Effects of curcumin in the interaction with cardiolipin-containg lipid monolayers and bilayers

Curcumin, a plant polyphenol extracted from the Chinese herb turmeric, has gained widespread attention in recent years because of its multifunctional properties as antioxidant, antinflammatory, antimicrobial, and anticancer agent. Effects of the molecule on mitochondrial membranes properties have also been evidenced. In this work, the interaction of curcumin with models of mitochondrial membranes composed of dimyristoylphosphatidylcholine (DMPC) or mixtures of DMPC and 4 mol% tetramyristoylcardiolipin (TMCL) has been investigated by using biophysical techniques. Spectrophotometry and fluorescence allowed to determine the association constant and the binding energy of curcumin with pure DMPC and mixed DMPC/TMCL aqueous bilayers. The molecular organization of pure DMPC and cardiolipin-containing Langmuir monolayers at the air-water interface were investigated and the morphology of the monolayers transferred into mica substrates were characterized through atomic force microscopy (AFM). It is found that curcumin associates at the polar/apolar interface of the lipid bilayers and the binding is favored in the presence of cardiolipin. At 2 mol%, curcumin is well miscible with lipid monolayers, particularly with mixed DMPC/TMCL ones, where compact terraces formation characterized by a reduction of the surface roughness is observed in the AFM topographic images. At 10 mol%, curcumin perturbs the stability of DMPC monolayers and morphologically are evident terraces surrounded by cur aggregates. In the presence of TMCL, very few curcumin aggregates and larger compact terraces are observed. The overall results indicate that cardiolipin augments the incorporation of curcumin in model membranes highlighting the mutual interplay cardiolipin-curcumin in mitochondrial membranes.