Noburu Konno

Changes in microsomal membrane phospholipids and fatty acids and in activities of membrane-bound enzyme in diabetic rat heart.

Diabetes mellitus is associated with alterations in lipid metabolism and cardiac dysfunction despite an absence of coronary arteriosclerotic changes. To investigate mechanisms of cardiac dysfunction in diabetic cardiomyopathy, we studied the relation between activities of membrane-bound enzymes and surrounding phospholipids in rats with diabetes induced with a single intravenous injection of streptozotocin (65 mg/kg). We found that total phospholipid content of sarcoplasmic reticulum membrane increased significantly 8 weeks after treatment with streptozotocin owing to increases in phosphatidylcholine and phosphatidylethanolamine, a decrease in arachidonic acid, and an increase in docosahexaenoic acid in the early stage of diabetes. Sarcolemmal Na+/K+-ATPase activity and the number of receptors decreased in isolated cardiomyoctes of diabetic rats 8 weeks after streptozotocin administration. The Ca2+ uptake of both sarcoplasmic reticulum and mitochondria decreased simultancously in permeabilized, isolated cardiomyocytes from diabetic rats. The depression of membrane-bound enzyme activities was correlated with alterations in phospholipids, which are closely related to the microenvironment of membrane-bound enzymes and influence intracellular Ca2+ metabolism. Because these changes in phospholipids and fatty acids were reversible with insulin therapy, they are diabetes-specific and might be a cause of cardiac dysfunction in diabetes.

Congestive heart failure is associated with the rate of bone loss

Abstract.  Nishio K, Mukae S, Aoki S, Itoh S, Konno N, Ozawa K, Satoh R, Katagiri T (School of Medicine Showa University, Hatanodai, Shinagawa‐ku, Tokyo, Japan). Congestive heart failure is associated with the rate of bone loss. J Intern Med 2003; 253: 439–446.

Comparison of bare metal stent with pioglitazone versus sirolimus-eluting stent for percutaneous coronary intervention in patients with Type 2 diabetes mellitus☆

BACKGROUND Drug-eluting stents (DESs) have been shown to decrease restenosis as compared with bare-metal stents. Recently, thiazolidinediones effectively reduced restenosis and the risk of repeat target vessel revascularization. We conducted a study to compare the performance of a DES with that of a bare-metal stent with pioglitazone in patients with Type 2 diabetes mellitus (DM). METHODS The study was a prospective cohort trial involving 38 Type 2 diabetic patients referred for coronary stenting who were assigned to either the sirolimus-eluting stent (SES) group or the pioglitazone group. Quantitative coronary angiography was performed at study entry and at 6 months of follow-up to evaluate in-stent late luminal loss and the percentage of the luminal diameter and the rate of restenosis. We also analyzed major adverse cardiac events (MACE) at 12 months. RESULTS There were no significant differences in glycemic control levels or in lipid levels in the two groups at follow up. The insulin and homeostasis model assessment insulin resistance at follow-up were significantly lower in the pioglitazone group than in the SES group. The percentage of restenosis was similar between the SES group and the pioglitazone group. The incidence of MACE at 1 year tended to be lower in the pioglitazone group than in the SES group. CONCLUSIONS The bare-metal stent with pioglitazone is not inferior to the SES in the present study and is one of therapeutic strategies of percutaneous coronary intervention for patients with DM.

The effect of pioglitazone on nitric oxide synthase in patients with type 2 diabetes mellitus.

The aim of this study was to evaluate the effect of pioglitazone on nitric oxide in patients with type 2 diabetes and coronary artery disease. Twenty-seven patients with coronary artery disease and diabetes mellitus who had received coronary stenting were eligible for the study. They were assigned to the no insulin resistance (NIR) group, the insulin resistance (IR) group, and the pioglitazone group (30 mg once a day). Endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-alpha), interleukin-6, leptin, and adiponectin were measured. In the pioglitazone group, eNOS, iNOS, and leptin were significantly lower and adiponectin was significantly higher than those in the IR group. Stepwise multiple regression analyses showed that eNOS correlated with TNF-alpha and iNOS correlated with leptin and TNF-alpha. Leptin was the strongest predictor of iNOS. Treatment with pioglitazone significantly reduced eNOS and iNOS by improving adipocytokine levels.

