BIO TO-2 Research Articles

Developmental Changes in the ECG of a Hamster Model of Muscular Dystrophy and Heart Failure

Aberrant autonomic signaling is being increasingly recognized as an important symptom in neuromuscular disorders. The δ-sarcoglycan-deficient BIO TO-2 hamster is recognized as a good model for studying mechanistic pathways and sequelae in muscular dystrophy and heart failure, including autonomic nervous system (ANS) dysfunction. Recent studies using the TO-2 hamster model have provided promising preclinical results demonstrating the efficacy of gene therapy to treat skeletal muscle weakness and heart failure. Methods to accelerate preclinical testing of gene therapy and new drugs for neuromuscular diseases are urgently needed. The purpose of this investigation was to demonstrate a rapid non-invasive screen for characterizing the ANS imbalance in dystrophic TO-2 hamsters. Electrocardiograms were recorded non-invasively in conscious ∼9-month old TO-2 hamsters (n = 10) and non-myopathic F1B control hamsters (n = 10). Heart rate was higher in TO-2 hamsters than controls (453 ± 12 bpm vs. 311 ± 25 bpm, P < 0.01). Time domain heart rate variability, an index of parasympathetic tone, was lower in TO-2 hamsters (12.2 ± 3.7 bpm vs. 38.2 ± 6.8, P < 0.05), as was the coefficient of variance of the RR interval (2.8 ± 0.9% vs. 16.2 ± 3.4%, P < 0.05) compared to control hamsters. Power spectral analysis demonstrated reduced high frequency and low frequency contributions, indicating autonomic imbalance with increased sympathetic tone and decreased parasympathetic tone in dystrophic TO-2 hamsters. Similar observations in newborn hamsters indicate autonomic nervous dysfunction may occur quite early in life in neuromuscular diseases. Our findings of autonomic abnormalities in newborn hamsters with a mutation in the δ-sarcoglycan gene suggest approaches to correct modulation of the heart rate as prevention or therapy for muscular dystrophies.

Abstract 17091: High Saturated Fat Intake Improves Survival in Genetic Cardiomyopathy Compared to a High Polyunsaturated Fat Diet or a Low Fat Diet

Surprisingly, a high fat diet comprised mainly of saturated fatty acids improves LV function and survival in rat models of heart failure induced by hypertension or myocardial infarction. The mechanism for this effect is not clear, nor is it known if a similar effect occurs with a high fat diet composed of plant derived polyunsaturated fatty acids (PUFA), or in genetic cardiomyopathies. We determined if survival in cardiomyopathic hamsters (Bio TO-2 strain) is prolonged by a high fat diet compared to a low fat diet (see table). Further, we compared the effect of high fat diets enriched with either saturated fat (palmitate and stearate), or PUFAs from plant sources(primarily linoleic and α-linolenic acids). Cardiomyopathic hamsters (6 wks old) were fed either a Low Fat diet; a High PUFA diet, or a High Saturated Fat diet. Survival was assessed (n=30/group), and subgroups were evaluated at 30 wks of age (n=12/group) for LV and mitochondrial function. The diet has no effect on LV function as assessed by echocardiography, and there was no difference in body weight or LV mass. Since there is impaired mitochondrial function in heart failure and dietary lipid composition might positively impact mitochondrial function, isolated mitochondria were assessed. Respiration and Ca 2+ -induced mitochondrial permeability transition were unaffected by diet. On the other hand, the high PUFA diet increased fat pad mass compared with the two other cardiomyopathic groups and elevated plasma free fatty acid concentration (p&lt;0.05). Importantly, there was a significant increase in survival in the high saturated sat group compared to the either the low fat or the high PUFA groups after 16 months of treatment (p&lt;0.0001). These results show that a high fat diet comprised largely of long chain saturated fatty acids increase survival in cardiomyopathic hamsters compared to either a low fat diet or a high fat diet comprised of PUFA from plant sources. The effect was independent of improved mitochondrial function.

