Shinichiro Niizuma

Analysis of Metabolic Remodeling in Compensated Left Ventricular Hypertrophy and Heart Failure

Background—Congestive heart failure (CHF) is associated with a change in cardiac energy metabolism. However, the mechanism by which this change is induced and causes the progression of CHF is unclear. Methods and Results—We analyzed the cardiac energy metabolism of Dahl salt-sensitive rats fed a high-salt diet, which showed a distinct transition from compensated left ventricular hypertrophy to CHF. Glucose uptake increased at the left ventricular hypertrophy stage, and glucose uptake further increased and fatty acid uptake decreased at the CHF stage. The gene expression related to glycolysis, fatty acid oxidation, and mitochondrial function was preserved at the left ventricular hypertrophy stage but decreased at the CHF stage and was associated with decreases in levels of transcriptional regulators. In a comprehensive metabolome analysis, the pentose phosphate pathway that regulates the cellular redox state was found to be activated at the CHF stage. Dichloroacetate (DCA), a compound known to enhance glucose oxidation, increased energy reserves and glucose uptake. DCA improved cardiac function and the survival of the animals. DCA activated the pentose phosphate pathway in the rat heart. DCA activated the pentose phosphate pathway, decreased oxidative stress, and prevented cell death of cultured cardiomyocytes. Conclusions—Left ventricular hypertrophy or CHF is associated with a distinct change in the metabolic profile of the heart. DCA attenuated the transition associated with increased energy reserves, activation of the pentose phosphate pathway, and reduced oxidative stress.

Suppression of Phosphoinositide 3-Kinase Prevents Cardiac Aging in Mice

Background— Heart failure is a typical age-associated disease. Although age-related changes of heart are likely to predispose aged people to heart failure, little is known about the molecular mechanism of cardiac aging. Methods and Results— We analyzed age-associated changes in murine heart and the manner in which suppression of the p110&agr; isoform of phosphoinositide 3-kinase activity modified cardiac aging. Cardiac function declined in old mice associated with the expression of senescence markers. Accumulation of ubiquitinated protein and lipofuscin, as well as comprehensive gene expression profiling, indicated that dysregulation of protein quality control was a characteristic of cardiac aging. Inhibition of phosphoinositide 3-kinase preserved cardiac function and attenuated expression of the senescence markers associated with enhanced autophagy. Suppression of target of rapamycin, a downstream effector of phosphoinositide 3-kinase, also prevented lipofuscin accumulation in the heart. Conclusions— Suppression of phosphoinositide 3-kinase prevented many age-associated changes in the heart and preserved cardiac function of aged mice.

Constitutive SIRT1 overexpression impairs mitochondria and reduces cardiac function in mice.

Heart failure is associated with a change in cardiac energy metabolism. SIRT1 is a NAD(+)-dependent protein deacetylase, and important in the regulation of cellular energy metabolism. To examine the role of SIRT1 in cardiac energy metabolism, we created transgenic mice overexpressing SIRT1 in a cardiac-specific manner, and investigated cardiac functional reserve, energy reserve, substrate uptake, and markers of mitochondrial function. High overexpression of SIRT1 caused dilated cardiomyopathy. Moderate overexpression of SIRT1 impaired cardiac diastolic function, but did not cause heart failure. Fatty acid uptake was decreased and the number of degenerated mitochondria was increased dependent on SIRT1 gene dosage. Markers of reactive oxygen species were decreased. Changes in morphology and reactive oxygen species were associated with the reduced expression of genes related to mitochondrial function and autophagy. In addition, the respiration of isolated mitochondria was decreased. Cardiac function was normal in transgenic mice expressing a low level of SIRT1 at baseline, but the mice developed cardiac dysfunction upon pressure overload. In summary, the constitutive overexpression of SIRT1 reduced cardiac function associated with impaired mitochondria in mice.

Impact of Left Ventricular End-Diastolic Wall Stress on Plasma B-Type Natriuretic Peptide in Heart Failure with Chronic Kidney Disease and End-Stage Renal Disease

BACKGROUND Plasma B-type natriuretic peptide (BNP) is a diagnostic and prognostic marker in heart failure (HF). Although renal function is reported as an important clinical determinant, precise evaluations of the relationships of renal function with hemodynamic factors in determining BNP have not been performed. Therefore, we evaluated the association of plasma BNP concentrations with LV end-diastolic wall stress (EDWS) in a broad range of HF patients including those with chronic kidney disease (CKD) and end-stage renal disease (ESRD). METHODS In 156 consecutive HF patients including those with CKD and ESRD, we measured plasma BNP and performed echocardiography and cardiac catheterization. LV EDWS was calculated as a crucial hemodynamic determinant of BNP. RESULTS Plasma BNP concentrations increased progressively with decreasing renal function across the groups (P < 0.01) and were correlated with LV EDWS (r = 0.47) in the HF patients overall. This relationship was also present when patients were subdivided into systolic and diastolic HF (P < 0.01). In multivariable analysis, higher EDWS was associated with increased BNP concentration independently of renal dysfunction (P < 0.01). Anemia, systolic HF, and decreased BMI also contributed to increased BNP concentrations. CONCLUSIONS These results suggest that LV EDWS is a strong determinant of BNP even in patients with CKD and ESRD. Anemia, obesity, and HF type (systolic or diastolic) should also be considered in interpreting plasma BNP concentrations in HF patients. These findings may contribute to the clinical management of HF patients, especially those complicated with CKD and ESRD.

