The relationship between plasma homocysteine and amino acid concentrations in patients with end-stage renal disease

Dynamic cellular changes in acute kidney injury caused by different ischemia time

Ischemia reperfusion injury (IRI), often related to surgical procedures, is one of the important causes of acute kidney injury (AKI). To decipher the dynamic process of AKI caused by IRI (with prolonged ischemia phase), we performed single-cell RNA sequencing (scRNA-seq) of clinically relevant IRI murine model with different ischemic intervals. We discovered that Slc5a2^hi proximal tubular cells were susceptible to AKI and highly expressed neutral amino acid transporter gene Slc6a19, which was dramatically decreased over the time course. With the usage of mass spectrometry-based metabolomic analysis, we detected that the level of neutral amino acid isoleucine dropped off in AKI mouse plasma metabolites. And the reduction of plasma isoleucine was also verified in patients with cardiac surgery-associated acute kidney injury (CSA-AKI). The findings advanced the understanding of dynamic process of AKI and introduced reduction of isoleucine as a potential biomarker for CSA-AKI.

Serum amino acid profile in chronic sinusitis

Objective: Serum amino acid profile is known to vary in many diseases. The changes in the serum amino acid profile provide important information about diagnosis and prognosis of related diseases and the effectiveness of treatment. The aim of this study is to investigate whether serum amino acids are effective in the development of CRS. Methods: A total of 23 healthy volunteers between the ages of 20 and 40 years were allocated to the control group (Group 1) and 27 patients with chronic rhinosinusitis were allocated to the study group (Group 2). The patients whose history, symptom, and examination findings were consistent with chronic sinusitis and who also who had sinusitis findings on a paranasal sinus tomography and were diagnosed with chronic sinusitis for at least one year were included in Group 2. A total of 32 serum-free amino acid levels were measured in both group using the LC-MS/MS system. Results: The serum taurine level was found to be statistically significantly lower in Group 2 compared to Group 1 (p:0.002). A significant alteration was not observed in the serum levels of remaining 31 amino acids. Conclusion: According to the data we obtained from the study, decreased serum taurine level may be a factor in the etiopathogenesis of chronic rhinosinusitis and therefore taurine supplementation may be considered as a new therapeutic target in the treatment of chronic rhinosinusitis.

The serum amino acid profile in COVID-19

The pandemic of the coronavirus disease (COVID-19) caused by SARS-CoV-2 affects millions of people worldwide. There are still many unknown aspects to this infection which affects the whole world. In addition, the potential impacts caused by this infection are still unclear. Amino acid metabolism, in particular, contains significant clues in terms of the development and prevention of many diseases. Therefore, this study aimed to compare amino acid profile of COVID-19 and healthy subject. In this study, the amino acid profiles of patients with asymptomatic, mild, moderate, and severe/critical SARS-CoV-2 infection were scanned with LC–MS/MS. The amino acid profile encompassing 30 amino acids in 142 people including 30 control and 112 COVID-19 patients was examined. 20 amino acids showed significant differences when compared to the control group in COVID-19 patient groups with different levels of severity in the statistical analyses conducted. It was detected that the branched-chain amino acids (BCAAs) changed in correlation with one another, and l-2-aminobutyric acid and l-phenylalanine had biomarker potential for COVID-19. Moreover, it was concluded that l-2-aminobutyric acid could provide prognostic information about the course of the disease. We believe that a new viewpoint will develop regarding the diagnosis, treatment, and prognosis as a result of the evaluation of the serum amino acid profiles of COVID-19 patients. Determining l-phenylalanine and l-2-aminobutyric levels can be used in laboratories as a COVID-19-biomarker. Also, supplementing COVID patients with taurine and BCAAs can be beneficial for treatment protocols.

Serum metabolite signatures of epithelial ovarian cancer based on targeted metabolomics

BACKGROUND

Epithelial ovarian cancer (EOC) is a common gynecological cancer with high mortality rates. The main objective of this study was to investigate the serum amino acid and organic acid profiles to distinguish key metabolites for screening EOC patients.

