Complexation of curcumin with cyclodextrins adjusts its binding to plasma proteins

Curcumin shows poor bioaccessibility due to its poor water solubility, which limits its application in aqueous formulations, and the weak binding to plasma proteins, which hinders its transportation to targeted sites through the systemic circulation. In this study, we explored the potential of a cyclodextrin derivative, succinic acid-β-cyclodextrin (SACD), to overcome these problems. Complexation of curcumin to SACD significantly increased its water-dispersibility and enhanced its binding to a model plasma protein: bovine serum albumin (BSA). The binding constant and number of binding sites of the ligand-protein system increased from 3.87 × 10³ to 1.52 × 10⁵ L mol^-1 s^-1 and from 0.80 to 1.15 in the absence and presence of SACD, respectively. The presence of SACD also reduced the ability of curcumin to promote conformational changes in BSA. For instance, the thermal denaturation temperatures of BSA in BSA-curcumin mixtures was 65.3 °C and 67.0 °C in the absence and presence of SACD, respectively, compared to 67.8 °C for pure BSA. These effects were attributed to the fact that SACD forms an inclusion complex with curcumin and modulates the binding of curcumin with BSA, which may affect the biological accessibility of curcumin in the systemic circulation.