Francis Puisieux

Effect of PEO surface density on long-circulating PLA-PEO nanoparticles which are very low complement activators.

The rapid uptake of injected nanoparticles by cells of the mononuclear phagocytes system (MPS) is a major obstacle when a long blood circulation time is needed. Whereas nanoparticles made from PLA and stabilized by surfactants (PLA-F68) are rapidly phagocytized, the rate of phagocytosis is strongly reduced in case of nanoparticles made from a diblock copolymer (PLA-PEO). Because of the role of the complement system in opsonization, this difference of phagocytosis was hypothesized to be related to this system. An important complement consumption was obtained in 5 min in the presence of PLA-F68 particles. In the presence of a higher surface area of PLA-PEO particles possessing a high PEO surface density, the consumption remained very low. When the average PEO surface density was decreased on such particles below a given threshold, a fast and strong complement consumption occurred again. These experimental data support the concept of steric repulsion towards proteins, by surfaces covered with terminally attached PEO chains and emphasize the prime importance of PEO surface density in such an effect. The major, but probably not exclusive, role of complement as an opsonin capable of inducing a fast phagocytosis by MPS should be taken into account concerning the in vitro evaluation of nanoparticles as candidates for a long blood circulation.

In vitro degradation of nanospheres from poly(D,L-lactides) of different molecular weights and polydispersities

Abstract The aim of this work was to study the stability of nanospheres from poly(D,L-lactide) in aqueous media. The influence of the poly(D,L-lactide) molecular weight and polydispersity, pH of the medium and temperature, was investigated. The degree of DL PLA degradation was estimated by monitoring the total acidity of the medium, the lactic acid production, the molecular weight of the polymer, the mean diameter of the nanospheres and the amount of polymer remaining insoluble. Poly(D,L-lactide) degradation rate depended on polymer molecular weight and polydispersity. The data suggested that it resulted from a hydrolysis which is much more catalysed at acidic and alkaline pH than at neutral pH. Two main hydrolysis mechanisms can be proposed: a random scission at acidic pH and a sequential cleavage from the chain end in alkaline medium. Higher temperature accelerated the degradation process. The best storage conditions for an aqueous dispersion of poly(D,L-lactide) nanospheres were deduced (temperature: 4°C, pH close to neutrality).

In vitro and in vivo antitumoral activity of free, and encapsulated taxol

The anti-tumoral activity of taxol encapsulated either in liposomes or in nanocapsules was compared with that of free taxol, using the P388 and L1210 leukaemia test systems. The in vitro inhibition of cell growth was measured after 48 h and 96 h exposure to various concentrations of taxol. With P388 cells, the inhibitory activities of the three forms of the drug were similar. With the L1210 cells, however, the concentrations required for a 50 per cent inhibition of cell growth (IC50) after 48 h exposure to the drug were greater for nanocapsules than for liposomes or free taxol, the values being 0.060, 0.043 and 0.035 micrograms ml-1, respectively. However, a greater efficiency of nanocapsules was observed after 96 h exposure. Using cytomorphometric analysis, no difference was found between L1210 cells treated either with free or encapsulated taxol. In vivo, mice bearing P388 leukaemia, and treated either with taxol solubilized with 5 per cent DMSO + 5 per cent cremophor in saline solution, or with taxol encapsulated in liposomes (IP daily dose of 12.5 mg Kg-1 body weight x 4 days) showed ILS values of 65.8% and 67.9% respectively. Nanocapsules proved to be toxic, apparently due to their composition: this problem is currently under investigation.

Combined poly(isobutylcyanoacrylate) and cyclodextrins nanoparticles for enhancing the encapsulation of lipophilic drugs.

