High-performance liquid chromatography-based assays of enzyme activities

Quantitative assessment of the exposure-efficacy relationship of glucocerebrosidase using Markovian elements in Gaucher patients treated with enzyme replacement therapy

AIMS

The aims of this study are (i) to develop a population pharmacokinetic model of enzyme activity in Gaucher-type 1 (GD1) patients after intravenous administration of enzyme replacement therapy (ERT) and, (ii) to establish an exposure-efficacy relationship for bone marrow infiltration to propose dose adjustments according to patient covariate values.

MATERIALS AND METHODS

A prospective follow-up, semi-experimental multi-centre study was conducted in four hospitals to evaluate the pharmacokinetics, efficacy and safety of ERT in GD1 patients. 25 individuals with 266 glucocerebrosidase (GCase) observations in plasma and leukocytes and 14 individuals with 68 Spanish Magnetic Resonance Imaging (S-MRI) observations were enrolled.

RESULTS

A two concatenated compartments with zero-order endogenous production and first-order distribution (CL₁ =3.85 x10^-1 L/d) and elimination (CL₂ = 1.25 L/d) allowed to describe GCase observations in plasma and leucocytes, respectively. An exponential time-dependency (k_T =6.14 x10^-1 d^-1 ) effect on CL₁ was incorporated. The final exposure-efficacy model was a longitudinal logistic regression model with a first-order Markov element. An Emax function (EC₅₀ =15.73 U/L and Emax=2.33) linked steady-state concentrations of GCase in leucocytes to the probability of transition across the different S-MRI stages.

CONCLUSION

A population pharmacokinetic model successfully characterized the leukocyte activity-time profiles of GCase following intravenous administration of ERT in GD1 patients together with an exposure-efficacy relationship in bone marrow using markovian elements. The information obtained from this study could be of high clinical relevance in individualization of ERT in GD1 patients, as this could lead to anticipate decision-making regarding clinical response in bone and optimal dosing strategy. NONSTANDARD ABBREVIATIONS: -2LL: -2xlog(likelihood); ERT: enzyme replacement therapy; GCase: glucocerebrosidase activity; GD1: Gaucher disease type 1; GOF: goodness-of-fit plots; IIV: inter-individual variability; NLME: non-linear mixed effects modelling; OFV: objective function value; pc-VPC: prediction-corrected visual predictive check; PK: pharmacokinetic; RSE: relative standard error; RUV: residual unexplained variability, S-MRI: Spanish Magnetic Resonance Imaging, TDM: therapeutic drug monitoring.

Capillary electrophoresis for enzyme-based studies: Applications to lipases and kinases

Capillary electrophoresis (CE) is a powerful technique continuously expanding into new application fields. One of these applications involves the study of enzymes, their catalytic activities and the alteration of this activity by specific ligands. In this review, two model enzymes, lipases and kinases, will be used since they differ substantially in their modes of action, reaction requirements and applications making them perfect subjects to demonstrate the advantages and limitations of CE-based enzymatic assays. Indeed, the ability to run CE in various operation modes and hyphenation to different detectors is essential for lipase-based studies. Additionally, the low sample consumption provided by CE promotes it as a promising technique to assay human and viral nucleoside kinases. Undeniably, these are rarely commercially available enzymes and must be frequently produced in the laboratory, a process which requires special sets of skills. CE-based lipase and kinase reactions can be performed outside the capillary (pre-capillary) where the reactants are mixed in a vial prior to their separation or, inside the capillary (in-capillary) where the reactants are mixed before the electrophoretic analysis. These enzyme-based applications of CE will be compared to those of liquid chromatography-based applications in terms of advantages and limitations. Binding assays based on affinity CE and the compelling microscale thermophoresis (MST) will be briefly presented as they allow a broad understanding of the molecular mechanism behind ligand binding and of the resulting modulation in activity.