Roles of saturated vs. polyunsaturated fat in heart failure survival: not all fats are created equal

This editorial refers to ‘High intake of saturated fat, but not polyunsaturated fat, improves survival in heart failure despite persistent mitochondrial defects’ by T.F. Galvao et al. , doi:10.1093/cvr/cvr258. Galvao et al. 1 compare the effects of two high-fat diets, both 45% kcal but sourced from either polyunsaturated fatty acids (PUFA; linoleic and α-linolenic acids) or saturated fat (palmitate and stearate) in a male δ-sarcoglycan null Bio TO2 hamster model of heart failure. Surprisingly, the heart failure hamsters fed the diet high in saturated fat showed increased survival compared with hamsters fed a diet high in PUFA or the control standard diet (12% kcal from fat). Importantly, in all three diet groups, the hamsters developed dysfunction at both the left ventricle and cardiac mitochondria levels. Despite the lack of a cardiac function phenotype, the PUFA-fed hamsters showed elevated Ca2+-induced mitochondrial permeability transition pore opening rates compared with both the saturated fat and standard fed hamsters. The clear distinction in obesity effects differentially driven by high-fat diets from different lipid sources, in the context of heart failure, has not been previously studied. The present study is important because it reveals the strong impact of fat source on cardiovascular events and survival rates in the setting of existing heart failure. A diet high in saturated fat promotes obesity by stimulating an inflammatory response that can induce cardiac concentric hypertrophy and alter the stress response.2 Obesity resulting either from saturated or PUFA …

High intake of saturated fat, but not polyunsaturated fat, improves survival in heart failure despite persistent mitochondrial defects

The impact of a high-fat diet on the failing heart is unclear, and the differences between polyunsaturated fatty acids (PUFA) and saturated fat have not been assessed. Here, we compared a standard low-fat diet to high-fat diets enriched with either saturated fat (palmitate and stearate) or PUFA (linoleic and α-linolenic acids) in hamsters with genetic cardiomyopathy. Male δ-sarcoglycan null Bio TO2 hamsters were fed a standard low-fat diet (12% energy from fat), or high-fat diets (45% fat) comprised of either saturated fat or PUFA. The median survival was increased by the high saturated fat diet (P< 0.01; 278 days with standard diet and 361 days with high saturated fat)), but not with high PUFA (260 days) (n = 30-35/group). Body mass was modestly elevated (∼10%) in both high fat groups. Subgroups evaluated after 24 weeks had similar left ventricular chamber size, function, and mass. Mitochondrial oxidative enzyme activity and the yield of interfibrillar mitochondria (IFM) were decreased to a similar extent in all TO2 groups compared with normal F1B hamsters. Ca(2+)-induced mitochondrial permeability transition pore opening was enhanced in IFM in all TO2 groups compared with F1B hamsters, but to a significantly greater extent in those fed the high PUFA diet compared with the standard or high saturated fat diet. These results show that a high intake of saturated fat improves survival in heart failure compared with a high PUFA diet or low-fat diet, despite persistent mitochondrial defects.

Body Temperature Circadian Rhythm Variability Corresponds to Left Ventricular Systolic Dysfunction in Decompensated Cardiomyopathic Hamsters

Background A declining amplitude of body temperature circadian rhythm (BTCR) predicts decompensation or death in cardiomyopathic hamsters. We tested the hypothesis that changes in BTCR amplitude accompany significant changes in left ventricular (LV) size and function. Methods and Results Using intraperitoneal transmitters, we continuously monitored the temperature of 30 male BIO TO-2 Syrian dilated cardiomyopathic hamsters. Cosinor analysis was used to detect significant changes—defined as changes >1 standard deviation from the baseline amplitude for 3 consecutive days—in BTCR amplitude over each hamster’s lifespan. The Student t-test was used to compare BTCR variability and LV size and function (as assessed by 2D echocardiography) between baseline and the time that BTCR amplitude declined. All hamsters received 10 mg/kg furosemide daily. At the time of BTCR amplitude decline, functional parameters had changed significantly ( P < .0001) from baseline: ejection fraction (0.31 ± 0.09% vs. 0.52 ± 0.08%), LV end-systolic volume (0.11 ± 0.03 vs. 0.05 ± 0.02 cm 3), and LV end-diastolic volume (0.16 ± 0.04 vs. 0.10 ± 0.03 cm 3). Conclusions In decompensated cardiomyopathic hamsters, a decline in BTCR amplitude was associated with progression of heart failure and cardiac decompensation. Variation in BTCR warrants further investigation because of its potential implications for the diagnosis and treatment of cardiovascular disorders.

