Kohzo Nagata

Mineralocorticoid Receptor Antagonism Attenuates Cardiac Hypertrophy and Failure in Low-Aldosterone Hypertensive Rats

Chronic elevation of plasma aldosterone contributes to heart failure. Mineralocorticoid receptor (MR) antagonism is cardioprotective in such a setting, but whether such protection occurs in the presence of low-aldosterone concentrations remains unclear. We investigated whether MR blockade attenuates cardiac hypertrophy and failure in rats with salt-sensitive hypertension. Dahl salt-sensitive (DS) rats fed a high-salt diet from 7 weeks develop concentric left ventricular (LV) hypertrophy secondary to hypertension at 12 weeks followed by heart failure at 19 weeks (DS-CHF). DS rats on such a diet were treated with a non-antihypertensive dose of the selective MR antagonist eplerenone from 12 to 19 weeks. Renin activity and aldosterone concentration in plasma were decreased in DS-CHF rats compared with controls. LV hypertrophy and fibrosis, as well as macrophage infiltration around coronary vessels, were apparent in DS-CHF rats. The amounts of mRNAs for 11&bgr;-hydroxysteroid dehydrogenase type 1, MR, monocyte chemoattractant protein 1, and osteopontin were increased in these hearts. Treatment of DS-CHF rats with eplerenone inhibited these changes in gene expression, as well as coronary vascular inflammation and heart failure. Eplerenone attenuated both the decrease in the ratio of reduced to oxidized glutathione and the increase in NADPH oxidase activity apparent in DS-CHF rat hearts. MR blockade with eplerenone thus resulted in attenuation of LV hypertrophy and failure, without an antihypertensive effect, in rats with low-aldosterone hypertension. The beneficial cardiac effects of eplerenone are likely attributable, at least in part, to attenuation of myocardial oxidative stress and coronary vascular inflammation induced by glucocorticoid-activated MRs.

Discrimination of Nonobstructive Hypertrophic Cardiomyopathy From Hypertensive Left Ventricular Hypertrophy on the Basis of Strain Rate Imaging by Tissue Doppler Ultrasonography

Background—The differentiation of hypertrophic cardiomyopathy (HCM) from hypertensive left ventricular hypertrophy (H-LVH) on the basis of morphological information obtained by conventional echocardiography is occasionally problematic. We investigated whether strain rate (SR) imaging derived from tissue Doppler imaging (TDI) is able to discriminate HCM from H-LVH. Methods and Results—Conventional echocardiography and TDI were performed with 34 patients with LVH and 16 reference subjects. Mean values of systolic strain (&egr;sys), peak systolic SR, and early diastolic SR obtained from 8 left ventricular (LV) segments were calculated. LV pressures were recorded simultaneously in the patients. Patients were diagnosed with HCM (n=20) or H-LVH (n=14) on the basis of conventional echocardiography and endomyocardial biopsy findings. Multivariate analysis revealed that septum/posterior wall thickness ratio (P=0.00013) and &egr;sys (P<0.0001) were each able to discriminate HCM from H-LVH. A &egr;sys cutoff value of −10.6% discriminated between HCM and H-LVH with a sensitivity of 85.0%, specificity of 100.0%, and predictive accuracy of 91.2%. The combination of the septum/posterior wall thickness ratio and &egr;sys discriminated HCM from H-LVH with a predictive accuracy of 96.1%. The &egr;sys parameter was significantly correlated with pulmonary arterial wedge pressure, LV end-diastolic pressure, the peak positive first derivative of LV pressure, and the time constant of LV pressure decay. Conclusions—SR imaging is able to discriminate HCM from H-LVH, with &egr;sys reflecting myocardial contractile and lusitropic properties.

