Multifunctional and highly sensitive precolumn reagents for amino acids in liquid chromatography/tandem mass spectrometry

Mass Spectrometry Imaging of Coniine and Other Hemlock Alkaloids after On-Tissue Derivatization Reveals Distinct Alkaloid Distributions in the Plant

Specialized metabolites play important roles in plants and can, for example, protect plants from predators or pathogens. Alkaloids, due to their pronounced biological activity on higher animals, are one of the most intriguing groups of specialized metabolites, and many of them are known as plant defense compounds. Poison hemlock, Conium maculatum, is well-known for its high content of piperidine alkaloids, of which coniine is the most famous. The distribution, localization, and diversity of these compounds in C. maculatum tissues have not yet been studied in detail. The hemlock alkaloids are low molecular weight compounds with relatively high volatility. They are thus difficult to analyze on-tissue by MALDI mass spectrometry imaging due to delocalization, which occurs even when using an atmospheric pressure ion source. In this manuscript, we describe an on-tissue derivatization method that allows the subsequent determination of the spatial distribution of hemlock alkaloids in different plant tissues by mass spectrometry imaging. Coniferyl aldehyde was found to be a suitable reagent for derivatization of the secondary amine alkaloids. The imaging analysis revealed that even chemically closely related hemlock alkaloids are discretely distributed in different plant tissues. Additionally, we detected a yet undescribed hemlock alkaloid in Conium maculatum seeds.

Comprehensive profiling of amino acids and derivatives in biological samples: A robust UHPLC-MS/MS method for investigating acute lung injury

The severe respiratory dysfunctions associated with acute lung injury (ALI) and its sequelae have a high morbidity and mortality rate, are multifactorial, and lack a viable treatment. Considering the critical function that amino acids and derivatives play in the genesis of illnesses and the regulation of metabolic processes, monitoring the levels of metabolites associated with amino acids in biological matrices is necessary and interesting to study their pathological mechanisms. Exploring the dynamics of amino acids and derivatives level and searching for biomarkers provides improved clinical ideas for the diagnosis and treatment of ALI. Therefore, we developed an ultra-high-performance liquid chromatography-electrospray tandem mass spectrometry (UHPLC-MS/MS) method that can simultaneously determine the amino acid and derivatives metabolic levels to study amino acid profiles in different biological samples to facilitate clinical research of ALI. In this study, 48 amino acids and derivatives, including neurotransmitters, polyamines, purines, and other types, were quantified simultaneously in a fast, high-throughput, sensitive, and reliable manner within a 15-minute run time without derivatization. No relevant studies have been reported to quantify these 48 amino acid metabolites in three biological samples simultaneously. Satisfactory linearity (R > 0.995), inter-day and intra-day accuracy (85.17-112.67 % and 85.29-111.60 %, respectively), inter-day and intra-day precision (RSD < 13.80 % and RSD < 12.01 %, respectively), matrix effects (81.00 %-118.00 %), recovery (85.09 %-114.65 %) and stability (RSD < 14.72 %) were all demonstrated by the optimized method's successful validation for all analytes. In addition, the suggested method was effectively implemented in plasma, urine, and lung tissue from normal mice and mice with ALI, with the aim of finding potential biomarkers associated with ALI. Potential biomarkers were screened through multivariate statistical analysis and volcanic map analysis, and the changes of markers in ALI were again identified through heat map analysis and correlation analysis with biochemical indicators, which provided ideas and references for subsequent mechanism studies. Here, the technique created in this work offers a quick and dependable way to perform an integrated analysis of amino acids in a variety of biological materials, which can provide research ideas for understanding the physiopathological state of various diseases.

Alkyl gallates inhibit serine O-acetyltransferase in bacteria and enhance susceptibility of drug-resistant Gram-negative bacteria to antibiotics

A principal concept in developing antibacterial agents with selective toxicity is blocking metabolic pathways that are critical for bacterial growth but that mammalian cells lack. Serine O-acetyltransferase (CysE) is an enzyme in many bacteria that catalyzes the first step in l-cysteine biosynthesis by transferring an acetyl group from acetyl coenzyme A (acetyl-CoA) to l-serine to form O-acetylserine. Because mammalian cells lack this l-cysteine biosynthesis pathway, developing an inhibitor of CysE has been thought to be a way to establish a new class of antibacterial agents. Here, we demonstrated that alkyl gallates such as octyl gallate (OGA) could act as potent CysE inhibitors in vitro and in bacteria. Mass spectrometry analyses indicated that OGA treatment markedly reduced intrabacterial levels of l-cysteine and its metabolites including glutathione and glutathione persulfide in Escherichia coli to a level similar to that found in E. coli lacking the cysE gene. Consistent with the reduction of those antioxidant molecules in bacteria, E. coli became vulnerable to hydrogen peroxide-mediated bacterial killing in the presence of OGA. More important, OGA treatment intensified susceptibilities of metallo-β-lactamase-expressing Gram-negative bacteria (E. coli and Klebsiella pneumoniae) to carbapenem. Structural analyses showed that alkyl gallate bound to the binding site for acetyl-CoA that limits access of acetyl-CoA to the active site. Our data thus suggest that CysE inhibitors may be used to treat infectious diseases caused by drug-resistant Gram-negative bacteria not only via direct antibacterial activity but also by enhancing therapeutic potentials of existing antibiotics.

A Practical Method for Amino Acid Analysis by LC-MS Using Precolumn Derivatization with Urea

Amino acid (AA) analysis is important in biochemistry, food science, and clinical medicine. However, due to intrinsic limitations, AAs usually require derivatization to improve their separation and determination. Here, we present a liquid chromatography-mass spectrometry (LC-MS) method for the derivatization of AAs using the simple agent urea. The reactions proceed quantitatively under a wide range of conditions without any pretreatment steps. Urea-derivatized products (carbamoyl amino acids) of 20 AAs exhibit better separation on reversed-phase columns and increased response in a UV detector compared to underivatized ones. We applied this approach to AA analysis in complex samples using a cell culture media as a model, and it showed potential for the determination of oligopeptides. This fast, simple, and inexpensive method should be useful for AA analysis in complex samples.

