Changes in the Composition of Bilirubin‐IX Isomers During Human Prenatal Development

Abstract

We analyzed the isomeric composition of bilirubin‐IX in human fetal bile using HPLC. The approximate ratio of the bilirubin‐IX isomers obtained from the fetal bile at 20 weeks of gestation was IXα, 6%; IXβ, 87%; IXγ, 0.5%; and IXδ, 6%. From 15 to 22 weeks, bilirubin‐IXβ was predominant and bilirubin‐IXδ and bilirubin‐IXα were also present in the bile as minor components. By 28 weeks, bilirubin‐IXα constituted about 50% of the total bilirubin. There was a general correlation between fetal age and the proportion of bilirubin‐IXβ to bilirubin‐IXβ in the bile and the small intestinal contents of fetuses. As development proceeded from mid‐gestation to near term, the isomeric composition dramatically changed, with a decrease in the IXβ isomer and a subsequent increment of the IXα isomer. In contrast, the IXβ isomer changes little. Recently, we identified four forms of biliverdin reductase including two biliverdin‐IXα reductases and two biliverdin‐IXβ reductases in human liver cytosolic fractions [Yamaguchi, T., Komoda, Y. & Nakajima, H. (1994) J. Biol. Chem. 269, 24343–24348]. The proportion of the total activity of biliverdin‐IXβ reductases to that of biliverdin‐IXα reductases was considerably higher in the fetal, than in the adult liver. Copyright © 1995, Wiley Blackwell. All rights reserved