Dietary and physical activity patterns in children with fatty liver.

BACKGROUND/OBJECTIVES: To examine lifestyle patterns (diet, physical activity, energy expenditure) and metabolic variables (insulin resistance, oxidative stress, inflammation) in children with fatty liver detected by sonography. SUBJECTS/METHODS: Body composition (fat-free mass, body mass index-z), waist circumference (WC), dietary intake and energy expenditure were determined in 38 patients (ages 5-19 years) with fatty liver in whom specific causative liver disorders had been excluded. Laboratory investigations included liver biochemistries, C-reactive protein, tumor necrosis factor-alpha, glutathione peroxidase, vitamin E, and erythrocyte-glutathione. RESULTS: In all, 36 of 38 children were overweight/obese; 37 had WC indicative of abdominal obesity. They displayed fasting hyperinsulinemia (n=15), hypertriglyceridemia (n=14), and hypoadiponectinemia (5.5+/-1.9 s.d. microg/ml; n=23) and insulin resistance (homeostasis model of insulin resistance (HOMA-IR)>3; n=21). Alanine aminotransferase (ALT) was elevated in 28 (43-556 U/l; median=56). Some inflammatory markers were elevated, whereas antioxidants were decreased. Diet was characterized by high saturated-, low polyunsaturated-fat, high fructose and sucrose intakes. Fructose intake was independently associated with insulin resistance and decreased serum adiponectin, regardless of serum ALT (P<0.05). Low and subnormal intakes of omega-3 fatty acids (C20:5 (n-3) and C22:6 (n-3)) were associated with abnormal serum ALT (P=0.006) and elevated HOMA-IR (P=0.01). Findings were similar in children 11 years old. Physical activity was low in both age groups. CONCLUSIONS: Children with fatty liver detected sonographically have metabolic features of non-alcoholic fatty liver disease. Their diets are high in fructose and low in polyunsaturated fatty acid. Their activity patterns are sedentary. These lifestyle features may contribute to liver damage and can be a focus for therapeutic intervention.

Re-feeding rapidly restores protection against Heligmosomoides bakeri (Nematoda) in protein-deficient mice.

This study determined whether the timing of re-feeding of protein-deficient mice restored functional protection against the gastrointestinal nematode, Heligmosomoides bakeri. Balb/c mice were fed a 3% protein-deficient (PD) diet and then transferred to 24% protein-sufficient (PS) diet either on the day of primary infection, 10 days after the primary infection, on the day of challenge infection, or 7 days after the challenge infection. Control mice were fed either the PD or PS diet. Onset of challenge, but not primary, infection caused short-term body weight loss, anorexia and reduced feed efficiency. Weight gain was delayed in mice when re-feeding commenced on the day of challenge infection; alkaline phosphatase (ALP) was also elevated in these mice on day 28 post-challenge. In contrast, other re-feeding groups attained similar body weights to PS mice within 4 days and had similar ALP at day 28. Serum leptin was higher in PD than PS mice and positively associated with food intake. As expected, worm survival was prolonged in mice fed the PD diet. However, egg production and worm burdens were similar in all re-feeding groups to the PS mice, indicating that protein re-feeding during either the primary or challenge infection rapidly restored normal parasite clearance.

Dietary pectin, but not cellulose, influences Heligmosomoides polygyrus (Nematoda) reproduction and intestinal morphology in the mouse.

Dietary texture has been reported to influence parasite establishment and survival, but to what degree this relationship is modified by either the type or quantity of dietary fibre is unknown. Using a 2 x 4 factorial design, we explored the relationship between fibre type (soluble pectin vs insoluble = cellulose) and fibre quantity (0, 5, 10 and 20% by dry weight) on parasitic outcomes in BALB/c mice infected with 100 Heligmosomoides polygyrus (Nematoda) larvae. Pectin, but not cellulose, exerted a significant effect on parasite egg production. Following in vitro culture of female worms, increasing levels of dietary pectin were associated with increasing release of eggs. Yet this pattern was not observed in vivo, where per capita egg production peaked at the 10% pectin concentration, but was very low in mice fed 20% pectin. Parasite establishment was elevated in mice fed 20% pectin, but was unaffected by cellulose concentration. Neither type nor quantity of fibre affected H. polygyrus survival or spatial distribution along the gastrointestinal tract. To what degree differences in parasite establishment and reproduction could be attributed to the marked effects of pectin on gut morphology (increased intestinal length, villus length, mucosa thickness and villus/crypt ratio) requires further exploration. Our data indicate that cellulose is preferable to pectin as the source of fibre for experimental diets as cellulose did not affect H. polygyrus establishment, reproduction or survival during a 4-week primary infection.

