OBJECTIVE-Blockade of the CB1 receptor is one of the promising strategies for the treatment of obesity. Although antagonists suppress food intake and reduce body weight, the role of central versus peripheral CB1 activation on weight loss and related metabolic parameters remains to be elucidated. We therefore specifically assessed and compared the respective potential relevance of central nervous system (CNS) versus peripheral CB1 receptors in the regulation of energy homeostasis and lipid and glucose metabolism in diet-induced obese (DIO) rats.RESEARCH DESIGN AND METHODS-Both lean and DIO rats were used for our experiments. The expression of key enzymes involved in lipid metabolism was measured by real-time PCR, and euglycemic-hyperinsulinemic clamps were used for insulin sensitivity and glucose metabolism studies.RESULTS-Specific CNS-CB1 blockade decreased body weight and food intake but, independent of those effects, had no beneficial influence on peripheral lipid and glucose metabolism. Peripheral treatment with CB1 antagonist (Rimonabant) also reduced food intake and body weight but, in addition, independently triggered lipid mobilization pathways in white adipose tissue and cellular glucose uptake. Insulin sensitivity and skeletal muscle glucose uptake were enhanced, while hepatic glucose production was decreased during peripheral infusion of the CB1 antagonist. However, these effects depended on the antagonistelicited reduction of food intake.CONCLUSIONS-Several relevant metabolic processes appear to independently benefit from peripheral blockade of CB1, while CNS-CB1 blockade alone predominantly affects food intake and body weight. Diabetes 57:2977-2991, 2008 T he incidence of obesity and the metabolic syndrome have grown to epidemic proportions, making increased research efforts toward discovery of novel anti-obesity therapies increasingly important. Endocannabinoids are key modulators of feeding behavior through the activation of the CB1 receptor (1,2), which is localized in the periphery as well as in many brain areas involved in the regulation of energy homeostasis and reward processes (3,4). Recent studies (5-11) have demonstrated that blocking the activity of the endogenous cannabinoid system may be a successful strategy for the treatment of obesity and the metabolic syndrome.It is well known that CB1 receptors in the hypothalamus might regulate food intake through the disinhibition of the release of melanin-concentrating hormone from lateral hypothalamic neurons (12) and the inhibition of the release and/or expression of corticotrophin-releasing hormone in the paraventricular nucleus (13). Both these effects are under the negative control of leptin, which is known to negatively control endocannabinoid tone in the hypothalamus (2). On the other hand, the effects of CB1 activation on ␣-melanocyte-stimulating hormone are controversial, since both inhibition and stimulation were reported in the study by Hentges et al. (14), and no downstream effects of ␣-melanocyte-stimulating hormone on endocannabinoi...

A study that was designed to identify plausible replacements for highly basic guanidine moiety contained in potent MC4R agonists, as exemplified by 1, led to the discovery of initial nonguanidine lead 5. Propyl analog 23 was subsequently found to be equipotent to 5, whereas analogs bearing smaller and branched alkyl groups at the 3 position of the oxopiperazine template demonstrated reduced binding affinity and agonist potency for MC4R. Acylation of the NH2 group of the 4F-D-Phe residue of 3-propyl analog 23 significantly increased the binding affinity and the functional activity for MC4R. Analogs with neutral and weakly basic capping groups of the D-Phe residue exhibited excellent MC4R selectivity against MC1R whereas those with an amino acid had moderate MC4R/MC1R selectivity. We have also demonstrated that compound 35 showed promising oral bioavailability and a moderate oral half life and induced significant weight loss in a 28-day rat obesity model.

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The melanin-concentrating hormone-1 receptor (MCH1R) is a G-protein-coupled receptor expressed in the brain and peripheral tissues that regulates energy storage and body weight. Here, we focused on discovery of the mechanism and site of action for a small-molecule MCH1R antagonist, which yields weight loss in a mouse model of human obesity. MCH1R is expressed throughout the brain but also found in peripheral tissues known to regulate fat storage and utilization, e.g., skeletal muscle and adipose tissue. Previous studies of MCH1R antagonist studies have not delineated the site that is critical for mediating the anorexigenic and weight-reducing actions. In this study, we evaluated the role of the brain and peripheral tissue receptors. We developed a novel nonbrain-permeable MCH antagonist analog with a carboxylic acid moiety to specifically test the site of action. Based on in vitro and in vivo assays, the analog is not able to cross the blood-brain barrier and does not lead to inhibition of food intake and reduced body weight. The data clearly demonstrate that MCH1R antagonists need access to the brain to reduce body weight and fat mass. The brainpermeable MCH1R antagonist leads to significant reduction in body weight and fat mass in diet-induced obese mice. The effect is dose-dependent and appears to be partially driven by a reduction in food intake. Finally, these studies show the utility of a medicinal chemistry approach to address an important biological and pharmacological question.The obesity epidemic continues to increase in many developed and developing countries (Ogden et al., 2003;Haslam and James, 2005). The 2004 National Health and Nutrition Examination Survey indicated that more than 50% of the United States population is either obese or overweight (Hedley et al., 2004;Ogden et al., 2006). More importantly, the incidence of obese and overweight children is also on the rise. Obesity is associated with multiple metabolic disorders, including diabetes and cardiovascular disease (Ogden et al., 2003). There is a great interest in identifying behavioral and pharmacological approaches to reduce body weight in obese and overweight individuals.Weight loss intervention strategies include targets for reducing hunger/appetite, enhancing satiety, increasing metabolism/ energy utilization, blocking fat absorption, inhibiting adipose tissue differentiation, and inducing adipose tissue apoptosis. The current therapeutic approaches for weight loss include diet, exercise, and pharmacotherapy. Efficacy is very modest, with a high rate of recidivism at the end of the treatment period (Schnee et al., 2006). Orlistat (Xenical) and sibutramine (Meridia) are currently the only two approved pharmacotherapy agents on the market. Orlistat blocks absorption of fat from the intestine, whereas sibutramine reduces appetite by acting on brain pathways that regulate hunger (Bray and Ryan, 2007). These drugs show limited efficacy, and considerable attention is focused on the development of new reagents to decrease body weight.

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