and controlled fashion with addition of PGE1 (group IV) for the initial 30 min. We evaluated regional blood flow in the left common iliac artery, cardiac output, systemic vascular resistance, oxygen and glucose consumption, muscle adenosine triphosphate (ATP), and potassium levels in iliac vein.

RESULTS

Benefits after reperfusion were observed in group IV compared with group III regarding regional blood flow at 60 min (P < 0.01) and 90 min (P < 0.01), glucose consumption at 30 min, (P < 0.05) and potassium regulation at 30 (P < 0.05) and 90 min (P < 0.05).

CONCLUSION

The addition of PGE1 to controlled reperfusion further reduces local hemodynamic effects of ischemia-reperfusion injury compared with standard controlled and uncontrolled reperfusion in an animal model.

HDL and its sphingosine-1-phosphate content in cardioprotection

Increasing evidence suggests that High-density lipoproteins (HDL) are a direct cardioprotective agent in the setting of acute myocardial ischemia/reperfusion injury, and that this cardioprotection occurs independently of their atheroprotective effect. Studies on the involved mechanisms have revealed that the biologically active HDL-compound sphingosine-1-phosphate (S1P) is responsible for the beneficial effect of HDL on the myocardium. There appears to be an intricate interplay between known preconditioning agents and components of the S1P synthesis machinery in the heart, which makes S1P signalling an attractive downstream convergence point of preconditioning and cardioprotection at the level of its G protein-coupled receptors. While local S1P production has been known to protect the heart against ischemia/reperfusion injury and to mediate preconditioning, systemic S1P supply via HDL adds a novel aspect to the regulation of cardioprotection. Thus the S1P-content of HDL may serve both as a potential cardiovascular risk marker and a novel therapeutic target. Strategies for short-term "acute" HDL elevation as well as S1P analogues may prove beneficial not only in the high-risk patient but also in any patient at risk of myocardial ischemia.

Cyclooxygenase-1 Mediates the Final Stage of Morphine-Induced Delayed Cardioprotection in Concert With Cyclooxygenase-2

OBJECTIVES

We sought to investigate the time course of morphine-induced delayed cardioprotection and examine the role of cyclooxygenase (COX) in this cardioprotective effect.

BACKGROUND

Cyclooxygenase-2 has been shown to be essential for the delayed cardioprotection induced by ischemic preconditioning and delta-opioid agonists.

METHODS

Male mice were subjected to 45 min of coronary artery occlusion followed by 120 min of reperfusion. Expressions of COX-2 and COX-1 were assessed by Western blotting, and the myocardial prostaglandin (PG)E2 and 6-keto-PGF(1-alpha) contents were measured using enzyme immunoassays.

RESULTS

A powerful infarct-sparing effect appeared 24 and 48 h after morphine preconditioning and faded after 72 h. After 24 h, the anti-infarct effect was associated with enhanced myocardial levels of COX-2, PGE2, and 6-keto-PGF(1-alpha), and no changes in COX-1 protein levels were found. Cardioprotection and increases in PGE2 and 6-keto-PGF(1-alpha) were completely abolished by the COX-2-selective inhibitor NS-398 and the non-selective COX inhibitor indomethacin, whereas the COX-1-selective inhibitor SC-560 had no effect. After 48 h, up-regulation of myocardial PGE2 and 6-keto-PGF(1-alpha) was also observed, and COX-1 expression was enhanced markedly, but only a slight increase in COX-2 expression was apparent. Cardioprotection and the increases in PGE2 and 6-keto-PGF(1-alpha) 48 h after morphine administration were abrogated only by indomethacin, and not by SC-560 or NS-398.

CONCLUSIONS

Morphine confers delayed cardioprotection via a COX-dependent pathway; COX-2 is essential for the cardioprotection observed in the initial stage (24 h), whereas, in the final stage (48 h), cardioprotection is mediated by COX-1 in concert with COX-2.

Cardioprotection During the Final Stage of the Late Phase of Ischemic Preconditioning Is Mediated by Neuronal NO Synthase in Concert With Cyclooxygenase-2

The infarct-sparing effect of the late phase of ischemic preconditioning (late PC) lasts for 72 hours. Upregulation of both cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS) has been shown to be essential to the protection in the initial stage of late PC (24 hours after PC); however, the mechanisms underlying the protection in the final stage of late PC (48 to 72 hours after PC) are unknown. Conscious rabbits were preconditioned with six cycles of 4-minute coronary occlusion/4-minute reperfusion. At 72 hours after PC, powerful protection against infarction was associated with increased myocardial levels of COX-2 mRNA, protein, and cardioprotective prostaglandins (PGI 2 and PGE 2 ). The COX-2–selective inhibitor NS-398 completely blocked the protection. Surprisingly, iNOS expression was not increased at 72 hours; instead, upregulation of neuronal NO synthase (nNOS) was evident at both the mRNA (+266±20%, P <0.005) and the protein levels (+195±66%, P <0.005), which was accompanied by an increase in myocardial nitrite/nitrate (+20±4%, P <0.05). The nNOS-selective inhibitors N -propyl- l -arginine or S -ethyl N -[4-(trifluoromethyl)phenyl]isothiourea completely blocked the protection of late PC at 72 hours, whereas the iNOS-selective inhibitor S -methylisothiourea had no effect. In line with these findings, the disappearance of protection at 120 hours after PC was associated with the return of nNOS mRNA, protein, and activity to control levels. Although expression of COX-2 protein was still elevated at 120 hours, only a marginal increase in PGI 2 and PGE 2 levels was detected. In contrast to 72 hour after PC, nNOS was not upregulated at 24 hour after PC. We conclude that (1) the cardioprotection observed in the final stage of late PC (72 hour) is mediated by nNOS, not by iNOS, in concert with COX-2, and (2) nNOS-derived NO is required to drive COX-2 activity. These data identify, for the first time, a cardioprotective role of nNOS and demonstrate, surprisingly, that the mechanism of late PC differs at 72 hours (nNOS) versus 24 hours (iNOS).

Microvascular in vivo assessment of reperfusion injury: significance of prostaglandin E1 and I2 in postischemic “no-reflow” and “reflow-paradox”

BACKGROUND

Microvascular ischemia-reperfusion (I/R) injury is characterized by failure of capillary perfusion ("no-reflow") and reoxygenation-associated phenomena ("reflow-paradox"), including activation of leukocyte-endothelium interaction with cytotoxic mediator-induced loss of endothelial integrity. The objectives of this study were to elucidate the impact of both prostaglandins E(1) (PGE(1)) and I(2) (PGI(2)) in microvascular reperfusion injury, with special focus on the distinct pathophysiology of no-reflow- and reflow-paradox phenomena.

