Pharmacology of Appetite Suppression: Implication for the Treatment of Obesity

Abstract

Given the current global epidemic of obesity there is a demand for new anti-obesity drugs to overcome the problem. Many pharmacological agents reduce food intake and significantly decrease body mass when administered to animals but affect feeding behaviour in a profoundly different way indicating the variety of biological mechanisms by which such agents act (appetite verses non-appetite). More limited clinical data demonstrates that some of the same drugs produce decreases in food intake and weight loss in humans. A few of these drugs do so by modifying the functioning of the appetite system as measured by subjective changes in feelings of hunger and fullness (indices of satiety). These drugs that modify the daily flux of appetite could be considered as 'appetite suppressants' with clinical potential as anti-obesity agents. Drugs that can be considered suitable candidates for appetite suppressants are agents that enhance peripherally satiety peptide systems (such as CCK, Bombesin/GRP, Enterostatin and GLP-1), alter the CNS levels of various hypothalamic neuropeptides (NPY, Galanin, Orexin, CART and Melanocortins) or monoamine neurotransmitters (such as serotonin, nor-adrenaline and possibly dopamine). Recently, the hormone leptin has become regarded as a key hormonal signal linking adipose tissue status with a number of key central nervous system circuits (NPY, CART, CRF, Melanocortins and possibly Orexins). This tonic system may also provide drug targets for the control of appetite. Any changes induced by a potential appetite suppressant should be considered in terms of the (i) psychological experience and behavioural expression of appetite, (ii) metabolism and peripheral physiology, and (iii) functioning of CNS neural pathways. In humans, such modulation of appetite will involve changes in total caloric consumption, subjective changes in feelings of hunger and fullness, preferences for specific food items, and general macronutrient preferences. These may be expressed behaviourally as changes in meal patterns, snacking behaviour and food choice. Within the next 20 years it is certain that clinicians will have a new range of anti-obesity compounds available to choose from. Such novel compounds may act on a single component of the appetite system or target a combination of these components detailed in this review. Such compounds used in combination with life style changes and dietary intervention may be critical in dealing with the rising world epidemic of obesity.