Quantitative methods for amino acid analysis in biological fluids

Heat shock interferes with the amino acid metabolism of bovine cumulus-oocyte complexes in vitro: a multistep analysis

By affecting the ovarian pool of follicles and their enclosed oocytes, heat stress has an impact on dairy cow fertility. This study aimed to determine how heat shock (HS) during in vitro maturation affected the ability of the bovine cumulus-oocyte complexes (COCs) to develop, as well as their metabolism of amino acids (AAs). In this study, COCs were in vitro matured for 23 h at 38.5 °C (control; n = 322), 39.5 °C (mild HS (MHS); n = 290), or 40.5 °C (severe HS (SHS); n = 245). In comparison to the control group, the MHS and SHS groups significantly decreased the percentage of metaphase-II oocytes, as well as cumulus cell expansion and viability. The SHS decreased the rates of cleavage and blastocyst formation in comparison to the control and MHS. Compared to the control and MHS-COCs, the SHS-COCs produced significantly more phenylalanine, threonine, valine, arginine, alanine, glutamic acid, and citrulline while depleting less leucine, glutamine, and serine. Data showed that SHS-COCs had the highest appearance and turnover of all AAs and essential AAs. Heat shock was positively correlated with the appearance of glutamic acid, glutamine, isoleucine, alanine, serine, valine, phenylalanine, and asparagine. Network analysis identified the relationship between HS and alanine or glutamic acid, as well as the relationship between blastocyst and cleavage rates and ornithine. The findings imply that SHS may have an impact on the quality and metabolism of AAs in COCs. Moreover, the use of a multistep analysis could simply identify the AAs most closely linked to HS and the developmental competence of bovine COCs.

Engineering microbial cells with metal chelating hydroxylated unnatural amino acids for removable of synthetic pollutants from water

Lead (Pb²⁺) is a well-known heavy metal and toxic synthetic industrial pollutant in the ecosystem and causes severe threats to living organisms. It is paramount to develop a sustainable microbial engineering approach to remove synthetic pollutants from the environment. Genetic code engineering is emerging as an important microbial engineering tool in biosciences to biosynthesis congener protein production beyond the canonical set of natural molecules and expand the chemistries of living cells. Here, we prepare cells expressing unnatural amino acid encoded congener proteins for effectively removable toxic synthetic industrial pollutants (Pb²⁺) with high binding efficiency. Native and the developed congener proteins expressing cells adapted the Langmuir and Sips adsorption model that recommends uniform adsorption with Pb²⁺ ions. This could be due to a more significant number of functional groups on the protein surface. Fluorescence spectroscopic, field emission scanning electron microscope, X-ray photoelectron spectroscopic analysis, and protein-metal molecular stimulation coordination allowed us to explore the role of hydroxylation on Pb²⁺ adsorption. The bioreactor filled with immobilized protein-containing active granules showed >90% of lead removal in the contaminated water samples. The desorption of bound Pb2+ from GFP and its variants were studied by varying the pH to reuse the proteins for subsequent usage. We observed that about 70% of the GFP and its variants could be recycled and >75% of fluorescence efficiency could be recovered. Among all the variants, GFPHPDP exhibits high affinity and maintains the reusability efficiency in 7 consecutive cycles. These results suggest that genetic code engineering of cells encoding unnatural amino acids could be a next-generation microbial engineering tool for manipulating and developing the microbial strain's selective and effective removal of synthetic pollutants from the environment.

Nutritional Composition of Bombyx mori Pupae: A Systematic Review

Simple Summary

The mulberry silkworm (Bombyx mori) is a domesticated insect traditionally reared to produce silk. Its pupae are historically eaten in Asian countries and are obtained as waste products from the silk reeling industry. Pupae are a promising novel food in Western countries as well as a source of proteins, lipids, and minerals. Several varied results are reported in the literature regarding the nutrient composition of silkworm pupa, and several factors must be considered when comparing the research. Some of the variables that could affect the pupal nutritional content include rearing techniques, diets, silkworm strains, killing, and drying techniques. This literature systematic review identifies the most important research areas and aids authorities and producers in the evaluation and development of silkworm pupae for novel uses.

Abstract

As insects have started to enter the eating habits of Western countries, an increasing amount of literature regarding the mulberry silkworm (Bombyx mori) prospective application as food has been published. Despite this growing interest, there is currently no systematic review of silkworm nutritional composition available. In this paper, we performed a systematic review of the recent available literature on the nutrient composition of mulberry silkworm pupae. After screening the titles and abstracts of 14,008 studies retrieved from three scientific databases, data about nutrients was extracted from 29 selected papers, together with their related variables. This systematic review provides an overview of the variety of data reported in the literature and highlights that many elements contribute to hindering a sound comparison of the different nutritional values reported for silkworm pupae. The observed variability of the composition data reported could be due to differences in diet, strains, pretreatments, and origin of the silkworm analyzed. However, all these variables were not always available and should be reported in future studies to simplify the data comparison.

Development of a robust 30-minute reverse-phase high pressure liquid chromatography method to measure amino acids using widely available equipment and its comparison to current clinical ion-exchange chromatography measurement

We have developed a fast and accurate method that uses a small volume of sample to determine over 25 of the typically reported amino acids in human plasma. Samples were prepped with a single step using a spin filter to remove proteins, avoiding the decreased sensitivity from dilution in acid precipitation. Using a reverse phase (RP) High Performance Liquid Chromatography (HPLC) system with O-phthaldehyde (OPA) as the pre-column derivatization reagent, and UV detection at 338 nm, we did a direct comparison with the most common ion exchange/ninhydrin method used in clinical labs on the same plasma samples with 95% concurrence, analysis of amino acid standard solutions returned 99% concurrence. With a sample preparation time of 30 min, utilizing less than 25 μl of sample and with a chromatography run of 30 min, this method can substantially increase access to analysis in both clinical and research laboratories using instruments that are more widely available.

Synopsis

We describe a rapid and easily deployed method for sensitive amino measurement in biological samples.

