Effects of the ametryn pesticide on biomembrane models based on Langmuir films and giant unilamellar vesicles (GUVs)

The plasma membrane plays a crucial role in regulating various physiological processes within cells, controlling the flow of substances in and out of the cell. It primarily comprises lipids, oligosaccharides, sterols, and proteins, which are responsible for its functionalization. In this study, we utilized 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) to create mono and bilayers as mimetic systems for the lipid structure of cell plasma membranes. This approach constitutes the initial phase of comprehending the impact of contaminants on in vivo systems. Thus, the impact of the pesticide ametryn (AMT) on DPPC monolayers, which were formed using Langmuir films at the air/water interface, as well as on DPPC bilayers formed by giant unilamellar vesicles (GUVs), was investigated. The use of Brewster Angle Microscopy revealed a significant influence of AMT when in the water subphase on the morphology of DPPC aggregates in Langmuir monolayers, whose surface pressure vs. mean molecular area (π-A) isotherms are shifted to larger areas for higher AMT concentrations. Phase modulation infrared reflection-absorption spectroscopy indicated interactions between AMT and DPPC in Langmuir films, specifically involving the phosphate and choline DPPC head groups. Basically, the negatively charged hydrophilic portion of AMT (SCH3) would be oriented towards the DPPC choline group. At the same time, the AMT triazine ring would be positioned closer to the DPPC phosphate group, leading also to a slight disturb of the vertical orientation of the DPPC alkyl chains. In line with the findings from the monolayer experiments, the confocal microscopy images obtained through phase contrast revealed that the presence of AMT resulted in approximately 85 % of the DPPC GUVs losing their phase contrast. This loss can be attributed to the exchange between the inner and outer contents of the DPPC bilayer.