Plasma free amino acid profiles are associated with serum high molecular weight adiponectin levels in Japanese medical check-up population without type 2 diabetes mellitus

To prevent the progression of type 2 diabetes mellitus (T2DM), early detection and intervention are important. Several studies have already shown that the serum adiponectin level could be useful for evaluating the future risk of T2DM. Recently, plasma free amino acid (PFAA) concentrations have also emerged as potential biomarkers that predict the future onset of T2DM. In this study, we aimed to further characterise PFAA profiles by elucidating the association with the serum high molecular weight (HMW) adiponectin level in this cross-sectional study. A total of 1000 Japanese subjects who underwent medical check-ups were enrolled, and their plasma concentrations of 21 amino acids and clinical parameters were measured. The subjects without T2DM were divided into quartiles (Q1-4) by serum HMW adiponectin level, and the association with between PFAA concentrations was analysed. Concentrations of glutamate, alanine, proline, tyrosine, histidine, methionine, lysine, branched-chain amino acids (BCAAs) and tryptophan varied significantly according to the adiponectin quartile. Furthermore, serum adiponectin levels showed significant inverse correlations with these amino acids. The change in the PFAA profile in the group with the lowest adiponectin concentrations (Q1) was similar to that of T2DM patients. Although both adiponectin levels and PFAA concentrations are known to be altered by the accumulation of visceral fat and insulin resistance, the levels of glutamate, BCAA, lysine and tryptophan remain significantly associated with adiponectin level after adjustment for age, body mass index and homeostasis model assessment of insulin resistance, showing the direct association between PFAA concentrations and the serum HMW adiponectin level. Registration number: University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) UMIN000029920, registered on Nov 13th 2017 (prospectively registered).

Profiling of amines in biological samples using polythioester-functionalized magnetic nanoprobe

Introduction: The metabolic balance of amines is closely related to human health. It remains a great challenge to analyze amines with high-throughput and high-coverage. Methods: Polythioester-functionalized magnetic nanoprobes (PMPs) have been prepared under mild conditions and applied in chemoselective capture of amides. With the introduction of polythioester, PMPs demonstrate remarkably increased capture efficiency, leading to the dramatically improved sensitivity of mass spectrometry detection. Results: The analysis method with PMPs treatment has been applied in rapid detection of more than 100 amines in lung adenocarcinoma cell lines, mouse organ tissues, and 103 human serum samples with high-throughput and high-coverage. Statistical analysis shows that arginine biosynthesis differed between lung adenocarcinoma cell lines. Discussion: Phenylalanine, tyrosine and tryptophan biosynthesis differed between tissues. The combination indicators demonstrate a great diagnostic accuracy for distinguishing between health and lung disease subjects as well as differentiating the patients with benign lung disease and lung cancer. With powerful capture ability, low-cost preparation, and convenient separation, the PMPs demonstrate promising application in the intensive study of metabolic pathways and early diagnosis of disease.high-throughput and high-coverage. Here, polythioester-functionalized magnetic nanoprobes (PMPs) have been prepared under mild conditions and applied in chemoselective capture of amides. With the introduction of polythioester, PMPs demonstrate remarkably increased capture efficiency, leading to the dramatically improved sensitivity of mass spectrometry detection. The analysis method with PMPs treatment has been applied in rapid detection of more than 100 amines in lung adenocarcinoma cell lines, mouse organ tissues, and 103 human serum samples with high-throughput and high-coverage. Statistical analysis shows that arginine biosynthesis differed between lung adenocarcinoma cell lines. Phenylalanine, tyrosine and tryptophan biosynthesis differed between tissues. The combination indicators demonstrate a great diagnostic accuracy for distinguishing between health and lung disease subjects as well as differentiating the patients with benign lung disease and lung cancer. With powerful capture ability, low-cost preparation, and convenient separation, the PMPs demonstrate promising application in the intensive study of metabolic pathways and early diagnosis of disease.

Associations of AminoIndex Cancer Screening (Breast) Grade with Clinical and Laboratory Variables

BACKGROUND

Altered metabolism in the blood of cancer patients is closely related to changes in amino acids. Amino acids play an important physiological role as essential metabolites and regulators of metabolism. AminoIndex Cancer Screening (AICS) uses multivariate analysis of plasma-free amino acid profiles to screen for seven cancer types, including breast cancer.

METHODS

To determine the clinical utility of AICS (breast), we retrospectively analyzed associations of AICS (breast) score with clinical and laboratory variables in 390 patients who underwent AICS (breast) testing. The mean age of participants was 50.7 years (range: 26-87 years) and all were female.

RESULTS

The AICS (breast) grade was A, B, and C for 250 (64.1%), 90 (23.1%), and 50 (12.8%) participants, respectively. AICS (breast) was significantly correlated with AICS (gastric) (r = 0.487, p < 0.0001) and AICS (lung) (r = 0.523, p < 0.0001). Multivariate linear regression analysis showed no significant difference of AICS (breast) grade with age, body mass index, estimated glomerular filtration rate, dyslipidemia, or blood pressure. However, neutrophil-to-lymphocyte ratio significantly differed in relation to AICS (breast) grade (cut-off value, 1.7; p = 0.030), although only data from 72 patients were analyzed.

CONCLUSION

To our knowledge, this is the first study to report associations of AICS (breast) grade with clinical variables.

