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P Bannasch

Publications and source records attributed to P Bannasch.

At least 19 recordsLinked to original sources
PubMed1996

Increase of lipid peroxidation in rat liver microsomes by dehydroepiandrosterone feeding.

Oral administration of the adrenal steroid dehydroepiandrosterone (DHEA), a peroxisome proliferator and hepatocarcinogen in the rat, caused an increase in NADPH-dependent lipid peroxidation in microsomes isolated from rat liver and kidney cortex, but not from brain. The increase of liver microsomal lipid peroxidation was greater in male than in female rats. the effect of DHEA on lipid peroxidation became discernible after feeding steroid-containing diet (0.6%) to male and female rats for 2 and 3 days and reached maximal levels at 1 and 2 weeks, respectively. The increase of microsomal lipid peroxidation reached a plateau stimulation at 0.05% in the diet. The addition of DHEA in the concentration range 0.1-100 microM to microsomes isolated from control rats had no effect on lipid peroxidation. Furthermore, a significant increase of the endogenous concentration of thiobarbituric acid reactive substances was found in microsomes after DHEA-administration at 0.05% in the diet. These results provide in vivo evidence that DHEA can cause lipid peroxidation in rat liver. Administration of DHEA at 0.6% in the diet for 7 consecutive days also significantly enhanced NADH- and ascorbate-dependent lipid peroxidation in liver microsomes. The DHEA-stimulated rat liver microsomal lipid peroxidation was completely inhibited by EDTA but not by superoxide dismutase, catalase or mannitol applied as OH-radical scavenger. The findings indicate that membrane lipid peroxidation is an early effect of DHEA, and that this process may be involved in the steroid-induced carcinogenesis in rats.

Adenosine Diphosphate↗
PubMed1996

Altered liver acini induced in diabetic rats by portal vein islet isografts resemble preneoplastic hepatic foci in their enzymic pattern.

As demonstrated previously, liver acini draining the blood from intraportally transplanted pancreatic islets in streptozotocin-diabetic rats are altered in various respects. The hepatocytes in these acini store glycogen and/or fat, and they show an increase in proliferation as well as in apoptotic activity. Thus, they are phenotypically similar to carcinogen-induced preneoplastic liver foci (glycogen-storing foci and sometimes also mixed cell foci). By means of catalytic enzyme histochemistry or immunohistochemistry, we investigated the activity of key enzymes of alternative pathways of carbohydrate metabolism and some additional marker enzymes (well known from studies on preneoplastic hepatic foci) in the altered liver acini surrounding the islet isografts. In addition, the expression of glucose transporter proteins 1 and 2 (GLUT-1 and GLUT-2) were investigated immunohistochemically. The activities of hexokinase, pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase, and glucose-6-phosphate dehydrogenase were increased, whereas the activities of glycogen phosphorylase, adenylate cyclase, glucose-6-phosphatase, and membrane-bound adenosine triphosphatase were decreased in the altered liver acini. The expression of GLUT-2 was also decreased. GLUT-1 and glutathione S-transferase placental form were not expressed, and the activities of glycogen synthase and gamma-glutamyl-transferase remained unchanged. All changes of the enzyme activities were in line with the well known effects of insulin and resembled alterations characteristic of preneoplastic liver foci observed in different models of hepatocarcinogenesis. It remains to be clarified in long-term experiments whether or not these foci represent preneoplastic lesions and may proceed to neoplasia.

Animals↗
PubMed1995

Synergistic hepatocarcinogenic effect of hepadnaviral infection and dietary aflatoxin B1 in woodchucks.

