Enzymhistochemische und autoradiographische Untersuchungen w�hrend der Cancerisierung der Rattenleber mit Di�thylnitrosamin

Biological markers of preneoplastic foci and neoplastic nodules in rodent liver

Foci of altered hepatocytes are regularly observed early during hepatocarcinogenesis in rodents. The abnormal hepatocytes may show a number of different phenotypes as characterized by various cytomorphological and cytochemical markers. The first appearance and the further development of the abnormal cell populations depend on the dose of the carcinogen given and on the duration of the carcinogenic treatment. According to cytochemical, morphometric and autoradiographic findings in rats receiving low doses (2–10% of the LD 50/kg bw/day) of hepatocarcinogens for limited periods (“stop” experiments), glycogenotic (clear or acidophilic) hepatocytes indicate the first step of the neoplastic cell transformation which can be detected by these methods at present. The glycogenotic cells undergo a characteristic metamorphosis and give rise to basophilic tumor cells poor in glycogen, but rich in ribosomes. Under extreme experimental conditions, such as a single or repeated application of higher doses of one or several chemical carcinogens a puzzling picture emerges which is “reversible” to a large extent after withdrawal of the respective compounds. This observation points to a phenotypic instability of the cellular changes induced in certain experimental systems. Foci of altered hepatocytes persisting after withdrawal of the carcinogenic compounds are considered preneoplastic lesions. They may transform into neoplastic nodules which are also persistent and share a number of cytomorphological and cytochemical markers with the focal lesions. The persistent nodules progress to hepatocarcinomas after lag periods of weeks or months. However, the foci may also progress to hepatocarcinomas without passing a nodular intermediate stage. The development of both neoplastic nodules and carcinomas from the preneoplastic glycogen storage foci can proceed independent of further administration of carcinogen. The sequence of cellular changes during hepatocarcinogenesis derived from the experimental results in rodents is strongly supported by observations in humans, especially by the increasing reports on the appearance of hepatic tumors in patients who suffer from inborn hepatic glycogenosis.

Myocardial glycogen storage disease in farmed rainbow trout, Oncorhynchus mykiss (Walbaum)

This paper is the first description of a spontaneous glycogen-storage disease in a lower vertebrate, as previous descriptions deal with humans and other mammals, or fish where the condition has been experimentally induced. Affected farmed rainbow trout experienced increased mortality from 60 days post-startfeeding and displayed clinical signs of heart failure with abnormal behaviour, exophthalmia, distended abdomen and ventral skin petechiation. Necropsy revealed alterations in cardiac shape with distended atria and rounded ventricles. Microscopically, the compact wall of the ventricle was absent, uneven or thinner than normal. The cardiac myocytes contained extensive amounts of glycogen in cytoplasmic vacuoles as demonstrated by periodic acid-Schiff staining that was abolished by saliva-diastase pretreatment on serial sections. Associated lesions included conspicuous subepicardial and myocardial vascularization, epicardial thickening and necrosis of the ventricular compactum/spongiosum interphase. The lesions in cardiac myocytes had a striking resemblance to glycogenosis type II (Pompe disease), a rare autosomal recessive lysosomal storage disease in humans. This condition was more severe and mortality was higher in a replicate/parallel fish group treated perorally with 17alpha-methyltestosterone to produce all-female progeny, indicating that the hormone treatment aggravated the condition resulting in earlier and more severe manifestation of the disease in this group.

Prevalidation of a rat liver foci bioassay (RLFB) based on results from 1600 rats: a study report

A rat liver foci bioassay (RLFB) based on an initiation-promotion protocol employing preneoplastic foci of altered hepatocytes (FAH) as an endpoint, was prevalidated in 5 different laboratories. FAH were identified by immunohistochemical demonstration of glutathione-S-transferase (placental form, GSTP) and by staining with hematoxilin/eosin (H&E), and their area fraction was quantified morphometrically. The four model hepatocarcinogens N-nitrosomorpholine, 2-acetylaminofluoren, phenobarbital, and clofibrate were selected according to characteristic differences in their presumed mode of action, and tested in a total of 1,600 male and female rats at 2 different dose levels. The chemicals were found to differ characteristically in their potency and dose-response relationship to induce FAH when given alone or when administered following initiation with diethylnitrosamine. The interlaboratory variation was small for results obtained with the GSTP-stain and somewhat larger with respect to H&E. The assessment of the carcinogenic potential of the four chemicals by the different laboratories was in the same range and the nature of their dose-response relationships did not differ essentially between laboratories. Our results suggest that this RLFB is a sensitive bioassay, providing potentially valuable information for risk assessment including the classification of carcinogenic chemicals according to their mode of action.

