Flow microfluorometric identification of liver cells with elevated gamma-glutamyltranspeptidase activity after carcinogen exposure.

We have developed a fluorometric cytochemical assay for gamma-glutamyltranspeptidase (gamma-GT) using the substrate gamma-glutamyl-4-methoxy-2-naphthylamide in which the released methoxynaphthylamine was coupled with 5-nitrosalicylaldehyde to form a yellow fluorescent crystalline product within the cells. Single cell suspensions were obtained by collagenase perfusion of livers from rats that had either received a two-thirds partial hepatectomy followed 24 hr later by a single injection of diethylnitrosamine (DEN) or received a partial hepatectomy alone. Cultured HTC cells were used as a source of gamma-GT+ cells. Fluorescence (gamma-GT activity) was low in most of the cells from both DEN-exposed and control rats, but high in HTC cells. The livers of both DEN-exposed and control rats had a subpopulation of cells that were gamma-GT+; this population could be quantitated and sorted by flow cytometry. Five weeks post injection the number of GT+ cells from the rats exposed to DEN was more than 20 times that from the control rats. Increased gamma-GT activity may be a useful cytochemical marker for preneoplastic liver cells.