METHODS

In total, 39 patients with EOC and 31 healthy controls were selected as the training set. Serum amino acid and organic acid profiles were determined using the targeted metabolomics approach. Metabolite profiles were processed via multivariate analysis to identify potential metabolites and construct a metabolic network. Finally, a test dataset derived from 29 patients and 28 healthy controls was constructed to validate the potential metabolites.

RESULTS

Distinct amino acid and organic acid profiles were obtained between EOC and healthy control groups. Methionine, glutamine, asparagine, glutamic acid and glycolic acid were identified as potential metabolites to distinguish EOC from control samples. The areas under the curve for methionine, glutamine, asparagine, glutamic acid and glycolic acid were 0.775, 0 778, 0.955, 0.874 and 0.897, respectively, in the validation study. Metabolic network analysis of the training set indicated key roles of alanine, aspartate and glutamate metabolism as well as D-glutamine and D-glutamate metabolism in the pathogenesis of EOC.

CONCLUSIONS

Amino acid and organic acid profiles may serve as potential screening tools for EOC. Data from this study provide useful information to bridge gaps in the understanding of the amino acid and organic acid alterations associated with epithelial ovarian cancer.

A multicentre clinical validation of AminoIndex Cancer Screening (AICS)

AminoIndex Cancer Screening (AICS) is a novel cancer screening test based on plasma free amino acid (PFAA) levels. This system categorises subjects as rank A, B, or C in order of increasing probability of each cancer incidence. The current study aimed to validate the potential of AICS for cancer detection. AICS values were determined from the PFAA levels in subjects examined at Chiba Cancer Center Cohort, Mitsui Memorial Hospital, and Saihaku Hospital, and the cancer incidence was investigated. The sensitivities of rank C for cancer diagnosis within 1 year after AICS examination were 83.3% (10/12) for gastric, 50.0% (2/4) for lung, 46.2% (6/13) for colorectal, 50.0% (8/16) for prostate, 43.8% (7/16) for breast, and 50.0% (1/2) for uterine/ovarian cancer. The total cancer detection rate via AICS was 0.33% (34/10,245). The sensitivities during the maximum follow-up period of 6.2 years were 51.7% (15/29) for gastric, 18.2% (2/11) for lung, 28.6% (8/28) for colorectal, 36.4% (8/22) for prostate, 29.0% (9/31) for breast, and 33.3% (2/6) for uterine/ovarian cancers. In conclusion, AICS is a more useful method for evaluating the probability of cancer incidence than for predicting onset, suggesting that annual AICS should be recommended to detect any malignancy.

Plasma-Free Amino Acid Profiling of Nasal Polyposis Patients

AIM AND OBJECTIVE

To determine the mechanisms present in the etiopathogenesis of nasal polyposis. It is not clear whether amino acids contribute in a causal way to the development of the disease. Therefore, the aim of this study was to determine the plasma-free amino acid profile in patients with nasal polyposis and to compare the results with a healthy control group.

MATERIALS AND METHODS

This was a prospective controlled study that took place in the Otolaryngology Department at the Harran University Faculty of Medicine between April 2017 and April 2018. Plasmafree amino acid profile levels were studied in serum samples taken from a patient group and a healthy control group. Patients who were diagnosed with bilateral diffuse nasal polyposis and were scheduled for surgical interventions were included in this study. Individuals whose age, gender, and body mass index values were compatible with that of the patient group and who did not have any health problems were included in the control group. All the participants whose levels of plasma-free amino acid were thought to be affected by one or more of the following factors were excluded from the study: smoking and alcohol use, allergic rhinitis presence, the presence of acute or chronic sinusitis, a history of endoscopic sinus surgery, unilateral nasal masses, a history of chronic drug use, systemic or topical steroid use in the last three months for any reason, and liver, kidney, hematological, cardiovascular, metabolic, neurological, or psychiatric disorders or malignancies.

