Separation and identification of purine nucleosides in the urine of patients with malignant cancer by reverse phase liquid chromatography/electrospray tandem mass spectrometry

The causal relationship between CSF metabolites and GBM: a two-sample mendelian randomization analysis

BACKGROUND

Glioblastoma multiforme (GBM) is a highly aggressive primary malignant brain tumor characterized by rapid progression, poor prognosis, and high mortality rates. Understanding the relationship between cerebrospinal fluid (CSF) metabolites and GBM is crucial for identifying potential biomarkers and pathways involved in the pathogenesis of this devastating disease.

METHODS

In this study, Mendelian randomization (MR) analysis was employed to investigate the causal relationship between 338 CSF metabolites and GBM. The data for metabolites were obtained from a genome-wide association study summary dataset based on 291 individuals, and the GBM data was derived from FinnGen included 91 cases and 174,006 controls of European descent. The Inverse Variance Weighted method was utilized to estimate the causal effects. Supplementary comprehensive assessments of causal effects between CSF metabolites and GBM were conducted using MR-Egger regression, Weighted Median, Simple Mode, and Weighted Mode methods. Additionally, tests for heterogeneity and pleiotropy were performed.

RESULTS

Through MR analysis, a total of 12 identified metabolites and 2 with unknown chemical properties were found to have a causal relationship with GBM. 1-palmitoyl-2-stearoyl-gpc (16:0/18:0), 7-alpha-hydroxy-3-oxo-4-cholestenoate, Alpha-tocopherol, Behenoyl sphingomyelin (d18:1/22:0), Cysteinylglycine, Maleate, Uracil, Valine, X-12,101, X-12,104 and Butyrate (4:0) are associated with an increased risk of GBM. N1-methylinosine, Stachydrine and Succinylcarnitine (c4-dc) are associated with decreased GBM risk.

CONCLUSION

In conclusion, this study sheds light on the intricate interplay between CSF metabolites and GBM, offering novel perspectives on disease mechanisms and potential treatment avenues. By elucidating the role of CSF metabolites in GBM pathogenesis, this research contributes to the advancement of diagnostic capabilities and targeted therapeutic interventions for this aggressive brain tumor. Further exploration of these findings may lead to improved management strategies and better outcomes for patients with GBM.

Targeted quantitative metabolomics with a linear mixed-effect model for analysis of urinary nucleosides and deoxynucleosides from bladder cancer patients before and after tumor resection

In the present study, we developed and validated a fast, simple, and sensitive quantitative method for the simultaneous determination of eleven nucleosides and deoxynucleosides from urine samples. The analyses were performed with the use of liquid chromatography coupled with triple quadrupole mass spectrometry. The sample pretreatment procedure was limited to centrifugation, vortex mixing of urine samples with a methanol/water solution (1:1, v/v), evaporation and dissolution steps. The analysis lasted 20 min and was performed in dynamic multiple reaction monitoring mode (dMRM) in positive polarity. Process validation was conducted to determine the linearity, precision, accuracy, limit of quantification, stability, recovery and matrix effect. All validation procedures were carried out in accordance with current FDA and EMA regulations. The validated method was applied for the analysis of 133 urine samples derived from bladder cancer patients before tumor resection and 24 h, 2 weeks, and 3, 6, 9, and 12 months after the surgery. The obtained data sets were analyzed using a linear mixed-effect model. The analysis revealed that concentration level of 2-methylthioadenosine was decreased, while for inosine, it was increased 24 h after tumor resection in comparison to the preoperative state. The presented quantitative longitudinal study of urine nucleosides and deoxynucleosides before and up to 12 months after bladder tumor resection brings additional prospective insight into the metabolite excretion pattern in bladder cancer disease. Moreover, incurred sample reanalysis was performed proving the robustness and repeatability of the developed targeted method.

