Glucose production, gluconeogenesis, and insulin sensitivity in children and adolescents: an evaluation of their reproducibility

Hypoglycemia in Patients With LAMA2-CMD

BACKGROUND

Hypoglycemia has been reported in patients with LAMA2-CMD, but the frequency, risk factors, and correlation to genotype/phenotype have not been systematically assessed to date.

METHODS

A retrospective cohort study was performed on 48 patients with LAMA2-CMD. Patients were divided into two groups: a hypoglycemic group, with at least one episode of hypoglycemia, and a nonhypoglycemic group. The groups were compared according to gait function, epilepsy, intellectual disability, constipation, gastroesophageal reflux, gastrostomy, weight percentile, scoliosis, the use of a ventilator device, the use of a feeding device, neuromuscular disease swallowing status scale, and type of mutation.

RESULTS

Fifteen patients (31.2%) presented with at least one episode of symptomatic hypoglycemia and eight (16.6% of the cohort) had two or more episodes. All patients who had hypoglycemia were in the nonambulant group. We observed a correlation between gait, the use of ventilator and feeding devices, and swallow function with hypoglycemia. Patients with extremely low weight were five times more likely to have recurrent episodes of hypoglycemia. The presence of at least one missense variant appears to be associated with a lower risk of hypoglycemia.

CONCLUSION

Patients with LAMA2-CMD are at risk of hypoglycemia. The risk is more relevant in patients with severe phenotype and patients with loss-of-function variants. For patients with extremely low weight, the risk is higher. Blood glucose should be actively measured in patients who are fasting or have infections, and health care providers should be prepared to identify and treat these patients.

Mifepristone Improves Adipose Tissue Insulin Sensitivity in Insulin Resistant Individuals

BACKGROUND

Increased tissue cortisol availability has been implicated in abnormal glucose and fat metabolism in patients with obesity, metabolic syndrome, and type 2 diabetes (T2DM). Our objective was to evaluate whether blockade of glucocorticoid receptor (GR) with mifepristone ameliorates insulin resistance (IR) in overweight/obese subjects with glucose intolerance.

METHODS

We conducted a randomized, double-blinded, placebo-controlled, crossover study in overweight/obese individuals (n = 16, 44% female) with prediabetes or mild T2DM but not clinical hypercortisolism. Mifepristone (50 mg every 6 h) or placebo was administered for 9 days, followed by crossover to the other treatment arm after a washout period of 6 to 8weeks. At baseline and following each treatment, oral glucose tolerance test (OGTT) and frequently sampled intravenous glucose tolerance test (FSIVGTT) were performed. Insulin sensitivity was measured using FSIVGTT [primary outcome: insulin sensitivity index (SI)] and OGTT [Matsuda index (MI) and oral glucose insulin sensitivity index (OGIS)]. Hepatic and adipose insulin resistance were assessed using hepatic insulin resistance index (HIRI), and adipose tissue insulin sensitivity index (Adipo-SI) and adipo-IR, derived from the FSIVGTT.

RESULTS

Mifepristone administration did not alter whole-body glucose disposal indices of insulin sensitivity (SI, MI, and OGIS). GR blockade significantly improved Adipo-SI (61.7 ± 32.9 vs 42.8 ± 23.9; P = 0.002) and reduced adipo-IR (49.9 ± 45.9 vs 65.5 ± 43.8; P = 0.004), and HIRI (50.2 ± 38.7 vs 70.0 ± 44.3; P = 0.08). Mifepristone increased insulin clearance but did not affect insulin secretion or β-cell glucose sensitivity.

CONCLUSION

Short-term mifepristone administration improves adipose and hepatic insulin sensitivity among obese individuals with hyperglycemia without hypercortisolism.

Metformin improves blood glucose by increasing incretins independent of changes in gluconeogenesis in youth with type 2 diabetes

AIMS/HYPOTHESIS

Metformin is the only approved oral agent for youth with type 2 diabetes but its mechanism of action remains controversial. Recent data in adults suggest a primary role for the enteroinsular pathway, but there are no data in youth, in whom metformin efficacy is only ~50%. Our objectives were to compare incretin concentrations and rates of glucose production and gluconeogenesis in youth with type 2 diabetes before and after short-term metformin therapy compared with peers with normal glucose tolerance (NGT).

METHODS

This is a case-control observational study in youth with type 2 diabetes who were not on metformin (n = 18) compared with youth with NGT (n = 10) who were evaluated with a 2 day protocol. A 75 g OGTT was administered to measure intact glucagon-like 1 peptide (iGLP-1), gastric inhibitory polypeptide (GIP) and peptide YY (PYY). Insulinogenic index (IGI) and whole-body insulin sensitivity were calculated using glucose and insulin levels from the OGTT. Basal rates of gluconeogenesis (²H₂O), glucose production ([6,6-²H₂]glucose) and whole-body lipolysis ([²H₅]glycerol) were measured after an overnight fast on study day 2. Youth with type 2 diabetes (n = 9) were subsequently evaluated with an identical 2 day protocol after 3 months on the metformin study.

RESULTS

Compared with individuals with NGT, those with type 2 diabetes had higher fasting (7.8 ± 2.5 vs 5.1 ± 0.3 mmol/l, mean ± SD p = 0.002) and 2 h glucose concentrations (13.8 ± 4.5 vs 5.9 ± 0.9 mmol/l, p = 0.001), higher rates of absolute gluconeogenesis (10.0 ± 1.7 vs 7.2 ± 1.1 μmol [kg fat-free mass (FFM)]^-1 min^-1, p < 0.001) and whole-body lipolysis (5.2 ± 0.9 vs 4.0 ± 1.4 μmol kg_FFM^-1 min^-1, p < 0.01), but lower fasting iGLP-1 concentrations (0.5 ± 0.5 vs 1.3 ± 0.7 pmol/l, p < 0.01). Metformin decreased 2 h glucose (pre metformin 11.4 ± 2.8 vs post metformin 9.9 ± 1.9 mmol/l, p = 0.04) and was associated with ~20-50% increase in IGI (median [25th-75th percentile] pre 1.39 [0.89-1.47] vs post 1.43 [0.88-2.70], p = 0.04), fasting iGLP-1 (pre 0.3 ± 0.2 vs post 1.0 ± 0.7 pmol/l, p = 0.02), 2 h iGLP (pre 0.4 ± 0.2 vs post 1.2 ± 0.9 pmol/l, p = 0.06), fasting PYY (pre 6.3 ± 2.2 vs post 10.5 ± 4.3 pmol/l, p < 0.01) and 2 h PYY (pre 6.6 ± 2.9 vs post 9.0 ± 4.0 pmol/l, p < 0.01). There was no change in BMI, insulin sensitivity or GIP concentrations pre vs post metformin. There were no differences pre vs post metformin in rates of glucose production (15.0 ± 3.9 vs 14.9 ± 2.2 μmol kg_FFM^-1 min^-1, p = 0.84), absolute gluconeogenesis (9.9 ± 1.8 vs 9.7 ± 1.7 μmol kg_FFM^-1 min^-1, p = 0.76) or whole-body lipolysis (5.0 ± 0.7 vs 5.3 ± 1.3 μmol kg_FFM^-1 min^-1, p = 0.20). Post metformin iGLP-1 and PYY concentrations in youth with type 2 diabetes were comparable to levels in youth with NGT.

CONCLUSIONS/INTERPRETATION

Overall, the improved postprandial blood glucose levels and increase in incretins observed in the absence of changes in insulin sensitivity and gluconeogenesis, support an enteroinsular mechanistic pathway in youth with type 2 diabetes treated with short-term metformin.

Hypoglycemia in patients with congenital muscle disease

BACKGROUND

Only a few small studies have previously reported episodes of hypoglycemia in children with neuromuscular diseases; however, there has been no broader investigation into the occurrence of hypoglycemia in children with congenital muscle disease (CMD).

METHODS

Pediatric patients enrolled in the CMD International Registry (CMDIR) with a history of hypoglycemia were included in this retrospective review. Hypoglycemic episodes and associated clinical and biochemical characteristics were characterized.

RESULTS

Ten patients with CMD (5 with LAMA2-related muscular dystrophy) reported at least one episode of hypoglycemia beginning at an average age of 3.5 years. Predominant symptoms included altered mental status and nausea/vomiting, and laboratory studies demonstrated metabolic acidosis and ketonuria, consistent with ketotic hypoglycemia.

CONCLUSION

Patients with CMD may have an increased risk of hypoglycemia during fasting, illness, or stress due to their relatively low muscle mass and hence, paucity of gluconeogenic substrate. Clinicians should therefore maintain a high index of suspicion for hypoglycemia in this high-risk patient population and caregivers should routinely be trained to recognize and treat hypoglycemia.