RESULTS

In patients with nasal polyposis, 3-methyl histidine (3-MHIS: nasal polyposis group (ng) = 3.22 (1.92 - 6.07); control group (cg) = 1.21 (0.77 - 1.68); p = 0.001); arginine (arg: ng = 98.95 (70.81 - 117.75); cg = 75.10 (54.49 - 79.88); p = 0.005); asparagine (asn: ng = 79.84 (57.50 - 101.44); cg = 60.66 (46.39 - 74.62); p = 0.021); citrulline (cit: ng = 51.83 (43.81 - 59.78); cg = 38.33 (27.81 - 53.73); p = 0.038); cystine (cys: ng = 4.29 (2.43 - 6.66); cg = 2.41 (1.51 - 4.16); p = 0.019); glutamic acid (glu: ng = 234.86 (128.75 - 286.66); cg = 152.37 (122.51 - 188.34); p = 0.045); histidine (his: ng = 94.19 (79.34 - 113.99); cg = 74.80 (62.76 - 98.91); p = 0.018); lysine (lys: ng = 297.22 (206.55 - 371.25); cg = 179.50 (151.58 - 238.02); p = 0.001); ornithine (ng = 160.62 (128.36 - 189.32); cg = 115.91 (97.03 - 159.91); p = 0.019); serine (ser: ng = 195.15 (151.58 - 253.07); cg = 83.07 (67.44 - 92.44); p = 0.001); taurine (tau: ng = 74.69 (47.00 - 112.13); cg = 53.14 (33.57 - 67.31); p = 0.006); tryptophan (trp: ng = 52.31 (33.81 - 80.11); cg = 34.44 (25.94 - 43.07); p = 0.005), homocitrulline (ng = 1.75 (1.27 - 2.59); cg = 0.00 (0.00 - 0.53); p = 0.001); norvaline (ng = 6.90 (5.61 - 9.18); cg = 4.93 (3.74 - 7.13); p = 0.021); argininosuccinic acid (ng = 14.33 (10.06 - 25.65); cg = 12.22 (5.77 - 16.87) p = 0.046); and plasma concentrations were significantly higher than in the healthy control group (p <0.05). However, the gamma-aminobutyric acid (gaba: ng = 0.16 (0.10 - 0.24); cg = 0.21 (0.19 - 0.29); p = 0.010) plasma concentration was significantly lower in the nasal polyposis group than in the healthy control group.

CONCLUSION

In this study, plasma levels of 15 free amino acids were significantly higher in the nasal polyposis group than in the healthy control group. A plasma level of 1 free amino acid was found to be significantly lower in the nasal polyposis group compared to the healthy control group. Therefore, it is important to determine the possibility of using the information obtained to prevent the recurrence of the condition and to develop effective treatment strategies. This study may be a milestone for studies of this subject. However, this study needs to be confirmed by further studies conducted in a larger series.

Vascular endothelium dysfunction: a conservative target in metabolic disorders

AIM

Vascular endothelium plays a role in capillary transport of nutrients and drugs and regulates angiogenesis, homeostasis, as well as vascular tone and permeability as a major regulator of local vascular homeostasis. The present study has been designed to investigate the role of endothelium in metabolic disorders.

METHODS

The endothelium maintains the balance between vasodilatation and vasoconstriction, procoagulant and anticoagulant, prothrombotic and antithrombotic mechanisms.

RESULTS

Diabetes mellitus causes the activation of aldose reductase, polyol pathway and advanced glycation-end-product formation that collectively affect the phosphorylation status and expression of endothelial nitric oxide synthatase (eNOS) and causes vascular endothelium dysfunction. Elevated homocysteine levels have been associated with increase in LDL oxidation, generation of hydrogen peroxides, superoxide anions that increased oxidative degradation of nitric oxide. Hyperhomocysteinemia has been reported to increase the endogenous competitive inhibitors of eNOS viz L-N-monomethyl arginine (L-NMMA) and asymmetric dimethyl arginine (ADMA) that may contribute to vascular endothelial dysfunction. Hypercholesterolemia stimulates oxidation of LDL cholesterol, release of endothelins, and generation of ROS. The increased cholesterol and triglyceride level and decreased protective HDL level, decreases the activity and expression of eNOS and disrupts the integrity of vascular endothelium, due to oxidative stress. Hypertension also stimulates release of endothelins, vasoconstrictor prostanoids, angiotensin II, inflammatory cytokines, xanthine oxidase and, thereby, reduces bioavailability of nitric oxide.

