[Cytomorphologic and morphometric studies on hepatocarcinogenesis. II. Reversibility of cell-nucleus changes in nitrosomorpholine poisoned rat liver]

Dose-dependent induction of preneoplastic lesions by the tobacco-specific nitrosamine carcinogen NNK in the in ovo carcinogenicity assessment (IOCA) assay

The potential of the carcinogenic tobacco specific nitrosamine 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-1-butanone (NNK) to induce preneoplastic hepatocellular altered foci (HAF) was tested in the in ovo carcinogenicity assessment (IOCA) assay. Single doses of NNK over a dose range from 0.1 mg to 6 mg were injected into fertilized turkey eggs prior to incubation for 24 days. The livers were investigated by histological, histochemical and morphometric methods. Mortality was increased for eggs exposed to 6 mg. In this group, the whole livers were severely altered, showing pronounced changes of nucleus size and signs of cell death. At the dose of 2 mg various types of foci of altered hepatocytes (HAF) were observed. Basophilic cell foci of the solid or tubular type were most frequent. The NNK-induced HAF were very similar to the preneoplastic lesions that occur in the livers of mammals during hepatocarcinogenesis which are regarded as early indicators of carcinogenesis. The similarity to the HAF in rodents included histochemically detectable alterations like decreased activities of glucose-6-phosphatase, adenosine triphosphatase and glycogen phosphorylase. At doses of 1 mg or below, no HAF were detected. At all dose levels an increased occurrence of enlarged hepatocytes with enlarged nuclei and prominent nucleoli (karyomegalic hepatocytes) were observed. The increase in karyomegalic hepatocytes was also statistically significant at the low dose of 0.1 mg/kg NNK but the dose-effect curve for their induction was clearly non-linear. Induction of HAF and karyomegalic hepatocytes in ovo is a simple (one dose), rapid (24 days) and inexpensive (no animal purchase or housing) experimental approach for studies on chemically induced hepatocarcinogenesis.

Nonlinearity of nuclear enlargement in hepatocytes induced by the carcinogen N'-nitrosomorpholine in Ovo

In this study we investigated the effects of different doses of the carcinogenic nitrosamine N'-nitrosomorpholine (NNM) on the occurrence of enlarged nuclei in embryonic turkey liver in order to evaluate whether this parameter might represent a quantitative indicator of chemically induced hepatocarcinogenesis. Therefore fertile embryo turkey eggs were injected with NNM over a dose range of 125 microg-8 mg/egg at the first day of incubation. After incubation for 24 days, the embryonic livers were removed and processed for histologic evaluation. The induction of hepatocytes with enlarged nuclei (nuclear profiles > 35 microm2 was quantitated morphometrically in hematoxylin and eosin (H&E)-stained sections. The NNM treatment increased both the number of enlarged hepatocyte nuclei and the areas of the individual profiles of the enlarged nuclei in a dose-dependent manner. Exposure to 500 microg-8 mg NNM/egg resulted in a statistically significant increase in the number of hepatocytes with enlarged nuclei. The lower doses of 250 microg and 125 microg NNM/egg showed a similar albeit not significant trend. Signs for cytotoxic effects on the hepatocytes, such as necrosis or enhanced cytoplasmic vacuolization, were observed in tissue samples of embryos exposed to 4 or 8 mg NNM, but not after treatment with lower doses. The dose-effect curve for the induction of the nuclear enlargement was nonlinear, with a moderate slope for lower dose levels of 125-500 microg/egg and a steep slope for higher dose levels of 1-8 mg. Findings in rodents indicate a pathogenic link between the occurrence of enlarged nuclei and hepatocarcinogenesis. Based on the results with NNM, it is suggested that the in ovo model may represent a rapid, convenient, and inexpensive experimental approach for dose effect investigations on chemically induced hepatocarcinogenesis.

