Hyperphenylalaninaemia in parenterally fed newborn babies

An Overview of Parenteral Nutrition from Birth to Adolescence Based on a Composite Fish Oil Containing Lipid Emulsion and a Pediatric Amino Acid Solution

Intestinal failure (IF) is characterized by a critical reduction in functional gut mass below the minimum needed for optimal growth in children. It requires parenteral nutrition (PN) and home-PN (HPN), which is challenging in terms of meeting nutritional needs according to age, growth velocity, clinical situation, and rapid changes in fluid and electrolyte requirements. Due to these complex requirements, age-adapted multi-chamber bags (MCBs) are important additions to the nutrition armamentarium. The launch of composite fish oil (FO)-containing intravenous lipid emulsions (ILEs) heralded the development of MCBs containing these ILEs in combination with a crystalline amino acid solution adapted for pediatric use. The safety and efficacy of lipid and amino acid components in this context have been widely documented in numerous published studies. This narrative manuscript includes a review of the articles published in PudMed, Embase, and Google Scholar up to June 2023 for the age groups of term infants to children and adolescents. Preterm infants with their highly specific demands are not included. It aims to offer an overview of the clinical experience regarding the use of a composite FO-based ILE and a developed specific amino acid solution.

Effect of hyperalimentation and insulin-treated hyperglycemia on tyrosine levels in very preterm infants receiving parenteral nutrition

BACKGROUND

Hyperalimentation describes the increase in glucose, amino acids (AAs), and lipid intake designed to overcome postnatal growth failure in preterm infants. Preterm infants are dependent on phenylalanine metabolism to maintain tyrosine levels because of tyrosine concentration limits in parenteral nutrition (PN). We hypothesized that hyperalimentation would increase individual AA levels when compared with the control group but avoid high phenylalanine/tyrosine levels.

AIM

To compare the plasma AA profiles on days 8-10 of life in preterm infants receiving a hyperalimentation vs a control regimen.

METHODS

Infants <29 weeks' gestation were randomized to receive hyperalimentation (30% more PN macronutrients) or a control regimen. Data were collected to measure macronutrient (including protein) intake and PN intolerance, including hyperglycemia, insulin use, urea, and AA profile. Plasma profiles of 23 individual AA levels were measured on days 8-10 using ion exchange chromatography.

RESULTS

One hundred forty-two infants were randomized with 118 AA profiles obtained on days 8-10. There were no differences in birth weight or gestation between groups. There was an increase (P < .05) in 8 of 23 median individual plasma AA levels when comparing hyperalimentation (n = 57) with controls (n = 61). Only tyrosine levels (median; interquartile range) were lower with hyperalimentation: 27 (15-52) µmol/L vs 43 (24-69) µmol/L (P < .01). Hyperalimentation resulted in more insulin-treated hyperglycemia. No difference between the groups was apparent in tyrosine levels when substratified for insulin-treated hyperglycemia. All insulin vs no insulin comparisons showed lower tyrosine levels with insulin treatment (P < .01).

CONCLUSION

Hyperalimentation can result in paradoxically low plasma tyrosine levels associated with an increase in insulin-treated hyperglycemia.

Neonatology/Paediatrics - Guidelines on Parenteral Nutrition, Chapter 13

There are special challenges in implementing parenteral nutrition (PN) in paediatric patients, which arises from the wide range of patients, ranging from extremely premature infants up to teenagers weighing up to and over 100 kg, and their varying substrate requirements. Age and maturity-related changes of the metabolism and fluid and nutrient requirements must be taken into consideration along with the clinical situation during which PN is applied. The indication, the procedure as well as the intake of fluid and substrates are very different to that known in PN-practice in adult patients, e.g. the fluid, nutrient and energy needs of premature infants and newborns per kg body weight are markedly higher than of older paediatric and adult patients. Premature infants <35 weeks of pregnancy and most sick term infants usually require full or partial PN. In neonates the actual amount of PN administered must be calculated (not estimated). Enteral nutrition should be gradually introduced and should replace PN as quickly as possible in order to minimise any side-effects from exposure to PN. Inadequate substrate intake in early infancy can cause long-term detrimental effects in terms of metabolic programming of the risk of illness in later life. If energy and nutrient demands in children and adolescents cannot be met through enteral nutrition, partial or total PN should be considered within 7 days or less depending on the nutritional state and clinical conditions.

