INS and obesity due to melanocortin 4 receptor deficiency: Although its biological functions are not fully understood, its action results in increased insulin sensitivity of peripheral tissues (through insulinomimetic properties), while its paracrine action may promote the increase in obesity through differentiation of fat cells and intensification of adipogenesis and up-regulation of other pro-inflammatory cytokines, such as IL-1β, IL-6, or TNF-α in vascular endothelial cells and peripheral blood monocytes [53,54].