Myocardial metabolism in insulin-deficient diabetic humans without coronary artery disease

The Interplay between Adipose Tissue Properties and Levels of NT-proBNP in People with HIV

Objective

We aimed to assess the association between low N-terminal pro-brain natriuretic peptide (NT-proBNP) and body mass index (BMI), adipose tissue distribution, adiponectin, and HIV-specific risk factors among people with HIV (PWH).

Methods

We included 811 PWH with measurement of height, weight and waist circumference, blood samples analyzed for NT-proBNP, and visceral-(VAT) and subcutaneous (SAT) adipose tissue areas measured from CT-scans. Low concentrations of NT-proBNP were defined as concentrations below the limit of quantification (5.9 pmol/L). Associations were explored with multivariable logistic regression analyses adjusted for relevant confounders.

Results

We identified 471 (58%) individuals with low concentrations of NT-proBNP. Increasing BMI was associated with higher odds of low NT-proBNP (adjusted OR (aOR) 1.06 (95% CI: 1.01-1.11) per 1 kg/m2). Central obesity and large areas of VAT were associated with higher odds of low NT-proBNP (aOR 1.66 (1.16-2.36) and aOR 1.69 (1.09-2.62), respectively). Higher adiponectin was associated with lower odds of low NT-proBNP (aOR 0.86 (0.79-0.95) per 10% increase). No associations were found between low NT-proBNP and HIV-specific risk factors.

Conclusions

In PWH, low NT-proBNP is associated with an adverse adipose tissue profile with high BMI, central obesity, accumulation of VAT, and low adiponectin.

Energy metabolism homeostasis in cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the general population. Energy metabolism disturbance is one of the early abnormalities in CVDs, such as coronary heart disease, diabetic cardiomyopathy, and heart failure. To explore the role of myocardial energy homeostasis disturbance in CVDs, it is important to understand myocardial metabolism in the normal heart and their function in the complex pathophysiology of CVDs. In this article, we summarized lipid metabolism/lipotoxicity and glucose metabolism/insulin resistance in the heart, focused on the metabolic regulation during neonatal and ageing heart, proposed potential metabolic mechanisms for cardiac regeneration and degeneration. We provided an overview of emerging molecular network among cardiac proliferation, regeneration, and metabolic disturbance. These novel targets promise a new era for the treatment of CVDs.

The Contribution of Cardiac Fatty Acid Oxidation to Diabetic Cardiomyopathy Severity

Diabetes is a major risk factor for the development of cardiovascular disease via contributing and/or triggering significant cellular signaling and metabolic and structural alterations at the level of the heart and the whole body. The main cause of mortality and morbidity in diabetic patients is cardiovascular disease including diabetic cardiomyopathy. Therefore, understanding how diabetes increases the incidence of diabetic cardiomyopathy and how it mediates the major perturbations in cell signaling and energy metabolism should help in the development of therapeutics to prevent these perturbations. One of the significant metabolic alterations in diabetes is a marked increase in cardiac fatty acid oxidation rates and the domination of fatty acids as the major energy source in the heart. This increased reliance of the heart on fatty acids in the diabetic has a negative impact on cardiac function and structure through a number of mechanisms. It also has a detrimental effect on cardiac efficiency and worsens the energy status in diabetes, mainly through inhibiting cardiac glucose oxidation. Furthermore, accelerated cardiac fatty acid oxidation rates in diabetes also make the heart more vulnerable to ischemic injury. In this review, we discuss how cardiac energy metabolism is altered in diabetic cardiomyopathy and the impact of cardiac insulin resistance on the contribution of glucose and fatty acid to overall cardiac ATP production and cardiac efficiency. Furthermore, how diabetes influences the susceptibility of the myocardium to ischemia/reperfusion injury and the role of the changes in glucose and fatty acid oxidation in mediating these effects are also discussed.

Lactate and Myocadiac Energy Metabolism

The myocardium is capable of utilizing different energy substrates, which is referred to as “metabolic flexibility.” This process assures ATP production from fatty acids, glucose, lactate, amino acids, and ketones, in the face of varying metabolic contexts. In the normal physiological state, the oxidation of fatty acids contributes to approximately 60% of energy required, and the oxidation of other substrates provides the rest. The accumulation of lactate in ischemic and hypoxic tissues has traditionally be considered as a by-product, and of little utility. However, recent evidence suggests that lactate may represent an important fuel for the myocardium during exercise or myocadiac stress. This new paradigm drives increasing interest in understanding its role in cardiac metabolism under both physiological and pathological conditions. In recent years, blood lactate has been regarded as a signal of stress in cardiac disease, linking to prognosis in patients with myocardial ischemia or heart failure. In this review, we discuss the importance of lactate as an energy source and its relevance to the progression and management of heart diseases.

Metabolic Profiling of the Diabetic Heart: Toward a Richer Picture

The increasing global prevalence of diabetes has been accompanied by a rise in diabetes-related conditions. This includes diabetic cardiomyopathy (DbCM), a progressive form of heart disease that occurs with both insulin-dependent (type-1) and insulin-independent (type-2) diabetes and arises in the absence of hypertension or coronary artery disease. Over time, DbCM can develop into overt heart failure. Like other forms of cardiomyopathy, DbCM is accompanied by alterations in metabolism which could lead to further progression of the pathology, with metabolic derangement postulated to precede functional changes in the diabetic heart. Moreover in the case of type-2 diabetes, underlying insulin resistance is likely to prevent the canonical substrate switch of the failing heart away from fatty acid oxidation toward increased use of glycolysis. Analytical chemistry techniques, collectively known as metabolomics, are useful tools for investigating the condition. In this article, we provide a comprehensive review of those studies that have employed metabolomic techniques, namely chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy, to profile metabolic remodeling in the diabetic heart of human patients and animal models. These studies collectively demonstrate that glycolysis and glucose oxidation are suppressed in the diabetic myocardium and highlight a complex picture regarding lipid metabolism. The diabetic heart typically shows an increased reliance on fatty acid oxidation, yet triacylglycerols and other lipids accumulate in the diabetic myocardium indicating probable lipotoxicity. The application of lipidomic techniques to the diabetic heart has identified specific lipid species that become enriched and which may in turn act as plasma-borne biomarkers for the condition. Metabolomics is proving to be a powerful approach, allowing a much richer analysis of the metabolic alterations that occur in the diabetic heart. Careful physiological interpretation of metabolomic results will now be key in order to establish which aspects of the metabolic derangement are causal to the progression of DbCM and might form the basis for novel therapeutic intervention.

