Treatment with recombinant human insulin-like growth factor (rhIGF)-I/rhIGF binding protein-3 complex improves metabolic control in subjects with severe insulin resistance

OBJECTIVE

Diabetes in the context of severe insulin resistance (SIR) presents a major therapeutic challenge because conventional therapies including insulin and insulin sensitizers often fail to achieve adequate metabolic control. Adjunctive therapy with recombinant human IGF-I (rhIGF-I)/recombinant human IGF binding protein-3 (rhIGFBP-3) has been shown to improve insulin sensitivity in both type 1 and type 2 diabetes and may have a role in the treatment of SIR. We report clinical and physiological outcomes after adjunctive therapy with rhIGF-I/rhIGFBP-3 in five subjects with SIR.

RESEARCH DESIGN AND METHODS

Five females (median age, 17 yr; range, 5-37) with SIR (two with pathogenic insulin receptor mutations) were treated with 0.5-2.0 mg/kg rhIGF-I/rhIGFBP-3 using a 16-wk dose escalation protocol. Glycosylated hemoglobin was recorded monthly. At baseline and end of treatment all patients were evaluated using continuous glucose monitoring sensing and admitted for overnight GH profiling and insulin-modified stable-label iv glucose tolerance test. Changes in body composition were assessed using dual-energy x-ray absorptiometry and magnetic resonance imaging.

RESULTS

Treatment with rhIGF-I/rhIGFBP-3 was well tolerated, and all subjects reported clinical improvements with reduction in acanthosis nigricans. Glycosylated hemoglobin was reduced (8.5% pretreatment to 7.1%; P < 0.03) with a trend toward reduction in mean continuous glucose monitoring sensing glucose (10.7 vs. 8.5 mmol/liter; P = 0.08). Effects of treatment on other biochemical measures were variable, but there was a trend toward improved C-peptide responses during the iv glucose tolerance test.

CONCLUSIONS

rhIGF-I/rhIGFBP-3 is well tolerated and clinically effective in subjects with SIR.

Metabolic effects of intensive insulin therapy in critically ill patients

Our aim was to investigate the effects of glycemic control and insulin concentration on lipolysis, glucose, and protein metabolism in critically ill medical patients. For our methods, the patients were studied twice. In study 1, blood glucose (BG) concentrations were maintained between 7 and 9 mmol/l with intravenous insulin. After study 1, patients entered one of four protocols for 48 h until study 2: low-insulin high-glucose (LIHG; variable insulin, BG of 7-9 mmol/l), low-insulin low-glucose (LILG; variable insulin of BG 4-6 mmol/l), high-insulin high-glucose [HIHG; insulin (2.0 mU . kg(-1).min(-1) plus insulin requirement from study 1), BG of 7-9 mmol/l], or high-insulin low-glucose [HILG; insulin (2.0 mU.kg(-1).min(-1) plus insulin requirement from study 1), BG of 4-6 mmol/l]. Age-matched healthy control subjects received two-step euglycemic hyperinsulinemic clamps achieving insulin levels similar to the LI and HI groups. In our results, whole body proteolysis was higher in patients in study 1 (P < 0.006) compared with control subjects at comparable insulin concentrations and was reduced with LI (P < 0.01) and HI (P = 0.001) in control subjects but not in patients. Endogenous glucose production rate (R(a)), glucose disposal, and lipolysis were not different in all patients in study 1 compared with control subjects at comparable insulin concentrations. Glucose R(a) and lipolysis did not change in any of the study 2 patient groups. HI increased glucose disposal in the patients (HIHG, P = 0.001; HILG, P = 0.07 vs. study 1), but this was less than in controls receiving HI (P < 0.03). In conclusion, low-dose intravenous insulin administered to maintain BG between 7-9 mmol/l is sufficient to limit lipolysis and endogenous glucose R(a) and increase glucose R(d). Neither hyperinsulinemia nor normoglycemia had any protein-sparing effect.

Differential effects of insulin detemir and neutral protamine Hagedorn (NPH) insulin on hepatic glucose production and peripheral glucose uptake during hypoglycaemia in type 1 diabetes

AIMS/HYPOTHESIS

We compared the symptoms of hypoglycaemia induced by insulin detemir (NN304) (B29Lys(epsilon-tetradecanoyl),desB30 human insulin) and equally effective doses of neutral protamine Hagedorn (NPH) insulin in relation to possible differential effects on hepatic glucose production and peripheral glucose uptake.

METHODS

After overnight intravenous infusion of soluble human insulin 18 participants with type 1 diabetes received subcutaneous injections of NPH insulin or insulin detemir (0.5 U/kg body weight) on separate occasions in random order. During the ensuing gradual development of hypoglycaemia cognitive function and levels of counter-regulatory hormones were measured and rates of endogenous glucose production and peripheral glucose uptake continuously evaluated using a primed constant infusion of [6,6-(2)H(2)]glucose. The study was terminated when plasma glucose concentration had fallen to 2.4 mmol/l or had reached a minimum at a higher concentration.

RESULTS

During the development of hypoglycaemia no difference between the two insulin preparations was observed in symptoms or hormonal responses. Significant differences were seen in rates of glucose flux. At and below plasma glucose concentrations of 3.5 mmol/l suppression of endogenous glucose production was greater with insulin detemir than with NPH insulin, whereas stimulation of peripheral glucose uptake was greater with NPH insulin than with insulin detemir.

CONCLUSIONS/INTERPRETATION

In participants with type 1 diabetes subcutaneously injected insulin detemir exhibits relative hepatoselectivity compared with NPH insulin, but symptoms of hypoglycaemia and hormonal counter-regulation are similar.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00760448.

Pegvisomant improves insulin sensitivity and reduces overnight free fatty acid concentrations in patients with acromegaly

INTRODUCTION

Acromegaly is complicated by an increased incidence of diabetes mellitus caused by impaired insulin sensitivity and reduced beta-cell function. Pegvisomant blocks activity at GH receptors, normalizing IGF-I in over 90% of patients and improving insulin sensitivity. The mechanisms for this increase in insulin sensitivity are not fully determined. We used stable isotope techniques to investigate the effects of pegvisomant on glucose and lipid metabolism in acromegaly.

METHODS

Five patients (age, 43 yr +/- sd) with active acromegaly were studied on two occasions: before pegvisomant and after 4 wk of pegvisomant (20 mg daily sc). (2)H(5)-glycerol was infused overnight to measure overnight and early morning (basal) glycerol production rate (Ra). The next morning (2)H(2)-glucose was infused for 2 h before and throughout a hyperinsulinemic euglycemic (1.5 mU/kg x min insulin) clamp to measure basal glucose Ra and insulin-stimulated peripheral glucose disposal (Rd).

RESULTS

Mean IGF-I was significantly reduced after pegvisomant treatment (mean, 539 +/- 176 vs. 198 +/- 168 microg/ml; P = 0.001). The insulin sensitivity of endogenous glucose production was significantly increased after pegvisomant [mean glucose Ra *insulin, 118.5 +/- 28 vs. 69.2 +/- 22 micromol/kg x min *(mU/liter); P = 0.04]. No differences in glucose Rd were seen after pegvisomant. All patients showed a reduction in glycerol Ra adjusted for insulin [mean, 18.12 +/- 1.75 vs. 14.4 +/- 4.75 micromol/kg x min *(mU/liter); P = 0.08] and overnight FFA concentrations (mean area under the curve, 278 +/- 84 vs. 203 +/- 71; P < 0.05) after pegvisomant.

CONCLUSION

Short-term administration of pegvisomant leads to a reduction in overnight endogenous glucose production, and this may be related to reduced levels of FFA.

Effects of rosiglitazone and pioglitazone on lipoprotein metabolism in patients with Type 2 diabetes and normal lipids

AIMS

Previous studies have suggested that plasma lipids are affected differently by the peroxisome proliferators-activated receptor (PPAR)-gamma agonists pioglitazone and rosiglitazone. The aim of this study was to perform a quantitative lipoprotein turnover study to determine the effects of PPAR-gamma agonists on lipoprotein metabolism.

METHODS

Twenty-four subjects with Type 2 diabetes treated with diet and/or metformin were randomized in a double-blind study to receive 30 mg pioglitazone, 8 mg rosiglitazone or placebo once daily for 3 months. Before and after treatment, absolute secretion rate (ASR) and fractional catabolic rate (FCR) of very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and low-density lipoprotein (LDL) apolipoprotein B100 were measured with a 10-h infusion of 1-13C leucine.

RESULTS

There was a significant decrease in glycated haemoglobin (HbA(1c)) and non-esterified fatty acids with pioglitazone (P = 0.01; P = 0.02) and rosiglitazone (P = 0.04; P = 0.003), respectively, but no change in plasma triglyceride or high-density lipoprotein (HDL) cholesterol. Following rosiglitazone, there was a significant reduction in VLDL apolipoprotein B100 (apoB) ASR (P = 0.01) compared with baseline, a decrease in VLDL triglyceride/apoB (P = 0.01), an increase in LDL2 cholesterol (P = 0.02) and a decrease in LDL3 cholesterol (P = 0.02). There was a decrease in VLDL triglyceride/apoB (P = 0.04) in the pioglitazone group. There was no significant difference in change in VLDL ASR or FCR among the three groups.

CONCLUSIONS

In patients with Type 2 diabetes and normal lipids, treatment with rosiglitazone or pioglitazone had no significant effect on lipoprotein metabolism compared with placebo.

Severe intrauterine growth retardation and atypical diabetes associated with a translocation breakpoint disrupting regulation of the insulin-like growth factor 2 gene

CONTEXT

IGF-II is an imprinted gene (predominantly transcribed from the paternally inherited allele), which has an important role in fetal growth in mice. IGF2 gene expression is regulated by a complex system of enhancers and promoters that determine tissue-specific and development-specific transcription. In mice, enhancers of the IGF2 gene are located up to 260 kb telomeric to the gene. The role of IGF-II in humans is unclear.