The effect of graded intake of glycyl-L-tyrosine on phenylalanine and tyrosine metabolism in parenterally fed neonates with an estimation of tyrosine requirement

Although tyrosine is considered indispensable during the neonatal period, its poor solubility has limited its inclusion in parenteral amino acid solutions to less than 1% of total amino acids. Dipeptides of tyrosine are highly soluble, have been shown to be well used and safe in animal models and humans, and, therefore, may be used as an effective means of providing tyrosine in the parenterally fed neonate. The goal of the present study was to determine the tyrosine requirement of the parenterally fed neonate receiving graded intakes of glycyl-L-tyrosine as a source of tyrosine. Thirteen infants receiving adequate energy (340 +/- 38 kJ. kg(-1).d(-1)) and protein (2.4 +/- 0.4 g.kg(-1).d(-1)) were randomized to receive parenteral nutrition with one of five graded levels of glycyl-L-tyrosine. The mean requirement and safe level of intake were estimated using a 1-(13)C-phenylalanine tracer and linear regression cross-over analysis that identified a break point in the response of label appearance in breath CO(2) (F(13)CO(2)) and phenylalanine oxidation to graded tyrosine intake. Based on the mean estimates of whole-body phenylalanine oxidation, the tyrosine mean requirement and safe level of intake were found to be 74 mg.kg(-1). d(-1) and 94 mg.kg(-1).d(-1), respectively. This represents 3.1 and 3.9% of total amino acids, respectively, considerably higher than levels found in present commercially available pediatric amino acid solutions. These data raise concern regarding the adequacy of aromatic amino acid intake in the parenterally fed neonate.

Current total parenteral nutrition solutions for the neonate are inadequate

The amino acid requirements of the parenterally fed neonate are poorly defined. Newborn infants are at risk for amino acid deficiency and toxicity, due to lack of small intestinal metabolism and metabolic immaturity. We discuss recent evidence that identifies inadequacies of commercial amino acid solutions with respect to the balance and quantity of aromatic amino acids, and sulphur amino acids. We present data demonstrating that impaired small intestinal metabolism (or lack of first pass metabolism) alters the whole body requirement for methionine, threonine, and arginine, and discuss the potential adverse effects of excess or inadequate parenteral amino acid intake.

Phenylalanine and tyrosine metabolism in neonates receiving parenteral nutrition differing in pattern of amino acids

Tyrosine is considered to be an indispensable dietary amino acid in the neonate, yet achieving adequate parenteral tyrosine intake is difficult due to its poor solubility. Increasing the supply of phenylalanine is the most common means of compensating for low tyrosine levels. Unfortunately, plasma phenylalanine concentrations are sometimes elevated in infants receiving high phenylalanine intake. This led us to study the phenylalanine and tyrosine metabolism in 16 neonates randomized to receive total parenteral nutrition with either a high or a moderate phenylalanine-containing amino acid solution. A primed, 24-h continuous stable isotope infusion of L-[1-13C]phenylalanine and L-[3,3-2H2]tyrosine was given to enable the measurement of phenylalanine and tyrosine kinetics. Results demonstrated that 1) phenylalanine hydroxylation was significantly greater in infants receiving high phenylalanine, 2) phenylalanine oxidation and percent dose oxidized was also significantly greater in infants receiving high phenylalanine, 3) apparent phenylalanine retention was greater in neonates receiving high phenylalanine, and 4) alternate catabolites of phenylalanine and tyrosine metabolism were significantly greater in infants receiving high phenylalanine compared with moderate phenylalanine. We conclude that neonates respond to increased parenteral phenylalanine intake by increasing their hydroxylation and oxidation rates. The greater oxidation of phenylalanine in infants receiving high phenylalanine in conjunction with the urinary excretion of alternate catabolites of phenylalanine and tyrosine suggests that the high phenylalanine intake may be in excess of needs. However, the lower apparent phenylalanine retention observed in infants receiving moderate phenylalanine suggests that the total aromatic amino acid level of moderate phenylalanine may be deficient for neonatal needs.

