Fumio Terasaki

Oxidative stress in skeletal muscle impairs mitochondrial respiration and limits exercise capacity in type 2 diabetic mice

Insulin resistance or diabetes is associated with limited exercise capacity, which can be caused by the abnormal energy metabolism in skeletal muscle. Oxidative stress is involved in mitochondrial dysfunction in diabetes. We hypothesized that increased oxidative stress could cause mitochondrial dysfunction in skeletal muscle and make contribution to exercise intolerance in diabetes. C57/BL6J mice were fed on normal diet or high fat diet (HFD) for 8 wk to induce obesity with insulin resistance and diabetes. Treadmill tests with expired gas analysis were performed to determine the exercise capacity and whole body oxygen uptake (Vo(2)). The work (vertical distance x body weight) to exhaustion was reduced in the HFD mice by 36%, accompanied by a 16% decrease of peak Vo(2). Mitochondrial ADP-stimulated respiration, electron transport chain complex I and III activities, and mitochondrial content in skeletal muscle were decreased in the HFD mice. Furthermore, superoxide production and NAD(P)H oxidase activity in skeletal muscle were significantly increased in the HFD mice. Intriguingly, the treatment of HFD-fed mice with apocynin [10 mmol/l; an inhibitor of NAD(P)H oxidase activation] improved exercise intolerance and mitochondrial dysfunction in skeletal muscle without affecting glucose metabolism itself. The exercise capacity and mitochondrial function in skeletal muscle were impaired in type 2 diabetes, which might be due to enhanced oxidative stress. Therapies designed to regulate oxidative stress and maintain mitochondrial function could be beneficial to improve the exercise capacity in type 2 diabetes.

Angiotensin II receptor blockade prevents microangiopathy and preserves diastolic function in the diabetic rat heart

Background: Cardiac microangiopathy may be involved in the development of heart failure in diabetes mellitus. Objective: To evaluate the effect of angiotensin II receptor blockade on cardiac function and fine structures in diabetes. Methods: Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 30), a model of spontaneously developing diabetes mellitus, and their diabetes resistant counterparts (n = 20) were used. At 30 weeks of age, when the OLETF rats show hyperglycaemic obesity with hyperinsulinaemia, the animals were divided into two groups and given candesartan, an angiotensin II receptor blocker, 0.2 mg/kg/day, or vehicle for six weeks. Capillary density was evaluated in the left ventricular myocardium by electron microscopy, matrix metalloproteinase (MMP) activity by zymography, and cytokines by reverse transcriptase polymerase chain reaction. Results: Compared with the control rats, the OLETF rats at 36 weeks showed decreased peak negative dP/dt (mean (SD): 2350 (250) v 3492 (286) mm Hg/s) and increased cardiomyocyte diameter (24.3 (0.6) v 18.9 (0.6) μm) (both p < 0.05). Thickening of the capillary basement membranes and decreased capillary density were observed. Angiotensin receptor blockade improved almost all the haemodynamic variables, and the histological findings became similar to those of the controls. Angiotensin receptor blockade also activated MMP-2 and prevented an increase of inflammatory cytokines, especially interleukin (IL)-1β and IL-6, in the diabetic heart. Conclusions: Angiotensin II receptor blockade preserved left ventricular diastolic function. It was also potent at improving cardiomyocyte diameter and the thickening of the capillary basement membrane, increasing MMP-2 activity, and decreasing inflammatory cytokines. With all these changes, candesartan could contribute to cardioprotection in diabetes mellitus.

Molecular Basis for Clinical Heterogeneity in Inherited Cardiomyopathies Due to Myopalladin Mutations

Abnormalities in Z-disc proteins cause hypertrophic (HCM), dilated (DCM) and/or restrictive cardiomyopathy (RCM), but disease-causing mechanisms are not fully understood. Myopalladin (MYPN) is a Z-disc protein expressed in striated muscle and functions as a structural, signaling and gene expression regulating molecule in response to muscle stress. MYPN was genetically screened in 900 patients with HCM, DCM and RCM, and disease-causing mechanisms were investigated using comparative immunohistochemical analysis of the patient myocardium and neonatal rat cardiomyocytes expressing mutant MYPN. Cardiac-restricted transgenic (Tg) mice were generated and protein-protein interactions were evaluated. Two nonsense and 13 missense MYPN variants were identified in subjects with DCM, HCM and RCM with the average cardiomyopathy prevalence of 1.66%. Functional studies were performed on two variants (Q529X and Y20C) associated with variable clinical phenotypes. Humans carrying the Y20C-MYPN variant developed HCM or DCM, whereas Q529X-MYPN was found in familial RCM. Disturbed myofibrillogenesis with disruption of α-actinin2, desmin and cardiac ankyrin repeat protein (CARP) was evident in rat cardiomyocytes expressing MYPN(Q529X). Cardiac-restricted MYPN(Y20C) Tg mice developed HCM and disrupted intercalated discs, with disturbed expression of desmin, desmoplakin, connexin43 and vinculin being evident. Failed nuclear translocation and reduced binding of Y20C-MYPN to CARP were demonstrated using in vitro and in vivo systems. MYPN mutations cause various forms of cardiomyopathy via different protein-protein interactions. Q529X-MYPN causes RCM via disturbed myofibrillogenesis, whereas Y20C-MYPN perturbs MYPN nuclear shuttling and leads to abnormal assembly of terminal Z-disc within the cardiac transitional junction and intercalated disc.

