Phospholipase A2 induces structural changes in phospholipid-containing cubosomes

The functionalization of cubosomes for their use in drug delivery, bioimaging, and biosensing can be achieved by incorporating molecules that are sensitive to physiological conditions, such as phospholipids. Considering this, it is relevant to investigate the interaction between phospholipid-containing cubosomes and phospholipase A2 (PLA2), a ubiquitous enzyme associated with inflammatory diseases, metabolic diseases, skin diseases, and certain cancer types. Therefore, in this study, the effect of the type and concentration of phospholipid, along with the concentration of calcium as co-factor, on the nature of PLA2-induced structural changes in phospholipid-containing cubosomes was investigated. Monoolein cubosomes containing 0–10 mol% of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC), or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were incubated with PLA2, and structural changes were investigated by cryo-transmission electron microscopy, small angle X-ray scattering and zeta potential determination. Incubation with PLA2 induced swelling of the bicontinuous cubic phase structure, ultimately leading to phase transitions. The effect was most pronounced for cubosomes with the highest phospholipid concentration and was dependent on the type of phospholipid, with the addition of DOPC and DMPC resulting in a greater effect than POPC and DPPC. Incubating phospholipid-containing cubosomes with PLA2 at increasing calcium levels lead to a higher degree of swelling of the internal structure until a tipping point, where calcium ions counteracted the structural change. These findings show that phospholipid-containing cubosomes are susceptible to structural changes induced by PLA2 hydrolysis and may be utilized for engineering PLA2-responsive systems in the future.