Improved synthesis of quaternary ammonium-chitosan conjugates (N+-Ch) for enhanced intestinal drug permeation

The pH-induced structural modifications of the reaction product between chitosan and 2-diethylaminoethyl chloride are studied with the purpose of testing and comparing the resulting chitosan derivatives on the basis of their intestinal drug permeability-enhancing properties. The reaction reproducibly yielded conjugates comprising short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan repeating unit. The more significant derivatives, N+-Ch-7 (degree of substitution, DS = 41%; n = 3) and N+-Ch-8 (DS = 59%; n = 1.7) were prepared at pH 7 and 8, respectively. The apparent permeability (Papp) of excised rat intestine was determined by means of Ussing type chambers. The hydrophilic fluorescein sodium (NaFlu) and fluorescein isothiocyanate dextran (MW 4400 Da) (FD-4), and the lipophilic rhodamine 123 (Rh-123), were applied in Ringer buffer to the apical side. Apical to basolateral transport was measured in the absence or presence of 0.5% (w/v) of the polymer under test. N+-Ch-7 and N+-Ch-8 were more effective Papp enhancers than N-trimethyl-chitosan. Both N+-Ch-7 and N+-Ch-8 enhanced the Papp of NaFlu (enhancement ratio, ER = 1.84 and 1.33, respectively), while N+-Ch-8 was the more effective enhancer for FD-4 (ER = 2.14). The Papp of Rh-123 was significantly enhanced only by N+-Ch-7 (ER = 1.37). Permeant-polymer binding counteracted the enhancement effect of polymer on transmembrane permeant flux. Contact with the chitosan conjugates did not impair the mucosal epithelium integrity.