Determination of Free Amino Acids in Bee Pollen by Liquid Chromatography with Fluorescence Detection

Bee pollen is one of the hive products that is of most interest today due to its multiple beneficial health properties, making it an increasingly popular food supplement. Bee pollen contains many bioactive compounds, such as fatty acids, vitamins, minerals, proteins, and amino acids, among others. In the present study, the free amino acid content was determined in bee pollen by using liquid chromatography coupled to a fluorescence detector. Sample treatment consisted of a solvent extraction of the free amino acids with ultrapure water and a further centrifugation of the extract, which was repeated twice. After that, it was necessary to perform a pre-column derivatization of the amino acids using a combination of two reagents (o-phthalaldehyde and 9-fluorenylmethyl chloroformate) prior to their separation in a Gemini® C18 reverse phase column in gradient elution mode. The analytical performance was evaluated, and several commercial bee pollen samples were analyzed. Significant differences in the free amino acid profile and concentration, which ranged between 19 and 192 mg/g, were observed depending on the botanical origin of the samples.

Valine feeding reduces ammonia production through rearrangement of metabolic fluxes in central carbon metabolism of CHO cells

Ammonia is a toxic byproduct of CHO cell metabolism, which inhibits cell growth, reduces cell viability, alters glycosylation, and decreases recombinant protein productivity. In an attempt to minimize the ammonium accumulation in cell culture media, different amino acids were added individually to the culture medium before the production phase to alleviate the negative effects of ammonium on cell culture performance. Among all the amino acids examined in this study, valine showed the most positive impact on CHO cell culture performance. When the cultured CHO cells were fed with 5 mM valine, EPO titer was increased by 25% compared to the control medium, and ammonium and lactate production were decreased by 23 and 26%, respectively, relative to the control culture. Moreover, the sialic acid content of the EPO protein in valine-fed culture was higher than in the control culture, most likely because of the lower ammonium concentration. Flux balance analysis (FBA) results demonstrated that the citric acid cycle was enriched by valine feeding. The measurement of TCA cycle activity supported this finding. The analysis revealed that there might be a link between promoting tricarboxylic acid (TCA) cycle metabolism in valine-fed culture and reduction in lactate and ammonia accumulation. Furthermore, in valine-fed culture, FBA outcomes showed that alanine was excreted into the medium as the primary mechanism for reducing ammonium concentration. It was predicted that the elevated TCA cycle metabolism was concurrent with an increment in recombinant protein production. Taken together, our data demonstrate that valine addition could be an effective strategy for mitigating the negative impacts of ammonium and enhancing glycoprotein production in both quality and quantity. KEY POINTS: • Valine feeding can mitigate the negative impacts of ammonia on CHO cell growth. • Valine addition assists the ammonia removal mechanism by enriching the TCA cycle. • Ammonia is removed from the media through alanine excretion in valine-fed culture.

Quantification of bovine plasma amino acids via liquid chromatography–electrospray ionization-mass spectrometry: Comparison of underivatized and precolumn derivatized methods

•

We validated and compared 2 methods for quantification of AA in bovine plasma.

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Our underivatized method may be a practical alternative for essential AA.

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The derivatized method has greater ¹²C area signal sensitivity, linearity, and accuracy.

The objectives of this experiment were to evaluate and compare underivatized (UND) and precolumn derivatized (DER) methods for quantification of bovine plasma AA by isotope dilution ratio via liquid chromatography-electrospray ionization (ESI)-single quadrupole mass spectrometry. Linearity of the mass-to-charge ratio signal and area signal sensitivity of ¹²C were evaluated for each AA with 5-point standard curves (range: 1.1–500 µM). Plasma from lactating dairy cows was isolated by centrifugation and deproteinized using 1 N perchloric acid with a final concentration of 0.5 N. Deproteinized plasma was filtered and injected into a 50 × 2-mm column (Imtakt) or extracted, derivatized, and injected into a 250 × 3-mm column (EZ:faast, Phenomenex) and analyzed via liquid chromatography-ESI-single quadrupole mass spectrometry. Coefficients of variation and recovery rates were evaluated using 4 replicates of pooled plasma samples spiked with each AA at concentrations of 10, 20, and 50 µM. In addition, a subset of 24 plasma samples was used to directly compare methods using linear regression, correlation coefficient (r), concordance correlation coefficient (CCC), and Bland-Altman plot test. Both methods showed linearity within the dynamic range analyzed for all essential AA (coefficient of determination, R² ≥ 0.995) and most other AA, although the UND samples had poor linearity (R² ≤ 0.990) or peak resolution problems for Asp, Gly, Tyr, and Ser. Moreover, area signal sensitivity for ¹²C AA was greater for DER samples than for UND samples [range: 2.2× (Pro) to 309.5× (Ala)]. Both methods had recovery rates ranging from 85.7 to 119.8.0%, and none differed from 100% except Gln [20 µM (85.7%) and 50 µM (87.6%)] and Val [50 µM (119.8%)] using the UND method. The UND method had a coefficient of variation ranging from 0.9% (Val) to 7.8% (His), whereas for the DER method the range was 2.2% (Glu) to 8.8% (Asp). The highest correlation coefficient (>0.90) and CCC (>0.90) were observed for Arg, Ile, Leu, Met, Thr, Trp, Val, and Gln, with the Bland-Altman plot test showing minimal mean bias for these AA. Lowest values were observed for His (r = 0.46; CCC = 0.45), Lys (r = 0.76; CCC = 0.75), Ala (r = 0.83; CCC = 0.73), and Glu (r = 0.65; CCC = 0.42). The UND method showed linearity, precision, and accurate recovery rates for most AA, with most essential AA having comparable values between the 2 methods. However, the DER method had greater ¹²C AA area signal sensitivity, linearity, and recovery rates.

Diminished Systemic Amino Acids Metabolome and Lipid Peroxidation in Ureteropelvic Junction Obstruction (UPJO) Infants Requiring Surgery

Congenital anomalies of the urinary tract, and particularly of obstructive nephropathy such as ureteropelvic junction obstruction (UPJO) in infants, can later lead to chronic kidney disease and hypertension. Fundamental questions regarding underlying mechanisms remain unanswered. The aim of the present study was to quantitate the systemic amino acids metabolome in 21 UPJO infants requiring surgery (Group A) and 21 UPJO infants under conservative treatment (Group B). Nineteen healthy age-matched infants served as controls (Group C). Serum amino acids involved in several pathways and representative metabolites, including the L-arginine-derived nitric oxide (NO) metabolites nitrite and nitrate and the lipid peroxidation biomarker malondialdehyde (MDA) were measured by gas chromatography–mass spectrometry (GC–MS) methods using their stable-isotope labeled analogs as internal standards after derivatization to their methyl esters N-pentafluoropropionic amides (amino acids) and to their pentafluorobenzyl derivatives (nitrite, nitrate, MDA). The concentrations of the majority of the biomarkers were found to be lower in Group A compared to Group B. Statistical analysis revealed clear differentiation between the examined study groups. Univariate statistical analysis highlighted serum homoarginine (q = 0.006), asymmetric dimethylarginine (q = 0.05) and malondialdehyde (q = 0.022) as potential biomarkers for UPJO infants requiring surgery. Group A also differed from Group B with respect to the diameter of the preoperative anterior–posterior renal pelvis (AP) as well as regarding the number and extent of inverse correlations between AP and the serum concentrations of the biomarkers. In Group A, but not in Group B, the AP diameter strongly correlated with hydroxy-proline (r = −0.746, p = 0.0002) and MDA (r = −0.754, p = 0.002). Our results indicate a diminished amino acids metabolome in the serum of UPJO infants requiring surgery comparing to a conservative group.

