Age-matched F1B Research Articles

Chronic Treatment With N-acetylcysteine Improves Cardiac Function but Does Not Prevent Progression of Cardiomyopathy in Syrian Cardiomyopathic Hamsters

Oxidative stress has been postulated to contribute to the onset and development of heart failure (HF). The efficacy of antioxidant therapy in HF, however, remains controversial. This study evaluates the effect of the antioxidant N-acetylcysteine (NAC, 1 g/kg per day) on cardiovascular function in 2- and 6-month-old Bio-TO2 Syrian cardiomyopathic hamsters (SCH) after treatment for 1 month and 5 months with this drug. Endothelial function, systolic blood pressure (SBP), and echocardiographic parameters were evaluated. Age-matched F1-B golden hamsters were used as controls. One month of NAC administration significantly decreased SBP in 2-month-old SCH (n = 5, P < 0.001) without modifying echocardiographic values. Five-month treatment of cardiomyopathic animals with the antioxidant improved the acetylcholine-induced relaxation in aortic rings by 24% (E( Max) value from 45.8% ± 4% to 55.3% ± 2% n = 7, P < .05) but did not modify EC(50) values for the acetylcholine concentration-response curve. In addition, 5-month administration of NAC to SCH increased ejection fraction from 39% ± 4% to 57% ± 4% (n = 11, P < .001) and decreased left ventricular end-diastolic and end-systolic volumes (from 0.38 ± 0.04 mL/100 g body weight (BW) and 0.22 ± 0.03 mL/100 g BW, before, to 0.24 ± 0.04 mL/100 g BW and 0.12 ± 0.03 mL/100 g BW after treatment, P < .01). Cardiac output index also improved after 5 months of treatment, although it did not reach statistical significance. These results suggest that antioxidant therapy alone decreases ventricular dilatation and improves cardiovascular function in this animal model of dilated cardiomyopathy, but it does not prevent the appearance of HF.

Reduced Ca2+ transport across sarcolemma but enhanced spontaneous activity in cardiomyocytes isolated from left atrium-pulmonary veins tissue of myopathic hamster

BackgroundSeveral lines of evidence point to a particularly important role of the left atrium (LA) in initiating and maintaining atrial fibrillation (AF). This role may be related to the location of pulmonary veins (PVs) in the LA. The aim of the present study was to investigate the action potential (AP) and ionic currents in LA-PV cardiomyocytes isolated from Bio14.6 myopathic Syrian hamsters (36-57 week-old) versus age-matched F1B healthy control hamsters.Methods and ResultsWhole-cell patch-clamp techniques were used to record AP in current-clamp mode and ionic currents in voltage-clamp mode. The results obtained show that in both healthy and myopathic LA-PV tissue spontaneously discharging cardiomyocytes can be found, but they are more numerous in myopathic (9/29) than in healthy hamsters (4/42, p < 0.05 by χ2 analysis). Myopathic myocytes have shorter AP duration (APD) with smaller ICa,L and INCX than the healthy control. The currents ITO, IK, IK1 and ICa,T are not significantly different in myopathic versus healthy cells.ConclusionsOur results indicate that in myopathic Syrian hamsters LA-PV cardiomyocytes are more prone to automatic rhythms. Also, they show altered electrophysiologic properties, which may be due to abnormal Ca2+ channels and may account for contractile dysfunction.

Synthetic prostacycline agonist, ONO-1301, ameliorates left ventricular dysfunction and cardiac fibrosis in cardiomyopathic hamsters

Impairment of cardiac function in cardiomyopathy has been postulated to be related to decreased blood flow and increased collagen synthesis. Administration of growth factors was reported to attenuate left ventricular (LV) remodeling and dysfunction in animal models of dilated cardiomyopathy. We previously reported that ONO-1301, a synthetic prostacyclin agonist with thromboxane-synthase inhibitory activity, promotes production of hepatocyte growth factor and vascular endothelial growth factor from various cell types and ameliorate ischemia-induced LV dysfunction in mice and pigs. We evaluated therapeutic efficacy of ONO-1301 in the Syrian hamster (TO-2), a model of genetically determined dilated cardiomyopathy. Either vehicle or a slow releasing form of ONO-1301 (ONO-1301-PLGA, 10 mg/kg/3 weeks) was administered subcutaneously every 3 weeks to TO-2 hamsters from 24 to 32 weeks of age ( n = 12 for each group). Age-matched F1B hamsters were used as a control. Plasma concentration of HGF was elevated in ONO-1301-PLGA group ( p < 0.05). Echocardiographic study demonstrated that LV fractional shortening was significantly improved in the ONO-1301-PLGA group (25 ± 4%, p < 0.01) compared with that in the vehicle group (19 ± 2%). Cardiac fibrosis was significantly reduced by ONO-1301-PLGA ( p < 0.05) as determined by Azan-Mallory staining. Capillary density of left ventricle was markedly reduced in TO-2 hamsters. ONO-1301-PLGA significantly increased capillary density in TO-2 group ( p < 0.05). ONO-1301 improved LV dysfunction and reduced cardiac fibrosis in the hamster model of dilated cardiomyopathy. ONO-1301 might hold a therapeutic potential in the treatment of dilated cardiomyopathy.

