P2X3 receptor antagonism attenuates the progression of heart failure

Despite advances in the treatment of heart failure, prognosis is poor, mortality high and there remains no cure. Heart failure is associated with reduced cardiac pump function, autonomic dysregulation, systemic inflammation and sleep-disordered breathing; these morbidities are exacerbated by peripheral chemoreceptor dysfunction. We reveal that in heart failure the carotid body generates spontaneous, episodic burst discharges coincident with the onset of disordered breathing in male rats. Purinergic (P2X3) receptors were upregulated two-fold in peripheral chemosensory afferents in heart failure, and when antagonized abolished these episodic discharges, normalized both peripheral chemoreceptor sensitivity and the breathing pattern, reinstated autonomic balance, improved cardiac function, and reduced both inflammation and biomarkers of cardiac failure. Aberrant ATP transmission in the carotid body triggers episodic discharges that via P2X3 receptors play a crucial role in the progression of heart failure and as such offer a distinct therapeutic angle to reverse multiple components of its pathogenesis.

Restoration of Cardiac Function After Myocardial Infarction by Long-Term Activation of the CNS Leptin-Melanocortin System

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Leptin protects against progression to heart failure after myocardial infarction.

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This beneficial effect requires activation of the brain melanocortin system.

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Stimulation of brain MC4R recapitulates the cardiac protective effects of leptin.

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Leptin-MC4R activation improves cardiac substrate oxidation and mitochondrial function.

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It also improves Ca²⁺ coupling and contractile function in viable cardiomyocytes after MI.

Heart failure has a high mortality rate, and current therapies offer limited benefits. The authors demonstrate that activation of the central nervous system leptin-melanocortin pathway confers remarkable protection against progressive heart failure following severe myocardial infarction. The beneficial cardiac-protective actions of leptin require activation of brain melanocortin-4 receptors and elicit improvements in cardiac substrate oxidation, cardiomyocyte contractility, Ca²⁺ coupling, and mitochondrial efficiency. These findings highlight a potentially novel therapeutic approach for myocardial infarction and heart failure.

Abstract 137: Impact of Leptin Deficiency Compared to Neuronal Specific Leptin Receptor Deletion on Cardiometabolic Regulation

The main goal of this study was to compare the impact of whole-body leptin deficiency with neuronal specific leptin receptor (LR) deletion on metabolic and cardiovascular regulation. Liver fat, diacylglycerol acyltransferase-2 (DGTA2) and CD36 protein content were measured in male and female wild-type (WT, n=5/sex), nervous system LR deficient (LR/Nestin-Cre, n=6/sex), and leptin deficient (ob/ob, n=5) mice. Blood pressure (BP) and heart rate (HR) were recorded by telemetry, and motor activity (MA) and oxygen consumption (VO 2 ) were monitored at 24 weeks of age. Female and male LR/Nestin-Cre and ob/ob mice were heavier than WT mice (62±5 and 61±3 vs 31±1 g), hyperphagic (6.2±0.5 and 6.1±0.7 vs 3.5±1.0 g/day), with reduced VO 2 (27±1 and 33±1 vs 49±3 ml/kg/min) and decreased MA (3±1 and 7±2 vs 676±105 cm/hr). LR/Nestin-Cre and ob/ob mice were also hyperinsulinemic and hyperglycemic compared to WT mice. LR/Nestin-Cre mice had high plasma leptin levels while ob/ob mice had undetectable leptin levels. Despite comparable obesity, LR/Nestin-Cre mice had lower liver fat content (83% reduced) and DGTA2 and CD36 protein levels than ob/ob mice. Male WT, LR/Nestin-Cre, and ob/ob mice exhibited similar BP (111±3, 110±1 and109±2 mmHg), whereas female LR/Nestin-Cre mice had higher BP compared to WT females despite similar metabolic phenotypes compared to male LR/Nestin-Cre mice. No significant increases in plasma aldosterone concentration was observed in male LR/Nestin-Cre compared to WT mice (495±48 vs. 440±62 pg/ml); however, female LR/Nestin-Cre mice had ~14 fold higher plasma aldosterone concentration compared to female WT mice (707±97 vs. 50±3 pg/ml). These results indicate that although nervous system LRs play a crucial role in regulating body weight and glucose homeostasis, peripheral LRs also regulate liver fat deposition and modulate BP in a sex dependent manner. (NHLBI-PO1HL51971, NIGMS P20GM104357 and U54GM115428)

Abstract 090: Intergenerational Inheritance of Obesity-Induced Diastolic Dysfunction With Preserved Ejection Fraction