Short- and intermediate-term carcinogenicity testing--a review. Part 1: the prototypes mouse skin tumour assay and rat liver focus assay

Carcinogenicity testing is by far the most expensive and time-consuming study type of toxicology. For many years, the lifetime exposure with the maximum tolerated dose in two rodent species has been the gold standard of carcinogenicity testing of pharmaceuticals. Major change was introduced by the Fourth International Conference on Harmonization in July 1997; a chronic rodent bioassay in one species and a short-term carcinogenicity assay are regarded as sufficient for registration. Such requirements provide the opportunity to redirect the vast resources previously spent on the lifetime study in the second species. Numerous experimental protocols for short- and intermediate-term carcinogenicity testing in many target tissues have been available for years. The first part of this review describes the basic principles of short- and intermediate-term carcinogenicity testing using the examples of the widely used mouse skin tumour assay and the rat liver foci assay. In the context of these experimental models, the discrimination and quantification of initiating and promoting activity and the use of preneoplastic lesions as endpoints in carcinogenicity testing are described. The review includes the limitations of the models with regard to the extrapolation from effects observed in animal experiments to a potential exposure of humans.

Sequential changes in growth kinetics and cellular phenotype during hepatocarcinogenesis

Sequential changes in cell proliferation and cellular phenotype during hepatocarcinogenesis induced in rats with N-nitrosomorpholine were investigated by autoradiographic determination of the [3H]thymidine-labelling index in morphologically defined focal lesions and extrafocal hepatic tissue at different times between 4 and 48 weeks after withdrawal of the carcinogen (stop model). The labelling index was found to be significantly increased in all types of preneoplastic and neoplastic hepatic lesions as compared to both the liver tissue of untreated controls and the extrafocal parenchyma of N-nitrosomorpholine-treated rats. However, the extent of the increase in labelling index differed in the phenotypically diverse types of preneoplastic and neoplastic lesions. There was a significant but relatively small increase in the labelling index in clear and acidophilic cell foci. A much stronger elevation of cell proliferation was characteristic of mixed and basophilic cell foci. The development of hepatocellular adenomas and carcinomas from preneoplastic hepatic foci was further characterized by an additional increase in cell proliferation. Each specific cellular phenotype was associated with a rather uniform proliferation rate, which remained elevated at all time points studied, suggesting that the rate of cell proliferation in the phenotypically diverse preneoplastic hepatic foci mainly reflects the intrinsic growth potential of the respective cellular phenotypes. The results support the concept that the predominant sequence of cellular changes in hepatocarcinogenesis induced by the stop model leads from the clear and acidophilic cell foci, storing glycogen in excess, through mixed and basophilic cell foci to hepatocellular adenomas and carcinomas. The fact that the labelling index of the extrafocal liver tissue of N-nitrosomorpholine-treated rats was also significantly higher than that of the normal parenchyma of untreated controls might indicate an involvement of extrafocal hepatocytes, in addition to that of foci of altered hepatocytes, in hepatocarcinogenesis.

Significance of sequential cellular changes inside and outside foci of altered hepatocytes during hepatocarcinogenesis

A variety of phenotypic cellular changes emerge in the liver of different species prior to the appearance of hepatocellular adenomas and carcinomas induced by carcinogenic agents (chemicals, radiation, hepadna viruses) or develop "spontaneously." Foci of altered hepatocytes have been studied most extensively in rats treated with chemical carcinogens; they are considered preneoplastic lesions and have been used in several laboratories as endpoints in carcinogenicity testing. The principles and problems of the morphological classification of foci of altered hepatocytes are presented. In addition to the 4 types of foci generally accepted (clear, acidophilic, basophilic and mixed cell foci), further subtypes (intermediate cell foci) or other types of foci, namely tigroid cell foci and amphophilic cell foci, have more recently been separated as distinct pathomorphological entities. Whereas the amphophilic foci might result from a modulation of clear and acidophilic cell foci, the tigroid cell foci apparently represent a stage in a separate cell lineage leading to hepatocellular adenomas. It remains open whether the tigroid cell foci may also progress to carcinomas. Extrafocal phenotypic changes of hepatocytes might also be involved in hepatocarcinogenesis. The cellular phenotypes within foci also depend strongly, among many other factors, on the dose and duration of the carcinogenic treatment. Cytomorphological, cytochemical, microbiochemical and stereological studies suggest that the predominant sequence of cellular changes during hepatocarcinogenesis leads from the clear and acidophilic cell foci storing glycogen in excess through mixed cell foci and nodules to basophilic cell populations prevailing in hepatocellular carcinomas. A multitude of metabolic aberrations is associated with the sequential cellular changes. Aberrations in carbohydrate metabolism are particularly prominent and might be causally related to the neoplastic transformation of the hepatocytes.

