Assessment of pharmacodynamic and pharmacokinetic characteristics of drugs using microdialysis sampling and capillary electrophoresis

Novel routes to either racemic or enantiopure α-amino-(4-hydroxy-pyrrolidin-3-yl)acetic acid derivatives and biological evaluation of a new promising pharmacological scaffold

Cycloaddition between (+) or (-)-menthone-derived nitrones and N-benzyl-3-pyrroline afforded enantiopure spiro-fused heterocycles. The reaction occurred enantio- and diastereo-selectively on the less hindered side of the nitrone, the 3-pyrroline N-benzyl group being oriented outwards, thus controlling the configurations of three simultaneously created chiral centers. From either (+) or (-)-menthone, both enantiomeric cycloadducts were synthesized in excellent yield. Removing the chiral auxiliary and the N-benzyl group delivered a series of enantiopure 4-hydroxy-3-glycinyl-pyrrolidine derivatives in 3-5 steps and 36 to 81 overall yields. Using two other achiral nitrones, shorter routes to racemic analogues were developed. Two of the synthesized compounds markedly lowered extracellular glutamate level and modestly interacted with cannabinoid type-1 receptors. As these two neuroactive compounds were devoid of in vitro toxicity and did not cross the blood brain interface, they might represent potential pharmacological agents to target peripheral organs.

Simultaneous determination of dihydroxybenzene and phenylenediamine positional isomers using capillary zone electrophoresis coupled with amperometric detection

In general capillary zone electrophoresis (CZE) separation models, o-, m-, and p-phenylenediamine isomers can be separated in a weak acidic running buffer for their pK(a) values being 4.52, 5.64, 6.04, respectively, while o-, m-, and p-dihydroxybenzene isomers can be separated in a weak basic buffer for their pK(a) values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE-AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10(-7) mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK(a) and had some advantages of high sensitivity, good repeatability and small sample requirement.

Current role of capillary electrophoretic/electrokinetic techniques in forensic toxicology

The current application of capillary electrophoresis in forensic toxicology has been critically reviewed with special focus on the areas where this technique has shown real advantages over chromatographic methods. For example, capillary electrophoresis has been most successfully applied to the chiral analysis of some drugs of forensic interest, including amphetamines and their congeners. Another typical application field of capillary electrophoresis is represented by protein analysis. Recently, special interest has been paid to carbohydrate deficient transferrin (CDT), the most important biological marker of chronic alcohol abuse. Other specific applications of capillary electrophoresis of potential forensic toxicological concern are also discussed. The review includes 62 references.

Sensitive analysis of two barbiturates in human urine by capillary electrophoresis with sample stacking induced by moving reaction boundary

An on-line stacking method based on moving reaction boundary (MRB) was developed for the sensitive determination of barbital and phenobarbital in human urine via capillary electrophoresis (CE). The optimized conditions for the method are: 60 mmol L(-1) pH 11.0 Gly-NaOH as the background electrolyte, 10 mmol L(-1) pH 5.5 Gly-HCl as sample buffer, secobarbital as the internal standard (IS), 12.5 kV, 1.4 psi 10s sample injection, 75 microm ID 60.2 cm total length (50 cm effective length) capillary and 214 nm detect wavelength. Under the optimized conditions, the method can well stack and separate barbital and phenobarbital in urine samples and result in 20.5-fold and 22.6-fold improvement in concentration sensitivity for barbital and phenobarbital, respectively. Furthermore, the method holds: (1) good linear calibration functions for the two target compounds (correlation coefficients r>0.999), (2) low limits of detection (0.27 microg mL(-1) for barbital and 0.26 microg mL(-1) for phenobarbital), (3) low limits of quantification (0.92 microg mL(-1) for barbital and 0.87 microg mL(-1) for phenobarbital), (4) good precision (R.S.D. of intra-day and inter-day less than 5.38% for barbital and 1.67% for phenobarbital, respectively) and (5) high recoveries at three concentration levels (90.27-106.36% for barbital and 93.05-113.60% for phenobarbital in urine). The method is simple, sensitive and efficient, and can fit to the need of clinical and forensic toxicology.

Continuous multi-element (Cu, Mn, Ni, Se) monitoring in saline and cell suspension using on-line microdialysis coupled with simultaneous electrothermal atomic absorption spectrometry

