Arylamine activation following chronic ethanol ingestion by rats: studies on the liver S9, microsomal and cytosolic fractions and comparison with Aroclor 1254 pretreatment

Abstract

That enzyme fractions derived from animals chronically fed alcohol can alter the metabolism of carcinogenic xenobiotic compounds has been documented. To further understand this relationship the mutagenicity of 3 aromatic amines was determined in the Ames test, employing activation systems derived from rats maintained on an alcohol-containing liquid diet, an isocaloric control liquid diet or Aroclor 1254-pretreated animals fed standard laboratory chow. Depending upon protein and substrate concentrations, S9 from ethanol-fed rats was 30-50% less efficient than S9 from pair-fed rats in activating arylamines (2-aminofluorene, 2-aminoanthracene and 2-acetylaminofluorene) to mutagens in Salmonella typhimurium TA98 and TA100. Cytosolic fractions from ethanol-fed animals always resulted in greater arylamine activation than that of controls whereas the opposite was true of the microsomal compartment in which the ethanol-treated group was consistently less active than the controls. The cytosolic N-acetyltransferase activities with respect to 2 different substrates, isoniazid and 2-aminofluorene, were unaffected by ethanol consumption, indicating that this activity probably does not account for the different activation profiles exhibited by the ethanol and pair-fed cytosolic systems. Both the cytosolic and microsomal compartments are required for maximal expression of the mutagenicity of each arylamine however, each compartment can activate arylamines independently of the other. Reconstituting cytosol with microsomes from ethanol- and pair-fed rats, but not Aroclor-pretreated rats, resulted in a synergistic activation of the aromatic amines and displayed an effect similar to that of S9. Compared to Aroclor pretreatment and pair-fed controls, microsomes from ethanol-fed rats displayed the least capacity for activating any of the arylamines to mutagens. Microsomes from Aroclor-pretreated rats accounted for at least 80% of the S9-mediated activation of each of the arylamines to mutagenic metabolites which was in marked contrast to the contribution of the microsomal fractions to the S9 activity in the ethanol- (5-20% of S9 activity) and pair-fed systems (22-30% of S9 activity). The data indicate that 2 opposing reactions occur in S9, a cytosolic activity that augments and a microsomal activity that attenuates the mutagenicity of arylamines. Both activities are modified by ethanol consumption and Aroclor pretreatment.