OBJECTIVE

A woman of short adult stature (1.46 m, -3 sd score) born with severe intrauterine growth retardation (1.25 kg at term, -5.4 SD score) and atypical diabetes diagnosed at the age of 23 yr had a balanced chromosomal translocation t(1;11) (p36.22; p15.5). We hypothesized that her phenotype resulted from disruption of her paternally derived IGF2 gene because her daughter who inherited the identical translocation had normal birth weight.

DESIGN

Both chromosomal break points were identified using fluorescent in situ hybridization. Sequence, methylation, and expression of the IGF2 gene was examined. Hyperinsulinemic, euglycemic clamp with glucose tracers and magnetic resonance imaging of the thorax, abdomen, and pelvis were performed.

RESULTS

The 11p15.5 break point mapped 184 kb telomeric of the IGF2 gene. Microsatellite markers confirmed paternal origin of this chromosome. IGF2 gene sequence and methylation was normal. IGF2 gene expression was reduced in lymphoblasts. Clamp studies showed marked hepatic and total insulin resistance. Massive excess sc fat was seen on magnetic resonance imaging despite slim body mass index (21.1 kg/m2).

CONCLUSIONS

A break point 184 kb upstream of the paternally derived IGF2 gene, separating it from some telomeric enhancers, resulted in reduced expression in some mesoderm-derived adult tissues causing intrauterine growth retardation, short stature, lactation failure, and insulin resistance with altered fat distribution.

Effect of 6-month supervised exercise on low-density lipoprotein apolipoprotein B kinetics in patients with type 2 diabetes mellitus

Although low-density lipoprotein (LDL) cholesterol is often normal in patients with type 2 diabetes mellitus, there is evidence for a reduced fractional catabolic rate and consequently an increased mean residence time (MRT), which can increase atherogenic risk. The dyslipidemia and insulin resistance of type 2 diabetes mellitus can be improved by aerobic exercise, but effects on LDL kinetics are unknown. The effect of 6-month supervised exercise on LDL apolipoprotein B kinetics was studied in a group of 17 patients with type 2 diabetes mellitus (mean age, 56.8 years; range, 38-68 years). Patients were randomized into a supervised group, who had a weekly training session, and an unsupervised group. LDL kinetics were measured with an infusion of 1-(13)C leucine at baseline in all groups and after 6 months of exercise in the patients. Eight body mass index-matched nondiabetic controls (mean age, 50.3 years; range, 40-67 years) were also studied at baseline only. At baseline, LDL MRT was significantly longer in the diabetic patients, whereas LDL production rate and fractional clearance rates were significantly lower than in controls. Percentage of glycated hemoglobin A(1c), body mass index, insulin sensitivity measured by the homeostasis model assessment, and very low-density lipoprotein triglyceride decreased (P < .02) in the supervised group, with no change in the unsupervised group. After 6 months, LDL cholesterol did not change in either the supervised or unsupervised group; but there was a significant change in LDL MRT between groups (P < .05) that correlated positively with very low-density lipoprotein triglyceride (r = 0.51, P < .04) and negatively with maximal oxygen uptake, a measure of fitness (r = -0.51, P = .035), in all patients. The LDL production and clearance rates did not change in either group. This study suggests that a supervised exercise program can reduce deleterious changes in LDL MRT.

The effects of growth hormone and/or testosterone on whole body protein kinetics and skeletal muscle gene expression in healthy elderly men: a randomized controlled trial

CONTEXT

Alterations of protein turnover may contribute to the progressive decline of muscle mass with aging.

OBJECTIVE

Our objective was to examine the effects of near-physiological recombinant human GH and/or testosterone (T) administration to older men on whole body protein kinetics and muscle gene expression.

DESIGN, SETTINGS, AND PARTICIPANTS

A 6-month randomized, double-blind, placebo-controlled trial in 21 healthy elderly men aged 65-75 yr, was performed. Participants were randomized to receive placebo GH and placebo T, rhGH and placebo T (GH), T and placebo GH (T), or rhGH and T (GHT).

INTERVENTIONS

The leucine rate of appearance (index of proteolysis), nonoxidative leucine disposal rate (an index of protein synthesis), and leucine oxidation rate were measured with an infusion of l-[1-(13)C] leucine. Muscle biopsies for the measurement of gene expression were performed. Body composition and aerobic capacity (maximal oxygen capacity) were measured.

RESULTS

Serum IGF-I levels increased significantly with GH and GHT (P < 0.001) compared with placebo. T increased significantly only in the T group (P = 0.028). Leucine rate of appearance and nonoxidative leucine disposal rate increased with GH (P = 0.015, P = 0.019) and GHT (P = 0.017, P = 0.02), but leucine oxidation did not change significantly in any treatment group. Midthigh muscle mass and maximal oxygen capacity increased (P < 0.04) with GHT only. Expression of muscle function genes did not change significantly, but the within-group comparisons revealed a significant increase of androgen receptor expression in the GHT group (P = 0.001).

CONCLUSION

This study showed that 6-month treatment with low-dose GH alone or with T in healthy elderly men produces comparable increments in whole body protein turnover and protein synthesis.

Isotope turnover studies in uncontrolled diabetes and the effects of insulin

Turnover rates of glucose, free fatty acids (FFA) and leucine have been measured in newly diagnosed, uncontrolled insulin-dependent diabetic (IDD) patients. The results have been compared with data collected from the same patients while on conventional insulin therapy as well as after overnight intravenous infusion of insulin with sustained normoglycaemia. The data have been analysed by compartmental and non-compartmental methods and the results have been compared with simultaneously collected data on respiratory exchange. Oxidation rates of 14C-labelled substrates have also been measured. Tracer studies were done on established diabetics after insulin withdrawal and subsequent intravenous infusion of insulin at different rates. The results confirm the in vivo importance of the glucose-fatty acid cycle, indicating that when glucose, FFA and ketone bodies are available in excess it is FFA and ketones that are metabolized in preference to glucose. The data emphasize the importance of increased production rates rather than decreased utilization rates in producing high concentrations of substrates in the plasma of insulin-deficient patients.

Impact of growth hormone and dehydroepiandrosterone on protein metabolism in glucocorticoid-treated patients

CONTEXT

Chronic pharmacological glucocorticoid (GC) use causes substantial morbidity from protein wasting. GH and androgens are anabolic agents that may potentially reverse GC-induced protein loss.

OBJECTIVE

Our objective was to assess the effect of GH and dehydroepiandrosterone (DHEA) on protein metabolism in subjects on long-term GC therapy.

DESIGN

This was an open, stepwise GH dose-finding study (study 1), followed by a randomized cross-over intervention study (study 2).

SETTING

The studies were performed at a clinical research facility.

PATIENTS AND INTERVENTION

In study 1, six subjects (age 69+/-4 yr) treated with long-term (>6 months) GCs (prednisone dose 8.3+/-0.8 mg/d) were studied before and after two sequential GH doses (0.8 and 1.6 mg/d) for 2 wk each. In study 2, 10 women (age 71+/-3 yr) treated with long-term GCs (prednisone dose 5.4+/-0.5 mg/d) were studied at baseline and after 2-wk treatment with GH 0.8 mg/d, DHEA 50 mg/d, or GH and DHEA (combination treatment).

MAIN OUTCOME MEASURE

Changes in whole body protein metabolism were assessed using a 3-h primed constant infusion of 1-[13C]leucine, from which rates of leucine appearance, leucine oxidation, and leucine incorporation into protein were estimated.

RESULTS

In study 1, GH 0.8 and 1.6 mg/d significantly reduced leucine oxidation by 19% (P=0.03) and 31% (P=0.02), and increased leucine incorporation into protein by 10% (P=0.13) and 19% (P=0.04), respectively. The lower GH dose did not cause hyperglycemia, whereas GH 1.6 mg/d resulted in fasting hyperglycemia in two of six subjects. In study 2, DHEA did not significantly change leucine metabolism alone or when combined with GH. Blood glucose was not affected by DHEA.

CONCLUSION

GH, at a modest supraphysiological dose of 0.8 mg/d, induces protein anabolism in chronic GC users without causing diabetes. DHEA 50 mg/d does not enhance the effect of GH. GH may safely prevent or reverse protein loss induced by chronic GC therapy.

Relationship between GH-induced metabolic changes and changes in body composition: a dose and time course study in GH-deficient adults

OBJECTIVE

Although growth hormone (GH)-induced changes in fat and protein metabolism are likely to underlie changes in body composition, the relationship has not been clearly defined. The aim was to study the effects of dose and time course on substrate metabolism and relate to body compositional changes during GH treatment.

DESIGN

In an open randomised-controlled study, 16 GH-deficient adults were randomised to treatment with GH 3 microg/kg/d (low dose, n=6) or 6 microg/kg/d (higher dose, n=10) for 12 weeks. Changes in whole body protein metabolism, estimated using the leucine turnover technique, and resting energy expenditure (REE) were assessed after short-term GH (two weeks) and longer-term GH (12 weeks). Changes in lean body mass (LBM) and fat mass (FM) over 12 weeks were assessed by DXA.

RESULTS

The maximal changes in leucine oxidation (Lox) (-3.9+/-1.1 versus +0.8+/-1.8 micromol/min, p=0.03) and REE (+132+/-36 versus -28+/-41 kcal/d, p=0.01) were significantly greater in the higher, than the low dose group. FM fell (-1.4+/-0.4 kg, p=0.005) and LBM increased (+2.2+/-0.7 kg, p=0.01) significantly in the higher dose group only. The acute reduction in Lox at two weeks in the higher dose group was no longer significant after 12 weeks. The change in Lox after two (r=-0.53, p=0.035), but not 12, weeks was significantly correlated with the change in LBM.

CONCLUSIONS

GH-induced changes in protein metabolism were influenced by the dose and duration of GH treatment. Suppression of protein oxidation occurred soon after initiation of GH in the higher dose group and predicted a later gain in LBM. Early assessment of whole body protein metabolism may allow prediction of the anabolic potential of GH.