We have developed a microdialysis sampling technique coupled on-line with simultaneous electrothermal atomic absorption spectrometry (SIMAAS) for the continuous monitoring of copper (Cu), manganese (Mn), nickel (Ni), and selenium (Se) in saline solutions and in cell suspensions. These trace elements are considered to be those associated most significantly with oxidative stress in biological systems. We employed ultrapure saline (0.9% NaCl) as the perfusate and, thus, the dialysate samples contained a high concentration of salt in the matrix. The use of modifiers [Pd coupled with Mg(NO3)2] prevented the target elements from undergoing evaporation at a pyrolysis temperature of 1200 degrees C, a process that effectively eliminated interference from NaCl. The excellent linearity, detection limits, and precision of the SIMAAS technique allowed the Cu, Mn, Ni, and Se concentrations to be determined in saline. For the on-line microdialysis-SIMAAS system, the ultrapure saline was perfused at a flow rate of 1 microL/min. The probe recoveries of Cu, Mn, Ni, and Se in saline were 57.9, 65.0, 65.5, and 67.9%, respectively. A standard saline solution was measured continuously by the on-line system to ensure long-term stability; each measurement fell within a range of two standard deviations. We determined the on-line spiked recoveries of Cu, Mn, Ni, and Se (101.3, 88.8, 91.3, and 98.5%, respectively) by adding a spiking standard into the stirred saline. The spiked recoveries (Cu, 37.5%; Mn, 3.8%; Ni, 71.1%; Se, 33.8%) were also determined through on-line spiking of a standard into the stirred cell suspension; these values demonstrate that Cu, Mn, and Se were depleted in the cell suspension, but Ni was not. The use of this on-line microdialysis-SIMAAS system permitted the in situ, dynamic, and continuous monitoring of Cu, Mn, Ni, and Se in cell suspensions at a temporal resolution of 20 min.

Analysis of serotonin in brain microdialysates using capillary electrophoresis and native laser-induced fluorescence detection

Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples.

Continuous in vivo Monitoring of Blood Diffusible Calcium Using On-line Microdialysis Sampling Coupled with Flame Atomic Absorption Spectrometry

A direct, rapid and continuous in vivo monitoring of diffusible calcium in the blood of living rabbits has been developed using microdialysis sampling coupled on-line with flame atomic absorption spectrometry. Microdialysates perfused through implanted microdialysis probes were collected with a sample loop on an injection valve and directly introduced into the flame atomizer by a carrier solution. An ultrapure saline solution (0.9% NaCI, pH 7.2) was used as the perfusion solution at a flow rate of 20 microI min(-1) via the microdialysis probe. A 0.1% La solution in 0.5% HNO3 solution was employed as the carrier solution at a nebulizer uptake flow rate of 2.5 ml min(-1). The interval for each determination was 2.5 min (2 min of sampling time, 20 s of read time and 10 s of washing time). The performance characteristics of the on-line microdialysis-FAAS system were validated as follows: linearity range, 0 - 100 mg l(-1); detection limit (3a, n = 7), 3.66 mg l(-1); precision (RSD, n = 50), 6.2%. For the evaluation of analytical accuracy, the proposed on-line method was compared with the in vivo no net flux method. The use of an on-line microdialysis-FAAS system permitted the in situ, dynamic and continuous in vivo monitoring of diffusible calcium in the blood of the living rabbits after CaCl2 administration with a temporal resolution of 2.5 min.

Investigation of the mechanism of pH-mediated stacking of anions for the analysis of physiological samples by capillary electrophoresis

Capillary electrophoresis has been widely used for the analysis of physiological samples such as plasma and microdialysate. However, sample destacking can occur during the analysis of these high-ionic strength samples, resulting in poor separation efficiency and reduced sensitivity. A technique termed pH-mediated stacking of anions (base stacking) has previously been developed to analyze microdialysate samples and achieve on-line preconcentration of analytes by following sample injection with an injection of sodium hydroxide. In this work, the mechanism of base stacking was investigated. Peak efficiency was shown to be a function of background electrolyte and sample ionic strength. Analytes representing several classes of compounds with a wide range of mobilities were used to study the effects of multiple parameters on sample stacking. The length of hydroxide injection required for stacking was shown to be dependent on analyte mobility and the type of amine background electrolyte used. Combinations of electrokinetic and hydrodynamic injections of sample and hydroxide were examined and it was concluded that although stacking could be achieved with several injection modes, electrokinetic injection of both sample and hydroxide was most effective for sample stacking. The mechanism of pH-mediated stacking for each of these modes is presented.

Automated capillary liquid chromatography for simultaneous determination of neuroactive amines and amino acids

A method for the separation and quantitative determination of neuroactive amino acids (aspartate, glutamate, citrulline, arginine, glycine, taurine, gamma-aminobutyric acid) and neuroactive amines (noradrenaline, dopamine and serotonin) in a single chromatographic analysis is presented. The method is based on pre-column derivatization with o-phthalaldehyde and tert.-butyl thiol, on-column preconcentration and separation using 50 microns I.D. packed capillary columns, and detection by amperometry. Mass limits of detection are 80-900 amol for all neurotransmitters with RSDs of 0.71 and 4.6% or better for retention time and peak area, respectively. The method was demonstrated by application to the determination of neurotransmitters in microdialysis samples collected from striatum of live rats and tissue samples extracted from butterfly brains.

