Evaluation of the Physicochemical and Antioxidative Properties of Curcumin Metallocomplexes in Self-Microemulsifying Drug Delivery Systems

Curcumin (CUR), an active constituent of turmeric which is capable of forming complexes with metal ions. Even though CUR metallocomplexes displayed better biological activities compared to the free CUR, their application in medicine is limited by their poor aqueous solubility. This research aimed to develop self-microemulsifying drug delivery systems (SMEDDSs) to improve the solubility and the antioxidative activity of CUR metallocomplexes. Mononuclear (1:1) CUR metallocomplexes (CUR-Cu, CUR-Mg and CUR-Fe) were synthesised with Cu2+, Mg2+ and Fe3+ salts. The CUR and CUR metallocomplexes were loaded into the microemulsions (MEs) which contains palm oil, Tween 80 and polyethylene glycol (PEG) 400 at the ratios of 1:7:2 and 1:8:1. All of the MEs formulations appeared to be monophasic and clear, where the pH values were in the range of 6.55-6.78. In both formulations, the solubility of all metallocomplexes were 1.3-3.4-folds higher than the CUR, where CUR-Cu MEs (1:7:2 and 1:8:1) exhibited the highest solubility (965.99 ± 102.59 µg/mL and 986.49 ± 75.31 µg/mL, respectively). In both formulations, CUR-Cu MEs displayed ~2-folds higher %RSA compared to CUR MEs, meanwhile; CUR-Fe displayed the lowest %RSA (~6-7%) which maybe due to the instability of the coordination of ligand-metal complex resulted from the high oxidation state in Fe3+ ion.