Metastasis-associated protein, S100A4 mediates cardiac fibrosis potentially through the modulation of p53 in cardiac fibroblasts

Metastasis-associated protein, S100A4 is suggested as a marker for fibrosis in several organs. It also modulates DNA binding of p53 and affects its function. However, the functional role of S100A4 in the myocardium has remained unclear. Therefore, we investigated the role of S100A4 and its relationship with p53 in cardiac fibrosis. In Dahl-rat hypertensive heart disease model, S100A4 was upregulated in the hypertrophic myocardium and further activated during transition to heart failure (HF). It was expressed in various cells including fibroblasts. In in vitro cardiac fibroblasts, the knockdown of S100A4 significantly suppressed both cell proliferation and collagen expressions. S100A4 co-localized and interacted with p53 in the nucleus. S100A4 knockdown increased the expression of p53-downstream genes, p21 and mdm2, and concomitant knockdown of p53 recovered cell proliferation and collagen expression. Transverse aortic constriction (TAC) was performed in S100A4 knockout (KO) mice, which showed a similar baseline-phenotype to wild type (WT) mice. Although there was no difference in hypertrophic response, KO mice showed reduced interstitial fibrosis, decreased myofibroblasts, and suppressed expressions of collagens and profibrotic cytokines in the left ventricle. Also, DNA microarray analysis showed that S100A4 knockout in vivo had a significant impact on expressions of p53-associated genes. These findings suggest that S100A4 modulates p53 function in fibroblasts and thereby mediates myocardial interstitial fibrosis through two distinct mechanisms; cell proliferation and collagen expression. Blockade of S100A4 may have therapeutic potential in cardiac hypertrophy and HF by attenuating cardiac fibrosis.

Analysis of liver metabolism in a rat model of heart failure

BACKGROUND Cachexia, namely body wasting, is a common complication in cases of congestive heart failure (CHF). Although, neurohumoral and immune abnormalities are associated with the condition, precisely how the imbalance of catabolism and anabolism is responsible for the wasting process is not known. METHODS We analyzed markers of cachexia in Dahl salt-sensitive rats which show marked hypertension with preserved systolic function at 11 weeks and CHF at 17-19 weeks of age. We also analyzed the change in hepatic metabolism associated with CHF since liver plays a central role in the systemic regulation of catabolism and anabolism. RESULTS In CHF rats, a failure to grow was observed and blood hepatic protein levels were decreased associated with increased blood proinflammatory cytokine levels, indicating that Dahl rats serve as a model of cardiac cachexia. Food intake was reduced, and blood sugar and insulin levels were decreased. Despite the apparent fasting condition, blood fatty acid levels were decreased and triglycerides levels were increased. In CHF rats, liver incorporated more glucose, the gene expression related to gluconeogenesis was decreased, the gene expression related to lipogenesis was increased, and the triglyceride content of the liver was increased. The paradoxical production of triglycerides synthesis in fasting rats was associated with a proinflammatory response in liver. CONCLUSIONS The Dahl salt-sensitive rat can be used as a model of cardiac cachexia. The cachexia was associated with abnormal hepatic metabolism that might work as a maladaptive response during the progression of CHF.

Asymptomatic renal infarction, due to fibromuscular dysplasia, in a young woman with 11 years of follow-up.

We report a 27-year-old woman with renovascular hypertension, renal infarction, and hepatic artery aneurysm due to fibromuscular dysplasia. The patient was first noted to have renal artery aneurysm and hepatic artery aneurysm at the age of 17. The renal infarction was asymptomatic and was incidentally detected by magnetic resonance imaging (MRI) examination. Because of the rather peripheral location of the aneurysms, percutaneous transluminal renal artery angioplasty was considered inappropriate. This case suggests the need for long-term and periodical follow-up of patients with fibromuscular dysplasia.

