Surfactant-associated protein B kinetics in vivo in newborn infants by stable isotopes.
Surfactant-associated protein B (SP-B) is critical to the biophysical function of pulmonary surfactant. No information is available on SP-B synthesis and kinetics in humans. We administered a 24-h i.v. infusion of 13C-valine as metabolic precursor of SP-B to six newborn infants (weight 3.5+/-0.5 kg; age 12 d, range 1-43 d). Three of the study infants also received i.v. 2H-palmitate to label surfactant disaturated phosphatidylcholine (DSPC). SP-B and DSPC were isolated from tracheal aspirates, and their respective 13C and 2H enrichments were measured by gas chromatography-mass spectrometry. SP-B kinetics was measured successfully in all six infants. SP-B median (range) fractional synthesis rate was 30% per day (20-78% per day), secretion time was 4.5 h (1-9 h), time to peak was 24 h (12-36 h), and half-life was 21 h (8-35 h). The ascending part of the SP-B kinetic curve was similar to the DSPC curve, suggesting similar secretion pathways. SP-B half-life seemed to be shorter than DSPC half-life. These results agree with existing animal data. We conclude that the measurement of SP-B kinetics is feasible in vivo in humans by stable isotope technology.
Cogo
Paola
P
Department of Pediatrics, University of Padova, Padova, and Pharmacy, Salesi Children Hospital, Ancona, Italy. cogo@pediatria.unipd.it
Baritussio
Aldo
A
Rosso
Federica
F
Gucciardi
Antonina
A
Moretti
Vincenzo
V
Badon
Tamara
T
Duner
Elena
E
Zimmernann
Luc
L
Carnielli
Virgilio P
VP
D002247:Carbon Isotopes / Q000378:metabolism; D003903:Deuterium / Q000378:metabolism; D006207:Half-Life; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D010168:Palmitates / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D037701:Pulmonary Surfactant-Associated Protein B / Q000096:biosynthesis / Q000378:metabolism*; D014633:Valine / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism
D002247:Carbon Isotopes; D010168:Palmitates; D010713:Phosphatidylcholines; D037701:Pulmonary Surfactant-Associated Protein B; D003903:Deuterium; D014633:Valine