Zhi-Qing Zhao

Gradual Reperfusion Reduces Infarct Size and Endothelial Injury but Augments Neutrophil Accumulation

BACKGROUND Reperfusion causes injury to the coronary artery endothelium primarily by neutrophil-mediated mechanisms. However, factors other than neutrophils may govern the extent of myocardial necrosis. This study tests the hypothesis that gradual initiation of reflow will reduce reperfusion injury and preserve postischemic endothelial function. METHODS In 16 anesthetized dogs, the left anterior descending artery was ligated for 60 minutes. In one group, reperfusion was initiated abruptly (abrupt, n = 8), whereas in the gradual reperfusion group (ramp, n = 8), flow was slowly initiated during the first 30 minutes of reperfusion. After reperfusion, coronary artery segments were isolated to assess postischemic endothelial function. RESULTS Infarct size (area of necrosis/area at risk) was significantly reduced in the ramp group (28.2% +/- 2.0%) compared with abrupt (41.6% +/- 1.4%). Neutrophil accumulation (myeloperoxidase) in the area at risk was significantly greater in the ramp group compared with abrupt (8.0 +/- 1.3 versus 3.5 +/- 0.8 U/g tissue). In isolated postischemic left anterior descending arterial rings, the concentration of acetylcholine that elicited a response 50% of the maximum possible response was significantly greater in abrupt (-6.88 +/- 0.04 log [mol/L]) than ramp (-7.62 +/- 0.04 log [mol/L]) and control (-7.68 +/- 0.003 log [mol/L]), suggesting endothelial dysfunction. The concentration of A23187 that elicited a response 50% of the maximum possible response was similarly greater in abrupt (-7.24 +/- 0.03 log [mol/L]) versus ramp (-7.62 +/- 0.03 log [mol/L]) and control (-7.8 +/- 0.04 log [mol/L]). Smooth muscle dysfunction (response to sodium nitrite) also occurred in the abrupt rings. CONCLUSIONS Gradual reperfusion of an ischemic area reduces infarct size and preserves endothelial function but paradoxically increases neutrophil accumulation within the area at risk.

Coronary artery endothelial dysfunction after global ischemia, blood cardioplegia, and reperfusion

This study tests the hypothesis that blood cardioplegia (BCP) attenuates endothelial dysfunction related to nitric oxide after global normothermic ischemia, cardioplegic arrest, and reperfusion in anesthetized open-chest dogs placed on cardiopulmonary bypass. The dogs were divided into five groups to identify the time when endothelial injury occurred: group 1 = control without ischemia; group 2 = 45 minutes of normothermic ischemia only; group 3 = 45 minutes of normothermic ischemia plus unmodified reperfusion; group 4 = 45 minutes of ischemia plus intermittent BCP without reperfusion; and group 5 = ischemia plus BCP and reperfusion. In vitro coronary vascular relaxation responses to the nitric oxide stimulator acetylcholine (endothelium-dependent, receptor-dependent), the calcium ionophore A23187 (endothelium-dependent, receptor-independent), and acidified NaNO2 (endothelium-independent) were measured at the end of the protocol. Maximum in vitro coronary vascular responses to acetylcholine were similar among groups 1, 2, and 4, indicating an absence of endothelial injury. In contrast, significantly impaired relaxations to acetylcholine were demonstrated in the two reperfused groups (groups 3 and 5). Relaxation responses to A23187 and NaNO2 were not altered markedly in any group. Electron microscopy showed intact endothelium in groups 1, 2, and 4. However, moderately severe endothelium damage was seen in groups 3 and 5. We conclude that morphologic and functional endothelial damage occurs after blood reperfusion with or without BCP, and 1-hour hypothermic BCP arrest after normothermic ischemia is not associated with extension of endothelial damage.

Intravascular adenosine at reperfusion reduces infarct size and neutrophil adherence

