Effect of crotamine on glucose uptake by brown adipose tissue: evaluation in an experimental model with 18FDG PET

Abstract

Brown adipose tissue /BAT plays an important role in thermoregulation. The decoupling between the electron transport chain and oxidative phosphorylation is mediated by uncoupling protein-1/UCP-1, which leads to the release of energy as heat, without ATP formation. BAT is activated by sympathetic noradrenergic stimuli, with exposure to cold being the main physiological stimulus. Positron emission tomography with 18F-fluorodeoxyglucose (FDG-PET) translates into images the in vivo glycolytic activity and has been increasingly used in the metabolic characterization of BAT, which in rodents is located predominantly in the interscapular region.Crotamine is a polypeptide isolated from the venom of the rattlesnake. Studies conducted by a researcher of the present project demonstrated that oral treatment with crotamine contributed not only to tumor remission in a murine melanoma model, but also allowed the first observation of the effect of this peptide on the differentiation and metabolic activation of BAT. Effects in rodents included reduced weight gain, reduced white fat, increased brown fat, changes in metabolic profile, and increased basal metabolism. Beta3 agonists are another option to increase the metabolic activity of BAT, since thermogenic activation is dependent on adrenergic pathways mediated by this class of receptors. There are possible indirect effects of crotamine in the adrenergic pathways, such as the reduction of mRNA expression of ²3 adrenergic receptors, and the hypothesis of a down-regulation of the receptor due to increased adrenergic tone has been raised. The present study will use FDG-PET to investigate the activation of BAT glycolytic metabolism in mice receiving crotamine after cold or beta3-agonist stimuli, with or without concomitant adrenergic beta-blocker. The results of this study will increase the understanding of the isolated or associated effects of drugs inducing the formation and activation of BAT, implying a better understanding of the mechanisms of metabolic regulation and the perspective of food or drug supplementation interventions in obesity and metabolic syndrome. Adult male mice of the C57BL-6 lineage will be evaluated longitudinally, with PET-FDG images at baseline, 10 days, and 21 days after starting daily oral treatment with crotamine 10 ¼g. Five groups with eight animals will be studied, according to the stimulus for BAT activation: none, cold (with or without beta-blocker), beta3-agonist (with or without beta-blocker). [Cold stimulus=cold chamber 6-7ºC, beta3-agonist = CL316,243 1 mg/kg iv, beta-blocker = 5 mg/kg intraperitoneal propranolol]PET images will be acquired in dedicated equipment for small animals, starting 45 minutes after intravenous administration of 18F-FDG. Volumes of interest (VOI) on the interscapular fat will be delimited in every animal. Metabolic activity measures will include by the maximum and average standardized uptake value (SUV) in the VOI. Total lesion glycolysis (TLG) will be obtained by multiplying SUV volume by volume of VOI. PET will also be acquired after administration of 11C-PK11195, a mitochondrial tracer proposed for the detection of BAT under thermoneutral conditions. The means and standard deviation of the variables in each group will be described. Continuous normal distribution data will be analyzed by Student's t-test and non-normal by the Kruskall-Wallis test, non-parametric quantities of the chi-square test or Fischer's exact test. In all situations a 5% significance will be adopted. (AU)