Impact of acute and chronic low-dose glucocorticoids on protein metabolism

CONTEXT

High-dose glucocorticoids cause acute protein loss by increasing protein breakdown and oxidation. Whether lower glucocorticoid doses, typical of therapeutic use, induce sustained catabolism has not been studied.

OBJECTIVE

Our objective was to assess the effect of acute and chronic therapeutic glucocorticoid doses on protein metabolism.

DESIGN AND SETTING

We conducted an open longitudinal and a cross-sectional study at a clinical research facility.

PATIENTS AND INTERVENTION

Ten healthy subjects were studied before and after a short course of prednisolone (5 and 10 mg/d sequentially for 7 d each). Twelve subjects with inactive polymyalgia rheumatica receiving chronic (>12 months) prednisone (mean = 5.0 +/- 0.8 mg/d) were compared with 12 age- and gender-matched normal subjects.

MAIN OUTCOME MEASURE

Whole-body protein metabolism was assessed using a 3-h primed constant infusion of 1-[(13)C]leucine, from which rates of leucine appearance (leucine Ra, an index of protein breakdown), leucine oxidation (Lox, index of protein oxidation) and leucine incorporation into protein (LIP, index of protein synthesis) were estimated.

RESULTS

Prednisolone induced an acute significant increase in Lox (P = 0.008) and a fall in LIP (P = 0.08) but did not affect leucine Ra. There was no significant difference between the effects of the 5- and 10-mg prednisolone doses on leucine metabolism. In subjects receiving chronic prednisone therapy, leucine Ra, Lox, and LIP were not significantly different from normal subjects.

CONCLUSION

Glucocorticoids stimulate protein oxidation after acute but not chronic administration. This time-related change suggests that glucocorticoid-induced stimulation of protein oxidation does not persist but that a metabolic adaptation occurs to limit protein loss.

Measurement of endogenous and exogenous triacylglycerol kinetics in the fed and fasted states

Emerging evidence has shown that an abnormal postprandial accumulation of dietary fat is atherogenic. However, there is a lack of data describing the mechanisms for accumulation of triacylglycerol (TAG) in the postprandial period. There is therefore a need to establish a specific measure of the kinetics of endogenous and exogenous TAG in the postprandial period.

Protein metabolism in acromegaly: differential effects of short- and long-term treatment

CONTEXT

GH acutely increases body protein by stimulating protein synthesis and reducing protein oxidation.

OBJECTIVE

The objective of the study was to determine whether these changes in protein metabolism are sustained in long-term GH excess and reversed by correction.

DESIGN

We conducted a cross-sectional study in 16 acromegalic and 18 normal subjects and a longitudinal study in which acromegalic subjects were studied before and after short-term (n=8) or long-term (n=10) treatment.

SETTING

The study was conducted at a clinical research center.

MAIN OUTCOME MEASURES

Whole-body rates of leucine appearance (leucine Ra; an index of protein breakdown), leucine oxidation, and nonoxidative leucine disposal (NOLD; an index of protein synthesis) estimated using infusion of 1-[13C] leucine were measured.

RESULTS

Leucine Ra and NOLD were greater (P<0.01) in acromegalic compared with normal subjects, whereas leucine oxidation did not differ. Leucine oxidation increased significantly (P<0.05) after short-term treatment but returned to baseline after long-term treatment. Both leucine Ra and NOLD decreased significantly (P<0.05) after short- and long-term treatment. Adjustment for body composition did not affect results.

CONCLUSIONS

In acromegalic subjects, protein breakdown and synthesis are increased, whereas protein oxidation does not differ from normal subjects. Protein oxidation increases transiently, whereas protein breakdown and synthesis are stably reduced after treatment. Because protein oxidation represents irreversible loss, we conclude that the normal state of protein oxidation found in acromegaly and after long-term treatment represents metabolic adaptation, which maintains protein mass at a steady state after stable changes in GH status.

Exercise training reduces fatty acid availability and improves the insulin sensitivity of glucose metabolism

AIMS/HYPOTHESIS

It is not known whether the beneficial effects of exercise training on insulin sensitivity are due to changes in hepatic and peripheral insulin sensitivity or whether the changes in insulin sensitivity can be explained by adaptive changes in fatty acid metabolism, changes in visceral fat or changes in liver and muscle triacylglycerol content. We investigated the effects of 6 weeks of supervised exercise in sedentary men on these variables.

SUBJECTS AND METHODS

We randomised 17 sedentary overweight male subjects (age 50 +/- 2.6 years, BMI 27.6 +/- 0.5 kg/m(2)) to a 6-week exercise programme (n = 10) or control group (n = 7). The insulin sensitivity of palmitic acid production rate (Ra), glycerol Ra, endogenous glucose Ra (EGP), glucose uptake and glucose metabolic clearance rate were measured at 0 and 6 weeks with a two-step hyperinsulinaemic-euglycaemic clamp [step 1, 0.3 (low dose); step 2, 1.5 (high dose) mU kg(-1) min(-1)]. In the exercise group subjects were studied >72 h after the last training session. Liver and skeletal muscle triacylglycerol content was measured by magnetic resonance spectroscopy and visceral adipose tissue by cross-sectional computer tomography scanning.

RESULTS

After 6 weeks, fasting glycerol, palmitic acid Ra (p = 0.003, p = 0.042) and NEFA concentration (p = 0.005) were decreased in the exercise group with no change in the control group. The effects of low-dose insulin on EGP and of high-dose insulin on glucose uptake and metabolic clearance rate were enhanced in the exercise group but not in the control group (p = 0.026; p = 0.007 and p = 0.04). There was no change in muscle triacylglycerol and liver fat in either group.

CONCLUSIONS/INTERPRETATION

Decreased availability of circulating NEFA may contribute to the observed improvement in the insulin sensitivity of EGP and glucose uptake following 6 weeks of moderate exercise.

Effects of growth hormone and/or testosterone on very low density lipoprotein apolipoprotein B100 kinetics and plasma lipids in healthy elderly men: a randomised controlled trial

OBJECTIVE

To assess the effects of low dose recombinant growth hormone (GH), testosterone (T) and combined GH and T, on lipid profiles and very low density lipoprotein apolipoprotein B (VLDL apoB) metabolism.

DESIGN AND PATIENTS

Sixty-nine healthy elderly men (65-80 yr) were studied in a six month double-blind, placebo-controlled trial. Participants were randomised to placebo GH and placebo T (P), GH and placebo T (GH), T and placebo GH (T) or GH and T (GHT).

MEASUREMENTS

Plasma lipid profiles were assessed before treatment and at 6 months. VLDL apoB absolute secretion rate (ASR) and fractional catabolic rate (FCR) were measured in a subset of 21 men: P (n=5); GH (n=5); T (n=6); GHT (n=5), with an infusion of 1-(13)C leucine. Fat mass (FM) was measured by DEXA and intra-abdominal fat (IAF) by CT scan.

RESULTS

IGF-I levels increased in the GH and GHT (P<0.001) groups: testosterone increased in the T (P=0.029) and GHT (P=0.05) groups. There was no change in total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, apolipoprotein A-I, apolipoprotein B or lipoprotein(a) in the GH, GHT or T groups. In the subset of 21 men, IGF-I levels increased similarly with GH and GHT (P<0.01) but T levels increased only with T (P<0.03). FM and IAF decreased significantly only with GHT (P<0.01, P=0.01). Treatment with GH, T or GHT had no effect on VLDL apoB ASR or VLDL FCR.

CONCLUSION

Co-administration of GH and T in near physiological doses in healthy elderly men resulted in favourable changes in body composition without altering the plasma lipid profile or VLDL apoB metabolism.

Effects of recombinant human IGF-I/IGF-binding protein-3 complex on glucose and glycerol metabolism in type 1 diabetes

Recombinant human IGF-I (rhIGF-I) complexed with its natural binding protein IGF-binding protein (IGFBP)-3 (rhIGF-I/IGFBP-3) is a novel formulation that has been shown to improve insulin sensitivity in type 1 diabetes, yet the mechanisms are not clear. We used stable isotopes to investigate the effects of rhIGF-I/IGFBP-3 on glucose and glycerol metabolism in type 1 diabetes. Fifteen subjects (age 13-24 years; 10 males) were studied on three occasions in random order. Each study period lasted for two days, and an injection of either placebo or rhIGF-I/IGFBP-3 (0.1-0.8 mg x kg(-1) x day (-1)) was given subcutaneously at 6:00 p.m. on days 1 and 2. Following the second injection, the subjects were kept euglycemic overnight by a variable rate insulin infusion, followed by a 4-h, two-step (insulin 0.6 and 1.5 mU x kg(-1) x min (-1)) hyperinsulinemic-euglycemic clamp. During the overnight basal steady state, rhIGF-I/IGFBP-3 dose-dependently reduced endogenous glucose production rate (R(a)) (P = 0.004), while peripheral glucose uptake (R(d)) was not different from placebo. The increase in glucose R(d) during hyperinsulinemic clamp was greater following rhIGF-I/IGFBP-3 than placebo, both during the first (P = 0.008) and second step (P = 0.008) of the clamp. No significant differences were found in glycerol R(a), a measure of lipolysis, between rhIGF-I/IGFBP-3 and placebo. In conclusion, rhIGF-I/IGFBP-3 enhances glucose metabolism by controlling both endogenous glucose output and peripheral glucose uptake.

Acute regulation of plasma leptin by isoprenaline in lean and obese fasted subjects

AIM

In human obesity, there is some evidence for impaired adrenergic sensitivity with respect to catecholamine-induced lipolysis. The beta-adrenoceptor agonist isoprenaline has been shown to suppress plasma leptin levels in lean humans in vivo. We hypothesized that a reduced adrenergic sensitivity in obese humans would result in impaired suppression of leptin secretion.

