Adipokine

Adipokines, also known as adipocytokines, are bioactive peptides and proteins secreted by adipose tissue. They function as signaling molecules that regulate a range of physiological processes, including appetite, energy expenditure, glucose and lipid metabolism, and immune or inflammatory responses. Adipose tissue releases adipokines from adipocytes as well as from resident stromal vascular cells, making it an endocrine organ. Obesity is associated with an altered adipokine profile and chronic low-grade inflammation, which contribute to insulin resistance and metabolic disease.

Key adipokines include leptin, adiponectin, resistin, visfatin (NAMPT), chemerin, omentin, apelin, and vaspin. Leptin informs the brain about energy stores and generally suppresses appetite while increasing energy expenditure; however, obesity often involves leptin resistance. Adiponectin enhances insulin sensitivity and has anti-inflammatory effects, with levels typically reduced in obesity. Resistin’s role in humans is less clear but has been linked to insulin resistance and inflammation in some studies. Visfatin, chemerin, omentin, apelin, and vaspin have diverse actions on metabolism and immune function, including modulation of insulin signaling, glucose uptake, lipid metabolism, and inflammatory cell recruitment. Receptor and signaling pathways vary among adipokines, with examples such as the leptin receptor and JAK-STAT signaling, and adiponectin receptors that activate AMPK and PPAR-α pathways.

Dysregulated adipokine signaling is implicated in obesity-related diseases, including type 2 diabetes, cardiovascular disease, and metabolic syndrome. Because adipokines reflect adipose tissue function, they are studied as potential biomarkers and therapeutic targets for metabolic and inflammatory disorders.