Hepatocyte growth factor prevents tissue fibrosis, remodeling, and dysfunction in cardiomyopathic hamster hearts

Structural remodeling of the myocardium, including myocyte hypertrophy, myocardial fibrosis, and dilatation, drives functional impairment in various forms of acquired and hereditary cardiomyopathy. Using cardiomyopathic Syrian hamsters with a genetic defect in delta-sarcoglycan, we investigated the potential involvement of hepatocyte growth factor (HGF) in the pathophysiology and therapeutics related to dilated cardiomyopathy, because HGF has previously been shown to be cytoprotective and to have benefits in acute heart injury. Late-stage TO-2 cardiomyopathic hamsters showed severe cardiac dysfunction and fibrosis, accompanied by increases in myocardial expression of transforming growth factor-beta1 (TGF-beta1), a growth factor responsible for tissue fibrosis. Conversely, HGF was downregulated in late-stage myopathic hearts. Treatment with recombinant human HGF for 3 wk suppressed cardiac fibrosis, accompanied by a decreased expression of TGF-beta1 and type I collagen. Suppression of TGF-beta1 and type I collagen by HGF was also shown in cultured cardiac myofibroblasts. Likewise, HGF suppressed myocardial hypertrophy, apoptosis in cardiomyocytes, and expression of atrial natriuretic polypeptide, a molecular marker of hypertrophy. Importantly, downregulation of the fibrogenic and hypertrophic genes by HGF treatment was associated with improved cardiac function. Thus the decrease in endogenous HGF levels may participate in the susceptibility of cardiac tissue to hypertrophy and fibrosis, and exogenous HGF led to therapeutic benefits in case of dilated cardiomyopathy in this model, even at the late-stage treatment.     

Implications of protease activation in cardiac dysfunction and development of genetic cardiomyopathy in hamsters

It has become evident that protein degradation by proteolytic enzymes, known as proteases, is partly responsible for cardiovascular dysfunction in various types of heart disease. Both extracellular and intracellular alterations in proteolytic activities are invariably seen in heart failure associated with hypertrophic cardiomyopathy, dilated cardiomyopathy, hypertensive cardiomyopathy, diabetic cardiomyopathy, and ischemic cardiomyopathy. Genetic cardiomyopathy displayed in different strains of hamsters provides a useful model for studying heart failure due to either cardiac hypertrophy or cardiac dilation. Alterations in the function of several myocardial organelles such as sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, as well as extracellular matrix have been shown to be due to subcellular remodeling as a consequence of changes in gene expression and protein content in failing hearts from cardiomyopathic hamsters. In view of the increased activities of various proteases, including calpains and matrix metalloproteinases in the hearts of genetically determined hamsters, it is proposed that the activation of different proteases may also represent an important determinant of subcellular remodeling and cardiac dysfunction associated with genetic cardiomyopathy.     

Alteration of extracellular matrix in dilated cardiomyopathic hamster heart

The purpose of this study was to characterize the collagen in hereditary dilated cardiomyopathic hamster hearts, and to examine the participation of the collagen in the occurrence and progression of cardiomyopathy.BIO 53.58 hamsters (5, 10, 20 weeks old) were used as the model of dilated cardiomyopathy. Flb hamsters were used as controls. The collagen content was almost constant at any age in the Flb hamsters, but increased with age in BIO 53.58 hamsters. Type III collagen increased significantly in BIO 53.58 hamsters at 10 weeks. The acetic acid solubility of collagen decreased in BIO 53.58 hamsters as the fibrosis progressed, but was unchanged in controls. Reducible crosslinks showed a tendency to decrease progressively in BIO 53.58 hamsters. There were no differences between Flb and BIO 53.58 hamsters at 5 weeks, but its expression in BIO 53.58 hamsters at 10 and 20 weeks of age increased compared to Flb controls.These findings indicate that in the early phase of cardiomyopathy the extracellular matrix of the myocardium is rich in type III collagen. In the later phase, the matrix resembles that of hard tissues, whose collagen is mainly of type I collagen and is insoluble. These data suggest that the increased collagen synthesis may impair the cardiac function in the development of cardiomyopathy.     

