Basal and ethanol-induced cardiac contractile response in lean and obese Zucker rat hearts

Obesity cardiomyopathy: evidence, mechanisms, and therapeutic implications

The prevalence of heart failure is on the rise and imposes a major health threat, in part, due to the rapidly increased prevalence of overweight and obesity. To this point, epidemiological, clinical, and experimental evidence supports the existence of a unique disease entity termed “obesity cardiomyopathy,” which develops independent of hypertension, coronary heart disease, and other heart diseases. Our contemporary review evaluates the evidence for this pathological condition, examines putative responsible mechanisms, and discusses therapeutic options for this disorder. Clinical findings have consolidated the presence of left ventricular dysfunction in obesity. Experimental investigations have uncovered pathophysiological changes in myocardial structure and function in genetically predisposed and diet-induced obesity. Indeed, contemporary evidence consolidates a wide array of cellular and molecular mechanisms underlying the etiology of obesity cardiomyopathy including adipose tissue dysfunction, systemic inflammation, metabolic disturbances (insulin resistance, abnormal glucose transport, spillover of free fatty acids, lipotoxicity, and amino acid derangement), altered intracellular especially mitochondrial Ca²⁺ homeostasis, oxidative stress, autophagy/mitophagy defect, myocardial fibrosis, dampened coronary flow reserve, coronary microvascular disease (microangiopathy), and endothelial impairment. Given the important role of obesity in the increased risk of heart failure, especially that with preserved systolic function and the recent rises in COVID-19-associated cardiovascular mortality, this review should provide compelling evidence for the presence of obesity cardiomyopathy, independent of various comorbid conditions, underlying mechanisms, and offer new insights into potential therapeutic approaches (pharmacological and lifestyle modification) for the clinical management of obesity cardiomyopathy.

AT1Receptor Blockade Improves Myocardial Functional Performance in Obesity

Fundamento

A obesidade tem sido associada com ativação crônica do sistema renina-angiotensina-aldosterona e importantes alterações no desempenho cardíaco.

Objetivo

Avaliar a influência do bloqueio de receptores de angiotensina-II do tipo 1 (AT₁) sobre a morfologia e desempenho cardíaco de ratos obesos por dieta

Métodos

Ratos Wistar (n=48) foram submetidos a dieta controle (2,9 kcal/g) ou hiperlipídica (3,6 kcal/g) durante 20 semanas. Após a 16ª semana, foram distribuídos em quatro grupos: Controle (CO), Obeso (OB), Controle Losartan (CL) e Obeso Losartan (OL). CL e OL receberam losartan (30 mg/kg/dia) na água durante quatro semanas. Posteriormente, foram analisadas composição corporal, pressão arterial sistólica (PAS) e ecocardiograma. A função de músculos papilares foi avaliada em situação basal com concentração de cálcio ([Ca²⁺]_o) de 2,50 mM e após manobras inotrópicas: potencial pós-pausa (PPP), elevação da [Ca²⁺]_o e durante estimulação beta-adrenérgica com isoproterenol. A análise dos resultados foi feita por meio de Two-Way ANOVA e teste de comparações apropriado. O nível de significância considerado foi de 5%.

Resultados

Embora a alteração da PAS não tenha se mantido ao final do experimento, a obesidade se associou com hipertrofia cardíaca e maior velocidade de encurtamento da parede posterior do ventrículo esquerdo.No estudo de músculos papilares em condição basal, CL mostrou menor velocidade máxima de variação negativa da tensão desenvolvida (-dT/dt) do que CO. O PPP de 60s promoveu menor -dT/dt e pico de tensão desenvolvida (TD) em OB e CL, comparados ao CO, e maior variação relativa de TD e velocidade máxima de variação positiva (+dT/dt) no OL em relação a CL e OB. Sob 1,5, 2,0 e 2,5mM de [Ca²⁺]_o, o grupo OL exibiu maior -dT/dt do que CL.

Conclusão

Losartan melhora a função miocárdica de ratos com obesidade induzida por dieta. (Arq Bras Cardiol. 2020; 115(1):17-28)

Cardiac Dysfunction Induced by Obesity Is Not Related to β-Adrenergic System Impairment at the Receptor-Signalling Pathway

Obesity has been shown to impair myocardial performance. Some factors have been suggested as responsible for possible cardiac abnormalities in models of obesity, among them beta-adrenergic (βA) system, an important mechanism of regulation of myocardial contraction and relaxation. The objective of present study was to evaluate the involvement of βA system components in myocardial dysfunction induced by obesity. Thirty-day-old male Wistar rats were distributed in control (C, n = 25) and obese (Ob, n = 25) groups. The C group was fed a standard diet and Ob group was fed four unsaturated high-fat diets for 15 weeks. Cardiac function was evaluated by isolated papillary muscle preparation and βA system evaluated by using cumulative concentrations of isoproterenol and Western blot. After 15 weeks, the Ob rats developed higher adiposity index than C rats and several comorbidities; however, were not associated with changes in systolic blood pressure. Obesity caused structural changes and the myocardial responsiveness to post-rest contraction stimulus and increased extracellular calcium (Ca²⁺) was compromised. There were no changes in cardiac function between groups after βA stimulation. The obesity was not accompanied by changes in protein expression of G protein subunit alpha (Gsα) and βA receptors (β₁AR and β₂AR). In conclusion, the myocardial dysfunction caused by unsaturated high-fat diet-induced obesity, after 15 weeks, is not related to βAR system impairment at the receptor-signalling pathway.

