N. C. Jackson

The metabolic consequences of critical illness: acute effects on glutamine and protein metabolism

Net protein loss and large decreases in plasma glutamine concentration are characteristics of critical illness. We have used [2-15N]glutamine and [1-13C]leucine to investigate whole body glutamine and leucine kinetics in a group of critically ill patients and matched healthy controls. Glutamine appearance rate (Ra,Gln) was similar in both groups. However, in the patients, the proportion of Ra,Gln arising from protein breakdown was higher than in the control group (43 +/- 3 vs. 32 +/- 2%, P < 0.05). Glutamine metabolic clearance rate (MCR) was 92 +/- 8% higher (P < 0.001), whereas plasma glutamine concentration was 38 +/- 5% lower (P < 0.001) than in the control group. Leucine appearance rate (whole body proteolysis) and nonoxidative leucine disposal (whole body protein synthesis) were 59 +/- 14 and 49 +/- 15% higher in the patients (P < 0.001). Leucine oxidation and MCR were increased in the patients by 104 +/- 37 and 129 +/- 39%, respectively (P < 0.05). These results demonstrate that critical illness is associated with a major increase in protein turnover. The acute decrease in plasma glutamine concentration and the unaltered plasma Ra,Gln suggest that the increase in proteolysis is insufficient to meet increased demand for glutamine in this severe catabolic state.Net protein loss and large decreases in plasma glutamine concentration are characteristics of critical illness. We have used [2-15N]glutamine and [1-13C]leucine to investigate whole body glutamine and leucine kinetics in a group of critically ill patients and matched healthy controls. Glutamine appearance rate (Ra,Gln) was similar in both groups. However, in the patients, the proportion of Ra,Gln arising from protein breakdown was higher than in the control group (43 ± 3 vs. 32 ± 2%, P < 0.05). Glutamine metabolic clearance rate (MCR) was 92 ± 8% higher ( P < 0.001), whereas plasma glutamine concentration was 38 ± 5% lower ( P < 0.001) than in the control group. Leucine appearance rate (whole body proteolysis) and nonoxidative leucine disposal (whole body protein synthesis) were 59 ± 14 and 49 ± 15% higher in the patients ( P < 0.001). Leucine oxidation and MCR were increased in the patients by 104 ± 37 and 129 ± 39%, respectively ( P < 0.05). These results demonstrate that critical illness is associated with a major increase in protein turnover. The acute decrease in plasma glutamine concentration and the unaltered plasma Ra,Gln suggest that the increase in proteolysis is insufficient to meet increased demand for glutamine in this severe catabolic state.

A comparison of the effects of IGF-I and insulin on glucose metabolism, fat metabolism and the cardiovascular system in normal human volunteers

Abstract. The metabolic and cardiovascular effects of recombinant human IGF‐I were compared to insulin in six normal subjects. Subjects were studied twice and intravenously received an infusion of [6,6‐2H2]glucose (0–480 min) and in random order either IGF‐I 20μg kg‐1 h‐1 (43.7 pmol kg‐1 min‐1) or insulin 0.5 mU kg‐1 min‐1 (3.4 pmol kg‐1 min‐1) with an euglycaemic clamp. One subject was withdrawn following a serious adverse event. During the IGF‐I infusion glucose appearance rate (Ra) decreased from 1.79 ± 0.13 at baseline (150–180 min) to 0.35 ± 0.26 mg kg‐1 min‐1 (P < 0.01) at 360min, and glucose utilization rate (Rd) increased from 1.79 ± 0.28 to 4.17 ± 0.84 mg kg‐1 min‐1 (P < 0.01). There was no change in free fatty acids (FFA) and an increase (percentage change from pre‐infusion mean) in cardiac output + 37.3%± 9% (P < 0.01), heart rate + 13%± 2% (P < 0.01) and stroke volume + 21%± 7% (P < 0.05). During the insulin infusion glucose Ra decreased from 1.89 ± 0.13 to 0.34 ± 0.33 mg kg‐1 min‐1 (P < 0.01) and FFA from 0.546 mmoll‐1 to 0.198 mmoll‐1 (P < 0.01), glucose Rd increased from l.89 ± 0.18 to 5.41 ± l.47mg kg‐1 min‐1 (P < 0.01) and there were no significant changes in the cardiovascular variables.

Measurement of glucose metabolism and insulin secretion during normal pregnancy and pregnancy complicated by gestational diabetes