Unusual histochemical pattern in preneoplastic hepatic foci characterized by hyperactivity of several enzymes

In a stop-experiment using the hepatocarcinogen N-nitrosomorpholine, as well as glycogenotic and related lesions, hepatocellular foci with a different histochemical pattern were identified. The outstanding features of these hepatic foci, which may progress to hepatocellular adenoma, were increased activities of mitochondrial glycerol-3-phosphate dehydrogenase (mG3PD), glycogen synthase, pyruvate kinase and glucose-6-phosphatase detected by enzyme histochemistry. Since no decrease in activity of any of the enzymes examined were seen in these foci, compared with normal liver, the term enzymatically hyperactive focus (EHF) is proposed for this type of lesion. Only at the stage of overtly nodular growth did these lesions exhibit some of the characteristic changes seen in nodules developing from glycogenotic foci, namely elevated activities of glucose-6-phosphate dehydrogenase, gamma-glutamyl transferase and glutathione-S-transferase P as well as decreased activities of adenosine-triphosphatase, glucose-6-phosphatase and adenylate cyclase. Some of these enzymes have been used widely in morphometric studies as markers for preneoplastic and neoplastic lesions. The inability to detect early EHF may lead to an underestimation of preneoplastic liver lesions in quantitative studies. Although there are apparent differences in the histochemical patterns of glycogen storing foci and early EHF, these differences tend to disappear during progression to overtly neoplastic lesions. In studies comparing the phenotypic alterations in different types of preneoplastic hepatic lesions, the recognition of EHF may contribute to the distinction of obligatory from facultative phenomena during transformation.

Quantitative morphometric comparison between the expression of two different "marker enzymes" in preneoplastic liver lesions induced in rats with low doses of N-nitrosodiethanolamine

Male Sprague-Dawley rats were treated with low doses of N-nitrosodiethanolamine (NDELA) (0.2, 0.63, 1.5, 6 and 25 mg/kg body wt per day). Foci of altered hepatocytes developed at all dose levels. The extent of foci positive for gamma-glutamyl transpeptidase (gamma-GT), as demonstrated histochemically in frozen sections, was quantitated morphometrically and compared with the data obtained earlier in the same livers by measuring the extent of foci positive for glucose-6-phosphate dehydrogenase (G6PDH). The area density of foci positive for gamma-GT was much smaller than that of foci positive for G6PDH at all dose levels and time points studied. However, there was an increase in the area density of both gamma-GT- and G6PDH-positive foci proportionally to the time of treatment and the total dose of the carcinogen administered. The dose-time relation for the induction of 0.5% gamma-GT positive liver tissue assessed as a double logarithmic plot gives a straight line. The same holds true for the induction of 1% G6PDH-positive liver tissue. The slopes of these straight lines are identical, and they have the same characteristics as the line indicating the time when 50% of the animals developed liver tumors at higher doses. Thus, a close statistical correlation of enzyme altered hepatic foci and the development of hepatocellular tumor exists irrespective of the absolute amount of the area density of the respective foci.

Immunohistochemical demonstration of decreased L-pyruvate kinase in enzyme altered rat liver lesions produced by different carcinogens

Preneoplastic liver lesions were produced in female Wistar rats by application of 25 mg/kg N-nitrosomorpholine (NNM), 14 mg/kg diethylnitrosamine (DENA), 0.075 mg/kg aflatoxin B1 (AFB1) or 160 mg/kg safrole. These carcinogens were administered in two equal doses 12 and 24 h after partial hepatectomy. The animals then received sodium phenobarbital (0.1% in tap water) for up to 410 days. Numerous altered hepatic foci (AHF) and hyperplastic nodules (HN) were detected enzyme histochemically by their negative ATPase reaction after application of AFB1, DENA and NNM; some AHF and HN were also caused by the weak carcinogen safrole. Immunohistochemically these lesions were also L-pyruvate kinase (L-PK)-negative with a high coincidence with regard to their number and area. These results confirm the role of L-PK, an enzyme affecting the pentose phosphate pathway, as a negative marker of preneoplastic liver lesions.

