Determination of arginine and methylated arginines in human plasma by liquid chromatography-tandem mass spectrometry

Validation and application of volumetric absorptive microsampling (VAMS) dried blood method for phenylalanine measurement in patients with phenylketonuria

BACKGROUND

Frequent blood phenylalanine (Phe) measurement is required for phenylketonuria (PKU) patients for diagnosis and disease status monitoring. Though various methods are available for blood Phe measurement, there is a lack of validated quantitative methods for measuring Phe with less than 15% variability. A method to allow at home blood sample collection for the PKU community is in high demand.

METHODS

A volumetric absorptive microsampling (VAMS) dried blood collection high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed and fully validated for blood Phe measurement in compliance with regulatory guidances. The method accuracy, precision, stability, selectivity, matrix and hematocrit effects were assessed. A venous plasma collection HPLC-MS/MS method was developed and validated as a reference method. 311 matching VAMS and plasma samples were collected from 24 PKU subjects in a Phase 2 clinical study. Phe measurements using the two methods were compared.

RESULTS

Both VAMS and the plasma sample collection methods met the acceptance criteria for Good Laboratory Practice (GLP) bioanalytical analysis. Comparisons showed a high Pearson's correlation of 0.9813. The Passing-Bablok analysis showed that the difference was estimated to be less than 5% and Bland Altman analysis indicated that the difference was proportional with Phe concentration and for the majority of samples (88.85%) the measurement was within ±20% difference. Following 7 days treatment with 60 or 20 mg/kg/day PTC923 (Sepiapterin) or 20 mg/kg/day sapropterin, PKU patients exhibited respectively -206.4, -146.9, and -91.5 µmol/L reductions of blood Phe as measured by the VAMS method.

CONCLUSIONS

Concordant results were obtained using VAMS and plasma methods, which demonstrated that VAMS is a reliable method for clinical applications to monitor blood Phe for PKU patients.

PMMA/paper hybrid microfluidic chip for simultaneous determination of arginine and valine in human plasma

The simultaneous determination is reported of arginine (Arg) and valine (Val) amino acids in plasma using flower-shaped μPADs and PMMA/paper hybrid microfluidic chip based on AuNPs capped with R-thiazolidine-4-carboxylic acid (THP). In this article, the evaluation procedure is based on the smartphone colorimetric detection mechanism that results from the aggregation of the THP-AuNPs with the addition of amino acids and visual color change from red to blue. Arg and Val were selectively determined with good reproducibility and an acceptable linearity range. The flower-shaped (μPADs) provides many advantages, including low cost, reasonable sensitivity, simple and fast performance, simultaneous detection, disposable use, and high sample throughput compared with conventional colorimetric method using cuvette cells. The ratios between the absorbance wavelength at (A₆₅₀/A₅₂₅) and (A₆₈₅/A₅₂₅) are linearly proportional to the concentration of Arg and Val. Under the optimum conditions, the calibration range in aqueous solutions is 0.0068-100.0 and 0.0056-75.0 µM with a limit of detection of 2.25 and 1.86 nM for Arg and Val at pH 7.0, respectively. In the case of μPADs, the calibration curves for Arg and Val showed good linearity in the concentration range 0.01-75.0 µM. The detection limits for the analytes were 3.51 nM and 3.44 nM for Arg and Val, respectively. In addition, a PMMA/paper hybrid microfluidic chip was successfully employed to determine Arg and Val in plasma samples with a relative error below 5%.

Binding the gap between experiments, statistics, and method comparison: A tutorial for computing limits of detection and quantification in univariate calibration for complex samples

The present tutorial aims to review the most frequently reported criteria for the calculation of the limits of detection (LOD) and quantification (LOQ) in univariate calibration, summarizing their fundamentals, advantages, and limitations. The current criteria for estimating LOD and LOQ are based on diverse theoretical and/or empirical assumptions and require different amounts of experimental data, making the calculation rather complex in some cases. Moreover, alternative forms for calculating LOD/LOQ frequently lead to dissimilar results. This scenario might worsen in the case of complex analytical systems. Throughout this tutorial, different forms of calculating LOD/LOQ are illustrated using previously reported experimental datasets in the environmental chemistry field as examples. The influence of the sample matrix during the estimation of LOD/LOQ parameters is investigated through one calibration approache. The discrepancies in the obtained results with different criteria for the calculation of LOD/LOQ are highlighted. Finally, general guidelines and recommendations regarding experimental and data processing issues are proposed, aiming to promote fair criteria for the comparison of different analytical methodologies in terms of prediction ability and detection capability.

Pyranopyrazole based Schiff base for rapid colorimetric detection of arginine in aqueous and real samples

A novel pyranopyrazole-based Schiff base PPS has been synthesized via a condensation reaction between aldehyde and hydrazide derivatives of pyranopyrazole.

Blood Microsampling to Monitor Metabolic Profiles During Physical Exercise

Monitoring approaches and technical improvements are key factors to improve a sportsman’s health, training, and recovery after an injury. In this study, a targeted metabolomics approach using microsampling with hemaPEN^® was developed to measure changes in blood concentrations of nine amino acids and four organic acids before, during, and after exercise. The aim of this research project was to investigate if a reliable monitoring of metabolite levels during sports activity can be achieved by collecting one drop of whole blood at different time points. A hemaPEN device is an easy-to-use and noninvasive microsampling technique designed to collect four accurate and precise blood volumes simultaneously (10.96 µl). Twenty healthy volunteers between 19 and 30 years of age were included in this study. Physical activity consisted in running as fast as possible 1,600 m after 400 m warm-up. One drop of blood was collected at five time points: before exercise, after 800-m running, after 1,600 m, and 30 min and 60 min after finishing the exercise. The influence of physical activity on metabolite levels was evaluated using two ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) methods. Analytical performance criteria such as metabolite stability, method precision, trueness, and accuracy were found to be satisfactory. Expected significant metabolic changes were identified for lactic acid, main TCA cycle intermediates, and some amino acids (e.g., creatinine, choline, and taurine). This preliminary study performed on a small cohort demonstrated a high interest of using microsampling for fluxomics analysis, not only to collect quickly and easily biological samples during sports events but also because it is much easier to store and to process the samples than classical plasma/serum samples obtained by venipuncture. The present results open new avenue for fluxomics analysis in the context of health care.

