Transamination of leucine and nitrogen accretion in human pregnancy and the newborn infant

Does Altered Cellular Metabolism Underpin the Normal Changes to the Maternal Immune System during Pregnancy?

Pregnancy is characterised by metabolic changes that occur to support the growth and development of the fetus over the course of gestation. These metabolic changes can be classified into two distinct phases: an initial anabolic phase to prepare an adequate store of substrates and energy which are then broken down and used during a catabolic phase to meet the energetic demands of the mother, placenta and fetus. Dynamic readjustment of immune homeostasis is also a feature of pregnancy and is likely linked to the changes in energy substrate utilisation at this time. As cellular metabolism is increasingly recognised as a key determinant of immune cell phenotype and function, we consider how changes in maternal metabolism might contribute to T cell plasticity during pregnancy.

Dietary Aromatic Amino Acid Requirements During Early and Late Gestation in Healthy Pregnant Women

BACKGROUND

Phenylalanine and tyrosine (referred to as total aromatic amino acids; TAAs) are essential for protein synthesis, and are precursors for important catecholamines. Current estimated average requirement (EAR) recommendations for TAA during pregnancy are 36 mg·kg-1·d-1, and has not been experimentally determined.

OBJECTIVES

The aim was to determine TAA requirements (dietary phenylalanine in the absence of tyrosine) during early and late gestation using the indicator amino acid oxidation (IAAO, with L-[1-13C]leucine) technique.

METHODS

Nineteen healthy pregnant women (age 22-38 y) were studied at a range of phenylalanine intakes (5 to 100 mg·kg-1·d-1) in early (13-19 wk) and/or late (33-39 wk) pregnancy for a total of 51 study days. Graded test intakes were provided as 8 hourly isonitrogenous and isocaloric meals. Breath samples were collected for 13C enrichment analysis on an isotope ratio mass spectrometer. A plasma sample was collected and analyzed for phenylalanine and tyrosine concentrations on an amino acid analyzer. The TAA requirement in early and late pregnancy was calculated using 2-phase linear regression crossover analysis that identified breakpoints in 13CO2 production (the requirement) in response to phenylalanine intakes.

RESULTS

TAA requirement during early pregnancy was 44 mg·kg-1·d-1 (95% CI: 28.3, 58.8) and during late pregnancy was 50 mg·kg-1·d-1 (95% CI: 36.1, 63.1). In early and late pregnancy, plasma phenylalanine and tyrosine concentrations rose linearly in response to graded phenylalanine intakes.

CONCLUSIONS

Our results suggest that the current EAR of 36 mg·kg-1·d-1 for TAAs is underestimated. When compared with results previously determined in nonpregnant adults, early pregnancy requirements were similar (43 compared with 44 mg·kg-1·d-1, respectively). During late pregnancy, a 14% higher TAA requirement was observed when compared with early pregnancy. The results from this study have potential implications for creating gestation stage-specific TAA recommendations.

Investigation of amino acids and minerals in Chinese breast milk

BACKGROUND

The nutrients in human milk, particularly amino acids and minerals, are important for infant growth and development. Since there are few reports of amino acids and minerals in Chinese breast milk, we conducted this study to establish a representative preliminary database of breast milk nutrients in Chinese breast milk. In this study, we collected breast milk from healthy mothers in seven cities in western, southern and central China. The composition, content and proportion of total amino acids and ten elements (potassium, sodium, calcium, magnesium, iron, zinc, manganese, copper, selenium and phosphorus) in human milk in different lactation stages were investigated.

RESULTS

In this study, it was found that the content of total essential amino acids (671.47 mg 100 mL^-1 ) in Chinese breast milk was higher compared with the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) (574 mg 100 mL^-1 ), but the content of leucine (LEU) (129.01 mg 100 mL^-1 ) and cysteine (CYS) (20.31 mg 100 mL^-1 ) was much lower than that recommended by ESPGHAN. Moreover, it was found that the content of most of these ten elements decreased during lactation, and the content of calcium in Chinese breast milk was lower compared with ESPGHAN. In addition, the content of selenium (7.23-20.55 mg 1000 mL^-1 ) in breast milk from the three cities Nanchang, Shanghai and Guangzhou in China was much higher than that recommended by ESPGHAN.

CONCLUSIONS

In a word, amino acids and minerals in Chinese human milk showed a significant difference from other countries. Human milk meal or infant food should be regulated to meet the requirements of the infant and to maintain the balance of the amino acids and minerals. © 2020 Society of Chemical Industry.

Dietary phenylalanine requirements during early and late gestation in healthy pregnant women

BACKGROUND

Phenylalanine is an indispensable amino acid and, via tyrosine, is the precursor for the neurotransmitters dopamine, norepinephrine, and epinephrine. Currently, dietary requirements for phenylalanine during pregnancy are unknown.