BACKGROUND Adenosine has been shown to reduce infarct size predominantly during reperfusion by adenosine A2-receptor-mediated processes. This cardioprotection may involve inhibition of events in the vascular compartment, such as adherence-independent and adherence-dependent actions of neutrophils. This study tested the hypothesis that adenosine exerts its cardioprotection during reperfusion by targeting effectors in the vascular compartment. METHODS Polyadenylic acid (molecular weight, 230,000 daltons) was used as an intravascularly confined adenosine mimetic. In anesthetized New Zealand white rabbits, the left coronary artery was occluded for 30 minutes and reperfused for 120 minutes. RESULTS Polyadenylic acid (1 mg/kg bolus, 0.5 mg kg-1 h-1) given 5 minutes before reperfusion significantly (p < 0.05) reduced infarct size compared with vehicle (23% +/- 2% versus 37% +/- 2% area at risk). The A1-antagonist KW-3902 had no effect on this polyadenylic acid-induced protection (17% +/- 3%), whereas the A1-A2 antagonist sulfophenytheophylline blocked this infarct size reduction (41% +/- 2%). In vitro adherence of platelet-activating factor-activated neutrophils to thoracic aortic endothelium was significantly diminished by polyadenylic acid (185 +/- 12 neutrophils/mm2 versus 36 +/- 4 neutrophils/mm2 endothelial surface). Sulfophenytheophylline inhibited this effect (280 +/- 6 neutrophils/mm2), whereas KW-3902 did not (31 +/- 7 neutrophils/mm2). CONCLUSIONS An intravascular adenosine mimetic agent exerts cardioprotection during reperfusion by targeting receptor-mediated mechanisms in the intravascular compartment, possibly involving inhibition of neutrophil-related processes.

Reduction in surgical ischemic-reperfusion injury with adenosine and nitric oxide therapy

Ischemia and reperfusion impair the inherent capacity of the heart to protect itself from related pathophysiologic events by reducing endogenous oxygen radical scavengers and inhibitors. However, other endogenously produced agents, notably adenosine and nitric oxide, are produced during ischemia, reperfusion, or both. These autacoids have several cardioprotection actions in common, particularly antineutrophil effects and inhibition of endothelial-neutrophil interactions, which are key initial steps in ischemic-reperfusion injury. Studies have shown that nitric oxide exerts cardioprotection primarily during reperfusion. Adenosine, on the other hand, protects the myocardium to some extent during both ischemia and reperfusion, thereby covering both periods during which myocardial injury may be sustained during a cardiac operation. Native adenosine or active analogues, or donors of nitric oxide, may be given before or in conjunction with cardioplegia solutions. However, these endogenous agents can also be pharmacologically recruited to provide a new potent therapeutic approach against surgical ischemic-reperfusion injury. This article reviews the cardioprotective effects of primarily endogenous nitric oxide and adenosine in both nonsurgical and surgical models of ischemia-reperfusion injury. Both adenosine and nitric oxide provide potent cardioprotection in surgical and nonsurgical models of ischemia-reperfusion. An important mechanism in this cardioprotection is attenuation of neutrophil-mediated damage.

Blood cardioplegia enhanced with nitric oxide donor SPM-5185 counteracts postischemic endothelial and ventricular dysfunction

This study tested the hypothesis that enhancement of blood cardioplegia with the nitric oxide donor agent SPM-5185 inhibits postischemic left ventricular and coronary endothelial dysfunction. Eighteen anesthetized dogs supported by total vented bypass were subjected to 30 minutes of normothermic ischemia followed by 4 degrees C multidose blood cardioplegia. Hearts received either standard blood cardioplegia (vehicle group; n = 6), blood cardioplegia with 1 mumol/L SPM-5185 (low-dose group; n = 6), or 10 mumol/L SPM-5185 (high-dose group; n = 6). After 60 minutes of cardioplegic arrest, the heart was reperfused for a total of 60 minutes, first in the beating empty state for 30 minutes and then after discontinuation of bypass for 30 minutes. Baseline and postischemic left ventricular function was assessed by the slope of the end-systolic pressure-volume (impedance catheter) relation. Postischemic end-systolic pressure-volume relation was depressed by 53.7% of preischemic values in the vehicle group (from 8.2 +/- 1.0 to 3.8 +/- 0.3 mm Hg/ml) and by 33.7% (from 9.2 +/- 1.1 to 6.1 +/- 0.5 mm Hg/ml) in the low-dose group. In contrast, there was complete postischemic functional recovery in the high-dose group (from 7.6 +/- 1.1 to 7.2 +/- 1.2 mm Hg/ml). In coronary arteries isolated from these hearts, endothelium-dependent maximal relaxation to acetylcholine was impaired by 27% in the vehicle group and by 18% in the low-dose group, whereas the high-dose group showed complete endothelium-dependent relaxation. Myeloperoxidase activity, an index of neutrophil accumulation in postischemic myocardium, was elevated in the vehicle and low-dose groups (3.36 +/- 0.58 and 2.56 +/- 0.68 U/100 mg tissue) but was significantly reduced in the high-dose group to 1.27 +/- 0.45 U/100 mg tissue. We conclude that inclusion of 10 mumol/L nitric oxide donor SPM-5185 in blood cardioplegia improves postischemic ventricular performance and endothelial function in ischemically injured hearts, possibly via inhibition of neutrophil-mediated damage.