Gluconeogenesis and risk for fasting hyperglycemia in Black and White women

Black women, compared with White women, have high rates of whole-body insulin resistance but a lower prevalence of fasting hyperglycemia and hepatic steatosis. This dissociation of whole-body insulin resistance from fasting hyperglycemia may be explained by racial differences in gluconeogenesis, hepatic fat, or tissue-specific insulin sensitivity. Two groups of premenopausal federally employed women, without diabetes were studied. Using stable isotope tracers, [2H2O] and [6,62-H2]glucose, basal glucose production was partitioned into its components (gluconeogenesis and glycogenolysis) and basal whole-body lipolysis ([2H5]glycerol) was measured. Indices of insulin sensitivity, whole-body (SI), hepatic (HISIGPR), and adipose tissue, were calculated. Hepatic fat was measured by proton magnetic resonance spectroscopy. Black women had less hepatic fat and lower fractional and absolute gluconeogenesis. Whole-body SI, HISIGPR, and adipose tissue sensitivity were similar by race, but at any given level of whole-body SI, Black women had higher HISIGPR. Therefore, fasting hyperglycemia may be a less common early pathological feature of prediabetes in Black women compared with White women, because gluconeogenesis remains lower despite similar whole-body SI.

Comprehensive assessment of insulin resistance in non-obese Asian Indian and Chinese men

Aims/Introduction

Indian individuals are more insulin resistant (IR) than Chinese individuals, even among those with a non‐obese body mass index (BMI). However, BMI often underestimates body fat in Indian individuals, and it remains unclear whether Indians would remain more IR than Chinese individuals when both BMI and body fat are equally matched.

Materials and Methods

Using the hyperinsulinemic‐euglycemic clamp with stable‐isotope infusion, we comprehensively assessed IR between 13 non‐obese Indian men with 13 Chinese men matched for age, BMI and body fat. We further compared the differences in insulin metabolic clearance rate (MCR) between the two groups and its relationship with various metabolic parameters. The response of lipid and amino acid metabolism to insulin stimulation was also evaluated using metabolomic profiling.

Results

The rates of endogenous glucose production during fasting were similar, and endogenous glucose production was completely suppressed during insulin clamp for both ethnic groups. Glucose disappearance during insulin clamp was also similar between the two groups, even after accounting for differences in insulin concentration. Metabolomic profiles of amino acids and various acylcarnitines were similar during both fasting and insulin clamp. However, plasma insulin during clamp was significantly higher in Indian men, indicating that insulin MCR was lower. Insulin MCR correlated significantly with total adiposity and skeletal muscle insulin sensitivity.

Conclusion

When equally matched for body fat, non‐obese Indian men had similar skeletal muscle insulin sensitivity and endogenous glucose production to Chinese men. The effects of insulin on lipid and amino acid metabolism were also similar. Low insulin MCR is associated with greater adiposity and lower skeletal muscle insulin sensitivity.

Triglyceride glucose index as a surrogate measure of insulin sensitivity in obese adolescents with normoglycemia, prediabetes, and type 2 diabetes mellitus: comparison with the hyperinsulinemic-euglycemic clamp

BACKGROUND

There is a need for simple surrogate estimates of insulin sensitivity in epidemiological studies of obese youth because the hyperinsulinemic-euglycemic clamp is not feasible on a large scale.

OBJECTIVE

(i) To examine the triglyceride glucose (TyG) index (Ln[fasting triglycerides (mg/dL) × fasting glucose (mg/dL)/2]) and its relationship to in vivo insulin sensitivity in obese adolescents (OB) along the spectrum of glucose tolerance and (ii) to compare TyG index with triglyceride/high-density lipoprotein TG/HDL and 1/fasting insulin (1/IF ), other surrogates of insulin sensitivity.

PATIENTS AND DESIGN

Cross-sectional data in 225 OB with normal glucose tolerance (NGT), prediabetes (preDM), and type 2 diabetes (T2DM) who had a 3-h hyperinsulinemic-euglycemic clamp and fasting lipid measurement.

RESULTS

Insulin-stimulated glucose disposal (Rd) declined significantly across the glycemic groups from OB-NGT to OB-preDM to OB-T2DM with a corresponding increase in TyG index (8.3 ± 0.5, 8.6 ± 0.5, 8.9 ± 0.6, p < 0.0001). The correlation of TyG index to Rd was -0.419 (p < 0.0001). The optimal TyG index for diagnosis of insulin resistance was 8.52 [receiver operating characteristic-area under the ROC curves (ROC-AUC) 0.750, p < 0.0001]. The ROC-AUC for 1/IF was 0.836. In multiple regression analysis, 64.8% of the variance in Rd was explained by TyG index, 1/IF , body mass index (BMI) z-score, glycemic group, and sex.

CONCLUSION

The TyG index affords an easily and widely available simple laboratory method as a surrogate estimate of insulin sensitivity that could be used repeatedly in large-scale observational and/or interventional cohorts of OB. Although not superior to 1/IF , TyG index offers the advantage of having a standardized method of measuring triglyceride and glucose, which is not the case for insulin assays.

What is a normal blood glucose?

Glucose is the key metabolic substrate for tissue energy production. In the perinatal period the mother supplies glucose to the fetus and for most of the gestational period the normal lower limit of fetal glucose concentration is around 3 mmol/L. Just after birth, for the first few hours of life in a normal term neonate appropriate for gestational age, blood glucose levels can range between 1.4 mmol/L and 6.2 mmol/L but by about 72 h of age fasting blood glucose levels reach normal infant, child and adult values (3.5-5.5 mmol/L). Normal blood glucose levels are maintained within this narrow range by factors which control glucose production and glucose utilisation. The key hormones which regulate glucose homoeostasis include insulin, glucagon, epinephrine, norepinephrine, cortisol and growth hormone. Pathological states that affect either glucose production or utilisation will lead to hypoglycaemia. Although hypoglycaemia is a common biochemical finding in children (especially in the newborn) it is not possible to define by a single (or a range of) blood glucose value/s. It can be defined as the concentration of glucose in the blood or plasma at which the individual demonstrates a unique response to the abnormal milieu caused by the inadequate delivery of glucose to a target organ (eg, the brain). Hypoglycaemia should therefore be considered as a continuum and the blood glucose level should be interpreted within the clinical scenario and with respect to the counter-regulatory hormonal responses and intermediate metabolites.

Measurements of Gluconeogenesis and Glycogenolysis: A Methodological Review

Gluconeogenesis is a complex metabolic process that involves multiple enzymatic steps regulated by myriad factors, including substrate concentrations, the redox state, activation and inhibition of specific enzyme steps, and hormonal modulation. At present, the most widely accepted technique to determine gluconeogenesis is by measuring the incorporation of deuterium from the body water pool into newly formed glucose. However, several techniques using radioactive and stable-labeled isotopes have been used to quantitate the contribution and regulation of gluconeogenesis in humans. Each method has its advantages, methodological assumptions, and set of propagated errors. In this review, we examine the strengths and weaknesses of the most commonly used stable isotopes methods to measure gluconeogenesis in vivo. We discuss the advantages and limitations of each method and summarize the applicability of these measurements in understanding normal and pathophysiological conditions.

Increased and early lipolysis in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency during fast

Children with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD) have a defect in the degradation of long-chain fatty acids and are at risk of hypoketotic hypoglycemia and insufficient energy production as well as accumulation of toxic fatty acid intermediates. Knowledge on substrate metabolism in children with LCHAD deficiency during fasting is limited. Treatment guidelines differ between centers, both as far as length of fasting periods and need for night feeds are concerned. To increase the understanding of fasting intolerance and improve treatment recommendations, children with LCHAD deficiency were investigated with stable isotope technique, microdialysis, and indirect calometry, in order to assess lipolysis and glucose production during 6 h of fasting. We found an early and increased lipolysis and accumulation of long chain acylcarnitines after 4 h of fasting, albeit no patients developed hypoglycemia. The rate of glycerol production, reflecting lipolysis, averaged 7.7 ± 1.6 µmol/kg/min, which is higher compared to that of peers. The rate of glucose production was normal for age; 19.6 ± 3.4 µmol/kg/min (3.5 ± 0.6 mg/kg/min). Resting energy expenditure was also normal, even though the respiratory quotient was increased indicating mainly glucose oxidation. The results show that lipolysis and accumulation of long chain acylcarnitines occurs before hypoglycemia in fasting children with LCHAD, which may indicate more limited fasting tolerance than previously suggested.

Increased gluconeogenesis in youth with newly diagnosed type 2 diabetes

AIMS/HYPOTHESIS

The role of increased gluconeogenesis as an important contributor to fasting hyperglycaemia at diabetes onset is not known. We evaluated the contribution of gluconeogenesis and glycogenolysis to fasting hyperglycaemia in newly diagnosed youths with type 2 diabetes following an overnight fast.

METHODS

Basal rates (μmol kg(FFM) (-1) min(-1)) of gluconeogenesis ((2)H2O), glycogenolysis and glycerol production ([(2)H5] glycerol) were measured in 18 adolescents (nine treatment naive diabetic and nine normal-glucose-tolerant obese adolescents).