Effect of Gegen Qinlian Decoction on Cardiac Gene Expression in Diabetic Mice

The aim of this research is to investigate the therapeutic effect of GGQL decoction on cardiac dysfunction and elucidate the pharmacological mechanisms. db/db mice were divided into DB group or GGQL group, and WT mice were used as control. All mice were accessed by echocardiography. And the total RNA of LV tissue samples was sequenced, then differential expression genes were analyzed. The RNA-seq results were validated by the results of RT-qPCR of 4 genes identified as differentially expressed. The content of pyruvate and ceramide in myocardial tissue was also measured. The results showed that GGQL decoction could significantly improve the diastolic dysfunction, increase the content of pyruvate, and had the trend to reduce the ceramide content. The results of RNA-seq showed that 2958 genes were differentially expressed when comparing the DB group with the WT group. Among them, compared with the DB group, 26 genes were differentially regulated in the GGQL group. The expression results of 4 genes were consistent with the RNA-seq results. Our study reveals that GGQL decoction has a therapeutic effect on diastolic dysfunction of the left ventricular and the effect may be related to its role in promoting myocardial glycolysis and decreasing the content of ceramide.

Diabetic Cardiomyopathy: An Immunometabolic Perspective

The heart possesses a remarkable inherent capability to adapt itself to a wide array of genetic and extrinsic factors to maintain contractile function. Failure to sustain its compensatory responses results in cardiac dysfunction, leading to cardiomyopathy. Diabetic cardiomyopathy (DCM) is characterized by left ventricular hypertrophy and reduced diastolic function, with or without concurrent systolic dysfunction in the absence of hypertension and coronary artery disease. Changes in substrate metabolism, oxidative stress, endoplasmic reticulum stress, formation of extracellular matrix proteins, and advanced glycation end products constitute the early stage in DCM. These early events are followed by steatosis (accumulation of lipid droplets) in cardiomyocytes, which is followed by apoptosis, changes in immune responses with a consequent increase in fibrosis, remodeling of cardiomyocytes, and the resultant decrease in cardiac function. The heart is an omnivore, metabolically flexible, and consumes the highest amount of ATP in the body. Altered myocardial substrate and energy metabolism initiate the development of DCM. Diabetic hearts shift away from the utilization of glucose, rely almost completely on fatty acids (FAs) as the energy source, and become metabolically inflexible. Oxidation of FAs is metabolically inefficient as it consumes more energy. In addition to metabolic inflexibility and energy inefficiency, the diabetic heart suffers from impaired calcium handling with consequent alteration of relaxation-contraction dynamics leading to diastolic and systolic dysfunction. Sarcoplasmic reticulum (SR) plays a key role in excitation-contraction coupling as Ca²⁺ is transported into the SR by the SERCA2a (sarcoplasmic/endoplasmic reticulum calcium-ATPase 2a) during cardiac relaxation. Diabetic cardiomyocytes display decreased SERCA2a activity and leaky Ca²⁺ release channel resulting in reduced SR calcium load. The diabetic heart also suffers from marked downregulation of novel cardioprotective microRNAs (miRNAs) discovered recently. Since immune responses and substrate energy metabolism are critically altered in diabetes, the present review will focus on immunometabolism and miRNAs.

A Comparative Metabolomics Approach Reveals Early Biomarkers for Metabolic Response to Acute Myocardial Infarction

Discovery of novel biomarkers is critical for early diagnosis of acute coronary syndrome (ACS). Serum metabolite profiling of ST-elevation myocardial infarction (STEMI), unstable angina (UA) and healthy controls was performed using gas chromatography mass spectrometry (GC/MS), solid-phase microextraction coupled to gas chromatography mass spectrometry (SPME-GC/MS) and nuclear magnetic resonance (¹H-NMR). Multivariate data analysis revealed a metabolic signature that could robustly discriminate STEMI patients from both healthy controls and UA patients. This panel of biomarkers consisted of 19 metabolites identified in the serum of STEMI patients. One of the most intriguing biomarkers among these metabolites is hydrogen sulfide (H₂S), an endogenous gasotransmitter with profound effect on the heart. Serum H₂S absolute levels were further investigated using a quantitative double-antibody sandwich enzyme-linked immunosorbent assay (ELISA). This highly sensitive immunoassay confirmed the elevation of serum H₂S in STEMI patients. H₂S level discriminated between UA and STEMI groups, providing an initial insight into serum-free H₂S bioavailability during ACS. In conclusion, the current study provides a detailed map illustrating the most predominant altered metabolic pathways and the biochemical linkages among the biomarker metabolites identified in STEMI patients. Metabolomics analysis may yield novel predictive biomarkers that will potentially allow for an earlier medical intervention.

Imaging of myocardial fatty acid oxidation

Myocardial fuel selection is a key feature of the health and function of the heart, with clear links between myocardial function and fuel selection and important impacts of fuel selection on ischemia tolerance. Radiopharmaceuticals provide uniquely valuable tools for in vivo, non-invasive assessment of these aspects of cardiac function and metabolism. Here we review the landscape of imaging probes developed to provide non-invasive assessment of myocardial fatty acid oxidation (MFAO). Also, we review the state of current knowledge that myocardial fatty acid imaging has helped establish of static and dynamic fuel selection that characterizes cardiac and cardiometabolic disease and the interplay between fuel selection and various aspects of cardiac function. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Mitochondrial pyruvate transport: a historical perspective and future research directions

