Regulation Of Systemic Metabolism Research Articles

Adaptive Immunity and Metabolic Health: Harmony Becomes Dissonant in Obesity and Aging.

Adipose tissue (AT) is the primary energy reservoir organ, and thereby plays a critical role in energy homeostasis and regulation of metabolism. AT expands in response to chronic overnutrition or aging and becomes a major source of inflammation that has marked influence on systemic metabolism. The chronic, sterile inflammation that occurs in the AT during the development of obesity or in aging contributes to onset of devastating diseases such as insulin resistance, diabetes, and cardiovascular pathologies. Numerous studies have shown that inflammation in the visceral AT of humans and animals is a critical trigger for the development of metabolic syndrome. This work underscores the well-supported conclusion that the inflammatory immune response and metabolic pathways in the AT are tightly interwoven by multiple layers of relatively conserved mechanisms. During the development of diet-induced obesity or age-associated adiposity, cells of the innate and the adaptive immune systems infiltrate and proliferate in the AT. Macrophages, which dominate AT-associated immune cells in mouse models of obesity, but are less dominant in obese people, have been studied extensively. However, cells of the adaptive immune system, including T cells and B cells, contribute significantly to AT inflammation, perhaps more in humans than in mice. Lymphocytes regulate recruitment of innate immune cells into AT, and produce cytokines that influence the helpful-to-harmful inflammatory balance that, in turn, regulates organismal metabolism. This review describes inflammation, or more precisely, metabolic inflammation (metaflammation) with an eye toward the AT and the roles lymphocytes play in regulation of systemic metabolism during obesity and aging. © 2017 American Physiological Society. Compr Physiol 7:1307-1337, 2017.

Ileectomy-induced Bile Overaccumulation in Mouse Intestine.

Intestinal resection is a common therapeutic approach for human diseases such as obesity, inflammatory bowel disease, Crohn's disease, and colon cancer that often results in severe short bowel syndrome-like adverse effects including bile acid diarrhea, dehydration, electrolyte disturbances, and nutrient malabsorption. Here we introduce a murine ileal resection model, termed ileectomy, to evaluate tissue communication and the maintenance of systemic homeostasis. After ileal resection, circulating blood is permanently devoid of the ileum-specific endocrine hormone fibroblast growth factor 15 (FGF15), which releases its endocrinal inhibition of bile acid synthesis in the liver. In combination with the increased production and abolished reabsorption of bile acids after removing the ileum, mice that underwent surgery suffer from bile salt overaccumulation in the intestine and associated diarrhea, morbidity, and mortality. Novel usage of the surgery model introduced in this study may provide mechanistic and functional insights into ileal control of systemic metabolic regulation in physiology and disease.

Lipid Processing in the Brain: A Key Regulator of Systemic Metabolism.

Metabolic disorders, particularly aberrations in lipid homeostasis, such as obesity, type 2 diabetes mellitus, and hypertriglyceridemia often manifest together as the metabolic syndrome (MetS). Despite major advances in our understanding of the pathogenesis of these disorders, the prevalence of the MetS continues to rise. It is becoming increasingly apparent that intermediary metabolism within the central nervous system is a major contributor to the regulation of systemic metabolism. In particular, lipid metabolism within the brain is tightly regulated to maintain neuronal structure and function and may signal nutrient status to modulate metabolism in key peripheral tissues such as the liver. There is now a growing body of evidence to suggest that fatty acid (FA) sensing in hypothalamic neurons via accumulation of FAs or FA metabolites may signal nutritional sufficiency and may decrease hepatic glucose production, lipogenesis, and VLDL-TG secretion. In addition, recent studies have highlighted the existence of liver-related neurons that have the potential to direct such signals through parasympathetic and sympathetic nervous system activity. However, to date whether these liver-related neurons are FA sensitive remain to be determined. The findings discussed in this review underscore the importance of the autonomic nervous system in the regulation of systemic metabolism and highlight the need for further research to determine the key features of FA neurons, which may serve as novel therapeutic targets for the treatment of metabolic disorders.

