Impact of low-dose or under-dose direct oral anticoagulant on coagulation and fibrinolytic markers in patients with atrial fibrillation

Background

Atrial fibrillation (AF) is known to increase the risks of cerebral and systemic embolism. Apart from vitamin K antagonists, edoxaban, a direct oral anticoagulant (DOAC), has been approved for oral anticoagulation in patients with non-valvular AF. On the other hand, DOACs are sometimes prescribed at off-label under-doses for patients who have undergone ablation for AF. Prothrombin fragment F1+2 is an activation peptide released from prothrombin during thrombin formation. The purpose of this study is to compare the effects of DOAC doses on coagulation and fibrinolytic markers.

Methods and results

A total of 88 patients with AF (age: 68±11 years, male:45%, paroxysmal AF n=49, persistent AF n=39) were recruited. All patients were received edoxaban (60mg or 30mg) once a day. For the purpose of the study, patients were divided into three groups according to whether they had been treated before the ablation procedure under an appropriate standard dose group (n=30 [34.1%]), appropriate low-dose group (n=35 [39.8%]), or off-label under-dose group (n=23 [26.1%]). We examined the coagulation and fibrinolytic markers, and echocardiographic parameters before ablation. All patients were followed up for 12 months after AF ablation. Creatinine clearance was significantly higher in appropriate standard-dose group than in appropriate low-dose or off-label under-dose group (101.1±38.4, 57.1±15.9 and 73.2±14.6 mL/min, respectively; P<0.001). There were no significant baseline differences in AF type, history of stroke/transient ischemic attack (TIA), plasma B-type natriuretic peptide, protein C, fibrinogen, D-dimer level, left ventricular ejection fraction or left atrium dimension among the three groups. Prothrombin fragment F1+2 level was significantly lower in the appropriate standard-dose group than the appropriate low-dose and off-label under-dose groups (105.9±29.4, 142.6±41.3 and 142.8±84.9 pmol/L, respectively; P=0.011, Figure). One patient in the appropriate low-dose group had a TIA and 1 patient in the off-label under-dose group had a bleeding event during the follow up period after ablation.

Conclusion

Our results suggest that an appropriate standard dose of edoxaban is needed to suppress hypercoagulability in patients with AF.

Funding Acknowledgement

Type of funding sources: None. Prothrombin fragment F1+2 level

P321A single factor related to left atrial pressure overload is useful for prognosis in elderly patients with heart failure with preserved ejection fraction: PURSUIT HFpEF study

Background

E/e' and the ratio of diastolic elastance (Ed)/arterial elastance (Ea) = (E/e')/(0.9 × systolic blood pressure), indices of left atrial (LA) pressure overload, are elevated in elderly women with heart failure with preserved ejection fraction (HFpEF). The severity of diastolic dysfunction is assessed by a combination of several indices of LA volume and pressure overload. However, which overload is more important as a single factor for the prognosis of these patients remains undefined.

Methods

We enrolled patients with HFpEF showing sinus rhythm (n=145; left ventricular ejection fraction >50%; men/women, 56/89; mean age, 80.5 years). Blood examination and transthoracic echocardiography were performed before discharge. All-cause mortality and admission for cardiac events were evaluated after more than 1 year (mean, 370 days).

Results

The all-cause mortality rate was 11% (16/145). There were significant differences in age (p=0.005), serum N-terminal pro-brain natriuretic peptide (NT-proBNP) level (p<0.001), LA volume index (p=0.018), E/e' (p=0.022), and Ed/Ea (p=0.016) between patients with and without all-cause mortality. When cutoff points for mortality by receiver operating characteristic curve analysis were examined, the area under the curve in LA volume index (0.564) was slightly smaller than that in age (0.734), NT-proBNP level (0.732), E/e' (0.695), and Ed/Ea (0.709). Kaplan-Meier survival analysis clearly showed that age >85 years (p<0.001), NT-proBNP level >888 pg/mL (p=0.003), E/e' >14.4 (p=0.020), and Ed/Ea >0.153 (p<0.001) were determinant factors for mortality. Cox hazard ratios were also significant in these indices (p=0.002, p=0.012, p=0.028, and p=0.001, respectively). In the case of all-cause mortality or admission for cardiac events, the results were nearly similar as those in the case of all-cause mortality. Ed/Ea exhibited a larger Cox hazard ratio for prognosis than E/e' in the multivariate analysis.

Conclusions

LA pressure overload compared to volume overload was a useful marker for prognosis in elderly patients with HFpEF. As a single index for LA pressure overload in noninvasive echocardiographic findings, Ed/Ea may be more suitable than E/e'.

P3395Arrival time at hyperemia of below the ankle as a determinant factor for limb salvage: evaluation by 2 dimension perfusion angiography

Background

In patients with critical limb ischemia, it is desirable to obtain enough skin perfusion pressure (SPP) levels through revascularization. 2D-perfusion angiography is an emerging technology for the quantification of tissue perfusion consisted of 6 parameters calculated by time-density curve of digital subtraction angiography (DSA).

Purpose

We evaluated the feasibility of 2D-perfusion angiography for below the knee (BTK) endovascular therapy (EVT). We aimed to clarify which angiographical parameters of lower limb are related to SPP after EVT.

Methods

Consecutive 33 limbs (mean age 74.5 years, men 55%), which successfully underwent EVT for isolated BTK lesions, were enrolled in this study. We excluded Rutherford 6 limbs with severe gangrene or tissue loss, consequently 26 limbs were Rutherford 4 or 5 critical limb ischemia. We treated total 47 lesions, including 26 chronic total occlusive lesions. 5Fr guiding sheath was advanced to popliteal artery. DSA images were obtained by mechanical contrast infusion. We quantified indexed blood flow on below the ankle area by using 2D-perfusion angiography, and examined 6 parameters [arrival time (AT), time to peak (TTP), wash-in rate, width, area under the curve and mean transit time (MTT)] from acquired DSA. Hyperemia was induced by 20mg papaverine intra-arterial infusion through the guiding sheath.

Results

The parameters except wash-in rate were significantly shortened after hyperemia induced by intra-arterial papaverine infusion below the ankle region. Dorsal and plantar SPP were significantly correlated with hyperemic AT, hyperemic wash-in rate and AT ratio (hyperemic/rest) of lower ankle regions after EVT. However, only AT ratio was independently associated with dorsal SPP in multivariate analysis (P=0.032). A receiver operating characteristic curve showed hyperemic AT <4.5 seconds and AT ratio <0.49 predicted to obtain SPP levels >50 mmHg after EVT with the area under the curve of 0.71 (95% confidence interval, 0.52–0.90) and 0.73 (95% confidence interval, 0.55–0.90), respectively.

Representative Case of 2D-perfusion

Conclusion

Hyperemic AT <4.5 seconds and AT ratio <0.49 of lower ankle regions may be essential to obtain the sufficient levels of SPP for limb salvage after BTK intervention. 2D perfusion angiography technique at hyperemic condition is feasible and has the potential to monitor lower limb tissue perfusion through EVT and to optimize the interventional treatment.

Relationship between evaluation by quantitative fatty acid myocardial scintigraphy and response to beta-blockade therapy in patients with dilated cardiomyopathy

Predicting the effect of beta-blockade therapy on the clinical outcome of patients with dilated cardiomyopathy (DCM) is difficult prior to the initiation of therapy. Myocardial fatty acid metabolism has been shown to be impaired in patients with DCM. We examined whether the extent of myocardial injury, as assessed by iodine-123 15-( p-iodophenyl)-3- R, S-methylpentadecanoic acid (BMIPP) myocardial scintigraphy, is related to the response of patients with DCM to beta-blockade therapy. Thirty-seven patients with DCM were examined using BMIPP myocardial scintigraphy before and after 6 months of treatment with metoprolol. Myocardial BMIPP uptake (%BM uptake) was estimated quantitatively as a percentage of the total injected count ratio. The left ventricular end-diastolic and end-systolic dimensions (LVDd, LVDs) and ejection fraction (LVEF) were also evaluated. The patients were divided into two groups according to their functional improvement (>10% elevation of LVEF) after 6 months of metoprolol therapy. Twenty-eight patients responded to the therapy, while nine did not. Prior to the therapy, no significant differences in LVDd, LVDs or LVEF were observed between the responders and non-responders. However, the %BM uptake was significantly lower in the non-responders than in the responders (1.0%+/-0.2% vs 2.1%+/-0.5%, P<0.001). The %BM uptake could be used to distinguish the responders from the non-responders with a sensitivity of 0.93 and a specificity of 1.00 at a threshold value of 1.4. After the metoprolol therapy, the %BM uptake improved significantly in the responders (2.5%+/-0.5%, P<0.01) but did not change in the non-responders. These results indicate that myocardial BMIPP uptake could predict the response of DCM patients to beta-blockade therapy.

Increased angiotensin-converting enzyme activity in coronary artery specimens from patients with acute coronary syndrome

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are effective in the secondary prevention of ischemic heart disease, but they do not reduce the rate of restenosis. Vascular ACE activity in the culprit coronary lesions of these patients, however, has never been quantified.