Mineralocorticoid Receptor Antagonism Ameliorates Left Ventricular Diastolic Dysfunction and Myocardial Fibrosis in Mildly Symptomatic Patients With Idiopathic Dilated Cardiomyopathy: A Pilot Study

Background— Mineralocorticoid receptor antagonism reduces mortality associated with heart failure by mechanisms that remain unclear. The effects of the mineralocorticoid receptor antagonist spironolactone on left ventricular (LV) function and chamber stiffness associated with myocardial fibrosis were investigated in mildly symptomatic patients with idiopathic dilated cardiomyopathy (DCM). Methods and Results— Twenty-five DCM patients with a New York Heart Association functional class of I or II were examined before and after treatment with spironolactone for 12 months. LV pressures and volumes were measured simultaneously, and LV endomyocardial biopsy specimens were obtained. Serum concentrations of the carboxyl-terminal propeptide (PIP) and carboxyl-terminal telopeptide (CITP) of collagen type I were measured. The patients were divided into 2 groups on the basis of the serum PIP/CITP ratio (≤35, group A, n=12; >35, group B, n=13), an index of myocardial collagen accumulation. LV diastolic chamber stiffness, the collagen volume fraction, and abundance of collagen type I and III mRNAs in biopsy tissue were greater and the LV early diastolic strain rate (tissue Doppler echocardiography) was smaller in group B than in group A at baseline. These differences and the difference in PIP/CITP were greatly reduced after treatment of patients in group B with spironolactone, with treatment having no effect on these parameters in group A. The collagen volume fraction was significantly correlated with PIP/CITP, LV early diastolic strain rate, and LV diastolic chamber stiffness for all patients before and after treatment with spironolactone. Conclusions— Spironolactone ameliorated LV diastolic dysfunction and reduced chamber stiffness in association with regression of myocardial fibrosis in mildly symptomatic patients with DCM. These effects appeared limited, however, to patients with increased myocardial collagen accumulation.

Dipeptidyl Peptidase-4 Modulates Left Ventricular Dysfunction in Chronic Heart Failure via Angiogenesis-Dependent and -Independent Actions

Background— The inhibition of dipeptidyl peptidase-4 (DPP4) protects the heart from acute myocardial ischemia. However, the role of DPP4 in chronic heart failure independent of coronary artery disease remains unclear. Methods and Results— We first localized the membrane-bound form of DPP4 to the capillary endothelia of rat and human heart tissue. Diabetes mellitus promoted the activation of the membrane-bound form of DPP4, leading to reduced myocardial stromal cell-derived factor-1&agr; concentrations and resultant angiogenic impairment in rats. The diabetic rats exhibited diastolic left ventricular dysfunction (DHF) with enhanced interstitial fibrosis caused partly by the increased ratio of matrix metalloproteinase-2 to tissue inhibitor of metalloproteinase-2 in a DPP4-dependent fashion. Both genetic and pharmacological DPP4 suppression reversed the stromal cell-derived factor-1&agr;–dependent microvasculopathy and DHF associated with diabetes mellitus. Pressure overload induced DHF, which was reversed by DPP4 inhibition via a glucagon-like peptide-1/cAMP-dependent mechanism distinct from that for diabetic heart. In patients with DHF, the circulating DPP4 activity in peripheral veins was associated with that in coronary sinus and with E/e′, an echocardiographic parameter representing DHF. Comorbid diabetes mellitus increased the circulating DPP4 activities in both peripheral veins and coronary sinus. Conclusions— DPP4 inhibition reverses DHF via membrane-bound DPP4/stromal cell-derived factor-1&agr;–dependent local actions on angiogenesis and circulating DPP4/glucagon-like peptide-1–mediated inotropic actions. Myocardium-derived DPP4 activity in coronary sinus can be monitored by peripheral vein sampling, which partly correlates with DHF index; thus, circulating DPP4 may potentially serve as a biomarker for monitoring DHF.