SummaryGestational diabetes affects 2–3% of pregnant women and is associated with foetal complications including macrosomia and an increased likelihood of developing diabetes in later life. We have therefore studied seven women with gestational diabetes and five control women both during the third trimester of pregnancy and again 2–3 months post-partum, using the minimal model analysis of the frequently sampled labelled ([6, 6-2H2]-glucose) intravenous glucose tolerance test. Glucose tolerance (glucose Kd) was significantly reduced in the women with gestational diabetes compared with the normal pregnant women both in pregnancy (1.16±0.11 vs 1.78±0.23%/min; p<0.05) and post-partum (1.47±0.22 vs 2.59±0.43%/min; p<0.05) and increased significantly in the control women after delivery (p<0.05). Glucose effectiveness was not significantly different between the women with gestational diabetes and the control group either during or after pregnancy. Insulin sensitivity was significantly lower during pregnancy than after delivery in the women with gestational diabetes (p<0.05). There was no significant difference in basal insulin secretion in the two groups during pregnancy or post-partum. However, during pregnancy the control subjects significantly increased (p<0.001) their insulin secretion over a period of 20 min in response to an intravenous glucose tolerance test (96.2±42.7 pmol/kg) compared with post-partum values (58.3±25.2 pmol/kg) while in the women with gestational diabetes insulin secretion was similar in pregnancy (65.5±9.3 pmol/kg) and after delivery (57.7±15.7 pmol/kg). These data suggest that the glucose intolerance in gestational diabetes compared to normal pregnancy is due to reduced insulin sensitivity and an impaired ability in gestational diabetes to increase insulin secretion in response to glucose.

Insulin Detemir Reduces Weight Gain as a Result of Reduced Food Intake in Patients With Type 1 Diabetes

OBJECTIVE Insulin detemir lacks the usual propensity for insulin to cause weight gain. We investigated whether this effect was a result of reduced energy intake and/or increased energy expenditure. RESEARCH DESIGN AND METHODS A 32-week, randomized crossover design trial was undertaken in 23 patients with type 1 diabetes. Patients on a basal-bolus regimen (with insulin aspart as the bolus insulin) were randomly assigned to insulin detemir or NPH insulin as a basal insulin for 16 weeks, followed by the other basal insulin for 16 weeks. At the end of each 16-week period, total energy expenditure, resting energy expenditure, diet-induced thermogenesis, activity energy expenditure, energy intake, weight change, glycemic control, hypoglycemic episodes, and hormones that affect satiety and fuel partitioning were measured. RESULTS After 16 weeks, weight change was −0.69 ± 1.85 kg with insulin detemir and +1.7 ± 2.46 kg with NPH insulin (P < 0.001). Total energy intake was significantly less with insulin detemir (2,016 ± 501 kcal/day) than with NPH insulin (2,181 ± 559 kcal/day) (P = 0.026). There was no significant difference in any measure of energy expenditure, HbA1c percentage, or number of hypoglycemic episodes. Leptin was lower and resistin was higher with insulin detemir compared with NPH insulin (P = 0.039, P = 0.047). After the meal, ghrelin and pancreatic polypeptide levels (P = 0.002, P = 0.001) were higher with insulin detemir. CONCLUSIONS The reduced weight gain with insulin detemir compared with NPH insulin is attributed to reduced energy intake rather than increased energy expenditure. This may be mediated by a direct or indirect effect of insulin detemir on the hormones that control satiety.

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.

Effect of growth hormone treatment on postprandial protein metabolism in growth hormone-deficient adults.

Growth hormone (GH) treatment of GH-deficient adults increases lean body mass. To investigate this anabolic effect of GH, body composition and postabsorptive and postprandial protein metabolism were measured in 12 GH-deficient adults randomized to placebo or GH treatment. Protein metabolism was measured after an infusion of [1-13C]leucine before and after a standard meal at 0 and 2 mo. After 2 mo, there was an increase in lean body mass in the GH group (P < 0. 05) but no change in the placebo group. In the postabsorptive state, there was increased nonoxidative leucine disappearance (NOLD; a measure of protein synthesis) and leucine metabolic clearance rate and decreased leucine oxidation in the GH group (P < 0.05) but no change in the placebo group. After the meal, there was an increase in NOLD and oxidation in all studies (P < 0.05), but the increase in NOLD, measured as area under the curve, was greater in the GH group (P < 0.05). This study clearly demonstrates for the first time that the increase in protein synthesis in the postabsorptive state after GH treatment of GH-deficient adults is maintained in the postprandial state.Growth hormone (GH) treatment of GH-deficient adults increases lean body mass. To investigate this anabolic effect of GH, body composition and postabsorptive and postprandial protein metabolism were measured in 12 GH-deficient adults randomized to placebo or GH treatment. Protein metabolism was measured after an infusion of [1-13C]leucine before and after a standard meal at 0 and 2 mo. After 2 mo, there was an increase in lean body mass in the GH group ( P < 0.05) but no change in the placebo group. In the postabsorptive state, there was increased nonoxidative leucine disappearance (NOLD; a measure of protein synthesis) and leucine metabolic clearance rate and decreased leucine oxidation in the GH group ( P < 0.05) but no change in the placebo group. After the meal, there was an increase in NOLD and oxidation in all studies ( P < 0.05), but the increase in NOLD, measured as area under the curve, was greater in the GH group ( P < 0.05). This study clearly demonstrates for the first time that the increase in protein synthesis in the postabsorptive state after GH treatment of GH-deficient adults is maintained in the postprandial state.

Quantitative measurement of 3-O-methyl-D-glucose by gas chromatography-mass spectrometry as a measure of glucose transport in vivo.