MATERIALS AND METHODS

By use of the hamster dorsal skinfold preparation and in vivo fluorescence microscopy, the microcirculation of a striated skin muscle was assessed before 4 h of pressure-induced ischemia and 0.5, 2, and 24 h after onset of reperfusion.

RESULTS

I/R was characterized by enhanced leukocyte-endothelium interaction in postcapillary venules, increase of macromolecular leakage, and reduction of functional capillary perfusion (P < 0.05). Intravenous 2-h infusion of PGE(1), starting with onset of reperfusion, reduced leukocyte adhesion and macromolecular leakage in postcapillary venules during early reperfusion (P < 0.05), while 6-h infusion, given during ischemia and early reperfusion, showed no significant effects. PGI(2) infusion also attenuated postischemic leukocyte adhesion, which was significant by a 6-h prolonged administration (P < 0.05), but did not influence the increase of microvascular permeability. Both prostaglandins were unable to prevent the postischemic failure of capillary perfusion (no-reflow).

CONCLUSIONS

Both prostaglandins did not significantly influence postischemic no-reflow phenomena, but appeared as potent inhibitors of reflow-paradox under the experimental circumstances of this study.

Moderate Systemic Hypotension During Reperfusion Reduces the Coronary Blood Flow and Increases the Size of Myocardial Infarction in Pigs

STUDY OBJECTIVE

s: To examine the effects of low arterial BP (ABP) during reperfusion on the extent of myocardial infarction and on coronary blood flow (CBF) in an occlusion/reperfusion experimental model.

DESIGN

Prospective, randomized animal study.

SETTING

University hospital.

PARTICIPANTS

Normal pigs that were anesthetized, intubated, and mechanically ventilated.

INTERVENTIONS

Twenty-seven open-chest pigs underwent occlusion of the mid left anterior descending (LAD) coronary artery for 1 h followed by reperfusion for 2 h. During reperfusion, the animals were randomly assigned to either continuous infusion of nitroglycerin in therapeutic doses and fluid infusion at rates to maintain a mean ABP >or= 80 mm Hg (group 1, n = 13), or continuous nitroglycerin infusion at rates to maintain a mean ABP between 60 mm Hg and 75 mm Hg (group 2, n = 14).

MEASUREMENTS AND RESULTS

The hemodynamics and the coronary ABP distal to the occlusion were recorded throughout the experiment. In addition, the LAD CBF and peak hyperemia CBF before occlusion and during reperfusion periods were measured by transit-time flowmetry. At the end of the experiment, the infarcted left ventricular myocardial size was measured. There were no significant hemodynamic differences, including the distal coronary arterial pressure, between the two groups before or during the LAD artery occlusion period. During reperfusion, mean ABP was 90 +/- 3 mm Hg in group 1 vs 69 +/- 3 mm Hg in group 2 (p < 0.001). In group 1, the infarcted myocardium represented 50.3 +/- 4.3% of the myocardium at risk, vs 69.4 +/- 7.2% in group 2 (p < 0.001). During reperfusion, CBF and peak hyperemia CBF were significantly higher in group 1 than in group 2.

CONCLUSIONS

Low ABP during reperfusion increases the size of myocardial infarction and decreases CBF.

[Pathophysiological roles of the prostanoids in the cardiovascular system: studies using mice deficient in prostanoid receptors]

Prostanoids, consisting of the prostaglandins (PGs) and thromboxanes (TXs), exert various actions through activation of their specific receptors. They include the DP, EP, FP, IP, and TP receptors for PGD2, PGE2, PGF2alpha, PGI2, and TXA2, respectively. Moreover, EP receptors are classified into four subtypes, the EP1, EP2, EP3 and EP4 receptors. Using mice lacking prostanoid receptors, we intended to clarify in vivo roles of prostanoids under pathophysiological conditions of the cardiovascular system, which include ischemia-induced cardiac injury, pressure overload-induced cardiac hypertrophy, renovascular hypertension, tachycardia during systemic inflammation and thromboembolism. The results demonstrated that 1) PGI2 plays an important role in attenuating the ischemic injury and the pressure overload-induced hypertrophy of the hearts, and also contributes to the development of renovascular hypertension; 2) PGE2 plays a cardioprotective role against the ischemic injury via both the EP3 and EP4, and also participates in acute thromboembolism via the EP3; and 3) both PGF2alpha and TXA2, which have been produced during systemic inflammation, are responsible for tachycardia.

BM-573, a dual thromboxane synthase inhibitor and thromboxane receptor antagonist, prevents pig myocardial infarction induced by coronary thrombosis

The aim of this study was to characterize the effects of BM-573 [N-terbutyl-N'-[2-(4'-methylphenylamino)-5-nitro-benzenesulfonyl] urea], a novel dual thromboxane A2 receptor antagonist and thromboxane synthase inhibitor, on myocardial infarction induced by topical ferric chloride (FeCl3) application to the left anterior descending (LAD) coronary artery in anesthetized pigs. All control animals (n = 6) developed an occlusive thrombus in the LAD coronary artery. The mean infarct size, revealed by triphenyl tetrazolium chloride (TTC), and the area at risk, evidenced by Evans blue, corresponded to 35.3 +/- 2.2 and 36.9 +/- 2.1% of the left ventricular mass, respectively. In the BM-573-treated group (n = 6), a drug infusion (10 mg. kg-1. h-1) started 30 min before FeCl3 application and continued throughout the experimentation. Among the BM-573-treated group, four pigs did not develop coronary artery thrombus and their myocardium appeared healthy. Histopathological examination of FeCl3-injured coronary artery revealed an occlusive and adherent thrombus in control group, while pretreatment with BM-573 prevented thrombus formation. In infarcted zones, lack of desmin staining and muscle structure disorganization were obvious. Depletion of myocardial ATP content was observed in the myocardial necrotic region of the control group, but not in myocardial samples of BM-573-treated pigs that did not develop myocardial infarction. When BM-573 prevented LAD artery occlusion, the area under the curve of plasmatic troponin T was reduced by 77% over 6 h. These data suggest that BM-573 could be useful for the prevention of myocardial infarction.

