TNF and obesity due to melanocortin 4 receptor deficiency: In a study that evaluated gene expression and cytokine dosage in plasma and tissue before and after induction of obesity in animals fed a high-fat diet, Matsuzawa-Nagata et al. demonstrated that up-regulation of ROS gene expression preceded the onset of obesity, and also the production of Tumor Necrosis Factor alpha (TNF-α), suggesting that the onset of obesity is related to an imbalance in ROS production (Matsuzawa-Nagata et al., 2008).