Systematic studies of the sequence of cellular changes during hepatocarcinogenesis induced predominantly in rats by stop experiments with
N-nitrosomorpholine (NNM) led to the following main results and conclusions: The development of hepatocellular
tumors is preceded by a multifocal
hepatic glycogen storage disease (
glycogenosis). Cytomorphological and cytochemical findings suggest a sequence of focal changes leading from clear and acidophilic
glycogen storage foci through mixed cell foci and neoplastic nodules to
hepatocellular carcinomas. The clear and acidophilic
glycogen storage cells persisting after withdrawal of the
carcinogen apparently represent a preneoplastic cell population, the neoplastic transformation of which is accompanied by a gradual reduction of
glycogen and a concomitant increase in ribosomes (basophilia). The first appearance and frequency of the different liver lesions investigated was shown to depend on the dose of
carcinogen administered. With increasing dose of NNM, the number of focal lesions considerably increased, and this was accompanied by an earlier development of mixed and basophilic cell populations. There was no indication of any reversibility of pronounced focal lesions under the experimental conditions chosen. On the contrary, the foci became larger and acquired phenotypic markers closer to
neoplasia independent of further action of the
carcinogen.
Enzyme histochemically, the majority of the pronounced
glycogen storage foci showed a reduction in the activities of
glycogen phosphorylase and
glucose-6-phosphatase while the activity of
glucose-6-phosphate dehydrogenase, a key
enzyme for the pentose phosphate pathway, was increased. The mixed cell foci, neoplastic nodules and
carcinomas which emerged at later stages were characterized by a progressive shift away from
glycogen metabolism towards glycolysis and the pentose phosphate pathway. as indicated by an increase in
glyceraldehyde-3-phosphate dehydrogenase and
glucose-6-phosphate dehydrogenase activities. These changes in
enzyme pattern are in keeping with a developmental sequence leading from
glycogen storage foci through mixed cell foci and neoplastic nodules to
hepatocellular carcinomas. Biochemical microanalysis of dissected
glycogen storage foci and mixed cell foci revealed that the foci composed exclusively of storage cells contained on an average 100% more
glycogen than the normal liver tissue. The overall
glycogen content of the mixed cell foci, which were composed of both glycogenotic and
glycogen-poor basophilic cells, was not distinguishable from that of normal tissue.(ABSTRACT TRUNCATED AT 400 WORDS)