Characterization of stereoselectivity and genetic polymorphism of the debrisoquine hydroxylation in man via analysis of urinary debrisoquine and 4-hydroxydebrisoquine by capillary electrophoresis

Cytochrome P450 2U1, a very peculiar member of the human P450s family

Cytochrome P450 2U1 (CYP2U1) exhibits several distinctive characteristics among the 57 human CYPs, such as its presence in almost all living organisms with a highly conserved sequence, its particular gene organization with only five exons, its major location in thymus and brain, and its protein sequence involving an unusually long N-terminal region containing 8 proline residues and an insert of about 20 amino acids containing 5 arginine residues after the transmembrane helix. Few substrates, including fatty acids, N-arachidonoylserotonin (AS), and some drugs, have been reported so far. However, its biological roles remain largely unknown, even though CYP2U1 mutations have been involved in some pathological situations, such as complicated forms of hereditary spastic paraplegia. These data together with its ability to hydroxylate some fatty acids and AS suggest its possible role in lipid metabolism.

DNA-based nanocomposite as electrochemical chiral sensing platform for the enantioselective interaction with quinine and quinidine

A DNA-based nanocomposite was prepared to develop a simple strategy for electrochemical chiral analysis.

Progress of capillary electrophoresis in therapeutic drug monitoring and clinical and forensic toxicology

During the past decade, capillary electrophoresis (CE) emerged as a promising, effective, and economical approach for the analysis of licit and illicit drugs and their metabolites in biologic samples. This review provides an overview of the principles of CE, the features of CE instrumentation, and the key aspects of CE-based drug assays that were developed for therapeutic drug monitoring (TDM), clinical and forensic toxicology, and assessment of drug metabolism and pharmacokinetics. CE performed in fused-silica capillaries has sufficiently matured and can thus be applied routinely, whereas chip-based instrumentation comprising fully integrated assays is still in development. Despite the attractive advantages of electrokinetic capillary technology, relatively few CE-based assays for TDM and for drug screening of clinical and forensic interest have been adopted in the routine arena. The lack of complete systems designed for unattended operation, the reluctance of bioanalysts to replace a satisfactory existing method, and tight budgets are believed to have hindered the widespread replacement of older (mainly chromatographic) technology. Another limitation of CE is that this technique is somewhat less sensitive than other analytic techniques used for drug analysis in biologic fluids. New instrumental developments featuring user-friendly software and the introduction of assay kits, however, should increase the number of validated CE drug tests becoming used on a routine basis.

Coupling continuous separation techniques to capillary electrophoresis

One of the weak points of capillary electrophoresis is the need to implement rigorously sample pretreatment because its great impact on the quality of the qualitative and quantitative results provided. One of the approaches to solve this problem is through the symbiosis of automatic continuous flow systems (CFSs) and capillary electrophoresis (CE). In this review a systematic approach to CFS-CE coupling is presented and discussed. The design of the corresponding interface depends on three factors, namely: (a) the characteristics of the CFS involved which can be non-chromatographic and chromatographic; (b) the type of CE equipment: laboratory-made or commercially available; and (c) the type of connection which can be in-line (on-capillary), on-line or mixed off/on-line. These are the basic criteria to qualify the hyphenation of CFS (solid-phase extraction, dialysis, gas diffusion, evaporation, direct leaching) with CE described so far and applied to determine a variety of analytes in many different types of samples. A critical discussion allows one to demonstrate that this symbiosis is an important topic in research and development, besides separation and detection, to consolidate CE as a routine analytical tool.

Capillary electrophoretic separation, immunochemical recognition and analysis of the diastereomers quinine and quinidine and two quinidine metabolites in body fluids

The capillary electrophoretic separation and immunochemical recognition of the two naturally fluorescing, cationic diastereomers quinine (QN) and quinidine (QD), their hydroderivatives and two major QD metabolites (3-hydroxyquinidine and quinidine-N-oxide) was investigated. Plain aqueous phosphate buffers and an alkaline buffer containing dodecyl sulfate micelles are shown to be incapable of resolving the two diastereomers. However, incorporation of an additional chemical equilibrium (with beta-cyclodextrin) in the case of capillary zone electrophoresis (CZE) and the presence of a small amount of an organic solvent as buffer modifier (2-propanol) in dodecyl sulfate based micellar electrokinetic capillary chromatography (MECC), were found to provide separation media which lead to complete resolution of QN, QD and the other compounds of interest. Furthermore, for MECC- and CZE-based immunoassay formats, a commercially available antibody against QD was found to be a perfect discriminator between QD and QN. It was determined to recognize QD and the two QD metabolites (cross reactivity of 20--30%) but not QN. MECC and CZE with laser induced fluorescence (LIF) detection are shown to be suitable to determine QD and metabolites in urine and plasma (quinidine-N-oxide only) collected after single dose intake of 50 mg QD sulfate and of QN in urine, saliva and serum samples that were collected after self-administration of 0.5 l of quinine water (25 mg of QN). With direct injection of a body fluid, MECC with LIF was found to provide 10 ng/ml detection limits for QD and QN. This ppb sensitivity is comparable to that obtained in HPLC assays that are based upon drug extraction. Furthermore, MECC and CZE assays with UV detection are shown to provide the ppm sensitivity required for therapeutic drug monitoring and clinical toxicology of QD and QN.