METHODS

Eight obese [Ob, body mass index (BMI) = 33.3 kg/m2] and seven lean (Ln, BMI = 21.8 kg/m2) men were studied after an overnight fast. Intravenous isoprenaline infusion was initiated at a rate of 8 ng/kg/min, titrated up to 24 ng/kg/min over 30 min and continued at this rate for a further 120 min with continuous electrocardiogram monitoring.

RESULTS

Baseline fasting plasma leptin was higher in obese compared with lean subjects (Ob 12.2 +/- 1.8, Ln 2.6 +/- 0.6 ng/ml, p < 0.05 unpaired t-test). Baseline fasting glycerol as a measure of lipolysis was similar in both groups (Ob 62.9 +/- 7.6, Ln 42.4 +/- 8.9 micromol/l) and increased from baseline to 150 min by equivalent amounts (Ob +66.9%, Ln +81.2%, p = NS). Plasma leptin decreased from baseline to 150 min with similar relative changes in both groups (Ob -29.2%, Ln -27.8%).

CONCLUSIONS

Obese subjects show a similar lipolytic and leptin response to acute isoprenaline infusion compared with lean subjects. Impaired beta-adrenergic-induced inhibition of leptin secretion does not appear to contribute to hyperleptinaemia in obese human subjects.

Low-density lipoprotein apolipoprotein B100 turnover in hypopituitary patients with GH deficiency: a stable isotope study

BACKGROUND

Epidemiological studies suggest that hypopituitary patients have an increased risk for cardiovascular mortality. The dyslipidaemia associated with this condition is often characterised by an increase in total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol (LDL-C) and may contribute to these findings. The underlying mechanisms are not fully elucidated.

MATERIALS AND METHODS

LDL apolipoprotein B (apoB) production rate and metabolic clearance rate were measured in seven patients with hypopituitarism (including GH deficiency) under stable conventional replacement therapy (three males and four females; age 40-16.1 years; body mass index 29.0-6.1 kg/m(2) (means +/- s.d.)) and seven age-, gender- and body mass index-matched control subjects with an infusion of 1-(13)C-leucine. Fasting lipid profile and lipid composition of LDL were also measured.

RESULTS

Fasting TC, triglycerides (TG), high-density lipoprotein-C, LDL-C and free fatty acid concentrations were not different between hypopituitary patients and control subjects. LDL-TG (P < 0.006) and LDL-TG/LDL apoB ratio (P < 0.02) were significantly increased in hypopituitary patients. LDL apoB pool size was not statistically different between patients and control subjects. In the hypopituitary patients, LDL apoB metabolic clearance rate (P < 0.05) and LDL apoB production rate (P < 0.02) were lower than in the control subjects.

CONCLUSIONS

The present results suggest that LDL apoB turnover and LDL composition is altered in hypopituitary patients. Whether these findings explain the increased risk for cardiovascular disease in hypopituitary patients remains to be established.

In treatment-naïve and antiretroviral-treated subjects with HIV, reduced plasma adiponectin is associated with a reduced fractional clearance rate of VLDL, IDL and LDL apolipoprotein B-100

AIMS/HYPOTHESIS

We hypothesised that loss of peripheral fat in HIV patients would result in decreased plasma adipocytokines, in particular adiponectin, and that this decrease would be associated with changes in VLDL, IDL and LDL apolipoprotein B kinetics.

METHODS

Plasma adiponectin, leptin and other cytokines were measured in uninfected control subjects (n=12) and three HIV-positive groups comprising treatment-naïve patients (n=15) and patients on triple antiretroviral therapy containing protease inhibitors (PI, n=15) or non-nucleoside reverse transcriptase inhibitors (NNRTI, n=25). VLDL, IDL and LDL apolipoprotein B kinetics were measured with an infusion of [1-(13)C] leucine. Regional body fat was measured with a dual energy X-ray absorptiometry scan. Insulin resistance was calculated using homeostasis model assessment (HOMA).

RESULTS

Adiponectin (median [interquartile range]) was reduced in the treatment-naive (5.4 microg/ml [4.7-8.5]), PI (5.0 microg/ml [3.3-6.4]) and NNRTI (5.0 microg/ml [3.1-6.7]) groups compared with controls (9.7 microg/ml [6.9-13.3]) (p<0.05). In all subjects adiponectin correlated positively with HDL-cholesterol levels, the VLDL, IDL and LDL apolipoprotein B fractional clearance rates, and with the limb fat:lean body mass ratio (all p<0.01). Adiponectin correlated negatively with plasma triglyceride levels and HOMA (p<0.001). In a linear regression model that included HOMA, adiponectin was an independent predictor of VLDL and HDL-cholesterol levels and the IDL fractional clearance rate. TNF was higher in treatment-naive and PI subjects, and soluble TNF receptor superfamily, members 1A and 1B (previously known as TNF receptors 1 and 2) was higher in PI patients than in control subjects (p<0.05).

CONCLUSIONS/INTERPRETATION

Adiponectin levels are significantly reduced in treated and untreated HIV patients and are predictive of VLDL and IDL apolipoprotein B fractional clearance rates. Adiponectin may have a direct effect on lipoprotein metabolism, which may be independent of insulin.

Contrasting insulin sensitivity of endogenous glucose production rate in subjects with hepatocyte nuclear factor-1beta and -1alpha mutations

Heterozygous mutations in the transcription factors hepatocyte nuclear factor (HNF)-1alpha and -1beta result in MODY (maturity-onset diabetes of the young). Despite structural similarity between HNF-1alpha and -1beta, HNF-1beta mutation carriers have hyperinsulinemia, whereas HNF-1alpha mutation carriers have normal or reduced insulin concentrations. We examined whether HNF-1beta mutation carriers are insulin resistant. The endogenous glucose production rate and rate of glucose uptake were measured with a two-step, low-dose (0.3 mU . kg(-1) . min(-1)) and high-dose (1.5 mU . kg(-1) . min(-1)) hyperinsulinemic-euglycemic clamp, with an infusion of [6,6-(2)H(2)]glucose, in six subjects with HNF-1alpha mutations, six subjects with HNF-1beta mutations, and six control subjects, matched for age, sex, and BMI. Endogenous glucose production rate was not suppressed by low-dose insulin in HNF-1beta subjects but was suppressed by 89% in HNF-1alpha subjects (P = 0.004) and 80% in control subjects (P < 0.001). Insulin-stimulated glucose uptake and suppression of lipolysis were similar in all groups at low- and high-dose insulin. Subjects with HNF-1beta mutations have reduced insulin sensitivity of endogenous glucose production but normal peripheral insulin sensitivity. This is likely to reflect reduced action of HNF-1beta in the liver and possibly the kidney. This may be mediated through regulation by HNF-1beta of the key gluconeogenic enzymes glucose-6-phosphatase or PEPCK.

Effects of high-dose growth hormone on glucose and glycerol metabolism at rest and during exercise in endurance-trained athletes

CONTEXT

Recombinant human-GH (r-hGH), in supraphysiological doses, is self-administered by athletes in the belief that it is performance enhancing.

OBJECTIVE

The objective of this study was to determine whether r-hGH alters whole-body glucose and glycerol metabolism in endurance-trained athletes at rest and during and after exercise.

DESIGN

This was a 4-wk double-blind placebo-controlled trial.

SETTING

This study was conducted at St. Thomas Hospital (London, UK).

PARTICIPANTS

Twelve endurance-trained male athletes were recruited and randomized to r-hGH (0.2 U/kg.d) (n = 6) or identical placebo (n = 6) for 4 wk. One (placebo group) withdrew after randomization.

INTERVENTION

Intervention was conducted by randomization to r-hGH (0.2 U/kg x d) or identical placebo for 4 wk.

MAIN OUTCOME MEASURES

Whole-body rates of appearance (Ra) of glucose and glycerol (an index of lipolysis) and rate of disappearance of glucose were measured using infusions of d-[6-6-2H2]glucose and 2H5-glycerol.

RESULTS

Plasma levels of glycerol and free fatty acids and glycerol Ra at rest and during and after exercise increased during r-hGH treatment (P < 0.05 vs. placebo). Glucose Ra and glucose rate of disappearance were greater after exercise during r-hGH treatment (P < 0.05 vs. placebo). Resting energy expenditure and fat oxidation were greater under resting conditions during r-hGH treatment (P < 0.05 vs. placebo).

CONCLUSIONS

r-hGH in endurance-trained athletes increased lipolysis and fatty acid availability at rest and during and after exercise. r-hGH increased glucose production and uptake rates after exercise. The relevance of these effects for athletic performance is not known.

GH secretion in acute exercise may result in post-exercise lipolysis

Exercise is a potent stimulator of growth hormone (GH) secretion. We hypothesised that after a short bout of intense exercise GH may increase lipolysis during recovery. In 7 moderately trained young male subjects (21.8 +/- 0.5 years) and 7 moderately trained older male subjects (56.0 +/- 1.0 years) [(2)H(5)] glycerol was infused for 370min to measure glycerol production rate (R(a)), a measure of lipolysis. At 130 min subjects exercised on a cycle ergonometer for 20 min at 70% V(O2 max), followed by rest for 220 min. On a separate occasion the study was repeated in the young subjects with a 1h GH infusion (4microgkg(-1)h(-1)) at 130 min instead of exercise. In response to exercise, catecholamines (p < 0.02) and glycerol R(a) (p < 0.01) increased, peaking during exercise. GH concentration increased in response to exercise (p < 0.01), peaking after exercise (150-160 min) in both groups with no significant difference in peak response between groups. A post-exercise rise in glycerol R(a) was demonstrated in both groups peaking at 265-295 min in the older group (p < 0.002, peak vs. basal) and continuing to rise until 370 min in the young group (p < 0.01, peak vs. basal). The timing and magnitude of this was reproduced with the GH infusion. There was a significant correlation between the peak GH response to exercise and the post-exercise rise in glycerol R(a) measured as area under the curve (r=0.57, p < 0.04). In conclusion, this study provides evidence that the GH response to acute exercise may increase lipolysis during recovery.

