Adipokines Is Adipose Tissue an Endocrine Organ

Beta Switch Program

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Although loss of fat tissue during cancer has not been considered as a very important alteration, compared to those affecting the quality of life or the prognosis of the cachectic cancer patient, we now know that adipose tissue is not just a fat reservoir. The concept of the adipocyte as an 'intelligent' cell that is able to communicate directly or indirectly with the brain is revolutionary compared to the previously held view of adipose tissue as a metabolically inactive fat deposit. Nowadays, we can go a step further and introduce the concept of the adipocyte as an 'intelligence' centre involved

Fig. 2. The adipocyte as an endocrine organ. Recent work suggests that adipose tissue behaves as a true endocrine organ, releasing many active compounds involved in maintaining the homeostatic response and energy balance. These compounds include cytokines, such as TNF and IL-6; leptin (involved in food intake and thermogenesis); acute-phase reac-tants, such as CRP; resistin (involved in insulin resistance); ASP (involved in lipid synthesis), Acrp30 (probably involved in adipocyte differentiation); and PAI-1 (a haemostatic factor)

Fig. 2. The adipocyte as an endocrine organ. Recent work suggests that adipose tissue behaves as a true endocrine organ, releasing many active compounds involved in maintaining the homeostatic response and energy balance. These compounds include cytokines, such as TNF and IL-6; leptin (involved in food intake and thermogenesis); acute-phase reac-tants, such as CRP; resistin (involved in insulin resistance); ASP (involved in lipid synthesis), Acrp30 (probably involved in adipocyte differentiation); and PAI-1 (a haemostatic factor)

in the regulation of body weigh. But how is regulation accomplished?

Discovery of the hormone leptin [34] radically changed the field of body weight control. Leptin, a16-kDa protein synthesised in adipose tissue and secreted into the bloodstream, is the product of the ob gene. The protein travels to the brain, where it acts as a ponderostat or adipostat signal informing the brain about adipose tissue mass, and mediates a loss of appetite. Actually, the word leptin comes from the Greek leptos, which means thin. Mice that are ob/ob have a defect in leptin production, resulting in hyperphagia and, consequently, obesity. In other experimental models, such as the fatty rat, leptin production is normal but there seems to be a defect in the brain receptor [35]. Based on its amino-acid sequence, the receptor appears to be similar to the members of the class I cytokine receptor family [36]. Leptin production is correlated with an increase in fat mass and adipocyte size [37]. In addition to leptin, adipocytes synthesise and secrete many other mol ecules, especially cytokines. Thus, TNF-a is expressed and produced in adipose tissue, in particular in obesity conditions.

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