Nonselective ETA/ETB-receptor blockade increases systemic blood pressure of Bio 14.6 cardiomyopathic hamsters

To examine the role of endothelin ETA and ETB receptors in congestive heart failure due to cardiomyopathy, the effect of chronic treatment with selective ETA- and ETB-receptor antagonists (atrasentan and A-192621, respectively), alone and in combination, was assessed on functional and biochemical parameters of 52-week-old Bio 14.6 cardiomyopathic hamsters. Compared with control animals, cardiomyopathic hamsters treated for 9 weeks with atrasentan showed no variation in MAP; however, selective ETB- and combined nonselective ETA- and ETB-receptor antagonists increased systemic blood pressure. After selective ETB-receptor blockade, plasma endothelin levels were augmented. Importantly, this increase was highly enhanced (more than 8-fold) by concomitant ETA-receptor antagonism. Furthermore, the left ventricle:body weight ratio of cardiomyopathic hamsters treated with A-192621, alone or in combination with atrasentan, was significantly increased. On the other hand, decreased left ventricular end-diastolic pressure was observed in cardiomyopathic hamsters after selective ETA- or combined nonselective ETA/ETB-receptor antagonism, while only selective ETA-receptor blockade reduced left ventricular endothelin levels. Our results suggest that, in congestive heart failure, ETB receptors are essential to limit circulating endothelin levels, which may argue for improved cardiac benefits after long-term treatment with highly selective ETA-receptor antagonists.     

Cardiac carnitine deficiency and altered carnitine transport in cardiomyopathic hamsters

The Bio 14.6 hamster has a well-documented cardiomyopathy which leads to congestive heart failure. Previous work demonstrated that hearts from these hamsters have depressed fatty acid oxidation and depressed carnitine concentrations compared to those of normal hamsters. Analyses of tissue carnitine concentrations from 40 to 464 days of age demonstrate that the cardiomyopathic hamsters have a cardiac carnitine deficiency throughout life. Therefore, the carnitine deficiency is not a secondary effect of an advanced stage of the cardiomyopathy. Both the observation that other tissues of the cardiomyopathic hamster have normal or markedly elevated carnitine concentrations and the observation that oral carnitine treatment could not increase the cardiac carnitine concentrations to those of normal hamsters are consistent with the hypothesis that the cardiac carnitine deficiency is the result of a defective cardiac transport mechanism. Cardiac carnitine-binding protein (which may function in the cardiac carnitine transport mechanism) prepared from hearts of cardiomyopathic hamsters had a lower maximal carnitine binding and an increased dissociation constant for carnitine compared to the cardiac carnitine-binding protein prepared from normal hamsters. Thus, several types of data indicate that the cardiomyopathic hamster has an altered cardiac carnitine transport mechanism.     

Cardiac matrix remodeling following intracoronary cell transplantation in dilated cardiomyopathic rabbits

Cellular cardiomyoplasty has been proposed as a promising therapeutic strategy for chronic heart failure. Previous studies focused on structural changes in cardiomyocytes to explain the potential benefits for contractile function. However, limited information is available about the cardiac matrix remodeling following cell transplantation in dilated cardiomyopathy (DCM). Here, we established a new animal model of intracoronary bone marrow mononuclear cells (BMMNCs) transplantation to explore extracellular matrix remodeling in adriamycin-induced cardiomyopathic rabbits. In vivo studies demonstrated that BMMNCs transplantation can dramatically delay the progress of collagen metabolism and decrease myocardial collagen volume fraction. The beneficial effects were mediated by attenuating stress-generated over-expression of matrix metalloproteinases (MMPs) in ventricular remodeling. Improved cardiac function may be contributed in part by stem-associated inhibition of extracellular matrix remodeling.     