RESULTS

Type 2 diabetes was associated with higher gluconeogenesis (9.2 ± 0.6 vs 7.0 ± 0.3 μmol kg(FFM) (-1) min(-1), p < 0.01), plasma fasting glucose (7.0 ± 0.6 vs 5.0 ± 0.2 mmol/l, p = 0.004) and insulin (300 ± 30 vs 126 ± 31 pmol/l, p = 0.001). Glucose production and glycogenolysis were similar between the groups (15.4 ± 0.3 vs 12.4 ± 1.4 μmol kg(FFM) (-1) min(-1), p = 0.06; and 6.2 ± 0.8 vs 5.3 ± 0.7 μmol kg(FFM) (-1) min(-1), p = 0.5, respectively). After controlling for differences in adiposity, gluconeogenesis, glycogenolysis and glucose production were higher in diabetic youth (p ≤ 0.02). Glycerol concentration (84 ± 6 vs 57 ± 6 μmol/l, p = 0.01) and glycerol production (5.0 ± 0.3 vs 3.6 ± 0.5 μmol kg(FFM) (-1) min(-1), p = 0.03) were 40% higher in youth with diabetes. The increased glycerol production could account for only ~1/3 of substrate needed for the increased gluconeogenesis in diabetic youth.

CONCLUSION/INTERPRETATIONS

Increased gluconeogenesis was a major contributor to fasting hyperglycaemia and hepatic insulin resistance in newly diagnosed untreated adolescents and was an early pathological feature of type 2 diabetes. Increased glycerol availability may represent a significant source of new carbon substrates for increased gluconeogenesis but would not account for all the carbons required to sustain the increased rates.

Endogenous glucose production from infancy to adulthood: a non-linear regression model

OBJECTIVE

To construct a regression model for endogenous glucose production (EGP) as a function of age, and compare this with glucose supplementation using commonly used dextrose-based saline solutions at fluid maintenance rate in children.

DESIGN

A model was constructed based on EGP data, as quantified by [6,6-(2)H2] glucose dilution after fasting overnight during normoglycaemia, in 40 healthy subjects aged 2.5-54.3 years old. The data were analysed using non-linear regression modelling with a 1-phase exponential decay curve fit. This model was compared to the amount of glucose provided with 2.5% or 5% dextrose-based saline solutions infused at fluid maintenance rate.

RESULTS

Non-linear regression analysis of the EGP data yielded the following regression model: EGP (mg/kg/min) = 6.50 × 2.72(-0.145 × age (y))+1.93. Glucose supplementation at fluid maintenance rate with a 5% dextrose-based saline solution ranged from 46% at age 1 year to 55% at age 18 years of the glucose required to preclude the need for EGP. With a 2.5% dextrose-based solution, these percentages are 23% at age 1 year to 27% at age 18 years.

CONCLUSIONS

we present an accurate non-linear regression model for EGP as a function of age. With standard dextrose-based saline solutions infused at fluid maintenance rate, only approximately 50% or less of EGP is provided. With prolonged infusion of these solutions, the deficit between exogenous glucose supplementation and EGP may induce a catabolic state and may ultimately lead to hypoglycaemia, especially in younger children.

Energy substrate metabolism in pyruvate dehydrogenase complex deficiency

Pyruvate dehydrogenase (PDH) deficiency is an inherited disorder of carbohydrate metabolism, resulting in lactic acidosis and neurological dysfunction. In order to provide energy for the brain, a ketogenic diet has been tried. Both the disorder and the ketogenic therapy may influence energy production. The aim of the study was to assess hepatic glucose production, lipolysis and resting energy expenditure (REE) in an infant, given a ketogenic diet due to neonatal onset of the disease. Lipolysis and glucose production were determined for two consecutive time periods by constant-rate infusions of [1,1,2,3,3-²H₅]-glycerol and [6,6-²H²]-glucose. The boy had been fasting for 2.5 h at the start of the sampling periods. REE was estimated by indirect calorimetry. Rates of glucose production and lipolysis were increased compared with those of term neonates. REE corresponded to 60% of normal values. Respiratory quotient (RQ) was increased, indicating a predominance of glucose oxidation. Blood lactate was within the normal range. Several mechanisms may underlie the increased rates of glucose production and lipolysis. A ketogenic diet will result in a low insulin secretion and reduced peripheral and hepatic insulin sensitivity, leading to increased production of glucose and decreased peripheral glucose uptake. Surprisingly, RQ was high, indicating active glucose oxidation, which may reflect a residual enzyme activity, sufficient during rest. Considering this, a strict ketogenic diet might not be the optimal choice for patients with PDH deficiency. We propose an individualised diet for this group of patients aiming at the highest glucose intake that each patient will tolerate without elevated lactate levels.

Effects of hyperglycemia on the developing brain in newborns

BACKGROUND

Hyperglycemia is a common problem in preterm neonates and is associated with increased risk of mortality and severe morbidities such as brain damage. However, available data about the effects of severity of hyperglycemia on the developing brain in the early life is limited. Therefore, we evaluated the effects of moderate and severe hyperglycemia on the developing brain.

METHOD

Thirty newborn Sprague-Dawley rats were randomly divided into three groups as control, moderate hyperglycemia (30% dextrose), and severe hyperglycemia (50% dextrose). Pups in the hyperglycemia groups were administered subcutaneous sterile dextrose solution at a dose of 4 mL/kg daily from the second day to the eleventh day of life. Blood glucose levels were measured every day in all study groups. Rat brain tissues were removed at the end of the study. Histopathologic and immunohistochemical (caspase-9, -8, and -3) examination and biochemical analysis including xanthine oxidase, total antioxidant status, total oxidant status, and malondialdehyde activities were performed.

RESULTS

Weight of the brain tissues in rats with hyperglycemia groups was significantly lower than the control group (P < 0.05). Weight of the brain tissues in rats with moderate hyperglycemia was lower than that of the severe hyperglycemia (P < 0.05). In the histopathologic and immunochemical evaluation, severity of brain damage and apoptosis were significantly higher in the severe hyperglycemia group, especially at the level of the hippocampus (P < 0.05). Tissue malondialdehyde, xanthine oxidase levels, and total oxidant status were significantly increased in the severe hyperglycemia group, whereas total antioxidant status was significantly decreased in the severe hyperglycemia group (P < 0.001).

CONCLUSION

Brain damaging effects of severe hyperglycemia were observed in the developing brains of the rat pups. It might be inferred that severe hyperglycemia can damage the developing brain especially in preterm infants.

Adaptation of glucose metabolism to fasting in young children with infectious diseases: a perspective

Hypoglycemia is a frequently encountered complication in young children with infectious diseases and may result in permanent neurological damage or even death. Mortality rate in young children under 5 years of age is increased four- to six-fold when severe infectious disease is complicated by hypoglycemia. Young age, prolonged fasting and severity of disease are considered important risk factors. This perspective describes the combined results of recently conducted studies on the effect of these risk factors on glucose metabolism in children with different infectious diseases. The results of these studies have nutritional implications for the approach in clinical practice towards young children with infectious diseases and specific recommendations are made. A unique finding is the existence of infectious disease-related differences in the adaptation of glucose metabolism during fasting in young children.

Water signal attenuation by D2O infusion as a novel contrast mechanism for 1H perfusion MRI

Deuterium oxide (D2 O), which is commercially available and nonradioactive, was proposed as a perfusion tracer before the clinical usage of conventional gadolinium-based MRI contrast agents. However, the sensitivity of direct deuterium detection is the major challenge for its application. In this study, we propose a contrast-enhanced strategy to indirectly trace administered D2 O by monitoring the signal attenuation of (1) H MRI. Experiments on D2 O concentration phantoms and in vivo rat brains were conducted to prove the concept of the proposed contrast mechanism. An average maximum signal drop ratio of 5.25 ± 0.91% was detected on (1) H MR images of rat brains with 2 mL of D2 O administered per 100 g of body weight. As a diffusible tracer for perfusion, D2 O infusion is a practicable method for the assessment of tissue perfusion and has the potential to provide different information from gadolinium-based contrast agents, which have limited permeability for blood vessels. Furthermore, the observed negative relaxivities of D2 O reveal the (1) H-D exchange effect. Therefore, applications of perfusion MRI with D2 O as a contrast agent are worthy of further investigation.

Fasting predisposes to hypoglycemia in Surinamese children with severe pneumonia, and young children are more at risk

The objective of this study was to investigate glucose kinetics during controlled fasting in children with severe pneumonia. Plasma glucose concentration, endogenous glucose production and gluconeogenesis were measured in 12 Surinamese children (six young: 1-3 years, six older: 3-5 years) with severe pneumonia during a controlled 16 h fast using stable isotopes [6,6-(2)H2]glucose and (2)H2O at a hospital-based research facility. On admission, the glucose concentrations were comparable in both groups: young children: 5.1 ± 1.3 mmol/l, older children: 4.8 ± 0.6 mmol/l, p = 0.685, with a decrease during the first 8 h of fasting in the young children only to 3.6 ± 0.5, p = 0.04. Glucose production was comparable in both groups: young: 24.5 ± 8.3, older: 24.9 ± 5.9 µmol/kg(•)min, p = 0.926. Between 8 and 16 h of fasting, the glucose concentration decreased comparably in both groups (young: - 0.9 ± 0.7, p = 0.004; older: -1.0 ± 0.4 mmol/l, p = 0.001), as did glucose production (young: -6.8 ± 6.3, p = 0.003; older: -5.3 ± 3.4 µmol/kg(•)min, p = 0.001). Gluconeogenesis decreased in young children only: -5.0 ± 7.4, p = 0.029. We conclude that fasting predisposes to hypoglycemia in children with severe pneumonia. Young children are more at risk than older children. Glucose production is an important determinant of the plasma glucose concentration in young children with pneumonia, indicating an inability to reduce glucose usage. Our results are largely in agreement with the literature on the adaptation of glucose metabolism in children with malaria, although there seem to be disease-specific differences in the regulation of gluconeogenesis.