Gait Disturbances in Dystrophic Hamsters

The delta-sarcoglycan-deficient hamster is an excellent model to study muscular dystrophy. Gait disturbances, important clinically, have not been described in this animal model. We applied ventral plane videography (DigiGait) to analyze gait in BIO TO-2 dystrophic and BIO F1B control hamsters walking on a transparent treadmill belt. Stride length was ∼13% shorter (P < .05) in TO-2 hamsters at 9 months of age compared to F1B hamsters. Hindlimb propulsion duration, an indicator of muscle strength, was shorter in 9-month-old TO-2 (247 ± 8 ms) compared to F1B hamsters (272 ± 11 ms; P < .05). Braking duration, reflecting generation of ground reaction forces, was delayed in 9-month-old TO-2 (147 ± 6 ms) compared to F1B hamsters (126 ± 8 ms; P < .05). Hindpaw eversion, evidence of muscle weakness, was greater in 9-month-old TO-2 than in F1B hamsters (17.7 ± 1.2° versus 8.7 ± 1.6°; P < .05). Incline and decline walking aggravated gait disturbances in TO-2 hamsters at 3 months of age. Several gait deficits were apparent in TO-2 hamsters at 1 month of age. Quantitative gait analysis demonstrates that dystrophic TO-2 hamsters recapitulate functional aspects of human muscular dystrophy. Early detection of gait abnormalities in a convenient animal model may accelerate the development of therapies for muscular dystrophy.

Enhancement of shortening velocity, power, and acto‐myosin crossbridge (CB) kinetics following long‐term treatment with propionyl‐L‐carnitine, coenzyme Q10, and omega‐3 fatty acids in BIO TO‐2 cardiomyopathic Syrian hamsters papillary muscle

Impaired functions of myocardial muscle cells in human and animals, is a primary defect associated with idiopathic dilated cardiomyopathy (DCM). The pathophysiological mechanisms implicated in the DCM are yet to be clarified and an effective therapy is still not available. The BIO TO-2 cardiomyopathic Syrian Hamsters (CMSHs) represent an animal model of idiopathic DCM. The aim of this study was to investigate the effect of long-term treatment (2 months) with propionyl-L-carnitine (PLC), coenzyme Q(10), omega-3 fatty acids and a combination of these three agents (formulation HS12607) on mechanical properties and acto-myosin crossbridges (CBs) kinetics of left ventricular (LV) papillary muscle from control and treated 10 month old BIO TO-2 CMSHs. Isometric and isotonic contractile properties of isolated papillary muscle from control and treated CMSHs were investigated, and acto-myosin CB number, force and kinetics were calculated using Huxley's equations. Mechanical parameter values were higher in treated than in control hamsters, particularly when substances were administered together in a coformulation (HS12607). Compared to control, HS12607-treated papillary muscles showed a significant increase of maximum peak isometric tension (P(o)) (30.06 +/- 4.91 vs. 19.74 +/- 5.00 mN/mm(2)), maximum extent of muscle shortening (0.13 +/- 0.03 vs. 0.07 +/- 0.02 L/L(max)), maximum unloaded shortening velocity (1.18 +/- 0.24 vs. 0.53 +/- 0.13 L/L(max) s(-1)) and maximum peak of power output (5.52 +/- 1.61 vs. 1.58 +/- 0.83). The curvature of the hyperbolic force-velocity relationships did not differ between control and treated hamsters. When compared to controls, acto-myosin CB number increased in treated hamsters [(6.67 +/- 1.91) 10(10)/mm(2) vs. (3.55 +/- 2.08) 10(10)/mm(2)], whereas the unitary force of single CB was similar in control and treated animals. The peak value of the rate constant for CB attachment (f(1)) and detachment (g(2)) was higher in treated animals when compared to control. (93.87 +/- 25.82 vs.47.28 +/- 10.88 s(-1) and 214.40 +/- 44.64 vs. 95.56 +/- 23.49 s(-1), respectively). In conclusion, the present study illustrates that supplementation with PLC, CoQ(10) and omega-3 fatty acids improved motor parameters, energetic, and CB kinetics of BIO TO-2 CMSH papillary muscle indicating that these naturally occurring substances may be a valid adjuvant to conventional therapy in DCM.