Interactive hepadnaviral and chemical hepatocarcinogenesis was studied in woodchucks inoculated as newborns with woodchuck hepatitis virus (WHV), which is closely related to the human hepatitis B virus. When the woodchucks reached 12 months of age, aflatoxin B1 (AFB1) was administered in the diet at dose levels of 40 micrograms/kg body weight/day for 4 months and subsequently 20 micrograms/kg body weight/day (5 days/week) for lifetime. WHV DNA was demonstrated by Southern blot hybridization in the serum and by PCR in the serum and/or liver tissue. The histo- and cytomorphology of the liver were investigated by light and electron microscopy. WHV carriers with and without AFB1 treatment developed a high incidence of preneoplastic foci of altered hepatocytes, hepatocellular adenomas, and hepatocellular carcinomas that appeared 6-26 months after the beginning of the combination experiment. Administration of AFB1 to WHV carriers resulted in a significantly earlier appearance of hepatocellular neoplasms and a higher incidence of hepatocellular carcinomas compared to WHV carriers not treated with AFB1. Neither hepatocellular adenomas nor carcinomas (but preneoplastic foci of altered hepatocytes) were detected in woodchucks receiving AFB1 alone, and no preneoplastic or neoplastic lesions were found in untreated controls. These results provide conclusive evidence of a synergistic hepatocarcinogenic effect of hepadnaviral infection and dietary AFB1. Except for the frequent presence of ground glass cells containing surface antigen filaments in the infected woodchucks, the phenotype of preneoplastic foci of altered hepatocytes was similar in WHV carriers with and without exposure to AFB1 and in animals treated with AFB1 alone. Clear cell foci excessively storing glycogen and/or fat, amphophilic cell foci crowded with mitochondria and peroxisomes, and mixed cell foci composed of various cell types including basophilic cells rich in ribosomes predominated. The cellular phenotype in neoplastic lesions varied from clear, amphophilic, and mixed cell populations in highly differentiated adenomas and carcinomas to basophilic cell populations prevailing in poorly differentiated carcinomas. The striking similarities in altered cellular phenotypes of preneoplastic hepatic foci emerging after both hepadnaviral infection and exposure to AFB1 suggest closely related underlying molecular mechanisms that may be mainly responsible for the synergistic hepatocarcinogenic effect of these oncogenic agents.

Aflatoxin B1↗
PubMed1995

Early detection of Knudson's two-hits in preneoplastic renal cells of the Eker rat model by the laser microdissection procedure.

Hereditary renal cell carcinomas invariably develop by the age of 1 year in Eker rats. At the histological level, renal cell carcinomas develop through multiple stages from early preneoplastic lesions (e.g., phenotypically altered tubules) to adenomas. We previously reported that ionizing radiation induces additional tumors (large adenomas and carcinomas) in a linear dose-response relationship and that loss of heterozygosity (LOH) at chromosome 10, where the predisposing tuberous sclerosis (Tsc2) gene is localized, was found in the renal cell carcinomas which developed from hybrid F1 rats carrying the Eker mutation, indicating that in heterozygotes two events (one inherited, one somatic) are necessary to produce at least large adenomas and carcinomas. This study was designed to examine LOH in the earliest preneoplastic lesions, using a laser microdissection procedure. We could accurately dissect single altered renal tubules out of freeze-dried sections and clearly detected LOH in 4 of 19 altered tubules (21%). This is the first demonstration of LOH in single renal tubules. Our present results support the theory of a second, somatic mutation (second hit) as rate-limiting step of renal carcinogenesis in the Eker rat model of dominantly inherited cancer and the tumor suppressor nature of the Tsc2 gene function.

Animals↗
PubMed1995

Elevated content of p53 protein in the absence of p53 gene mutations as a possible prognostic marker for human renal cell tumors.

p53 tumour suppressor gene expression was estimated immunohistochemically using DO-1 monoclonal antibody (recognising both wild-type and mutant p53 in 88 human renal tumours. Single strand conformation polymorphism (SSCP) analysis of possible mutations within exons 4-8 of the p53 gene was performed in 29 of the tumours (mostly immunostaining-positive cases). Obviously elevated p53 content was detected with DO-1 antibody in chromophobic cell carcinomas and most clear/chromophilic cell tumours (in chromophilic cell populations). In contrast, clear cell carcinomas demonstrated either complete absence of p53 expression or the presence of single immunopositive nuclei. Oncocytomas were completely negative. Additional immunostaining of the positive samples with mutant p53-specific Pab240 monoclonal antibody failed to detect immunopositive material. No p53 mutation was found in any of the samples analysed by SSCP. Our results suggest that the elevated p53 content in human renal cell carcinomas does not result from gene mutation and the p53 gene alterations are probably not an important mechanism in the development of human renal cell carcinomas. Accumulation of the wild-type p53 protein may be a useful prognostic marker indicating neoplastic progression malignancy.

