Endogenous surfactant metabolism in critically ill infants measured with stable isotope labeled fatty acids

Paola E. Cogo, Virgilio P. Carnielli, J. E H Bunt, Tamara Badon, Giuseppe Giordano, Franco Zacchello, P. J J Sauer, L. J I Zimmermann

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Abstract

Little is known about endogenous surfactant metabolism in infants, because radioactive isotopes used for this purpose in animals cannot be used in humans. We developed a novel and safe method to measure the endogenous surfactant kinetics in vivo in humans by using stable isotope labeled fatty acids. We infused albumin-bound [U-13C]palmitic acid (PA) and [U- 13C]linoleic acid (LLA) for 24 h in eight critically ill infants (mean ± SD; weight: 3.7 ± 1.3 kg; age: 51.3 ± 61.6 d) who required mechanical ventilation. The 13C enrichment of PA and LLA in surfactant phosphatidylcholine (PC), obtained from tracheal aspirates, was measured by gas chromatography combustion interface-isotope ratio mass spectrometry. We measured a significant incorporation of both 13C-PA and 13C-LLA into surfactant PC. PC-PA and PC-LLA became enriched after 8.7 ± 4.9 h (range: 3.4-17.3) and 10.0 ± 7.2 h (range: 3.0-22.4), respectively; the times at maximum enrichment were 49.2 ± 8.9 and 45.6 ± 19.3 h, respectively. The fractional synthesis rate of surfactant PC-PA ranged from 0.4 to 3.4% per h, whereas the fractional synthesis rate of PC-LLA ranged from 0.5 to 3.8% per h. The surfactant PC-PA and PC-LLA half-lives ranged from 16.8 to 177.7 and 23.8 to 144.4 h, respectively. This method provides new data on surfactant metabolism in infants requiting mechanical ventilation. We found that synthesis of surfactant from plasma PA and LLA is a slow process and that there were marked differences in PC kinetics among infants. This variability could be related to differences in lung disease and could affect the clinical course of the respiratory failure.

Original languageEnglish
Pages (from-to)242-246
Number of pages5
JournalPediatric Research
Volume45
Issue number2
Publication statusPublished - Feb 1999

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ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health

Cite this

Cogo, P. E., Carnielli, V. P., Bunt, J. E. H., Badon, T., Giordano, G., Zacchello, F., Sauer, P. J. J., & Zimmermann, L. J. I. (1999). Endogenous surfactant metabolism in critically ill infants measured with stable isotope labeled fatty acids. Pediatric Research, 45(2), 242-246.