Mário Mateus Sugizaki

A Hypercaloric pellet-diet cycle induces obesity and co-morbidities in wistar rats

The present study was carried to develop and analyze the consequences of hypercaloric pellet-diet cycle that promotes obesity in rats. Male Wistar rats were randomly distributed into two groups that received either normal diet (ND; n =32; 3,5 Kcal/g) or a hypercaloric diet (HD; n =32; 4,6 Kcal/g). The ND group received commercial Labina rat feeding while the HD animals received a cycle of five hypercaloric diets over a 14-week period. The effects of the diets were analyzed in terms of body weight, body composition, hormone-metabolite levels, systolic arterial pressure and glucose tolerance at the 5% significance level. The hypercaloric pellet diet cycle promoted an increase in body weight and fat, systolic arterial pressure and a high serum level of glucose, triacylglycerol, insulin and leptin. The HD group also presented an impaired glucose tolerance. In conclusion, the results of this study show that the hypercaloric pellet-diet cycle promoted obesity in Wistar rats and displayed several characteristics that are commonly associated with human obesity, such as high arterial pressure, insulin resistance, hyperglycaemia, hyperinsulinaemia, hyperleptinaemia and dyslipidaemia.

Heart failure alters matrix metalloproteinase gene expression and activity in rat skeletal muscle.

Heart failure is associated with a skeletal muscle myopathy with cellular and extracellular alterations. The hypothesis of this investigation is that extracellular changes may be associated with enhanced mRNA expression and activity of matrix metalloproteinases (MMP). We examined MMP mRNA expression and MMP activity in Soleus (SOL), extensor digitorum longus (EDL), and diaphragm (DIA) muscles of young Wistar rat with monocrotaline‐induced heart failure. Rats injected with saline served as age‐matched controls. MMP2 and MMP9 mRNA contents were determined by RT‐PCR and MMP activity by electrophoresis in gelatin‐containing polyacrylamide gels in the presence of SDS under non‐reducing conditions. Heart failure increased MMP9 mRNA expression and activity in SOL, EDL and DIA and MMP2 mRNA expression in DIA. These results suggest that MMP changes may contribute to the skeletal muscle myopathy during heart failure.

Misclassification probability as obese or lean in hypercaloric and normocaloric diet

The aim of the present study was to determine the classification error probabilities, as lean or obese, in hypercaloric diet-induced obesity, which depends on the variable used to characterize animal obesity. In addition, the misclassification probabilities in animals submitted to normocaloric diet were also evaluated. Male Wistar rats were randomly distributed into two groups: normal diet (ND; n=31; 3.5 Kcal/g) and hypercaloric diet (HD; n=31; 4.6 Kcal/g). The ND group received commercial Labina rat feed and HD animals a cycle of five hypercaloric diets for a 14-week period. The variables analysed were body weight, body composition, body weight to length ratio, Lee Index, body mass Index and misclassification probability. A 5% significance level was used. The hypercaloric pellet-diet cycle promoted increase of body weight, carcass fat, body weight to length ratio and Lee Index. The total misclassification probabilities ranged from 19.21% to 40.91%. In conclusion, the results of this experiment show that misclassification probabilities occur when dietary manipulation is used to promote obesity in animals. This misjudgement ranges from 19.49% to 40.52% in hypercaloric diet and 18.94% to 41.30% in normocaloric diet.

Involvement of L-type calcium channel and SERCA2a in myocardial dysfunction induced by obesity.

Obesity has been shown to impair myocardial performance. Nevertheless, the mechanisms underlying the participation of calcium (Ca2+) handling on cardiac dysfunction in obesity models remain unknown. L‐type Ca2+ channels and sarcoplasmic reticulum (SR) Ca2+‐ATPase (SERCA2a), may contribute to the cardiac dysfunction induced by obesity. The purpose of this study was to investigate whether myocardial dysfunction in obese rats is related to decreased activity and/or expression of L‐type Ca2+ channels and SERCA2a. Male 30‐day‐old Wistar rats were fed standard (C) and alternately four palatable high‐fat diets (Ob) for 15 weeks. Obesity was determined by adiposity index and comorbidities were evaluated. Myocardial function was evaluated in isolated left ventricle papillary muscles under basal conditions and after inotropic and lusitropic maneuvers. L‐type Ca2+ channels and SERCA2a activity were determined using specific blockers, while changes in the amount of channels were evaluated by Western blot analysis. Phospholamban (PLB) protein expression and the SERCA2a/PLB ratio were also determined. Compared with C rats, the Ob rats had increased body fat, adiposity index and several comorbidities. The Ob muscles developed similar baseline data, but myocardial responsiveness to post‐rest contraction stimulus and increased extracellular Ca2+ was compromised. The diltiazem promoted higher inhibition on developed tension in obese rats. In addition, there were no changes in the L‐type Ca2+ channel protein content and SERCA2a behavior (activity and expression). In conclusion, the myocardial dysfunction caused by obesity is related to L‐type Ca2+ channel activity impairment without significant changes in SERCA2a expression and function as well as L‐type Ca2+ protein levels. J. Cell. Physiol. 226: 2934–2942, 2011.