Influence of Enalapril Therapy Schedule on the Progression of the Disease in Dilated Cardiomyopathic Syrian Hamsters (Bio TO-2 strain)

The influence of enalapril therapy schedule on the progression of the disease in terms of hemodynamics, cardiac remodeling and survival was assessed in cardiomyopathic Syrian hamsters (CMHs). CMHs (Bio TO-2 dilated strain) were treated orally with enalapril at 20 mg/kg/day from 60 to 200 (early treatment), from 120 to 200 (late treatment) or 120 to 250 (prolonged treatment) days of age. In survival studies, CMHs were treated until 90% of controls are death. Early, late and prolonged treatments significantly decreased mean arterial blood pressure (-23%, -27% and -22%, respectively), but had no effects on cardiac output and stroke volume. Late and prolonged treatments significantly decreased total peripheral resistance (-38% and -24%, respectively), but not early treatment. Only, prolonged treatment significantly decreased left ventricle (LV) end diastolic blood pressure (-60%). Early, late and prolonged treatments significantly decreased LV collagen density (-44%, -31% and -54%, respectively) and LV cavity area (-26%, -21% and -29%, respectively). Survival was significantly improved when enalapril was administered from 120 days of age, but not significantly when administered earlier. In conclusion, enalapril exerted beneficial effects (improvement of cardiac function and prolonged survival) more marked when the treatment was begun late in the evolution of congestive heart failure.

Passive Stress in Myofibrils from Cardiomyopathic Hamsters

Dilated cardiomyopahty (DCM) is a frequent heart disease characterized by cardiac dilation and contractile dysfunction. The Bio TO-2 hamster is a genetic animal model of human DCM. The purpose of this research is to study the progression of DCM by comparing over time the passive mechanical properties of left ventricular wall myofibrils from TO-2 hamsters to those from F1B control hamsters. To date, we measured the passive stress-sarcomere length relations for two myofibrils each from experimental and control animals aged 36 weeks. Myofibrils were attached at one end to a glass needle controlled by a motor for stretching, and at the other end to a silicon-nitride nanolever of known stiffness for force measurements. Sarcomere lengths were measured from the myofibrillar striation patterns. Passive stresses in the experimental and control myofibrils were comparable. More passive mechanical experiments will be performed to confirm this result. In a single myofibril, titin is thought to be responsible for essentially all of the passive stress response to stretch (Linke et al., 1994; Bartoo et al., 1997). Titin depletion experiments and titin molecular weight determination will therefore also be performed to detect changes in titin isoform.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Cardiomyopathic Syrian Hamster as a Model of Congestive Heart Failure

Cardiomyopathic Syrian hamsters (Bio TO-2 dilated strain) constitute an animal model of congestive heart failure, which progressively develops an alteration of cardiac function leading to decreased arterial blood pressure and musculo-cutaneous blood flow associated with a complex process of cardiac remodeling including left ventricle dilation, wall thinning, and greater collagen density. The protocols described in this unit are designed to assess the pharmacological effects of new therapeutic strategies on cardiac and systemic hemodynamics, morphometry (body and target organs weight), cardiac remodeling (left ventricle dilation and collagen density), and survival in this model of dilated cardiomyopathy. Examples of results obtained with enalapril, an angiotensin I converting enzyme inhibitor, are provided for illustrative purposes.