ATF6 is important under both pathological and physiological states in the heart

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) evokes the ER stress response, including activating transcription factor 6 (ATF6), a key transcriptional activator to maintain cellular homeostasis. The ER stress has recently been reported to cause various diseases, but the role of ATF6 in the heart remains unknown. We clarified the role of ATF6 in the heart. The ATF6 activity was increased in the murine heart after myocardial infarction (MI). Treatment of mice with 4-(2-aminoethyl) benzenesulfonyl fluoride, an inhibitor of ATF6, further reduced cardiac function and increased the mortality rate at 14days after MI. Pharmacological inhibition of ATF6 induced dilatation of left ventricle and depression of cardiac function even in sham-operated murine hearts. The transgenic mice that expressed dominant negative mutant of ATF6 showed larger left ventricular dimension and reduced fractional shortening compared with wild-type littermates, resulting in death of heart failure at approximately 8weeks of age. In contrast, cardiac function after MI was better in transgenic mice that expressed constitutively active mutant of ATF6, compared with wild-type littermates. These results suggest that activation of the ER stress response factor ATF6 plays a critical role in not only protecting hearts under the pathological state but also maintaining cardiac function under the physiological state.

Angiotensin II Type 1a Receptor Is Involved in Cell Infiltration, Cytokine Production, and Neovascularization in Infarcted Myocardium

Objective—Angiotensin II is critically involved in left ventricular remodeling after myocardial infarction. Neovascularization has been thought to prevent the development of left ventricular remodeling and deterioration to heart failure. To elucidate the role of angiotensin II in neovascularization during cardiac remodeling, we induced myocardial infarction in angiotensin II type1a receptor (AT1) knockout (KO) mice. Methods and Results—There were more vessels in the border zone of infarcted hearts of wild-type (WT) mice and AT1KO mice at 14 days after operation, compared with in the left ventricle of sham-operated mice, and the number was larger in WT mice than in AT1KO mice. Consistent with these observations, the infarcted heart of AT1KO mice expressed lower levels of matrix metalloproteinase and endothelial nitric oxide synthase activity. More inflammatory cells such as granulocytes and macrophages were infiltrated in the infarcted hearts of WT mice than AT1KO mice at 4 days. A variety of cytokines and chemokines were increased in infarcted hearts of WT and AT1KO mice, and many of them were more remarkable in WT mice than in AT1KO mice at 14 days. Conclusions—AT1 plays a critical role in inflammatory cell infiltration, cytokine production, and neovascularization in infarcted hearts.

Increased serum levels and expression of S100A8/A9 complex in infiltrated neutrophils in atherosclerotic plaque of unstable angina

Background: The S100A8/A9 complex is expressed in a subset of activated neutrophils and macrophages in acute inflammatory lesions associated with various diseases. Objective: To investigate (a) whether serum S100A8/A9 levels are increased in patients with unstable angina (UA); and (b) whether S100A8/A9 expression is upregulated in coronary atherosclerotic plaques of patients with UA. Design: Serum S100A8/A9 levels in 39 patients with stable angina (SA) and 53 patients with UA were measured. In addition, the presence of the S100A8/A9 complex in directional coronary atherectomy specimens was studied immunohistochemically. Cell types which stain positive for S100A8/A9 were identified by immunodouble staining with neutrophils and macrophages. Results: Mean (SD) serum S100A8/A9 levels were significantly higher in patients with UA than in those with SA (3.25 (3.08) μg/ml vs 0.77 (0.31) μg/ml, p<0.05). In patients with UA, immunodouble staining clearly showed that the S100A8/A9 complex was expressed in infiltrated neutrophils and occasional macrophages. The S100A8/A9-positive area was significantly higher in UA than in SA (mean (SD) 18.3 (14.2)% vs 1.3 (2.4)%, respectively, p<0.001). Conclusions: The S100A8/A9 complex may be involved in the inflammatory process of coronary atherosclerotic plaques in patients with UA.