CONCLUSION

Thus, the cellular and molecular mechanisms underlying diabetes mellitus, hyperhomocysteinemia, hypercholesterolemia hypertension and hyperuricemia leads to an imbalance of phosphorylation and dephosphorylation status of lipid and protein kinase that cause modulation of vascular endothelial L-arginine/nitric oxide synthetase (eNOS), to produce vascular endothelium dysfunction.

Plasma amino acid profiles in healthy East Asian subpopulations living in Japan

OBJECTIVES

Profiles of plasma free amino acids (PFAAs) have been utilized as biomarkers to detect various diseases. However, few studies have investigated whether ethnicity or specific subpopulations within East Asia influence PFAA concentrations.

METHODS

A total of 95 healthy volunteers living in Japan, including 31 Japanese individuals, 36 Korean individuals and 28 Chinese individuals, were enrolled. Participants' PFAA levels were measured by high-performance liquid chromatography mass spectrometry, and the effects of factors such as sex, age, body mass index (BMI) and subpopulation on PFAA profiles were analyzed.

RESULTS

With the exception of glutamine and α-aminobutyric acid, there were no significant differences among the three examined subpopulations with respect to either the means or the distributions of PFAA concentrations. A multiple regression analysis revealed that most of the PFAA concentrations were significantly related to sex. Ornithine concentrations, glutamate concentrations, and glutamine and α-aminobutyric acid concentrations were significantly associated with age, BMI, and Chinese subpopulation, respectively.

CONCLUSION

The study results indicate that the contributions of subpopulation within East Asia to PFAA profiles are small, particularly relative to the contributions provided by sex.

A Novel Multivariate Index for Pancreatic Cancer Detection Based On the Plasma Free Amino Acid Profile

Background

The incidence of pancreatic cancer (PC) continues to increase in the world, while most patients are diagnosed with advanced stages and survive <12 months. This poor prognosis is attributable to difficulty of early detection. Here we developed and evaluated a multivariate index composed of plasma free amino acids (PFAAs) for early detection of PC.

Methods

We conducted a cross-sectional study in multi-institutions in Japan. Fasting plasma samples from PC patients (n = 360), chronic pancreatitis (CP) patients (n = 28), and healthy control (HC) subjects (n = 8372) without apparent cancers who were undergoing comprehensive medical examinations were collected. Concentrations of 19 PFAAs were measured by liquid chromatography–mass spectrometry. We generated an index consisting of the following six PFAAs: serine, asparagine, isoleucine, alanine, histidine, and tryptophan as variables for discrimination in a training set (120 PC and matching 600 HC) and evaluation in a validation set (240 PC, 28 CP, and 7772 HC).

Results

Several amino acid concentrations in plasma were significantly altered in PC. Plasma tryptophan and histidine concentrations in PC were particularly low, while serine was particularly higher than that of HC. The area under curve (AUC) based on receiver operating characteristic (ROC) curve analysis of the resulting index to discriminate PC from HC were 0.89 [95% confidence interval (CI), 0.86–0.93] in the training set. In the validation set, AUCs based on ROC curve analysis of the PFAA index were 0.86 (95% CI, 0.84–0.89) for all PC patients versus HC subjects, 0.81 (95% CI, 0.75–0.86) for PC patients from stage IIA to IIB versus HC subjects, and 0.87 (95% CI, 0.80–0.93) for all PC patients versus CP patients.

Conclusions

These findings suggest that the PFAA profile of PC was significantly different from that of HC. The PFAA index is a promising biomarker for screening and diagnosis of PC.

