Reinduction of T-type calcium channels by endothelin-1 in failing hearts in vivo and in adult rat ventricular myocytes in vitro.

BACKGROUND: In ventricular myocardium, the T-type Ca2+ current (ICa,T), which is temporarily observed during fetal and neonatal periods, has been shown to reappear in failing/remodeling hearts. However, its pathophysiological regulation has not been elucidated. METHODS AND RESULTS: We utilized Dahl salt-sensitive (DS) rats with hypertension at the stage of concentric left ventricular (LV) hypertrophy (11 weeks old, LVH) and at the heart failure stage (16 to 18 weeks old, CHF). Some were treated with bosentan (100 mg/kg per day) during the period from LVH to CHF. In LVH, neither the presence of ICa,T (measured in the freshly isolated LV myocytes) nor an increase in alpha-1G mRNA expression were detected. This condition was associated with increases in tissue angiotensin II (AII) but not with endothelin (ET)-1 peptides. In contrast, in CHF, when the tissue AII remained elevated and ET-1 de novo increased, ICa,T was recorded in most of the cells (-0.87+/-0.18 pA/pF at -30 mV, P<0.01 versus LVH). This was associated with a significant increase in the alpha-1G mRNA level. The chronic bosentan treatment eliminated both the elevation of alpha-1G mRNA level and ICa,T from the cells, whereas it did not affect the cell size and membrane capacitance. In addition, 48-hour exposure to ET-1 but not AII induced ICa,T in normal adult myocytes in culture from Sprague-Dawley rats. CONCLUSIONS: ICa,T channels reappear in failing but not in hypertrophied LV cardiomyocytes in a manner depending on the tissue ET-1 activation.

Excessive activation of matrix metalloproteinases coincides with left ventricular remodeling during transition from hypertrophy to heart failure in hypertensive rats.

OBJECTIVES: We sought to elucidate how the local activation of matrix metalloproteinases (MMPs) is balanced by that of the endogenous tissue inhibitors of MMP (TIMPs) during left ventricular (LV) remodeling. BACKGROUND: Although it is known that the extracellular matrix (ECM) must be altered during LV remodeling, its local regulation has not been fully elucidated. METHODS: In Dahl salt-sensitive rats with hypertension, in which a stage of concentric, compensated left ventricular hypertrophy (LVH) at 11 weeks is followed by a distinct stage of congestive heart failure (CHF) with LV enlargement and dysfunction at 17 weeks, we determined protein and messenger ribonucleic acid (mRNA) levels of LV myocardial TIMP-2 and -4 and MMP-2, as well as their concomitant activities. RESULTS: No changes were found at the LVH stage. However, during the transition to CHF, TIMP-2 and -4 activities, protein and mRNA levels were all sharply increased. At the same time, the MMP-2 mRNA and protein levels and activities, as determined by gelatin zymography, as well as by an antibody capture assay, showed a substantial increase during the transition to CHF. The net MMP activities were closely related to increases in LV diameter (r = 0.763) and to systolic wall stress (r = 0.858) in vivo. CONCLUSIONS: Both TIMPs and MMP-2 remained inactive during hypertrophy, per se; they were activated during the transition to CHF. At this time, the activation of MMP-2 surpassed that of TIMPs, possibly resulting in ECM breakdown and progression of LV enlargement.

Angiotensin II, oxidative stress, and extracellular matrix degradation during transition to LV failure in rats with hypertension.

Angiotensin II (Ang-II) plays pivotal roles in the progression of left ventricular (LV) remodeling in diseased hearts; it remains to be elucidated how Ang-II links to degradation of the extracellular matrix (ECM). Using hypertensive Dahl salt-sensitive rats that show the distinctive transition from concentric LV hypertrophy to LV remodeling, we chronically treated them with an angiotensin type-1 receptor blocker (telmisartan 5 mg/kg/day, ARB group) or vehicle (0.5% CMC, CHF group). During the process of LV remodeling, we assessed, (1) in-vivo LV shape and function; (2) animal survival; (3) amounts of ECM in LV using a scanning electron microscope (SEM); (4) mRNA (by real time RT-PCR) and protein (by immunoblotting) levels in LV of NADPH oxidase, glutathione peroxidase-1 (GPX-1), and matrix metalloproteinase (MMP)-2, -9, and -13; (5) immunohistochemical staining of myocardial 4-hydroxy-2-nonenal and 8-hydroxy-2'-deoxyguanosine; (6) nuclear factor kappa-B (NFkappaB) protein levels in the nuclear extract; and (7) endogenous activities of MMP-2 and -9 by an antibody capture method. Compared with CHF, ARB group showed an improvement of survival and preserved LV shape and function, and ECM density in SEM that was accompanied by decreases in oxidative stress-mediated protein degenerations, activities of GPX-1, NADPH oxidase, NFkappaB, and MMP-2, -9, and -13. Local activation of Ang-II in hypertrophic LV triggers MMP-mediated ECM degradation, namely LV remodeling, at least in part, through NADPH oxidase-induced oxidative stress and the subsequent NFkappaB activation.

