Leucine incorporation into mixed skeletal muscle protein in humans

Nair, K. Sreekumaran; Halliday, D.; Griggs, Robert C.

doi:10.1152/ajpendo.1988.254.2.e208

Cited by 115 publications

(119 citation statements)

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“…At 0600 h, arterialized blood samples were taken every 10 min until 0630 h for [6,6-2 H 2 ]-D-glucose isotopic enrichment measurements. At 0630 h, a percutaneous needle muscle biopsy (350 -400 mg) was obtained from the vastus lateralis muscle under local anesthesia (22). Approximately 40 mg of muscle was immediately used for measurement of MAPR, as previously described (5), and the remaining tissue was frozen in liquid nitrogen and stored at Ϫ80°F for other analyses.…”

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confidence: 99%

Endurance Exercise as a Countermeasure for Aging

et al. 2008

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OBJECTIVE-We determined whether reduced insulin sensitivity, mitochondrial dysfunction, and other age-related dysfunctions are inevitable consequences of aging or secondary to physical inactivity.RESEARCH DESIGN AND METHODS-Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp and ATP production in mitochondria isolated from vastus lateralis biopsies of 42 healthy sedentary and endurance-trained young (18 -30 years old) and older (59 -76 years old) subjects. Expression of proteins involved in fuel metabolism was measured by mass spectrometry. Citrate synthase activity, mitochondrial DNA (mtDNA) abundance, and expression of nuclear-encoded transcription factors for mitochondrial biogenesis were measured. SIRT3, a mitochondrial sirtuin linked to lifespan-enhancing effects of caloric restriction, was measured by immunoblot.RESULTS-Insulin-induced glucose disposal and suppression of endogenous glucose production were higher in the trained young and older subjects, but no age effect was noted. Age-related decline in mitochondrial oxidative capacity was absent in endurance-trained individuals. Although endurance-trained individuals exhibited higher expression of mitochondrial proteins, mtDNA, and mitochondrial transcription factors, there were persisting effects of age. SIRT3 expression was lower with age in sedentary but equally elevated regardless of age in endurance-trained individuals.CONCLUSIONS-The results demonstrate that reduced insulin sensitivity is likely related to changes in adiposity and to physical inactivity rather than being an inevitable consequence of aging. The results also show that regular endurance exercise partly normalizes age-related mitochondrial dysfunction, although there are persisting effects of age on mtDNA abundance and expression of nuclear transcription factors and mitochondrial protein. Furthermore, exercise may promote longevity through pathways common to effects of caloric restriction. Diabetes 57: 2933-2942, 2008 R educed insulin sensitivity is a common factor in the metabolic syndrome, a cluster of clinical conditions that shows increased risk with age (1-3). Mitochondrial dysfunction is also prevalent in the elderly (4,5), with reductions in mitochondrial enzyme activities (6), protein synthesis (7) and expression (5), and DNA (mtDNA) abundance (5,8). A close association between insulin sensitivity and muscle mitochondrial function has been reported in aging (4,5), type 2 diabetes (9), and obesity (10) as well as in offspring of type 2 diabetic individuals (11), prompting a hypothesis that either reduced insulin sensitivity results from muscle mitochondrial dysfunction (4,11) or vice versa (5,12).Endurance exercise increases insulin sensitivity (13,14) and mitochondrial enzyme activities (15,16). Short-term and longitudinal studies have documented that older populations respond favorably to endurance exercise but that there are persisting age effects that cannot be eliminated by short-term exercise programs (8,17). For practical reasons, most training studies ar...

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confidence: 99%

Endurance Exercise as a Countermeasure for Aging

et al. 2008

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“…L-(1-13 C)Leucine (99% at.%, Tracer Technologies, Somerville, Massachusetts) was mixed with natural leucine (Sigma Chemical Co., St Louis, Missouri) to make serial standard dilutions of (1-13 C)leucine enrichment in the range expected in muscle hydrolysates obtained from subjects infused with this tracer (~ 1.08-1.19 at.% 1-13 C in the carboxyl position, which is equivalent to ~0.001-0.011 at.% excess 13 C in all carbons of the combusted chemical derivative of the leucine molecule). Analytical procedures for the standards were identical to those used for muscle tissue analysis described below.…”

Section: Experimental Standard Mixturementioning

confidence: 99%

“…This requires biopsy sampling of the muscle tissue during the infusion of labeled amino acid, separating the amino acids from an acid hydrolysate of the tissue using preparative gas chromatography (GC) or liquid chromatography (LC), isolating the labeled amino acid using a post-column splitter and a liquid nitrogen trap or a fraction collector, releasing the labeled carboxyl group as CO 2 by reaction with ninhydrin, and determining the 13 CO 2 / 12 CO 2 ratio using isotope ratio mass spectrometry (IRMS). 12,13 Unfortunately, this approach is time and labor intensive, requires relatively large muscle samples (~25-100 mg) for adequate recovery of leucine and CO 2 , and has the potential for contamination with natural carbon, predominantly 12 C, because of the numerous preparative steps.…”

Section: Introductionmentioning

confidence: 99%

Measurement of muscle protein fractional synthetic rate by capillary gas chromatography/combustion isotope ratio mass spectrometry

Yarasheski

Smith

Rennie

et al. 1992

Biol. Mass Spectrom.