Simultaneous Quantitation of Lipid Biomarkers for Inflammatory Bowel Disease Using LC-MS/MS

Eicosanoids are key mediators and regulators of inflammation and oxidative stress that are often used as biomarkers for severity and therapeutic responses in various diseases. We here report a highly sensitive LC-MS/MS method for the simultaneous quantification of at least 66 key eicosanoids in a widely used murine model of colitis. Chromatographic separation was achieved with Shim-Pack XR-ODSIII, 150 × 2.00 mm, 2.2 µm. The mobile phase was operated in gradient conditions and consisted of acetonitrile and 0.1% acetic acid in water with a total flow of 0.37 mL/min. This method is sensitive, with a limit of quantification ranging from 0.01 to 1 ng/mL for the various analytes, has a large dynamic range (200 ng/mL), and a total run time of 25 min. The inter- and intraday accuracy (85-115%), precision (≥85%), and recovery (40-90%) met the acceptance criteria per the US Food and Drug Administration guidelines. This method was successfully applied to evaluate eicosanoid metabolites in mice subjected to colitis versus untreated, healthy control mice. In summary, we developed a highly sensitive and fast LC-MS/MS method that can be used to identify biomarkers for inflammation and potentially help in prognosis of the disease in inflammatory bowel disease (IBD) patients, including the response to therapy.

Role of Carbon Monoxide in Host-Gut Microbiome Communication

Nature is full of examples of symbiotic relationships. The critical symbiotic relation between host and mutualistic bacteria is attracting increasing attention to the degree that the gut microbiome is proposed by some as a new organ system. The microbiome exerts its systemic effect through a diverse range of metabolites, which include gaseous molecules such as H₂, CO₂, NH₃, CH₄, NO, H₂S, and CO. In turn, the human host can influence the microbiome through these gaseous molecules as well in a reciprocal manner. Among these gaseous molecules, NO, H₂S, and CO occupy a special place because of their widely known physiological functions in the host and their overlap and similarity in both targets and functions. The roles that NO and H₂S play have been extensively examined by others. Herein, the roles of CO in host-gut microbiome communication are examined through a discussion of (1) host production and function of CO, (2) available CO donors as research tools, (3) CO production from diet and bacterial sources, (4) effect of CO on bacteria including CO sensing, and (5) gut microbiome production of CO. There is a large amount of literature suggesting the "messenger" role of CO in host-gut microbiome communication. However, much more work is needed to begin achieving a systematic understanding of this issue.

Targeted ultra-performance liquid chromatography/tandem mass spectrometric quantification of methylated amines and selected amino acids in biofluids

RATIONALE

Methylated amino compounds and basic amino acids are important analyte classes with high relevance in nutrition, physical activity and physiology. Reliable and easy quantification methods covering a variety of metabolites in body fluids are a prerequisite for efficient investigations in the field of food and nutrition.

METHODS

Targeted ultra-performance liquid chromatography/tandem mass spectrometric (UHPLC/MS) analysis was performed using HILIC separation and timed ESI-MRM detection, combined with a short sample preparation. Calibration in urine and blood plasma was achieved by matrix-matched standards, isotope-labelled internal standards and standard addition. The method was fully validated and the performance was evaluated using a subset from the Karlsruhe Metabolomics and Nutrition (KarMeN) study.

RESULTS

Within this method, a total of 30 compounds could be quantified simultaneously in a short run of 9 min in both body fluids. This covers a variety of free amino compounds which are present in very different concentrations. The method is easy, precise and robust, and has a broad working range. As a proof of principle, literature-based associations of certain metabolites with dietary intake of respective foods were clearly confirmed in the KarMeN subset.

CONCLUSIONS

Overall, the method turned out to be well suited for application in nutrition studies, as shown for the example of food intake biomarkers in KarMeN. Application to a variety of questions such as food-related effects or physical activity will support future studies in the context of nutrition and health.

Nitric oxide, asymmetric dimethylarginine, symmetric dimethylarginine and L-arginine levels in psychotic exacerbation of schizophrenia and bipolar disorder manic episode

OBJECTIVES

To examine the changes in nitric oxide (NO), asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and L-arginine levels in schizophrenia during acute psychotic exacerbation and in bipolar disorder during mania and to compare those changes to healthy controls.

METHODS

Thirty schizophrenia patients with acute psychotic exacerbation and 30 bipolar disorder patients with mania, who attended the Psychiatry Department,  Erenköy Hospital for Mental and Nervous Diseases, Istanbul, Turkey, in 2010. Thirty healthy controls were included. The diagnosis was made using the Structured Clinical Interview for Axis I Disorders (SCID-I) interviews. Patients' demographic data were recorded, and NO, SDMA, L-arginine, and ADMA levels were studied.

RESULTS

Nitric oxide levels in schizophrenia patients were significantly lower than the control group. Nitric oxide levels in the bipolar group were lower than the control group but the difference was not statistically significant. The levels of SDMA, ADMA, and L-arginine were found to be significantly higher in schizophrenia and bipolar disorder patients than the control group. The disease duration was slightly negatively correlated with NO levels in bipolar patients. In schizophrenia patients, the disease severity was slightly positively correlated with NO levels.

CONCLUSION

Significant changes in NO, SDMA, ADMA, and L-arginine levels in schizophrenia and bipolar disorder patients suggest that NO and inhibitors of NO might be implicated in the neurobiology of schizophrenia and bipolar disorder.

Deep Protein Methylation Profiling by Combined Chemical and Immunoaffinity Approaches Reveals Novel PRMT1 Targets

Protein methylation has been implicated in many important biological contexts including signaling, metabolism, and transcriptional control. Despite the importance of this post-translational modification, the global analysis of protein methylation by mass spectrometry-based proteomics has not been extensively studied because of the lack of robust, well-characterized techniques for methyl peptide enrichment. Here, to better investigate protein methylation, we compared two methods for methyl peptide enrichment: immunoaffinity purification (IAP) and high pH strong cation exchange (SCX). Using both methods, we identified 1720 methylation sites on 778 proteins. Comparison of these methods revealed that they are largely orthogonal, suggesting that the usage of both techniques is required to provide a global view of protein methylation. Using both IAP and SCX, we then investigated changes in protein methylation downstream of protein arginine methyltransferase 1 (PRMT1). PRMT1 knockdown resulted in significant changes to 127 arginine methylation sites on 78 proteins. In contrast, only a single lysine methylation site was significantly changed upon PRMT1 knockdown. In PRMT1 knockdown cells, we found 114 MMA sites that were either significantly downregulated or upregulated on proteins enriched for mRNA metabolic processes. PRMT1 knockdown also induced significant changes in both asymmetric dimethyl arginine (ADMA) and symmetric dimethyl arginine (SDMA). Using characteristic neutral loss fragmentation ions, we annotated dimethylarginines as either ADMA or SDMA. Through integrative analysis of methyl forms, we identified 18 high confidence PRMT1 substrates and 12 methylation sites that are scavenged by other non-PRMT1 arginine methyltransferases in the absence of PRMT1 activity. We also identified one methylation site, HNRNPA1 R206, which switched from ADMA to SDMA upon PRMT1 knockdown. Taken together, our results suggest that deep protein methylation profiling by mass spectrometry requires orthogonal enrichment techniques to identify novel PRMT1 methylation targets and highlight the dynamic interplay between methyltransferases in mammalian cells.

