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

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

San Luis

Congreso; XLVIII 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 pests and low toxicity for mammals. It exerts its action by blocking the passage of chloride ions in the central nervous system GABA and GluCl receptors. Given that these are membrane intrinsic proteins and that Fipronil is a highly lipophilic compound, non-specific effects on the physical properties of the membrane cannot be discarded. In a previous work, we have demonstrated that Fipronil interacts with lipid membranes using DPPC Langmuir films as the membrane model. In this work, we complement those experimental results with studies in DPPC large unilamellar vesicles (LUVs). Moreover, we contrast these experimental results with molecular dynamics simulations (MDS) in mono- and bilayer systems. Free diffusion MDS of DPPC monolayers in three different molecular packing states and a DPPC liquid-crystalline bilayer confirmed the strong tendency of Fipronil to partition in lipidic phases. The NH2 group of Fipronil forms hydrogen bonds with the glycerol region of DPPC, and to a lesser extent with the phosphate group. Bilayer MDS show that Fipronil is not be able to pass from one hemilayer to the other or to cross the bilayer. We obtained spatially resolved free energy profiles of Fipronil partition into the DPPC bilayer based on umbrella sampling. These profiles allowed us to determine that the most favorable partition site of Fipronil would be located between the glycerol region and the acyl chain of dpPC. This result was confirmed by Fluorescence anisotropy studies of DPPC-LUVs in the presence of Fipronil where a stronger effect on anisotropy was observed for DPH probe compared to TMA-DPH, which locates closer to the phospholipid polar head groups. These experiments also showed that Fipronil has an ordering effect in the liquid-crystalline phase of the liposomes and a fluidizing effect in the gel phase. The same behavior was shown by the deuterium order parameter obtained from the MDS.