Cannabinoid receptor 1 (CB1) antagonism enhances glucose utilisation and activates brown adipose tissue in diet-induced obese mice

Abstract

Aims/hypothesis: We examined the physiological mechanisms by which cannabinoid receptor 1 (CB1) antagonism improves glucose metabolism and insulin sensitivity independent of its anorectic and weight-reducing effects, as well as the effects of CB1 antagonism on brown adipose tissue (BAT) function.

Methods: Three groups of diet-induced obese mice received for 1 month: vehicle; the selective CB1 antagonist SR141716; or vehicle/pair-feeding. After measurements of body composition and energy expenditure, mice underwent euglycaemic-hyperinsulinaemic clamp studies to assess in vivo insulin action. In separate cohorts, we assessed insulin action in weight-reduced mice with diet-induced obesity (DIO), and the effect of CB1 antagonism on BAT thermogenesis. Surgical denervation of interscapular BAT (iBAT) was carried out in order to study the requirement for the sympathetic nervous system in mediating the effects of CB1 antagonism on BAT function.

Results: Weight loss associated with chronic CB1 antagonism was accompanied by increased energy expenditure, enhanced insulin-stimulated glucose utilisation, and marked activation of BAT thermogenesis. Insulin-dependent glucose uptake was significantly increased in white adipose tissue and BAT, whereas glycogen synthesis was increased in liver, fat and muscle. Despite marked weight loss in the mice, SR141716 treatment did not improve insulin-mediated suppression of hepatic glucose production nor increase skeletal muscle glucose uptake. Denervation of iBAT blunted the effect of SR141716 on iBAT differentiation and insulin-mediated glucose uptake.

Conclusions/interpretation: Chronic CB1 antagonism markedly enhances insulin-mediated glucose utilisation in DIO mice, independent of its anorectic and weight-reducing effects. The potent effect on insulin-stimulated BAT glucose uptake reveals a novel role for CB1 receptors as regulators of glucose metabolism.

Fig. 1

Energy balance and body composition in DIO C57BL/6 mice treated with 10 mg/kg SR i.p. or vehicle. After 4 weeks of treatment mice were moved to indirect calorimetry cages for 4 days. a Food intake and (b) body weight of VEH (white squares), PF (triangles) and SR (black squares) mice. c Fat mass and (d) percentage change in fat mass from baseline of VEH (white bars), PF (hatched bars) and SR (black bars) mice measured by MRI. e Energy expenditure and (f) locomotor activity were measured by indirect calorimetry cages equipped with a beam-break measurement system. In all groups, n=11; *p<0.05 SR group vs PF and VEH groups; ^†p<0.05 SR group vs VEH group only

Fig. 2

Hyperinsulinaemic–euglycaemic clamp studies. After 7 weeks of treatment with VEH (white bars), PF (hatched bars) and SR (black bars), mice underwent a hyperinsulinaemic–euglycaemic clamp. Graphs show: (a) glucose infusion rate; (b) glucose disposal rate; (c) glucose production rate; (d) whole-body glycolysis rate. Glucose uptake was measured by 2-deoxy-[U-¹⁴C]glucose in WAT (e) and iBAT (f). In all groups, n=11. *p<0.05 SR group vs PF and VEH groups; ^†p<0.05 SR group vs VEH group only

Fig. 3

Rate of tissue glucose uptake and glycogen synthesis. a Glucose uptake in several muscles measured by 2-deoxy-[U-¹⁴C] glucose. b Glycogen synthesis rate in several muscles, liver and WAT in VEH (white bars), PF (hatched bars) and SR (black bars) groups. In all groups, n=11. EDL, extensor digitorum longus; Gast, gastrocnemius; Sol, soleus. *p<0.05 SR group vs PF and VEH groups; ^†p<0.05 SR group vs VEH group only

Fig. 4

SR141716 treatment induces BAT thermogenesis. iBAT temperature measurement with implantable probes during (a) the first 3 days and (b) the last 3 days of treatment with 10 mg/kg SR141716 i.p. (black squares) or vehicle (white squares). The shaded area indicates the dark period, while the vertical line indicates time of injection. c AUCs of iBAT temperature during days 1–3 and 10–12 in VEH (white bars) and SR (black bars). d Expression of Pgc-1α, Ucp1 and Pparδ in iBAT from VEH (white bars), SR (black bars) and PF (hatched bars) groups. For a–c, n=6, and for d, n=11; *p<0.05 (SR group vs other groups on the same graph). a.u., arbitrary units

Fig. 5

Effect of CB1 antagonism on iBAT morphology in sham-operated or denervated mice. a–d Haematoxylin and eosin staining of iBAT after chronic treatment with 10 mg/kg SR (b,d) or vehicle (a,c) in sham-operated (a,b) and denervated (c,d) mice. In order to confirm effectiveness of the surgical denervation, tyrosine hydroxylase, a marker of SNS innervation, was measured by western blot (e). In all groups, n=4. D-VEH, denervated VEH group; D-SR, denervated SR group; S-SR, sham-operated SR group; S-VEH, sham-operated VEH group; β-Tub, β-tubulin; TH, tyrosine hydroxylase

Fig. 6

Effect of denervation on body weight, adiposity and iBAT glucose uptake and gene expression. a Body weight of SR and VEH animals (black and white symbols, respectively) that had sham operation or iBAT denervation (squares and triangles, respectively). In b–e, white bars and black bars represent VEH and SR groups, respectively. b Fat mass of SR and VEH animals that had sham operation or iBAT denervation. c–e Activation of iBAT in sham-operated and denervated animals after chronic treatment with SR141716. c Glucose uptake in iBAT measured by 2-deoxy-[U-¹⁴C]glucose under hyperinsulinaemic conditions. d Ucp1mRNA expression (by two-way ANOVA: main effect of SR and denervation p≤0.05). e Pgc-1α mRNA expression. For a and b, n=13/group; for c, n=8/group; and for d and e, n=5/group; *p<0.05 SR group vs VEH group. a.u., arbitrary units; Denerv, denervated