Total sulfur amino acid requirement in young men as determined by indicator amino acid oxidation with L-[1-13C]phenylalanine.

BACKGROUND: Determining the sulfur amino acid (SAA) requirements of humans has remained elusive because of the complex nature of SAA metabolism. Current recommendations are based on nitrogen balance studies. OBJECTIVE: The goal of the present study was to determine the methionine requirement of men fed a diet devoid of cysteine (total SAA requirement). DESIGN: Six men were randomly assigned to receive 6 graded intakes of methionine: 0, 6.5, 13.0, 19.5, 26.0, and 32.0 mg x kg(-1) x d(-1). The total SAA requirement was determined by measuring the oxidation of L-[1-13C]phenylalanine to 13CO2 (F(13)CO2)). The mean total SAA requirement was estimated with use of a linear regression crossover analysis, which identified a breakpoint of the F(13)CO2 response to methionine intake. RESULTS: On the basis of the mean measures of F(13)CO2, the mean requirement and population-safe intake (upper limit of the 95% CI) of total SAAs were found to be 12.6 and 21 mg x kg(-1) x d(-1), respectively. CONCLUSION: Although the mean SAA requirement is consistent with current guidelines for the total SAA intake, the population-safe intake is substantially higher than the currently recommended total SAA intake.

Dietary cysteine reduces the methionine requirement in men.

BACKGROUND: Despite early evidence suggesting that dietary cysteine has a sparing effect on methionine requirements, some recent reports question the existence of a measurable sparing capacity. OBJECTIVE: The goal of the present study was to determine whether dietary cysteine could reduce the requirement for methionine in men consuming diets with and without cysteine. DESIGN: Six men were randomly assigned to receive graded intakes of methionine while fed a diet containing either no exogenous cysteine or an excess of cysteine (21 mg x kg(-1) x d(-1)). The methionine requirement was determined by measuring the oxidation of L-[1-13C]phenylalanine to 13CO2 and estimated by using a linear regression crossover analysis. RESULTS: The mean and population-safe (upper limit of the 95% CI) methionine requirements in the absence of exogenous cysteine were found to be 12.6 and 21 mg x kg(-1) x d(-1), respectively. The mean and population-safe methionine requirements in the presence of excess dietary cysteine were found to be 4.5 and 10.1 mg x kg(-1) x d(-1), respectively, representing a cysteine sparing effect of 64% in a comparison of mean methionine requirements and of 52% in a comparison of population-safe methionine intakes. Furthermore, the difference between population-safe intakes with and without dietary cysteine establishes a safe cysteine intake of 10.9 mg x kg(-1) x d(-1) in the presence of adequate methionine intakes. CONCLUSION: Our data suggest that dietary cysteine can reduce the exogenous requirement for methionine in men. These results strongly support the existence of a cysteine sparing effect in humans.

Comparison of the effect of dietary fat restriction with that of energy restriction on human lipid metabolism.

