Adipose Tissue: The New Endocrine Organ? A Review Article

Abstract

Fat is either white or brown, the latter being found principally in neonates. White fat, which comprises adipocytes, pre-adipocytes, macrophages, endothelial cells, fibroblasts, and leukocytes, actively participates in hormonal and inflammatory systems. Adipokines include hormones such as leptin, adiponectin, visfatin, apelin, vaspin, hepcidine, chemerin, omentin, and inflammatory cytokines, including tumor necrosis factor alpha (TNF), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator protein (PAI). Multiple roles in metabolic and inflammatory responses have been assigned to adipokines; this review describes the molecular actions and clinical significance of the more important adipokines. The array of adipokines evidences diverse roles for adipose tissue, which looms large in the mediators of inflammation and metabolism. For this reason, treating obesity is more than a reduction of excess fat; it is also the treatment of obesity's comorbidities, many of which will some day be treated by drugs that counteract derangements induced by adipokine excesses.

ChemR23 knockout mice display mild obesity but no deficit in adipocyte differentiation

“…Some adipokines also influence adipose tissue development and inflammatory cell recruitment. Leptin and adiponectin are the most studied members of the adipokine family (Maffei et al 1995, Hu et al 1996, but several new members have been discovered recently (MacDougald & Burant 2007, Wozniak et al 2009, Ouchi et al 2011, and since 2007, chemerin has been included in this family of extracellular mediators (Bozaoglu et al 2007, Goralski et al 2007.…”

Virgin olive oil in preventive medicine: From legend to epigenetics

“…Until a few years ago, obesity was considered only a condition in which there is an excess accumulation of fat in adipocytes. Recently, however, some studies have shown that the white fat accounting for more than half of mature adipocytes and the remaining of pre-adipocytes, fibroblasts, endothelial cells and macrophages, is a true endocrine organ that plays an important role in both inflammatory and metabolic mechanisms [80,81]. In fact, adipocytes produce at least 50 adipokines, several substances that release chemotactic proteins, complement proteins (adipsin), proteins involved in blood pressure control, angiogenesis, and molecules involved in the metabolism of glucose and lipids including adiponectin, resistin, visfatin, apelin, vaspin, hepcidin, chemeria, and omentin [81,82].…”

“…Recently, however, some studies have shown that the white fat accounting for more than half of mature adipocytes and the remaining of pre-adipocytes, fibroblasts, endothelial cells and macrophages, is a true endocrine organ that plays an important role in both inflammatory and metabolic mechanisms [80,81]. In fact, adipocytes produce at least 50 adipokines, several substances that release chemotactic proteins, complement proteins (adipsin), proteins involved in blood pressure control, angiogenesis, and molecules involved in the metabolism of glucose and lipids including adiponectin, resistin, visfatin, apelin, vaspin, hepcidin, chemeria, and omentin [81,82]. Adipocytes in obese subjects, unlike subjects with normal weight, release a larger amount of proteins from white fat with pro coagulant activity, such as plasminogen activator inhibitor type 1 (PAI-1), factor VII and the inducible form of nitric oxide synthase (iNOS), which at least partly explains the increased risk of cardiovascular disease in obese subjects.…”

“…They also release cytokines with typical pro-inflammatory activities including leptin, the MCP-1, the tumor necrosis factor-alpha (TNFalpha), and the interleukin-6 (IL-6), thereby promoting a state of chronic inflammation, as shown by the abundant number of macrophages secreted in circulation by white adipose tissue. They also release free fatty acids and glycerol, promoting resistance to insulin, and leading to type 2 diabetes and metabolic syndrome, although the mechanisms behind this remain uncharacterized [80,81,[82][83][84][85][86]. They are consistently elevated in obese subjects and in type 2 diabetes in subjects with a high risk of coronary heart disease and rheumatoid arthritis, leading to an increase in lipolysis and lipid oxidation [80,[82][83][84][87][88][89].…”

Fuzzy logic as a decision-making support system for the indication of bariatric surgery based on an index (MAFOI) generated by the association between body fat and body mass index.

“…An excess of fat tissue (obesity) has been shown to be harmful for multiple organs and systems through trobogenic, atherogenic, oncogenic, hemodynamic, and neuro-humoral mechanisms [7][8][9][10][11] . Recently, obesity and related diseases (comorbidities), including diabetes mellitus, hypertension, coronary artery disease, cancer, sleep apnea, and osteoartrosis, have replaced tobacco use as a leading cause of death, where obesity contributes directly to the severity of the comorbities [12][13][14][15] .…”