RNA-seq and metabolomic analyses of Akt1-mediated muscle growth reveals regulation of regenerative pathways and changes in the muscle secretome

BackgroundSkeletal muscle is a major regulator of systemic metabolism as it serves as the major site for glucose disposal and the main reservoir for amino acids. With aging, cachexia, starvation, and myositis, there is a preferential loss of fast glycolytic muscle fibers. We previously reported a mouse model in which a constitutively-active Akt transgene is induced to express in a subset of muscle groups leading to the hypertrophy of type IIb myofibers with an accompanying increase in strength. This muscle growth protects mice in various cardio-metabolic disease models, but little is known about the underlying cellular and molecular mechanisms by which fast-twitch muscle impacts disease processes and regulates distant tissues. In the present study, poly (A) + tail mRNA-seq and non-targeted metabolomics were performed to characterize the transcriptome and metabolome of the hypertrophic gastrocnemius muscle from Akt1-transgenic mice.ResultsCombined metabolomics and transcriptomic analyses revealed that Akt1-induced muscle growth mediated a metabolic shift involving reductions in glycolysis and oxidative phosphorylation, but enhanced pentose phosphate pathway activation and increased branch chain amino acid accumulation. Pathway analysis for the 4,027 differentially expressed genes in muscle identified enriched signaling pathways involving growth, cell cycle regulation, and inflammation. Consistent with a regenerative transcriptional signature, the transgenic muscle tissue was found to be comprised of fibers with centralized nuclei that are positive for embryonic myosin heavy chain. Immunohistochemical analysis also revealed the presence of inflammatory cells associated with the regenerating fibers. Signal peptide prediction analysis revealed 240 differentially expressed in muscle transcripts that potentially encode secreted proteins. A number of these secreted factors have signaling properties that are consistent with the myogenic, metabolic and cardiovascular-protective properties that have previously been associated with type IIb muscle growth.ConclusionsThis study provides the first extensive transcriptomic sequencing/metabolomics analysis for a model of fast-twitch myofiber growth. These data reveal that enhanced Akt signaling promotes the activation of pathways that are important for the production of proteins and nucleic acids. Numerous transcripts potentially encoding muscle secreted proteins were identified, indicating the importance of fast-twitch muscle in inter-tissue communication.

MTORC2 signalling regulates M2 macrophage differentiation in response to helminth infection and adaptive thermogenesis

Alternatively activated macrophages (M2) have an important function in innate immune responses to parasitic helminths, and emerging evidence also indicates these cells are regulators of systemic metabolism. Here we show a critical role for mTORC2 signalling in the generation of M2 macrophages. Abrogation of mTORC2 signalling in macrophages by selective conditional deletion of the adaptor molecule Rictor inhibits the generation of M2 macrophages while leaving the generation of classically activated macrophages (M1) intact. Selective deletion of Rictor in macrophages prevents M2 differentiation and clearance of a parasitic helminth infection in mice, and also abrogates the ability of mice to regulate brown fat and maintain core body temperature. Our findings define a role for mTORC2 in macrophages in integrating signals from the immune microenvironment to promote innate type 2 immunity, and also to integrate systemic metabolic and thermogenic responses.

Endoplasmic Reticulum Stress and Obesity.