Plasma amino acid profiles at various reproductive stages in female rats

We measured the plasma levels of amino acids at various reproductive stages in female rats, including the estrous cycle, pregnancy and lactation, and compared the resulting amino acid profiles using two- or three-dimensional figures. These figures revealed that the amino acid profiles of pregnant and lactating dams differed considerably from those during the estrous cycle or in male rats. The plasma levels of individual amino acids were almost the same between proestrus, estrus, metestrus and diestrus, and their profiles did not differ significantly. However, the amino acid profiles changed during pregnancy and lactation in dams. The plasma Ser level decreased significantly in mid and late pregnancy, whereas Tyr, Gly and His decreased significantly in the late and end stages of pregnancy, and Trp and Lys significantly decreased and increased at the end of pregnancy, respectively. Much larger changes in amino acid profiles were observed during lactation, when the levels of many amino acids increased significantly, and none showed a significant decrease. Plasma Pro, Ser and Gly levels increased continuously from day 1 until day 15 of lactation, whereas Asn and Met increased significantly from days 1 and 5 respectively until the end of lactation. These results suggest that the profiles of plasma amino acids show characteristic changes according to reproductive stage and that it may be necessary to consider such differences when performing amino acid-based diagnosis.

Plasma amino acid profiling of cancer patients with abnormal savda based on high-performance liquid chromatography

OBJECTIVE

To investigate metabolic signatures in plasma of cancer patients with abnormal Savda using plasma-free amino acid profiles, and to evaluate the diagnostic potential of these profiles for the detection and explanation of the mechanisms of different symptoms in traditional Uyghur medicine.

METHODS

Plasma samples from cancer patients with abnormal Savda (n = 85) or non-abnormal Savda (n = 105) and a healthy control group (n = 65) were analyzed using high-performance liquid chromatography (HPLC). Orthogonal projection to latent structures with discriminant analysis was used for the classification and prediction of abnormal Savda, and spectral profiles were subjected to Student's t-tests to assess statistical significance.

RESULTS

Compared with the healthy group, the levels of aspartic acid, glutamate, glycine, histidine, arginine, threonine, alanine, proline, methionine, isoleucine, leucine and phenylalanine decreased significantly in plasma of cancer patients with abnormal Savda (all P < 0.05). Serine, cystine, tyrosine, valine and lysine levels showed no significant differences (all P > 0.05). Compared with non-abnormal Savda syndrome patients, abnormal Savda syndrome patients showed high concentrations of glutamate, serine, valine, isoleucine, leucine and phenylalanine (all P < 0.05). The remaining plasma amino acids showed no significant differences (all P > 0.05).

CONCLUSION

Plasma-free amino acid profiling has the potential to assist in understanding and determining abnormal Savda. A HPLC-based metabonomic platform could be a powerful tool for the classification of symptoms in traditional medicine.

A new approach for quantitative analysis of L-phenylalanine using a novel semi-sandwich immunometric assay

Here, we describe a novel method for L-phenylalanine analysis using a sandwich-type immunometric assay approach for use as a new method for amino acid analysis. To overcome difficulties of the preparation of high-affinity and selectivity monoclonal antibodies against L-phenylalanine and the inability to use sandwich-type immunometric assays due to their small molecular weight, three procedures were examined. First, amino groups of L-phenylalanine were modified by "N-Fmoc-L-cysteine" (FC) residues and the derivative (FC-Phe) was used as a hapten. Immunization of mice with bovine serum albumin/FC-Phe conjugate successfully yielded specific monoclonal anti-FC-Phe antibodies. Second, a new derivatization reagent, "biotin linker conjugate of FC-Phe N-succinimidyl ester" (FC(Biotin)-NHS), was synthesized to convert L-phenylalanine to FC-(Biotin)-Phe as a hapten structure. The biotin moiety linked to the thiol group of cysteine formed a second binding site for streptavidin/horseradish peroxidase (HRP) conjugates for optical detection. Third, a new semi-sandwich-type immunometric assay was established using pre-derivatized L-phenylalanine, the monoclonal anti-FC-Phe antibody, and streptavidin/HRP conjugate (without second antibody). Using the new "semi-sandwich" immunometric assay system, a detection limit of 35 nM (60 amol per analysis) and a detection range of 0.1-20 μM were attained using a standard L-phenylalanine solution. Rat plasma samples were analyzed to test reliability. Intra-day assay precision was within 6% of the coefficient of variation; inter-day variation was 0.1%. The recovery rates were from 92.4 to 123.7%. This is the first report of the quantitative determination of L-phenylalanine using a reliable semi-sandwich immunometric assay approach and will be applicable to the quantitative determination of other amino acids.

