In vitro release of curcumin from vehicles containing alginate and cyclodextrin. Studies of curcumin and curcuminoides. XXXIII.

Combinations of cyclodextrins and alginates were used to solubilize the hydrophobic compound curcumin in aqueous vehicles intended for topical delivery. A careful selection of the excipients is necessary to achieve a sufficient release of curcumin towards a membrane of hydrophilic character, e.g. mucosa. The aim of the study was to investigate the effect of different combinations of cyclodextrins and alginates on curcumin release towards hydrophilic membranes in vitro. The curcumin flux through semi-permeable membranes of different molecular weight cut-off was measured to differentiate between the flux of curcumin in its uncomplexed form (restricted flux), its uncomplexed form together with its inclusion complexes (partly restricted flux) and the overall flux of curcumin-cyclodextrin complexes and uncomplexed curcumin (unrestricted flux). A high viscosity of the vehicle was expected to inhibit curcumin flux. Vehicles containing 3% alginate were found to have lower unrestricted flux than the vehicles containing 0.5% alginate independent of the type of cyclodextrin used. The results indicate that the unrestricted curcumin flux (e.g. in the case of wounded skin) is rather independent of the composition of the hydrophilic vehicle and mostly limited by the viscosity. However, partly restricted and restricted curcumin flux were found to depend on both the viscosity and the composition of the vehicles. The cyclodextrin with the demonstrated lowest solubilisation capacity (i.e. hydroxypropyl-beta-cyclodextrin) resulted in the highest values of both the restricted and unrestricted curcumin flux. In conclusion, a combination of hydroxypropyl-beta-cyclodextrin and propylene glycol alginate seemed to be the best choice with respect to curcumin solubility and release from the vehicle.