Selective cannabinoid-1 receptor blockade benefits fatty acid and triglyceride metabolism significantly in weight-stable nonhuman primates

The goal of this study was to determine whether administration of the CB₁ cannabinoid receptor antagonist rimonabant would alter fatty acid flux in nonhuman primates. Five adult baboons (Papio Sp) aged 12.1 ± 4.7 yr (body weight: 31.9 ± 2.1 kg) underwent repeated metabolic tests to determine fatty acid and TG flux before and after 7 wk of treatment with rimonabant (15 mg/day). Animals were fed ad libitum diets, and stable isotopes were administered via diet (d₃₁-tripalmitin) and intravenously (¹³C₄-palmitate, ¹³C₁-acetate). Plasma was collected in the fed and fasted states, and blood lipids were analyzed by GC-MS. DEXA was used to assess body composition and a hyperinsulinemic euglycemic clamp used to assess insulin-mediated glucose disposal. During the study, no changes were observed in food intake, body weight, plasma, and tissue endocannabinoid concentrations or the quantity of liver-TG fatty acids originating from de novo lipogenesis (19 ± 6 vs. 16 ± 5%, for pre- and posttreatment, respectively, P = 0.39). However, waist circumference was significantly reduced 4% in the treated animals (P < 0.04), glucose disposal increased 30% (P = 0.03), and FFA turnover increased 37% (P = 0.02). The faster FFA flux was consistent with a 43% reduction in these fatty acids used for TRL-TG synthesis (40 ± 3 vs. 23 ± 4%, P = 0.02) and a twofold increase in TRL-TG turnover (1.5 ± 0.9 vs. 3.1 ± 1.4 μmol·kg⁻¹·h⁻¹, P = 0.03). These data support the potential for a strong effect of CB₁ receptor antagonism at the level of adipose tissue, resulting in improvements in fasting turnover of fatty acids at the whole body level, central adipose storage, and significant improvements in glucose homeostasis.

Regression dilution bias: tools for correction methods and sample size calculation

BACKGROUND

Random errors in measurement of a risk factor will introduce downward bias of an estimated association to a disease or a disease marker. This phenomenon is called regression dilution bias. A bias correction may be made with data from a validity study or a reliability study.

AIMS AND METHODS

In this article we give a non-technical description of designs of reliability studies with emphasis on selection of individuals for a repeated measurement, assumptions of measurement error models, and correction methods for the slope in a simple linear regression model where the dependent variable is a continuous variable. Also, we describe situations where correction for regression dilution bias is not appropriate.

RESULTS

The methods are illustrated with the association between insulin sensitivity measured with the euglycaemic insulin clamp technique and fasting insulin, where measurement of the latter variable carries noticeable random error. We provide software tools for estimation of a corrected slope in a simple linear regression model assuming data for a continuous dependent variable and a continuous risk factor from a main study and an additional measurement of the risk factor in a reliability study. Also, we supply programs for estimation of the number of individuals needed in the reliability study and for choice of its design.

CONCLUSIONS

Our conclusion is that correction for regression dilution bias is seldom applied in epidemiological studies. This may cause important effects of risk factors with large measurement errors to be neglected.

Surrogate estimates of insulin sensitivity in obese youth along the spectrum of glucose tolerance from normal to prediabetes to diabetes

CONTEXT

In epidemiological studies of childhood obesity, simple and reliable surrogate estimates of insulin sensitivity are needed because the gold standard, the hyperinsulinemic-euglycemic clamp, is not feasible on a large scale.

OBJECTIVE

To examine the correlation of fasting and oral glucose tolerance test (OGTT)-derived surrogate indices of insulin sensitivity with the hyperinsulinemic-euglycemic clamp in obese adolescents with normal glucose tolerance, prediabetes, and diabetes.

PATIENTS AND DESIGN

A total of 188 overweight/obese adolescents (10 to <20 yr old) who completed a standard 2-h OGTT and 3-h hyperinsulinemic-euglycemic clamp were included. Fasting-derived surrogates [fasting glucose (G(F)), fasting insulin (I(F)), 1/I(F), G(F)/I(F), homeostasis model assessment and quantitative insulin sensitivity check index] and OGTT-derived surrogates [whole-body insulin sensitivity index and the ratio of glucose and insulin areas under the curve (Gluc(AUC)/Ins(AUC))] were calculated.

MAIN OUTCOME MEASURES

We evaluated the correlations between the clamp-measured insulin sensitivity and the surrogate estimates and area under the receiver operating characteristic curves.

RESULTS

Fasting indices (1/I(F), G(F)/I(F), homeostasis model assessment of insulin sensitivity, and quantitative insulin sensitivity check index) correlated significantly with clamp insulin sensitivity (r = 0.82, 0.78, 0.81, and 0.80, respectively), with lower correlations between the OGTT surrogates and clamp (whole-body insulin sensitivity index, r = 0.77; Gluc(AUC)/Ins(AUC), r = 0.62). The area under the receiver operating characteristic curves was more than or equal to 0.94 for all surrogates except Gluc(AUC)/Ins(AUC.) Across quartiles of clamp-measured insulin sensitivity, there was a significant overlap in individual values of I(F), 1/I(F), and G(F)/I(F).

CONCLUSION

In obese adolescents with normal or impaired glucose tolerance or diabetes, OGTT-derived surrogates do not offer any advantage over the simpler fasting indices, which correlate strongly with clamp insulin sensitivity. Surrogate indices of insulin sensitivity could be used in epidemiological studies but not to define insulin resistance in individual patients or research subjects.

Protocol for the measurement of fatty acid and glycerol turnover in vivo in baboons

Recognition of the strength of nonhuman primate models in investigating metabolic disorders has resulted in an expanded need for in vivo research techniques. We studied adipose metabolism in 10 baboons (13.0 ± 4.2 years old, 29.5 ± 5.5 kg). Part 1 evaluated the effect of different sedatives on the rate of appearance of plasma free fatty acids (RaFFA), assessed using ¹³C₄-labeled palmitate infusion (7 µmol/kg/min). Animals, were studied with no sedation, with complete isoflurane sedation, and with minimal midazolam infusion (0.04 mg/kg/h), with the last scheme allowing for the most consistent values and animals that were visually more calm. In Part 2, RaFFA and RaGlycerol (D₅-glycerol, 5 mg/kg lean body mass/h) were measured. From midnight to 0300, flux fell and came to a steady state between 0500 and 0700 h (RaFFA, 39.4 ± 29.8 μmol/kg fat mass/min; and RaGlycerol, 26.9 ± 7.3 μmol/kg/min). The RaFFA-to-RaGlycerol ratio was 1.5 ± 0.8 (49% reesterification). The decline in turnover throughout the night reflects natural circadian processes and was mirrored by reductions in FFA and glycerol to 0.62 and ± 0.14 and 0.16 and ± 0.03 mmol/l, respectively. The concurrent changes in both FFA and glycerol kinetics indicate physiologic validity of the method. These techniques will support needed research to determine mechanisms by which treatments act upon the adipocyte in vivo.

Galactose promotes fat mobilization in obese lactating and nonlactating women

BACKGROUND

Galactose consumption as the only carbohydrate source results in little increase in plasma glucose and insulin concentrations when compared with fasting. Lower insulin might promote endogenous lipolysis during meal absorption, which may facilitate fat loss.

OBJECTIVE

The objective was to test the hypothesis that consumption of an isocaloric, isonitrogenous galactose drink will result in higher rates of lipolysis and fat oxidation than consumption of a glucose drink in obese lactating and nonlactating women.

DESIGN

Seven healthy, obese, exclusively breastfeeding women and 7 healthy, obese, nonlactating women were studied on 2 occasions according to a randomized, crossover, single-blinded design. Subjects received drinks providing ≈70% of the daily estimated energy requirement, of which 60% was either glucose or galactose. The primary outcomes were the rate of appearance (Ra) of glycerol and palmitate, and the secondary outcomes were glucose Ra, milk production, energy expenditure, and substrate oxidation.

RESULTS

Plasma glucose and insulin concentrations were lower (P < 0.05) and those of glycerol, palmitate, free fatty acids, and triglycerides were higher (P < 0.05) during galactose than during glucose feeding in both nonlactating and lactating women. During galactose feeding, glucose Ra was lower (P < 0.01) and glycerol, palmitate, and free fatty acid Ra were higher (P < 0.01) in both groups. During galactose feeding in all women combined, fat oxidation was higher (P = 0.01) and protein oxidation was lower (P < 0.01). Milk production, energy expenditure, and carbohydrate oxidation were similar between glucose and galactose feeding.