Pyruvate is the end-product of glycolysis, a major substrate for oxidative metabolism, and a branching point for glucose, lactate, fatty acid and amino acid synthesis. The mitochondrial enzymes that metabolize pyruvate are physically separated from cytosolic pyruvate pools and rely on a membrane transport system to shuttle pyruvate across the impermeable inner mitochondrial membrane (IMM). Despite long-standing acceptance that transport of pyruvate into the mitochondrial matrix by a carrier-mediated process is required for the bulk of its metabolism, it has taken almost 40 years to determine the molecular identity of an IMM pyruvate carrier. Our current understanding is that two proteins, mitochondrial pyruvate carriers MPC1 and MPC2, form a hetero-oligomeric complex in the IMM to facilitate pyruvate transport. This step is required for mitochondrial pyruvate oxidation and carboxylation-critical reactions in intermediary metabolism that are dysregulated in several common diseases. The identification of these transporter constituents opens the door to the identification of novel compounds that modulate MPC activity, with potential utility for treating diabetes, cardiovascular disease, cancer, neurodegenerative diseases, and other common causes of morbidity and mortality. The purpose of the present review is to detail the historical, current and future research investigations concerning mitochondrial pyruvate transport, and discuss the possible consequences of altered pyruvate transport in various metabolic tissues.

1H-NMR-based metabolic analysis of human serum reveals novel markers of myocardial energy expenditure in heart failure patients

OBJECTIVE

Elevated myocardial energy expenditure (MEE) is related with reduced left ventricular ejection fraction, and has also been documented as an independent predictor of cardiovascular mortality. However, the serum small-molecule metabolite profiles and pathophysiological mechanisms of elevated MEE in heart failure (HF) are still lacking. Herein, we used 1H-NMR-based metabolomics analysis to screen for potential biomarkers of MEE in HF.

METHODS

A total of 61 subjects were enrolled, including 46 patients with heart failure and 15 age-matched controls. Venous serum samples were collected from subjects after an 8-hour fast. An INOVA 600 MHz nuclear magnetic resonance spectrometer with Carr-Purcell-Melboom-Gill (CPMG) pulse sequence was employed for the metabolomics analysis and MEE was calculated using colored Doppler echocardiography. Metabolomics data were processed using orthogonal signal correction and regression analysis was performed using the partial least squares method.

RESULTS

The mean MEE levels of HF patients and controls were 139.61±58.18 cal/min and 61.09±23.54 cal/min, respectively. Serum metabolomics varied with MEE changed, and 3-hydroxybutyrate, acetone and succinate were significantly elevated with the increasing MEE. Importantly, these three metabolites were independent of administration of angiotensin converting enzyme inhibitor, β-receptor blockers, diuretics and statins (P>0.05).

CONCLUSIONS

These results suggested that in patients with heart failure, MEE elevation was associated with significant changes in serum metabolomics profiles, especially the concentration of 3-hydroxybutyrate, acetone and succinate. These compounds could be used as potential serum biomarkers to study myocardial energy mechanism in HF patients.

CardioNet: a human metabolic network suited for the study of cardiomyocyte metabolism

Background

Availability of oxygen and nutrients in the coronary circulation is a crucial determinant of cardiac performance. Nutrient composition of coronary blood may significantly vary in specific physiological and pathological conditions, for example, administration of special diets, long-term starvation, physical exercise or diabetes. Quantitative analysis of cardiac metabolism from a systems biology perspective may help to a better understanding of the relationship between nutrient supply and efficiency of metabolic processes required for an adequate cardiac output.

Results

Here we present CardioNet, the first large-scale reconstruction of the metabolic network of the human cardiomyocyte comprising 1793 metabolic reactions, including 560 transport processes in six compartments. We use flux-balance analysis to demonstrate the capability of the network to accomplish a set of 368 metabolic functions required for maintaining the structural and functional integrity of the cell. Taking the maintenance of ATP, biosynthesis of ceramide, cardiolipin and further important phospholipids as examples, we analyse how a changed supply of glucose, lactate, fatty acids and ketone bodies may influence the efficiency of these essential processes.

Conclusions

CardioNet is a functionally validated metabolic network of the human cardiomyocyte that enables theorectical studies of cellular metabolic processes crucial for the accomplishment of an adequate cardiac output.

Role of oxidative stress in disease progression in Stage B, a pre-cursor of heart failure

Oxidative stress represents a persistent imbalance between the production and the compensation of reactive oxygen species. Though predominantly found in advanced heart failure, the most frequent "at-risk" condition has been associated with underlying oxidative stress. It is therefore conceivable that timely detection and early intervention to reduce oxidative stress processes provide an opportunity to prevent disease progression to overt heart failure. This article reviews the current understanding of the current evidence of oxidative stress involvement in the pathophysiology of human heart failure and its potential therapeutic interventions in patients with Stage A and B heart failure.

Parallel effects of β-adrenoceptor blockade on cardiac function and fatty acid oxidation in the diabetic heart: Confronting the maze

Diabetic cardiomyopathy is a disease process in which diabetes produces a direct and continuous myocardial insult even in the absence of ischemic, hypertensive or valvular disease. The β-blocking agents bisoprolol, carvedilol and metoprolol have been shown in large-scale randomized controlled trials to reduce heart failure mortality. In this review, we summarize the results of our studies investigating the effects of β-blocking agents on cardiac function and metabolism in diabetic heart failure, and the complex inter-related mechanisms involved. Metoprolol inhibits fatty acid oxidation at the mitochondrial level but does not prevent lipotoxicity; its beneficial effects are more likely to be due to pro-survival effects of chronic treatment. These studies have expanded our understanding of the range of effects produced by β-adrenergic blockade and show how interconnected the signaling pathways of function and metabolism are in the heart. Although our initial hypothesis that inhibition of fatty acid oxidation would be a key mechanism of action was disproved, unexpected results led us to some intriguing regulatory mechanisms of cardiac metabolism. The first was upstream stimulatory factor-2-mediated repression of transcriptional master regulator PGC-1α, most likely occurring as a consequence of the improved function; it is unclear whether this effect is unique to β-blockers, although repression of carnitine palmitoyltransferase (CPT)-1 has not been reported with other drugs which improve function. The second was the identification of a range of covalent modifications which can regulate CPT-1 directly, mediated by a signalome at the level of the mitochondria. We also identified an important interaction between β-adrenergic signaling and caveolins, which may be a key mechanism of action of β-adrenergic blockade. Our experience with this labyrinthine signaling web illustrates that initial hypotheses and anticipated directions do not have to be right in order to open up meaningful directions or reveal new information.