Base Sequence↗
PubMed1995

Damage to mitochondrial DNA induced by the hepatocarcinogen diethylnitrosamine in ovo.

Different doses of the hepatocarcinogen diethylnitrosamine (DEN) were injected into fertilized turkey eggs 8 days before hatching. The embryos were removed from the eggs after 4 days and liver samples were shock frozen. Mitochondrial DNA (mtDNA) was purified from the samples. Electrophoresis on agarose gels with native mitochondrial DNA and with ribonuclease-treated mitochondrial DNA revealed a DEN-induced effect on the molecular size of the mtDNA. The content of mtDNA of the regular size of 16 kb dose-dependently decreased, whereas the amount of mtDNA fragments of various size increased. Fluorescent staining of the electrophoresis gels allowed the densitometric quantification of the mitochondrial DNA of the regular band at 16 kb and the amount of fragments of irregular size (smear). The diethylnitrosamine-induced effect was dose-dependent over the whole dose range from 1.24 to 6.2 mmol/kg. Even the lowest dose (10 mg DEN per egg) showed clear-cut effects. Mitochondrial damage and malfunction may be mechanistically involved in the neoplastic transformation and in aging phenomena. The in ovo model is a simple and rapid approach for investigations on chemically induced alterations of mtDNA.

Animals↗
PubMed1995

Dose dependence of diethylnitrosamine-induced nuclear enlargement in embryonal turkey liver.

Avian embryos (turkey) were exposed to diethylnitrosamine in ovo. On the first day of incubation doses of 0.5-5.0 mg/egg were injected into the white of the fertilized egg. The experiment was terminated 4 days before hatching. Livers were removed and prepared for subsequent histological examination. In haematoxylin and eosin stained sections the areas of hepatocyte nuclear profiles were measured by semi-automatic image analysis. In liver samples of diethylnitrosamine-exposed embryos hepatocyte nuclei of more than twice the size of normal hepatocyte nuclei were found. The incidence of the enlarged nuclei was clearly dose dependent. An increase in the size of hepatocyte nuclei was observed after low doses of diethylnitrosamine that did not induce common signs of non-specific toxic effects, e.g. cell death, fat vacuoles or loss of glycogen. The slope of the dose-response curve was rather steep. A 10-fold increase in the dose of the carcinogen resulted in a 100-fold increase in the incidence of enlarged hepatocyte nuclei. In combination with preneoplastic foci of altered hepatocytes, the quantification of nuclear enlargement can provide a valuable complementary parameter for the evaluation of carcinogen-induced effects in ovo.

Animals↗
PubMed1995

Spongiotic pericytoma: a benign neoplasm deriving from the perisinusoidal (Ito) cells in rat liver.

Spongiosis hepatis has been known for some time to develop frequently in livers of rats and fish treated with hepatocarcinogens and was considered to derive from the perisinusoidal (Ito) cells (PSC). Using rat liver treated with N-nitrosomorpholine at different dose levels, we studied the cellular composition and origin as well as the proliferation kinetics of spongiosis hepatis by immunohistochemical demonstration of desmin, vimentin, and alpha-smooth-muscle actin, and by autoradiographic determination of [3H]-thymidine incorporation, respectively. The vast majority of the cells forming spongiosis hepatis were positive for desmin and vimentin but negative for alpha-smooth-muscle actin, confirming the cellular origin of spongiosis hepatis from PSC. In addition, immunohistochemical demonstration of desmin and vimentin revealed that spongiosis hepatis is an integral part of larger lesions consisting of focal PSC aggregates. These aggregates show a significantly increased incorporation of [3H]-thymidine compared with PSC in the extrafocal tissue and in the liver tissue of untreated control animals. In stop experiments, this increased labeling index was maintained many months after withdrawal of the carcinogen, in line with the earlier observation of a progressive behavior of spongiosis hepatis. We conclude that PSC may give rise to proliferative lesions appearing as PSC aggregates associated with more or less pronounced spongiosis hepatis. The persistence, the proliferative activity, and the slow expansive growth of these lesions suggest a benign neoplastic behavior. We therefore propose to classify these lesions as spongiotic pericytoma. Malignant tumors possibly originating from spongiotic pericytoma should consequently by classified as perisinusoidal (Ito) cell sarcomas.