Growth hormone and testosterone interact positively to enhance protein and energy metabolism in hypopituitary men

We investigated the impact of growth hormone (GH) alone, testosterone (T) alone, and combined GH and T on whole body protein metabolism. Twelve hypopituitary men participated in two studies. Study 1 compared the effects of GH alone with GH plus T, and study 2 compared the effects of T alone with GH plus T. IGF-I, resting energy expenditure (REE), and fat oxidation (F(ox)) and rates of whole body leucine appearance (R(a)), oxidation (L(ox)), and nonoxidative leucine disposal (NOLD) were measured. In study 1, GH treatment increased mean plasma IGF-I (P < 0.001). GH did not change leucine R(a) but reduced L(ox) (P < 0.02) and increased NOLD (P < 0.02). Addition of T resulted in an additional increase in IGF-I (P < 0.05), reduction in Lox (P < 0.002), and increase in NOLD (P < 0.002). In study 2, T alone did not alter IGF-I levels. T alone did not change leucine R(a) but reduced L(ox) (P < 0.01) and increased NOLD (P < 0.01). Addition of GH further reduced L(ox) (P < 0.05) and increased NOLD (P < 0.05). In both studies, combined treatments on REE and F(ox) were greater than either alone. In summary, GH-induced increase of circulating IGF-I is augmented by T, which does not increase IGF-I in the absence of GH. T and GH exerted independent and additive effects on protein metabolism, F(ox) and REE. The anabolic effects of T are independent of circulating IGF-I.

Low Density Lipoprotein Apolipoprotein B Metabolism in Treatment-Naive HIV Patients and Patients on Antiretroviral Therapy

Background

Dyslipidaemia and lipodystrophy have been described in treated HIV patients and in a small percentage of untreated HIV patients. Lipodystrophy in these patients has been shown to be associated with a lower expression of low density lipoprotein (LDL) receptors.

Methods

We have investigated the effect of antiretroviral treatment with either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) on body fat distribution and LDL apolipoprotein B (apoB) kinetics in 12 HIV-negative controls and 52 HIV-infected patients, including antiretroviral treatment-naive (TN) patients ( n=13) and patients taking two nucleoside analogues plus either a PI ( n=15) or an NNRTI ( n=24).

Results

LDL cholesterol was not different between groups. Compared with the controls, LDL apoB absolute synthetic rate (ASR) and fractional catabolic rate (FCR) were lower and residence time (RT) was higher in the PI and NNRTI groups ( P<0.05). In the TN patients, LDL ASR was lower ( P<0.05) and there was a trend for a lower FCR and higher RT compared with the controls ( P=0.07). LDL apoB pool size was greater in the PI group compared with the controls ( P<0.05). In the PI group, patients on ritonavir (RTV)-containing regimens had a lower LDL apoB ASR ( P=0.009) and a trend to a lower LDL apoB FCR and increased RT compared with non-RTV-containing PI regimens ( P=0.05). There was a positive correlation between LDL apoB FCR and limb fat/lean body mass ( P=0.004) in all subjects.

Conclusions

Decreased LDL FCR, despite unchanged LDL cholesterol, was demonstrated in both treated and untreated HIV patients. It was more marked with RTV-containing regimens and was associated with reduced limb fat. The increased LDL RT may lead to an increased risk of atherogenesis thus contributing to the risk for cardiovascular disease in these patients.

Comparison of the effects on glucose and lipid metabolism of equipotent doses of insulin detemir and NPH insulin with a 16-h euglycaemic clamp

AIMS/HYPOTHESIS

The association of insulin detemir with non-esterified fatty acid binding sites on albumin may limit its transfer from the circulation into the extravascular extracellular space in adipose tissue and muscle, due to the capillary endothelial cell barrier. In the liver, the open sinusoids may expose hepatocytes to insulin detemir, enabling it to have a greater effect in the liver than in peripheral tissues.

METHODS

We investigated the effects of equipotent doses of insulin detemir and NPH insulin on hepatic glucose rate of appearance (Ra), peripheral glucose rate of disposal (Rd) and glycerol Ra (a measure of lipolysis) using stable isotope techniques. We also investigated the effects of these insulins on NEFA concentrations in seven healthy volunteers during a 16-h euglycaemic clamp. A higher dose of insulin detemir was also studied.

RESULTS

There was no difference in the glucose infusion profile between insulin detemir and NPH. Insulin detemir had a greater effect on mean suppression of glucose Ra (mean difference 0.24 mg kg(-1) min(-1); CI 0.09-0.39; p<0.01), and minimum glucose Ra, with minimum low dose detemir -0.10+/-0.15 mg.kg(-1).min(-1) and minimum NPH 0.17+/-0.10 mg.kg(-1).min(-1) (p<0.02). However, it had a lesser effect on mean suppression of NEFA concentrations (mean difference -0.10 mmol/l; CI -0.03 to -0.17; ANOVA, p<0.02) than NPH. The effect of insulin detemir on glucose Rd and glycerol Ra was not different from NPH. Following high-dose detemir, total glucose infused and maximum glucose Rd were higher (p<0.02, p<0.03) and plasma NEFA concentrations lower (p<0.01) than with low-dose determir.

CONCLUSIONS/INTERPRETATION

This study suggests that insulin detemir, when compared to NPH insulin, has a greater effect on the liver than on peripheral tissues and thus has the potential to restore the physiological insulin gradient.

Antiretroviral treatment reduces very-low-density lipoprotein and intermediate-density lipoprotein apolipoprotein B fractional catabolic rate in human immunodeficiency virus-infected patients with mild dyslipidemia

The relationship between antiretroviral treatment of HIV infection, body fat distribution, insulin resistance, and very-low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) apolipoprotein-B (apoB) kinetics was investigated in 55 HIV-infected patients taking two nucleoside analogs plus either a protease inhibitor (n = 15) or a nonnucleoside reverse transcriptase inhibitor (n = 25), 15 antiretroviral therapy-naive patients, and 12 HIV-negative controls. Compared with the controls, high-density lipoprotein cholesterol was reduced in all groups (P < 0.01). Plasma triglyceride was increased in patients taking protease inhibitors (P < 0.05). VLDL and IDL apoB fractional catabolic rate (FCR) was lower in all treatment groups (P < 0.05) compared with controls. Trunk fat, VLDL apoB absolute secretion rate, and insulin resistance were not different between groups. Peripheral fat was lower in the treated patients (P < 0.05) and correlated with duration of therapy (r = -0.55; P < 0.001). There was a positive correlation between peripheral fat and VLDL apoB FCR (P = 0.002) and IDL apoB FCR (P = 0.002) and a negative correlation with VLDL apoB pool size, VLDL cholesterol, and triglyceride (P < 0.03; P < 0.01; P < 0.002). These results suggest that mild dyslipidemia resulting from antiretroviral therapy is caused by a decrease in VLDL and IDL apoB FCR, which is associated with a loss of peripheral fat.

Low density lipoprotein apolipoprotein B metabolism in treatment-naive HIV patients and patients on antiretroviral therapy

BACKGROUND

Dyslipidaemia and lipodystrophy have been described in treated HIV patients and in a small percentage of untreated HIV patients. Lipodystrophy in these patients has been shown to be associated with a lower expression of low density lipoprotein (LDL) receptors.

METHODS

We have investigated the effect of antiretroviral treatment with either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) on body fat distribution and LDL apolipoprotein B (apoB) kinetics in 12 HIV-negative controls and 52 HIV-infected patients, including antiretroviral treatment-naive (TN) patients (n=13) and patients taking two nucleoside analogues plus either a PI (n=15) or an NNRTI (n=24).

RESULTS

LDL cholesterol was not different between groups. Compared with the controls, LDL apoB absolute synthetic rate (ASR) and fractional catabolic rate (FCR) were lower and residence time (RT) was higher in the PI and NNRTI groups (P<0.05). In the TN patients, LDL ASR was lower (P<0.05) and there was a trend for a lower FCR and higher RT compared with the controls (P=0.07). LDL apoB pool size was greater in the PI group compared with the controls (P<0.05). In the PI group, patients on ritonavir (RTV)-containing regimens had a lower LDL apoB ASR (P=0.009) and a trend to a lower LDL apoB FCR and increased RT compared with non-RTV-containing PI regimens (P=0.05). There was a positive correlation between LDL apoB FCR and limb fat/lean body mass (P=0.004) in all subjects.

CONCLUSIONS

Decreased LDL FCR, despite unchanged LDL cholesterol, was demonstrated in both treated and untreated HIV patients. It was more marked with RTV-containing regimens and was associated with reduced limb fat. The increased LDL RT may lead to an increased risk of atherogenesis thus contributing to the risk for cardiovascular disease in these patients.

Dose-dependent effects of recombinant human insulin-like growth factor (IGF)-I/IGF binding protein-3 complex on overnight growth hormone secretion and insulin sensitivity in type 1 diabetes

GH hypersecretion in type 1 diabetes has been implicated in the pathogenesis of insulin resistance, and microangiopathic complications, and may result from reduced circulating IGF levels. We examined the effects of recombinant human (rh)IGF-I [complexed in equimolar ratio with rhIGF binding protein (BP)-3 (rhIGF-I/IGFBP-3)] replacement on overnight GH levels and insulin sensitivity in type 1 diabetes. Fifteen subjects, 13-24 yr old (10 male), were given rhIGF-I/IGFBP-3 or placebo as a daily sc injection for 2 d. After the second injection overnight, insulin requirements for euglycemia were determined (0400-0800 h), followed by a 4-h, two-step (insulin, 0.6 and 1.5 mU/kg.min) hyperinsulinemic euglycemic [90 mg/dl (5 mmol/liter)] clamp. In each subject, the protocol was repeated on three occasions in random order. Seven subjects received placebo and rhIGF-I/IGFBP-3 (0.1 mg/kg.d and 0.4 mg/kg.d), and eight subjects received placebo and rhIGF-I/IGFBP-3 (0.2 mg/kg.d and 0.8 mg/kg.d). We found dose-dependent increases in circulating IGF-I and IGFBP-3 concentrations after rhIGF-I/IGFBP-3. These were paralleled by significant reductions in mean overnight GH levels and GH pulse amplitude. We also observed dose-dependent effects of rhIGF-I/IGFBP-3 on overnight insulin requirements for euglycemia, with reductions of up to 41%. Insulin sensitivity, defined by M-values, was improved with rhIGF-I/IGFBP-3 (0.4 and 0.8 mg/kg.d). Thus, restoration of circulating IGF-I and IGFBP-3 levels with rhIGF-I/IGFBP-3 suppresses GH secretion in adolescents with type 1 diabetes, leading to reduced insulin requirements and improvements in insulin sensitivity.

