Development of simultaneous analysis of tryptophan metabolites in serum and gastric juice - an investigation towards establishing a biomarker test for gastric cancer diagnosis

Determination of indoxyl sulfate by spectrofluorimetric method in human plasma through extraction with deep eutectic solvent

A rapid and efficient analytical method was established to quantify indoxyl sulfate (IS) in plasma through extraction technique with a deep eutectic solvent (DES) and spectrofluorimetric method. DES (choline chloride: urea) was mixed with plasma samples for the extraction of IS, followed by the addition of dipotassium hydrogen phosphate (K2HPO4) solution to form an aqueous two-phase system. The fluorescence intensity of IS which was first extracted to the DES-rich-phase and then back-extracted into the salt-rich-phase, was measured by spectrofluorimetric method. Some key factors such as pH, centrifugation speed and time, the volume ratio of DES/salt, and salt concentration were optimized. Under the optimized conditions, the suggested method had a dynamic range between 20 and 160 µg/mL with a coefficient of determination (R2) of 0.99. Precision (relative standard deviation) was less than 15% and accuracy (% relative recovery) was ± 15% at the nominal concentration level. In addition, results showed that IS levels in real samples were higher than 40 µg/mL which was compatible with reported IS levels in end-stage renal disease (ESRD) patients. Overall, all the results reflect the fact that the presented analytical method can potentially be used for the determination of IS in real plasma samples.

Liquid chromatography-tandem mass spectrometry based simultaneous quantification of tryptophan, serotonin and kynurenine pathway metabolites in tissues and cell culture systems

BACKGROUND

Kynurenine and respective metabolites exhibit bioactivity as well as tryptophan, an essential amino acid, and the neurotransmitter serotonin. Dysregulations in the kynurenine pathway are involved in neurodegenerative/neuropsychiatric disorders and diabetes mellitus type 2 but also in cancer. Therefore, measurements of kynurenine-related metabolites will improve the general understanding for kynurenine pathway relevance in disease pathogenesis.

METHODS

Tryptophan, serotonin, picolinic acid, quinolinic acid, 3-OH-kynurenine, kynurenine, 3-OH-anthranilic acid, kynurenic acid, anthranilic acid as well as nicotinic acid and the redox cofactor NAD+ were analyzed in heterogeneous matrices by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). After validation, the described method was applied for measurements of native metabolite concentrations in murine tissues and cellular systems including pathway-shift monitoring after treatment with the tryptophan-2,3-dioxygenase-inhibitor 680C91. In addition, the method was evaluated for its ability for integration into multi-omics approaches using a single sample metabolite extraction procedure.

RESULTS

A simple and sensitive UPLC-MS/MS method for simultaneous quantification of up to 10 kynurenine-related metabolites in four biological matrices was developed. Within a run time of 6.5 min, chromatographic separation of kynurenine-related metabolites, including the isomers nicotinic acid and picolinic acid, was achieved without derivatization. Validation parameters, including interday precision (<14.8%), mean accuracy (102.4% ± 12.9%) and linear detection ranges of more than three orders of magnitude, indicate method reliability. Depending the investigated sample matrix, the majority of metabolites were successfully detected and quantified in native murine and cell culture derived sample materials. Furthermore, the method allowed to monitor the impact of a tryptophan-2,3-dioxygenase-inhibitor on kynurenine pathway in a cellular system and is suitable for multi-assay analyses using aliquots from the same cell extract.

CONCLUSION

The described UPLC-MS/MS method provides a simple tool for the simultaneous quantification of kynurenine pathway metabolites. Due to its suitability for many physiological matrices, the method provides wide application for disease-related experimental settings.

Could circulating biomarkers of nitrosative stress and protein glycoxidation be useful in patients with gastric cancer?

Background

Nitrosative stress leads to protein glycoxidation, but both processes may be strongly related to the cancer development. Therefore, the aim of this study was to assess the nitrosative stress and protein glycoxidation products in patients with gastric cancer in comparison with healthy controls. We are also the first to evaluate the diagnostic utility of nitrosative stress and protein glycoxidation markers in gastric cancer patients in respect to histopathological classifications (TNM, Lauren's and Goseki's classification) and histopathological parameters such as histological type, histological differentiation grade, presence of vascular or neural invasion, desmoplasia and Helicobacter pylori infection.

Methods

The study included 50 patients with gastric cancer and 50 healthy controls matched for sex and age. Nitrosative stress parameters and protein glycoxidation products were measured colorimetrically/fluorometrically in plasma or serum samples. Student's t-test or Mann-Whitney U-test were used for statistical analysis.

Results

NO, S-nitrosothiols, nitrotyrosine, kynurenine, N-formylkynurenine, dityrosine, AGE and Amadori products were significantly increased whereas tryptophan fluorescence was decreased in patients with gastric cancer compared to the healthy control. Nitrosative stress and glycoxidation products may be useful in diagnosis of gastric cancer because they differentiate patients with gastric cancer from healthy individuals with high sensitivity and specificity. Some of the determined parameters are characterised by high AUC value in differentiation of GC patients according to the histopathological parameters.

Conclusions

Gastric cancer is associated with enhanced circulating nitrosative stress and protein glycation. Although further research on a tissue model is needed, plasma/serum biomarkers may be dependent on tumour size, histological type, tumour invasion depth, presence of lymph node and distant metastasis, vascular and neural invasion and Helicobacter pylori infection. Thus, circulating biomarkers of nitrosative stress/protein glycoxidation may have potential diagnostic significance in gastric cancer patients.

Advances in kynurenine analysis

Kynurenine, the first product of tryptophan degradation via the kynurenine pathway, has become one of the most frequently mentioned biomarkers in recent years. Its levels in the body indicate the state of the human physiology. Human serum and plasma are the main matrixes used to evaluate kynurenine levels and liquid chromatography is the dominant technique for its determination. However, their concentrations in blood do not always correspond to the levels in other matrixes obtained from the affected individuals. It is therefore important to decide when it is appropriate to analyse kynurenine in alternative matrices. However, liquid chromatography may not be the best option for the analysis. This review presents alternatives that can be used and summarizes the features that need to be considered prior to kynurenine determination. Possible approaches to kynurenine analysis in a variety of human matrixes, their challenges, and limitations are critically discussed.

