LEP and obesity due to melanocortin 4 receptor deficiency: In obesity, type 2 diabetes mellitus (T2DM), and metabolic syndrome, the insulin and leptin signaling pathways are attenuated as a result of long-term exposure to hyperinsulinemia and hyperleptinemia; thus, the use of PTP1B inhibitors may become one of the approaches to restore them and increase tissue sensitivity to insulin and leptin [1,6].