Marie-Christine Andry

Determination of free amino group content of serum albumin microcapsules using trinitrobenzenesulfonic acid: effect of variations in polycondensation pH

Microcapsules were prepared from human serum albumin (HSA) through an interfacial cross-linking process using terephthaloyl chloride at various pH values (5.9–11). Determination of free amino groups was performed on lyophilized microcapsules by means of a back titration method using trinitrobenzenesulfonic acid (TNBS). Increasing reaction pH was shown to result in a progressive decrease of microcapsule free amino groups. Moreover, two groups of microcapsules could be distinguished with respect to their -NH2 content: those obtained at low pH values (8 and < 8) which contained more than 400 μmolg dry weight, and those prepared from pH 9, whose -NH2 content did not exceed 110 μmolg dry weight. These results were compared with previous findings concerning the involvement of hydroxy and carboxy groups of HSA microcapsules as a function of pH, that had been obtained from FT-IR spectroscopic studies.

Cross-linked β-cyclodextrin microcapsules : preparation and properties

Abstract Microcapsules were prepared by interfacial cross-linking of β-cyclodextrins (β-CD) with terephthaloyl chloride (TC). Batches were prepared from β-CD solutions in 1 M NaOH, using 5% TC and a 30 min reaction time. Microcapsules were studied with respect to morphology (microscopy), size (laser diffraction technique) and, for selected batches, IR spectroscopy, determination of β-CD content (polarimetry after alkaline dissolution of microcapsules) and complexing properties, evaluated using p -nitrophenol (pNP) as the guest molecule. Well-formed microcapsules were obtained from 5, 7.5, and 10% β-CD solutions. The mean size of all batches was in the 10–35 μm range. The IR spectrum showed bands at 1724, 1280 and 731 cm −1 , reflecting the formation of esters. The β-CD contents were 46, 56–58 or 60–66% for batches prepared from 5, 7.5 or 10% β-CD solutions, respectively. The experiments conducted with 1 mM pNP showed a rapid complexation reaching a maximum within 1 h. When incubating 50 mg lyophilized microcapsules in 10 ml pNP solution, the maximal fixation (97.8 μmol/g microcapsules) was observed for small-sized particles (≈11 μm) prepared from a 7.5% β-CD solution. The method then appears as a simple and rapid procedure to provide stable microcapsules, having an interesting guest-binding ability.

Cross-linked β-cyclodextrin microcapsules. II. Retarding effect on drug release through semi-permeable membranes

Microcapsules were prepared by interfacial cross-linking of beta-cyclodextrins (beta-CD) with terephthaloylchloride (TC) as described previously. Complexation assays were conducted with propranolol HCl. After 1 h incubation of 50 mg lyophilized microcapsules in 10 ml propranolol solution, the amounts of fixed drug were 507.5+/-8.6 micromol and 811.2+/-16.0 micromol per g lyophilized microcapsules with 1 mM and 2 mM solutions, respectively. A dialysis experiment was then performed. After 1 h incubation of microcapsules (10 or 50 mg) in 10 ml of 2 mM propranolol solution, the suspension was dialysed against a phosphate buffer pH 7.4 at 37 degrees C. The drug diffusion was all the more retarded that the amount of added beta-CD microcapsules was higher. Finally, double microcapsules were prepared using a suspension of beta-CD microcapsules (10-100 mg) in a solution of methylene blue in an acetate buffer pH 7.4. After adding human serum albumin (HSA), the suspension was emulsified in cyclohexane and double microcapsules were obtained by cross-linking the HSA with TC. In vitro release studies showed that the incorporation of beta-CD microcapsules resulted in a decrease in release rate of methylene blue, the decrease being related to the amount of encapsulated beta-CD microcapsules. The study then suggests interesting applications of beta-CD microcapsules for modulating the release rate of drugs through semi-permeable membranes.