Plasma free amino acid profiling of five types of cancer patients and its application for early detection

Background

Recently, rapid advances have been made in metabolomics-based, easy-to-use early cancer detection methods using blood samples. Among metabolites, profiling of plasma free amino acids (PFAAs) is a promising approach because PFAAs link all organ systems and have important roles in metabolism. Furthermore, PFAA profiles are known to be influenced by specific diseases, including cancers. Therefore, the purpose of the present study was to determine the characteristics of the PFAA profiles in cancer patients and the possibility of using this information for early detection.

Methods and Findings

Plasma samples were collected from approximately 200 patients from multiple institutes, each diagnosed with one of the following five types of cancer: lung, gastric, colorectal, breast, or prostate cancer. Patients were compared to gender- and age- matched controls also used in this study. The PFAA levels were measured using high-performance liquid chromatography (HPLC)–electrospray ionization (ESI)–mass spectrometry (MS). Univariate analysis revealed significant differences in the PFAA profiles between the controls and the patients with any of the five types of cancer listed above, even those with asymptomatic early-stage disease. Furthermore, multivariate analysis clearly discriminated the cancer patients from the controls in terms of the area under the receiver-operator characteristics curve (AUC of ROC >0.75 for each cancer), regardless of cancer stage. Because this study was designed as case-control study, further investigations, including model construction and validation using cohorts with larger sample sizes, are necessary to determine the usefulness of PFAA profiling.

Conclusions

These findings suggest that PFAA profiling has great potential for improving cancer screening and diagnosis and understanding disease pathogenesis. PFAA profiles can also be used to determine various disease diagnoses from a single blood sample, which involves a relatively simple plasma assay and imposes a lower physical burden on subjects when compared to existing screening methods.

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.

Characteristic metabolism of free amino acids in cetacean plasma: cluster analysis and comparison with mice

From an evolutionary perspective, the ancestors of cetaceans first lived in terrestrial environments prior to adapting to aquatic environments. Whereas anatomical and morphological adaptations to aquatic environments have been well studied, few studies have focused on physiological changes. We focused on plasma amino acid concentrations (aminograms) since they show distinct patterns under various physiological conditions. Plasma and urine aminograms were obtained from bottlenose dolphins, pacific white-sided dolphins, Risso's dolphins, false-killer whales and C57BL/6J and ICR mice. Hierarchical cluster analyses were employed to uncover a multitude of amino acid relationships among different species, which can help us understand the complex interrelations comprising metabolic adaptations. The cetacean aminograms formed a cluster that was markedly distinguishable from the mouse cluster, indicating that cetaceans and terrestrial mammals have quite different metabolic machinery for amino acids. Levels of carnosine and 3-methylhistidine, both of which are antioxidants, were substantially higher in cetaceans. Urea was markedly elevated in cetaceans, whereas the level of urea cycle-related amino acids was lower. Because diving mammals must cope with high rates of reactive oxygen species generation due to alterations in apnea/reoxygenation and ischemia-reperfusion processes, high concentrations of antioxidative amino acids are advantageous. Moreover, shifting the set point of urea cycle may be an adaption used for body water conservation in the hyperosmotic sea water environment, because urea functions as a major blood osmolyte. Furthermore, since dolphins are kept in many aquariums for observation, the evaluation of these aminograms may provide useful diagnostic indices for the assessment of cetacean health in artificial environments in the future.

Determining important regulatory relations of amino acids from dynamic network analysis of plasma amino acids

The changes in the concentrations of plasma amino acids do not always follow the flow-based metabolic pathway network. We have previously shown that there is a control-based network structure among plasma amino acids besides the metabolic pathway map. Based on this network structure, in this study, we performed dynamic analysis using time-course data of the plasma samples of rats fed single essential amino acid deficient diet. Using S-system model (conceptual mathematical model represented by power-law formalism), we inferred the dynamic network structure which reproduces the actual time-courses within the error allowance of 13.17%. By performing sensitivity analysis, three of the most dominant relations in this network were selected; the control paths from leucine to valine, from methionine to threonine, and from leucine to isoleucine. This result is in good agreement with the biological knowledge regarding branched-chain amino acids, and suggests the biological importance of the effect from methionine to threonine.

