Rasmané Semde

Studies of pectin HM/Eudragit® RL/Eudragit® NE film-coating formulations intended for colonic drug delivery

Theophylline pellets were coated with Eudragit NE30D aqueous dispersions, containing various pectin HM/Eudragit RL30D ionic complexes, using an Uni-Glatt fluidized-bed apparatus. Dissolution studies were then carried out on the coated pellets at pH 6.0, in absence and in presence of commercial pectinolytic enzymes. The theophylline release from the coated pellets, after an initial latency phase, occurred linearly as a function of time. The theophylline release rate was dependent on the pectin HM content of the complexes incorporated in the coatings. The lowest theophylline release from the coated pellets was obtained when the pectin HM content of the complexes was 20.0% w/w (related to Eudragit RL), i.e. when the complexation between pectin HM and Eudragit RL is optimal. The theophylline release from the coated pellets was slower in presence of the pectinolytic enzymes when the pectin content of complexes is higher than 20% w/w. On the other hand, the effect of the enzymes induced an increase of the theophylline release when the pectin HM content of the coatings ranged between 10.0 and 15.0% w/w (related to Eudragit RL).

Effect of pectinolytic enzymes on the theophylline release from pellets coated with water insoluble polymers containing pectin HM or calcium pectinate

Theophylline pellets were coated with cellulosic (Aquacoat ECD 30, Surelease clear) or acrylic (Eudragit NE30D, RS30D) polymer aqueous dispersions, containing 10% (related to the insoluble polymer content) of pectin HM or calcium pectinate, using a Uni-Glatt fluidized-bed coating apparatus. When commercial pectinolytic enzymes were added to the dissolution media (0.05 M acetate - phosphate buffer, pH 6.0), the release of theophylline from the coated pellets was generally slower than that observed in the media without enzymes. The enzymatic slowing down of the drug release, depending on the type of the aqueous polymer dispersion used, is more important with mixed Eudragit NE/calcium pectinate coated pellets. The results obtained have been examined with regard to the validity of the approach based on the combination of pectins and the insoluble polymer aqueous dispersions intended for specific-delivery of drugs to the colon. The mechanism of the hydrophilic drug release from pellets coated with insoluble polymer aqueous dispersions containing an aqueous gel-forming polymer has been also discussed.

Leaching of pectin from mixed pectin/insoluble polymer films intended for colonic drug delivery

Investigations intended to combine pectin HM or calcium pectinates with commercially available aqueous polymer dispersions for colon-specific drug delivery have been conducted on isolated films. The mixed films were prepared from Aquacoat® ECD 30, Surelease® clear, Eudragit® RS30D or Eudragit® NE30D containing 5, 10 or 15% w/w (related to insoluble polymer content) of pectin HM or 10% w/w of calcium pectinates. The kinetics of pectin leaching from the mixed films, incubated in 0.05 M acetate–phosphate buffer (pH 4.5, 37°C) in the absence of pectinolytic enzymes, showed that pectin HM or calcium pectinates were quickly released from the different films except from the mixed pectin/Eudragit® RS films. Moreover, in these cases, the leaching of pectin from Eudragit® RS films containing up to 10% w/w (related to Eudragit® RS polymer content) of pectin HM or pectin LM, was significantly faster in the presence of enzymes than in absence. These results indicate that the associations of pectin HM or LM and Eudragit RS are likely to give more suitable coating materials for colon-specific drug delivery than the other combinations.

Study of some important factors involved in azo derivative reduction by Clostridium perfringens

In order to design azo polymers having potential for use as colonic coating materials, the most important factors able to affect the bacterial degradation of azo derivatives were evaluated by a reliable method, using Clostridium perfringens ATCC 3626 as colonic bacteria. The azo degradation was followed by recording the decrease of the absorbance of azo dye solutions in phosphate buffer salt (PBS), pH 7.2, containing Clostridium perfringens, vs time. The results obtained show that the degradation of azo substrates is linear (zero order), faster in basic media and when a redox mediator, such as riboflavin or benzylviologen, is introduced in the incubation medium. Moreover, the substrate redox potential was shown not to affect significantly the degradation rates. However, when several azo dyes are introduced simultaneously into the incubation medium, the microbial azo reduction occurs sequentially as a function of the substrate redox potential, the substrate having the smallest negative redox potential being degraded first. Finally, when Eudragit® RL/RS films containing an azo dye (amaranth) are incubated with Clostridium perfringens or NADPH, the time required to bleach the films decreases dramatically when the percentage of Eudragit® RL in the films increases, as a result of the increase of the film permeability.

