What are
The term adipokine was coined to identify in a generic way all the molecules synthesized and secreted by adipose tissue.
Obesity and Inflammation
In addition to its primary function as an energy reservoir, in fact, the white adipose tissue is now considered a real source of hormones. In obesity, this secretion, in particular that of the adipokines acting as peptide hormones (see leptin and adiponectin) is altered. In fact, it seems that the excessive increase in size of the mature adipocyte, typical of obese people, somehow stimulates the "infiltration of macrophages responsible for the" digestion "of the enormous lipid vacuole of dead adipocytes (perhaps due to hypoxia). The consequent release of pro-inflammatory substances has particularly negative consequences on the health of the organism and predisposes to various diseases typically associated with obesity: diabetes, and various cardiovascular diseases.
How do they work
Some adipokines act in an autocrine way, others with paracrine mechanisms and still others in an endocrine way. The role of these substances - at times still to be clarified - is quite variable in relation to the adipokine considered; many of these are involved in the immune response and inflammation, while others participate in the regulation of energy metabolisms.
Which ones are they
Among the best known adipokines we remember leptin, interleukin-6, tumor necrosis factor (TNF-a), acylation stimulating protein (ASP), plasminogen activator / inhibitor (PAI-1) and " adiponectin.
Some of these, such as the classic cytokines [interleukin 1 (IL-1), interleukin 6 (IL-6), Tumor necrosis factor α (TNFα)], presumably derive from inflammatory cells infiltrated in the adipose tissue, whose concentration is proportional to the volume of adipocytes.
Some of the main adipokines:
- LEPTIN: is a fundamental signal of satiety in the brain; it also influences various bodily activities, such as hematopoiesis and reproduction; expression and
leptin secretion increase in obesity. - ADIPONECTIN: important in the regulation of energy metabolism, it promotes the oxidation of triglycerides and increases the insulin sensitivity of muscles and liver; the expression and secretion of adiponectin decrease in obesity.
- ASP: increases glucose uptake in adipocytes, inhibits hormone-sensitive lipase and activates diacylglycerol acyltransferase. It therefore has a stimulating activity on the synthesis of triglycerides and inhibits the oxidation of fatty acids.
- TNF-α: the excessive production of this substance by the adipose tissue is correlated in the insulin resistance in the obese. In fact, it increases liposis and the consequent increase in circulating FFAs; at the level of muscle tissue it reduces the expression of the glucose transporter GLUT-4. It also causes the brown adipose cells, responsible for auxiliary thermogenesis, to apoptosis and reduces their functionality.
- PAI-1: is a causal factor of vascular thrombosis.
- RESISTIN: inhibits glucose uptake in skeletal muscle cells.
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