Adipokines and etiopathology of metabolic disorders

White adipose tissue is an endocrine organ producing numerous proteins known as adipokines, which include leptin, adiponectin, resistin, visfatin, and other factors, which are involved in most metabolic disorders. In obesity, plasma leptin concentrations are high due to leptin resistance that may result from the attenuation of leptin signaling in the hypothalamus. Leptin acts to inhibit appetite, stimulate thermogenesis, enhance fatty acid oxidation, decrease glucose, and reduce body weight, and fat. A reduced adiponectin level has been associated with insulin resistance, dyslipidemia, and atherosclerosis, and its low level is a predictor of later development of type 2 diabetes. Resistin expression is low in adipose tissue and high in bone marrow and lungs, its role in glucose homeostasis remains controversial, it has been associated with insulin resistance and obesity. Visfatin is a secretory protein highly enriched in visceral adipocytes, liver, muscle, and lymphocytes. An increase of visfatin levels in obesity was related to preservation of insulin sensitivity, it enhances glucose uptake by adipocytes and inhibits hepatocyte glucose release, it induces tyrosine phosphorylation, and interacts with insulin receptors. Many studies are still being conducted to highlight the role of adipokines in metabolic disorders.