Challenging the status quo: A comparison of ion exchange chromatography with liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry methods for the measurement of amino acids in human plasma

BACKGROUND

Plasma amino acid analysis is key to the diagnosis and monitoring of inherited disorders of amino acid synthesis, catabolism and transport. Ion exchange chromatography (IEC) is widely accepted as the gold standard method of analysis, but with the introduction of liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography mass spectrometry (LC-MS) methods, this should now be questioned.

METHODS

The analytical performance of three commercially available reagent kits, Waters AccQ Tag™ ULTRA LC-MS, SpOtOn Amino Acids LC-MS/MS and Chromsystems MassChrom® Amino Acid Analysis LC-MS/MS, were evaluated and compared with Biochrom Physiological Amino Acids ion exchange chromatography. Correlation with IEC was assessed by Passing-Bablok regression, concordance correlation coefficients (CCC) and Bland-Altman analysis for 21 common amino acids. Calculation of the total error from imprecision and bias was also used to benchmark performance.

RESULTS

The MassChrom® and SpOtOn kits demonstrated acceptable inter-batch imprecision (CV < 10%) and accuracy (mean bias < 10%), whereas the AccQ Tag™ ULTRA kit did not. Good correlation (CCC > 0.95) with Biochrom IEC was demonstrated for 10/21 analytes in both the MassChrom® and SpOtOn kits and 6/21 in the AccQ Tag™ ULTRA kit.

CONCLUSIONS

The LC-MS assay demonstrated variable analytical performance and correlated poorly with ion exchange chromatography. Both LC-MS/MS assays demonstrated comparable analytical performance and reasonable correlation with ion exchange chromatography. They also confer practical advantages which cannot be realized by ion exchange chromatography, superior specificity and significantly faster analysis time, suggesting that ion exchange chromatography should no longer be described as the gold standard method for plasma amino acid analysis.

Cyanobacteria-Derived Proline Increases Stress Tolerance in Arabidopsis thaliana Root Hairs by Suppressing Programmed Cell Death

Nitrogen-fixing heterocystous cyanobacteria are used as biofertilizer inoculants for stimulating plant growth but can also alleviate plant stress by exometabolite secretion. However, only a small number of studies have focused on elucidating the identity of said bioactives because of the wide array of exuded compounds. Here, we used the root hair assay (RHA) as a rapid programmed cell death (PCD) screening tool for characterizing the bioactivity of cyanobacteria Nostoc muscorum conditioned medium (CM) on Arabidopsis thaliana root hair stress tolerance. We found that heat-stressed A. thaliana pre-treated with N. muscorum CM fractions exhibited significantly lower root hair PCD levels compared to untreated seedlings. Treatment with CM increased stress tolerance by suppressing PCD in root hairs but not necrosis, indicating the bioactive compound was specifically modulating the PCD pathway and not a general stress response. Based on documented N. muscorum exometabolites, we identified the stress-responsive proline as a compound of interest and strong evidence from the ninhydrin assay and HPLC indicate that proline is present in N. muscorum CM. To establish whether proline was capable of suppressing PCD, we conducted proline supplementation experiments. Our results showed that exogenous proline had a similar effect on root hairs as N. muscorum CM treatment, with comparable PCD suppression levels and insignificant necrosis changes. To verify proline as one of the biologically active compounds in N. muscorum CM, we used three mutant A. thaliana lines with proline transporter mutations (lht1, aap1 and atprot1-1::atprot2-3::atprot3-2). Compared with the wild-type seedlings, PCD-suppression in lht1and aap1 mutants was significantly reduced when supplied with low proline (1-5 μM) levels. Similarly, pre-treatment with N. muscorum CM resulted in elevated PCD levels in all three mutant lines compared to wild-type seedlings. Our results show that plant uptake of cyanobacteria-derived proline alters their root hair PCD sensitivity threshold. This offers evidence of a novel biofertilizer mechanism for reducing stress-induced PCD levels, independent of the existing mechanisms documented in the literature.

Development and validation of chemical kindling in adult zebrafish: A simple and improved chronic model for screening of antiepileptic agents

BACKGROUND

Zebrafish has emerged as a potential animal model of acute convulsion for early screening of antiepileptic agents. There is a need for alternative chronic zebrafish models of epilepsy with more correlation to the clinical condition.

NEW METHOD

Adult zebrafish were repeatedly exposed to subeffective concentrations of pentylenetetrazole (PTZ), until appearance to tonic-clonic seizures, considered as kindled. Valproic acid (VPA) exposure was given during kindling and in kindled fish in 2 different groups. The neurotransmitters level and expression of the genes associated with kindling were studied in the fish brain.

RESULTS

There was an increase in seizure severity score at 1.25 mM concentration of PTZ, and 66.66 % of fish achieved kindling after 22 days' exposure. A marked increase in c-fos, crebbpa and crebbpbexpression, and glutamate/GABA level was observed in the brain of kindled fish. VPA inhibited the induction of PTZ-mediated kindling and reduced seizure severity in kindled fish.

COMPARISON WITH EXISTING METHOD

In contrast to an existing adult zebrafish kindling method, the present protocol is of longer duration, with more similarity to clinical epilepsy. Moreover, the induction of kindling involves a simple non-invasive technique without the use of anesthesia. The protocol can be used for evaluation of both antiepileptic and antiepileptogenic agents.

CONCLUSION

Repeated exposure of 1.25 mM PTZ induced kindling in zebrafish, altering the brain neurotransmitter levels and gene expression. Inhibition of kindling induction and decrease in seizures in normal and kindled fish, respectively by VPA validated application of the model for preclinical testing of agents against epilepsy.

