Chitosan: a unique polysaccharide for drug delivery

Characterization of chitosan hydrochloride-mucin interaction by means of viscosimetric and turbidimetric measurements

In the present work the interaction between chitosan hydrochloride (HCS) and two different types of mucin - one obtained from bovine submaxillary glands and the other from porcine stomach - was investigated. Two hydration media were tested: distilled water and 0. 1 M HCl. Intrinsic viscosity, which provides information about polymeric chain conformation, was assessed in both media for HCS and bovine submaxillary mucin. Changes in the specific viscosity of HCS-mucin mixtures were observed as a function of the polymer:mucin weight ratio. The formation of interaction products was indicated by a minimum in the specific viscosity. Such a minimum occurred at different polymer:mucin weight ratios depending on the hydration medium and mucin type. This suggested a different stoichiometry of interaction. Turbidimetric measurements were also effected in order to evidentiate the eventual precipitation of the polymer-mucin interaction products. While in distilled water the precipitation of the interaction product did occur, in acidic medium, although a minimum in specific viscosity was observed, no precipitate was formed. The two techniques employed, viscosimetric and turbidimetric, allowed us to investigate for both mucins the influence of hydration medium on the formation of the HCS-mucin interaction products and to conclude that a slightly acid-neutral pH favours the interaction between HCS and mucins.

Carbohydrate biopolymers enhance antibody responses to mucosally delivered vaccine antigens

We have evaluated the ability of two carbohydrate biopolymers, chitosan and gellan, to enhance antibody responses to subunit influenza virus vaccines delivered to the respiratory tracts of mice. Groups of mice were vaccinated three times intranasally (i.n.) with 10 microg of purified influenza B/Panama virus surface antigens (PSAs), which consist of hemagglutinin (HA) and neuraminidase (NA), either alone or admixed with chitosan or gellan solutions. Separate groups were vaccinated subcutaneously (s.c.) with PSAs adsorbed to Alhydrogel or chitosan or gellan alone i.n. Serum antibody responses were determined by enzyme-linked immunosorbent assay (ELISA) for influenza virus-specific immunoglobulin G (IgG) and by HA inhibition (HAI) and NA inhibition (NAI) assays. The local respiratory immune response was measured by assaying for influenza virus-specific IgA antibody in nasal secretions and by enumerating nasal and pulmonary lymphocytes secreting IgA, IgG, and IgM anti-influenza virus-specific antibodies by enzyme-linked immunospotting (ELISPOT). When administered alone i.n., B/Panama PSA was poorly immunogenic. Parenteral immunization with B/Panama PSA with Alhydrogel elicited high titers of anti-B/Panama antibodies in serum but a very poor respiratory anti-B/Panama IgA response. In contrast, i.n. immunization with PSA plus chitosan stimulated very strong local and systemic anti-B/Panama responses. Gellan also enhanced the local and serum antibody responses to i.n. PSA but not to the same extent as chitosan. The ability of chitosan to augment the immunogenicity of influenza vaccines given i.n. was confirmed using PSA prepared from an influenza A virus (A/Texas H1N1).

Chitin deacetylases: new, versatile tools in biotechnology

Chitin deacetylases have been identified in several fungi and insects. They catalyse the hydrolysis of N-acetamido bonds of chitin, converting it to chitosan. Chitosans, which are produced by a harsh thermochemical procedure, have several applications in areas such as biomedicine, food ingredients, cosmetics and pharmaceuticals. The use of chitin deacetylases for the conversion of chitin to chitosan, in contrast to the presently used chemical procedure, offers the possibility of a controlled, non-degradable process, resulting in the production of novel, well-defined chitosan oligomers and polymers.

Gadolinium neutron-capture therapy using novel gadopentetic acid-chitosan complex nanoparticles: in vivo growth suppression of experimental melanoma solid tumor

The potential of gadolinium neutron-capture therapy (Gd-NCT) for cancer was evaluated using chitosan nanoparticles as a novel gadolinium device. The nanoparticles, incorporating 1200 microg of natural gadolinium, were administered intratumorally twice in mice bearing subcutaneous B16F10 melanoma. The thermal neutron irradiation was performed for the tumor site, with the fluence of 6. 32x10(12) neutrons/cm(2), 8 h after the second gadolinium administration. After the irradiation, the tumor growth in the nanoparticle-administered group was significantly suppressed compared to that in the gadopentetate solution-administered group, despite radioresistance of melanoma and the smaller Gd dose than that administered in past Gd-NCT trials. This study demonstrated the potential usefulness of Gd-NCT using gadolinium-loaded nanoparticles.