Positive inotropic effect of coenzyme Q10, omega‐3 fatty acids and propionyl‐L‐carnitine on papillary muscle force‐frequency responses of BIO TO‐2 cardiomyopathic Syrian hamsters

The inability of heart muscle to generate ventricular pressure to adequately propel blood through the cardiovascular system is a primary defect associated with congestive heart failure (CHF). Force-frequency relationship (FFR) is one of the main cardiac defects associated with congestive heart failure. Thus FFR is a convenient methodological tool for evaluating the severity of muscle contractile dysfunction and the effectiveness of therapeutic agents. Papillary muscle isolated from BIO TO-2 cardiomyopathic Syrian hamsters (CMSHs), show a depressed FFR and represents an animal model of human idiopathic dilated cardiomyopathy. In the present study we investigated the effect of CoQ10, omega-3 fatty acids, propionyl-L-carnitine (PLC) and a combination of these 3 agents (formulation HS12607) on FFR in 8 month old BIO TO-2 CMSHs. Papillary muscles isolated from the anesthetized animals were placed in an incubation bath and attached to an isometric force transducer. A digital computer with an analog/digital interface allowed control of both muscle developed force and electrical stimulus parameters. Force-frequency response was evaluated, at Lmax, with increasing frequencies: 0.06, 0.12, 0.25, 0.5, 1, 2 and 4 Hz. HS12607-treatment produced a positive inotropic effect resulting in a significant enhancement (p < 0.05) of the peak force at the highest frequencies (1-4 Hz). In the range of frequency of 1-4 Hz also CoQ10 and omega-3 significantly (p < 0.05) attenuated the fractional decline in developed force. The significant improvement (p < 0.05) of the timing parameter peak rate of tension rise (+ T') and peak rate of tension fall (-T') indicating a faster rate of muscle contraction and relaxation respectively, found in CoQ10, omega-3 and PLC-treated CMSHs, may be due to the positive effects of these substances on sarcoplasmic reticulum functions. These findings suggest that naturally occurring CoQ10, omega-3 and PLC, particularly when administered together in a coformulation, might be a valid adjuvant to conventional therapy in dilated cardiomyopathy especially when considering that they are natural substances, devoid of side effects.

Combined Strategy Using Myoblasts and Hepatocyte Growth Factor in Dilated Cardiomyopathic Hamsters

There are few reports on treating dilated cardiomyopathy (DCM) with myoblast transplantation, and these show limited efficacy. Hepatocyte growth factor has cardioprotective effects on failed myocardium. Here, we combined these two treatments and analyzed cardiac function in DCM hamsters. Twenty-seven-week-old BIO TO-2 hamsters, which show moderate cardiac remodeling, were divided into four treatment groups: myoblast transplantation (T group, n = 24), human hepatocyte growth factor gene transfection (H group, n = 29), combined treatment (T+H group, n = 21), and medium alone (C group, n = 26). Significantly better fractional shortening was observed in the T+H group compared with the others (14.9% +/- 1.0%, 11.7% +/- 1.5%, 11.3% +/- 1.3%, and 8.6% +/- 1.1 %, in the T+H, H, T, and C groups, respectively). Immunohistochemical analysis showed alpha- and beta-sarcoglycan expression in the hearts of the H and T+H groups but not in the other groups. There was less myocardial fibrosis in the H and T+H groups than in the other two, and neovascularization in the T+H group was significantly greater than in the other groups (266 +/- 24, 209 +/- 27, 199 +/- 36, and 96 +/- 17 vessels/mm2, in the T+H, H, T, and C groups, respectively). Survival was significantly prolonged in the H and T+H groups compared with the other groups. Hepatocyte growth factor gene transfection and myoblast transplantation preserved the cardiac function of DCM hamsters, probably through different mechanisms, and the combined treatments preserved cardiac performance better than either treatment alone. The combined therapy is a promising strategy for treating DCM.

