Changes in membrane fluidity evoked by organophosphorus insecticide bromfenvinfos and its methylated analogue

Abstract

The interaction of organophosphorus insecticides bromfenvinfos and methyl bromfenvinfos with model and native membranes was investigated by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), a probe located in the hydrophobic core of the bilayer and 1,3-bis-(1-pyrene)propane, a probe distributed in the outer region of the bilayer. DPH reported a broadening of the transition profile and solidifying effects in the fluid phase of liposomes formed from dimyristoyl (DMPC), dipalmitoyl (DPPC), and distearoyl (DSPC) phosphatidylcholine in the presence of the insecticides. A shift of the transition temperature towards a lower temperature was observed in DPPC- and DSPC-bromfenvinfos-treated vesicles. Py(3)Py detected an ordering effect of the insecticides in the fluid state of the lipids and abolished pre-transition in DPPC and DSPC vesicles. These results suggest that the insecticides localize in the co-operative region of the bilayer. Cholesterol added to DMPC decreased the influence of the insecticides as reported by both DPH and Py(3)Py. The effect of the insecticides on the fluidity of some native membranes, namely erythrocytes, lymphocytes, brain microsomes, and sarcoplasmic reticulum, depended on the cholesterol content in these membranes, the higher the cholesterol content, the smaller the solidifying effect. The physical mechanism of action of the insecticides on membrane lipids can be similar to that of cholesterol. All observed effects were more pronounced for bromfenvinfos than for its methylated analogue which correlates with the toxicity of these compounds for mammals.