Chitosan for enhanced intestinal permeability: prospects for derivatives soluble in neutral and basic environments.

In this study the effects of two chitosan salts, namely chitosan hydrochloride and chitosan glutamate (0.5 and 1.5% w/v), on the transepithelial electrical resistance (TEER) and permeability of Caco-2 cell monolayers, using the radioactive marker [14C]-mannitol, were investigated in a slightly acidic (pH 6.2) and neutral (pH 7.4) environment. Both salts are soluble in acidic conditions up to a concentration of 1.5% w/v and solutions of this strength, at a pH of 6.2, caused a pronounced lowering in the TEER of Caco-2 cell monolayers in the order of 70+/-1% (chitosan glutamate) and 77+/-3% (chitosan hydrochloride), 20 min after incubation started. In agreement with the TEER results the transport of the radioactive marker, [14C]-mannitol, was increased 25-fold (chitosan glutamate) and 36-fold (chitosan hydrochloride), respectively, at this pH. However, at a pH of 7.4 both salts are insoluble and prove to be ineffective since no reduction in the TEER values or increase in the transport of [14C]-mannitol were found. The results show that these chitosan salts are potent absorption enhancers in acidic environments. We conclude that there is a need for chitosan derivatives with increased solubility, especially at neutral and basic pH values, for use as absorption enhancers aimed at the delivery of therapeutic compounds in the more basic environment of the large intestine and colon.