Metabolic codependencies in the tumor microenvironment and gastric cancer: Difficulties and opportunities

Oncogenesis and the development of tumors affect metabolism throughout the body. Metabolic reprogramming (also known as metabolic remodeling) is a feature of malignant tumors that is driven by oncogenic changes in the cancer cells themselves as well as by cytokines in the tumor microenvironment. These include endothelial cells, matrix fibroblasts, immune cells, and malignant tumor cells. The heterogeneity of mutant clones is affected by the actions of other cells in the tumor and by metabolites and cytokines in the microenvironment. Metabolism can also influence immune cell phenotype and function. Metabolic reprogramming of cancer cells is the result of a convergence of both internal and external signals. The basal metabolic state is maintained by internal signaling, while external signaling fine-tunes the metabolic process based on metabolite availability and cellular needs. This paper reviews the metabolic characteristics of gastric cancer, focusing on the intrinsic and extrinsic mechanisms that drive cancer metabolism in the tumor microenvironment, and interactions between tumor cell metabolic changes and microenvironment metabolic changes. This information will be helpful for the individualized metabolic treatment of gastric cancers.

Metabolomics Reveals Novel Serum Metabolic Signatures in Gastric Cancer by a Mass Spectrometry Platform

Gastric cancer (GAS) is one of the malignant tumors of the gastrointestinal system. Alterations in metabolite composition can reflect pathological processes of GAS and constitute a basis for diagnosis and treatment improvements. In this study, a total of 301 serum samples from 150 GAS patients at different tumor-node-metastasis (TNM) stages and 151 healthy controls were collected. Mass spectrometry platforms were performed to investigate the changes in GAS-related metabolites and explore the new potential serum biomarkers and the metabolic dysregulation associated with GAS progression. Twelve differential metabolites (ethyl 2,4-dimethyl-1,3-dioxolane-2-acetate, D-urobilinogen, 14-HDoHE, 13-hydroxy-9-methoxy-10-oxo-11-octadecenoic acid, 5,6-dihydroxyprostaglandin F1a, 9'-carboxy-gamma-tocotrienol, glutaric acid, alanine, tyrosine, C18:2(FFA), adipic acid, and suberic acid) were identified to establish the diagnosis model for GAS. The defined biomarker panel was also statistically significant for GAS progression with different TNM stages. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment revealed the metabolic dysregulation associated with GAS progression. In conclusion, a diagnostic panel was established and validated, which could be used to further stage the early and advanced GAS patients from healthy controls. These findings may provide useful information for explaining the GAS metabolic alterations and try to facilitate the characterization of GAS patients in the early stage.

Simultaneous determination of serum tryptophan metabolites in an older Chinese population

Tryptophan (TRP) and its metabolites exhibit significant biological effects and are strongly associated with age-related disease and mortality. However, reports on quantitatively analyzing these metabolites in older individuals are not available. We used ultra-high-performance liquid chromatography-tandem mass spectrometry to optimize and validate a method for isotope dilution analysis of TRP metabolites in older individuals. The targeted analytes are TRP, serotonin or 5-hydroxytryptamine, kynurenine, kynurenic acid, xanthurenic acid, indole-3-acetic acid, indole-3-propionic acid, and tryptamine. The serum sample was purified using solid-phase extraction and was separated on a Waters HSS T3 column (100 mm × 2.1 mm, 1.8 μm). The analytes were detected in the multiple reaction monitoring mode under positive ionization. TRP was confirmed and measured after being diluted 100 times. This method exhibited satisfactory linearity (r > 0.99). The intrabatch and interbatch accuracies (85.7-114%) and precisions (<15%) were acceptable. The standard-normalized matrix effects ranged from 51.6 to 145%. This method was successfully applied to a cohort of 1021 older Chinese individuals, and this study may enable further understanding of the metabolic phenotypes associated with TRP in other populations.

Progress with Metabolomic Blood Tests for Gastrointestinal Cancer Diagnosis-An Assessment of Biomarker Translation

There is an urgent need for cost-effective, non-invasive tools to detect early stages of gastrointestinal cancer (colorectal, gastric, and esophageal cancers). Despite many publications suggesting circulating metabolites acting as accurate cancer biomarkers, few have reached the clinic. In upper gastrointestinal cancer this is critically important, as there is no test to complement gold-standard endoscopic evaluation in patients with mild symptoms that do not meet referral criteria. Therefore, this study aimed to describe and solve this translational gap. Studies reporting diagnostic accuracy of metabolomic blood-based gastrointestinal cancer biomarkers from 2007 to 2020 were systematically reviewed and progress of each biomarker along the discovery-validation-adoption pathway was mapped. Successful biomarker translation was defined as a composite endpoint, including patent protection/FDA approval/recommendation in national guidelines. The review found 77 biomarker panels of gastrointestinal cancer, including 25 with an AUROC >0.9. All but one was stalled at the discovery phase, 9.09% were patented and none were clinically approved, confirming the extent of biomarker translational gap. In addition, there were numerous "re-discoveries," including histidine, discovered in 7 colorectal studies. Finally, this study quantitatively supports the presence of a translational gap between discovery and clinical adoption, despite clear evidence of highly performing biomarkers with significant potential clinical value.