Enantioselectivity of debrisoquine 4-hydroxylation in Brazilian Caucasian hypertensive patients phenotyped as extensive metabolizers

Debrisoquine (D), an antihypertensive drug metabolized to 4-hydroxydebrisoquine (4-OHD) by CYP2D6, is commonly used as an in vivo probe of CYP2D6 activity and can be used to phenotype individuals as either extensive (EMs) or poor metabolizers (PMs) of such drugs as beta-adrenergic blockers, tricyclic antidepressants, and class 1C antiarrhythmics. This report describes reversed-phase HPLC systems by which D and 4-OHD or S-(+) and R-(-)-4-OHD in urine are more selectively quantified without the need for derivatization techniques. We also studied the urinary excretion of R-(-)- and S-(+)-4-hydroxydebrisoquine in EM hypertensive patients in order to determine weather 4-OHD formation exhibits enantioselectivity. Twelve patients with mild to severe essential hypertension were admitted to the study. They received a single tablet of Declinax containing 10 mg debrisoquine sulfate. All the urine excreted during the following 8 h was collected. The debrisoquine metabolic ratio (DMR) was calculated as % of dose excreted as D/% of dose excreted as 4-OHD and the debrisoquine recovery ratio (DRR) was calculated as % of dose excreted as 4-OHD/% of dose excreted as D+4-OHD. Debrisoquine and its metabolite were determined in urine by HPLC using a reversed-phase Select B LiChrospher column, a mobile phase of 0.25 N acetate buffer, pH 5-acetonitrile (9:1, v/v) and a fluorescence detector. The limit of quantitation was determined to be 25.0 ng/ml for D and 18.75 ng/ml for 4-OHD. Intra- and inter-day relative standard deviations (RSDs) were less than 10%. All hypertensive patients studied showed a DMR of less than 12.6 or a DRR higher than 0.12 and were classified as EMs. Direct enantioselective separation on chiral stationary phase involved resolution of S-(+)-4-OHD and R-(-)-4-OHD on a Chiralcel OD-R column with a mobile phase of 0.125 N sodium perchlorate, pH 5-acetonitrile-methanol (85:12:3, v/v/v). The quantitation limit of each enantiomer was 3.75 ng/ml of urine. Intra- and inter-day RSDs were less than 10% for each enantiomer. A high degree of enantioselectivity in the 4-hydroxylation of D favouring the S-(+) enantiomer was observed, resulting in R-(-)-4-OHD not detected in the urine of the EM hypertensive patients studied.

Enantiospecific analysis by capillary electrophoresis: applications in drug metabolism and pharmacokinetics

Enantiospecific analysis has an important role in drug metabolism and pharmacokinetic investigations and its now no longer acceptable to determine total drug, or metabolite, concentrations following the administration of a racemate. Inspite of the fact that capillary electrophoresis (CE) has become an essential technique in pharmaceutical and enantiospecific analysis, the chromatographic methodologies remain the most commonly used approach for the determination of the enantiomeric composition of drugs in biological fluids. The application of CE to bioanalysis has been slow, which is in part associated with the complexity of biological matrices together with the relatively poor concentration limits of detection achievable. However, as a result of its versatility, high separation efficiency, minimal sample requirements, speed of analysis and low consumable expense CE is likely to play an increasingly significant role in the area. This review present an overview of enantiospecific CE in bioanalysis in which the approaches to enantiomeric resolution and the problems associated with biological matrices are briefly discussed. The application of enantiospecific CE to samples of biological origin is illustrated using examples where the methodology has either solved an analytical problem, or provided a useful alternative to the currently available chromatographic methods. Such improvements in methodology are associated with either the high separation efficiency and/or microanalytical capabilities of the technique. Enantiospecific CE will not replace the chromatographic methodologies but does provide the bioanalyst with a useful addition to his armamentarium.

Enantioselective determination of drugs in body fluids by capillary electrophoresis

During the past decade, chiral capillary electrophoresis (CE) emerged as a promising, effective and economic approach for the enantioselective determination of drugs in body fluids, hair and microsomal preparations. This review discusses the principles and important aspects of CE-based chiral bioassays, provides a survey of the assays developed and presents an overview of the key achievements encountered. Applications discussed encompass the pharmacokinetics of drug enantiomers, the elucidation of the stereoselectivity of drug metabolism and bioanalysis of drug enantiomers of toxicological and forensic interest.

