Yellow hyaline membrane disease. Identification of the pigment and bilirubin binding

The distinguishing feature of yellow hyaline membrane disease (YHM) in the newborn is the presence of nonfading, bright yellow membrane lining the luminal aspects of conventional pink hyaline membranes (HM). Examination of yellow membranes, stained and unstained, under fluorescent microscopy reveals on orange-red fluorescent material heterogeneously dispersed within the membranes. Homogenates of lungs with YHM and HM were extracted with chloroform and tested spectrophotometrically, by thin layer chromatography, and for diazotized sulfanilic acid reactivity. Spectrophotometric profiles of YHM differed from those of HM by a unique absorption shoulder at 454 nm. in the former. This shoulder corresponded to the absorbance of unconjugated bilirubin. This profile could be reproduced by adding purified unconjugated bilirubin to non-YHM lung homogenate prior to extraction. Thin layer chromatography of the extracted YHM material produced two unique spots not found in extracts prepared from normal or HM-diseased lungs. These spots could be duplicated by thin layer chromatography using pure unconjugated bilirubin. The spots also fluoresced orange-red, the same color initially observed in the membranous preparations under fluorescent microscopy. Additional in vitro binding studies suggest that polymyxin, a decapeptide antibiotic used in endotracheal irrigation of newborn infants, binds bilirubin in pH-dependent, small molecular ratios. Although subsequent clinical studies disproved the etiologic significance of this particular drug, the unique properties of the bilirubin present in the YHMD lungs strongly suggest that the bilirubin there is bound by some yet unelucidated mechanism.