Treatment with brain natriuretic peptide prevents the development of cardiac dysfunction in obese diabetic db/db mice

Longitudinal assessment of N-terminal pro-B-type natriuretic peptide and risk of diabetes in older adults: The cardiovascular health study

INTRODUCTION

Natriuretic peptides have a well-recognized role in cardiovascular homeostasis. Recently, higher levels of B-type natriuretic peptide (BNP) have also been associated with decreased risk of diabetes in middle-aged adults. Whether this association persists into older age, where the pathophysiology of diabetes changes, has not been established, nor has its intermediate pathways.

METHODS

We investigated the relationship between N-terminal (NT)-proBNP and incident diabetes in 2359 older adults free of cardiovascular disease or chronic kidney disease in the Cardiovascular Health Study.

RESULTS

We documented 348 incident cases of diabetes over 12.6years of median follow-up. After adjusting for age, sex, race, body mass index, systolic blood pressure, anti-hypertensive treatment, smoking, alcohol use, and LDL, each doubling of NT-proBNP was associated with a 9% lower risk of incident diabetes (HR=0.91 [95% CI: 0.84-0.99]). Additional adjustment for waist circumference, physical activity, estimated glomerular filtration rate or C-reactive protein did not influence the association. Among putative mediators, HDL and triglycerides, adiponectin, and especially homeostasis model assessment of insulin resistance, all appeared to account for a portion of the lower risk associated with NT-proBNP.

CONCLUSION

In older adults without prevalent cardiovascular or kidney disease, higher NT-proBNP is associated with decreased risk of incident diabetes even after adjustment for traditional risk factors. These findings suggest that the metabolic effects of natriuretic peptides persist late in life and offer a potential therapeutic target for prevention of diabetes in older people.

Oxytocin and cardioprotection in diabetes and obesity

Oxytocin (OT) emerges as a drug for the treatment of diabetes and obesity. The entire OT system is synthesized in the rat and human heart. The direct myocardial infusion with OT into an ischemic or failing heart has the potential to elicit a variety of cardioprotective effects. OT treatment attenuates cardiomyocyte (CMs) death induced by ischemia-reperfusion by activating pro-survival pathways within injured CMs in vivo and in isolated cells. OT treatment reduces cardiac apoptosis, fibrosis, and hypertrophy. The OT/OT receptor (OTR) system is downregulated in the db/db mouse model of type 2 diabetes which develops genetic diabetic cardiomyopathy (DC) similar to human disease. We have shown that chronic OT treatment prevents the development of DC in the db/db mouse. In addition, OT stimulates glucose uptake in both cardiac stem cells and CMs, and increases cell resistance to diabetic conditions. OT may help replace lost CMs by stimulating the in situ differentiation of cardiac stem cells into functional mature CMs. Lastly, adult stem cells amenable for transplantation such as MSCs could be preconditioned with OT ex vivo and implanted into the injured heart to aid in tissue regeneration through direct differentiation, secretion of protective and cardiomyogenic factors and/or their fusion with injured CMs.

LXRα improves myocardial glucose tolerance and reduces cardiac hypertrophy in a mouse model of obesity-induced type 2 diabetes

AIMS/HYPOTHESIS

Diabetic cardiomyopathy is a myocardial disease triggered by impaired insulin signalling, increased fatty acid uptake and diminished glucose utilisation. Liver X receptors (LXRs) are key transcriptional regulators of metabolic homeostasis. However, their effect in the diabetic heart is largely unknown.

METHODS

We cloned murine Lxrα (also known as Nr1h3) behind the α-myosin heavy chain (αMhc; also known as Myh6) promoter to create transgenic (Lxrα-Tg) mice and transgene-negative littermates (wild-type [WT]). A mouse model of type 2 diabetes was induced by a high-fat diet (HFD, 60% energy from fat) over 16 weeks and compared with a low-fat diet (10% energy from fat). A mouse model of type 1 diabetes was induced via streptozotocin injection over 12 weeks.

