Shinji Inaba

Clinical significance of global two-dimensional strain as a surrogate parameter of myocardial fibrosis and cardiac events in patients with hypertrophic cardiomyopathy

AIMS Late gadolinium enhancement (LGE) on contrast-enhanced magnetic resonance imaging (MRI) in hypertrophic cardiomyopathy (HCM) has been reported to be associated with myocardial fibrosis and cardiac events. In patients with HCM, two-dimensional (2D) strain can identify subclinical global systolic dysfunction despite normal left ventricular (LV) chamber function. Therefore, this study tested the hypothesis that global 2D strain could detect subtle myocardial fibrosis and serve as a novel prognostic parameter in HCM patients. METHODS AND RESULTS Echocardiography and MRI were performed in 48 consecutive patients with HCM and normal chamber function. We measured global longitudinal strain (GLS) in apical two-chamber, four-chamber, and long-axis views using speckle-tracking analysis. The extent of LGE (%LGE = LGE volume/total LV volume) and LV mass index were calculated by MRI using Simpsons rule and custom software. All patients were followed up for major cardiac events. Global longitudinal strain in patients with LGE was significantly lower than that without LGE (-11.8 ± 2.8 vs. -15.0 ± 1.7%, P < 0.001). Multivariate analysis showed that GLS was an independent predictor of %LGE (standard coefficient = 0.627, P < 0.001). During a mean follow-up period of 42 ± 12 months, five patients had cardiac events. When the patients were stratified based on the median level of GLS (-12.9%), all events were observed in the worse GLS group (P = 0.018). CONCLUSION These results suggest that global 2D strain might provide useful information on myocardial fibrosis and cardiac events in HCM patients with normal chamber function.

Continuous Activation of Renin-Angiotensin System Impairs Cognitive Function in Renin/Angiotensinogen Transgenic Mice

We examined the possibility that continuous activation of the human brain renin-angiotensin system causes cognitive impairment, using human renin (hRN) and human angiotensinogen (hANG) gene chimeric transgenic (Tg) mice. Cognitive function was evaluated by the shuttle avoidance test once a week from 10 to 20 weeks of age. The avoidance rate in wild-type mice gradually increased. In contrast, the avoidance rate in chimeric hRN/hANG-Tg mice also increased; however, no further increase in avoidance rate was observed from 14 weeks of age, and it decreased thereafter. Cerebral surface blood flow was markedly reduced in 20-week-old hRN/hANG-Tg mice. Superoxide anion production in the brain was already higher in 10-week-old hRN/hANG-Tg mice and further increased thereafter with an increase in NADPH oxidase activity. Moreover, expression of p47phox and Nox4 in the brain of hRN/hANG-Tg mice also increased. Administration of an angiotensin II type 1 receptor blocker, olmesartan (5.0 mg/kg per day), attenuated the increase in blood pressure and ameliorated cognitive decline with enhancement of cerebral surface blood flow and a reduction of oxidative stress in hRN/hANG-Tg mice. On the other hand, hydralazine (0.5 mg/kg per day) did not improve the decrease in avoidance rate, and did not influence cerebral surface blood flow or oxidative stress in hRN/hANG-Tg mice, in spite of a similar reduction of blood pressure to that by olmesartan. Moreover, we observed that treatment with Tempol improved impaired cognitive function in hRN/hANG-Tg mice. These results suggest that continuous activation of the brain renin-angiotensin system impairs cognitive function via stimulation of the angiotensin II type 1 receptor with a decrease in cerebral surface blood flow and an increase in oxidative stress.

Blockade of AT1 Receptor Improves Adipocyte Differentiation in Atherosclerotic and Diabetic Models