A multilevel analysis identifies the different relationships between amino acids and the competence of oocytes matured individually or in groups

High-protein diets contribute to an increase in urea follicular concentrations associated with decreased fertility. Urea has been shown to interfere with the epidermal growth factor (EGF)/EGFR system, which has been shown to have a beneficial effect during in vitro maturation (IVM) of oocytes. Of note, the number of cumulus-oocyte complexes (COCs) in the maturation medium can change the maturation and the developmental competence of COCs. Therefore, it was hypothesized that, the presence of urea and EGF may have a differential effect on the depletion/appearance of AAs and competence of COCs matured individually (I-IVM system) or in groups (G-IVM system). In the G-IVM system, COCs increased consumption (depletion) of AAs compared with other groups in the presence of high-level urea (40 mg/dl) + EGF (10 ng/ml). In the I-IVM system, the non-cleaved COCs depleted more AAs than the cleaved COCs, in particular in the presence of urea. The combination of urea and EGF increased the depletion of AAs in the G-IVM system. However, the EGF abrogated the urea-induced depletion of AAs by the I-IVM COCs. The use of N-acetyl-L-cysteine as an EGFR inhibitor canceled urea-induced depletion of AAs. This shows the inhibiting effect of urea over the EGF/EGFR system. In the presence of urea + EGF, COCs had a lower degree of developmental competence than control in both I- and G-IVM systems. Arginine had the best predictive power to identify highly competent COCs in the G-IVM system, while glutamine was the best predictor of the cleavage in the I-IVM system. In conclusion, this multi-level study shows that COCs matured individually or in groups may have different association with AAs metabolism. These findings provide new insights into the relationships between AA metabolism and the subsequent developmental competence of COCs.

A global Slc7a7 knockout mouse model demonstrates characteristic phenotypes of human lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an inborn error of cationic amino acid (arginine, lysine, ornithine) transport caused by biallelic pathogenic variants in SLC7A7, which encodes the light subunit of the y+LAT1 transporter. Treatments for the complications of LPI, including growth failure, renal disease, pulmonary alveolar proteinosis, autoimmune disorders and osteoporosis, are limited. Given the early lethality of the only published global Slc7a7 knockout mouse model, a viable animal model to investigate global SLC7A7 deficiency is needed. Hence, we generated two mouse models with global Slc7a7 deficiency (Slc7a7em1Lbu/em1Lbu; Slc7a7Lbu/Lbu and Slc7a7em1(IMPC)Bay/em1(IMPC)Bay; Slc7a7Bay/Bay) using CRISPR/Cas9 technology by introducing a deletion of exons 3 and 4. Perinatal lethality was observed in Slc7a7Lbu/Lbu and Slc7a7Bay/Bay mice on the C57BL/6 and C57BL/6NJ inbred genetic backgrounds, respectively. We noted improved survival of Slc7a7Lbu/Lbu mice on the 129 Sv/Ev × C57BL/6 F2 background, but postnatal growth failure occurred. Consistent with human LPI, these Slc7a7Lbu/Lbu mice exhibited reduced plasma and increased urinary concentrations of the cationic amino acids. Histopathological assessment revealed loss of brush border and lipid vacuolation in the renal cortex of Slc7a7Lbu/Lbu mice, which combined with aminoaciduria suggests proximal tubular dysfunction. Micro-computed tomography of L4 vertebrae and skeletal radiographs showed delayed skeletal development and suggested decreased mineralization in Slc7a7Lbu/Lbu mice, respectively. In addition to delayed skeletal development and delayed development in the kidneys, the lungs and liver were observed based on histopathological assessment. Overall, our Slc7a7Lbu/Lbu mouse model on the F2 mixed background recapitulates multiple human LPI phenotypes and may be useful for future studies of LPI pathology.

Why Not Glycine Electrochemical Biosensors?

Glycine monitoring is gaining importance as a biomarker in clinical analysis due to its involvement in multiple physiological functions, which results in glycine being one of the most analyzed biomolecules for diagnostics. This growing demand requires faster and more reliable, while affordable, analytical methods that can replace the current gold standard for glycine detection, which is based on sample extraction with subsequent use of liquid chromatography or fluorometric kits for its quantification in centralized laboratories. This work discusses electrochemical sensors and biosensors as an alternative option, focusing on their potential application for glycine determination in blood, urine, and cerebrospinal fluid, the three most widely used matrices for glycine analysis with clinical meaning. For electrochemical sensors, voltammetry/amperometry is the preferred readout (10 of the 13 papers collected in this review) and metal-based redox mediator modification is the predominant approach for electrode fabrication (11 of the 13 papers). However, none of the reported electrochemical sensors fulfill the requirements for direct analysis of biological fluids, most of them lacking appropriate selectivity, linear range of response, and/or capability of measuring at physiological conditions. Enhanced selectivity has been recently reported using biosensors (with an enzyme element in the electrode design), although this is still a very incipient approach. Currently, despite the benefits of electrochemistry, only optical biosensors have been successfully reported for glycine detection and, from all the inspected works, it is clear that bioengineering efforts will play a key role in the embellishment of selectivity and storage stability of the sensing element in the sensor.

Measurement of homocysteine: a historical perspective

Elevated plasma level of homocysteine is being increasingly associated with many diseases. There is a significant interest in the development of methods to determine the total homocysteine in biologically relevant tissues. Over the years, researchers use various methods to determine the exact concentrations of homocysteine in these tissues. However, the precise method used in many studies earlier was questionable. We have reviewed various methodologies for the measurement of homocysteine. We list the commonly used methodologies currently in use to determine homocysteine levels. Through extensive literature search, we have come up with the most popular as well as the newest measurement modalities and listed them with a brief discussion of each of the methodology. In conclusion, we have presented the historical perspective of homocysteine measurement in biological fluids in this manuscript. Thus, the precise understanding of its concentration in biological fluids coupled with its importance in health and disease should justify a newer but reliable technique in the area of ongoing research in homocysteine.