BACKGROUND: Dietary fat and energy have been implicated as factors controlling circulating total and LDL-cholesterol concentrations. Whether these factors work independently or synergistically in regulating human cholesterol metabolism remains to be fully elucidated. OBJECTIVE: The objective was to determine whether the effects of fat restriction on circulating lipid concentrations and synthesis differ from those of energy restriction in hypercholesterolemic subjects fed controlled diets. DESIGN: Eleven men (LDL > 3.6 mmol/L) participated in a randomized crossover study. Subjects consumed 4 prepared diets, each for 4 wk and separated by 6 wk, that contained either typical amounts of fat and energy (TF), low amounts of fat but adequate energy (LF), low amounts of fat and energy through carbohydrate restriction (LFE), or typical amounts of fat and low energy through carbohydrate restriction (LE). RESULTS: Body weights declined (P < 0.001) after the LE and LFE diets. Total cholesterol concentrations were not significantly different between the diets. LDL cholesterol was lower (P < 0.05) after the LF and LFE diets (8.2% and 8.0%, respectively) than after the TF diet. The LE diet increased HDL cholesterol (46.8%) and decreased triacylglycerols (22.7%), whereas the LF diet increased triacylglycerols (23.6%), relative to the TF diet. LDL:HDL decreased after the LE and LFE diets (P < 0.05). Cholesterol fractional synthesis rates after the LF, LE, and LFE diets were lower (35.2%, 27.7%, and 25.5%, respectively; P < 0.05) relative to the TF diet. CONCLUSION: Reductions in both dietary fat and energy may modify LDL cholesterol by lowering cholesterol biosynthesis; however, the increase in HDL cholesterol and the suppression of triacylglycerol concentrations and LDL:HDL suggests that favorable plasma lipid profiles were also achieved through energy restriction alone.

Comparison of deuterium incorporation and mass isotopomer distribution analysis for measurement of human cholesterol biosynthesis.

To compare endogenous cholesterol biosynthesis measured by deuterium incorporation (DI) and mass isotopomer distribution analysis (MIDA), cholesterol fractional and absolute synthetic rates were measured simultaneously by both techniques under identical physiological conditions. Twelve subjects (22 to 39 years of age) underwent a dual stable isotope protocol, involving oral deuterium oxide administration and measurement of incorporation of deuterium into cholesterol coincident with constant infusion of sodium [1-(13)C]acetate and measurement of the mass isotopomer distribution pattern of newly synthesized cholesterol. Synthesis was determined over 24 h with a 7-h feeding period. Both methods yielded similar measurements of fractional cholesterol synthesis (7.8 +/- 2.5% day(-)(1) for DI vs. 6.9 +/- 2.2% day(-)(1) for MIDA). Correlation of fractional synthesis across techniques was strong (r = 0.84, P = 0.0007). Absolute synthesis rates were also not different at 24 h (13.4 +/- 4.3 mg kg(-)(1) day(-)(1) for DI vs. 11.9 +/- 3.6 mg kg(-)(1) day(-)(1) for MIDA, r = 0.79, P < 0.002). We conclude that despite different assumptions and analytical requirements, deuterium incorporation and MIDA yield similar rates of cholesterogenesis in humans when measurements are made over 24 h. The decision as to which method to adopt depends on available clinical and analytical facilities

Isotopic enrichment of amino acids in urine following oral infusions of L-[1-(13)C]phenylalanine and L-[1-(13)C]lysine in humans: confounding effect of D-[13C]amino acids.

Urine sampling of the free amino acid pool serves to reflect plasma enrichment and is used as a noninvasive means to determine isotope enrichment in studies of amino acid metabolism. We determined the effect of D-[13C]phenylalanine and D-[13C]lysine content of tracers on urinary amino acid enrichment following oral infusion of L-[13C]phenylalanine in 18 preterm infants and L-[1-(13)C]lysine in seven healthy adult females. Urinary [13C]phenylalanine enrichment was higher (P < .0001) for L-[13C]phenylalanine containing 0.4% D-[13C]phenylalanine (28.6 +/- 7.1) versus L-[1-(13)C]phenylalanine that contained undetectable D-[13C]phenylalanine (10.2 +/- 1.5). D-[13C]phenylalanine, measured by chiral column gas chromatography-mass spectrometry (GC-MS), accounted for 10% to 30% (20.5% +/- 7%) of total phenylalanine in the urine of infants who received 0.4% D-[13C]phenylalanine, and was absent from the urine of infants receiving tracer with undetectable [13C]phenylalanine. Urinary L-[13C]phenylalanine enrichment did not differ between tracer groups (9.8 +/- 1.5 and 9.8 +/- 2.5). In adult females, the use of L-[1-(13)C]lysine (1.6% D-lysine) resulted in a higher (P < .02) urine total L,D-[13C]lysine enrichment compared with plasma enrichment (40.8 +/- 4.1 v 11.1 +/- 0.7). This study demonstrates the significant presence of D-[13C]amino acids in urine that originate as contaminants from commercially manufactured tracers, as a result of renal tubular discrimination of D-amino acids. A tracer containing detectable amounts of D-[13C]isomer cannot be recommended for any study in which urine will be used to reflect enrichment in the arterial plasma pool.

