Simultaneous measurement of phosphatidylglycerol and disaturated‐phosphatidylcholine palmitate kinetics from alveolar surfactant. Study in infants with stable isotope tracer, coupled with isotope ratio mass spectrometry

Abstract

Disaturated-phosphatidylcholine (DSPC) and phosphatidylglycerol (PG) are respectively the first and the third most abundant phospholipid in human alveolar surfactant. Their concentration decreases in airway surfactant of adults and infants with respiratory distress syndrome and cystic fibrosis. In this study, we used mass spectrometry (IRMS) to investigate the turnover of DSPC and PG in tracheal aspirates (TA) obtained from infants with normal or diseased lungs. We studied eight infants requiring mechanical ventilation: two with no lung disease, four with diaphragmatic hernia, one with ATP-binding cassette sub-family A member 3 heterozygote mutation and one with sepsis. Patients received deuterated water for 48 h as metabolic precursors of palmitate-DSPC and palmitate-PG. Serial TAs were obtained every 6 h for five days or until extubation. DSPC and PG were isolated from TA by column and high-performance thin layer chromatography. Deuterium enrichments of palmitate-DSPC and PG residues were measured by IRMS coupled with a gas chromatographer. Median secretion time (ST), peak time (PT) and fractional synthesis rate (FSR) were 3.7 [0.9- 13.4] h, 71.0 [52.2 - 85.2] h and 6.6 [6.3 - 11.1] %/day for DSPC and 19.3 [6.4 - 22.8] h, 49.0 [33.0 - 52.5] h and 5.8 [4.8 - 10.9] %/day for PG. This study shows that it is feasible to use deuterium derived from body water to trace simultaneously airway surfactant DSPC and PG in humans. When compared within the same patient, DSPC and PG had similar fractional synthesis rates, but PG had a shorter PT, suggesting differences in the life cycle of these essential surfactant components.

Surfactant protein C metabolism in human infants and adult patients by stable isotope tracer and mass spectrometry

“…Stable isotopes have been used to study the turnover of surfactant components [18,26]. We now add the turnover of SP-C with the hope that this may help to clarify the pathophysiology of lung disease.…”

“…As shown in Fig. 3, incorporation of 13 C leucine into SP-C increased until 20-25 h after the start of isotope infusion with a PT of 24 h [20][21][22][23][24][25][26][27] like in SP-B. The maximum enrichment of 13 C leucine was higher for SP-B than for SP-C.…”

Tracing exogenous surfactant in vivo in rabbits by the natural variation of 13C

“…Briefly, we verified the suitability of our method in lung-lavaged adult rabbits by assessing the constancy of poractant alfa DSPC-PA carbon stable isotopes ratio among different batches, the difference in carbon stable isotopes abundance between endogenous and exogenous surfactant, and the effect of poractant alfa administration on rabbit alveolar DSPC-PA 13 C content. Our novel method allowed to discriminate an endogenous/exogenous (and vice versa) ratio of 1/49 (2%), without the need for dispensing any artificially labelled compound [14, 15]. This aspect makes the stable isotope natural abundance approach safe and exploitable to study in vivo different doses and surfactant administration methods.…”

Estimating the contribution of surfactant replacement therapy to the alveolar pool: An in vivo study based on 13C natural abundance in rabbits

“…RDS is characterised by lung immaturity and lack of lung surfactant, a thin layer of lipids and proteins with tension‐lowering proprieties. The lipid portion of pulmonary surfactant is mainly composed of phospholipids (PL, 80%–85% by weight), with a predominant presence of disaturated‐phosphatidylcholine (DSPC, approximately 50% of total PL) . In RDS newborns, treatment with exogenous surfactant improves gas exchange and survival, and the InSurE (Intubation‐Surfactant‐Extubation) procedure has been widely used since has been shown to reduce both the need for mechanical ventilation and death.…”