Obesity is strongly associated with cardiomyopathy and heart failure. We examined the impact of paternal and maternal obesity on systolic and diastolic function in male adult offspring. The following groups were studied: 1) offspring fed normal diet (ND) born from ND parents (ND-F1-ND, n=5); 2) offspring fed high fat diet (HFD) born from ND parents (HFD-F1-ND, n=6); 3) offspring fed ND born from HFD parents (ND-F1-HFD, n=7); and 4) offspring fed HFD born from HFD parents (HFD-F1-HFD, n=7). Parents were fed HFD or ND from weaning until the end of lactation, while the offspring were placed on ND or HFD from weaning until the end of experiments. Body weight, fat and lean mass, measured using EchoMRI4-in-1 System, were measured weekly. Cardiac function including ejection fraction (EF), isovolumetric relaxation time (IVRT), late filling velocity (A’), E and E’ early filling velocities were determined at 22 weeks of age using long and short axis left ventricle dimensions, pulse wave and tissue Doppler (VisualSonics 30 MHZ transducer, VEVO3100®). Compared to lean control ND-F1-ND mice, ND-F1-HFD mice had similar body weight (28.9±1.0 vs. 27.9±0.4 g) but higher fat mass (4.5±0.9 vs. 3.0±0.3 g) and lower lean mass (22.9±0.4 vs. 24.6±0.3 g). Both groups of mice fed HFD after weaning were heavier than offspring fed ND. However, HFD-F1-HFD mice were heavier than HFD-F1-ND mice (47.3±0.8 vs. 42.5±1.9 g) due to greater fat mass (19.4±0.6 vs. 15.7±1.6 g) and lean mass (28.3±0.6 vs. 26.9 vs. 0.3 g). Despite no major differences in ejection fraction among all 4 groups, mice fed HFD or born from parents fed HFD exhibited diastolic dysfunction; worse indicators of diastolic function were observed in mice from HFD parents as indicated by increased IVRT (30.4±1.8, 25.0±1.8, 22.1±2.0 vs. 21.4±0.9 ms) and E/E’ ratio (36.6±3.6, 32.3±1.8, 31.8±1.2 vs. 27.9±2.5) and reduced E’/A’ ratio (0.9±0.1, 0.7±0.1, 1.5±0.2 vs. 1.4±0.1) for HFD-F1-HFD, ND-F1-HFD, HFD-F1-ND and ND-F1-ND, respectively. These results indicate that diet-induced parental obesity is associated with diastolic dysfunction and preserved EF in the offspring, which is exacerbated by HFD-induced obesity. (NHLBI-PO1HL51971, NIGMS P20GM104357 and U54GM115428)

Impact of leptin deficiency compared with neuronal-specific leptin receptor deletion on cardiometabolic regulation

The main goal of this study was to compare the impact of total body leptin deficiency with neuronal-specific leptin receptor (LR) deletion on metabolic and cardiovascular regulation. Liver fat, diacylglycerol acyltransferase-2 (DGTA2), and CD36 protein content were measured in wild-type (WT), nervous system LR-deficient (LR/Nestin-Cre), and leptin deficient (ob/ob) mice. Blood pressure (BP) and heart rate (HR) were recorded by telemetry, and motor activity (MA) and oxygen consumption (V̇o₂) were monitored at 24 wk of age. Female and male LR/Nestin-Cre and ob/ob mice were heavier than WT mice (62 ± 5 and 61 ± 3 vs. 31 ± 1 g) and hyperphagic (6.2 ± 0.5 and 6.1 ± 0.7 vs. 3.5 ± 1.0 g/day), with reduced V̇o₂ (27 ± 1 and 33 ± 1 vs 49 ± 3 ml·kg^-1·min^-1) and decreased MA (3 ± 1 and 7 ± 2 vs 676 ± 105 cm/h). They were also hyperinsulinemic and hyperglycemic compared with WT mice. LR/Nestin-Cre mice had high levels of plasma leptin, while ob/ob mice had undetectable leptin levels. Despite comparable obesity, LR/Nestin-Cre mice had lower liver fat content, DGTA2, and CD36 protein levels than ob/ob mice. Male WT, LR/Nestin-Cre, and ob/ob mice exhibited similar BP (111 ± 3, 110 ± 1 and 109 ± 2 mmHg). Female LR/Nestin-Cre and ob/ob mice, however, had higher BP than WT females despite similar metabolic phenotypes compared with male LR/Nestin-Cre and ob/ob mice. These results indicate that although nervous system LRs play a crucial role in regulating body weight and glucose homeostasis, peripheral LRs regulate liver fat deposition. In addition, our results suggest potential sex differences in the impact of obesity on BP regulation.

