Sequential functional and morphological alterations during hepatocarcinogenesis induced in rats by feeding of a low dose of 2-acetylaminofluorene.
The early cellular events in liver carcinogenesis were studied in Fischer-344 male rats that either were fed 200 ppm 2-acetylaminofluorene (AAF) for up to 10 wk or were fed the carcinogen for 8 wk followed by maintenance for an additional 24 wk. By 1 wk of exposure, AAF caused a reduction in the number of glutamine synthetase (GS)-positive centrilobular hepatocytes, an increase in DNA synthesizing hepatocytes in the central areas of the hepatic lobules, and a shift from multinucleated to mononucleated hepatocytes, although overt hepatocellular necrosis was not evident. By 3 wk, altered hepatocellular foci characterized by deficiencies in iron storage (IS-) and collagen production and by expression of gamma-glutamyl transferase (GGT+) and placental-type glutathione transferase (PGT+) activity appeared. Single PGT+ cells were also found. During continued exposure, foci increased in number, size, and total area with the increases escalating between 8 and 10 wk of exposure. Cessation of AAF exposure at 8 wk resulted in a slight decrease in the number of foci after a further 6 wk of maintenance, but with continued maintenance for another 6 and 12 wk, the number again increased. IS- characterized the majority of foci during carcinogen administration, whereas after cessation of exposure, GGT+ and PGT+ foci predominated. None of the foci were positive for GS. After AAF exposure for 10 wk, a few neoplasms developed and greater numbers occurred after maintenance for a further 24 wk of rats exposed for 8 wk. We conclude the following: (a) the low dose of AAF caused subtle alterations in function and proliferation of normal hepatocytes and converted hepatocytes into focus cells; (b) reduction of the GS+ area is a sensitive indicator of cytotoxicity of AAF; (c) the development of some foci at an early stage depends on a promoting action of AAF, which ceased when the carcinogen was withdrawn, allowing some foci to undergo reversion; (d) a strong linkage exists in expression of IS-, GGT+, and PGT+ in foci; (e) the carcinogenic process accelerates in the absence of any indication of increased cytotoxicity by AAF; and (f) under the conditions of this study, no GS+ foci, adenomas, and carcinomas were found, indicating that no carcinogen-induced expression of GS occurred in these lesions and that GS expression is not linked to other phenotypic abnormalities.
Stenbäck
F
F
Department of Pathology, University of Oulu, Finland.
Gebhardt
R
R
Sirma
H
H
Garbay
J M
JM
Williams
G M
GM
D015073:2-Acetylaminofluorene / Q000633:toxicity*; D000284:Administration, Oral; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D005974:Glutamate-Ammonia Ligase / Q000032:analysis; D005982:Glutathione Transferase / Q000032:analysis; D007124:Immunoenzyme Techniques; D007501:Iron / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D005723:gamma-Glutamyltransferase / Q000032:analysis
D015073:2-Acetylaminofluorene; D007501:Iron; D005723:gamma-Glutamyltransferase; D005982:Glutathione Transferase; D005974:Glutamate-Ammonia Ligase