Obesity induces upregulation of genes involved in myocardial Ca2+ handling

Obesity is a complex multifactorial disorder that is often associated with cardiovascular diseases. Research on experimental models has suggested that cardiac dysfunction in obesity might be related to alterations in myocardial intracellular calcium (Ca2+) handling. However, information about the expression of Ca2+-related genes that lead to this abnormality is scarce. We evaluated the effects of obesity induced by a high-fat diet in the expression of Ca2+-related genes, focusing the L-type Ca2+ channel (Cacna1c), sarcolemmal Na+/Ca2+ exchanger (NCX), sarcoplasmic reticulum Ca2+ ATPase (SERCA2a), ryanodine receptor (RyR2), and phospholamban (PLB) mRNA in rat myocardium. Male 30-day-old Wistar rats were fed a standard (control) or high-fat diet (obese) for 15 weeks. Obesity was defined as increased percent of body fat in carcass. The mRNA expression of Ca2+-related genes in the left ventricle was measured by RT-PCR. Compared with control rats, the obese rats had increased percent of body fat, area under the curve for glucose, and leptin and insulin plasma concentrations. Obesity also caused an increase in the levels of SERCA2a, RyR2 and PLB mRNA (P < 0.05) but did not modify the mRNA levels of Cacna1c and NCX. These findings show that obesity induced by high-fat diet causes cardiac upregulation of Ca2+ transport_related genes in the sarcoplasmic reticulum.

Disfunção miocárdica e alterações no trânsito de cálcio intracelular em ratos obesos

FUNDAMENTO: Varios mecanismos tem sido propostos contribuir para a disfuncao cardiaca em modelos de obesidade, tais como alteracoes nas proteinas do trânsito de calcio (Ca+2) e nos receptores beta-adrenergicos. Todavia, o papel desses fatores no desenvolvimento da disfuncao miocardica induzida pela obesidade ainda nao esta claro. OBJETIVO: Este estudo pretende investigar se a obesidade induzida por um ciclo de dieta hipercaloricas resulta em disfuncao cardiaca. Alem disso, foi avaliado se essa alteracao funcional em ratos obesos esta relacionada com o prejuizo do trânsito de Ca+2 e do sistema beta-adrenergico. METODOS: Ratos Wistar machos, 30 dias de idade, foram alimentados com racao padrao (C) e um ciclo de cinco dietas hipercaloricas (Ob) por 15 semanas. A obesidade foi definida pelo aumento da porcentagem de gordura corporal dos ratos. A funcao cardiaca foi avaliada mediante analise isolada do musculo papilar do ventriculo esquerdo em condicoes basais e apos manobras inotropicas e lusitropicas. RESULTADOS: Em comparacao com o grupo controle, os ratos obesos apresentaram aumento da gordura corporal e intolerância a glicose. Os musculos dos ratos obesos desenvolveram valores basais semelhantes; entretanto, as respostas miocardicas ao potencial pos-pausa e aumento de Ca+2 extracelular foram comprometidas. Nao houve alteracoes na funcao cardiaca entre os grupos apos a estimulacao beta-adrenergica. CONCLUSAO: A obesidade promove disfuncao cardiaca relacionada com alteracoes no trânsito de Ca+2 intracelular. Esse prejuizo funcional e provavelmente ocasionado pela reducao da atividade da bomba de Ca+2 do reticulo sarcoplasmatico (SERCA2a) via Ca+2 calmodulina-quinase.

Heart failure alters MyoD and MRF4 expressions in rat skeletal muscle

Heart failure (HF) is characterized by a skeletal muscle myopathy with increased expression of fast myosin heavy chains (MHCs). The skeletal muscle‐specific molecular regulatory mechanisms controlling MHC expression during HF have not been described. Myogenic regulatory factors (MRFs), a family of transcriptional factors that control the expression of several skeletal muscle‐specific genes, may be related to these alterations. This investigation was undertaken in order to examine potential relationships between MRF mRNA expression and MHC protein isoforms in Wistar rat skeletal muscle with monocrotaline‐induced HF. We studied soleus (Sol) and extensor digitorum longus (EDL) muscles from both HF and control Wistar rats. MyoD, myogenin and MRF4 contents were determined using reverse transcription‐polymerase chain reaction while MHC isoforms were separated using polyacrylamide gel electrophoresis. Despite no change in MHC composition of Wistar rat skeletal muscles with HF, the mRNA relative expression of MyoD in Sol and EDL muscles and that of MRF4 in Sol muscle were significantly reduced, whereas myogenin was not changed in both muscles. This down‐regulation in the mRNA relative expression of MRF4 in Sol was associated with atrophy in response to HF while these alterations were not present in EDL muscle. Taken together, our results show a potential role for MRFs in skeletal muscle myopathy during HF.