Characterization of Aroma-Active Compounds, Phenolics, and Antioxidant Properties in Fresh and Fermented Capers (Capparis spinosa) by GC-MS-Olfactometry and LC-DAD-ESI-MS/MS

Caper (Capparis spinosa) is an important food ingredient whose fresh parts, particularly the flower buds, are consumed as a starter with olives, cheese, and nuts, or are used as a component in other foods. It is one of the most popular species of aromatic plants grown in the Mediterranean zone. Fermentation makes the caper edible and affects the overall aroma as well as sensory and nutritional characteristics. This study aimed to evaluate the changes in aroma, aroma-active, and phenolic compounds of caper as affected by fermentation. Purge and trap method was used for the extraction of the aroma compounds, while gas chromatography-mass spectrometry olfactometry and Liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry (LC-DAD-ESI-MS/MS) were employed for the detection of aroma-active compounds and phenolics, respectively. The results showed that the total amount of aroma compounds decreased drastically (62,616 to 21,471 µg/kg) in fermented sample. Twelve and 10 aroma-active compounds were detected in fresh and fermented caper buds, respectively, for the first time by the application of aroma extract dilution analysis. Among these compounds, methyl isothiocyanate (flavor dilution [FD] factor = 512) in fresh caper and acetic acid (FD factor = 128) in the fermented caper had the highest FD factor. With regard to the phenolic compounds, a total of 16 components were identified in fresh and fermented capers. As observed in aroma compounds, the total phenolic concentration decreased as a result of fermentation. Two phenolic compounds being kaempferol-3-O-glucosyl-rhamnosyl-glucoside and isorhamnetin hexoside were newly identified in caper. PRACTICAL APPLICATIONS: Capparis spinosa is one of the most popular sources of different secondary metabolites of interest to consumers. The results of the present study showed that the fermentation process of the capers is highly influential on the neutral composition of the sample. The total concentrations of aroma and phenolic compounds were reduced by 66% and 78%, respectively, in response to fermentation process.

Development, validation and comparison of four methods for quantifying endogenous 25OH-D3 in human plasma

To meet the increasing clinical needs for 25-hydroxyvitamin D3 (25OH-D3) detection, the development of an efficient and accurate high-performance liquid chromatography-mass spectrometry (HPLC-MS) method for plasma 25OH-D3 quantitation is important. Since 25OH-D3 is an endogenous compound, the lack of a plasma blank increases the difficulty of accurately quantifying 25OH-D3. Selection of a method suitable for clinical monitoring among various methods for endogenous compound quantification is necessary. Methyl tert butyl ether was chosen for the sample treatment in a liquid-liquid extraction protocol. Water as a blank matrix, 5% human serum albumin in water as a blank matrix, surrogate analyte and background subtraction were designed to address the problem of a deficiency of a plasma blank. Four liquid chromatography-tandem mass spectrometry methods were fully validated to verify the advantages and limitations owing to regulatory deficiencies for endogenous compound validation. All four methods met the criteria and could be used to monitor clinical samples. Overall 30 human plasma samples were quantified in parallel using the four methods. The difference between any two methods was <12.6% and the total relative standard deviation was <5.2%. Background subtraction and 5% human serum albumin in water as a blank matrix may be better choices considering data quality, matrix similarity, cost and practicality.

Amphiphilicity Regulation of AgI Nanoclusters: Self-Assembly and Its Application as a Luminescent Probe

Research on the self-assembly of various amphiphilic molecules is a relatively new research area and of great significance. However, new kinds of metal-nanocluster (NC)-based amphiphilic molecule have rarely been explored. Herein, hydrophobic cation 1-hexadecyl-3-methylimidazolium (C₁₆ mim⁺ ) was chosen to modify hydrophilic (NH₄ )₆ [Ag₆ (mna)₆ ] (Ag₆ -NCs, H₂ mna=2-mercaptonicotinic acid) and Ag₆ @C₁₆ mim-NCs were obtained. Ag₆ @C₁₆ mim-NCs displayed thermotropic liquid crystal and thermofluorescent properties. Moreover, the Ag₆ @C₁₆ mim-NCs exhibits benign amphiphilicity, and it can self-assemble into ordered nanosheets and nanorods through aggregation in water/dimethyl sulfoxide (DMSO) binary solvent mixtures, whereas single Ag₆ -NCs do not. Meanwhile, the Ag₆ @C₁₆ mim-NCs also displays aggregation-induced emission properties owing to the restriction of intramolecular vibrations of the capping ligands. Furthermore, the luminescent aggregates could detect arginine selectively with the detection limit at 28 μm. This study introduces a new kind of metal-NC-based amphiphilic molecule in a supramolecular self-assembly field, and they have potential to be used as optical materials in applied research.

Interplay between Plasmodium falciparum haemozoin and L-arginine: implication for nitric oxide production

Background

Plasmodium falciparum haemozoin, a detoxification product of digested haemoglobin from infected erythrocytes, is released into the bloodstream upon schizont rupture and accumulates in leukocytes. High levels of haemozoin correlate with disease severity. Some studies have shown that concentrations of the substrate of inducible nitric oxide synthase (iNOS), l-arginine, as well as nitric oxide are low in patients infected with P. falciparum malaria. The present study investigates, in vitro, the role of P. falciparum haemozoin on nitric oxide production, iNOS expression in macrophages, and the possible interaction between l-arginine and haemozoin.

Methods

Plasmodium falciparum haemozoin was obtained from in vitro cultures through magnetic isolation. Phagocytosis of haemozoin by immortalized bone marrow derived macrophages was detected by confocal reflection combined with fluorescence microscopy. Nitrite concentrations in the supernatants was evaluated by Griess assay as a standard indication of nitric oxide production, while iNOS expression was detected on cell extracts by western blotting. Detection of l-arginine in haemozoin-treated or untreated media was achieved by liquid chromatography–tandem mass spectrometry (LC–MS/MS).

