title: The in vivo effect of bilirubin on the N-methyl-D-aspartate receptor/ion channel complex in the brains of newborn piglets.
abstract: Bilirubin neurotoxicity can be mediated by numerous mechanisms due to its increased permeability in neuronal membranes. The present study tests the hypothesis that a prolonged bilirubin infusion modifies the N-methyl-D-aspartate (NMDA) receptor/ ion channel complex in the cerebral cortex of newborn piglets. Studies were performed in seven control and six bilirubin-exposed piglets, 2-4 d of age. Piglets in the bilirubin group received a 35 mg/kg bolus of bilirubin followed by a 4-h infusion (25 mg/kg/h) of a buffer solution containing 0.1 N NaOH, 5% human albumin, and 0.055 Na2HPO4 with 3 mg/mL bilirubin. The final mean bilirubin concentration in the bilirubin group was 495.9 +/- 85.5 mumol/L (29.0 +/- 5.0 mg/dL). The control group received a bilirubin-free buffer solution. Sulfisoxazole was administered to animals in both groups. P2 membrane fractions were prepared from the cerebral cortex. [3H]MK-801 binding assays were performed to study NMDA receptor modification. The Bmax in the control and bilirubin groups were 1.20 +/- 0.10 (mean +/- SD) and 1.32 +/- 0.14 pmol/mg protein, respectively. The value for Kd in the control brains was 6.97 +/- 0.80 nM compared with 4.80 +/- 0.28 nM in the bilirubin-exposed brains (p < 0.001). [3H]Glutamate binding studies did not show a significant difference in the Bmax and Kd for the NMDA-specific glutamate site in the two groups. The results show that in vivo exposure to bilirubin increases the affinity of the receptor (decreased Kd) for [3H]MK-801, indicating that bilirubin modifies the function of the NMDA receptor/ion channel complex in the brain of the newborn piglet. We speculate that the affinity of bilirubin for neuronal membranes leads to bilirubin-mediated neurotoxicity, resulting in either short- or long-term disruption of neuronal function.
authors.affiliation: Department of Pediatrics, Medical College of Pennsylvania/Hahnemann University School of Medicine, Philadelphia 19129, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hoffman
authors.forename: S A
authors.initials: SA
authors.lastname: Zanelli
authors.forename: J
authors.initials: J
authors.lastname: Kubin
authors.forename: O P
authors.initials: OP
authors.lastname: Mishra
authors.forename: M
authors.initials: M
authors.lastname: Delivoria-Papadopoulos
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001663:Bilirubin / Q000494:pharmacology*; D001921:Brain / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D016291:Dizocilpine Maleate / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*; D012016:Reference Values; D012709:Serum Albumin; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013552:Swine
chemical_list: D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D012709:Serum Albumin; D010725:Phosphocreatine; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D001663:Bilirubin