BACKGROUND The roles of the angiotensin (Ang) II type 1 (AT(1)) receptor in the changes in white adipose tissue were explored in an animal model of atherosclerosis using apolipoprotein E-deficient (ApoEKO) mice. METHODS Apolipoprotein E-deficient (ApoEKO) mice and KK-A(y) mice were used. Expression of markers for adipocyte differentiation and inflammation was determined by real-time reverse-transcription polymerase chain reaction. RESULTS Adipose tissue weight and adipocyte size in epididymal white adipose tissue were increased in ApoEKO mice and KK-A(y) mice. In the adipose tissue of these models, expression of adiponectin and peroxisome proliferator-activated receptor-gamma (PPARgamma), which induce adipocyte differentiation, and expression of transcription factors of adipocyte differentiation, such as CCAAT-enhancer-binding protein-alpha (C/EBPalpha) and aP2, were decreased. Expression of inflammatory markers and nicotinamide adenine dinucleotide phosphate oxidase subunits was also increased. Deletion of AT(1)a receptor in ApoEKO mice and administration of an AT(1) receptor blocker, valsartan, to KK-A(y) mice reduced epididymal adipose tissue weight and adipocyte size significantly. Blockade of the AT(1) receptor also reduced the expression of inflammatory chemokines and oxidative stress markers. Moreover, AT(1)a receptor deletion in ApoEKO mice and AT(1) receptor blockade in KK-A(y) mice prevented the decrease in expression of adiponectin, PPARgamma, C/EBPalpha, and aP2. Valsartan also increased glucose uptake induced by insulin in adipose tissue of KK-A(y) mice. CONCLUSIONS These results suggest that enlargement and weakened differentiation of adipocytes are observed in atherosclerosis and diabetes, and that AT(1) receptor blockade prevented adipocyte enlargement and promoted adipocyte differentiation in these models.

Direct renin inhibition improved insulin resistance and adipose tissue dysfunction in type 2 diabetic KK-Ay mice

Objective The renin–angiotensin system affects insulin sensitivity mainly through the angiotensin II type 1 receptor. In this study, the effects of renin inhibition on insulin resistance and adipose tissue dysfunction were explored in type 2 diabetic KK-Ay mice. Methods and results Male KK-Ay mice were treated with a direct renin inhibitor, aliskiren, administered subcutaneously at a dose of 50 mg/kg per day for 14 days using an osmotic minipump. This dose of aliskiren strongly inhibited plasma renin activity and lowered blood pressure about 17% in KK-Ay mice. Aliskiren decreased body weight and plasma glucose level, and increased plasma insulin level in a fed condition. Aliskiren also lowered the plasma levels of cholesterol, fatty acids and triglycerides. In the oral glucose tolerant test, the plasma glucose elevation after glucose load was reduced by aliskiren, without a significant change in insulin level. Insulin tolerance test showed that aliskiren enhanced insulins effect on plasma glucose. Aliskiren also reduced the epididymal adipose tissue mass by 25% and retroperitoneal adipose tissue mass by 35%. In adipose tissue, expression of the insulin receptor was not changed by aliskiren; however, expression of insulin receptor substrate-1, glucose transporter type 4, adiponectin, peroxisome proliferator-activated receptor-gamma and CCAAT/enhancer-binding proteinδ was increased by aliskiren. Moreover, NADPH oxidase activity and expression of inflammatory factors were reduced in adipose tissue. Aliskiren increased the pancreatic β-cell area in KK-Ay mice. Conclusion These results suggest that renin inhibition by aliskiren improved insulin resistance and adipose tissue dysfunction in type 2 diabetic mice through an increase in insulin sensitivity, insulin secretion and adipocyte differentiation, and a reduction of oxidative stress.

AT2 Receptor Deficiency Attenuates Adipocyte Differentiation and Decreases Adipocyte Number in Atherosclerotic Mice

BACKGROUND Previous reports indicated that blockade of AT(1) receptor stimulation attenuated adipocyte dysfunction. However, the effects of AT(2) receptor stimulation on adipose tissue were not yet clear. In the present study, we examined the adipose tissue dysfunction in atherosclerotic apolipoprotein E knockout (ApoEKO) mice with AT(2) receptor deficiency. METHODS Male ApoEKO and AT(2) receptor/ApoE knockout (AT(2)/ApoEKO) mice at 6 weeks of age were treated with a normal diet or a high-cholesterol diet (HCD: 1.25% cholesterol). Markers for adipocyte differentiation and inflammation in adipose tissue were assayed with real-time reverse-transcription-PCR and western blot. RESULTS Compared with ApoEKO mice, AT(2)/ApoEKO mice with a normal diet showed only a decrease in expression of adiponectin and CCAAT/enhancer binding protein delta (C/EBPdelta) in epididymal adipose tissue without changes in body weight, adipose tissue weight, and adipocyte number even at 6 months of age. After HCD for 4 weeks, the weight of both epididymal and retroperitoneal adipose tissue in AT(2)/ApoEKO mice was greater than that in ApoEKO mice without a change in body weight. Plasma concentrations of cholesterol and fatty acids were higher in AT(2)/ApoEKO mice than in ApoEKO mice. In adipose tissue of AT(2)/ApoEKO mice, the adipocyte number was decreased and the expression of peroxisome proliferator-activated receptor gamma (PPARgamma), C/EBPalpha, and aP2 was lower than that in ApoEKO mice, in association with an increase in nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. CONCLUSIONS These results suggest that AT(2) receptor stimulation in adipose tissue is involved in the improvement of adipocyte differentiation and adipose tissue dysfunction in atherosclerotic model.