Results

Haemozoin synergizes in vitro with interferon-gamma to produce nitric oxide. However, when mouse macrophages were stimulated with haemozoin, a proportional increase of nitric oxide was observed up to 25 μM of haemozoin, followed by a decrease with doses up to 100 μM, when nitric oxide release was completely abrogated. This was not due to reactive oxygen species production, nor to an effect on iNOS activity. Interestingly, when at 24 h, haemozoin-treated macrophages were washed and incubated in fresh medium for further 24 h, the nitric oxide production was restored in a dose–response manner. Similar results were seen when l-arginine-enriched media was used in the stimulation. Moreover, muramyldipeptide, a strong nitric oxide inducer, was unable to activate macrophages to release nitric oxide in the presence of haemozoin-treated medium. By LC–MS/MS a complete depletion of l-arginine was observed in this haemozoin-treated, conditioned medium.

Conclusions

It is proposed that haemozoin interacts with l-arginine reducing its availability for iNOS, and thus decreasing nitric oxide production. The clinical (or pathological) implications of these results are discussed.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2602-0) contains supplementary material, which is available to authorized users.

Quantification of ADMA: analytical approaches

Methylated L-arginine analogs are involved in nitric oxide synthase activity regulation. Methods based on high-performance liquid chromatography with fluorescence, capillary electrophoresis, or ion exchange chromatography with absorbance detection were first applied for the quantitative determination of N-monomethyl-L-arginine (NMMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in human blood and urine. These assays revealed elevated circulating levels of ADMA in various diseases and gave accumulating evidence of the usefulness of ADMA as a cardiovascular risk factor. However, the methods used are hampered by the fact that NMMA, ADMA and SDMA can be distinguished from L-arginine only by means of chromatographic separation. This has promoted the development of alternatives that involve mass spectrometry (MS) technology. Today, various MS-based approaches such as liquid chromatography (LC)-MS, LC-MS/MS, gas chromatography (GC)-MS, and GC-MS/MS are available. L-arginine and its analogs have been subjected to LC-MS analysis with and without further derivatization to their o-phthaldialdehyde derivatives. For these methods, labelled L-arginine was used as the internal standard. The first MS-based method that distinguishes NMMA, ADMA, SDMA and L-arginine by mass-to-charge (m/z)- ratio has been reported by Tsikas et al. This GC-MS approach has been further improved by Albsmeier et al by introducing labelled ADMA as an internal standard. As an alternative to existing methods, a commercially available ELISA kit has recently been developed and validated.

12-months metabolic changes among gender dysphoric individuals under cross-sex hormone treatment: a targeted metabolomics study

Metabolomic analyses in epidemiological studies have demonstrated a strong sexual dimorphism for most metabolites. Cross-sex hormone treatment (CSH) in transgender individuals enables the study of metabolites in a cross-gender setting. Targeted metabolomic profiling of serum of fasting transmen and transwomen at baseline and following 12 months of CSH (N = 20/group) was performed. Changes in 186 serum metabolites and metabolite ratios were determined by targeted metabolomics analysis based on ESI-LC-MS/MS. RandomForest (RF) analysis was applied to detect metabolites of highest interest for grouping of transwomen and transmen before and after initiation of CSH. Principal component analysis (PCA) was performed to check whether group differentiation was achievable according to these variables and to see if changes in metabolite levels could be explained by a priori gender differences. PCA predicted grouping of individuals-determined by the citrulline/arginine-ratio and the amino acids lysine, alanine and asymmetric dimethylarginine - in addition to the expected grouping due to changes in sex steroids and body composition. The fact that most of the investigated metabolites did, however, not change, indicates that the majority of sex dependent differences in metabolites reported in the literature before may primarily not be attributable to sex hormones but to other gender-differences.

Determination of Asymmetric and Symmetric Dimethylarginine in Serum from Patients with Chronic Kidney Disease: UPLC-MS/MS versus ELISA

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis, and its structural isomer symmetric dimethylarginine (SDMA) are uremic toxins accumulating in chronic kidney disease (CKD) patients. The objective of this study was to develop and validate a robust UPLC-MS/MS method for the simultaneous determination of ADMA and SDMA in human serum. Chromatographic separation after butyl ester derivatization was achieved on an Acquity UPLC BEH C18 column, followed by tandem mass spectrometric detection. After validation, the applicability of the method was evaluated by the analysis of serum samples from 10 healthy controls and 77 CKD patients on hemodialysis (CKD5HD). Both ADMA (0.84 ± 0.19 µM vs. 0.52 ± 0.07 µM) and SDMA concentrations (2.06 ± 0.82 µM vs. 0.59 ± 0.13 µM) were significantly (p < 0.001) elevated in CKD5HD patients compared to healthy controls. In general, low degrees of protein binding were found for both ADMA and SDMA. In addition, an established commercially available ELISA kit was utilized on the same samples (n = 87) to compare values obtained both with ELISA and UPLC-MS/MS. Regression analysis between these two methods was significant (p < 0.0001) but moderate for both ADMA (R = 0.78) and SDMA (R = 0.72).

Levels of nitric oxide, asymmetric dimethyl arginine, symmetric dimethyl arginine,and L-arginine in patients with obsessive-compulsive disorder

BACKGROUND/AIM

We aimed to investigate and compare to healthy controls the variations in the levels of nitric oxide (NO), asymmetric dimethyl arginine (ADMA), symmetric dimethyl arginine (SDMA), and L-arginine levels in patients with obsessive-compulsive disorder (OCD).

MATERIALS AND METHODS

We enrolled 30 patients with OCD and 30 healthy controls in the study consecutively. Diagnostic interviews of all participants were conducted with the Structured Clinical Interview for Axis I Disorders (SCID-I), and sociodemographic data of the participants were recorded. Patients scoring 10 points or more on the Yale-Brown Obsessive-Compulsive Scale were enrolled in the study.

RESULTS

The NO levels of patients with OCD were increased compared to the control group, but the increase was not statistically significant (P > 0.05). However, patients with OCD had significantly lower levels of ADMA, SDMA, and L-arginine compared with the controls (P < 0.001).

CONCLUSION

We found a significant decrease in ADMA, SDMA, and L-arginine as NO inhibitors between the groups, possibly because of an increase in NO. However, the insignificant increase in NO suggests that ADMA, SDMA, and L-arginine play direct and potentially important roles in OCD biology.