Animals↗
PubMed1995

[Sequential cellular and molecular changes during hepatocarcinogenesis].

Oncogenic agents may hit at least four different types of target cells in the liver, namely the hepatocytes, the cholangiolar cells, the sinusoidal endothelial and the perisinusoidal cells. All of these cell types may give rise to neoplasms which develop from phenotypically altered preneoplastic cell populations via various intermediate stages to benign and/or malignant neoplasms. The manifestation of hepatocellular neoplasms induced by chemicals, radiation or viruses in different species including primates is regularly preceded by focal metabolic and morphological alterations which emerge in the liver parenchyma long before the neoplasms appear. The predominant sequence of metabolic changes leads from a focal excessive storage of glycogen (glycogenosis) through intermediate stages, in which the glycogenosis is frequently replaced by a lipidosis, to glycogen-poor hepatocellular carcinomas. The early hepatocellular glycogenosis is due to a disturbance in glycogen breakdown, which is associated with a dysfunction of signal transduction and glucose transport. During progression from the preneoplastic hepatocellular glycogenosis to glycogen-poor hepatocellular neoplasms a fundamental shift in carbohydrate metabolism takes place, gradually redirecting metabolites such as glucose-6-phosphate toward alternative metabolic pathways such as the pentose phosphate pathway and glycolysis. Studies on about 70 resected or explanted livers from patients bearing hepatocellular carcinomas or suffering from cirrhosis provided evidence for focal changes in glycogen metabolism similar to those observed in laboratory animals. An alternative sequence of cellular changes involving oncocytes and amphophilic cell populations rich in mitochondria and sometimes also peroxisomes has been observed in rats after administration of non-genotoxic hepatocarcinogens, particularly peroxisomal proliferators, and in woodchucks during hepadnaviral hepatocarcinogenesis. Our observations suggest fundamental changes in the cellular energy metabolism during hepatocarcinogenesis, which are most probably due to a disturbance in signal transduction pathways and may be causally linked to neoplastic cell conversion.

Animals↗
PubMed1994

Differences in expression and intracellular distribution of hexokinase isoenzymes in rat liver cells of different transformation stages.

The activity, intracellular distribution and mRNA expression of hexokinase isoenzymes were studied in normal rat liver, and in epithelial liver cells at different stages of neoplastic transformation, including non-tumorigenic and tumorigenic cell lines. In contrast to liver, all transformed cells exhibited only hexokinase I and II, which both showed significantly increased activity, hexokinase II being the more abundant form. In parallel, the mRNA expression of the two isoenzymes was elevated, indicating transcriptional control of gene expression. Hexokinase I and II were found in the cytosol and bound to mitochondrial membranes; the percentage of membrane-bound enzyme activity increased with the grade of transformation from 32% of total activity in normal liver up to 69% in dedifferentiated tumor cells. The ratio of hexokinase I/II was higher in the membrane fraction than in the cytosol. In all tissues studied hexokinase II could be resolved in two subtypes IIa and IIb by hydrophobic interaction chromatography. The relative proportion of cytosolic IIa and IIb varied significantly between normal liver (1:1) and transformed cells, and among cells of different transformation stages (4:1 to 1:10). IIa demonstrated the main activity in the more differentiated, IIb in the less differentiated cell lines. IIa-activity showed a good correlation with the intracellular glucose 6-phosphate concentration of the cells. The data indicate that neoplastic cell transformation is accompanied by progressive alterations in the proportion and subcellular distribution of hexokinase isoenzymes I and II.

Animals↗
PubMed1994

Microheterogeneity of cytosolic and membrane-bound hexokinase II in Morris hepatoma 3924A.