In recent years, the world has seen an alarming increase in obesity and closely associated with insulin resistance which is a state of low-grade inflammation, the latter characterized by elevated levels of proinflammatory cytokines in blood and tissues. A shift in energy balance alters systemic metabolic regulation and the important role that chronic inflammation, endoplasmic reticulum (ER) dysfunction, and activation of the unfolded protein response (UPR) play in this process.Why obesity is so closely associated with insulin resistance and inflammation is not understood well. This suggests that there are probably other causes for obesity-related insulin resistance and inflammation. One of these appears to be endoplasmic reticulum (ER) stress.The ER is a vast membranous network responsible for the trafficking of a wide range of proteins and plays a central role in integrating multiple metabolic signals critical in cellular homeostasis. Conditions that may trigger unfolded protein response activation include increased protein synthesis, the presence of mutant or misfolded proteins, inhibition of protein glycosylation, imbalance of ER calcium levels, glucose and energy deprivation, hypoxia, pathogens or pathogen-associated components and toxins. Thus, characterizing the mechanisms contributing to obesity and identifying potential targets for its prevention and treatment will have a great impact on the control of associated conditions, particularly T2D.

The GATOR1 Complex Regulates Metabolic Homeostasis and the Response to Nutrient Stress in Drosophila melanogaster.

TORC1 regulates metabolism and growth in response to a large array of upstream inputs. The evolutionarily conserved trimeric GATOR1 complex inhibits TORC1 activity in response to amino acid limitation. In humans, the GATOR1 complex has been implicated in a wide array of pathologies including cancer and hereditary forms of epilepsy. However, the precise role of GATOR1 in animal physiology remains largely undefined. Here, we characterize null mutants of the GATOR1 components nprl2, nprl3, and iml1 in Drosophila melanogaster. We demonstrate that all three mutants have inappropriately high baseline levels of TORC1 activity and decreased adult viability. Consistent with increased TORC1 activity, GATOR1 mutants exhibit a cell autonomous increase in cell growth. Notably, escaper nprl2 and nprl3 mutant adults have a profound locomotion defect. In line with a nonautonomous role in the regulation of systemic metabolism, expressing the Nprl3 protein in the fat body, a nutrient storage organ, and hemocytes but not muscles and neurons rescues the motility of nprl3 mutants. Finally, we show that nprl2 and nprl3 mutants fail to activate autophagy in response to amino acid limitation and are extremely sensitive to both amino acid and complete starvation. Thus, in Drosophila, in addition to maintaining baseline levels of TORC1 activity, the GATOR1 complex has retained a critical role in the response to nutrient stress. In summary, the TORC1 inhibitor GATOR1 contributes to multiple aspects of the development and physiology of Drosophila.

Extracellular Redox Regulation of Intracellular Reactive Oxygen Generation, Mitochondrial Function and Lipid Turnover in Cultured Human Adipocytes.

BackgroundMany tissues play an important role in metabolic homeostasis and the development of diabetes and obesity. We hypothesized that the circulating redox metabolome is a master metabolic regulatory system that impacts all organs and modulates reactive oxygen species (ROS) production, lipid peroxidation, energy production and changes in lipid turnover in many cells including adipocytes.MethodsDifferentiated human preadipocytes were exposed to the redox couples, lactate (L) and pyruvate (P), β–hydroxybutyrate (βOHB) and acetoacetate (Acoc), and the thiol-disulfides cysteine/ cystine (Cys/CySS) and GSH/GSSG for 1.5–4 hours. ROS measurements were done with CM-H2DCFDA. Lipid peroxidation (LPO) was assessed by a modification of the thiobarbituric acid method. Lipolysis was measured as glycerol release. Lipid synthesis was measured as 14C-glucose incorporated into lipid. Respiration was assessed using the SeaHorse XF24 analyzer and the proton leak was determined from the difference in respiration with oligomycin and antimycin A.ResultsMetabolites with increasing oxidation potentials (GSSG, CySS, Acoc) increased adipocyte ROS. In contrast, P caused a decrease in ROS compared with L. Acoc also induced a significant increase in both LPO and lipid synthesis. L and Acoc increased lipolysis. βOHB increased respiration, mainly due to an increased proton leak. GSSG, when present throughout 14 days of differentiation significantly increased fat accumulation, but not when added later.ConclusionsWe demonstrated that in human adipocytes changes in the external redox state impacted ROS production, LPO, energy efficiency, lipid handling, and differentiation. A more oxidized state generally led to increased ROS, LPO and lipid turnover and more reduction led to increased respiration and a proton leak. However, not all of the redox couples were the same suggesting compartmentalization. These data are consistent with the concept of the circulating redox metabolome as a master metabolic regulatory system.

