Localisation of a tumor-associated phenotype of benz-aldehyde dehydrogenase in liver carcinogenesis of flounder by quantitative histochemistry

Aldehyde dehydrogenases (ALDHs) oxidize endogeneous reactive aldehydes including lipid peroxidation products (propionaldehyde, malondialdehyde) and are also inducible by xenobiotics like DDT and TCDD. ALDHs are found in injured livers and cancers of contaminant-exposed flounder (Platichthys flesus L.) and showed identical characteristics as in hepatocellular carcinomas of rats by its cytosolic localisation, the preferential oxidation of aromatic compounds (benzaldehyde), dependency on NADP as coenzyme and sensitivity to the specific inhibitor disulfiram. Image analysis showed increased activity of NADP-dependent benzaldehyde dehydrogenase localised in a few cells of early eosinophilic foci and in basophilic adenomas, carcinomas and their invasively growing protrusions (satellites). Disulfiram sensitivity to differentiate between the xenobiotic-inducible isozyme and the tumor-specific isozyme in rats was highest in the early stages of carcinogenesis in the liver of fish. Moderate disulfiram inhibition was observed in non-neoplastic and extrafocal tissue. In neoplastic livers of flounder from contaminated areas (Elbe estuary), hepatocytes in early stages of carcinogenesis were best protected against accumulation of toxic aldehydes by increased activity of the specific tumor-associated isozyme.