A new Schiff base and its metal complex as colorimetric and fluorescent–colorimetric sensors for rapid detection of arginine

A new Schiff base (L) and its Pb²⁺-complex have been utilized for rapid detection of arginine in aqueous medium.Lexhibits an excellent selective colorimetric response whereas its Pb²⁺-complex exploits fluorescent-colorimetric response towards arginine with very low detection limits.

LC-MS metabolite fingerprinting and MtSK-based screening of an endophyte Bartalinia pondoensis Marinc of Citrus aurantum L

An endophyte Bartalinia pondoensis Marinc of Citrus aurantum L. var. dulcis was isolated and studied for its secondary metabolites and for their Mycobacterium tuberculosis shikimate kinase (MtSK) inhibitory activities. Using LC-MS metabolite fingerprinting of the constituents of the methanol extract, 19 compounds pertaining to various classes were identified: amino acids, proto-alkaloids, fatty acid amides and oxazole, aniline derivatives and aromatic compounds. We report here for the first time the presence of the [N-(ethyloxy, hydroxymethyl)phenylethylamine] as a new proto-alkaloid and 18 other known compounds are reported for the first time in the genus of Bartalinia. MtSK inhibitory activities of methanol extract and fractions obtained by solid phase extraction (SPE) at a concentration of 50 μg/mL may be attributed to the presence of aniline and oxazole derivatives present in all fractions in varying concentrations.

Hypothermia decreases cerebrospinal fluid asymmetric dimethylarginine levels in children with traumatic brain injury

OBJECTIVES

Pathological increases in asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, have been implicated in endothelial dysfunction and vascular diseases. Reduced nitric oxide early after traumatic brain injury may contribute to hypoperfusion. Currently, methods to quantify asymmetric dimethylarginine in the cerebrospinal fluid have not been fully explored. We aimed to develop and validate a method to determine asymmetric dimethylarginine in the cerebrospinal fluid of a pediatric traumatic brain injury population and to use this method to assess the effects of 1) traumatic brain injury and 2) therapeutic hypothermia on this mediator.

DESIGN, SETTING, AND PATIENTS

An ancillary study to a prospective, phase II randomized clinical trial of early hypothermia in a tertiary care pediatric intensive care unit for children with Traumatic brain injury admitted to Children's Hospital of Pittsburgh.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A UPLC-MS/MS method was developed and validated to quantitate asymmetric dimethylarginine. A total of 56 samples collected over 3 days with injury onset were analyzed from the cerebrospinal fluid of consented therapeutic hypothermia (n = 9) and normothermia (n = 10) children. Children undergoing diagnostic lumbar puncture (n = 5) were enrolled as controls. Asymmetric dimethylarginine was present at a quantifiable level in all samples. Mean asymmetric dimethylarginine levels were significantly increased in normothermic Traumatic brain injury children compared with that in control (0.19 ± 0.08 µmol/L and 0.11 ± 0.02 µmol/L, respectively, p = 0.01), and hypothermic children had significantly reduced mean asymmetric dimethylarginine levels (0.11 ± 0.05 µmol/L) vs. normothermic (p = 0.03) measured on day 3. Patient demographics including age, gender, and nitric oxide levels (measured as nitrite and nitrate using liquid chromatography coupled with Griess reaction) did not significantly differ between normothermia and hypothermia groups. Also, nitric oxide levels did not correlate with asymmetric dimethylarginine concentrations.

CONCLUSIONS

Asymmetric dimethylarginine levels were significantly increased in the cerebrospinal fluid of traumatic brain injury children. Early hypothermia attenuated this increase. The implications of attenuated asymmetric dimethylarginine on nitric oxide synthases activity and regional cerebral blood flow after traumatic brain injury by therapeutic hypothermia deserve future study.

Quantification of arginine and dimethylated arginines in human plasma by field-amplified sample injection capillary electrophoresis UV detection

We report a capillary electrophoresis method by field-amplified sample injection (FASI) for the separation and detection of free plasma arginine and dimethylated arginines. Protein elimination from plasma was performed by acetonitrile/ammonia precipitation. Supernatants were dried, reswollen in water, and directly injected on capillary without complex cleanup by solid-phase extraction and/or tedious sample derivatization procedures. Analytes were baseline-separated within 22 min by using 50 mmol/L Tris phosphate pH 2.3 as running buffer. Due to the stacking effects of electrokinetic injection, it is possible to perform a considerable on-line preconcentration of the analytes before running the electrophoresis. This procedure allows to reach a detection limit in real sample of 10 nmol/L for dimethylated arginines and 20 nmol/L for arginine. Recovery of plasma ADMA was 99-104 % and inter-day CV was less than 3 %.

A new derivatization method coupled with LC-MS/MS to enable baseline separation and quantification of dimethylarginines in human plasma from patients to receive on-pump CABG surgery

Asymmetric dimethylarginine (ADMA) is an inhibitor of nitric oxide synthase and a risk factor for cardiovascular events. We have developed a new derivatization method to enable baseline separation of the regio-isomers, ADMA, and symmetric dimethylarginine (SDMA), within 15 min on a C18 reverse phase column. Reacting naphthalene-2,3-dicarboxaldehyde with ADMA and SDMA in the presence of 2-mercaptoethanol produces corresponding 2,3-dihydro-benzo[f]isoindol-1-ones that are more stable than previously reported ortho-phthaldialdehyde and 2-mercaptoethanol derivatives. LC-MS/MS quantitation of these derivatives can be used to determine ADMA and SDMA concentrations in the plasma of patients to receive on-pump coronary artery bypass grafting (CABG) surgery. The LOD, LOQ and lower LOQ (LLOQ) of this method were determined to be 2.6, 8.7, and 25 nM for ADMA, and 2.5, 8.3, and 25 nM for SDMA, respectively, with consumption of only 50 μL of plasma. The relative standard deviations and relative errors of the intraday and interday determinations, as measurements of reproducibility and accuracy, are all within 15%. The ADMA and SDMA concentrations in patient plasma are 298.1 ± 11.2 nM (mean ± S.E.M., n = 123) and 457.7 ± 19.8 nM (mean ± S.E.M., n = 123), respectively. Upon unblinding of our clinical trial, these predetermined values might explain patient clinical outcomes associated with on-pump CABG surgery, as ADMA is known to inhibit nitric oxide production. Furthermore, this derivatization reaction in conjunction with LC-MS/MS analysis may open a venue to explore alternative chemical labeling modes for LC-MS/MS applications, such as analysis of other amino acids, metabolites, and peptides containing primary amine group(s).

