Chronic exposure to
ethionine (0.05%) combined with dietary
choline deficiency was used to study changes in
aldehyde dehydrogenase (ALDH) activity during hepatocarcinogenesis in male Sprague-Dawley rats. Over a period of 43 weeks, animals were sacrificed at intervals and the ALDH phenotype of normal liver and any lesions was characterized by histochemical analysis, total activity assays, and gel electrophoresis, using
propionaldehyde and
nicotinamide adenine dinucleotide (
NAD+) to detect normal liver ALDH activity and
benzaldehyde and
nicotinamide adenine dinucleotide phosphate (
NADP+) for
tumor-associated ALDH. In animals receiving
ethionine plus
choline deficiency, significant changes in ALDH were observed histochemically by 9 weeks, when there was a distinct shift in activity from its normal centrilobular pattern to a periportal distribution. The first
NAD+- and
NADP+-dependent ALDH-positive
enzyme-altered foci were also seen at 9 weeks. There was no correlation between the ALDH and
gamma-glutamyl transpeptidase phenotypes of an individual focus. Areas of cholangiofibrosis, cystic degeneration, and bile duct proliferation were distinctly ALDH negative. No significant changes in
benzaldehyde and NADP+ ALDH activity were detectable by total activity assays or gel electrophoresis prior to the appearance of overt
neoplasms at 26 weeks. No significant changes in ALDH activity occurred in animals receiving either
ethionine or
choline deficient diet alone. By histochemistry, total activity assays and gel electrophoresis, only 7 of the 28 (25%) of the
hepatic neoplasms examined expressed the
tumor-associated ALDH phenotype. An additional five
neoplasms had barely detectable levels of
benzaldehyde and NADP+ ALDH activity. These results are in striking contrast to changes in ALDH activity occurring during hepatocarcinogenesis induced by other protocols we have tested previously in which from 50 to 96% of all
neoplasms were ALDH positive.