The vitamin D receptor activator paricalcitol prevents fibrosis and diastolic dysfunction in a murine model of pressure overload

BACKGROUND: Activation of the vitamin D-vitamin D receptor (VDR) axis has been shown to reduce blood pressure and left ventricular (LV) hypertrophy. Besides cardiac hypertrophy, cardiac fibrosis is a key element of adverse cardiac remodeling. We hypothesized that activation of the VDR by paricalcitol would prevent fibrosis and LV diastolic dysfunction in an established murine model of cardiac remodeling. METHODS: Mice were subjected to transverse aortic constriction (TAC) to induce cardiac hypertrophy. Mice were treated with paricalcitol, losartan, or a combination of both for a period of four consecutive weeks. RESULTS: The fixed aortic constriction caused similar increase in blood pressure, both in untreated and paricalcitol- or losartan-treated mice. TAC significantly increased LV weight compared to sham operated animals (10.2±0.7 vs. 6.9±0.3mg/mm, p<0.05). Administration of either paricalcitol (10.5±0.7), losartan (10.8±0.4), or a combination of both (9.2±0.6) did not reduce LV weight. Fibrosis was significantly increased in mice undergoing TAC (5.9±1.0 vs. sham 2.4±0.8%, p<0.05). Treatment with losartan and paricalcitol reduced fibrosis (paricalcitol 1.6±0.3% and losartan 2.9±0.6%, both p<0.05 vs. TAC). This reduction in fibrosis in paricalcitol treated mice was associated with improved indices of LV contraction and relaxation, e.g. dPdtmax and dPdtmin and lower LV end diastolic pressure, and relaxation constant Tau. Also, treatment with paricalcitol and losartan reduced mRNA expression of ANP, fibronectin, collagen III and TIMP-1. DISCUSSION: Treatment with the selective VDR activator paricalcitol reduces myocardial fibrosis and preserves diastolic LV function due to pressure overload in a mouse model. This is associated with a reduced percentage of fibrosis and a decreased expression of ANP and several other tissue markers.     

Interaction between AT1 and AT2 receptors during postinfarction left ventricular remodeling

The relative contribution of the angiotensin II type 1 and 2 receptors (AT1-R and AT2-R) in postmyocardial infarction (MI) remodeling remains incompletely understood. We studied five groups of C57Bl/6 mice after 1 h of left anterior descending artery occlusion-reperfusion: 1) wild type, untreated (n = 12); 2) wild type, treated with the AT1-R blocker losartan (10-20 mg.kg(-1).day(-1) in drinking water) from day 1 to day 28 post-MI (n = 10); 3) cardiac overexpression of the AT2-R [AT2-transgenic (TG); n = 14]; 4) AT2-TG treated with losartan (n = 13); and 5) AT2-TG and null for the AT1a-R [AT2-TG/AT1 knockout (KO); n = 10]. Cardiac magnetic resonance imaging (CMR) measured ejection fraction and left ventricular end-diastolic and end-systolic volume (EDVI and ESVI) and mass indexed to weight on days 0, 1, 7, and 28 post-MI. Infarct size was measured on day 1 by late gadolinium-enhanced CMR. Regional myocyte hypertrophy and collagen content were measured on day 28 post-MI. Infarct size was similar among groups. Systolic blood pressure was lowest in AT2-TG/AT1KO. By day 28 post-MI, when corrected for baseline differences, EDVI and ESVI were higher and ejection fraction was lower in wild type than other groups. Ejection fraction was highest and EDVI and mass index were lowest in AT2-TG/AT1KO at day 28. The AT2-TG/AT1KO demonstrated less fibrosis in adjacent regions. Regional myocyte hypertrophy was similar in all groups. The AT1-R and AT2-R are intricately intertwined in post-MI remodeling. Pharmacological blockade of AT1-R is equivalent to AT2-R overexpression in attenuating post-MI remodeling. Genetic knockout of the AT1a-R is additive to AT2-R overexpression, due, at least in part, to blood pressure lowering.     

