Giacomo Di Colo

Controlled drug release from implantable matrices based on hydrophobia polymers

Abstract Reports on the controlled release of drugs, including macromolecular drugs, from sillcone elastomers and ethylene-vinyl acetate copolymers, based on the formation of channels and cracks in the polymer, are reviewed. Aqueous interconnected pores are produced by osmotically active additives or by using loads of water-soluble drugs exceeding the percolation threshold. The release is generally proportional to the square root of time ( t 1 2 ). Nevertheless, pseudozero-order release kinetics can be obtained by adequately controlling the formulation variables. The factors controlling the release pattern and rate are discussed. In vivo applications of these types of systems are also considered.

Improved synthesis of quaternary ammonium-chitosan conjugates (N+-Ch) for enhanced intestinal drug permeation

The pH-induced structural modifications of the reaction product between chitosan and 2-diethylaminoethyl chloride are studied with the purpose of testing and comparing the resulting chitosan derivatives on the basis of their intestinal drug permeability-enhancing properties. The reaction reproducibly yielded conjugates comprising short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan repeating unit. The more significant derivatives, N(+)-Ch-7 (degree of substitution, DS=41%; n=3) and N(+)-Ch-8 (DS=59%; n=1.7) were prepared at pH 7 and 8, respectively. The apparent permeability (P(app)) of excised rat intestine was determined by means of Ussing type chambers. The hydrophilic fluorescein sodium (NaFlu) and fluorescein isothiocyanate dextran (MW 4400 Da) (FD-4), and the lipophilic rhodamine 123 (Rh-123), were applied in Ringer buffer to the apical side. Apical to basolateral transport was measured in the absence or presence of 0.5% (w/v) of the polymer under test. N(+)-Ch-7 and N(+)-Ch-8 were more effective P(app) enhancers than N-trimethyl-chitosan. Both N(+)-Ch-7 and N(+)-Ch-8 enhanced the P(app) of NaFlu (enhancement ratio, ER=1.84 and 1.33, respectively), while N(+)-Ch-8 was the more effective enhancer for FD-4 (ER=2.14). The P(app) of Rh-123 was significantly enhanced only by N(+)-Ch-7 (ER=1.37). Permeant-polymer binding counteracted the enhancement effect of polymer on transmembrane permeant flux. Contact with the chitosan conjugates did not impair the mucosal epithelium integrity.

Red grape skin and seeds polyphenols: Evidence of their protective effects on endothelial progenitor cells and improvement of their intestinal absorption.

SCOPE To evaluate the ability of grape skin and seeds to protect endothelial progenitor cells (EPC) from oxidative stress induced by hyperglycemia (HG) compared to red wine (RW) and prepare innovative pharmaceutical systems for the oral administration of red grape extract allowing the overcoming of its poor intestinal absorption. METHODS AND RESULTS Human EPC were characterized by expression of cell surface markers. Cells were incubated with different concentrations of total polyphenols from grape components or RW in the presence or absence of HG. Cell viability, migration, adhesion, and reactive oxygen species (ROS) production were assayed. Intestinal permeation of polyphenols was studied in the absence or presence of a quaternary ammonium-chitosan conjugate (N⁺(60)-Ch). Grape components and RW increased EPC viability, adhesion and migration, and prevented the HG effect (P < 0.01). ROS production induced by HG was significantly reduced only by grape seed extract and RW (P < 0.01). N⁺(60)-Ch acted as an effective enhancer of polyphenol permeability across the excised rat intestine. CONCLUSIONS Red grape components are a source of antioxidant compounds that ameliorate EPC viability and function, while preventing endothelial dysfunction. The use of polycationic chitosan derivatives can promote the absorption of polyphenols across intestinal epithelium, thus increasing their bioavailability and potential therapeutic value in atherosclerosis.

Synergistic interaction between TS-polysaccharide and hyaluronic acid: implications in the formulation of eye drops.

