INDUCTION OF 3 HISTOCHEMICALLY DISTINCT POPULATIONS OF HEPATIC FOCI IN C57BL 6J MICE/

Although expression of the enzyme gamma-glutamyl transpeptidase (GGT) is the most common phenotypic marker of preneoplastic foci in the live rs of carcinogen-treated rats, it is not generally expressed in mouse liver tumors or hepatic foci. However, several carcinogens, including safrole and ortho-azoaminotoluene (OAT), have been reported to induce GGT-positive foci in mice. We asked whether safrole and OAT induce GGT expression in preneoplastic foci or if these compounds select for a d istinct set of lesions that can be identified by their GGT-positive ph enotype. We treated 12-day-old male and female C57BL/6J mice with NN-d iethylnitrosamine (DEN) (0.20 mumol/g body wt) to initiate hepatocarci nogenesis. From 6 to 24 weeks of age, during the promotion phase of he patocarcinogenesis, groups of mice were treated with 3,4,5,3',4',5'-he xabromobiphenyl (HBB), safrole or OAT. Additional groups of female mic e were ovariectomized at 6 weeks of age with or without subsequent chr onic treatment with testosterone. All the animals were killed at 24 we eks of age and serial liver sections were stained for glucose-6-phosph atase (G6Pase) or GGT. Both testosterone and HBB were strong promoters of the development of G6Pase-deficient foci. No GGT-positive foci wer e observed in animals treated with these agents or with DEN alone. In mice fed safrole or OAT during the promotion period, female mice devel oped more G6Pase-deficient foci than male mice, and GGT-positive foci were observed. Analysis of serial sections revealed that the G6Pase-de ficient foci and the GGT-positive foci were independent populations. T he relative number of these two classes of foci varied according to th e treatment regimen. In females fed safrole, 7% of the foci in the liv er were GGT-positive while in female mice fed OAT, 45% were GGT-positi ve. In all groups of mice in which we observed GGT-positive foci and i n ovariectomized female mice, we noted a third independent population of foci which demonstrated significantly increased expression of G6Pas e relative to surrounding normal liver. These data indicate that diffe rent treatments during the promotion stage of hepatocarcinogenesis in the mouse may give rise to distinct populations of preneoplastic lesio ns. Further studies of the molecular events giving rise to these disti nct lesions will provide insights into the multiple pathways that resu lt in hepatocarcinogenesis.