Gastric cancer detection by non-blood-based liquid biopsies: A systematic review looking into the last decade of research

Gastric cancer (GC) screening is arguable in most Western countries. Liquid biopsies are a great promise to answer the unmet need for less invasive diagnostic biomarkers in GC. Thus, we aimed at systematically reviewing the current knowledge on liquid biopsy-based biomarkers in GC screening. A systematic search on PubMed/MEDLINE and Scopus databases was performed on published articles reporting the use of non-blood specimen (saliva, gastric juice [GJ], urine and stool) on GC diagnosis. 3208 records were retrieved by June 2022. After removal of duplicate records, 2379 abstracts were screened, and 84 full texts included in this systematic review. More than 90% of studies were reported on Asian populations. Overall, 9 studies explored stool-, 12 saliva-, and 29 urine-derived biomarkers for GC detection. Additionally, 37 studies, representing the majority, analyzed GJ, focusing on nucleic acid molecules. Several miRNAs and lncRNA molecules have been associated with GC risk, particularly miR-21 (area under the curve [AUC] = 0.97, 95% CI: 0.94-1.00). Considering salivary biomarkers, the best described model in validation sets included the soybean agglutinin and Vicia villosa agglutinin lectins (AUC = 0.89, 95% CI: 0.80-0.99). Most studies in urine carried out metabolomic approaches, with two discriminatory models presenting AUC values superior to 0.97. This systematic review emphasizes the potential role of non-blood-based biomarkers, although further validation, particularly in Western countries, is mandatory, namely for non-invasive screening and/or monitoring, as well as the use of GJ as a tool to enhance upper gastrointestinal endoscopy accuracy.

Metabolite biomarker discovery for human gastric cancer using dried blood spot mass spectrometry metabolomic approach

As one of the most common malignancies, gastric cancer (GC) is the third leading cause of cancer-related deaths in China. GC is asymptomatic in early stages, and the majority of GC mortality is due to delayed symptoms. It is an urgent task to find reliable biomarkers for the identification of GC in order to improve outcomes. A combination of dried blood spot sampling and direct infusion mass spectrometry (MS) technology was used to measure blood metabolic profiles for 166 patients with GC and 183 healthy individuals, and 93 metabolites including amino acids, carnitine/acylcarnitines and their derivatives, and related ratios were quantified. Multiple algorithms were used to characterize the changes of metabolic profiles in patients with GC compared to healthy individuals. A biomarker panel was identified in training set, and assessed by tenfold cross-validation and external test data set. After systematic selection of 93 metabolites, a biomarker panel consisting of Ala, Arg, Gly, Orn, Tyr/Cit, Val/Phe, C4-OH, C5/C3, C10:2 shows the potential to distinguish patients with GC from healthy individuals in tenfold cross-validation model (sensitivity: 0.8750, specificity: 0.9006) and test set (sensitivity: 0.9545, specificity: 0.8636). This metabolomic analysis makes contribution to the identification of disease-associated biomarkers and to the development of new diagnostic tools for patients with GC.

Gastric Cancer Cell-Derived Kynurenines Hyperactive Regulatory T Cells to Promote Chemoresistance via the IL-10/STAT3/BCL2 Signaling Pathway

Chemotherapy resistance is frequently observed in gastric cancer patients and is associated with poor prognosis; tryptophan (Trp) catabolism has been recognized as a key metabolic regulator of many types of cancer progression. Regulatory T cells (Tregs) and Trp metabolite kynurenine (Kyn) were analyzed using tumor tissues. Chemotherapy resistance induced by IL-10 or Treg was detected by flow cytometry assay. The activation of STAT3/BCL2 signaling pathways in gastric cells cocultured by Treg was illustrated by western blotting. Patients' Treg and human gastric cancer organoid model were established to examine the anticancer effects of STAT3 inhibitor. We found that a higher level of IL-10 secreted by Kyn-induced Tregs was responsible for the 5-fluorouracil-induced resistance of gastric cancer cell lines. STAT3 and BCL2 knockout significantly abrogated Treg supernatant- or IL-10-induced chemoresistance in SGC7901 and BGC823 cell lines. Furthermore, STAT3 inhibitor significantly reduced the organoid and clonogenicity of organoids cocultured with Treg. Our data suggested that tumor-derived Kyn may hyperactivate Tregs and induce chemoresistance through the IL-10/STAT3/BCL2 signaling pathway.

Kynurenine and Anthranilic Acid in the Peritoneum Correlate With the Stage of Gastric Cancer Disease

Background:

This study aimed to assess the importance of selected kynurenines measured in peritoneal fluid, lavage washings, and blood serum in patients with advanced gastric cancer (GC) based on the clinical and pathological staging of TNM for a more precise evaluation of the stage of the disease.

Methods:

Data were collected from a prospectively maintained database of all patients operated on advanced GC between July 2018 and August 2020. In total, 98 patients were eligible for the analysis according to the REMARK guidelines.

Results:

Among the various kynurenines analyzed in this study, we found that the median concentration of anthranilic acid (AA) in the peritoneal lavage washings was significantly higher in patients with positive nodes (pN1-3) compared to those with negative nodes (pN0) (P = 0.0100). Based on the ROC analysis, AA showed diagnostic utility in the differentiation of the pN staging (P = 0.0047). Furthermore, there was a positive correlation between AA in peritoneal fluid with stage pN (P = 0.0116) and a positive correlation between AA in peritoneal lavage washings with stage cT (P = 0.0101). We found that the median concentration of kynurenine (Kyn) in peritoneal lavage washings was significantly higher in patients with cM1 compared to cM0 patients (P = 0.0047). Based on the ROC analysis, Kyn showed diagnostic utility in cM staging differentiation (P < 0.0001). There was a positive correlation between peritoneal Kyn and stage of cM (P = 0.0079).

Conclusions:

AA and Kyn measured in peritoneal lavage indicate advanced GC and may be considered in the future as valuable adjunct tools in TNM staging of advanced GC.

Tissue-based metabolomics reveals metabolic signatures and major metabolic pathways of gastric cancer with help of transcriptomic data from TCGA

PURPOSE

The aim of the present study was to screen differential metabolites of gastric cancer (GC) and identify the key metabolic pathways of GC.

METHODS

GC (n=28) and matched paracancerous (PC) tissues were collected, and LC-MS/MS analysis were performed to detect metabolites of GC and PC tissues. Metabolite pathways based on differential metabolites were enriched by MetaboAnalyst, and genes related to metabolite pathways were identified using the KEGGREST function of the R software package. Transcriptomics data from The Cancer Genome Atlas (TCGA) was analyzed to obtain differentially expressed genes (DEGs) of GC. Overlapping genes were acquired from metabonimics and transcriptomics data. Pathway enrichment analysis was performed using String. The protein expression of genes was validated by the Human Protein Atlas (HPA) database.

