2862 Diabetes Volume 65, October 2016 Marlou L. Dirks,1 Benjamin T. Wall,1 Bas van de Valk,1 Tanya M. Holloway,2 Graham P. Holloway,2 Adrian Chabowski,3 Gijs H. Goossens,1 and Luc J.C. van Loon1 One Week of Bed Rest Leads to Substantial Muscle Atrophy and Induces Whole-Body Insulin Resistance in the Absence of Skeletal Muscle Lipid Accumulation Diabetes 2016;65:2862–2875 | DOI: 10.2337/db15-1661 Short (<10 days) periods of muscle disuse, often neces- mechanisms implicated in high-fat diet–induced insulin sary for recovery from illness or injury, lead to various resistance. negative health consequences. The current study inves- tigated mechanisms underlying disuse-induced insulin resistance, taking into account muscle atrophy. Ten Recovery from injury or illness generally necessitates a healthy, young males (age: 23 6 1 years; BMI: 23.0 6 period of bed rest, often as a consequence of hospitali- 0.9 kg $ m22) were subjected to 1 week of strict bed zation. Prolonged (.10 days) periods of bed rest have rest. Prior to and after bed rest, lean body mass (dual- been shown to induce substantial changes in body com- energy X-ray absorptiometry) and quadriceps cross- position and are accompanied by overall metabolic decline METABOLISM sectional area (CSA; computed tomography) were (1,2). Though this model of prolonged physical inactivity assessed, and peak oxygen uptake (VO2peak) and leg has taught us much about muscle disuse atrophy, it may strength were determined. Whole-body insulin sensitiv- be of limited clinical relevance to most patients who are, ity was measured using a hyperinsulinemic-euglycemic on average, hospitalized for ,7 days (3). Recent data clamp. Additionally, muscle biopsies were collected to from our laboratory as well as others show that merely assess muscle lipid (fraction) content and various a few days of disuse substantially reduces skeletal muscle markers of mitochondrial and vascular content. Bed rest mass and strength (2,4–6). As a consequence, it has been resulted in 1.4 6 0.2 kg lean tissue loss and a 3.2 6 0.9% suggested that the accumulation of such short (,10 days), decline in quadriceps CSA (both P < 0.01). VO2peak and successive periods of bed rest or immobilization may one-repetition maximum declined by 6.4 6 2.3 (P < 0.05) largely be responsible for the loss of muscle mass and and 6.9 6 1.4% (P < 0.01), respectively. Bed rest induced metabolic decline observed throughout the life span (7,8). a296 5% decrease in whole-body insulin sensitivity Impairments in metabolic health following prolonged (P < 0.01). This was accompanied by a decline in muscle disuse have been well described and include a decline in oxidative capacity, without alterations in skeletal muscle glucose tolerance and insulin sensitivity (1,9), a decrease lipid content or saturation level, markers of oxidative in resting fat oxidation (10), an increase in mitochondrial stress, or capillary density. In conclusion, 1 week of bed reactive oxygen species (ROS) production (11), and a de- rest substantially reduces skeletal muscle mass and cline in basal metabolic rate (12). As the decline in meta- lowers whole-body insulin sensitivity, without affecting bolic health predisposes to greater morbidity and mortality 1NUTRIM School of Nutrition and Translational Research in Metabolism, Maas- This article contains Supplementary Data online at http://diabetes tricht University Medical Centre, Maastrict, the Netherlands .diabetesjournals.org/lookup/suppl/doi:10.2337/db15-1661/-/DC1. 2 Human Health & Nutritional Sciences, University of Guelph, Guelph, Ontario, This article is featured in a podcast available at http://www.diabetesjournals.org/ Canada content/diabetes-core-update-podcasts. 3Department of Physiology, Medical University of Bialystok, Bialystok, Poland © 2016 by the American Diabetes Association. Readers may use this article as Corresponding author: Luc J.C. van Loon, [email protected]. long as the work is properly cited, the use is educational and not for profit, and the Received 15 December 2015 and accepted 23 June 2016. work is not altered. More information is available at http://www.diabetesjournals Clinical trial reg. no. NCT02109380, clinicaltrials.gov. .org/content/license. diabetes.diabetesjournals.org Dirks and Associates 2863 of patients (13), it is of major clinical relevance to under- obesity-related insulin resistance such as skeletal muscle stand the mechanisms responsible for this decline in met- lipid accumulation, oxidative stress, and micro- and/or abolic health. Prolonged disuse has been associated with macrovascular dysfunction. substantial loss of muscle mass and/or gain in fat mass RESEARCH DESIGN AND METHODS (2). Such changes in body composition lower the body’s capacity for blood glucose disposal and may contribute to Subjects the decline in metabolic health. However, changes in body Ten healthy young men (age 23 6 1 years) were included in composition can only partly explain the observed metabolic the current study. Subjects’ characteristics are presented in decline, as reduced insulin sensitivity has been observed dur- Table 1. Prior to inclusion in the study, subjects filled out a ing bed rest before measurable changes in body composition general health questionnaire and completed a routine medical became apparent (1,2). We hypothesize that the substantial screening to ensure their eligibility to take part in the study. 