S-Protected Thiolated Chitosan for Oral Delivery of Hydrophilic Macromolecules: Evaluation of Permeation Enhancing and Efflux Pump Inhibitory Properties

Abstract

The objective of this study was the investigation of permeation enhancing and P-glycoprotein (P-gp) inhibition effects of a novel thiolated chitosan, the so-named S-protected thiolated chitosan. Mediated by a carbodiimide, increasing amounts of thioglycolic acid (TGA) were covalently bound to chitosan (CS) in the first step of modification. In the second step, these thiol groups of thiolated chitosan were protected by disulfide bond formation with the thiolated aromatic residue 6-mercaptonicotinamide (6-MNA). Mucoadhesive properties of all conjugates were evaluated in vitro on porcine intestinal mucosa based on tensile strength investigations. Permeation enhancing effects were evaluated ex vivo using rat intestinal mucosa and in vitro via Caco-2 cells using the hydrophilic macromolecule FD(4) as the model drug. Caco-2 cells were further used to show P-gp inhibition effects by using Rho-123 as P-gp substrate. Apparent permeability coefficients (P(app)) were calculated and compared to values obtained from each buffer control. Three different thiolated chitosans were generated in the first step of modification, which displayed increasing amounts of covalently attached free thiol groups on the polymer backbone. In the second modification step, more than 50% of these free thiol groups were covalently linked with 6-MNA. Within 3 h of permeation studies on excised rat intestine, P(app) values of all S-protected chitosans were at least 1.3-fold higher compared to those of corresponding thiomers and more than twice as high as that of unmodified chitosan. Additional permeation studies on Caco-2 cells confirmed these results. Because of the chemical modification and higher amount of reactive thiol groups, all S-protected thiolated chitosans exhibit at least 1.4-fold pronounced P-gp inhibition effects in contrast to their corresponding thiomers. These features approve S-protected thiolated chitosan as a promising excipient for various drug delivery systems providing improved permeation enhancing and efflux inhibition effects.

Design and evaluation of an intravesical delivery system for superficial bladder cancer: preparation of gemcitabine HCl-loaded chitosan–thioglycolic acid nanoparticles and comparison of chitosan/poloxamer gels as carriers

“…The underlying mechanism for this permeation-enhancing effect of chitosan seems to be based on its positive charge, which interacts with the negatively charged cell membrane and affects the tight junctions of umbrella cells. 13 In addition, in the current study, this permeation-enhancing effect of chitosan was much more pronounced by the immobilization of thiol groups on the polymeric backbone. This improved effect of thiomers seems to be based on the inhibition of protein tyrosine phosphatase enzyme, which is involved in the opening process of tight junctions.…”

“…12 The amount of thiol groups immobilized on chitosan was determined photometrically with Ellman's reagent. 13 …”

Chitosan microparticles loaded with yeast-derived PCV2 virus-like particles elicit antigen-specific cellular immune response in mice after oral administration

“…The functionalized (chemically modified) form of chitosan used for preparing microparticles has attracted considerable interest of late due to improved mucoadhesivity, permeability, stability, and a controlled/extended antigen release profile at mucosal sites [11, 26]. Therefore, our future studies will explore the use of these functionalized forms of chitosan for the preparation of microencapsulated PCV2 antigens and their optimization for use as oral vaccines.…”

Design and application of chitosan microspheres as oral and nasal vaccine carriers: an updated review

“…In the second step, the thiol group of thiolated chitosan was protected by the formation of disulfide bonds with aromatic thiol-bearing ligands. The S-protected thiolated chitosan exhibited improved mucoadhesivity, enhanced permeation effect, inhibited efflux pump, bioavailability, and controlled release profile compared to the corresponding thiolated and unmodified polymers, 109,127,128 demonstrating that TCMs prepared using S-protected thiolated chitosan are a promising chitosan-based mucoadhesive polymer for the development of various mucosal vaccine delivery systems.…”

“…126 Recently, Bernkop-Schnurch et al performed several studies using aromatic thiol-bearing ligands for the synthesis of S-protected thiolated chitosan and evaluated their efficacy as mucosal drug delivery carriers. 109,127,128 To prepare the S-protected thiolated chitosan, the thiol-bearing ligand was covalently attached to chitosan as the first step of modification. In the second step, the thiol group of thiolated chitosan was protected by the formation of disulfide bonds with aromatic thiol-bearing ligands.…”