Pyrimidine and Purine Concentrations in Cord, Preterm and Term Infant Plasma Compared to Maternal Values—An Observational Study

Background: Purines and pyrimidines are essential for the synthesis of nucleotides for DNA/RNA synthesis and for intermediate lipids, carbohydrates, and one-carbon metabolism. They are defined as nonessential as they can be synthesized de novo in vivo. However, the rate of de novo synthesis may be below requirements during rapid growth. Accordingly, nucleotide supplementation has been associated with potential benefits for growth in newborn infants. Therefore, nucleotides have been considered conditionally essential, and adequate availability may be relevant during periods of growth and development, particularly in preterm infants. Aims: To investigate plasma concentrations of purines and pyrimidines in cord blood in relation to (1) gestational age, (2) the blood of the corresponding mother, and (3) postnatal preterm infants’ blood. Methods: 155 infant–mother pairs (23 6/7–41 5/7 weeks postmenstrual age) from 10/2020–11/2022 were included. Purines and pyrimidines were analyzed with tandem mass spectrometry. Data are expressed as the median and interquartile range. Results: Cytidine, uridine, inosine, xanthine, hypoxanthine, adenosine, adenosine monophosphate, and guanosine monophosphate concentrations were above the lower limits of detection. Fetal plasma concentrations were significantly higher than those in corresponding mothers. The more immature the fetuses, the higher were the concentrations in umbilical cord plasma. Cytidine, inosine, xanthine, and hypoxanthine plasma concentrations significantly decreased within 14 days after birth. Conclusions: Fetal plasma concentrations of several purines and pyrimidines were higher than corresponding maternal concentrations, and concentrations of several metabolites decreased markedly after birth, demonstrating substantial changes in purine and pyrimidine concentrations across the fetal-to-postnatal transition. The underlying mechanisms (including potential contributions of placental transport, endogenous metabolism, tissue uptake, elimination, and nutritional intake) require further investigation.