Shigeki Muramatsu

Stereoselective determination of the active metabolites of a new anti-inflammatory agent (CS-670) in human and rat plasma using antibody-mediated extraction and high-performance liquid chromatography

The main metabolites of (+-)-2-[4-(2-oxocyclohexylidenemethyl)phenyl]propionic acid (CS-670), a new pro-drug anti-inflammatory agent of the 2-arylpropionic acid type, have one or two chiral centres arising from reduction of the oxocyclohexylidene moiety in addition to an original chiral centre in the propionic acid moiety. To determine these metabolites stereoselectively, antibody-mediated extraction was investigated as a stereoselective clean-up method prior to chiral HPLC. Immunoglobulin G, which recognizes each stereoisomeric cyclohexanol moiety, was coupled to cyanogen bromide-activated Sepharose 4B to prepare re-usable immobilized antibody, and its specificity was improved by examination of a washing process after charging of samples. Plasma extracted with the immobilized antibody column was derivatized with a chiral reagent to separate the enantiomers of the propionic acid moiety by HPLC. This newly developed analytical method clarified the stereoselective biotransformation of the pro-drug to pharmacologically active forms in humans and rats related to reduction of the oxocyclohexylidene moiety and chiral inversion in the propionic acid moiety.

Preparation of immunoaffinity mini-columns for the analysis of platelet activating factor (PAF) in biological samples

Using an antibody to BN 52719, an analogue of platelet activating factor (PAF), immunoaffinity mini-columns for the separation of PAF from biological samples were prepared. Rabbits were immunized with BN 52719 and immunoglobulin G (IgG) from the antiserum was coupled with Sepharose 4B. The resulting suspension of the IgG-coated Sepharose 4B in 25 mM phosphate buffer (pH 6.9) was poured into a plastic mini-column (bed volume 2.0 x 0.8 cm). Stepwise elution of the column with methanol revealed that lyso-PAF is eluted with 20-30% methanol in water whereas PAF is eluted with 50-80% methanol. For the determination of PAF in biological samples, it is recommended that lipids are extracted from the samples and the extract, reconstituted in 20% methanol, is loaded on the column. The column is then washed with 50% methanol followed by elution of PAF with 80% methanol. A small amount of [3H]PAF is added to the samples for measurement of the recoveries of PAF during the procedures of extraction and elution. The PAF is then quantified by radioimmunoassay or bioassay. Employing the immunoaffinity mini-column and radioimmunoassay, the contents of PAF in macrophages and conditioned medium after stimulation with calcium ionophore A23187, or tumor promoters such as TPA and thapsigargin, were measured.

Enzyme-linked immunosorbent assay of pravastatin, a HMG-CoA reductase inhibitor, in human plasma.

An enzyme-linked immunosorbent assay (ELISA) was developed for sensitive and specific determination of pravastatin (PS) sodium, a HMG-CoA reductase inhibitor. Preparation of immunogens to obtain antisera was carried out using chemically modified PS; beta-alanine derivative of PS (for ELISA-1) and 5-deoxy- PS (for ELISA-2) were linked to bovine serum albumin via its terminal carboxylic acid by the N-succinimidyl ester method, to avoid intramolecular lactonization of PS. Enzyme-labeled antigens were prepared similarly by coupling with horseradish peroxidase, and were used by homogeneous combination of antisera. The enzymic activity was determined using a microtiter plate coated with second antibody and tetramethylbenzidine as a chromogenic substrate. Both of the ELISA systems enabled the determination of PS in a range of 5 to 500 pg/well, with an IC50 of 36 to 130 pg/well. Cross-reactivties with main metabolites in plasma, which differed from PS in decaline moiety, were less than a few percent. When ELISA-1 was applied to the determination of PS in human plasma directly after dilution with the ELISA buffer, the detection limit and the intra-assay coefficient (5 ng/ml of PS) were 500 pg/ml and 4.5%, respectively. Further, ELISA-1 was validated by gas chromatography-mass spectrometry with the determination of PS in human plasma after oral administration at a dose of 10 mg/body.

Determination of Furosine in Hair by Liquid Chromatography–Tandem Mass Spectrometry

A sensitive and reliable analytical method for determining furosine in hair has been developed using liquid chromatography-tandem mass spectrometry. Fructose-N(omega)-formyl-d4-DL-lysine was synthesized and used as an internal standard. By the present method, glycated lysine levels in hair could be determined as fructose-lysine in only 0.1 mg of hair sample, ranging from 35.1-72.6 ng/mg hair among five healthy volunteers, which corresponded to 0.0635-0.153% of the total lysine contents in hair determined by amino acid analysis.