Exaggeration of Focal Cerebral Ischemia in Transgenic Mice Carrying Human Renin and Human Angiotensinogen Genes

Background and Purpose— We examined the possibility that activation of the human brain renin–angiotensin system is involved in enhancement of ischemic brain damage using chimeric transgenic mice with human renin (hRN) and human angiotensinogen (hANG) genes. Methods— Chimeric (hRN/hANG-Tg) mice were generated by mating of hRN and hANG transgenic mice. Permanent occlusion of the middle cerebral artery (MCA) by an intraluminal filament technique induced focal ischemic brain lesions. Results— hRN/hANG-Tg mice showed higher angiotensin II levels in the plasma and brain. The ischemic brain area at 24 hours after MCA occlusion was significantly enlarged in hRN/hANG-Tg mice with an enhanced neurological deficit compared to that in wild-type, hRN-Tg and hANG-Tg mice. The reduction of cerebral blood flow in the periphery region of the MCA territory after MCA occlusion was markedly exaggerated in hRN/hANG-Tg mice. Superoxide anion production in the brain and arteries was also increased significantly in hRN/hANG-Tg mice even before MCA occlusion and was further enhanced after MCA occlusion. Treatment with an AT1 receptor blocker, valsartan (3.0 mg/kg per day), for 2 weeks significantly reduced the ischemic brain area and improved the neurological deficit after MCA occlusion in hRN/hANG-Tg mice, similar to those in wild-type, hRN-Tg, and hANG-Tg mice, with restoration of cerebral blood flow in the peripheral region and decreases in superoxide anion production and blood pressure. Conclusions— These results indicate that activation of the human renin–angiotensin system exaggerates ischemic brain damage mainly through stimulation of the AT1 receptor and marked reduction of cerebral blood flow and enhanced oxidative stress.

Effect of cilostazol on vasomotor reactivity in patients with vasospastic angina pectoris

We examined the effects of cilostazol on impaired coronary arterial responses in patients with vasospastic angina (VSA). Thirty patients who were diagnosed with VSA based on an acetylcholine provocation test and 10 subjects with normal coronary arteries were enrolled. The patients were divided into the following 3 groups: no antiplatelet agent treatment group, aspirin treatment, or cilostazol treatment groups. Coronary flow reserve (CFR), coronary flow volume at maximum hyperemia, and epicardial coronary artery diameter after administration of N(G)-monomethyl-L-arginine (L-NMMA) were examined using a Doppler flow wire before and 6 months after the start of this study. CFR, coronary flow volume at maximum hyperemia, and diameter changes by L-NMMA were significantly increased in the cilostazol treatment group compared with the other 2 groups. In conclusion, cilostazol increased CFR and flow-dependent coronary dilation; these changes were attributable to nitric oxide. Cilostazol may improve coronary vascular endothelial dysfunction and coronary hemodynamics in patients with VSA.

Prevention of Vascular Injury by Combination of an AT1 Receptor Blocker, Olmesartan, With Various Calcium Antagonists