CONCLUSIONS

Galactose consumption is associated with higher endogenous fat mobilization and oxidation during meal absorption. Long-term studies are required to determine whether galactose as an exclusive carbohydrate source would promote body fat loss in obese subjects.

Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth

INTRODUCTION

Data on the metabolic effects of resistance exercise (strength training) in adolescents are limited.

PURPOSE

The objective of this study was to determine whether a controlled resistance exercise program without dietary intervention or weight loss reduces body fat accumulation, increases lean body mass, and improves insulin sensitivity and glucose metabolism in sedentary obese Hispanic adolescents.

METHODS

Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 h·wk, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques.

RESULTS

All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (∼80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05).

CONCLUSIONS

We conclude that a controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.

Determination of the BMI threshold that predicts cardiovascular risk and insulin resistance in late childhood

AIMS

Body mass index (BMI, kg/m(2)) thresholds of children predicting cardiovascular risk, reported in previous studies were inconsistent and that predicting increased insulin resistance is lacking. We determined the BMI threshold that predicts increased cardiovascular risk and insulin resistance in children.

METHODS

The entire 4th grade students (187 boys and 218 girls) from 5 schools were included. Cardiovascular risk was defined as the presence of three or more of cardiovascular risk factors. Increased insulin resistance was estimated using homeostasis model assessment of insulin resistance and fasting insulin level.

RESULTS

The BMI percentile predicting cardiovascular risk was the 71.3th percentile for boys and the 77.1th percentile for girls. The BMI value was 21.4 kg/m(2) for boys and 20.6 kg/m(2) for girls. 34% of boys and 42% of girls with a BMI above the cut-off values had cardiovascular risk. The BMI percentile predicting increased insulin resistance was the 66.3th percentile for boys and the 67.9th percentile for girls. The children with cardiovascular risk had significantly greater (P<0.01) insulin resistance than those without risk.

CONCLUSION

This study demonstrated that the BMI thresholds at which cardiovascular risk and insulin resistance begin to increase in Korean children were lower than current definition of childhood obesity, proposed by the international obesity task force.

Evidence that multiple genetic variants of MC4R play a functional role in the regulation of energy expenditure and appetite in Hispanic children

BACKGROUND

Melanocortin-4-receptor (MC4R) haploinsufficiency is the most common form of monogenic obesity; however, the frequency of MC4R variants and their functional effects in general populations remain uncertain.

OBJECTIVE

The aim was to identify and characterize the effects of MC4R variants in Hispanic children.

DESIGN

MC4R was resequenced in 376 parents, and the identified single nucleotide polymorphisms (SNPs) were genotyped in 613 parents and 1016 children from the Viva la Familia cohort. Measured genotype analysis (MGA) tested associations between SNPs and phenotypes. Bayesian quantitative trait nucleotide (BQTN) analysis was used to infer the most likely functional polymorphisms influencing obesity-related traits.

RESULTS

Seven rare SNPs in coding and 18 SNPs in flanking regions of MC4R were identified. MGA showed suggestive associations between MC4R variants and body size, adiposity, glucose, insulin, leptin, ghrelin, energy expenditure, physical activity, and food intake. BQTN analysis identified SNP 1704 in a predicted micro-RNA target sequence in the downstream flanking region of MC4R as a strong, probable functional variant influencing total, sedentary, and moderate activities with posterior probabilities of 1.0. SNP 2132 was identified as a variant with a high probability (1.0) of exerting a functional effect on total energy expenditure and sleeping metabolic rate. SNP rs34114122 was selected as having likely functional effects on the appetite hormone ghrelin, with a posterior probability of 0.81.

CONCLUSION

This comprehensive investigation provides strong evidence that MC4R genetic variants are likely to play a functional role in the regulation of weight, not only through energy intake but through energy expenditure.

Aerobic exercise increases peripheral and hepatic insulin sensitivity in sedentary adolescents

CONTEXT

Data are limited on the effects of controlled aerobic exercise programs (without weight loss) on insulin sensitivity and glucose metabolism in children and adolescents.

OBJECTIVE

To determine whether a controlled aerobic exercise program (without weight loss) improves peripheral and hepatic insulin sensitivity and affects glucose production (GPR), gluconeogenesis and glycogenolysis in sedentary lean and obese Hispanic adolescents.

PATIENTS AND DESIGN

Twenty-nine post-pubertal adolescents (14 lean: 15.1 +/- 0.3 y; 20.6 +/- 0.8 kg/m(2); 18.9+/-1.5% body fat and 15 obese: 15.6 +/- 0.4 y; 33.2 +/- 0.9 kg/m(2); 38.4 +/- 1.4% body fat) (mean +/- SE), completed a 12 wk aerobic exercise program (4 x 30 min/week at >or=70% of VO(2) peak). Peripheral and hepatic insulin sensitivity and glucose kinetics were quantified using GCMS pre- and post-exercise.

RESULTS

No weight loss occurred. Lean and obese participants complied well with the program ( approximately 90% of the exercise sessions attended, resulting in approximately 15% increase in fitness in both groups). Peripheral and hepatic insulin sensitivity were higher in lean than obese adolescents but increased in both groups; peripheral insulin sensitivity by 35 +/- 14% (lean) (p < 0.05) and 59 +/- 19% (obese) (p < 0.01) and hepatic insulin sensitivity by 19 +/- 7% (lean) (p < 0.05) and 23 +/- 4% (obese) (p < 0.01). GPR, gluconeogenesis and glycogenolysis did not differ between the groups. GPR decreased slightly, 3 +/- 1% (lean) (p < 0.05) and 4 +/- 1% (obese) (p < 0.01). Gluconeogenesis remained unchanged, while glycogenolysis decreased slightly in the obese group (p < 0.01).

CONCLUSION

This well accepted aerobic exercise program, without weight loss, is a promising strategy to improve peripheral and hepatic insulin sensitivity in lean and obese sedentary adolescents. The small decrease in GPR is probably of limited clinical relevance.

Mechanisms to conserve glucose in lactating women during a 42-h fast

Little is known about how lactating women accommodate for their increased glucose demands during fasting to avoid maternal hypoglycemia. The objective of this study was to determine whether lactating women conserve plasma glucose by reducing maternal glucose utilization by increasing utilization of FFA and ketone bodies and/or increasing gluconeogenesis and mammary gland hexoneogenesis. Six healthy exclusively breastfeeding women and six nonlactating controls were studied during 42 h of fasting and 6 h of refeeding. Glucose and protein kinetic parameters were measured using stable isotopes and GCMS and energy expenditure and substrate oxidation using indirect calorimetry. After 42 h of fasting, milk production decreased by 16% but remained within normal range. Glucose, insulin, and C-peptide concentrations decreased with the duration of fasting in both groups but were lower (P < 0.05) in lactating women. Glucagon, FFA, and beta-hydroxybutyrate concentrations increased with fasting time (P < 0.001) and were higher (P < 0.0001) in lactating women during both fasting and refeeding. During 42 h of fasting, gluconeogenesis was higher in lactating women compared with nonlactating controls (7.7 +/- 0.4 vs. 6.5 +/- 0.2 micromol kg(-1) min(-1), P < 0.05), whereas glycogenolysis was suppressed to similar values (0.4 +/- 0.1 vs. 0.9 +/- 0.2 micromol kg(-1) min(-1), respectively). Mammary hexoneogenesis did not increase with the duration of fasting. Carbohydrate oxidation was lower and fat and protein oxidations higher (P < 0.05) in lactating women. In summary, lactating women are at risk for hypoglycemia if fasting is extended beyond 30 h. The extra glucose demands of extended fasting during lactation appear to be compensated by increasing gluconeogenesis associated with ketosis, decreasing carbohydrate oxidation, and increasing protein and FFA oxidations.

Glucose metabolism in children: influence of age, fasting, and infectious diseases

This review describes the occurrence of hypoglycemia in young children as a common and serious complication that needs to be avoided because of the high risk of brain damage and mortality. Young age, fasting, and severe infectious disease are considered important risk factors. The limited data on the effect of these risk factors on glucose metabolism in children are discussed and compared with data on glucose metabolism in adults. The observations discussed may have implications for further research on glucose kinetics in young children with infectious disease.