Left ventricular systolic function deterioration during dobutamine stress echocardiography as an early manifestation of diabetic cardiomyopathy and reversal by optimized therapeutic approach

Diabetes mellitus has been associated with changes in the structure and function of the myocardium manifesting in the early stages of the disease as subtle systolic and diastolic dysfunction; the role of dobutamine stress echocardiography (DSE) in this setting remains unclear. We sought to evaluate the prevalence of dobutamine-induced systolic dysfunction amongst diabetic patients with normal at rest left ventricular ejection fraction and no coronary artery disease and to investigate whether an optimized therapeutic approach can reverse these abnormalities. 1,363 patients with DM referred to our echocardiography laboratory for DSE between January 2008 and June 2010 were prospectively investigated. Patients with normal left ventricular ejection fraction (LVEF) at rest and significant deterioration during peak dobutamine infusion (defined as a ≥10% decrease) in the absence of coronary artery disease or vasospasm were enrolled. They received on top of their usual treatment 5 mg perindopril and had their glycemic control intensified. At 60 days, all of them were controlled for clinical status and underwent a control DSE. 18 patients were included, there were 9 males and 9 females, mean age was 66.1 ± 10.2 years. All the patients had type II DM with a mean duration of 12.7 ± 6.6 years. They all had normal at rest echocardiographic findings with no wall motion abnormalities; mean LVEF was 62 ± 6%. At peak dobutamine, LVEF significantly deteriorated in all the patients with a mean 15 ± 5% decrease compared to baseline. After therapeutic optimization, Glycated haemoglobin improved from 8.53 ± 2.05% to 6.8 ± 0.6% (δ HbA1C = 1.73%, P = 0.001), mean LVEF at peak dobutamine infusion evolved from 47.17 ± 4.2% pre-optimization to 58 ± 4.8% at control (10.83% improvement; P < 0.001). In patients with DM and normal at rest LVEF, Dobutamine infusion during DSE can induce a significant deterioration in LVEF in the absence of coronary artery disease or vasospasm. This specific condition could be largely reversed through an optimized therapy based on a tighter metabolic control and a more stringent renin-angiotensin-aldosterone system inhibition.

Adaptation of myocardial substrate metabolism to a ketogenic nutrient environment

Heart muscle is metabolically versatile, converting energy stored in fatty acids, glucose, lactate, amino acids, and ketone bodies. Here, we use mouse models in ketotic nutritional states (24 h of fasting and a very low carbohydrate ketogenic diet) to demonstrate that heart muscle engages a metabolic response that limits ketone body utilization. Pathway reconstruction from microarray data sets, gene expression analysis, protein immunoblotting, and immunohistochemical analysis of myocardial tissue from nutritionally modified mouse models reveal that ketotic states promote transcriptional suppression of the key ketolytic enzyme, succinyl-CoA:3-oxoacid CoA transferase (SCOT; encoded by Oxct1), as well as peroxisome proliferator-activated receptor alpha-dependent induction of the key ketogenic enzyme HMGCS2. Consistent with reduction of SCOT, NMR profiling demonstrates that maintenance on a ketogenic diet causes a 25% reduction of myocardial (13)C enrichment of glutamate when (13)C-labeled ketone bodies are delivered in vivo or ex vivo, indicating reduced procession of ketones through oxidative metabolism. Accordingly, unmetabolized substrate concentrations are higher within the hearts of ketogenic diet-fed mice challenged with ketones compared with those of chow-fed controls. Furthermore, reduced ketone body oxidation correlates with failure of ketone bodies to inhibit fatty acid oxidation. These results indicate that ketotic nutrient environments engage mechanisms that curtail ketolytic capacity, controlling the utilization of ketone bodies in ketotic states.

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Cleavage of protein kinase D after acute hypoinsulinemia prevents excessive lipoprotein lipase-mediated cardiac triglyceride accumulation

OBJECTIVE

During hypoinsulinemia, when cardiac glucose utilization is impaired, the heart rapidly adapts to using more fatty acids. One means by which this is achieved is through lipoprotein lipase (LPL). We determined the mechanisms by which the heart regulates LPL after acute hypoinsulinemia.

RESEARCH DESIGN AND METHODS

We used two different doses of streptozocin (55 [D-55] and 100 [D-100] mg/kg) to induce moderate and severe hypoinsulinemia, respectively, in rats. Isolated cardiomyocytes were also used for transfection or silencing of protein kinase D (PKD) and caspase-3.

RESULTS

There was substantial increase in LPL in D-55 hearts, an effect that was absent in severely hypoinsulinemic D-100 animals. Measurement of PKD, a key element involved in increasing LPL, revealed that only D-100 hearts showed an increase in proteolysis of PKD, an effect that required activation of caspase-3 together with loss of 14-3-3zeta, a binding protein that protects enzymes against degradation. In vitro, phosphomimetic PKD colocalized with LPL in the trans-golgi. PKD, when mutated to prevent its cleavage by caspase-3 and silencing of caspase-3, was able to increase LPL activity. Using a caspase inhibitor (Z-DEVD) in D-100 animals, we effectively lowered caspase-3 activity, prevented PKD cleavage, and increased LPL vesicle formation and translocation to the vascular lumen. This increase in cardiac luminal LPL was associated with a striking accumulation of cardiac triglyceride in Z-DEVD-treated D-100 rats. CONCLUSIONS After severe hypoinsulinemia, activation of caspase-3 can restrict LPL translocation to the vascular lumen. When caspase-3 is inhibited, this compensatory response is lost, leading to lipid accumulation in the heart.

PET detection of the impact of dobutamine on myocardial glucose metabolism in women with type 1 diabetes mellitus

BACKGROUND

Our objective was to determine, in the hearts of women with type 1 diabetes mellitus (T1DM), whether the fate of extracted glucose is altered and, if so, what the impact of dobutamine is on myocardial substrate metabolism. In experimental models of T1DM, myocardial glycolysis and glucose oxidation are reduced with the impairment becoming more pronounced with dobutamine. Whether similar changes occur in humans with T1DM is unclear.