OBJECTIVES

This study's aim was to determine phenylalanine requirements (in the presence of excess tyrosine) during early and late gestation using direct amino acid oxidation (DAAO; with l-[1-13C]phenylalanine) and indicator amino acid oxidation (IAAO; with l-[1-13C]leucine).

METHODS

Twenty-three healthy women (age: 30.4 ± 3.1 y, mean ± SD) were studied at a range of phenylalanine intakes (5.5-30.5 mg · kg-1 · d-1 in early and late pregnancy using DAAO, and 2.5-30.5 mg · kg-1 · d-1 in late pregnancy using IAAO) for a total of 76 study days. Test intakes were provided as 8 isocaloric and isonitrogenous meals with 1.5 g · kg-1 · d-1 protein and energy at 1.7 times the measured resting energy expenditure. Breath samples were analyzed on an isotope ratio mass spectrometer for 13C enrichment. Phenylalanine requirement was determined using a 2-phase linear regression crossover model to identify a breakpoint in 13CO2 production (representing the mean requirement) in response to phenylalanine intakes.

RESULTS

Phenylalanine requirement during early pregnancy was determined to be 15 mg · kg-1 · d-1 (95% CI: 10.4, 19.9 mg · kg-1 · d-1); during late pregnancy, it was determined to be 21 mg · kg-1 · d-1 by DAAO (95% CI: 17.4, 24.7 mg · kg-1 · d-1) and IAAO (95% CI: 10.5, 32.2 mg · kg-1 · d-1).

CONCLUSIONS

Our results suggest a higher requirement (40%) for phenylalanine during late pregnancy than during early pregnancy. Moreover, the early pregnancy requirements are higher than the previous adult male requirement (9.1 mg · kg-1 · d-1; 95% CI: 4.6, 13.6 mg · kg-1 · d-1), although the 95% CIs overlap. Both DAAO and IAAO methods provided similar breakpoints in late pregnancy, showing that the DAAO method was appropriate even though low phenylalanine intakes could not be tested. These results have potential implications for gestation stage-specific dietary phenylalanine recommendations in future.This trial was registered at clinicaltrials.gov as NCT02669381.

Perinatal western-type diet and associated gestational weight gain alter postpartum maternal mood

INTRODUCTION

The role of perinatal diet in postpartum maternal mood disorders, including depression and anxiety, remains unclear. We investigated whether perinatal consumption of a Western-type diet (high in fat and branched-chain amino acids [BCAA]) and associated gestational weight gain (GWG) cause serotonin dysregulation in the central nervous system (CNS), resulting in postpartum depression and anxiety (PPD/A).

METHODS

Mouse dams were fed one of four diets (high-fat/high BCAA, low-fat/high BCAA, high-fat, and low-fat) prior to mating and throughout gestation and lactation. Postpartum behavioral assessments were conducted, and plasma and brain tissues assayed. To evaluate potential clinical utility, we conducted preliminary human studies using data from an extant sample of 17 primiparous women with high GWG, comparing across self-reported postpartum mood symptoms using the Edinburgh Postnatal Depression Scale (EPDS) for percent GWG and plasma amino acid levels.

RESULTS

Mouse dams fed the high-fat/high BCAA diet gained more weight per kcal consumed, and BCAA-supplemented dams lost weight more slowly postpartum. Dams on BCAA-supplemented diets exhibited increased PPD/A-like behavior, decreased dopaminergic function, and decreased plasma tyrosine and histidine levels when assessed on postnatal day (P)8. Preliminary human data showed that GWG accounted for 29% of the variance in EPDS scores. Histidine was also lower in women with higher EPDS scores.

CONCLUSIONS

These findings highlight the role of perinatal diet and excess GWG in the development of postpartum mood disorders.

Protein and Amino Acid Requirements during Pregnancy

Protein forms an essential component of a healthy diet in humans to support both growth and maintenance. During pregnancy, an exceptional stage of life defined by rapid growth and development, adequate dietary protein is crucial to ensure a healthy outcome. Protein deposition in maternal and fetal tissues increases throughout pregnancy, with most occurring during the third trimester. Dietary protein intake recommendations are based on factorial estimates because the traditional method of determining protein requirements, nitrogen balance, is invasive and undesirable during pregnancy. The current Estimated Average Requirement and RDA recommendations of 0.88 and 1.1 g · kg(-1) · d(-1), respectively, are for all stages of pregnancy. The single recommendation does not take into account the changing needs during different stages of pregnancy. Recently, with the use of the minimally invasive indicator amino acid oxidation method, we defined the requirements to be, on average, 1.2 and 1.52 g · kg(-1) · d(-1) during early (∼16 wk) and late (∼36 wk) stages of pregnancy, respectively. Although the requirements are substantially higher than current recommendations, our values are ∼14-18% of total energy and fit within the Acceptable Macronutrient Distribution Range. Using swine as an animal model we showed that the requirements for several indispensable amino acids increase dramatically during late gestation compared with early gestation. Additional studies should be conducted during pregnancy to confirm the newly determined protein requirements and to determine the indispensable amino acid requirements during pregnancy in humans.