A family with severe insulin resistance and diabetes due to a mutation in AKT2

Inherited defects in signaling pathways downstream of the insulin receptor have long been suggested to contribute to human type 2 diabetes mellitus. Here we describe a mutation in the gene encoding the protein kinase AKT2/PKBbeta in a family that shows autosomal dominant inheritance of severe insulin resistance and diabetes mellitus. Expression of the mutant kinase in cultured cells disrupted insulin signaling to metabolic end points and inhibited the function of coexpressed, wild-type AKT. These findings demonstrate the central importance of AKT signaling to insulin sensitivity in humans.

Effects of growth hormone (GH) replacement therapy on low-density lipoprotein apolipoprotein B100 kinetics in adult patients with GH deficiency: a stable isotope study

GH replacement therapy has been shown to improve the dyslipidemic condition in a substantial proportion of patients with adult GH deficiency. The mechanisms are not yet fully elucidated. Low-density lipoprotein (LDL) apolipoprotein B100 (apoB) formation and catabolism are important determinants of plasma cholesterol concentrations. This study examined the effect of GH replacement therapy on LDL apoB metabolism using a stable isotope turnover technique. LDL apoB kinetics was determined in 13 adult patients with GH deficiency before and after 3 months GH/placebo treatment in a randomized, double-blind, placebo-controlled study. LDL apoB (13)C-leucine enrichment was determined by isotope-ratio mass spectrometry. Plasma volume was assessed by standardized radionuclide dilution technique. GH replacement therapy significantly decreased LDL cholesterol, LDL apoB concentrations, and LDL apoB pool size compared with placebo. Compared with baseline, GH replacement therapy resulted in a significant increase in plasma volume and fractional catabolic rate, whereas LDL formation rate remained unchanged. LDL lipid content did not significantly change after GH and placebo. This study suggests that short-term GH replacement therapy decreases the LDL apoB pool by increasing removal of LDL particles without changing LDL composition or LDL apoB production rate. In addition, it is possible that the beneficial effects of GH on the cardiovascular system contribute to these findings.

The effect of a six-month exercise program on very low-density lipoprotein apolipoprotein B secretion in type 2 diabetes

The dyslipidemia and insulin resistance of type 2 diabetes can be improved by aerobic exercise. The effect of 6 months supervised exercise on very low-density lipoprotein (VLDL) apolipoprotein B metabolism was investigated in patients with type 2 diabetes. Moderately obese patients (n = 18) were randomized into supervised (n = 9) and unsupervised (n = 9) exercise groups. All patients were given a training session and a personal exercise program and asked to exercise four times per week at 70% maximal oxygen uptake for 6 months. Patients in the supervised group had a weekly session with an exercise trainer. VLDL apolipoprotein (apo)B metabolism was measured with an infusion of 1-(13)C leucine before and after 6 months of the exercise program. Supervised exercise for 6 months resulted in a significant within-group decrease in percent hemoglobin A1c (P < 0.001), body fat (P < 0.004), nonesterified fatty acid (P < 0.04), and triglycerides (P < 0.05) and an increase in insulin sensitivity (P < 0.01). There was a decrease in VLDL apoB pool size (160.8 +/- 42.6 to 84.9 +/- 23.2 mg, P < 0.01) and VLDL apoB secretion rate (11.3 +/- 2.6 to 5.5 +/- 2.0 mg/kg.d, P < 0.05) with no change in fractional catabolic rate. In a between-group comparison, the decrease in VLDL apoB secretion rate in the supervised group did not achieve significance. This study demonstrates that in type 2 diabetes, a supervised exercise program reduces VLDL apoB pool size, which may be due to a decrease in VLDL apoB secretion rate.

Insulin-like growth factor I has a direct effect on glucose and protein metabolism, but no effect on lipid metabolism in type 1 diabetes

There is evidence of a metabolic role for IGF-I in type 1 diabetes, but it is unclear whether IGF-I acts indirectly by reducing GH secretion or has direct effects. Using stable isotopes we have investigated, on three separate occasions, the effect of a pulse of recombinant human GH, a sc injection of recombinant human IGF-I, and a placebo on glucose, lipid, and protein metabolism in subjects with type 1 diabetes during a basal insulin infusion and a hyperinsulinemic euglycemic clamp. Endogenous GH secretion was suppressed with octreotide. IGF-I reduced the hepatic glucose production rate (Ra), increased peripheral glucose uptake, and reduced protein breakdown during the basal insulin infusion (P < 0.05, P < 0.005, and P < 0.05, respectively, vs. placebo) and the hyperinsulinemic euglycemic clamp (P < 0.05, P < 0.005, and P < 0.05, respectively, vs. placebo). IGF-I had no effect on glycerol Ra, an index of lipolysis. GH increased glucose and glycerol Ra during the basal insulin infusion (P < 0.005 vs. placebo study), but the effects were no different from placebo during the clamp. In conclusion, IGF-I had a direct effect on glucose and protein metabolism, which was maintained during the hyperinsulinemic euglycemic clamp. This suggests that IGF-I acts in concert with insulin and may have an important role in maintaining glucose homeostasis and protein metabolism in type 1 diabetes.

Combined growth hormone/insulin-like growth factor I in addition to glutamine-supplemented TPN results in net protein anabolism in critical illness

Protein loss leading to reduced lean body mass is recognized to contribute to the high levels of morbidity and mortality seen in critical illness. This prospective, randomized, controlled study compared the effects of conventional parenteral nutrition (TPN), glutamine-supplemented (0.4 g.kg-1.day-1) TPN (TPNGLN), and TPNGLN with combined growth hormone (GH, 0.2 IU.kg-1.day-1) and IGF-I (160 microg.kg-1.day-1) on protein metabolism in critical illness. Nineteen mechanically ventilated subjects [64 +/- 3 yr, body mass index (BMI) 23.8 +/- 1.3, kg/m2] were initially studied in the fasting state (study 1) and subsequently after 3 days of nutritional with/without hormonal support (study 2). All had recently been admitted to the ICU and the majority were postemergency abdominal surgery (APACHE II 17.5 +/- 1.0). Protein metabolism was assessed using a primed constant infusion of [1-13C]leucine. Conventional TPN contained mixed amino acids, Intralipid, and 50% dextrose. TPNGLN, unlike TPN alone, resulted in an increase in plasma glutamine concentration ( approximately 50%, P < 0.05). Both TPN and TPNGLN decreased the rate of protein breakdown (TPN 15%, P < 0.002; TPNGLN 16%, P < 0.05), but during these treatments the patients remained in a net negative protein balance. Combined treatment with TPNGLN + GH/IGF-I increased plasma IGF-I levels (10.3 +/- 0.8 vs. 48.1 +/- 9.1 nmol/l, study 1 vs. study 2, P < 0.05), and in contrast to therapy with nutrition alone, resulted in net protein gain (-0.75 +/- 0.14 vs. 0.33 +/- 0.12 g protein.kg-1.day-1, study 1 vs. study 2, P < 0.05). Therapy with GH/IGF-I + TPNGLN, unlike nutrition alone, resulted in net positive protein balance in a group of critically ill patients.

High dose growth hormone exerts an anabolic effect at rest and during exercise in endurance-trained athletes

The anabolic actions of GH in GH-deficient adults and children are well documented. Replacement with GH in such individuals promotes protein synthesis and reduces irreversible loss of protein through oxidation. Although GH is known to be self-administered by athletes, its protein metabolic effects in this context are unknown. This study was designed to determine whether 4 wk of high dose recombinant human GH (r-hGH) administration altered whole body leucine kinetics in endurance-trained athletes at rest and during and after 30 min of exercise at 60% of maximal oxygen uptake. Eleven endurance-trained male athletes were studied, six randomized to receive r-hGH (0.067 mg/kg.d), and five to receive placebo. Whole body leucine turnover was measured at rest and during and after exercise, using a 5-h primed constant infusion of 1-[(13)C]leucine, from which rates of leucine appearance (an index of protein breakdown), leucine oxidation, and nonoxidative leucine disposal (an index of protein synthesis) were estimated. Under resting conditions, r-hGH administration increased rate of leucine appearance and nonoxidative leucine disposal, and reduced leucine oxidation (P < 0.01). This effect was apparent after 1 wk, and was accentuated after 4 wk, of r-hGH administration (P < 0.05). During and after exercise, GH attenuated the exercise-induced increase in leucine oxidation (P < 0.05). There were no changes observed in placebo-treated subjects compared with the baseline study. We conclude that GH administration to endurance-trained male athletes has a net anabolic effect on whole body protein metabolism at rest and during and after exercise.

The effects of a specific growth hormone antagonist on overnight insulin requirements and insulin sensitivity in young adults with Type 1 diabetes mellitus

AIMS/HYPOTHESIS

Growth hormone hypersecretion in Type 1 diabetes could exacerbate insulin resistance and contribute to declining glycaemic control. Our aim was to determine the effects of specific growth hormone blockade on insulin sensitivity and lipolysis in young adults with Type 1 diabetes.

METHODS

We studied the effects of two doses of a specific growth hormone antagonist (B2036-PEG; Somavert, Pharmacia Corporation, Milton Keynes, UK) on insulin sensitivity in seven young adults (17-22 yrs, 3M) with Type 1 diabetes. Subjects received 5 and 10 mg B2036-PEG, in random order for 3 weeks, with a 3-week washout. At baseline and following each treatment block, an overnight (03:00 to 08:00 h) insulin infusion for euglycaemia (5 mmol/l), followed by two-step hyperinsulinaemic euglycaemic clamp, using [6,6 2H2] glucose and 2H5 glycerol to measure glucose and glycerol turnover was performed.

