Effects of the insecticide Fipronil on membrane models. Experimental and computational studies

FELSZTYNA, IVÁN; SÁNCHEZ-BORZONE, MARIELA EUGENIA; MIGUEL, VIRGINIA; GARCÍA, DANIEL ASMED

San Luis

Congreso; XLVII Reunión Anual de la Sociedad Argentina de Biofísica; 2019

Sociedad Argentina de Biofísica

Fipronil is a widely used phenylpyrazole insecticide with high activity against insect pestsand low toxicity for mammals. It exerts its action by blocking the passage of chloride ionsin the central nervous system GABA and GluCl receptors. Given that these aremembrane intrinsic proteins and that Fipronil is a highly lipophilic compound, non-specific effects on the physical properties of the membrane cannot be discarded. In aprevious work, we have demonstrated that Fipronil interacts with lipid membranes usingDPPC Langmuir films as the membrane model. In this work, we complement thoseexperimental results with studies in DPPC large unilamellar vesicles (LUVs). Moreover, wecontrast these experimental results with molecular dynamics simulations (MDS) in mono-and bilayer systems. Free diffusion MDS of DPPC monolayers in three different molecularpacking states and in a DPPC liquid-crystalline bilayer confirmed the strong tendency ofFipronil to partition in lipidic phases. The NH2 group of Fipronil forms hydrogen bondswith the glycerol region of DPPC and, to a lesser extent, with the phosphate group.Bilayer MDS show that Fipronil is not able to pass from one hemilayer to the other or tocross the bilayer. We obtained spatially resolved free energy profiles of Fipronil partitioninto the DPPC bilayer based on umbrella sampling. These profiles allowed us todetermine that the most favorable partition site of Fipronil would be located between theglycerol region and the acyl chain of DPPC. This result was confirmed by fluorescenceanisotropy studies of DPPC-LUVs in the presence of Fipronil, where a stronger effect onanisotropy was observed for DPH probe compared to TMA-DPH, which locates closer tothe phospholipid polar head groups. These experiments also showed that Fipronil has anordering effect in the liquid-crystalline phase of the liposomes and a fluidizing effect inthe gel phase. The same behavior was shown by the deuterium order parameterobtained from the MDS