P36: Nitrite and nitrate concentrations and metabolism in breast milk, artificial milk, and parenteral nutrition of term and preterm infants

Abstract

Background In the adult, dietary nitrate is converted to nitrite by bacteria in the mouth. In the acidic environment of the stomach, the ingested nitrite is converted to NO where it is has a protective effect by increasing blood flow and mucus production, and by modulating the microbial flora of the GI tract. Ingested nitrite has also been linked to improved cardiovascular function in adults. However, the intake and importance of nitrate and nitrite in newborn infants is largely unknown. The purpose of this work is to determine nitrite and nitrate concentrations in both the diet and total parenteral nutrition (TPN) of term and preterm infants, and to characterize the means by which nitrite is metabolized in fresh and freeze–thawed breast milk. Methods We measured nitrate and nitrite levels in breast milk collected from mothers of preterm and term infants, ten different brands of commonly used infant formula, and TPN. We also measured the effect of freeze–thawing, temperature and oxygen tension variation, and several metal-containing enzyme antagonists on the metabolism of nitrite in samples of breast milk. Results Nitrite concentrations averaged 0.07 ± 0.01 μM in the milk of mothers of preterm infants, significantly less than in the milk of mothers of term infants (0.13 ± 0.02 μM) ( P N -ethylmaleimide to block thiol groups, or the addition of allopurinol to block xanthine oxidase. The metabolism of nitrite was inhibited by the addition of ferricyanide. Nitrite metabolism was also inhibited through the use of three different blockers of lactoperoxidase, a normal constituent of breast milk, and was increased by the addition of purified lactoperoxidase, suggesting that this enzyme is involved in nitrite metabolism. Nitrite concentrations in infant formula varied widely and ranged from 0.01 to 1.3 μM, and nitrate concentrations ranged from 12 to 67 μM. The nitrite (0.08 ± 0.02 μM) and nitrate (9.5 ± 0.8 μM) concentrations in TPN were similar to those measured in fresh breast milk. Conclusions Overall nitrite and nitrate ingestion by term and preterm infants is low compared to adults, and decreases further in infants receiving freeze–thawed breast milk due to metabolism of nitrite by lactoperoxidase. Given recent evidence for the importance of dietary nitrite in adults, we speculate that low levels of ingestion may negatively impact the gastric and cardiovascular health of the newborn. Disclosure Nothing to disclose.