Longitudinal Metabolomic Profiling of Amino Acids and Lipids across Healthy Pregnancy

Pregnancy is characterized by a complexity of metabolic processes that may impact fetal development and ultimately, infant health outcomes. However, our understanding of whole body maternal and fetal metabolism during this critical life stage remains incomplete. The objective of this study is to utilize metabolomics to profile longitudinal patterns of fasting maternal metabolites among a cohort of non-diabetic, healthy pregnant women in order to advance our understanding of changes in protein and lipid concentrations across gestation, the biochemical pathways by which they are metabolized and to describe variation in maternal metabolites between ethnic groups. Among 160 pregnant women, amino acids, tricarboxylic acid (TCA) cycle intermediates, keto-bodies and non-esterified fatty acids were detected by liquid chromatography coupled with mass spectrometry, while polar lipids were detected through flow-injected mass spectrometry. The maternal plasma concentration of several essential and non-essential amino acids, long-chain polyunsaturated fatty acids, free carnitine, acetylcarnitine, phosphatidylcholines and sphingomyelins significantly decreased across pregnancy. Concentrations of several TCA intermediates increase as pregnancy progresses, as well as the keto-body β-hydroxybutyrate. Ratios of specific acylcarnitines used as indicators of metabolic pathways suggest a decreased beta-oxidation rate and increased carnitine palmitoyltransferase-1 enzyme activity with advancing gestation. Decreasing amino acid concentrations likely reflects placental uptake and tissue biosynthesis. The absence of any increase in plasma non-esterified fatty acids is unexpected in the catabolic phase of later pregnancy and may reflect enhanced placental fatty acid uptake and utilization for fetal tissue growth. While it appears that energy production through the TCA cycle increases as pregnancy progresses, decreasing patterns of free carnitine and acetylcarnitine as well as increased carnitine palmitoyltransferase-1 rate and β-hydroxybutyrate levels suggest a concomitant upregulation of ketogenesis to ensure sufficient energy supply in the fasting state. Several differences in metabolomic profiles between Hispanic and non-Hispanic women demonstrate phenotypic variations in prenatal metabolism which should be considered in future studies.

Transamination governs nitrogen isotope heterogeneity of amino acids in rats

The nitrogen isotope composition (δ¹⁵N) of different amino acids carries different dietary information. We hypothesized that transamination and de novo synthesis create three groups that largely explain their dietary information. Rats were fed with ¹⁵N-labeled amino acids. The redistribution of the dietary ¹⁵N labels among the muscular amino acids was analyzed. Subsequently, the labeling was changed and the nitrogen isotope turnover was analyzed. The amino acids had a common nitrogen half-life of ∼20 d, but differed in δ¹⁵N. Nontransaminating and essential amino acids largely conserved the δ¹⁵N of the source and, hence, trace the origin in heterogeneous diets. Nonessential and nontransaminating amino acids showed a nitrogen isotope composition between their dietary composition and that of their de novo synthesis pool, likely indicating their fraction of de novo synthesis. The bulk of amino acids, which are transaminating, derived their N from a common N pool and hence their δ¹⁵N was similar.

Protein and amino acid metabolism in the human newborn

Birth and adaptation to extrauterine life involve major shifts in the protein and energy metabolism of the human newborn. These include a shift from a state of continuous supply of nutrients including amino acids from the mother to cyclic periodic oral intake, a change in the redox state of organs, thermogenesis, and a significant change in the mobilization and use of oxidative substrates. The development of safe, stable isotopic tracer methods has allowed the study of protein and amino acid metabolism not only in the healthy newborn but also in those born prematurely and of low birth weight. These studies have identified the unique and quantitative aspects of amino acid/protein metabolism in the neonate, thus contributing to rational nutritional care of these babies. The present review summarizes the contemporary data on some of the significant developments in essential and dispensable amino acids and their relationship to overall protein metabolism. Specifically, the recent data of kinetics of leucine, phenylalanine, glutamine, sulfur amino acid, and threonine and their relation to whole-body protein turnover are presented. Finally, the physiological rationale and the impact of nutrient (amino acids) interventions on the dynamics of protein metabolism are discussed.

Transport of amino acids through the placenta and their role

Amino acids are transported across the human placenta mediated by transporter proteins that differ in structure, mechanism and substrate specificity. Some of them are Na+-dependent systems, whereas others are Na+-independent. Among these there are transporters composed of a heavy chain, a glycoprotein, and a light chain. Moreover, they can be differently distributed in the two membranes forming the syncytiotrophoblast. The transport mechanisms involved and their regulation are only partially known. In the placenta itself, part of the amino acids is metabolized to form other compounds important for the fetus. This occurs for instance for arginine, which gives rise to polyamines and to NO. Interconversion occurs among few other amino acids Transport is altered in pregnancy complications, such as restricted fetal growth.