TNF‐α‐mediated signal transduction pathway is a major determinant of apoptosis in dilated cardiomyopathy

Although J2N-k strain of cardiomyopathic hamsters is an excellent model of dilated cardiomyopathy, the presence and mechanisms of apoptosis in the hearts of these genetically modified animals have not been investigated. This study examined the hypothesis that cardiac dysfunction and apoptosis in the cardiomyopathic hamsters were associated with tumour necrosis factor-alpha (TNF-α)-mediated signalling pathway involving the activation of some pro-apoptotic proteins and/or deactivation of some antiapoptotic proteins. Echocardiographic assessment of 31-week-old hamsters indicated an increase in the internal dimension of the left ventricle as well as decreases in the ejection fraction, fractional shortening and cardiac output without any evidence of cardiac hypertrophy. Increased level of TNF-α and apoptosis in cardiomyopathic hearts were accompanied by increased protein content for protein kinase C (PKC) -α and -ɛ isozymes as well as caspases 3 and 9. Phosphorylated protein content for p38 MAPK and NFκB was increased whereas that for Erk1/2, BAD and Bcl-2 was decreased in cardiomyopathic hearts. These results support the view that TNF-α and PKC isozymes may promote apoptosis due to the activation of p38 MAPK and deactivation of Erk1/2 pathways, and these changes may contribute toward the development of cardiac dysfunction in dilated cardiomyopathy.     

Acetylcholine induces vasoconstriction in the microcirculation of cardiomyopathic hamsters: reversal by L-arginine.

The goal of this study was to determine whether endothelium-dependent responses of the microcirculation are altered during cardiomyopathy. We examined in vivo responses of cheek pouch arterioles to an endothelium-dependent agonist (acetylcholine) and an endothelium-independent agonist (nitroglycerin) in normal and in cardiomyopathic hamsters. In normal hamsters, acetylcholine produced dose-related dilatation of arterioles. In contrast, acetylcholine produced constriction of arterioles in cardiomyopathic hamsters. Nitroglycerin produced similar dose-related dilatation in normal and cardiomyopathic hamsters. We also examined whether impaired responses to acetylcholine in cardiomyopathic hamsters were related to an alteration in the L-arginine/nitric oxide pathway. We found that L-arginine (100 microM) restored endothelium-dependent vasodilatation to acetylcholine in cardiomyopathic hamsters. Thus, cardiomyopathy impairs endothelium-dependent responses of the microcirculation which is reversed by L-arginine.     

Matrix remodeling in experimental and human heart failure: a possible regulatory role for TIMP-3

In the failing heart, an imbalance in matrix metalloproteinases (MMPs) and their biological regulators, the tissue inhibitors of MMPs (TIMPs), may result in cardiac dilatation from matrix degradation. We hypothesized that a reduction of myocardial TIMP-3 is associated with adverse matrix remodeling in both human and experimental heart failure. Cardiomyopathic hamsters at age 15 wk (normal), 25 wk (compensated stage), and 35 wk (overt failure) were compared with age-matched normal controls. MMP activity (gelatinase bioassay) was increased in cardiomyopathic hearts (P = 0.03) and peaked during the transition to overt heart failure. TIMP-3 content (immunoblot) was decreased compared with normal controls (74 +/- 5% at 25 wk, 69 +/- 10% at 35 wk; P = 0.001) and its reduction was associated with increased MMP activity (r = -0.6; P = 0.004). TIMP-1 increased progressively (P = 0.001), whereas TIMP-2, TIMP-4, and MMP protein levels were unchanged. Myocardial collagen (hydroxyproline content) increased with time during the progression to end-stage cardiac failure (P < 0.0001). Collagen synthesis ([(14)C]proline uptake) was elevated in cardiomyopathy at 15 and 25 wk (P < 0.05). The collagen cross-linking ratio (insoluble:soluble collagen) was reduced (P = 0.003) as the left ventricle dilated. By confocal microscopy restricted to viable myocardium, collagen content was reduced (P = 0.04) with fragmentation (P < 0.0001) and thinning (P = 0.003) of perimysial collagen fibers. Similarly, patients with end-stage congestive heart failure (n = 7) compared with nonfailing controls (n = 2) had elevated gelatinase MMP activity (P = 0.02) associated with isolated reductions in TIMP-3 (55 +/- 5% of normal; P = 0.003). Reductions of TIMP-3 parallel adverse matrix remodeling in the cardiomyopathic hamster and the failing human heart. TIMP-3 may contribute to the regulation of myocardial remodeling and its reduction may promote a transition from compensated to end-stage congestive heart failure.     

