Design and in vitro evaluation of thiolated alginates with N-acetyl-L-cysteine/L-cysteine substructures

A new generation S-protected thiolated alginate was synthesized using a ligand based on l-cysteine ​​protected with N-acetyl-l-cysteine (NACys-Cys) ​​in order to obtain a thiomer with improved mucoadhesive properties. Two types of alginate with different molar mass were evaluated with two ligand concentrations. The successful protection with NACys-Cys was confirmed with FT-IR, NMR and free amino group quantification. Quantification of disulfide and thiol groups showed a maximum of 546.93 ± 58.27 µmol S-S/g polymer and 35.48 ± 1.79 µmol -SH/g polymer. Evaluation of swelling behavior showed a ∼5-fold increase in weight at 2 h in buffer pH 6.8. Ex vivo mucoadhesion tests were performed with porcine intestinal mucosa where the S-protected thiomers remained adhered for an average of 70.9 ± 7.0 h, which was ∼15-fold longer than unmodified alginate (p < 0.0001). Cytotoxicity of S-protected thiomers was evaluated on human colorectal carcinoma cells (Caco-2) by resazurin assay. Both unmodified polymer and thiomers did not show a significant decrease in cell viability (p > 0.05). The results indicate that this novel third-generation S-protected thiomer provides remarkable ex vivo mucoadhesive properties, adequate swelling capacity and no in vitro cytotoxicity. According to results it might be a promising material for medical and pharmaceutical applications.