RESULTS

Compared to baseline, overnight insulin requirements decreased with both doses: (means+/-SEM) 0.34+/-0.02 mU/Kg/min vs 0.25+/-0.01 (5 mg) (p=0.04), and 0.24+/-0.01 (10 mg) (p=0.004). IGF-I (ng/ml) decreased following 10 mg [223.5+/-23.9 vs 154.6+/-28.1 (p=0.005], but not 5 mg. Mean overnight non esterified fatty acid concentrations (mmol/l) decreased with 10 mg [0.51+/-0.04 vs 0.38+/-0.04 (p=0.03)], as did beta-hydroxybutyrate (mmol/l); [0.31+/-0.04 vs 0.15+/-0.02 (p=0.004)]. Glycerol production rate, an index of lipolysis, was lower following 10 mg (p=0.04), but insulin sensitivity during the clamp did not change with either dose.

CONCLUSION/INTERPRETATION

Treatment with both doses of B2036-PEG reduced overnight insulin requirements. The 10 mg dose suppressed lipolysis and reduced IGF-I. Failure to show enhanced insulin sensitivity during the clamp with the 10 mg dose could reflect opposing actions of growth hormone and IGF-I.

Effect of growth hormone (GH) on glycerol and free fatty acid metabolism during exhaustive exercise in GH-deficient adults

GH is an important regulator of fat metabolism at rest, but it is not known whether it regulates fat metabolism during exercise. To determine whether physiologic concentrations of GH influence fat metabolism during exercise, we randomized 16 GH-deficient adults, receiving long-term (mean duration, 5 yr) GH replacement, to either continue GH (n = 8) or receive identical placebo (n = 8) for a 3-month period. Metabolic studies, at rest, during and following exhaustive exercise were carried out at baseline and at the end of the 3 months. The rate of appearance of glycerol (glycerol Ra, an index of lipolysis) and free fatty acids (FFA, FFA Ra) and the rate of disappearance of FFA (FFA Rd) in the plasma were measured using infusions of (2)H(5)-glycerol and 1-(13)C-palmitic acid. Changes in body composition were assessed using dual-energy x-ray absorptiometry scanning and anthropometric measurements. In the baseline studies, exercise resulted in an increase in plasma glycerol and FFA concentrations, glycerol Ra, FFA Ra, and FFA Rd (P < 0.001). Three months of GH withdrawal resulted in reductions in plasma glycerol and FFA, glycerol Ra, FFA Ra, and FFA Rd at rest (P < 0.05 vs. baseline) and during exercise (P < 0.05 vs. baseline and vs. GH treated). Lean body mass decreased after 3 months of GH withdrawal, but total body fat, trunk fat, waist circumference, and the sum of skinfold thicknesses increased after 3 months of GH withdrawal (P < 0.05 vs. baseline and vs. GH treated). Fasting insulin and homeostasis model assessment of insulin resistance decreased after 3 months of GH withdrawal (P < 0.05 vs. baseline and vs. GH treated). In summary, GH withdrawal for 3 months resulted in reductions in release of glycerol and FFA into the circulation and uptake of FFA into the tissues during intense exercise. These changes were accompanied by reduced lean body mass and increased total body and trunk fat. Further studies are required to determine whether reduced mobilization of fat during exercise contributes to reduced exercise capacity and increased body fat in GH-deficient adults.

Human metabolic syndrome resulting from dominant-negative mutations in the nuclear receptor peroxisome proliferator-activated receptor-gamma

We previously reported a syndrome of severe hyperinsulinemia and early-onset hypertension in three patients with dominant-negative mutations in the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-gamma. We now report the results of further detailed pathophysiological evaluation of these subjects, the identification of affected prepubertal children within one of the original families, and the effects of thiazolidinedione therapy in two subjects. These studies 1) definitively demonstrate the presence of severe peripheral and hepatic insulin resistance in the affected subjects; 2) describe a stereotyped pattern of partial lipodystrophy associated with all the features of the metabolic syndrome and nonalcoholic steatohepatitis; 3) document abnormalities in the in vivo function of remaining adipose tissue, including the inability of subcutaneous abdominal adipose tissue to trap and store free fatty acids postprandially and the presence of very low circulating levels of adiponectin; 4) document the presence of severe hyperinsulinemia in prepubertal carriers of the proline-467-leucine (P467L) PPAR-gamma mutation; 5) provide the first direct evidence of cellular resistance to PPAR-gamma agonists in mononuclear cells derived from the patients; and 6) report on the metabolic response to thiazolidinedione therapy in two affected subjects. Although the condition is rare, the study of humans with dominant-negative mutations in PPAR-gamma can provide important insight into the roles of this nuclear receptor in human metabolism.

The role of hepatic portal glucose sensing in modulating responses to hypoglycaemia in man

AIMS/HYPOTHESIS

The role of glucose sensing cells in the human hepatic portal system in the initiation of the neuroendocrine responses to acute hypoglycaemia is not known. We investigated the effect of raising blood glucose concentrations in the hepatic-portal vein on neurohumoral responses during induction of systemic hypoglycaemia in nine healthy male volunteers.

METHODS

Each subject received an insulin infusion (3 mU.kg(-1).min(-1)) on two occasions, in random order. Variable rate glucose infusion was used to maintain plasma glucose at 5 mmol/l for 60 min, then 3.2 mmol/l for 60 min. At 20 min prior to hypoglycaemia, subjects drank 20 g of glucose in water or water sweetened with saccharin. In five of the volunteers, the oral glucose was labelled with U-13C6 glucose, which showed peak systemic glucose absorption between 90 and 110 min. Five volunteers also repeated the study with a euglycaemic clamp.

RESULTS

Oral glucose was associated with a reduction in the early adrenaline response to hypoglycaemia, the area under the curve from 90 to 110 min falling from 24.02+/-20.84 (means +/- SD) to 15.26+/-13.65 nmol/l per 20 min, p<0.05. Symptom scores (area under curve) decreased from 99.72+/-91.86 to 16.39+/-94.71, p=0.008 (total), 51.8+/-68.61 to 7.78+/-41.61, p=0.03 (autonomic) and 54.17+/-50.61 to 8.6+/-57.99 with oral glucose, p=0.001 (neuroglycopenic). Oral glucose did not influence symptoms during euglycaemia.

CONCLUSION/INTERPRETATION

Our data are compatible with the hypothesis that centrally mediated symptomatic and neuroendocrine responses are attenuated by glucose detection in the hepatic portal vein in humans.

Partitioning glucose distribution/transport, disposal, and endogenous production during IVGTT

We have separated the effect of insulin on glucose distribution/transport, glucose disposal, and endogenous production (EGP) during an intravenous glucose tolerance test (IVGTT) by use of a dual-tracer dilution methodology. Six healthy lean male subjects (age 33 +/- 3 yr, body mass index 22.7 +/- 0.6 kg/m(2)) underwent a 4-h IVGTT (0.3 g/kg glucose enriched with 3-6% D-[U-(13)C]glucose and 5-10% 3-O-methyl-D-glucose) preceded by a 2-h investigation under basal conditions (5 mg/kg of D-[U-(13)C]glucose and 8 mg/kg of 3-O-methyl-D-glucose). A new model described the kinetics of the two glucose tracers and native glucose with the use of a two-compartment structure for glucose and a one-compartment structure for insulin effects. Insulin sensitivities of distribution/transport, disposal, and EGP were similar (11.5 +/- 3.8 vs. 10.4 +/- 3.9 vs. 11.1 +/- 2.7 x 10(-2) ml small middle dot kg(-1) small middle dot min(-1) per mU/l; P = nonsignificant, ANOVA). When expressed in terms of ability to lower glucose concentration, stimulation of disposal and stimulation of distribution/transport accounted each independently for 25 and 30%, respectively, of the overall effect. Suppression of EGP was more effective (P < 0.01, ANOVA) and accounted for 50% of the overall effect. EGP was suppressed by 70% (52-82%) (95% confidence interval relative to basal) within 60 min of the IVGTT; glucose distribution/transport was least responsive to insulin and was maximally activated by 62% (34-96%) above basal at 80 min compared with maximum 279% (116-565%) activation of glucose disposal at 20 min. The deactivation of glucose distribution/transport was slower than that of glucose disposal and EGP (P < 0.02) with half-times of 207 (84-510), 12 (7-22), and 29 (16-54) min, respectively. The minimal-model insulin sensitivity was tightly correlated with and linearly related to sensitivity of EGP (r = 0.96, P < 0.005) and correlated positively but nonsignificantly with distribution/transport sensitivity (r = 0.73, P = 0.10) and disposal sensitivity (r = 0.55, P = 0.26). We conclude that, in healthy subjects during an IVGTT, the two peripheral insulin effects account jointly for approximately one-half of the overall insulin-stimulated glucose lowering, each effect contributing equally. Suppression of EGP matches the effect in the periphery.