RESULTS

HFD manifested comparable increases in body weight, plasma triacylglycerol and insulin resistance per OGTT in Lxrα-Tg and WT mice. HFD significantly increased left ventricular weight by 21% in WT hearts, but only by 5% in Lxrα-Tg. To elucidate metabolic effects in the heart, microPET (positron emission tomography) imaging revealed that cardiac glucose uptake was increased by 1.4-fold in WT mice on an HFD, but further augmented by 1.7-fold in Lxrα-Tg hearts, in part through 5' adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and restoration of glucose transporter 4 (GLUT4). By contrast, streptozotocin-induced ablation of insulin signalling diminished cardiac glucose uptake levels and caused cardiac dysfunction, indicating that insulin may be important in LXRα-mediated glucose uptake. Chromatin immunoprecipitation assays identified natriuretic peptides, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), as potential direct targets of cardiac LXRα overexpression.

CONCLUSIONS/INTERPRETATION

Cardiac-specific LXRα overexpression ameliorates the progression of HFD-induced left ventricular hypertrophy in association with increased glucose reliance and natriuretic peptide signalling during the early phase of diabetic cardiomyopathy. These findings implicate a potential protective role for LXR in targeting metabolic disturbances underlying diabetes.

AMPK in cardiac fibrosis and repair: Actions beyond metabolic regulation

Fibrosis is a general term encompassing a plethora of pathologies that span all systems and is marked by increased deposition of collagen. Injury of variable etiology gives rise to complex cascades involving several cell-types and molecular signals, leading to the excessive accumulation of extracellular matrix that promotes fibrosis and eventually leads to organ failure. Cardiac fibrosis is a dynamic process associated notably with ischemia, hypertrophy, volume- and pressure-overload, aging and diabetes mellitus. It has profoundly deleterious consequences on the normal architecture and functioning of the myocardium and is associated with considerable mortality and morbidity. The AMP-activated protein kinase (AMPK) is a ubiquitously expressed cellular energy sensor and an essential component of the adaptive response to cardiomyocyte stress that occurs during ischemia. Nevertheless, its actions extend well beyond its energy-regulating role and it appears to possess an essential role in regulating fibrosis of the myocardium. In this review paper, we will summarize the main elements and crucial players of cardiac fibrosis. In addition, we will provide an overview of the diverse roles of AMPK in the heart and discuss in detail its implication in cardiac fibrosis. Lastly, we will highlight the recently published literature concerning AMPK-targeting current therapy and novel strategies aiming to attenuate fibrosis.

Defective Natriuretic Peptide Receptor Signaling in Skeletal Muscle Links Obesity to Type 2 Diabetes

Circulating natriuretic peptide (NP) levels are reduced in obesity and predict the risk of type 2 diabetes (T2D). Since skeletal muscle was recently shown as a key target tissue of NP, we aimed to investigate muscle NP receptor (NPR) expression in the context of obesity and T2D. Muscle NPRA correlated positively with whole-body insulin sensitivity in humans and was strikingly downregulated in obese subjects and recovered in response to diet-induced weight loss. In addition, muscle NP clearance receptor (NPRC) increased in individuals with impaired glucose tolerance and T2D. Similar results were found in obese diabetic mice. Although no acute effect of brain NP (BNP) on insulin sensitivity was observed in lean mice, chronic BNP infusion improved blood glucose control and insulin sensitivity in skeletal muscle of obese and diabetic mice. This occurred in parallel with a reduced lipotoxic pressure in skeletal muscle due to an upregulation of lipid oxidative capacity. In addition, chronic NP treatment in human primary myotubes increased lipid oxidation in a PGC1α-dependent manner and reduced palmitate-induced lipotoxicity. Collectively, our data show that activation of NPRA signaling in skeletal muscle is important for the maintenance of long-term insulin sensitivity and has the potential to treat obesity-related metabolic disorders.

Nutrient sensing and utilization: Getting to the heart of metabolic flexibility

A central feature of obesity-related cardiometabolic diseases is the impaired ability to transition between fatty acid and glucose metabolism. This impairment, referred to as "metabolic inflexibility", occurs in a number of tissues, including the heart. Although the heart normally prefers to metabolize fatty acids over glucose, the inability to upregulate glucose metabolism under energetically demanding conditions contributes to a pathological state involving energy imbalance, impaired contractility, and post-translational protein modifications. This review discusses pathophysiologic processes that contribute to cardiac metabolic inflexibility and speculates on the potential physiologic origins that lead to the current state of cardiometabolic disease in an obesogenic environment.