Microcapsules prepared through interfacial cross-linking of starch derivatives

Abstract An interfacial cross-linking process was applied to hydrosoluble starch derivatives: hydroxyethylstarch (HES) and carboxymethylstarch (CMS). It resulted in stable microcapsules, which could be easily lyophilized and gave free-flowing powders. Sodium salicylate was encapsulated in HES microcapsules. In vitro dissolution studies indicated that these walls allow a prolonged release of the tracer. CMS microcapsules exhibited hydrophilic properties, as shown by water-induced swelling and gel formation. All cross-linked polysaccharide microcapsules were characterized by a total resistance to digestive media. However, when a protein, human serum albumin (HSA) or gelatin, was added to the starch derivatives in the aqueous phase, the process provided biodegradable microcapsules.

Free amino group content of serum albumin microcapsules. III. A study at low pH values

Abstract Microcapsules were prepared by interfacial cross-linking of human serum albumin (HSA) with terephthaloyl chloride (TC). Determination of free amino groups was performed on lyophilized microcapsules with trinitrobenzene-sulfonic acid (TNBS). In two series of assays conducted with phosphate buffers, pH 7.4 and 8, respectively, microcapsules exhibited a high −NH 2 content (> 330 μmol/g dry weight), with only a slight decrease when raising TC concentration from 2.5 to 5% TC (w/v) and/or reaction time from 30 to 60 min. When the phosphate buffer, pH 7.4 (ionic strength (μ): 0.40), was replaced by an acetate buffer, pH 7.4 (μ: 0.66), supplemented with 0.125 or 0.25 M CaCl 2 , microcapsule −NH 2 content was reduced from 346 to 134 and 168 μmol/g, respectively. Control batches prepared with the acetate buffer without adding CaCI 2 also had a reduced −NH 2 content (182, μmol/g), while a higher value (302 μmol/g) was found for microcapsules prepared using a phosphate buffer with a 0.66 ionic strength. Finally, a sharp decrease in −NH 2 , content was also found for microcapsules prepared from acetate buffers at pH 5.9 (174 μmol/g) and 6.8 (158 μmol/g), as compared with microcapsules prepared from phosphate buffers at the same pH values (438 and 388 μmol/g, respectively).

Etoposide encapsulation in surface-modified poly(lactide-co-glycolide) nanoparticles strongly enhances glioma antitumor efficiency†

Etoposide (VP-16) is a hydrophobic anticancer agent inhibiting Topoisomerase II, commonly used in pediatric brain chemotherapeutic schemes as mildly toxic. Unfortunately, despite its appropriate solubilization in vehicle solvents, its poor bioavailability and limited passage of the blood-brain barrier concur to disappointing results requiring the development of new delivery system forms. In this study, etoposide formulated as a parenteral injectable solution (Teva®) was loaded into all-biocompatible poly(lactide-co-glycolide) (PLGA) or PLGA/P188-blended nanoparticles (size 110-130 nm) using a fully biocompatible nanoprecipitation technique. The presence of coprecipitated P188 on encapsulation efficacies and in vitro drug release was investigated. Drug encapsulation was determined using HPLC. Inflammatory response was checked by FACS analysis on human monocytes. Cytotoxic activity of the various simple (Teva®) or double (Teva®-loaded NPs) formulations was studied on the murine C6 and F98 cell lines. Obtained results suggest that, although noninflammatory neither nontoxic by themselves, the use of PLGA and PLGA/P188 nanoencapsulations over pre-existing etoposide formulation could induce a greatly improved cytotoxic activity. This approach demonstrated a promising perspective for parenteral delivery of VP16 and potential development of a therapeutic entity.

Determination of free amino group content of serum albumin microcapsules: II. Effect of variations in reaction time and in terephthaloyl chloride concentration

Abstract Microcapsules were prepared through interfacial cross-linking of human serum albumin (HSA) using terephthaloyl chloride (TC) at a constant pH of 9.8. Variations were performed in reaction time (for a 2.5% w/v TC concentration) and in TC concentration (for a 30 min reaction time). Determination of free amino groups was performed on lyophilized microcapsules by means of a back titration method using trinitrobenzenesulfonic acid (TNBS). When prolonging the reaction time from 2 to 30 min. microcapsule-NH 2 content progressively decreased from 154 to 60 μmol/g dry weight. These results were in good agreement with those of a previous study conducted using Fourier transform infrared spectroscopy. A slight recovery of free-NH 2 was observed after 60 and 120 min. Increasing TC concentration from 1 to 5% (w/v) resulted in a progressive decrease in microcapsule-NH 2 content from 99 to 38 μmol/g.