Effect of IGF-I therapy on VLDL apolipoprotein B100 metabolism in type 1 diabetes mellitus

Abnormal lipid metabolism may be related to the increased cardiovascular risk in type 1 diabetes. Secretion and clearance rates of very low density lipoprotein (VLDL) apolipoprotein B100 (apoB) determine plasma lipid concentrations. Type 1 diabetes is characterized by increased growth hormone (GH) secretion and decreased insulin-like growth factor (IGF) I concentrations. High-dose IGF-I therapy improves the lipid profile in type 1 diabetes. This study examined the effect of low-dose (40 microg.kg(-1).day(-1)) IGF-I therapy on VLDL apoB metabolism, VLDL composition, and the GH-IGF-I axis during euglycemia in type 1 diabetes. Using a stable isotope technique, VLDL apoB kinetics were estimated before and after 1 wk of IGF-I therapy in 12 patients with type 1 diabetes in a double-blind, placebo-controlled trial. Fasting plasma triglyceride (P < 0.03), VLDL-triglyceride concentrations (P < 0.05), and the VLDL-triglyceride-to-VLDL apoB ratio (P < 0.002) significantly decreased after IGF-I therapy, whereas VLDL apoB kinetics were not significantly affected by IGF-I therapy. IGF-I therapy resulted in a significant increase in IGF-I and a significant reduction in GH concentrations. The mean overnight insulin concentrations during euglycemia decreased by 25% after IGF-I therapy. These results indicate that low-dose IGF-I therapy restores the GH-IGF-I axis in type 1 diabetes. IGF-I therapy changes fasting triglyceride concentrations and VLDL composition probably because of an increase in insulin sensitivity.

Normal VLDL metabolism despite altered lipoprotein composition in type 1 diabetes mellitus

OBJECTIVES

Patients with type 1 diabetes are at increased risk of cardiovascular disease, which may be related to abnormal lipid metabolism. Secretion and clearance of VLDL apolipoprotein B100 (apoB) are important determinants of plasma lipid concentrations and are known to be influenced by hormones, including insulin and growth hormone.

PATIENTS

This study examined overnight VLDL apoB metabolism and VLDL composition in six lean patients with type 1 diabetes during euglycaemia (controlled by a varying insulin infusion) and in six age-, sex- and BMI-matched control subjects.

METHODS

VLDL apoB kinetics were determined using a primed constant 1-13C leucine infusion, and VLDL apoB enrichment was measured by gas-chromatography mass-spectrometry. Fasting lipid profile, IGF-I, IGFBP-3, overnight GH profiles and free insulin concentrations were also assessed.

RESULTS

Fasting concentrations of triglycerides (TG), total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C) were similar in both groups. The VLDL apoB secretion and metabolic clearance rates were not significantly different between the two groups, but the VLDL-TGNLDL apoB and the VLDL-CNLDL apoB ratios were significantly increased in those with diabetes (P < 0.02 and P < 0.03, respectively). Total IGF-I concentrations were similar between the two groups; however, the GH area under the curve and free insulin concentrations were increased in patients with type 1 diabetes (GH: diabetes: 94.8 +/- 15.1 vs. controls: 45.6 +/- 10-6, mU/L/h, P < 0.04; free insulin: diabetes: 78.4 +/- 5.0 vs. controls: 28.3 +/- 3.26, pmol/l, P < 0.001). IGFBP-3 concentrations were lower in diabetic patients (diabetes: 2,454.2 +/- 68.7 vs. controls: 3,219.4 +/- 76.4, ng/ml, P < 0.001). In the control group overnight GH secretion correlated negatively with fasting TC (P < 0.01) and LDL-C (P < 0.03) concentrations, whereas free insulin concentrations correlated positively with fasting TG concentrations (P < 0.009). No significant correlations were found in the patients with diabetes.

CONCLUSION

This study suggests that in euglycaemic conditions patients with type 1 diabetes mellitus have normal VLDL apoB kinetics but altered VLDL composition. The altered VLDL composition may be associated with accelerated atherogenesis. We speculate that the disrupted hormonal balance and, in particular, the increased GH secretion might be responsible for the compositional changes of VLDL particles in type 1 diabetes mellitus.

Temporal changes in insulin sensitivity following the development of acute liver failure secondary to acetaminophen

Insulin resistance in chronic liver disease (CLD) is well documented. This study investigated whether similar changes occur in acute liver failure (ALF). Patients with ALF (n = 10) were recruited within 72 hours of their peak prothrombin time (range 42-120 seconds). All patients were ventilated for encephalopathy (grade III-IV). Peripheral and endogenous insulin sensitivity were assessed by a hyperinsulinemic euglycemic clamp (Human Actrapid 1.5 mU/min/kg) with an infusion of D-[6,6-(2)H(2)] glucose. The clamp was performed on day 0 and then on day 7 and day 14. During the insulin infusion, the mean total peripheral glucose uptake (area under the curve [AUC]) was 1,422 (SD, 1,253), 2,244 (SD, 1,392), and 4,500 (SD, 1,120) micromol/kg on days 0, 7, and 14, respectively. Significant changes occurred from day 0 to 14 (day 14-day 0: 3,078 [95% CI, 1,798 to 4,359]; P =.001) and day 7 to 14 (day 14-day 7: 2,256 [95% CI, 923 to 3,589]; P =.001). No significant difference in endogenous glucose production was demonstrated over time. Mean peripheral insulin sensitivity altered over time, increasing from 0.09 (SD, 0.09) micromol/kg/min/mU/L on day 0 to 0.24 (SD, 0.16) on day 7 and 0.5 (SD, 0.1) on day 14. Significant changes occurred between days 0, 7, and 14 (day 7-day 0: 0.15 [95% CI, 0.04 to 0.26], P =.006; day 14-day 0: 0.4 [95% CI, 0.28 to 0.5], P =.001; day 14-day 7: 0.2 [95% CI, 0.12 to 0.38], P =.001). This study demonstrates that in ALF, impaired peripheral uptake of glucose occurs, peripheral insulin sensitivity being restored at 2 weeks in subjects who survived.

IGF-I treatment in adults with type 1 diabetes: effects on glucose and protein metabolism in the fasting state and during a hyperinsulinemic-euglycemic amino acid clamp

Type 1 diabetes is associated with abnormalities of the growth hormone (GH)-IGF-I axis. Such abnormalities include decreased circulating levels of IGF-I. We studied the effects of IGF-I therapy (40 microg x kg(-1) x day(-1)) on protein and glucose metabolism in adults with type 1 diabetes in a randomized placebo-controlled trial. A total of 12 subjects participated, and each subject was studied at baseline and after 7 days of treatment, both in the fasting state and during a hyperinsulinemic-euglycemic amino acid clamp. Protein and glucose metabolism were assessed using infusions of [1-13C]leucine and [6-6-2H2]glucose. IGF-I administration resulted in a 51% rise in circulating IGF-I levels (P < 0.005) and a 56% decrease in the mean overnight GH concentration (P < 0.05). After IGF-I treatment, a decrease in the overnight insulin requirement (0.26+/-0.07 vs. 0.17+/-0.06 U/kg, P < 0.05) and an increase in the glucose infusion requirement were observed during the hyperinsulinemic clamp (approximately 67%, P < 0.05). Basal glucose kinetics were unchanged, but an increase in insulin-stimulated peripheral glucose disposal was observed after IGF-I therapy (37+/-6 vs. 52+/-10 micromol x kg(-1) x min(-1), P < 0.05). IGF-I administration increased the basal metabolic clearance rate for leucine (approximately 28%, P < 0.05) and resulted in a net increase in leucine balance, both in the basal state and during the hyperinsulinemic amino acid clamp (-0.17+/-0.03 vs. -0.10+/-0.02, P < 0.01, and 0.25+/-0.08 vs. 0.40+/-0.06, P < 0.05, respectively). No changes in these variables were recorded in the subjects after administration of placebo. These findings demonstrated that IGF-I replacement resulted in significant alterations in glucose and protein metabolism in the basal and insulin-stimulated states. These effects were associated with increased insulin sensitivity, and they underline the major role of IGF-I in protein and glucose metabolism in type 1 diabetes.

Effects of glutamine supplementation, GH, and IGF-I on glutamine metabolism in critically ill patients

During critical illness glutamine deficiency may develop. Glutamine supplementation can restore plasma concentration to normal, but the effect on glutamine metabolism is unknown. The use of growth hormone (GH) and insulin-like growth factor I (IGF-I) to prevent protein catabolism in these patients may exacerbate the glutamine deficiency. We have investigated, in critically ill patients, the effects of 72 h of treatment with standard parenteral nutrition (TPN; n = 6), TPN supplemented with glutamine (TPNGLN; 0.4 g x kg(-1) x day(-1), n = 6), or TPNGLN with combined GH (0.2 IU. kg(-1). day(-1)) and IGF-I (160 microg x kg (-1) x day(-1)) (TPNGLN+GH/IGF-I; n = 5) on glutamine metabolism using [2-(15)N]glutamine. In patients receiving TPNGLN and TPNGLN+GH/IGF-I, plasma glutamine concentration was increased (338 +/- 22 vs. 461 +/- 24 micromol/l, P < 0.001, and 307 +/- 65 vs. 524 +/- 71 micromol/l, P < 0.05, respectively) and glutamine uptake was increased (5.2 +/- 0.5 vs. 7.4 +/- 0.7 micromol x kg(-1) x min(-1), P < 0.05 and 5.2 +/- 1.1 vs. 7.6 +/- 0.8 micromol x kg(-1) x min(-1), P < 0.05). Glutamine production and metabolic clearance rates were not altered by the three treatments. These results suggest that there is an increased requirement for glutamine in critically ill patients. Combined GH/IGF-I treatment with TPNGLN did not have adverse effects on glutamine metabolism.

Estimating protein turnover with a [15N,13C]leucine tracer: a study using simulated data

We explore the use of [15N,13C]leucine tracer to estimate whole-body fractional rates of a fast-turning-over protein pool employing synthetic data. The kinetics of [15N,13C]leucine tracer are simplified compared with those of traditional leucine tracers and benefit from irreversible transamination to [13C]alpha-ketoisocaproaic acid (KIC) resulting in a simplified model structure. A three-compartment model of [15N,13C]leucine kinetics was proposed and evaluated using data generated by a Reference Model (based on a model by Cobelli et al.). The results suggest that fractional turnover rates of a fast-turning-over protein pool can be estimated with a low but acceptable precision during a six-hour constant intravenous infusion of [15N,13C]leucine with frequent sampling of plasma tracer-to-tracee ratio (TTR) of [15N,13C]leucine. We conclude that [15N,13C]leucine may be useful for the measurement of protein kinetics and its full potential should be explored in clinical studies with compartmental data analysis.