Plasma and Urinary Amino Acid-Derived Catabolites as Potential Biomarkers of Protein and Amino Acid Deficiency in Rats.

OBJECTIVE: Dietary intakes must cover protein and essential amino acid (EAA) requirements. For this purpose, different methods have been developed such as the nitrogen balance method, factorial method, or AA tracer studies. However, these methods are either invasive or imprecise, and the Food and Agriculture Organization of the United Nations (FAO, 2013) recommends new methods and, in particular, metabolomics. The aim of this study is to determine total protein/EAA requirement in the plasma and urine of growing rats. METHODS: 36 weanling rats were fed with diets containing 3, 5, 8, 12, 15, and 20% protein for 3 weeks. During experimentation, urine was collected using metabolic cages, and blood from the portal vein and vena was taken at the end of the experiment. Metabolomics analyses were performed using LC-MS, and the data were analyzed with a multivariate analysis model, partial least Squares (PLS) regression, and independent component-discriminant analysis (ICDA). Each discriminant metabolite identified by PLS or ICDA was tested by one-way ANOVA to evaluate the effect of diet. RESULTS: PLS and ICDA allowed us to identify discriminating metabolites between different diet groups. Protein deficiency led to an increase in the AA catabolism enzyme systems inducing the production of breakdown metabolites in the plasma and urine. CONCLUSION: These results indicate that metabolites are specific for the state of EAA deficiency and sufficiency. Some types of biomarkers such as AA degradation metabolites appear to be specific candidates for protein/EAA requirement.

Pediatric reference intervals for plasma and urine essential amino acids in a Turkish population.

AIM: To establish age- and sex-specific reference intervals for essential amino acids in a healthy Turkish pediatric population. MATERIALS AND METHODS: A total of 945 clinically healthy children (531 boys and 414 girls, ranging in age from birth to 14 years) were enrolled. Plasma and urine amino acids' concentrations were measured by high-performance liquid chromatography. RESULTS: Concentrations of essential amino acids in plasma were higher in girls than in boys in the age groups of 0-1 months and 7-14 years; however, there was no difference in the other age groups. Concentrations of essential amino acids in urine were higher in girls than in boys in the age group of 0-1 months; however, there was no difference in the other age groups. Our results demonstrated the sex-related differences in concentrations ofleucine, isoleucine, valine, phenylalanine, lysine, and histidine in plasma, which increased with age in boys but not in girls. The concentrations of leucine, tryptophan, methionine, and lysine in urine declined with age in girls but not in boys, which were sex-related differences, too. CONCLUSION: We defined essential amino acids' reference intervals in a Turkish pediatric population.

Altered amino acid excretion in children with autism.

Autism is a complex and life-long behavioural disorder of unknown aetiology. Recent reports have indicated the involvement of digestive tract dysfunction and possible complications from inadequate nutrition. In this study, 34 autistic children (12 untreated and 22 receiving therapeutic treatments related to digestive function and nutritional uptake) and 29 control subjects (all 5-15 years of age) were investigated to determine whether there were any anomalies in the urinary excretion of amino acids, glucose, sucrose, arabinose and tartaric acid using GC/FID and GC/MS analysis techniques. Significantly lower relative urinary levels of essential amino acids were revealed for both the untreated (mean +/- SEM, 32.53 +/- 3.09%) and treated (31.98 +/- 2.87%) autistic children compared with the controls (37.87 +/- 1.50%). There were no significant differences in measured excretions of sugars or tartaric acid. It was concluded that the untreated autistic children had evidence of altered metabolic homeostasis.

Higher urinary excretion of essential amino acids in preterm infants fed protein hydrolysates.

AIM: Protein hydrolysates have been introduced in preterm formulae, but it is not clear whether they are needed for the feeding of preterm infants. We designed a randomized, controlled trial to test the effects of a preterm formula with hydrolysed cow's milk proteins on short-term growth and urinary and plasma amino acids levels. METHODS: Infants with a birthweight < or = 1750 g and gestational age < or = 34 wk fed a conventional preterm infant formula (formula B) or a hydrolysed formula (formula A). Weight was measured daily; length, head circumference, mid-arm circumference and total skinfold thickness were measured weekly. Blood and urine were analysed for amino acid concentrations at start, 14 and 28 d. RESULTS: Twenty-one infants met the criteria for randomization. The daily feeding volumes were: formula A 172.8 +/- 5.6 vs formula B 170.1 +/- 2.8 ml/kg/d. Infants fed with formula A showed slower weight gain (17.4 +/- 3.4 vs 20.5 +/- 3.3 g/kg/d; p = 0.045) and lower mean change in Z-scores for weight (-0.18 +/- 0.16 vs 0.00 +/- 0.09; p = 0.009) and for head circumference (-0.06 +/- 0.13 vs 0.06 +/- 0.13; p = 0.049). After 14 d, infants receiving formula A had statistically significant higher urinary levels of essential amino acids compared to infants receiving formula B. CONCLUSION: Our results support the hypothesis of less nutritional value of hydrolysed versus conventional preterm formulae. Higher renal excretion of essential amino acids may be one of the mechanisms involved. These findings must be confirmed by further studies with larger sample sizes and protein hydrolysates with different degrees of hydrolysis.