Rapid screen for heart failure autonomic nervous system imbalance in cardiomyopathic BIO TO‐2 hamsters

The cardiomyopathic BIO TO-2 hamster is a recognized model for heart failure including autonomic nervous system dysfunction. Recent studies using BIO TO-2 hamster that has a large deletion in the -sarcoglycan gene have provided promising results showing the efficacy of gene therapy in heart failure. Methods to accelerate preclinical testing of gene therapy and new drugs for heart disease are urgently needed. This study demonstrates a rapid non-invasive screen for characterizing autonomic nervous system imbalance in BIO TO-2 hamsters thus showing its usefulness in the preclinical testing of drugs for heart failure. EKGs were recorded non-invasively through the underside of the paws in conscious BIO TO-2 hamsters and controls (BIO F1-B) using an electrode-embedded platform. Each recording took only a few minutes. Heart rate was significantly higher in BIO TO-2 hamsters. Time domain heart rate variability, an index of parasympathetic tone, was significantly lower, as was the coefficient of variance of the RR interval. Power spectrum analysis showed a reduced high-frequency power spectrum and an increased low/high-frequency ratio, indicating autonomic imbalance with an increased sympathetic tone and a decreased parasympathetic tone in BIO TO-2 hamsters. Thus, autonomic nervous system dysfunction of the heart in hamsters can be quickly and noninvasively quantified. This technique and the findings are of practical significance in accelerating the testing of new therapeutic modalities in the treatment of heart failure.

Cardiomyopathic BIO hamsters are excellent animal models for heart failure and for gene therapy in myopathies

A spontaneous mutation affecting the striatal muscle in a Syrian hamster strain was discovered in 1959 (Homburger et al, New hereditary disease of Syrian hamsters. Primary, generalized polymyopathy and cardiac necrosis, Arch Intern Med. 1962;110:–2). Subsequent research over the past many years has revealed that this mutation in BIO hamsters is confined to a single autosomal-recessive gene that affects all muscle systems (striated, smooth and cardiac muscles). Currently, there are two distinctly different yet related myopathic BIO hamster strains (BIO 14.6 & BIO TO-2) and these are widely being used as animal models for autosomal recessive cardiomyopathy. One important feature of these hamsters is premature death due to progressive myocardial necrosis and eventual heart failure. At the molecular level, the defective gene has been identified as being related to the delta-sarcoglycan gene and this finding has stimulated a great deal of interest in gene therapy in diseases involving the three muscle groups (striated, smooth and cardiac). While there is an extensive literature on these BIO hamster models for various applications, there is a need to provide updated information on their characteristics as compared with control BIO hamsters. These include physical measurements such as body weight changes throughout their life span, survival curves, blood chemistries including lipid profiles, and hemodyamics. Additional applications for these BIO hamster models are also being recognized.

Longer preservation of cardiac performance by sheet-shaped myoblast implantation in dilated cardiomyopathic hamsters

Cell therapy is a promising strategy for ischemic cardiomyopathy. However, the direct injection method has limitations for generalized cell delivery, especially in dilated cardiomyopathy (DCM). We hypothesized that a sheet-shaped myoblast graft would be superior to direct injection for improving cardiac performance in DCM. Male 27-week-old BIO TO-2 (DCM) hamsters that showed moderate cardiac remodeling were used as recipients. Myoblasts isolated from BIO F1B hamsters were cultured on dishes coated with poly(N-isopropylacrylamide), a temperature-responsive polymer, and spontaneously detached as a sheet-shaped graft at 20 degrees C without enzymatic treatment. Three different therapies were conducted: (1) sheet-shaped myoblast graft implantation (S group, n=29); (2) myoblast injection (M group, n=28); and (3) sham operation (C group, n=28). In the S group, two sheet-shaped myoblast grafts were implanted on the left ventricle (LV) wall, and in the M group, myoblasts were injected into the right ventricle (RV) and LV walls. After the sheet-shaped myoblast grafts were implanted, echocardiography demonstrated that the dilated LV dimension was significantly reduced, whereas the hearts in other groups showed a progression of LV dilation. The fractional shortening in the M and C groups decreased significantly while that in the S group was maintained at the preoperative level for 3 months after the operation. Histological examination demonstrated that in the S group, the LV wall thickness was increased, with viable myoblasts, and myocardial fibrosis was decreased compared with the other groups. Immunohistochemical staining demonstrated alpha-sarcoglycan and beta-sarcoglycan expression on the basement membrane of the cardiomyocytes in the S group but not in the other groups. The life expectancy was significantly prolonged in the S group. Sheet-shaped myoblast graft implantation improved cardiac performance and prolonged life expectancy, associated with a reduction in myocardial fibrosis and re-organization of the cytoskeletal proteins in DCM hamsters. Thus, sheet-shaped autologous myoblast graft implantation may induce restoration of the heart in DCM.