High-density lipoproteins protect isolated rat hearts from ischemia-reperfusion injury by reducing cardiac tumor necrosis factor-alpha content and enhancing prostaglandin release

The incidence and severity of primary cardiac events are inversely related to the plasma concentration of high-density lipoproteins (HDLs). We investigated whether HDLs may exert a direct cardioprotection in buffer-perfused isolated rat hearts, which underwent a 20-minute low-flow ischemia followed by a 30-minute reperfusion. The administration of HDLs at physiological concentrations (0.5 and 1.0 mg/mL) during the 10 minutes immediately before ischemia rapidly and remarkably improved postischemic functional recovery and decreased creatine kinase release in the coronary effluent. Reconstituted HDLs containing apolipoprotein A-I (apoA-I) and phosphatidylcholine, but not lipid-free apoA-I or phosphatidylcholine liposomes, were also effective in protecting the heart from ischemia-reperfusion injury. HDLs at reperfusion were less effective than when given before ischemia. HDLs caused a dose-dependent reduction of ischemia-induced cardiac tumor necrosis factor-alpha (TNF-alpha) expression and content, which correlated with the improved functional recovery. A parallel increase of TNF-alpha release in the coronary effluent was observed, due to a direct binding of cardiac TNF-alpha to HDLs. Taken together, these findings argue for a cause-effect relationship between the HDL-mediated removal of TNF-alpha from the ischemic myocardium and the HDL-induced cardioprotection. Indeed, etanercept, a recombinant TNF-alpha-blocking protein, caused a dose-dependent improvement of postischemic functional recovery. HDLs also enhanced ischemia-induced prostaglandin release, which may contribute to the cardioprotective effect. A low plasma HDL level may expose the heart to excessive ischemia-reperfusion damage, and HDL-targeted therapies may be helpful to induce immediate or delayed myocardial protection from ischemia-reperfusion injury.

alpha(4)-integrin mediates neutrophil-induced free radical injury to cardiac myocytes

Previous work has demonstrated that circulating neutrophils (polymorphonuclear leukocytes [PMNs]) adhere to cardiac myocytes via beta(2)-integrins and cause cellular injury via the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme system. Since PMNs induced to leave the vasculature (emigrated PMNs) express the alpha(4)-integrin, we asked whether (a) these PMNs also induce myocyte injury via NADPH oxidase; (b) beta(2)-integrins (CD18) still signal oxidant production, or if this process is now coupled to the alpha(4)-integrin; and (c) dysfunction is superoxide dependent within the myocyte or at the myocyte-PMN interface. Emigrated PMNs exposed to cardiac myocytes quickly induced significant changes in myocyte function. Myocyte shortening was decreased by 30-50% and rates of contraction and relaxation were reduced by 30% within the first 10 min. Both alpha(4)-integrin antibody (Ab)-treated PMNs and NADPH oxidase-deficient PMNs were unable to reduce myocyte shortening. An increased level of oxidative stress was detected in myocytes within 5 min of PMN adhesion. Addition of an anti-alpha(4)-integrin Ab, but not an anti-CD18 Ab, prevented oxidant production, suggesting that in emigrated PMNs the NADPH oxidase system is uncoupled from CD18 and can be activated via the alpha(4)-integrin. Addition of exogenous superoxide dismutase (SOD) inhibited all parameters of dysfunction measured, whereas overexpression of intracellular SOD within the myocytes did not inhibit the oxidative stress or the myocyte dysfunction caused by the emigrated PMNs. These findings demonstrate that profound molecular changes occur within PMNs as they emigrate, such that CD18 and associated intracellular signaling pathways leading to oxidant production are uncoupled and newly expressed alpha(4)-integrin functions as the ligand that signals oxidant production. The results also provide pathological relevance as the emigrated PMNs have the capacity to injure cardiac myocytes through the alpha(4)-integrin-coupled NADPH oxidase pathway that can be inhibited by extracellular, but not intracellular SOD.

Do prostaglandins have a salutary role in skeletal muscle ischaemia-reperfusion injury?

OBJECTIVES

the effects of prostaglandins (PG) E1, E2, and the prostacyclin analogue iloprost with and without the addition of free-radical scavengers catalase and superoxide dismutase on gastrocnemius blood flow and oedema were studied in a rodent model of hindlimb ischaemia-reperfusion.

METHODS

male Sprague-Dawley rats underwent 6-h hindlimb ischaemia with 4-h reperfusion. Prostaglandins were infused prior to reperfusion and their effects on limb blood flow and oedema examined.

RESULTS

control animals exhibited a triphasic pattern of muscle blood flow during reperfusion compared to normal animals. PGE1 did not abolish low reflow at 10 min, relative reperfusion was preserved but reperfusion injury was abolished at 120 min. Muscle blood flow was increased at 240 min compared to controls. Increased limb swelling was also seen. Addition of free-radical scavengers caused the abolition of low reflow. Similar results were seen with iloprost. PGE2 abolished low reflow at 10 min and increased perfusion at 120 min but did not prevent reperfusion injury at 240 min.

CONCLUSIONS

PGE1 and iloprost enhance muscle blood flow at 4-h reperfusion, though neither abolishes low reflow; PGE2 improved flow at 10 and 120 min but not after 240 min. This study demonstrates a potentially beneficial role for prostaglandins in improving muscle blood flow in skeletal muscle ischaemia-reperfusion injury.

Intravenous aspirin at reperfusion does not reduce infarct size in the dog with a residual critical stenosis

Platelet-related events being associated with the increment of infarct size at reperfusion in the presence of a residual stenosis, we tested in dogs whether intravenous aspirin (ASA) could limit infarct size. The left anterior descending coronary artery was occluded for 90 min and reperfused for 6 h in the presence of a residual critical stenosis. Controls received saline, and treated groups were given 2, 6, or 12 mg/kg ASA, i.v., 5 min before reperfusion. Infarct size did not differ significantly between groups (control, 43.80+/-6.28%; ASA, 2 mg/kg: 41.07+/-7.78%; ASA, 6 mg/kg: 37.55+/-3.44%; ASA, 12 mg/kg: 29.40+/-5.41%), as well as transmural collateral blood flow and [111In]-platelet accumulation in the infarcted myocardium (2.5-3.6 x 10(5) platelets/g). However, myocardial neutrophil accumulation was significantly reduced (p < 0.05) in groups given 6 (15.0+/-2.6 x 10(6)/g tissue) and 12 mg/kg (18.4 +/-3.8) ASA, but not in the 2-mg/kg group (21.0+/-5.2), as compared with control group (32.0+/-7.2). Ex vivo platelet aggregation to collagen was abolished during reperfusion in all treated groups (p < 0.05). Transcardiac arteriovenous differences in 6-keto-PGF1alpha were reduced significantly 1 h after reperfusion in groups given 6 or 12 mg/kg ASA (94.7+/-13.1 and 71.7+/-19.2 pg/ml, respectively) but not in the 2-mg/kg group (178.3+/-78.2 pg/ml), as compared with control (405.4+/-171.6 pg/ml). ASA-insensitive platelet activation at the site of stenosis or inhibition by ASA of prostacyclin production by jeopardized myocardium may explain the observed lack of benefit of ASA.