AbstractPurpose. The aim of this study was to prepare and characterize nanoparticulate systems constituted of poly(isobutylcyanoacrylate) and cyclodextrins and intended for increasing the loading of the particles with lipophilic substances. Progesterone was used as a model substance. Methods. Nanoparticles were prepared by polymerization of isobutyl-cyanoacrylate in presence of cyclodextrins or progesterone/ hydroxy-propyl-β-cyclodextrin complex. Particle size, zeta potential, cyclodextrin and progesterone loading of the particles were determined. Results. Nanoparticles could be easily prepared in presence of cyclodextrins. An increase in hydroxypropyl-β-cyclodextrin concentration resulted in small nanoparticles (less than 50 nm). It was found that large amounts of cyclodextrins remained associated to the particles, resulting in a 50 fold increase in progesterone loading compared to nanoparticles prepared in absence of cyclodextrins. Conclusions. The poly(isobutylcyanoacrylate)—cyclodextrin nanoparticles were characterized by the presence of many lipophilic sites belonging to the cyclodextrins which were firmly anchored to the structure of the particles. Therefore, this new type of nanoparticles offers probably an opportunity for increasing the loading of nanoparticles with various lipophilic drugs.

Characterization of a new ocular delivery system based on a dispersion of liposomes in a thermosensitive gel

Abstract This paper describes a novel approach for designing an ocular delivery system based on the dispersion of liposomes into a thermosensitive gel made of a copolymer of ethylene oxide and propylene oxide (poloxamer 407). At high copolymer concentrations (20–30%), and from a temperature of approximately 20°C, poloxamer 407 passes from a solution to a gel. In order to stabilize liposomes in the gel, PEG2000-DSPE was introduced in their composition. Adsorption studies investigated by size and ζ-potential measurements have shown that the adsorption was higher for positively charged or neutral non-sterically stabilized liposomes. Poloxamer 407 adsorbed to a lower extent with negatively charged or PEG-DSPE containing liposomes. Furthermore, using a fluorescent aqueous marker, it was shown that liposome permeability was dramatically reduced in the presence of poloxamer 407 when PEG-DSPE was incorporated into the liposomes. This data suggests that poloxamer 407 could adsorb, at different extents, to all types of vesicles but that bilayer destabilization by the copolymer was reduced when liposomes were sterically stabilized. This was explained by the poor accessibility of the poloxamer to the phospholipidic which is the possible consequence of the steric repulsion effect induced by polyethylene glycol. Finally, it was shown that the thermosensitivity of poloxamer 407 was maintained after introducing the liposomes into the gel. In conclusion, a new system based on a dispersion of peggylated liposomes into thermosensitive poloxamer 407 is proposed, offering new potentialities for delivery of drugs.

Mucoadhesion of Latexes. II. Adsorption Isotherms and Desorption Studies

Adsorption isotherms of poly(styrene) latexes on rat intestinal mucosa were studied under static conditions and analyzed according to different isotherm classifications. Isotherms of latexes with a particle size up to 670 nm had the characteristic shape of a disperse adsorbate on a porous adsorbent. Plateaus were reached at latex concentrations of about 2.5 g/L. The results indicated an increase in adsorption with the size and the hydrophilicity of the latexes. Typically, a surfactant-free carboxylate latex of 230 nm had a plateau of 0.66 g/m2, and a latex of 320 nm with added sodium dodecyl sulfate had a plateau of 0.881 g/m2. Surfactant-free carboxylate latex of 2 µm had a Langmuirian isotherm with a plateau level of 2.616 g/m2, which corresponded to a monolayer of adsorbed particles on the surface of mucosa. Desorption studies showed that the adsorption was irreversible. Adhesion to the mucous gel layer would therefore be limited by the mucus turnover.

Formulation study of a transdermal delivery system of primaquine

Abstract A potential transdermal application of an anti-malarial drug, primaquine, was investigated. In-vitro percutaneous absorption through hairless rat skin using either the salt or free base form of this drug was studied. Investigations were performed in order to choose an adequate vehicle for transdermal delivery of the free base form. The vehicles studied were Mygliol ® 840 (M), Labrafac Hydrophile ® (LH), Transcutol ® (T), propylene glycol (PG), oleic acid (OA) and a mixture LH/T 50:50. Finally, transdermal release of primaquine from different matrix transdermal therapeutic systems (TTS) was compared. In this optimization we studied the influence of polymer type (Eudragit ® RL 100 or ethyl cellulose), adhesive layer and drug concentration in the polymeric matrix on the release profiles. Primaquine free base was found to be very suitable for transdermal delivery. Mygliol ® 840 showed the best enhancement factor of the percutaneous flux of primaquine. The optimized TTS, which was an ethyl cellulose-based formulation with Mygliol ® 840 as vehicle, showed a percutaneous flux of 180 μg cm −2 h −1 .