Recent developments in DNA adduct analysis using liquid chromatography coupled with mass spectrometry

The formation of DNA adducts by genotoxic agents is an early event in cancer development, and it may lead to gene mutations, thereby initiating tumor development. The measurement of DNA adducts can provide critical information about the genotoxic potential of a chemical and its mechanism of carcinogenesis. In recent decades, liquid chromatography coupled with mass spectrometry has become the most important technique for analyzing DNA adducts. The improvements in resolution achievable with new chromatographic separation techniques coupled with the high specificity and sensitivity and wide dynamic range of new mass spectrometry systems have been used for both qualitative and quantitative analyses of DNA adducts. This review discusses the challenges in qualitative and quantitative analyses of DNA adducts by liquid chromatography coupled with mass spectrometry and highlights recent developments towards overcoming the limitations of liquid chromatography coupled with mass spectrometry methods. The key steps and new solutions, such as sample preparation, mass spectrometry fragmentation, and method validation, are summarized. In addition, the fundamental principles and latest advances in DNA adductomic approaches are reviewed.

Urinary Nucleosides and Deoxynucleosides

Urinary nucleosides and deoxynucleosides are mainly known as metabolites of RNA turnover and oxidative damage of DNA. For several decades these metabolites have been examined for their potential use in disease states including cancer and oxidative stress. Subsequent improvements in analytical sensitivity and specificity have provided a reliable means to measure these unique molecules to better assess their relationship to physiologic and pathophysiologic conditions. In fact, some are currently used as antiviral and antitumor agents. In this review we provide insight into their molecular characteristics, highlight current separation techniques and detection methods, and explore potential clinical usefulness.

Application of DNA adductomics to soil bacterium Sphingobium sp. strain KK22

Toward the development of ecotoxicology methods to investigate microbial markers of impacts of hydrocarbon processing activities, DNA adductomic analyses were conducted on a sphingomonad soil bacterium. From growing cells that were exposed or unexposed to acrolein, a commonly used biocide in hydraulic fracturing processes, DNA was extracted, digested to 2'-deoxynucleosides and analyzed by liquid chromatography-positive ionization electrospray-tandem mass spectrometry in selected reaction monitoring mode transmitting the [M + H](+) > [M + H - 116](+) transition over 100 transitions. Overall data shown as DNA adductome maps revealed numerous putative DNA adducts under both conditions with some occurring specifically for each condition. Adductomic analyses of triplicate samples indicated that elevated levels of some targeted putative adducts occurred in exposed cells. Two exposure-specific adducts were identified in exposed cells as 3-(2'-deoxyribosyl)-5,6,7,8-tetrahydro-6-hydroxy-(and 8-hydroxy-)pyrimido[1,2-a]- purine-(3H)-one (6- and 8-hydroxy-PdG) following synthesis of authentic standards of these compounds and subsequent analyses. A time course experiment showed that 6- and 8-hydroxy-PdG were detected in bacterial DNA within 30 min of acrolein exposure but were not detected in unexposed cells. This work demonstrated the first application of DNA adductomics to examine DNA damage in a bacterium and sets a foundation for future work.

A novel method of liquid chromatography-tandem mass spectrometry combined with chemical derivatization for the determination of ribonucleosides in urine

Ribonucleosides are the end products of RNA metabolism. These metabolites, especially the modified ribonucleosides, have been extensively evaluated as cancer-related biomarkers. However, the determination of urinary ribonucleosides is still a challenge due to their low abundance, high polarity and serious matrix interferences in urine samples. In this study, a derivatization method based on a chemical reaction between ribonucleosides and acetone to form acetonides was developed for the determination of urinary ribonucleosides. The derivative products, acetonides, were detected by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The methodological evaluation was performed by quantifying four nucleosides for linear range, average recovery, precision, accuracy and stability. The validated procedures were applied to screen modified ribonucleosides in urine samples. Improvement of separation and enhancement of sensitivity were obtained in the analysis. To identify ribonucleosides, inexpensive isotope labeling acetone (acetone-d6) and label-free acetone were applied to form ordinary and deuterated acetonides, respectively. The two groups of samples were separated with orthogonal partial least squares (OPLS). The ordinary and deuterated pairs of acetonides were symmetrically distributed in the S-plot for easy and visual signal identification. After structural confirmation, a total of 56 ribonucleosides were detected, 52 of which were modified ribonucleosides. The application of derivatization, deuterium-labeling and multivariate statistical analysis offers a new option for selective detection of ribonucleosides in biological samples.