Contribution of galactose and fructose to glucose homeostasis

To determine the contributions of galactose and fructose to glucose formation, 6 subjects (26 +/- 2 years old; body mass index, 22.4 +/- 0.2 kg/m(2)) (mean +/- SE) were studied during fasting conditions. Three subjects received a primed constant intravenous infusion of [6,6-(2)H(2)]glucose for 3 hours followed by oral bolus ingestion of galactose labeled to 2% with [U-(13)C]galactose (0.72 g/kg); the other 3 subjects received a primed constant intravenous infusion of [6,6-(2)H(2)]glucose followed by either a bolus ingestion of fructose alone (0.72 g/kg) (labeled to 2% with [U-(13)C]fructose) or coingestion of fructose (labeled with [U-(13)C]fructose) (0.72 g/kg) and unlabeled glucose (0.72 g/kg). Four hours after ingestion, subjects received 1 mg of glucagon intravenously to stimulate glycogenolysis. When galactose was ingested alone, the area under the curve (AUC) of [(13)C(6)]glucose and [(13)C(3)]glucose was 7.28 +/- 0.39 and 3.52 +/- 0.05 mmol/L per 4 hours, respectively. When [U-(13)C]fructose was ingested with unlabeled fructose or unlabeled fructose plus glucose, no [(13)C(6)]glucose was detected in plasma. The AUC of [(13)C(3)]glucose after fructose and fructose plus glucose ingestion was 20.21 +/- 2.41 and 6.25 +/- 0.34 mmol/L per 4 hours, respectively. Comparing the AUC for the (13)C(3) vs (13)C(6) enrichments, 67% of oral galactose enters the systemic circulation via a direct route and 33% via an indirect route. In contrast, fructose only enters the systemic circulation via the indirect route. Finally, when ingested alone, fructose and galactose contribute little to glycogen synthesis. After the coingestion of fructose and glucose with the resultant insulin response from the glucose, fructose is a significant contributor to glycogen synthesis.

beta-Cell function and insulin sensitivity in adolescents from an OGTT

Given the increase in the incidence of insulin resistance, obesity, and type 2 diabetes in children and adolescents, it would be of paramount importance to assess quantitative indices of insulin secretion and action during a physiological perturbation, such as a meal or an oral glucose-tolerance test (OGTT). A minimal model method is proposed to measure quantitative indices of insulin secretion and action in adolescents from an oral test. A 7 h, 21-sample OGTT was performed in 11 adolescents. The C-peptide minimal model was identified on C-peptide and glucose data to quantify indices of beta-cell function: static phi(s) and dynamic phi(d) responsivity to glucose from which total responsivity phi was also measured. The glucose minimal model was identified on glucose and insulin data to estimate insulin sensitivity, S(I), which was compared to a reference measure, S(I)(ref), provided by a tracer method. Disposition indices, which adjust insulin secretion for insulin action, were then calculated. Indices of beta-cell function were phi(s) = 51.35 +/- 8.89 x 10(-9)min(-1), phi(d) = 1,392 +/- 258 x 10(-9), and phi = 82.09 +/- 17.70 x 10(-9)min(-1). Insulin sensitivity was S(I) = 14.19 +/- 2.73 x 10(-4), not significantly different from S(I)(ref) = 14.96 +/- 3.04 x 10(-4) dl/kg.min per microU/ml, and well correlated: r = 0.98, P < 0.0001, thus indicating that S(I) can be accurately measured from an oral test. Disposition indices were DI(s) = 1,040 +/- 201 x 10(-14) dl/kg/min(2) per pmol/l, DI(d) = 33,178 +/- 10,720 x 10(-14) dl/kg/min per pmol/l, DI = 1,844 +/- 522 x 10(-14) dl/kg/min(2) per pmol/l. Virtually the same minimal model assessment was obtained with a reduced 3 h, 9-sample protocol. OGTT interpreted with C-peptide and glucose minimal model has the potential to provide novel insight regarding the regulation of glucose metabolism in adolescents, and to evaluate the effect of obesity and interventions such as diet and exercise.

Resting energy expenditure in insulin resistance falls with decompensation of insulin secretion in obese children

BACKGROUND

Low resting energy expenditure (REE) and respiratory quotient (RQ) have been shown in adults to predispose to obesity and diabetes mellitus.

AIM

To correlate REE and RQ in 73 obese children and young adults (body mass index [BMI] 37 +/- 10 kg/m2) with measures of insulin secretion and resistance (IR) indices, percent carbohydrate and fat oxidation, and prolactin and leptin levels.

DESIGN

During a 3-day admission, REE and RQ were determined by indirect calorimetry. Blood chemistries and oral glucose tolerance test (OGTT) were obtained, and intravenous glucose tolerance test (IVGTT) modified by tolbutamide was conducted after an overnight fast, permitting calculation of acute insulin response (AIR), insulin resistance (SiIVGTT), and disposition index (DI).

RESULTS

Patients fell into two groups according to their SiIVGTT: those with normal insulin sensitivity (NIS) and those with insulin resistance (IR). IR patients were subdivided on the basis of DI (cut-off value 0.13 min(-1)) into compensated (CIR) or decompensated (DIR) groups. CIR patients had higher RQ, REE corrected by BMI, AIR, and carbohydrate oxidation and lower fat oxidation than NIS and DIR patients. REE correlated positively with BMI, leptin, and AIR, and negatively with SiIVGTT.

CONCLUSIONS

Findings in the CIR and DIR groups support the correlation of REE with metabolic changes consistent with an increased risk of diabetes mellitus.

Very young children with uncomplicated falciparum malaria have higher risk of hypoglycaemia: a study from Suriname

OBJECTIVE

To measure glucose kinetics and the influence of age, nutritional status and fasting duration in children with uncomplicated falciparum malaria (UFM) under the age of 5 years.

METHODS

Plasma glucose concentration, endogenous glucose production (EGP) and gluconeogenesis (GNG) were measured using [6,6-(2)H(2)]glucose and (2)H(2)O in 17 very young (<3 years) and 7 older (3-5 years) Surinamese children with UFM admitted to the Distrikt Hospital Stoelmanseiland and Diakonessen Hospital Paramaribo over 17 months.

RESULTS

Plasma glucose concentration was lower in the group of very young children than in the older children (P = 0.028). There were no differences in EGP and GNG between the groups. Overall GNG contributed 56% (median, range 17-87%) to EGP, with no differences between the groups (P = 0.240). Glucose clearance was lower in the older children (P = 0.026). Glucose concentration did not differ between children with weight for length/height less than -1.3 SD and children with weight for length/height greater than -1.3 SD (P = 0.266). Plasma glucose concentration was not predicted by fasting duration (P = 0.762).

CONCLUSIONS

Our data suggest a higher risk of hypoglycaemia in very young children with uncomplicated malaria as plasma glucose concentration was lower in this study group. Since this could not be attributed to an impaired EGP, and because glucose clearance was lower in the older children, we presume that older children were better capable of reducing glucose utilization during fasting. Studies on glucose kinetics are feasible in very young children with malaria and give more insight in the pathophysiology of hypoglycaemia.

Measurement of gluconeogenesis using glucose fragments and mass spectrometry after ingestion of deuterium oxide

We report a new method to measure the fraction of glucose derived from gluconeogenesis using gas chromatography-mass spectrometry and positive chemical ionization. After ingestion of deuterium oxide by subjects, glucose derived from gluconeogenesis is labeled with deuterium. Our calculations of gluconeogenesis are based on measurements of the average enrichment of deuterium on carbon 1, 3, 4, 5, and 6 of glucose and the deuterium enrichment in body water. In a sample from an adult volunteer after ingestion of deuterium oxide, fractional gluconeogenesis using the "average deuterium enrichment method" was 48.3 +/- 0.5% (mean +/- SD) and that with the C-5 hexamethylenetetramine (HMT) method by Landau et al. (Landau BR, Wahren J, Chandramouli V, Schumann WC, Ekberg K, Kalhan SC; J Clin Invest 98: 378-385, 1996) was 46.9 +/- 5.4%. The coefficient of variation of 10 replicate analyses using the new method was 1.0% compared with 11.5% for the C-5 HMT method. In samples derived from an infant receiving total parenteral nutrition, fractional gluconeogenesis was 13.3 +/- 0.3% using the new method and 13.7 +/- 0.8% using the C-5 HMT method. Fractional gluconeogenesis measured in six adult volunteers after 66 h of continuous fasting was 83.7 +/- 2.3% using the new method and 84.2 +/- 5.0% using the C-5 HMT method. In conclusion, the average deuterium enrichment method is simple, highly reproducible, and cost effective. Furthermore, it requires only small blood sample volumes. With the use of an additional tracer, glucose rate of appearance can also be measured during the same analysis. Thus the new method makes measurements of gluconeogenesis available and affordable to large numbers of investigators under conditions of low and high fractional gluconeogenesis ( approximately 10 to approximately 90) in all subject populations.

Glucose fluxes during OGTT in adolescents assessed by a stable isotope triple tracer method

Virtually no information is available on glucose fluxes during a meal or glucose ingestion in adolescents.

AIM

To use a triple tracer approach to measure rates of appearance of ingested glucose (Ra(ogtt)), endogenous glucose production (EGP) and glucose disappearance (Rd) following an oral glucose bolus in adolescents.

METHODS

Eleven adolescents (4 M/7 F, 15 +/- 1 yr; 67.3 +/- 4.7 kg; 24 +/-2 kg/m2) underwent a frequent sampled oral glucose tolerance test (OGTT) (labelled with [6,6-2H2]glucose) combined with intravenous infusion of [1-(13)C]glucose and [U-(13)C6]glucose following an overnight fast. Formulas were developed to estimate glucose fluxes using one- or two-compartment models.