METHODS AND RESULTS

Myocardial perfusion, oxygen consumption, and glucose and fatty acid metabolism were measured with positron emission tomography in 19 women, 7 normal volunteers (NVs) and 12 with T1DM. The NVs and 6 T1DM (DM1) patients were studied under baseline metabolic conditions and 6 T1DM patients were studied during hyperinsulinemic-euglycemic clamp (DM1-C), both at rest and during dobutamine. At rest, myocardial glucose uptake, glycolysis, glycogen storage, and oxidation were reduced by similar levels in DM1 patients compared with NVs (P < .05). During dobutamine, although myocardial glucose uptake was not different from DM1 patients at rest, fractional glycolysis was lower compared with NVs or DM1-C patients and reflected a lower glucose oxidation rate (P < .001). Measurements of myocardial glucose metabolism at rest and during dobutamine were comparable between NVs and DM1-C patients. During dobutamine, myocardial fatty acid uptake and oxidation increased in all 3 groups.

CONCLUSIONS

In women with T1DM, (1) myocardial glucose metabolism is impaired downstream from initial uptake, (2) these abnormalities become more pronounced with dobutamine and are paralleled by an increase in myocardial fatty acid metabolism, and (3) insulin restores glucose metabolism to levels observed in normal control subjects.

Translation of myocardial metabolic imaging concepts into the clinics

Flexibility in myocardial substrate metabolism for energy production is fundamental to cardiac health. This loss in plasticity or flexibility leads to overdependence on the metabolism of an individual category of substrates, with the predominance in fatty acid metabolism characteristic of diabetic heart disease and the accelerated glucose use associated with pressure-overload left ventricular hypertrophy being prime examples. There is a strong demand for accurate noninvasive imaging approaches of myocardial substrate metabolism that can facilitate the crosstalk between the bench and the bedside, leading to improved patient management paradigms. In this article potential future applications of metabolic imaging, particularly radionuclide approaches, for assessment of cardiovascular disease are discussed.

Myocardial glucose and lactate metabolism during rest and atrial pacing in humans

There is minimal in vivo data in humans evaluating myocardial substrate utilization during increased heart work. This study was performed to determine the balance of myocardial glucose and lactate metabolism during rest and increased heart work induced by atrial pacing in seven healthy men and women (age, 49.7 +/- 3.9 years; body mass index, 23.4 +/- 1.1 kg m(-2), maximum oxygen consumption, 35.5 +/- 3.0 ml kg(-1) min(-1), ejection fraction, 68 +/- 3%). After 3 days of dietary control, catheters were placed in coronary sinus, femoral arterial and venous, and peripheral venous blood vessels. Subjects received a primed continuous infusion of [3,3,3-(2)H]lactate and [6,6-(2)H]glucose throughout the study. Arterial and coronary sinus blood sampling and measurements of coronary sinus blood flow were made during rest and atrial pacing at approximately 111 beats min(-1). Myocardial oxygen consumption increased (P = 0.04) from rest to atrial pacing. Net glucose uptake increased (P = 0.04) from rest to atrial pacing with unchanged fractional extraction (rest: 9.1 +/- 2.7%, atrial pacing 9.8 +/- 2.9%). The percentage of whole body glucose disposal from myocardial uptake also increased from rest to atrial pacing. Isotopically measured lactate uptake also increased significantly from rest to atrial pacing with no significant differences in fractional extraction. The myocardium released lactate throughout the experiment, which increased significantly from rest and atrial pacing (P < 0.05). The heart accounted for a significantly greater percentage of whole body lactate disposal during atrial pacing (15.0 +/- 4.4%) compared to rest (4.9 +/- 0.9%, P = 0.03). These data suggest: (1) in the absence of ischaemia the myocardium is constantly taking up and releasing lactate at rest which increases during atrial pacing, and (2) when arterial substrate delivery is unchanged, increased myocardial work is accomplished with similar proportions of glucose and lactate utilization in healthy humans in vivo.

Endothelial heparanase secretion after acute hypoinsulinemia is regulated by glucose and fatty acid

Following diabetes, the heart increases its lipoprotein lipase (LPL) at the coronary lumen by transferring LPL from the cardiomyocyte to the endothelial lumen. We examined how hyperglycemia controls secretion of heparanase, the enzyme that cleaves myocyte heparan sulphate proteoglycan to initiate this movement. Diazoxide (DZ) was used to decrease serum insulin and generate hyperglycemia. A modified Langendorff technique was used to separate coronary from interstitial effluent, which were assayed for heparanase and LPL. Within 30 min of DZ, interstitial heparanase increased, an effect that closely mirrored an augmentation in interstitial LPL. Endothelial cells were incubated with palmitic acid (PA) or glucose, and heparanase secretion was determined. PA increased intracellular heparanase, with no effect on secretion of this enzyme. Unlike PA, glucose dose-dependently lowered endothelial intracellular heparanase, which was strongly associated with increased heparanase activity in the incubation medium. Preincubation with cytochalasin D or nocodazole prevented the high glucose-induced depletion of intracellular heparanase. Our data suggest that following hyperglycemia, translocation of LPL from the cardiomyocyte cell surface to the apical side of endothelial cells is dependent on the ability of the fatty acid to increase endothelial intracellular heparanase followed by rapid secretion of this enzyme by glucose, which requires an intact microtubule and actin cytoskeleton.

