The pharmacological features of bilirubin: the question of the century.

This review looks at the toxicity and metabolism of bilirubin in terms of its pharmacological potential. Its role has gained importance as more research has revealed the functional significance and interrelationship between the gasotransmitters nitric oxide and carbon monoxide. The biological actions of bilirubin have mostly been characterized in the high micromolar range where toxic effects occur. However, it could also prove to be an important cytoprotector for brain tissue, which is inherently less equipped for antioxidant defense. Plasma bilirubin levels negatively correlate to a number of disease states. Higher levels of bilirubin that are still within the normal range provide a protective effect to the body. The effects on various disorders could be tested using controlled pharmacological upregulation of the molecule with animal models. At nanomolar concentrations, considerable benefits have been obtained when the molecule was delivered pharmacologically under in vitro or in vivo test conditions, particularly in neurodegenerative disorders and after tissue or organ transplantation. The induction of heme oxygenase-1 (HMOX-1) via the activation of nuclear factor erythroid 2-related factor or the use of bile pigments in the harvesting of diseased tissue are novel applications, and like every new therapy, should be used with caution. HMOX-1 is tissue specific, and in exceptional states, such as schizophrenia and specific types of renal disorder, the same therapy may have disastrous effects.