Tamoxifen alone or in combination with estradiol-17 beta inhibits the growth and malignant transformation of hepatic hyperplastic nodules

Hepatic hyperplastic nodules (HHNs) induced by the 'resistant hepatocyte method' of Solt et al. were studied as an experimental prototype of oral contraceptive-related tumors. Cytoplasmic estrogen receptors were present in all HHNs harvested and their concentration was always less than that in normal liver. No specific cytoplasmic progestin receptors could be measured in the above tumor or liver specimens. The long-term administration of estradiol-17 beta (4.8-24.0 micrograms/day) resulted in the death of all but one of 20 animals prior to termination at 10 months. Tamoxifen (0.25-2.5 mg biweekly), which did not lead to excess mortality, decreased HHN grade (proportion of liver slice occupied by HHN) and inhibited malignant transformation. Combination therapy with single-dose estradiol-17 beta (4.8 micrograms/day) and various doses of tamoxifen (0.25-2.5 mg biweekly) in most cases reduced mortality, HHN grade and malignant transformation. Cytoplasmic progestin receptors were absent and estrogen receptors were either undetectable or present in low concentrations in hepatic tumors harvested at the time of termination. Our results indicated that HHNs are hormone-dependent and that malignant transformation can be inhibited by tamoxifen alone or in combination with estradiol-17 beta.

Intestinal metaplasia as a common option of oval cells in relation to cholangiofibrosis in liver of rats exposed to 2-acetylaminofluorene

Oval cell proliferation in the liver was studied in rats exposed to dietary 2-acetylaminofluorene for 2 weeks with partial hepatectomy performed midway at 1 week. Using autoradiography after either continuous or pulse exposure to [3H]thymidine, histochemical staining for leucine aminopeptidase and gamma-glutamyltransferase, and transmission electron microscopy, we found that every animal showed islands of oval cells with small intestinal metaplasia at 3 weeks. Transitions from these islands of metaplasia to cholangiofibrosis were commonly seen. The importance of small intestinal metaplasia of oval cells in the genesis of cholangiofibrosis is presented and discussed.

Concepts of disease, medical research and the challenges to the schools of the healing professions

The study of disease is a significant part of the pattern of funding for medical research in North America and elsewhere. Also, the existence of disease and its importance in all branches of the healing professions is the major justification for separate professional schools of medicine. These considerations should encourage a vigorous exploration and development of concepts of disease as an important part of any medical education. Based on much of the current research activities, concepts of disease, especially chronic disease, seem largely outdated and not intimately reflecting the realization that the development of disease is often a physiological response to perturbations in the internal or external environment and not abnormal or pathological in the etymological sense. The importance of viewing cancer and other chronic diseases from this physiological point of view and not from the point of view of end-stage disease is emphasized by the use of one example, the development of cancer with chemicals. The challenge to the healing professions to develop more modern programs for educating the prospective research worker for the study of disease is discussed briefly.

Tamoxifen alone or in combination with estradiol-17 beta inhibits the growth and malignant transformation of hepatic hyperplastic nodules

Hepatic hyperplastic nodules (HHNs) induced by the 'resistant hepatocyte method' of Solt and Farber were studied as an experimental prototype of oral contraceptive-related tumors. Cytoplasmic estrogen receptors were present in all HHNs harvested and their concentration was always less than that in normal liver. No specific cytoplasmic progestin receptors could be measured in the above tumor or liver specimens. The long-term administration of estradiol-17 beta (4.8-24.0 micrograms/day) resulted in the death of all but one of 20 animals prior to termination at 10 months. Tamoxifen (0.25-2.5 mg biweekly) which did not lead to excess mortality, decreased HHN grade (proportion of liver slice occupied by HHN) and inhibited malignant transformation. Combination therapy with single-dose estradiol-17 beta (4.8 micrograms/day) and various doses of tamoxifen (0.25-2.5 mg biweekly) in most cases reduced mortality, HHN grade and malignant transformation. Cytoplasmic progestin receptors were absent and estrogen receptors were either undetectable or present in low concentration in hepatic tumors harvested at the time of termination. Our results indicate that HHNs are hormone-dependent and that malignant transformation can be inhibited by tamoxifen alone or in combination with estradiol-17 beta.