Altered microvasculature is involved in remodeling processes in cardiomyopathic hamsters.

The cardiomyopathic hamster (BIO TO2) is a well-established model of heart failure. Deterioration of cardiac function in BIO TO2 is attributed to a defect in delta-sarcoglycan, whereas cardiac dysfunction in delta-sarcoglycan knockout mice is caused by microvascular abnormalities. We examined the relation between cardiac function and the microvasculature, including angiogenic factors, in BIO TO2. At the age of 5 weeks, percent fractional shortening (%FS) and positive rate of change in left ventricular pressure over time (dP/dt max) were lower in BIO TO2 than in age-matched F1B controls. Capillary density, capillary/myocyte (CM) ratio, capillary domain area (CDA), and myocyte density were similar between BIO TO2 and F1B controls. At the ages of 13 and 20 weeks, BIO had significantly lower capillary and myocyte densities and a significantly higher CM ratio and CDA. Myocyte density positively correlated with %FS and dP/dt max. There were no significant differences in mRNA expression for VEGF, Flt-1, angiopoietin-1, or angiopoietin-2 between BIO TO2 and F1B control. Progressive myocyte loss is responsible for deterioration of cardiac function in BIO TO2. The impaired neovascularization may be involved in the progress of cardiac remodeling in cardiomyopathic hamsters.

Ameliorating effects of amlodipine on plasma and myocardial catecholamines in BIO 53.58 Syrian hamsters, a model of dilated cardiomyopathy

Our previous study has shown that the concentrations of norepinephrine, epinephrine and dopamine in the plasma of BIO 53.58 hamsters (a model of dilated cardiomyopathy: DCM) at 18 weeks of age (severe cardiomyopathic stage) were twice those of age-matched F1B control and conversely the myocardial norepinephrine level was decreased. The present study was undertaken to examine the effect of amlodipine on catecholamine concentration, myocardial receptors and histopathological changes in BIO 53.58 hamsters. Oral administration of amlodipine (10 mg/kg/day) for 7 weeks in 11 week-old-BIO 53.58 hamsters brought about marked decreases in the concentrations of norepinephrine, epinephrine and dopamine in the plasma, compared with those in vehicle-treated BIO 53.58 hamsters. This was accompanied by a concomitant increase in the concentration of myocardial catecholamine concentration. In other words, the concentrations of catecholamines in plasma and myocardium of amlodipine administered BIO 53.58 hamsters approximated to the control level in age-matched F1B. In addition, amlodipine administration caused a significant reduction of calcium deposition with a tendency toward a decrease in the myocardial necrosis, and it had little effect on the affinity and number of specific binding for (+)-[ 3H]PN 200–110, (−)-[ 125I]iodocyanopindolol (CYP) and [ 3H]prazosin in the myocardium. In conclusion, the present study shows that administration of amlodipine in BIO 53.58 hamsters may exhibit ameliorating effect on plasma and myocardial catecholamines with a significant reduction of calcium deposition. These data may offer further support for the use of amlodipine in patients with DCM.

Extracellular Matrix Regulation in the Development of Syrian Cardiomyopathic Bio 14.6 and Bio 53.58 Hamsters

The myocardium contains a collagen matrix composed primarily of collagen and fibronectin, which are major determinants of the myocardial architecture, structural integrity and mechanical properties. The present study was undertaken to determine the age-related changes of the accumulation and degradation of the collagen matrix in Syrian myopathic hamsters, of the Bio 14.6 and Bio 53.58 strains. Those hamsters were used as models for hypertrophic and dilated cardiomyopathy, respectively. The heart to body weight ratio in the Bio 14.6 strains was higher (P<0.05) than that in the age-matched F1b strains. In the Bio 53.58 strains, the heart to body weight ratio was higher at 8 and 42 weeks of age than that in the F1b strains. The collagen content increased from 22 weeks of age in both Bio hamsters compared with age-matched F1b hamsters (P<0.05). In both cardiomyopathic hamsters, the mRNA expressions for type I and type III collagen and fibronectin all increased with aging; however, the fibronectin expression in the Bio 14.6 strains increased more at 22 weeks of age than at 42 weeks of age. The left ventricular MMP-1, MMP-2 and MMP-9 activities in Bio 53.58 strains increased with aging. However, in the Bio 14.6 strains, although MMP-1 activities increased with aging, MMP-2 and MMP-9 activities decreased at 42 weeks of age in comparison to those at 22 weeks of age. Thus, the MMP activation differed between two cardiomyopathic models at the stage of heart failure, although the collagen synthesis was elevated in both models. In conclusion, it would seem that the relative balance between the synthesis and the removal of collagen may contribute to the changes in the left ventricular geometry in two different types of cardiomyopathy.