Disruption of sarcolemmal integrity during ischemia and reperfusion of canine hearts as monitored by use of lathanum ions and a specific probe

Myocellular injury induced by acute ischemia and subsequent reperfusion was studied in 38 dogs, with special reference to sarcolemmal permeability as determined by the vital ionic lanthanum (La3+) probe technique and electron microscopy. The left anterior descending coronary artery (LAD) was occluded in 14 dogs for 10 to 60 min, and the ischemic zone was perfused slowly for 7 min with a La3+-containing solution. In 21 dogs, the LAD was released for 10 min after occlusion and was then reperfused for 7 min with arterial blood plus the La3+-containing solution. Subsequently, in both groups of animals, the ischemic myocardium was subjected to perfusion fixation in preparation for electron microscopy. In normal cardiac myocytes, La3+ was localized exclusively in the extracellular space. After 10 to 20 min of ischemia, more than 80% of myocytes appeared normal or were damaged only slightly, and the majority continued to exclude La3+. After 10 min of ischemia, deposits of lanthanum were detected in 1 and 6 % of myocytes in the absence or presence of reperfusion, respectively. The number of cells with such deposits was markedly increased after 30 min of ischemia (19%), as well as after 20 min of ischemia followed by reperfusion (17%), prior to the development of irreversible myocardial damage. After 60 min of ischemia with or without reperfusion, about 30% of myocytes showed severe injury with particulate deposits of lanthanum throughout the entire cell.These results indicate that sarcolemmal permeability increases during the early stage of myocardial injury due to ischemia or ischemiareperfusion and contributes to the development of myocardial damage.

Production of hydrogen peroxide in situ in cardiac myocytes during hypoxia-reoxygenation as assessed with cerium.

 Free radicals have been implicated in myocardial reperfusion injury. Hydrogen peroxide (H2O2) is one possible source of reactive oxygen intermediates. We studied the formation and toxicity of H2O2 in isolated myocytes during hypoxia-reoxygenation with the use of cerium. This method involves formation of an electron-dense precipitate when H2O2 reacts with cerium chloride (CeCl3). Single myocytes were obtained from rat hearts by collagenase digestion. Isolated myocytes were reoxygenated for 15 min after 30 min of hypoxia. The cells were treated with digitonin to increase the permeability of the plasma membrane, and CeCl3 was added to detect intracellular H2O2 on electron microscopy. In the nonhypoxia control group, the ultrastructure of cells was well preserved, and no dense deposits were found in myocytes. In the hypoxia-reoxygenation group, precipitates, i.e., Ce–H2O2 reaction products, were found inside and along swollen mitochondria, and cell viability was reduced to 72.3% of control. These results indicate that endogenous H2O2 is generated by mitochondria and that its release into the cytosol may lead to myocyte death under pathological situations such as hypoxia-reoxygenation.

Histochemical studies of myocardial injury caused by hydrogen peroxide after reperfusion using the cerium method

Free radicals have been implicated in myocardial reperfusion injury. Hydrogen peroxide (H2O2) is a precursor of highly reactive oxygen intermediates. In this study, we investigated myocardial injury caused by endogenous H2O2 during the early reperfusion period following brief ischemia with electron microscopy and the cerium method. This method involves formation of an electrondense precipitate when H2O2 reacts with cerium chloride (CeCl3). We used isolated, functioning hearts prepared according to the working heart model, which were reperfused with a solution containing 0.5mM CeCl3 for 5 min after 10 min of ischemia. Some hearts were treated with 3-amino-1,2,4-triazole (ATZ) to inhibit catalase; others were treated with ATZ and superoxide dismutase (SOD), which dismutates the superoxide anion to hydrogen peroxide. In the control group (no drugs given) and the ATZ-treated group, the CeCl3−H2O2-dependent reaction products during the reperfusion period appeared in 12% and 28%, respectively, of the microvascular spaces. Treatment with SOD did not produce a decrease in electron-dense precipitates or a decrease in myocardial injury during ischemia-reperfusion. Moreover, in the ATZ group, moderately injured myocytes were seen (swelling of mitocondria, intermyofibrillar edema). Our results indicate that in myocytes, catalase plays an important role in the defense against H2O2 and that the increase in H2O2 is a cause of reperfusion injury. However, SOD does not protect against H2O2 in the absence of catalase.