Obesity Preserves Myocardial Function During Blockade of the Glycolytic Pathway

Background Obesity is defined by excessive accumulation of body fat relative to lean tissue. Studies during the last few years indicate that cardiac function in obese animals may be preserved, increased or diminished. Objective Study the energy balance of the myocardium with the hypothesis that the increase in fatty acid oxidation and reduced glucose leads to cardiac dysfunction in obesity. Methods 30-day-old male Wistar rats were fed standard and hypercaloric diet for 30 weeks. Cardiac function and morphology were assessed. In this paper was viewed the general characteristics and comorbities associated to obesity. The structure cardiac was determined by weights of the heart and left ventricle (LV). Myocardial function was evaluated by studying isolated papillary muscles from the LV, under the baseline condition and after inotropic and lusitropic maneuvers: myocardial stiffness; postrest contraction; increase in extracellular Ca2+ concentration; change in heart rate and inhibitor of glycolytic pathway. Results Compared with control group, the obese rats had increased body fat and co-morbities associated with obesity. Functional assessment after blocking iodoacetate shows no difference in the linear regression of DT, however, the RT showed a statistically significant difference in behavior between the control and the obese group, most notable being the slope in group C. Conclusion The energy imbalance on obesity did not cause cardiac dysfunction. On the contrary, the prioritization of fatty acids utilization provides protection to cardiac muscle during the inhibition of glycolysis, suggesting that this pathway is fewer used by obese cardiac muscle.

A comparative study of myocardial function and morphology during fasting/refeeding and food restriction in rats

BACKGROUND This study compared the influence of fasting/refeeding cycles and food restriction on rat myocardial performance and morphology. METHODS Sixty-day-old male Wistar rats were submitted to food ad libitum (C), 50% food restriction (R50), and fasting/refeeding cycles (RF) for 12 weeks. Myocardial function was evaluated under baseline conditions and after progressive increase in calcium and isoproterenol. Myocardium ultrastructure was examined in the papillary muscle. RESULTS Fasting/refeeding cycles maintained rat body weight and left ventricle weight between control and food-restricted rats. Under baseline conditions, the time to peak tension (TPT) was more prolonged in R50 than in RF and C rats. Furthermore, the maximum tension decline rate (-dT/dt) increased less in R50 than in RF with calcium elevation. While the R50 group showed focal changes in many muscle fibers, such as the disorganization or loss of myofilaments, polymorphic mitochondria with disrupted cristae, and irregular appearance or infolding of the plasma membrane, the RF rats displayed few alterations such as loss or disorganization of myofibrils. CONCLUSION Food restriction promotes myocardial dysfunction, not observed in RF rats, and higher morphological damage than with fasting/refeeding. The increase in TPT may be attributed possibly to the disorganization and loss of myofibrils; however, the mechanisms responsible for the alteration in -dT/dt in R50 needs to be further clarified.

Effect of unsaturated fatty acids on myocardial performance, metabolism and morphology

Diets rich in saturated fatty acids are one of the most important causes of atherosclerosis in men, and have been replaced with diets rich in unsaturated fatty acids (UFA) for the prevention of this disorder. However, the effect of UFA on myocardial performance, metabolism and morphology has not been completely characterized. The objective of the present investigation was to evaluate the effects of a UFA-rich diet on cardiac muscle function, oxidative stress, and morphology. Sixty-day-old male Wistar rats were fed a control (N = 8) or a UFA-rich diet (N = 8) for 60 days. Myocardial performance was studied in isolated papillary muscle by isometric and isotonic contractions under basal conditions after calcium chloride (5.2 mM) and ss-adrenergic stimulation with 1.0 microM isoproterenol. Fragments of the left ventricle free wall were used to study oxidative stress and were analyzed by light microscopy, and the myocardial ultrastructure was examined in left ventricle papillary muscle. After 60 days the UFA-rich diet did not change myocardial function. However, it caused high lipid hydroperoxide (176 +/- 5 vs 158 +/- 5, P < 0.0005) and low catalase (7 +/- 1 vs 9 +/- 1, P < 0.005) and superoxide-dismutase (18 +/- 2 vs 27 +/- 5, P < 0.005) levels, and discrete morphological changes in UFA-rich diet hearts such as lipid deposits and mitochondrial membrane alterations compared to control rats. These data show that a UFA-rich diet caused myocardial oxidative stress and mild structural alterations, but did not change mechanical function.