Phosphorylation of glucose by hexokinase is the key step in glucose and energy metabolism of the cell. In the Morris hepatoma 3924A, hexokinase II is the predominant hexokinase isoenzyme and occurs in the cytosol as well as bound to membranes. Hexokinase II was isolated by DEAE-cellulose chromatography from both the cytosolic and the mitochondria-enriched fractions and further resolved by hydrophobic-interaction chromatography on phenyl-Sepharose into two components designated hexokinase IIa and IIb. In both the soluble and the mitochondria-enriched fractions, type IIb was the predominant form, but the IIb/IIa ratio was higher in the particulate (6-8) as compared with the cytosolic fraction (1.5-2.0). Binding of the isolated forms of the enzyme to rat liver mitochondria resulted in a 2-10-fold activation of both subtypes. Biochemical characterization showed that both subtypes are closely related to the isoenzyme commonly referred to as hexokinase II, and that the microheterogeneity was not a consequence of contamination with hexokinase I or III. Both subtypes had a molecular mass of 110 kDa, they were inhibited by Pi at concentrations higher than 5 mM, and activated by the detergent CHAPS. The two subtypes differed in electrophoretic mobility (IIa > IIb), in Km values for glucose (IIa, 0.109 mM; IIb, 0.216 mM), in Ki values for glucose 6-phosphate (IIa, 25 microM; IIb, 0.106 mM), and in Ki values for glucose 1,6-biphosphate (IIa, 12.2 microM; IIb, 5.5 microM). An artificial proteolytic cleavage as cause of the hexokinase II microheterogeneity can be excluded, since both subtypes show the same molecular mass and the ability to bind to mitochondria and phenyl-Sepharose. In addition, the relative proportions of the two subtypes did not vary markedly between several enzyme preparations. Northern-blot analysis with a hexokinase II-specific cDNA probe revealed two distinct mRNA transcripts of 5.2 and 6.3 kb in length, which offers the possibility that hexokinase II microheterogeneity is due to differential RNA transcription and/or processing.

Animals↗
PubMed1994

Preneoplastic foci of altered hepatocytes induced in rats by irradiation with alpha-particles of Thorotrast and neutrons.

Prestages of hepatocellular neoplasms induced in rats by continuous internal alpha-radiation of Thorotrast or by fractionated external radiation with neutrons were studied by cytomorphological, cytochemical and morphometric methods. Irradiation with both Thorotrast and neutrons resulted in a significant increase in the number and volume fraction of foci of altered hepatocytes (FAH), the occurrence of which at 14 months correlated well with the previously reported increased incidence of hepatocellular neoplasms appearing after long lag periods. The morphological and biochemical phenotypes of radiation-induced FAH were similar to those of preneoplastic lesions described earlier in hepatocarcinogenesis elicited by chemicals or viruses.

Alpha Particles↗
PubMed1994

Over-expression of glucose transporter isoform GLUT1 and hexokinase I in rat renal oncocytic tubules and oncocytomas.

Renal oncocytomas, which have previously been shown to originate from the collecting duct system, were induced in male Sprague-Dawley rats by oral administration of N-nitrosomorpholine (NNM) for 7 weeks. The expression of glucose transporter isoforms GLUT1 and GLUT2, and of several enzymes involved in glucose metabolism [hexokinase (HK), pyruvate kinase (PK), lactate dehydrogenase (LDH), malate dehydrogenase (MDH)] were studied by cytochemical approaches in serial cryostat sections of the kidney 12, 23 and 34 weeks after withdrawal of NNM. Oncocytic tubules connected with collecting ducts were first observed 23 weeks, and oncocytomas 34 weeks after withdrawal. The cytochemical pattern of oncocytic tubules and oncocytomas was similar, but differed markedly from that of normal collecting ducts in nearly all variables studied; expression of GLUT1 and hexokinase I proteins were strongly increased; activities of HK, PK and MDH were elevated, while LDH activity was reduced. These results suggest that oncocytic transformation is associated with fundamental changes in energy metabolism which differ from those in cell lineages leading to other types of renal cell tumours, such as clear/acidophilic and basophilic cell tumours. The characteristic over-expression of GLUT1 may be used as a diagnostic criterion for the discrimination between oncocytes and acidophilic (granular) cells in clear/acidophilic renal cell tumours which show a reduced expression of this glucose transporter protein.

