Plasma Amino Acids Stimulate Uncoupled Respiration of Muscle Subsarcolemmal Mitochondria in Lean but Not Obese Humans

Abstract

Context: Obesity is associated with mitochondrial dysfunction in skeletal muscle. Increasing the plasma amino acid (AA) concentrations stimulates mitochondrial adenosine triphosphate (ATP) production in lean individuals.

Objective: To determine whether acute elevation in plasma AAs enhances muscle mitochondrial respiration and ATP production in subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria in obese adults.

Design: Assessment of SS and IMF mitochondrial function during saline (i.e., control) and AA infusions.

Participants: Eligible participants were healthy lean (body mass index, <25 kg/m2; age, 37 ± 3 years; n = 10) and obese (body mass index >30 kg/m2; age 35 ± 3 years; n = 11) subjects.

Intervention: Single trial of saline infusion followed by AA infusion. SS and IMF mitochondria were isolated from muscle biopsies collected at the end of the saline and AA infusions.

Main outcomes: Mitochondrial respiration and ATP production.

Results: AA infusion increased adenosine 5'-diphosphate (ADP)-stimulated respiration and ATP production rates of SS mitochondria in the lean (P < 0.05), but not obese, subjects. Furthermore, AA infusion increased the uncoupled (i.e., non-ADP-stimulated) respiration of SS mitochondria in the lean subjects only (P < 0.05). AA infusion had no effect on any of these parameters in IMF mitochondria in either lean or obese subjects (P > 0.05).

Conclusions: Increasing the plasma AA concentrations enhances the capacity for respiration and ATP production of muscle SS, but not IMF, mitochondria in lean individuals, in parallel with increases in uncoupled respiration. However, neither of these parameters increases in muscle SS or IMF mitochondria in obese individuals.

Trial registration: ClinicalTrials.gov NCT01824173.

Copyright © 2017 Endocrine Society

Figures

Figure 1.

Hormone and glucose concentrations. (A, C, E) Measurements were performed at the initiation of the experiments [time (t) = 60 minutes], at the end of the saline infusion period (t = 300 minutes), 30 minutes after the start of the AA infusion (t = 330 minutes), and at the end of the AA infusion period (t = 540 minutes). (B, D, F) The corresponding AUCs describing the hormone and glucose responses during the saline and AA infusion periods. Data presented as the mean ± standard error of the mean. Two-way with repeated measures ANOVA was used to analyze the data. Bonferroni correction was performed for multiple comparison tests (***P < 0.001, **P < 0.01, *P < 0.05 vs saline infusion, unless otherwise stated).

Figure 2.

State 3 oxygen consumption (State 3 JO) and ATP production (State 3 JP). State 3 JO and JP of (A, C, E, G) SS and (B, D, F, H) IMF mitochondria were measured at the end of the saline (Saline Infusion) and AA (AA Infusion) infusion periods. State 3 JO and JP were measured in the presence of MPG (malate, 1 mM; pyruvate, 1 mM; glutamate, 10 mM) or SUCC (10 mM) as substrates, and maximal rates for JO and JP were stimulated by the addition of ADP (0.67 mM). Data presented as the mean ± standard error of the mean. Two-way with repeated measures ANOVA was used to analyze the data. Bonferroni correction was performed for multiple comparison tests (**P < 0.01, *P < 0.05 vs saline infusion).

Figure 3.

State 2 JO and state 4 JO oxygen consumption. State 2 JO and state 4 JO of (A, C, E, G) SS and (B, D, F, H) IMF mitochondria were measured at the end of the saline (Saline Infusion) and AA (AA Infusion) infusion periods. State 2 JO was measured in the presence of MPG (malate, 1 mM; pyruvate, 1 mM; glutamate, 10 mM) or SUCC (10 mM) as substrates. State 4 JO was measured following state 3 JO after depletion of ADP in the medium. Data presented as the mean ± standard error of the mean. Two-way with repeated measures ANOVA was used to analyze the data. Bonferroni correction was performed for multiple comparison tests (***P < 0.001, *P < 0.05 vs saline infusion).

Figure 4.

RCR (state 3 JO/state 4 JO) and ADP/O ratio. The RCR and ADP/O ratio were measured in the presence of MPG (malate, 1 mM; pyruvate, 1 mM; glutamate, 10 mM) or SUCC (10 mM) as substrates; Data presented as the mean ± standard error of the mean. Two-way with repeated measures ANOVA was used to analyze the data. Bonferroni correction was performed for multiple comparison tests (**P < 0.01, *P < 0.05 vs saline infusion).