Table 1.

Overview of adipokines.

Adipokine	Description	Receptor/Signaling	Functions	Refs.
Leptin	cytokine-like hormone encoded by LEP gene (obese gene, ob). secreted by WAT, brain, intestines, skeletal muscle, placenta, etc.	LEP-R (encoded by LEPR), which have at least six isoforms LEP-R long isoform signals via JAK–STAT activation or, alternatively, via p38 MAPK, JNK, ERK1/2, PI3K/Akt or PKC signaling	controls appetite and body weight at the hypothalamus level regulates insulin secretion, thermogenesis, lipid homeostasis, reproductive functions, inflammation, infection, angiogenesis, and homeostasis of cartilage and bone	[6,22,23]
Adiponectin (ACRP30, AdipoQ, GBP28 or apM1)	encoded by ADIPOQ gene homologous to C1q, collagen VIII and collagen X 12–18-monomers, trimers, and hexamers forms produced by AT, bone marrow, skeletal muscle, and cardiac tissue	AdipoR1 (mainly present in skeletal muscle) and AdipoR2 (prevalent in the liver) signals through AMPK, PPARα or PPARγ	augments FA oxidation and glucose uptake in the muscle decreases glucose synthesis in the liver affects obesity, metabolic syndrome, lipodystrophy, and cardiovascular disease.	[24,25]
Ghrelin	hormone expressed by the stomach’s oxyntic glands, pancreatic islets, hypothalamus, lung, testis, and ovary	acylation catalyzed by GOAT (UAG to AG conversion) AG activates, while UAG antagonizes, GHSR1a	triggers food intake and adiposity regulates glucose metabolism, reward behavior, gut motility, and immune system	[26,27]
Resistin (ADSF or FIZZ3)	found as dimers in human blood produced in macrophages, mononuclear leukocytes, bone marrow cells, and spleen	ROR-1, IGF-1R and CAP1 are potential receptors toll-like receptor (TLR) 4 mediate resistin-induced pro- inflammatory cytokines secretion via NF-κB and C/EBPβ.	regulates blood glucose levels and lipid metabolism and promotes IR induces pro-inflammatory cytokines secretion and monocytes differentiation into macrophages.	[28]
RBP4	member of the lipocalin family expressed by liver, AT, retinal pigment epithelium, kidney, peritubular, and Sertoli cells of the testis bound to TTR in the circulation	STRA6 mediates retinol influx from the blood to target cells	transports retinol (essential for the visual cycle) contributes to IR, dyslipidemia, T2DM and cardiovascular dysfunction	[29]
Visfatin (PBEF or NAMPT)	homodimeric cytokine-like peptide with intracellular (iNAMPT) and extracellular (eNAMPT) forms	unidentified specific receptor iNAMPT is the rate-limiting enzyme of NAD biosynthesis from nicotinamide.	iNAMPT modulates cellular metabolism, differentiation, and stress response eNAMPT induces pro-inflammatory cytokines production and associates with metabolic and inflammatory diseases	[30,31]
Chemerin (TIG2 or RARRES2)	secreted as an inactive precursor (prochemerin) activated by proteases of the coagulation cascade, neutrophil-derived proteases (elastase and cathepsin G), bacterial proteases, and mast cell products (tryptase)	CMKLR1 mediates chemerin’s chemotactic activity GPR1 and CCRL2 also binds chemerin, but their functional relevance is unknown	Regulates adipocyte differentiation, insulin sensitivity, glucose, and lipid metabolism bridges innate and adaptive immunity through CMKLR1 (expressed in antigen-presenting cells, natural killer cells, and macrophages)	[32]
AFABP (ap2 or FABP4)	belongs to the lipocalin family abundant cytosolic protein of mature adipocytes also produced by endothelial cells and macrophages	unidentified receptor high affinity and selectivity for long-chain fatty acids induced by FA, TLRs agonists, oxLDL, and advanced glycation end products	modulates lipolysis in adipocytes promotes cholesterol esters accumulation and foam-cell formation induces endothelial dysfunction	[33]