THE PATHOGENESIS OF TUMORS OF THE LIVER PRODUCED BY BUTTER YELLOW

Metaplastic pancreatic cells in liver tumors induced by diethylnitrosamine

Metaplastic pancreatic cells have been infrequently observed in fish liver tumors induced by chemical carcinogens. An investigation with nitrosamine-exposed trout was undertaken to characterize the relationships of metaplastic pancreatic cells with other cell types. Eight-week-old rainbow trout (Salmo gairdneri) were fed a control diet or diets containing 500 ppm beta-naphthoflavone (BNF), 2000 ppm indole-3-carbinol (13C), or 100 ppm Aroclor 1254 (PCB) for 6 weeks. The fish were then exposed to 250 ppm diethylnitrosamine for 24 hr in an aqueous aquarium bath and reared on control diet for 39 weeks postexposure. Livers were excised, processed to paraffin sections, and stained with hematoxylin and eosin for histological evaluation. Metaplastic pancreatic cells were found only in tumors. Of the tumors with metaplastic pancreatic cells, 100/105 (95.2%) contained neoplastic cholangiolar components. Only 5/105 (4.76%) were hepatocellular carcinomas. 13C pretreatment inhibited the incidence of cholangiolar tumors (cholangioma 3.6% vs 31.3%, cholangiocarcinoma 3.6% vs 13.0%) and metaplastic pancreatic cells (5.1% vs 19.1%), whereas BNF and PCB had no effect. A hepatocellular origin for metaplastic pancreatic cells is supported. Cholangiolar neoplasia is associated with the expression, growth, or survival of metaplastic pancreatic cells in liver tumors. Hepatocarcinogenicity should not be described entirely by hepatocellular events since cholangiolar and metaplastic pancreatic cells can respond associatively to carcinogens and dietary modulators.

Macroregenerative nodule of the liver. A clinicopathologic study of 345 autopsy cases of chronic liver disease

The livers of 345 autopsy cases of chronic liver disease were examined for macroregenerative nodule (MRN), a large nodular lesion more than 10 mm in diameter. A total of 86 lesions of MRN was found in 49 cases (14.2%): 32 were from 191 cases of hepatocellular carcinoma (HCC), 16 were from 148 cases of cirrhosis only, and one was from six cases of chronic hepatitis. The incidence (19.6%) and the size (12.1 mm) of MRN in macronodular type of cirrhosis were significantly higher and larger than those in other types of cirrhosis. Also, the average size of MRN lesions of cases with HCC (12 mm) was significantly larger than that of cases with cirrhosis only (10.5 mm). The incidence of liver cell dysplasia (LCD) in cases of MRN (67.3%) was significantly higher than that in cases without MRN (40.9%). The MRN lesions were divided into Type I and Type II, the latter having proliferative foci distinguishable from the surrounding tissue. Three of them contained atypical cells regarded as cancer. Type II lesions were larger in size, and cases with multiple MRN lesions were seen more frequently in cases of HCC. The average age of the patients with Type II lesion was 5 years older than those with Type I lesions. These findings suggest that MRN should not be ignored in the morphogenesis of HCC.

Cellular events during hepatocarcinogenesis in rats and the question of premalignancy

The cellular, biochemical, and genetic changes that occur in the liver of rats exposed to chemical hepatocarcinogens are reviewed. Multiple new cell types appear in the liver of carcinogen-treated rats including foci, nodules, ducts, oval cells, and atypical hyperplastic areas. The application of phenotypic markers for these cell types suggests that hepatocellular carcinomas may arise from more than one cell type, including a putative liver stem cell that proliferates following carcinogen exposure. Study of DNA, RNA, and proteins produced by hepatocellular carcinomas and putative premalignant cells has so far failed to identify a gene or gene product clearly associated with the malignant or premalignant phenotype. Understanding the cellular lineage from normal cell through putative premalignant cell to cancer is critical to understanding the process of carcinogenesis. Application of new immunological (monoclonal antibody, transplantation) and molecular biological (gene cloning, oncogene identification) approaches to this problem holds promise that the process of hepatocarcinogenesis will be better known in the near future.

National Toxicology Program nomenclature for hepatoproliferative lesions of rats

Diagnostic criteria for hepatoproliferative lesions of Fischer 344 rats are presented to permit more complete categorization of the spectrum of lesions observed in two-year chemical carcinogenicity studies. A nomenclature recently adopted by the National Toxicology Program differs from previous classification schemes in that hepatocellular hyperplasia and hepatocellular adenoma are to be used for lesions which were previously combined under the diagnosis of neoplastic nodule. The term hyperplasia is reserved for proliferative lesions that are perceived to be secondary, nonneoplastic responses to degenerative changes in the liver. Foci of cellular alteration, hepatocellular adenoma, and hepatocellular carcinoma are believed to represent a spectrum of changes that comprise the natural history of neoplasia. This change in nomenclature was made subsequent to a peer review of representative hepatoproliferative lesions from two-year carcinogenicity studies. The revised nomenclature is consistent with traditional pathologic diagnoses for proliferative lesions in other epithelial tissues and should facilitate the interpretation of conventional toxicity and carcinogenicity studies in rats. Morphologic features of other selected rat liver lesions are also presented.

