title: Bilirubin selectively inhibits cytochrome c oxidase activity and induces apoptosis in immature cortical neurons: assessment of the protective effects of glycoursodeoxycholic acid.
abstract: High levels of unconjugated bilirubin (UCB) may initiate encephalopathy in neonatal life, mainly in pre-mature infants. The molecular mechanisms of this bilirubin-induced neurologic dysfunction (BIND) are not yet clarified and no neuroprotective strategy is currently worldwide accepted. Here, we show that UCB, at conditions mimicking those of hyperbilirubinemic newborns (50 microM UCB in the presence of 100 muM human serum albumin), rapidly (within 1 h) inhibited cytochrome c oxidase activity and ascorbate-driven oxygen consumption in 3 days in vitro rat cortical neurons. This was accompanied by a bioenergetic and oxidative crisis, and apoptotic cell death, as judged by the collapse of the inner-mitochondrial membrane potential, increased glycolytic activity, superoxide anion radical production, and ATP release, as well as disruption of glutathione redox status. Furthermore, the antioxidant compound glycoursodeoxycholic acid (GUDCA) fully abrogated UCB-induced cytochrome c oxidase inhibition and significantly prevented oxidative stress, metabolic alterations, and cell demise. These results suggest that the neurotoxicity associated with neonatal bilirubin-induced encephalopathy occur through a dysregulation of energy metabolism, and supports the notion that GUDCA may be useful in the treatment of BIND.
authors.affiliation: Centro de Patogénese Molecular - UBMBE/iMed.UL, Faculdade de Farmácia, University of Lisbon, Lisbon, Portugal.
authors.forename: Ana Rita
authors.initials: AR
authors.lastname: Vaz
authors.forename: Maria
authors.initials: M
authors.lastname: Delgado-Esteban
authors.forename: Maria Alexandra
authors.initials: MA
authors.lastname: Brito
authors.forename: Juan P
authors.initials: JP
authors.lastname: Bolaños
authors.forename: Dora
authors.initials: D
authors.lastname: Brites
authors.forename: Angeles
authors.initials: A
authors.lastname: Almeida
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001663:Bilirubin / Q000502:physiology / Q000633:toxicity*; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000633:toxicity; D005260:Female; D006801:Humans; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014580:Ursodeoxycholic Acid / Q000031:analogs & derivatives* / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D018696:Neuroprotective Agents; C024033:glycoursodeoxycholic acid; D014580:Ursodeoxycholic Acid; D003576:Electron Transport Complex IV; D001663:Bilirubin