The use of high pressure liquid chromatography in clinical chemistry and biomedical research

Micellar electrokinetic chromatographic and capillary zone electrophoretic methods for screening urinary biomarkers of human disorders: a critical review of the state-of-the-art

Human urine plays a central role in clinical diagnostic being one of the most-frequently used body fluid for detection of biological markers. Samples from patients with different diseases display patterns of biomarkers that differ significantly from those obtained from healthy subjects. The availability of fast, reproducible, and easy-to-apply analytical techniques that would allow identification of a large number of these analytes is thus highly desiderable since they may provide detailed information about the progression of a pathological process. From among the variety of methods so far applied for the determination of urinary metabolites, capillary electrophoresis, both in the capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) modes, represents a robust and reliable analytical tool widely used in this area. The aim of the present article is to focus the interest of the reader on recent applications of MEKC and CZE in the field of urinary biomarkers and to discuss advantages and/or limitations of each mode.

The metal coordination of sCD39 during ATP hydrolysis

BACKGROUND

The hydrolysis of ATP and ADP by ecto-nucleoside triphosphate diphosphohydrolase 1 (CD39) requires divalent cations, like Ca2+ and Mg2+. In spite of considerable work, it is not clear whether divalent cations bind to the enzyme in the absence of nucleotide or only as nucleotide-Me+2 complex. Here we study the protein ligands for Me+2.

RESULTS

When VO2+ was used as a substitute for Ca2+, the ATPase activity of soluble CD39 was 25% of that with Ca2+ as cofactor. Protein ligands of the VO2+-nucleotide complex bound to the catalytic site of soluble CD39 were characterized by electron paramagnetic resonance (EPR) spectroscopy. The EPR spectrum contained one species designated T with VO2+-AMPPNP as ligand. Two species D1 and D2 were observed when VO2+-AMPCP was bound to soluble CD39. The results suggest that species D1 and D2 represent the metal-ADP complexes at the catalytic site of soluble CD39 corresponding to the intermediate formed during ATP hydrolysis and the substrate for further hydrolysis, respectively.

CONCLUSIONS

VO2+ can functionally substitute for Ca2+ as a cofactor of sCD39, and it produces four different EPR features when bound in the presence of different nucleotides or in the absence of nucleotide. The metal coordination for each conformation corresponding to each EPR species is proposed, and the mechanism of sCD39 catalysis is discussed.

Soluble apyrases release adp during ATP hydrolysis

A soluble form of CD39 was expressed and purified from High-Five insect cells. The soluble CD39 is a monomer with a molecular weight of 54,000. The k(cat) and K(m) of the purified soluble CD39 were 4.6 s(-1) and 12 microM for ATP and 1.3 s(-1) and 7 microM for ADP as substrates, respectively. One nucleotide binding site was detected on the monomer only in the presence of Ca(2+). In contrast to the membrane bound CD39, soluble CD39 released ADP as an intermediate during ATP hydrolysis, as did the soluble potato apyrase.

New approaches in clinical chemistry: on-line analyte concentration and microreaction capillary electrophoresis for the determination of drugs, metabolic intermediates, and biopolymers in biological fluids

The use of capillary electrophoresis (CE) for clinically relevant assays is attractive since it often presents many advantages over contemporary methods. The small-diameter tubing that holds the separation medium has led to the development of multicapillary instruments, and simultaneous sample analysis. Furthermore, CE is compatible with a wide range of detectors, including UV-Vis, fluorescence, laser-induced fluorescence, electrochemistry, mass spectrometry, radiometric, and more recently nuclear magnetic resonance, and laser-induced circular dichroism systems. Selection of an appropriate detector can yield highly specific analyte detection with good mass sensitivity. Another attractive feature of CE is the low consumption of sample and reagents. However, it is paradoxical that this advantage also leads to severe limitation, namely poor concentration sensitivity. Often high analyte concentrations are required in order to have injection of sufficient material for detection. In this regard, a series of devices that are broadly termed 'analyte concentrators' have been developed for analyte preconcentration on-line with the CE capillary. These devices have been used primarily for non-specific analyte preconcentration using packing material of the C18 type. Alternatively, the use of very specific antibody-containing cartridges and enzyme-immobilized microreactors have been demonstrated. In the current report, we review the likely impact of the technology of capillary electrophoresis and the role of the CE analyte concentrator-microreactor on the analysis of biomolecules, present on complex matrices, in a clinical laboratory. Specific examples of the direct analysis of physiologically-derived fluids and microdialysates are presented, and a personal view of the future of CE in the clinical environment is given.

Useful sample handlings for reversed phase high performance liquid chromatography in emergency toxicology

Some physicochemical treatments of biological samples, before being injected into a liquid chromatograph, are discussed. The advantages of dilution, liquid and solid extraction are compared referring mainly to unpublished results. Assays of antiepileptic drugs, caffeine, theophylline, tricyclic antidepressants, valproic acid, and meprobamate are used to demonstrate the importance of sample handlings in toxicological analyses in which reversed phase high performance liquid chromatographies are applied.