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.     

Histochemical studies on the early proliferative lesion induced in the rat liver by aflatoxin

Male inbred Fischer rats were fed a diet containing 5 p.p.m. aflatoxin for 1, 3, 4½ and 6 weeks at which times groups were killed for histological and histochemical study. Aflatoxin produced a scattered individual cell necrosis of parenchymal cells by 1 week. At 3 weeks small basophilic proliferative foci were seen which increased in size and abundance to 6 weeks. These foci showed starvation-resistant glycogen, variable depletion of glucose-6-phosphatase, succinic dehydrogenase, aniline hydrogenase, membrane ATPase and acid phosphatase. At 6 weeks the foci showed the presence of gamma glutamyl transpeptidase and glucose-6-phosphate dehydrogenase. The basophilic foci were not preceded by other focal histological and histochemical change. The basophilic proliferative lesions are observed when an irreversible change has been induced in the liver. The role of such lesions in the histogenesis of hepatocellular carcinoma is discussed.     

Decreased fibronectin in rat liver altered foci and adenomas induced by N-2-fluorenylacetamide

The disposition of fibronectin in N-2-fluorenylacetamide-induced rat liver lesions was studied by immunohistochemical staining. Male rats were fed the carcinogen for 7 weeks to induce hepatocellular altered foci and then given no chemical or phenobarbital in the diet for 24 weeks until adenomas developed. Regardless of the exposure conditions, the amount of extracellular fibronectin was unchanged in about 60% of the liver altered foci and decreased in about 40%. In contrast, 90% of the adenomas demonstrated a significantly decreased staining pattern for fibronectin. In some adenomas, the fibronectin staining pattern demonstrated irregular, wide, and distorted deposits. In nonlesional regions of the livers of rats exposed to N-2-fluorenylacetamide, the amount of fibronectin was decreased in the centrilobular and midlobular zones. The decrease of fibronectin in hepatocellular altered foci and adenomas demonstrates another abnormality in these lesions, which may be important in their biologic behavior. Foci with decreased fibronectin may have a greater potential to progress to adenomas.     

Hepatocarcinogenic activity of N-butyl-N-(4-hydroxybutyl)nitrosamine in rats is not modified by sodium L-ascorbate

Male F344 and Wistar Shionogi (WS) rats were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks and then killed at week 36 (experiment 1). Although reduction of body weight increase was found, no effects on liver weights were noted. Formalin-fixed and paraffin-embedded liver tissues from rats killed terminally were cut and stained for glutathione S-transferase placental form (GST-P) immunohistochemically. Marked elevation of quantitative values of small GST-P positive (GST-P+) foci were apparent in both strains of rat administered BBN. In experiment 2, both sexes of F344 rats were given 0.05% BBN in the drinking water for 4 weeks and then fed diet containing 0 or 5.0% sodium L-ascorbate (SA) for 32 weeks. No body and liver weight changes were evident in any group. Quantitative values for small GST-P+ foci were increased in both sexes of rats exposed to BBN but were not modified by additional SA treatment. Thus, it was confirmed that the selective bladder carcinogen BBN also acts as a liver carcinogen. These results, from the quantitative analysis of small GST-P+ foci as end point marker lesions, indicate that the liver tumor modifying potential of test chemicals can be evaluated in rats by using an initiation/promotion protocol for urinary bladder carcinogenesis.     

Induction and modulation of hepatic preneoplasia and neoplasia in the rat by dehydroepiandrosterone