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.

Reperfusion injury: experimental evidence and clinical implications

Postischemic reperfusion may profoundly alter cardiac function. Principal mediators of this phenomenon are oxygen radicals and neutrophils. Upon reflow, oxygen radicals are generated in large amounts, overwhelming cellular defenses and inducing oxidative tissue damage; biochemical markers of oxygen radical formation and attack can be found in postischemic myocardium. Reintroduction of neutrophils in postischemic tissues is accompanied by their activation, with release of lytic enzymes that directly induce tissue damage and proinflammatory mediators that amplify the local inflammatory reaction. Neutrophils may also plug capillaries, mechanically blocking flow. Oxidants can also modulate various events, ultimately leading to tissue injury, such as nitric oxide formation, platelet-activating factor metabolism, tissue factor synthesis, and exposure of adhesion molecules. In the clinical setting, important consequences of postischemic reperfusion are reversible contractile dysfunction ("stunning"), which is mostly caused by oxygen radical attack, and impairment to flow at the microvascular level ("no-reflow") secondary to neutrophil plugging and vasoconstriction.

Emigrated neutrophils regulate ventricular contractility via alpha4 integrin

We have previously shown that CD18 and alpha4 integrin were important in the adherence of emigrated neutrophils to cardiac myocytes. Whether either of these molecules is important in myocyte dysfunction is unclear. In this study, we measured contractility as an index of myocyte function. Control contractility was compared with shortening response in myocytes exposed to neutrophils in the presence and absence of anti-CD18 or anti-alpha4 antibodies. Control unloaded cell shortening, expressed as a percentage of resting cell length, measured 10.06+/-1.16% (n=10) at 5 minutes. Circulating neutrophils caused a 35% reduction in cell shortening, an event prevented by anti-CD18, but not by anti-alpha4 antibody. When emigrated neutrophils were added to the myocytes, a profound reduction (50%) in unloaded cell shortening was noted. A significant increase in CD18 and alpha4 integrin was found on emigrated neutrophils. Addition of anti-CD18 antibody did not protect the myocyte from the emigrated neutrophils, whereas the addition of an anti-alpha4 antibody significantly reduced neutrophil-induced cell shortening, despite some neutrophils still adhering to the myocytes. Furthermore, emigrated neutrophils were able to cause myocytes to go into contracture within 5 minutes in the presence of neutrophils with or without anti-CD18 antibody. In addition to the impairment in unloaded cell shortening, at later times (10 minutes), neutrophils also caused a 40% reduction in the rate of contraction and relaxation. The addition of either anti-CD18 or anti-alpha4 antibody protected the myocytes from these changes. The data suggest that immunosuppression of CD18 on emigrated neutrophils was only partially effective in reducing myocyte dysfunction. In contrast, immunosuppression of the alpha4 integrin alone was sufficient to dramatically reduce all parameters of cell dysfunction measured in this study.

Nitric oxide deficiency, leukocyte activation, and resultant ischemia are crucial to the pathogenesis of diabetic retinopathy/neuropathy--preventive potential of antioxidants, essential fatty acids, chromium, ginkgolides, and pentoxifylline

Impaired microcirculatory perfusion appears to be crucial to the pathogenesis of both neuropathy and retinopathy in diabetics. This in turn reflects a hyperglycemically mediated perturbation of vascular endothelial function that entails overactivation of protein kinase C, reduced availability of nitric oxide, increased production of superoxide and endothelin, impaired insulin function, diminished synthesis of prostacyclin/PGE1, and increased activation and endothelial adherence of leukocytes. These dysfunctions may be addressed with a supplementation program that includes high-dose antioxidants, fish oil, gamma-linolenic acid, chromium, arginine, carnitine, and ginkgolides. Pharmaceuticals likely to be of benefit in this regard include pentoxifylline, probucol, replacement estrogens, and inhibitors of angiotensin converting enzyme and aldose reductase.

Spinal cord complications of thoracoabdominal aneurysm surgery

BACKGROUND

Although rare, paralysis secondary to spinal cord ischaemia after aortic aneurysm surgery is a devastating complication. Many papers have been published on this topic but without a clear consensus on the best way of minimizing the problem. Recent articles have included advanced pharmacological approaches and the literature has been reviewed in light of these.

METHODS

Relevant papers were identified by an extensive text word search of the Medline database and a review of quoted articles.

RESULTS

Spinal cord complications are commoner after the repair of Crawford type II aneurysms than less extensive aneurysms. The presence of dissection, rupture and prolonged clamp times are associated with an increased incidence. About a quarter of all cord problems develop over 24 h after surgery and this may be due to a reperfusion type injury, although the exact mechanisms are by no means clear.

CONCLUSION

A combination of rapid surgery, left heart bypass for the repair of more extensive aneurysms, free spinal drainage and the avoidance of postoperative hypoxia and hypotension help to minimize spinal cord ischaemia. No pharmacological agent has yet been shown conclusively to improve outcome in the clinical setting.

The inflammatory response and extracorporeal circulation

Defining the cause of organ and tissue dysfunction associated with the use of perfusion systems will produce methods of prevention or treatment and improve patient outcome. The problem is the plethora of triggers, effectors, and mediators in this process, which can now be measured. Each new measureable compound becomes another biochemical "smoking gun" without physiological data to show any relevance to the human problem. This review critically compares and contrasts the role of certain, largely novel, initiation, amplification, and cytotoxic mechanisms in the inflammatory response of the myocardium and pulmonary systems after a period of cardiopulmonary bypass. The available evidence strongly points to the process being different for each of these tissue beds. These data suggest that ensuring normal lung and heart functions after surgery will require separate therapeutic strategies.

Prolonged coronary artery occlusion-reperfusion sequences reduce myocardial free radical production: an electron paramagnetic resonance study

Our purpose was to determine whether prolonged myocardial ischemia attenuates free radical production after early reperfusion. Twenty-two mongrel dogs underwent left anterior descending coronary artery occlusion for 20, 40, or 60 minutes followed by 30 minutes of reperfusion. Electron paramagnetic resonance spectroscopy was used to measure ascorbate free radical in the coronary vein effluent. Ascorbate free radical production during reperfusion was significantly (p < 0.05) reduced in the dogs undergoing 60 minutes of coronary artery occlusion compared with the dogs undergoing 40 and 20 minutes of occlusion. We conclude that prolonged myocardial ischemia results in less free radical production on reperfusion than do shorter periods of ischemia followed by reperfusion.