Evidence that phenylalanine hydroxylation rates are overestimated in neonatal subjects receiving total parenteral nutrition with a high phenylalanine content

Recent publications have indicated that the parenterally fed neonate has a substantial ability to hydroxylate phenylalanine. Examination of these data suggests that, at high phenylalanine intakes, estimated rates of hydroxylation exceed rates of intake. This implies significant net tissue breakdown. However, the quantitative validity of the estimates of phenylalanine hydroxylation cannot be assessed without nitrogen balance data. We have recently developed a parenterally fed neonatal piglet model and have used this to study aromatic amino acid metabolism in piglets fed different amino acid solutions. Reappraisal of the data from these studies has allowed us to estimate both phenylalanine hydroxylation and tissue protein accretion. Piglets were parenterally fed Vamin [292 micromol of Phe x kg(-1) x h(-1), 26 micromol of Tyr x kg(-1) x h(-1)], Vaminolact + Phe [VLP, 277 micromol of Phe x kg(-1) x h(-1), 26 micromol Tyr x kg(-1) x h(-1)], or Vaminolact + glycyl-L-tyrosine [VLGT, 152 micromol of Phe x kg(-1) x h(-1), 159 micromol of Tyr x kg(-1) x h(-1)] for 8 d. Nitrogen balance was measured over the last 5 study d, and aromatic amino acid kinetics were determined using a primed continuous infusion of L-[1-4C]phenylalanine on d 8. Average body protein gain, derived from nitrogen balance, was 11 g x kg(-1) x d(-1). For the Vamin and VLP groups, the rates of phenylalanine hydroxylation were estimated to be 139 and 90% of intake, respectively. However, phenylalanine hydroxylation was only 16% of intake for the VLGT group. In view of the tissue protein accretion data, it appears that the rate of phenylalanine hydroxylation may be overestimated in neonates fed high phenylalanine parenteral nutrition. The extent to which the parenterally fed neonate can adapt to a high phenylalanine intake, by increasing the rate of phenylalanine hydroxylation, remains to be determined.

Tyrosine kinetics and requirements during total parenteral nutrition in the neonatal piglet: the effect of glycyl-L-tyrosine supplementation

Tyrosine may be a conditionally indispensable amino acid in the neonate; however, the provision of aromatic amino acids to neonates receiving total parenteral nutrition (TPN) is complicated by the poor solubility of crystalline tyrosine. In the present study, we investigated tyrosine kinetics and requirements during TPN, when tyrosine was supplied as the soluble dipeptide, glycyl-L-tyrosine in a neonatal piglet model. Fifteen 3-d-old male Yorkshire piglets were fitted with external jugular and femoral catheters and randomized to one of five tyrosine intakes: 0.11, 0.31, 0.41, 0.51 and 0.71 g.kg-1.d-1. Total parenteral amino acid and energy intakes were 15.0 g.kg-1.d-1 and 1.1 MJ.kg-1.d-1, respectively. Piglets were maintained on TPN for 6 d, with nitrogen balance measured over the final 3 d of the study. On the final study day, tyrosine kinetics were measured during a 4-h primed-constant infusion of L-[l14C]tyrosine. Nitrogen retention was 67% at the lowest tyrosine intake and increased significantly (p < 0.05) at intakes of 0.31 g.kg-1.d-1 and above (84, 86, 87, and 88% for intakes of 0.31, 0.41, 0.51, and 0.71 g.kg-1.d-1, respectively). Plasma tyrosine concentrations and tyrosine oxidation (expressed as either a percentage of the dose oxidized or when corrected for flux) were low and similar at the two lowest intakes, but increased significantly at the higher intakes. Two-phase regression analysis of the data (plasma tyrosine, tyrosine oxidation) yielded estimates of a mean tyrosine requirement of 0.31 and 0.35, respectively, with estimated safe intakes (upper 95% confidence limit) of 0.44 and 0.42 g.kg-1.d-1. The present work also indicates that oxidation techniques may be suitable for the estimation of amino acid requirements during TPN in the neonate.

Amino acid solutions for premature neonates during the first week of life: the role of N-acetyl-L-cysteine and N-acetyl-L-tyrosine