Development of an integrated capillary electrophoresis/sensor for L-ascorbic acid detection

A CE/biosensor for measuring ascorbic acid was developed by coupling a polyaniline optical sensor and capillary electrophoresis (CE). The capillary column was partially modified with a thin film of polyaniline redox sensitive material. Ascorbic acid was detected by monitoring the changes in optical absorbance occurring to the polyaniline film upon the reduction reaction. The sensor response (change in optical absorbance at 650 nm) is proportional to the concentration of ascorbic acid over a range of 2.5-250 mg/L and the response range has shown a clear dependence on the characteristics of the polymerized film. High specificity and sensitivity of the present method, low sample consumption, short times of response (ca. 2 min) and the reproducibility of the results demonstrate that the CE/polyaniline-sensor could be further employed in the study of the relation between the content of L-ascorbic acid in body fluids and clinical parameters, e.g., cell ageing.

Biomedical applications of capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis (CE) is a high-efficiency analytical technique that has had a great impact as a tool in biomedical research, clinical and forensic practice in the last ten years. Only in one of the applications, the DNA analysis, it has had an explosive exponential growth in the last few years. This impact is expressed in an enormous amount of CE articles and many reviews. The CE advantages with respect to other analytical techniques: the required very small sample volume, rapid analysis, great resolution power and low costs, have made this technique ideal for the analysis of a numerous endogenous and exogenous substances present in biological fluids. The different modes of CE have been coupled to different detection techniques such as UV-absorbance, electrochemical, mass spectrometry and laser-induced fluorescence detection (LIFD) to detect different nature and molecular size separated analytes. This review focuses mostly on the applications of CE-LIFD, to measure drugs and endogenous neuroactive substances such as amino acids and monoamines, especially in microdialysis samples from experimental animals and humans. CE-LIFD trends are discussed: automated faster analysis with capillary array systems, resolution power improvement, higher detection sensitivity, and CE systems miniaturization for extremely small sample volume, in order to make CE easier and affordable to the lab bench or the clinical bed.

Micellar electrokinetic chromatography for the analysis of cefpirome in microdialysis and plasma samples obtained in vivo from human volunteers

Pharmacokinetics of drugs in the human interstitial space fluid can be monitored by means of microdialysis. However, the small-volume microdialysis samples containing low drug concentrations require a sensitive analytical method. In the present study, micellar electrokinetic chromatography (MEKC) is described for the quantification of cefpirome in human microdialysis and plasma samples. Sample preparation of human plasma samples by ultracentrifugation was suitable for comparison of plasma and microdialysate concentrations. Limits of quantification were 2 microg/mL and 0.3 microg/mL for plasma and microdialysate samples, respectively. The limit of detection (LOD) was estimated at 0.2 microg/mL for the plasma and microdialysate samples. In conclusion, MEKC is a reliable and reproducible technique for measuring cefpirome concentrations in microdialysates as well as centrifuged plasma samples.

Pharmacokinetic applications of capillary electrophoresis

This review briefly discusses the use of capillary electrophoretic (CE) methods for the investigations of different aspects of pharmacokinetics. In most investigations, CE was the method of choice because of its unique features, including high resolving power for chiral or metabolite separation, small sample volume for pediatric pharmacokinetics or for cell-based investigations, in situ microdialysis sampling for rapid eliminations, low UV wavelength detection for nonderivatized analytes, fast and simplified sample processing for existing methods that require tedious sample preparation, or as a second method for verifications. Moreover, instrumental aspects of CE-based assays for pharmacokinetic studies, such as different modes of CE methods for analyzing biological samples, sample stacking for increasing detection sensitivity, and coupling techniques with microdialysis and mass spectrometry, are also discussed in this review. Furthermore, the advantages and limitations of CE methods as well as the future outlook for pharmacokinetic studies are summarized.

Overview of capillary electrophoresis and capillary electrochromatography

This paper provides an overview on the current status of capillary electrophoresis (CE) and capillary electrochromatography (CEC). The focus is largely on the current application areas of CE where routine methods are now in place. These application areas include the analysis of DNA, clinical and forensic samples, carbohydrates, inorganic anions and metal ions, pharmaceuticals, enantiomeric species and proteins and peptides. More specific areas such the determination of physical properties, microchip CE and instrumentation developments are also covered. The application, advantages and limitations of CEC are covered. Recent review articles and textbooks are frequently cited to provide readers with a source of information regarding pioneering work and theoretical treatments.

Capillary electrophoresis in drug analysis

Capillary electrophoresis has become one of the advanced analytical methods for drugs in pharmaceutical, therapeutic, diagnostic and forensic applications. This review discusses key issues and provides key references to the topic of drug analysis using capillary electrophoresis. It gives readers a brief summary of the current status of the technology and serves as an editorial for the paper symposium "Capillary electrophoresis in drug analysis".