Morphometric study of alterations of extrafocal hepatocytes of rat liver treated with N-nitrosomorpholine

Male Sprague-Dawley rats were treated with the hepatocarcinogen N-nitrosomorpholine for 7 weeks and observed for up to 40 weeks after withdrawal of the carcinogen. In addition to the focal preneoplastic lesions described earlier there were also alterations in extrafocal hepatocytes and these changes have been quantified morphometrically. Since the periportal and perivenous hepatocytes were not altered to the same extent, cells of the periportal zone (PPZ) and cells of the perivenous zone (PVZ) were measured separately. Immediately after stopping treatment there was marked enlargement of the hepatocellular cytoplasm and of the nuclei in both the PPZ and the PVZ and a reduction in the number of binuclear hepatocytes. While these alterations were totally reversed during the first 10 weeks after treatment ceased in the PPZ, statistically significant changes in nuclear size, nuclear-cytoplasmic ratio and number of binuclear cells persisted in the PVZ up to 40 weeks after the end of treatment. We suggest that both the foci of altered hepatocytes as well as the persisting changes in extrafocal hepatocytes may be involved in the process of hepatocarcinogenesis.

Karyometry of pseudostratified, metaplastic and dysplastic nasal epithelium by morphometry and stereology. 2. Automated image analysis (IBAS) of the basal layer of nickel workers

A mathematical model for the stereological analysis of parallel-oriented, spheroidal nuclei has been applied to the basal layers of respiratory, metaplastic and dysplastic nasal epithelia. Nuclear profiles seen on tissue sections were measured with an automatic image analyser (IBAS). Nuclear profile area distributions were used to assess possible polyploidies. The result are compared to the histopathological grading, consisting of pseudostratified (respiratory), cuboidal, mixed cuboidal/squamous, squamous, and dysplastic epithelia. The estimated nuclear axis lengths, volumes, surface areas and volume/surface ratios are, in the great majority of cases, significantly smaller in pseudostratified or cuboidal epithelium than in squamous metaplasia and dysplasia. Correspondingly, the numerical density of the nuclei is lower in the latter cases, in which is also noted a smaller nuclear eccentricity. No significant difference is found between the nuclei of squamous and dysplastic epithelia. There is a clear correlation between the mean profile areas and the stereologically estimated volumes of the nuclei. When classifying the mean profile areas into four classes, a progressive shift from the smaller towards the larger size classes is observed when passing from pseudostratified to dysplastic epithelia, through the different metaplastic stages. The nuclear profile area plots often show several peaks, even in some pseudostratified and cuboidal epithelia, probably reflecting polyploidy. There is a marked tendency towards larger profile areas in squamous metaplasia and dysplasia. One histopathologically typical dysplasia showed only small-sized nuclei and another had a notable contribution of those in its profile area plot, in contrast with all the other dysplasias and squamous metaplasias, which displayed practically no small nuclei. The possible implications of the existence of "small-sized-nuclei-dysplasias" are discussed. The literature dealing with nuclear volumes or DNA quantities in putative preneoplastic situations in reviewed. Our method adds some valuable objective criteria to those used in classical histopathological grading. It should be possible to apply this method to other epithelial tissues.

Application of fine-needle aspiration biopsy for the diagnosis of dysplastic and neoplastic liver cell changes induced by N-nitrosomorpholine in rats

Male rats were treated with the hepatocarcinogen, N-nitrosomorpholine (NNM, 10 mg ad 100 ml drinking water) for 19 weeks. Repeated fine-needle aspiration biopsies of the liver were performed percutaneously. Cytomorphologic and cytochemical criteria were used for the characterization of dysplastic and carcinoma cells. The alterations seen in the smears were correlated with histopathologic findings in the punctured liver lobes. Cells showing type I dysplasia were recognized in smears obtained from day 7 on. They corresponded to the swollen, glycogen-free cells developing in zone 3 of the Rappaport acinus during the early treatment phases. In later stages type I dysplastic cells were observed in smears. This coincided with the development of neoplastic nodules seen in histopathologic preparations. Carcinoma cells were recognized first after 15 weeks. Marked gamma-glutamyl transpeptidase (gamma-GT) activity could be demonstrated cytochemically in biopsy smears and biochemically in biopsy homogenates during the early phases of NNM-treatment. Simultaneously, a rise in gamma-GT activity was also observed in the serum.