AT1 Receptor Blockade Reduces Cardiac Calcineurin Activity in Hypertensive Rats

The possible role of calcineurin in the attenuation of cardiac hypertrophy and fibrosis by blockade of the angiotensin II type 1 (AT1) receptor was investigated in Dahl salt-sensitive (DS) rats. The effect of the calcineurin inhibitor FK506 was also studied. DS rats progressively developed severe hypertension when fed a diet containing 8% NaCl from 7 weeks of age. In addition, marked cardiac hypertrophy and fibrosis were apparent and the activity of calcineurin and its mRNA expression in the myocardium was increased in these animals at 12 weeks in comparison with age-matched Dahl salt-resistant rats. The abundance of angiotensin-converting enzyme (ACE) and transforming growth factor (TGF)-&bgr;1 mRNAs was also increased in the hearts of DS rats at 12 weeks. Treatment of DS rats with a non-antihypertensive dose of the selective AT1 receptor blocker candesartan (1 mg/kg per day) or FK506 (0.1 mg/kg per day) from 7 to 12 weeks attenuated both calcineurin activity and its mRNA expression in the heart, as well as the development of cardiac hypertrophy and fibrosis, without affecting cardiac function. Treatment with candesartan, but not FK506, prevented the upregulation of ACE and TGF-&bgr;1 gene expression. Both candesartan and FK506 prevented the load-induced induction of fetal-type cardiac genes. These results demonstrate that AT1 receptor blockade attenuates the development of cardiac hypertrophy and fibrosis as well as the activation of calcineurin, without an antihypertensive effect, in rats with salt-sensitive hypertension. Calcineurin may be downstream from TGF-&bgr;1 in AT1 receptor-mediated angiotensin II signaling in vivo.

Continuous positive airway pressure improves daytime baroreflex sensitivity and nitric oxide production in patients with moderate to severe obstructive sleep apnea syndrome.

Individuals with obstructive sleep apnea syndrome (OSAS) are at high risk for cardiovascular morbidity and mortality. The effects of OSAS severity and nocturnal continuous positive airway pressure (CPAP) on daytime baroreflex sensitivity (BRS) and nitric oxide (NO) production were investigated in OSAS patients. Fifty-one consecutive males with OSAS and 29 age-matched healthy men underwent the Valsalva test and standard polysomnography. Patients with an apnea-hypopnea index (AHI) of ≥20 episodes per hour were randomized to receive CPAP treatment for 3 months (n=14) or no such treatment (n=19). The BRS index measured from the overshoot phase (phase IV) of the Valsalva maneuver and plasma NO concentration were significantly lower, whereas the AHI, oxygen desaturation time, arousal index, percentage of sleep stage 1, and systolic blood pressure were significantly greater, in patients with an AHI of ≥20/h than in those with an AHI of <20/h or in controls. The 24-h urinary excretion of norepinephrine was significantly reduced and the plasma NO concentration was significantly increased after one night of CPAP. The BRS index for phase IV and the Valsalva ratio were significantly increased in the CPAP group after the 3-month treatment period but remained unchanged in the non-CPAP group of OSAS patients. The daytime BRS index and NO production were thus inversely related to the severity of OSAS, and successful CPAP treatment improved these parameters in patients with moderate to severe OSAS. CPAP may therefore reduce the risk of cardiovascular complications due to endothelial dysfunction or increased sympathetic activity.

Elastolytic Cathepsin Induction/Activation System Exists in Myocardium and Is Upregulated in Hypertensive Heart Failure

Cathepsins are cysteine proteases that participate in various types of tissue remodeling. However, their expressions during myocardial remodeling have not been examined. In this study, we investigated their expressions in the left ventricular (LV) myocardium of rats and humans with hypertension-induced LV hypertrophy or heart failure (HF). Real-time PCR and immunoblot analysis revealed that the abundance of cathepsin S mRNA or protein in the LV tissues was greater in rats or humans with HF than in those with hypertrophy or in control subjects. Immunostaining showed that cathepsin S was localized predominantly to cardiac myocytes and coronary vascular smooth muscle cells, but also overlapped in part with macrophages. Elastic lamina fragmentations significantly increased in the LV intramyocardial coronary arteries of HF rats. The amount of elastolytic activity in the extract of the LV myocardium was markedly increased for HF rats compared with controls, and this activity was mostly because of cathepsin S. Although the amount of elastin mRNA was increased in the LV myocardium of HF rats, the area of interstitial elastin was not. The expression of interleukin 1β was increased in the LV myocardium of HF rats, and this cytokine was found to increase the expression and activity of cathepsin S in cultured neonatal cardiomyocytes. These results suggest that cathepsin S participates in pathological LV remodeling associated with hypertension-induced HF. This protease is, thus, a potential target for therapeutics aimed at preventing or reversing cardiac remodeling.