l-Arginine inhibits neutrophil adherence and coronary artery dysfunction

BACKGROUND Nitric oxide (NO) attenuates neutrophil (PMN)-mediated damage, partly by inhibiting superoxide anion (O2-) generation and adherence to the coronary artery endothelium. L-Arginine is the endogenous substrate for production of NO via the NO synthase pathway. This study tested the hypothesis that the endogenous NO precursor L-arginine (L-Arg) would reduce PMN-induced coronary artery dysfunction by attenuating O2- production and neutrophil adherence. METHODS Neutrophils and left anterior descending (LAD) coronary artery segments were isolated from normal, anesthetised (30 mg/kg i.v. pentobarbitone) dogs. LAD segments were either cut into 2-3 mm rings and mounted in organ chambers to measure vascular tone responses to acetylcholine (endothelium-receptor-dependent) and acidified NaNO2 (smooth muscle), or cut into segments to measure adherence of fluorescently labeled neutrophils by epifluorescence microscopy. RESULTS L-Arg had no direct inhibitory effect on O2- production (cytochrome c reduction) by PMN activated with platelet activating factor (PAF) (34.6 +/- 4.8 nmol vs. 34.2 +/- 4.1 nmol). L-Arg (10 mmol) reduced adherence of fluorescently labeled PMN to isolated canine coronary artery endothelium activated by 100 nM PAF from 187 +/- 11 to 41 +/- 6 PMN/mm2, P < 0.05. This inhibition of adherence was reversed by N-var pi-nitro-L-arginine (L-NA, 1 mmol) (175 +/- 20 PMN/mm2) and by the NO scavenger, carboxy-PTIO (600 mu M, 157 +/- 23 PMN/mm2). D-arginine, the nonmetabolised enantiomer of L-arginine, (D-Arg, 10 mmol) did not reduce adherence (162 +/- 20 PMN/mm2). To determine the effect of PMN on coronary artery endothelial function, canine coronary artery rings were transiently incubated with activated PMNs in organ chambers to induce dysfunction. After washout of PMN, the EC50 (- log M) derived from post-injury concentration-relaxation responses to acetylcholine was significantly less in 10 mmol L-Arg (6.94 +/- 0.08) than untreated rings (6.47 +/- 0.06). In contrast, 10 mmol D-Arg could not reverse this dysfunction (6.48 +/- 0.11). CONCLUSIONS L-Arg reduces PMN-induced coronary endothelial dysfunction by inhibition of adherence via the L-arginine-NO pathway.

Adenosine in blood cardioplegia prevents postischemic dysfunction in ischemically injured hearts

Adenosine (ADO) is an endogenous cardioprotective autacoid that exerts receptor-mediated cardioprotection from ischemic-reperfusion injury. This study tested the hypothesis that blood cardioplegia (BCP) supplemented with ADO reduces postischemic left ventricular dysfunction in ischemically injured hearts. Twenty-one anesthetized dogs on total bypass were subjected to 30 minutes of normothermic global ischemia. Cold (4 degrees C) potassium BCP was then delivered every 20 minutes for 60 minutes of cardioplegic arrest. In 7 dogs, unsupplemented BCP was used; in 7 dogs, BCP was supplemented with 400 mumol/L ADO; and, in 7 dogs, ADO receptors were blocked with 8-p-sulfophenyltheophylline (30 mg/kg) given with 400 mumol/L ADO in BCP. Preischemic and postischemic left ventricular systolic function was assessed by the slope and volume axis intercept of the end-systolic pressure-volume (impedance catheter) relationship (ESPVR). In unsupplemented BCP, the postischemic slope of the ESPVR was significantly depressed by 42% versus the preischemic value (from 6.8 +/- 1.2 mm Hg/mL to 3.9 +/- 0.4 mm Hg/mL; p < 0.05 versus the preischemic value). In contrast, BCP supplemented with ADO was found to restore the postischemic ESPVR slope to preischemic levels (7.7 +/- 1.0 mm Hg/mL versus 7.4 +/- 1.2 mm Hg/mL, respectively). This cardioprotection was reversed by 8-p-sulfophenyltheophylline (9.9 +/- 1.5 mm Hg/mL versus 4.5 +/- 0.7 mm Hg/mL; p < 0.05 versus the preischemic value). Postischemic plasma creatinine kinase activity was elevated equally in all groups over the baseline values. We conclude that ADO in BCP attenuates postcardioplegia dysfunction in severely injured hearts through the operation of receptor-mediated mechanisms.