Chlorine substitution promotes phenyl radical loss from C8-phenoxy-2'-deoxyguanosine adducts: implications for biomarker identification from chlorophenol exposure

Chlorophenols are persistent organic pollutants, which undergo peroxidase-mediated oxidation to afford phenolic radical intermediates that react at the C8-site of 2'-deoxyguanosine (dG) to generate oxygen-linked C8-dG adducts. Such adducts are expected to contribute to chlorophenol toxicity and serve as effective dose biomarkers for chlorophenol exposure. Electrospray ionization mass spectrometry (ESI-MS) was employed to study collision induced dissociation (CID) for a family of such phenolic O-linked C8-dG adducts. Fragmentation of the deprotonated nucleosides demonstrates that an unexpected homolytic cleavage of the ether linkage to release phenyl radicals and a nucleoside distonic ion with m/z 281 competes effectively with commonly observed breakage of the glycosidic bond to release the deprotonated nucleobase. Increased chlorination of the phenyl ring enhances phenyl radical loss. Density functional theory calculations demonstrate that Cl-substitution decreases phenyl radical stability but promotes homolytic breakage of the C8-phenyl bond in the C8-dG adduct. The calculations suggest that phenyl radical loss is driven by destabilizing steric (electrostatic repulsion) interactions between the ether oxygen atom and ortho-chlorines on the phenyl ring. The distonic ion at m/z 281 represents a unique dissociation product for deprotonated O-linked C8-dG adducts and may prove useful for selective detection of relevant biomarkers for chlorophenol exposure by tandem mass spectrometry using selective reaction monitoring.

Development of urinary pseudotargeted LC-MS-based metabolomics method and its application in hepatocellular carcinoma biomarker discovery

Hepatocellular carcinoma (HCC) is one of the pestilent malignancies leading to cancer-related death. Discovering effective biomarkers for HCC diagnosis is an urgent demand. To identify potential metabolite biomarkers, we developed a urinary pseudotargeted method based on liquid chromatography-hybrid triple quadrupole linear ion trap mass spectrometry (LC-QTRAP MS). Compared with nontargeted method, the pseudotargeted method can achieve better data quality, which benefits differential metabolites discovery. The established method was applied to cirrhosis (CIR) and HCC investigation. It was found that urinary nucleosides, bile acids, citric acid, and several amino acids were significantly changed in liver disease groups compared with the controls, featuring the dysregulation of purine metabolism, energy metabolism, and amino metabolism in liver diseases. Furthermore, some metabolites such as cyclic adenosine monophosphate, glutamine, and short- and medium-chain acylcarnitines were the differential metabolites of HCC and CIR. On the basis of binary logistic regression, butyrylcarnitine (carnitine C4:0) and hydantoin-5-propionic acid were defined as combinational markers to distinguish HCC from CIR. The area under curve was 0.786 and 0.773 for discovery stage and validation stage samples, respectively. These data show that the established pseudotargeted method is a complementary one of targeted and nontargeted methods for metabolomics study.

Mass spectrometry analysis of nucleosides and nucleotides

Mass spectrometry has been widely utilised in the study of nucleobases, nucleosides and nucleotides as components of nucleic acids and as bioactive metabolites in their own right. In this review, the application of mass spectrometry to such analysis is overviewed in relation to various aspects regarding the analytical mass spectrometric and chromatographic techniques applied and also the various applications of such analysis.

