Ultrastructural and immunocytochemical characterization of the cellular phenotype in primary adenoid liver tumours of the rat

Electron microscopic alterations in intermediate hepatocyte-like cells in children with chronic hepatitis B: the first report in pediatric patients

OBJECTIVE

The study objective was an in-depth ultrastructural analysis of intermediate hepatocyte-like cells (IHCs), constituting a subpopulation of liver progenitor/oval cells, in children with chronic hepatitis B viral (HBV) infection.

METHODS

Ultrastructural investigations were conducted on liver biopsy material, fixed in a solution of 2.5% glutaraldehyde, 2% paraformaldehyde, and 0.1 mol/l cacodylate buffer, obtained from 40 children, aged 3-16 years, with chronic hepatitis B.

RESULTS

Transmission-electron microscopic analysis of liver progenitor/oval cells showed, apart from a morphologically unchanged population of oval cells, the presence of IHCs displaying variously pronounced ultrastructural changes, including degeneration. Interesting was that damaged IHCs were mainly observed in patients with a coexisting advanced liver fibrosis, where they frequently adhered to bundles of collagen fibers. Submicroscopic abnormalities in these cells referred mainly to mitochondria and granular endoplasmic reticulum. The most pronounced mitochondrial alterations observed in degenerating IHCs in the course of chronic HBV infection were characterized by distinct swelling, loss of mitochondrial crests, and the presence of myelin structures within the matrix. In granular endoplasmic reticulum, shortening and segmental degranulation of the reticulum were observed. The above changes were accompanied by the appearance of primitive phagosome-like structures with absorbed biliary pigment. In the vicinity of altered IHCs, transitional hepatic stellate cells could be found.

CONCLUSION

Our study seems to suggest that chronic HBV infection, lasting from childhood and coexisting with intensive fibrosis may, with the involvement of other carcinogenic factors, promote degenerating IHCs towards neoplastic transformation in adulthood.

Rapid induction of preneoplastic liver foci in embryonal turkey liver by diethylnitrosamine

Diethylnitrosamine (DEN) was injected into fertilized turkey eggs. After incubation for 24 days, the livers of the embryos were removed and investigated by means of histological and enzyme-histochemical methods. Doses of 2 and 5 mg DEN per egg had no effect on mortality and embryo weight but induced various types of foci of altered hepatocytes. In addition, a replacement of the trabecular structure of the liver by a tubular arrangement of the hepatocytes and markedly enlarged hepatocytes were found. The diethylnitrosamine-induced foci of altered hepatocytes were very similar to the preneoplastic lesions that occur in the liver of mammals during hepatocarcinogenesis and are regarded as early indicators of carcinogenicity. The presented in ovo model is a simple (1 dose), rapid (24 days), and inexpensive (no animal housing) approach for the induction of foci of altered hepatocytes. The sensitivity of this carcinogenesis bioassay appears to be comparable to that of lifetime studies in rodents. It is proposed that the induction of preneoplastic foci of altered hepatocytes in ovo is a valuable screening model for hepatocarcinogenic effects.

The stem cells of the liver ? a selective review

The current status of the much-debated question of the still-hypothetical stem cells of the liver is reviewed, with an emphasis on their role in hepatocarcinogenesis. The widely held view of the primacy of the hepatocyte, notably of the mononuclear diploid type, in this process--the "hepatocytic theory"--has been compared with variants of the "stem cell hypothesis" based on the "non-parenchymal epithelial cells" of the liver--the "oval" or biliary ductular cells, the "nondescript periductular" cells and the "primitive" bipotential epithelial cells. An attempt has been made to concentrate mainly on the more recent publications, in an effort to balance the conflicting opinions expressed by comparing results obtained by the newer procedures currently in use. Despite some interesting and relevant findings it appears that the evidence in favour of the stem-cell hypothesis is still circumstantial and that the hepatocytic theory has not been invalidated. Presumably the question of the hepatic stem cells will be answered when the riddle of hepatocarcinogenesis has been solved.