Dehydroepiandrosterone (DHEA), the main adrenal steroid in humans and a precursor in androgen and estrogen biosynthesis, acts as a peroxisome proliferator and as a hepatocarcinogen in rats. Neoplasms emerge from a glycogenotic/amphophilic/basophilic preneoplastic cell lineage. A higher female tumor incidence suggests a relevant influence of sex hormones. DHEA enhances hepatocarcinogenesis induced by N-nitrosomorpholine (NNM), which is characterized by the glycogenotic/basophilic cell lineage. The tumor promoting effect is related to an additional amphophilic/basophilic preneoplastic lesion sequence and to faster proliferation of the basophilic preneoplastic lesions. Nevertheless, hepatocellular carcinomas provided under DHEA treatment seem to have a less malignant phenotype compared to tumors induced by NNM only. Further, DHEA treatment reduces growth and generation of glycogen storage foci (GSF) in initial NNM-treated rats. Thus, DHEA treatment results in both, a growth stimulation of the late basophilic lesion type with an additional amphophilic lesion sequence, and in a growth inhibition of early preneoplastic lesions, addressing especially GSF. DHEA also inhibits the growth of physiologically proliferating liver tissue. This might be explained by a DHEA related cellular metabolism, which results in significant energy consumption. Additionally, a DHEA-induced alteration of cytokine levels might contribute to this growth inhibition as well.     

Post-exercise glycogen resynthesis in trained high-protein or high-fat-fed rats after glucose feeding

Summary This study examined the effect on glycogen resynthesis during recovery from exercise of feeding glucose orally to physically trained rats which had been fed for 5 weeks on high-protein low fat (HP), high-protein/long-chain triglyceride (LCT) or high carbohydrate (CHO) diets. Muscle glycogen remained low and hepatic gluconeogenesis was stimulated by long-term fat or high-protein diets. The trained rats received, via a stomach tube, 3 ml of a 34% glucose solution immediately after exercise (2 h at 20 m · min^–1), followed by 1ml portions at hourly intervals until the end of the experiments. When fed glucose soleus muscle glycogen overcompensation occurred rapidly in the rats fed all three diets following prolonged exercise. In LCT- and CHO-fed rats, glucose feeding appeared more effective for soleus muscle repletion than in HP-fed rats. The liver demonstrated no appreciable glycogen overcompensation. A complete restoration of liver glycogen occurred within a 2- to 4-h recovery period in the rats fed HP-diet, while the liver glycogen store had been restored by only 67% in CHO-fed rats and 84% in LCT-fed rats within a 6-h recovery period. This coincides with low gluconeogenesis efficiency in these animals.     

Isolation and enrichment of cells resistant to iron accumulation from carcinogen-induced rat liver altered foci

Enrichment of cells from rat liver iron-excluding foci induced by 2-acetylaminofluorene was performed using density gradients. Rats were continuously fed a diet containing the carcinogen for 8 to 13 weeks to induce altered foci that were iron excluding and positive for γ-glutamyl transpeptidase activity. At weekly intervals, and after loading with iron by subcutaneous injection, the livers were perfused with collagenase and dissociated. Fractionation of dissociated control and treated liver cells on Ficoll gradients yielded three cellular fractions. In preparations from carcinogen-exposed rats the percentage of hepatocytes excluding iron and positive for γ-glutamyl transpeptidase was always higher in the top (least dense) fraction than in the other lower fractions or the original population of dissociated hepatocytes. Moreover, the total number of hepatocytes in the top fraction increased progressively with the duration of feeding. These observations indicate that iron-excluding hepatocytes of enzyme-altered foci are less dense than other hepatocytes and can be enriched by gradient centrifugation. The progressive increase in the number of these altered liver cells with continued carcinogen exposure is consistent with a role for these cells in the development of liver tumors.     

Evidence of a threshold-effect for 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline liver carcinogenicity in F344/DuCrj rats

To estimate potential human risk of exposure to a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a 2-year carcinogenicity test was conducted using male F344 rats administered MeIQx-containing diet at doses of 0 (control), 0.001, 1, and 100 ppm. The lowest dose 0.001 ppm was established as equivalent to the daily intake of this carcinogen in humans (0.2 to 2.6 microg/man/day). Significant decreases of survival rate and body weight gain were observed in rats treated with 100 ppm MeIQx. Histopathological examination revealed significant induction of hepatocellular carcinomas, adenomas, and development of glutathione S-transferase placental form-positive foci with MeIQx at 100 ppm. Moreover, the incidences of Zymbal's glands carcinoma, mammary fibroadenoma, and subcutaneous fibroma were found significantly increased in a 100 ppm MeIQx group. However, no significant induction of altered preneoplastic hepatocellular foci was observed in 0.001 and 1 ppm groups as compared to the controls. 8-Hydroxy-2'-deoxyguanosine levels in the rat liver DNA of the 100 ppm-treated group were not elevated, but MeIQx-DNA adduct formation increased as compared with the 1 ppm case, albeit without significance. No significant induction of any other neoplastic lesions related to the carcinogen administration was found in MeIQx-administered groups except for 100 ppm. These results imply that 1 ppm may be a no-effect level for MeIQx carcinogenesis.     

