Almost all enteral aspartate is taken up in first-pass metabolism in enterally fed preterm infants (Article)

2010-06-01T00:00:00Z

Background & aims: The intestine is a major site of amino acid metabolism, especially in neonates. Neonatal animals derive energy needed for metabolic processes from dietary glucose and amino acids. Rats were found to oxidize non-essential amino acids such as aspartate, glutamate and glutamine in the intestine at a high rate. We have previously found that glutamate and glucose are important sources of energy for the splanchnic tissues in fully fed preterm infants. However, no data are available on splanchnic aspartate metabolism in human preterm infants. In the present study we studied whole-body and splanchnic aspartate metabolism and determined the metabolic fate of aspartate. Methods: In eight, enterally fed, preterm infants (gestational age 31 weeks (wk)±3 SD, range: 26-34wk) splanchnic and whole-body aspartate kinetics were assessed by dual tracer ([U-13C]aspartate and [D3]aspartate) techniques. Results: Splanchnic first-pass aspartate uptake was almost complete (77±15%). Almost all (80±9%) of the13C administered as [U-13C]aspartate used in first-pass was recovered as CO2in expired breath. Conclusion: The splanchnic tissues extract almost all of the dietary aspartate in preterm infants. The majority of the labeled carbon is recovered in expired breath, making it most likely that the sequestered carbon skeleton of aspartate is utilized for energy generation.

Neonatal sulfur amino acid metabolism (Doctoral Thesis)

2008-05-30T00:00:00Z

At birth, infants can be classified either by gestational age (GA) or by weight. Neonates born < 37 weeks are classified as preterm, < 28 weeks as very preterm and < 26 weeks as extremely preterm infants. Prematurely born infants can also be classified by birth weight as follows (1): - Low birth weight (LBW) < 2500 g - Very low birth weight (VLBW) < 1500 g - Extremely low birth weight (ELBW) < 1000 g However, both classifications are used arbitrary in the clinical setting and obviously the infant born very prematurely has most likely a birth weight < 1500 g. Over the past 25 years life support in the neonate born prematurely has improved tremendously and has created major advantages in medical treatment possibilities and survival. Nowadays it is generally accepted to treat the very preterm infant and even the extremely preterm infant since survival rates for these infants are still increasing.

Cyst(e)ine requirements in enterally fed very low birth weight preterm infants (Article)

2008-03-01T00:00:00Z

OBJECTIVE. Optimal nutrition is of utmost importance for the preterm infant's later health and developmental outcome. Amino acid requirements for preterm infants differ from those for term and older Infants, because growth rates differ. Some nonessential amino acids, however, cannot be sufficiently synthesized endog-enously. Cyst(e)ine is supposed to be such a conditionally essential amino acid in preterm infants. The objective of this study was to determine, at 32 and 35 weeks' postmenstrual age, cyst(e)ine requirements in fully enterally fed very low birth weight preterm infants with gestational ages of <29 weeks. METHODS. Infants were randomly assigned to 1 of the 5 graded cystine test diets that contained generous amounts of methionine. Cyst(e)ine requirement was determined with the indicator amino acid oxidation technique ([I-13C]phenylaIanlne) after 24-hour adaptation. RESULTS.Fractional [I13-CJphenylalanine oxidation was established in 47 very low birth weight preterm infants (mean gestational age: 28 weeks ± 1 week SD; birth weight: 1.07 kg ± 0.21 kg SD). Increase in dietary cyst(e)ine intake did not result in a decrease in fractional [l-13,CJphenylalanine oxidation. CONCLUSIONS.These data do not support the hypothesis that endogenous cyst(e)ine synthesis is limited in very low birth weight preterm infants with gestational ages of <29 weeks, both at 32 and 35 weeks postmenstrual age. It is safe to conclude that cyst(e)ine requirement is

Splanchnic oxidation is the major metabolic fate of dietary glutamate in enterally fed preterm infants (Article)

2007-10-01T00:00:00Z

The intestine is a major site of amino acid metabolism, especially in neonates. The energy needed for the metabolic processes in neonatal animals is derived from dietary glucose and amino acids. No data are available showing that dietary amino acids function as intestinal fuel source in human neonates as well. We hypothesized that preterm infants show a high splanchnic first-pass glutamate metabolism and the primary metabolic fate of glutamate is oxidation. Five preterm infants (birth weight 1.2 ± 0.2 kg, gestational age 29 ± 1 wk) were studied by dual tracer ([U-C]glutamate and [D3]glutamate) techniques on two study days (within postnatal d 14-19). Splanchnic and whole-body glutamate kinetics were assessed by plasma isotopic enrichment of [U-C]glutamate and [D3]glutamate and breath CO2 enrichment. Fractional first-pass glutamate uptake was 77 ± 18% on d 1, and 70 ± 7% on d 2, mean 74 ± 13%. Almost all (86 ± 7%) of the glutamate used in the first pass is directed toward oxidation. There is a high splanchnic fractional first-pass uptake and a high oxidation rate of glutamate in preterm infants. Glutamate is an important source of energy for the splanchnic tissues in preterm infants receiving full enteral feeding.