Acadesine reduces myocardial infarct size by an adenosine mediated mechanism

OBJECTIVE The aim was to test the hypotheses that acadesine (1) augments endogenous interstitial fluid (ISF) adenosine during ischaemia, and (2) reduces infarct size by adenosine receptor mediated mechanisms. METHODS To test these hypotheses, the left coronary artery of anaesthetised rabbits (n = 33) was occluded for 30 min and reperfused for 120 min. Acadesine (1 mg.kg-1.min-1 for 5 min, then 0.2 mg.kg-1.min-1) was infused intravenously beginning 30 min before coronary occlusion and ending 30 min after reperfusion. The area at risk was comparable in all groups, averaging 34.7 (SEM 2.2%) of the left ventricle. In separate studies (n = 22), estimates of ISF adenosine and adenosine metabolites were obtained by cardiac microdialysis. Although dialysate adenosine levels increased significantly in the area at risk during ischaemia in the untreated group [from 0.044(0.008) to 0.339(0.146) microM], acadesine did not significantly augment dialysate adenosine levels before or during ischaemia [preischaemia = 0.094(0.032) microM; ischaemia = 0.542(0.262) microM]. In addition, there was no significant difference in dialysate adenosine concentrations during the first 10 min of reperfusion, after which adenosine levels returned to baseline levels. A 2.5-fold large dose failed to increase interstitial fluid adenosine. However, the adenosine receptor blocker 8-p-sulphophenyltheophylline (SPT) in the presence of acadesine increased ISF adenosine fourfold. Acadesine significantly (P < 0.05) reduced infarct size [n = 8, 19.7(2.9)% of risk area] compared with the untreated group [n = 8, 29.4(1.3)%]. This infarct size reduction with acadesine was antagonised by SPT given during ischaemia-reperfusion [n = 8, 46.2(3.0)%] or only during reperfusion [n = 9, 42.7(2.6)%. CONCLUSIONS Acadesine reduces infarct size by an adenosine mediated mechanism, but this cardioprotective action is not associated with significantly augmented interstitial fluid adenosine levels.

Pentostatin-augmented interstitial adenosine prevents postcardioplegia injury in damaged hearts

This study tests the hypothesis that the adenosine deaminase inhibitor pentostatin (2-deoxycoformycin), when given before ischemia or during infusions of blood cardioplegia, augments interstitial adenosine levels and prevents postcardioplegia dysfunction in hearts with antecedent ischemia. Twenty-one anesthetized dogs were placed on cardiopulmonary bypass, and the hearts were made globally ischemic for 30 minutes. Dogs received blood cardioplegia with no pentostatin (BCP group, n = 6), pretreatment pentostatin (0.2 mg/kg) infused 5 minutes before global ischemia (PS-PTx group, n = 7), or pentostatin included only in the blood cardioplegia without pretreatment (PS-BCP group, n = 8). Microdialysate myocardial adenosine levels (an index of interstitial fluid levels) increased only modestly in the BCP group (from 0.55 +/- 0.13 microM to 2.64 +/- 0.50 microM) and the PS-BCP group (from 0.55 +/- 0.18 microM to 1.08 +/- 0.48 microM) during normothermic ischemia, but interstitial adenosine levels were not augmented further during cardioplegic arrest in either group. In contrast, the adenosine level in the PS-PTx group was significantly (p < 0.05) augmented during global ischemia (from 0.50 +/- 0.13 microM to 63.16 +/- 28.08 microM) and cardioplegia infusion (to 15.26 microM +/- 5.61 microM). Relative to baseline, postischemic left ventricular performance (end-systolic pressure-volume relation) was depressed in both the BCP (from 5.5 +/- 1.2 mm Hg/mL to 3.8 +/- 0.4 mm Hg/mL) and PS-BCP groups (from 7.1 +/- 0.9 mm Hg/mL to 3.8 +/- 0.7 mm Hg/mL). In contrast, PS-PTx restored postischemic performance (from 6.2 +/- 0.5 mm Hg/mL to 7.5 +/- 0.9 mm Hg/mL).(ABSTRACT TRUNCATED AT 250 WORDS)