Abstract 082: Chronic Angiotensin-(1-7) Attenuates the Development of Obesity in Mice by Enhancing Energy Expenditure

Activation of the renin-angiotensin system, and in particular angiotensin (Ang) II, is observed in obese patients and closely correlates with insulin resistance. Obesity is also associated with deficiency of Ang-(1-7), a vasodilatory peptide that mitigates Ang II actions. Accumulating evidence suggests that Ang-(1-7) has direct positive metabolic effects including reducing adiposity and reversing whole-body glucose intolerance and insulin resistance in animal models of cardiometabolic syndrome. In this study, we tested the hypothesis that chronic Ang-(1-7) administration would prevent high fat diet-induced obesity in mice, and determined potential mechanisms underlying this effect. To test this hypothesis, adult male C57BL/6J mice received a 12-week systemic infusion of Ang-(1-7) (400 ng/kg/min; n=7) or saline (n=6) via subcutaneous osmotic mini-pumps. Immediately following mini-pump implantation, mice were placed on a 60% high fat diet, with body mass measured weekly. Body composition (mq10 nuclear magnetic resonance analyzer), food and water intake, and energy expenditure (indirect calorimetry) were measured during the last week of treatment. Ang-(1-7) attenuated high fat diet-induced weight gain [39.7±1.3 Ang-(1-7) vs. 43.9±0.7 g saline at 12 weeks; p=0.023) and adiposity [32±1 Ang-(1-7) vs. 29±1% saline; p=0.050). The reduced gain in body weight following Ang-(1-7) was associated with increased average energy expenditure [0.55±0.02 Ang-(1-7) vs. 0.42±0.06 kcal/hour saline, p=0.038] and oxygen consumption [1.84±0.07 Ang-(1-7) vs. 1.39±0.23 ml/min saline, p=0.049] during the dark cycle, with no effect on locomotor activity. A similar trend for Ang-(1-7) to increase energy expenditure and oxygen consumption was observed during the light cycle. There were no significant differences in food or water intake following chronic Ang-(1-7) versus saline infusion. These findings suggest that targeting of Ang-(1-7) may be a novel strategy to prevent the development of obesity by enhancing energy expenditure, and further highlight the importance of the renin-angiotensin system in metabolic regulation.

Deciphering the Principles of Bacterial Nitrogen Dietary Preferences: a Strategy for Nutrient Containment.

ABSTRACTA fundamental question in microbial physiology concerns why organisms prefer certain nutrients to others. For example, among different nitrogen sources, ammonium is the preferred nitrogen source, supporting fast growth, whereas alternative nitrogen sources, such as certain amino acids, are considered to be poor nitrogen sources, supporting much slower exponential growth. However, the physiological/regulatory logic behind such nitrogen dietary choices remains elusive. In this study, by engineering Escherichia coli, we switched the dietary preferences toward amino acids, with growth rates equivalent to that of the wild-type strain grown on ammonia. However, when the engineered strain was cultured together with wild-type E. coli, this growth advantage was diminished as a consequence of ammonium leakage from the transport-and-catabolism (TC)-enhanced (TCE) cells, which are preferentially utilized by wild-type bacteria. Our results reveal that the nitrogen regulatory (Ntr) system fine tunes the expression of amino acid transport and catabolism components to match the flux through the ammonia assimilation pathway such that essential nutrients are retained, but, as a consequence, the fast growth rate on amino acids is sacrificed.