Capillary electrophoresis in clinical and forensic analysis: recent advances and breakthrough to routine applications

This paper is a comprehensive review article on capillary electrophoresis (CE) in clinical and forensic analysis. It is based upon the literature of 1997 and 1998, presents CE examples in major fields of application, and provides an overview of the key achievements encountered, including those associated with the analysis of drugs, serum proteins, hemoglobin variants, and nucleic acids. For CE in clinical and forensic analysis, the past two years witnessed a breakthrough to routine applications. As most coauthors of this review are associated with diagnostic or forensic laboratories now using CE on a routine basis, this review also contains data from routine applications in drug, protein, and DNA analysis. With the first-hand experience of providing analytical service under stringent quality control conditions, aspects of quality assurance, assay specifications for clinical and forensic CE and the pros and cons of this maturing, cost-and pollution-controlled age technology are also discussed.

Capillary electrophoresis as a versatile tool for the bioanalysis of drugs--a review

This review article presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The principles of capillary electrophoresis and its various separation and detection modes are briefly discussed. Sample pretreatment methods which have been used for clean-up and concentration are discussed. Finally, an extensive overview of bioanalytical applications is presented. The bioanalyses of more than 200 drugs have been summarised, including the applied sample pretreatment methods and the achieved detection limits.

Characterization of the stereoselective metabolism of thiopental and its metabolite pentobarbital via analysis of their enantiomers in human plasma by capillary electrophoresis

Using capillary zone electrophoresis (CZE) with a 75 mM phosphate buffer at pH 8.5 containing 5 mM hydroxypropyl-gamma-cyclodextrin (OHP-gamma-CD) as chiral selector, the separation of the enantiomers of thiopental and its oxybarbiturate metabolite, pentobarbital, is reported. Enantiomer assignment was performed via preparation of enantiomerically enriched fractions using chiral recycling isotachophoresis (rITP) processing of racemic barbiturates and analysis of rITP fractions by chiral CZE and circular dichroism spectroscopy. Thiopental and pentobarbital enantiomers in plasma were extracted at low pH using dichloromethane and extracts were reconstituted in acetonitrile or 10-fold diluted, achiral running buffer. The stereoselectivity of the thiopental and pentobarbital metabolism was assessed via analysis of 12 plasma samples that stemmed from patients undergoing prolonged or having completed long-term racemic thiopental infusion. The data obtained revealed a modest stereoselectivity with R-(+)-thiopental/S-(-)-thiopental and R-(+)-pentobarbital/S-(-)-pentobarbital plasma ratios being < 1 (P < 0.05 compared to data obtained with racemic controls) and > 1 (P < 0.001), respectively. The total S-(-)-thiopental plasma concentration was found to be on average about 24% higher compared to the concentration of R-(+)-thiopental, whereas the total R-(+)-pentobarbital plasma level was observed to be on average 29% higher compared to the S-(-)-pentobarbital concentration.

Enantiomeric separation of methadone by cyclodextrin-based capillary and recycling isotachophoresis

The separation of methadone enantiomers by cationic capillary isotachophoresis (CITP) and recycling isotachophoresis (RITP) having (2-hydroxypropyl)-beta-cyclodextrin (OHP-beta-CD) as chiral selector in the leading electrolyte is described. Sodium acetate/acetic acid (pH between 4 and 5) served as leading electrolyte (catholyte) and acetic acid as terminator (anolyte). Complete separation of the enantiomers was obtained by CITP in a 50 microm internal diameter (ID) fused-silica capillary and in a 500 microm ID Teflon capillary. In the first approach, enantiomeric separation could be monitored via UV absorbance detection at low wavelength. With the second instrumental setup, an additional conductivity sensor permitted the visualization of the enantiomeric separation and the characterization of the buffer system employed. A 10 mM sodium acetate/acetic acid leading buffer of pH 4.3, containing 5 mM OHP-beta-CD, was found to provide best enantiomeric separation and was thus chosen for RITP. With RITP processing of a few mg of racemic methadone, partial separation of methadone enantiomers was obtained. R-(-)-methadone and S-(+)-methadone were found to be significantly (up to about 80%) enriched at the front and back side, respectively, of the isotachophoretic zone. The enantiomeric composition of methadone in the collected fractions was assessed by chiral capillary zone electrophoresis (CZE) and circular dichroism spectroscopy. CZE was found to represent a simple and efficient method for the determination of the enantiomeric excess, whereas the latter technology was noted to be the superior approach for properly characterizing fractions that contain similar amounts of the two enantiomers. Furthermore, chiral RITP and analysis of the collected fractions by circular dichroism spectroscopy is shown to be potentially useful for identification of single enantiomers in absence of pure chiral standards.