METHODS AND RESULTS

We measured the ACE activity of vascular tissue obtained by directional coronary atherectomy in patients with acute coronary syndrome (n=17) and in patients with stable ischemic heart disease (n=36), with and without restenosis. The ACE activity of the culprit coronary lesions was significantly increased in patients with acute coronary syndrome (0.87+/-0.12 nmol. min(-1). mg protein(-1); P:<0.01) but not in patients with ischemic heart disease with restenosis (n=11, 0.19+/-0.05 nmol. min(-1). mg protein(-1)) when compared with those patients with ischemic heart disease without restenosis (n=25, 0.20+/-0.05 nmol. min(-1). mg protein(-1)). There was no difference between the ACE activity of the coronary tissue of the in-stent (n=5) and stent-unrelated (n=6) restenosis patients (0.24+/-0.10 versus 0.15+/-0.04 nmol. min(-1). mg protein(-1)). Serum ACE activity did not differ significantly among the patients.

CONCLUSIONS

The present study demonstrates increased ACE activity in culprit lesions in acute coronary syndrome, indicating that enhanced ACE activity is related to the causative mechanism of active coronary lesions.

FR167653, a cytokine-suppressive agent, reduces myocardial ischemia-reperfusion injury in rats

FR167653 inhibits the production of inflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) in human monocytes in a dose-dependent manner. We examined the effects of FR167653 on the propagation of myocardial infarction resulting from coronary occlusion-reperfusion and the time course of expression of these cytokines in myocardial tissue in rats. Myocardial infarction was induced by coronary ligation for 20 minutes followed by 2 hours of reperfusion. Although hemodynamic parameters did not differ significantly during coronary occlusion-reperfusion, the size of the infarct was significantly reduced by intravenous administration of FR167653 before occlusion (p < 0.01). mRNA levels of IL-1beta and TNF-alpha assessed by the reverse-transcriptase polymerase chain reaction method were significantly increased during coronary occlusion-reperfusion in the ischemic myocardium. Treatment with FR167653, however, significantly reduced the increased expression of these cytokines. These results indicate that the expression of inflammatory cytokines increases in the ischemic-reperfused myocardium and that the inhibition of the increased expression of cytokines by FR167653 effectively reduces myocardial ischemia-reperfusion injury.

Involvement of cytokines in the mechanism of whole-body hyperthermia-induced cardioprotection

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury and activates manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger, in myocardium in a biphasic manner. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) induced a biphasic cardioprotection that corresponded to the activation of Mn-SOD. However, a direct association between Mn-SOD activation in myocardium and the acquisition of tolerance to ischemia/reperfusion injury induced by hyperthermia and the involvement of the cytokines in the signal transduction pathway for the hyperthermia-induced cardioprotection have not yet been elucidated.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. At 0.5 and 72 hours after hyperthermia, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. Inhibition of the increases in Mn-SOD content and activity 72 hours after hyperthermia by the administration of antisense oligodeoxynucleotides to Mn-SOD abolished the expected decrease in myocardial infarct size. The simultaneous administration of neutralizing antibodies to TNF-alpha and IL-1beta before hyperthermia abolished the biphasic cardioprotection and increase in Mn-SOD activity.

CONCLUSIONS

The increase in Mn-SOD activity mediated through the production of TNF-alpha and IL-1beta by whole-body hyperthermia is important in the acquisition of early- and late-phase cardioprotection against ischemia/reperfusion injury in rats.

Time to recover from atrial hormonal, mechanical, and electrical dysfunction after successful electrical cardioversion of persistent atrial fibrillation

Although transient atrial dysfunction has been reported after electrical cardioversion of atrial fibrillation (AF), the difference in the time to recover from the atrial hormonal, mechanical, and electrical dysfunction has not been described. Thus, we evaluated the time course of recovery from atrial hormonal, mechanical, and electrical dysfunction after cardioversion in patients with nonvalvular AF. We attempted electrical cardioversion in 87 consecutive patients with nonvalvular AF that had persisted for > or =6 months, and in 24 patients (28%) with maintained sinus rhythm for > or =6 months. To evaluate atrial hormonal, mechanical, and electrical dysfunction in these 24 patients, we measured plasma concentration of atrial natriuretic peptide, the atrial peak velocity in transmitral flow, and the ratio of peak systolic-to-diastolic pulmonary venous flow (S/D ratio) using echocardiography, and the duration and the root mean voltage for the terminal 20 ms (LP20) of the filtered P wave using P-wave signal-averaged electrocardiography. Atrial natriuretic peptide rapidly returned to baseline within 1 day after cardioversion, and maintained these levels for 6 months. Atrial peak velocity in transmitral flow and S/D ratio were significantly increased at 2 weeks, and continued to increase until 1 month, and then reached a plateau. The duration and LP20 began to recover only 6 months after cardioversion. One to 3 years after conversion, the duration and LP20 had nearly reached a plateau, but the latter value remained below normal. In patients with nonvalvular AF of prolonged duration, recovery from atrial electrical dysfunction after sinus conversion took much longer than that from either atrial hormonal or mechanical dysfunction.

Differential effects of long-term renin-angiotensin system blockade on limitation of infarct size in cholesterol-fed rabbits

We evaluated the effects of chronic inhibition of angiotensin-converting enzyme (ACE) or receptor blockade of angiotensin II type I on the size of myocardial infarcts induced by coronary occlusion-reperfusion in rabbits fed a high-cholesterol or normal diet for 10 weeks. In treated rabbits, myocardial infarction occurred 24 h after the last dose of enalapril or L-158809, an angiotensin II type I receptor antagonist, because of the drugs' waning effects on hemodynamic parameters. The size of the infarct was significantly larger in cholesterol-fed rabbits than in rabbits fed a normal diet. This augmentation of infarct size in cholesterol-fed rabbits was reversed by long-term treatment with enalapril, but not L-158809. The favorable effects of enalapril treatment disappeared after pretreatment with the bradykinin B(2) receptor blocker HOE 140. Long-term enalapril or L-158809 administration did not reduce the size of the infarct in rabbits fed a normal diet. ACE activity in ischemic myocardium significantly exceeded that in nonischemic myocardium and was further increased in cholesterol-fed rabbits, but was significantly reduced by long-term enalapril, but not L-158809. Moreover, treatment with enalapril, but not L-158809, restored acetylcholine-induced endothelium-dependent relaxation of aortic rings from cholesterol-fed rabbits. These results demonstrate that long-term ACE inhibition, but not angiotensin II type I receptor blockade, effectively reduces the size of myocardial infarcts in cholesterol-fed rabbits. The favorable effects of enalapril treatment may involve primarily a bradykinin B(2) receptor-mediated pathway.

Cholesterol feeding exacerbates myocardial injury in Zucker diabetic fatty rats

We measured infarct size after coronary occlusion (30 min) and reperfusion (24 h) in genetic non-insulin-dependent Zucker diabetic fatty (ZDF) rats with and without 4-wk cholesterol feeding. Infarct size was similar in ZDF rats and lean control rats but was significantly larger in cholesterol-fed diabetic rats than in cholesterol-fed lean rats (P < 0.05). Plasma levels of glucose, insulin, and triglycerides were significantly higher in diabetic rats and were not influenced by cholesterol feeding. The increase in total plasma cholesterol induced by cholesterol feeding was significantly greater in diabetic rats than in lean rats (P < 0.05). A significant positive correlation was found between total plasma cholesterol and infarct size (P < 0.05). Myeloperoxidase activity, as an index of neutrophil accumulation, was significantly higher and expression of P-selectin was more marked in the ischemic myocardium of cholesterol-fed diabetic rats than of cholesterol-fed lean rats. Acetylcholine-induced endothelium-dependent relaxation (EDR) of aortic rings was markedly impaired in cholesterol-fed diabetic rats. Thus cholesterol feeding significantly exacerbated myocardial injury produced by coronary occlusion-reperfusion in non-insulin-dependent diabetic rats, possibly because of enhanced expression of P-selectin and impairment of EDR in the coronary bed.

Exercise provides direct biphasic cardioprotection via manganese superoxide dismutase activation

Epidemiologic investigations have shown that exercise reduces morbidity and mortality from coronary artery disease. In this study, using a rat model, we attempted to determine whether exercise can reduce ischemic injury to the heart and elucidate a mechanism for the cardioprotective effect of exercise. Results showed that exercise significantly reduced the magnitude of a myocardial infarction in biphasic manner. The time course for cardioprotection resembled that of the change in manganese superoxide dismutase (Mn-SOD) activity. The administration of the antisense oligodeoxyribonucleotide to Mn-SOD abolished the expected decrease in infarct size. We showed that the level of tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) increased after exercise. The simultaneous administration of the neutralizing antibodies to the cytokines abolished the exercise-induced cardioprotection and the activation of Mn-SOD. Furthermore, TNF-alpha can mimic the biphasic pattern of cardioprotection and activation of Mn-SOD. An antioxidant completely abolished cardioprotection and the activation of Mn-SOD by exercise or the injection of TNF-alpha as well as exercise-induced increase in TNF-alpha and IL-1beta. The production of reactive oxygen species and endogenous TNF-alpha and IL-1beta induced by exercise leads to the activation of Mn-SOD, which plays major roles in the acquisition of biphasic cardioprotection against ischemia/reperfusion injury in rats.

