Chemical carcinogenesis: a current biological perspective.
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Carcinogens↗
Biomedical subjects
E Farber
Publications and source records attributed to E Farber.
The induction of liver cancer by dietary deficiency of choline and methionine without added carcinogens.
Fischer 344 male rats fed a choline-methionine deficient diet for from 13 to 24 months developed a 100% incidence of putative preneoplastic hepatocyte nodules and a 51% incidence of hepatocellular carcinoma. The addition of 0.8% choline chloride completely prevented the development of both the nodules and the cancer. The diet contained no added known carcinogen. Analysis of the deficient and supplemented diets revealed no detectable volatile nitrosamines or nitrosamides, nitrite, nitrate or malonaldehyde, less than 0.9 p.p.b. aflatoxin B1 and barely detectable levels of Ames positive material with one strain of Salmonella typhimurium. These findings indicate that a dietary deficiency of choline and methionine can be a major rate limiting factor in the development of liver cancer.
Animals↗
The biochemistry of preneoplastic liver: a common metabolic pattern in hepatocyte nodules.
The biochemical properties of putative preneoplastic hepatocyte nodules as they relate to the metabolism of xenobiotics have been reviewed briefly. A common pattern with low phase I components and elevated phase II components appears evident. The phase I components included microsomal cytochromes P-450 in composite and four different mixed function oxygenase activities. The activities in the nodules were 50% or less of the control values. The phase II components included glutathione, glutathione S-transferases and UDP-glucuronyl transferase 1 and showed two- to five-fold elevations. In addition, activities of microsomal epoxide hydrolase, cytosolic DT-diaphorase, and gamma-glutamyl transferase were all elevated in nodules. The possible significance of this biochemical pattern in analyzing the diversity of biochemical expressions of cancer, in the mechanism of cancer development, and in understanding the suggested role of physiological adaptation in carcinogenesis is discussed.
Animals↗
Chemical carcinogenesis: hepatocyte nodules with a special phenotype as a common step at the crossroads.
Unlike the great heterogeneity and diversity in the initial interactions of a chemical carcinogen with DNA and in the phenotypes of the late malignant neoplasms, the intermediate steps in liver carcinogenesis, the hepatocyte nodules, are remarkably similar. This commonality is seen in six different models of liver cancer development using carcinogens and promoters of quite different chemical structure and properties. The hepatocytes in the nodules show a similar arrangement and architecture, cytology and cytochemistry, blood supply, biological behavior, and biochemical pattern. These observations, coupled with the program nature of the remodeling of the hepatocyte nodules, strongly suggest that at least some of the earlier steps in carcinogenesis are of a physiological adaptive nature.
Adaptation, Physiological↗
Cell cycle kinetics of rat hepatocytes in early putative preneoplastic lesions in hepatocarcinogenesis.
This set of experiments is the first of a series designed to explore facets of cell proliferation of hepatocytes during the carcinogenic process induced in liver by chemical carcinogens. A rat model for hepatocarcinogenesis, the resistant hepatocyte model, was used. A major advantage of this model is the unusual degree of synchrony in the early steps. Carcinogenesis was initiated by the administration of a necrogenic dose of diethylnitrosamine. Resistant hepatocytes so induced were stimulated rapidly to proliferate by partial hepatectomy in the presence of a brief exposure to dietary 2-acetylaminofluorene sufficient to inhibit the proliferation of the majority of hepatocytes, the nonresistant population. Cell cycle parameters were measured in the early carcinogen-altered resistant hepatocyte populations and in regenerating hepatocytes. Growth fraction and doubling time were experimentally determined in the altered hepatocytes. The mean cell cycle length of the resistant cells was 38.6 hr, somewhat longer than that of regenerating hepatocytes, which was 33.6 hr. Most of the increase was due to a prolonged S phase which was 13.6 hr in the altered cell population as compared to 7.0 hr in hepatocytes in regenerating control liver. The hepatocytes in normal regenerating liver had a mean duration of 21.6 hr for G1 as compared to 20.4 hr for the altered hepatocytes and a G2 of 3.4 hr as compared to 3.0 hr for carcinogen-altered hepatocyte. M was assumed to be 1.6 hr in both populations. The growth fraction in the altered cell population was determined to be a minimum of 0.83, and the doubling time was about 45 hr. Thus, the resistant hepatocytes which represent an early putative preneoplastic population show, in general, a prolongation of the cell cycle, mostly due to a prolonged S phase.
