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Gamma-carboxyglutamic acid in urine of newborn infants
Insights
Newborn infants, including preterm and small-for-gestational age, excrete similar amounts of urinary Gamma-Carboxyglutamic acid (GLA) as adults, indicating efficient carboxylation and high bone turnover in neonates.
Area of Science:
- Biochemistry
- Neonatal Physiology
- Pediatric Endocrinology
Background:
- Vitamin K deficiency is common in newborns, affecting coagulation factors.
- Gamma-Carboxyglutamic acid (GLA) is a vitamin K-dependent amino acid crucial for bone metabolism.
- Neonatal bone turnover is known to be high.
Purpose of the Study:
- To measure urinary Gamma-Carboxyglutamic acid (GLA) excretion in term, preterm AGA, and preterm SGA infants.
- To compare neonatal urinary GLA levels with those of adult controls.
- To investigate the relationship between urinary GLA and other physiological markers in neonates.
Main Methods:
- Urine samples were collected from 11 full-term, 48 preterm AGA, and 25 preterm SGA infants.
- Gamma-Carboxyglutamic acid (GLA) was quantified using high-resolution anion exchange chromatography.
- Urinary GLA excretion was measured in micromoles per kilogram per 24 hours (μmol·kg⁻¹·24h⁻¹).
Main Results:
- Urinary GLA levels in low birth weight infants (preterm AGA and SGA) were higher in the first 3 days of life compared to full-term infants and adults.
- In low birth weight infants, urinary GLA decreased significantly from days 1-3 to day 8, then gradually increased by day 45.
- No correlation was found between urinary GLA and birth weight, gestational age, urinary hydroxyproline, or serum alkaline phosphatase in these infants.
- Neonatal urinary GLA excretion was comparable to adult levels, despite reduced vitamin K-dependent coagulation factors.
Conclusions:
- Neonates, including preterm and SGA infants, demonstrate efficient carboxylation of glutamic acid.
- High urinary GLA excretion in newborns suggests a high rate of bone turnover.
- The findings indicate that neonatal carboxylase activity is functional and supports rapid bone metabolism.
Abstract:
Gamma-Carboxyglutamic acid (GLA) was measured in the urines obtained from 11 full-term infants, 48 pre-term infants appropriate for gestational age (AGA), and 25 small-for-gestational age (SGA) infants. Separation was performed by high resolution anion exchange chromatography. The results were similar in both AGA and SGA infants. During the first 3 days of life, urinary GLA mean (and range) was 1.66 (0.34-4.60) in the low birth weight infants versus 0.88 (0.26-1.38) in the full-term infants and 0.76 (0.62-1.15) mumol . kg-1 X 24 h-1 in the control adults. In the low birth weight infants, urinary GLA fell from 2.79 (0.61-5.75) at age 1-3 days, to 1.55 (0.26-4.04) mumol/24 h at day 8 (p less than 0.01); it then rose again slowly to 2.12 (0.65-3.93) mumol/24 h at day 45. In these infants there was no correlation between urinary GLA excretion and birth weight or gestational age, or urinary hydroxyproline or serum alkaline phosphatase. Despite the well-known reduced blood levels of vitamin K dependent coagulation factors in neonates, these results show that urinary GLA excretion is at least similar to the excretion in adults. These data suggest that these neonates can carboxylate glutamic acid and that the newborn infant has a high bone turnover.