RESULTS

A total of 325 key metabolites were identified, 111 of which were differentially expressed between the GC and PC groups. Seven metabolite pathways enriched by MetaboAnalyst were chosen, and 361 genes were identified by KEGGREST. A total of 2831 DEGs were identified from the TCGA cohort. Of these, 1317 were down-regulated, and 1636 were up-regulated. Twenty-two overlapping genes were identified between genes related to metabolism and DEGs. Glycerophospholipid (GPL) metabolism is likely associated with GC, of which AGPAT9 and ETNPPL showed lower expressed in GC tissues.

CONCLUSIONS

We investigated the tissue-based metabolomics profile of GC, and several differential metabolites were identified. GPL metabolism may affect on progression of GC.

A systematic review of metabolomic profiling of gastric cancer and esophageal cancer

Objective: Upper gastrointestinal (UGI) cancers, predominantly gastric cancer (GC) and esophageal cancer (EC), are malignant tumor types with high morbidity and mortality rates. Accumulating studies have focused on metabolomic profiling of UGI cancers in recent years. In this systematic review, we have provided a collective summary of previous findings on metabolites and metabolomic profiling associated with GC and EC.

Methods: A systematic search of three databases (Embase, PubMed, and Web of Science) for molecular epidemiologic studies on the metabolomic profiles of GC and EC was conducted. The Newcastle–Ottawa Scale (NOS) was used to assess the quality of the included articles.

Results: A total of 52 original studies were included for review. A number of metabolites were differentially distributed between GC and EC cases and non-cases, including those involved in glycolysis, anaerobic respiration, tricarboxylic acid cycle, and protein and lipid metabolism. Lactic acid, glucose, citrate, and fumaric acid were among the most frequently reported metabolites of cellular respiration while glutamine, glutamate, and valine were among the most commonly reported amino acids. The lipid metabolites identified previously included saturated and unsaturated free fatty acids, aldehydes, and ketones. However, the key findings across studies to date have been inconsistent, potentially due to limited sample sizes and the majority being hospital-based case-control analyses lacking an independent replication group.

Conclusions: Studies on metabolomics have thus far provided insights into etiological factors and biomarkers for UGI cancers, supporting the potential of applying metabolomic profiling in cancer prevention and management efforts.

Metabolic Profiling Revealed Prediction Biomarkers for Infantile Hemangioma in Umbilical Cord Blood Sera: A Prospective Study

Infantile hemangioma (IH), the most common benign tumor in infancy, mostly arises and has rapid growth before 3 months of age. Because irreversible skin changes occur in the early proliferative stage, early medical treatment is essential to reduce the permanent sequelae caused by IH. Yet there are still no early screening biomarkers for IH before its visible emergence. This study aimed to explore prediction biomarkers using noninvasive umbilical cord blood (UCB). A prospective study of the metabolic profiling approach was performed on UCB sera from 28 infants with IH and 132 matched healthy controls from a UCB population comprising over 1500 infants (PeptideAtlas: PASS01675) using liquid chromatography-mass spectrometry. The metabolic profiling results exhibited the characteristic metabolic aberrance of IH. Machine learning suggested a panel of biomarkers to predict the occurrence of IH, with the area under curve (AUC) values in the receiver operating characteristic analysis all >0.943. Phenylacetic acid had potential to predict infants with large IH (diameter >2 cm) from those with small IH (diameter <2 cm), with an AUC of 0.756. The novel biomarkers in noninvasive UCB sera for predicting IH before its emergence might lead to a revolutionary clinical utility.

UHPLC-ESI-MS/MS Quantification of Relevant Substrates and Metabolites of the Kynurenine Pathway Present in Serum and Peritoneal Fluid from Gastric Cancer Patients-Method Development and Validation

Metabolites and enzymes involved in the kynurenine pathway (KP) are highly promising targets for cancer treatment, including gastrointestinal tract diseases. Thus, accurate quantification of these compounds in body fluids becomes increasingly important. The aim of this study was the development and validation of the UHPLC-ESI-MS/MS methods for targeted quantification of biologically important KP substrates (tryptophan and nicotinamide) and metabolites(kynurenines) in samples of serum and peritoneal fluid from gastric cancer patients. The serum samples were simply pretreated with trichloroacetic acid to precipitate proteins. The peritoneal fluid was purified by solid-phase extraction before analysis. Validation was carried out for both matrices independently. Analysis of the samples from gastric cancer patients showed different accumulations of tryptophan and its metabolites in different biofluids of the same patient. The protocols will be used for the evaluation of tryptophan and kynurenines in blood and peritoneal fluid to determine correlation with the clinicopathological status of gastric cancer or the disease's prognosis.

Efficacy of Analytical Technologies in Metabolomics Studies of the Gastrointestinal Cancers

According to the reports of the World Health Organization and the International Agency for Research on Cancer, cancer is the second leading cause of human death worldwide. However, early-stage detection of cancers can efficiently enhance the chance of therapy and saving lives. Metabolomics strategies apply a variety of approaches to discover new potential diagnoses, prognoses, and/or therapeutic biomarkers of various diseases. Metabolomics aims to identify and measure different low-molecular-weight biomolecules in physiological environments. In these studies, special metabolites are extracted from biological samples and identified using analytical techniques. Afterward, using data processing programs discovering significantly associated biomarkers is pursued. In the present review, we aimed to discuss recently reported analytical approaches on the metabolomics studies of gastrointestinal cancers including gastric, colorectal, and esophageal cancers. The gas- and liquid-chromatography with different detectors have been shown that are the main analytical techniques and for metabolites quantification, nuclear magnetic resonance has been utilized as a master method.

Serum Metabolic Profiling Analysis of Chronic Gastritis and Gastric Cancer by Untargeted Metabolomics

Purpose

Gastric cancer is a common tumor of the digestive system. Identification of potential molecules associated with gastric cancer progression and validation of potential biomarkers for gastric cancer diagnosis are very important. Thus, the aim of our study was to determine the serum metabolic characteristics of the serum of patients with chronic gastritis (CG) or gastric cancer (GC) and validate candidate biomarkers for disease diagnosis.