22 muscle atrophy caused by short-term bed rest will contribute Exclusion criteria were a BMI ,18.5 or .30 kg $ m ,a to, but not fully explain, the vast decline in metabolic health. (family) history of thrombosis, type 2 diabetes mellitus (de- . $ 21 One of the key hallmarks of metabolic health is insulin termined by HbA1c values 7.0% [53 mmol mol ]), and sensitivity. Earlier studies have demonstrated that short any back, knee, or shoulder complaints. Furthermore, sub- periods of bed rest impair glucose tolerance and lower jects who had been involved in structured and prolonged whole-body and/or peripheral insulin sensitivity (14–18). resistance-type exercise training during the 6 months prior The development of insulin resistance under conditions of to the study were also excluded. All subjects were informed lipid oversupply (e.g., type 2 diabetes mellitus and [high- on the nature and risks of the experiment before written fat] overfeeding) has been associated with lipid deposition informed consent was obtained. During the screening visit, in skeletal muscle (19) and, more specifically, with an a fasting blood sample was taken to assess HbA1c,resting increase in intramuscular lipid intermediates such as diac- energy expenditure was measured with the use of a venti- ylglycerols (DAGs), ceramides, and long-chain fatty acyl- lated hood, and a one-repetition maximum (1RM) estimation CoA, which impair insulin signaling (as reviewed in Ref. test was performed. The current study was approved by 20). Furthermore, both muscle disuse atrophy (21,22) and the Medical Ethical Committee of Maastricht University the development of insulin resistance (23) have also been Medical Centre (registration number 14-3-013) in accor- attributed to a decline in mitochondrial content and/or im- dance with the Declaration of Helsinki. pairments in skeletal muscle mitochondrial function. Addi- Experimental Outline tionally, impairments in micro- and macrovascular function The experimental protocol is depicted in Supplementary have been linked to peripheral insulin resistance (24). So far, Fig. 1. After inclusion into the study, subjects visited the it is unclear which mechanism(s) contribute to the proposed university for a pretesting visit during which the 1RM and development of insulin resistance during short-term bed rest. peak oxygen uptake (VO2peak) tests were performed. Fol- The objective of the current study was to assess mech- lowing this visit, a 7-day period of standardized nutrition anisms that may contribute to the development of insulin was started. On day 6 of the controlled diet, a mixed-meal resistance during short-term muscle disuse, taking into tolerance test was performed. The day after, on day 7 of account the expected muscle atrophy. To achieve this, we the standardized diet and the day prior to bed rest, test subjected healthy, young males to 1 week of strict bed rest day 1 was scheduled. During this day, a muscle biopsy was and used comprehensive measures of muscle mass and taken from the m. vastus lateralis, and a hyperinsulinemic- muscle function in combination with detailed metabolic euglycemic clamp and computed tomography (CT) and dual- phenotyping (e.g., whole-body insulin sensitivity, sub- energy X-ray absorptiometry (DXA) scans were performed. strate metabolism, skeletal muscle lipid content and The next morning, subjects arrived at the laboratory to composition, muscle oxidative capacity, and capillary start the bed rest period. The meal tolerance test was re- density) to determine their possible contribution to the peated on day 6 of bed rest. After exactly 7 days of bed development of disuse-induced whole-body insulin re- rest, test day 1 was repeated, and subjects were allowed to sistance. Importantly, this was conducted under energy- balanced conditions to eliminate the contribution of Table 1—Subjects’ characteristics overfeeding to our results. We hypothesized that bed Age (years) 23 6 1 rest–induced insulin resistance is attributed to mecha- Body mass (kg) 74.9 6 2.3 nisms known to induce insulin resistance in chronic met- 6 abolic disease (i.e., ectopic lipid deposition, intramuscular Height (m) 1.81 0.02 22 accumulation of lipid intermediates, a decline in mito- BMI (kg $ m ) 23.0 6 0.9 2 chondrial content and/or impairment in skeletal muscle Fasting glucose (mmol $ L 1) 5.7 6 0.2 capillarization). In this study, we demonstrate that short- Fasting insulin (mU $ L21) 7.2 6 1.8 21 term bed rest leads to skeletal muscle atrophy, pro- HbA1c (% [mmol $ mol ]) 5.1 6 0.1 [32.4 6 0.9] nounced whole-body insulin resistance, and a decline in RMR (MJ $ d21) 7.2 6 0.2 skeletal muscle oxidative capacity.