The bile pigment [bilirubin](https://ul.orna.me/KOge/librarybiomarker?id=170) is commonly measured as a marker of liver health, and high levels can indicate disease. However, researchers found bilirubin in the brains of mice — in concentrations 5 to 10 times higher than in their rodent livers. The researchers set out to find out what the function of bilirubin in brain tissue was. They found that bilirubin is an antioxidant, important for protecting the brain from oxidative stress. ## Evidence base For their experiments, the team used lab-grown mouse neurons that had been genetically engineered not to produce bilirubin. As the cells grew, the researchers exposed them to oxidative stress. Compared to normal brain cells, the genetically modified neurons were much more vulnerable, especially when exposed to a harmful form of oxygen called superoxide. Study author Chirag Vasavda, M.D., suspected that oxidative stress reduced learning ability, memory, and brain development. To test this theory, the researchers stimulated excessive brain cell activity in normal mice and mice deprived of bilirubin. They found that the bilirubin-deprived mice suffered about two to three times more brain damage than their "normal" counterparts. The experiment showed that bilirubin may play an important role in controlling superoxide levels in the brain. This broadens the scientific understanding of the role of bilirubin and could lead to new treatments for neurodegenerative diseases such as Huntington's disease and Parkinson's disease. __Sources__: Chirag Vasavda et al, Bilirubin Links Heme Metabolism to Neuroprotection by Scavenging Superoxide, Cell Chemical Biology (2019). DOI: 10.1016/j.chembiol.2019.07.006