Role of endothelin in deterioration of heart failure due to cardiomyopathy in hamsters: increase in endothelin-1 production in the heart and beneficial effect of endothelin-A receptor antagonist on survival and cardiac function.

We previously reported that chronic endothelin (ET) receptor blockade ameliorated the survival rate and cardiac hemodynamics in rats with chronic heart failure (CHF) due to myocardial infarction. However, it remains unclear whether ET-1 is involved in the pathophysiology of cardiomyopathy, which is one of the major causes of CHF. Accordingly, we investigated the production of ET-1 in the heart and the effect of chronic ETA receptor blockade on survival rate and cardiac function in the Bio 14.6 hamster, which is an idiopathic model of CHF caused by cardiomyopathy. We used 52-week-old Bio 14.6 cardiomyopathic hamsters and age-matched F1b normal hamsters. The expression of preproET-1 mRNA and the ET-1 level in the hearts were markedly higher in the cardiomyopathic hamsters than in the normal hamsters. The cardiomyopathic hamsters showed severe CHF, illustrated by lower left ventricular (LV) +dP/dt/Pmax and right ventricular (RV) +dP/dt/Pmax and by higher LV end-diastolic pressure (EDP), RVEDP, and central venous pressure compared with the normal hamsters. Long-term (9 weeks) treatment with an ETA antagonist (TA-0201, 1.3 mg. kg-1. d-1) markedly increased survival of cardiomyopathic hamsters (untreated, 16%; TA-0201-treated, 65.2%; P<0.001). After 6 weeks of treatment, LV +dP/dt/Pmax and RV +dP/dt/Pmax were significantly higher and LVEDP and RVEDP were lower in the TA-0201-treated group than in the untreated group, suggesting that chronic TA-0201 treatment effectively prevented deterioration of cardiac dysfunction. In the cardiomyopathic hamsters with CHF, the production of ET-1 in the heart was markedly increased, and chronic ETA receptor blockade greatly ameliorated survival and cardiac dysfunction. These results suggest that ET-1 plays an important role in the deterioration of CHF caused by cardiomyopathy, and ETA antagonists may exert therapeutic effects in CHF due to cardiomyopathy.

A role of myofilament Ca 2+ sensitivity in enhanced vascular reactivity in cardiomyopathic hamsters

We compared the contractile responses to vasoconstrictors in aortas from 20- to 22-week old cardiomyopathic hamsters, BIO 53.58 strain, and age-matched F1b strain controls. Aortas from cardiomyopathic hamsters exhibited greater contractions in response to phenylephrine, angiotensin II, and high K + than did the controls. Neither endothelium removal nor the presence of indomethacin and N ω-nitro- l-arginine ( l-NNA) affected the enhanced contractile responses to these vasoconstrictors, indicating no involvement of endogenous prostanoids and nitric oxide from the endothelium. The contractile response to phorbol-12,13-dibutyrate (PDB) was also more markedly increased in cardiomyopathic aortas regardless of whether extracellular Ca 2+ was present. The contractile response of cardiomyopathic aorta to phenylephrine was more sensitive to the inhibitory actions of the protein kinase C inhibitors staurosporine and calphostin C than was that of control aorta. These results suggest that activation of protein kinase C is partly involved in the enhanced phenylephrine response of cardiomyopathic aorta. None of nifedipine, ryanodine, and cyclopiazonic acid modified the maximum contractions induced by phenylephrine in either cardiomyopathic aortas or controls. The Ca 2+ sensitivity of tension was significantly increased in β-escin-skinned smooth muscle of mesenteric artery from cardiomyopathic hamsters compared to that of controls. PDB induced Ca 2+ sensitization, but significantly only in cardiomyopathic hamsters. We propose that the enhanced vascular reactivity in cardiomyopathic hamsters may primarily result from increased Ca 2+ sensitivity of contractile proteins. In addition, protein kinase C-mediated Ca 2+ sensitization may further contribute to the enhanced vascular response to agonists.