Plasma amino acid analysis for diagnosis and amino acid-based metabolic networks

PURPOSE OF REVIEW

To highlight the usefulness of amino acid profiling in clinical diagnosis and current developments in analysis revealing underlying metabolic relationships.

RECENT FINDINGS

Recent innovations in metabolomics and systems biology enable high throughput measurement of diverse amino acids and the subsequent data mining for various uses. Recent studies show new possibilities of using plasma amino acid analysis as biomarker discovery tools by generating diagnostic indices through systematic computation. Such studies show that amino acid-based clinical diagnostic indices for hepatic fibrosis in type C hepatitis patients can be generated. In addition, several studies show the potential of treating amino acid profile data as a metabolomic subset, which can be integrated through the analysis of correlation with different types of 'omics' data for describing metabolite-to-metabolite or metabolite-to-gene interaction networks.

CONCLUSION

Amino acid profiling of biological samples could be used to generate indices that could be used for clinical diagnosis and is a useful tool for understanding metabolic implications under various physiological conditions. Although further improvements in analytical methods are needed, amino acids could be useful indicators for facilitating nutritional management of specific physiological and pathological states.

Multi-layered network structure of amino acid (AA) metabolism characterized by each essential AA-deficient condition

The concentrations of free amino acids in plasma change coordinately and their profiles show distinctive features in various physiological conditions; however, their behavior can not always be explained by the conventional flow-based metabolic pathway network. In this study, we have revealed the interrelatedness of the plasma amino acids and inferred their network structure with threshold-test analysis and multilevel-digraph analysis methods using the plasma samples of rats which are fed diet deficient in single essential amino acid.

In the inferred network, we could draw some interesting interrelations between plasma amino acids as follows: 1) Lysine is located at the top control level and has effects on almost all of the other plasma amino acids. 2) Threonine plays a role in a hub in the network, which has direct links to the most number of other amino acids. 3) Threonine and methionine are interrelated to each other and form a loop structure.

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.

A tale of two homocysteines--and two hemodialysis units

Pharmacologic doses of folic acid are commonly used to reduce the hyperhomocysteinemia of end-stage renal disease (ESRD). Vitamin B12 acts at the same metabolic locus as folic acid, but information is lacking about the specific effects of high doses of this vitamin on homocysteine levels in renal failure. We therefore compared the plasma homocysteine concentrations of maintenance hemodialysis patients in two McGill University-affiliated urban tertiary-care medical centers that differed in the use of vitamin B12 and folic acid therapy. Patients in the first hemodialysis unit are routinely prescribed high-dose folic acid (HI-F, 6 mg/d), whereas those in the second unit receive high-dose vitamin B12 in the form of a monthly 1-mg intravenous injection, along with conventional oral folic acid (HI-B12, 1 mg/d). Predialysis homocysteine was 23.4 +/- 6.8 micromol/L (mean +/- SD) in the HI-F unit and 18.2 +/- 6.1 micromol/L in the HI-B12 unit (P < .002). Postdialysis homocysteine was 14.5 +/- 4.1 in the HI-F unit and 10.6 +/- 3.4 micromol/L in the HI-B12 unit (P = .0001). Multiple regression analysis indicated that high-dose parenteral vitamin B12 was associated with a lower homocysteine concentration even after controlling for the potential confounders of sex, serum urea, serum creatinine, urea reduction ratio, and plasma cysteine. Because this was a cross-sectional observational study, we cannot exclude the possibility that unidentified factors, rather than the different vitamin therapies, account for the different homocysteine levels in the two units. Careful prospective studies of the homocysteine-lowering effect of high-dose parenteral vitamin B12 in ESRD should be undertaken.