Effect of sulfo-N-succinimidyl palmitate on the rat heart: Myocardial long-chain fatty acid uptake and cardiac hypertrophy

Abnormal long-chain fatty acid metabolism has been suggested as having a role in the genesis of certain cardiac diseases, and depressed myocardial long-chain fatty acid uptake has been clinically demonstrated in some patients with hypertrophic cardiomyopathy. However, the site where long-chain fatty acid metabolism is affected in cardiomyopathy remains unclear. Although cardiac hypertrophy is reported to be induced in rats by a fat-free diet, little is known of the consequences of depressed myocardial long-chain fatty acid uptake. Sulfo-N-succinimidyl derivatives of long-chain fatty acids have been shown to irreversibly inhibit long-chain fatty acid transport. To investigate the possible linkage of abnormal long-chain fatty acid uptake with cardiac hypertrophy, myocardial long-chain fatty acid uptake was blocked in rats using a sulfo-N-succinimidyl derivative of palmitate (SSP). SSP was intraperitoneally administered to rats for 12 weeks, and its effects on physiological parameters, and cardiac morphology were studied, SSP treatment (20 mg/kg) caused a 12% increase in heart weight (663.7 +/- 33.6 mg in controls v 741.2 +/- 26.5 mg after SSP treatment) and an 11% increase in the heart weight to body weight ratio (2.46 +/- 0.10 in controls v 2.72 +/- 0.17 after SSP) without any significant change of body weight. No significant differences were observed in blood pressure, heart rate, and serum hormones (insulin and triiodothyronine) between the control and SSP-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Incremental Prognostic Values of Serum Tenascin-C Levels With Blood B-type Natriuretic Peptide Testing at Discharge in Patients With Dilated Cardiomyopathy and Decompensated Heart Failure

BACKGROUND This study investigates the predictive value of serum tenascin-C (TN-C), which is observed at the active sites of ongoing tissue remodeling, for cardiac events of patients with dilated cardiomyopathy (DCM). METHODS AND RESULTS In this trial, 110 consecutive patients hospitalized with heart failure (HF) resulting from DCM underwent assessments of serum TN-C and plasma brain natriuretic peptide (BNP) levels at discharge and were followed up for 22.4 months. Cardiac function and hemodynamics were assessed invasively in 60 of these patients at discharge. There were 19 cardiac events (14 rehospitalizations, 3 deaths from refractory HF, and 2 sudden deaths) during follow-up. The average levels of TN-C and BNP were 73 +/- 38 ng/mL and 279 +/- 414 pg/mL, respectively. The optimal cutoff value for serum TN-C levels predicted cardiac events were >or=78.4 ng/mL, whereas BNP levels were >or=219 pg/mL. Patients with levels higher than this had significantly higher cardiac events and serum TN-C >or=78.4 ng/mL had an incremental predictive power with BNP for cardiac events. Left ventricular end-diastolic volume was significantly larger, and mean pulmonary arterial pressure was elevated in patients with serum TN-C >or=78.4 ng/mL. CONCLUSIONS The combined index of serum levels for TN-C and BNP at discharge predicts cardiac events from decompensated HF. Additionally, elevated serum TN-C levels reflect left ventricular and pulmonary vascular remodeling in DCM patients.

A Case of Cardiomyopathy Showing Progression From the Hypertrophic to the Dilated Form

This report describes a case of cardiomyopathy with a novel point mutation of mitochondrial DNA coding lysine tRNA in association with severe ultrastructural alterations of the mitochondria in the cardiomyocytes. Abnormalities of energy production and/or abnormal protein synthesis because of the mutation of mitochondrial DNA may have played an important role in the pathogenesis of this case, which showed severe cardiomyocyte degeneration and deterioration from hypertrophic cardiomyopathy to severe dilated cardiomyopathy.

Evolution to dilated cardiomyopathy from acute eosinophilic pancarditis in Churg-Strauss syndrome

SummaryWe describe the clinical manifestations of a patient with Churg-Strauss syndrome who presented with severe acute cardiac involvement and whose disease evolved to dilated cardiomyopathy (DCM), with special reference to the histopathological findings. Endomyocardial biopsies, conducted sequentially, three times within 10 months, revealed severe eosinophilic endomyocarditis in the acute phase, interstitial fibrosis in the subacute phase, and endocardial thickening with mural thrombi, at 10 months. Although acute inflammation associated with elevation of eosinophil granule proteins subsided with steroid therapy, left ventricular dilatation with reduced contractility progressed. A subgroup of DCM is not considered to be idiopathic but, rather, an aftereffect of hypereosinophilic heart disease.