Sequential analysis of hepatic carcinogenesis: a comparative study of the ultrastructure of preneoplastic, malignant, prenatal, postnatal, and regenerating liver.

The objective of this study was to compare the fine structure of presumptive preneoplastic hepatocytes at various times during liver carcinogenesis with that of normal, developing, and regenerating liver and of hepatocellular carcinomas, using transmission and scanning electron microscopy. A new model of liver carcinogenesis was used in which several of the early steps are quite well synchronized. A single initiating dose of diethylnitrosamine induced isolated islands of altered hepatocytes. The cells were characterized by persistence of glycogen despite starvation, increase in smooth endoplasmic reticulum, and hypertrophic nucleoli. Following intense selection of the altered hepatocytes by dietary 2-acetylaminofluorene plus partial hepatectomy, the affected hepatocytes proliferated rapidly to produce basophilic foci. These early hyperplastic lesions revealed stellate-shaped dilated bile canaliculi lined by blebs and abnormally thick elongated microvilli, a decreased number of microvilli on the sinusoidal surface, a marked increase in smooth endoplasmic reticulum, large nucleoli, and bundles of pericanalicular microfilaments. A majority of the proliferating lesions reacquired a normal organizational pattern within several weeks after partial hepatectomy and could not be distinguished from normal liver. A small number continued to grow and become typical persistent hyperplastic nodules. These showed significant widening of intercellular spaces between hepatocytes, elongated microvilli over large regions of the cell surface, many invaginations of the cell membrane, and irregularly shaped bile canaliculi. Sequential changes in focal hyperplastic hepatocytes during carcinogenesis could be distinguished from normal, developing, and regenerating liver. The major differences involved the cell surfaces and cytoplasmic organelles. The findings are compatible with the hypothesis that a carcinogen may act by inducing alterations in a small number of hepatocytes and that hepatocellular carcinomas arise through stepwise evolutional changes in these cells.     

ADENOMA WITH MULTIPLE HYPERPLASTIC NODULES IN NONCIRRHOTIC LIVER POSSIBLY RELATED TO LONG-TERM ADMINISTRATION OF A HYPOLIPIDEMIC DRUG

Described here is an autopsy case of a 76-year-old woman with preneoplastic and other adenomatous hepatocellular lesions. Multiple small hyperplastic liver foci with PAS positive reaction and adenomatous nodular lesions were noted in a non-cirrhotic liver. These lesions resembled altered foci or neoplastic nodules which are currently regarded as premalignant changes in experimental animal models. It is suggested that the liver lesions of this woman may be related to long-term administration of hypolipidemic drug cloflbrate for hypercholesteremia and the lesions could be one of the precursor changes of human hepatocellular carcinoma.     

The ultrastructural features of aflatoxin B1-induced lesions in the rat liver.

Hepatocellular carcinoma was induced in rats by administering aflatoxin B1 (AFB1) for 6 weeks. Malignant tumours were preceded by foci and nodules of altered hepatocytes. The ultrastructural characteristics of the nodular lesions have been studied and compared with those of the hepatocellular carcinoma cells. Alterations in the endoplasmic reticulum, junctional complexes and nuclei were common to both the basophilic and eosinophilic nodular cells and the carcinoma cells. These most likely represent hyperplastic changes rather than malignant alterations. The eosinophilic nodules were distinguished from other lesions by the abundance of concentric, membranous whorls in the cytoplasm of nodular cells. These cytoplasmic structures were also present in some hepatocellular carcinoma cells. The observations provided further evidence suggesting that the eosinophilic nodule, rather than the basophilic nodule, may play a role in the development of malignancy in the rat liver.     