Decrease in glucokinase and glucose-6-phosphatase and increase in hexokinase in putative preneoplastic lesions of rat liver

Preneoplastic liver lesions were produced in female Wistar rats by oral administration of 2-acetylaminofluorene for 165 days succeeded by a carcinogen-free standard diet up to 420 days. During the treatment numerous altered hepatic foci (AHF) and hyperplastic nodules (HN) were detected histochemically by a focal decrease or lack of adenosine-5-triphosphatase and glucose-6-phosphatase (G-6-Pase) activities. In addition, the immunohistochemically demonstrable amount of L-type pyruvate kinase was clearly reduced. The histochemically demonstrated decrease of G-6-Pase was substantiated by microbiochemical determination of the enzyme activity in microdissected material. Moreover, during the experimental period a continuous decrease in glucokinase and an increase in hexokinase was detected microbiochemically within AHF and HN. These alterations indicate a shift in the carbohydrate metabolism from gluconeogenesis to glucose utilization and pentose-phosphate-pathway for biosynthesis of nucleic acids. Beside other oncofetal markers, HK may be used as indicator of the early stages of liver carcinogenesis.

Histology and histochemistry of the liver of chickens after DENA induced hepatocarcinogenesis and ingestion of low chlorinated biphenyls

Studies are presented which demonstrate the pathological effects of diethylnitrosamine (DENA) and polychlorinated biphenyls (PCB) in the liver of chickens. DENA, which has been shown to cause tumors in rats and chickens, was tested on 80 laying hens to determine whether changes in the liver during hepatocarcinogenesis were similar to those observed in rats. In addition, the hepatocarcinogenic and cocarcinogenic properties of Clophen C (CC), a technical mixture of low chlorinated biphenyls was tested on chickens. The livers of test animals were examined histologically for preneoplastic and neoplastic lesions. Histochemical methods were used to determine lipid and glycogen contents as well as changes in activity of alkaline phosphatase and gamma-glutamyl-transpeptidase. Putative preneoplastic lesions in the liver were first observed according to the substance and dosage applied as follows: DENA 1 X weekly (group II), beginning on day 258; DENA 2 X weekly (group III), beginning on day 183; and CC + DENA 2 X weekly (group V), beginning on day 231. Application of CC alone did not induce lesions. The concept that CC has cocarcinogenic capability was substantiated by the fact that animals from group V (CC + DENA 2 X weekly) developed twice as many tumors as did animals from group III (DENA 2 X weekly). Additionally, tumors developed earlier in the former group than in the latter.

Liver tumors in rodents: extrapolation to man

Man is a poor model for the prediction of agents that are hepatocarcinogenic for laboratory rodents. Relatively few agents are known to cause any form of primary liver cancer in man. The most important is hepatitis B virus, for which there is possibly a model in the woodchuck but not one in rats or mice. The only other agents known to cause primary liver cancer in man are certain steroid hormones, vinyl chloride, and thorium dioxide. There are animal models for the first two of these and a reasonable expectation that thorium dioxide would produce liver tumors in animals if the appropriate experiments were done. Aflatoxin, a potent hepatocarcinogen in rats and other species but not mice, is strongly suspected of being an important human hepatocarcinogen in certain geographical areas of the world, but the evidence is circumstantial. There is no more than a weak association between the nutritional type of cirrhosis secondary to excessive intake of alcohol and increased primary liver cancer in man, and no evidence at all that ethanol per se causes liver tumors in mice, rats, hamsters, or mastomys. By contrast, a very large number of chemicals to which people in the West have been exposed for many decades have been found to be hepatocarcinogens in laboratory rodents. In most cases the levels of exposure required to produce liver tumors in rodents far exceed those to which man is normally exposed. The problem is to guess whether low-level exposure to such rodent hepatocarcinogens poses any real liver cancer threat to man?The mortality from primary liver cancer is very low in countries such as England and Wales where there is widespread exposure to low doses of both natural and synthetic agents which, in high dosage, cause liver tumors in rodents. This suggests that, if there is any risk, it can only be very small. Death rate data collected in England and Wales by the Registrar General are consistent with there having been a small increase in the incidence of primary liver cancer in England and Wales during the past 20 years, but the apparent increase might well be a consequence of revisions in the International Classification of Diseases system and not real. During the first half of the present century the age-standardized incidence of primary liver cancer in England and Wales was falling.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzymes of glutathione metabolism as biochemical markers during hepatocarcinogenesis

