Early biological markers during liver carcinogenesis.

Abstract

Morphological and biochemical markers of early events during liver carcinogenesis have been detected by such micromethods as electron microscopy and cytochemistry. Morphological markers: During hepatocarcinogenesis at least 4 different types of altered hepatocytes can be distinguished in routine hematoxylin- and eosin-stained tissue sections: 1. clear cells, 2. acidophilic cells, 3. vacuolated cells, and 4. basophilic (tumour) cells. Under the electron microscope, the clear cells can be characterized by large glycogen zones and by a dislocation and relative reduction of the granular endoplasmic reticulum. The acidophilic cells show a pronounced prnliferation of the agranular endoplasmic reticulum. The vacuolated cells contain many fat droplets. The basophilic cells are rich in ribosomes, but poor in glycogen particles. While the clear and the acidophilic cells emerge very early after the application of carcinogens, the vacuolated cells and especially the basophilic cells appear only later, when neoplastic nodules and hepatocellular carcinomas develop. Intermediate cell types with an unusual mixture of clear, acidophilic, vacuolated and basophilic cytoplasmic components are frequently found in neoplastic nodules and sometimes also in carcinomas. The morphological results suggest that the clear and the acidophilic hepatocytes comprise a preneoplastic cell population giving rise to hepatocellular tumours. The sequence of cellular changes leading to cholangiocellular tumours starts with a ductular (oval) cell proliferation which may progress to cholangiofibrotic areas, cystic cholangiomas, cholangiofibromas and cholangiocarcinomas. The first sign of the development of malignant mesenchymal liver tumours (hemangiosarcomas, fibrosarcomas) which has been detected by morphological methods is a proliferation of atypical mesenchymal cells along the liver cell cords or inside the sinusoids. Biochemical markers: The earliest change which can be demonstrated by cytochemical methods in hepatocytes during carcinogenesis is an excessive storage of glycogen (hepatocellular glycogenosis). The hepatic glycogenosis has been recently confirmed by biochemical methods. This accumulation of glycogen is responsible for the clear cytoplasm of the cells mentioned above. The acidophilic cells may also contain considerable amounts of glycogen. Both the clear and the acidophilic cells form glycogen storage foci during the preneoplastic phase. Enzyme histochemical investigations of these foci show that the activities of most enzymes studied up to several weeks after application of the carcinogen remain unchanged. A possible exception is glycogen Phosphorylase, the activity of which seems to increase during the very early stages. Later on, however, characteristic changes occur in many glycogen storage foci: The activities of Phosphorylase and glucose-6-phosphatase decrease, while that of glucose-6-phosphate dehydrogenase increases. Further steps toward malignancy are associated with additional enzyme histochemical changes and a reduction of glycogen. It is concluded that a gradual shift of cellular carbohydrate metabolism occurs during hepatocarcinogenesis. A phenomenon very similar to hepatocellular glycogenosis can be observed in preneoplastic ductular cells which store and secrete abundant acid and neutral mucopolysaccharides (cholangiocellular mucopolysaccharidosis). The production of mucopolysaccharides persists in one type of cholangiocellular tumours (cholangiofi-broma), but in cystic cholangiomas and in cholangiocarcinomas the mucopolysaccharidosis gradually disappears. Up to now comparable changes in carbohydrate metabolism have not been found during the development of mesenchymal liver tumours. The hepatocellular glycogenosis and the cholangiocellular mucopolysaccharidosis may be considered useful markers for the recognition and perhaps also for the isolation of preneoplastic cells for further biochemical investigation.