Experimental Design

A total of 123 human serum samples from patients with CG or GC were collected for untargeted metabolomic analysis via UHPLC-Q-TOF/MS to determine characteristics of the serum. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and heat map were used for multivariate analysis. In addition, commercial databases were used to identify the pathways of metabolites. Differential metabolites were identified based on a heat map with a t-test threshold (p < 0.05), fold-change threshold (FC > 1.5 or FC < 2/3) and variable importance in the projection (VIP >1). Then, differential metabolites were analyzed by receiver operating characteristic (ROC) curve to determine candidate biomarkers. All samples were analyzed for fasting lipid profiles.

Results

Analysis of serum metabolomic profiles indicated that most of the altered metabolic pathways in the three groups were associated with lipid metabolism (p < 0.05) and lipids and lipid-like molecules were the predominating metabolites within the top 100 differential metabolites (p < 0.05, FC > 1.5 or FC < 2/3, and VIP >1). Moreover, differential metabolites, including hexadecasphinganine, linoleamide, and N-Hydroxy arachidonoyl amine had high diagnostic performance according to PLS-DA. In addition, fasting lipid profile analysis showed the serum levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A1 (Apo-A1) were decreased concomitant to the progression of the progression of the disease compared with those in the control group (p < 0.05).

Conclusions

Thus, this study demonstrated that lipid metabolism may influence the development of CG to GC. Hexadecasphinganine, linoleamide, and N-Hydroxy arachidonoyl amine were selected as candidate diagnostic markers for CG and GC.

The Distinctive Serum Metabolomes of Gastric, Esophageal and Colorectal Cancers

Simple Summary

Cancer of the stomach, esophagus and colon are often fatal. Ways are being sought to establish patient-friendly screening tests that would allow these cancers to be detected earlier. Examination of the metabolomics results of cancer patient’s serum for certain metabolites unique for a particular cancer was the goal of this review. From studies conducted within the past five years several metabolites were found to be changed in cancer compared to non-cancer patients for each of the three cancers. Further confirmation of what was discovered in this review coupled with establishment of standard protocols may allow for cancer screening on patient blood samples to become routine clinical tests.

Abstract

Three of the most lethal cancers in the world are the gastrointestinal cancers—gastric (GC), esophageal (EC) and colorectal cancer (CRC)—which are ranked as third, sixth and fourth in cancer deaths globally. Early detection of these cancers is difficult, and a quest is currently on to find non-invasive screening tests to detect these cancers. The reprogramming of energy metabolism is a hallmark of cancer, notably, an increased dependence on aerobic glycolysis which is often referred to as the Warburg effect. This metabolic change results in a unique metabolic profile that distinguishes cancer cells from normal cells. Serum metabolomics analyses allow one to measure the end products of both host and microbiota metabolism present at the time of sample collection. It is a non-invasive procedure requiring only blood collection which encourages greater patient compliance to have more frequent screenings for cancer. In the following review we will examine some of the most current serum metabolomics studies in order to compare their results and test a hypothesis that different tumors, notably, from EC, GC and CRC, have distinguishing serum metabolite profiles.

The footprint of kynurenine pathway in every cancer: a new target for chemotherapy

Treatment of cancers has always been a challenge for physicians. Typically, several groups of anti-cancer medications are needed for effective management of an invasive and metastatic cancer. Recently, therapeutic potentiation of immune system markedly improved treatment of cancers. Kynurenine pathway has an interwoven correlation with immune system. Kynurenine promotes T Reg (regulatory) differentiation, which leads to increased production of anti-inflammatory cytokines and suppression of cytotoxic activity of T cells. Overactivation of kynurenine pathway in cancers provides an immunologically susceptible microenvironment for mutant cells to survive and invade surrounding tissues. Interestingly, kynurenine pathway vigorously interacts with other molecular pathways involved in tumorigenesis. For instance, kynurenine pathway interacts with phospoinosisitide-3 kinase (PI3K), extracellular signal-regulated kinase (ERK), Wnt/β-catenin, P53, bridging integrator 1 (BIN-1), cyclooxygenase 2 (COX-2), cyclin-dependent kinase (CDK) and collagen type XII α1 chain (COL12A1). Overactivation of kynurenine pathway, particularly overactivation of indoleamine 2,3-dioxygenase (IDO) predicts poor prognosis of several cancers such as gastrointestinal cancers, gynecological cancers, hematologic malignancies, breast cancer, lung cancer, glioma, melanoma, prostate cancer and pancreatic cancer. Furthermore, kynurenine increases the invasion, metastasis and chemoresistance of cancer cells. Recently, IDO inhibitors entered clinical trials and successfully passed their safety tests and showed promising therapeutic efficacy for cancers such as melanoma, brain cancer, renal cell carcinoma, prostate cancer and pancreatic cancer. However, a phase III trial of epacadostat, an IDO inhibitor, could not increase the efficacy of treatment with pembrolizumab for melanoma. In this review the expanding knowledge towards kynurenine pathway and its application in each cancer is discussed separately.

UHPLC-MS/MS profiling of histidine and bile acid metabolism in human gastric fluid for diagnosis of gastric diseases

Bile acids (BAs) are synthesized in the liver and can mediate homeostasis and various metabolism processes in the human body. Their levels in the gastrointestinal tract are closely related to various gastrointestinal diseases. In particular, farnesoid X receptor activated by free BAs is associated with overexpression of histidine decarboxylase in tumorigenesis. Therefore, comprehensive profiling of histamine (HIST), histidine (His), and BAs in biological samples can provide insight into the pathological mechanisms of gastrointestinal diseases. However, development of an analytical platform to profile HIST, His, and BAs in biological samples has several challenges such as highly different polarities between acidic and basic targets, low physiological concentrations of analytes, and high matrix interference of biological samples. In this study, an ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method combined with serial derivatization was developed to simultaneously determine HIST, His, and 5 BAs (cholic acid, deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid, and lithocholic acid) in human gastric fluid. In serial derivatization, benzoyl chloride (BzCl) and N,N-dimethylethylenediamine (DMED) were used to selectively derivatize amino and carboxyl groups of analytes, respectively. After serial derivatization, all target derivatives were determined using a reverse-phase C18 LC column and positive multiple reaction monitoring (MRM) mode, with reasonable chromatographic separation and sensitive MS detection. To accurately quantify target metabolites, 7 stable isotope-labeled internal standards were used. The MS/MS spectra of DMED and Bz derivatives exhibited specific fragments via loss of a neutral molecule (dimethylamine; 45 Da) and inductive cleavage (benzoyl; m/z 105) from protonated molecules, enabling selection of appropriate MRM transition ions for selective and sensitive detection. The developed method was validated with respect to limits of detection and quantification, linearity, precision, accuracy, stability, and matrix effect. The established method was successfully applied to human gastric fluid samples. This method provides reliable quantification of HIST, His, and BAs in human gastric fluid and will be helpful to understand pathophysiological mechanisms of gastric diseases.