Enantioselective metabolomics by liquid chromatography-mass spectrometry

Metabolomics strives to capture the entirety of the metabolites in a biological system by comprehensive analysis, often by liquid chromatography hyphenated to mass spectrometry. A particular challenge thereby is the differentiation of structural isomers. Common achiral targeted and untargeted assays do not distinguish between enantiomers. This may lead to information loss. An increasing number of publications demonstrate that the enantiomeric ratio of certain metabolites can be meaningful biomarkers of certain diseases emphasizing the importance of introducing enantioselective analytical procedures in metabolomics. In this work, the state-of-the-art in the field of LC-MS based metabolomics is summarized with focus on developments in the recent decade. Methodologies, tagging strategies, workflows and general concepts are outlined. Selected biological applications in which enantioselective metabolomics has documented its usefulness are briefly discussed. In general, targeted enantioselective metabolomics assays are often based on a direct approach using chiral stationary phases (CSP) with polysaccharide derivatives, macrocyclic antibiotics, chiral crown ethers, chiral ion exchangers, donor-acceptor phases as chiral selectors. Rarely, these targeted assays focus on more than 20 analytes and usually are restricted to a certain metabolite class. In a variety of cases, pre-column derivatization of metabolites has been performed, especially for amino acids, to improve separation and detection sensitivity. Triple quadrupole instruments are the detection methods of first choice in targeted assays. Here, issues like matrix effect, absence of blank matrix impair accuracy of results. In selected applications, multiple heart cutting 2D-LC (RP followed by chiral separation) has been pursued to overcome this problem and alleviate bias due to interferences. Non-targeted assays, on the other hand, are based on indirect approach involving tagging with a chiral derivatizing agent (CDA). Besides classical CDAs numerous innovative reagents and workflows have been proposed and are discussed. Thereby, a critical issue for the accuracy is often neglected, viz. the validation of the enantiomeric impurity in the CDA. The majority of applications focus on amino acids, hydroxy acids, oxidized fatty acids and oxylipins. Some potential clinical applications are highlighted.

Mass spectrometry-based lipid analysis and imaging

Mass spectrometry imaging (MSI) is a powerful tool for in situ mapping of analytes across a sample. With growing interest in lipid biochemistry, the ability to perform such mapping without antibodies has opened many opportunities for MSI and lipid analysis. Herein, we discuss the basics of MSI with particular emphasis on MALDI mass spectrometry and lipid analysis. A discussion of critical advancements as well as protocol details are provided to the reader. In addition, strategies for improving the detection of lipids, as well as applications in biomedical research, are presented.

Association of Plasma Branched-Chain and Aromatic Amino Acids with Reduction in Kidney Function Evaluated in Apparently Healthy Adults

The published literature on the association of circulatory branched-chain amino acids (BCAAs) and aromatic amino acids (AAAs) with reduced kidney function is inconsistent or conflicting. Clarification of it might help to better understand the underlying pathophysiology and to determine potential biomarkers for early detection and evaluation of kidney function decline. Our main purpose was to explore and clarify the potential relationships of individual BCAAs and AAAs with estimated glomerular filtration rate (eGFR) decline. We included the data from 2804 healthy subjects and categorized them into three groups based on eGFR tertiles. The associations between individual amino acids and eGFR were explored by covariate-adjusted logistic regression models. There was a progressive increase in the concentrations of BCAAs and AAAs from the upper to the lower tertiles. We revealed significant positive associations of isoleucine, leucine, and phenylalanine with lower tertiles of eGFR in the adjusted models (p < 0.01-0.001). The findings hold a promising potential of using plasma isoleucine, leucine, and phenylalanine levels for evaluation of kidney function decline. Future longitudinal studies should investigate the causal association between altered levels of these amino acids and impaired kidney function and also the utility of the former as potential biomarkers for evaluating the risk and early detection of the latter.

Characterization and Determination of 13C-Labeled Nonessential Amino Acids in a 13C5-Glutamine Isotope Tracer Experiment with a Mass Spectrometry Strategy Combining Parallel Reaction Monitoring and Multiple Reaction Monitoring

Isotopic tracer, a powerful technique for metabolic pathway analysis, is currently widely applied in metabolic flux analysis. However, the qualitative and quantitative analyses of ¹³C-labeled metabolites pose great challenges, especially in complex biological sample matrices. Here, we present an integrated method for the qualitative and quantitative analyses of various isotopologues and isotopomers of ¹³C-labeled nonessential amino acids (NEAAs) in HepG2 cells incubated with ¹³C₅-glutamine (Gln) based on ultra-high-performance liquid chromatography (UHPLC) coupled with tandem mass spectrometry (MS). First, accurate mass-to-charge (m/z) values of protonated isotopologues and elution time of standards were simultaneously analyzed to characterize ¹³C-labeled NEAAs by high-resolution Orbitrap MS in the parallel reaction monitoring (PRM) mode. Second, isotopologues and isotopomers of ¹³C-labeled NEAAs were investigated in HepG2 cells incubated with ¹³C₅-Gln at different time points. Ultimately, a total of 66 multiple reaction monitoring (MRM) transitions were performed by UHPLC coupled with triple quadrupole MS. Among them, 29 MRM transitions were monitored for pure metabolites (unambiguously identified). The other 37 MRM transitions were monitored for mixtures with exactly identical MRM transitions and retention time. The application of targeted profiling of ¹³C-labeled NEAAs in the dynamic ¹³C-labeling experiment indicated that the concentration-time profiles of NEAAs were different from each other. The concentrations of most ¹³C-labeled Gln, Glu, Pro, and Asp altered after ¹³C₅-Gln incubation, indicating that Gln plays a fundamental role in the biosynthesis of Glu, Pro, and Asp. The proposed PRM-MRM combination mode LC-MS approach is expected to provide valuable insights into analyses of isotope-labeled metabolites in isotope tracer experiments.

On-tissue chemical derivatization reagents for matrix-assisted laser desorption/ionization mass spectrometry imaging

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is a key tool for the analysis of biological tissues. It provides spatial and quantitative information about different types of analytes within tissue sections. Despite the increasing improvements of this technique, the low detection sensitivity of some compounds remains an important challenge to overcome. Poor sensitivity is related to weak ionization efficiency, low abundance of analytes and matrix ions, or endogenous interferences. On-tissue chemical derivatization (OTCD) has proven to be an important solution to these issues and is increasingly employed in MALDI MSI studies. OTCD reagents, synthesized or commercially available, have been essentially used for the detection of small exogenous or endogenous molecules within tissues. Optimally, an OTCD reaction is performed in mild conditions, in an acceptable range of time, preserves the integrity of the tissues, and prevents the delocalization. In addition to their reactivity with a targeted chemical function, some OTCD reagents can also be used as a matrix, which simplifies the sample preparation procedure. In this review, we present an exhaustive overview of OTCD reagents and methods used in MALDI MSI studies.