Enzymes of glutathione metabolism, particularly gamma-glutamyltransferase (GGT) and glutathione S-transferase (GST), play a role in multistage hepatocarcinogenesis. The enhanced expression of these enzymes in preneoplastic altered hepatic foci, nodules, and hepatocellular carcinomas has been demonstrated after treatment with a variety of initiating and promoting agents. Glutathione is necessary for the detoxification of xenobiotics and carcinogens and for cell replication. Induction of GGT in altered hepatocytes may permit these cells to utilize extracellular glutathione to preserve their internal glutathione levels. GST induction allows glutathione utilization for the protection of the altered hepatocyte in an environment of exposure to xenobiotics, such as promoting agents. Thus, the combined effects of GGT and GST, in a toxic environment, may provide for the enhanced proliferation observed in preneoplastic hepatocytes. New clinical and research opportunities may involve the use of GGT and the placental isozyme of GST (PGST) as markers of preneoplasia and neoplasia in humans. Many factors, such as hormones, diet, and exposure to initiating and promoting agents, influence GGT and GST expression. The recent cloning of cDNAs to GGT and PGST offers opportunities for the study of factors involved in the genetic expression of these two enzymes. Coupled with the use of hepatocyte culture and transplantation, the factors involved at the molecular level in the creation of hepatocellular neoplasia may be discovered.

Histochemical and immunohistochemical detection of putative preneoplastic liver foci in women after long-term use of oral contraceptives

Localized areas with altered enzyme patterns were observed in liver tissue surrounding focal nodular hyperplasia in women after long-term use of oral contraceptives. These localized lesions were of three different types. Type I lesions were characterized by glycogen storage, a reduction in ATPase and an increase in gamma-glutamyltranspeptidase (gamma-GT) and UDP-glucuronyltransferase (UDP-GT) detected immunohistochemically. Type II lesions, which were morphologically very similar to small hyperplastic nodules, showed only a decreased ATPase reaction. Type III lesions showed an increase in gamma-GT (detected histochemically) and a slight reduction in ATPase. The results indicated that in human liver from patients given oral contraceptives long-term, localized lesions with altered enzyme patterns may occur which are very similar to those observed in animal models during experimental hepatic carcinogenesis.

Increased UDP-glucuronyltransferase and gamma-glutamyltranspeptidase in enzyme-altered rat liver lesions produced by low doses of aflatoxin B1

Preneoplastic liver lesions were produced in female Wistar rats by low doses of aflatoxin B1 (Model 1: administration of 37.5 micrograms/kg 12 and 24 h after partial hepatectomy; Model 2: continuous application of 3.5 micrograms/kg in tap water daily for 28 days with partial hepatectomy after 14 days. The animals then received sodium phenobarbital, 0.1% in tap water, for 180 to 400 days). In both models numerous altered hepatic foci (AHF) and hyperplastic nodules (HN) were detected enzyme histochemically by their negative ATPase and positive gamma-glutamyltranspeptidase reactions. Immunohistochemically these lesions were also UDP-glucuronyltransferase positive. Increased UDP-glucuronyltransferase adds to permanent alterations of a number of drug metabolizing enzymes observed in a variety of different tumor models. These alterations are responsible for the toxin-resistant phenotype (Faber 1984b). Increased gamma-glutamyltranspeptidase was detected both enzyme histochemically and immunohistochemically; whereas gamma-glutamyltranspeptidase activity was present in both AHF/HN and in periportal areas by enzyme histochemistry, the immunohistochemical method selectively stained gamma-glutamyltranspeptidase in AHF and HN. Immunohistochemically detectable UDP-glucuronyltransferase and gamma-glutamyltranspeptidase are markers of putative precancerous liver lesions which may be useful in the analysis of the prestages of liver carcinogenesis.

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.

Three-dimensional observations by scanning electron microscopy on the blood supply and organization of vasculature during hepatocarcinogenesis in rats

Three-dimensional vascular changes in rats during hepatocarcinogenesis were studied by stereoscopic and scanning electron microscopic observation of vascular casts of sinusoids by injecting resin from hepatic artery (red color) and portal vein (blue color). Neoplastic lesions were synchronously induced by injection of diethylnitrosamine (DENA) followed by feeding of 2-acetylaminofluorene (2-AAF) plus partial hepatectomy, then periodically killed for examination. At 6 weeks after DENA injection sinusoids of hyperplastic foci (HF) were filled with blue resin similar to surrounding tissue, then at 8 weeks some HF and hyperplastic nodules (HN) took up red resin leaving surrounding sinusoids blue. At 12 to 18 weeks, red HN became more discrete with obvious compression of surroundings but decreased their number whereas blue HN were not. Red HN had incomplete anastomosing sinusoids giving a coral-like appearance. Spongy or cystic areas contained little or no resin, suggesting ischemic condition. Hepatocellular carcinomas (HCC) at 40 weeks took exclusively arterial red resin forming irregularly shaped anastomosing sinusoids. These findings indicate that acquisition of arterial blood supply by HF may relate to their further development to persistent HN and HCC.