2-Acetylaminofluorene↗
Studies on the proliferation and fate of oval cells in the liver of rats treated with 2-acetylaminofluorene and partial hepatectomy.
The kinetics of oval cell proliferation in the liver and their fate were studied by combined autoradiography and immunohistochemical staining for epidermal prekeratin and epoxide hydrolase (EH). The oval cell proliferation was induced in rats by exposure to dietary 2-acetylaminofluorene (2-AAF) for 2 weeks with the midway performance of partial hepatectomy (PH). The labeling with 3H-thymidine [3H-TdR] was done in different groups of rats by two procedures: continuous exposure for 1 week with the aid of a minipump and brief exposure by the administration of a single dose. The livers of groups of animals were examined from 1 to 10 weeks after PH. Oval cells and duct epithelium showed positive staining for prekeratin and negative for EH, whereas hepatocytes showed the reverse pattern of staining. A critical finding was the observation that the exposure to the 2-AAF inhibited virtually completely the labeling of hepatocytes with [3H]-TdR in the caudate lobe and incompletely in the right lobe without interfering with the labeling of the oval cells in either lobe. This made it possible to study the fate of the oval cells vis-à-vis hepatocytes. This qualitative-quantitative study of oval cells and hepatocytes clearly indicates that oval cells under these experimental conditions do not become hepatocytes within 10 weeks. Over 80% of oval cells disappear within this period, and the remainder persist as such. These results indicate that under one set of experimental conditions related to hepatocarcino-genesis in the rat, no evidence for the conversion of oval cells to hepatocytes was obtained.
2-Acetylaminofluorene↗
Cellular biochemistry of the stepwise development of cancer with chemicals: G. H. A. Clowes memorial lecture.
The sequence of possible cellular, tissue, biochemical, and molecular changes that are important during the development of experimental liver cancer with chemicals is reviewed from the viewpoint of the author's experience in carcinogenesis over the past 25 years. The development of a new model for the analysis of liver carcinogenesis, the resistant hepatocyte model, is briefly described, as are the known steps between exposure to an initiating dose of a chemical carcinogen to the appearance of hepatocellular carcinoma. These steps include: (a) the interactions with DNA; (b) the dependence on a round of cell proliferation for initiation; (c) one type of initiated hepatocyte, a resistant hepatocyte; (d) the selection of these new hepatocytes, probably by clonal expansion, to form synchronously the first type of hepatocyte nodules, early nodules; (e) the election of the majority of these nodules to undergo remodeling to normal-appearing liver by differentiation ("redifferentiation"); (f) the election of a minority of early nodules to persist; (g) the slow growth of the few persistent nodules; and (h) the precursor role of persistent nodules in the development of hepatocellular carcinoma. The evidence for such a precursor role includes: (a) the common occurrence in persistent nodules of a subsequent precancerous step, "nodules in nodules"; (b) the occurrence of metastasizing cancer inside nodules without cancer elsewhere in the liver; and (c) the high rate of evolution to cancer of persistent nodules, but not of early nodules, when transplanted to the spleen. Based on the common architecture, organization, blood supply, and biochemical pattern of properties relating to the metabolism of xenobiotics in hepatocyte nodules in six different models of liver carcinogenesis and on the common occurrence of a highly programmed redifferentiation pattern of carcinogen-induced hepatocyte nodules, it is concluded that heterogeneity and diversity seen in many phenotypic properties of cancers, including liver cancers, is preceded by a precursor population that is unusually homogeneous and uniform in phenotype. Thus, the heterogeneity and diversity of cancers are probably late manifestations in carcinogenesis. The available evidence is very suggestive that the hepatocyte nodules are an expression of physiological adaptation to exposure to hazardous xenobiotics and not a form of aberration or mutation. The data also suggest that hepatocyte nodules are an additional pattern of liver differentiation and that liver cancer, to be understood, should be compared with this precursor new state rather than the conventional adult, fetal, or embryonic states.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
The multistep nature of cancer development.
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Animals↗
A characteristic electrophoretic pattern of cytosolic polypeptides from hepatocyte nodules generated during liver carcinogenesis in several models.
The cytosolic polypeptides of hepatocyte nodules in six models of liver carcinogenesis were analysed by SDS-polyacrylamide gel electrophoresis and their patterns compared with these of control and variously treated livers. The amount of a polypeptide of Mr 21,000 was about tenfold elevated in the cytosol of five of the six types of nodules and moderately elevated in the sixth. Certain other polypeptides, particularly one of Mr 26,000, also varied in amount, so that all of the nodules analysed could be distinguished from liver by their electrophoretic patterns. Some possible identities of the two polypeptides are discussed. Their study may have mechanistic as well as diagnostic importance.
