ABSTRACT: Inhibition of cannabinoid receptor 1 (CB1) has shown efficacy in reducing body weight and improving metabolic parameters, with the effects correlating with target engagement in the brain. Recently, the peripheral effects of inhibiting the CB1 receptor has been appreciated through studies in diet-induced obese and liver-specific CB1 KO mice. In this report, we systematically investigated gene expression changes in peripheral tissues of DIO mice treated with the CB1 inverse agonist AM251. CB1 receptor inhibition led to down-regulation of genes within the de novo fatty acid and cholesterol synthetic pathways, including SREBP-1 and -2, and their downstream targets in both liver and adipose tissue. In addition, genes involved in fatty acid Beta-oxidation were up-regulated with AM251 treatment, probably through the activation of PPARalpha. In adipose tissue, CB1 receptor inhibition led to the down-regulation of genes in the TNFalpha signal transduction pathway and possibly to the activation of PPARgamma, both of which would result in improved insulin sensitivity. CB1-/- mice were obtained from A. Zimmer (University of Bonn) (Zimmer et al., 1999) and back-crossed onto C57BL/6J genetic background for ten generations by A. Zimmer before homozygous CB1-/- mice were re-derived at Taconic Farms (German Town, NY) onto the C57BL/6N genetic background. Male CB1-/- mice and control littermates (n=5-7 in each group) at 2 months of age were fed with regular chow (Teklad 7012, 13 % kcal from fat, 3.41 kcal/g, Harlan Laboratories, Indianapolis, IN, USA) or high fat diet (S3282, 59.4% kcal from fat; 24.5% kcal from carbohydrate; 16.2% kcal from protein; 5.29 kcal/g, Bio-Serv, Frenchtown, NJ, USA) for 14 weeks, and were individually caged 1 week before drug treatment. Vehicle (0.5% methylcellulose) or AM251 (10 mg/kg, Sigma, St Louis, MO, USA) were dosed by oral gavage at 5:00 PM daily for 2 days. Body weight was measured at 5:00 PM on day 1 and 2, and at 10:00 AM on day 3 before tissue collection. Food was measured at 5:00 PM on day 1 and at 10:00 AM on day 3 before tissue collection. Food intake is calculated as the difference in food weight at the start minus at the end of the study. Mice were euthanized by CO2 asphyxiation at 10:00 AM following the second dose.