Renin-angiotensin system inhibition on noradrenergic nerve terminal function in pacing-induced heart failure

Chronic angiotensin-converting enzyme (ACE) inhibition has been shown to improve cardiac sympathetic nerve terminal function in heart failure. To determine whether similar effects could be produced by angiotensin II AT(1) receptor blockade, we administered the ACE inhibitor quinapril, angiotensin II AT(1) receptor blocker losartan, or both agents together, to rabbits with pacing-induced heart failure. Chronic rapid pacing produced left ventricular dilation and decline of fractional shortening, increased plasma norepinephrine (NE), and caused reductions of myocardial NE uptake activity, NE histofluorescence profile, and tyrosine hydroxylase immunostained profile. Administration of quinapril or losartan retarded the progression of left ventricular dysfunction and attenuated cardiac sympathetic nerve terminal abnormalities in heart failure. Quinapril and losartan together produced greater effects than either agent alone. The effect of renin-angiotensin system inhibition on improvement of left ventricular function and remodeling, however, was not sustained. Our results suggest that the effects of ACE inhibitors are mediated via the reduction of angiotensin II and that angiotensin II plays a pivotal role in modulating cardiac sympathetic nerve terminal function during development of heart failure. The combined effect of ACE inhibition and angiotensin II AT(1) receptor blockade on cardiac sympathetic nerve terminal dysfunction may contribute to the beneficial effects on cardiac function in heart failure.     

Stimulatory guanine nucleotide-binding protein and adenylate cyclase activities in Bio 14.6 cardiomyopathic hamsters at the hypertrophic stage

The Bio 14.6 cardiomyopathic Syrian hamster is an animal model of human idiopathic cardiomyopathy. The pathogenesis of the disease in this animal has not yet been clearly elucidated. It is well known that α- and β-adrenergic receptors are increased in the myocardium of this animal, but that isoprenaline does not produce an augmented response. We examined the activity of cardiac stimulatory GTP-binding protein (Gs), which couple with β-adrenergic receptors to stimulate adenylate cyclase, in Bio 14.6 cardiomyopathic hamsters at 90 and 160 days of age. The cardiac norepinephrine concentration was significantly increased in Bio 14.6 hamsters compared with control hamsters (F1B) at 90 days of age (1,739±120 vs 1,470±161 ng/g wet tissue weight, p<0.05). Cardiac forskolin-stimulated adenylate cyclase activities at 90 and 160 days of age were lower in the cardiomyopathic hamsters than in the F1B controls (90 days old: 98±24 vs 122±29 pmol/min/mg protein, p<0.05; 160 days old: 74±13 vs 124±28 pmol/min/mg protein, p<0.01). Cardiac Gs activities at 90 and 160 days of age were significantly lower in Bio 14.6 hamsters than those in F1B hamsters (90 days old: 204±42 vs 259±49 pmol/min/mg protein, p<0.05; 160 days old: 156±39 vs 211±60 pmol/min/mg protein, p<0.05). We thus demonstrated functional defects in cardiac Gs protein and adenylate cyclase activity in the Bio 14.6 cardiomyopathic hamsters at 90 to 160 days of age (the hypertrophic stage of cardiomyopathy). Such defects could be one possible mechanism preventing an enhanced response to β-adrenergic stimulation in this animal and could also contribute to myocardial decompensation in the late stage of cardiomyopathy.     