Natriuretic peptides, heart, and adipose tissue: new findings and future developments for diabetes research

Natriuretic peptides (NPs) play a key role in cardiovascular homeostasis, counteracting the deleterious effects of volume and pressure overload and activating antibrotic and antihypertrophic pathways in the heart. N-terminal B-type NP (NT-proBNP) also is a promising biomarker of global cardiovascular risk in the general population, and there is increasing interest on its potential use in diabetic patients for screening of silent cardiovascular abnormalities, cardiovascular risk stratification, and guided intervention. Recently, both atrial NP (ANP) and B-type NP (BNP) have emerged as key mediators in the control of metabolic processes including the heart in the network of organs that regulate energy usage and metabolism. Epidemiological studies have shown that ANP and BNP are reduced in people with obesity, insulin resistance, and diabetes, and this deficiency may contribute to enhance their global cardiovascular risk. Moreover, ANP and BNP have receptors in the adipose tissue, enhance lipolysis and energy expenditure, and modulate adipokine release and food intake. Therefore, low ANP and BNP levels may be not only a consequence but also a cause of obesity, and recent prospective studies have shown that low levels of NT-proBNP and midregional proANP (MR-proANP) are a strong predictor of type 2 diabetes onset. Whether ANP and BNP supplementation may result in either cardiovascular or metabolic benefits in humans remains, however, to be established.

Diabetes Mellitus and Heart Failure

Diabetes mellitus and heart failure are two multifaceted entities characterised by high morbidity and mortality. Early epidemiological and prospective studies have observed the frequent co-existence of both conditions. Importantly, diabetes mellitus can precipitate or worsen heart failure due to the accumulation of advanced glycation end products, oxidative stress, inflammatory status impairment, decay of intracellular calcium, changes in microRNAs expression, not to mention atherosclerosis progression and coronary artery disease. Heart failure also impairs glucose metabolism through less well-known mechanisms. Attention must especially be given in the treatment as there are frequently adverse interactions between the two diseases and novel agents against diabetic cardiomyopathy are under investigation. As several missing links still exist in the connection between heart failure and diabetes mellitus we will review, in this article, the most recent data underlying the interaction of them and provide an overview of the most important clinical perspectives.

All-trans retinoic acid stimulates gene expression of the cardioprotective natriuretic peptide system and prevents fibrosis and apoptosis in cardiomyocytes of obese ob/ob mice

In hypertensive rodents, retinoic acid (RA) prevents adverse cardiac remodelling and improves myocardial infarction outcome, but its role in obesity-related changes of cardiac tissue are unclear. We hypothesized that all-trans RA (ATRA) treatment will improve the cardioprotective oxytocin-natriuretic peptides (OT-NP) system, preventing apoptosis and collagen accumulation in hearts of ob/ob mice, a mouse model of obesity and insulin resistance. Female 9-week-old B6.V-Lep/J ob/ob mice (n = 16) were divided into 2 groups: 1 group (n = 8) treated with 100 μg of ATRA dissolved in 100 μL of corn oil (vehicle) delivered daily (∼2 μg·g body weight(-1)·day(-1)) by stomach intubation for 16 days, and 1 group (n = 8) that received the vehicle alone. A group of nonobese littermate mice (n = 9) served as controls. Ob/ob mice exhibited obesity, hyperglycaemia, and downregulation of the cardiac OT-NP system, including the mRNA for the transcription factor GATA4, OT receptor and brain NP, and the protein expression for endothelial nitric oxide synthase. Hearts from ob/ob mice also demonstrated increased apoptosis and collagen accumulation. ATRA treatment induced weight loss and decreased adipocytes diameter in the visceral fat, thus reducing visceral obesity, which is associated with a high risk for cardiovascular disease. RA treatment was associated with a reduction in hyperglycemia and a normalization of the OT-NP system's expression in the hearts of ob/ob mice. Furthermore, ATRA treatment prevented apoptosis and collagen accumulation in hearts of ob/ob mice. The present study indicates that ATRA treatment was effective in restoring the cardioprotective OT-NP system and in preventing abnormal cardiac remodelling in the ob/ob mice.