Effect of nodularin on the expression of glutathione S-transferase placental form and proliferating cell nuclear antigen in N-nitrosodiethylamine initiated hepatocarcinogenesis in the male Fischer 344 rat

The tumor-promoting effect of nodularin during carcinogenesis was investiga ted, Male Fischer 344 rats were injected with nodularin for 10 weeks from w eek 3 after N-nitrosodiethylamine initiation without partial hepatectomy. R ats were further maintained for 10 weeks after the cessation of nodularin a nd were periodically killed, In contrast to the minimal foci in the DEN and nodularin alone groups, treatment with DEN and nodularin produced four kin ds of nodules with eosinophilic, clear, mixed and basophilic cells, After t he cessation of nodularin, the maximally increased number, but not the area , of glutathione S-transferase placental form-positive [GST-P(+)] nodules a t week 12 decreased significantly and the appearance of two types of hyperp lastic nodules was noted by GST-P immunostaining; homogeneously stained den se nodules (DN) and heterogeneously stained pale nodules (PN), which appear ed only after the cessation of nodularin, DN were well circumscribed by enz yme-altered cells, as opposed to poorly in PN, Moreover, normal-appearing h epatocytes replaced the enzyme-altered cells in PN, In contrast to the high er PCNA index in GST-P(+) DN, the background level returned to that of the control at week 15, PCNA indices in DN were significantly higher than in PN , which were still higher than the control, indicating that nodularin affec ted the PCNA index differentially in the altered and unaltered hepatocytes. However, nodularin without DEN initiation significantly increased the PCNA index through initial cell death and subsequent hepatocyte proliferation, These results suggest that: (i) nodularin has a promoting effect by inducin g hepatocyte proliferation in both enzyme-altered hyperplastic nodules and the surrounding parenchyma; (ii) proliferation is transient in background c ells but not in enzyme-altered hepatocytes; (iii) GST-P(+) DN can be regard ed as progressive and GST-P(+) PN as regressive, revealed by both immunohis tochemistry and PCNA index.