Blockade of AT1 receptors by losartan did not affect renin gene expression in kidney medulla

This study was designed to determine particular changes in the renin gene expression and activity in renal cortex and medulla after AT(1) receptor blockade. It was found that two-week-treatment with AT(1) blocker losartan induced an increase in tissue renin activity in both parts of kidney causing subsequent elevation of plasma renin activity. Renin mRNA in losartan-treated rats was increased only in cortex, suggesting cortex origin of elevated renin activity in medulla. Medullary renin mRNA indicated local synthesis of renin within the whole kidney and supported the idea of the presence of tissue renin-angiotensin system. Our results show that gene expression of renin in kidney medulla is insensitive to AT(1) receptor blockade and this points out that the regulation of kidney renin-angiotensin system probably differs from that in cortex.     

Angiotensin receptors contribute to blood pressure homeostasis in salt-depleted SHR

This study evaluated the contribution of angiotensin peptides acting at various receptor subtypes to the arterial pressure and heart rate of adult 9-wk-old male conscious salt-depleted spontaneously hypertensive rats (SHR). Plasma ANG II and ANG I in salt-depleted SHR were elevated sevenfold compared with peptide levels measured in sodium-replete SHR, whereas plasma ANG-(1-7) was twofold greater in salt-depleted SHR compared with salt-replete SHR. Losartan (32.5 micromol/kg), PD-123319 (0.12 micromol. kg(-1). min(-1)), [d-Ala(7)]ANG-(1-7) (10 and 100 pmol/min), and a polyclonal ANG II antibody (0.08 mg/min) were infused intravenously alone or in combination. Combined blockade of AT(2) and AT((1-7)) receptors significantly increased the blood pressure of losartan-treated SHR (+15 +/- 1 mmHg; P < 0.01); this change did not differ from the blood pressure elevation produced by the sole blockade of AT((1-7)) receptors (15 +/- 4 mmHg). On the other hand, sole blockade of AT(2) receptors in losartan-treated SHR increased mean arterial pressure by 8 +/- 1 mmHg (P < 0.05 vs. 5% dextrose in water as vehicle), and this increase was less than the pressor response produced by blockade of AT((1-7)) receptors alone or combined blockade of AT((1-7)) and AT(2) receptors. The ANG II antibody increased blood pressure to the greatest extent in salt-depleted SHR pretreated with only losartan (+11 +/- 2 mmHg) and to the least extent in salt-depleted SHR previously treated with the combination of losartan, PD-123319, and [d-Ala(7)]ANG-(1-7) (+7 +/- 1 mmHg; P < 0.01). Losartan significantly increased heart rate, whereas other combinations of receptor antagonists or the ANG II antibody did not alter heart rate. Our results demonstrate that ANG II and ANG-(1-7) act through non-AT(1) receptors to oppose the vasoconstrictor actions of ANG II in salt-depleted SHR. Combined blockade of AT(2) and AT((1-7)) receptors and ANG II neutralization by the ANG II antibody reversed as much as 67% of the blood pressure-lowering effect of losartan.     