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The measurement of skeletal muscle protein fractional synthetic rate using an infusion of (1-13 C)leucine and measuring the isotopic abundance of the tracer in skeletal muscle protein by preparative gas chromatography (GC)/ninhydrin isotope ratio mass spectrometry (IRMS) is laborious and subject to errors owing to contamination by 12 C. The purpose of this study was to compare muscle ( 13 C)leucine enrichment measured with the conventional preparative GC/ ninhydrin IRMS approach to a new, continuous-flow technique using capillary GC/combustion IRMS. Quadriceps muscles were removed from four Sprague-Dawley rats after each was infused at a different rate with (1-13 C)leucine for 6-8 h. Muscle leucine enrichment (at.% excess) measured by both methods differed by less than 4%, except at low ( 13 C)leucine enrichments (<0.03 at.% excess). In addition, capillary GC/combustion IRMS was used to assess muscle ( 13 C)leucine enrichment and fractional muscle protein synthesis rate in ten normal young men and women infused with (1,2-13 C 2 )leucine for 12-14 h. This approach reduced the variability of the isotope abundance measure and gave estimates of muscle protein synthesis rate (0.050 ± 0.011% h −1 (mean ± SEM); range = 0.023-0.147% h −1 ) that agree with published values determined using the standard analytical approach. The measurement of ( 13 C)leucine enrichment from skeletal muscle protein by capillary GC/combustion IRMS provides a simple, acceptable and practical alternative to preparative GC/ninhydrin IRMS.

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“…During the D 2 Ϫ phase of the study, all subjects were given a constant intravenous normal saline (Baxter, Deerfield, IL) infusion at a rate of 1 ml ⅐ kg Ϫ1 ⅐ h Ϫ1 during the night before the study. Muscle needle biopsies were performed at 7:00 A.M. under local anesthesia, as previously described (23), and the samples were instantly frozen in liquid nitrogen and stored at Ϫ80°C for gene expression analysis. The control subjects were also admitted to the Clinical Research Center and were given a standard meal on the day before the study.…”

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Gene Expression Profile in Skeletal Muscle of Type 2 Diabetes and the Effect of Insulin Treatment

et al. 2002

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Type 2 diabetes is characterized by muscle insulin resistance. Nondiabetic first-degree relatives of type 2 diabetic patients have also been reported to have insulin resistance. A polygenic basis for pathogenesis of type 2 diabetes has been proposed. A gene expression profile was evaluated in the skeletal muscle of patients with type 2 diabetes while not on treatment for 2 weeks and after 10 days of intensive insulin treatment. Comparison of gene expression pattern with age-, sex-, and BMI-matched people with no family history of diabetes was performed using a microarray technique (Hu6800 arrays; Affymetrix, Santa Clara, CA). Only those gene transcripts showing >1.9-fold changes and an average difference in fluorescence intensity of >1,000 in all subjects are reported. Insulin sensitivity (SI) was measured using an intravenous glucose tolerance test. Of 6,451 genes surveyed, transcriptional patterns of 85 genes showed alterations in the diabetic patients after withdrawal of treatment, when compared with patterns in the nondiabetic control subjects. Insulin treatment reduced the difference in patterns between diabetic and nondiabetic control subjects (improved) in all but 11 gene transcripts, which included genes involved in structural and contractile functions, growth and tissue development, stress response, and energy metabolism. These improved transcripts included genes involved in insulin signaling, transcription factors, and mitochondrial maintenance. However, insulin treatment altered the transcription of 29 additional genes involved in signal transduction; structural and contractile functions; growth and tissue development; and protein, fat, and energy metabolism. Type 2 diabetic patients had elevated circulating insulin during the insulin-treated phase, although their blood glucose levels (98.8 ؎ 6.4 vs. 90.0 ؎ 2.9 mg/dl for diabetic vs. control) were similar to those of the control subjects. In contrast, after withdrawal of treatment, the diabetic patients had reduced SI and elevated blood glucose (224.0 ؎ 26.2 mg/dl), although their insulin levels were similar to those of the nondiabetic control subjects. This study identified several candidate genes for muscle insulin resistance, complications associated with poor glycemic control, and effects of insulin treatment in people with type 2 diabetes. Diabetes

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Leucine incorporation into mixed skeletal muscle protein in humans

Cited by 115 publications

References 19 publications

Endurance Exercise as a Countermeasure for Aging

Endurance Exercise as a Countermeasure for Aging

Measurement of muscle protein fractional synthetic rate by capillary gas chromatography/combustion isotope ratio mass spectrometry

Gene Expression Profile in Skeletal Muscle of Type 2 Diabetes and the Effect of Insulin Treatment

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