Urinary nucleosides as biomarkers of breast, colon, lung, and gastric cancer in Taiwanese

Urinary nucleosides are associated with many types of cancer. In this study, six targeted urinary nucleosides, namely adenosine, cytidine, 3-methylcytidine, 1-methyladenosine, inosine, and 2-deoxyguanosine, were chosen to evaluate their role as biomarkers of four different types of cancer: lung cancer, gastric cancer, colon cancer, and breast cancer. Urine samples were purified using solid-phase extraction (SPE) and then analyzed using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The Mann-Whitney U test and Principal Component Analysis (PCA) were used to compare differences in urinary nucleosides between patients with one of four types of cancer and healthy controls. The diagnostic sensitivity of single nucleosides for different types of cancer ranged from 14% to 69%. In contrast, the diagnostic sensitivity of a set of six nucleosides ranged from 37% to 69%. The false-positive identification rate associated with the set of six nucleosides in urine was less than 2% compared with that of less than 5% for a single nucleoside. Furthermore, combining the set of six urinary nucleosides with carcinoembryonic antigen improved the diagnostic sensitivity for colon cancer. In summary, the study show that a set of six targeted nucleosides is a good diagnostic marker for breast and colon cancers but not for lung and gastric cancers.

Hydrophilic interaction ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry for determination of nucleotides, nucleosides and nucleobases in Ziziphus plants

In this study, a rapid and sensitive analytical method was developed for the determination of 20 nucleobases, nucleosides and nucleotides in Ziziphus plants at trace levels by using hydrophilic interaction ultra-high performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry (HILIC-UHPLC-TQ-MS/MS) in multiple-reaction monitoring (MRM) mode. Under the optimized chromatographic conditions, good separation for 20 target compounds were obtained on a UHPLC Amide column with sub-2μm particles within 10min. The overall LODs and LOQs were between 0.11-3.12ngmL(-1) and 0.29-12.48ngmL(-1) for the 20 analytes, respectively. It is the first report about simultaneous analysis of nucleobases, nucleosides and nucleotides in medicinal plants using HILIC-UHPLC-TQ-MS/MS method, which affords good linearity, precision, repeatability and accuracy. The developed method was successfully applied to Ziziphus plant (Z. jujuba, Z. jujuba var. spinosa and Z. mauritiana) samples. The analysis showed that the fruits and leaves of Ziziphus plants are rich in nucleosides and nucleobases as well as nucleotides, and could be selected as the healthy food resources. Our results in present study suggest that HILIC-UHPLC-TQ-MS/MS method could be employed as a useful tool for quality assessment of the samples from the Ziziphus plants as well as other medicinal plants or food samples using nucleotides, nucleosides and nucleobases as markers.

Concurrent profiling of indole-3-acetic acid, abscisic acid, and cytokinins and structurally related purines by high-performance-liquid-chromatography tandem electrospray mass spectrometry

BACKGROUND

Cytokinins (CKs) are a group of plant growth regulators that are involved in several plant developmental processes. Despite the breadth of knowledge surrounding CKs and their diverse functions, much remains to be discovered about the full potential of CKs, including their relationship with the purine salvage pathway, and other phytohormones. The most widely used approach to query unknown facets of CK biology utilized functional genomics coupled with CK metabolite assays and screening of CK associated phenotypes. There are numerous different types of assays for determining CK quantity, however, none of these methods screen for the compendium of metabolites that are necessary for elucidating all roles, including purine salvage pathway enzymes in CK metabolism, and CK cross-talk with other phytohormones. Furthermore, all published analytical methods have drawbacks ranging from the required use of radiolabelled compounds, or hazardous derivatization reagents, poor sensitivity, lack of resolution between CK isomers and lengthy run times.