Assessing the progression of gastric cancer via profiling of histamine, histidine, and bile acids in gastric juice using LC-MS/MS

Bile acid (BA) imbalance may be directly associated with gastric cancer and indirectly influence stomach carcinogenesis via overexpression of histidine decarboxylase (HDC), which converts histidine (His) into histamine (HIST). Moreover, the progression of gastric cancer, could change the gut microbiome, including bacteria spp. that produce secondary BAs. Gastric juice has various metabolites that could indicate gastric cancer-related stomach conditions. Therefore, profiling of HIST, His, and BAs in gastric juice is crucial for understanding the etiological mechanisms of gastric cancer. We used a profiling method to simultaneously determine targeted metabolites in gastric juice using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We successfully analyzed 70 human gastric juice samples from patients with chronic superficial gastritis (CSG, n = 20), intestinal metaplasia (IM, n = 12), and gastric cancer (n = 38). Furthermore, we investigated the relevance between BA metabolism and gastric cancer. There were statistical differences in the metabolism of cholic acid (CA) into deoxycholic acid (DCA) based on the progression of CSG into IM and gastric cancer. Hence, the progression of gastric cancer might be related to the alterations in gut microbiome composition. We provide insight into the etiological mechanisms of the progression of gastric cancer and biomarkers to diagnose and treat gastric cancer.

Metabolomics studies in gastrointestinal cancer: a systematic review

Introduction: This systemic review provides an overview of metabolic perturbations and possible mechanisms in gastrointestinal cancer. The authors discuss emerging challenges of technical and clinical applications.Areas covered: In this systemic review, the authors summarized the currently available results of metabolomic biomarkers linked to GI cancer, and discussed the altered metabolism pathways including carbohydrate metabolism, amino acid metabolism, lipids, and nucleotide metabolism and other metabolisms. Furthermore, future efforts need to adhere to normalize analysis procedures, validate with the larger cohort and utilize multiple-omics technologies. The search was conducted in PubMed with the following search terms (biomarker, gastrointestinal cancer, colorectal cancer, and esophageal cancer) from 2013 to 2019.Expert opinion: This systemic review summarized the currently available results of metabolomic biomarkers linked to gastrointestinal cancer, and discussed the altered metabolism pathways. The authors believe that metabolomics will benefit deeper understandings of the pathogenic mechanism, discovery of biomarkers and aid the search for drug targets as we move toward the era of personalized medicine. Personalized medication for tumors can improve the curative effect, avoid side effects and medical resource waste. As a promisingtool, metabolomics that targets the entire cancer-specific metabolite network should be applied more widely in cancer research.

Ultra-performance liquid chromatography-tandem mass spectrometry quantitative profiling of tryptophan metabolites in human plasma and its application to clinical study

A sensitive, rapid and reliable ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to assay tryptophan (TRP) and its nine metabolites, including kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HAA), xanthurenic acid (XA), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), 3-indolepropionic acid (IPA) and 3-indoleacetic acid (IAA) in human plasma. Tryptophan-d5 (TRP-d5) and carbamazepine (CAR) were applied to the method quantification, where TRP-d5 was the corresponding internal standard (IS) for TRP and KYN, and CAR was the corresponding IS for the other analytes. Plasma samples were processed by deproteinisation with acetonitrile, followed by separation on an Acquity UPLC HSS T3 column by using gradient elution with 0.1% (v/v) formic acid in water and acetonitrile and detection by electrospray ionisation tandem mass spectrometry in positive ion multiple reaction monitoring (MRM) within a total run time of 5 min. The calibration ranges were 3-600 ng/mL for 3-HK, 1.5-300 ng/mL for 5-HT, 25-5000 ng/mL for KYN, 1-200 ng/mL for XA, 100-20,000 ng/mL for TRP, 5-1000 ng/mL for KYNA, 2-400 ng/mL for 3-HAA, 2.5-500 ng/mL for 5-HIAA and 10-2000 ng/mL for IAA and IPA. All intra- and inter-day analytical variations were acceptable. Matrix effect and recovery evaluation proved that matrix effect can be negligible, and sample preparation approach was effective. The newly developed method can simultaneously determine a panel of TRP metabolites and was successfully applied in the clinical study characterising TRP metabolism in healthy volunteers.

Ex Vivo Analysis of Tryptophan Metabolism Using 19F NMR

Tryptophan, an essential amino acid, is metabolized into a variety of small molecules capable of impacting human physiology, and aberrant tryptophan metabolism has been linked to a number of diseases. There are three principal routes by which tryptophan is degraded, and thus methods for measuring metabolic flux through these pathways can be used to understand the factors that perturb tryptophan metabolism and potentially to measure disease biomarkers. Here, we describe a method utilizing 6-fluorotryptophan as a probe for detecting tryptophan metabolites in ex vivo tissue samples via ¹⁹F nuclear magnetic resonance. As a proof of concept, we demonstrate that 6-fluorotryptophan can be used to measure changes in tryptophan metabolism resulting from antibiotic-induced changes in gut microbiota composition. Taken together, we describe a general strategy for monitoring amino acid metabolism using ¹⁹F nuclear magnetic resonance that is operationally simple and does not require chromatographic separation of metabolites.