Amelioration by quinapril of myocardial infarction induced by coronary occlusion/reperfusion in a rabbit model of atherosclerosis: possible mechanisms

BACKGROUND

The increased severity of the myocardial injury produced by coronary occlusion-reperfusion in models of atherosclerosis is associated with an increase in leukocyte accumulation in the ischemic myocardium. Expression of P-selectin, an adhesion molecule involved in the interaction between leukocytes and endothelium, is increased in atherosclerotic vessels. Long-term angiotensin-converting enzyme (ACE) inhibition has been shown to reduce atherosclerotic vascular change in experimental models.

METHODS AND RESULTS

We examined changes in the size of the infarct resulting from coronary occlusion/reperfusion in normally fed and cholesterol-fed rabbits that were chronically treated with quinapril. Infarct size was significantly larger in the cholesterol-fed versus normally fed rabbits. ACE activity in the ischemic and nonischemic myocardium was significantly reduced by quinapril. Chronic quinapril administration significantly ameliorated the increased myocardial injury in cholesterol-fed rabbits. Quinapril administration markedly increased the myocardial cGMP content and reduced the myeloperoxidase activity in the border region of the ischemic myocardium in cholesterol-fed rabbits. The enhanced expression of P-selectin in myocardial tissue of cholesterol-fed rabbits was also effectively reduced by quinapril treatment. The above effects of quinapril were eliminated by blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis.

CONCLUSIONS

Chronic quinapril treatment ameliorated the severity of myocardial injury produced by coronary occlusion/reperfusion in cholesterol-fed rabbits, possibly because of reversal of the enhanced interaction between leukocytes and endothelium in the ischemic myocardium via a bradykinin-related pathway.

Whole-body hyperthermia provides biphasic cardioprotection against ischemia/reperfusion injury in the rat

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury 24 hours after the heat stress. Free radicals and redox mechanisms have been implicated in such tolerance. However, the time course and its relation to the induction of antioxidative enzymes in the protection induced by whole-body hyperthermia against ischemia/reperfusion injury are unknown.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. After the defined recovery interval(s) at room temperature, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. The exposure to hyperthermia led to a recovery interval- dependent, biphasic reduction in the incidence of ventricular fibrillation during ischemia and in the size of the myocardial infarct as determined after 48 hours of reperfusion. The time course of the late-phase (24- to 96-hour recovery interval) but not the early-phase (0.5 hour) cardioprotection depended on the degree of hyperthermia. The time course of the increase in myocardial manganese superoxide dismutase (Mn-SOD) activity corresponded to that of the cardioprotective effects, although an increase in the content of Mn-SOD and of heat shock protein 72 corresponded only to the late-phase effects. Administration of an antioxidant before hyperthermia abolished the early- and late-phase cardioprotection and the increase in Mn-SOD activity.

CONCLUSIONS

THe activation of Mn-SOD mediated by free radical production during hyperthermia is important in the acquisition of early-phase and late-phase cardioprotection against ischemia/reperfusion injury in rats.

A "second window of protection" occurs 24 h after ischemic preconditioning in the rat heart

We and others found that cardioprotection is acquired not only soon after, but also 24 h after ischemic preconditioning in canine and rabbit myocardial infarction models (second window of protection). However, a second window phenomenon against myocardial infarction was dependent on species limitations and has not been observed in porcine hearts. In this study, we examined whether the "second window of protection" against myocardial infarction is observed in the rat heart. In the ischemic preconditioning (IP) group, the left main coronary artery (LCA) of rats was occluded four times for 3 min. each separated by reperfusion for 10 min. After 0, 3, and 24 h, the rats were subjected to a 20-min LCA occlusion followed by 48-h reperfusion. At 0 and 24 h after IP, infarct size and the incidence of ventricular fibrillation (VF) during ischemia were significantly reduced compared with corresponding sham-operated groups without preconditioning. After 3 h of IP, there were no differences either in the incidence of VF during ischemia or in infarct size. Manganese superoxide dismutase (Mn-SOD) content in ischemic (LCA) region of myocardium significantly increased as compared with that of sham-operated rats 24 h after IP. Treatment with N-2-mercaptopropionyl glycine, an antioxidant and a hydroxyl radical scavenger, during IP abolished the early-phase (0 h after IP) and late-phase (24 h after IP) cardioprotection and the corresponding late increase in Mn-SOD content. These results indicate that a "second window of protection" against myocardial infarction also exists in rat hearts and the induction of an intrinsic scavenger, Mn-SOD, via free radical production during IP may be important in the second window of protection.

Reduction in infarct size by chronic amlodipine treatment in cholesterol-fed rabbits

Calcium (Ca)-dependent factors, including cholesterol-induced changes in membrane Ca permeability and Ca deposition into lesions, may contribute to plaque formation and stability during the early and late stages of atherogenesis. Amlodipine can reduce atheroma formation in cholesterol-fed rabbits and may be cardioprotective. We therefore examined the effects of chronic amlodipine treatment (5 mg/kg daily for 10 weeks, p.o.) on infarct size after 30-min coronary occlusion/48-h reperfusion in rabbits fed a diet with or without 1% cholesterol. Infarct size was significantly larger in cholesterol-fed rabbits (72.0 +/- 3.5%, n = 9, mean +/- S.E.M.) than in normal-fed rabbits (47.1 +/- 4.9%, n = 9, P < 0.05). Amlodipine treatment effectively reversed the infarct size augmentation in cholesterol-fed rabbits (46.3 +/- 6.3%, n = 9, P < 0.05), but did not affect infarct size in normal-fed rabbits (51.0 +/- 4.7%, n = 8). In both cholesterol-fed and normal-fed rabbits, Ca content and leukocyte accumulation as assessed by myeloperoxidase activity were significantly higher in the ischemic myocardium than in the nonischemic myocardium. However, Ca content and leukocyte accumulation were markedly elevated in the ischemic myocardium of cholesterol-fed rabbits compared with normal-fed rabbits. Amlodipine treatment effectively reversed this elevation. Acetylcholine showed a marked reduction in endothelium-dependent relaxation in the aorta of cholesterol-fed rabbits, which also was reversed by amlodipine treatment. These results indicate that chronic amlodipine treatment reduces infarct size only in cholesterol-fed rabbits.

Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

The effects of nitric oxide (NO) produced by cardiac inducible NO synthase (iNOS) on myocardial injury after oxidative stress were examined: Interleukin-1 beta induced cultured rat neonatal cardiac myocytes to express iNOS. After induction of iNOS, L-arginine enhanced NO production in a concentration-dependent manner. Glutathione peroxidase (GPX) activity in myocytes was attenuated by elevated iNOS activity and by an NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). Although NO production by iNOS did not induce myocardial injury, NO augmented release of lactate dehydrogenase from myocyte cultures after addition of H2O2 (0.1 mM, 1 h). Inhibition of iNOS with N omega-nitro-L-arginine methyl ester ameliorated the effects of NO-enhancing treatments on myocardial injury and GPX activity. SNAP augmented the myocardial injury induced by H2O2. Inhibition of GPX activity with antisense oligodeoxyribonucleotide for GPX mRNA increased myocardial injury by H2O2. Results suggest that the induction of cardiac iNOS promotes myocardial injury due to oxidative stress via inactivation of the intrinsic antioxidant enzyme, GPX.

Long-term probucol treatment reverses the severity of myocardial injury in watanabe heritable hyperlipidemic rabbits

We previously reported that administration of NO donors ameliorates the severity of myocardial injury in cholesterol-fed rabbits. We now evaluated the effects of probucol, a lipid-lowering antioxidant that can preserve endothelium-dependent relaxation (EDR), in the aortas of cholesterol-fed rabbits. We examined the effects of short-term (7 days) or long-term (24 weeks) administration of 1% probucol on the size of infarcts resulting from 30 minutes of coronary occlusion followed by reperfusion (for 48 hours) in Watanabe heritable hyperlipidemic (WHHL) rabbits. Infarcts in untreated WHHL rabbits were significantly larger than those in the rabbits receiving the long-term but not the short-term treatment with probucol (72.2 +/- 5.4%, 37.6 +/- 6.4%, and 66.7 +/- 3.5%, respectively). Long-term probucol treatment also significantly reduced myeloperoxidase activity in both ischemic and nonischemic myocardium and suppressed P-selectin expression in the coronary vasculature. No significant differences were observed in hemodynamic parameters during myocardial ischemia/reperfusion. Long-term probucol treatment significantly reduced the surface area of atherosclerotic plaque lesions in the aorta (24.4 +/- 3.8% vs 46.3 +/- 6.3, P < .05). Moreover, long-term probucol treatment restored acetylcholine-induced EDR in aortic rings but did not affect sodium nitroprusside-induced relaxation. Finally, long-term probucol treatment resulted in significantly elevated cGMP levels in the aorta. These results indicate that long-term probucol treatment significantly ameliorates myocardial injury in heritable atherosclerotic rabbits, perhaps by reducing the accumulation of leukocytes in the myocardium and atherosclerotic vascular lesions. Thus, long-term administration appears to suppress the progression of atherosclerotic vascular disease in this animal model.