Self-assembled biotransesterified cyclodextrins as Artemisinin nanocarriers – I: Formulation, lyoavailability and in vitro antimalarial activity assessment

We recently reported a one-step transesterification of cyclodextrins (CDs) by vinyl-acyl fatty esters catalyzed by thermolysin. By using the solvent displacement method and depending on the experimental conditions, the CD derivatives grafted with decanoic alkyl chains (CD-C(10)) yielded either nanosphere or nanoreservoir-type systems with a size ranging from 70 to 220 nm. Both types of nanostructures were able to associate artemisinin (ART), a well-known antimalarial lipophilic drug. The formulation parameters were optimized to reach stable and high ART dosage corresponding to drug levels of 0.3 and 1.6 mg mL(-1) in the colloidal suspension, for the spherical and reservoir-type nanosystems, respectively. PEG surface-decorated nanoparticles were also prepared by co-nanoprecipitation of PEG fatty acid esters and CD-C(10) molecules. The integration of the PEGylated amphiphiles within the CD-C(10) nanostructures did not influence the ART lyoavailability. Both types of ART-loaded nanosystems showed a sustained in vitro release profile over 96 (nanoreservoirs) and 240 h (nanospheres). Finally, the in vitro antimalarial activity was evaluated using the lactate dehydrogenase assay. ART-containing colloidal suspensions inhibited the growth of cultured Plasmodium falciparum, both multi-resistant K1 and susceptible 3D7 strains with IC(50) values (2.8 and 7.0 ng mL(-1)) close to those of reference ART solution. These colloidal nanosystems based on CD derivatives and containing ART may provide a promising alternative formulation for injectable use of ART.

Monoolein-water liquid crystalline gels of gentamicin as bioresorbable implants for the local treatment of chronic osteomyelitis: in vitro characterization.

To maximize the efficacy of chronic osteomyelitis antibiotherapy while reducing antibiotic systemic toxicity, as well as time and costs of hospitalizations, it has been thought that monoolein–water gels incorporating gentamicin sulfate could be used as local, bioresorbable, and sustained-release implants. For this purpose, four formulations were examined with regard to their physicochemical and in vitro drug release characteristics. Hot stage microscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction showed cubic liquid crystalline and eutectic structures. The more suitable formulation consisting of 80–15–5% wt/wt monoolein–water–gentamicin sulfate progressively released the antibiotic for a period of 3 weeks without burst effect. Moreover, the content and the release profile of gentamicin sulfate were not significantly changed after storage at 2–6°C for a period of 10 months.

Progress in Developing Amphiphilic Cyclodextrin-Based Nanodevices for Drug Delivery

Nowadays, colloidal drug carriers represent an alternative to solve drug bioavailabily problems. During the past two decades, colloidal drug carriers have proved to improve the therapeutic index of drugs and thus increase their efficacy and/or reduce their toxicity. However, the major challenge in the development of these drug carriers remains the search for materials able to self-organize into stable nanoscale systems. In particular, amphiphilic α-, β- and γ-cyclodextrins (CDs), grafted on their secondary or primary side with different aliphatic chains, have been investigated as drug delivery vehicles due to their ability to self-assemble and form various stable colloidal systems such as micellar aggregates, nanoreservoirs or nanoparticles exhibiting a matricial, multilamellar or hexagonal supramolecular organization. These self-assembled CD-based nanodevices show some advantages in terms of stability, good ability to associate lipophilic drugs and good in vivo tolerance. This review focuses on the potential of the structured nanoparticles obtained from nonionic amphiphilic CDs in drug delivery and targeting. We discuss the synthesis and characterization of the building blocks as well as the preparation and characterization of colloidal particles made from these materials. We also considered some pharmaceutical applications and identified opportunities for an optimum use of this CD-based nanotechnology approach in addressing worldwide priority health problems.