The ultrastructural features of aflatoxin B1-induced lesions in the rat liver

Hepatocellular carcinoma was induced in rats by administering aflatoxin B1 (AFB1) for 6 weeks. Malignant tumours were preceded by foci and nodules of altered hepatocytes. The ultrastructural characteristics of the nodular lesions have been studied and compared with those of the hepatocellular carcinoma cells. Alterations in the endoplasmic reticulum, junctional complexes and nuclei were common to both the basophilic and eosinophilic nodular cells and the carcinoma cells. These most likely represent hyperplastic changes rather than malignant alterations. The eosinophilic nodules were distinguished from other lesions by the abundance of concentric, membranous whorls in the cytoplasm of nodular cells. These cytoplasmic structures were also present in some hepatocellular carcinoma cells. The observations provided further evidence suggesting that the eosinophilic nodule, rather than the basophilic nodule, may play a role in the development of malignancy in the rat liver.     

Mice deficient in glycerol-3-phosphate acyltransferase-1 have a reduced susceptibility to liver cancer

The risk of hepatocellular carcinoma increases with the persistence of non-alcoholic fatty liver disease. Triacylglycerol synthesis is initiated by glycerol-3-phosphate acyltransferase (GPAT). Of four isoforms, GPAT1 contributes 30-50% of total liver GPAT activity, and we hypothesized that it might influence liver susceptibility to tumorigenesis. C57Bl/6 mice deficient in GPAT1 were backcrossed 6 times to C3H mice. After exposure to the carcinogen diethylnitrosamine (DEN) and the tumor promoter phenobarbital, male Gpat1?/? mice, compared with controls (Gpat1?/?), had 93% fewer macroscopically visible nodules per liver at 21 weeks of age and 39% fewer at 34 weeks of age. Microscopically, control mice had increased numbers of foci of altered hepatocytes, particularly the basophilic subtype, as well as more, and malignant, liver neoplasms than did the Gpat1?/? mice. At 21 weeks of age, 50% (4/8) of control mice (50%) had hepatocellular adenomas with an average multiplicity (tumors per tumor-bearing-animal) of 4.3, while none occurred in 8 Gpat1?/? mice. At 34 weeks of age, all 15 control mice (100%) had hepatocellular adenomas with an average multiplicity of 5.2 compared to an incidence of 93% in Gpat1?/? mice and multiplicity of 3.1. HCCs were observed in 13% of control mice and in only 6% of Gpat1?/? mice. These data show that alterations in the formation of complex lipids catalyzed by Gpat1 reduce susceptibility to DEN-induced liver tumorigenesis.     

Transgenic mice expressing hepatitis B virus X protein are more susceptible to carcinogen induced hepatocarcinogenesis

The hepatitis B virus X (HBx) protein is thought to be implicated in the development of human hepatocellular carcinoma (HCC), but its exact function remains controversial. To investigate whether the expression of the HBx gene alone can induce HCC on an inbred C57BL/6 strain that displays a lower spontaneous rate of liver cancer, and to determine if HBx transgenic mice are more susceptible to the effects of hepatocarcinogens, C57-TgN (HBx) X transgenic mice were bred with normal C57BL/6 mice strain. The F1 mice (about 50% HBx positive and 50% HBx negative) were treated with a single dose of diethylnitrosamine (DEN) at 7 days of age, or were untreated. Mice were killed at appropriate time points and were analyzed for histological change in the liver. The expression of HBx protein were examined by using immunohistochemical staining. Glycogen storage foci were examined by using periodic acid-Schiff (PAS) staining. In HBx transgenic mice untreated with DEN, HBx expression and glycogen storage foci were always observed in the liver after 8 weeks, but not obvious histological pathologic changes. Histological examination of liver tissue confirmed that DEN-treated HBx mice developed approximately twice as many focal lesions of basophilic hepatocytes as treated wild-type littermates. Hepatocellular adenomas and carcinomas were also more frequent in DEN-treated HBx-positive than HBx-negative mice. Taken together, our results suggest that HBx gene expression alone is not sufficient for carcinogenesis, but may act as a promoter for malignant transformation.     