RESULTS

In this paper, a method is described for the concurrent extraction, purification and analysis of several CKs (freebases, ribosides, glucosides, nucleotides), purines (adenosine monophosphate, inosine, adenosine, and adenine), indole-3-acetic acid, and abscisic acid from hundred-milligram (mg) quantities of Arabidopsis thaliana leaf tissue. This method utilizes conventional Bieleski solvents extraction, solid phase purification, and is unique because of its diverse range of detectable analytes, and implementation of a conventional HPLC system with a fused core column that enables good sensitivity without the requirement of a UHPLC system. Using this method we were able to resolve CKs about twice as fast as our previous method. Similarly, analysis of adenosine, indole-3-acetic acid, and abscisic acid, was comparatively rapid. A further enhancement of the method was the utilization of a QTRAP 5500 mass analyzer, which improved upon several aspects of our previous analytical method carried out on a Quattro mass analyzer. Notable improvements included much superior sensitivity, and number of analytes detectable within a single run. Limits of detection ranged from 2 pM for (9G)Z to almost 750 pM for indole-3-acetic acid.

CONCLUSIONS

This method is well suited for functional genomics platforms tailored to understanding CK metabolism, CK interrelationships with purine recycling and associated hormonal cross-talk.

Revisiting the reactivity of uracil during collision induced dissociation: tautomerism and charge-directed processes

In our recent work towards the nontarget identification of products of nucleic acid (NA) damage in urine, we have found previous work describing the dissociation of NA bases not adequate to fully explain their observed reactivity. Here we revisit the gas-phase chemistry of protonated uracil (U) during collision induced dissociation (CID) using two modern tandem mass spectrometry techniques; quadrupole ion trap (QIT) and quadrupole time of flight (Q-TOF). We present detailed mechanistic proposals that account for all observed products of our experiments and from previous isotope labeling data, and that are supported by previous ion spectroscopy results and theoretical work. The diverse product-ions of U cannot be explained adequately by only considering the lowest energy form of protonated U as a precursor. The tautomers adopted by U during collisional excitation make it possible to relate the complex reactivity observed to reasonable mechanistic proposals and feasible product-ion structures for this small highly conjugated heterocycle. These reactions proceed from four different stable tautomers, which are excited to a specific activated precursor from which dissociation can occur via a charge-directed process through a favorable transition state to give a stabilized product. Understanding the chemistry of uracil at this level will facilitate the identification of new modified uracil derivatives in biological samples based solely on their reactivity during CID. Our integrated approach to describing ion dissociation is widely applicable to other NA bases and similar classes of biomolecules.

3-(3-amino-3-carboxypropyl)-5,6-dihydrouridine is one of two novel post-transcriptional modifications in tRNALys(UUU) from Trypanosoma brucei

tRNA is the most heavily modified of all RNA types, with typically 10-20% of the residues being post-transcriptionally altered. Unravelling the modification pattern of a tRNA is a challenging task; there are 92 currently known tRNA modifications, many of which are chemically similar. Furthermore, the tRNA has to be investigated with single-nucleotide resolution in order to ensure complete mapping of all modifications. In the present work, we characterized tRNA(Lys)(UUU) from Trypanosoma brucei, and provide a complete overview of its post-transcriptional modifications. The first step was MALDI-TOF MS of two independent digests of the tRNA, with RNase A and RNase T1, respectively. This revealed digestion products harbouring mass-changing modifications. Next, the modifications were mapped at the nucleotide level in the RNase products by tandem MS. Comparison with the sequence of the unmodified tRNA revealed the modified residues. The modifications were further characterized at the nucleoside level by chromatographic retention time and fragmentation pattern upon higher-order tandem MS. Phylogenetic comparison with modifications in tRNA(Lys) from other organisms was used through the entire analysis. We identified modifications on 12 nucleosides in tRNA(Lys)(UUU), where U47 exhibited a novel modification, 3-(3-amino-3-carboxypropyl)-5,6-dihydrouridine, based on identical chromatographic retention and MS fragmentation as the synthetic nucleoside. A37 was observed in two versions: a minor fraction with the previously described 2-methylthio-N(6)-threonylcarbamoyl-modification, and a major fraction with A37 being modified by a 294.0-Da moiety. The latter product is the largest adenosine modification reported so far, and we discuss its nature and origin.

