INS and obesity due to melanocortin 4 receptor deficiency: In reference to insulin sensitivity, experimental data in mice models showed that bilirubin administration improves hyperglycemia and obesity by increasing insulin sensitivity and suggest that bilirubin or bilirubin-increasing drugs might be useful as an insulin sensitizer for the treatment of obesity-induced insulin resistance and type 2 diabetes based on its profound anti-ER stress and anti-inflammatory properties (46).