Proanthocyanidin microcapsules: preparation, properties and free radical scavenging activity

Abstract Microcapsules were prepared by interfacial cross-linking of grape proanthocyanidin (GPO) with terephthaloyl chloride (TC). Using 5% TC, 30-min reaction time and a stirring speed of 5000 rpm, batches were prepared from 10% GPO solutions in buffers pH 8, 9.8, and 11, respectively. Microcapsules were studied with respect to morphology (microscopy), size (laser diffraction technique), stability in water at 45°C and, for stable batches, IR spectroscopy, degradation in human plasma, and free radical scavenging activity studied by electron paramagnetic resonance (EPR) using both extinction of the stable radical DPPH (2,2-diphenyl-picryl-hydrazyl), and scavenging of OH° (evaluated using 5,5-dimethyl-pyrrolidine-N-oxide; DMPO). All particles had a mean size 5 months). Using a stirring speed of 3000 rpm at pH 11 provided 15-μm particles which gave a yellow supernatant after 3 weeks. The IR spectra of the two stable batches (pH 9.8 and 11) showed bands at 1736 and 1267 cm−1 reflecting the formation of esters. They were slowly degraded in plasma, and although less active than the initial GPO, they exhibited a significant antioxidant activity. The method appears to be an efficient means of stabilizing the polyphenol without suppressing the free radical scavenging activity.

Development and physicochemical characterization of copper complexes-loaded PLGA nanoparticles

PLGA nanoparticles were prepared via a modified W/O/W emulsion solvent diffusion process, in which all formulation components were fully biocompatible and biodegradable. Different independent processing parameters were systematically studied. Nanoparticles were characterized by DLS (particle size, polydispersity, zeta-potential) and TEM/AFM (surface morphology). An optimized formulation was used to encapsulate copper complexes of cyclen and DOTA as potential PET imaging agents. Results showed that the predominant formulation factors appeared to be the lactide-to-glycolide (L:G) ratio of PLGA, the nature of the diffusion phase, and the presence of hydroxyl ions in the first-emulsion aqueous phase. By regulating those 3 parameters, PLGA nanoparticles were prepared with very good preparation yields (>95%), a size less than 200 nm and a polydispersity index less than 0.1. TEM pictures showed nanoparticles with a narrow size distribution, a spherical shape and a smooth surface. The optimized formulation allowed to encapsulate Cu-cyclen and Cu-DOTA complexes with an encapsulation efficiency between 20% and 25%.

A new magnetic resonance imaging contrast agent loaded into poly(lacide-co-glycolide) nanoparticles for long-term detection of tumors

The incorporation of a lipophilic Gd chelate (GdDO3A-C12) in biocompatible PLGA poly(D, L-lactide-co-glycolide) nanoparticles was explored as an approach to increase the relaxivity of contrast agents for magnetic resonance imaging. By nanoprecipitation, it was possible to obtain PEGylated gadolinium nanoparticles (mean diameter of 155 nm) with high Gd loading (1.1 × 10(4) Gd centers per nanoparticle). The corresponding GdDO3AC12 ⊂ NPs nanoparticles exhibited an enhanced relaxivity (up to sixfold greater than DOTAREM® at 40 MHz) because the nanoparticle framework constrained the lipophilic Gd chelate motion and favorably impacted the Gd chelate rotational correlation time. T1-weighted imaging at 3 T on phantoms showed enhanced contrast for the GdDO3AC12 ⊂ NPs. Importantly, Gd chelate leakage was almost nonexistent, which suggested that these GdDO3AC12 ⊂ NPs could be useful for long-term MRI detection.