title: Synergistic cytotoxic effect of tetrachlorocatechol and sodium azide in Escherichia coli: toxicity, metabolism, and mechanistic aspects.
abstract: Pentachlorophenol (PCP) is used in industrial and domestic applications, including as a biocide and a wood preservative. Metabolism of PCP undergoes oxidative dechlorination, forming tetrachlorocatechol (TCC) and tetrachlorohydroquinone (TCHQ). Both sodium azide (NaN(3)) and TCC appear naturally in soil. None of them are cytotoxic by themselves or facilitate autooxidation. Here, we show that their combination leads to synergistic cytotoxicity (>6 log bacterial killing) to Escherichia coli. The rate of oxygen consumption in a cell-free system showed that NaN(3) increases TCC oxidation by 520-fold. The synergism coefficient to cells was calculated as 96 or greater, and we have shown the formation of a new compound. It is suggested that the intermediate species, o-tetrachlorosemiquinine, and an unknown, nitrogen-centered free radical, both visualized by electron-spin resonance, are harmful species responsible for the synergistic cytotoxicity of TCC/NaN(3), rather than the endproduct formed during the reaction. Desferrioxamine and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide offered nearly complete protection, but through radical scavenging rather than through chelating properties. The mechanism of damage for TCC compared to its analogue, TCHQ, were investigated, and whereas the cellular damage of TCHQ/NaN(3) is through a site-specific mechanism, in the case of TCC/NaN(3) it is through the accumulation of the component(s) in the bacterial cell membrane, eventually leading to dysfunction, as evidenced by electron microscopy.
authors.affiliation: Department of Cellular Biochemistry and Human Genetics, Hebrew University-Hadassah Schools of Medicine and Dental Medicine, Jerusalem 91120, Israel.
authors.forename: Smadar
authors.initials: S
authors.lastname: Levy
authors.forename: Mordechai
authors.initials: M
authors.lastname: Chevion
mesh_terms: D002396:Catechols / Q000737:chemistry / Q000633:toxicity*; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004785:Environmental Pollutants / Q000737:chemistry / Q000633:toxicity*; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010101:Oxygen Consumption / Q000187:drug effects; D019810:Sodium Azide / Q000737:chemistry / Q000633:toxicity*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002396:Catechols; D004785:Environmental Pollutants; C423629:3,4,5,6-tetrachlorocatechol; D019810:Sodium Azide