Evaluation of the hydrophobic drug loading characteristics in nanoprecipitated amphiphilic cyclodextrin nanospheres

The aim of this work was to evaluate the loading capacity and the association characteristics of the hydrophobic drug progesterone on amphiphilic cyclodextrin nanospheres prepared by the nanoprecipitation method. The colloidal suspensions were prepared in the presence or absence of two different surfactants, Pluronic F68 and Tween 80. The physicochemical characteristics of the nanospheres were assessed using a nanosizer, zetameter, and transmission electron microscope. The physical state of the drug was verified using differential scanning calorimetry (DSC) and x-ray diffraction (XRD) methods. The in vitro progesterone release was investigated at 37 degrees C after dilution of the suspensions in sink conditions. Nanospheres with a mean diameter from 100 to 300 nm and a low degree of polydispersity were prepared from amphiphilic hexanoyl-gamma-cyclodextrin. The progesterone loading capacity was not affected by the formulation parameters tested. The DSC and XRD studies demonstrated the absence of the crystalline domains of progesterone in loaded nanospheres. The DSC studies also demonstrated the presence of interactions between the drug and carrier. The release of the drug from the carrier was extremely rapid and was governed by a partition phenomenon that depends only on the solubility of the drug in the release medium. From these results, we concluded that with this method, the progesterone is molecularly associated at the surface of the cyclodextrin nanospheres, probably through hydrophobic interactions in specific sites. The release profiles obtained can be of value when an improvement in the bioavailability of the drug is desired.

Mucoadhesion of Latexes. I. Analytical Methods and Kinetic Studies

A Fourier transform infrared spectroscopy/attenuated total reflection technique for direct quantification of adsorbed poly(styrene) latexes on rat intestinal mucosa was developed for deposited latex amounts up to 1.5 g/m2. The method agreed well with another dosage assay of adsorbed particles by turbidimetry after denaturation of the mucus. Adsorption kinetics were made under static conditions at latex concentrations of 4 g/L in physiological saline. Ninety percent of equilibrium was reached after 10 min for a particle size of 230 nm, 20 min for a size of 320 nm, and 30 min for a size of 670 nm. The plateaus were between 0.6 and 0.9 g/m2 (adsorbed mass per apparent surface of mucosa). The first phase of the kinetics was theoretically approached by a diffusion model in the suspension medium. Mucosa from rat jejunum and ileum could be considered as a homogeneous biological model for latex adsorption.

Surface modification of alumina particles by nonionic surfactants: Adsorption of steroids, barbiturates and pilocarpine

Abstract The sorption isotherms of several drugs (progesterone, testosterone, hydrocortisone, amobarbital, barbital, butobarbital (sodium salt), pilocarpine hydrochloride) on C alumina particles as a function of surfactant concentration (Triton X-100) were constructed. It was found that the adsorption of the drugs is considerably enhanced by the nonionic surfactant above a concentration threshold of the order of 5 × 10 −5 mol/l, although Triton X-100 itself is poorly adsorbed on the alumina particles. The maximum increase in drug adsorption due to the surfactant is found to occur close to the critical micelle concentration (CMC); the increase is by a factor of 10 for all compounds studied. Due to the poor adsorption ability of Triton X-100, the drug mole fraction at the particle surface is above 0.8 for all compounds except for pilocarpine. The sorption isotherms were of two types: the more hydrophobic compounds displayed a plateau adsorption above the CMC; for the most hydrophilic compounds and the ionic drugs, the adsorption decreased from its maximum at the CMC to almost zero at higher surfactant concentration. The above phenomena seem to be the consequence of surface particle modifications induced by the surfactant monomers rather than an adsolubilization effect.