Hepatocellular injury, hyperplasia and putative premalignancy in rats fed 2-acetylaminofluorene

Hepatocellular growth inhibition and restorative hyperplasia were studied in 80 young male Buffalo rats that were fed .02% 2-AAF for up to four weeks. Between 30 and 58 days of age, the control rats tripled their body weights and more than doubled their liver weights. But these increases were respectively inhibited by 25 and 22% in 2-AAF fed rats. Because the rats were in a phase of rapid growth, it was necessary to evaluate the age-related hepatic changes in control animals prior to analyzing the experimental data. Thirty-seven-day-old control rats had 3H-thymidine labeling indices of hepatocytes that were two to five times higher than in 58-day-old rats. A replicative gradient was also noted in the hepatic acini. At three ages of sacrifice (37, 44 and 58 days), the control hepatocytes in the periportal regions (Zone 1) had labeling indices that were at least three times higher than those surrounding the terminal hepatic veins (Zone 3). Histochemical GGTase activity also showed age-related zonal changes. Particularly prominent was the decrease with age in the enzyme activity of the most actively replicating Zone 1 hepatocytes. GGTase activity was observed in hepatocytes occupying 7.6% of tissue section areas in rats sacrificed at 30 days of age, but this decreased to 0.3% by the fourth week of the study. After four weeks of feeding the carcinogen toxic growth inhibition was most impressive in midzonal (Zone 2) hepatocytes, which also showed decreased glycogen, and decreased cytoplasmic RNA. The localization of injury to acinar midzones is particularly noteworthy in view of the extreme rarity of the finding in the hepatic toxicology literature. Growth inhibition was already apparent after only one week of 2-AAF feeding, when the 3H-thymidine labeling indices of Zone 2 hepatocytes were 90% lower (0.9%) than in control rats (8.6%). Hepatocellular hyperplasia, presumably a restorative response to the midzonal growth inhibition, was prominent in Zone 1, but also noted in Zone 3, after four weeks of the study. However, most of the Zone 1 hyperplastic cells showed canalicular GGTase activity, while none of the Zone 3 hyperplastic cells showed this phenotype. Occasional discrete foci of hyperplastic hepatocytes that were considered putatively premalignant because of their very high GGTase activity and low G6Pase and ATPase activities were also noted after four weeks of 2-AAF feeding. The foci were usually in close physical association with hyperplastic Zone 1 hepatocytes, but could be distinguished by their higher GGTase and lower G6Pase activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatocellular glycogenosis and related pattern of enzymatic changes during hepatocarcinogenesis

Systematic studies of the sequence of cellular changes during hepatocarcinogenesis induced predominantly in rats by stop experiments with N-nitrosomorpholine (NNM) led to the following main results and conclusions: The development of hepatocellular tumors is preceded by a multifocal hepatic glycogen storage disease (glycogenosis). Cytomorphological and cytochemical findings suggest a sequence of focal changes leading from clear and acidophilic glycogen storage foci through mixed cell foci and neoplastic nodules to hepatocellular carcinomas. The clear and acidophilic glycogen storage cells persisting after withdrawal of the carcinogen apparently represent a preneoplastic cell population, the neoplastic transformation of which is accompanied by a gradual reduction of glycogen and a concomitant increase in ribosomes (basophilia). The first appearance and frequency of the different liver lesions investigated was shown to depend on the dose of carcinogen administered. With increasing dose of NNM, the number of focal lesions considerably increased, and this was accompanied by an earlier development of mixed and basophilic cell populations. There was no indication of any reversibility of pronounced focal lesions under the experimental conditions chosen. On the contrary, the foci became larger and acquired phenotypic markers closer to neoplasia independent of further action of the carcinogen. Enzyme histochemically, the majority of the pronounced glycogen storage foci showed a reduction in the activities of glycogen phosphorylase and glucose-6-phosphatase while the activity of glucose-6-phosphate dehydrogenase, a key enzyme for the pentose phosphate pathway, was increased. The mixed cell foci, neoplastic nodules and carcinomas which emerged at later stages were characterized by a progressive shift away from glycogen metabolism towards glycolysis and the pentose phosphate pathway. as indicated by an increase in glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase activities. These changes in enzyme pattern are in keeping with a developmental sequence leading from glycogen storage foci through mixed cell foci and neoplastic nodules to hepatocellular carcinomas. Biochemical microanalysis of dissected glycogen storage foci and mixed cell foci revealed that the foci composed exclusively of storage cells contained on an average 100% more glycogen than the normal liver tissue. The overall glycogen content of the mixed cell foci, which were composed of both glycogenotic and glycogen-poor basophilic cells, was not distinguishable from that of normal tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunohistochemical and biochemical detection of uridine-diphosphate-glucuronyltransferase (UDP-GT) activity in putative preneoplastic liver foci