Reduction of progressive burn injury by a stable prostaglandin I2 analogue, beraprost sodium (Procylin): an experimental study in rats

Beraprost sodium is a chemically stable prostaglandin I2 analogue with antiplatelet and vasodilator actions. Burn injury causes thrombosis and vessel occlusion by increasing the blood viscosity and by thermal damage to the vascular network in the dermis. A vascular response also occurs in the uninjured dermis surrounding the site of injury. Diminished blood flow and spreading tissue oedema lead to progressive ischaemia and necrosis around the burn site (zone of stasis), with the final necrotic tissue area being larger than the initial one. If blood flow could be restored in the zone of stasis, secondary tissue damage would be minimized. In this study, we examined the effects of a prostaglandin I2 analogue, beraprost sodium (Procylin, Kaken Pharmaceutical Company, Tokyo, Japan) on burn injury in rats. Twenty male Sprague-Dawley rats weighing an average of 450 g were burned with a comb-shaped brass probe that produced a row of three burns measuring 10 x 30 mm each and two intervening unburned areas measuring 5 x 30 mm each. The rats were divided into two groups of 10 animals. One group received 0.015 mg of beraprost sodium intraperitoneally immediately after burn injury, while the control group received the same volume of saline. Skin blood flow was measured with a laser Doppler flowmeter, and the development of oedema as well as the area of necrotic tissue were also determined. The extent of skin necrosis and oedema were significantly reduced in the beraprost sodium-treated rats, and blood flow in the zone of stasis was increased. These findings demonstrate that prostaglandin I2 plays an important role in burn injury and that beraprost sodium can reduce secondary necrosis in the zone of stasis.

Reduction of canine infarct size by bolus intravenous administration of liposomal prostaglandin E1: comparison with control, placebo liposomes, and continuous intravenous infusion of prostaglandin E1

Prostaglandin E1 (PGE1) reduces experimental infarct size when administered by prolonged low-dose left atrial infusion during coronary occlusion. Liposomal delivery of PGE1 may enhance biologic activity and limit adverse hemodynamic effects. The purpose of this study was to test the hypothesis that intravenous bolus administration of liposomal PGE1 (TLC C-53, The Liposome Company, Princeton, N.J.) during coronary occlusion would result in myocardial salvage. We compared TLC C-53 (0.5 microgram/kg intravenous bolus at 10 and 100 min of occlusion of the left anterior descending coronary artery [LAD]), free PGE1 (0.1 microgram/kg/min infused 10 min after LAD occlusion until reperfusion), placebo liposomes, and control (n = 7 for each group) in an open-chest canine model of 2 hours of LAD occlusion and reperfusion. Infarct size as a percentage of risk area (mean +/- SD) in the control group (58.4% +/- 20.0%) was similar to that in animals given placebo liposomes (53.1% +/- 12.6%) but was significantly reduced in the groups given TLC C-53 (33.5% +/- 9.2%; p < 0.01) or free PGE1 (37.2% +/- 4.8%; p < 0.05) groups. Infarct salvage was significant (p < 0.05) for the TLC C-53-and PGE1-treated dogs compared with the control dogs, independent of collateral blood flow by analysis of covariance. Moreover, the ischemic-zone blood flow during reperfusion was significantly higher in the TLC C-53 group compared with the control group or the group receiving free PGE1. Neutrophil infiltration of ischemic myocardium was significantly inhibited by TLC C-53 as determined by myeloperoxidase assay. Unlike free PGE1, TLC C-53 did not cause significant tachycardia or hypotension during therapy. In conclusion, TLC C-53 administered intravenously during coronary occlusion significantly reduced infarct size, limited neutrophil infiltration, and improved myocardial blood flow during reperfusion without adverse hemodynamic consequences.

Influence of pentoxifylline on cytokine levels and inflammatory parameters in septic shock

OBJECTIVE

To evaluate the influence of pentoxifylline (PTX), a phosphodiesterase inhibitor, on cytokines and inflammatory proteins in patients suffering from septic shock.

DESIGN

Prospective study comparing a therapy group to a matched control group.

SETTING

Medical intensive care unit at a university hospital.

PATIENTS

Twenty four patients fulfilling the criteria of septic shock were included in this study. Twelve patients received PTX (therapy group) and 12 patients matched for diagnosis, age and gender served as the control group.

INTERVENTIONS

Pentoxifylline at 1 mg/kg per hour over 24 h in the therapy group.

MEASUREMENTS AND RESULTS

Cytokine levels [tumor necrosis factor-alpha (TNF)], soluble TNF receptor [TNF-R], and interleukin-6 [IL-6] and inflammatory proteins [C-reactive protein, alpha-1-antitrypsin (AAT), fibronectin, and haptoglobin], as well as hemodynamic parameters and the APACHE III score were evaluated before initiation of therapy and 24 h-later. After 24 h, TNF levels were significantly lower in the therapy group (p = 0.013), while IL-6 levels were significantly higher in the therapy group (p = 0.030). Within the 24 h TNF declined significantly in the therapy group (p = 0.006), while IL-6 showed a significant increase (p = 0.043). AAT and the APACHE III score tended to differ significantly after 24 h between the groups [AAT levels higher in the therapy group (p = 0.05), APACHE III score lower (p = 0.05)]. In the therapy group, the systemic vascular resistance index was significantly higher after 24 h (p = 0.0026) whereas the cardiac index declined (p = 0.035).

CONCLUSIONS

PTX does influence TNF levels in septic shock patients. Nevertheless, inhibiting a single mediator in severe septic shock cannot stop the inflammatory overreaction.