RESULTS

During the 7 h following the OGTT bolus, 9.8 +/- 2.3% of the ingested glucose was extracted by the liver, EGP was suppressed by 45 +/- 4% and Rd increased by 21 +/- 5%.

CONCLUSIONS

The triple tracer method provided accurate assessment of Ra(ogtt), EGP and Rd fluxes during an OGTT in adolescents. Thus, this method might provide novel insight on postprandial glucose fluxes in children/adolescents under various conditions.

Body size, body composition, and metabolic profile explain higher energy expenditure in overweight children

Lower relative rates of energy expenditure (EE), increased energetic efficiency, and altered fuel utilization purportedly associated with obesity have not been demonstrated indisputably in overweight children. We hypothesized that differences in energy metabolism between nonoverweight and overweight children are attributable to differences in body size and composition, circulating thyroid hormones, sympathetic nervous system, and adrenomedullary activity. A total of 836 Hispanic children, 5-19 y old, participated in 24-h calorimetry, anthropometric, and dual-energy X-ray absorptiometry measurements. Biochemistries were determined by standard techniques. Absolute total EE (TEE) and its components (sleep EE, basal EE, sedentary EE, cycling EE, walking EE, activity EE, nonexercising activity thermogenesis) were higher in overweight children (P = 0.001). Net mechanical energetic efficiency of cycling was lower in overweight children (P = 0.001). Adjusting for body size and composition accounted for differences in TEE, its components, and energetic efficiency. Net carbohydrate and fat utilization did not differ between groups. TEE was independently influenced by sex, Tanner stage, fat free mass, fat mass (FM), fasting serum nonesterified fatty acids (NEFA), leptin, free thyroxine, triiodothyronine, and 24-h urinary norepinephrine and epinephrine. Fat utilization was independently associated with age2, sex, FM, fasting serum NEFA, triacylglycerol, adiponectin, leptin, total thyroxine, and free triiodothyronine. Higher EE in overweight children was largely explained by differences in body size and composition, with minor contributions of thyroid and sympathoadrenal systems. Alterations in EE, energetic efficiency, and substrate utilization were not evident in the overweight children.

Exercise alone reduces insulin resistance in obese children independently of changes in body composition

CONTEXT

The number of obese children with insulin resistance and type 2 diabetes is increasing, but the best management strategy is not clear.

OBJECTIVE

The objective of this study was to assess the effect of a structured 8-wk exercise training program on insulin resistance and changes in body composition in obese children.

DESIGN

The study was 8 wk of structured supervised exercise intervention with outcome measures before and after the exercise period.

SUBJECTS

Fourteen obese children (12.70 +/- 2.32 yr; eight male, six female) with high fasting insulin levels were enrolled into the study.

INTERVENTION

INTERVENTION consisted of 8 wk of supervised circuit-based exercise training, composed of three fully supervised 1-h sessions per week.

OUTCOME MEASURES

Outcome measures were assessed pretraining program and posttraining program and included insulin sensitivity (euglycemic-hyperinsulinemic clamp studies), fasting insulin and glucose levels, body composition using dual energy x-ray absorptiometry scan, lipid profile, and liver function tests.

RESULTS

Insulin sensitivity improved significantly after 8 wk of training (M(lbm) 8.20 +/- 3.44 to 10.03 +/- 4.33 mg/kg.min, P < 0.05). Submaximal exercise heart rate responses were significantly lower following the training (P < 0.05), indicating an improvement in cardiorespiratory fitness. Dual energy x-ray absorptiometry scans revealed no differences in lean body mass or abdominal fat mass.

CONCLUSION

An 8-wk exercise training program increases insulin sensitivity in obese children, and this improvement occurred in the presence of increased cardiorespiratory fitness but is independent of measurable changes in body composition.

Insufficient ketone body use is the cause of ketotic hypoglycemia in one of a pair of homozygotic twins

CONTEXT

Childhood ketotic hypoglycemia (KH) is a disease characterized by fasting hypoglycemia and increased levels of ketone bodies. The cause is unknown.

OBJECTIVE

The objective of the study was to study a pair of homozygotic twin boys, one of whom had severe KH from the age of 14 months, whereas the other boy was apparently healthy.

DESIGN AND RESULTS

At the age of 6 yr, the boys were thoroughly investigated. During a 24-h fasting tolerance test, the twin with KH showed hypoglycemia (blood glucose 2.0 mmol/liter) after 18 h. Three h before the occurrence of hypoglycemia, he had had 10 times higher beta-hydroxybutyrate levels than his brother, who showed no signs of hypoglycemia. Their glucose production rates were normal and similar (23.3 and 21.7 micromol/kg body weight per minute in the healthy and KH twin, respectively) as well as their lipolysis rates (5.8 and 6.8 micromol/kg body weight per minute, respectively). During repeated 60-min infusions of beta-hydroxybutyrate, the plasma level of beta-hydroxybutyrate increased 5-10 times more in the twin with KH (mean 1.1 mmol/liter in the healthy and 10.8 mmol/liter in the KH twin), indicating a disturbed clearance or metabolism of beta-hydroxybutyrate. No mutations were found in genes involved in ketone body metabolism or transport.

CONCLUSION

In the affected boy, KH seems to be the result of a reduced capacity to use ketone bodies, leading to increased peripheral metabolism of glucose that cannot be met by hepatic glucose production. Because the boys are homozygotic twins and only one of them is affected, the ketotic hypoglycemia is most likely caused by an altered imprinting of gene(s) involved in regulating metabolic pathways.

Dietary glutamate is almost entirely removed in its first pass through the splanchnic bed in premature infants

Breast milk glutamate is a potential gluconeogenic substrate. However, in piglets, most dietary glutamate undergoes first pass extraction by the gut, limiting its contribution to glucose formation. The objectives of the study were to determine in preterm infants, whether dietary glutamate increases plasma [glutamate] in a dose-dependent fashion and whether glutamate carbon appears in plasma glucose to an appreciable extent. Five enterally fed infants (31 +/- 0 wk; 1555 +/- 131 g) (mean +/- SE) were studied twice (postnatal age 10 +/- 1 d and 17 +/- 1 d, respectively), while receiving an intragastric infusion of glutamate (labeled to 4% +/- by [U-13C] glutamate) at 2.4 (study 1) and 4.8 micromol/kg/min (study 2) for 1.5 h (n=2) or 5 h (n=3). Plasma [glutamate] was 82 +/- 8 microM at baseline, and 84 +/- 11 and 90 +/- 13 microM after glutamate supplementation at 2.4 and 4.8 micromol/kg/min, respectively, values not different from baseline. Plasma [glutamate] was not affected by the duration of the glutamate infusion (1.5 versus 5 h). Plasma 13C glucose enrichment was only 0.3% (after 5 h ingestion of glutamate labeled to 4%) indicating insignificant contribution of dietary glutamate carbon to glucose. Thus, in premature infants, splanchnic extraction is the major fate of dietary glutamate, which is not a significant gluconeogenic substrate in these infants.

Assessment of beta-cell function in humans, simultaneously with insulin sensitivity and hepatic extraction, from intravenous and oral glucose tests

Assessment of insulin secretion in humans under physiological conditions has been a challenge because of its complex interplay with insulin action and hepatic insulin extraction. The possibility of simultaneously assessing beta-cell function, insulin sensitivity, and hepatic insulin extraction under physiological conditions using a simple protocol is appealing, since it has the potential to provide novel insights regarding the regulation of fasting and postprandial glucose metabolism in diabetic and nondiabetic humans. In this Perspective, we review data indicating that an oral glucose tolerance test (OGTT) or a meal test is able to accomplish this goal when interpreted with the oral beta-cell minimal model. We begin by using the well-established intravenous minimal model to highlight how the oral minimal model was developed and how the oral assessment parallels that of an intravenous glucose tolerance test (IVGTT). We also point out the unique aspects of both approaches in relation to their ability to assess different aspects of the beta-cell secretory cascade. We review the ability of the oral model to concurrently measure insulin sensitivity and hepatic insulin extraction, thereby enabling it to quantitatively portray the complex relationship among beta-cell function, hepatic insulin extraction, and insulin action. In addition, data from 204 individuals (54 young and 159 elderly) who underwent both IVGTT and meal tolerance tests are used to illustrate how these different approaches provide complementary but differing insights regarding the regulation of beta-cell function in humans.

Metabolic and behavioral predictors of weight gain in Hispanic children: the Viva la Familia Study

BACKGROUND

Despite the high prevalence of overweight among Hispanic children in the United States, definitive predictors of weight gain have not been identified in this population.

OBJECTIVE

The study objective was to test sociodemographic, metabolic, and behavioral predictors of 1-y weight gains in a large cohort of Hispanic children studied longitudinally.