Profibrotic influence of high glucose concentration on cardiac fibroblast functions: effects of losartan and vitamin E

Long-standing diabetes can result in the development of cardiomyopathy, which can be accompanied by myocardial fibrosis. Although exposure of cultured kidney and skin fibroblasts to high glucose (HG) concentration is known to increase collagen synthesis, little is known about cardiac fibroblasts (CFs). Therefore, we determined the influence of HG conditions on CF functions and the effects of losartan and vitamin E in these responses. We cultured rat CFs in either normal glucose (NG; 5.5 mM) or HG (25 mM) media and assessed changes in protein and collagen synthesis, matrix metalloproteinase (MMP) activity, and levels of mRNA for ANG II type 1 (AT(1)) receptors. Results indicate that HG-level CFs synthesized more protein and collagen, and these effects were not due to changes in osmotic pressure. The addition of ANG II stimulated protein and collagen synthesis in NG-concentration but not HG-concentration CFs. Interestingly, losartan pretreatment blocked the HG- or ANG II-induced increases in both protein and collagen synthesis. HG or ANG II decreased total MMP activity. Decreases in MMP activity were blocked by losartan. AT(1) mRNA levels were upregulated with HG concentration. Vitamin E pretreatment blocked the effects of HG on total protein synthesis and stimulated MMP activity. Results suggest that HG levels may promote fibrosis by increasing CF protein and collagen synthesis and decreasing MMP activity. HG levels may cause these effects via the upregulation of AT(1) receptors, which can be blocked by losartan. However, vitamin E can alter HG concentration-induced changes in CF functions independently of AT(1) mRNA levels.     

A metabolic approach to the treatment of dilated cardiomyopathy in BIO T0-2 cardiomyopathic Syrian hamsters

Mechanisms underlying dilated cardiomyopathy (DCM) are poorly understood and effective therapy is still unavailable. The aim of this study was to examine the heart ultrastructure and dynamic of BIO T0-2 cardiomyopathic hamsters, an animal model of DCM, and to study in these animals, the effects of a co-formulation (HS12607) of propionyl-L-carnitine, coenzyme Q(10) and omega-3 fatty acids on cardiac mechanical parameters. Sarcomere length, Frank-Starling mechanism and force-frequency relations were studied on isolated ventricular papillary muscle from age-matched BIO F1B normal Syrian hamsters, BIO T0-2 control and BIO T0-2 HS12607-treated cardiomyopathic Syrian hamsters. At the optimum length to maximum active force, electron microscopy of left ventricular papillary muscle revealed that seven out of ten muscles studied showed shorter sarcomeres (1.20 +/- 0.29 microm), and the remaining three showed longer sarcomeres (2.80 +/- 0.13 microm), compared to those of normal hamsters (2.05 +/- 0.06 microm, n = 10). Severe alterations of the Frank-Starling mechanism, force-frequency relations and derivative parameters of contractile waves were also observed in vitro in the BIO T0-2 control hamsters. Long-term (8 weeks) treatment with HS12607 prevented alterations in sarcomere length in the BIO T0-2 cardiomyopathic hamsters; the Frank-Starling mechanism and force-frequency relations were also significantly (P < 0.05) improved in these hamsters. Therefore results of the present study strongly suggest the need for clinical studies on metabolic therapeutic intervention in the effort to stop the progression of dilated cardiomyopathy.     

Chronic losartan administration reduces mortality and preserves cardiac but not skeletal muscle function in dystrophic mice

Duchenne muscular dystrophy (DMD) is a degenerative disorder affecting skeletal and cardiac muscle for which there is no effective therapy. Angiotension receptor blockade (ARB) has excellent therapeutic potential in DMD based on recent data demonstrating attenuation of skeletal muscle disease progression during 6–9 months of therapy in the mdx mouse model of DMD. Since cardiac-related death is major cause of mortality in DMD, it is important to evaluate the effect of any novel treatment on the heart. Therefore, we evaluated the long-term impact of ARB on both the skeletal muscle and cardiac phenotype of the mdx mouse. Mdx mice received either losartan (0.6 g/L) (n = 8) or standard drinking water (n = 9) for two years, after which echocardiography was performed to assess cardiac function. Skeletal muscle weight, morphology, and function were assessed. Fibrosis was evaluated in the diaphragm and heart by Trichrome stain and by determination of tissue hydroxyproline content. By the study endpoint, 88% of treated mice were alive compared to only 44% of untreated (p = 0.05). No difference in skeletal muscle morphology, function, or fibrosis was noted in losartan-treated animals. Cardiac function was significantly preserved with losartan treatment, with a trend towards reduction in cardiac fibrosis. We saw no impact on the skeletal muscle disease progression, suggesting that other pathways that trigger fibrosis dominate over angiotensin II in skeletal muscle long term, unlike the situation in the heart. Our study suggests that ARB may be an important prophylactic treatment for DMD-associated cardiomyopathy, but will not impact skeletal muscle disease.     