The EZ:Faast Family of Amino Acid Analysis Kits: Application of the GC-FID Kit for Rapid Determination of Plasma Tryptophan and Other Amino Acids

Plasma tryptophan (Trp) and other amino acids (AA) can be determined rapidly by gas (GC) or liquid (LC) chromatography using the Phenomenex EZ:Faast™ family of kits. Three kits are available: (1) GC-FID or -NPD, (2) GC-MS, and (3) LC-MS. The two GC kits can determine 32 AA, whereas the LC-MS can determine 5 additional AA. All three kits, however, share the same experimental procedure up to and including the preparation of derivatized AA. The method is based on solid-phase extraction (SPE), thus saving time on prior removal of plasma or other proteins and interfering substances and can be applied to other body fluids and experimental media and to supernatants of extracts of solid material. Briefly, SPE is performed using a proprietary cation-exchange mechanism. The acid solution of the internal standard ensures that the free amino acids are in an anionic form suitable for cationic binding. The alkaline nature of the elution medium ensures that the AA cations are released prior to derivatization. The latter involves production of chloroformate derivatives of both the amino and carboxylic acid groups. With experience, six plasma samples can be so processed within 12 min. The shortest analytical run is <7 min per sample using the GC-FID/NPD kit. Despite its many steps, the procedure becomes second nature and an enjoyable task. I have now used the GC-FID kit with manual injection to process >1600 plasma and other samples. Limit of detection of AA is 1 μM or less. The procedure has been validated and optimized for Trp and its main five brain uptake competitors.

Urea influences amino acid turnover in bovine cumulus-oocyte complexes, cumulus cells and denuded oocytes, and affects in vitro fertilization outcome

High-protein diets often lead to an increase in urea concentration in follicular fluid of dairy cows, which may reduce oocyte competence. In the present study, maturation media were supplemented with urea (0, 20, 40 mg/dl), and amino acids (AAs) turnover was evaluated in the 24-h spent media of specimens (cell types), bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), or denuded oocytes (DOs). The main effects of urea and cell type, and their interaction were significant on the individual turnover (expect threonine, glycine, and tyrosine) and total turnover, depletion, and appearance of AAs. The results showed a high level of urea and DOs increased the depletion of all AAs and that of essential and non-AAs, respectively. Sensitivity analysis revealed the highest sensitivity of isoleucine, lysine, and tryptophan to urea, especially in DOs. Principal component analysis (PCA) evaluated the strong correlations between the turnover of: (1) glutamine, aspartic acid or glycine, and developmental competence and fertilization of COCs; (2) serine, isoleucine, valine or glutamic acid, and cleavage rate of DOs; and (3) serine, glutamine, aspartic acid or alanine, and CCs viability. In conclusion, urea significantly changed the turnover of AAs by COCs, CCs and DOs, and reduced the subsequent developmental competence of bovine oocytes.

Endogenous glutamine decrease is associated with pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is becoming the second leading cause of cancer-related death in the Western world. The mortality is very high, which emphasizes the need to identify biomarkers for early detection. As glutamine metabolism alteration is a feature of PDAC, its in vivo evaluation may provide a useful tool for biomarker identification. Our aim was to identify a handy method to evaluate blood glutamine consumption in mouse models of PDAC. We quantified the in vitro glutamine uptake by Mass Spectrometry (MS) in tumor cell supernatants and showed that it was higher in PDAC compared to non-PDAC tumor and pancreatic control human cells. The increased glutamine uptake was paralleled by higher activity of most glutamine pathway-related enzymes supporting nucleotide and ATP production. Free glutamine blood levels were evaluated in orthotopic and spontaneous mouse models of PDAC and other pancreatic-related disorders by High-Performance Liquid Chromatography (HPLC) and/or MS. Notably we observed a reduction of blood glutamine as much as the tumor progressed from pancreatic intraepithelial lesions to invasive PDAC, but was not related to chronic pancreatitis-associated inflammation or diabetes. In parallel the increased levels of branched-chain amino acids (BCAA) were observed. By contrast blood glutamine levels were stable in non-tumor bearing mice. These findings demonstrated that glutamine uptake is measurable both in vitro and in vivo. The higher in vitro avidity of PDAC cells corresponded to a lower blood glutamine level as soon as the tumor mass grew. The reduction in circulating glutamine represents a novel tool exploitable to implement other diagnostic or prognostic PDAC biomarkers.

Bioanalytical LC separation techniques for quantitative analysis of free amino acids in human plasma

The quantitative analysis of free amino acids in human plasma has become an important and essential analysis parameter in different areas of life sciences. Free amino acid concentrations in human plasma samples are generally determined by means of GC or LC after chemical derivatization followed by UV, fluorescent or MS detection of the amino acid derivatives. Derivatization of free amino acids is done either pre- or post-column, and the amino acid derivatives obtained posess improved chromatographic behavior, increased detection sensitivity and selectivity compared with non-derivatized free amino acids. This work gives an overview of different chemical derivatization methods applied and their liquid separation techniques in bioanalytical assays for quantitative free amino acid analysis in human plasma samples. Important plasma preparation procedures, pre- and post-column derivatization, and different LC separation techniques are presented.

HPLC method for amino acids profile in biological fluids and inborn metabolic disorders of aminoacidopathies

Quantification of total and individual amino acids in biological fluids such as plasma, urine and cerebrospinal fluid has an important diagnostic implication in laboratory medicine. The present paper describes protocols for the assay of total amino acids by modified method based on dinitrophenyl and HPLC profile involving pre-column derivatization with o-pthalaldehyde (OPA) derivatization, respectively. The method, based on the alkylation of-SH groups prior to OPA derivatization of amino acids followed by reverse phase high performance liquid chromatography, provide a comprehensive profile of more than twenty amino acids (including-SH group containing) in a single run lasting about 45 minutes. The present study, apart from establishing the normal profile of amino acids in plasma of Indian sub population, also presents HPLC profile for some of the rare amino acidopathies.

The EZ:Faast family of amino acid analysis kits: application of the GC-FID kit for rapid determination of plasma tryptophan and other amino acids

Plasma tryptophan (Trp) and other amino acids (AA) can be determined rapidly by gas (GC) or liquid (LC) chromatography using the Phenomenex EZ:Faast(™) family of kits. Three kits are available: (1) GC-FID or -NPD, (2) GC-MS, (3) LC-MS. The two GC kits can determine 32 AA, whereas the LC-MS can determine five additional AA. All three kits, however, share the same experimental procedure up to and including the preparation of derivatised AA. The method is based on solid-phase extraction (SPE), thus saving time on prior removal of plasma or other proteins and interfering substances, and can be applied to other body fluids and experimental media and to supernatants of extracts of solid material. Briefly, SPE is performed using a proprietary cation-exchange mechanism. The acid solution of the internal standard ensures that the free amino acids are in an anionic form suitable for cationic binding. The alkaline nature of the elution medium ensures that the AA cations are released prior to derivatisation. The latter involves production of chloroformate derivatives of both the amino and carboxylic acid groups. With experience, six plasma samples can be so processed within 12 min. The shortest analytical run is <7 min per sample using the GC-FID/NPD kit. Despite its many steps, the procedure becomes second nature and an enjoyable task. I have now used the GC-FID kit with manual injection to process >1,600 plasma and other samples. Limit of detection of AA is 1 μM or less. The procedure has been validated and optimised for Trp and its main five brain uptake competitors.