Effect of Angiotensin II Type 1 Receptor Blocker on Cardiac Angiotensin-Converting Enzyme and Chymase-Like Activities, and Cardiac Fibrosis in Cardiomyopathic Hamsters

It has been reported that cardiac chymase has an effect on cardiac fibrosis through the Angiotensin (Ang) II formation and an Ang II-independent mechanism. In the present study, Ang II type 1 (AT1) receptor blocker (candesartan cilexetil) was administered to dilated cardiomyopathic (DCM; Bio TO2) hamsters for 4 weeks to study the effect of AT1 receptor blocker on cardiac chymase-like activity and cardiac fibrosis. Echocardiography, histological examination, and assessment of cardiac angiotensin-converting enzyme (ACE)/chymase-like activities were conducted. Hamsters showed cardiac dysfunction due to increased left ventricular dimensions and decreased ventricular wall thickness, significant increase in cardiac chymase-like activity, and fibrosis. This result indicates that the cardiac chymase-like activity is responsible for cardiac fibrosis. When candesartan cilexetil was administered to Bio TO2 hamsters, cardiac chymase-like activity increased significantly, whereas cardiac fibrosis decreased significantly. Cardiac ACE and chymase-like activities were unchanged in non-DCM hamsters with candesartan cilexetil. This suggests that the cardiac Ang II formation mechanism was stimulated by suppressing the effect of cardiac Ang II, and cardiac chymase-like activity could be increased. Moreover, this mechanism may be more highly activated if cardiac Ang II is activated in the heart. In conclusion, we demonstrated that AT1 receptor blocker reduced cardiac fibrosis, although cardiac chymase-like activity increased. Because the Ang II-forming pathway and the effect of chymase in hamsters is similar to that in dogs, the results of the present study may supplement the available information for dogs.

Reorganization of cytoskeletal proteins and prolonged life expectancy caused by hepatocyte growth factor in a hamster model of late-phase dilated cardiomyopathy

It has been postulated recently that changes in cytoskeletal and sarcolemmal proteins initiate a final common pathway for contractile dysfunction in dilated cardiomyopathy. In ischemic cardiomyopathy, hepatocyte growth factor plays an important role in reorganizing the impaired cytoskeletal proteins in several cell types. We have tested the hypothesis that hepatocyte growth factor might improve life expectancy through modification of the molecular process that contributes to impairment in dilated cardiomyopathy. Adult male 27-week-old BIO TO-2 hamsters, which show moderate cardiac remodeling, were divided into treatment groups that received (1) hemagglutinating virus of Japan liposomes containing human hepatocyte growth factor cDNA (H group), (2) culture medium (C group), or (3) sham operation (S group). After the operation, echocardiography demonstrated that the enlarged left ventricular end-systolic dimension and decreased fractional shortening were significantly attenuated in the H group compared with the C group. There was significantly less myocardial fibrosis in the H group compared with the C group. Immunohistochemical analysis showed alpha-dystroglycan and alpha- and beta-sarcoglycan expression in the basement membrane beneath the cardiomyocytes in the H group, whereas no expression of these proteins was seen in the C group. The 40-week survival was significantly better in the H group than in the C and S groups. An improved survival associated with transient reorganization of the cytoskeletal proteins and reduction in myocardial fibrosis was achieved by hepatocyte growth factor treatment in an adult hamster model of dilated cardiomyopathy. The results suggest a therapeutic potential of hepatocyte growth factor in the treatment of dilated cardiomyopathy.