Chitosan and its derivatives: potential excipients for peroral peptide delivery systems

In the 1990s chitosan turned out to be a useful excipient in various pharmaceutical formulations. By modifications of the primary amino group at the 2-position of this poly(beta1-->4 D-glucosamine), the features of chitosan can even be optimised according to a given task in drug delivery systems. For peroral peptide delivery these tasks focus on overcoming the absorption (I) and enzymatic barrier (II) of the gut. On the one hand, even unmodified chitosan proved to display a permeation enhancing effect for peptide drugs. On the other hand, a protective effect for polymer embedded peptides towards degradation by intestinal peptidases can be achieved by the immobilisation of enzyme inhibitors on the polymer. Whereas serine proteases are inhibited by the covalent attachment of competitive inhibitors such as the Bowman-Birk inhibitor, metallo-peptidases are inhibited by chitosan derivatives displaying complexing properties such as chitosan-EDTA conjugates. In addition, because of the mucoadhesive properties of chitosan and most of its derivatives, a presystemic metabolism of peptides on the way between the dosage form and the absorption membrane can be strongly reduced. Based on these unique features, the co-administration of chitosan and its derivatives leads to a strongly improved bioavailability of many perorally given peptide drugs such as insulin, calcitonin and buserelin. These polymers are therefore useful excipients for the peroral administration of peptide drugs.

N-trimethylated chitosan chloride (TMC) improves the intestinal permeation of the peptide drug buserelin in vitro (Caco-2 cells) and in vivo (rats)

PURPOSE

To evaluate N-trimethyl chitosan chloride (TMC) of high degrees of substitution as intestinal permeation enhancers for the peptide drug buserelin in vitro using Caco-2 cell monolayers, and to investigate TMCs as enhancers of the intestinal absorption of buserelin in vivo, in rats.

METHODS

TMCs were tested on Caco-2 cells for their efficiency to increase the paracellular permeability of the peptide buserelin. For the in vivo studies male Wistar rats were used and buserelin was administered with or without the polymers intraduodenally. Both types of experiments were performed at pH 7.2.

RESULTS

Transport studies with Caco-2 cell monolayers confirmed that the increase in buserelin permeation is dependent on the degree of trimethylation of TMC. In agreement with the in vitro results, in vivo data revealed highly increased bioavailability of buserelin following intraduodenal co-administration with 1.0% (w/v) TMCs. Intraduodenally applied buserelin resulted in 0.8% absolute bioavailability, whereas co-administrations with TMCs resulted in mean bioavailability values between 6 and 13 %. Chitosan HCl (1.0%; pH = 7.2) did not significantly increase the intestinal absorption of buserelin.

CONCLUSIONS

Both the in vitro and in vivo results indicate that TMCs are potent mucosal permeation enhancers of the peptide drug buserelin at neutral pH values.

Chitosan-gadopentetic acid complex nanoparticles for gadolinium neutron-capture therapy of cancer: preparation by novel emulsion-droplet coalescence technique and characterization

PURPOSE

The gadopentetic acid (Gd-DTPA)-loaded chitosan nanoparticles (Gd-nanoCPs) were prepared for gadolinium neutron-capture therapy (Gd-NCT) and characterized and evaluated as a device for intratumoral (i.t.) injection.

METHODS

Gd-nanoCPs were prepared by a novel emulsion-droplet coalescence technique. The effects of the deacetylation degree of chitosan and Gd-DTPA concentration in chitosan medium on the particle size and the gadolinium content in Gd-nanoCPs were examined. In vitro Gd-DTPA release from Gd-nanoCPs was evaluated using an isotonic phosphate-buffered saline solution (PBS, pH 7.4) and human plasma. In vivo Gd-DTPA retention in the tumor after i.t. injection of Gd-nanoCPs was estimated on mice bearing s.c. B16F10 melanoma.

RESULTS

Gd-nanoCPs with the highest Gd content, which were obtained using 100% deacetylated chitosan in 15% Gd-DTPA aqueous solution, were 452 nm in diameter and 45% in Gd-DTPA content. A lower deacetylation degree of chitosan led to an increase in particle size and a decrease in Gd-DTPA content in Gd-nanoCPs. As Gd-DTPA concentration in the chitosan solution increased, Gd-DTPA content in Gd-nanoCPs increased but the particle size did not vary. Gd-DTPA loaded to Gd-nanoCPs was hardly released over 7 days in PBS (1.8%) despite the high water solubility of Gd-DTPA. In contrast, 91% of Gd-DTPA was released in plasma over 24 hours. When Gd-nanoCPs were i.t. injected, 92% of Gd-DTPA injected effectually without outflow was held in the tumor tissue for 24 hours, which was different from the case of gadopentetate solution injection (only 1.2%).

CONCLUSIONS

Gd-nanoCPs highly incorporating Gd-DTPA were successfully prepared by the emulsion-droplet coalescence technique. Their releasing properties and their ability for long-term retention of Gd-DTPA in the tumor indicated that Gd-nanoCPs might be useful as an i.t. injectable device for Gd-NCT.