Effect of colchicine on circulating and myocardial neutrophils and on infarct size in a canine model of ischemia and reperfusion

Myocardial injury after ischemia/reperfusion has been attributed in part to the effects of neutrophils. We examined whether colchicine, a potent and rapid inhibitor of neutrophils, may reduce inflammatory leukocytosis, prevent postischemic myocardial neutrophil accumulation, and reduce infarct size (IS). Twenty-four dogs were randomized to either a control (saline administration) or a colchicine (1 mg/kg intravenously, i.v.) group. Anesthetized open-chest dogs underwent 120-min coronary artery occlusion followed by 6-h reperfusion. Determinants of IS [area-at-risk (AAR) and collateral flow] and IS were measured in 22 dogs (11 in each group). We evaluated neutrophil toxicity by measuring ex vivo production of reactive oxygen species by chemiluminescence. Myocardial localization and accumulation of neutrophils were histologically evaluated by independent observers. The number of circulating neutrophils (p < 0.01), neutrophil cytotoxicity (p < 0.05), and neutrophil myocardial accumulation after 6-h reperfusion (p = 0.006) were reduced in treated dogs. Left ventricular (LV) peak rate of pressure increase was similar in both groups during ischemia /reperfusion. However, whereas collateral blood flow and AAR, the main determinants of IS, were similar in control and treated dogs, there was no reduction in IS: 37.1 +/- 7% of AAR in controls and 37.4 +/- 8% in treated dogs. Despite marked reduction of neutrophil toxicity and postischemic myocardial neutrophil accumulation, no myocardial protection could be detected in this dog model.

Effect of beraprost sodium (Procylin), a stable prostaglandin I2 analogue, on a dorsal skin flap model in rats

Beraprost sodium, a chemically stable prostaglandin I2 analogue with antiplatelet vasodilator actions, was tested by comparing the extent of viability of random pattern skin flaps in control rats and rats treated with beraprost sodium. An isolated tail based 2 x 7 cm flap was constructed in 50 Sprague-Dawley rats. In group 1 (beraprost sodium treated group, n = 25) 0.015 mg beraprost sodium were injected intraperitoneally immediately after the flap had been raised. In group 2 (control group, n = 25) the animals were injected intraperitoneally with the same volume of saline immediately after the flap had been raised. At the end of the seventh day the flap survival area was documented using digital planimetry. The difference between the results showed that beraprost sodium had significantly beneficial effect on skin flap survival (p < 0.01, Welch's test).

Influence of prostaglandin E1 on tissue ischemia during surgical repair of the abdominal aorta

OBJECTIVE

To evaluate tissue protection by PGE1 during leg ischemia in patients undergoing aortic surgery.

DESIGN

Randomized, controlled prospective clinical trial.

SETTING

Single university hospital.

PARTICIPANTS

19 consecutive patients undergoing abdominal aortic aneurysm repair.

INTERVENTIONS

Patients received infusions of 30 ng/kg/min of PGE1 or saline.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables, lactate, creatine phosphokinase, and thromboxane B2 (TXB2) were measured. In the control group, the decrease in cardiac index (CI) after aortic cross-clamping (AXC) persisted until unclamping together with a decrease in femoral venous O2 content (CfvO2). In the PGE1 group, CI returned to baseline with a trend toward greater CfvO2 levels. During reperfusion in the PGE1 group, O2 consumption and lactate levels exceeded preclamp values. Pulmonary hypertension occurred equally in both groups but did not correlate with TXB2, which was not altered by surgery or by PGE1 infusion.

CONCLUSIONS

Intraoperative PGE1 treatment offers no benefit and may exacerbate tissue ischemia during AXC by redistributing microcirculatory flow or limiting cellular oxygen utilization in a manner that overwhelms any possible protective effect.

Endogenous reactive oxygen metabolites mediate sublethal endothelial cell dysfunction during reoxygenation

PURPOSE

Endothelial cells (EC) secrete vasoactive eicosanoids, which maintain organ blood flow. Because EC are a major source of eicosanoids, we studied the effects of reoxygenation on EC prostacyclin production.

METHODS

Bovine aortic EC cultures were exposed to 2 hours of normoxia, then 1 hour of hypoxia (PO2 = 10 +/- 3.5 mm Hg), followed by 1.5 hours of reoxygenation in either normal medium or medium plus either superoxide dismutase (SOD, 300 units/ml), catalase (1200 units/ml), allopurinol (5.0 x 10(-4) mol/L), or dinitrophenol (10(-4) mol/L).

RESULTS

Prostacyclin production decreased to 40% (p < 0.05) of basal prostacyclin production after 1 hour of hypoxia. EC reoxygenated with control medium recovered to 48% of basal prostacyclin production. EC reoxygenated in SOD resulted in recovery (p < 0.05) to 154% of basal prostacyclin production after 60 minutes. Catalase treatment resulted in recovery to 105% (p < 0.05) of basal prostacyclin production within 30 minutes of reoxygenation. Allopurinol treatment resulted in 77% recovery (p < 0.05) of basal prostacyclin production only during 30 minutes of reoxygenation. Dinitrophenol treatment resulted in significant (> or = 85%, p < 0.05) sustained recovery of basal prostacyclin production at 30, 60, and 90 minutes of experimental reperfusion.

CONCLUSIONS

The hypoxia-induced decrease in EC prostacyclin does not recover during reoxygenation. Catalase/SOD allowed return to baseline prostacyclin production during reoxygenation, implicating reactive oxygen metabolites as mediators of decreased eicosanoid biosynthesis. Recovery of prostacyclin production after 60 minutes reoxygenation with dinitrophenol but not allopurinol suggests a mitochondrial origin of the oxygen metabolites responsible for decreased prostacyclin biosynthesis.

Protective Effect of Elastase Inhibition Against Myocardial Dysfunction and Injury Induced by Ischemia and Reperfusion in Isolated Rat Hearts

BACKGROUND: Elastase release has been incriminated in the genesis of reperfusion-induced myocardial dysfunction and injury, and elastase inhibitors have been reported to reduce myocardial dysfunction in dogs subjected to coronary artery occlusion and reperfusion. METHODS AND RESULTS: To examine if elastase inhibition will modify myocardial dysfunction and injured induced by ischemia and reperfusion in isolated hearts, hearts from male Sprague Dawley rats were subjected to 30 minutes of total ischemia followed by 30 minutes of reperfusion. Ischemia-reperfusion resulted in myocardial dysfunction (increase in coronary perfusion pressure and decrease in myocardial contraction), injury (measured as creatine kinase release), and lipid peroxidation (myocardial malondialdehyde). Perfusion of hearts with an elastase inhibitor, ICI200,880, protected against myocardial dysfunction, injury and lipid peroxidation following ischemia-reperfusion. As expected, perfusion with superoxide dismutase protected the hearts against hemodynamic deterioration following ischemia-reperfusion. In in vitro studies, there was no direct effect of ICI200,880 on superoxide anion generation. CONCLUSIONS: ICI200,880 seems to exert cardioprotective effects against ischemia-reperfusion-induced injury and myocardial dysfunction in isolated buffer-perfused hearts, most likely by an elastase-like protease inhibitory activity.