The Cutoff Value of Aldosterone-to-Renin Ratio for the Diagnosis of Primary Aldosteronism in Patients Taking Antihypertensive Medicine

Background. Primary aldosteronism (PA) may account for as much as 6–20% of cases of refractory hypertension referred to hypertension clinics. Because antihypertensive agents affect the physiologic renin-angiotensin-aldosterone system, screening diagnostic tests for PA are generally performed after antihypertensive agents are discontinued. However, such tests can be dangerous for patients with severe hypertension or other cardiovascular complications. However, a reliable cutoff value for the aldosterone-to-renin ratio (ARR) has not been established, especially for Asians, including the Japanese. Method. Fifty-five consecutive patients with clinically suspected PA were evaluated from July 10, 2001, to March 1, 2005, at the National Cardiovascular Center in Japan. Every referred patient was screened prospectively for PA with the ARR at the outpatient clinic. The patients tested continued to be treated with a variety of antihypertensive agents. We reviewed the sensitivity, specificity, and accuracy of the ARR without modifying the antihypertensive agents. The diagnosis of PA was established with the results of both abdominal computed tomography and adrenal scintigraphy. Results. Of the 55 patients, 27 were found to have PA, including adrenal adenoma (n = 18) and bilateral adrenal hyperplasia (n = 9). The mean ARR of patients with PA was significantly higher than that of patients without PA. By assuming a cutoff value of the ARR ≥ 69 calculated from the receiver operating characteristics curve, the highest sensitivity (81%), specificity (82%), positive-predictive value (81%), and negative-predictive value (81%) were obtained. Conclusion. The data suggest that an ARR ≥ 69 strongly indicates PA in Japanese patients with hypertension being treated with antihypertensive agents.

Measurement of Technetium-99m Sestamibi Signals in Rats Administered a Mitochondrial Uncoupler and in a Rat Model of Heart Failure

Background Many methods have been used to assess mitochondrial function. Technetium-99m sestamibi (99mTc-MIBI), a lipophilic cation, is rapidly incorporated into myocardial cells by diffusion and mainly localizes to the mitochondria. The purpose of this study was to investigate whether measurement of 99mTc-MIBI signals in animal models could be used as a tool to quantify mitochondrial membrane potential at the organ level. Methods and Results We analyzed 99mTc-MIBI signals in Sprague-Dawley (SD) rat hearts perfused with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler known to reduce the mitochondrial membrane potential. 99mTc-MIBI signals could be used to detect changes in the mitochondrial membrane potential with sensitivity comparable to that obtained by two-photon laser microscopy with the cationic probe tetramethylrhodamine ethyl ester (TMRE). We also measured 99mTc-MIBI signals in the hearts of SD rats administered CCCP (4 mg/kg intraperitoneally) or vehicle. 99mTc-MIBI signals decreased in rat hearts administered CCCP, and the ATP content, as measured by 31P magnetic resonance spectroscopy, decreased simultaneously. Next, we administered 99mTc-MIBI to Dahl salt-sensitive rats fed a high-salt diet, which leads to hypertension and heart failure. The 99mTc-MIBI signal per heart tissue weight was inversely correlated with heart weight, cardiac function, and the expression of atrial natriuretic factor, a marker of heart failure, and positively correlated with the accumulation of labeled fatty acid analog. The 99mTc-MIBI signal per liver tissue weight was lower than that per heart tissue weight. Conclusion Measurement of 99mTc-MIBI signals can be an effective tool for semiquantitative investigation of cardiac mitochondrial membrane potential in the SD rat model by using a chemical to decrease the mitochondrial membrane potential. The 99mTc-MIBI signal per heart tissue weight was inversely correlated with the severity of heart failure in the Dahl rat model.

Effect of persistent activation of phosphoinositide 3-kinase on heart.

AIMS Insulin/insulin-like growth factor-1 (IGF-1) signaling plays an important role in many biological processes. The class IA isoform of phosphoinositide 3-kinase (PI3K) is an important downstream effector of the insulin/IGF-1 signaling pathway. The aim of this study is to examine the effect of persistent activation of PI3K on gene expression and markers of cellular senescence in murine hearts. MAIN METHODS Transgenic mice expressing a constitutively active PI3K in a heart-specific manner were analyzed at the ages of 3 and 20 months. Effects of persistent activation of PI3K on gene expression were comprehensively analyzed using microarrays. KEY FINDINGS Upon comprehensive gene expression profiling, the genes whose expression was increased included those for several heat shock chaperons. The amount and nuclear localization of a forkhead box O (FOXO) protein was increased. In addition, the gene expression of insulin receptor substrate-2 decreased, and that of phosphatase and tensin homolog deleted on chromosome ten (PTEN) increased, suggesting that the persistent activation of PI3K modified the expression of molecules of insulin/IGF-1 signaling. The expression of markers of cellular senescence, such as senescence-associated beta-galactosidase activity, cell cycle inhibitors, proinflammatory cytokines, and lipofuscin, did not differ between old wild-type and caPI3K mice. SIGNIFICANCE The persistent activation of PI3K modified the expression of molecules of insulin/IGF-1 signaling pathway in a transgenic mouse line. Markers of cellular senescence were not changed in the aged mutant mice.