Effects of induced hyperthyroidism in normal and cardiomyopathic hamsters

Thyroid hormones (TH) enhance cardiac function and reverse gene changes typical of pathological hypertrophy. However, reports in humans, but not animals, indicate that excess TH can cause heart failure. Also, the effects of TH on normal and cardiomyopathic hearts are likely to be different. The goal of this study was to characterize the effects of prolonged hyperthyroidism on cardiac function, chamber and cellular remodeling, and protein expression in both normal and cardiomyopathic hearts. Hyperthyroidism was induced in 3-mo-old normal BIO F1B and dilated cardiomyopathic BIO TO2 hamsters. After TH treatment for 10 days and 2 mo, hemodynamics, echos, myocyte length, histology, and protein expression were assessed. After 10 days and 2 mo, there were no differences between TO2-treated (Tx) and TO2-untreated (Untx) hamsters in chamber diameters or left ventricular function. After 2 mo of treatment, however, F1B-Tx showed evidence of dilated heart failure vs. F1B-Untx. Chamber diameters were increased, and ejection fraction and positive and negative changes in pressure over time were reduced. In F1B-Tx and TO2-Tx hamsters, beta-myosin isoform expression was reduced, whereas alpha-myosin increased significantly in F1B-Tx only. In TO2-Tx hamsters, the percent of viable myocardium was increased, and percent fibronecrosis was reduced vs. TO2-Untx. Myocyte length increased with TH treatment in both hamster strains. We conclude that 1) excess TH can induce heart failure in normal animals as observed in humans, 2) reversal of myosin heavy chain expression does not necessarily improve heart function, and 3) excess TH altered cellular remodeling but did not adversely affect chamber function or dimensions in TO2 hamsters.

Contractile dysfunction of cardiomyopathic hamster myocytes is pronounced under high load conditions

To understand the pathophysiology of hereditary cardiomyopathy, the contractile function of cardiomyopathic hamsters has been studied at the cellular level. However, most of the studies to date have described the cell shortening under the unloaded condition. Using a novel force–length measurement system for single cardiomyocytes, we studied the contractile function of cardiomyopathic hamster myocytes over a wide range of loading conditions. Cardiomyocytes were isolated from the ventricles of eight- to 10-week-old cardiomyopathic (CMP) hamsters (Bio TO-2 strain), as well as control (CTRL) Syrian hamsters. A pair of carbon fibers was attached to both ends of single cardiomyocytes and their contractile characteristics were recorded while changing the after-load by controlling the fiber motion. Under the unloaded condition, the shortening fraction (CMP 9.2 ± 0.5% vs. CTRL 10.7 ± 0.8%, P = 0.06) and maximum shortening velocity (CMP 98.2 ± 7.3 μm/s vs. CTRL 147.2 ± 6.5 μm/s, P < 0.05) were decreased in CMP hamster myocytes. The peak force under the isometric condition (CMP 35.8 ± 2.2 mN/mm 2 vs. CTRL 69.0 ± 8.4 mN/mm 2, P < 0.05) and external work (CMP 898 ± 130 J/m 3 vs. CTRL 3058 ± 576 J/m 3, P < 0.05) under physiologically loaded conditions were also decreased, but the differences were more pronounced under the loaded conditions. Calcium transients measured by Indo-1 revealed elevated diastolic level, decreased peak level, and slower diastolic decay in CMP myocytes thus being consistent with the observed contractile dysfunction. These results clearly indicate the importance of the loading conditions in evaluating the contractile function of CMP hamster myocytes, and may provide insights into the mechanism of contractile dysfunction in this disease.

Contractile protein isoform and its concentration in ventricular muscle of dilated cardiomyopathic hamster (Bio TO-2 strain)

Contractile protein isoform and its concentration in ventricular muscle of dilated cardiomyopathic hamster (Bio TO-2 strain)