Oral Supplementation of Collagen Peptides Improves Skin Hydration by Increasing the Natural Moisturizing Factor Content in the Stratum Corneum: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

INTRODUCTION

We aimed to investigate the effect of orally ingested collagen peptides (CPs) on skin condition and elucidate their mechanism of action.

METHODS

A randomized, placebo-controlled, double-blind trial was conducted in 99 healthy Japanese women, aged 35-50 years. The subjects were randomized into 3 groups (33 subjects/group) to receive 1 or 5 g of CP or placebo once daily for 12 weeks. Skin water content, transepidermal water loss (TEWL), skin elasticity, and skin thickness were evaluated before treatment and after 4, 8, and 12 weeks of treatment. The level of natural moisturizing factor (NMF) constituents in the stratum corneum (SC) was quantified before treatment and after 12 weeks of treatment.

RESULTS

Oral ingestion of CP increased the water content in the SC and epidermis and decreased TEWL. Furthermore, the NMF level in the SC was increased. However, skin elasticity and skin thickness remained unchanged.

CONCLUSIONS

The improvement in skin water content following the oral ingestion of CP can be attributed to an increase in the level of NMF in the SC.

TRIAL REGISTRATION

UMIN000030375 (retrospectively registered).

Chemical labeling strategies for small molecule natural product detection and isolation

Covering: Up to 2020.It is widely accepted that small molecule natural products (NPs) evolved to carry out a particular ecological function and that these finely-tuned molecules can sometimes be appropriated for the treatment of disease in humans. Unfortunately, for the natural products chemist, NPs did not evolve to possess favorable physicochemical properties needed for HPLC-MS analysis. The process known as derivatization, whereby an NP in a complex mixture is decorated with a nonnatural moiety using a derivatizing agent (DA), arose from this sad state of affairs. Here, NPs are freed from the limitations of natural functionality and endowed, usually with some degree of chemoselectivity, with additional structural features that make HPLC-MS analysis more informative. DAs that selectively label amines, carboxylic acids, alcohols, phenols, thiols, ketones, and aldehydes, terminal alkynes, electrophiles, conjugated alkenes, and isocyanides have been developed and will be discussed here in detail. Although usually employed for targeted metabolomics, chemical labeling strategies have been effectively applied to uncharacterized NP extracts and may play an increasing role in the detection and isolation of certain classes of NPs in the future.

Significance of serum branched-chain amino acid to tyrosine ratio measurement in athletes with high skeletal muscle mass

BACKGROUND

Few nutritional markers reflect the hypermetabolic state of athletes with high levels of skeletal muscle. Although branched-chain amino acids (BCAA) play crucial roles in protein metabolism in skeletal muscle, the relationship between skeletal muscle mass and amino acid imbalances caused by the metabolism of BCAA and aromatic amino acids remains unclear. The aim of this study is to test the hypothesis that athletes with high levels of skeletal muscle mass have plasma amino acid imbalances, assessed by serum BCAA to tyrosine ratio (BTR) which can be measured conveniently.

METHODS

The study enrolled 111 young Japanese men: 70 wrestling athletes and 41 controls. None of them were under any medications, extreme dietary restrictions or intense exercise regimens. Each participant's body composition, serum concentrations of albumin and rapid turnover proteins including transthyretin and transferrin, BTR, and thyroid function were assessed.

RESULTS

Compared to the controls, the athletes had significantly higher skeletal muscle index (SMI) (p < 0.001), and lower serum albumin concentration (p < 0.001) and BTR (p < 0.001). Kruskal-Wallis tests showed that serum albumin concentration and BTR were significantly lower in the participants with higher SMI. Serum albumin concentration and BTR were inversely correlated with SMI by multiple regression analysis (logarithmic albumin, β = - 0.358, p < 0.001; BTR, β = - 0.299, p = 0.001). SMI was inversely and transthyretin was positively correlated with serum albumin (SMI, β = - 0.554, p < 0.001; transthyretin, β = 0.379, p < 0.001). Serum concentration of free 3,5,3'-triiodothyronine (FT₃) was inversely correlated with BTR, and, along with SMI and albumin, was independent predictor of BTR (SMI, β = - 0.321, p < 0.001; FT₃, β = - 0.253, p = 0.001; logarithmic albumin, β = 0.261, p = 0.003). However, FT₃ was not correlated with SMI or serum albumin. Serum concentrations of rapid turnover proteins were not correlated with BTR.

CONCLUSIONS

Increased skeletal muscle mass enhances the circulating amino acid imbalances, and is independently facilitated by thyroid hormones. Serum BTR may be a useful biomarker to assess the hypermetabolic state of wrestling athletes with high levels of skeletal muscle.

Chemical Isotope Labeling LC-MS for Metabolomics

Due to the great diversity of chemical and physical properties of metabolites as well as a wide range of concentrations of metabolites present in metabolomic samples, performing comprehensive and quantitative metabolome analysis is a major analytical challenge. Conventional approach of combining various techniques and methods with each detecting a fraction of the metabolome can lead to the increase in overall metabolomic coverage. However, this approach requires extensive investment in equipment and analytical expertise with still relatively low coverage and low sample throughput. Chemical isotope labeling (CIL) liquid chromatography mass spectrometry (LC-MS) offers an alternative means of increasing metabolomic coverage while maintaining high quantification precision and accuracy. This chapter describes the CIL LC-MS method and its key features for metabolomic analysis.

Plasma Branched-Chain and Aromatic Amino Acids in Relation to Hypertension

Findings of the available studies regarding the roles of branched-chain amino acids (BCAAs) and aromatic amino acids (AAAs) in hypertension are inconsistent, conflicting and inconclusive. The purpose of this study was to explore and clarify the existence of any relationships of individual BCAAs and AAAs with hypertension with adjustments for potential relevant confounders. A total of 2805 healthy controls and 2736 hypertensive patients were included in the current analysis. The associations between individual amino acids and hypertension were explored by logistic regression analyses adjusted for potential confounding variables. Among the investigated amino acids, only the BCAAs showed consistently significant positive associations with hypertension in the adjusted models (p-trend < 0.05 to 0.001). However, compared with the corresponding lowest quartile of individual BCAAs, the positive association with hypertension remained significant only in the highest quartile (p < 0.01 to 0.001). We confirmed in a relatively large cohort of subjects that BCAAs, not AAAs, demonstrated consistent positive associations with hypertension. The results display the promising potential for the use of BCAAs as relevant and accessible biomarkers, and provide perspectives on interventions directed towards the reduction in plasma BCAA levels in the prevention and management of hypertension.