Protein kinetics determined in vivo with a multiple-tracer, single-sample protocol: application to lactase synthesis.

Precise analysis of the kinetics of protein/enzyme turnover in vivo has been hampered by the need to obtain multiple tissue samples at different times during the course of a continuous tracer infusion. We hypothesized that the problem could be overcome by using an overlapping (i.e., staggered) infusion of multiple stable amino acid isotopomers, which would take the place of multiple tissue samples. We have measured, in pigs, the in vivo synthesis rates of precursor (rapidly turning over) and mature (slowly turning over) polypeptides of lactase phlorizin hydrolase (LPH), a model for glycoprotein synthesis, by using an overlapping infusion of [2H3]leucine, [13C1]leucine, [13C1]phenylalanine, [2H5]phenylalanine, [13C6]phenylalanine, and [2H8]phenylalanine. Blood samples were collected at timed intervals, and the small intestine was collected at the end of the infusion. The tracer-to-tracee ratios of each isotopomer were measured in the plasma and jejunal free amino acid pools as well as in purified LPH polypeptides. These values were used to estimate kinetic parameters in vivo using a linear steady-state compartmental model. The fractional synthesis rates of the high-mannose, complex glycosylated and mature brush-border LPH polypeptides, so determined, were 3.3 +/- 1.1%/min, 17.4 +/- 11%/min, and 0.089 +/- 0.02%/min, respectively. We conclude that this multiple-tracer, single-sample protocol is a practicable approach to the in vivo measurement of protein fractional synthesis rates when only a single tissue sample can be obtained. This method has broad application and should be particularly useful for studies in humans.

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.

Gluconeogenesis measured with [U-13C]glucose and mass isotopomer analysis of apoB-100 amino acids in pigs.

Infant pigs (8.5 kg) were fasted for 16 h and infused for 6 h with [U-13C]glucose. The fractional abundances of all 13C mass isotopomers of plasma glucose, lactate, and pyruvate and of plasma, hepatic, and very low density lipoprotein apolipoprotein B-100 (apoB-100) alanine, glutamate, and aspartate were measured. The ratios of [13C3]aspartate. [13C3]glutamate, and [13C3]alanine in apoB-100 were used to estimate the positional equilibrium of [13C3]oxaloacetate, the fractional contribution of pyruvate carboxylase to the hepatic oxaloacetate flux, and the activity of hepatic pyruvate dehydrogenase. The values were compared with those based on glucose labeling and previously published equations. The two methods [Katz and Lee method (J. Katz, P.A. Wals., and W.-N. P. Lee. J. Biol. Chem. 264: 12994-13001, 1989) and apoB method] gave similar estimates of the positional equilibrium of [13C3]oxaloacetate (0.59, Katz and Lee method; 0.61, apoB method) but slightly different estimates of the contribution of pyruvate carboxylase to the oxaloacetate flux (0.36, Katz and Lee; 0.31 apoB). Gluconeogenesis apparently contributed between 71 (Katz and Lee method) and 80% (apoB method) of the glucose entry rate (25 mumol.kg-1.min-1), and pyruvate dehydrogenase contributed 20% of the hepatic acetyl-CoA. We conclude that the labeling of aspartate in apoB-100 provides a good estimate of the isotopomer distribution in hepatic oxaloacetate but may underestimate the absolute isotopic enrichment by 50%.

Parenteral nutrition selectively decreases protein synthesis in the small intestine.