Mass spectrometric dereplication of nitrogen-containing constituents of black cohosh (Cimicifuga racemosa L.)

Black cohosh preparations are popular dietary supplements among women seeking alternative treatments for menopausal complaints. For decades, triterpene glycosides and phenolic acids have dominated the phytochemical and biomedical research on this plant. In this study, we provide evidence that black cohosh contains an unexpected and highly diverse group of secondary nitrogenous metabolites previously unknown to exist in this plant. Using a dereplication approach that combines accurate mass measurements, database searches and general knowledge of biosynthetic pathways of natural products, we identified or tentatively identified 73 nitrogen-containing metabolites, many of which are new natural products. The identified compounds belong to several structural groups including alkaloids, amides or esters of hydroxycinnamic acids and betains. Among the alkaloids, several classes such as guanidino alkaloids, isoquinolines and β-carbolines were identified. Fragmentation patterns for major compound classes are discussed, which provides a framework for the discovery of these compounds from other sources. Identification of alkaloids as a well-known group of bioactive natural products represents an important advance in better understanding of the pharmacological profile of black cohosh.

Quantitation of L-arginine and asymmetric dimethylarginine in human plasma by LC-selective ion mode-MS for Type 2 diabetes mellitus study

The article reports a simple, sensitive and fast LC/MS method for the analysis of L-arginine (L-Arg), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in human plasma. The homoarginine was used as the internal standard (IS). The chromatographic separation was achieved on C₁₈(150 mm×2.1 mm, 5 µm) column with a mobile phase consisting of ammonium acetate (0.25 mmol/l) and methanol (93 : 7, v/v), at a flow rate of 0.2 ml/min. L-Arg, ADMA and SDMA were well separated by LC/MS with selective ion mode (SIM). The method was successfully applied to type 2 diabetes mellitus (T2DM) study. Twenty-one healthy controls and twenty-two T2DM patients before and after treatment two years were investigated. The results indicated that the level of ADMA in T2DM was significantly higher than that in healthy controls. Furthermore, ADMA has important association with the development of cardiovascular diseases.

Update of uremic toxin research by mass spectrometry

Mass spectrometry (MS) has been successfully applied for the identification and quantification of uremic toxins and uremia-associated modified proteins. This review focuses on the recent progress in the MS analysis of uremic toxins. Uremic toxins include low-molecular weight solutes, protein-bound low-molecular weight solutes, and middle molecules (peptides and proteins). Based on MS analysis of these uremic toxins, the pathogenesis of the uremic symptoms will be elucidated to prevent and manage the symptoms. Notably, protein-bound uremic toxins such as indoxyl sulfate, p-cresyl sulfate, and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid have emerged as important targets of therapeutic removal. Hemodialysis even with a high-flux membrane cannot efficiently remove the protein-bound uremic toxins because of their high albumin-binding property. The accumulation of these protein-bound uremic toxins in the blood of dialysis patients might play an important role in the development of uremic complications such as cardiovascular disease. Indoxyl sulfate is the most promising protein-bound uremic toxin as a biomarker of progress in chronic kidney disease. Novel dialysis techniques or membranes should be developed to efficiently remove these protein-bound uremic toxins for the prevention and management of uremic complications.

Simultaneous bioanalysis of L-arginine, L-citrulline, and dimethylarginines by LC-MS/MS

PURPOSE

L-Arginine (ARG) is converted to nitric oxide (NO) and L-citrulline (CIT) by endothelial nitric oxide synthase which is competitively inhibited by asymmetric dimethylarginine (ADMA). We have developed a liquid chromatography-mass spectrometric method for the simultaneous determination of endogenous ARG, labeled ARG (¹⁵N₄-ARG), CIT, ADMA, and its inactive isomer, symmetric dimethylarginine (SDMA) in biological samples.

METHODS

Concentrations of unlabeled ARG, ¹⁵N₄-ARG, CIT, ADMA, and SDMA in EA.hy926 human endothelial cell lysate, cell incubation media, rat plasma or rat urine were measured by hydrophilic-interaction liquid chromatography electrospray tandem mass spectrometry. ¹³C₆-ARG, D₄-CIT and D₇-ADMA were used as internal standards for ARG and ¹⁵N₄-ARG, CIT, and dimethylarginines, respectively.

RESULTS

The calibration curves of ARG, ¹⁵N₄-ARG, CIT, ADMA, and SDMA were linear and independent of several sample matrices. Intra- and inter-day variabilities for the quantification of all the compounds were below 15% in quality control samples. Application of this method to determine the uptake as well as efflux of these compounds was illustrated through in vitro cell study by exposing human endothelial cells to ¹⁵N₄-ARG, which allowed the observation of generation of ¹⁵N₃-CIT and ¹⁵N₃-ARG in the cell lyate. Use of these isotopes adds insights into the cellular handling of endogenous vs. exogenous ARG. Application of this method for rat plasma and rat urine assays was demonstrated after ARG oral supplementation in rats.

CONCLUSION

An LC-MS/MS method was developed to quantify 6 ARG-related compounds simultaneously, utilizing 3 separate internal standards. This assay allows concurrent monitoring of uptake, efflux and metabolic processes when isotope-labeled ARG and CIT are measured, and can be applied for determination of these compounds in rat plasma and rat urine.

Improved method for plasma ADMA, SDMA, and arginine quantification by field-amplified sample injection capillary electrophoresis UV detection

Here, we describe an easy field-amplified sample injection capillary electrophoresis method with UV detection for the separation and detection of free plasma arginine and dimethylated arginines. The analytes were baseline-separated within 22 min by using 50 mmol/L Tris phosphate pH 2.3 as running buffer. The plasma samples were treated with acetonitrile/ammonia for protein elimination, the supernatants were dried, re-swollen in water and directly injected in the capillary without complex cleanup by solid phase extraction and/or tedious sample derivatization procedures. Due to the stacking effects of the electrokinetic injection, it was possible to operate a consistent on-line pre-concentration of the analytes before running the electrophoresis. This procedure allowed to reach a detection limit in the real sample of 10 nmol/L for dimethylated arginines and 20 nmol/L for arginine, thus improving about threefold our previous method, that required a more complicated pre-analytical procedure to concentrate samples. The recovery of plasma ADMA was 99-104% and inter-day CV was less than 3%. The assay performance was evaluated measuring the levels of arginine and its dimethyl derivatives in 50 subjects. The statistical tests for the methods comparison suggest that the data obtained by our new method and by our previous CE assay are similar.