The relationship between the urinary level of some amino acids and the occurrence of metabolic diseases associated with psychic disorders.

Assays of the branched chain amino acids, of those with basic character, of phenylalanine and glutamic acid were performed in the 24 hrs urines of 50 patients with psychic disorders, ranging in age from 0 to 20 years, and in 30 normal controls. Similar investigations were carried out in the patients' parents. Abnormal levels of urinary amino acids in some of the adults suggested the existence of mutant genes in one or both parents of one or two descendents with mental handicap. The levels of urinary amino acids correlated with the severity of the predominant psychic manifestations, which were more severe in the cases with a wide deviation from normal of aminoaciduria.

Evaluation of parenteral nutrition in the postoperative patient.

A variety of investigators have attempted to improve nitrogen balance during the postoperative period by modifying the composition of the infused nutrient solutions. This study compared the metabolic effects of administering standard amino acid solutions with a solution enriched with branched chain amino acids (BCAA). A prospective, randomized clinical study was performed in patients who had undergone subtotal gastrectomy or hemicolectomy, and subsequently cared for in the metabolic care unit. The patients were selected from specific entry criteria so that two groups of individuals were comparable. All patients underwent operation without complications. The plasma concentrations of valine and leucine were significantly increased (p less than 0.05 and p less than 0.01, respectively) two days after administration of solutions enriched with BCAA and throughout the entire postoperative period. The plasma glutamine concentrations tended to decrease in both groups; no concentration difference occurred between groups. Nitrogen balance tended to be more positive in the group receiving BCAA but there was no significant difference between groups after operation. Urinary excretion of 3-methylhistidine tended to increase postoperatively in both groups, but no difference occurred between groups. However, the urine excretion of isoleucine increased significantly in the patients receiving infusions enriched with BCAA. Both standard balanced amino acid and amino solutions enriched with BCAA were well tolerated in all patients.

Anticatabolic properties of branched chain amino acids in trauma.

The anticatabolic properties of branched chain amino acids enriched protein solutions in 22 patients with multiple trauma have been evaluated. Nitrogen balance, nitrogen output, the daily change of blood urea nitrogen, plasma albumin and total protein levels were recorded daily. Each 2 days free amino acids and 3-methyl histidine urinary concentrations were measured. The results obtained in the study suggest that in trauma patients high ratios of essential amino acids/total nitrogen are needed and that amino acid solutions enriched in branched chain amino acids are most effective in preventing muscle catabolism and promoting protein synthesis.

[Clinical study on the concentration of free amino acids in plasma and urine during postaggression metabolism. I]. / Klinische Untersuchungen über die Konzentration freier Aminosäuren im Plasma und Urin im Postaggressionsstoffwechsel. I. Mitteilung.

We studied the changes in the concentration pattern of free plasma amino acids in 30 surgical patients during standardized parenteral nutrition and exclusive water and electrolyte supply. Distinct reproducible differences were found in comparison to normal subjects. The concentration of branched-chain amino acids continuously increases during the post-operative period. The decrease of alanine is closely related. Phenylalanine also increases continuously due to insufficient transformation in the liver and increased release from the muscles. During post-aggression metabolism, cystine is probably not sufficiently formed from methionine and should be substituted. It may be that tyrosine is also essential for patients in the post-operative post-traumatic period. The glycine concentration of some amino acid mixtures is regarded as too high; the glycine content can be reduced in favour of serine supply.

Urinary excretion of amino acids in patients receiving intravenous hyperalimentation.

Urinary outputs of amino acids in nine patients receiving intravenous hyperalimentation were estimated for evaluating adequacy of dosage and composition of the infusage for the maintenance of normal metabolism of tissue proteins in the subjects. The daily outputs of the methylated amino acids (3-methylhistidine, epsilon-N-methylated lysines and guanidino-N-methylated arginines), which are thought to be derived from tissue proteins, remained in the normal ranges, suggesting that the normal metabolism of tissue proteins was sustained during intravenous hyperalimentation. Relatively large urinary excretion of threonine, serine and glycine might reflect the large dosage of glucose in the infusate and disuse of these amino acids during the treatment, especially in the patients with hepatic dysfunction. Diurnal rhythms in urinary outputs of amino acids in patients receiving intravenous hyperalimentation were not observed, except for the outputs of threonine, serine and glycine, which were large during the 3.00-9.00 h and 15.00-21.00 h periods. The absence of daily fluctuations of the methylated amino acids in urine suggested that there were no diurnal rhythms in the metabolism of tissue proteins in the subjects.