Affinity of Oxybenzone and Avobenzone toward Lipids in Model Membrane Systems: On the Role of Membranes in the Harmful Effect of UV Filters on Living Organisms

Avobenzone (Avo) and oxybenzone (Oxy) are organic UV filters that are consistently released into the environment and extensively studied in terms of their toxicity and bioaccumulation potential. This study aimed to verify the affinity of these compounds and their mixture to model membranes (lipid monolayers) and to discuss the potential role of lipids in the harmful effects of Avo and Oxy on living organisms. The experiments were performed for structurally different lipids building the membranes of, e.g., mammals, fish, or crustaceans: phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and cholesterol, and for a monolayer imitating adipocyte membranes. On the basis of the surface pressure/area isotherms, the penetration studies, and Brewster angle microscopy, the following conclusions were drawn. Avobenzone and oxybenzone affect the monolayer properties by increasing their fluidity, decreasing stability, and inducing morphological changes. Although Avo reveals a significantly stronger effect than Oxy, both filters show selectivity in their interactions with the lipids. The studies on the mixed monolayers indicate that not only the lipid type but also their content in the membrane correlates with the impact of UV filters. Finally, the direct influence of Avo and Oxy on the biomembrane may not be the ground for their toxicity mechanism; however, their affinity to particular lipids may correlate with their bioaccumulation potential.