Generic HPLC platform for automated enzyme reaction monitoring: Advancing the assay toolbox for transaminases and other PLP-dependent enzymes

Methods for rapid and direct quantification of enzyme kinetics independent of the substrate stand in high demand for both fundamental research and bioprocess development. This study addresses the need for a generic method by developing an automated, standardizable HPLC platform monitoring reaction progress in near real-time. The method was applied to amine transaminase (ATA) catalyzed reactions intensifying process development for chiral amine synthesis. Autosampler-assisted pipetting facilitates integrated mixing and sampling under controlled temperature. Crude enzyme formulations in high and low substrate concentrations can be employed. Sequential, small (1 µL) sample injections and immediate detection after separation permits fast reaction monitoring with excellent sensitivity, accuracy and reproducibility. Due to its modular design, different chromatographic techniques, e.g. reverse phase and size exclusion chromatography (SEC) can be employed. A novel assay for pyridoxal 5'-phosphate-dependent enzymes is presented using SEC for direct monitoring of enzyme-bound and free reaction intermediates. Time-resolved changes of the different cofactor states, e.g. pyridoxal 5'-phosphate, pyridoxamine 5'-phosphate and the internal aldimine were traced in both half reactions. The combination of the automated HPLC platform with SEC offers a method for substrate-independent screening, which renders a missing piece in the assay and screening toolbox for ATAs and other PLP-dependent enzymes.

Methods for purification of glutathione peroxidase and related enzymes

The different preparative techniques and related analytical methods used for purification of glutathione peroxidase, glutathione transferase and glutathione reductase, described in papers published in the last ten years, have been reviewed in this article. Among the different purification techniques, chromatography has played a relevant role, being reported in all the papers reviewed, whereas other preparative techniques such as electrophoresis and isoelectric focusing were less employed and have been reported in only ca. 3% of cases. Frequently, several different chromatographic modes and several rechromatography steps have been employed. The use of at least three different chromatographic modes has been reported in 53% of total reviewed papers, whereas 41% of them employed two differents modes and in only 6% a single preparative chromatographic step was used. To evaluate losses and improve recovery, analytical methods for quantitation of protein and assay of enzymatic activity must be used in each purification step. Among these analytical techniques, gel electrophoresis, under denaturing conditions, has been widely used to assess purity of enzyme preparation. A discussion of the different activity assay methods used for these three enzymes is also presented in this article.

Methods for chromatographic and electrophoretic separation and assay of NADP oxidoreductases

The different techniques described in purification protocols for pyridine nucleotide-dependent enzymes have been reviewed, covering mainly the papers published in the past six years. Chromatography was reported in 100% of reviewed papers and among the chromatographic techniques, affinity chromatography was the most used (ca. 92%), followed by ion-exchange chromatography (ca. 79%), size-exclusion chromatography (ca. 64%) and hydrophobic chromatography (ca. 24%). Other chromatographic techniques were used infrequently. Each chromatographic technique has a different specific capacity and chemical selectivity and, therefore, the order of selection should be based on a precise knowledge of the nature of the sample and the amount of the target enzyme that it contains. Analytical electrophoresis was used in about 95% of the reviewed papers, with denaturing polyacrylamide gel electrophoresis (PAGE) being the most widely used mode (ca. 92%), followed by native PAGE (ca. 48%). The use of isoelectric focusing was reported in 14% of the papers, while preparative gel electrophoresis was used in only 8% of the cases. The use of other electrophoretic techniques was reported in only a few papers. The use of continuous enzymatic activity assay methods (spectrophotometric) was found in most papers, while high-performance liquid chromatography-based methods (discontinuous assays) were reported in only 11% of the reviewed articles.

High-performance liquid chromatographic study of the aromatic nitrile metabolism in soil bacteria

Simultaneous HPLC determination of bromoxynil, ioxynil and dichlobenil, three arylnitrile herbicides, and their metabolic products in soil extracts and microbiological media is described. Limits of detection (LODs) ranged from 0.56 to 3.97 ppb. Slight modification of the mobile phase composition allowed determination of 13 other aromatic nitriles. Assay of aromatic nitrile hydratase, amidase or nitrilase activities is possible by the method developed.