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Background:Acylcarnitines are biomarkers of fatty acid metabolism, and examining their patterns in preterm newborn may reveal metabolic changes associated with particular conditions related to prematurity. Isomeric acylcarnitines in dried blood spots (DBS) and plasma have never been assessed in preterm infants.Methods:We studied 157 newborn divided into four groups by weeks of gestational age (GA), as follows: 22–27?wk in group 1; 28–31?wk in group 2; 32–36?wk in group 3; and 37–42?wk in group 4. Samples were collected on the third day of life. Acylcarnitines were separated and quantified using ultra-performance liquid chromatography tandem mass spectrometry.Results:Acylcarnitine concentrations correlated significantly with GA and birth weight in both DBS and plasma samples. Concentrations were lower in preterm newborn, except for acylcarnitines derived from branched-chain amino acids, which were higher and correlated with enteral feeding. On day 3 of life, no correlations emerged with gender, respiratory distress syndrome, bronchopulmonary dysplasia, surfactant administration, or mechanical ventilation.Conclusion:We established GA-based reference ranges for isomeric acylcarnitine concentrations in preterm newborn, which could be used to assess nutritional status and the putative neuroprotective role of acylcarnitines.

The aim of the study was to determine surfactant palmitate disaturated‐phosphatidylcholine (DSPC‐PA) synthesis in vivo in humans by the incorporation of deuterium from total body water into DSPC‐PA under steady state condition. We studied three newborns and one infant (body weight (BW) 4.6 ± 2.9 kg, gestational age 37.5 ± 2 weeks, age 9 ± 9 days) and four preterm newborns (BW 1.3 ± 0.6 kg, gestational age 30.3 ± 2.5 weeks, postnatal age 8.8 ± 9.2 h). All infants were mechanically ventilated during the study and the four preterm infants received exogenous surfactant at the start of the study.We administered 0.44 g 2H2O/kg BW as a bolus intravenously, followed by 0.0125 g 2H2O/kg BW every 6 h to maintain deuterium enrichment at plateau over 2 days. Urine samples and tracheal aspirates (TA) were obtained prior to dosing and every 6 h thereafter. Isotopic enrichment curves of DSPC‐PA from sequential TA and urine deuterium enrichments were analyzed by Gas Chromatography‐Isotope Ratio—Mass Spectrometry (GC‐IRMS) and normalized for Vienna Standard Mean Ocean Water. Enrichment data were used to measure DSPC‐PA fractional synthesis rate (FSR) from the linear portion of the DSPC‐PA enrichment rise over time, relative to plateau enrichment of urine deuterium. Secretion time (ST) was defined as the time lag between the start of the study and the appearance of DSPC‐PA deuterium enrichment in TA. Data were given as mean ± SD.All study infants reached deuterium‐steady state in urine. DSPC‐PA FSR was 6.5 ± 2.8%/day (range 2.6–10.2). FSR for infants who did not receive exogenous surfactant was 5.7 ± 3.5%/day (range 2.6–9.9%/day) and 7.3 ± 2.1%/day (range 5.1–10.2%/day) in the preterms, whereas DSPC‐PA ST was 10 ± 10 h and 31 ± 10 h respectively.Surfactant DSPC‐PA synthesis can be measured in humans by the incorporation of deuterium from body water. This study is a simpler and less invasive method compared to previously published methods on surfactant kinetics by means of stable isotopes. Copyright © 2005 John Wiley & Sons, Ltd.

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 vivoin humans by stable isotope technology.

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.