Aldehyde dehydrogenase and glucose-6-phosphate dehydrogenase as markers for enzyme-altered foci in the liver of dab (Limanda limanda L.)

The activities of the most important aldehyde oxidizing enzymes, the aldehyde dehydrogenases (ALDH), were detected histochemically in liver cryosections of dab (Limanda limanda L.) caught at differently polluted stations along the North Sea coast. In parallel, glucose-6-phospate dehydrogenase (G6PDH) as an NADPH-generating enzyme was measured. Increased activities of both enzymes localized putatively preneoplastic hepatocytes (foci), but ALDH in combination with propionaldehyde and NAD marked 50% more foci than G6PDH alone. Nevertheless, at the more contaminated stations with highest prevalences of foci, ALDH activities showed a shift in substrate and coenzyme dependence from propionaldehyde and NAD to benzaldehyde and NADP in altered hepatocytes, a possible result of physiological adaption to the toxic environment. Increased G6PDH activities in focal hepatocytes indicated elevated NADPH production in contrast to the injured extrafocal liver parenchyma showing reduced G6PDH activities compared to normal livers. Using the ALDH inhibitor disulfiram, the existence of a specific tumor-associated isozyme previously found in rats could not be clearly demonstrated in early enzyme-altered hepatocellular foci of dab. However, based on the total inhibition of Bz-NADP-dependent ALDH, the presence of a xenobiotic-induced ALDH isozyme can be anticipated.