Cardiac contractile dysfunction in J2N-k cardiomyopathic hamsters is associated with impaired SR function and regulation

Although dilated cardiomyopathy (DCM) is known to result in cardiac contractile dysfunction, the underlying mechanisms are unclear. The sarcoplasmic reticulum (SR) is the main regulator of intracellular Ca²⁺ required for cardiac contraction and relaxation. We therefore hypothesized that abnormalities in both SR function and regulation will contribute to cardiac contractile dysfunction of the J2N-k cardiomyopathic hamster, an appropriate model of DCM. Echocardiographic assessment indicated contractile dysfunction, because the ejection fraction, fractional shortening, cardiac output, and heart rate were all significantly reduced in J2N-k hamsters compared with controls. Depressed cardiac function was associated with decreased cardiac SR Ca²⁺ uptake in the cardiomyopathic hamsters. Reduced SR Ca²⁺ uptake could be further linked to a decrease in the expression of the SR Ca²⁺-ATPase and cAMP-dependent protein kinase (PKA)-mediated phospholamban (PLB) phosphorylation at serine-16. Depressed PLB phosphorylation was paralleled with a reduction in the activity of SR-associated PKA, as well as an elevation in protein phosphatase activity in J2N-k hamster. The results of this study suggest that an alteration in SR function and its regulation contribute to cardiac contractile dysfunction in the J2N-k cardiomyopathic hamster. sarcoplasmic reticulum; cardiomyopathy; cAMP-dependent protein kinase; Ca²⁺/calmodulin-dependent protein kinase; sarco(endo)plasmic reticulum ATPase; phospholamban     

Expression of matrix metalloproteinase activity in idiopathic dilated cardiomyopathy: A marker of cardiac dilatation

BACKGROUND: Idiopathic dilated cardiomyopathy (DCM), ventricular systolic dysfunction and chamber dilatation are accompanied by architectural remodeling, wall thinning and cardiac myocyte slippage. Recent work has demonstrated an association between collagen degradation and an increased expression of matrix metalloproteinases (MMPs). Accordingly, we have sought to correlate (a) collagen degradation with MMP elevations and, (b) assay the neutralizing potential of a known inhibitor of MMP, tetracycline on MMPs in DCM. METHODS: Assessment of LV volume and shape by 2-D echocardiography was performed. Light microscopic assessment of histopathology in picrosirius red stained biopsy samples of 11 DCM patients and six post-transplant patients was performed. Zymographic estimation of MMP activity and influence of tetracycline on MMP activity was assessed. RESULTS: Small amount of interstitial collagen was noted in the control group, whereas in the DCM hearts, chamber dilatation was associated with areas of scanty myocyte necrosis, islands of excess collagen, and focal areas of absent or scanty collagen with intact myocytes. In cardiomyopathic tissue, collagenase activity was markedly elevated at 63% compared with 8% in post-transplant tissue. Tetracycline at a concentration of 285+/-10 microM (IC50) inhibited collagenase activity by 50% in cardiomyopathic tissue. CONCLUSIONS: Areas of focal interstitial collagen accumulation were accompanied by collagen fiber lysis and increased collagenase activity in dilated cardiomyopathy. This enhanced collagenolytic activity found in endomyocardial biopsy tissue was inhibited by tetracycline. The non-antibiotic property of tetracycline may be of potential value in the prevention of ventricular dilatation in idiopathic dilated cardiomyopathy.