Design, synthesis, fabrication and in vitro evalution of mucoadhesive 5-amino-2-mercaptobenzimidazole chitosan as low water soluble drug carriers

Mucoadhesive thiolated chitosan suitable as a carrier for low water soluble drugs was designed and synthesized by conjugating 5-amino-2-mercaptobenzimidazole (MBI) using methylacrylate (MA) as the linking agent. A 14.4% degree of substitution of MA, as determined by (1)H NMR analysis, and 11.86±0.01μmol thiol groups/g of polymer, as determined by Ellman's method, was obtained. The MBI-MA-chitosan had an 11-fold stronger mucoadhesive property compared to unmodified chitosan at pH 1.2, as determined by the periodic acid: Schiff colorimetric method. Chitosan, MA-chitosan and MBI-MA-chitosan were fabricated as well-formed microspheres using electrospray ionization, including an entrapment efficiency of simvastatin (SV) of over 80% for the MBI-MA-chitosan. The mucoadhesiveness of the SV-loaded MBI-MA-CS microspheres was still higher than that for SV-loaded chitosan at pH 1.2 and 6.4. The SV-loaded MBI-MA-CS microspheres revealed a reduced burst effect and an increased release rate (more than fivefold higher than pure SV) of SV over 12h.

Enhanced water-solubility and mucoadhesion of N,N,N-trimethyl-N-gluconate-N-homocysteine thiolactone chitosan

A water-soluble chitosan with improved mucoadhesion was prepared by modifying 19.4% of the amine groups of chitosan to trimethylammonium and conjugation of gluconolactone (GLU) and homocysteine thiolactone (HT) onto the remaining amine groups of the chitosan backbone. The derived trimethyl-gluconate-HT-chitosan (TM-GN-HT-chitosan) was confirmed by Fourier Transform Infrared spectroscopy, NMR and thermogravimetric analysis. The total thiol and disulfide group level on the TM-GN-HT-chitosan were 17.96 ± 0.03 and 7.36 ± 0.03 μmol/g, respectively. The water solubility of the TM-GN-HT-chitosan conjugate was 79.0 ± 0.15%, more than that of TM-chitosan and chitosan, with an enhanced solubility over a broad pH range ranging from 85.6 ± 10.4% to 58.5±1.1% maximal solubility at pH 2 to 11. Finally, TM-GN-HT-chitosan showed a nearly ∼9.5-, 5.0- and 5.6-fold higher mucoadhesiveness than chitosan at pH 1.2, 4.0 and 6.4, respectively, and was optimal at pH 4.0.