Peter F. Whitington, Gilbert J. Burckart, Sharon R. Gross, Sheldon B. Korones, Richard A. Helms

Alterations in Reserve Bilirubin Binding Capacity of Albumin by Free Fatty Acids. II. In Vitro and In Vivo Studies Using Difference Spectroscopy

  • Gastroenterology
  • Pediatrics, Perinatology and Child Health

SummaryThe effects of free fatty acids (FFA) on reserve bilirubin binding capacity of solutions of human serum albumin (Alb) were determined in vitro using difference spectroscopy. Additionally, sera from 15 infants requiring parenteral nutrition were obtained before, during, and after the administration of a 1.0 g/kg intravenous dose of safflower oil emulsion, and determinations of FFA/Alb molar ratios and reserve bilirobin binding capacities were made for in vivo confirmation. The in vitro experiments demonstrated that increasing the linoleic acid/Alb molar ratio from 0 to 3.5 produced a 37% increase in binding capacity, but further increases to 9 ultimately resulted in a 32% decrease. Similar results were obtained using Alb at pH 7.4 and using defatted whole human serum. Using salicylate to block secondary binding sites demonstrated that linoleic acid enhanced binding at primary sites. In contrast to linoleic acid, octanoic acid did not alter binding at primary sites but lowered total binding capacity when its concentration exceeded 2.5 times that of the Alb in the sample. The in vivo measurements demonstrated that the total reserve bilirubin binding capacity dropped to 30% below base line only when the FFA/Alb molar ratio was greater than 7:1. Increases in total reserve bilirubin binding capacity above 30% over base line occurred in the range of FFA/Alb molar ratios of 1.6:4.0. Binding at primary sites was enhanced in a like manner at moderate FFA concentrations and did not fall below base line even at very high concentrations. These data support the concept of a positive cooperative binding effect between fatty acids and bilirubin at moderate fatty acid/Alb molar ratios and reconfirm the negative effect of fatty acids on bilirubin binding at high molar ratios. These data suggest that hyperbilirubinemic infants may be offered the nutritional benefits of intravenous safflower oil emulsion without additional risk of kernicterus as long as the FFA/Alb molar ratio is kept below 4 or the reserve bilirubin binding capacity is not decreased.

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