Gamma-Glutamyl Transpeptidase: A Positive Marker for Cultured Rat Liver Cells Derived From Putative Premalignant and Malignant Lesions2

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Abstract
The utility of γ-glutamyl transpeptldase (γ-GT) as a positive in vitro marker for isolated hepatocytes derived from chemical carclnogen-induced presumptive premalignant and malignant hepatocyte lesions was assessed. The distribution of γ-GT activity in vitro was analyzed by histochemical techniques in acetone-fixed primary liver cell cultures and smear preparations derived from normal and carcinogen-treated adult F344 rats. High levels of γ-GT activity were located in hepatocytes derived from macroscopic, chemical carcinogen-induced hepatocyte lesions at every stage of hepatocarcinogenesis tested. Hepatocytes derived from “normal-looking” liver surrounding carcinogen-induced, macroscopic “early” lesions were γ-GT-negative. γ-GT activity in vitro was often localized as spots or bands in hepatocytes, and γ-GT-positive bile duct cells were easily discerned. After continuous exposure of rats to 2-acetylaminofluorene or to diethylnitrosamine (DEN), γ-GT-positive hepatocytes appeared in vitro only when derived from livers containing γ-GT-positive microscopic or macroscopic lesions. With cells isolated from early lesions, the relative proportions of γ-GT-positive hepatocytes were greater when the cells were derived specifically from individual lesions rather than from “total liver” and were observed to increase in total liver isolates when the lesions increased in size. “Grey-white” hyperplastic nodules yielded primary cultures containing 29.0–44.0% γ-GT-positive hepatocytes, with no selective attachment of γ-GT-positive hepatocytes to the cell culture vessels. No γ-GT-positive hepatocytes were observed in primary cultures derived from 1) normal, adult male or female F344 rats, 2) rats subjected to two-thirds partial hepatectomy at various intervals prior to cell culture, or 3) rats subjected to acute doses of DEN or dimethylnitrosamine. γ-GT activity could not be induced in cultured, normal hepatocytes by exposure to various chemical carcinogens in vitro. No γ-GT-positlve proliferating cells could be isolated from any of the stages of hepatocarcinogenesls investigated, except obvious hepatocellular carcinoma.