Amino Acid profiles in human tear fluids analyzed by high-performance liquid chromatography and electrospray ionization tandem mass spectrometry

PURPOSE

To identify the 23 amino acid profiles in human tear fluids, and to evaluate whether the ocular disease conditions reflect the amino acid profiles.

DESIGN

Laboratory investigation.

METHODS

We evaluated the concentrations and relative composition of 23 amino acids in tear fluids obtained from 31 healthy volunteers using reversed-phase high-performance liquid chromatography and electrospray ionization tandem mass spectrometry, and compared them with those in plasma and aqueous humor. We also evaluated the tear-fluid amino acid profiles from 33 affected subjects.

RESULTS

The amino acid profiles of the basal tear and reflex tear were found to be similar, and 4 distinct groups of healthy volunteers (male, female, young, and elderly) showed similar profiles. Absolute concentrations of taurine (Tau) and L-glutamine were significantly dominant in these tear fluids. The relative compositions of Tau, L-glutamic acid, L-arginine (Arg), and citrulline in the tear fluid were significantly higher than those in the plasma and aqueous humor. Analysis of the hierarchical clustering of the amino acid profiles clearly distinguished severe ocular surface diseases from non-ocular surface diseases. The relative compositions of Tau, L-methionine, and Arg decreased in severe ocular surface disease subjects compared with non-ocular surface disease subjects.

CONCLUSIONS

Tear-fluid amino acid profiles differ from those in plasma and aqueous humor. Steady-state tear-fluid amino acid profiles might reflect ocular-surface homeostasis and the observed changes of amino acids might have a close relation with the disease conditions on the ocular surface.

Plasma free tryptophan revisited: what you need to know and do before measuring it

Plasma free tryptophan (Trp) is an important peripheral parameter widely used by psychopharmacologists to assess Trp entry into the brain for cerebral serotonin synthesis, although, along with total Trp, it can give much more information on Trp metabolism and disposition. Plasma free Trp is, however, a labile parameter easily influenced by a great many modulators, including fasting, food intake, many prescribed and over the counter medications, consumption of alcoholic and of common hot beverages, illicit drug use, some hormones, exercise and mild stressors. Interpretation of changes in plasma free Trp requires appropriate preparation of ultrafiltrates from freshly isolated plasma or serum, accurate analytical methodology and awareness of the multitude of physiological and pharmacological modulators of its concentration. This article highlights these points and makes recommendations aimed at avoiding pitfalls in studies involving this parameter.

Application of the Phenomenex EZ:faasttrade mark amino acid analysis kit for rapid gas-chromatographic determination of concentrations of plasma tryptophan and its brain uptake competitors

The Phenomenex EZ:faast™ amino acid analysis kit is available for gas (GC) or liquid (LC) chromatographic analysis of amino acids (AA) using mass spectrometry (MS) and other GC detectors. We used it for rapid GC determination of plasma tryptophan, its brain uptake competitors (Val, Leu, Ile, Phe and Tyr) and many other amino acids. Based on solid-phase extraction, this fast method enables one person to process two plasma samples in 8–10 min and six samples in ∼15 min up to GC injection and a 7-min GC run per plasma sample. Using a Perkin-Elmer Clarus 500 GC, a Total Chrome software, a flame-ionisation detector (FID) and norvaline as internal standard, we used this method to analyse ∼1,000 plasma samples from normal subjects undergoing acute tryptophan depletion and loading tests. The limit of detection for most amino acids is 1 nmol/ml (1 μM) and in many cases less. With manual injection, coefficients of variation for the above six amino acids were 1.5–6.2% (intra-assay) and 3.8–9.7% (inter-assay). This simple, rapid and elegant method will be valuable to the amino acid analyst and researcher, as it can save much manpower time and meet urgent emergency requests and the demands of a high-throughput laboratory.

Plasma and Urine Amino Acid Profiles in a Healthy Adult Population of Singapore

Introduction: The analysis of amino acids in plasma and urine was introduced in Singapore when a laboratory for the investigation of inherited metabolic disorders was established by the Ministry of Health. Reference ranges are required for interpreting test results and making diagnoses. Initially, reference ranges established for Caucasians were used as there were no local data and we were unable to find data obtained by the same analytical method for Asian populations. This was not considered an ideal and long-term solution, as Singaporeans may have amino acid concentrations quite different from those of Caucasians due to genetic factors, dietary difference, environment, and other influences. This study was therefore undertaken when a number of healthy laboratory personnel volunteered to provide specimens for the study. Materials and Methods: Sixty healthy male and female laboratory workers not on any form of medication were recruited. They consisted of 24 males (range, 23 to 58 years) and 36 females (range, 20 to 60 years), with a mean age of 38.7 years. Non-fasting random blood and urine specimens were collected on ice. Removal of protein and peptides from heparinised plasma and urine was achieved by ultrafiltration through protein-exclusion membrane. Amino acid analysis on the ultrafiltrate was performed by a dedicated Beckman 6300 Amino Acid Analyzer using a cation exchange resin column and post-column colour reaction with ninhydrin reagent. Urine creatinine was measured by a Beckman LX 20 PRO Analyzer. Results for urine amino acids were expressed as µmol/mmol of creatinine. Results: Reference ranges for 32 amino acids in blood plasma and 36 amino acids in urine were calculated by a non-parametric method using the SPSS statistical calculation software. The ranges cover 95% of the population and the low and high limits of each reference range represent the 2.5th percentile and 97.5th percentile of the frequency distribution respectively. Conclusions: We observed differences in the reference ranges of several plasma and urine amino acids between Singaporean and Caucasian populations. Moreover, the list of urine amino acids for Caucasian population is incomplete. We have therefore discontinued the use of reference values established for Caucasians and adopted the results of this study for our patient diagnostic work. Key words: Blood amino acid, Normal ranges, Reference values, Urine amino acids

Network analysis of plasma and tissue amino acids and the generation of an amino index for potential diagnostic use

BACKGROUND

Few studies exist on the use of metabolic profiling of amino acids to examine underlying physiologic and disease states.