Orotic acid, a new promoter for experimental liver carcinogenesis

Male Fischer 344 rats initiated with 1,2-dimethylhydrazine 2HCl (100 mg/kg) given 18 hr after partial hepatectomy and exposed to a diet containing 1% orotic acid for 13 months developed a 100% incidence of hepatocellular carcinoma. The creation of nucleotide pool imbalances by dietary orotic acid, for e.g., an increase in uridine nucleotides and a decrease in adenine nucleotides, was considered as a possible mechanism for the promotional effect of orotic acid on liver carcinogenesis. The significance of this hypothesis is that altered nucleotide pools affect both genomic as well as membrane organization. Consistent with this hypothesis is our finding that feeding rats with a diet containing 1% orotic acid for 10 weeks resulted in a liver DNA damage as monitored by its slower sedimentation in alkaline sucrose gradients compared to the corresponding controls. To assess the general applicability of this hypothesis, nucleotide pool imbalances were created by using methods other than feeding orotic acid and their effect on the incidence of gamma-glutamyltransferase positive foci in carcinogen initiated rats was determined. The results obtained indicated that rats initiated with 1,2-dimethylhydrazine.2HCl (100 mg/kg) given 18 hr after partial hepatectomy and exposed to diet deficient in arginine, a regimen that causes an increased synthesis and excretion of orotic acid, or were fed diets containing 1% thymidine or 1% thymine developed greater number of gamma-glutamyltransferase positive foci compared to the corresponding controls fed the basal diets. These results were interpreted to indicate that orotic acid exerts its promotional effect probably by creating an imbalance in nucleotide pools. One of the mechanisms by which an imbalance of nucleotide pools influences the pathogenesis of the carcinogenic process may be by inducing perturbations in the DNA.     

Placental glutathione S-transferase (GST-P) as a new marker for hepatocarcinogenesis: in vivo short-term screening for hepatocarcinogens

Our laboratory has developed an in vivo short-term screening test for hepatocarcinogens based on quantitation of gamma-glutamyl transpeptidase (gamma-GT) positive foci. However, gamma-GT positive hepatocytes appear in periportal areas under a variety of circumstances apparently unrelated to hepatocarcinogenesis. Glutathione S-transferase placental type (GST-P), which is hardly detectable in normal rat liver, was recently demonstrated as a new marker protein for preneoplastic liver foci. In experiment I, rats were initially given a single dose (200 mg/kg) of diethylnitrosamine intraperitoneally and 2 weeks later were treated with test compounds for 6 weeks. All rats were subjected to partial hepatectomy at week 3. The long-term development of preneoplastic lesions was followed in rats for 50 weeks. The immunohistochemical investigation of GST-P binding and the histochemical demonstration of gamma-GT in serial sections revealed that almost all gamma-GT foci were GST-P positive, but 5-10% of GST-P foci could not be detected by gamma-GT staining. From week 8, many gamma-GT foci partially lost gamma-GT activity. However, no comparable disappearance of GST-P was evident in the lesions. All hepatocellular carcinomas (HC) found at week 50 consisted of GST-P positive HC cells. In contrast, 37.9% (11/29) of HC were negative for gamma-GT. In experiment II (in vivo short-term screening test for hepatocarcinogens), rats were treated in the same manner as for experiment I and killed at week 8. Fifty-eight chemicals were investigated for their potential to modify GST-P positive foci development.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occurrence of cell death (apoptosis) in preneoplastic and neoplastic liver cells. A sequential study.