Synthesis and enzymatic degradation of epichlorohydrin cross-linked pectins.

Abstract The water solubility of pectin was successfully decreased by cross-linking with increasing amounts of epichlorohydrin in the reaction media. The initial molar ratios of epichlorohydrin/ galacturonic acid monomer in the reaction mixtures were 0, 0.37, 0.56, 0.74, 1.00, 1.47, and 2.44. The resulting epichlorohydrin cross-linked pectins were thus referred to as C-LP0, C-LP37, C-LP56, C-LP75, C-LP100, C-LP150, and C-LP250, respectively. Methoxylation degrees ranged from 60.5 ± 0.9% to 68.0 ± 0.6%, and the effective cross-linking degrees, determined by quantification of the hydroxyl anions consumed during the reaction, were 0, 17.8, 26.0, 38.3, 46.5, 53.5, and 58.7%, respectively. After incubating the different cross-linked pectins (0.5% w/v) in 25 mL of 0.05 M acetate–phosphate buffer (pH 4.5), containing 50 µL of Pectinex® Ultra SP-L (pectinolytic enzymes), between 60 and 80% of the pectin osidic bounds were broken in less than 1 hr. Moreover, increasing the cross-linking degree only resulted in a weak slowing on the enzymatic degradation velocity.

Self-assembled biotransesterified cyclodextrins as potential Artemisinin nanocarriers. II: In vitro behavior toward the immune system and in vivo biodistribution assessment of unloaded nanoparticles.

In a previous study, we reported on the formulation of Artemisinin-loaded surface-decorated nanoparticles (nanospheres and nanoreservoirs) by co-nanoprecipitation of PEG derivatives (PEG1500 and PEG4000-stearate, polysorbate 80) and biosynthesized γ-CD fatty esters. In the present study, the co-nanoprecipitation was extended to the use of a PEGylated phospholipid, namely DMPE-PEG2000. As our goal was to prepare long-circulating nanocarriers for further systemic delivery of Artemisinin (ART), here, we have investigated, on the one hand, the in vitro behavior of these surface-modified γ-CD-C10 particles toward the immune system (complement activation and macrophage uptake assays) and, on the other hand, their biodistribution features in mice. These experiments showed that the in vitro plasma protein adsorption and phagocytosis by macrophage cells triggered by γ-CD-C10 nanoparticles were significantly reduced when their surface was decorated with amphiphilic PEGylated molecules, in particular PEG1500-stearate, DMPE-mPEG2000 or polysorbate 80. The prolonged blood circulation time assessed by fluorescence imaging was demonstrated for unloaded γ-CD-C10-based nanospheres and nanoreservoir particles containing DMPE-PEG2000 and polysorbate80, respectively. These nanoparticles also proved to be non-hemolytic at the concentration range used in vivo. Within the limits of the conducted experiments, the co-nanoprecipitation technique may be considered as an alternative for surface modification of amphiphilic CD-based drug delivery systems and may be applied to the systemic delivery of ART.

Effect of hydroxyapatite on the physicochemical characteristics of a gentamicin-loaded monoolein gel intended to treat chronic osteomyelitis.

Many works have demonstrated the real potential of gentamicin-monoolein-water formulations as bioresorbable and sustained-release implants for the local treatment of the chronic osteomyelitis. In order to improve the efficacy of this type of implant, the incorporation of hydroxyapatite, a well-known osteointegrator material, is thought to be an interesting approach. Five formulations incorporating 0, 2.5, 5, 10, and 20% of hydroxyapatite were examined with regard to their physicochemical and in vitro drug release characteristics. The rheological, thermal (differential scanning calorimetric and thermogravimetric diffraction analysis), X-ray diffraction, and dissolution studies have showed that the presence of hydroxyapatite does not dramatically disturb the cubic liquid crystalline structure of the monoolein-water gel and their ability to progressively release the antibiotic. Implant 20% that was capable to release gentamicin sulfate over a period of four weeks without marked burst effect could be used as a more suitable biodegradable delivery system for the local management of chronic osteomyelitis.