A 2-year dose-response study of lesion sequences during hepatocellular carcinogenesis in the male B6C3F(1) mouse given the drinking water chemical dichloroacetic acid

Dichloroacetic acid (DCA) is carcinogenic to the B6C3F(1) mouse and the F344 rat. Given the carcinogenic potential of DCA in rodent liver and the known concentrations of this compound in drinking water, reliable biologically based models to reduce the uncertainty of risk assessment for human exposure to DCA are needed. Development of such models requires identification and quantification of premalignant hepatic lesions, identification of the doses at which these lesions occur, and determination of the likelihood that these lesions will progress to cancer. In this study we determined the dose response of histopathologic changes occurring in the livers of mice exposed to DCA (0.05-3.5 g/L) for 26-100 weeks. Lesions were classified as foci of cellular alteration smaller than one liver lobule (altered hepatic foci; AHF), foci of cellular alteration larger than one liver lobule (large foci of cellular alteration; LFCA), adenomas (ADs), or carcinomas (CAs). Histopathologic analysis of 598 premalignant lesions revealed that (a)) each lesion class had a predominant phenotype; (b)) AHF, LFCA, and AD demonstrated neoplastic progression with time; and (c)) independent of DCA dose and length of exposure effects, some toxic/adaptive changes in non-involved liver were related to this neoplastic progression. A lesion sequence for carcinogenesis in male B6C3F(1) mouse liver has been proposed that will enable development of a biologically based mathematical model for DCA. Because all classes of premalignant lesions and CAs were found at both lower and higher doses, these data are consistent with the conclusion that nongenotoxic mechanisms, such as negative selection, are relevant to DCA carcinogenesis at lower doses where DCA genotoxicity has not been observed.

Hepatic progenitor cells in hepatocellular adenomas

Hepatocellular adenoma is a benign tumor of the liver that has a small but not negligible risk of malignant transformation into hepatocellular carcinoma. In analogy with the established role of oval cells in hepatocarcinogenesis in rodent models, human hepatic progenitor cells may have a function in the development of liver tumors. To investigate this issue, we performed immunohistochemistry on biopsies of 10 consecutively resected hepatocellular adenomas using markers for hepatic progenitor cells. Sections of paraffin-embedded and frozen biopsies were stained using antibodies against cytokeratins 7, 8, 18, and 19, chromogranin-A, OV-6, and neural cell adhesion molecule. Hepatic progenitor cells were observed in five of 10 hepatocellular adenomas. These five tumors also contained cells with an immunohistochemical phenotype intermediate between hepatic progenitor cells and hepatocytes. Hepatic progenitor cells and intermediate hepatocyte-like cells were scattered throughout the tumors with a density that varied from area to area. Ultrastructural examination confirmed the presence of hepatic progenitor cells. Our study shows that hepatic progenitor cells are present in a considerable proportion of hepatocellular adenomas, supporting the hypothesis that human hepatic progenitor cells can play a role in the development of hepatocellular tumors.

Diagnostic impact of fluorescence in situ hybridization in the differentiation of hepatocellular adenoma and well-differentiated hepatocellular carcinoma

Histopathological differentiation between hepatocellular adenoma and well differentiated hepatocellular carcinoma (HCC) may be a difficult task in small biopsies and occasionally in resected tumor specimens. Whether the analysis of chromosome aberrations can contribute to a more precise discrimination has not been analyzed systematically up to now. Therefore, fluorescence in situ hybridization was applied to 28 cases of adenoma and well differentiated carcinoma, using centromeric probes for chromosomes 1, 6, 7, 8, and X. None of 14 adenomas revealed an aberrant count in the analyses performed. By contrast, 13/14 carcinomas demonstrated aberrations for 2-5 chromosomes/case. Chromosome 1 was aberrant in 8/12 cases informative for this probe (67%), chromosomes 6 and 7 were aberrant in 9/14 cases (64%), chromosome 8 was aberrant in 11/14 cases (79%), and chromosome X in 7/14 cases (50%). Taking results for chromosomes 1 and 8 together, 13/14 HCC revealed aberrations for at least one of these chromosomes. Probes for 6, 7, and X revealed no additional aberrant cases.Thus, FISH for chromosomes 1 and 8, extended by probes for chromosomes 6, 7 and X, represents a promising approach toward a more accurate differentiation between hepatocellular adenoma and carcinoma.

Immunocytochemical investigation of catalase and peroxisomal lipid beta-oxidation enzymes in human hepatocellular tumors and liver cirrhosis

A significant reduction of catalase activity, a peroxisomal marker enzyme, occurs in human hepatic neoplasias, but no information is available on other peroxisomal proteins. We have studied by means of immunohistochemistry four specific proteins of peroxisomes (catalase and three enzymes of lipid beta-oxidation) in human hepatocellular tumors of various differentiation grades from adenoma to anaplastic carcinoma. In all tumors, except the adenomas, the tumor cells contained fewer peroxisomes than extrafocal hepatocytes and the reduction of antigenic sites in the tumor types generally correlated with the degree of tumor dedifferentiation as assessed by classical histopathological criteria. Two poorly differentiated tumors had no detectable peroxisomes at all. There were no major differences in the intensities of the immunocytochemical staining for all four studied peroxisomal antigens in different tumors, suggesting that the neoplastic transformation affects the biogenesis of the entire organelle and not merely the individual peroxisomal enzyme proteins. Some tumors exhibited a distinct peripheral distribution of peroxisomes. In cases with associated liver cirrhosis, the hepatocytes in the adjacent liver showed marked peroxisome proliferation, forming large perinuclear aggregates, occupying occasionally the entire cytoplasm. Taken together, our observations indicate that peroxisomes are significantly altered in both hepatocellular tumors and liver cirrhosis and, thus, could be responsible for some of the metabolic derangements observed in those disease processes.

Benign myxoid hepatocellular tumor: a variant of liver cell adenoma

A case of myxoid hepatocellular adenoma in the non-cirrhotic liver of a 26-year-old man is described. Grossly, the tumor was well circumscribed, rounded and measured 16 cm in diameter. Histologically, the tumor was characterized by nests and strands of polygonal cells embedded in a myxoid extracellular matrix. Electron microscopy confirmed the hepatocellular nature of the neoplastic cells. The patient is alive and well, without evidence of disease, 2 years after a local excision.

Light and electron microscopic analysis of liver sinusoids during hepatocarcinogenesis with 2-acetylaminofluorene in rats

To clarify the sequential changes and morphological differences of the sinusoidal structures between hepatocellular carcinoma (HCC) and hepatocellular adenoma (HA), we examined morphological changes of sinusoidal cells and related structures such as basement membrane during hepatocarcinogenesis in the rat. During continuous feeding of carcinogenic diets containing 2-acetylaminofluorene to rats, HA appeared at the 8th week in the peripheral area and then extended toward the centrolobular area. The appearance of HCC was recognized at the 27th week. In the HA lesion, the morphology of sinusoidal cells and related structures was basically the same as that of normal liver except for a slight thickening of the basement membrane and a decreased amount of vitamin A-lipid droplets of stellate cells. In HCC, the fenestrations of endothelial cells disappeared and the basement membrane became continuous, thick and often multilayered. Stellate cells contained almost no vitamin A-lipid droplets and were associated with abundant collagen fibers. Kupffer cells and pit cells were not seen inside the sinusoid. All these features of the sinusoids in HCC resembled the morphological characteristics of the capillary. The present study has revealed that HCC possesses sinusoid structures distinct from those of HA. This suggests that HCC may not derive directly from HA but may develop newly within the HA.