Heat shock-induced manganese superoxide dismutase enhances the tolerance of cardiac myocytes to hypoxia-reoxygenation injury

We evaluated the mechanism of the heat shock-induced tolerance to ischemia-reperfusion using a model of hypoxia-reoxygenation tolerance in neonatal rat cardiac myocytes. Myocytes exposed to heat shock (42 degrees C, 1 h) exhibited a 1.8-fold increase in levels of manganese superoxide dismutase (Mn-SOD) mRNA after 40 min v control cells. The concentration of Mn-SOD increased from 0.49+/-0.04 microg/mg protein to 0.68+/-0.05 microg/mg protein after 24 h (P<0. 05). Levels of heat shock protein 72 (hsp72; inducible form) mRNA and protein also increased markedly after heat shock exposure. The release of creatine kinase (CK) from the myocytes and the depletion of ATP level in the myocytes exposed to hypoxia (pO2: 7 mmHg, 3 h) and reoxygenation (pO2: 143 mmHg) were significantly reduced following heat shock pretreatment (CK: 1.18+/-0.14 U/l v 0.62+/-0.13 U/l, ATP: 11.9+/-1.1 nmol/mg protein v 16.2+/-1.0 nmol/mg protein, P<0.05). Treatment with antisense oligodeoxyribonucleotides to Mn-SOD (1.5 micromol/l) completely inhibited the heat shock-associated induction of Mn-SOD (0.47+/-0.05 microg/mg protein), but not hsp72, and abolished the heat shock-induced decrease in CK release (1.04+/-0.15 U/l, P<0.05) and depletion of ATP level (11. 2+/-1.1 nmol/mg protein, P<0.05). Results indicate that Mn-SOD induction, not hsp72 induction, plays a pivotal role in the heat shock-induced acquisition of tolerance to hypoxia-reoxygenation in neonatal rat cardiac myocytes.

Time course of tolerance to ischemia-reperfusion injury and induction of heat shock protein 72 by heat stress in the rat heart

We compared the time course of tolerance to myocardial ischemia-reperfusion injury with the time course of heat shock protein 72 (hsp72; inducible form) induction after heat stress in a rat model. The size of the infarct resulting from ischemia-reperfusion was increased 12 h after whole-body hyperthermia (42 degrees C for 15 min), but was significantly decreased 48 and 72 h after hyperthermia, compared with the sham control. The infarct size was decreased as late as 96 h after hyperthermia, although the infarct-limiting effect was smaller at that time. The myocardial content of hsp72 was markedly increased for 3-72 h after hyperthermic treatment, and was decreased after 72 h in association with an increase in the infarct size. The hsp72 content remained elevated during the period of tolerance to ischemia-reperfusion injury, but the infarct size decreased after the hsp72 content peaked. Pretreatment with a protein kinase C (PKC) inhibitor, chelerythrine chloride, immediately before hyperthermia, significantly suppressed the delayed cardioprotective effect of hyperthermia and reduced hsp72 induction. These results suggest that newly synthesized hsp72 through PKC activation after heat stress may have to be post-translationally modified and compartmentalized prior to assuming to the development of the delayed tolerance to ischemia-reperfusion injury in rats.

Effects of preconditioning with ebselen on glutathione metabolism and stress protein expression

Selenium induces several proteins, including glutathione and stress proteins. These proteins have been shown to be cardioprotective against oxidative injury. To determine whether ebselen, a seleno-organic compound, can also induce these proteins and exert cardioprotective action, we examined the effects of preconditioning with ebselen on glutathione metabolism and stress protein expression and on myocyte injury induced by oxidative stress. Treatment of cultured cardiac myocytes with ebselen (0.3-30 microM) for 24 hr increased the reduced glutathione content. Glutathione reductase activity, but not glutathione peroxidase activity, was significantly elevated in a dose-dependent manner. Pretreatment with ebselen increased the expression of such stress proteins as heat shock protein 70 and heme oxygenase-1 (heat shock protein 32) in cardiac myocytes, as assessed by Western blotting. Expression of heat shock protein 70 was increased only at a higher dose of ebselen (30 microM), whereas expression of heme oxygenase-1 was markedly increased at a lower dose of ebselen (3 microM). Under these conditions, the myocyte injury induced by hydrogen peroxide or simulated ischemia/reperfusion, assessed by the release of lactate dehydrogenase into the culture medium, was reduced by ebselen pretreatment in a dose-dependent manner. Results indicated that cardiac myocytes pharmacologically preconditioned with ebselen for 24 hr exhibited resistance to oxidative injury, possibly via the up-regulation of glutathione metabolism and the expression of stress proteins.

Intravascular ultrasonic evidence by constant cross-sectional area of atherosclerotic plaques during coronary vasomotion in humans

AIMS

This study aims to visualize ultrasonically deformation of atherosclerotic plaques in human coronary arteries during vasoconstriction and vasodilatation.

METHODS AND RESULTS

Intravascular ultrasound detected occult atherosclerosis in angiographically normal coronary arteries of eight patients with chest pain at rest. During the acetylcholine provocative test, intravascular ultrasound monitored deformation of the atherosclerotic plaques. At the last step of the test, intracoronary injection of isosorbide dinitrate caused vasodilation. Under control, acetylcholine-treated, and isosorbide dinitrate-treated conditions, cross-sectional areas of sonolucent circle and vessel lumen were measured. Subtraction of the latter from the former gave the area of atherosclerotic plaque. In the process of vasoconstriction and vasodilation, the plaque area did not change significantly.

CONCLUSION

The cross-sectional area of the atherosclerotic plaque appeared to be constant during vasomotion of human coronary arteries.

Vascular angiotensin-converting enzyme activity in cholesterol-fed rabbits: effects of enalapril

Many reports have shown inhibitory effects of angiotensin-converting enzyme (ACE) inhibitors on the progression of atherosclerotic plaque lesions in vascular tissue of experimental models. However, no report has shown alterations of ACE activity in vascular tissue during the process of atherosclerosis. We measured ACE activity in plasma and aortic tissue in rabbits fed a cholesterol-rich (1%) or normal diet for 10 weeks. We also evaluated the blood pressure response to angiotensin (Ang) I and II. These data were compared in untreated rabbits and in rabbits receiving chronic treatment with an ACE inhibitor, enalapril (3 mg/kg/day for 10 weeks). ACE activity in aortic tissue, but not in plasma, in cholesterol-fed rabbits was gradually but significantly increased compared with that in noncholesterol-fed rabbits even after the 4-week feeding period, when no atherosclerotic lesion was observed in the aortic tissue. Treatment with enalapril for 10 weeks, but not 4 weeks, significantly reduced the ACE activity in aortic tissue in association with the reductions in the elevated Ang II level and the atherosclerotic plaque area of the aortic tissue. These results indicated that ACE activity in aortic tissue was increased during the early phase of atherosclerotic process.

Alpha 1-adrenergic stimulation induces cardiac tolerance to hypoxia via induction and activation of Mn-SOD

We examined whether or not alpha 1-adrenergic stimulation increases the tolerance of the heart to ischemia using a hypoxia-reoxygenation model of cardiac myocytes. After exposure to norepinephrine (NE; 0.2 microM) for 24 h, the manganese superoxide dismutase (Mn-SOD) content and activity in the cells were increased from 0.61 +/- 0.03 to 0.87 +/- 0.04 microgram/dish and 22 +/- 1 to 55 +/- 4 U/dish, respectively. The specific activity of Mn-SOD was also increased from 36 to 63 U/microgram Mn-SOD protein after the stimulation with NE. Prazosin (2 microM) abolished the increase in Mn-SOD activity (U/mg total protein). Creatine kinase (CK) release after hypoxia (PO2 7 mmHg; 3 h)-reoxygenation (1 h) from cells pretreated with NE in the presence of propranolol and yohimbine for 24 h was attenuated by 48% compared with that from cells without NE stimulation. When antisense oligodeoxyribonucleotides to Mn-SOD were added to myocyte cultures, the increase in Mn-SOD activity (U/mg total protein) and the attenuation of CK release after the addition of NE in the presence of propranolol and yohimbine were not observed. These results suggest that alpha 1-adrenergic stimulation increases the tolerance of myocytes to hypoxia through induction and activation of Mn-SOD.