Aging↗
Comparison of formalin- and acetone-fixation for immunohistochemical detection of carcinoembryonic antigen (CEA) and keratin.
The purpose of the present study was to compare the relative merits of cold acetone and buffered formalin as fixatives for the detection of carcinoembryonic antigen and keratin in permanently embedded tissues using a peroxidase-antiperoxidase (PAP) immunohistochemical procedure. The effect of treatment with the proteolytic enzyme pronase also was examined in the formalin-fixed tissues. Cold acetone was found to be superior to formalin for the preservation of CEA and keratin antigenic activities in a variety of benign and malignant tissues. Pronase treatment markedly increased the staining intensities of both antigens in formalin-fixed tissues. For many tissues, however, superior results were obtained using the cold acetone method, and this technic is recommended for the optimum retention of antigenic activity in permanently embedded tissues.
Acetone↗
Failure of glutathione to prevent liver cancer development in rats initiated with diethylnitrosamine in the resistant hepatocyte model.
This study was undertaken to observe whether the administration of reduced glutathione intragastrically to male Fischer 344 rats during the precancerous steps of liver carcinogenesis has any protective effect on the development of hepatocellular carcinoma. Hepatocyte nodules were induced in the liver with a single initiating dose of diethylnitrosamine followed by selection of resistant hepatocytes to generate nodules by a two week exposure to dietary 2-acetylaminofluorene coupled with partial hepatectomy. Animals had hepatocyte ('hyperplastic') nodules when examined by laparotomy at three months. At that time, the animals were divided into two groups. One received daily intragastric glutathione for 8 months while the other received no further treatment. An additional control group received only the selecting (promoting) regimen with no initiator or glutathione. At 12 months, the animals receiving the initiator and promoter regimen had a 65% incidence of hepatocellular carcinoma and those receiving glutathione in addition had a 71% incidence. Under these experimental conditions, the long term administration of glutathione appears to have no observable influence on liver cancer development in this model.
Animals↗
The induction of resistant hepatocytes during initiation of liver carcinogenesis with chemicals in rats fed a choline deficient methionine low diet.
Feeding a choline deficient methionine low (CLD) diet for two weeks can substitute for partial hepatectomy in the genesis with benzo[a]pyrene (B[a]P) or 1,2-dimethylhydrazine (1,2-DMH) of resistant hepatocytes that can be selected with dietary 2-acetylaminofluorene plus partial hepatectomy. With single doses of B[a]P or 1,2-DMH during the feeding of the CLD diet for 3 weeks, the number of foci of hepatocytes positive for gamma-glutamyl transferase is approximately the same as with the same dose of each carcinogen given after partial hepatectomy. DL-ethionine was now found to be positive when given as a single dose to animals on the CLD diet. Feeding ethionine for 6 or 12 weeks in a similar choline lipotrope deficient diet also induced a significant increase in foci of enzyme altered hepatocytes. The results indicate that dietary imbalance can have an important influence on initiation of chemical carcinogenesis.
1,2-Dimethylhydrazine↗
Distinctive biochemical pattern associated with resistance of hepatocytes in hepatocyte nodules during liver carcinogenesis.
Hepatocyte ("hyperplastic") nodules induced in the liver by initiation with diethylnitrosamine and selected by dietary 2-acetylaminofluorene plus partial hepatectomy ("resistant hepatocyte model") have a special pattern of biochemical behavior and metabolic activity different than that seen acutely with many xenobiotics including many promoting agents and carcinogens. The nodule cells show a very low uptake of 2-acetylaminofluorene, relative to surrounding and normal liver, low levels of activity in the cytochromes P-450 and aryl hydrocarbon hydroxylase, high levels of activity in gamma-glutamyltransferase, microsomal epoxide hydrolase, soluble glutathione-S-transferase and soluble UDP-glucuronyltransferase (UDP-GT(1)) and elevated levels of glutathione. This metabolic pattern appears to maximize the resistance of the nodules to xenobiotics generally, such as 2-acetylaminofluorene, and thereby may account for the resistant behavior of nodule hepatocytes to the inhibition of cell proliferation and the cytotoxicity by 2-acetylaminofluorene and other carcinogens. The possible importance of this seemingly new metabolic program in carcinogenesis is discussed briefly.