Influence of 5,10-methylenetetrahydrofolate reductase gene polymorphism on plasma homocysteine concentration in patients with end-stage renal disease

The purpose of this study is to observe the influence of the methylenetetrahydrofolate reductase (MTHFR) gene (677C-->T substitution) on plasma homocysteine levels in end-stage renal disease (ESRD) patients who received a relatively large amount of folate (2 mg/d) and are undergoing hemodialysis. A cross-sectional study of plasma homocysteine, vitamin B(12), and folate was performed in patients with ESRD. The study population for the MTHFR gene study included 312 healthy subjects and 106 patients with ESRD undergoing hemodialysis. The C677T transition in the MTHFR gene was detected by HinF 1 restriction enzyme analysis and subsequent electrophoresis in a 3% agarose gel. The genotype of the MTHFR gene in 106 patients with ESRD was homozygous C677T mutation (VV) in 17 patients (16.1%) and heterozygous (AV) in 63 patients (58.4%); 26 patients (24.5%) did not carry this mutation (AA). The mean levels of homocysteine, vitamin B(12), and folate in the patients with ESRD were 23.3 +/- 14.0 mmol/L, 620.2 +/- 98.5 pmol/L, and 138.6 +/- 55.6 nmol/L, respectively. There was no significant difference in homocysteine levels among the three genotypes: 28.2 +/- 19.4 mmol/L for VV, 22.7 +/- 14.9 mmol/L for AV, and 23.4 +/- 11.1 mmol/L for AA genotype (P > 0.05). There was no difference in genotype distribution between the patient groups of less than 25th and greater than 75th percentiles, classified according to plasma homocysteine levels (P = 0.47). In conclusion, with high-dose folate supplementation, the hyperhomocysteinemia in patients with ESRD does not seem to be caused by the 677C-->T mutation in the MTHFR gene.

Effects of high-dose folic acid and pyridoxine on plasma and erythrocyte sulfur amino acids in hemodialysis patients

In this investigation, sulfur amino acids (sAA) and sulfhydryls were determined in the plasma and erythrocytes (RBC) of 10 uremic patients on regular hemodialysis (HD) treatment and 10 healthy subjects, before and after supplementation with 15 mg/d of folic acid and 200 mg/d of pyridoxine for 4 wk. The basal total plasma concentrations of homocysteine (Hcy), cysteine (Cys), cysteinylglycine (Cys-Gly), gamma-glutamylcysteine (gamma-Glu-Cys), glutathione (GSH), and free cysteinesulfinic acid (CSA) were significantly higher in HD patients when compared to healthy subjects, whereas methionine (Met) and taurine (Tau) concentrations were the same in the two groups. HD patients showed significantly higher RBC levels of Hcy and Cys-Gly, whereas the RBC concentrations of Met, Cys, Tau, and GSH were not different from those in the healthy subjects. The plasma concentrations of sAA and sulfhydryls differed compared with RBC levels in the healthy subjects and HD patients. In both groups, supplementation with high doses of folic acid and pyridoxine reduced the plasma Hcy concentration. In addition, increased plasma concentrations of Cys-Gly and GSH were found in the HD patients and of CSA in the healthy subjects. After vitamin supplementation, the RBC concentrations of Hcy, Cys, and GSH increased and that of Tau decreased in healthy subjects. The only significant finding in RBC of HD patients was an increase in GSH levels after supplementation. This study shows several RBC and plasma sAA and sulfhydryl abnormalities in HD patients, which confirms earlier findings that RBC and plasma pools play independent roles in interorgan amino acid transport and metabolism. Moreover, high-dose supplementation with folic acid and pyridoxine significantly reduced Hcy levels, but did not restore the sAA and sulfhydryl abnormalities to normal levels. The increase that was observed in GSH after vitamin supplementation may have a beneficial effect in improving blood antioxidant status in uremic patients. Finally, the findings of elevated plasma Cys levels correlating to the elevated plasma Hcy levels in the presence of elevated plasma CSA levels, both before and after vitamin supplementation, led to the hypothesis that a block in decarboxylation of CSA is linked to hyperhomocysteinemia in end-stage renal failure.