Purpose: To investigate different structures of modified chitosan containing different chain lengths and aromatic moieties for vaccine delivery capacity.

Methods: The characteristics of the modified chitosan, namely, methylated N-(4-N,N-dimethylaminobenzyl) chitosan (TM-Bz-CS), methylated N-(4-N,N-dimethylaminocinnamyl) chitosan (TM-CM-CS) and methylated N-(4-pyridinylmethyl) chitosan (TM-Py-CS), with Eqiva degree (equivalent degree) were studied by in vitro absorption enhancement on the transepithelial electrical resistance (TEER) in Caco-2 cell monolayers as well as by in vivo adjuvant activity against ovalbumin (OVA), a model antigen, via oral administration to BALB/c mice.

Results: At the same concentration and pH (0.1 mg/ml, pH 7.4), TM₆₅CM₅₀CS exhibited the highest in vitro enhancing paracellular permeability and also the highest in vivo adjuvant activity following oral administration to mice. OVA-specific serum immunoglobulin G (IgG) antibody levels of mice that received OVA in TM₆₅CM₅₀CS were significantly (p < 0.05) higher than those that received OVA in TM₆₅CS, TM₅₆Bz₄₂CS and TM₅₃Py₄₀CS. On the other hand, TM₆₅CS and TM₅₆Bz₄₂CS exhibited in vitro enhancing paracellular permeability but showed no immune responses, while TM₅₃Py₄₀CS failed to enhance paracellular permeability and did not elicit immune responses as well.

Conclusion: This study demonstrates that addition of hydrophobic moiety (dimethylaminocinnamyl) to CS backbone can increase both its absorption enhancing property and adjuvant activity. The chemical structure and the positive charge location play an important role for binding affinity, absorption enhancement and immune responses.