Comparative study of abnormality in glycogen storing capacity and other histochemical phenotypic changes in carcinogen-induced hepatocellular preneoplastic lesions in rats

A sequential comparison was made between abnormal glycogen storage and other histochemical phenotypic changes in hepatocellular precancerous lesions (altered foci and neoplastic nodules) during various stages in the process of development of cancer in rat liver. N-2-fluorenylacetamide was fed to male rats for 8 weeks and groups of rats were killed at the end of carcinogen feeding and at 12 and 24 weeks on control diet. Foci rich in glycogen storage accounted for a majority of all foci over the course of experiment, while foci devoid of glycogen storage, which were absent at the end of carcinogen feeding, gradually increased in number during maintenance. Glycogen-deficient lesions that might appear to arise from glycogen-rich lesions displayed hyperbasophilia demonstrated by toluidine blue reaction, but often lacked gamma-glutamyl transpeptidase activity. Resistance to iron accumulation was consistently shown in all precursor lesions for hepatocellular carcinoma in the siderotic liver regardless of abundance or absence of cellular glycogen. It was suggested that properties such as loss of glycogen storing capacity, hyperbasophilia, and some cellular atypicality resembling those of carcinoma cells might be essential elements for malignant progression.

Carcinomas and other lesions of the liver in mice ingesting organochlorine pesticides

Carcinomas of the liver were readily induced in male and female mice given organochlorine pesticides orally. The carcinomas were predominantly hepatocellular, with a few being cholangiocellular, and varied from well differentiated to poorly differentiated to undifferentiated. They are capable of invading, metastasizing, and killing the mice. Hemangiosarcomas, leimyosarcomas, and reticulum cell sarcomas were also occasionally seen in mice receiving these chemicals. Hepatic vein thrombosis and hepatic necrosis was observed in some mice.

Polychlorinated biphenyl(s) as a promotor in experimental hepatocarcinogenesis in rats

The effects of dietary polychlorinated biphenyls (PCBs) on hepatocarcinogenesis in female rats of Donryu strain receiving 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) were investigated. Oral administration of PCBs after administration of 3'-Me-DAB resulted in a high incidence (64%) of hepatocarcinoma. In contrast, administration of a similar amount of PCBs before, or together with 3'-Me-DAB did not induce hepatic tumors. Administration of a slightly larger amount of PCBs alone did not induce liver tumors, while administration of a slightly larger amount of 3'-Me-DAB alone caused only a low incidence (13%) of hepatocarcinoma. These results strongly suggest that PCBs exert a potent promoting action in experimental azo dye hepatocarcinogenesis.

Development of tumours in Syrian hamsters during prolonged experimental exposure to nas

In several series of experiments, nas was introduced into the buccal pouch or oesophagus of Syrian hamsters or applied to the dorsal skin. In one series, nas was administered to six consecutive generations of hamsters. No tumours appeared at the site of administration, although changes appeared in the mucosa of the buccal pouch and the oesophagus. Tumours in organs remote from the site of application developed only in those series in which nas was introduced into the buccal pouch. The commonest site of tumorigenesis was the liver, followed by the adrenal glands, the forestomach, and the genital organs. Tumours occurred in 17.6% of the experimental animals compared with 3.5% of the controls.

Fine structural changes induced in rat hepatocytes by single doses of 3'-methyl-4-dimethylaminoazobenzene

Male Leeds rats were given single oral doses of 150 or 300 mg/kg body weight of 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB). They were sacrificed 24 or 48 h after treatment and their hepatic tissues examined by electron microscopy. The development was observed of an unusual cytoplasmic change, which consisted of large perinuclear areas of decreased hyaloplasmic density, devoid of glycogen or organized structures, which displaced the organelles to the cell periphery. This arose by the formation of large glycogen lakes, which coalesced and then lost their glycogen content, and this was accompanied by nuclear irregularity and shrinkage. Other changes, affecting the endoplasmic reticulum and the cell surface, appeared to be similar to those induced by chronic azo dye feeding. It was concluded that the acute lesion observed may limit any specific responses of the hepatocytes to the presence of 3'-MeDAB.

THE EFFECTS OF THE CARCINOGEN, 2-ACETYLAMINOFLUORENE, ON LARVAL AND ADULT FROGS

2-Acetylaminofluorene is a powerful carcinogen capable of inducing a variety of benign and malignant neoplasms in several species of animals and is required only in very small amounts for relatively short periods of time. It is somewhat soluble (1.3 mgm. per 100 cc.) in water. Frog tadpoles were raised in solutions of various strengths. Even dilute solutions proved to be highly toxic to these animals. In those animals that survived it was found that 2-acetylaminofluorene inhibits both total body growth and rate of tail regeneration; that the tadpoles remained dark (melanophores dilated) even on a light background; that lesions of the liver developed resembling those described in mammals resulting from treatment with the same and other carcinogens. It is not certain that these lesions are neoplastic, but they may be of the type that precede or accompany liver cell carcinoma. This carcinogen was also fed to or injected into adult frogs. Even small amounts were toxic to them and only a small number survived for more than a few days. In the survivors, after six to eight weeks, lesions of the liver, including necrosis and cirrhosis, appeared. No distinct neoplasms were produced.