TNF and obesity due to melanocortin 4 receptor deficiency: Moreover, several studies have demonstrated that inflammatory mediators, such as tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and C reactive protein, are elevated in obesity (27–29) and are involved in the increase of circulating leptin concentrations in rodents and humans, suggesting that these factors may be related to hyperleptinemia and leptin resistance onset (30, 31).