Effect of vitamin E on human aortic endothelial cell responses to oxidative injury

Reactive oxygen species produced by the cells present in the arterial wall may cause oxidative damage to cellular components altering endothelial cell (EC) function. Changes in the EC function appear to play a key role in the pathogenesis of atherosclerosis. Human aortic endothelial cells (HAEC) were employed to investigate the protective role of vitamin E upon exposure of endothelial cells to oxidative stress in vitro. HAEC assimilate d-alpha-tocopherol from the media in a dose-dependent manner. Exposure of HAEC to 16.5 mM of the free radical generator 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) for 16 h decreased cell viability (assessed by trypan blue exclusion) from 90 to 28%. HAEC preincubated with vitamin E at 15, 30, and 60 microM prior to the AAPH exposure resulted in a dose-dependent increase in resistance to oxidative stress and increased cell viability by 37, 66, and 85%, respectively. An increase in prostacyclin (PGI2) production by HAEC in response to AAPH exposure was correlated positively with cell damage and negatively with vitamin E concentration. Interleukin (IL)-1 production also increased in parallel with cell damage induced by AAPH. Vitamin E treatment significantly reduced IL-1 production after AAPH exposure. This modulatory role of vitamin E on HAEC function following exposure to an oxidative stress may reflect its antioxidant protection against lipid peroxidation.

Neutrophils and myocardial reperfusion injury

Ischaemia induces an acute inflammatory response in myocardial tissue with an early phase of neutrophil accumulation, which is accelerated by reperfusion. In experimental models, interventions that deplete neutrophils or inhibit their function cause a significant reduction in myocardial infarct size. These cells, therefore, may exacerbate tissue injury through the release of free radicals and proteolytic enzymes. Neutrophil recruitment depends on the presence of inflammatory mediators. Leukotriene B4, interleukin 8 and the complement fragment C5a have been implicated in this process. Studies using antibodies to the selectin, integrin and immunoglobulin superfamily adhesion molecules indicate that they also have a crucial role in myocardial neutrophil recruitment.

Bypass conduit vessel wall biology substantially influences downstream myocardial contractile response to injury from ischemia and reperfusion

Coronary vascular intraluminal release of endogenous endothelium-derived substances, such as prostacyclin, may affect downstream cardiac myocyte contractile function. With a "chronic" canine model of endothelialized and deendothelialized internal thoracic artery coronary grafts, we tested the hypothesis that higher basal release of endothelium-derived prostacyclin in internal thoracic artery bypass conduit effluent accelerates functional recovery of postischemic stunned myocardium in the intact circulation. Eleven dogs underwent left internal thoracic artery-left circumflex artery bypass, and the proximal circumflex artery was then ligated. Internal thoracic artery conduit endothelium was denuded by balloon catheter in five dogs before grafting and left intact in six dogs. After 7 days, awake dogs were studied to measure myocardial segment length in the circumflex region with ultrasonic dimension transducers, left ventricular pressure with micromanometers, and circumflex artery flow with an ultrasonic flow probe. Regional contractile function was quantified by the area beneath the linear preload recruitable stroke work relationship at baseline and at intervals after a 15-minute circumflex graft occlusion followed by 3 hours of reperfusion. Heart rate, left ventricular peak pressure, left ventricular end-diastolic pressure, left ventricular peak first derivative of pressure (dP/dt), and circumflex flow were similar (all p not significant) in endothelialized and nonendothelialized dogs during ischemia and reperfusion. Ischemia reduced the preload recruitable stroke work relationship to 44% +/- 35% of control values (p < 0.01) in endothelialized dogs and to 47% +/- 18% of control values in nonendothelialized dogs (p < 0.01) at 15 minutes of reperfusion, indicating a similar (p not significant) initial degree of injury. During 3 hours of reperfusion, the preload recruitable stroke work relationship returned to 51% +/- 17% of control values in endothelialized dogs but to only 35% +/- 20% of control values in nonendothelialized dogs (p < 0.02). Basal intraluminal release of endogenous prostanoids in excised internal thoracic artery conduits was subsequently quantified by ex vivo bioassay of vasoactive properties of conduit effluent on normal coronary artery smooth muscle. Endothelialized conduits induced greater smooth muscle relaxation than did nonendothelialized conduits (67% vs 23%), and this increased relaxation by endothelialized conduits was eliminated by indomethacin, a blocker of prostanoid synthesis. These data indicate that coronary bypass conduit endothelium-derived substances, such as prostacyclin, significantly influence downstream myocardial contractile response to ischemia and reperfusion, independent of alterations in coronary flow in the intact circulation.

The influence of prostacyclin (PGI2) on contractile properties of isolated right ventricle of rat heart

The mechanism of the positive inotropic effect of prostacyclin (PGI2) (2.6 x 10(-6) mol/l) on the isolated right ventricle of rat heart was studied. Our results show that the positive inotropic effect of prostacyclin is produced indirectly through beta adrenoceptors and slow Ca2+ channels, because blockade of slow Ca2+ channels with verapamil (10(-6) mol/l) and beta adrenoceptors with propranolol (10(-6) mol/l) abolishes this effect. Alpha adrenoceptors do not mediate the action of PGI2.

Adjunctive selectin blockade successfully reduces infarct size beyond thrombolysis in the electrolytic canine coronary artery model

BACKGROUND

An adjunctive pharmacological strategy to thrombolytic therapy that is tailored to limit reperfusion injury after thrombolysis could further maximize the unquestioned benefit of restoring flow to ischemic myocardium. Ischemia-reperfusion injury exhibits features characteristic of an acute inflammatory response, including the rapid activation and infiltration of neutrophils. The initial process of neutrophil migration from the circulation to injured tissue is modulated by a group of adhesion molecules called selectins. The purpose of the present study was to assess the efficacy of a selectin blocker (CY 1503) given as an adjunct to thrombolytic therapy to interfere with the inflammatory response after ischemia-reperfusion and subsequently reduce myocardial infarct size in the electrolytic canine model.