BACKGROUND A combination of different types of antihypertensive drugs is widely used for the treatment of hypertension. We examined the inhibitory effects of a combination of an AT(1) receptor blocker (ARB), olmesartan, with various calcium channel blockers (CCBs) on inflammatory vascular remodeling. METHODS Inflammatory vascular remodeling was induced by polyethylene-cuff placement around the femoral artery of C57BL/6J mice at 10 weeks of age. Olmesartan (0.5 mg/kg/day) was administered intraperitoneally using an osmotic minipump. CCBs (nifedipine 1.0 mg/kg/day, amlodipine 0.1 mg/kg/day, azelnidipine 0.1 mg/kg/day), and hydrochlorothiazide (HCTZ 0.5 mg/kg/day) were administered orally. RESULTS In the injured artery, superoxide anion production and expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits p47(phox) and Rac-1 were markedly increased, together with expression of monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor (TNF)-alpha. Administration of a single drug alone at each concentration did not significantly inhibit these changes in the injured artery. However, a combination of olmesartan with various CCBs inhibited neointimal formation as well as oxidative stress and inflammatory markers in the injured artery. Moreover, among these CCBs, inhibition of these markers by olmesartan with azelnidipine was stronger than that caused by a combination with other CCBs. On the other hand, a combination of subeffective doses of olmesartan and HCTZ did not significantly affect vascular changes after cuff placement. CONCLUSIONS These results suggest that the combination of ARB with CCB synergistically inhibits vascular remodeling and that the inhibitory actions of ARB on vascular remodeling may vary depending on the combined CCB.

Role of angiotensin-converting enzyme 2 in cardiac hypertrophy induced by nitric oxide synthase inhibition.

Objective Angiotensin-converting enzyme 2 (ACE2) generates angiotensin-(1–7) [Ang-(1–7)], a peptide highlighted as exerting a pivotal role in cardiovascular remodeling. Moreover, the ACE2/Ang-(1–7)/Mas axis directly activates endothelial nitric oxide (NO) synthase and NO generation in the heart. However, the role of ACE2 in cardiovascular remodeling induced by persistent inhibition of NO under chronic activation of the renin–angiotensin system (RAS) remains poorly understood. Methods and results Chimeric hypertensive mice that exhibit activation of the human RAS were produced by mating human renin (hRN) and human angiotensinogen (hANG) transgenic mice. Persistent NO inhibition with NG-nitro-L-arginine methyl ester (L-NAME) was started at 8 weeks of age for 4 weeks. After administration of L-NAME, blood pressure (BP) markedly increased in the chimeric mice (hRN/hANG-Tg), whereas wild-type mice (C57BL/6J) showed little increase in BP. Cardiovascular remodeling with enhanced oxidative stress in hRN/hANG-Tg was markedly accelerated by NO inhibition compared with that in wild-type mice. Moreover, ACE2 mRNA expression and activity in cardiac tissue were markedly reduced in L-NAME-treated hRN/hANG-Tg. Co-administration of an angiotensin II type 1 (AT1) receptor blocker (ARB), olmesartan, inhibited L-NAME-induced cardiovascular remodeling and improved the reduction in cardiac ACE2. The preventive effect of olmesartan on cardiac hypertrophy was blunted by co-administration of a selective Ang-(1–7) antagonist, [D-Ala7]-Ang-(1–7). Conclusion Our findings demonstrate that cardiovascular remodeling induced by persistent NO inhibition was enhanced in hRN/hANG-Tg. An ARB, olmesartan, blunted cardiac remodeling induced by NO inhibition with RAS activation partially through the ACE2/Ang-(1–7)/Mas axis in addition to directly through its classical ACE/Ang II/AT1 receptor axis-blocking action.

The differences in left ventricular torsional behavior between patients with hypertrophic cardiomyopathy and hypertensive heart disease.

BACKGROUND The aim of this study was to investigate the differences in left ventricular (LV) twisting behavior between patients with hypertrophic cardiomyopathy (HCM) and hypertensive heart disease (HHD). METHODS Forty-four patients with HCM (mean age, 63±15 years), 35 patients with HHD (mean age, 63±13 years) and 20 age and sex-matched control subjects were evaluated. After a standard echocardiographic examination, LV twist and twisting velocity profiles from apical and basal short-axis images were analyzed using two-dimensional speckle tracking imaging. RESULTS LV diastolic and systolic dimensions, and ejection fraction were not significantly different among the groups. LV mass index and early diastolic mitral annular velocity were not significantly different between the HCM and HHD groups. The peak torsion in the HCM and HHD groups was significantly greater than that in the control group. The peak untwisting velocity in the HCM group was comparable with that in the control group. However, when the peak untwisting velocity was corrected by peak torsion, this ratio was significantly decreased in the HCM group compared with the values in the HHD and control groups. The time to peak untwisting velocity in the HCM group was significantly longer than the values in the HHD and control groups. CONCLUSIONS These results suggest that enhanced peak torsion in HCM may improve untwisting behavior, but this mechanism fails to fully compensate for impaired untwisting behavior compared with HHD.