Nobuyuki Hieda

The effects of lipoxygenase inhibitor and peptidoleukotriene antagonist on myocardial injury in a canine coronary occlusion-reperfusion model

UNLABELLED We studied effects of lipoxygenase inhibitor (AA-861) and peptidoleukotriene antagonist (ONO-1078) on infarct size, polymorphonuclear leukocyte (PMNs) infiltration, gross myocardial hemorrhage and ventricular arrhythmias in canine coronary occlusion (2 hr)-reperfusion (5 hr) model. Infarct size (IS) and risk area (RA) were determined by dual staining technique. Thirty minutes before coronary occlusion dogs were randomly assigned to one of the following three groups: lipoxygenase inhibitor group (n = 11) receiving AA-861 3 mg/kg i.v., peptidoleukotriene antagonist group (n = 11) receiving continuous intravenous infusion of ONO-1078 1 micrograms/kg/min and vehicle control group (n = 15). Both AA-861 and ONO-1078 reduced infarct size [AA-861: 21.8 +/- 1.3% of RA (mean +/- SEM), ONO-1078: 22.5 +/- 4.4% vs CONTROL 54.0 +/- 6.4%, p less than 0.01 and p less than 0.01, respectively] and area of gross myocardial hemorrhage (AA-861: 5.1 +/- 2.4% of IS, ONO-1078: 5.2 +/- 2.5% vs CONTROL 22.3 +/- 3.9%, p less than 0.01 and p less than 0.01, respectively). Both drugs also decreased frequency of ventricular premature contractions both during occlusion and during reperfusion, and that of ventricular tachycardia during reperfusion. AA-861 inhibited PMNs recruitment into infarcted area. However, ONO-1078 had no significant influence on degree of PMNs infiltration. These results suggest that lipoxygenase products, especially peptidoleukotrienes (LTC4, D4 and E4) may play important roles in the pathogenesis of myocardial ischemic and reperfusion injuries.

The role of leukotoxin (9,10-epoxy-12-octadecenoate) in the genesis of coagulation abnormalities.

This study was designed to clarify whether or not leukotoxin (9, 10-epoxy-12-octadecenoate), which is biosynthesized by neutrophils, might be involved in the genesis of coagulating abnormalities. Twelve dogs were divided into 2 groups. In the test group (n = 6), 100 mumol/kg of leukotoxin was injected intravenously, and in the control group (n = 6), 100 mumol/kg of linoleate was injected. In each group, a series of blood samples were collected and used for coagulation studies. After the end of the experimental period, a histological study was performed on organs removed from the dogs. In the leukotoxin group, fibrin and fibrinogen degradation products (FDP) was increased time-dependently. Fibrinogen was decreased, and prothrombin time and activated partial thromboplastin time were prolonged in parallel with the increase in FDP. A decrease in number of platelets was also observed. Intravascular coagulation was observed in sections of lung. These data were compatible with a diagnosis of disseminated intravascular coagulation (DIC). No significant changes in these parameters were observed in the linoleate group. Leukotoxin has been confirmed to show antifungal and antibacterial activity, and its production might be a defensive response to infection. Over-production of leukotoxin associated with severe infection might therefore account for infection-induced DIC.

Cardioprotective effects of various class I antiarrhythmic drugs in canine hearts