LC-MS/MS-based quantification of tryptophan metabolites and neurotransmitters in the serum and brain of mice

l-Tryptophan (Trp) metabolites and related neurotransmitters play crucial roles in physiological functions, and their imbalances are implicated in the pathology of depression, Alzheimer's disease and other diseases. Measurement of Trp metabolites and related neurotransmitters possesses a great potential to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of Trp, l-kynurenine (Kyn), kynurenic acid (Kyna), 3-hydroxykynurenine (3-HK), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE), l-glutamic acid (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) in mice serum and the brain tissues in a single chromatographic run. Samples were spiked with the internal standard, mixed with trifluoroacetic acid to precipitate protein and analyzed by LC-MS/MS. Chromatographic separation was achieved using a Restek Ultra Aqueous C18 column in combination with a gradient elution within 8 min. Mass spectrometric detection was performed using multiple reaction monitoring with electrospray ionization source in positive mode. The method exhibited good selectivity and correlation coefficient values for the calibration curves of each analyte were >0.99. The limit of detection and quantification ranged from 0.96 to 24.48 nmol/L and 3.42 to 244.82 nmol/L, respectively. The intra- and inter-day precision were ≤13.92%. All analytes were stable in prepared samples at room temperature in the autosampler for 24 h. This method was successfully applied to the analysis of biological samples from control and chronic mild stress (CMS) induced depression mice. It was found that Kyn and 3-HK pathways were enhanced by CMS, while the levels of Trp, Kyna, 5-HIAA, Glu, GABA and ACh were significantly reduced. The changes in 5-HT and NE levels were not uniform in the periphery and the brain. This method can therefore be applied to analyze Trp metabolites and related neurotransmitters levels to monitor disease states, study the mechanisms and outcomes of therapeutic interventions.

Quantitation of Neurotoxic Metabolites of the Kynurenine Pathway by Laser Desorption Ionization Mass Spectrometry (LDI-MS)

The metabolites of the mammalian kynurenine (KYN) pathway are generated from a branch of tryptophan metabolic pathway. The latter generates 3-hydroxykynurenine (3-HK), kynurenic acid (KYNA), quinolinic acid (QUIN), and picolinic acid (PIC) which are all strongly neuroactive, often with dramatically contrasting functional outcomes. Whereas KYNA and PIC are neuroprotective, 3-HK and QUIN are potently neurotoxic and attributed in major neurodegenerative diseases like schizophrenia, Alzheimer's disease, Huntington's disease, bipolar disorder, and depression. It is increasingly evident that the ratio(s) between the neurotoxic and neuroprotective metabolites may help predict the manifestations of disease vs. health. Therefore high-throughput platforms for determining the relative levels of these kynurenine metabolites in biofluids offer considerable potential. Current analytical tools for studying KYN pathway include assays of branching enzymes, PCR, immunoanalysis, and LCMS. None of these offer high-throughput, cost-effective analyses suited for clinical or drug-screening applications. In this report a laser desorption ionization mass spectrometry (LDI-MS) method is described using SBA-15 mesoporous silica. The system allows fast, high-resolution quantitation of neurotoxic kynurenines using targeted metabolomics on conventional MALDI platforms.

Simultaneous determination of tryptophan and its 31 catabolites in mouse tissues by polarity switching UHPLC-SRM-MS

Tryptophan (TRP) and its catabolites have attracted a lot of attention because of their clinical significance to human health. Recently, microbiome-gut-brain axis was found to have links to many diseases based on the imbalance of TRP catabolism. By using ultra-high performance liquid chromatography coupled to electrospray ionization triple quadrupole mass spectrometry, we present a rapid, robust and comprehensive method to determine 31 TRP catabolites covering three major pathways - kynurenic, serotonergic and bacterial degradation - within 5 min. Polarity switching was employed to analyze catabolites in both ionization modes simultaneously for greatly improved analytical throughput. The intra-day and inter-day precision were 0.5-15.8% and 1.5-16.7%, respectively. Accuracy was between 75.8 and 126.9%. The developed method was applied to study the tissue level of TRP catabolites in the liver, ileum, ileal contents, brain and plasma samples from 8 mice, and clear differences in the distribution of TRP catabolites were observed in different tissues. Ratios of key catabolites to TRP were used to evaluate the activities of specific enzyme and pathway in respective tissues. This method has potential in high throughput analysis of TRP catabolites in biological matrices, which can facilitate understanding the influence of TRP catabolites on microbiome-gut-brain axis and on human health.

Discovery and Validation of Clinical Biomarkers of Cancer: A Review Combining Metabolomics and Proteomics

Early detection and diagnosis of cancer can allow timely medical intervention, which greatly improves chances of survival and enhances quality of life. Biomarkers play an important role in assisting clinicians and health care providers in cancer diagnosis and treatment follow-up. In spite of years of research and the discovery of thousands of candidate cancer biomarkers, only a few have transitioned to routine usage in the clinic. This review highlights advances in proteomics technologies that have enabled high rates of discovery of candidate cancer biomarkers and evaluates integration with other omics technologies to improve their progress through to validation and clinical translation. Furthermore, it gauges the role of metabolomics technology in cancer biomarker research and assesses it as a complementary tool in aiding cancer biomarker discovery and validation.

Determination of Tryptophan and Its Major Metabolites in Fluid from the Anterior Chamber of the Eye in Diabetic Patients with Cataract by Liquid Chromotography Mass Spectrometry (LC-MS/MS)

Tryptophan (TRP) is to an essential amino acid and its catabolites are significant to human health. By using ultra-high-performance liquid chromatography coupled to electrospray ionization triple quadrupole mass spectrometry (UHPLC-ESI-MS/MS), levels of three major components of kynurenic pathway namely tryptophan (TRP), kynurenic acid (KYNA) and kynurenine (KYN) in fluid from the anterior chamber of the eye were determined. The analysis was carried out on a Synergi 4 μ Fusion-RP column using gradient elution mode. For quantitative determination, l-tryptophan-amino-15N, 99 ATOM % 15N was used as an internal standard. The method was linear in the concentration range 4–2000 ng mL⁻¹ for TRP, KYNA and KYN. The mean recoveries measured at four concentration levels for TRP, KYN and KYNA included the following ranges 94.3–96.1; 91.0–95.0; and 96.0–97.6%, respectively. The intra-day precision parameters were smaller than 4.4, 6.4 and 5% respectively. The developed method was applied to study the level of TRP, KYNA and KYN in eye fluid for the retrospective case series which included 28 patients suffering from cataracts and diabetes (n = 8). The experimental data was subjected to statistical analysis. The Mann-Whitney U-test revealed clear differences in the level of TRP catabolites and the ratios of TRP/KYN representing the activities of specific enzyme of kynurenine pathway in examined groups of patients. A level of probability p < 0.05 was used throughout a paper to denote statistically significant differences between the groups.