A sequential study was performed to investigate the occurrence of cell death in preneoplastic and neoplastic liver cells of F-344 rats. The animals were administered a single initiator dose of 1,2-dimethylhydrazine and were then subjected to a liver carcinogenesis promotion regimen, consisting of a diet containing 1% orotic acid. Cell death, morphologically similar to that described as apoptosis, was evident in foci of preneoplastic hepatocytes at 10 weeks after orotic acid feeding. An increased frequency of apoptotic bodies was observed in nodules, but not in the surrounding liver, 20 weeks after starting the dietary regimen, and in hepatocellular carcinomas that developed after 1 year of continuous promotion. Occurrence of this type of cell death was also observed in liver foci of rats subjected to two other promoting regimens, suggesting, thus, a possible relevance of apoptosis to the carcinogenic process in the liver.     

Hepatocellular neoplasms induced by low-number pancreatic islet transplants in streptozotocin diabetic rats.

We have previously demonstrated in short-term experiments that altered hepatocytes in liver acini draining the blood from intraportally transplanted pancreatic islets in streptozotocin-induced diabetic rats with mild persisting diabetes resemble those in preneoplastic foci of altered hepatocytes. We now present the results of long-term studies (up to 22 months) in this animal model. Glycogen-storing foci (which were the first parenchymal alteration observed some days after transplantation) persisted at least for 6 months, when the first mixed-cell foci and the first hepatocellular adenoma emerged. After 15 to 22 months, 86% of the animals exhibited at least one hepatocellular adenoma and four animals (19%) showed a hepatocellular carcinoma. The transplants were found in a close spatial relationship with the preneoplastic foci and the hepatocellular neoplasms. The mitotic indices, the 5-bromo-2'-desoxyuridine labeling indices and the apoptotic indices showed significant differences between the unaltered liver parenchyma, different types of preneoplastic foci, and hepatocellular neoplasms. The immunohistochemical expression of transforming growth factor-alpha increased during the stepwise development from glycogen-storing liver acini to hepatocellular carcinomas. Hepatocarcinogenesis in this new animal model is probably due to the hormonal and growth-stimulating effects of insulin secreted by the intraportally transplanted islets of Langerhans in diabetic rats.     

Characterization of the promoting activity of thiobenzamide on liver carcinogenesis

To characterize the promoting activity of thiobenzamide (TB), a thiono-sulfur-containing xenobiotic, rats of both sexes were treated with the compound for 4 or 8 weeks after an initiating dose of diethyl-nitrosamine. The number, area (volume), and phenotypic complexity of the enzyme-altered hepatocyte foci were studied in serial sections stained with hematoxylin/eosin and reacted for glycogen, iron, and gamma-glutamyltranspeptidase activity. The TB-induced changes on the drug metabolizing systems were also investigated. The main findings were: When fed in a dose range of 500-2,000 mg/kg of diet, TB induced a number of foci greater than controls, especially in female rats. Benzamide, a major TB metabolite, was ineffective. The appearance of hepatocyte foci upon TB feeding was nearly synchronized. An increase of the phenotypic complexity of the hepatocyte foci occurred only during the first 4 weeks of TB administration; it correlated with an increase in size. The liver microsome content of cytochrome P-450 as well as the activity of many monooxygenases was decreased, some of the phase II reactions being increased. In conclusion TB behaves as an efficient promoter of liver carcinogenesis, possibly as a consequence of an induced adaptive response.     

Evidence for the stem cell origin of hepatocellular carcinoma and cholangiocarcinoma.

A review of the morphologic, autoradiographic, and phenotypic analysis of the cellular changes seen during induction of cancer of the liver in rats by chemical carcinogens is used to develop an alternative to the established hypothesis that chemically induced hepatocellular carcinoma arises from premalignant nodules. The authors propose that hepatocellular and ductular carcinomas arise from a pluripotent liver stem cell and that enzyme-altered foci and nodular changes are adaptive non-oncogenic responses to the toxic effects of carcinogens. It is further postulated that persistent nodules may provide an environment that nurtures development of neoplastic cells other than the altered hepatocytes that originally form the nodule. It is possible, however, that there may be more than one cellular lineage to hepatocellular cancer and that persistent nodules contain these different lineages.