Bilirubin: bad, yet good?

Bilirubin: Bad, yet good?

As an end product of the breakdown of red blood cells inmammals, bilirubin can cause problems if it accumulates in tissues in abnormal amounts, and it is particularly destructive when concentrated in the nervous system. Although normally excreted with body wastes, the fat-soluble bilirubin can cause dangerous jaundice, such as that seen in hemolytic disease of newborns. But there may be a good-news side to bilirubin's story, according to a report in the Feb. 27 SCIENCE.

Researchers at the University of California at Berkeley andSan Francisco found that very small concentrations of bilirubin "scavenge' harmful oxygen radicals in laboratory tests. Hydrogen peroxide and other oxygen radicals, by-products of the oxygen used during normal cellular metabolism, can damage cell membranes and enzymes through chemical reactions. They have been suggested as causes of a wide range of conditions, from cancer and heart disease to aging.

The study suggests that bilirubin in the body routinely actsas an antioxidant, disarming the oxygen radicals and thereby speeding repair of cell damage. Laboratory experiments show that when the oxygen concentration is equivalent to that found in living cells, the antioxidant activity of bilirubin exceeds that of well-known antioxidants found in mammalian cells.