Takuo Ogawa

Massive conversion of guanosine to 8-hydroxy-guanosine in mouse liver mitochondrial DNA by administration of azidothymidine.

As typical mitochondrial myopathy has been reported to be expressed among many patients with AIDS treated with long-term azidothymidine (AZT) therapy, we examined changes in mouse liver mitochondrial DNA (mtDNA) after 4-week administration of AZT. Even below 1/10th the dose given to the patients (AZT, 1 mg/kg/day), 25% of the total deoxyguanosine (dG) was converted to be 8-hydroxy-deoxyguanosine (8-OH-dG). 38% of the total dG was converted to 8-OH-dG with AZT 5 mg/kg/day. In vitro, the conversion of dG to 8-OH-dG was demonstrated by incubating mtDNA in the oxygen radical producing system containing NADH and KCN treated mitochondrial inner membrane. Thus it is concluded that, by lack of repairing system, damaged mtDNA with AZT results in impaired mitochondrial respiratory chain causing oxygen radicals which are responsible for 8-OH-dG formation. These results suggest that the oxygen damage of mtDNA is the primary cause of mitochondrial myopathy with AZT therapy.

Hydroxyl radical and leukotoxin biosynthesis in neutrophil plasma membrane

We measured O2-, H2O2, .OH and leukotoxin biosynthesis in neutrophil plasma membrane. O2- was produced by respiratory burst oxidase in the membrane coupling with NADPH oxidation. Leukotoxin was biosynthesized in the system containing linoleate. Addition of SOD into the system doubled the amount of leukotoxin synthesized. Further addition of catalase into the system decreased leukotoxin formation. .OH and leukotoxin formation in the system was substantially increased by the presence of cytochrome c. In addition, leukotoxin was detected in the non-biological reaction mixture containing H2O2 and linoleate in the presence of heme iron. In this mixture, .OH and leukotoxin formation also showed a good correlation. From these results, it is evident that, in neutrophil cell membrane, leukotoxin is synthesized by .OH with linoleate.

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.

Changes in myocardial mitochondrial electron transport activity in rats administered with acetylcholinesterase inhibitor.

This study was designed to elucidate harmful effects of acetylcholine on myocardial mitochondrial electron transport activity. Rats were cervically dislocated 3 h and 6 h after oral administration of pyridostigmine, an acetylcholinesterase inhibitor. The myocardial mitochondrial electron-transport activity (NADH-cytochrome c reductase, succinate-cytochrome c reductase and cytochrome c oxidase), and myocardial acetylcholine and norepinephrine concentrations were measured. Activities of cytochrome c oxidase were significantly decreased in the pyridostigmine-3h and the pyridostigmine-6h groups compared with untreated rats. Activity of NADH-cytochrome c reductase was significantly decreased 6 h after administration. No significant changes were observed in those of succinate-cytochrome c reductase among all groups. Pyridostigmine increased significantly myocardial acetylcholine concentration, however, no significant changes of myocardial norepinephrine concentrations were observed among all groups. It is indicated that these mitochondrial injuries might be dependent on an increase in acetylcholine level and independent of norepinephrine.