Development and validation of a hydrophilic interaction chromatography-tandem mass spectrometry method with on-line polar extraction for the analysis of urinary nucleosides. Potential application in clinical diagnosis

The present paper describes the development, validation and application of a quantitative method for the determination of endogenous nucleosides and nucleobases in urine based on the on-line coupling of a solid-phase extraction step with hydrophilic interaction chromatography-tandem mass spectrometry. The method combines the use of a highly polar restricted-access material (RAM), based on an N-vinylacetamide copolymer, for efficient analyte extraction and matrix removal, with separation by zwitterionic hydrophilic interaction chromatography (ZIC-HILIC), that revealed a satisfactory retention of the polar analytes studied. Detection using a triple quadrupole analyser allowed reliable identification and high-sensitivity quantitation of the target compounds. The on-line configuration developed, RAM-ZIC-HILIC-MS/MS, provides a convenient approach to automate the application to urine analysis, with minimum sample manipulation. The whole method was validated according to European Legislation for bioanalytical methods. The validation steps included the verification of matrix effects, calibration curve, precision, accuracy, selectivity, stability and carry-over in real samples. The results of the validation process revealed that the proposed method is suitable for the reliable determination of nucleosides and nucleobases in human urine, showing limits of detection from 0.1 to 1.3 ng mL(-1). The application to clinical samples was also checked; the results obtained in analyses of urine samples from healthy volunteers and cancer patients using Principal Component Analysis, Hierarchical Cluster Analysis and Soft Independent Modeling of Class Analogy are also shown.

Evaluation of urinary ribonucleoside profiling for clinical biomarker discovery using constant neutral loss scanning liquid chromatography/tandem mass spectrometry

The patterns and levels of urinary excreted ribonucleosides which reflect RNA turnover and metabolism in humans offer the potential for early detection of disease and monitoring of therapeutic intervention. A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method employing constant neutral loss (CNL) scanning for the loss of the ribose moiety (132 u) was used to detect ribonucleosides in human urine and to evaluate this analytical platform for biomarker research in clinical trials. Ribonucleosides were stable and not influenced by the time spent at room temperature prior to freezing or long-term storage at -80 °C. Matrix effects caused variation in the mass spectrometer response which was dependent on the concentration of the analysed urine sample. For the use of urinary ribonucleoside profiling in clinical biomarker studies, adjustment of the urine samples to a common concentration prior to sample preparation is therefore advocated. Changes in the mass spectrometer response should be accounted for by the use of an internal standard added after sample preparation. Diurnal variation exceeded inter-day variation of an individual's ribonucleoside profile, but inter-person differences were predominant and allowed the separation of individuals against each other in a multivariate space. Due to considerable diurnal variation the use of spot urine samples would introduce unnecessary variation and should be replaced by the collection of multiple spot urine samples across the day, where possible. Should such a protocol not be feasible, biological intra-day and inter-day variation must be considered and accounted for in the data interpretation.

Exploring the roles of nucleobase desolvation and shape complementarity during the misreplication of O(6)-methylguanine

O(6)-methylguanine (O(6)-MeG) is a miscoding DNA lesion arising from the alkylation of guanine. This report uses the bacteriophage T4 DNA polymerase as a model to probe the roles of hydrogen-bonding interactions, shape/size, and nucleobase desolvation during the replication of this miscoding lesion. This was accomplished by using transient kinetic techniques to monitor the kinetic parameters for incorporating and extending natural and nonnatural nucleotides. In general, the efficiency of nucleotide incorporation does not depend on the hydrogen-bonding potential of the incoming nucleotide. Instead, nucleobase hydrophobicity and shape complementarity appear to be the preeminent factors controlling nucleotide incorporation. In addition, shape complementarity plays a large role in controlling the extension of various mispairs containing O(6)-MeG. This is evident as the rate constants for extension correlate with proper interglycosyl distances and symmetry between the base angles of the formed mispair. Base pairs not conforming to an acceptable geometry within the polymerase's active site are refractory to elongation and are processed via exonuclease proofreading. The collective data set encompassing nucleotide incorporation, extension, and excision is used to generate a model accounting for the mutagenic potential of O(6)-MeG observed in vivo. In addition, kinetic studies monitoring the incorporation and extension of nonnatural nucleotides identified an analog that displays high selectivity for incorporation opposite O(6)-MeG compared to unmodified purines. The unusual selectivity of this analog for replicating damaged DNA provides a novel biochemical tool to study translesion DNA synthesis.