Tyrosine and cyst(e)ine are amino acids that are thought to be essential for preterm neonates. These amino acids have low stability (cyst(e)ine) or low solubility (tyrosine) and are therefore usually present only in small amounts in amino acid solutions. Acetylation improves the stability and solubility of amino acids, facilitating a higher concentration in the solution. We compared three commercially available amino acid solutions, Aminovenös-N-päd 10%, Vaminolact 6.5%, and Primène 10%, administered to 20 low-birth-weight neonates on total parenteral nutrition from postnatal day 2 onward. Aminovenös-N-päd 10% contains acetylated tyrosine and acetylated cysteine; the other solutions do not contain acetylated amino acids and differ in the amount of tyrosine and cysteine added. On postnatal day 7, plasma amino acids were measured together with urinary excretion of amino acids and the total nitrogen excretion; 38% of the intake of N-acetyl-L-tyrosine and 53% of the intake of N-acetyl-L-cysteine were excreted in urine. Plasma levels of N-acetyl-L-tyrosine (331 +/- 74 mumol/L) and N-acetyl-L-cysteine (18 +/- 29 mumol/L) were higher than those of tyrosine (105 +/- 108 mumol/L) and cystine (11 +/- 9 mumol/L), respectively. Plasma tyrosine levels in the groups receiving small amounts of tyrosine remained just below the reference range. We show a linear correlation of plasma cystine with the intake of cysteine (r = .75, p = 0.01), but not with N-acetyl-L-cysteine. The estimated intake of cysteine should be 500 mumol.kg-1.d-1 in order to obtain levels comparable with those shown in normal term, breast-fed neonates. Nitrogen retention did not differ among the three groups (247 to 273 mg.kg-1.d-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperphenylalaninaemia and outcome in intravenously fed preterm neonates

Hyperphenylalaninaemia is likely to have occurred in many infants fed the intravenous amino acid solution Vamin 9. In this study of 336 preterm infants plasma phenylalanine was measured weekly during their hospital stay. Reference data on plasma phenylalanine were prepared for 243 infants who did not receive Vamin. Only 1% of these infants had a peak plasma phenylalanine concentration greater than 150 mumol/l (maximum 202 mumol/l) compared with 23% in 93 infants fed Vamin 9, seven of whom had concentrations > 300 mumol/l (maximum 704 mumol/l). High concentrations only occurred when the total energy to protein energy ratio in the intravenous solutions decreased to less than 8.5:1 and always occurred with a ratio less than 6.5:1, implying that hyperphenylalaninaemia may be minimised with an intravenous energy intake of greater than 34 kcal (142 kJ)/g protein. Nevertheless, follow up at 18 months post-term showed that increased plasma phenylalanine in this instance was not associated with any impairment of the Bayley mental development index (or subscales including fine motor, cognitive, or language development), the psychomotor development index, or the social maturity quotient. Thus, despite theoretical concern, an adverse outcome after hyperphenylalaninaemia induced by intravenous feeding has not been observed.

Plasma amino acid profiles in preterm infants receiving Vamin 9 glucose or Vamin infant

Amino acid profiles were measured in 29 low-birth-weight infants receiving either Vamin 9 glucose (n = 18, group A) or Vamin Infant (n = 11, group B) as the amino acid source in parenteral nutrition; intake was otherwise identical. Infants were sampled when receiving 430 mgN/kg per day (3.2 g/kg per day amino acids) and 90 non-protein kcal/kg per day. There was no difference between groups in birth weight, gestational or postnatal age. The percentage N retention was similar in both (68 and 60%, groups A and B respectively). Phenylalanine and tyrosine levels were higher in those who received Vamin 9 glucose but 55% of infants given Vamin Infant had tyrosine levels below the lower limit of the target range. Cysteine levels were low in both groups. Further modification of the amino acid composition of parenteral solutions for the newborn is necessary. If sufficient non-protein energy can be provided the risk of abnormally high amino acid levels is reduced.

Evaluation of a taurine containing amino acid solution in parenteral nutrition

Vaminolact, an amino acid solution containing taurine, was given to 15 sick newborn babies. They were compared with a group of 10 babies who received a solution that did not contain taurine (Vamin glucose). Efficacy and safety were evaluated by monitoring plasma amino acid patterns, growth patterns, nitrogen balance, and biochemical and haematological profiles. No serious abnormalities in amino acid concentrations were found. After an initial fall the taurine concentration recovered more rapidly in those receiving the taurine supplement, though this difference was not significant. Phenylalanine concentrations were within the reference range in the group receiving Vaminolact, and were significantly lower than in the group receiving Vamin glucose. Metabolic acidosis, which occurred in several subjects in each group, was not a serious problem. Liver function tests remained satisfactory. Nitrogen retention was greater among those receiving Vaminolact than in the control group. Vaminolact is a safe and effective amino acid solution for use in critically ill babies.