Mitochondria controlled by UCP2 determine hypoxia-induced synaptic remodeling in the cortex and hippocampus

We have established that mitochondrial dynamics, under metabolic control, play crucial roles in the regulation of systemic metabolism by hypothalamic circuits. The role of mitochondrial dynamics in neurons in higher brain regions is, however, ill-defined. Here we show that early postnatal exposure of animals to temporal hypoxia followed by normoxia, a major metabolic challenge on brain cells, resulted in adaptive responses of neuronal mitochondria. The number and oxygen consumption of mitochondria in cortical and hippocampal neurons were altered, while mitochondria–endoplasmic reticulum (ER) interactions were preserved. These changes coincided with increased synaptic input of neurons in the cortex and hippocampus. We identified that the changing oxygen tension triggered mitochondrial uncoupling protein 2 (UCP2) expression and showed that UCP2 is crucial for these adaptive mitochondrial responses. In UCP2 KO mice, changing oxygen tension did not induce changes in mitochondrial parameters and function but decreased mitochondria–ER contacts and resulted in loss of synapses both in the cortex and hippocampus. These observations establish that mitochondrial location controlled by UCP2 is relevant for adaptive responses of neurons in cortical and hippocampal neurons and are relevant to perinatal hypoxia-triggered circuit adaptations.

Noninvasive evaluation of the correlation between regional cerebral blood flow and intraventricular brain temperature in temporal lobe epilepsy

IntroductionIn temporal lobe epilepsy (TLE), an uncoupling of cerebral blood flow (CBF) and metabolism is indicated. The aim of this study was to clarify this relationship by investigating intraventricular brain temperature (BT) and CBF in TLE using a noninvasive MRI technique. Material and methodsWe recruited 38 subjects with left TLE and 39 subjects with right TLE. All patients underwent an MRI examination including diffusion-weighted imaging (DWI) and pseudo-continuous arterial spin labeling (pCASL). Intraventricular BT was calculated by a DWI thermometric technique, and regional CBF was obtained from pCASL images, and we analyzed the relationship between them using the statistical parametric mapping 8 software (SPM8). ResultsIn only the left TLE group, there was a significant negative correlation between CBF and BT in the left inferior frontal gyrus. Positive correlations in the bilateral posterior poles were also found at the trend level in left TLE group. The patients with right TLE showed no significant correlation. ConclusionOur results may reflect a regional uncoupling of blood flow and metabolism in those brain areas, and they may indicate that TLE has different metabolic regulation systems in the brain.

Mathematical Modeling of the Blood Glucose Regulation System in Diabetes Mellitus Patients

Interest in the mathematical modeling of the carbohydrate metabolism regulation system increases in recent years. This is associated with a "closed loop" insulin pump development (it controls an insulin infusion depending on the blood glucose level). To create an algorithm for the automatic control of insulin (and other hormones) infusion using an insulin pump it is necessary to accurately predict glycaemia level. So, the primary objective of mathematical modeling is to predict the blood glucose level changes, caused by the wide range of external factors. This review discusses the main mathematical models of blood glucose level control physiological system (simplified insulin-glucose system). The two major classes of models--empirical and theoretical--are described in detail. The ideal mathematical model of carbohydrate metabolism regulatory system is absent. However, the success in the field of blood glucose level control modeling and simulating is essentialfor the further development of diabetes prevention and treatment technologies, and creating an artificial pancreas in particular.

Pancreatic hyperplasia after gastric bypass surgery in a GK rat model of non-obese type 2 diabetes.

Gastric bypass surgery produces clear antidiabetic effects in a substantial proportion of morbidly obese patients. In view of the recent trend away from 'bariatric' surgery and toward 'metabolic' surgery, it is important to elucidate the enhancing effect of bypass surgery on pancreatic β-cell mass, which is related to diabetes remission in non-obese patients. We investigated the effects of gastric bypass surgery on glycemic control and other pancreatic changes in a spontaneous non-obese type 2 diabetes Goto-Kakizaki rat model. Significant improvements in postprandial hyperglycemia and plasma c-peptide level were observed when glucose was administered orally post-surgery. Other important events observed after surgery were enhanced first phase insulin secretion in a in site pancreatic perfusion experiment, pancreatic hyperplasia, improved islet structure (revealed by immunohistochemical analysis), striking increase in β-cell mass, slight increase in ratio of β-cell area to total pancreas area, and increased number of small islets closely related to exocrine ducts. No notable changes were observed in ratio of β-cell to non-β endocrine cell area, β-cell apoptosis, or β-cell proliferation. These findings demonstrate that gastric bypass surgery in this rat model increases endocrine cells and pancreatic hyperplasia, and reflect the important role of the gastrointestinal system in regulation of metabolism.

