Adipokines are a group of peptide hormones (polypeptides) that are predominantly produced and secreted in adipocytes of adipose tissue. Currently, more than 600 adipokines have been described in the human body with different biological properties. The most widely used classification focuses on their inflammatory properties and distinguishes between pro- and anti-inflammatory adipokines. The upregulation of pro-inflammatory adipokines leads to the development of a chronic, low-grade inflammatory state and contributes to metabolic dysfunction (Kovács D et al. 2020).
Many adipins transmit their signals via specific receptors. Others, however, act via receptors of various cytokines and hormones Kovács D et al. 2020). For example, adiponectin exerts its effect via two receptors. AdipoR1 is expressed by skeletal muscle and other tissues, and AdipoR2 is expressed by hepatocytes. Leptin, for example, exerts its biological effects via the leptin receptor (Ob-R), which belongs to the type I cytokine receptor family (Gorska E et al. 2010). The receptors for chemerin, monocyte chemoattractant protein-1 (MCP-1), and apelin are G protein-coupled receptors (GPRs) (Kovács D et al. (2020), whereas the effects of resistin, visfatin, and fetuin-A are mediated via the insulin receptor and a pattern recognition receptor (Toll-like receptor [TLR] (Fasshauer, M et al. (2015). Adiponectin receptors are members of the progestin and AdipoQ receptor families, whereas zinc-α2-glycoprotein (ZAG) is a β2-adrenoreceptor agonist. SERPINE1 binds to the urokinase receptor, lipocalin 2 (LCN2) may act through its own specific 24p3 receptor, and in the case of omentin-1, no specific receptor has yet been identified.