Adipose tissue as a source of inflammatory cytokines in health and disease: focus on end-stage renal disease.

Adipose tissue is a necessary survival characteristic of species that do not have constant access to food. TNF-alpha is a very fundamental "internal regulator" (intra-system) of adipose tissue metabolism, and IL-6 and IL-1 beta are relevant control factors, as well. Leptin and IL-6, but not TNF-alpha, appear to be the major signals linking adipose tissue to the systemic immunologic response. In ESRD, it has been coherently observed that acute-phase reactants like CRP and serum amyloid A are independently associated to atherosclerosis, death, and cardiovascular complications. Leptin is inversely related with plasma creatinine, suggesting that reduced renal clearance is a primary factor responsible for hyperleptinemia in ESRD. On the other hand, this adipose tissue hormone behaves as an inverse acute-phase reactant (i.e., it decreases during spontaneous episodes of the acute-phase response). Dialysis patients with hyperleptinemia have more severe degrees of insulin resistance but further studies are required to see whether leptin plays a role in insulin resistance in these patients. The most abundant protein synthesized in the adipose tissue, adiponectin, is inversely related to metabolic risk factors like glucose, triglycerides, insulin, and HDL cholesterol in uremic patients, suggesting that this cytokine is a protective factor for the cardiovascular system. Accordingly, plasma adiponectin is an independent, inverse predictor of incident cardiovascular events in dialysis patients.