Heme oxygenase-1 expression and its relation to oxidative stress during primary culture of cardiomyocytes

The inducible form of heme oxygenase (heme oxygenase-1) is a heat shock protein 32 (HSP32) whose expression is induced by numerous agents, including heme compounds and heavy metals, and during oxidative stress. The purpose of this study was to examine whether heme oxygenase-1 is induced during primary cell culture of cardiomyocytes and the relation of heme oxygenase-1 expression to oxidative stress levels. Western blot analysis and reverse transcription-polymerase chain reaction analysis showed heme oxygenase-1 expression 12-48 h after isolation of rat neonatal cardiomyocyte for culture. Its expression was barely detected immediately after isolation. Actinomycin D or cycloheximide completely suppressed such expression. Myocardial cells were exposed to oxidative stress during the first 12 h after isolation as assessed by their glutathione redox state; the ratio of reduced glutathione/oxidized glutathione was less than 10. The expression of heme oxygenase-1 was significantly reduced by treatment with reduced glutathione (58% reduction, P < 0.05), but markedly increased by treatment with hydrogen peroxide (65% increase, P < 0.05) 12 h after isolation. Expression of heat shock protein 70 was not significantly changed during primary culture incubation. Results indicate that heme oxygenase-1 is expressed during primary culture of cardiomyocytes. Its expression is closely related to the oxidative stress level of the cultured cells.

A nitric oxide donor reverses myocardial injury in rabbits with acute hypercholesterolemia

We evaluated the propagation of myocardial injury in a model of coronary artery occlusion and reperfusion in control and hypercholesterolemic rabbits. This was done by examining the differences in the infarct size and in the extent of leukocyte accumulation resulting from coronary artery occlusion (30 min) followed by reperfusion (2 or 48 hr) in rabbits fed 1% cholesterol for 4 days vs. controls not fed cholesterol. There was no significant difference in the infarct size in the 2-hr (45.7 +/- 6.7%, n = 8) vs. 48-hr (48.8 +/- 5.8%, n = 9) models of reperfusion in control rabbits. However, infarct size in the cholesterol-fed rabbits at 2 hr (64.0 +/- 4.1%, n = 6) or 48 hr (72.3 +/- 3.0%, n = 8) of reperfusion significantly exceeded that in the corresponding controls (P < .05). The infarct in cholesterol-fed rabbits at 2 hr of reperfusion was smaller than that at 48 hr of reperfusion, but not significantly. Treatment with S-nitroso-N-acetylpenicillamine, a nitric oxide donor, effectively reduced the size of infarct in the cholesterol-fed rabbits. However, treatment with N-acetylpenicillamine had no infarct-limiting effect. When we evaluated the extent of leukocyte accumulation in the ischemic myocardium, as assessed by myeloperoxidase activity, a positive correlation was observed between myeloperoxidase activity and infarct size at 48 hr of reperfusion. Results indicate that the propagation of myocardial ischemia and reperfusion injury in acutely hypercholesterolemic rabbits differed from that in controls. An exogenous nitric oxide donor effectively reduced the size of infarct associated with the reduction in the accumulation of leukocytes 48 hr after reperfusion, which suggests that a reduction in the production of endogenous nitric oxide during ischemia and reperfusion may aggravate the severity of myocardial injury in acutely hypercholesterolemic rabbits.

Amelioration of severity of myocardial injury by a nitric oxide donor in rabbits fed a cholesterol-rich diet

OBJECTIVES

This study compared the effect of a nitric oxide donor on limiting the size of infarct resulting from myocardial ischemia-reperfusion between atherosclerotic and nonatherosclerotic models.

BACKGROUND

Endothelial-derived relaxation in coronary arteries affected by ischemia is substantially impaired after reperfusion, and this impairment may exacerbate the myocardial ischemia-reperfusion injury. In animals with experimental atherosclerosis, release of endothelial-derived relaxing factor is also decreased, and the propagation of myocardial infarction could be exacerbated.

METHODS

We examined the extent of myocardial injury induced by ischemia (30 min) and reperfusion (48 hr) in rabbits fed a cholesterol-rich (1%) or normal diet for 10 weeks. We also evaluated the effect of a nitric oxide donor (S-nitroso-N-acetylpenicillamine [SNAP], a nitric oxide precursor (L-arginine) or a degradation product of SNAP (N-acetylpenicillamine) on infarct size in these models.

RESULTS

Severity of myocardial injury was significantly exacerbated in cholesterol-fed rabbits (75.2 +/- 4.4% [mean +/- SEM]) compared with that in non-cholesterol-fed rabbits (53.2 +/- 5.2%). This exacerbation was prevented by treatment with SNAP (50.2 +/- 6.4%) but not with L-arginine (70.5 +/- 6.0%) or N-acetylpenicillamine (70.4 +/- 4.8%) in cholesterol-fed-rabbits. However, SNAP did not limit infarct size in non-cholesterol-fed rabbits (60.8 +/- 4.2%). The rate-pressure product was similar during the course of the experiment in all the groups.

CONCLUSIONS

Myocardial damage induced by ischemia-reperfusion was significantly exacerbated in rabbits fed a long-term cholesterol-rich diet but was effectively reversed by treatment with a nitric oxide donor. However, this agent did not limit infarct size in normal rabbits. Thus, a nitric oxide donor reduces myocardial infarct size in atherosclerotic but not in nonatherosclerotic rabbits.

Nitric oxide synthase protects the heart against ischemia-reperfusion injury in rabbits

The role of nitric oxide (NO) in myocardial ischemia-reperfusion injury is still controversial. To determine the role of NO in the propagation of myocardial injury in a coronary artery occlusion-reperfusion model, we examined the effect of a competitive NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), with and without L-arginine, on the size of the infarct resulting from coronary artery occlusion (30 min) followed by reperfusion (48 hr) in rabbits. L-NAME (300 micrograms/kg, as a bolus, and 100 micrograms/kg/min, i.v.) with and without L-arginine (30 mg/kg, as a bolus, and 10 mg/kg/min, i.v.) was administered immediately before coronary occlusion to 60 min after reperfusion. The infarct size in the L-NAME-treated rabbits (75.1% +/- 5.0%, n = 7), assessed as a percentage of infarcted region/ischemic region, was significantly larger than that of control rabbits (51.2% +/- 7.4%, n = 7; P < .05). The increase in infarct size was significantly attenuated by the treatment with L-NAME and L-arginine (62.0% +/- 4.0%, n = 7). However, the infarct size for the treatment with L-NAME and D-arginine (76.7% +/- 5.7%, n = 6) did not differ from that in the L-NAME-treated rabbits. There was no significant difference in the infarct size between L-arginine-treated (60.1% +/- 7.3%, n = 6) and control rabbits. Rate-pressure products, as an index of myocardial oxygen consumption, were comparable in all the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Ebselen protects against ischemia-reperfusion injury in a canine model of myocardial infarction

We investigated the infarct-limiting effect of a selenoorganic compound, ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], in a canine coronary artery occlusion-reperfusion model of myocardial infarction. Ebselen, administered 1 h before coronary artery occlusion (50 mg/kg po), significantly reduced infarct size resulting from 90-min coronary artery occlusion followed by 5-h reperfusion (P < 0.05). When we examined the relation between infarct size and plasma ebselen level, infarct size in dogs with plasma ebselen level > 5 microM before reperfusion was significantly smaller (P < 0.05) than that in dogs with plasma ebselen level < or = 5 microM or in the control dogs. This infarct limitation produced by ebselen treatment was associated with an increase in reduced glutathione content and a reduction in myeloperoxidase activity in the ischemic myocardium. No differences between the control and treated groups were found in hemodynamic parameters or regional myocardial blood flow in the course of the experiment. The findings of this study demonstrate that ebselen effectively reduced the myocardial ischemia-reperfusion injury associated with preservation of the glutathione redox state and a reduction in neutrophil infiltration into the ischemic myocardium.

Induction of manganese superoxide dismutase in rat cardiac myocytes increases tolerance to hypoxia 24 hours after preconditioning

Manganese superoxide dismutase (Mn-SOD) is induced in ischemic hearts 24 h after ischemic preconditioning, when tolerance to ischemia is acquired. We examined the relationship between Mn-SOD induction and the protective effect of preconditioning using cultured rat cardiac myocytes. Exposure of cardiac myocytes to brief hypoxia (1 h) decreased creatine kinase release induced by sustained hypoxia (3 h) that follows when the sustained hypoxia was applied 24 h after hypoxic preconditioning (57% of that in cells without preconditioning). The activity and content of Mn-SOD in cardiac myocytes were increased 24 h after hypoxic preconditioning (activity, 170%; content, 139% compared with cells without preconditioning) coincidentally with the acquisition of tolerance to hypoxia. Mn-SOD mRNA was also increased 20-40 min after preconditioning. Antisense oligodeoxyribonucleotides corresponding to the initiation site of Mn-SOD translation inhibited the increases in the Mn-SOD content and activity and abolished the expected decrease in creatine kinase release induced by sustained hypoxia after 24 h of hypoxic preconditioning. Sense oligodeoxyribonucleotides did not abolish either Mn-SOD induction or tolerance to hypoxia. These results suggest that the induction of Mn-SOD in myocytes by preconditioning plays a pivotal role in the acquisition of tolerance to ischemia at a later phase (24 h) of ischemic preconditioning.

