Biomedical subjects

Alain Astier

Publications and source records attributed to Alain Astier.

8 recordsLinked to original sources

PubMed2006

Distribution of calcineurin activity in blood cell fractions and impact of tacrolimus inhibition.

The aim of this study was to investigate calcineurin (PP2B) activity in different blood cell fractions and its inhibition by tacrolimus. Basal PP2B activity was measured in each blood cellular fraction collected from healthy volunteers. The inhibition profile of PP2B activity was explored in isolated peripheral blood mononuclear cells (PBMC) and platelets exposed directly to tacrolimus and in PBMC and platelets isolated from whole blood previously exposed to tacrolimus. Contrasting with red blood cells (30%) and platelets (25%), PBMC represented only 8.7% of PP2B activity of unfractionated whole blood. After tacrolimus exposure of isolated PBMC and platelets, the concentration of tacrolimus required to inhibit 50% of PP2B activity (EC(50)) in PBMC was significantly lower than in platelets (0.26 ng/mL vs. 0.83 ng/mL, P < 0.001). EC(50) values were similar in PBMC and platelets isolated from whole blood previously exposed to tacrolimus (7.69 ng/mL vs. 7.42 ng/mL, respectively). These results suggest PBMC is a very suitable matrix for PP2B measurement in monitoring transplant recipients but clinical studies are necessary to solve clearly this issue.

Blood Platelets↗

PubMed2006

Pharmacokinetics of hydroxyurea 1,000 mg coated breakable tablets and 500 mg capsules in pediatric and adult patients with sickle cell disease.

Little is known about the pharmacokinetics of hydroxyurea in patients with sickle cell disease (SCD). Our aims were to evaluate bioequivalence between standard hydroxyurea capsules and a new formulation of 1,000 mg coated breakable tablets in adults and to compare pharmacokinetic parameters in adults and children with SCD. Fifteen adults received hydroxyurea capsules and tablets in a randomized cross-over study. Eleven children received hydroxyurea tablets. The results showed bioequivalence between capsules and tablets in adults. Pharmacokinetic parameters were not significantly different between adults and children. Considerable inter-individual variability was noted.

Adolescent↗

PubMed2005

Melarsoprol-cyclodextrins inclusion complexes.

Melarsoprol, a water-insoluble drug, is mainly used in the treatment of trypanosomiasis and has demonstrated an in vitro activity on myeloid and lymphoid leukemia derived cell lines. It is marketed as a very poorly tolerated non-aqueous solution (Arsobal). The aim of our work was to develop melarsoprol-cyclodextrin complexes in order to improve the tolerability and the bioavailability of melarsoprol. Phase-solubility analysis showed A(L)-type diagrams with beta-cyclodextrin (betaCD), randomly methylated beta-cyclodextrin (RAMEbetaCD) and hydroxypropyl-beta-cyclodextrin (HPbetaCD), which suggested the formation of 1:1 inclusion complexes. The solubility enhancement factor of melarsoprol (solubility in 250 mM of cyclodextrin/solubility in water) was about 7.2x10(3) with both beta-cyclodextrin derivatives. The 1:1 stoichiometry was confirmed in the aqueous solutions by the UV spectrophotometer using Job's plot method. The apparent stability constants K(1:1), calculated from mole-ratio titration plots, were 57 143+/-4 425M(-1) for RAMEbetaCD and 50 761+/-5 070 M(-1) for HPbetaCD. Data from 1H-NMR and ROESY experiments provided a clear evidence of inclusion complexation of melarsoprol with its dithiaarsane extremity inserted into the wide rim of the cyclodextrin torus. Moreover, RAMEbetaCD had a pronounced effect on the drug hydrolysis and the dissolution rate of melarsoprol. However, the cytotoxic properties of melarsoprol on K562 and U937 human leukemia cell lines was not modified by complexation.

Antineoplastic Agents↗

PubMed2004

Poly(epsilon-caprolactone) and Eudragit microparticles containing fludrocortisone acetate.

Substitutive hormonal therapies have to be administered for long periods. Thus, the development of sustained-release forms, as microparticle suspensions, is interesting in order to improve patient compliance by reducing dosing frequencies and side effects. The aim of this work was to compare different formulations of fludrocortisone microparticles for the treatment of mineralocorticoid insufficiency. The study was done with different polymers (poly(epsilon-caprolactone), Eudragit RS and Eudragit RL) and different processes (O/W solvent evaporation methods and S/O/W evaporation methods). The use of a suspension of micronized drug in dichloromethane as dispersed phase (S/O/W method) significantly improved the process. Whereas low concentrations of FLU dissolved in the dispersed phase led to smooth-surface homogeneous microparticles and poor incorporation efficiency (5.8-7.3%); suspensions of FLU led to microparticles with numerous crystals on their surfaces (S/O/W microparticles) and high incorporation efficiency (about 79%). However, the best release profiles were obtained with microparticles prepared with 7.5 mg/ml of dichloromethane, near saturation. Moreover, the use of mixtures of poly(epsilon-caprolactone), Eudragit RS and RL did not improve the release profiles.