Animals↗
PubMed1994

Sex differences in dehydroepiandrosterone metabolism in the rat: different plasma levels following ingestion of DHEA-supplemented diet and different metabolite patterns in plasma, bile and urine.

Plasma dehydroepiandrosterone (DHEA) and DHEA sulfate levels were determined by an enzyme immunoassay in male and female Sprague-Dawley rats fed a diet containing 0.6% or 0.3% DHEA. A significant difference in DHEA plasma levels was observed in male and female animals. In male rats, total DHEA plasma concentrations were found in the range of 0.4-1.5 microgram/ml (0.6% DHEA chow) and 0.3-0.5 microgram/ml (0.3% DHEA chow). In female animals several times higher DHEA plasma levels were determined: 17.5-33 micrograms/ml (0.6% DHEA chow) and 8.3-14.8 micrograms/ml (0.3% DHEA chow). DHEA was present in rat plasma of both sexes preferably as the sulfate conjugate. Significant sex differences were also found in the DHEA metabolite patterns obtained by TLC separation of extracts from plasma, bile and urine following administration of 3H-DHEA. In female rats, DHEA is present predominantly as the sulfate conjugate in considerable amounts in all materials investigated, whereas in male rats polar metabolites dominate in the patterns.

Animals↗
PubMed1994

Cell proliferation and cell death (apoptosis) in hepatic preneoplasia and neoplasia are closely related to phenotypic cellular diversity and instability.

Preneoplastic and neoplastic hepatic lesions were induced in male Sprague-Dawley rats by oral exposure to N-nitrosomorpholine (12 mg/kg body wt/day) for 7 weeks (stop model). Twelve, 23 and 34 weeks after withdrawal of the carcinogen, cell proliferation and cell death (apoptosis) were studied in defined phenotypes of preneoplastic foci of altered hepatocytes (FAH), hepatocellular adenomas (HCA) and carcinomas (HCC) by autoradiographic determination of the labelling index (LI) resulting from continuous administration of [3H]thymidine for 48 h and by simultaneous counting of apoptotic bodies respectively. Compared with the liver parenchyma of untreated controls and the extrafocal parenchyma of treated animals, the mean LI was elevated in all types of FAH, HCA and HCC, but the extent of this increase differed markedly between the diverse phenotypes. The increase in the LI was significant for clear/acidophilic, intermediate and mixed/basophilic cell foci, but remained insignificant for the relatively rare tigroid and amphophilic cell foci. The previously established progression-linked phenotypic instability in the predominant cell lineage leading to HCC was associated with a gradual increase in the mean LI showing four significantly different proliferative stages: (i) clear/acidophilic and intermediate cell foci excessively storing glycogen, (ii) mixed/basophilic cell populations in FAH and glycogen-storing HCA, (iii) glycogen-poor HCA and glycogen-storing HCC and (iv) glycogen-poor HCC. The inverse correlation between glycogen accumulation and cell proliferation during progression from glycogenotic FAH to glycogen-poor HCC indicates that the fundamental metabolic shift associated with the gradual disappearance of the glycogenosis is essential for the evolution of the malignant phenotype. The mean ratio of necrotic cells (RN) was somewhat higher in all types of FAH compared to the normal and extrafocal liver parenchyma, but this was not statistically significant. Only when HCA and HCC appeared was there a significant increase in the mean RN, proceeding with the progression of neoplastic development. Our results do not support the concept that cell death (apoptosis) plays a major role in counterbalancing cell replication in FAH, but rather suggest that cell death occurs more frequently in the course of hepatocarcinogenesis the more neoplastic development advances.

Animals↗
PubMed1994

Dose and time dependence of the cellular phenotype in rat hepatic preneoplasia and neoplasia induced by single oral exposures to N-nitrosomorpholine.