Pathophysiological Behavior of the Myocardium in Acute Ischemia and Reperfusion, with Special Emphasis on the Sarcoplasmic Reticulum

The myocardium under severe ischemia and reperfusion exhibits four types of different pathophysiologic behaviors: coagulation necrosis, stunning, ischemic preconditioning, and reperfusion injury. This chapter describes these changes in the postischemic myocardium in relation to the length of ischemia. Canine hearts were made ischemic by occludmg the left anterior descending coronary artery (LAD), and the sarcoplasmic reticulum (SR) from the ischemia-reperfused myocardium was analyzed. In permanent occlusion of the LAD, Ca2+-ATPase activity of the SR was reduced simultaneously with the degradation of the major ATPase protein in ischemia for 20 to 30 minutes. In the stunned myocardium, with occlusion of the LAD for 15 minutes and reperfusion, long-term reduction in the activity of the SR was noted simultaneously with a reduction in the percent of segment shortening, but without degradation of the ATPase protein of the SR. In the preconditioned myocardium, in which the LAD was occluded four times for five minutes each prior to LAD occlusion for 60 minutes and reperfusion, both ATPase activity and the SR ATPase protein were preserved In reperfusion of the LAD after occlusion for 10 to 30 minutes, reduction in Ca2+-ATPase activity and degradation of the ATPase protein occurred earlier, simultaneously with generation of free radicals, suggesting reperfusion injury. We conclude that pathophysiologic behaviors of the postischemic myocardium proceed in quite different ways depending upon the length of ischemia and will only be fully understood in the light of studies on ischemia and reperfusion of the heart muscle.

Oxygen Consumption and Mitochondrial Membrane Potential in Postischemic Myocardium

Oxygen consumption may be disproportionately high relative to contractile function in postischemic reperfused myocardium. The study reported in this chapter investigated the mechanism of the dissociation between oxygen consumption and contractile function in postischemic reperfused myocardium using isolated rat hearts. Mitochondrial dysfunction secondary to increased calcium uptake has been implicated as an important mediator of reperfusion injury in the heart. In postischemic, isovolumic, antegrate-perfused rat hearts, the myocardial oxygen consumption rate (MVO2) and contractile function were studied in relation to mitochondrial function. Left ventricular pressure, coronary blood flow, and oxygen consumption were determined. Mitochondrial respiration and the mitochondrial membrane potential were measured by polarography and flow cytometry, respectively. To examine the role of mitochondrial calcium uptake in ischemia reperfusion injury, isolated rat hearts perfused with ruthenium red, which inhibits calcium uptake by mitochondria, were compared to control perfused hearts. After stabilization, hearts were subjected to 60 minutes of no-flow ischemia, followed by 60 minutes of reperfusion. At 15 minutes after the onset of reperfusion, there was poor recovery of left ventricular developed pressure to 64% of the control level, but myocardial oxygen consumption was increased to 134% of control. The addition of 2.5 μM ruthenium red to the perfusate resulted in a decrease of myocardial oxygen consumption. The oxygen consumption rate in state 3 of mitochondria decreased similarly following reperfusion in control and ruthenium red hearts. The mitochondrial membrane potential was reduced to 89% (logarithmic scale) after 15 minutes of reperfusion and then returned to preischemic level. These data suggest that the dissociation between oxygen consumption and contractile function following early reperfusion is partly caused by the repair of intracellular damage resulting from calcium accumulation to mitochondria.

Production of Hydrogen Peroxide During Hypoxia-Reoxygenation in Isolated Myocytes

Active oxygen species, including hydrogen peroxide (H2O2), have been implicated in myocardial reperfusion injury. Recently, spin-trap agents and biochemical techniques applied to intact hearts have shown that H2O2 is generated by leukocytes, by endothelial cells, and by mitochondria in myocytes. In this study, we used electron microscopy and the cerium (Ce) method to histologically investigate H2O2 formation during hypoxia—reoxygenation and its toxic effects on myocardium. This Ce method involves the formation of an electron-dense precipitate when H2O2 reacts with cerium chloride (CeCl3). Single myocytes were obtained from rat hearts by the collagenase method. Isolated myocytes were reoxygenated for 15 minutes after 30 minutes of hypoxia. Digitonin and CeCl3, were added to make cell membranes permeable and to detect intracellular H2O2 by electron microscopy. In the control group, the ultrastructure was well preserved and no dense deposits were found in myocytes. However, in the hypoxia—reoxygenation group, precipitates, which were cerium—H2O2 reaction products, were found along swollen mitochondria. Moreover, in the hypoxia-reoxygenation group, cell viability was reduced to 72% of control. These results indicate that H2O2 is generated by mitochondria and that its relese into cytosol may lead to myocyte death during hypoxia—reperfusion.