OBJECTIVE

We aimed to introduce a new method for studying relations among amino acids and to generate a diagnostic index, or amino index, based on amino acid concentrations.

DESIGN

For network analysis, 35 Fischer-344 rats were randomly divided into 7 groups and fed diets containing 5%, 10%, 15%, 20%, 30%, 50%, or 70% protein. Amino acid concentrations in plasma and various organs were used to derive correlation coefficients that were then used to construct correlation networks. To build a diagnostic index for diabetic rats, the plasma amino acid concentrations of diabetic and normal rats were analyzed by using a novel algorithm developed to generate amino acid-based indexes. Plasma amino acid concentrations from human growth hormone transgenic rats and insulin-treated diabetic rats were used to evaluate the index obtained for diabetes. Dimethylnitrosamine-treated Sprague-Dawley rats were used to generate an index for hepatic fibrosis.

RESULTS

The scatter plots of plasma amino acid concentrations showed distinct patterns in different organs that were due to the different protein contents of the diets. Network analysis showed that data-driven networks for blood and tissue could be obtained. We derived a diagnostic index for the discrimination of diabetic rats with both sensitivity and specificity >97% and another surrogate index for liver hydroxyproline with a correlation of r2= 0.85.

CONCLUSIONS

Correlation-based network analysis may help to uncover specific physiologic conditions or states. A novel approach using amino acid molar ratios was shown to generate indexes that can be used to separate animal disease models and monitor the progression of a disease parameter. Some of the methods described here may be applicable to the clinical setting.

Optimization of a free separation of 30 free amino acids and peptides by capillary zone electrophoresis with indirect absorbance detection: a potential for quantification in physiological fluids

This report describes a rapid, single-run procedure, based on the optimization of capillary electrophoresis (CE) and indirect absorbance detection capabilities, which was developed for the separation and quantification of 30 underivatized physiological amino acids and peptides, usually present in biological fluids. p-Aminosalicylic acid buffered with sodium carbonate at pH 10.2+/-0.1 was used as the running electrolyte. Electrophoresis, carried out in a capillary (87 cm x 75 microm) at 15 kV potential (normal polarity), separated the examined compounds within 30 min. Limits of detection ranged from 1.93 to 20.08 micromol/l (median 6.71 micromol/l). The method was linear within the 50-200 micromol/l concentration range (r ranged from 0.684 to 0.989, median r=0.934). Within run migration times precision was good (median C.V.=0.7%). Less favorable within run peak area precision (median C.V.=6.6%) was obtained. The analytical procedure presented was successfully tested for separation and quantification of amino acids in physiological fluids, such as plasma or supernatant of macrophage cultures. Sample preparations require only a protein precipitation and dilution step.

Regression-based reference limits for urinary amino acids in a pediatric population

Age-related variation of the urinary excretion of amino acids has been widely reported. Instead of the conventional reference intervals, continuous reference limits might be a more practical approach during periods of rapid changes such as infancy or childhood. Regression-based reference limits have been produced for the urinary excretion of 23 amino acids analyzed in 148 healthy individuals from 0 to 12 years of age. Urinary excretion was modeled as a function of age by two parametric procedures: the polynomial and the piece-wise linear regression methods. Likewise, age-specific standard deviation was estimated by the regression of the absolute values of the residuals on age. Residual analysis was employed to select the best-fitting model and the 95% reference limits, and their 95% confidence intervals were calculated and plotted against the raw data. The urinary excretion of 19 amino acids decreased rapidly during the first year of life with a further slow decline thereafter. These amino acids fit better the piecewise model. The other four amino acids displayed a steady decrease in the urinary excretion from birth to puberty, and the excretion patterns fit better the quadratic or linear model. Fifteen amino acids showed a significant change in standard deviation with age. Regression-based reference limits differed consistently from conventional limits (<3 years) and narrower confidence intervals were obtained throughout the entire period studied. Avoiding partitioning gave rise to smoothly changing limits. Therefore, such alternative way of presenting amino acid reference limits may facilitate the follow-up of patients with inborn errors of amino acid metabolism.

Separation of free amino acids in human plasma by capillary electrophoresis with laser induced fluorescence: potential for emergency diagnosis of inborn errors of metabolism

Free amino acids (AAs) in human plasma are derivatized with 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA) and analyzed by capillary electrophoresis (CE) with laser induced fluorescence (LIF) detection. The labeling procedure is significantly improved over results reported previously. Derivatization can be completed in 40 min, with concentrations as low as 4 x 10(-8) M successfully labeled in favourable cases. Twenty-nine AAs (including 2 internal standards) are identified and can be reproducibly separated in 70 min. Migration time RSD values for 23 of these AAs were calculated and found in the range from 0.5 to 4%. The rapid derivatization procedure and the resolution obtained in the separation are sufficient for a semi-quantitative, emergency diagnosis of several inborn errors of metabolism (IEM). Amino acid profiles for both normal donor plasma samples and plasma samples of patients suffering from phenylketonuria, tyrosinemia, maple syrup urinary disease, hyperornithinemia, and citrullinemia are studied.

Year-Long Validation Study and Reference Values for Urinary Amino Acids Using a Reversed-Phase HPLC Method

Background: Reversed-phase HPLC (RP-HPLC) has become an alternative to ion-exchange chromatography for amino acid analysis in biological fluids. However, validation studies for its urine application are limited, and the corresponding reference values have not been reported extensively. We studied the long-term performance of a commercial HPLC method for urine amino acid analysis and established specific age-related reference values for urine amino acid excretion.

Methods: Method performance was continuously assessed by recovery and precision studies with urine samples and controls, respectively. Healthy individuals were prospectively analyzed throughout a 5-year period. Excretion of individual amino acids, expressed as mmol/mol of creatinine, was included in six age-related groups for random urine samples (0–1 month, 1–12 months, 1–3 years, 3–8 years, 8–16 years, and &gt;16 years) and in two groups for 24-h urine collections (8–16 years and &gt;16 years).