Cardioprotective effects of carvedilol on acute autoimmune myocarditis: anti-inflammatory effects associated with antioxidant property.

Carvedilol, a new beta-blocker with antioxidant properties, has been shown to be cardioprotective in experimental models of myocardial damage. We investigated whether carvedilol protects against experimental autoimmune myocarditis (EAM) because of its suppression of inflammatory cytokines and its antioxidant properties. We orally administered a vehicle, various doses of carvedilol, racemic carvedilol [R(+)-carvedilol, an enantiomer of carvedilol without beta-blocking activity], metoprolol, or propranolol to rats with EAM induced by porcine myosin for 3 wk. Echocardiographic study showed that the three beta-blockers, except R(+)-carvedilol, suppressed left ventricular fractional shortening and decreased heart rates to the same extent. Carvedilol and R(+)-carvedilol, but not metoprolol or propranolol, markedly reduced the severity of myocarditis at the two different doses and suppressed thickening of the left ventricular posterior wall in rats with EAM. Only carvedilol suppressed myocardial mRNA expression of inflammatory cytokines and IL-1beta protein expression in myocarditis. In addition, carvedilol and R(+)-carvedilol decreased myocardial protein carbonyl contents and myocardial thiobarbituric acid-reactive substance products in rats with EAM. The in vitro study showed that carvedilol and R(+)-carvedilol suppressed IL-1beta production in LPS-stimulated U937 cells and that carvedilol and R(+)-carvedilol, but not metoprolol or propranolol, suppressed thiobarbituric acid-reactive substance products in myocardial membrane challenged by oxidative stress. It was also confirmed that probucol, an antioxidant, ameliorated EAM in vivo. Carvedilol protects against acute EAM in rats, and the superior cardioprotective effect of carvedilol compared with metoprolol and propranolol may be due to suppression of inflammatory cytokines associated with the antioxidant properties in addition to the hemodynamic modifications.

RhoA expression is not a critical determinant in hypertension evolution in salt-sensitive Dahl rats.

BACKGROUND: The Rho/Rho kinase pathway plays an important role in regulation of vascular smooth muscle cell contraction and is involved in the pathogenesis of hypertension. However, little is known about the role of this pathway in the evolution of salt-sensitive hypertension and vascular remodeling. The aim of this study was to examine whether the age-dependent surge of blood pressure after exposure to a high salt-containing diet, which is well-established for Dahl salt-sensitive rats, is primarily regulated by the level of expression of RhoA in arterial vessels. MATERIAL/METHODS: We examined Dahl salt-sensitive rats at 3 weeks, 6 weeks, and 9 weeks of age (n=10, each). In each group, animals were switched to being fed a diet containing 8% NaCl from one containing 0.3% NaCl. After 7 days, mRNA and protein levels of RhoA from the thoracic aorta were quantified. RESULTS: At the time of examination, increases in systolic blood pressure were significantly different depending on the age at which the high salt diet was initiated. The % increases were 34+/-3% (3-weeks), 20+/-2% (6-weeks), and 13+/-2% (9-weeks). Despite these differing changes in blood pressure, mRNA and protein levels of RhoA in the arteries did not differ among the groups. CONCLUSIONS: RhoA expression and activity appear not to be the critical determinant of the surge in hypertension when Dahl salt-sensitive rats are exposed to salt-rich diets. Hence, the age-dependent salt-sensitivity must be mediated by alternative pathways.

Tissue angiotensin II during progression or ventricular hypertrophy to heart failure in hypertensive rats; differential effects on PKC epsilon and PKC beta.

The protein kinase C (PKC) family has been implicated as second messengers in mechanosensitive modulation of cardiac hypertrophy. However, little information is available on the role of expression and activation of specific cardiac PKC isozymes during development of left ventricular hypertrophy (LVH) and failure (LVF). Dahl salt-sensitive rats fed an 8% salt diet developed systemic hypertension and concentric LVH at 11 weeks of age that is followed by left ventricle (LV) dilatation and global hypokinesis at 17 weeks. Among several PKC isozymes expressed in the LV myocardium, only PKC epsilon showed a 94% increase at the LVH stage. At the LVF stage, however, PKC epsilon returned to the control level, whereas PKC beta I and beta II increased by 158% and 155%, respectively. Hearts were studied at each stage using the Langendorff set-up, and a LV balloon was inflated to achieve an equivalent diastolic wall stress. Following mechanical stretch, PKC epsilon was significantly activated in LVH myocardium in which tissue angiotensin II levels were increased by 59%. Pre-treatment with valsartan, an AT(1)-receptor blocker, abolished the stretch-mediated PKC epsilon activation. Mechanical stretch no longer induced PKC epsilon activation in LVF. Chronic administration of valsartan blunted the progression of LVF and inhibited the increase in PKC beta. Mechanosensitive PKC epsilon activation is augmented and therefore may contribute to the development of compensatory hypertrophy. This effect was dependent on activation of tissue angiotensin II. However, this compensatory mechanism becomes inactive in LVF, where PKC beta may participate in the progression to cardiac dysfunction and LV remodeling.