Effect of alkyl-gamma-cyclodextrins on the stability of retinol

Inclusion complexation between retinol (RET) and two synthetic alkyl carbonates of c-cyclodextrin (alkyl-c-CD) derivatives, ethyl-c-cyclodextrin (E-CD) and octyl-c-cyclodextrin (O-CD), was investigated by means of different techniques. The complexes were characterized by differential scanning calorimetry (DSC). Phase solubility studies, according to the method of Higuchi and Connors [1] were used to evaluate the complexation in aqueous solution at room temperature. In the present study inclusion complexes of retinol with E-CD and with O-CD were prepared to prevent its rapid degradation. In order to investigate the behavior of retinol under UV light, test of irradiation was performed separately on samples prepared dispersing retinol (0.1% w/w) or an equivalent amount of retinol/alkyl-c-CD respectively in hydroxyethylcellulose (HEC) gel and in an O/W emulsion. The stability over time of retinol was also investigated storing the samples at 40 C. Moreover retinol permeation through porcine skin has been evaluated employing Franz cells [2]. Retinol solubility was increased in presence of cyclodextrins while DSC analysis suggest that this inclusion agents are able to interact with retinol. Data for skin accumulation in porcine ear skin showed that alkyl-CDs increase of approximatively 1,5-fold retinol skin accumulation. Studies on the stability showed that both the inclusion complexes considered are able to increase retinol stability to light exposure and also to heat.