Polymorphonuclear leukocytes-induced injury in hypoxic cardiac myocytes

Growing evidence suggests that free radicals derived from polymorphonuclear leukocytes (PMNs) play an important role in myocardial ischemia-reperfusion injury. To elucidate the cellular mechanism by which activated PMNs exacerbate ischemic myocardial damage, we investigated the extent of cell injury, assessed by the morphological deterioration, free radical generation, and lipid peroxidation in mouse embryo myocardial cells coincubated with activated PMNs. The generation of PMN-derived free radicals was related to the extent of myocardial cell injury. When myocardial cell sheets were subjected to hypoxia and glucose-free media, myocardial cells were injured (cristalysis in the mitochondria and disruption of the sarcolemma) after adding various PMN activators, and the injury extended to the adjacent cells. Chemiluminescent emission and production of thiobarbituric acid-reactive substances in the coincubated cells increased markedly compared with myocardial cells or PMNs alone. The augmented lipid peroxidation coincided with the progression of myocardial cell injury. Catalase inhibited the myocardial cell injury by 52%, the chemiluminescence by 46%, and lipid peroxidation by 50%, whereas superoxide dismutase exhibited less pronounced inhibition. These results indicate that a chain reaction of lipid peroxidation in myocardial cells induced by PMN-derived free radicals closely correlates with membrane damage and contributes to the propagation of irreversible myocardial cell damage.

gamma-Glutamylcysteine ethyl ester for myocardial protection in dogs during ischemia and reperfusion

OBJECTIVES

The aim of this study was to examine the infarct-limiting effects of gamma-glutamylcysteine ethyl ester, a newly discovered synthetic precursor of glutathione biosynthesis, in a canine model of myocardial infarction.

BACKGROUND

Reduced glutathione plays an important role in protecting cells against damage induced by reactive oxygen species during myocardial ischemia and reperfusion. Gamma-glutamylcysteine ethyl ester is capable of penetrating into cells in its intact form and increasing intracellular glutathione levels.

METHODS

Dogs were subjected to a 90-min coronary occlusion followed by 5 h of reperfusion. An intravenous bolus injection of gamma-glutamylcysteine ethyl ester (3 or 10 mg/kg body weight) was administered immediately before reperfusion. Regional myocardial blood flow was measured with the use of colored microspheres.

RESULTS

Gamma-glutamylcysteine ethyl ester effectively reduced infarct size in a dose-dependent manner (mean +/- SEM 26.4 +/- 3.5% in the low dose group [3 mg/kg, n = 10] and 19.0 +/- 3.4% in the high dose group [10 mg/kg, n = 10]; each p < 0.05 vs. the value in the control group [40.6 +/- 4.8%, n = 10]). There were no differences between the control and treated groups in hemodynamic variables or regional myocardial blood flow either during the ischemic period or after reperfusion. The reduced glutathione content of ischemic myocardium in the control group (0.62 +/- 0.11 mumol/g, p < 0.01) was significantly lower than that in nonischemic myocardium (1.46 +/- 0.07 mumol/g), and it was preserved by treatment in a dose-dependent manner (3 mg/kg, 0.83 +/- 0.06 mumol/g; 10 mg/kg, 0.92 +/- 0.14 mumol/g; each p < 0.05 vs. control level). There were no differences in oxidized glutathione content between nonischemic and ischemic myocardium or among the three groups.

CONCLUSIONS

Gamma-glutamylcysteine ethyl ester, a precursor of glutathione, significantly attenuates myocardial ischemia and reperfusion injury when administered immediately before reperfusion.

Calcium overload and cardiac myocyte cell damage induced by arachidonate lipoxygenation

The accumulation of arachidonic acid and lipoxygenase metabolites of arachidonate occurs in ischemic-reperfused myocardium. Although lipoxygenase inhibitors have been shown to attenuate myocardial infarct size after ischemia-reperfusion, the relationship between arachidonate lipoxygenation and myocardial injury remains unclear. To investigate the direct effect of arachidonate lipoxygenation on cardiac myocytes, isolated rat cardiac myocytes loaded with indo 1 were superfused with Tyrode solution containing arachidonic acid mixed with soybean lipoxygenase. Although neither arachidonic acid nor lipoxygenase alone had any effects, arachidonic acid plus lipoxygenase induced an increase in the twitch amplitude associated with an increased intracellular Ca2+ concentration ([Ca2+]i) and irreversible hypercontracture. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, blocked these effects. Linolenic acid, which is also a lipoxygenase substrate, caused the same effects as arachidonic acid in the presence of lipoxygenase, whereas oleic and stearic acid, which do not function as lipoxygenase substrates, did not. Both ascorbic acid and alpha-tocopherol attenuated an increase in [Ca2+]i and the cellular damage, whereas nicardipine and superoxide dismutase had no effects. These results suggest that lipoxygenase metabolites of arachidonic acid cause intracellular Ca2+ overload and cellular damage to cardiomyocytes, probably through augmentation of lipid peroxidation of the cell membranes by free radicals.

Adenosine blockade during reperfusion reverses the infarct limiting effect in preconditioned canine hearts

OBJECTIVES

The aim was to investigate whether adenosine release after reperfusion contributes to infarct limitation by ischaemic preconditioning.

METHODS

Dogs underwent preconditioning with four 5 min cycles of left anterior descending coronary artery (LAD) occlusion and reperfusion, followed by 90 min LAD occlusion and 5 h reperfusion with or without the non-specific adenosine receptor blocker, 8-phenyltheophylline (8-PT). Infarct size was assessed by a dual staining method with triphenyltetrazolium chloride and Evans blue. Blood flow measurements in the subendocardial region were made by infusion of coloured microspheres before occlusion and midway through the sustained occlusion. Transcardiac alteration of neutrophillic function was assessed by luminol-enhanced whole blood chemiluminescence induced by zymosan.

RESULTS

Infarct size was significantly reduced in the preconditioned dogs [12.5(SEM 4.0)%, n = 10, p < 0.01] compared with the control dogs [40.5(6.1)%, n = 10], an effect significantly reduced by the 8-PT treatment [23.4(4.9)%, n = 8]. Treatment with 8-PT without ischaemic preconditioning had no effect on infarct size [42.8(6.3)%, n = 7]. There was no difference in myocardial blood flow in the ischaemic or non-ischaemic subendocardial tissue between any pair of the four groups. The ratio of whole blood chemiluminescence in the cardiac vein to that in the carotid artery was considerably reduced in preconditioned dogs compared with that in control dogs after reperfusion. Myeloperoxidase activity in the ischaemic myocardium and the peripheral neutrophil count at the end of the experiment were both also decreased compared with control dogs. In preconditioned dogs treated with 8-PT, neutrophillic function in the coronary circulation after reperfusion was increased compared with that in both controls and preconditioned dogs with no 8-PT treatment. There was no difference in neutrophillic function between the 8-PT-treated dogs with or without ischaemic preconditioning. Treatment with 8-PT increased myeloperoxidase activity in the ischaemic myocardium of the preconditioned dogs, and no difference was seen in activity between dogs treated with 8-PT with or without ischaemic preconditioning.

CONCLUSIONS

An adenosine receptor blocker caused a moderate but significant reversal of infarct limitation by ischaemic preconditioning associated with a significant increase of neutrophillic function in the coronary circulation during early reperfusion.

Brief myocardial ischemia affects free radical generating and scavenging systems in dogs

This study examined whether brief repeated myocardial ischemia altered free radical generating and scavenging activity in a dog model. In dogs preconditioned with four 5-min left anterior descending coronary artery (LAD) occlusions and reperfusions, we examined transcardiac changes in both the function of neutrophils, cells which are major free radical generators, and in myocardial antioxidant enzyme activity, as an indication of free radical scavenging. Neutrophil function was assessed by determining luminol-enhanced whole blood chemiluminescence (CL) induced by zymosan. Blood was taken simultaneously from the carotid artery and the cardiac vein running along the occluded LAD. Preconditioning with sublethal ischemia significantly reduced whole blood CL in the cardiac vein compared with the carotid artery after the first and fourth 5-min reperfusions, while there was no difference in neutrophil count between these sampling sites. Immediately after brief repeated ischemia and reperfusion, manganese-superoxide dismutase (SOD) activity was significantly enhanced, and glutathione reductase activity was markedly reduced in the ischemic, compared with the non-ischemic, myocardium. There were no differences in the myocardial activities of copper, zinc-SOD, glutathione peroxidase, and glutathione S-transferase between the ischemic and non-ischemic regions. Also, no difference was observed between the reduced myocardial glutathione levels in these regions, although the oxidized glutathione level was significantly higher in the ischemic regions of the subepicardial and subendocardial areas. We demonstrated that brief repeated ischemia affects free radical generating and scavenging systems in the ischemic myocardium.

Free radical generation coupled with arachidonate lipoxygenase reaction relates to reoxygenation induced myocardial cell injury

OBJECTIVE

The role of arachidonate lipoxygenase activity in reoxygenation induced cell injury in adult canine cardiac myocytes was investigated.

METHODS

The production of hydroxyeicosatetraenoic acids (HETEs), which are lipoxygenase metabolites, was measured with high pressure liquid chromatography in canine cardiac myocytes cultured under hypoxic conditions and then reoxygenated. Free radical generation was evaluated by electron paramagnetic resonance spectroscopy with a spin trapper, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and luminol enhanced chemiluminescence emission. Cell injury was estimated in terms of morphological changes and release of intracellular enzymes. Morphological damage to myocytes was quantified in terms of the percentage of hypercontracted "round" cells. The effects of nordihydroguaiaretic acid, AA-861, mepacrine, indomethacin, aspirin, alpha tocopherol, and 2-0-octadecylascorbic acid (CV-3611) on lipoxygenase metabolism, free radical generation and cell injury were also assessed.