Myocardial FFA metabolism during rest and atrial pacing in humans

There is limited in vivo data in humans evaluating myocardial fat utilization during increased heart work. This study was done to determine myocardial free fatty acid (FFA) metabolism during rest and atrial pacing, which increases cardiac work without changing arterial substrate concentration. We studied seven healthy men and women (age = 49.7 +/- 3.9 yr, BMI = 23.4 +/- 1.1 kg/m(2), Vo(2max) = 35.5 +/- 3.0 ml.kg(-1).min(-1), ejection fraction = 68 +/- 3%). After 3 days of dietary control, coronary sinus, femoral arterial and venous, and peripheral venous catheters were placed. Subjects received [(13)C]bicarbonate followed by a continuous infusion of [1-(13)C]palmitate through the end of the study. Arterial and coronary sinus blood sampling and measurements of resting coronary sinus blood flow were made during rest and atrial pacing to 120 beats/min. MVo(2) increased (P < 0.05) from rest to atrial pacing. Coronary sinus FFA concentration was significantly lower than arterial through rest and atrial pacing (P = 0.007). Isotopically measured myocardial palmitate uptake increased significantly from rest to atrial pacing (P = 0.03). Approximately one-third of palmitate delivery was extracted by the myocardium during rest and atrial pacing. Myocardial V(13)CO(2) production and palmitate oxidation increased significantly from rest (P < 0.01) to atrial pacing. Net glycerol balance was significantly greater than zero during rest (P = 0.04) but not different from zero during atrial pacing (P = 0.13). These data suggest that myocardial lipid uptake and oxidation increase with greater heart work during atrial pacing, with a similar relative proportion of fat oxidation to total myocardial energy expenditure.

Time course of alterations in myocardial glucose utilization in the Zucker diabetic fatty rat with correlation to gene expression of glucose transporters: a small-animal PET investigation

Diabetic cardiomyopathy is associated with abnormalities in glucose metabolism. We evaluated myocardial glucose metabolism in a rodent model of type 2 diabetes, namely the Zucker diabetic fatty (ZDF) rat, and validated PET measurements of glucose uptake against gene and protein expression of glucose transporters (GLUTs).

METHODS

Six lean and ZDF rats underwent small-animal PET at the age of 14 wk and at the age of 19 wk. The imaging protocol consisted of a 60-min dynamic acquisition with 18F-FDG (18.5-29.6 MBq). Dynamic images were reconstructed using filtered backprojection with a 2.5 zoom on the heart and 40 frames per imaging session. PET measurements of myocardial glucose uptake (MGUp) rate and utilization were determined with an input function derived by the hybrid image-blood-sampling algorithm on recovery-corrected anterolateral myocardial regions of interest. After the PET session at week 19 (W19), hearts were extracted for gene and protein expression analysis of GLUT-1 and GLUT-4. The dependence of MGUp on gene expression of GLUT-1 and GLUT-4 was characterized by multiple-regression analysis.

RESULTS

MGUp in ZDF rats at both week 14 (W14) and W19 (P < 0.006) was significantly lower than MGUp in lean littermate control rats. Moreover, lean rats at W19 displayed significantly higher MGUp than they did at W14 (P = 0.007). Consistent with a diminished MGUp result, gene expression of GLUT-4 was significantly (P = 0.004) lower in ZDF rats. Finally, MGUp significantly (P = 0.0003) correlated with gene expression of GLUT-4.

CONCLUSION

Using small-animal PET, we confirmed alterations in myocardial glucose utilization and validated PET measurement of MGUp against gene and protein expression of GLUTs in the diabetic heart of an animal model of type 2 diabetes.

Fatty acids and insulin modulate myocardial substrate metabolism in humans with type 1 diabetes

OBJECTIVE

Normal human myocardium switches substrate metabolism preference, adapting to the prevailing plasma substrate levels and hormonal milieu, but in type 1 diabetes, the myocardium relies heavily on fatty acid metabolism for energy. Whether conditions that affect myocardial glucose use and fatty acid utilization, oxidation, and storage in nondiabetic subjects alter them in type 1 diabetes is not well known.

RESEARCH DESIGN AND METHODS

To test the hypotheses that in humans with type 1 diabetes, myocardial glucose and fatty acid metabolism can be manipulated by altering plasma free fatty acid (FFA) and insulin levels, we quantified myocardial oxygen consumption (MVo(2)), glucose, and fatty acid metabolism in nondiabetic subjects and three groups of type 1 diabetic subjects (those studied during euglycemia, hyperlipidemia, and a hyperinsulinemic-euglycemic clamp) using positron emission tomography.

RESULTS

Type 1 diabetic subjects had higher MVo(2) and lower myocardial glucose utilization rate/insulin than control subjects. In type 1 diabetes, glucose utilization increased with increasing plasma insulin and decreasing FFA levels. Myocardial fatty acid utilization, oxidation, and esterification rates increased with increasing plasma FFA. Increasing plasma insulin levels decreased myocardial fatty acid esterification rates but increased the percentage of fatty acids going into esterification.

CONCLUSIONS

Type 1 diabetes myocardium has increased MVo(2) and is insulin resistant during euglycemia. However, its myocardial glucose and fatty acid metabolism still responds to changes in plasma insulin and plasma FFA levels. Moreover, insulin and plasma FFA levels can regulate the intramyocardial fate of fatty acids in humans with type 1 diabetes.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Regulation of myocardial substrate metabolism during increased energy expenditure: insights from computational studies

In response to exercise, the heart increases its metabolic rate severalfold while maintaining energy species (e.g., ATP, ADP, and Pi) concentrations constant; however, the mechanisms that regulate this response are unclear. Limited experimental studies show that the classic regulatory species NADH and NAD+ are also maintained nearly constant with increased cardiac power generation, but current measurements lump the cytosol and mitochondria and do not provide dynamic information during the early phase of the transition from low to high work states. In the present study, we modified our previously published computational model of cardiac metabolism by incorporating parallel activation of ATP hydrolysis, glycolysis, mitochondrial dehydrogenases, the electron transport chain, and oxidative phosphorylation, and simulated the metabolic responses of the heart to an abrupt increase in energy expenditure. Model simulations showed that myocardial oxygen consumption, pyruvate oxidation, fatty acids oxidation, and ATP generation were all increased with increased energy expenditure, whereas ATP and ADP remained constant. Both cytosolic and mitochondrial NADH/NAD+ increased during the first minutes (by 40% and 20%, respectively) and returned to the resting values by 10-15 min. Furthermore, model simulations showed that an altered substrate selection, induced by either elevated arterial lactate or diabetic conditions, affected cytosolic NADH/NAD+ but had minimal effects on the mitochondrial NADH/NAD+, myocardial oxygen consumption, or ATP production. In conclusion, these results support the concept of parallel activation of metabolic processes generating reducing equivalents during an abrupt increase in cardiac energy expenditure and suggest there is a transient increase in the mitochondrial NADH/NAD+ ratio that is independent of substrate supply.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Imaging of myocardial metabolism