Free amino acids in African indigenous vegetables: Analysis with improved hydrophilic interaction ultra-high performance liquid chromatography tandem mass spectrometry and interactive machine learning

A hydrophilic interaction (HILIC) ultra-high performance liquid chromatography (UHPLC) with triple quadrupole tandem mass spectrometry (MS/MS) method was developed and validated for the quantification of 21 free amino acids (AAs). Compared to published reports, our method renders collectively improved sensitivity with lower limit of quantification (LLOQ) at 0.5~42.19 ng/mL with 0.3 μL injection volume (or equivalently 0.15~12.6 pg injected on column), robust linear range from LLOQ up to 3521~5720 ng/mL (or 1056 ~ 1716 pg on column) and a high throughput with total time of 6 min per sample, as well as easier experimental setup, less maintenance and higher adaptation flexibility. Ammonium formate in the mobile phase, though commonly used in HILIC, was found unnecessary in our experimental setup, and its removal from mobile phase was key for significant improvement in sensitivity (4~74 times higher than with 5 mM ammonium formate). Addition of 10 (or up to100 mM) hydrochloric acid (HCl) in the sample diluent was crucial to keep response linearity for basic amino acids of histidine, lysine and arginine. Different HCl concentration (10~100 mM) in sample diluent also excreted an effect on detection sensitivity, and it is of importance to keep the final prepared sample and calibrators in the same HCl level. Leucine and isoleucine were distinguished using different transitions. Validated at seven concentration levels, accuracy was bound within 75~125%, matrix effect generally within 90~110%, and precision error mostly below 2.5%. Using this newly developed method, the free amino acids were then quantified in a total of 544 African indigenous vegetables (AIVs) samples from African nightshades (AN), Ethiopian mustards (EM), amaranths (AM) and spider plants (SP), comprising a total of 8 identified species and 43 accessions, cultivated and harvested in USA, Kenya and Tanzania over several years, 2013~2018. The AN, EM, AM and SP were distinguished based on free AAs profile using machine learning methods (ML) including principle component analysis, discriminant analysis, naïve Bayes, elastic net-regularized logistic regression, random forest and support vector machine, with prediction accuracy achieved at ca. 83~97% on the test set (train/test ratio at 7/3). An interactive ML platform was constructed using R Shiny at https://boyuan.shinyapps.io/AIV_Classifier/ for modeling train-test simulation and category prediction of unknown AIV sample(s). This new method presents a robust and rapid approach to quantifying free amino acids in plants for use in evaluating plants, biofortification, botanical authentication, safety, adulteration and with applications to nutrition, health and food product development.

Use of plasma-free amino acids as biomarkers for detecting and predicting disease risk

This paper reviews developments regarding the use of plasma-free amino acid (PFAA) profiles as biomarkers for detecting and predicting disease risk. This work was initiated and first published in 2006 and was subsequently developed by Ajinomoto Co., Inc. After commercialization in 2011, PFAA-based tests were adopted in over 1500 clinics and hospitals in Japan, and numerous clinician-led studies have been performed to validate these tests. Evidence is accumulating that PFAA profiles can be used for diabetes prediction and evaluation of frailty; in particular, decreased plasma essential amino acids could contribute to the pathophysiology of severe frailty. Integration of PFAA evaluation as a biomarker and effective essential amino acid supplementation, which improves physical and mental functions in the elderly, could facilitate the development of precision nutrition, including personalized solutions. This present review provides the background for the technology as well as more recent clinical findings, and offers future possibilities regarding the implementation of precision nutrition.

Recent developments of novel matrices and on-tissue chemical derivatization reagents for MALDI-MSI

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a fast-growing technique for visualization of the spatial distribution of the small molecular and macromolecular biomolecules in tissue sections. Challenges in MALDI-MSI, such as poor sensitivity for some classes of molecules or limited specificity, for instance resulting from the presence of isobaric molecules or limited resolving power of the instrument, have encouraged the MSI scientific community to improve MALDI-MSI sample preparation workflows with innovations in chemistry. Recent developments of novel small organic MALDI matrices play a part in the improvement of image quality and the expansion of the application areas of MALDI-MSI. This includes rationally designed/synthesized as well as commercially available small organic molecules whose superior matrix properties in comparison with common matrices have only recently been discovered. Furthermore, on-tissue chemical derivatization (OTCD) processes get more focused attention, because of their advantages for localization of poorly ionizable metabolites and their‚ in several cases‚ more specific imaging of metabolites in tissue sections. This review will provide an overview about the latest developments of novel small organic matrices and on-tissue chemical derivatization reagents for MALDI-MSI.

Preoperative AminoIndex Cancer Screening (AICS) abnormalities predict postoperative recurrence in patients undergoing curative resection for non-small cell lung cancer

BACKGROUND

AminoIndex™ Cancer Screening (AICS (lung)) was developed as a screening test for lung cancer using a multivariate analysis of plasma-free amino acid (PFAA) profiles. According to the developed index composed of PFAA, the probability of lung cancer was categorized into AICS (lung) ranks A, B, and C in order of increasing risk. The aim of the present study was to investigate the relationship between the preoperative AICS (lung) rank and surgical outcomes in patients who underwent curative resection for non-small cell lung cancer (NSCLC).

METHODS

Preoperative blood samples were collected from 297 patients who underwent curative resection for NSCLC between 2006 and 2015. PFAA concentrations were measured. The relationship between the preoperative AICS (lung) rank and clinicopathological factors was examined. The effects of the preoperative AICS (lung) rank on postoperative outcomes were also analyzed.