RESULTS

Cardiac myocytes produced 5-HETE and 12-HETE at less than 0.1 ng.mg-1 protein under normoxic conditions. Production of HETE was greatly increased at five hours of reoxygenation after 45 minutes of hypoxia [5-HETE = 12.0(SEM 0.5), 12-HETE = 23.6(1.1) ng.mg-1 protein]. Both DMPO-OH adduct generation and chemiluminescence emission were considerably increased after one to three hours of reoxygenation, although they increased only slightly after 45 minutes of hypoxia. After five hours of reoxygenation, long rod cells gradually became deformed; 92.0% of the cells were converted to hypercontracted "round" cells. Cell injury and HETE production were significantly suppressed by nordihydroguaiaretic acid (10 microM), AA-861 (2 microM), and mepacrine (10 microM). Indomethacin (10 microM) and aspirin (50 microM) enhanced cell injury and HETE production. alpha Tocopherol and CV-3611 greatly suppressed cell injury and free radical generation, but not HETE production.

CONCLUSION

The arachidonate lipoxygenase metabolic pathway may have an important role in reoxygenation induced myocardial cell injury in adult cardiac myocytes, possibly because of the generation of free radicals.

Delayed effects of sublethal ischemia on the acquisition of tolerance to ischemia

The infarct-limiting effect of ischemic preconditioning is believed to be a transient phenomenon. We examined the delayed effects of repetitive brief ischemia on limiting infarct size in an open-chest dog model by an occlusion (90 minutes) of the left anterior descending coronary artery (LAD) followed by reperfusion (5 hours). The dogs were preconditioned with four brief repeated ischemic episodes induced by 5-minute LAD occlusions with subsequent reperfusion. The size of infarcts initiated by a sustained occlusion immediately or 24 hours after preconditioning was significantly smaller when compared with infarcts in sham-operated dogs (for the immediate occlusion, 14.4 +/- 2.0% versus 39.0 +/- 3.7%, respectively [p < 0.01]; and for the delayed occlusion, 18.8 +/- 3.4% versus 35.1 +/- 4.6%, respectively [p < 0.05]); however, when the infarction was induced 3 hours (31.2 +/- 3.7% versus 37.5 +/- 4.2%, respectively) or 12 hours (25.4 +/- 4.8% versus 35.0 +/- 5.3%, respectively) after repetitive ischemia, the infarct size did not differ. No differences were seen in regional myocardial blood flow or rate-pressure products between the two groups. These results indicate that an infarct-limiting effect of brief repeated ischemia can be observed 24 hours after sublethal preconditioning.

Transcardiac alteration of neutrophil function relates to myocardial ischaemia/reperfusion injury

OBJECTIVE

The aim was to define the relation between transcardiac changes in neutrophil function in myocardial ischaemia and the progression of myocardial necrosis.

METHODS

Samples of blood from carotid artery, jugular vein, and cardiac vein streaming from the ischaemic area were taken simultaneously in a canine coronary occlusion-reperfusion model of myocardial infarction. Neutrophil function was evaluated by neutrophil count, whole blood chemiluminescence and leucocyte infiltration into the ischaemic myocardium. Myocardial necrosis was assessed by plasma creatine kinase and dual staining technique using Evans blue dye and triphenyltetrazolium chloride. Effects of a free radical scavenger, N-2-mercaptopropionyl glycine (MPG), initiated 15 min before reperfusion and continued during the reperfusion phase, were also examined.

RESULTS

Whole blood chemiluminescence of the cardiac vein was reduced at 90 min after coronary artery occlusion as compared to carotid artery [5.8(SEM 0.5) v 7.5(0.7) count x 10(3) cell neutrophil-1 x 10 min-1, p < 0.05], and then increased abruptly after reperfusion to peak after 10 min of reperfusion [7.1(0.7) count x 10(3) cell neutrophil-1 x 10 min-1]. The neutrophil count in cardiac venous blood was significantly reduced within 5 min of reperfusion. MPG significantly attenuated the reperfusion associated increase in cardiac vein whole blood chemiluminescence and the decrease in the cardiac venous blood neutrophil count. The increase in myocardial free radical generation 1-3 h after reperfusion, as assessed by the electron paramagnetic resonance spin trapping technique, was reduced markedly, as was the extent of leucocyte infiltration into the ischaemic myocardium. Under these conditions, administration of MPG significantly reduced myocardial infarct size [40.3(4.5)% v 21.4(4.2)%, p < 0.05]. A marked increase in transcardiac creatine kinase release after reperfusion observed in control dogs was also reduced significantly.

CONCLUSIONS

A transient alteration of neutrophil function occurs in the coronary circulation immediately after reperfusion, which may augment neutrophil infiltration and free radical generation in the ischaemic myocardium, leading to the propagation of myocardial ischaemia/reperfusion injury.

Sublethal ischemia alters myocardial antioxidant activity in canine heart

We examined antioxidant activity in the pre-conditioned canine myocardium with four 5-min episodes of regional ischemia and reperfusion. Immediately after repetitive brief ischemia, mitochondrial Mn-superoxide dismutase (SOD) activity in the ischemic myocardium significantly increased compared with that in the nonischemic myocardium (18.7 +/- 2.1 vs. 14.9 +/- 1.0 U/mg protein, P < 0.05). Although no difference was seen in the activity between these regions after 3 h of the sublethal ischemia, a significant increase in the activity of the ischemic myocardium reappeared after 24 h compared with that of the nonischemic myocardium (26.7 +/- 0.9 vs. 20.8 +/- 0.9 U/mg protein, P < 0.05). Mn-SOD content increased gradually in the ischemic myocardium after sublethal ischemia, with a peak after 24 h (2.8 +/- 0.1 vs. 2.1 +/- 0.1 microgram/mg protein, P < 0.05). There were no differences in the activity and content of Cu, Zn-SOD between these regions after sublethal ischemia. Activities of glutathione peroxidase and reductase were significantly higher and lower, respectively, in the ischemic myocardium than those of the nonischemic myocardium immediately after repetitive brief ischemia, but no differences between these regions were seen in activities after 3 or 24 h. These results indicate that a brief ischemic insult alters myocardial antioxidant activity not only immediately after but also 24 h after sublethal ischemia.

Neutrophil-induced myocardial cell damage and active oxygen metabolites

Free radicals derived from polymorphonuclear leukocytes (PMN) have been suggested to play an important role in myocardial ischemia-reperfusion injury. To define the mechanism by which activated PMN exacerbate ischemic myocardial damage, we investigated the extent of cell injury, free radical generation and lipid peroxidation in embryo mouse myocardial cells co-incubated with activated PMN. The generation of free radicals derived from PMN correlated with the extent of myocardial cell injury. Among the cell sheets preconditioned with hypoxic and glucose free medium, PMN-adhered myocardial cells were initially injured after adding PMN activator, extending to adjacent cells. Chemiluminescence emission and thiobarbituric acid reactive substance in the co-incubated cells were markedly increased and sustained compared with those in each cell monoincubation. The augmented lipid peroxidation was related to the progression of myocardial cell injury. These results indicate that PMN-derived free radicals cause membrane disruption, contributing to the progression of myocardial injury.

Transcardiac alteration of neutrophil function before and after coronary thrombolysis in human myocardial infarction

We examined function of isolated neutrophils taken from aorta and coronary sinus before and after thrombolytic reperfusion in 17 patients whose infarct-related coronary arteries were totally occluded. Before reperfusion in left coronary artery disease, free radical generation by activated neutrophils in coronary sinus, assessed by ferricytochrome c reduction (phorbol myristate acetate, 10 ng/ml) and luminol-enhanced chemiluminescence (A23187, 2 microM), was reduced by 20% (P less than 0.05) and 30% (P less than 0.05), respectively, compared with those in aorta. Neutrophil aggregation (A23187, 10 microM) and chemotactic activity (formyl-methionyl-leucyl-phenylalanine, 5 microM) were also reduced in coronary sinus by 21% and 20%. After reperfusion the extent of such neutrophil function in coronary sinus recovered and was similar to that in aorta. There were no significant differences between neutrophil counts in aorta and coronary sinus before and after reperfusion. In right coronary artery disease, no significant changes were seen in these functions of neutrophils of aorta and coronary sinus before and after reperfusion. These results indicate that function of neutrophils passing through coronary circulation fluctuated significantly in association with reperfusion, suggesting (1) factor(s) that depress neutrophil function are produced in coronary circulation during myocardial ischemia and their effects are overcome after reperfusion or (2) activated neutrophils, trapped in the ischemic coronary bed, are washed out to coronary sinus after reperfusion.