DESIGN

Subjects (n = 879) were siblings from 319 Hispanic families enrolled in the Viva la Familia Study. Families were required to have at least one overweight child aged 4-19 y. One-year changes in weight and body composition by dual-energy X-ray absorptiometry were measured. Data were from parental interviews, birth certificates, multiple-pass 24-h dietary recalls, 3-d accelerometry, 24-h respiration calorimetry, measurements of eating in the absence of hunger, and measurement of fasting blood biochemistry indexes by radioimmunoassay. Generalized estimating equations and principal component analysis were applied.

RESULTS

Weight gain increased with age (P = 0.001), peaking at approximately 10 y of age in girls and approximately 11 y of age in boys. Mean (+/-SD) weight gain was significantly higher in overweight (7.5 +/- 3.7 kg/y) than in nonoverweight (4.4 +/- 2.4 kg/y) children and in boys than in girls. When adjusted for age, age squared, sex, and Tanner stage, the final model indicated a child's body mass index (BMI; kg/m2) status, maternal BMI, energy expenditure (total energy expenditure, basal metabolic rate, and sleeping metabolic rate), and fasting blood biochemistry indexes (total triiodothyronine, insulin, leptin, and ghrelin) as independent, positive predictors of weight gain (P = 0.01-0.001).

CONCLUSION

Knowledge of the metabolic and behavioral predictors of weight gain in Hispanic children will inform prevention and treatment efforts to address this serious public health problem in the United States.

Insulin-like growth factor binding protein-1 to screen for insulin resistance in children

BACKGROUND

Diabetes and atherosclerosis are burgeoning health problems complicating obesity-associated insulin resistance (IR). Early detection of IR in children is a key to preventative strategies. Since peripheral insulin levels insensitively reflect hepatic insulin fluxes, we studied the insulin-regulated hepatic insulin-like growth factor binding proteins (IGFBPs)-1 and -3 as possible screening markers of childhood IR.

METHODS

The tolbutamide-modified frequently sampled intravenous glucose tolerance test (FSIVGTT) and the oral glucose tolerance test (OGTT) were performed in 118 subjects < 21 years old with obesity. The relationships between insulin sensitivity index by minimal modeling (SiIVGTT), other Sis derived from fasting and OGTT insulin and glucose values, and the candidate serum markers were sought.

RESULTS

Significant correlation was found between IGFBP-1 and SiIVGTT, similar to the correlations of insulin sensitivity indices with SiIVGTT. In children < or = 10 years old, correlation of IGFBP-1 with SiIVGTT was the strongest. All (100%) subjects with IR defined by SiIVGTT < 4.5 +/- 0.5 x 10(-4) min(-1) /(microIU/mL) had inappropriately low IGFBP-1 levels. IGFBP-3 was not correlated with SiIVGTT.

CONCLUSIONS

IGFBP-1 levels decrease with obesity and IR. We propose that in young subjects, especially children under the age of 10 years, IGFBP-1 is a convenient and sensitive marker of IR, whereas elevated fasting insulin is less sensitive but more specific.

Correction for regression dilution bias using replicates from subjects with extreme first measurements

The least squares estimator of the slope in a simple linear regression model will be biased towards zero when the predictor is measured with random error, i.e. intra-individual variation or technical measurement error. A correction factor can be estimated from a reliability study where one replicate is available on a subset of subjects from the main study. Previous work in this field has assumed that the reliability study constitutes a random subsample from the main study. We propose that a more efficient design is to collect replicates for subjects with extreme values on their first measurement. A variance formula for this estimator of the correction factor is presented. The variance for the corrected estimated regression coefficient for the extreme selection technique is also derived and compared with random subsampling. Results show that variances for corrected regression coefficients can be markedly reduced with extreme selection. The variance gain can be estimated from the main study data. The results are illustrated using Monte Carlo simulations and an application on the relation between insulin sensitivity and fasting insulin using data from the population-based ULSAM study. In conclusion, an investigator faced with the planning of a reliability study may wish to consider an extreme selection design in order to improve precision at a given number of subjects or alternatively decrease the number of subjects at a given precision.

Impaired tricarboxylic acid cycle activity in mouse livers lacking cytosolic phosphoenolpyruvate carboxykinase

Liver-specific phosphoenolpyruvate carboxykinase (PEPCK) null mice, when fasted, maintain normal whole body glucose kinetics but develop dramatic hepatic steatosis. To identify the abnormalities of hepatic energy generation that lead to steatosis during fasting, we studied metabolic fluxes in livers lacking hepatic cytosolic PEPCK by NMR using 2H and 13C tracers. After a 4-h fast, glucose production from glycogenolysis and conversion of glycerol to glucose remains normal, whereas gluconeogenesis from tricarboxylic acid (TCA) cycle intermediates was nearly absent. Upon an extended 24-h fast, livers that lack PEPCK exhibit both 2-fold lower glucose production and oxygen consumption, compared with the controls, with all glucose production being derived only from glycerol. The mitochondrial reduction-oxidation (red-ox) state, as indicated by the NADH/NAD+ ratio, is 5-fold higher, and hepatic TCA cycle intermediate concentrations are dramatically increased in the PEPCK null livers. Consistent with this, flux through the TCA cycle and pyruvate cycling pathways is 10- and 40-fold lower, respectively. Disruption of hepatic cataplerosis due to loss of PEPCK leads to the accumulation of TCA cycle intermediates and a nearly complete blockage of gluconeogenesis from amino acids and lactate (an energy demanding process) but intact gluconeogenesis from glycerol (which contributes to net NADH production). Inhibition of the TCA cycle and fatty acid oxidation due to increased TCA cycle intermediate concentrations and reduced mitochondrial red-ox state lead to the development of steatosis.

Insulin resistance syndrome in children

The insulin resistance syndrome (syndrome X, metabolic syndrome) has become the major health problem of our times. Associated obesity, dyslipidemia, atherosclerosis, hypertension, and type 2 diabetes conspire to shorten life spans, while hyperandrogenism with polycystic ovarian syndrome affect the quality of life and fertility of increasing numbers of women. Whereas a growing number of single genetic diseases affecting satiety or energy metabolism have been found to produce the clinical phenotype, strong familial occurrences, especially in racially prone groups such as those from the Indian subcontinent, or individuals of African, Hispanic, and American Indian descents, together with emerging genetic findings, are revealing the polygenetic nature of the syndrome. However, the strong lifestyle factors of excessive carbohydrate and fat consumption and lack of exercise are important keys to the phenotypic expression of the syndrome. The natural history includes small for gestational age birth weight, excessive weight gains during childhood, premature pubarche, an allergic diathesis, acanthosis nigricans, striae compounded by gynecomastia, hypertriglyceridemia, hepatic steatosis, premature atherosclerosis, hypertension, polycystic ovarian syndrome, and focal glomerulonephritis appearing increasingly through adolescence into adulthood. Type 2 diabetes, which develops because of an inherent and/or an acquired failure of an insulin compensatory response, is increasingly seen from early puberty onward, as is atheromatous disease leading to coronary heart disease and stroke. A predisposition to certain cancers and Alzheimer's disease is also now recognized. The looming tragedy from growing numbers of individuals affected by obesity/insulin resistance syndrome requires urgent public health approaches directed at their early identification and intervention during childhood. Such measures include educating the public on the topic, limiting the consumption of sucrose-containing drinks and foods with high carbohydrate and fat contents, and promoting exercise programs in our nation's homes and schools.

Glucose production pathways by2H and13C NMR in patients with HIV-associated lipoatrophy

Patients with HIV taking protease inhibitors were selected for the presence (five subjects) or absence (five subjects) of lipoatrophy. Following an overnight fast, subjects were given oral (2)H(2)O in divided doses (5 mL/kg body water), [U-(13)C(3)] propionate (10 mg/kg), and acetaminophen (1000 mg). Glucose (from plasma) or acetaminophen glucuronide (from urine) were converted to monoacetone glucose for (2)H NMR and (13)C NMR analysis. The fraction of plasma glucose derived from gluconeogenesis was not significantly different between groups. However, flux from glycerol into gluconeogenesis relative to glucose production was increased from 0.20 +/- 0.13 among subjects without lipoatrophy to 0.42 +/- 0.12 (P < 0.05) among subjects with lipoatrophy, and the TCA cycle contribution was reduced. Lipoatrophy was associated with an abnormal profile of glucose production as assessed by (13)C and (2)H NMR of plasma and urine.

Sources of plasma glucose by automated bayesian analysis of2H NMR spectra

Sources of blood glucose can be determined after oral ingestion of (2)H(2)O followed by isolation of plasma glucose and measurement of the relative (2)H enrichments in select positions within the glucose molecule. Typically, (2)H enrichments are obtained by mass spectrometry but (2)H NMR offers an alternative. Here it is demonstrated that the entire analysis may be automated by Bayesian analysis of a (2)H free induction decay signal of monoacetone glucose to obtain a direct readout of the relative contributions of glycogenolysis, glycerol, and phosphoenol pyruvate to plasma glucose production. Furthermore, Markov Chain Monte Carlo (MCMC) simulations of the posterior probability density provide uncertainties in all metabolic parameters from a single patient, thereby allowing comparisons in glucose metabolism from one individual to another. The combined MCMC Bayesian methodology is operationally simple and requires little intervention from the operator.