A validated UPLC-MS/MS assay for the quantification of amino acids and biogenic amines in rat urine

Study of arginine metabolism in medication overuse chronic migraine: possible defect in NO synthesis

BACKGROUND AND AIM

The pathogenesis of the pain that occurs in episodic migraine attack is due to the activation of the trigeminal system's first neuron receptors located on vessel wall. The release from the endothelium of nitric oxide, a product of arginine metabolism, causes vasodilation and stretching of the vascular trigeminal system and promotes pain. It is unknown whether this same metabolic event is involved in the pain accompanying chronic migraine. To understand the possible role of arginine in the pathogenesis of chronic migraine patients, we evaluated the metabolism of arginine in plasma of chronic migraine and control subjects.

METHODS

We evaluated the metabolism of arginine in a group of patients affected by chronic migraine. Quantification of arginine, ornithine, citrulline, monomethyl arginine (NMMA), dimethylarginines (ADMA, SDMA), and tyramine was performed by ultra-performance liquid chromatography coupled with a triple quadrupole mass spectrometer.

RESULTS

Chronic migraine patients showed low plasma levels of arginine, significantly elevated levels of ornithine, ADMA, and NMMA whereas the levels of citrulline and SDMA were in the range of controls.

CONCLUSIONS

The elevated levels of ADMA and NMMA, inhibitors of nitric oxide synthase, suggest that the metabolism of arginine may be inhibited with a possible reduction of NO release in the circulation of chronic patients. This suggests that the origin of pain may not be related to the vasodilation of trigeminal vascular system that occurs in episodic migraine patients.

Incomplete Systemic Recovery and Metabolic Phenoreversion in Post-Acute-Phase Nonhospitalized COVID-19 Patients: Implications for Assessment of Post-Acute COVID-19 Syndrome

We present a multivariate metabotyping approach to assess the functional recovery of nonhospitalized COVID-19 patients and the possible biochemical sequelae of "Post-Acute COVID-19 Syndrome", colloquially known as long-COVID. Blood samples were taken from patients ca. 3 months after acute COVID-19 infection with further assessment of symptoms at 6 months. Some 57% of the patients had one or more persistent symptoms including respiratory-related symptoms like cough, dyspnea, and rhinorrhea or other nonrespiratory symptoms including chronic fatigue, anosmia, myalgia, or joint pain. Plasma samples were quantitatively analyzed for lipoproteins, glycoproteins, amino acids, biogenic amines, and tryptophan pathway intermediates using Nuclear Magnetic Resonance (NMR) spectroscopy and mass spectrometry. Metabolic data for the follow-up patients (n = 27) were compared with controls (n = 41) and hospitalized severe acute respiratory syndrome SARS-CoV-2 positive patients (n = 18, with multiple time-points). Univariate and multivariate statistics revealed variable patterns of functional recovery with many patients exhibiting residual COVID-19 biomarker signatures. Several parameters were persistently perturbed, e.g., elevated taurine (p = 3.6 × 10-3 versus controls) and reduced glutamine/glutamate ratio (p = 6.95 × 10-8 versus controls), indicative of possible liver and muscle damage and a high energy demand linked to more generalized tissue repair or immune function. Some parameters showed near-complete normalization, e.g., the plasma apolipoprotein B100/A1 ratio was similar to that of healthy controls but significantly lower (p = 4.2 × 10-3) than post-acute COVID-19 patients, reflecting partial reversion of the metabolic phenotype (phenoreversion) toward the healthy metabolic state. Plasma neopterin was normalized in all follow-up patients, indicative of a reduction in the adaptive immune activity that has been previously detected in active SARS-CoV-2 infection. Other systemic inflammatory biomarkers such as GlycA and the kynurenine/tryptophan ratio remained elevated in some, but not all, patients. Correlation analysis, principal component analysis (PCA), and orthogonal-partial least-squares discriminant analysis (O-PLS-DA) showed that the follow-up patients were, as a group, metabolically distinct from controls and partially comapped with the acute-phase patients. Significant systematic metabolic differences between asymptomatic and symptomatic follow-up patients were also observed for multiple metabolites. The overall metabolic variance of the symptomatic patients was significantly greater than that of nonsymptomatic patients for multiple parameters (χ2p = 0.014). Thus, asymptomatic follow-up patients including those with post-acute COVID-19 Syndrome displayed a spectrum of multiple persistent biochemical pathophysiology, suggesting that the metabolic phenotyping approach may be deployed for multisystem functional assessment of individual post-acute COVID-19 patients.

Quantification of endogenous aminoacids and aminoacid derivatives in urine by hydrophilic interaction liquid chromatography tandem mass spectrometry

Aminoacids and their derivatives are key biologically important metabolites and reliable, rapid and accurate, quantification for these analytes in urine remains an important analytical challenge. Here a fast and reliable HILIC-tandem MS method is presented for application in clinical or nutritional studies. The developed method was validated according to existing guidelines adapted for endogenous analytes. The validation strategy provided evidence of linearity, LOD and LOQ, accuracy, precision, matrix effect and recovery. The surrogate matrix approach was applied for calibration proving satisfactory accuracy and precision based on standard criteria over the working concentration ranges. Intra and inter day accuracy was found to range between 0.8 and 20% for the LQC (low QC) and between 0.05 and 15 % for MQC (medium QC) and HQC (high QC). Inter and intraday precision were found to be between 3 and 20 % for the LQC and between 1 and 15% for the MQC and HQC. The stability of the analytes, in both surrogate and pooled urine QC samples, was found to be within 15% over a short period at 4 °C or after a up to 3 freeze-thaw cycles. The uncertainty of the method was also assessed to provide increased confidence for the acquired measurements. The method was successfully applied to a subset of human urine samples involved in a study of amino acids dietary uptake. This method may provide a valuable tool for many applications or studies where amino acid metabolic signatures in the excreted urine are under investigation.

Racemization without deamidation: Effect of racemization conditions on 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate tagged amino acids

The aim of this research study was to provide a more thorough understanding of the underlying mechanism and to broaden the application field of the recently introduced racemization method employing the amino acid derivatization tag 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC, AccQ) for heat-induced stereoisomerization of common amino acids as well as uniformly isotopically labeled [U-¹³C¹⁵N]-amino acids. The influence of different buffer types such as sodium borate buffer and sodium carbonate buffer as well as their pH and molarity on the racemization and deamidation of amino acids were investigated. It was found that a 0.4 M borate buffer with a pH of 8.0 +/- 0.2 was the most suitable derivatization as well as racemization buffer to ensure degradation free racemization of deamidation prone compounds such as glutamine. Hereby essential was the in-solution pH measurement before and after derivatization with AQC as well as after heat-induced racemization. This strategy provided further insight at which pH an actual racemization event was observed and when an unwanted deamidation of glutamine to glutamic acid occurred. In addition also the influence of the presence of oxygen during racemization was studied. In this context it was possible to determine ideal oxidation and racemization conditions for the production of scalemic mixtures of chiral isotopically labeled methionine AQC-DL-[U-¹³C¹⁵N]-Met as well as its oxidation products, AQC-DL-[U-¹³C¹⁵N]-Met-O and AQC-DL-[U-¹³C¹⁵N]-Met-O₂. All stereoselective separations were performed on the zwitterionic Chiralpak ZWIX(+) column combined with HPLC-ESI-QTOF-MS analysis in positive ionization mode.