Defective calcium inactivation causes long QT in obese insulin-resistant rat

The majority of diabetic patients who are overweight or obese die of heart disease. We suspect that the obesity-induced insulin resistance may lead to abnormal cardiac electrophysiology. We tested this hypothesis by studying an obese insulin-resistant rat model, the obese Zucker rat (OZR). Compared with the age-matched control, lean Zucker rat (LZR), OZR of 16-17 wk old exhibited an increase in QTc interval, action potential duration, and cell capacitance. Furthermore, the L-type calcium current (I(CaL)) in OZR exhibited defective inactivation and lost the complete inactivation back to the closed state, leading to increased Ca(2+) influx. The current density of I(CaL) was reduced in OZR, whereas the threshold activation and the current-voltage relationship of I(CaL) were not significantly altered. L-type Ba(2+) current (I(BaL)) in OZR also exhibited defective inactivation, and steady-state inactivation was not significantly altered. However, the current-voltage relationship and activation threshold of I(BaL) in OZR exhibited a depolarized shift compared with LZR. The total and membrane protein expression levels of Cav1.2 [pore-forming subunit of L-type calcium channels (LTCC)], but not the insulin receptors, were decreased in OZR. The insulin receptor was found to be associated with the Cav1.2, which was weakened in OZR. The total protein expression of calmodulin was reduced, but that of Cavβ2 subunit was not altered in OZR. Together, these results suggested that the 16- to 17-wk-old OZR has 1) developed cardiac hypertrophy, 2) exhibited altered electrophysiology manifested by the prolonged QTc interval, 3) increased duration of action potential in isolated ventricular myocytes, 4) defective inactivation of I(CaL) and I(BaL), 5) weakened the association of LTCC with the insulin receptor, and 6) decreased protein expression of Cav1.2 and calmodulin. These results also provided mechanistic insights into a remodeled cardiac electrophysiology under the condition of insulin resistance, enhancing our understanding of long QT associated with obese type 2 diabetic patients.

Dietary interaction of high fat and marginal copper deficiency on cardiac contractile function

OBJECTIVE

High-fat and marginally copper-deficient diets impair heart function, leading to cardiac hypertrophy, increased lipid droplet volume, and compromised contractile function, resembling lipotoxic cardiac dysfunction. However, the combined effect of the two on cardiac function is unknown. This study was designed to examine the interaction between high-fat and marginally copper-deficient diets on cardiomyocyte contractile function.

RESEARCH METHODS AND PROCEDURES

Weanling male rats were fed diets incorporating a low- or high-fat diet (10% or 45% of kcal from fat, respectively) with adequate (6 mg/kg) or marginally deficient (1.5 mg/kg) copper content for 12 weeks. Contractile function was determined with an IonOptix system including peak shortening (PS), time-to-PS, time-to-90% relengthening, maximal velocity of shortening/relengthening, and intracellular Ca(2+) ([Ca(2+)](I)) rise and decay.

RESULTS

Neither dietary treatment affected blood pressure or glucose levels, although the high-fat diet elicited obesity and glucose intolerance. Both diets depressed PS, maximal velocity of shortening/relengthening, and intracellular Ca(2+) ([Ca(2+)](I)) rise and prolonged time-to-90% relengthening and Ca(2+) decay without an additive effect between the two. Ca(2+) sensitivity, apoptosis, lipid peroxidation, nitrosative damage, tissue ceramide, and triglyceride levels were unaffected by either diet or in combination. Phospholamban (PLB) but not sarco(endo)plasmic reticulum Ca(2+)-ATPase was increased by both diets. Endothelial NO synthase was depressed with concurrent treatments. The electron transport chain was unaffected, although mitochondrial aconitase activity was inhibited by the high-fat diet.

DISCUSSION

These data suggest that high-fat and marginally copper deficient diets impaired cardiomyocyte contractile function and [Ca(2+)](i) homeostasis, possibly through a similar mechanism, without obvious lipotoxicity, nitrosative damage, and apoptosis.

Angiotensin-converting enzyme inhibition reduces lipid deposits in myocardium and improves left ventricular function of obese zucker rats

OBJECTIVE

Alterations in the renin angiotensin system, cardiac lipotoxicity, and left ventricular (LV) dysfunction have been reported in obese rats. The present study examined whether angiotensin-converting enzyme inhibition could ameliorate lipid deposition and ventricular function in the myocardium of obese Zucker rats (OZRs).

