A Role for Endocannabinoids in the Control of Dietary Fat Intake

项目总结/抽象。哺乳动物在寻找美味的富含脂肪的食物方面具有适应性优势

Project Summary/Abstract. Mammals have an adaptive advantage in seeking palatable fat-rich foods, which are nutritionally essential but scarce in most natural habitats. In modern societies, where fatty foods are readily available and the energy necessary to find them is minimal, this innate drive can become maladaptive and is considered a primary contributing factor for obesity, cardiovascular disease, and diabetes. Despite its theoretical and practical significance, the neural mechanisms controlling fat preference and compulsive eating are largely unknown. The endocannabinoid (eCB) system, in particular, has gained attention for its key roles in the acquisition and sensory evaluation of natural (e.g., food) and non-natural (e.g., drugs of abuse) reinforcers. The eCBs are endogenous lipids that bind to and activate the same receptors as ∆9-THC, the psychoactive component in cannabis. Recent data from our laboratory indicate that oral exposure to dietary fat stimulates eCB mobilization in the rat small intestine, and localized blockade of this signaling event suppresses fat sham feeding. These results suggest that the intestinal eCB system exerts a powerful regulatory control over fat intake, and provide novel insights into physiological mechanisms that govern preference for fats, which are posited to possess addictive-like properties. The long-term goal of this research program is to utilize state-of- the-art experimental tools to probe the interface of food intake and reward, and thus, elucidate the biological substrates of fat preference and compulsive eating. The central hypothesis of this proposal is that the mobilization of eCBs in the small intestine, elicited by orosensory stimulation by fat-rich foods, contributes to the physiological control of fat intake and the pathophysiological state of obesity. We have three specific aims and unique approaches pertinent to a test of this hypothesis: (i) to identify lipid classes that stimulate intestinal eCB mobilization and promote dietary fat intake by utilizing a combination of surgical, biochemical, and pharmacological tools to identify select lipid classes responsible for driving intestinal eCB signaling and its role in fat preference; (ii) to define changes in intestinal eCB-metabolizing enzymes involved in cephalic-phase fat intake by characterizing modifications to intestinal gene transcripts and proteins involved in eCB metabolism; (iii) to identify oral fatty-acid receptors and neural pathways that maintain intestinal eCB mobilization and fat intake by investigating the ability for fat sham feeding to enhance intestinal eCB signaling in animals that lack the putative fat receptors, and identify the neural pathways that normally transmit this information to the gut. Collectively, the proposed plan will identify physiological mechanisms that control the positive feedback obtained from a fatty meal based on its orosensory properties. Furthermore, the proposal is highly novel because it focuses on an eCB signal in the gut, discovered in our preliminary work, that drives fat intake. Thus, these studies will provide support for the development of anti-obesity drugs that target the eCB system in the periphery, without disrupting central mechanisms that may lead to psychiatric side effects.