Existing methods of measuring glucose kinetics are subject to errors. There is considerable interest in improved methods of measuring glucose kinetics to allow the development of new regimes for the treatment of diabetes mellitus. 3-O-Methyl-D-glucose is transported but not metabolized and therefore allows independent estimation of transport parameters. We describe a method by which 3-O-methyl-D-glucose in plasma samples can be measured in protocols during which glucose flux is assessed with simultaneous use of two isotopically labeled glucoses to quantitate and validate measurements of the rate of glucose appearance and disappearance. Quantitative gas chromatographic/mass spectrometric (GC/MS) analysis of 3-O-methyl-D-glucose, D-glucose, D-[U-13C] glucose and D-[6,6-2H2] glucose in human plasma using methoxime-trimethylsilyl ether derivatives is described. Measurements of all four derivatives were performed together in a small sample volume (50 microliters) with high precision. The intra-assay (inter-assay) coefficients of variation at an isotope content of 0.25 atom% excess for D-[6,6-2H2] glucose, D-[U-13C] glucose and 3-O-methyl-D-glucose were 0.8% (1.0%), 0.5% (4.0%) and 0.1% (3.7%), respectively. This method provides the basis for quantitative estimation of parameters of glucose kinetics in man and the rates of glucose flux across the cell membrane.

Dissociation between exercise-induced reduction in liver fat and changes in hepatic and peripheral glucose homoeostasis in obese patients with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is associated with multi-organ (hepatic, skeletal muscle, adipose tissue) insulin resistance (IR). Exercise is an effective treatment for lowering liver fat but its effect on IR in NAFLD is unknown. We aimed to determine whether supervised exercise in NAFLD would reduce liver fat and improve hepatic and peripheral (skeletal muscle and adipose tissue) insulin sensitivity. Sixty nine NAFLD patients were randomized to 16 weeks exercise supervision (n=38) or counselling (n=31) without dietary modification. All participants underwent MRI/spectroscopy to assess changes in body fat and in liver and skeletal muscle triglyceride, before and following exercise/counselling. To quantify changes in hepatic and peripheral insulin sensitivity, a pre-determined subset (n=12 per group) underwent a two-stage hyperinsulinaemic euglycaemic clamp pre- and post-intervention. Results are shown as mean [95% confidence interval (CI)]. Fifty participants (30 exercise, 20 counselling), 51 years (IQR 40, 56), body mass index (BMI) 31 kg/m(2) (IQR 29, 35) with baseline liver fat/water % of 18.8% (IQR 10.7, 34.6) completed the study (12/12 exercise and 7/12 counselling completed the clamp studies). Supervised exercise mediated a greater reduction in liver fat/water percentage than counselling [Δ mean change 4.7% (0.01, 9.4); P<0.05], which correlated with the change in cardiorespiratory fitness (r=-0.34, P=0.0173). With exercise, peripheral insulin sensitivity significantly increased (following high-dose insulin) despite no significant change in hepatic glucose production (HGP; following low-dose insulin); no changes were observed in the control group. Although supervised exercise effectively reduced liver fat, improving peripheral IR in NAFLD, the reduction in liver fat was insufficient to improve hepatic IR.

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.

Short-term administration of pegvisomant improves hepatic insulin sensitivity and reduces soleus muscle intramyocellular lipid content in young adults with type 1 diabetes.

CONTEXT Data on the metabolic effects of GH derived from studies using GH suppression by pharmacological agents may not reflect selective actions. OBJECTIVE The purpose of this study was to evaluate the effects of GH antagonism on glucose and lipid metabolism using pegvisomant, a selective GH receptor antagonist in patients with type 1 diabetes (T1D). DESIGN AND PARTICIPANTS In a randomized, placebo-controlled, crossover study, 10 young adults with T1D were evaluated at baseline and after 4 weeks of treatment with either 10 mg of pegvisomant or placebo. The assessments included an overnight euglycemic steady state followed by a hyperinsulinemic euglycemic clamp and used glucose and glycerol cold stable isotopes. OUTCOME MEASURES Hepatic and peripheral insulin sensitivity (IS), lipid turnover, and intramyocellular lipid (IMCL) were measured. RESULTS Compared with placebo, pegvisomant treatment resulted in lower IGF-I levels (P < .001). During the overnight steady state, insulin requirements for euglycemia (P = .019), insulin levels (P = .008), and glucose production rates (Ra) (P = .033) were reduced. During the clamp study, glucose infusion rates (P = .031) increased and glucose Ra (P = .015) decreased whereas glucose disposal rates were unchanged. Free fatty acid levels were similar during the steady state but were lower during the clamp (P = .040) after pegvisomant. Soleus muscle IMCL decreased after treatment (P = .024); however, no change in tibialis anterior muscle was observed. CONCLUSIONS The study demonstrates that GH antagonism in T1D results in improved hepatic insulin sensitivity. Lack of consistent changes in free fatty acid levels may suggest a direct effect of GH on IS. Unchanged peripheral IS despite reductions in IMCL indicate that GH-induced alterations in IMCL may not be causally linked to glucose metabolism.