Recent developments and applications of EMMA in enzymatic and derivatization reactions

Optimized on-line enantioselective capillary electrophoretic method for kinetic and inhibition studies of drug metabolism mediated by cytochrome P450 enzymes

Pharmacokinetic and pharmacodynamic properties of a chiral drug can significantly differ between application of the racemate and single enantiomers. During drug development, the characteristics of candidate compounds have to be assessed prior to clinical testing. Since biotransformation significantly influences drug actions in an organism, metabolism studies represent a crucial part of such tests. Hence, an optimized and economical capillary electrophoretic method for on-line studies of the enantioselective drug metabolism mediated by cytochrome P450 enzymes was developed. It comprises a diffusion-based procedure, which enables mixing of the enzyme with virtually any compound inside the nanoliter-scale capillary reactor and without the need of additional optimization of mixing conditions. For CYP3A4, ketamine as probe substrate and highly sulfated γ-cyclodextrin as chiral selector, improved separation conditions for ketamine and norketamine enantiomers compared to a previously published electrophoretically mediated microanalysis method were elucidated. The new approach was thoroughly validated for the CYP3A4-mediated N-demethylation pathway of ketamine and applied to the determination of its kinetic parameters and the inhibition characteristics in presence of ketoconazole and dexmedetomidine. The determined parameters were found to be comparable to literature data obtained with different techniques. The presented method constitutes a miniaturized and cost-effective tool, which should be suitable for the assessment of the stereoselective aspects of kinetic and inhibition studies of cytochrome P450-mediated metabolic steps within early stages of the development of a new drug.

Isolation and characterization of bioactive compounds from plant resources: the role of analysis in the ethnopharmacological approach

The phytochemical research based on ethnopharmacology is considered an effective approach in the discovery of novel chemicals entities with potential as drug leads. Plants/plant extracts/decoctions, used by folklore traditions for treating several diseases, represent a source of chemical entities but no information are available on their nature. Starting from this viewpoint, the aim of this review is to address natural-products chemists to the choice of the best methodologies, which include the combination of extraction/sample preparation tools and analytical techniques, for isolating and characterizing bioactive secondary metabolites from plants, as potential lead compounds in the drug discovery process. The work is distributed according to the different steps involved in the ethnopharmacological approach (extraction, sample preparation, biological screening, etc.), discussing the analytical techniques employed for the isolation and identification of compound/s responsible for the biological activity claimed in the traditional use (separation, spectroscopic, hyphenated techniques, etc.). Particular emphasis will be on herbal medicines applications and developments achieved from 2010 up to date.

Capillary electrophoretic enzyme assays

In the past years, capillary electrophoresis has become a frequently used technique for enzyme assays due to the high separation efficiency and versatility as well as small sample size and low consumption of chemicals. The capillary electrophoresis assays can be divided into two general categories: pre-capillary (or offline) assays and in-capillary (or online) assays. In pre-capillary assays, the incubation is performed offline and substrate(s) and product(s) are subsequently analyzed by capillary electrophoresis. In in-capillary assays enzyme reaction and separation of the analytes are performed inside the same capillary. In such assays the enzyme is either immobilized or in solution. The latter techniques is also referred to as electrophoretically mediated microanalysis (EMMA) indicating that the individual steps of the incubation as well as analysis are performed via electrophoretic phenomena. This chapter describes both techniques using the deacetylation of acetyl-lysine residues in model peptides by sirtuin enzymes as well as the hydrolysis of acetylthiocholine by acetylcholinesterase as examples.

