Bilirubin has several physiological functions, both beneficial and harmful. In addition to reactive oxygen species-scavenging activities, bilirubin has potent immunosuppressive effects associated with long-term pathophysiological sequelae. It has been recently recognized as a hormone with endocrine actions and interconnected effects on various cellular signaling pathways. Current studies show that bilirubin also decreases adiposity and prevents metabolic and cardiovascular diseases. All in all, the physiological importance of bilirubin is only now coming to light, and strategies for increasing plasma bilirubin levels to combat chronic diseases are starting to be considered. This review discusses the beneficial effects of increasing plasma bilirubin, incorporates emerging areas of bilirubin biology, and provides key concepts to advance the field.

• Keywords
• BVRA, Blvra, HO-1, Hmox1, bilirubin, cardiovascular disease, cell signaling, heme oxygenase, metabolism, nuclear receptors,
• MeSH
• Bilirubin * metabolism   pharmacology   MeSH
• Heme Oxygenase-1 metabolism   MeSH
• Cardiovascular Diseases * MeSH
• Humans MeSH
• Reactive Oxygen Species metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Bilirubin * MeSH
• Heme Oxygenase-1 MeSH
• Reactive Oxygen Species MeSH

Neonatal hyperbilirubinemia or jaundice is associated with kernicterus, resulting in permanent neurological damage or even death. Conventional phototherapy does not prevent hyperbilirubinemia or eliminate the need for exchange transfusion. Here we investigated the potential of therapeutic bile acids ursodeoxycholic acid (UDCA) and obeticholic acid (OCA, 6-α-ethyl-CDCA), a farnesoid-X-receptor (FXR) agonist, as preventive treatment options for neonatal hyperbilirubinemia using the hUGT1*1 humanized mice and Ugt1a-deficient Gunn rats. Treatment of hUGT1*1 mice with UDCA or OCA at postnatal days 10-14 effectively decreased bilirubin in plasma (by 82% and 62%) and brain (by 72% and 69%), respectively. Mechanistically, our findings indicate that these effects are mediated through induction of protein levels of hUGT1A1 in the intestine, but not in liver. We further demonstrate that in Ugt1a-deficient Gunn rats, UDCA but not OCA significantly decreases plasma bilirubin, indicating that at least some of the hypobilirubinemic effects of UDCA are independent of UGT1A1. Finally, using the synthetic, non-bile acid, FXR-agonist GW4064, we show that some of these effects are mediated through direct or indirect activation of FXR. Together, our study shows that therapeutic bile acids UDCA and OCA effectively reduce both plasma and brain bilirubin, highlighting their potential in the treatment of neonatal hyperbilirubinemia.

• MeSH
• Bilirubin blood   MeSH
• Ileum drug effects   metabolism   MeSH
• Isoxazoles pharmacology   MeSH
• Liver drug effects   metabolism   MeSH
• Rats MeSH
• Chenodeoxycholic Acid analogs & derivatives   therapeutic use   MeSH
• Ursodeoxycholic Acid therapeutic use   MeSH
• Mice MeSH
• Hyperbilirubinemia, Neonatal blood   drug therapy   MeSH
• Rats, Gunn MeSH
• Receptors, Cytoplasmic and Nuclear agonists   metabolism   MeSH
• Treatment Outcome MeSH
• Bile Acids and Salts therapeutic use   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bilirubin MeSH
• farnesoid X-activated receptor MeSH Browser
• GW 4064 MeSH Browser
• Isoxazoles MeSH
• Chenodeoxycholic Acid MeSH
• Ursodeoxycholic Acid MeSH
• obeticholic acid MeSH Browser
• Receptors, Cytoplasmic and Nuclear MeSH
• Bile Acids and Salts MeSH

Bilirubin is a yellow endogenous derivate of the heme catabolism. Since the 1980s, it has been recognized as one of the most potent antioxidants in nature, able to counteract 10,000× higher intracellular concentrations of H2O2. In the recent years, not only bilirubin, but also its precursor biliverdin, and the enzymes involved in their productions (namely heme oxygenase and biliverdin reductase; altogether the "yellow players"-YPs) have been recognized playing a protective role in diseases characterized by a chronic prooxidant status. Based on that, there is an ongoing effort in inducing their activity as a therapeutic option. Nevertheless, the understanding of their specific contributions to pathological conditions of the central nervous system (CNS) and their role in these diseases are limited. In this review, we will focus on the most recent evidence linking the role of the YPs specifically to neurodegenerative and neurological conditions. Both the protective, as well as potentially worsening effects of the YP's activity will be discussed.

• Keywords
• bilirubin, bilirubin oxidation products, biliverdin, biliverdin reductase, central nervous system (CNS), heme, heme oxygenase, neurodegenerative diseases, yellow players,
• Publication type
• Journal Article MeSH
• Review MeSH