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract (Article)

2007-02-27T00:00:00Z

Methionine is an indispensable sulfur amino acid that functions as a key precursor for the synthesis of homocysteine and cysteine. Studies in adult humans suggest that splanchnic tissues convert dietary methionine to homocysteine and cysteine by means of transmethylation and transsulfuration, respectively. Studies in piglets show that significant metabolism of dietary indispensable amino acids occurs in the gastrointestinal tissues (GIT), yet the metabolic fate of methionine in GIT is unknown. We show here that 20% of the dietary methionine intake is metabolized by the GIT in piglets implanted with portal and arterial catheters and fed milk formula. Based on analyses from intraduodenal and intravenous infusions of [1-13C]methionine and [2H3]methionine, we found that the whole-body methionine transmethylation and remethylation rates were significantly higher during duodenal than intravenous tracer infusion. First-pass splanchnic metabolism accounted for 18% and 43% of the whole-body transmethylation and remethylation, respectively. Significant transmethylation and transsulfuration was demonstrated in the GIT, representing ≈27% and ≈23% of whole-body fluxes, respectively. The methionine used by the GIT was metabolized into homocysteine (31%), CO2(40%), or tissue protein (29%). Cystathionine β-synthase mRNA and activity was present in multiple GITs, including intestinal epithelial cells, but was significantly lower than liver. We conclude that the GIT consumes 20% of the dietary methionine and is a significant site of net homocysteine production. Moreover, the GITs represent a significant site of whole-body transmethylation and transsulfuration, and these two pathways account for a majority of methionine used by the GITs.

Parenteral amino acid and energy administration to premature infants in early life (Article)

2007-02-01T00:00:00Z

After birth, the nutritional supply through the umbilical cord ceases. Premature infants do not immediately tolerate full enteral feedings, yet they retain high nutritional needs for both growth and metabolic maintenance. Parenteral nutrition should therefore be initiated as quickly as possible after premature birth, thereby reducing the dependence on endogenous substrates. Intrauterine studies show very high amino acid uptake, clearly exceeding accretion rates. Studies covering the early neonatal period demonstrate that the initiation of high-dose amino acid administration directly after birth is safe and effective, even at low energy intakes. Future research should reveal whether usage could be improved through better amino acid solutions or by providing more energy via lipids from birth onwards as well.

Splanchnic metabolism of ingested amino acids in neonates (Article)

2007-01-01T00:00:00Z

PURPOSE OF REVIEW: Neonates typically show rapid growth. Nutrient absorption in the neonatal period is higher than during any other time in life so as to meet the requirements for this rapid growth. Generally, nutrients are administered enterally, and in the past the gut was considered to absorb and digest these nutrients without major metabolism. Recent animal and human work has, however, revealed that the intestine and other splanchnic tissues contribute significantly to whole-body metabolism, and have their own specific functions. This review focuses on these observations. RECENT FINDINGS: The splanchnic tissues take up greatly different proportions of each of the amino acids, ranging from 80-100% for threonine and several nonessential amino acids to 15-30% for lysine. The metabolic fates of the utilized substrates differ as well. Some are predominantly used for constitutive protein synthesis, others for energy generation or for formation of (glyco-)proteins that are secreted into the lumen. Glucose appears to be the major contributor to energy generation, but amino acids are important as well. SUMMARY: Both animal and human studies have shown that the intestine uses substantial amounts of dietary amino acids. This has several implications for the nutritional needs of infants to maintain growth, especially during times of inadequate enteral nutrition.

Use of [13C]bicarbonate for metabolic studies in preterm infants: intragastric versus intravenous administration. (Article)

2005-11-01T00:00:00Z

The metabolic fate of substrates in humans can be examined by the use of stable isotopes, one of which, [13C]bicarbonate, may serve to estimate CO2 production rate. In view of minimizing the burden of metabolic studies for preterm infants, the authors determined whether intragastric and intravenous infusions of [13C]bicarbonate would achieve the same 13CO2 enrichment in expired air during steady state. A second aim of this study was to determine the minimum time required to reach steady state during intragastric infusion. Ten preterm infants received a primed continuous [13C]bicarbonate infusion intragastrically, followed by an intravenous infusion the next day. Breath samples were obtained every 30 min by the direct sampling method. 13CO2 isotopic enrichment, expressed as atom percent excess, was measured by isotopic ratio mass spectrometry. Two-tailed t tests were used to detect statistically significant differences between the infusion routes. The isotopic enrichment at plateau did not differ between intragastric and intravenous infusion. A steady state of 13CO2 enrichment was achieved after 60 min of intravenous infusion and after 120 min of intragastric infusion. In conclusion, intragastric infusion of [13C]bicarbonate may serve to estimate the whole-body CO2 production rate in preterm infants. To reach 13CO2 steady state, a minimum of 120 min of bicarbonate administration is required.

Riedijk, M.A.