Chemistry, Pharmaceutical↗

PubMed2003

Determination of serine/threonine protein phosphatase type 2B PP2B in lymphocytes by HPLC.

Current cyclosporin (CsA) and tacrolimus (FK506) monitoring methods are based on blood concentrations determination, but the optimal sampling times are not clearly defined. An alternative pharmacodynamic approach has recently been introduced, based on assaying lymphocytes activity of calcineurin (PP2B), a phosphatase that is partially inhibited by CsA and FK506. However, the princeps method uses large amounts of radioactive [32P]substrate, raising a number of safety issues. Here we describe an alternative method for PP2B activity determination, based on HPLC coupled with spectrophotometric detection. A 19-amino-acid peptide is phosphorylated by a protein kinase, and further dephosphorylated by lymphocyte PP2B in the presence of okadaic acid. The two peptides are separated by using reverse-phase chromatography with a detection wavelength of 205 nm. After lymphocyte isolation by density-gradient centrifugation, PP2B activity is derived from the dephosphorylated peptide concentration measured during the first 6 min of the enzymatic reaction. This technique gives reproducible results and good analytical sensitivity with 10(6) lymphocytes. With an average isolation rate of 59.6%, only 7 ml of blood is required, making the method suitable for lymphopenic patients. Moreover, PP2B activity is stable in blood samples kept for 24h at room temperature and in isolated lymphocytes stored for 48 h at -20 degrees C. We validated the method by comparing median PP2B activity in 10 healthy volunteers (285.0+/-46.5 pmol/min/10(6)lymphocytes) and in 10 liver transplant patients (147.8+/-71.0 pmol/min/10(6)lymphocytes) (p<0.001). The relation between calcineurin activity and tacrolimus blood concentrations was also studied.

Amino Acid Sequence↗

PubMed2002

Slow-release melarsoprol microparticles.

The present study compares two methods of preparation of microparticles of melarsoprol for the treatment of the human trypanosomiasis. Melarsoprol is poorly soluble in water and in organic media. Microparticles were formulated with modified O/W and W/O/W methods, Poly(epsilon -caprolactone) microparticles were prepared either with a suspension-in-oil-in-water (S/O/W) solvent evaporation method or by complexation of melarsoprol with methyl ss-cyclodextrin followed by a water-in-oil-in-water (W(CD)/O/W) solvent evaporation method. Results showed a poor incorporation of melarsoprol (2.89 +/- 0.20 microg mg(-1)) using the W(CD)/O/W process, while the S/O/W process allowed achieving 161 +/- 5 microg mg(-1) and seemed to be very effective for the preparation of a sustained release form of melarsoprol. Moreover S/O/W microparticles showed a slow release of the drug in 70% of phosphate buffer pH 7.4, 0.1 M and 30% of propylene glycol (about 50% in 2 h and 80% after 7 h).

Chemistry, Pharmaceutical↗

PubMed2002

Preparation of 3,4-diaminopyridine microparticles by solvent-evaporation methods.

The present study compares two methods of preparation of microparticles of 3,4-diaminopyridine (3,4-DAP) for the treatment for multiple sclerosis and Lambert-Eaton myasthenia syndrome. Poly( epsilon -caprolactone) microparticles were prepared with a solvent-evaporation W/O method. The 3,4-DAP was dispersed in dichloromethane, leading to a suspension. The dispersion and the solidification of the dichloromethane droplets in an aqueous phase have led to microparticles of 55.3+/-34.7 microm. The incorporation of the drug by milligram of powder was very low (1.91 micrograms/mg) and the scanning electron microscopy (SEM) did not show any crystal but marks of dissolved crystals were observed on the polymeric surface. EudragitRS microspheres containing 3,4-DAP were prepared by a solvent-evaporation technique using light mineral oil as continuous phase. The drug and the polymer were completely dissolved in an acetone solution, used as discontinuous phase. This formulation have led to a higher incorporation of the drug (88.25 micrograms/mg). The particle size was 91.8+/-44.3 microm. The observation, by SEM, shows many crystals on the surface and inside the microparticles. A slow-release of the drug in a phosphate buffer pH 7.4 was observed (50% in 60 min and about 70% in 4 h).

4-Aminopyridine↗

PubMed2002

Capillary gas chromatographic determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine.

This article describes two methods for the determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine using capillary gas chromatography. For 1,4-butanediol, plasma or urine samples (500 microl) were extracted by protein precipitation whereas for gamma-hydroxybutyrate, plasma or urine samples (500 microl) were extracted and derivatised with BF3-butanol. The compounds were separated on a Supelcowax-10 column and detection was achieved using a flame ionization detector. The methods are linear over the specific ranges investigated, accurate (with a percentage of the nominal concentration <109.8%) and showed intra-day and inter-day precision within the ranges of 5.0-12.0 and 7.0-10.1%, respectively. No interferences were observed in plasma and urine from hospitalized patients.

Butylene Glycols↗