The dose and time dependence of the cellular phenotype in preneoplastic and neoplastic liver lesions was studied quantitatively in groups of male Sprague-Dawley rats exposed to single oral doses of 0, 200 and 320 mg/kg body wt of N-nitrosomorpholine (NNM) and killed at different time points between 7 and 80 weeks. Compared with the untreated controls, NNM-treated rats showed a dose- and time-dependent increase in the total number and volume of preneoplastic foci of altered hepatocytes (FAH) and in the incidence of hepatocellular adenomas (HCA). In controls, two major phenotypes of FAH were found in low numbers, namely clear and combined clear/acidophilic cell foci which both store excessive amounts of glycogen. The increase in the total number and volume of FAH by single doses of NNM was associated with changes in their cellular phenotype. Clear cell foci were more frequent in the lower dose group than in the higher dose group throughout the observation period. With the exception of the first 15 weeks, combined clear/acidophilic cell foci represented the most frequent phenotype at both dose levels and all time points studied. In contrast, mixed cell foci, which were completely lacking in controls, showed a high relative frequency after a single NNM dose of 320 mg/kg body wt throughout the observation period, but emerged at later time points and in lower numbers when the lower single dose was given. At both dose levels, mixed-cell foci represented the largest phenotype of FAH; their volume fraction correlated positively with the incidence of HCA, indicating a direct precursor-product relationship between these lesions. The size class distribution and temporal appearance of the different phenotypes of FAH and of the adenomas suggest a progression-linked phenotypic instability of the altered cellular phenotypes, resulting in a predominant sequence of cellular changes which leads from glycogenotic clear and acidophilic cell foci to mixed and basophilic cell populations, the latter being poor in glycogen. In addition to these types of FAH, tigroid cell foci, which were very rare in controls, developed in significantly greater numbers after single-dose treatment with NNM at both dose levels. This type of focus may either represent a side lineage of the predominant lineage or an intermediate stage in an alternative lineage of hepatocellular changes, but in any case has the potential to give rise to HCA.

Administration, Oral↗
PubMed1994

Dose and time dependence of the cellular phenotype in rat hepatic preneoplasia and neoplasia induced in stop experiments by oral exposure to N-nitrosomorpholine.

The dose and time dependence of the cellular phenotype in preneoplastic and neoplastic liver lesions was evaluated quantitatively in groups of male Sprague-Dawley rats exposed for 7 weeks to 0, 12 and 24 mg/kg body wt of N-nitrosomorpholine (NNM) and studied at different time points up to 80 weeks after withdrawal of NNM (stop model). NNM-treated rats showed a dose- and time-dependent increase in the total number and volume of preneoplastic foci of altered hepatocytes (FAH) and in the incidence of hepatocellular adenomas (HCA) and carcinomas (HCC) at both dose levels, compared with the untreated controls. After stopping treatment with 12 mg/kg body wt, the well-known sequence of cellular changes leading from glycogenotic clear and clear/acidophilic cell foci to mixed and diffusely basophilic cell populations poor in glycogen was found. In contrast, at the higher NNM dose level (24 mg/kg) predominantly mixed and diffusely basophilic cell foci appeared immediately after cessation of treatment, but their number rapidly declined up to 13 weeks after withdrawal. At the same time, there was a reciprocal increase in the number of the less altered clear/acidophilic cell foci, indicating an early reversion-linked phenotypic instability of FAH. However, in spite of this reversion higher numbers of mixed and diffusely basophilic cell foci were retained after treatment with 24 compared to 12 mg/kg of NNM at all time points studied, and there was even a slow additional increase in the number of these types of FAH 20 weeks after withdrawal of NNM. At both dose levels, the volume fraction of the persistent mixed cell foci correlated positively with the incidence of HCA and HCC, suggesting that this phenotype of FAH represents a direct precursor of the neoplastic lesions. Tigroid cell foci, which appeared most frequently after treatment with the lower dose of NNM, were not integrated into the predominant sequence of cellular changes leading to HCC, but they may represent an intermediate stage in a side lineage of this sequence, endowed with the potential to progress at least to HCA. Our results show that reversion-linked phenotypic instability of FAH occurs mainly after high dose treatment, possibly resulting from rapid adaptive cellular responses to the primary carcinogenic lesion(s) which may be fixed by genetic or epigenetic mechanisms. In contrast, progression-linked phenotypic instability of FAH is a slow process developing in a dose- and time-dependent manner at all dose levels leading to hepatic neoplasia.

Administration, Oral↗