Toxic liver injury and carcinogenesis. Methylation of rat-liver nucleic acids by dimethylnitrosamine in vivo

Abstract

In the preceding paper (Magee & Hultin, 1962) it was shown that methylation of proteins of ratliver slices occurred during incubation of the slices with the hepatotoxin and carcinogen dimethylnitrosamine. This finding supports the hypothesis that dimethylnitrosamine undergoes enzymic oxidative N-demethylation in the liver with subsequent intracellular fornation of a methylating agent, possibly diazomethane. Evidence for reaction with nucleic acids was also obtained. The reactions of nucleic acids and their components with alkylating agents have been studied very extensively in vitro

Carcinogens are Mutagens: A Simple Test System Combining Liver Homogenates for Activation and Bacteria for Detection

“…The compounds were chosen for testing because they were known to be carcinogenic in humans or in animals (7,15). Control values are presented both for the number of revertant colonies on plates with compound and no S-9 Mix, and for the number of colonies on plates [8][9] fraction and carcinogen concentration on mutagenesis of TA1538. (A) The procedure was as described in Methods except that the amount of S-9 fraction in the Mix was varied.…”

“…4-Aminobiphenyl (100 Isg per assay) had about 0.1 the activity of 2-acetylaminofluorene (50 jsg per assay), and the results plotted should be multiplied by 100 rather than 1000. Controls with S-9 Mix, but no compound, and with compound, omitting [8][9] Mix, were less than 25 colonies. (B) With human S-9, 0.5 ml was used per assay, and with rat S-9 the usual 0.15 ml was used.…”

“…With this test we have also shown that the active forms of a large number of known carcinogens are mutagens (1)(2)(3)(4)(5). The active forms of carcinogens such as aflatoxin, polycyclic hydrocarbons, dimethylnitrosamine, and various aromatic amines are formed by mammalian metabolism, in particular by the TPNH-dependent microsomal enzymes of liver (6)(7)(8)(9)(10)(11). The principal limitation of any bacterial system for detecting carcinogens as mutagens is that bacteria do not duplicate mammalian metabolism in activating carcinogens.…”

The induction of tumours in the rat by a single oral dose of N-nitrosomethylurea.

“…1) (Magee and Hultin, 1962;Magee and Farber, 1962;Craddock and Magee, 1963). This compound was shown to alkylate nucleic acids and proteins of various organs in rat and mouse in vivo to different degrees and there was some correlation between the degree of methylation of the nucleic acids and the sites at which tumours were induced (Lee et al, 1964).…”

New Developments in Mutagenicity Screening Techniques with Yeast

“…Mitotic gene conver-sayed at both the ade 2 and try 5 sites of sion is a nonreciprocal event, probably in-strain D-4 in all experiments. Since the re- In Vitro Hydroxylation System Dimethylnitrosamine (DMNA) and diethylnitrosamine (DENA) require conversion to alkylating agents for their activity, presumably through a mechanism involving an initial a-carbon hydroxylation followed by spontaneous dealkylation (52)(53)(54)(55). Studies of aromatic amines indicate that they are carcinogenic only after metabolic conversion by a hydroxylation mechanism to active breakdown products (56).…”