Björn Arvidsson

Interferon-β affects the tryptophan metabolism in multiple sclerosis patients

Tryptophan and its metabolites are of great interest in understanding the pathogenesis of multiple sclerosis (MS). The total levels of tryptophan and its metabolites, kynurenine and kynurenic acid were determined in plasma by capillary liquid chromatography electrospray ionisation tandem mass spectrometry. This is the first report of the plasma levels of these analytes in healthy controls and relapsing–remitting MS patients receiving long‐term and acute interferon‐β (IFN‐β) treatment. Twenty‐four hours post‐administration increased kynurenine levels (first IFN MS versus healthy, P = 0.042) and kynurenine/tryptophan ratio (K/T; first IFN MS versus healthy, P =0.027; first IFN MS versus long‐term IFN MS, P = 0.036) were found. The long‐term IFN MS group had higher K/T ratios at 4 and 12 h post‐administration (P = 0.015 and 0.009, respectively). The increase of K/T ratio in the first IFN MS group indicate an induction of the enzyme indolamine‐2,3‐dioxygenase (IDO), as reported earlier in experimental allergic encephalomyelitis. As IDO is participating in both inflammatory and neurodegenerative processes, further knowledge of its involvement in the pathogenesis of MS is of great importance.

Characterization of Human Urinary Metabolites of the Antimalarial Piperaquine

Five metabolites of the antimalarial piperaquine (PQ) (1,3-bis-[4-(7-chloroquinolyl-4)-piperazinyl-1]-propane) have been identified and their molecular structures characterized. After a p.o. dose of dihydroartemisinin-piperaquine, urine collected over 16 h from two healthy subjects was analyzed using liquid chromatography (LC)/UV, LC/tandem mass spectrometry (MS/MS), Fourier transform ion cyclotron resonance (FTICR)/MS, and H NMR. Five different peaks were recognized as possible metabolites [M1, 320 m/z; M2, M3, and M4, 551 m/z (PQ + 16 m/z); and M5, 567 m/z (PQ + 32 m/z)] using LC/MS/MS with gradient elution. The proposed carboxylic M1 has a theoretical monoisotopic molecular mass of 320.1166 m/z, which is in accordance with the FTICR/MS (320.1168 m/z) findings. The LC/MS/MS results also showed a 551 m/z metabolite (M2) with a distinct difference both in polarity and fragmentation pattern compared with PQ, 7-hydroxypiperaquine, and the other 551 m/z metabolites. We suggest that this is caused by N-oxidation of PQ. The results showed two metabolites (M3 and M4) with a molecular ion at 551 m/z and similar fragmentation pattern as both PQ and 7-hydroxypiperaquine; therefore, they are likely to be hydroxylated PQ metabolites. The molecular structures of M1 and M2 were also confirmed using H NMR. Urinary excretion rate in one subject suggested a terminal elimination half-life of about 53 days for M1. Assuming formation rate-limiting kinetics, this would support recent findings that the terminal elimination half-life of PQ has been underestimated previously.

Vascular permeability to fluorescent protein tracer in trigeminal nerve and gasserian ganglion

SummaryA study was made on the microvascular permeability in various regions of the fifth cranial nerve by comparing the distribution of intravenously injected fluorescent labelled albumin in ophthalmic nerve, Gasserian ganglion and adjacent parts of the roots in mice, rats and rabbits. The following observations were made:1.The tracer passed within 15 min after the injection out of the vessels both in the Gasserian ganglion and in the adjacent parts of the trigeminal nerve and its roots.2.The endoneurium of the ophthalmic branch of rat trigeminal nerve did not contain extravascular signs of the tracer. However, there was a marked outpouring of tracer in the epineurium of the same nerve.3.In the Gasserian ganglion the tracer spread mainly in intercellular spaces and accumulated around neurons. Nerve cells containing fluorescent tracer were only exceptionally observed even 24 h after the injection. The blood vessels in the intracranial portion of the fifth cranial nerve, particularly those in the Gasserian ganglion therefore differ from cerebral vessels in being permeable with regard to albumin. In the rat the peripheral branches of the same nerve are similar to the sciatic nerve with regard to the permeability properties; the endoneurial vessels are impermeable whereas epineurial vessels are permeable to fluorescent labelled albumin.