A replaceable dual-enzyme capillary microreactor using magnetic beads and its application for simultaneous detection of acetaldehyde and pyruvate

A novel replaceable dual-enzyme capillary microreactor was developed and evaluated using magnetic fields to immobilize the alcohol dehydrogenase (ADH)- and lactate dehydrogenase (LDH)-coated magnetic beads at desired positions in the capillary. The dual-enzyme assay was achieved by measuring the two consumption peaks of the coenzyme β-nicotinamide adenine dinucleotide (NADH), which were related to the ADH reaction and LDH reaction. The dual-enzyme capillary microreactor was constructed using magnetic beads without any modification of the inner surface of the capillary, and showed great stability and reproducibility. The electrophoretic resolution for different analytes can be easily controlled by altering the relative distance of different enzyme-coated magnetic beads. The apparent K(m) values for acetaldehyde with ADH-catalyzed reaction and for pyruvate with LDH-catalyzed reaction were determined. The detection limits for acetaldehyde and pyruvate determination are 0.01 and 0.016 mM (S/N = 3), respectively. The proposed method was successfully applied to simultaneously determine the acetaldehyde and pyruvate contents in beer samples. The results indicated that combing magnetic beads with CE is of great value to perform replaceable and controllable multienzyme capillary microreactor for investigation of a series of enzyme reactions and determination of multisubstrates.

Inhibitor screening of pharmacological chaperones for lysosomal β-glucocerebrosidase by capillary electrophoresis

Pharmacological chaperones (PCs) represent a promising therapeutic strategy for treatment of lysosomal storage disorders based on enhanced stabilization and trafficking of mutant protein upon orthosteric and/or allosteric binding. Herein, we introduce a simple yet reliable enzyme assay using capillary electrophoresis (CE) for inhibitor screening of PCs that target the lysosomal enzyme, β-glucocerebrosidase (GCase). The rate of GCase-catalyzed hydrolysis of the synthetic substrate, 4-methylumbelliferyl-β-D: -glucopyranoside was performed using different classes of PCs by CE with UV detection under standardized conditions. The pH and surfactant dependence of inhibitor binding on recombinant GCase activity was also examined. Enzyme inhibition studies were investigated for five putative PCs including isofagomine (IFG), ambroxol, bromhexine, diltiazem, and fluphenazine. IFG was confirmed as a potent competitive inhibitor of recombinant GCase with half-maximal inhibitory concentration (IC(50)) of 47.5 ± 0.1 and 4.6 ± 1.4 nM at pH 5.2 and pH 7.2, respectively. In contrast, the four other non-carbohydrate amines were demonstrated to function as mixed-type inhibitors with high micromolar activity at neutral pH relative to acidic pH conditions reflective of the lysosome. CE offers a convenient platform for characterization of PCs as a way to accelerate the clinical translation of previously approved drugs for oral treatment of rare genetic disorders, such as Gaucher disease.

Fundamental aspects of chiral electromigration techniques and application in pharmaceutical and biomedical analysis

Capillary electromigration techniques are often considered ideal methods for the analysis of chiral compounds due to the high resolution power and flexibility of the technique. Therefore, especially capillary electrophoresis using a chiral selector in the background electrolyte, also termed electrokinetic chromatography, has found widespread acceptance in analytical enantioseparations of drug compounds in pharmaceuticals and biological media. Moreover, mechanistic studies on analyte complexation by the chiral selectors have continuously been conducted in an effort to rationalize enantioseparation phenomena. These studies combined capillary electrophoresis with spectroscopic techniques such as nuclear magnetic resonance and/or molecular modeling. The present review focuses on recent examples of mechanistic aspects of capillary electromigration enantioseparations and summarizes recent applications of chiral pharmaceutical and biomedical analysis published between January 2009 and August 2010.

Advances in capillary electrophoretic enzyme assays

In recent years, capillary electrophoresis (CE) has become a frequently used tool for enzyme assays due to its well-recognized advantages such as high separation efficiency, short analysis time, small sample and chemicals consumption. The published applications cover all aspects of enzyme characterization and analysis including the determination of the enzyme activity, substrate and modulator characterization and identification, as well as the investigation of enzyme-mediated metabolic pathways of bioactive molecules. The CE assays may be classified into two general categories: (1) pre-capillary assays where the reactions are performed offline followed by CE analysis of the substrates and products and (2) online assays when the enzyme reaction and separation of the analytes are performed in the same capillary. In online assays, the enzyme may be either immobilized or in solution. The latter is also referred to as electrophoretically mediated microanalysis (EMMA). The present review will highlight the literature of CE-based enzyme assays from 2006 to November 2009. One section will be devoted to applications of microfluidic devices.