There is compelling evidence that alterations in myocardial substrate use play a key role in a variety of normal and abnormal cardiac conditions such as aging, left ventricular hypertrophy, and diabetic heart disease. However, it is unclear whether the metabolic changes are adaptive or maladaptive. Development of transgenic models targeting key aspects of myocardial substrate use, such as uptake, oxidation, and storage, is accelerating our understanding of the metabolic perturbations of cardiac disease. However, whether the metabolic phenotype in these models is relevant to the human condition is frequently unknown. The importance of altered myocardial metabolism in the pathogenesis of cardiac disease is underscored by the current robust development of novel therapeutics that target myocardial substrate use. Currently, magnetic resonance spectroscopy, single photon emission computed tomography, and positron emission tomography are the 3 methods available to image myocardial substrate metabolism. In this review the role of metabolic imaging in the study of specific cardiac disease processes will be discussed. Both the current and future capabilities of metabolic imaging to furthering our understanding of cardiac disease are highlighted.

beta-Hydroxybutyrate inhibits myocardial fatty acid oxidation in vivo independent of changes in malonyl-CoA content

This study tested the hypothesis that an acute infusion of beta-hydroxybutyrate inhibits myocardial fatty acid uptake and oxidation in vivo. Anesthetized pigs were untreated (n = 6) or treated with an intravenous infusion of fat emulsion (n = 7) to elevate plasma free fatty acid levels. A third group received fat emulsion plus an intravenous infusion of beta-hydroxybutyrate (25 micromol.kg-1.min-1; n = 7) for 60 min. All animals received a continuous infusion of [3H]palmitate, and myocardial fatty acid oxidation was measured from the cardiac production of 3H2O. Plasma free fatty acid concentrations were elevated in the fat emulsion group (0.77 +/- 0.11 mM) compared with the untreated group (0.15 +/- 0.03 mM), which resulted in greater myocardial free fatty acid oxidation. In contrast, the group receiving beta-hydroxybutyrate in addition to fat emulsion had elevated beta-hydroxybutyrate concentration (0.87 +/- 0.11 vs. 0.04 +/- 0.01 mM), but suppressed fatty acid oxidation (0.053 +/- 0.013 micromol.g-1.min-1) (P < 0.05) compared with the fat emulsion group (0.116 +/- 0.029 micromol.g-1.min-1). There were no differences among the three groups in the tissue content for malonyl-CoA, acetyl-CoA, or free CoA or the activity of acetyl-CoA carboxylase; thus the inhibition of fatty acid oxidation by elevated beta-hydroxybutyrate did not appear to be due to malonyl-CoA inhibition of carnitine palmitoyl transferase-I or to an increase in the acetyl-CoA-to-free CoA ratio. In conclusion, fatty acid uptake and oxidation is blocked by an infusion of beta-hydroxybutyrate; this effect was not due to elevated myocardial malonyl-CoA content.

Shift in metabolic substrate uptake by the heart during development of alloxan-induced diabetes

Inhibition of endothelial nitric oxide (NO) synthase (eNOS) is associated with an increase in glucose uptake by the heart. We have already shown that Type I diabetes also causes a decrease in eNOS protein expression and altered NO control of both coronary vascular resistance and oxygen consumption. Therefore, we predict that the increase in plasma glucose and the reduction in eNOS during diabetes together would result in a large increase in cardiac glucose uptake. Arterial (A) and coronary sinus (C) plasma levels of glucose, free fatty acid (FFA), beta-hydroxybutyric acid (beta-HBA), and lactate were measured, and myocardial uptake was calculated before and at week 1, 2, 3, and 4 of alloxan-induced diabetes. The heart of healthy dogs consumed FFA (19.2 +/- 2.6 microeq/min) and lactate (19.7 +/- 3.4 micromol/min). Dogs in the late stage of diabetes (at week 4) had elevated arterial beta-HBA concentrations (1.6 +/- 0.7 micromol/l) that were accompanied by an increased beta-HBA uptake (0.3 +/- 0.2 micromol/min). In contrast, myocardial lactate (-4.8 +/- 3.0 micromol/min) and FFA uptake (2.5 +/- 1.9 microeq/min) were significantly reduced in diabetic animals. Despite a marked hyperglycemia (449 +/- 25 mg/dl), the heart did not take up glucose (-7.9 +/- 4.1 mg/dl). Our results indicate significant changes in the myocardial substrate utilization in dogs only in the late stage of diabetes, at a time when myocardial NO production is already decreased.

Effects of treatment with sulfonylurea drugs or insulin on ischemia-induced myocardial dysfunction in type 2 diabetes

In patients with diabetes and coronary artery disease, the potential negative role of sulfonylurea drugs is under intensive investigation. We assessed the effects of treatment with glibenclamide or insulin on the extension of left ventricular myocardial dysfunction induced by acute ischemia. Nineteen consecutive patients with type 2 diabetes and coronary artery disease entered the study. Each patient was randomly assigned to either insulin or glibenclamide therapy. Treatment was crossed over after 12 weeks and maintained for another 12 weeks. At the end of each treatment, left ventricular myocardial function at rest and during dipyridamole infusion was studied by two-dimensional echocardiography under the same conditions of metabolic control. Glibenclamide or insulin treatment did not influence the rest values of left ventricular dimensions, left ventricular ejection fraction (LVEF), or wall motion score index (WMSI). Dipyridamole infusion, in patients receiving glibenclamide treatment, decreased LVEF (43 +/- 7 vs. 37 +/- 12%, P < 0.005) and increased WMSI (1.4 +/- 0.28 vs. 1.98 +/- 0.24, P < 0.001) compared with baseline values; during insulin treatment, LVEF (46 +/- 8 vs. 45 +/- 11%, NS) and WMSI (1.4 +/- 0.29 vs. 1.6 +/- 0.4, NS) did not change significantly. Peak stress LVEF was higher (45 +/- 11 vs. 37 +/- 12%, P < 0.001) and WMSI lower (1.6 +/- 0.4 vs. 1.98 +/- 0.24, P < 0.001) in patients receiving insulin. The results indicate that in patients with type 2 diabetes and coronary artery disease, ischemic myocardial dysfunction induced by dipyridamole infusion is less severe during treatment with insulin than with glibenclamide. Restitution of a preconditioning mechanism in insulin-treated patients may be the potential beneficial mechanism.