RESULTS

The AICS (lung) rank was A in 93 patients (31.3%), B in 82 (27.6%), and C in 122 (41.1%). The AICS (lung) rank did not correlate with any clinicopathological factors, except for age. Based on follow-up data (median follow-up period of 6 years), postoperative recurrence was observed in 22 rank A patients (23.7%), 15 rank B (18.3%) and 49 rank C (40.2%). In the univariate analysis, preoperative AICS (lung) rank C was a worse factor of recurrence-free survival (p = 0.0002). The multivariate analysis identified preoperative AICS (lung) rank C (HR: 2.17, p = 0.0005) as a significant predictor of postoperative recurrence, particularly in patients with early-stage disease or adenocarcinoma.

CONCLUSION

Preoperative AICS (lung) rank C is a high-risk predictor of postoperative recurrence in patients undergoing curative resection for NSCLC.

Permanently Positively Charged Stable Isotope Labeling Agents and Its Application in the Accurate Quantitation of Alkylphenols Migrated from Plastics to Edible Oils

A new permanently positively charged stable isotope labeling (SIL) agent pair, 4-(((2,5-dioxopyrrolidin-1-yl)oxy)carbonyl)-N,N,N-trimethylbenzenaminium iodide(DPTBA) and its deuterated counterpart d₃-DPTBA, was designed and synthesized. The SIL agents were applied to the liquid chromatography-tandem mass spectrometry analysis of alkylphenols. Light labeled standards and heavy labeled samples were mixed and analyzed simultaneously. Matrix effect which mainly occurred during the ionization process was minimized because of the identical ionization processes between samples and standards. Meanwhile, derivatization made alkylphenols be positively charged, and thus the sensitivity was enhanced. The limits of detection were in the range of 1.5-1.8 ng/L, and the limits of quantitation were in the range of 4.8-6.1 ng/L. The developed method was applied to analyze alkylphenols migrated from plastics to edible oils. The recoveries for all analytes were in the range of 88.6-95.3%, while the matrix effects for all analytes were in the range of 96.2-99.6%.

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.

Relationship of reduced glomerular filtration rate with alterations in plasma free amino acids and uric acid evaluated in healthy control and hypertensive subjects

The potential association between altered levels of plasma free amino acids (PFAAs) and uric acid (UA) with estimated glomerular filtration rate (eGFR) remains unknown among patients with hypertension. A total of 2804 healthy controls and 2455 hypertensive patients were included in the current analysis. eGFR was defined as reduced when it was <60 ml/min/1.73 m². The associations between reduced eGFR and individual PFAAs and UA in the healthy control and hypertension groups were explored by logistic regression analyses adjusted for potential confounding variables. Results show that UA had a significant positive association with reduced eGFR in both healthy control and hypertension groups (P < 0.001). Among the PFAAs, citrulline, glycine and phenylalanine showed significant positive associations with reduced eGFR in both healthy control (P < 0.01 to 0.001) and hypertension (P < 0.001) groups. Moreover, alanine, asparagine and methionine achieved significant positive associations with reduced eGFR only in the hypertension group (P < 0.01 to 0.001). Conversely, serine showed significant inverse associations with reduced eGFR in the hypertension group only (P < 0.001). Our findings provide first evidence for a strong relationship between distinct patterns of PFAAs and elevated UA with reduced eGFR in hypertension. The findings may appear useful in developing effective strategies for the prevention or early detection and treatment of declined kidney function in hypertension.

Genetic basis for plasma amino acid concentrations based on absolute quantification: a genome-wide association study in the Japanese population

To assess the use of plasma free amino acids (PFAAs) as biomarkers for metabolic disorders, it is essential to identify genetic factors that influence PFAA concentrations. PFAA concentrations were absolutely quantified by liquid chromatography–mass spectrometry using plasma samples from 1338 Japanese individuals, and genome-wide quantitative trait locus (QTL) analysis was performed for the concentrations of 21 PFAAs. We next conducted a conditional QTL analysis using the concentration of each PFAA adjusted by the other 20 PFAAs as covariates to elucidate genetic determinants that influence PFAA concentrations. We identified eight genes that showed a significant association with PFAA concentrations, of which two, SLC7A2 and PKD1L2, were identified. SLC7A2 was associated with the plasma levels of arginine and ornithine, and PKD1L2 with the level of glycine. The significant associations of these two genes were revealed in the conditional QTL analysis, but a significant association between serine and the CPS1 gene disappeared when glycine was used as a covariate. We demonstrated that conditional QTL analysis is useful for determining the metabolic pathways predominantly used for PFAA metabolism. Our findings will help elucidate the physiological roles of genetic components that control the metabolism of amino acids.

DL-Amino Acid Analysis Based on Labeling with Light and Heavy Isotopic Reagents Followed by UPLC-ESI-MS/MS

L-Pyroglutamic acid succinimidyl ester (L-PGA-OSu) and its isotopic variant (L-PGA[d₅]-OSu) were synthesized and used as the chiral labeling reagents for the enantioseparation of amino acids by reversed-phase UPLC-ESI-MS/MS. The enantiomers of amino acids were labeled with the reagents at 60 °C for 10 min in an alkaline medium. The resulting diastereomers were well separated by the reversed-phase chromatography using an ODS column, packed with small particles (1.7 μm) (Rs = 1.95-8.05). A highly sensitive detection at a low-fmol level (0.5-3.2 fmol) was obtained from the selected reaction monitoring (SRM) chromatograms. An isotope labeling strategy using light and heavy variants for the differential analysis of the DL-amino acids in different sample groups is also presented in this paper. The ratios of D/L-alanine in different yogurt products were successfully determined by the proposed method. The D/L ratios were almost comparable to those obtained from only using light reagent (i.e., L-PGA-OSu). Therefore, the proposed strategy seems to be useful for the differential analysis of DL-amino acids, not only in food products but also in biological samples.

Age-dependent Changes in Plasma Amino Acids Contribute to Alterations in Glycoxidation Products

BACKGROUND

Glycative stress is involved in the pathogenesis of various degenerative disorders. This study sought to determine the effect of age-related changes in amino acids on serum levels of pentosidine and carboxymethyl-lysine (CML) in healthy individuals.