This study was designed to clarify the cardioprotective effects of various class I antiarrhythmic drugs, i.e., aprindine, disopyramide, flecainide, lidocaine, mexiletine, pentisomide and propafenone, on the ischemic heart. Sixty-one adult mongrel dogs were classified into eight groups according to premedication: 1) control group, physiologic saline solution was administered intravenously 25 min before left anterior descending coronary artery ligation; 2) aprindine group, 3 mg/kg body weight of aprindine intravenously; 3) disopyramide group, 2 mg/kg of disopyramide intravenously; 4) flecainide group, 2 mg/kg of flecainide intravenously followed by drip infusion of 100 micrograms/kg per min; 5) lidocaine group, 2 mg/kg of lidocaine intravenously followed by drip infusion of 100 micrograms/kg per min; 6) mexiletine group, 3 mg/kg per min of mexiletine intravenously followed by drip infusion of 15 micrograms/kg per min; 7) pentisomide group, 5 mg/kg intravenously; and 8) propafenone group, 2 mg/kg intravenously. Arterial blood pressure and electrocardiogram were monitored throughout the experiment. Two hours after coronary occlusion, the heart was excised. Myocardial mitochondria were prepared and mitochondrial function (the respiratory control index and the rate of oxygen consumption in state III) was measured polarographically. Fractionation of myocardial tissues was performed and the lysosomal enzyme (N-acetyl-beta-glucosaminidase and beta-glucuronidase) activities among fractions were measured. No significant hemodynamic changes were observed compared with the control group except for those in the disopyramide and flecainide groups; that is, decrease in heart rate without changes in blood pressure compared with the control group was observed. All antiarrhythmic drugs effectively prevented the development of ventricular arrhythmias associated with ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of SUN 1165, a novel sodium channel blocker, on ischemia-induced mitochondrial dysfunction and leakage of lysosomal enzymes in canine hearts.

The cardioprotective effect of SUN 1165, a novel sodium channel blocker, was investigated on ischemic myocardium. Nineteen anesthetized dogs were subjected to 2 hours coronary occlusion, and divided into 2 groups. In the control group, physiological saline was infused. In the SUN 1165 group, 2 mg/kg of SUN 1165 was injected intravenously. Two hours after occlusion, heart mitochondria were prepared from both ischemic and non-ischemic areas in each group, and their functions (RCI and St.III O2) were measured polarographically with succinate as a substrate. Fractionation of myocardial tissue from both non-ischemic and ischemic areas was performed according to the method of Weglicki et al., and the activities of lysosomal enzymes (NAG and beta-gluc) were measured. In the control group, mitochondrial dysfunction and leakage of lysosomal enzymes induced by 2 hours occlusion were observed. Administration of SUN 1165 maintained mitochondrial function, and prevented the leakage of lysosomal enzymes caused by ischemia significantly. These results indicated that SUN 1165 has a cardioprotective effect in ischemic heart.

Cardioprotective and antiarrhythmic effects ofβ-blockers, propranolol, bisoprolol, and nipradilol in a canine model of regional ischemia

SummaryCardioprotective and antiarrhythmic effects of threeβ-blockers with different pharmacological properties were investigated in 33 anesthetized dogs with a 2-h coronary occlusion. Dogs were divided into 4 groups and received physiological saline or one of the following drugs using a 10-min infusion at 25 min before the occlusion: saline or control (n=12), propranolol (0.3 mg/kg,n=7), bisoprolol (0.05 mg/kg,n=7), and nipradilol (0.2 mg/kg,n=7) groups.Blood pressure did not significantly differ among the 4 experimental groups throughout the entire observation period. On the contrary, the postocclusion change (fall) in heart rate from the preocclusion value was significantly (P<0.05–0.01) greater in the drug-treated groups than in the control group. Each of theβ-blockers effectively prevented the development of ventricular arrhythmias associated with the 2-h coronary occlusion. In terms of assessing a cardioprotective effect, the respiratory control index and rate of oxygen consumption in State III in mitochondria, and lysosomal enzyme activities (N-acetyl-β-glucosaminidase orβ-glucuronidase) in myocardial tissues, all prepared from both ischemic and non-ischemic areas, were measured using the respective, established methods. The 2-h coronary occlusion induced a mitochondrial dysfunction and leakage of lysosomal enzymes in the control group, whereas eachβ-blocker significantly (P < 0.05–0.01) protected mitochondria against ischemia and prevented the lysosomal enzyme leakage. The results indicate that the antiarrhythmic effects ofβ-blockers on ischemic myocardium are, at least in part, due to their cardioprotective action, and these effects appear to be unrelated to the ancillary pharmacological properties of these drugs.