Abstract 008: Chronic Central Melanocortin 4 Receptor Activation Attenuates Cardiac Dysfunction After Myocardial Infarction In Rats

The melanocortin pathway plays an important role in multiple physiological functions besides its effect on energy homeostasis. In the present study we tested whether activation of the brain melanocortin 4 receptors (MC4R) confers protection against cardiac dysfunction after myocardial infarction (MI). Male Sprague-Dawley rats at 12 weeks of age were implanted with blood pressure telemetry transmitters and an intracerebroventricular (ICV) cannula was inserted into the lateral ventricle. After 10 days of recovery, food intake, mean arterial pressure (MAP) and heart rate (HR) were measured 24-hrs/day by telemetry and cardiac function was assessed by echocardiography (VEVO 3100 @ ). After stable baseline measurements for 4 days, the left coronary descending artery was permanently ligated and vehicle (n=6) or the MC4R agonist (MTII, 10 ng/hr, n=7) was infused ICV via osmotic minipump for 28 consecutive days. Chronic MC4R activation significantly decreased cumulative food intake (-121±17 g) and body weight (385±5 to 378±4 g) compared to vehicle treatment (-51±10 g and 358±9 to 427±9 g). Chronic MTII infusion did not significantly alter MAP and HR (113±1 to 115±2 mmHg and 356±3 to 349±9 bpm) whereas MAP and HR were slightly reduced in vehicle-treated rats with MI (109±1 to 105±3 mmHg and HR 357±3 to 324±5). Compared to vehicle, MTII infusion for 4 weeks attenuated cardiac dysfunction caused by MI as evidenced by normalization of global cardiac radial strain (39±4 to 39±3 vs. 37±4 to 25±3 %), cardiac output (117±9 to 117±8 vs. 105±6 to 83±9 ml/min) and improvement of ejection fraction (72±2 to 47±3 vs. 70±2 to 30±2 %). These results suggest that chronic central MC4R activation attenuates the progression of heart failure after MI in rats. (NHLBI-PO1HL51971, NIGMS- P20GM104357 and U54GM115428)

Abstract P294: Intergenerational Obesity: Impact on Cardiac Function and Reserve in Mice Fed a High Fat Diet

Obesity is associated with structural and functional changes in the heart and abnormal cardiovascular responses to exercise in humans and experimental animals. However, the impact of intergenerational obesity on cardiac function and reserve during increased stress is still unknown. In this study we examined if intergenerational obesity alters cardiac function and responses to a stress test induced by dobutamine in 22-week-old male lean mice fed a control diet (n=5) and obese mice fed a high fat diet (HFD) after birth and that were offspring of mothers who were fed a HFD (F1-HFD, n=7). Mice were instrumented with venous catheters for continuous infusion of saline and progressively increasing doses of dobutamine (2-12 ng/g/min, 2 min at each dose). Long and short axis left ventricle dimensions were obtained before and one minute after each dose of dobutamine using a 30 MHZ transducer (VEVO3100). Baseline heart rate (HR) was similar in F1-HFD (388±15 bpm) and control (426±22 bpm). Compared to controls, F1-HFD mice exhibited impaired diastolic function (E’/A’ ratio: 0.9±0.1 vs. 1.4±0.1 mm/s and isovolumetric relaxation time: 30±2 vs. 21±1 ms) but increased baseline ejection fraction (EF) (84±1 vs. 64±4 %). Dobutamine infusion increased HR by 6±3 and 41±11 bpm, and EF (84±1 to 93±2 and 64±4 to 94±2 %) in F1-HFD and controls, respectively. These results indicate that intergenerational obesity is associated with diastolic dysfunction, but no major alterations in cardiac reserve in response to a cardiovascular stress test. (NHLBI-PO1HL51971, NIGMS P20GM104357 and U54GM115428)

Matrix metalloproteinases 2 and 9 in rabbits with doxorubicin-induced cardiomyopathy

ABSTRACT: Some studies have shown the role played by matrix metalloproteinases and their inhibitors in doxorubicin cardiotoxicity. In this study, we sought to investigate how plasma and myocardial MMP 2 and 9 perform in rabbits with doxorubicin-induced cardiomyopathy, searching for a correlation between the activity of these collagenases and cardiac remodeling. Cardiomyopathy was induced by doxorubicin given intravenously twice a week for six consecutive weeks. Plasma MMP activity and the echocardiogram were assessed at baseline, and at 15 and 45 days after first injection of doxorubicin. The myocardial activity of these enzymes was solely evaluated in nine rabbits at 45 days, and results were compared with nine healthy controls. We only identified the full-length forms of both MMP 2 and 9 throughout the study. The plasma pro-MMP 2 reduced along the deterioration of cardiac function, while the pro-MMP 9 increased significantly at T45 as compared to baseline and T15. A negative significant correlation was found to exist between the plasma activity of pro-MMP 2 and mitral E-to-mitral septal annular early diastolic velocity ratio, which is an estimate of mean left atrial pressure and congestion. Only pro-MMP 2 was found in myocardial samples, and mean activity of such enzyme was statistically lower than that recorded for healthy controls. Although no active form was documented for either collagenase, the duration of the treatment with doxorubicin played a role in the alteration of plasma pro-forms activity. However, these changes could not be associated with most echocardiographic parameters that are supportive of cardiac remodeling.