Int J Obes (Lond). 2006 Apr;30 Suppl 1:S33-8.
The role of the endocannabinoid system in the control of energy homeostasis.
Osei-Hyiaman D, Harvey-White J, Batkai S, Kunos G.
1Laboratory of Physiologic Studies, National Institute on Alcohol Abuse & Alcoholism, National Institutes of Health, Bethesda, MD, USA.
The endocannabinoid system has recently emerged as an important regulator of energy homeostasis, involved in the control of both appetite and peripheral fat metabolism. We briefly review current understanding of the possible sites of action and cellular mechanisms involved in the central appetitive and peripheral metabolic effects of endocannabinoids. Studies in our laboratory, using leptin-deficient obese rodents and CB1 cannabinoid receptor (CB1)-deficient mice, have indicated that endocannabinoids acting via CB1 are involved in the hunger-induced increase in food intake and are negatively regulated by leptin in brain areas involved in appetite control, including the hypothalamus, limbic forebrain and amygdala. CB1(-/-) mice are lean and are resistant to diet-induced obesity (DIO) despite similar energy intake to wild-type mice with DIO, suggesting that CB1 regulation of body weight involves additional peripheral targets. Such targets appear to include both adipose tissue and the liver. CB1 expressed in adipocytes has been implicated in the control of adiponectin secretion and lipoprotein lipase activity. Recent findings indicate that both endocannabinoids and CB1 are present in the liver and are upregulated in DIO. CB1 stimulation increases de novo hepatic lipogenesis through activation of the fatty acid biosynthetic pathway. Components of this pathway are also expressed in the hypothalamus where they have been implicated in the regulation of appetite. The fatty acid biosynthetic pathway may thus represent a common molecular target for the central appetitive and peripheral metabolic effects of endocannabinoids.
Int J Obes (Lond). 2006 Apr;30 Suppl 1:S30-2.
The unfolding cannabinoid story on energy homeostasis: central or peripheral site of action?
Horvath TL.
[1] 1Department of Ob/Gyn and Reproductive Sciences, Yale University School of Medicine, New Haven, CT, USA [2] 2Department of Neurobiology and Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT, USA.
Presentations in this symposium addressed effects and modes of action of endocannabinoids in various tissues in relation to metabolic disorders. Endocannabinoids are produced and exert their effect in various brain sites, including the mesolimbic reward circuitry and the hypothalamus. Both of these regions have direct ties to energy metabolism regulation, particularly food intake and energy expenditure. These data clearly suggest that the observed beneficial effects of CB1 (cannabinoid receptor 1) receptor antagonists on obesity may be related to the central endocannabinoid system. On the other hand, data presented on cannabinoid action in the liver and white adipose tissues clearly indicate that CB1-mediated events in affecting metabolic phenotype may occur in peripheral tissues as well. This together with the reported results from human trials on CB1 antagonists showing that the initial anorectic effect of rimonabant is diminished after the first weeks while longer lasting weight loss is achieved do indicate that peripheral action of cannabinoids are very important in body weight regulation. Should this hold true in the long run, antagonizing CB1 receptors with compound not crossing the blood-brain barrier could revolutionize pharmaceutical approaches to obesity by offering a tool that short cuts the central nervous system.
Int J Obes (Lond). 2006 Apr;30 Suppl 1:S19-23.
Mechanisms of CB1 receptor signaling: endocannabinoid modulation of synaptic strength.
Mackie K.
1Department of Anesthesiology, University of Washington School of Medicine, Seattle, WA, USA.
The CB1 cannabinoid receptor has attracted much recent interest because of the observation that CB1 receptor antagonists have efficacy in treating metabolic syndrome and obesity. CB1 receptors also mediate most of the psychotropic effects of Delta(9)-tetrahydrocannabinol (Delta(9)THC), the principal psychoactive component of cannabis. In addition, they are one component of an interesting and widespread paracrine signaling system, the endocannabinoid system. The endocannabinoid system is comprised of cannabinoid receptors, endogenous cannabinoids, and the metabolic pathways responsible for their synthesis and degradation. The details of the endocannabinoid system have been most thoroughly studied in the brain. Here it has been shown to be intimately involved in several forms of neuronal plasticity. That is, activation of CB1 receptors by endocannabinoids produces either short- or long-term changes in the efficacy of synaptic transmission. The behavioral consequences of these changes are many, but some of the most striking and relevant to the current symposium are those associated with endogenous reward and consumptive behavior. |
