ИСТИНА

Alkyl-triphenyl phosphonium is a recognition pattern for substrates/inhibitors of the major E. coli MDR transporter AcrAB-TolC Background: Alkyl-triphenyl phosphoniums (Cn-TPPs) are permeating cations which uncouple oxidative phosphorylation in mitochondria and the Gram-positive bacteria Bacillus subtilis (Khailova et al., Biochemistry (Mosc.) 2015). Methods: 2-fold broth microdilution MIC determination, measurement of B. subtilis membrane potential by the potential-sensitive dye DiS-C3-(5), propidium iodide membrane permeability test, measurement of accumulation of ethidium bromide, bacterial growth suppression screening of TolC-requiring transporters, DNA damage and inhibition of translation tests, HeLa cell line viability test. Results: Here, we report that Cn-TPP (n=8-12) produced severe antibacterial effect on other Gram-positive bacteria, Mycobacterium sp. and Staphylococcus aureus, at submicromolar and micromolar concentrations, as determined by 2-fold broth microdilution and visualized by plots showing changes in optical density (OD) at 620 nm over time. Cn-TPPs exhibited much lower antibiotic activity towards Escherichia coli obviously due to the presence of the highly effective multidrug resistance pump AcrAB-TolC. By measuring fluorescence of the potential-sensitive dye DiS-C3-(5), we examined the effect of Cn-TPPs on the membrane potential of B. subtilis. Micromolar concentrations of Cn-TPPs caused a decrease in the membrane potential of B. subtilis in the minute time scale, whereas higher concentrations of Cn-TPPs caused a rapid drop of membrane potential to the level observed with the channel-forming antibiotic gramicidin A. Cn-TPPs increased fluorescence of ethidium bromide but did not cause an increase in fluorescence of the cell membrane-impermeant probe propidium iodide, therefore the action of Cn-TPPs on the membrane potential of B. subtilis was not due to a detergent effect on bacterial membrane. The mechanism of Cn-TPP toxicity towards bacterial cells was neither associated with DNA damage, nor with inhibition of translation. Lowering of the bacterial membrane potential by Cn-TPPs might be involved in the mechanism of its bactericidal action. No significant cytotoxic effect on mammalian HeLa cells was observed at bacteriotoxic concentrations of C12-TPP. E. coli mutants, lacking any of AcrAB-TolC transporter proteins, showed similar Cn-TPPs sensitivity, as B. subtilis. Other TolC-requiring transporters do not affect the E. coli sensitivity to Cn-TPPs. According to our recent findings (Nazarov et al., Sci.Rep. 2017), the mitochondria-targeted antioxidant SkQ1 (C10-TPP conjugated to a quinone moiety), exhibiting strong antibacterial activity, is expelled from E. coli cells only by the AcrAB-TolC pump. Conclusions: Therefore, compounds of the Cn-TPPs-R chemical structure are substrates and/or inhibitors of AcrAB-TolC, with Cn-TPP serving as a recognition pattern for the transporter. Cn-TPPs may be effective in protection of the infected mammals by killing invading bacteria.