Metabolomic analysis of human plasma from haemodialysis patients

BACKGROUND

Urea and creatinine are widely used as biomarkers for disease. However, these parameters have been criticized as markers for several reasons. Thus, we conducted this study to identify novel biomarkers that can be used as alternatives to urea and creatinine to estimate the adequate dialysis dose by metabolomic analyses of plasma samples from patients undergoing haemodialysis.

MATERIAL AND METHODS

Liquid chromatography-electrospray ionization (ESI)-time-of-flight mass spectrometry (MS) was used to analyse low molecular weight molecules present in the plasma samples of 10 patients with end-stage renal disease (ESRD) who were being treated with haemodialysis, and in 16 healthy subjects.

RESULTS

In plasma samples obtained after haemodialysis, the relative quantities of 54 peaks were significantly (P < 0·05) decreased when compared with those in the plasma before haemodialysis. The candidate biomarkers were allocated to three groups. Molecules in Group A improved completely with a large variance, molecules in Group B improved partially but with a large variance, and molecules in Group C improved partially with low variance after haemodialysis. Small cohort validation study consisting of the patients with ESRD undergoing haemodialysis indicates that three candidate biomarkers in Group C would be a very useful marker to estimate adequate haemodialysis dose.

CONCLUSIONS

1-Methylinosine and two unknown molecules whose m/z at ESI-positive mode are 257·1033 and 413·1359 were found as effective candidate biomarkers to estimate adequate haemodialysis dose, which has to be confirmed in prospective studies.

Targeted serum metabolite profiling of nucleosides in esophageal adenocarcinoma

Nucleosides are indicators of the whole-body turnover of transfer RNA. Based on the activity of cancer cells these molecules could potentially be used as cancer biomarkers, and several studies have determined that the metabolic levels of nucleosides are significantly altered in cancer patients compared to control groups. Here we report a targeted metabolite investigation of serum nucleosides in esophageal adenocarcinoma specimens. We quantified eight nucleosides using high-performance liquid chromatography/triple quadrupole mass spectrometry (HPLC/TQMS) and determined that the metabolic levels of 1-methyladenosine (p <2.14 × 10(-7)), N(2),N(2)-dimethylguanosine (p <2.78 × 10(-7)), N(2)-methylguanosine (p <2.48 × 10(-6)) and cytidine (p <6.98 × 10(-4)) were significantly elevated while the concentration of uridine (p <3.74 × 10(-3)) was significantly lowered in serum samples from cancer patients compared to those of control group. Our results suggest that nucleosides could potentially serve as useful biomarkers to identify esophageal adenocarcinoma.

Identification of a 2-cell stage specific inhibitor of the cleavage of preimplantation mouse embryos synthesized by rat hepatoma cells as 5′-deoxy-5′-methylthioadenosine

Rat hepatoma Reuber H-35 cells produce a unique compound designated as Fr.B-25, a 2-cell stage-specific inhibitor of the cleavage of preimplantation mouse embryos culturedin vitro. Here, we identified Fr.B-25 as a purine nucleoside, 5′-deoxy-5′-methylthioadenosine (MTA), by mass spectroscopic analysis. All of the biological activities examined of authentic MTA on the development of mouse zygotes were indistinguishable from those of Fr.B-25. The mechanism of MTA action in the development of preimplantation mouse embryos was probably different from those of hypoxanthine and adenosine, which are well-characterized purine nucleosides that act as inhibitors of the cleavage of mouse 2-cell embryos. From the shared molecular and biological properties of Fr.B-25 and MTA, we concluded that Fr.B-25 is MTA. To the best of our knowledge, this is the first delineation of the effect of MTA on the development of preimplantation mammalian embryos culturedin vitro.