Analysis of arginine and methylated metabolites in human plasma by field amplified sample injection capillary electrophoresis tandem mass spectrometry

A CE ion trap tandem MS method was optimised for the analysis of arginine, monomethyl- and (symmetric and asymmetric) dimethylarginines in human plasma after a very reduced sample pretreatment step involving a simple protein precipitation with ACN. Several parameters affecting the analytes MS ionization and the capillary electrophoretic separation were carefully studied and optimised. The complete separation of arginine, monomethylarginine and symmetric and asymmetric dimethylarginine was obtained in formic acid BGE in short analysis time with high specificity due to MS(2) detection of specific analytes fragments. In order to achieve the detection sensitivity suitable for the analysis of asymmetric and symmetric dimethylarginine in human plasma, the field amplified sample injection was applied. Due to stacking effects, this methodology allowed to operate a consistent on-line preconcentration of the analytes before running the electrophoresis. The method was validated for linearity, repeatability, recovery and accuracy and applied to the quantitative analysis of arginine, monomethyl- and dimethylarginines in human plasma of healthy subjects.

Association of homocysteine, asymmetric dimethylarginine, and nitric oxide with preeclampsia

PURPOSE

Endothelial dysfunction underlies the pathogenesis of preeclampsia, but its mechanism has not yet been completely understood. In this study we have aimed to measure homocysteine (Hcy), asymmetric dimethylarginine (ADMA), and nitric oxide (NO) levels as endothelial dysfunction markers in preeclamptic women.

METHODS

Control-case study with 62 preeclamptic patients and 30 controls without pregnancy complications was conducted. Plasma total Hcy, determined by capillary column gas chromatography/mass spectrometry (GC/MS), was correlated with serum ADMA (determined by liquid chromatography/tandem mass spectrometry using (13)C(6)-L: -arginine as the internal standard) and NO (analyzed by GC/MS).

RESULTS

There was a highly significant increase in the plasma concentration of homocysteine (P < 0.001) and ADMA (P < 0.001) and a highly significant decrease in the plasma concentration of nitric oxide (P < 0.001) among the preeclamptic patients. The differences were more significant between mild and severe preeclampsia, with and without eclampsia, with and without HELLP (hemolysis, elevated serum level of liver enzymes, and low platelets). In the combined patients and control groups a highly significant positive correlation was found between the plasma concentrations of homocysteine and ADMA (r = 0.853, P < 0.001). In addition, significant negative correlations were detected between the plasma concentrations of nitric oxide and the plasma concentration of homocysteine (r = -0.870, P < 0.001) and ADMA (r = -0.895, P < 0.001). These significant correlations were found to persist, even when they were restricted to the preeclamptic patients.

CONCLUSIONS

The homocysteine-ADMA-NO may be at least partly responsible for etiology in preeclampsia and could be regarded as markers for the severity of the disease. Therefore, L: -arginine may represent a novel therapy for the treatment of preeclampsia.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonist, AVE8134, attenuates the progression of heart failure and increases survival in rats

AIM

To investigate the efficacy of the peroxisome proliferator-activated receptor-alpha (PPARalpha) agonist, AVE8134, in cellular and experimental models of cardiac dysfunction and heart failure.

METHODS

In Sprague Dawley rats with permanent ligation of the left coronary artery (post-MI), AVE8134 was compared to the PPARgamma agonist rosiglitazone and in a second study to the ACE inhibitor ramipril. In DOCA-salt sensitive rats, efficacy of AVE8134 on cardiac hypertrophy and fibrosis was investigated. Finally, AVE8134 was administered to old spontaneously hypertensive rats (SHR) at a non-blood pressure lowering dose with survival as endpoint. In cellular models, we studied AVE8134 on hypertrophy in rat cardiomyocytes, nitric oxide signaling in human endothelial cells (HUVEC) and LDL-uptake in human MonoMac-6 cells.

RESULTS

In post-MI rats, AVE8134 dose-dependently improved cardiac output, myocardial contractility and relaxation and reduced lung and left ventricular weight and fibrosis. In contrast, rosiglitazone exacerbated cardiac dysfunction. Treatment at AVE8134 decreased plasma proBNP and arginine and increased plasma citrulline and urinary NOx/creatinine ratio. In DOCA rats, AVE8134 prevented development of high blood pressure, myocardial hypertrophy and cardiac fibrosis, and ameliorated endothelial dysfunction. Compound treatment increased cardiac protein expression and phosphorylation of eNOS. In old SHR, treatment with a low dose of AVE8134 improved cardiac and vascular function and increased life expectancy without lowering blood pressure. AVE8134 reduced phenylephrine-induced hypertrophy in adult rat cardiomyocytes. In HUVEC, Ser-1177-eNOS phosphorylation but not eNOS expression was increased. In monocytes, AVE8134 increased the expression of CD36 and the macrophage scavenger receptor 1, resulting in enhanced uptake of oxidized LDL.

CONCLUSION

The PPARalpha agonist AVE8134 prevents post-MI myocardial hypertrophy, fibrosis and cardiac dysfunction. AVE8134 has beneficial effects against hypertension-induced organ damages, resulting in decreased mortality. The compound exerts its protective properties by a direct effect on cardiomyocyte hypertrophy, but also indirectly via monocyte signaling and increased endothelial NO production.Acta Pharmacologica Sinica (2009) 30: 935-946; doi: 10.1038/aps.2009.58; published online 8 June 2009.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

Recent progress in the analysis of uremic toxins by mass spectrometry

Mass spectrometry (MS) has been successfully applied for the identification and quantification of uremic toxins and uremia-associated modified proteins. This review focuses on recent progress in the analysis of uremic toxins by using MS. Uremic toxins include low-molecular-weight compounds (e.g., indoxyl sulfate, p-cresol sulfate, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, asymmetric dimethylarginine), middle-molecular-weight peptides, and proteins modified with advanced glycation and oxidation. These uremic toxins are considered to be involved in a variety of symptoms which may appear in patients with stage 5 chronic kidney disease. Based on MS analysis of these uremic toxins, the pathogenesis of the uremic symptoms will be elucidated to prevent and manage the symptoms.

Development and validation of a fast quantitative method for plasma dimethylarginines analysis using liquid chromatography-tandem mass spectrometry

OBJECTIVES

The aim of this work was to implement a fast, accurate and simple method to quantify plasma ADMA and SDMA, in a run time suitable for routine analysis.