A common biochemical pattern in preneoplastic hepatocyte nodules generated in four different models in the rat

Hepatocyte nodules, structures consistently seen in every model of liver carcinogenesis well before the first appearance of cancer, were examined with respect to some Phase I and Phase II components considered to be important in the metabolism of carcinogens and other xenobiotics. Phase I components are those related to the metabolism of xenobiotics and include microsomal cytochromes P-450 and mixed-function oxygenase activities. Phase II components are those related to the conjugation and detoxification reactions of xenobiotics and their metabolites and include glutathione S-transferases and glutathione. Nodules were induced by the resistant hepatocyte, choline-deficient, methionine-low diet, phenobarbital and orotic acid models of liver carcinogenesis. Also, nodules generated by the resistant hepatocyte model were examined after transplantation to the spleen of syngeneic animals. The hepatocyte nodules show a common biochemical pattern, consisting of decreased microsomal cytochromes P-450, cytochrome b5, and aminopyrine N-demethylase activity and increased glutathione and gamma-glutamyltransferase in whole homogenates and glutathione S-transferase activity in the cytosol. This similarity, appropriate to a resistance phenotype, adds additional support for the hypothesis that hepatocyte nodules may be a common step in liver carcinogenesis in several different models.

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)

Rapid lipid peroxidation in the nuclear fraction of rat liver induced by a diet deficient in choline and methionine

A diet deficient in choline and methionine, known to produce hepatocellular carcinoma in the absence of any added chemical carcinogen, induced lipid peroxidation in the nuclear fraction of the liver when fed to male Fischer 344 rats. This lipid peroxidation was detected within 1 day of feeding the diet by the appearance of diene conjugates and increased progressively up to 3 days. It was prevented completely by the addition of choline chloride to the diet. The close proximity of DNA may make it a possible target for attack by free radicals.

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.

Comparative influences of different PB-type and 3-MC-type polychlorinated biphenyl-induced phenotypes on cytocidal hepatotoxicity of bromobenzene and acetaminophen

The influences of in vivo treatment with two pure PCB congeners, 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) and 3,3',4,4'-tetrachlorobiphenyl (TCBP), on the lethal cytotoxicity of bromobenzene and acetaminophen were examined in short-term primary cultures of isolated rat hepatocytes. Lethal injury was measured by release of lactate dehydrogenase (LDH) into culture medium after 20 hr exposure to the hepatotoxins. The HCBP, a PB-type inducer of cytochrome P-450, resembled phenobarbitone (PB) in its ability to increase susceptibility of hepatocytes to bromobenzene (0.5 to 1.6 mM) and acetaminophen (1 to 16 mM). This induced sensitivity was consistently inhibited by SKF-525-A (10 microM) but not alpha-naphthoflavone (ANF, 10 microM) in culture. The 3,3',4,4'-TCPB, a 3-MC-type inducer of cytochrome P-450, resembled 3-methylcholanthrene (3-MC) in its inability to induce susceptibility to bromobenzene. TCBP and 3-MC each increased (20- to 30-fold) cytotoxicity of acetaminophen by a mechanism substantially inhibitable by ANF but not SKF-525-A. These results demonstrate that categorizing pure PCB isomers and congeners into groups according to their different induction capabilities is predictive for their ability to modulate acute hepatocellular necrosis by bromobenzene and acetaminophen.

Nutrition and cancer

Nutrition has a close association with cancer. Carcinogens in foods, macronutrients, micronutrients such as vitamins A, C and E and selenium, dietary fiber, the modulation of metabolism by diet, food additives and anticarcinogens in foods all affect the development of cancer. In particular, macronutrients (especially meat and animal fat) appear to have a significant effect on the development of cancer of the colon, breast and uterus. This article discusses research on the links between nutrition and cancer, and describes current dietary recommendations to decrease the likelihood of cancer.

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.

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.

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.

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.

Influences of various xenobiotic inducers on cytocidal toxicity of lasiocarpine and senecionine in primary cultures of rat hepatocytes

The influences of in vivo pretreatment with phenobarbitone (PB), 3-methylcholanthrene (3-MC), 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP), and 3,3',4,4'-tetrachlorobiphenyl (TCBP) on cytocidal hepatotoxicity of two pyrrolizidine alkaloids, lasiocarpine (LC) and senecionine (SC), were compared in short-term primary cultures of rat hepatocytes. Toxicity was measured by release of lactate dehydrogenase (LDH) into culture medium at 24 h. LC was slightly more toxic to control hepatocytes than SC in the graded response range of 10-160 microM. PB and HCBP (a PB-type polychlorobiphenyl inducer) similarly potentiated toxicity of SC, and each diminished the degree to which cell killing by LC and SC was inhibited by SKF-525-A. By comparison, 3-MC and TCBP (a 3-MC-type PCB inducer) each diminished toxicity of SC but had little effect on toxicity of LC. Alpha-naphthoflavone (ANF) potentiated toxicity of both LC and SC in hepatocytes induced by 3-MC or TCBP but had little effect on responses of hepatocytes induced by either PB or HDBP. These results indicate that xenobiotics that induce similar patterns of cytochrome P-450 isozymes have qualitatively similar modulating influences on cytocidal hepatotoxicity of pyrrolizidine alkaloids in primary cultures. However, the observed modulating effects could not be explained solely on the basis of altered activation rates by the cytochrome P-450 species known to be induced by the various xenobiotics.

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.

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.

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.

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.