Cameroni R

AIR COMPARTMENT MULTIPLE – UNIT SYSTEM FOR PROLONGED GASTRIC RESIDENCE (PART I. FORMULATION STUDY)

Abstract A pre-formulation study was directed to optimize the in vitro floating ability of an air compartment multiple-unit system. Each unit was formed by a coated bead composed of a calcium alginate core separated by an air compartment from a calcium alginate or calcium alginate/polyvinylalcohol (PVA) membrane. The floating ability depended on the presence of the air compartment and on membrane porosity. The porous structure generated by the leaching of PVA, employed as a water-soluble additive in the coating composition, increased the membrane permeability preventing air compartment shrinkage. In this way, units were produced which were able to float immediately upon contact with artificial gastric juice and for a long period of time. The floating ability increased with the increase in PVA concentration and molecular weight and it was found to be excellent when using PVA 100 000 at a concentration of at least 5%.

Doxorubicin-loaded gelatin nanoparticles stabilized by glutaraldehyde: Involvement of the drug in the cross-linking process

Abstract The possible involvement of the primary amino group of doxorubicin (DXR) in the cross-linking process of gelatin nanoparticles stabilized by glutaraldehyde was investigated. Nanoparticles were characterized with regard to particle size, drug content, enzymatic degradation and cross-linking degree. The size of nanoparticles was around 100–200 nm and DXR was loaded with an entrapment efficiency of 42%. Upon the study of crosslinking rate, DXR-loaded nanoparticles showed a greater number of free amino groups than the unloaded ones. This should be due to a competition between the amino group of DXR and the amino groups of the gelatin chains during the cross-linking process. Hence, a binding of a drug fraction to the protein matrix via glutaraldehyde was hypothesized and confirmed by the results of a thin-layer chromatography (TLC) analysis. According to the in vitro study only a little fraction of DXR was released as free drug (8%) when the nanoparticles were put in saline solution. The addition of proteolytic enzymes disrupts the matrix structure producing the release of a further 10–15% of the drug loading which was entrapped in the nanoparticle matrix. The remaining part of the drug corresponds to DXR covalently linked to peptide residues produced by nanoparticle digestion.

Chitosan-Alginate Microparticles as a Protein Carrier

The oral administration of peptidic drugs requires their protection from degradation in the gastric environment and the improvement of their absorption in the intestinal tract. For these requirements, a microsystem based on cross-linked alginate as the carrier of bovine serum albumin (BSA), used as a model protein, was proposed. A spray-drying technique was applied to BSA/sodium alginate solutions to obtain spherical particles having a mean diameter less than 10 μm. The microparticles were hardened using first a solution of calcium chloride and then a solution of chitosan (CS) to obtain stable microsystems. The cross-linking process was carried out at different CS concentrations and pH values of the cross-linking medium. The CS concentration affected the BSA loading in the microparticles prepared at a pH value less than the protein isoelectric point (pI). Moreover, the BSA loading at a pH value less than the pI was higher than that at a pH similar to the pI regardless of the CS concentration. This finding could be attributable to the formation of a BSA/alginate complex. The evaluation of the interaction between BSA and alginate at different pH values by means rheological measurements confirmed this hypothesis. This approach may represent a promising way to devise a microcarrier system with appropriate size for targeting the Peyers patches, with appropriate immobilization capacity, and suitable for the oral administration of peptidic drugs.

Dynamic dialysis for the drug release evaluation from doxorubicin–gelatin nanoparticle conjugates

The drug release from doxorubicin (DXR)-gelatin nanoparticle conjugates was evaluated by means of a dynamic dialysis technique. The study was carried out in absence and in presence of a proteolytic enzyme (trypsin) able to degrade the carrier. In a preliminary study the apparent permeability constant (Kcv) of the drug through the dialysis bag was evaluated in several media. On the basis of this screening, a saline solution (NaCl 0.9%, w/v) resulted appropriate to carry out the dialysis study since, in this medium, the Kcv did not depend on the drug concentration in the donor solution. In absence of the enzyme only a little fraction (from 9 to 13%, w/w of the drug content) was released from nanoparticles. This fraction was considered as the evidence of the free drug fraction. After the addition of trypsin, the diffusion of a further drug fraction was observed. This fraction is probably due to a fraction of the DXR-peptide conjugates characterised by a molecular weight lower than membrane cut-off (3500 Da).

