Cr(vi) permanently binds to the lipid bilayer in an inverted hexagonal phase throughout the reduction process

Cr(VI) is a harmful, carcinogenic agent with a high permeability rate throughout the lipid membranes. In an intracellular environment and during interactions with cellular membranes, it undergoes an instant reduction to lower oxidation states throughout radical states, recognized as the most dangerous factor for cells. The cellular membrane is the most visible cellular organelle in the interior and exterior of a cell. In this study, liposomes and non-lamellar inverted hexagonal phase lipid structures based on phosphoethanolamine (PE) were used as model cellular bilayers because of their simple composition, preparation procedure, and the many other properties of natural systems. The lipid membranes were subjected to 0.075 mM Cr(VI) for 15 min, after which the Cr content was removed via dialysis. This way, the remaining Cr content could be studied qualitatively and quantitatively. Using the combined XRF/XAS/ EPR approach, we revealed that some Cr content (Cr(III) and Cr(VI)) was still present in the samples even after long-term dialysis at a temperature significantly above the phase transition for the chosen liposome. The amount of bound Cr increased with increasing PE and -(CC)-C-=- bond content in lipid mixtures. Internal membrane order decreased in less fluid membranes, while in more liquified ones, internal order was only slightly changed after subjecting them to the Cr(VI) agent. The results suggest that the inverted hexagonal phase of lipid structures is much more sensitive to oxidation than the lamellar lipid phase, which can play an important role in the strong cytotoxicity of Cr(VI).

Automated summary

Cr(VI) is a harmful and carcinogenic agent that can quickly undergo reduction to lower oxidation states in cellular membranes, posing a significant threat to cells. This study investigated the effects of Cr(VI) on liposomes and non-lamellar inverted hexagonal phase lipid structures, revealing that these structures are more sensitive to oxidation compared to lamellar lipid phases. The results suggest that the high cytotoxicity of Cr(VI) may be attributed to its impact on the inverted hexagonal phase of lipid structures.