In situ forming gels as subcutaneous delivery systems of curcumin and piperine.

In this study an in situ forming gel for curcumin and piperine delivery is investigated as a long-lasting strategy in the local treatment of inflammatory and degenerative joint disease, such as osteoarthritis and rheumatoid arthritis. Particularly glyceryl monooleate, in association with phosphatidylcholine and ethanol, were employed. Different ratios between excipients were tested, with the aim to obtain a liquid form suitable for subcutaneous injection, gaining a semisolid consistency in contact with biological fluids. A formulative study was conducted to assess the composition impact on the structural properties of the formulations, particularly focusing on injectability and phase transition. Curcumin and piperine were loaded, singularly or jointly, in selected in situ forming gels. Structural characterization, performed by X-ray scattering, revealed disordered reverse micellar phases, undergoing transition to hexagonal and cubic Pn3m phase upon hydration. In vitro dialysis release study demonstrated a sustained release of both drugs over 96 h, with a faster release in the case of jointly loaded drugs. Mechanistic analysis and water uptake studies indicated a drug release governed by both diffusion and swelling/erosion of the lipid supramolecular structure. Furthermore, an ex vivo release analysis performed using human skin explants suggested the formulation suitability for subcutaneous injection, indicating that the presence of piperine in the in situ formed gel allowed to double the curcumin release with respect to the simple curcumin loaded gel.