title: Toxicity of 1-methyl-4-phenylpyridinium derivatives in Escherichia coli.
abstract: Several derivatives of 1-methyl-4-phenylpyridinium (MPP+), i.e., 1-methyl-4-(4'-nitrophenyl)pyridinium (1), 1-methyl-4-(4'-cyanophenyl)pyridinium (2), 1-methyl-4-(3'-nitrophenyl)pyridinium (3), 1-methyl-4-(4'-chlorophenyl)pyridinium (4), 1-methyl-4-(4'-acetamidophenyl)pyridinium (5), and 1-methyl-4-(4'-aminophenyl)pyridinium (6), were synthesized in order to compare their toxicity with that of paraquat (PQ2+) in Escherichia coli. Addition of compounds 1, 2, and 3 to aerobic E. coli cell suspensions caused extracellular ferricytochrome c reduction, which was inhibited by superoxide dismutase in the same manner as that in the case of PQ2+. The rate of the ferricytochrome c (cyt. c) reduction was in the order of PQ2+ greater than 1 greater than 2 greater than 3, which is the same as that of the redox potentials of these compounds. On the other hand, MPP+, 4, 5, and 6, which have more negative potentials, had no effect on the cyt. c reduction. Compound 1 inhibited the growth of E. coli under aerobic conditions, but not under anaerobic conditions. The results show that compound 1 can act as a mediator for production of superoxide (O2-.), which seriously injures E. coli cells. However, though compounds 2 and 3 catalyzed the production of O2-. in E. coli cells, their activity of O2-. production was much lower than that of compound 1 or PQ2+. Thus, compound 3 had no effect on growth or survival of E. coli at 1 mM, while compounds 2 and 4 had both bacteriostatic and bacteriocidal effects which were independent of dioxygen (O2). The results show that the toxic mechanism is different from that of compound 1. MPP+, 5, and 6 had no effect on growth of E. coli. This paper shows that compound 1 is a novel enhancer of intracellular superoxide production, though the mechanism of toxicity of compounds 2 and 4 is not clear yet. The results suggest that the redox potential is a crucial factor for manifestation of the activity.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Mitsumoto
authors.forename: T
authors.initials: T
authors.lastname: Nagano
authors.forename: M
authors.initials: M
authors.lastname: Hirobe
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000031:analogs & derivatives* / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010269:Paraquat / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D013481:Superoxides; D010269:Paraquat; D015655:1-Methyl-4-phenylpyridinium