Mucoadhesive S-protected thiolated cyclodextrin-iodine complexes: a promising strategy to prolong mucosal residence time of iodine

Abstract

Aim: The purpose of this study was to develop S-protected thiolated α-cyclodextrin–iodine complexes providing prolonged mucosal residence time and sustained release of the antimicrobial agent. Materials & methods: First, L-cysteine was conjugated with 2-mercaptonicotinic acid to generate cysteine-2-mercaptonicotinic acid (Cys-MNA). Subsequently, α-CD was oxidized with NaIO4 and Cys-MNA was bound to the resulting aldehyde groups via reductive amination. Finally, iodine was incorporated into complex. Result: S-protected thiolated α-CD displayed 3804 μmol/g MNA groups. The inclusion constant (KC) between iodine and S-protected thiolated α-CD was 5.37 × 104 M-1. In vitro release of iodine was around 15% per hour, whereas mucoadhesive properties showed 38-fold improvement in mucoadhesion. The complex did not show cytotoxicity at a concentration of 0.5% (m/v). In addition, complexes exhibited pronounced antimicrobial activity against Staphylococcus aureus and Escherichia coli. Conclusion: According to these results, S-protected thiolated α-CD-iodine complex might be a promising novel formulation for the mucosal use of iodine.