An interaction between tamarind seed polysaccharide (TSP) and hyaluronic acid (HA) in aqueous solution has been ascertained. Various TSP/HA mixtures have been studied as the basis for the development of a potential excipient for eye drops synergistically improved over those of the separate polymers. Information about the nature of interpolymer interactions, and their dependence on TSP/HA ratios were obtained by NMR spectroscopy in solution. Superior mucin affinity of TSP/HA mixtures with respect to the single polysaccharides was assessed by NMR proton selective relaxation rate measurements. The mucoadhesivity of the TSP/HA (3/2) mixture, evaluated in vitro by NMR or viscometry, and in vivo by its mean and maximum residence time in rabbit precorneal area, is stronger than that of the component polysaccharides or the TSP/HA mixtures of different composition. TSP/HA (3/2) is little viscous and well tolerated by rabbit eyes. It stabilizes the tear film, thereby prolonging the residence of ketotifen fumarate and diclofenac sodium in tear fluid, but is unable to permeabilize the cornea. In conclusion, mucoadhesivity is responsible for the TSP/HA (3/2) synergistic enhancement of either extra- or intra-ocular drug bioavailability.

Mucoadhesive nanoparticles made of thiolated quaternary chitosan crosslinked with hyaluronan

Mucoadhesive polymeric nanoparticles intended for drug transport across the gastrointestinal mucosa were prepared from quaternary ammonium-chitosan conjugates synthesised from reduced-MW chitosan (32 kDa). Conjugates contained pendant moieties of 2-4 adjacent diethyl-dimethylene-ammonium groups substituted on repeating units (26-55%). Conjugates were thiolated via amide bonds with thioglycolic acid to yield products with thiol content in the 35-87 μmol/g range. Nanoparticles with mean size in the 270-370 nm range and positive zeta-potential (+3.7 to +12.5 mV) resulted from ionotropic gelation of the thiolated conjugates with de-polymerised hyaluronic acid (470 kDa). The nanoparticles were fairly stable in size and thiol content and showed a significant mucoadhesivity, matching and even exceeding that of the constituent polymers. Nanoparticles were internalised by endothelial progenitor cells in direct relation to their surface charge intensity. Nanoparticle uptake significantly improved cell viability and resistance to oxidation. The lyophilised nanoparticles were re-dispersible and could make a manageable formulation for oral use.

Bile acids as enhancers of steroid penetration through excised hairless mouse skin

Abstract Excised hairless mouse skin (EHMS) is used to evaluate the potential of sodium choleate (NaCOL), an ox bile extract containing the sodium salts of taurocholic, glycoeolic, desoxycholic and cholic acids, and of the free choleic acids (HCOL) to enhance the transcutaneous penetration of progesterone (PGT) and prednisolone (PDN). EHMS is pretreated with aqueous dispersions of the enhancers, then the steroids are allowed to permeate through the pretreated EHMS from normal saline under occluded conditions. NaCOL is ineffective whereas HCOL produces structural modifications of the stratum corneum, resulting in increased skin permeability of both steroids. The chloroform-soluble components of HCOL interact strongly with stratum corneum lipids, as demonstrated by differential scanning calorimetry, thus facilitating PGT penetration. The chloroform-insoluble components of HCOL interact with more polar structures of stratum corneum, thereby promoting PDN transport. The data also suggest the existence of a parallel drug co-transport mechanism by the more lipophilic HCOL components.

Selected polysaccharides at comparison for their mucoadhesiveness and effect on precorneal residence of different drugs in the rabbit model.

Mucoadhesive polysaccharides may prolong the residence of ophthalmic drugs in precorneal area. In this article, the mucoadhesiveness of arabinogalactan, tamarind seed polysaccharide, hyaluronan, hydroxyethylcellulose is compared in vivo, by the polymer residence time in rabbit tear fluid, and in vitro, by the polymer-induced increase of viscosity of a mucin dispersion. Polymer residence is prolonged by increased viscosity but shortened by reflex tearing caused by excessive viscosity. Tamarind seed polysaccharide is the most effective in prolonging the residence of ketotifen and diclofenac in precorneal area; hence, it is the optimal eyedrop additive as it is mucoadhesive while not increasing viscosity excessively.