Toll-Like Receptor 3 Influences Glucose Homeostasis and β-Cell Insulin Secretion.

Toll-like receptors (TLRs) have been implicated in the pathogenesis of type 2 diabetes. We examined the function of TLR3 in glucose metabolism and type 2 diabetes-related phenotypes in animals and humans. TLR3 is highly expressed in the pancreas, suggesting that it can influence metabolism. Using a diet-induced obesity model, we show that TLR3-deficient mice had enhanced glycemic control, facilitated by elevated insulin secretion. Despite having high insulin levels, Tlr3(-/-) mice did not experience disturbances in whole-body insulin sensitivity, suggesting that they have a robust metabolic system that manages increased insulin secretion. Increase in insulin secretion was associated with upregulation of islet glucose phosphorylation as well as exocytotic protein VAMP-2 in Tlr3(-/-) islets. TLR3 deficiency also modified the plasma lipid profile, decreasing VLDL levels due to decreased triglyceride biosynthesis. Moreover, a meta-analysis of two healthy human populations showed that a missense single nucleotide polymorphism in TLR3 (encoding L412F) was linked to elevated insulin levels, consistent with our experimental findings. In conclusion, our results increase the understanding of the function of innate receptors in metabolic disorders and implicate TLR3 as a key control system in metabolic regulation.

Usual breakfast eating habits affect response to breakfast skipping in overweight women.

This randomized, cross-over trial was designed to investigate the metabolic and appetitive responses to skipping breakfast in overweight women who were habitual breakfast Eaters or Skippers. Nine Eaters and nine Skippers were studied on two separate days during which subjects ate breakfast (B) or had no breakfast (NB), followed by a standard lunch meal 4 h later. Blood sampling for hormones and metabolites was performed after lunch, and appetite was rated throughout the day. Interactions between day and habitual breakfast pattern were seen for area under the curve (AUC) for insulin and free fatty acids (FFA). Both insulin (P = 0.020) and FFA (P = 0.023) AUC were higher on the NB day for Eaters but similar on both days for Skippers. Eaters had higher pre lunch hunger AUC on the NB day (P = 0.015) as well as lower pre lunch satiety AUC under both conditions (P = 0.019). Overall, this study showed that the adverse effects of skipping breakfast (higher insulin and FFA responses to lunch, increased hunger, and decreased satiety) were found primarily in habitual breakfast eaters. This suggests that meal skipping may have enhanced effects in habitual Eaters due to entrainment of metabolic and appetitive regulatory systems.

Interplay between the immune system and adipose tissue in obesity.

Obesity is a major risk factor for metabolic disease, with white adipose tissue (WAT) inflammation emerging as a key underlying pathology. Alongside its major role in energy storage, WAT is an important endocrine organ, producing many bioactive molecules, termed adipokines, which not only serve as regulators of systemic metabolism, but also possess immunoregulatory properties. Furthermore, WAT contains a unique immune cell repertoire, including an accumulation of leukocytes that are rare in other locations. These include alternatively activated macrophages, invariant natural killer T cells, and regulatory T cells. Disruption of resident adipose leukocyte homeostasis contributes to obesity-associated inflammation and consequent metabolic disorder. Despite many recent advances in this new field of immuno-metabolism, fundamental questions of why and how inflammation arises as obesity develops are not yet fully understood. Exploring the distinct immune system of adipose tissue is fundamental to our understanding of the endocrine as well as immune systems. In this review, we discuss the roles of adipose tissue leukocytes in the transition to obesity and progression of inflammation and highlight potential anti-inflammatory therapies for combating obesity-related pathology.

