DNA binding,adduct characterisation and metabolic activation of aflatoxin B1 catalysed by isolated rat liver parenchymal,Kupffer and endothelial cells

In vitro studies with rat liver parenchymal, Kupffer and endothelial cells isolated from male Sprague-Dawley rats were undertaken to investigate cell-specific bioactivation of aflatoxin B₁, DNA binding and adduct formation. In the mutagenicity studies, using homogenates of all three separated liver cell populations (co-incubated with NADP⁺ and glucose-6-phosphate as cofactors for the cytochrome P-450 monooxygenase system) parenchymal, Kupffer and endothelial cells were able to activate aflatoxin B₁ to a metabolite mutagenic to Salmonella typhimurium TA 98. In the case of nonparenchymal cells (i.e. Kupffer and endothelial cells) 10-fold higher concentrations of aflatoxin B₁ had to be used to obtain a similar number of revertants to that observed with parenchymal cells. Induction studies with Aroclor 1254 led to a striking decrease in the activation of aflatoxin B₁ in parenchymal cells, whereas nonparenchymal cells had a slightly enhanced metabolic activation capacity for aflatoxin B₁. Metabolism studies with microsomes from induced and noninduced cells using testosterone as substrate revealed comparable results: after induction with Aroclor 1254, parenchymal cells showed a 60% decrease in the formation rate of 2-hydroxytestosterone, whereas the formation rate of this metabolite remained unchanged in nonparenchymal cells; 2-hydroxytestosterone is specifically formed by cytochrome P-450 IIC11, which also catalyses the activation of aflatoxin B₁ to its epoxide. When freshly isolated, intact cells were incubated with tritiated aflatoxin B₁, a dose-dependent aflatoxin B₁ binding to DNA in parenchymal and nonparenchymal cells was observed. HPLC analysis of DNA acid hydrolysates of all three cell types showed the major adduct to be 8,9-dihydro-8-(N⁷-guanyl)-9-hydroxyaflatoxin B₁.This project was supported by the Deutsche Forschungsgemeinschaft (SFB 302). B. Schlemper was the recipient of a European Science Foundation Scholarship