Preneoplastic liver foci were produced in female Wistar rats by the administration of 2-acetylaminofluorene (0.03% w/w) in the diet for 174 days. Increased UDP-glucuronyltransferase (UDP-GT) could be visualized immunohistochemically in the same focal areas which were ATPase-negative and gamma-glutamyltranspeptidase-positive. Immunohistochemical detection was possible using rabbit anti-UDP-GT and peroxidase-labeled swine anti-rabbit immunoglobulins. The results of immunohistochemistry were substantiated by enzyme determination in microdissected material. UDP-GT activity was 5-fold higher in focal areas in comparison with the surrounding liver tissue. Increased UDP-GT activity in conjunction with the altered pattern of other drug-metabolizing enzymes is consistent with increased resistance of preneoplastic cells to the cytotoxicity of carcinogens. Immunohistochemical detection of UDP-GT may provide a new marker for preneoplastic lesions which, in conjunction with other markers, may prove useful in analyzing the various stages of liver carcinogenesis and the remodeling of preneoplastic lesions after cessation of carcinogenic stimuli.

Biochemical correlation of glycogen content and activity of some enzymes of carbohydrate metabolism in rat liver during early stages of carcinogenesis

The livers of rats treated for 12 weeks with N-nitrosomorpholine (80 mg/1 drinking water) were investigated on the day of carcinogen withdrawal (12 + 0 weeks) and 8 weeks after cessation of treatment (12 + 8 weeks). The glycogen content in relation to the DNA and protein content of the liver and the activities of glycogen synthetase, glycogen phosphorylase, glucose-6-phosphatase, and glucose-6-phosphate dehydrogenase were determined in the liver homogenates. The glycogen content of the livers was slightly elevated at both times investigated. Phosphorylase and synthetase activities showed no clear alterations in livers of treated animals as compared with controls. Glucose-6-phosphatase activity was significantly reduced at 12 + 0 weeks and returned to normal values at 12 + 8 weeks. The activity of glucose-6-phosphate dehydrogenase was unchanged at 12 + 0 weeks, but exhibited a significant increase at 12 + 8 weeks. Polyacrylamide gel electrophoresis with staining of the gels by an assay specific for the glucose-6-phosphate-dehydrogenase-catalysed reaction revealed the same pattern of active bands in treated and untreated animals but with higher activities in two bands originating from extracts of nitrosomorpholine-treated livers.

Fatal nitrosamine poisoning

A case is reported in which progressive liver symptoms with rise in bilirubin concentration, hemorrhagic diathesis, and signs of portal hypertension developed three years before death in liver coma. The pathologic and neuropathologic findings are described. The case was clarified after dimethylnitrosamine was demonstrated in food intended for the patient and after it was established that small amounts of nitrosamine could have been repeatedly ingested by the patient over a period of years. Comparable cases of human dimethylnitrosamine poisonings published in the literature are presented. The relatively typical morphologic alterations in the liver are described. Problems involved in the histological interpretation of such liver changes as well as the forensic conclusions to be drawn are discussed.