RESEARCH METHODS AND PROCEDURES

For 6 months, rats were treated as follows: Group (G) 1, OZR, no treatment; G2, OZR + ramipril (R); G3, OZR + amlodipine (AML); and G4, lean Zucker rats. LV function was assessed by echocardiogram and lipid deposits in cardiomyocytes (LDCM) by light microscopy using Oil red O.

RESULTS

At the end of the experiment, both OZR + R and OZR + AML groups presented similar reduction in blood pressure in comparison with untreated OZR (p < 0.01). OZR with R presented lower insulin-to-glucose ratio and lower serum triglycerides and cholesterol when compared with both untreated OZR and OZR with AML (p < 0.01). Fractional shortening by echocardiogram was as follows: G1, 25.4 +/- 3.8 (vs. G2 and G4, p < 0.05); G2, 37.2 +/- 2.4; G3, 29.3 +/- 4.4 (vs. G2 and G4, p < 0.05); and G4, 40.8 +/- 2.3. Percentage LDCM was as follows: G1, 12.4 +/- 2.7 (vs. G2 and G4, p < 0.05); G2, 0.8 +/- 0.2; G3, 11.1 +/- 2.1 (vs. G2 and G4, p < 0.05); and G4, 0.1 +/- 0.1. There was a negative correlation between fractional shortening and LDCM percentage in OZR (r = -0.93) and in OZR + AML (r = -0.87).

DISCUSSION

AML reduced blood pressure significantly; however, it failed to modify both metabolic parameters and LDCM. In contrast, R showed a substantial reduction in LDCM, together with LV function preservation.

Leptin-induced suppression of cardiomyocyte contraction is amplified by ceramide

Uncorrected obesity is often accompanied by ventricular contractile dysfunction, elevation of the lipotoxic mediator ceramide and the obesity gene product leptin. Both ceramide and leptin participate in the regulation of cardiac function and are speculated to play roles in obesity-related cardiac dysfunctions. The purpose of this study was to examine the effect of ceramide on leptin-elicited cardiac contractile response. Adult rat left ventricular myocytes were incubated for 24 h with low (5 nM) or high (50 nM) concentration of leptin in the absence or presence of the active ceramide analog C2-dihydroceramide (25 microM). Contractile and intracellular Ca2+ properties were evaluated using an IonOptix MyoCam system including peak shortening (PS), maximal velocity of shortening/relengthening (+/-dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), intracellular Ca2+ rise (Delta[Ca2+]) and intracellular Ca2+ decay. While ceramide did not elicit any effect on cell mechanics and intracellular Ca2+ transients, it sensitized leptin-induced effects on myocyte shortening and intracellular Ca2+ transients. In the absence of ceramide, 5 nM leptin had no effect on cell mechanics while 50 nM depressed PS, +/-dL/dt, Delta[Ca2+] and prolonged TR90. With ceramide co-incubation, 5 nM leptin depressed PS, +/-dL/dt, Delta[Ca2+] and prolonged TR90 whereas 50 nM leptin-elicited effects on PS, +/-dL/dt, Delta[Ca2+] and TR90 were significantly potentiated in addition to slowing intracellular Ca2+ decay. In summary, our data demonstrated that ceramide sensitizes cardiac depressive effects of leptin and may contribute to hyperleptinemia-related cardiac contractile dysfunction.

High-fat diet-induced juvenile obesity leads to cardiomyocyte dysfunction and upregulation of Foxo3a transcription factor independent of lipotoxicity and apoptosis

BACKGROUND

Obesity is associated with dyslipidemia, which leads to elevated triglyceride and ceramide levels, apoptosis and compromised cardiac function.

METHODS

To determine the role of high-fat diet-induced obesity on cardiomyocyte function, weanling male Sprague-Dawley rats were fed diets incorporating 10% of kcal or 45% of kcal from fat. Mechanical function of ventricular myocytes was evaluated including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening and relengthening (+/- dl/dt). Intracellular Ca properties were assessed using fluorescent microscopy.

RESULTS

High-fat diet induced hyperinsulinemic insulin-resistant obesity with depressed PS, +/- dl/dt, prolonged TPS/TR90 reduced intracellular Ca release and Ca clearing rate in the absence of hypertension, diabetes, lipotoxicity and apoptosis. Myocyte responsiveness to increased stimulus frequency and extracellular Ca was compromised. SERCA2a and phospholamban levels were increased, whereas phosphorylated phospholamban and potassium channel (Kv1,2) were reduced in high-fat diet group. High-fat diet upregulated the forkhead transcription factor Foxo3a, and suppressed mitochondrial aconitase activity without affecting expression of the caloric sensitive gene silent information regulator 2 (Sir2), protein nitrotyrosine formation, lipid peroxidation and apoptosis. Levels of endothelial nitric oxide synthase (NOS), inducible NOS, triglycerides and ceramide were similar between the two groups.

CONCLUSIONS

Collectively, our data show that high-fat diet-induced obesity resulted in impaired cardiomyocyte function, upregulated Foxo3a transcription factor and mitochondrial damage without overt lipotoxicity or apoptosis.