Gαi2 but Not Gαi3 Is Required for Muscarinic Inhibition of Contractility and Calcium Currents in Adult Cardiomyocytes

Parasympathetic stimulation of the heart acts through M(2)-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins Galpha(i/o), the specific signal transduction requirements of Galpha(i2) and Galpha(i3) in mediating muscarinic regulated L-type calcium currents (I(Ca, L)), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from Galpha(i2)-null mice, Galpha(i3)-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, and I(Ca, L) were all measured in response to isoproterenol, a beta-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and Galpha(i3)-null cells but had no effect in Galpha(i2)-null cells. This study demonstrates that Galpha(i2), but not Galpha(i3), is required for muscarinic inhibition of the beta-adrenergic response in adult murine ventricular myocytes.

Exercise Training Alters Left Ventricular Geometry and Attenuates Heart Failure in Dahl Salt-Sensitive Hypertensive Rats

The clinical efficacy of exercise training in individuals with heart failure is well established, but the mechanism underlying such efficacy has remained unclear. An imbalance between cardiac hypertrophy and angiogenesis is implicated in the transition to heart failure. We investigated the effects of exercise training on cardiac pathophysiology in hypertensive rats. Dahl salt-sensitive rats fed a high-salt diet from 6 weeks of age were assigned to sedentary or exercise (swimming)-trained groups at 9 weeks. Exercise training attenuated the development of heart failure and increased survival, without affecting blood pressure, at 18 weeks. It also attenuated left ventricular concentricity without a reduction in left ventricular mass or impairment of cardiac function. Interstitial fibrosis was increased and myocardial capillary density was decreased in the heart of sedentary rats, and these effects were attenuated by exercise. Exercise potentiated increases in the phosphorylation of Akt and mammalian target of rapamycin observed in the heart of sedentary rats, whereas it inhibited the downregulation of proangiogenic gene expression apparent in these animals. The abundance of the p110&agr; isoform of phosphatidylinositol 3-kinase was decreased, whereas those of the p110&ggr; isoform of phosphatidylinositol 3-kinase and the phosphorylation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase were increased, in the heart of sedentary rats, and all of these effects were prevented by exercise. Thus, exercise training had a beneficial effect on cardiac remodeling and attenuated heart failure in hypertensive rats, with these effects likely being attributable to the attenuation of left ventricular concentricity and restoration of coronary angiogenesis through activation of phosphatidylinositol 3-kinase(p110&agr;)-Akt-mammalian target of rapamycin signaling.

Myocardial velocity gradient as a noninvasively determined index of left ventricular diastolic dysfunction in patients with hypertrophic cardiomyopathy.

OBJECTIVES We investigated the utility of the peak negative myocardial velocity gradient (MVG) derived from tissue Doppler imaging (TDI) for evaluation of diastolic dysfunction in patients with hypertrophic cardiomyopathy (HCM). BACKGROUND Hypertrophic cardiomyopathy is characterized by impaired diastolic function with abnormal stiffness and prolonged relaxation. However, it remains difficult to evaluate these defects noninvasively. METHODS Both TDI and conventional echocardiography were performed in 36 patients with HCM and in 47 control subjects. Left ventricular (LV) pressure was measured simultaneously in all HCM patients and in 26 controls. RESULTS The peak negative MVG occurred soon after the isovolumic relaxation period during the initial phase of rapid filling (auxotonic relaxation). It was significantly smaller in HCM patients than in control subjects (2.32 +/- 0.52/s vs. 4.82 +/- 1.15/s, p < 0.0001); the cutoff value for differentiation between all HCM patients and 47 normal individuals was determined as 3.2/s. Both the left ventricular end-diastolic pressure (LVEDP) (19.6 +/- 6.1 mm Hg vs. 6.5 +/- 1.7 mm Hg, p < 0.0001) and the time constant of LV pressure decay during isovolumic diastole (tau) (44.0 +/- 6.7 ms vs. 32.1 +/- 5.5 ms, p < 0.0001) were increased in HCM patients compared with controls. The peak negative MVG was negatively correlated with both LVEDP (r = -0.75, p < 0.0001) and tau (r = -0.58, p < 0.0001). CONCLUSIONS A reduced peak negative MVG reflects both prolonged relaxation and elevated LVEDP. The peak negative MVG might thus provide a noninvasive index of diastolic function, yielding unique information about auxotonic relaxation in patients with HCM.