The endocannabinoid system: a new pharmacological target for obesity treatment?

An H2R-dependent medial septum histaminergic circuit mediates feeding behavior

Novel targets for treating feeding-related diseases are of great importance, and histamine has long been considered an anorexigenic agent. However, understanding its functions in feeding in a circuit-specific way is still limited. Here, we report a medial septum (MS)-projecting histaminergic circuit mediating feeding behavior. This MS-projecting histaminergic circuit is functionally inhibited during food consumption, and bidirectionally modulates feeding behavior via downstream H2, but not H1, receptors on MS glutamatergic neurons. Further, we observed a pathological decrease of histamine 2 receptors (H2Rs) expression in MS glutamatergic neurons in diet-induced obesity (DIO) mice. Genetically, down-regulation of H2Rs expression in MS glutamatergic neurons accelerates body-weight gain. Importantly, chronic activation of H2Rs in MS glutamatergic neurons (with its clinical agonist amthamine) significantly slowed down the body-weight gain in DIO mice, providing a possible clinical utility to treat obesity. Together, our results demonstrate that this MS-projecting histaminergic circuit is critically involved in feeding, and H2Rs in MS glutamatergic neurons is a promising target for treating body-weight problems.

New insights into bisphenols induced obesity in zebrafish (Danio rerio): Activation of cannabinoid receptor CB1

Bisphenols (BPs), as widely used plastic additives, penetrate into our daily lives. BPs are considered endocrine disruptors and could potentially induce obesity. In this study, the effects of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA) on food intake and lipid metabolism in zebrafish were determined. Moreover, the impact of BPA and TBBPA on the endocannabinoid system (ECS) of zebrafish was further explored by metabolomics, transcriptomics, and molecular docking analysis. Here we show that exposure to BPA and TBBPA at concentrations commonly found in the environment (20, 100, and 500 μg/L) led to hyperphagia and obesity in adult male zebrafish. Metabolomics and histopathological analysis revealed significant lipid accumulation in the liver of zebrafish exposed to BPA and TBBPA. The expression of ECS-related genes, in conjunction with RNA-Seq results, further indicated that BPA and TBBPA increased appetite and induced obesity by activating cannabinoid receptor type 1(CB1). Furthermore, molecular docking revealed that six representative BPs including BPA and TBBPA could bind to the CB1 receptor. Collectively, these findings indicate that CB1 may be a potential target for BPs to induce obesity.

Fighting food temptations: the modulating effects of short-term cognitive reappraisal, suppression and up-regulation on mesocorticolimbic activity related to appetitive motivation

The premise of cognitive therapy is that one can overcome the irresistible temptation of highly palatable foods by actively restructuring the way one thinks about food. Testing this idea, participants in the present study were instructed to passively view foods, up-regulate food palatability thoughts, apply cognitive reappraisal (e.g., thinking about health consequences), or suppress food palatability thoughts and cravings. We examined whether these strategies affect self-reported food craving and mesocorticolimbic activity as assessed by functional magnetic resonance imaging. It was hypothesized that cognitive reappraisal would most effectively inhibit the mesocorticolimbic activity and associated food craving as compared to suppression. In addition, it was hypothesized that suppression would lead to more prefrontal cortex activity, reflecting the use of more control resources, as compared to cognitive reappraisal. Self-report results indicated that up-regulation increased food craving compared to the other two conditions, but that there was no difference in craving between the suppression and cognitive reappraisal strategy. Corroborating self-report results, the neuroimaging results showed that up-regulation increased activity in important regions of the mesocorticolimbic circuitry, including the ventral tegmental area, ventral striatum, operculum, posterior insular gyrus, medial orbitofrontal cortex and ventromedial prefrontal cortex. Contrary to our hypothesis, suppression more effectively decreased activity in the core of the mesocorticolimbic circuitry (i.e., ventral tegmental area and ventral striatum) compared to cognitive reappraisal. Overall, the results support the contention that appetitive motivation can be modulated by the application of short-term cognitive control strategies.

Effects of the cannabinoid-1 receptor antagonist rimonabant on psychiatric symptoms in overweight people with schizophrenia: a randomized, double-blind, pilot study

Weight gain is a major adverse effect of several second-generation antipsychotic medications. Rimonabant is a cannabinoid-1 receptor antagonist that promotes weight loss in the general population. We conducted a 16-week, double-blind, placebo-controlled study of rimonabant (20 mg/d) in people with schizophrenia or schizoaffective disorder, based on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria, who were clinically stable on second-generation antipsychotics. Participants had a body mass index of 27 kg/m or higher with hyperlipidemia or body mass index of 30 kg/m or higher, and no current substance abuse/dependence (except nicotine), more than weekly cannabis use, or recent depressive symptoms/suicidality. An exercise and dietary counseling group was offered weekly. Target enrollment was 60; the trial was terminated early because of withdrawal of rimonabant from the European market. Fifteen participants were randomized (7 rimonabant, 8 placebo); 5 completed in each group. Rimonabant was associated with a greater reduction in Brief Psychiatric Rating Scale total score versus placebo (mean ± SE difference, -1.9 ± 0.8, P = 0.02), driven by differences in the Brief Psychiatric Rating Scale anxiety/depression (-1.4 ± 0.35, P = 0.0004) and hostility (-0.7 ± 0.3, P = 0.02) factors. Group differences were not significant for the Calgary Depression Scale total score (P = 0.24), Scale for the Assessment of Negative Symptoms total score (P = 0.13), weight, blood pressure, or fasting lipids or glucose. Rimonabant was well tolerated with no significant adverse events. No significant weight loss, metabolic effects, or adverse psychiatric effects were associated with the cannabinoid-1 receptor antagonist rimonabant in this small sample of people with schizophrenia. The endocannabinoid system remains a promising target for pharmacotherapy of schizophrenia and obesity.