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.

Relationship Between Glucocerebrosidase Activity and Clinical Response to Enzyme Replacement Therapy in Patients With Gaucher Disease Type I

The quantification of enzyme activity in the patient treated with enzyme replacement therapy (ERT) has been suggested as a tool for dosage individualization, so we conducted a study to evaluate the relationship between glucocerebrosidase activity and clinical response in patients with Gaucher disease type I (GD1) to ERT. The study included patients diagnosed with GD1, who were being treated with ERT, and healthy individuals. Markers based on glucocerebrosidase activity measurement in patients' leucocytes were studied: enzyme activity at 15 min. post-infusion (Act₇₅ ) reflects the amount of enzyme that is distributed in the body post-ERT infusion, and accumulated glucocerebrosidase activity during ERT infusion (Act_75-0 ) indicates the total drug exposure during infusion. The clinical response was evaluated based on criteria established by Pastores et al. and Gaucher Severity Score Index. Statistical analysis included ROC analysis and area under the curve test. Act₇₅ and Act_75-0 were found to be moderate predictive markers of an optimal clinical response (area under the ROC of Act₇₅ was 0.733 and Act_75-0 was 0.817). Act_75-0 showed statistical significance in its discriminative capacity (p < 0.05) for obtaining an optimal response to ERT. The cut-off point was 58% (RR = 1.800; 95% CI: 1.003-3.229; p < 0.05). Moreover, Act₇₅ showed a significant and inverse correlation with the Gaucher Severity Score Index, and Act₇₅ and Act_75-0 presented a significant correlation with residual enzyme activity at diagnosis. Markers based on glucocerebrosidase activity have a good correlation with clinical response to ERT. Therefore, it could provide supporting clinical data for dose management in GD1 patients.

Enantiomeric quality control of antihistamines in pharmaceuticals by affinity electrokinetic chromatography with human serum albumin as chiral selector

The present paper deals with the enantiomeric separation of six antihistaminic enantiomers by affinity electrokinetic chromatography (AEKC)-partial filling technique using human serum albumin (HSA) as chiral selector. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and HSA plug length (SPL) was carried out since there are interactions between variables that could not be considered in an univariate optimization. The estimated and experimental resolution values obtained for antihistaminic enantiomers varied from 1.13 (for orphenadrine) to 2.15 (for brompheniramine). The optimum experimental conditions for enantioresolution of each compound were: brompheniramine, pH 8.5, [HSA] 180 microM, SPL 180 s; chlorcyclizine, pH 6.5, [HSA] 180 microM, SPL 150 s; chlorpheniramine, pH 8.25, [HSA] 160 microM, SPL 150 s; hydroxyzine, pH 7.0, [HSA] 180 microM, SPL 150 s; and orphenadrine, pH 7.8, [HSA] 160 microM, SPL 150 s. pH and the quadratic term of pH seem to be the most critical factors that determine enantioresolution of antihistamines. The validity of the developed methodologies to enantiomeric quality control of antihistamines in pharmaceutical formulations is demonstrated analyzing the content of brompheniramine, chlorpheniramine and hyroxyzine enantiomers in commercially available pharmaceutical formulations containing racemic mixtures of compounds. Resolution, accuracy, reproducibility, cost and sample throughput of the proposed methodologies make them suitable for quality control of the enantiomeric composition of antihistamines in pharmaceutical preparations.

Characterization of antihistamine–human serum protein interactions by capillary electrophoresis

An important topic in the drug discovery and development process is the role of drug binding to plasma proteins. In this paper the characterization of the interaction between antihistamines (cationic drugs) towards human serum albumin (HSA) and alpha(1)-acid glycoprotein (AGP) under physiological conditions by capillary electrophoresis-frontal analysis is presented. Furthermore, the binding of these drugs to all plasma proteins is evaluated by using ultrafiltration and capillary electrophoresis. Antihistamines present a wide-ranging behaviour with respect to their affinities towards plasma proteins. Orphenadrine, phenindamine, tripelenamine and tripolidine principally bind to HSA; carbinoxamine, dimetindene and etintidine principally bind to AGP; brompheniramine, chlorpheniramine and ranitidine present an important binding to lipoproteins and/or globulins and finally, chlorcyclizine, cinarizine, cyclizine, doxylamine, hydroxyzine, perphenazine and terfenadine do not bind to lipoproteins and/or globulins but bind to HSA and AGP in different extension. The interaction of antihistamines with HSA is determined by the hydrophobicity (direct relationship) and the polar surface area (indirect relationship) of the compounds. The steric parameters and hydrogen bonding character of compounds seems to be related with the binding of antihistamines to AGP. The antihistamine-HSA affinity constants were evaluated and the K(1) values ranged from 7 x 10(2)M(-1) (for doxylamine) to 4 x 10(4)M(-1) (for phenindamine).

Chiral separation of oxprenolol by affinity electrokinetic chromatography-partial filling technique using human serum albumin as chiral selector

The intrinsic characteristics of capillary electrophoresis have made this technique a powerful tool in the chiral separation field. The present paper deals with the enantiomeric separation of oxprenolol enantiomers by affinity electrokinetic chromatography-partial filling technique using human serum albumin (HSA) as chiral selector. Several experimental conditions and variables affecting the separation such as pH, HSA concentration and plug length, background electrolyte concentration, temperature and voltage were studied. Baseline separation of oxprenolol enantiomers was obtained in less than 8 min under the following selected conditions: electrophoretic buffer composed of 50 mM Tris-(hydroximethyl)-aminomethane (Tris) at pH 8.5; 190 microM HSA solution applied at 50 mbar for 225 s as chiral selector; oxprenolol samples contained 190 microM HSA solution injected hydrodynamically at 30 mbar for 2s and the electrophoretic runs performed at 30 degrees C applying 15 kV voltage. The proposed methodology was applied for the analysis of two pharmaceutical preparations. Resolution, accuracy, reproducibility, speed and cost of the proposed method make it suitable for quality control of the enantiomeric composition of oxprenolol in drugs. The results show that a different affinity between oxprenolol enantiomers and HSA exists and can contribute to the pharmacokinetic differentiation of these enantiomers.