Synthesis, characterization and evaluation of thiolated quaternary ammonium-chitosan conjugates for enhanced intestinal drug permeation

In a previous report quaternary ammonium-chitosan conjugates (N(+)-Chs) endowed with intestinal drug permeability-enhancing properties were described. They are characterized by short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan (Ch) repeating units. In the present work two N(+)-Chs, one having DS (degree of substitution)=59.2+/-4.5%, n=1.7+/-0.1 (N(+)(60)-Ch), the other one having DS=40.6+/-1.3%, n=3.0+/-0.2 (N(+)(40)-Ch) were used to synthesize novel multifunctional non-cytotoxic Ch derivatives, each carrying thiol along with quaternary ammonium groups (N(+)-Ch-SH), with increased potential to enhance transepithelial drug transport. They have been obtained by transforming the residual free amino groups of N(+)(60)-Ch and N(+)(40)-Ch into 3-mercaptopropionamide moieties. The former yielded 4.5+/-0.7% thiol-bearing groups, the latter, 5.2+/-1.1% of such groups, on a Ch repeating unit basis. The multifunctional derivatives have improved the ability of the parent N(+)-Chs to enhance the permeability of the water-soluble macromolecular fluorescein isothiocyanate dextran, MW 4400 Da (FD4) and that of the lipophilic dexamethasone (DMS) across the excised rat intestinal mucosa and Caco-2 cell monolayer, respectively. The data from the present work altogether point to a synergism of quaternary ammonium and thiol groups to improve the intestinal drug absorption enhancing properties of the multifunctional Ch derivatives.

Thiolated quaternary ammonium–chitosan conjugates for enhanced precorneal retention, transcorneal permeation and intraocular absorption of dexamethasone

Previously, a quaternary ammonium (N(+))-chitosan (Ch) conjugate (N(+)(60)-Ch) characterized by short pendant chains, made of 1.7+/-0.1 adjacent diethyl-dimethylene-ammonium groups, substituted onto the primary amino group of the chitosan repeating units (degree of substitution, 59.2+/-4.5%) was used to synthesize a multifunctional non-cytotoxic thiomer (N(+)(60)-Ch-SH(5)), carrying 4.5+/-0.7% thiol-bearing 3-mercaptopropionamide besides quaternary ammonium groups. The present work was aimed at evaluating the potential of N(+)(60)-Ch-SH(5) and N(+)(60)-Ch as bioactive excipients for dexamethasone (DMS) eyedrops. The DMS permeability across excised rabbit cornea was enhanced over the control value by the thiomer and the parent polymer to about the same extent (3.8 vs. 4.1 times). The mean precorneal retention time and AUC in the aqueous of DMS instilled in rabbit eyes via eyedrops were enhanced by the thiomer (MRT=77.96+/-3.57 min, AUC=33.19+/-6.96 microg ml(-1) min) more than the parent polymer (MRT=65.74+/-4.91 min, AUC=21.48+/-3.81 microg ml(-1) min) over the control (MRT=5.07+/-0.25 min, AUC=6.25+/-0.65 microg ml(-1) min). The quaternary ammonium ions were responsible for both permeabilization of corneal epithelium and polymer adhesion to precorneal mucus, while the thiols increased the latter. This synergistic action is the basis of the higher thiomer bioactivity in vivo. A good ocular tolerability of the chitosan derivatives resulted from in vivo experiments.

Evaluation of a silicone based matrix containing a crosslinked polyethylene glycol as a controlled drug delivery system for potential oral application

Abstract A silicone based matrix containing dispersed medicated granules of a crosslinked polyethylene glycol with high swelling capacity is evaluated for its potential to release in vitro substantial fractions of drugs of different solubilities within 6 hours at controlled rates. Papaverine- HCl, clonidine- HCl and salicylamide are the model drugs. With a matrix shape of a 0.1-cm thick disc, a weight fraction of granules in matrix of around 35% and an appropriate granule size, dose fractions of around 80% are released with √t-type kinetics. The particular drug type and the drug content in granules, within the range of 5–20%, are without influence on the pattern and rate of fractional release. The release pattern depends on the pH of the elution medium, but the pH effects can be offset by properly controlling the granule size. Thus, the above features of release are obtained with normal saline as the elution medium, using granules of 354–425 μm, or with a medium whose pH is gradually increased from 1.2 to 7.4 to simulate the conditions of the GI tract, using granules of 105–250 μm. Drug release is initially controlled by the rate of increase of the number and size of interconnections among granules in course of swelling. Drug diffusion in the interconnected hydrogel gradually takes control of release.