Bilirubin, a pigment found in bile, is best known for lending itself to the yellow hue seen in the skin of people with jaundice. Yet, recent research shows that this pigment could play a surprising role in protecting brain cells against the damage caused by oxidative stress.
Recently, Johns Hopkins Medicine researchers reported that, in mice studies, the compound was found in high doses in the brain. Bilirubin is known to be found in the liver and the blood and is often used as a measure to look for disease. While it has previously been unknown whether the compound has an effect on healthy people, researchers were surprised to discover bilirubin in “exceptional levels” within mouse brains. In fact, its concentration was five to 10 times higher than it is in their livers.
Researchers note that while bilirubin was originally deemed a waste product, the body uses a significant amount of metabolic energy to produce the compound. It, therefore, seemed strange for it to have no function. Thus, the researchers set out to discover why there would be so much bilirubin present in the brain. Because the brain is both metabolically active yet vulnerable to oxidative damage, they thought that the compound could serve as an important antioxidant.
To test their theory, they genetically engineered mouse neurons to not produce bilirubin. They then exposed the neurons to different sources of oxidative stress. Compared to normal mouse neurons, these cells were much more vulnerable to stressors, and in particular, were damaged by a chemical cell messenger called superoxide. While superoxide is important for learning and memory, it can lead to oxidative stress and brain damage in abnormally high levels. Uncontrolled superoxide levels could be caused by excessive neuron activity. According to the researchers, the study findings suggest that bilirubin may be integral to controlling superoxide levels within the brain.
Although research is still in its infancy, the team believes their discovery could help to uncover new treatment options for neurodegenerative diseases. In specific, Parkinson’s and Huntington’s diseases are characterized by high levels of oxidative stress and superoxide, so this finding could be particularly useful for researching new therapies for these conditions.