A novel mouse model of lipotoxic cardiomyopathy

Inherited and acquired cardiomyopathies are associated with marked intracellular lipid accumulation in the heart. To test the hypothesis that mismatch between myocardial fatty acid uptake and utilization leads to the accumulation of cardiotoxic lipid species, and to establish a mouse model of metabolic cardiomyopathy, we generated transgenic mouse lines that overexpress long-chain acyl-CoA synthetase in the heart (MHC-ACS). This protein plays an important role in vectorial fatty acid transport across the plasma membrane. MHC-ACS mice demonstrate cardiac-restricted expression of the transgene and marked cardiac myocyte triglyceride accumulation. Lipid accumulation is associated with initial cardiac hypertrophy, followed by the development of left-ventricular dysfunction and premature death. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and cytochrome c release in transgenic hearts suggest that cardiac myocyte death occurs, in part, by lipid-induced programmed cell death. Taken together, our data demonstrate that fatty acid uptake/utilization mismatch in the heart leads to accumulation of lipid species toxic to cardiac myocytes. This novel mouse model will provide insight into the role of perturbations in myocardial lipid metabolism in the pathogenesis of inherited and acquired forms of heart failure.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Propionyl-L-carnitine effects on postischemic recovery of heart function and substrate oxidation in the diabetic rat

Previous studies have shown that propionyl-L-carnitine (PLC) can exert cardiac antiischemic effects in models of diabetes. In the nonischemic diabetic rat heart, PLC improves ventricular function secondary to stimulation in the oxidation of glucose and palmitate. Whether this increase in the oxidation of these substrates can explain the beneficial effects of PLC in the ischemic reperfused diabetic rat heart has yet to be determined. Diabetes was induced in male Sprague-Dawley rats by an intravenous injection of streptozotocin (60 mg/kg). Treatment was initiated by supplementing the drinking water with propionyl-L-carnitine at the concentration of 1 g/L. After a 6-week treatment period, exogenous substrate oxidation and recovery of mechanical function following ischemia were determined in isolated working hearts. In aerobically perfused diabetic hearts, compared with those of controls, rates of glucose oxidation were lower, but those of palmitate oxidation were similar. Diabetes was also characterized by a pronounced decrease in heart function. Following treatment with by propionyl-L-carnitine, however, there was a marked increase in rates at which glucose and palmitate were oxidized by diabetic hearts and a significant improvement in heart performance. Postischemic recovery of function in diabetic hearts was also improved with PLC. This improvement in contractile function was accompanied by an increase in both glucose and palmitate oxidation. Our findings show that postischemic diabetic rat heart function can be improved following chronic PLC treatment. This beneficial effect of propionyl-L-carnitine can be explained, in part, by an improvement in the oxidation of glucose and palmitate.

Intracellular lactate- and pyruvate-interconversion rates are increased in muscle tissue of non-insulin-dependent diabetic individuals

The contribution of muscle tissues of non-insulin-dependent diabetes mellitus (NIDDM) patients to blood lactate appearance remains undefined. To gain insight on intracellular pyruvate/lactate metabolism, the postabsorptive forearm metabolism of glucose, lactate, FFA, and ketone bodies (KB) was assessed in seven obese non-insulin-dependent diabetic patients (BMI = 28.0 +/- 0.5 kg/m2) and seven control individuals (BMI = 24.8 +/- 0.5 kg/m2) by using arteriovenous balance across forearm tissues along with continuous infusion of [3-13C1]-lactate and indirect calorimetry. Fasting plasma concentrations of glucose (10.0 +/- 0.3 vs. 4.7 +/- 0.2 mmol/liter), insulin (68 +/- 5 vs. 43 +/- 6 pmol/liter), FFA (0.57 +/- 0.02 vs. 0.51 +/- 0.02 mmol/liter), and blood levels of lactate (1.05 +/- 0.04 vs. 0.60 +/- 0.06 mmol/liter), and KB (0.48 +/- 0.04 vs. 0.29 +/- 0.02 mmol/liter) were higher in NIDDM patients (P < 0.01). Forearm glucose uptake was similar in the two groups (10.3 +/- 1.4 vs. 9.6 +/ 1.1 micromol/min/liter of forearm tissue), while KB uptake was twice as much in NIDDM patients as compared to control subjects. Lactate balance was only slightly increased in NIDDM patients (5.6 +/- 1.4 vs. 3.3 +/- 1.0 micromol/min/liter; P = NS). A two-compartment model of lactate and pyruvate kinetics in the forearm tissue was used to dissect out the rates of lactate to pyruvate and pyruvate to lactate interconversions. In spite of minor differences in the lactate balance, a fourfold increase in both lactate- (44.8 +/- 9.0 vs. 12.6 +/- 4.6 micromol/min/liter) and pyruvate-(50.4 +/- 9.8 vs. 16.0 +/- 5.0 micromol/min/liter) interconversion rates (both P < 0.01) were found. Whole body lactate turnover, assessed by using the classic isotope dilution principle, was higher in NIDDM individuals (46 +/- 9 vs. 21 +/- 3 micromol/min/kg; P < 0.01). Insights into the physiological meaning of this parameter were obtained by using a whole body noncompartmental model of lactate/pyruvate kinetics which provides a lower and upper bound for total lactate and pyruvate turnover (NIDDM = 46 +/- 9 vs. 108 +/- 31; controls = 21 +/- 3 - 50 +/-13 micromol/min/kg). In conclusion, in the postabsorptive state, despite a trivial lactate release by muscle, lactate- and pyruvate-interconversion rates are greatly enhanced in NIDDM patients, possibly due to concomitant impairment in the oxidative pathway of glucose metabolism. This finding strongly suggest a major disturbance in intracellular lactate/pyruvate metabolism in NIDDM.