A new technique for studying the relationship between maternal diabetes and the sialic acid content of fetal pulmonary surfactant

Abstract

By adapting a standard method for precipitation of high-density lipoprotein cholesterol with phosphotungstic acid (PTA) and Mg2+, fetal pulmonary surfactant can be rapidly isolated from human amniotic fluid, 97% of the total disaturated phosphatidylcholine being precipitated from the sample. The lecithin/sphingomyelin ratio for 17 separate specimens correlated reasonably well (r = 0.76) with the concentration of disaturated phosphatidylcholine in the PTA precipitate. Using thiobarbituric acid as the chromophore, I measured sialic acid in the PTA precipitate after overnight treatment with neuraminidase. The sialic acid/protein ratio for the PTA precipitate was identical to that of the surfactant, as isolated by ultracentrifugation. The concentrations of insulin and C-peptide were significantly greater in specimens of amniotic fluid from mothers with diabetes than from non-diabetic mothers (p < 0.001). When the specimens were segregated according to a C-peptide cutoff value of 4 μg/L, there was a small, significant decrease in PTA-precipitated concentrations of siliac acid in the samples with C-peptide >4 μg/L. The results suggest a possible mechanism for the increased incidence of respiratory distress among infants born to diabetic mothers.