Use of stable isotope labeling technique and mass isotopomer distribution analysis of [C-13]palmitate isolated from surfactant disaturated phospholipids to study surfactant in vivo kinetics in a premature infant

Pulmonary surfactant is a complex mixture of phospholipids and proteins whi ch lowers surface tension and maintains alveolar expansion at end expiratio n. Developmental and genetic disruption of pulmonary surfactant metabolism leads to respiratory distress in newborns. Stable isotope labeling of metab olic precursors of disaturated phospholipids, the most abundant and specifi c component of pulmonary surfactant, permits the measurement of the kinetic s of surfactant metabolism in vivo. We measured [U-C-13(6)]glucose incorpor ation into palmitic acid derived from disaturated surfactant phospholipids. A 24 h infusion of [U-C-13(6)]glucose (140 mg kg(-1)) was administered to a premature infant who required mechanical ventilation For respiratory dist ress syndrome; tracheal aspirate samples were obtained at the start of the infusion and at regular intervals for the next 70 h, Each tracheal aspirate sample was incubated with osmium tetroxide to isolate disaturated surfacta nt phospholipids. Methyl esters of the fatty acids in the disaturated phosp holipids were prepared and the enrichment of [C-13]methyl palmitate was mea sured by gas chromatography/mass spectrometry (GC/MS) and gas chromatograph y/combination/isotope ratio mass spectrometry (GC/C/IRMS). Mass isotopomer distribution analysis (MIDA) was used to calculate the fractional synthetic rate (FSR) of palmitate synthesized from acetate, With both GC/MS and GC/C /IRMS, palmitate C-13 enrichment was first detected 12.3 h after the start of the tracer infusion. The enrichment increased in a linear fashion, reach ed a peak at. 47 h and remained constant in the remainder of the samples. T he FSR of palmitate from acetate was 5.2% per day, Stable isotope technique s and MIDA will provide insights into the kinetics of surfactant metabolism in newborns with respiratory dysfunction, Copyright (C) 2000 John Wiley & Sons, Ltd.