DESIGN AND METHODS

We developed and validated a hydrophilic interaction chromatographic method coupled to tandem mass spectrometry (HILIC-MS/MS) for separation and simultaneous quantification of Arginine (Arg) and its dimethylarginines, ADMA and SDMA, with a short run time (less than 5 min) using a small volume of human plasma (0.02 mL).

RESULTS

Correlation coefficients (r) of the calibration curves ranged from 0.9926 to 0.9984. Within-day and between-day imprecision (CV%) and inaccuracy (%), carry-over and recovery were also evaluated for validation. Preliminary data of Arg, ADMA and SDMA from 30 apparently healthy subjects and type 2 diabetic patients (n=33) with and without kidney dysfunction were calculated and some statistical differences occurred among them (p<0.05).

CONCLUSIONS

Data from calibration curves and quality controls reveal that the method is accurate and precise. Healthy subjects and diabetic patients' values are in agreement with those reported in other studies.

Determination of asymmetric dimethylarginine in biological fluids: a paradigm for a successful analytical story

PURPOSE OF REVIEW

To review recently reported analytical methods for the quantification in biological fluids of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthesis, and to evaluate their impact on clinical research.

RECENT FINDINGS

Recently developed and increasingly used analytical methods in this area are based on mass spectrometry coupled with gas chromatography (i.e., gas chromatography-mass spectrometry and gas chromatography-mass spectrometry/mass spectrometry) or liquid chromatography (i.e., liquid chromatography-mass spectrometry and liquid chromatography-mass spectrometry/mass spectrometry). These approaches revealed asymmetric dimethylarginine concentrations in plasma and serum of healthy adults in the range 400-500 nmol/l. High-performance liquid chromatography methods with fluorescence detection provide asymmetric dimethylarginine plasma/serum concentrations comparable to those of mass spectrometry-based methods. This interval for circulating asymmetric dimethylarginine and the mass spectrometry/mass spectrometry-based methods have the potential to serve as reference values and analytical methods, respectively. An enzyme-linked immunosorbent assay method for asymmetric dimethylarginine has become commercially available and is increasingly used in clinical studies. Comparative studies revealed that the enzyme-linked immunosorbent assay method produces considerably higher asymmetric dimethylarginine concentrations in plasma or serum in healthy humans in the basal state than mass spectrometry and high-performance liquid chromatography methods and runs varyingly in different laboratories.

SUMMARY

At present, many analytical methods allow for the accurate and precise quantification of asymmetric dimethylarginine in biological fluids. However, reliable quantification of biological asymmetric dimethylarginine remains an analytical challenge in basic and clinical research.

Biosynthetic intermediate analysis and functional homology reveal a saxitoxin gene cluster in cyanobacteria

Saxitoxin (STX) and its analogues cause the paralytic shellfish poisoning (PSP) syndrome, which afflicts human health and impacts coastal shellfish economies worldwide. PSP toxins are unique alkaloids, being produced by both prokaryotes and eukaryotes. Here we describe a candidate PSP toxin biosynthesis gene cluster (sxt) from Cylindrospermopsis raciborskii T3. The saxitoxin biosynthetic pathway is encoded by more than 35 kb, and comparative sequence analysis assigns 30 catalytic functions to 26 proteins. STX biosynthesis is initiated with arginine, S-adenosylmethionine, and acetate by a new type of polyketide synthase, which can putatively perform a methylation of acetate, and a Claisen condensation reaction between propionate and arginine. Further steps involve enzymes catalyzing three heterocyclizations and various tailoring reactions that result in the numerous isoforms of saxitoxin. In the absence of a gene transfer system in these microorganisms, we have revised the description of the known STX biosynthetic pathway, with in silico functional inferences based on sxt open reading frames combined with liquid chromatography-tandem mass spectrometry analysis of the biosynthetic intermediates. Our results indicate the evolutionary origin for the production of PSP toxins in an ancestral cyanobacterium with genetic contributions from diverse phylogenetic lineages of bacteria and provide a quantum addition to the catalytic collective available for future combinatorial biosyntheses. The distribution of these genes also supports the idea of the involvement of this gene cluster in STX production in various cyanobacteria.

Association of an endogenous inhibitor of nitric oxide synthase with cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage

OBJECT

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) may be evoked by the decreased availability of nitric oxide (NO). Increased cerebrospinal fluid (CSF) levels of asymmetric dimethyl-L-arginine (ADMA), an endogenous inhibitor of NO synthase (NOS), have been associated with the course and degree of cerebral vasospasm in a primate model of SAH. In this study, the authors sought to determine if similar changes in CSF ADMA levels are observed in patients with SAH, and whether these changes are associated with NO and NOS metabolite levels in the CSF and the presence of cerebral vasospasm.

METHODS

Asymmetric dimethyl-L-arginine, L-arginine, L-citrulline, and nitrite levels were measured in CSF and serum samples collected during the 21-day period after a single aneurysmal SAH in 18 consecutive patients. Samples were also obtained in a control group consisting of seven patients with Chiari malformation Type I and five patients with spontaneous intracerebral hemorrhage without SAH. Vasospasm, defined as a greater than 11% reduction in the anterior circulation vessel diameter ratio compared with the ratio calculated from the initial arteriogram, was assessed on cerebral arteriography performed around Day 7.

RESULTS

In 13 patients with SAH, arteriographic cerebral vasospasm developed. Cerebrospinal fluid ADMA levels in patients with SAH were higher than in those in the control group (p < 0.001). The CSF ADMA level remained unchanged in the five patients with SAH without vasospasm, but was significantly increased in patients with vasospasm after Day 3 (6.2 +/- 1.7 microM) peaking during Days 7 through 9 (13.3 +/- 6.7 microM; p < 0.001) and then gradually decreasing between Days 12 and 21 (8.8 +/- 3.2 microM; p < 0.05). Nitrite levels in the CSF were lower in patients with vasospasm compared to patients without vasospasm (p < 0.03). Cerebrospinal fluid ADMA levels positively correlated with the degree of vasospasm (correlation coefficient [CC] = 0.88, p = 0.0001; 95% confidence interval [CI] 0.74-0.95) and negatively correlated with CSF nitrite levels (CC = -0.55; p = 0.017; 95% CI -0.81 to -0.12).

CONCLUSIONS

These results support the hypothesis that ADMA is involved in the progression of cerebral vasospasm. Asymmetric dimethyl-L-arginine and its metabolizing enzymes may be a future target for treatment of cerebral vasospasm after SAH.