Rapid capillary electrophoresis time-of-flight mass spectrometry separations of peptides and proteins using a monoquaternarized piperazine compound (M7C4I) for capillary coatings.

A monoquaternarized piperazine, 1‐(4‐iodobutyl) 4‐aza‐1‐azoniabicyclo[2,2,2] octane iodide (M7C4I), has been evaluated as a surface derivatization reagent for CE in combination with TOF MS for the analysis of proteins, peptides, and protein digests. The M7C4I piperazine, at alkaline pH, forms a covalent bond via alkylation of the ionized silanols producing a cationic surface with a highly stable and reversed EOF. The obtained surface yields rapid separations (less than 5 min) of peptides and proteins at acidic pH with high separation efficiencies (up to 1.1×106 plates/m for peptides and up to 1.8×106 plates/m for proteins) and no observed bleeding of the coating reagent into the mass spectrometer. The simplicity of the coating procedure also enables fast (2 min) regeneration of the surface, if necessary. This is useful in the analysis of complex samples in order to prevent possible memory effects. The potential of using M7C4I‐coated capillaries for MS analysis of complex samples is demonstrated by the separation of peptides, proteins, and protein digests. Even more, the spectacular thing in which large intact proteins with molecular masses over 0.5 MDa could be separated. The coating showed good ability to handle these large proteins with high efficiency and retained peak shape as demonstrated by separation of IgG1 (150 kDa) and thyroglobulin (669 kDa).

Quantitative aspects of analyzing small molecules - monitoring singly or doubly charged ions? A case study of ximelagatran.

Precision, reproducibility and lower limit of quantitation (LLOQ) are important characteristics of a quantitative method. We have investigated these properties for Ximelagatran (Xi), which has a high tendency to form doubly charged ions in electrospray ionization (ESI), by studying the percentage of doubly charged species formed when varying the formic acid (FA) concentration, analyte concentration, amount of organic modifier and flow rate. It was found that the percentage of [Xi + 2H](2+) can be controlled to be more than 90% or less than 10% by varying the amount of FA present, and that the change between these values is dramatic. Furthermore, the percentage of [Xi + 2H](2+) formed decreases with increased analyte concentration and increased flow rate. No apparent relationship with the amount of organic modifier was found. The results have the implication that, by carefully controlling the selected parameters, the LLOQ, precision and reproducibility can be improved. We have compared the fragmentation of the singly and doubly charged species and concluded that the [Xi + 2H](2+) ion is more inclined to undergo fragmentation than [Xi + H](+). As a consequence, unusual instrumental settings had to be used for the experiments. The fragmentation patterns are to a great extent similar, but the doubly charged species is more inclined to generate low-mass product ions.

Online capillary solid phase extraction and liquid chromatographic separation with quantitative tandem mass spectrometric detection (SPE-LC–MS/MS) of ximelagatran and its metabolites in a complex matrix

This work presents the development and validation of a fully automated quantitative analysis method of melagatran, its prodrug ximelagatran, and its major metabolites for the study of drug behavior in biofluids. The method involves online sample clean-up and enrichment on a C(4) capillary column followed by separation on a capillary C(18) column. Electrospray ionization tandem mass spectrometric detection in positive ion mode was performed with multiple reactions monitoring of eight different transients, divided into two time segments with four transients each. The structural similarity, the complexity of the matrix (pig liver extract) and the formation of isobaric fragment ions, made efficient chromatographic separation necessary. The analysis method provides valid accuracy (<9%; RSD%), precision (<8%; RSD%), linearity (<1.2 nM-1 microM; R(2)>0.999), limit of quantitation (<3.6 nM), retention repeatability (<1.2%; RSD%), selectivity, as well as analyte and column stabilities over a wide concentration range.