The role of guanine nucleotide binding proteins in hamsters with myocardial hypertrophy.

To clarify the role of the guanine nucleotide binding proteins (G-proteins) in the pathogenesis of myocardial hypertrophy, we investigated the alterations in myocardial G proteins in 20-week-old F1b hamsters with pressure overload induced for 3 days (3-day AS), 7 days (7-day AS) and 14 days (14-day AS) by the stenosis of the abdominal aorta, and in 4- and 20 week-old BIO 14.6 Syrian hamsters (4-wk and 20-wk BIO) with genetic myocardial hypertrophy. The hearts of 7-day AS, 14-day AS and 20-wk BIO with left ventricular hypertrophy exhibited a decrease in the mRNA levels detected by Northern blot analysis and protein levels of G protein detected by Western blot analysis as compared with sham-operated and age-matched F1b hearts. The function of Gs or Gi showed a concomitant reduction in both models of myocardial hypertrophy. The hearts of 3-day AS and 4-wk BIO without myocardial hypertrophy showed no changes in G proteins as compared with sham-operated and age-matched F1b hearts. These results suggest that a decrease in G proteins is not involved in the pathogenesis of myocardial hypertrophy, but that myocardial hypertrophy reduced the G proteins.

Decreased Na,K-ATPase gene expression in cardiomyopathic hamster hearts

We studied Na, K-ATPase mRNA expression in cardiomyopathic (Bio 14.6) and normal (F1b) Syrian hamster ventricles. In Northern blot analysis, Na,K-ATPase α1, α2, α3 and β1 isoform mRNAs were detected in 3-week-old Bio 14.6 and F1b hamster venticles. We then investigated the expression of α1 subunit mRNA in Bio 14.6 hamster ventricles at the ages of 3 weeks prehypertrophic and 30 weeks hypertrophic, and in age-matched F1b hamster ventricles. The α1 subunit mRNA levels in Bio 14.6 hamster ventricles were approximately 50% lower than those in F1b hamster ventricles at both 3 and 30 weeks of age. Na,K-ATPase activity measured in membrane fractions from the venticles of 3-week-old Bio 14.6 hamsters was also approximately 20% lower than that of F1b hamsters, suggesting that the differences in the mRNA level were associated with the differences in the protein level. We conclude that Na,K-ATPase mRNA expression and enzyme activity are significantly decreased in the hearts of Bio 14.6 hamsters even before the onset of hypertrophy and cardiomyopathy, suggesting that the altered expression of Na,K-ATPase gene is an early event in the pathogenesis of cardiomyopathy in this animal model.

Diminished beta-adrenergic receptor responsiveness and cardiac dilation in hearts of myopathic Syrian hamsters (BIO 53.58) are associated with a functional abnormality of the G stimulatory protein.

Previous studies have demonstrated a diminution in the bioactivity of the guanine nucleotide-binding regulatory protein that stimulates adenylyl cyclase (Gs) in hearts of the hypertrophic BIO 14.6 Syrian hamster. In this study, we measured functional activity and immunodetectable levels of Gs in a mutant strain of hamsters (BIO 53.58) that develop a dilated cardiomyopathy. Pathological studies demonstrated that 100-day-old BIO 53.58 hamsters had substantial ventricular dilation when compared with age-matched F1B controls. Additionally, these 100-day-old hamsters demonstrated diminished contractile response to beta-adrenergic receptor stimulation. The pathological and hemodynamic changes were associated with defective coupling of Gs to adenylyl cyclase as adenylyl cyclase activation was distinctly decreased in the presence of isoproterenol, fluoride ion, guanine nucleotides, and forskolin. Additionally, the ability of the alpha-subunit of Gs to reconstitute isoproterenol-stimulated adenylyl cyclase activity in S49 cyc- membranes was reduced approximately 65%. By contrast, cyc- complementation assays did not reveal a difference between the functional activity of Gs in hearts from 30-day-old BIO 53.58 hamsters and F1B controls. Furthermore, beta-adrenergic receptor stimulation of adenylyl cyclase in the membranes of the young BIO 53.58 hamsters was not significantly different from controls. The substantial alterations in Gs bioactivity in hearts of the 100-day-old BIO 53.58 hamsters was not associated with alterations in the immunodetectable levels of either alpha Gs or alpha Gi on Western Blots. These results suggest that G protein changes are associated with ventricular dilation in BIO 53.58 hamsters and that G protein levels are not always reflective of G protein bioactivity.