Abstract
Extract: Titrations of albumin with bilirubin were performed at pH 7.0 and pH 7.4. Unbound bilirubin concentrations were determined using a horseradish peroxidase assay. Titrations of infant serum indicated that 1 mol bilirubin was bound tightly/mol albumin at either pH with an association constant of approximately 6.2 × 107 M-1. When binding occurred at secondary sites, data were more scattered, but no pH differences could be detected. The effect of bilirubin on cells was studied by determining the viability of plated L cells after a pulse of bilirubin. The lethal unbound bilirubin concentrations for 50% of cells at pH 7.4 was about 0.7 μM compared with 0.3 μM at pH 7.0. Cell uptake of unbound bilirubin was rapid at either pH. In the essential absence of albumin (20/1 molar ratio), about 66% of the added bilirubin appeared in the cell pellet in 10 min at pH 7.0; initial uptake at pH 7.4 was 44% (P < 0.001).
Our data do not support the hypothesis that acidemia decreases albumin binding of bilirubin. The increased sensitivity appeared to be related to a greater cell uptake of bilirubin at the lower pH.
Speculation: Although albumin binding of bilirubin is clearly an important factor in the pathogenesis of kernicterus, this study emphasizes the importance of cell-bilirubin interaction as a determinant of bilirubin distribution and toxicity. Intervention to decrease the serum bilirubin concentration in a jaundiced neonate must respond both to the status of albumin-bilirubin binding and to conditions which alter the cellular affinity for bilirubin.
The peroxidase method provides a sensitive new technique for analyzing protein bilirubin interaction.
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Nelson, T., Jacobsen, J. & Wennberg, R. Effect of pH on the Interaction of Bilirubin with Albumin and Tissue Culture Cells. Pediatr Res 8, 963–967 (1974). https://doi.org/10.1203/00006450-197412000-00010
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DOI: https://doi.org/10.1203/00006450-197412000-00010
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