title: Increased brown adipose tissue oxidative capacity in cold-acclimated humans.
abstract: BACKGROUND
  Recent studies examining brown adipose tissue (BAT) metabolism in adult humans have provided convincing evidence of its thermogenic potential and role in clearing circulating glucose and fatty acids under acute mild cold exposure. In contrast, early indications suggest that BAT metabolism is defective in obesity and type 2 diabetes, which may have important pathological and therapeutic implications. Although many mammalian models have demonstrated the phenotypic flexibility of this tissue through chronic cold exposure, little is known about the metabolic plasticity of BAT in humans.
  
  
  OBJECTIVE
  Our objective was to determine whether 4 weeks of daily cold exposure could increase both the volume of metabolically active BAT and its oxidative capacity.
  
  
  METHODS
  Six nonacclimated men were exposed to 10°C for 2 hours daily for 4 weeks (5 d/wk), using a liquid-conditioned suit. Using electromyography combined with positron emission tomography with [(11)C]acetate and [(18)F]fluorodeoxyglucose, shivering intensity and BAT oxidative metabolism, glucose uptake, and volume before and after 4 weeks of cold acclimation were examined under controlled acute cold-exposure conditions.
  
  
  RESULTS
  The 4-week acclimation protocol elicited a 45% increase in BAT volume of activity (from 66 ± 30 to 95 ± 28 mL, P < .05) and a 2.2-fold increase in cold-induced total BAT oxidative metabolism (from 0.725 ± 0.300 to 1.591 ± 0.326 mL·s(-1), P < .05). Shivering intensity was not significantly different before compared with after acclimation (2.1% ± 0.7% vs 2.0% ± 0.5% maximal voluntary contraction, respectively). Fractional glucose uptake in BAT increased after acclimation (from 0.035 ± 0.014 to 0.048 ± 0.012 min(-1)), and net glucose uptake also trended toward an increase (from 163 ± 60 to 209 ± 50 nmol·g(-1)·min(-1)).
  
  
  CONCLUSIONS
  These findings demonstrate that daily cold exposure not only increases the volume of metabolically active BAT but also increases its oxidative capacity and thus its contribution to cold-induced thermogenesis.
authors.affiliation: Faculty of Health Sciences (D.P.B., H.C.T., F.H.), University of Ottawa, Ottawa, Ontario, Canada K1N 6N5; Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec (S.M.L., D.R.), Université Laval, Québec City, Québec, Canada G1V 4G5; Department of Medicine (C.N., M.K., S.P., A.C.C.), Centre de Recherche Clinique Etienne-Le Bel, Université de Sherbrooke, Sherbrooke, Québec, Canada; and Department of Nuclear Medicine and Radiobiology (S.P., B.G., E.E.T.), Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4.
authors.forename: Denis P
authors.initials: DP
authors.lastname: Blondin
authors.forename: Sébastien M
authors.initials: SM
authors.lastname: Labbé
authors.forename: Hans C
authors.initials: HC
authors.lastname: Tingelstad
authors.forename: Christophe
authors.initials: C
authors.lastname: Noll
authors.forename: Margaret
authors.initials: M
authors.lastname: Kunach
authors.forename: Serge
authors.initials: S
authors.lastname: Phoenix
authors.forename: Brigitte
authors.initials: B
authors.lastname: Guérin
authors.forename: Eric E
authors.initials: EE
authors.lastname: Turcotte
authors.forename: André C
authors.initials: AC
authors.lastname: Carpentier
authors.forename: Denis
authors.initials: D
authors.lastname: Richard
authors.forename: François
authors.initials: F
authors.lastname: Haman
mesh_terms: D000064:Acclimatization; D019342:Acetic Acid; D002001:Adipose Tissue, Brown / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000378:metabolism*; D000328:Adult; D001833:Body Temperature Regulation; D002250:Carbon Radioisotopes; D003080:Cold Temperature; D004734:Energy Metabolism; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D009929:Organ Size; D010084:Oxidation-Reduction; D049268:Positron-Emission Tomography; D055815:Young Adult
chemical_list: D002250:Carbon Radioisotopes; D019788:Fluorodeoxyglucose F18; D019342:Acetic Acid