Presence of blood in gastric juice: A sensitive marker for gastric cancer screening in a poor resource setting

BACKGROUND

Gastric cancer survival rates in Africa are low as many cases are diagnosed late. Currently, there are no inexpensive, non-invasive and simple techniques that can be employed in poor resource settings for early case detection. In this study, we explored the possibility using blood in gastric juice as a screening tool to identify patients requiring referral for endoscopy.

METHODS

The study was conducted at the University Teaching Hospital endoscopy unit in Lusaka, Zambia. During esophagogastroduodenoscopy, gastric juice was aspirated and the pH determined using pH paper test strips. The presence of blood was tested using urinalysis reagent strips.

RESULTS

We enrolled 276 patients; 147(53%) were female and median age was 49 years (IQR 40-64 years). The presence of blood was associated with mucosal lesions, [OR 2.1; 95% CI 1.2-3.7, P = 0.004]. It was also associated with gastric cancer, [OR 6.7; 95% CI 2-35, P = 0.0005], even at 1:10 and 1:100 dilutions, [OR 5.4; 95% CI 2.3-13.8, P<0.0001] and [OR 9.1; 95% CI 3.5-23, P<0.0001] respectively. The sensitivity for gastric cancer detection using blood in gastric juice was 91% and the specificity was 41%. Analysis using the intensity of blood in gastric juice yielded an area under the receiver operating characteristic curve of 0.78; 95% CI 0.71-0.86 with a sensitivity of 79% and a specificity of 77%.

CONCLUSIONS

The presence of blood in gastric juice is associated with gastric mucosal lesions. It has a high sensitivity but low specificity for gastric cancer detection.

Tetraspanin family identified as the central genes detected in gastric cancer using bioinformatics analysis

Gastric cancer has become a serious disease in the past decade. It has the second highest mortality rate among the four most common cancer types, leading to ~700,000 mortalities annually. Previous studies have attempted to elucidate the underlying biological mechanisms of gastric cancer. The present study aimed to obtain useful biomarkers and to improve the understanding of gastric cancer mechanisms at the genetic level. The present study used bioinformatics analysis to identify 1,829 differentially expressed genes (DEGs) which were obtained from the GSE54129 dataset. Using protein‑protein interaction information from the Search Tool for the Retrieval of Interacting Genes database, disease modules were constructed for gastric cancer using Cytoscape software. In the Gene Ontology analysis of biology processes, upregulated genes were significantly enriched in 'extracellular matrix organization', 'cell adhesion' and 'inflammatory response', whereas downregulated DEGs were significantly enriched in 'xenobiotic metabolic process', 'oxidation‑reduction process' and 'steroid metabolic process'. During Kyoto Encyclopedia of Genes and Genomes analysis, upregulated DEGs were significantly enriched in 'extracellular matrix‑receptor interaction', 'focal adhesion' and 'PI3K‑Akt signaling pathway', whereas the downregulated DEGs were significantly enriched in 'chemical carcinogenesis', 'metabolism of xenobiotics by cytochrome P450' and 'peroxisome'. The present study additionally identified 10 hub genes from the DEGs: Tumor protein p53 (TP53), C‑X‑C motif chemokine ligand 8 (CXCL8), tetraspanin 4 (TSPAN4), lysophosphatidic acid receptor 2 (LPAR2), adenylate cyclase 3 (ADCY3), phosphoinositide‑3‑kinase regulatory subunit 1 (PIK3R1), neuromedin U (NMU), C‑X‑C motif chemokine ligand (CXCL12), fos proto‑oncogene, AP‑1 transcription factor subunit (FOS) and sphingosine‑1‑phosphate receptor 1 (S1PR1), which have high degrees with other DEGs. The survival analysis revealed that the high expression of ADCY3, LPAR2, S1PR1, TP53 and TSPAN4 was associated with a lower survival rate, whereas high expression of CXCL8, FOS, NMU and PIK3R1 was associated with a higher survival rate. No significant association was identified between CXCL12 and survival rate. Additionally, TSPAN1 and TSPAN8 appeared in the top 100 DEGs. Finally, it was observed that 4 hub genes were highly expressed in gastric cancer tissue compared with para‑carcinoma tissue in the 12 patients; the increased TSPAN4 was significant (>5‑fold). Tetraspanin family genes may be novel biomarkers of gastric cancer. The findings of the present study may improve the understanding of the molecular mechanisms underlying the development of gastric cancer.

Gastric cancer: Metabolic and metabolomics perspectives (Review)

Gastric cancer is one of the most malignant tumors worldwide and remains a major health threat in Asia-Pacific regions, while its pathological mechanism is generally unknown. Recent research has advanced the understanding of the relationship between metabolic reprogramming and carcinogenesis. In particular, metabolic regulation and cancer research are being further brought into sharp focus with the emergence of metabolomics. Not only can metabolomics provide global information on metabolic profiles of specific tumors, but it can also act as a promising tool to discover biomarkers regarding diagnosis, metastatic surveillance and chemotherapeutic sensitivity prediction. Meanwhile, metabolism-based anticancer therapies will be further discovered. Up to now, accumulative studies have highlighted the application of metabolomics in gastric cancer research regarding different aspects; therefore we summarized the current available results of how metabolic changes are linked to gastric carcinogenesis, and how metabolomics holds promise for the diagnosis, metastatic surveillance, treatment and prognosis prediction of gastric cancer.