METHODS AND RESULTS

A fully occlusive thrombus was formed in the left circumflex coronary artery by electrolytic injury in 20 anesthetized open-chest dogs. After occlusion, an infusion of 1 mg/kg recombinant tissue-type plasminogen activator (rTPA) was administered over 20 minutes with either a bolus of placebo or the selectin blocker CY 1503 (40 mg/kg). At the onset of reperfusion, 20 micrograms/kg per minute rTPA was administered for 1 hour to prevent reocclusion. After 1 hour of reperfusion, infarct size, myocardial myeloperoxidase activity, and reperfusion arrhythmias were measured. In CY 1503-treated dogs, there was a significant 69% reduction in infarct size when expressed as a percentage of the area at risk (6.7 +/- 8.4% versus 21.8 +/- 13.6%; P = .008) and a marked reduction in myeloperoxidase activity (0.014 +/- 0.009 versus 0.0370 +/- 0.025 U/min per gram; P = .02) compared with the placebo group. There was no difference between the groups in the occurrence of reperfusion arrhythmias.

CONCLUSIONS

Selectin blockade as an adjunct to rTPA-mediated thrombolysis significantly reduces infarct size and myocardial neutrophil infiltration well beyond thrombolysis alone in the electrolytic canine model. These data suggest that selectin blockade is extremely effective at reducing ischemia-reperfusion injury and myocardial infarct size in this model and that the neutrophil is a potent mediator of ischemia-reperfusion injury.

Beneficial effects of prostacyclin treatment on reperfusion of the myocardium

A total of 20 patients with coronary artery disease were studied in order to assess the benefits of prostacyclin administration on reperfusion of the ischaemic myocardium after cardiopulmonary bypass. Ten received prostacyclin (25 ng/kg per min) while ten were untreated controls. There was no difference between groups with regard to age, preoperative ejection fraction and aortic cross-clamping times. There were no in-hospital deaths in either group. The administration of prostacyclin significantly altered the metabolic side effects of reperfusion followed by hypothermic cardioplegic arrest. Myocardial oxygen consumption after cardiopulmonary bypass was significantly higher in the prostacyclin-treated group than in controls (18.5 ml versus 13 ml; P < 0.01). Prostacyclin treatment significantly reduced the leucocyte activity: leukotriene B4 concentrations were 58 pmol/l in prostacyclin-treated patients compared with 93 pmol/l in controls (P < 0.01). Such recovery of metabolic status during reperfusion resulted in better haemodynamic function in patients receiving prostacyclin.

The prooxidant properties of captopril

The thiol drug captopril has been reported to possess reducing and transition metal-binding properties, which could result in specific changes in iron and copper prooxidant capacity. Thus, the effects of captopril on iron- and copper-induced oxidative injury were evaluated using deoxyribose as the oxidizable substrate in the presence of physiological phosphate concentrations but in the absence of the non-physiological chelator EDTA. In an iron(III)/H2O2/ascorbate oxidant system, captopril enhanced deoxyribose oxidation only when it was pre-mixed with iron, whereas it did not influence sugar degradation when not pre-mixed with the metal or when ascorbate was omitted. The physiological thiol GSH acted in a similar manner, whereas the SH-lacking angiotensin-converting enzyme inhibitor ramiprilat did not influence iron-induced deoxyribose oxidation, indicating that the thiol group is crucial in favouring enhanced iron reactivity due to 'malignant' chelation. Further specific experiments designed to evaluate possible thiol-dependent iron(III) reduction failed to demonstrate ferric to ferrous reduction by either captopril or reduced glutathione (GSH). When iron(III) was replaced by copper(II) to induce deoxyribose oxidation, captopril was prooxidant both in the presence and absence of ascorbate, and when pre-mixed or not with copper. On the other hand, GSH was prooxidant up to 2:1 molar ratio with respect to copper but markedly inhibited copper-dependent sugar oxidation beginning at molar ratio of 4:1. Ramiprilat did not significantly influence copper-induced deoxyribose oxidation. Moreover, unlike the experiments performed with iron, captopril, as well as GSH, readily reduced copper(II) to copper(I). Hence, captopril can act as prooxidant in the presence of iron or copper. In the former case, only 'malignant' iron chelation by the drug is involved in oxidant injury, whereas in the latter both copper chelation and reduction are operative, although specific chelating mechanisms are crucial in enhancing copper-induced oxidant injury. Captopril, therefore, cannot be considered simply as an 'antioxidant drug', and its catalytic transition metal-related prooxidant capacity should be taken into account in experimental and clinical investigations.

Polydeoxyribonucleotides and nitric oxide release from guinea-pig hearts during ischaemia and reperfusion

1. Two polydeoxyribonucleotides, produced by the controlled hydrolysis of DNA of mammalian lung (defibrotide and its lower molecular weight fraction, P.O. 085 DV), were studied for their ability to modify the release of nitrite and the coronary flow in perfusates collected from isolated, normally perfused hearts of guinea-pigs and from hearts subjected to regional ischaemia and reperfusion. 2. In guinea-pig normally perfused hearts, both defibrotide (DFT) and its fraction, P.O. 085 DV, increase the amount of nitrite appearing in perfusates in a concentration-dependent fashion. At the highest concentration studied (10(-6) M), P.O. 085 DV was more effective than DFT. A concomitant increase in the coronary flow was observed. 3. The increase in nitrite in perfusates and the increase in coronary flow induced by both DFT and P.O. 085 DV were significantly reduced by NG-monomethyl-L-arginine (L-NMMA, 10(-4) M), an inhibitor of nitric oxide synthase (NOS). 4. The endothelium-dependent vasodilator, acetylcholine (ACh), enhances the formation of nitrite and the coronary flow. Both the increase in coronary flow and in the formation of nitrite were significantly reduced by L-NMMA (10(-4) M). 5. In guinea-pig hearts subjected to ischaemia and reperfusion, the effect of both compounds in increasing the amount of nitrite in perfusates was more evident and more pronounced with P.O. 085 DV. 6. Reperfusion-induced arrhythmias were significantly reduced by both compounds to the extent of complete protection afforded by compound P.O. 085 DV. 7. The cardioprotective and antiarrhythmic effects of DFT and P.O. 085 DV are discussed.

Role of neutrophils in myocardial ischemia and reperfusion

In the intact organism, ischemic myocardial injury initiates an acute inflammatory response in which polymorphonuclear leukocytes (PMNs) are major participants. Evidence indicates that the interplaying inflammatory reactions are augmented by reperfusion and that accumulating PMNs can contribute to myocardial damage, eg, by release of oxygen-derived free radicals, proteases, and leukotrienes. In experimental models, interventions aimed at PMN inhibition can exert cardioprotective effects, and some of these strategies raise hope for future clinical applications. A greater understanding of the mechanisms involved in PMN-mediated myocardial damage is necessary for designing a rational approach to reduce the putative detrimental effects of PMNs without antagonizing their favorable consequences in tissue healing.