In vitro metabolism and activation of carcinogenic aromatic amines by subcellular fractions of human liver
Dybing, E.; Von Bahr, C.; Aune, T.; Glaumann, H.; Levitt, D.S.; Thorgeirsson, S.S.
Cancer Research 39(10): 4206-4211
1979
ISSN/ISBN: 0008-5472 PMID: 476655 Document Number: 150734
In vitro metabolism and metabolic activation of 2-acetylaminofluorene (AAF), 2-aminofluorene and 2,4-diaminoanisole to mutagenic (Salmonella typhimurium test system) and covalently protein-bound intermediates were evaluated in subcellular fractions from 7 human livers. The cytochrome P-450 content, aryl hydrocarbon hydroxylase activity and sodium dodecyl sulfate:polyacrylamide gel electrophoresis of the human liver microsomes were concomitantly studied. AAF was extensively metabolized (both C- and N-hydroxylated) by all of the human liver microsomal samples, but several-fold variations between the individual metabolites were observed among the different microsomal fractions. Similar variation was also observed for aryl hydrocarbon hydroxylase activity. Electrophoresis of the microsomal fractions revealed several polypeptides with a MW range of 40,000-60,000. Of these polypeptides, 2 with MW of .apprx. 54,000 and 55,000, correspond to those seen in rat liver microsomes following pretreatment with 3-methylcholanthrene. The in vitro mutagenicity of AAF with the individual samples corresponded well with those of 2-aminofluorene and 2,4-diaminoanisole, as did the degree of AAF N-hydroxylation. N-hydroxy-2-acetylaminofluorene was converted to mutagen(s) by both human liver microsomal and cytosol fractions, presumably via deacetylation. A poor association between the extent of covalent binding of AAF to liver microsomal proteins and the degree of mutagenicity in the S. typhimurium system was observed among the samples, possibly indicating that the reactive metabolite(s) arylating the protein differs from that causing the frame-shift mutation in the S. typhimurium. The results from the present study on AAF and benzo(a)pyrene hydroxylation; the metabolic activation of AAF, 2-aminofluorene, and 2,4-diaminoanisole; and, the electrophoretic characterization of hepatic cytochrome P-450 indicate great qualitative similarities between the subcellular fractions from human liver and those from the rat, the mouse and the rhesus monkey.