Protein immobilization in crosslinked alginate microparticles

Oral administration of peptide and protein drugs requires their protection from the acidic and enzymatic degradation in the gastro-intestinal environment and their targeting to the absorption zone. For this purpose, an alginate microsystem, as a carrier of bovine serum albumin (BSA), as a model protein, was developed using a spray-drying technique. A hardening process with Ca 2+ and chitosan (CS) provided a system with resistance to the gastro-intestinal barriers and of appropriate size for targeting to the Peyers patches. The present work aims to evaluate the effects of the ratio of sodium alginate (Na-A) and BSA as well as the pH of the crosslinking medium on the microsystem properties. Microparticle morphological and dimensional characteristics did not change significantly with the formulation variables. BSA loading at a pH value less than the protein isoelectric point (pI) was higher than that at a pH similar to the pI owing to an electrostatic interaction between the charged protein and the polyanionic alginate. The maximum encapsulation efficiency was obtained at the highest Na-A/BSA ratio. Protein release in a simulated gastro-intestinal fluid was not affected by the preparative variables, but was controlled by the pH-dependent nature of the polymer material. Polyacrylamide gel electrophoresis (PAGE) demonstrated the stability of the protein to both the preparative conditions and the gastro-intestinal pH values.

Alginate microparticles for enzyme peroral administration

In order to protect protein and peptide drugs against inactivation by different barriers in the gastro-intestinal tract and to improve their absorption, alginate microparticles as a carrier of L-lactate dehydrogenase, were developed by spray-drying technique. However, alginate complexation and spray-drying conditions led to enzyme activity loss. Such a drawback was overcome by using protectant additives (carboxymethylcellulose sodium salt, polyacrylic acid sodium salt, lactose) preventing the enzyme inactivation by both interaction with alginate and experimental conditions, lactose having the most protective effect. Nevertheless, only polyacrylic acid sodium salt provided a microparticulate structure required for the target of the Peyers patches.

Influence of drug loading level on drug release and dynamic swelling of crosslinked gelatin microspheres

The effect of drug loading level both on dynamic swelling and drug release was evaluated using crosslinked gelatin microspheres. Owing to water penetration the microsphere diameter went first to a maximum value, which was not affected by the payload; the diameter gradually approached to an equilibrium swollen value, which was affected by drug loading level. Water absorption increases and drug diffusion decreases the microsphere diameter. Obviously, the diameter variation depends on the factor (water absorption or drug diffusion) predominating in the process. As the payload affected only the equilibrium swollen value it is reasonable to hypothesize that drug loading level has a greater effect on drug diffusion than on polymer relaxation. This rationale could explain the increase of the diffusion component of the drug release process as the payload increased.

Biodegradable intraoperative system for bone infection treatment. II. In vivo evaluation

Abstract A biodegradable implant containing gentamicin sulphate for the prevention or the treatment of bone infections was designed by using, as the polymer material, sodium alginate containing a high proportion of mannuronic sequences capable of forming a complex with the drug. By a crosslinking procedure with calcium ions, insoluble but biodegradable calcium alginate spheres were obtained and formed into a chain by means a surgical wire. To evaluate the implant effectiveness, the implant was inserted at the femur level of Wistar rats and gentamicin levels in plasma, bone and soft tissues were detected by microbiological assay. The gentamicin concentrations were found to be sufficiently high to control pathogens for at least 30 and 7 days in the bone and soft tissue, respectively, whereas plasma levels were low and detectable for only 1 day. The complete implant bioabsorption occurred within 8–10 days after implantation and no signs of rejection or inflammatory reactions were observed at the level of the surrounding tissues.

Biodegradable intraoperative system for bone infection treatment. I. The drug/polymer interaction

In order to design and evaluate an implantable device of calcium alginate spheres releasing gentamicin sulphate to prevent or treat bone infections, the interaction between the cationic gentamicin and the polyanionic alginate was examined. Such an interaction took place, both in sodium alginate solution—as shown by theological study, and during the Ca-induced polymer gelation which led to the formation of the calcium alginate spheres. Gentamicin sulphate was found to interact selectively on the mannuronic residues of alginate without competition with calcium ions involved in the polymer gelation. In contrast, calcium ions were found to interact preferentially at the level of the polyguluronic sequences, though polymannuronic sequences can also play a role. This prevented the saturation of the polymannuronic sequences by the drug. Therefore, the alginate having a higher mannuronic acid content, i.e. capable of associating a greater amount of drug, could be considered the more suitable material for the implant design.

The Influence of 2-Hydroxypropyl-β-cyclodextrin on the Haemolysis Induced by Bile Acids

Cyclodextrins improve the water‐solubility of drugs and can mask their haemolytic effect in parenteral use. Because the mechanism by which bile acids induce haemolysis is poorly understood, it has been investigated in the presence of 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CyD).