We investigated the effects of an elemental diet fed parenterally or enterally on total mucosal protein and lactase phlorizin hydrolase (LPH) synthesis. Catheters were placed in the stomach, jugular vein, and carotid artery of 12 3-day-old pigs. Half of the animals were given an elemental regimen enterally and the other half parenterally. Six days later, animals were infused intravenously with [2H3]leucine for 6 h and killed, and the midjejunum of each animal was collected for analysis. The weight of the midjejunum was 8 +/- 1.5 and 17 +/- 1.6 g in parenterally fed and enterally fed piglets, respectively. LPH activities (mumol.min-1.g protein-1) were significantly higher in parenterally vs. enterally fed piglets. Total small intestinal LPH activities were lower in parenterally vs. enterally fed animals. The abundance of LPH mRNA relative to elongation factor-1 alpha mRNA was not different between groups. The fractional synthesis rate of total mucosal protein and LPH was significantly lower in parenterally fed animals (67 +/- 7 and 66 +/- 7%/day, respectively) than in enterally fed animals (96 +/- 7 and 90 +/- 6%/day, respectively). The absolute synthesis rate (the amount of protein synthesized per gram of mucosa) of total mucosal protein was significantly lower in parenterally fed than in enterally fed piglets. However, the absolute synthesis rate of LPH was unaffected by the route of nutrient administration. These results suggest that the small intestine partially compensates for the effects of parenteral feeding by maintaining the absolute synthesis rate of LPH at the same levels as in enterally fed animals.

Integration of amino acid and carbon intermediary metabolism: studies with uniformly labeled tracers and mass isotopomer analysis.

The central pathways of metabolism include glycolysis and gluconeogenesis, fatty acid synthesis and beta-oxidation, the citric acid cycle and ureagenesis. Because these pathways intersect, changes in one pathway, due to inborn error or disease, affect pathways that may seem remote from the initial metabolic defect. These metabolic interrelationships also present difficulties for isotopic studies, because once carbon derived from isotopic tracers is introduced into metabolism it is extensively recycled. The use of multiple labeled (especially uniformly 13C-labeled ([U-13C]), metabolic tracers, in conjunction with mass isotopomer distribution analysis of mass and nuclear magnetic spectra, has enabled the development of methods that resolve some of these difficulties. Suitable choices of tracers and analytes allow the simultaneous measurement of multiple pathways and, importantly, their kinetic interrelationships. We illustrate three uses of the technique: (1) the unequivocal determination of trace fluxes; (2) the quantification of biosynthetic pathways: and (3) the dissection, in vivo, of the citric acid (Krebs) cycle. In each case, different combinations of [U-13C]tracer and metabolic end product have revealed metabolic phenomena that otherwise would remain unidentified. A particularly striking, and unexpected, observation that has emerged from recent studies using the technique, suggests that the key dehydrogenase reactions in the Krebs cycle may be reversible. Although this approach is of relatively recent development, it has already given a number of novel insights into the organization of the central metabolic pathways. It should provide a powerful method of investigating the metabolic impact of genetic disease and provide invaluable support of the assessment of new therapeutic interventions.

Chronic low protein intake reduces tissue protein synthesis in a pig model of protein malnutrition.

To determine the effect of severe chronic protein deficiency on protein synthesis in different tissues and total protein in plasma, and on plasma biochemical constituents involved in amino acid metabolism, we fed diets containing either 20 or 3% protein to two groups of four age-matched piglets. After consuming the diets for 8 wk, the pigs received a primed-constant infusion of 2 H3-leucine for 8 h to measure the fractional synthesis rates (FSR) of tissue protein and total protein in plasma. Plasma urea and amino acid concentrations, particularly indispensable amino acids, were significantly lower in protein-deficient pigs. Fractional protein synthesis rates were lower in skin by 66% (P < 0.01), in jejunal mucosa by 50% (P < 0.05), in masseter muscle by 40% (P < 0.05), and in liver by 25% (P < 0.02); the fractional synthesis rate of the longissimus muscle was not different than controls. Although plasma protein concentration was significantly (P < 0.01) lower in protein-deficient pigs, the fractional synthesis rate of the total intravascular plasma protein pool was not different. We conclude that adaptation to a low protein diet involves a reduction in the rate of protein synthesis in most body tissues, with the most marked changes occurring in skin and intestine, two tissues which frequently exhibit severe functional impairment in protein malnutrition.