Correlation between growth rate and cytochemistry in Morris hepatomas

The correlation between the cytochemistry (glycoprotein, glycogen, glucose-6-phosphatase, catalase, alkaline phosphatase) and the growth rate of the fast-growing Morris hepatoma 3924A and the slow-growing Morris hepatoma 9618A was studied by utracytochemical techniques. By the chromic acid-phosphotungstic acid technique, acid glycoprotein is stained in glycocalyx, Golgi saccules and vesicles, and secretory granules of the tumor cells of both hepatomas. However, the hepatoma 3924A cells contain thicker glycocalyx and more numerous glycoprotein-rich granules than hepatoma 9618A cells. Abundant alpha and beta glycogen particles are found in hepatoma 3924A. Moderate glucose-6-phosphatase activity is observed in the cisternae of endoplasmic reticulum and nuclear envelope of hepatoma 9618A, but it is totally absent in hepatoma 3924A. High catalase activity is present in numerous peroxisomes of hepatoma 9618A. Hepatoma 3924A contains only a few catalase-positive microperoxisomes. Weak to moderate alkaline phosphatase is present in the plasma membrane and nuclear envelope of hepatoma 9618A cells, while hepatoma 3924A shows no activity of the enzyme. All the cytochemical parameters except glycoprotein show an inverse relationship with the growth rate of the hepatomas. The higher intracellular glycoprotein content of hepatoma 3924A may be related to differences in cell coat secretion (composition and activity) from the slower-growing hepatoma 9618A

Glucose phosphatase in benign and malignant tumours of the prostate. (Preliminary communication)

Histochemical studies of benign and malignant prostatic tumours for their differences in glucose-6-phosphatase activities are of interest by contributing to the accuracy of diagnosis of prostatic tumours. Studies by means of further histochemical methods are in progress.

Age-, sex-, and strain-dependent differences in the induction of enzyme-altered islands in rat liver by diethylnitrosamine

The formation of foci with loss of ATPase and emergence of gamma-GTase was studied histochemically in livers of male and female Wistar and Sprague-Dawley rats of 3--4 and 6--7 weeks of age, respectively, after application of diethylnitrosamine. A single dose of 8 mg/kg body weight induced a considerable island formation in weanlings of both sexes. Island induction in adults was observed only after repeated application. No difference in island size and number was observed with the exception of greater island size and Sprague-Dawley females. Sex-dependent differences in susceptibility to island induction were observed in weanlings, females being more sensitivity than males and Sprague-Dawley females being the most sensitive of all. No correlation was seen between monooxygenase activity and the extent of island formation. The coincidence of ATPase-deficiency and emergence of gamma-GTase was highest in Sprague-Dawley females. The importance of this result in respect to cancer formation is discussed. Weanling Sprague-Dawley females seemed to be the most suitable for use in a screening test system for chemical carcinogenicity, especially for testing low doses or weak carcinogens.

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, 4 1/2 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.

Separate isolation of cells from nodules and surrounding parenchyma of the same precancerous rat liver: biochemical and cytochemical characterization

Various enzyme and metabolic alterations have been observed in the hyperplastic nodules which appear during the hepatocarcinogenesis. These alterations have been mainly specified by histochemical observations. In this report, a technique of hepatocyte isolation is described which enables the separation of 2 cellular fractions, respectively, from the nodules and from the surrounding parenchyma of the same liver of a rat previously treated with a hepatocarcinogen. Such a technique allowed parallel analysis of both cellular populations by biochemical and cytochemical techniques.

Vinyl chloride and trichloroethylene: comparison of alkylating effects of metabolites and induction of preneoplastic enzyme deficiencies in rat liver

[1,2-14C] Vinyl chloride and [1,2-14C] trichloroethylene were incubated with rat liver microsomes, NADPH and RNA (from yeast). Whereas trichloroethylene metabolites were irreversibly bound to proteins in microsomal incubations to a higher extent than vinyl chloride metabolites, irreversible binding to RNA was lower for trichloroethylene metabolites. Hydrolysis of the RNA which was reisolated from microsomal incubations with 14C-vinyl chloride or 14C-trichloroethylene and separation of the nucleosides showed different alkylation products arising from vinyl chloride and from trichloroethylene, characteristic for vinyl chloride being formation of 1,N6-ethenoadenosine and 3,N4-enthenocytidine. The different reactivities of metabolites of vinyl chloride and of trichloroethylene prompted a comparison of the oncogenic effects of both compounds against the rat liver cell. Newborn rats were exposed for 10 weeks to 2000 ppm vinyl chloride or trichloroethylene (8 h/day; 5 days/week). After this period livers of the animals were stained for nucleoside-5-triphosphatase. Whereas the vinyl chloride exposed rats showed focal hepatocellular deficiencies in this enzyme, which are supposed to represent an early sign of malignancy, no such changes were induced by trichloroethylene exposure. The data therefore suggest differences between the hepatocarcinogenic activity of vinyl chloride and possible effects of trichloroethylene on the liver.