CCL2 and obesity due to melanocortin 4 receptor deficiency: Several studies reported that the low-grade inflammation is characterized by the overexpression of proinflammatory cytokines, such as tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), interleukin 1β (IL-1β), and monocyte chemoattractant protein-1 (MCP-1), in the obesity-induced insulin resistance, reduced insulin sensitivity, and pathogenesis of T2DM [10, 11].