2-Acetylaminofluorene↗
Redifferentiation as a basis for remodeling of carcinogen-induced hepatocyte nodules to normal appearing liver.
A system is described for the detailed study of the remodeling of hepatic nodules that appear regularly during liver carcinogenesis with chemicals. With the use of the resistant hepatocyte model and by focusing on the caudate lobe, it has been possible to label with [3H]thymidine all the hepatocytes in hepatocyte nodules without any significant degree of labeling of the surrounding hepatocytes. Through such a model, the persistence of the label, in relation to the organization and appearance of the hepatocytes in the nodules, has been followed for 26 weeks. Nodules do not "disappear" to any significant degree by regression or by replacement with hepatocytes from the surrounding liver. Rather, nodule hepatocytes undergo differentiation to an adult liver phenotype. Thus, differentiation ("redifferentiation") of a carcinogen-induced altered hepatocyte population is seen regularly during carcinogenesis despite the irreversible nature of some of the changes induced by a chemical carcinogen during initiation.
2-Acetylaminofluorene↗
Promotion of liver cancer development by brief exposure to dietary 2-acetylaminofluorene plus partial hepatectomy or carbon tetrachloride.
Adult male Fischer rats were exposed to a necrogenic dose (200 mg/kg) of diethylnitrosamine or to nonnecrogenic doses of N-methyl-N-nitrosourea, 1,2-dimethylhydrazine, or benzo(a)pyrene following partial hepatectomy or sham hepatectomy. This treatment by itself led to no hepatocellular carcinomas by 8 to 18 months, except in animals given N-methyl-N-nitrosourea, which showed a 30% incidence by 12 months. With each treatment regimen, exposure to dietary 2-acetylaminofluorene for 2 weeks coupled with partial hepatectomy or the administration of a necrogenic dose of CCl4, was associated with an incidence of 68 to 94% of cancer at 8, 12, or 18 months, depending upon the initiating carcinogen used. Appropriate controls showed either no hepatocellular carcinoma or a much lower incidence. It is concluded that the 2-week exposure to dietary 2-acetylaminofluorene plus partial hepatectomy or the administration of CCl4 has a strong promoting effect on liver carcinogenesis with four different chemical carcinogens.
1,2-Dimethylhydrazine↗
Transplantation of hepatocytes from normal and preneoplastic livers into spleens of syngeneic host rats.
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Animals↗
Resistance to hepatotoxins acquired by hepatocytes during liver regeneration.
The appearance of resistance to a number of hepatotoxins in primary cultures of hepatocytes prepared at various time intervals up to 2 weeks after partial hepatectomy is the major focus in this study. Resistance to the cytocidal effect of aflatoxin B1, 2-acetylaminofluorene, N-hydroxy-2-acetylaminofluorene, methotrexate, or methyl methanesulfonate shows a progressive increase until 48 hr and then returns to the resting level of susceptibility by 2 weeks. The genesis of mutagens from 2-acetylaminofluorene and aflatoxin B1 by S-9 liver fractions shows a decrease from and return to control values after partial hepatectomy that parallels the resistance. The levels of total cellular cytochromes P-450 also decrease following partial hepatectomy and remain from 28 to 36% less than those of controls for at least 1 week. The glutathione and total soluble sulfhydryl ("glutathione") content increase following partial hepatectomy, and the pattern is consistent with a partial role for glutathione in the resistance phenomenon as it relates to 2-acetylaminofluorene. The possible relationship between resistance to the cytocidal effects in vitro and the resistance to inhibition of cell proliferation in vivo during liver carcinogenesis is discussed.
2-Acetylaminofluorene↗
The rapid induction of liver cell death in rats fed a choline-deficient methionine-low diet.
This study was undertaken to test the hypothesis that the basis for the cell proliferation seen in the livers of rats fed a choline-deficient methionine-low (CMD) diet is regeneration following hepatocyte cell death and necrosis. Exposure of rats to a CMD diet for 2 weeks was found to induce liver cell loss and necrosis as monitored by three different approaches: 1) histologic examination, 2) serum sorbitol dehydrogenase assay, and 3) measurement of the total radioactivity in liver DNA prelabeled during a prior period of regeneration. These observations suggest that the basis for liver cell proliferation in rats fed a CMD diet probably resides in the cell loss and necrosis induced in the liver by the deficient diet.
Animals↗