Recent advances in methods of assessing dietary amino acid requirements for adult humans.

The requirements for the indispensable amino acids have been determined by a number of different methods. Historically, descriptive or gross measures like growth and nitrogen balance have been used. However, technological advancements in recent years have resulted in the use of more precise and mechanistic metabolic approaches (i.e., plasma amino acid concentrations, amino acid oxidation, indicator amino acid oxidation) to examine requirement. Nevertheless, the current recommendations are still based on nitrogen balance studies. Requirement estimates based on other methodologies, such as plasma amino acid concentrations and direct amino acid oxidation, suggest that the requirement estimates derived from nitrogen balance experiments are too low. However, these higher estimates have also been criticized on conceptual and methodological grounds, resulting in considerable controversy in the area of indispensable amino acid requirements. A new technique, indicator amino acid oxidation, addresses many of the criticisms directed toward the alternative methods and the proposed higher requirement estimates. This paper reviews the current knowledge of amino acid requirements and makes recommendations in light of new information that has been provided from recent indicator amino acid oxidation research. It is concluded that the nitrogen balance-based estimates of amino acid requirement are too low.

Protein-deficient pigs cannot maintain reduced glutathione homeostasis when subjected to the stress of inflammation.

The mechanisms responsible for depletion of systemic glutathione levels in nutritional deprivation and/or in infective and inflammatory conditions have not been fully established. We quantified the effects of protein undernutrition and experimental inflammation on the concentration and synthesis of reduced glutathione in the erythrocytes, liver and jejunal mucosa of young pigs. Two groups of five piglets consumed diets containing either 23 or 3% protein and, after 4 wk, were infused intravenously with [13C2]glycine before and 48 h after subcutaneous injections of turpentine. Erythrocyte, hepatic and intestinal mucosal reduced glutathione was quantified as the monobromobimane derivative by HPLC. Reduced glutathione synthesis was determined by measurements of the tracer/tracee ratio of reduced glutathione-bound glycine. In well-nourished piglets, turpentine injection had no effect on erythrocyte reduced glutathione concentrations or rate of synthesis. Protein undernutrition was associated with lower erythrocyte reduced glutathione concentrations (1.05 +/- 0.04 vs. 1.32 +/- 0.06 mmol/L, P < 0.01) and synthesis (42 +/- 5 vs. 60 +/- 5%/d), and turpentine inflammation caused a further fall in erythrocyte reduced glutathione concentration to 0.96 +/- 0.05 mmol/L, despite a significant (P < 0.05) increase in reduced glutathione synthesis. The combination of protein undernutrition and inflammation had a marked effect on mucosal reduced glutathione concentration (37 +/- 3% of control) and synthesis (65 +/- 5% of control). Hepatic reduced glutathione concentration and synthesis did not differ in the two groups. We conclude that the biosynthetic supply of reduced glutathione is sufficient to withstand an inflammatory challenge in well-nourished piglets but not in protein-deficient animals.

Aromatic amino acid metabolism of neonatal piglets receiving TPN: effect of tyrosine precursors.

Low tyrosine solubility in total parenteral nutrition (TPN) solutions complicates meeting the aromatic amino acid needs of infants. This study compared the effectiveness of two tyrosine precursors to supply the aromatic amino acid needs of TPN-fed neonatal piglets with a control group in which total aromatic acid needs were met by the addition of phenylalanine (Phe). Eighteen 3-day-old male Yorkshire piglets (6/group) received TPN for 8 days by central line. The solution was supplemented with Phe or one of the following two tyrosine precursors: N-acetyltyrosine (N-AcTyr) or glycyltyrosine (GlyTyr). Aromatic amino acid metabolism, growth, and nitrogen utilization were measured. Average amino acid and energy intakes were 14.6 g.kg-1.day-1 and 1,050 kJ.kg-1.day-1. Nitrogen balance and utilization were significantly higher (P < 0.05) in piglets in the control Phe group and on the GlyTyr regimen. The high urinary excretion of N-AcTyr (65%) confirms its low bioavailability. Flux and oxidation were significantly higher (P < 0.05) in the Phe group. High plasma Phe levels and excretion of Phe catabolites, as well as the high plasma tyrosine in the GlyTyr group, indicate that current strategies employed to meet the aromatic amino acid needs of neonates on TPN need further refinement.