METHODS

The subjects were 78 healthy individuals categorized into three age groups. The ages of the groups were as follows: 26 young adults (20-30 y, 25.2±3.03), 26 middle-aged adults (35-50 y, 39.46±6.97) and 26 older adults (60 y or older, 69.80±10.01). Serum levels of pentosidine and CML were measured by ELISA and levels of plasma amino acids were determined using HPLC.

RESULTS

Serum levels of pentosidine and CML in the youngest group were higher than in the oldest group (p=0.026, 0.029, respectively). There was a positive correlation between the serum levels of pentosidine and CML and the levels of plasmaTyrosine (p=0.032, r=0.211 and p=0.037, r=0.224), Valine (p=0.037, r=0.224 and p=0.021, r=0.247) and Isoleucine (p=0.041, r=0.203 and p=0.021, r=0.247), respectively. Serum levels of pentosidine and CML may be modulated by the plasma levels of selected amino acids.

CONCLUSIONS

Better understanding of the role of these selective amino acids might provide new perception of how glycation pathways may be altered and pave the way for new therapeutic principles.

Post-operative AICS status in completely resected lung cancer patients with pre-operative AICS abnormalities: predictive significance of disease recurrence

The AminoIndex^TM Cancer Screening (AICS) system, a plasma-free amino acid (PFAA)-based multivariate discrimination index, is a blood screening test for lung cancer based on the comparison of PFAA concentrations between patients with lung cancer and healthy controls. Pre- and post-operative AICS values were compared among 72 patients who underwent curative resection for lung cancer. Post-operative changes in PFAA concentrations were also evaluated. AICS values were classified as rank A (0.0–4.9), B (5.0–7.9), or C (8.0–10.0). Rank B–C patients were evaluated for outcomes and post-operative changes in their AICS values. Twenty-three of the 44 pre-operative rank B–C patients experienced post-operative reductions in AICS rank. Only one patient experienced cancer recurrence. Post-operative changes in PFAA concentrations were associated with the risk of post-operative cancer recurrence (p = 0.001). Multivariate analysis revealed that the absence of a post-operative reduction in AICS rank independently predicted cancer recurrence (hazard ratio: 14.28; p = 0.012). The majority of patients had high pre-operative AICS values and exhibited a reduction in AICS rank after curative resection. However, the absence of a post-operative reduction in AICS rank was associated with cancer recurrence, suggesting that AICS rank may be a sensitive marker of post-operative recurrence.

Role of dietary amino acid balance in diet restriction-mediated lifespan extension, renoprotection, and muscle weakness in aged mice

Extending healthy lifespan is an emerging issue in an aging society. This study was designed to identify a dietary method of extending lifespan, promoting renoprotection, and preventing muscle weakness in aged mice, with a focus on the importance of the balance between dietary essential (EAAs) and nonessential amino acids (NEAAs) on the dietary restriction (DR)‐induced antiaging effect. Groups of aged mice were fed ad libitum, a simple DR, or a DR with recovering NEAAs or EAAs. Simple DR significantly extended lifespan and ameliorated age‐related kidney injury; however, the beneficial effects of DR were canceled by recovering dietary EAA but not NEAA. Simple DR prevented the age‐dependent decrease in slow‐twitch muscle fiber function but reduced absolute fast‐twitch muscle fiber function. DR‐induced fast‐twitch muscle fiber dysfunction was improved by recovering either dietary NEAAs or EAAs. In the ad libitum‐fed and the DR plus EAA groups, the renal content of methionine, an EAA, was significantly higher, accompanied by lower renal production of hydrogen sulfide (H₂S), an endogenous antioxidant. Finally, removal of methionine from the dietary EAA supplement diminished the adverse effects of dietary EAA on lifespan and kidney injury in the diet‐restricted aged mice, which were accompanied by a recovery in H₂S production capacity and lower oxidative stress. These data imply that a dietary approach could combat kidney aging and prolong lifespan, while preventing muscle weakness, and suggest that renal methionine metabolism and the trans‐sulfuration pathway could be therapeutic targets for preventing kidney aging and subsequently promoting healthy aging.

Perioperative dynamics and significance of plasma-free amino acid profiles in colorectal cancer

Background

For early detection of cancer, we have previously developed the AminoIndex Cancer Screening (AICS) system, which quantifies 6 plasma-free amino acids (PFAAs) in blood samples. Herein, we examined the usefulness of the AICS in patients with colorectal cancer (CRC) by comparing the preoperative and postoperative PFAA profiles.

Methods

Our study cohort consisted of 62 patients who had undergone curative resection for CRC at our cancer center, with no recurrence at the time of the study. Blood samples were collected from fasted patients within 1 week before the resection and at 0.5–6.5 years post-resection. Following plasmapheresis, the PFAA levels were measured via liquid chromatography/mass spectrometry, and the AICS values were computed (the higher the value, the greater the probability of cancer). Risk was calculated from the AICS value and ranked as A, B, or C, with rank C representing the highest risk. All patients in our study were rank B + C.

Results

The postoperative AICS value was lower than the preoperative value in 57 of the 62 patients; the rank was also lower postoperatively (49 patients, p < 0.001). The decline in both was stage-independent, even occurring in patients with right-sided tumors or poorly differentiated adenocarcinomas. For comparative purposes, the levels of 2 tumor markers (carbohydrate antigen 19–9 and carcinoembryonic antigen) were also examined; these were within the reference ranges in 70–80% of patients preoperatively and in 80–90% postoperatively.

Conclusion

We suggest that tumor-bearing conditions alter the PFAA profiles, which may be used to predict prognosis and monitor for recurrence in CRC patients after tumor resection.

Trial registration

This trial has been retrospectively registered at UMIN-CTR R000028005, Oct 06, 2016.