Detection of oxygen-derived free radical generation in the canine postischemic heart during late phase of reperfusion

To define the relation between oxygen-derived free radical (oxy-radical) generation in the reperfused ischemic myocardium and the progression of myocardial damage, we measured oxy-radical generation in the ischemic myocardium and the propagating infarct size in a model of canine coronary occlusion (90 minutes) and reperfusion. We used electron paramagnetic resonance spin-trapping techniques (5,5-dimethyl-1-pyrroline N-oxide [DMPO]) to detect oxy-radicals in the rapidly frozen myocardial samples taken by needle biopsy. There was no detectable generation of DMPO adducts in the normal myocardium before or after reperfusion. In the reperfused ischemic myocardium, electron paramagnetic resonance signals of DMPO-OOH (superoxide anion) and DMPO-OH (hydroxyl radical) were detected, with peak concentrations at 1 hour after reperfusion for DMPO-OOH and at 3 hours after reperfusion for DMPO-OH, respectively. These DMPO adducts were also detected during the early phase (15 seconds) of reperfusion, but the concentrations of these signals were much less than those during the late phase of reperfusion. Treatment with human recombinant superoxide dismutase (2.5 mg/kg/hr) and catalase (2.5 mg/kg/hr) during the course of experiments abolished DMPO-OOH formation but had little effect on DMPO-OH formation. Infarct size (percent of risk area infarcted), quantified by a dual staining method with Evans blue dye and triphenyltetrazolium chloride, was 18.3 +/- 4.8% (mean +/- SEM) at 90 minutes of occlusion. After 5 hours of reperfusion, infarct size increased to 43.6 +/- 7.2%. These results indicate that a greater magnitude of oxy-radical generation was sustained in the ischemic myocardial tissue during the late phase (1-3 hours) of reperfusion, associated with the progression of myocardial infarction. The concurrent appearance of oxy-radicals and progressive infarction may support the view that a chain reaction of oxy-radicals contributes to the propagation of myocardial cell damage in the postischemic heart.

Polymorphonuclear leukocytes induced vasoconstriction in isolated canine coronary arteries

To assess how polymorphonuclear leukocytes (PMNs) act on coronary vasoactivity, we measured the changes in isometric tension of isolated rings of canine coronary arteries upon addition of autologous PMNs to organ chambers in which the rings were suspended. When PMNs isolated by the colloidal polyvinylpyrrolidone-coated silica (Percoll) gradient method were added to the chambers, ring preparations of left circumflex coronary arteries developed isometric tension. The increase in tension was dependent on the amount of PMNs (1 X 10(4) to 5 X 10(6) cells/ml). Maximal tension obtained by an optimal amount of PMNs (5 X 10(5) cells/ml) was almost comparable to that produced by prostaglandin F2 alpha (5 microM). Integrity of endothelial cells was not disrupted after the addition of PMNs because the developed tension could be reversed by the addition of acetylcholine in an endothelium-dependent manner. Mechanical rubbing of endothelium abolished the PMN-induced vasoconstriction, which was regained by placing an endothelium-unrubbed ring inside a rubbed ring ("sandwich preparation"). When PMN suspensions were pretreated with 5-lipoxygenase inhibitors of arachidonate, PMN-induced vasoconstriction was greatly suppressed, although the pretreatment of vascular preparations did not alter the development of isometric tension. These findings indicate that PMNs induce the contraction of coronary arterial rings in the presence of intact endothelial cells. The mechanism by which PMNs induce the contraction is the release of vasoconstrictive substances by metabolic interaction between PMNs and endothelial cells. Vasoconstrictive substances produced by the PMN-endothelial system, such as 5-lipoxygenase metabolites through a "leukotriene A4 steal" mechanism, may contribute to the contraction of vascular smooth muscle.

Role of free radicals and neutrophils in canine myocardial reperfusion injury: myocardial salvage by a novel free radical scavenger, 2-octadecylascorbic acid

To define the role of oxygen free radicals and neutrophil involvement in evolving myocardial reperfusion injury, we evaluated the effect of 2-octadecylascorbic acid (CV-3611), a novel free radical scavenger, on neutrophil function and the extent of myocardial damage resulting from 90 min of ischaemia followed by 5 h of reperfusion in an experimental model of myocardial infarction. Dogs were randomly assigned to receive CV-3611 (5 mg.kg-1.[5 min]-1, intravenously) just before the onset of reperfusion. Infarct size, as a percent of area at risk, was reduced by 60% in CV-3611 treated group as compared with control, at 16.7(SEM 3.1)% v 41.5(4.5)%, p less than 0.01. Administration of CV-3611 markedly reduced function of neutrophils isolated from peripheral circulation during reperfusion ex vivo as estimated by free radical generation (ferricytochrome c reduction and luminol enhanced chemiluminescence), chemotactic activity, and aggregation induced by A23187. Under these conditions, the enhancement in neutrophil infiltration and free radical generation (luminol enhanced chemiluminescence) in myocardium within area at risk, especially in the border zone between viable and irreversible injured myocardium, was markedly reduced. Haemodynamic profiles were similar between control and CV-3611 treated group. These results suggest that activated neutrophils, especially their generation of oxygen free radicals, contribute to reperfusion induced myocardial injury.

Attenuation of neutrophil function by inhibitors of arachidonate metabolism reduces the extent of canine myocardial infarction

To assess the role of neutrophils and arachidonate metabolites in evolving myocardial infarction, the effect of inhibitors of arachidonate metabolism on the extent of myocardial damage and neutrophil function was examined in a 90-minute occlusion/5-hour reperfusion model of canine myocardial infarction. A thromboxane A2 synthetase inhibitor, CV-4151, and a lipoxygenase inhibitor, AA-861, greatly reduced the infarct size. They also attenuated the production of chemoattractant leukotriene B4 and chemotactic activity of neutrophils isolated from peripheral circulation. Under these conditions, both the increases in peripheral leukocyte count and neutrophil infiltration in ischemic myocardium were inhibited. These results indicate that the inhibition of 2 pathways of arachidonate metabolism may decrease infiltration of activated neutrophils in ischemic myocardium by attenuating chemotactic function of neutrophils, resulting in reduction of the extent of myocardial infarction.

The effect of CV-4151, a selective inhibitor of thromboxane synthetase, on prostanoid formation and platelet aggregation in humans

The pharmacokinetics and pharmacologic effects of a potent, selective inhibitor of thromboxane synthetase, CV-4151 [(E)-7-phenyl-7-(3-pyridyl)-6-heptenoic acid] on prostanoid formation and platelet aggregation were studied in 42 healthy male volunteers. The drug was well tolerated. After oral administration of 10 to 100 mg of CV-4151, peak plasma levels of 1-6 micrograms/mL were reached in a dose-dependent manner within 1 hour. Elimination followed first-order fashion with elimination half-life of about 1 hour. Serum levels of thromboxane B2 reduced to 4% to 15% of control at 2 hours after drug ingestion dose-dependently. Serum levels of 6-keto-prostaglandin F1 alpha increased to about four to six times basal levels. Platelet aggregation induced by collagen and arachidonate was inhibited in most cases. Such pharmacologic effects outlasted serum drug levels. In repeated administration, stable inhibition of serum thromboxane B2 production and platelet aggregation in proportion to the enhancement of serum 6-keto-prostaglandin F1 alpha production was observed although no drug accumulation was found. These results indicate that CV-4151 may be suitable for clinical trials in cardiovascular diseases in which imbalance between thromboxane and prostacyclin may be involved in the pathogenesis.

Polymorphonuclear leukocyte activity and ventricular arrhythmia in acute myocardial infarction

Polymorphonuclear leukocyte activity was compared with the incidence and severity of ventricular arrhythmia evaluated by Holter electrocardiographic monitoring in 21 patients with acute myocardial infarction. A positive correlation (r = 0.706) was seen between peripheral polymorphonuclear leukocyte count and the amount of leukotriene B4 produced by A23187 (20 microM)-stimulated polymorphonuclear leukocytes on the first hospital day (p less than 0.01). Patients were divided into 3 groups according to the severity of ventricular arrhythmia: no or mild (unifocal, maximal hourly ventricular premature complex rate less than 30, n = 6), moderate (maximal hourly ventricular premature complex rate greater than or equal to 30 or multifocal, n = 6) or severe (R on T, greater than or equal to 2 consecutive ventricular premature complexes or ventricular fibrillation, n = 9). Polymorphonuclear leukocyte count and its leukotriene B4 production were increased with the increase in severity of ventricular arrhythmia among 3 groups. Polymorphonuclear leukocyte count (13,300 +/- 900/microliter, mean +/- standard error of the mean) and its leukotriene B4 production (194 +/- 24 ng/10(7) cells) in patients exhibiting severe ventricular arrhythmia were significantly increased compared with those in patients exhibiting no or mild ventricular arrhythmia (10,300 +/- 1,000/microliter, p less than 0.05 and 120 +/- 21 ng/10(7) cells, p less than 0.05, respectively). Enzymatically estimated infarct size in the latter patient group was significantly smaller than those of the other 2 groups, between which there was no difference in infarct size. These results suggest that polymorphonuclear leukocyte activity is closely related to the incidence and severity of ventricular arrhythmia during the early phase of myocardial infarction.