Amino acid levels in the critically ill preterm infant given mother's milk fortified with protein from human or cow's milk

Twenty preterm infants undergoing neonatal intensive care were randomly allocated to one of two feeding regimens: human milk enriched with either human milk protein (HMP) or adapted cow's milk protein (CMP). The birthweights (1076 +/- 301 g; 1031 +/- 309 g) and the gestational ages (28.4 +/- 1.6 weeks; 27.7 +/- 2.1 weeks) were comparable. The amount of protein added to the milk was set at 0.7 g/100 ml in order to provide a total supply of 3.0-3.5 g/kg/24 h. All infants received additional amounts of carbohydrate, calcium, phosphorous, and sodium chloride. Capillary whole blood amino acids were measured with high pressure liquid chromatography (HPLC). The amino acid levels did not differ significantly when the feeding groups were compared week by week, but the glycine/valine ratio was higher (p less than 0.05) in the HMP group after three weeks of fortification. Longitudinal changes after protein enrichment could be demonstrated in both groups. Alanine and threonine increased after one week (p less than 0.01) in both groups. Glycine in the HMP group peaked after two weeks (p less than 0.02), and valine in the CMP group increased (p less than 0.02) after one week on the feeding regimen. However, the amino acids never reached levels above those seen after a meal in normal term newborns. Other variables related to protein intake, such as protein and urea in serum, did not vary between the groups. Growth, expressed as gains in weight, length, and head circumference was poor but comparable. The quality of the protein, whether a human milk protein isolate or a cow's milk whey protein product, used for the fortification of human milk up to a protein load of 3.0-3.5 g/kg/24 h, did not cause any alterations of significance in the amino acid profiles of peripheral blood.

Amino acid profiles by HPLC after filter paper sampling: 'appropriate technology' for monitoring of nutritional status

This paper describes a rapid analysis of free amino acid levels in capillary blood samples using a modified HPLC system. Capillary whole blood (25 microliters) is dried on a filter paper, extracted and the equivalent of 0.25 microliter of the initial blood sample is used for each amino acid analysis. Nineteen free amino acid levels are determined with a reproducibility of better than +/- 10% for the entire procedure of sampling, preparation and analysis, with the exception of ornithine (+/- 19%) and lysine (+/- 12%). Cystine and proline cannot easily be determined by this method. Alanine, tyrosine, methionine, valine, phenylalanine, isoleucine and leucine concentrations on the filter paper are unaltered after 1, 2 and 21 wk. Storage at room temperature should not be for longer than 2 wk, but storage at +4 degrees C, -18 degrees C and -70 degrees C is acceptable for 21 wk. This new micromethod seems to be a practical and reliable tool. Because of its simplicity and, above all, the need for a minimal amount of capillary blood, it is a valid means for the routine monitoring of amino acid profiles in sick preterm infants on different protein regimens. The sampling and storage methods are also examples of 'appropriate technology' for field studies of nutritional adequacy in population samples derived from infants. This is because centrifugation is not necessary and the fact that the relevant amino acids on the dried filter paper samples display high stability.

Egg and breast milk based nitrogen sources compared

A nitrogen source based on egg protein (Vamin 9 glucose) and an alternative with an amino acid profile more similar to breast milk (Vaminolact), were compared in 14 parenterally fed infants. Subjects were randomly allocated to receive one or other amino acid solution, but were otherwise given identical diets. At the start of the study the two groups did not differ significantly in postconceptual age, postnatal age, or weight. Over a six day study period on a stable intake of intravenous nutrients there was no significant difference in growth or nitrogen retention between the two groups. Plasma amino acid profiles in those receiving Vamin 9 glucose, however, were frequently abnormal. Notably, mean concentrations of potentially neurotoxic phenylalanine and tyrosine were significantly higher (140% and 420%, respectively) in patients fed Vamin 9 compared with those given Vaminolact. An amino acid solution based on the composition of breast milk protein therefore brings plasma amino acid profiles during parenteral nutrition closer to those found in breast fed infants, and reduces in particular, the risks of hyperphenylalaninaemia and hypertyrosinaemia.

Plasma amino acid concentrations in parenterally fed preterm infants

One hundred and nine sick preterm infants were studied, and the data obtained show that hyperphenylalaninaemia is an extremely rare occurrence as long as an adequate source of energy is provided. High concentrations of the other aromatic amino acid (tyrosine) on the other hand, were often encountered and seem to be due to immaturity of an isolated hepatic enzyme as there was no correlation between phenylalanine and tyrosine concentrations. Possible adverse consequences of hypertyrosinaemia are discussed in relation to toxicity and the assessment of hepatic function. We provide reference centiles for plasma amino acid concentrations in this population.

The nutrition team in a children's hospital

This paper discusses the reasons for a paediatric nutritional care team, the members involved, and their role within the team. The methods used for nutritional assessment are described and the cost effectiveness of the nutrition team's involvement is discussed.