文摘
A substantial number of structurally diverse carcinogens may be metabolized to electrophilic sulfuric acid esters. This activation pathway is not taken into account in most short-term tests for the detection of mutagens and carcinogens. The reason is (i) that the commonly used bacterial and mammalian target cells do not express xenobiotic-metabolizing sulfotransferases (STs) and (ii) that the STs present in hepatic S9 mix, used as external activating system, are inactive due to the lack of cofactor, 5′-phosphoadenosine-3′-phosphosulfate. Even if this cofactor is supplemented to the S9 mix or if freshly isolated hepatocytes are used as external activating systems, the reactive sulfuric acid conjugates formed may not readily penetrate the target cell membrane, since they are ionized at physiological pH values. This problem can be avoided by the use of ST-proficient target cells. We have expressed various rat and human STs in Escherichia coli XL-1 Blue cells,his− Salmonella typhimurium strains and Chinese hamster V79 cells. Cytosol preparations of these cells were used as external metabolizing system in mutagenicity tests, and mutagenicity was also studied directly in the ST-proficient S. typhimurium strains and V79-derived cells. The study included the following food-borne genotoxicants and their phase-I metabolites: benzylic alcohols derived from polycyclic aromatic hydrocarbons,N -hydroxylated metabolites of heterocyclic amines, 1′-hydroxysafrole, 5-hydroxymethylfurfural and and 3-hydroxymethylindole. Special attention was given to (i) the comparison of internal versus external activation, (ii) the comparison of different STs from the same species, (iii) and the comparison of rat and human STs.
