Evaluation of monooleine aqueous dispersions as tools for topical administration of curcumin: characterization, in vitro and ex-vivo studies

Curcumin (CUR) is a well-known natural compound showing antioxidant, anti-inflammatory, and antitumor abilities but characterized by poor bioavailability and chemical instability, which drastically reduce its application in the treatment of chronic diseases such as osteoarthritis. The aim of the present study is the design and evaluation of monooleine aqueous dispersion (MAD) as novel carriers for the topical administration of CUR. CUR-loaded MAD was formulated using two different emulsifier systems, namely poloxamer 407 (MAD-A) and sodium cholate-sodium caseinate (MAD-B). These vehicles were characterized, and their influence on in vitro percutaneous absorption of CUR was also evaluated. Furthermore, an oxygen radical absorbance capacity assay was used to determine their antioxidant activity, and a Western blot analysis was performed to evaluate the inhibitory effect of the formulations on inducible nitric oxide synthase and cyclooxygenase 2 expressions. From the obtained results, CUR encapsulation efficiency was higher than 98% for MAD-A and 82% for MAD-B. Shelf-life studies showed that MAD-A maintains CUR stability better than MAD-B, and both vehicles demonstrated, in vitro, control of drug diffusion through the skin. Finally, MAD-A and MAD-B were able to extend the antioxidant/anti-inflammatory effects of CUR, also confirming the protective effect toward CUR chemical stability.