Results: Over a 1-year period, CVs for retention times were &lt;0.5% and 3.3% for within- and between-run imprecision, respectively. For amino acid concentrations, within-run CVs were 2.9–17% and between-run CVs were 7.1–46% for the same period. Amino acid recoveries were 78–122%. Reference intervals for 35 amino acids were calculated and compared with the concentrations observed in patients diagnosed with specific pathologies. A few statistically significant differences were found between the reference intervals derived using random and 24-h urine collections.

Conclusions: Long-term reliability of the RP-HPLC method for urine amino acid analysis has been demonstrated. Representative age-related reference intervals for the RP-HPLC method in both random urine and 24-h urine collections have been established, and their feasibility for diagnosis of aminoaciduria has been shown. These intervals could serve as a guide for laboratories changing to HPLC methods.

Developments in the measurement of plasma total homocysteine

Elevated plasma homocysteine is considered to be a graded risk factor for cardiovascular disease, and for this reason there is great interest in high-performance analytical techniques. Methods have evolved from ion-exchange chromatography to embrace high-performance liquid chromatography with fluorescence or electrochemical detection, immunoassays, gas chromatography-mass spectroscopy and liquid chromatography with tandem mass spectrometry. Immunoassays and high-performance liquid chromatography methods are currently available in kit form, fluorescence polarization immunoassay showing the best performance.

Recommended approaches for the laboratory measurement of homocysteine in the diagnosis and monitoring of patients with hyperhomocysteinaemia

Several recent studies have indicated that an increased concentration of plasma homocysteine is an independent risk factor for the premature development of vascular disease. These important findings emphasize the need for careful selection of an appropriate analytical approach to diagnose and treat individuals who may be at risk. We compared the results obtained from the measurement of plasma total homocysteine (free + protein-bound fractions) by high-performance liquid chromatography (HPLC) with the measurement of plasma free homocystine (free fraction) by conventional ion-exchange chromatography in 10 patients with inherited defects of homocysteine metabolism and 13 obligate heterozygote individuals. This study can be used to formulate recommendations on the appropriate use of these assays in different clinical circumstances. Our results show that the concentration of total plasma homocysteine must exceed 60 mumol/L before plasma free homocystine becomes detectable by conventional ion-exchange chromatography. Similarly, assessment of the urinary excretion of homocysteine in these patients indicates that it may not become consistently detectable by conventional ion-exchange chromatography or HPLC until plasma total homocysteine exceeds 150 mumol/L. On this basis, while most patients with classical homocystinuria would be detected by analysis of plasma using conventional ion-exchange chromatography or by measurement of of the urinary homocysteine excretion, occasional patients would be missed. When monitoring patients receiving treatment for classical homocystinuria, in whom metabolic control is good, and when investigating individuals with a suspected inherited defect of cobalamin or folate metabolism, a method which measures plasma total homocysteine should be used. The identification of moderate hyperhomocysteinaemia of undefined cause investigated in relation to a history of early vacsular disease can only be identified by this approach.

Measurement of phenylalanine and tyrosine in plasma by high-performance liquid chromatography using the inherent fluorescence of aromatic amino acids

An isocratic high-performance liquid chromatography (HPLC) method is described using the natural fluorescence of phenylalanine and tyrosine compared with that of an internal standard N-methyl phenylalanine. Plasma precipitated with 6% perchloric acid was separated isocratically using a base-deactivated C18 column with 5% acetonitrile in water as the mobile phase. Fluorescent measurements at an excitation wavelength of 215 nm and emission 283 nm showed only three peaks for tyrosine, phenylalanine and the internal standard eluting within 9 min. Inter-batch coefficients of variation for phenylalanine were 2.9% and 1.8% at levels of 70 and 567 mumol/L, respectively, and 2.9% at a level of 63 mumol/L for tyrosine. The results for phenylalanine for this method showed a small mean positive bias (11 mumol/L) when compared with the target all-method means for UK National External Quality Assessment Scheme samples (n = 31). The results for tyrosine showed a small positive mean bias (10 mumol/L) when compared with an ion-exchange chromatographic method (n = 40). This method provides a quick and simple alternative to those using HPLC with pre- or post-column derivatization for monitoring patients with phenylketonuria. It is also less subject to interferences than HPLC methods using ultraviolet detection, particularly for the early eluting tyrosine peak.

A simple bacterial bioassay for the measurement of L-glutamine

The amino acid L-glutamine has been shown to be important to numerous cells in the body. However, the routine measurement of glutamine in biological solutions is complicated by its relative instability, particularly at extremes of pH. We report a simple bacterial bioassay method for the estimation of glutamine, carried out at neutral pH, using an Escherichia coli that is specifically dependent on the presence of glutamine for replication. The assay is simple to perform and we have shown it to be highly reproducible. Furthermore, we observed significant correlation between the estimations of glutamine by the bioassay system and current methodologies. The levels of glutamine recorded were higher than by other methods. We also found that deproteinization and neutralization of samples allowed them to be stored at -70 degrees C for up to 24 weeks without deterioration.

Age-specific distribution of plasma amino acid concentrations in a healthy pediatric population

Reference values were determined for 23 plasma free amino acids from measurements done in 148 healthy children ranging from 0 to 18 years of age. Amino acid analysis was performed by ion-exchange chromatography. We propose a graphic form of presenting the age-specific distribution of plasma amino acid concentrations where the 10th, 50th, and 90th quantiles are illustrated. Although each amino acid possesses its own pattern of distribution, we can identify five different profiles. Nine amino acids (alanine, arginine, asparagine, methionine, ornithine, phenylalanine, proline, threonine, and tyrosine) demonstrate a decrease in their concentrations during the first year of life; their concentrations then tend to increase throughout childhood and adolescence. Nine others (cystine, glutamine, glycine, histidine, isoleucine, leucine, lysine, tryptophan, and valine) show a steady increase throughout infancy, childhood, and adolescence. Five amino acids (aspartic acid, citrulline, glutamic acid, serine, and taurine) do not follow these two common profiles. For the first time, quantile curves are produced to illustrate the age-dependent variation of amino acid concentrations from infancy to adulthood. This alternative way of presenting amino acid concentrations may facilitate the follow-up of patients with inborn errors of amino acid metabolism.

Decision support techniques for the interpretation of quantitative amino acid data

Quantitative amino acid profiles are traditionally reported as a list of individual concentrations and reference intervals. By the use of selected examples it is shown that alternative methods of presenting and assessing these results can enhance both the quantity and quality of information. A candidate decision support tool is offered as an aid to the interpretation of amino acid profiles.