Effects of a new thromboxane A2-antagonist (ONO-3708) and a new leukotriene-antagonist (ONO-1078) on thromboxane A2 analogue-, leukotriene C4-, and D4-induced regional myocardial blood flow reduction

SummaryEffects of the administration of a thromboxane A2 (TXA2) analogue (STA2), a leukotriene C4 (LTC4), and a leukotriene D4 (LTD4) on regional myocardial blood flow (RMBF) and hemodynamics were studied in anesthetized, open-chest dogs. The blocking ability of a recently synthesized TXA2 selective antagonist, ONO-3708, and a peptidoleukotriene-selective antagonist, ONO-1078, was also investigated. RMBF was measured continuously in three areas: the left anterior descending coronary artery (LAD) area, the circumflex artery (Cx) area, and the area between LAD and Cx. STA2, LTC4, and LTD4 caused a significant dose-dependent reduction of the RMBF in the LAD area. The peak percentage decrease in RMBF followed by a 10 µg dose of STA2, 1 µg dose of LTC4, and 1 µg dose of LTD4 is 38.6%±3.0%, 39.0%±3.1%, and 36.2%±2.4%, respectively. ED50 for the action of LTC4, LTD4, and STA2 on RMBF is 3, 3, and 50 µg, respectively. Pretreatment with the newly developed TXA2 antagonist, ONO-3708 (1 µg/kg/min for 10 min), completely inhibited the RMBF reduction induced by STA2 (10 µg). Pretreatment with the peptidoleukotriene antagonist, ONO-1078 (1 mg), inhibited the RMBF reduction induced by LTC4 or LTD4 (0.3–3 µg). Following pretreatment with a 1 mg dose of ONO-1078, the peak percentage decrease of RMBF caused by a 1 µg dose of LTC4 and LTD4 was reduced to 21.1%±2.3% and 19.8%±3.1%, respectively. However, the LTC4 (1 µg)-induced reduction of the RMBF was not affected by pretreatment with a TXA2 antagonist, ONO-3708, or an inhibitor of the endogenous production of TXA2, OKY-046. Likewise, the reduction of the RMBF induced by STA2 (10 µg) was not affected by pretreatment with a leukotriene-antagonist, ONO-1078. These results suggest that the reduction of RMBF induced by TXA2, LTC4, and LTD4 is mediated in vivo through different vascular receptors for each.

The role of phospholipase in plasmocid-induced mitochondrial dysfunction in rat hearts

This study was designed to clarify the role of phospholipase in the mechanism of plasmocid-induced mitochondrial dysfunction in the rat heart. Rats were divided into two groups: the control group, untreated; and the plasmocid group,in which plasmocid (30 mg/kg) was injected subcutaneously. In each group,the level of lipid peroxides and the phospholipase activity in heart homogenate were measured, and mitochondrial function (respiratory control index and the rate of oxygen consumption in State III) was determined polarographically. The activity of lysosomal enzymes (N-acetyl-β-glucosaminidase and β-glucuronidase) were also measured. The plasmocid group showed significant increases in lipid peroxide levels and phospholipase activity. Administration of plasmocid also caused mitochondrial dysfunction, while no significant changes were observed in the lysosomal enzyme activity of either group. These results suggested that plasmocid induced mitochondrial dysfunction is based on the degrading of phospholipids by membrane bound phospholipase, and that lysosomal enzymes are unlikely to be involved in plasmocid-induced mitochondrial dysfunction.

Alterations in Autonomic Nervous System and Heart Mitochondrial Function in Rats Treated with Cyclophosphamide

This study was designed to determine the changes in the autonomic nervous system and heart mitochondrial function in rats treated with cyclophosphamide, an antitumor agent. Rats were divided into two groups: the control group, which remained untreated, and the cyclophosphamide group, which received cyclophosphamide (100mg/kg) intraperitoneally once a day for four consecutive days. In both groups, enzymic activities of the heart mitochondrial electron transport chain were measured. Acetylcholine and norepinephrine contents in the left ventricles were also determined. Significant decreases in mitochondrial electron transport activities were observed in rats treated with cyclophosphamide. Cyclophosphamide treatment also increased acetylcholine and norepinephrine contents. It is well known that the sympathetic nervous system plays an important role in the genesis of cardio-myopathy, and we reported the involvement of the parasympathic nervous system in the pathogenesis of cardiomyopathy. Accordingly, alterations in autonomic nervous function might be linked to the development of mitochondrial dysfunction, although it remains unclear whether the effects of cyclophosphamide on mitochondrial function are direct or indirect.