Electronic supplementary material

The online version of this article (10.1186/s12893-018-0344-0) contains supplementary material, which is available to authorized users.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Plasma amino acid profile associated with fatty liver disease and co-occurrence of metabolic risk factors

Fatty liver disease (FLD) increases the risk of diabetes, cardiovascular disease, and steatohepatitis, which leads to fibrosis, cirrhosis, and hepatocellular carcinoma. Thus, the early detection of FLD is necessary. We aimed to find a quantitative and feasible model for discriminating the FLD, based on plasma free amino acid (PFAA) profiles. We constructed models of the relationship between PFAA levels in 2,000 generally healthy Japanese subjects and the diagnosis of FLD by abdominal ultrasound scan by multiple logistic regression analysis with variable selection. The performance of these models for FLD discrimination was validated using an independent data set of 2,160 subjects. The generated PFAA-based model was able to identify FLD patients. The area under the receiver operating characteristic curve for the model was 0.83, which was higher than those of other existing liver function-associated markers ranging from 0.53 to 0.80. The value of the linear discriminant in the model yielded the adjusted odds ratio (with 95% confidence intervals) for a 1 standard deviation increase of 2.63 (2.14–3.25) in the multiple logistic regression analysis with known liver function-associated covariates. Interestingly, the linear discriminant values were significantly associated with the progression of FLD, and patients with nonalcoholic steatohepatitis also exhibited higher values.

Dependence of matrix effect on ionization polarity during LC-ESI-MS analysis of derivatized amino acids in some natural samples

Matrix effect, the influence of co-eluting components on the ionization efficiency of the analyte, affects the trueness and precision of the LC-ESI-MS analysis. Derivatization can reduce or eliminate matrix effect, for example, diethyl ethoxymethylenemalonate (DEEMM) derivatives have shown less matrix effect compared to other derivatives. Moreover, the use of negative ion mode can further reduce matrix effect. In order to investigate the combination of derivatization and different ionization modes, an LC-ESI-MS/MS method using alternating positive/negative ion mode was developed and validated. The analyses in positive and negative ion modes had comparable limit of quantitation values. The influence of ESI polarity on matrix effect was investigated during the analysis of 22 DEEMM-derivatized amino acids in herbal extracts and honeys. Sample dilution approach was used for the evaluation of the presence of matrix effect. Altogether, 4 honeys and 11 herbal extracts were analyzed, and the concentrations of 22 amino acids in the samples are presented. In the positive ion mode, matrix effect was observed for several amino acid derivatives and the matrix effect was stronger in honey samples compared to the herbal extracts. The negative ion mode was free from matrix effect, with only few exceptions in honeys (average relative standard deviation over all analytes and matrices was 8%; SD = 7%). The matrix effect was eliminated in the positive ion mode by sample dilution and agreement between concentrations from the two ion modes was achieved for most amino acids. In conclusion, it was shown that the combination of derivatization and negative ion mode can be a powerful tool for minimizing matrix effect in more complicated applications.

Long-term effect of dietary overload lithium on the glucose metabolism in broiler chickens

Lithium, like insulin, activates glycogen synthase and stimulates glucose transport in rat adipocytes. To investigate the effect of dietary overload lithium on glucose metabolism in broiler chickens, one-day-old chicks were fed a basal diet supplemented with 0 (control) or 100mg lithium/kg (overload lithium) for 35days. Compared to controls, glucose disappearance rates were lower (p=0.035) 15-120min after glucose gavage, and blood glucose concentrations were lower (p=0.038) 30min after insulin injection in overload lithium broilers. Overload lithium decreased (p<0.05) glycogen and glucose-6-phosphate concentrations in liver, but increased (p<0.05) their concentrations in pectoralis major. Overload lithium increased (p<0.05) mRNA expression of glucose transporter (GLUT) 3 and GLUT9 in liver, and GLUT1, GLUT3, GLUT8, and GLUT9 in pectoralis major, but decreased (p<0.05) cytosolic phosphoenolpyruvate carboxykinase (PEPCK) in liver and mitochondrial PEPCK in pectoralis major. These results suggest that dietary overload lithium decreases glucose tolerance and gluconeogenesis, but increases insulin sensitivity and glucose transport in broiler chickens.

Enhanced detection of amino acids in hydrophilic interaction chromatography electrospray tandem mass spectrometry with carboxylic acids as mobile phase additives

Liquid chromatography coupled with mass spectrometry technique has been widely used in the analysis of biological targets such as amino acids, peptides, and proteins. In this work, eight common single carboxylic acids or diacids, which contain different pKa have been investigated as the additives to the analysis of amino acids. As the results, carboxylic acid additive can improve the signal intensity of acidity amino acids such as Asp and Glu and the chromatographic separation of basic amino acids such as Arg, His, and Lys. In particular, the diacids have better performance than single acids. The proposed mechanism is that the diacid has hydrogen bond interaction with amino acids to reduce their polarity/amphiprotic characteristics. Besides, oxalic acid has been found having better enhancement than phthalic acid by overall consideration. Therefore, we successfully quantified the 15 amino acids in Sepia bulk pharmaceutical chemical by using oxalic acid as the additive.

Plasma free amino acid profiles evaluate risk of metabolic syndrome, diabetes, dyslipidemia, and hypertension in a large Asian population

Background

Recently, the association of plasma free amino acid (PFAA) profile and lifestyle-related diseases has been reported. However, few studies have been reported in large Asian populations, about the usefulness of PFAAs for evaluating disease risks. We examined the ability of PFAA profiles to evaluate lifestyle-related diseases in so far the largest Asian population.

Methods

We examined plasma concentrations of 19 amino acids in 8589 Japanese subjects, and determined the association with variables associated with obesity, blood glucose, lipid, and blood pressure. We also evaluated the PFAA indexes that reflect visceral fat obesity and insulin resistance. The contribution of single PFAA level and relevant PFAA indexes was also examined in the risk assessment of lifestyle-related diseases.

Results

Of the 19 amino acids, branched-chain amino acids and aromatic amino acids showed association with obesity and lipid variables. The PFAA index related to visceral fat obesity showed relatively higher correlation with variables than that of any PFAA. In the evaluation of lifestyle-related disease risks, the odds ratios of the PFAA index related to visceral fat obesity or insulin resistance with the diseases were higher than most of those of individual amino acid levels even after adjusting for potential confounding factors. The association pattern of the indexes and PFAA with each lifestyle-related disease was distinct.

Conclusions

We confirmed the usefulness of PFAA profiles and indexes as markers for evaluating the risks of lifestyle-related diseases, including diabetes mellitus, metabolic syndrome, dyslipidemia, and hypertension in a large Asian population.