Participation of the central melanocortin system in metabolic regulation and energy homeostasis.

Obesity and metabolic disorders, such as type 2 diabetes and hypertension, have attracted considerable attention as life-threatening diseases not only in developed countries but also worldwide. Additionally, the rate of obesity in young people all over the world is rapidly increasing. Accumulated evidence suggests that the central nervous system may participate in the development of and/or protection from obesity. For example, in the brain, the hypothalamic melanocortin system senses and integrates central and peripheral metabolic signals and controls the degree of energy expenditure and feeding behavior, in concert with metabolic status, to regulate whole-body energy homeostasis. Currently, researchers are studying the mechanisms by which peripheral metabolic molecules control feeding behavior and energy balance through the central melanocortin system. Accordingly, recent studies have revealed that some inflammatory molecules and transcription factors participate in feeding behavior and energy balance by controlling the central melanocortin pathway, and have thus become new candidates as therapeutic targets to fight metabolic diseases such as obesity and diabetes.

Invited commentary: nighttime light exposure as a risk factor for obesity through disruption of circadian and circannual rhythms.

In this issue of the American Journal of Epidemiology, McFadden et al. (Am J Epidemiol. 2014;180(3):245-250) report findings on the relationship between light exposure at night and obesity from a cross-sectional study of United Kingdom women. Their research extends findings from a previous study with elderly participants by including a larger sample size of over 100,000 women and a broader age range of 16 years or older. The findings are consistent with animal studies showing that prolonged light exposure leads to weight gain. Humans' circadian, circannual, and metabolic regulatory systems evolved to be adaptive in environments that were quite different from those faced in modern industrial society. Technology has allowed exposures to levels and timing of light, nutrient intake, and physical activity never before possible. This commentary discusses how nighttime light exposure can increase the risk of obesity and the metabolic syndrome by disrupting circadian and circannual rhythms.

The gut hormone ghrelin partially reverses energy substrate metabolic alterations in the failing heart.

The gut-derived hormone ghrelin, especially its acylated form, plays a major role in the regulation of systemic metabolism and exerts also relevant cardioprotective effects; hence, it has been proposed for the treatment of heart failure (HF). We tested the hypothesis that ghrelin can directly modulate cardiac energy substrate metabolism. We used chronically instrumented dogs, 8 with pacing-induced HF and 6 normal controls. Human des-acyl ghrelin [1.2 nmol/kg per hour] was infused intravenously for 15 minutes, followed by washout (rebaseline) and infusion of acyl ghrelin at the same dose. (3)H-oleate and (14)C-glucose were coinfused and arterial and coronary sinus blood sampled to measure cardiac free fatty acid and glucose oxidation and lactate uptake. As expected, cardiac substrate metabolism was profoundly altered in HF because baseline oxidation levels of free fatty acids and glucose were, respectively, >70% lower and >160% higher compared with control. Neither des-acyl ghrelin nor acyl ghrelin significantly affected function and metabolism in normal hearts. However, in HF, des-acyl and acyl ghrelin enhanced myocardial oxygen consumption by 10.2±3.5% and 9.9±3.7%, respectively (P<0.05), and cardiac mechanical efficiency was not significantly altered. This was associated, respectively, with a 41.3±6.7% and 32.5±10.9% increase in free fatty acid oxidation and a 31.3±9.2% and 41.4±8.9% decrease in glucose oxidation (all P<0.05). Acute increases in des-acyl or acyl ghrelin do not interfere with cardiac metabolism in normal dogs, whereas they enhance free fatty acid oxidation and reduce glucose oxidation in HF dogs, thus partially correcting metabolic alterations in HF. This novel mechanism might contribute to the cardioprotective effects of ghrelin in HF.