Amino acid profile and aromatic amino acid concentration in total parenteral nutrition: effect on growth, protein metabolism and aromatic amino acid metabolism in the neonatal piglet.

1. The protein and amino acid utilization of two commercially available amino acid solutions, one egg-patterned (Vamin), the other human-milk-patterned (Vaminolact), were studied in piglets receiving total parenteral nutrition. It was hypothesized that Vaminolact was deficient in total aromatic amino acids, so a third group received a human-milk-patterned amino acid solution with added phenylalanine. 2. The piglets were on total parenteral nutrition for 8 days from day 2 or 3 of life. They all received a total energy intake of 1040 kJ day-1 kg-1 with macronutrient intakes of 14.6 g of amino acid, 27.4 g of glucose and 9.4 g of fat day-1 kg-1. 3. Nitrogen balances were performed on days 3-8 of total parenteral nutrition. On day 8 a primed constant infusion of (1-14C]-phenylalanine was given to measure phenylalanine flux and fractional conversion to tyrosine. Transamination catabolites of phenylalanine and tyrosine were measured in urine on day 7. 4. The piglets receiving Vaminolact gained significantly less weight (0.86 kg compared with 1.18 kg for Vamin and 1.20 kg for phenylalanine-supplemented Vaminolact; P < 0.02) and nitrogen (1435 mg day-1 kg-1 compared with 1601 mg and 1836 mg day-1 kg-1 for the other groups; P < 0.0001). 5. The piglets receiving Vamin had high plasma phenylalanine levels (2234 mumol/l compared with 156 mumol/l for Vaminolact and 399 mumol for phenylalanine-supplemented vaminolact; P < 0.0001). Those receiving Vamin also had an elevated excretion of phenylalanine transamination metabolites and low plasma lysine levels. Phenylalanine flux was highest in the Vamin group, intermediate in the phenylalanine-supplemented Vaminolact group and lowest in the Vaminolact group. 6. We conclude that Vaminolact is limiting in aromatic amino acids and that the addition of phenylalanine to the level in Vamin significantly improves growth and nitrogen retention; however, increasing the phenylalanine content of total parenteral nutrition is not the most metabolically suitable way to provide aromatic amino acids in neonatal total parenteral nutrition.

Development and validation of a total parenteral nutrition model in the neonatal piglet.

A model was developed for total parenteral nutrition (TPN) in neonatal piglets, with ingredients typical of those in clinical use. Our goal was to characterize the model and to compare growth and body composition of TPN-fed piglets with a reference sow-fed group. Forty piglets (1 to 3 d of age) received TPN (1040 kJ.-1.d-1, 14.6 g.kg-1.d-1 of amino acids, with nonprotein energy supplied equally by glucose and fat) for 8 d. Weight gain, linear growth, serum biochemistry, hematology and body composition were compared with the reference group of 20 sow-raised piglets. Piglets receiving TPN gained 63 +/- 12 g.kg-1.d-1, less than the mean (79 +/- 21 g.kg-1.d-1, P < 0.01), but within the range (49-118 g.kg-1.d-1), of sow-raised piglets. The TPN-fed piglets used the amino acids in TPN effectively, retaining 80% of infused nitrogen. At postmortem, dry-matter analysis of the bodies yielded similar findings in both groups. Wet-tissue protein concentration was lower in TPN-fed animals (12.5 +/- 0.8 vs 13.8 +/- 1.8 g.100 g body wt) because TPN-fed piglets were more hydrated. Ash concentration was lower in TPN-fed piglets, reflecting limitations in calcium and phosphorous supply.