Histogenesis and the role of p53 and K-ras mutations in hepatocarcinogenesis by glyceryl trinitrate (nitroglycerin) in male F344 rats.

Glyceryl trinitrate (GTN) was previously reported to induce hepatocellular carcinoma (HCC) in rats after prolonged feeding. The present experiments were undertaken to evaluate the histogenesis and molecular biology of these tumors and the possible role of nitric oxide (NO), a GTN metabolite, in their development. Male F344 rats received a single i.g. intubation of GTN (1.2 g/kg) at 6 weeks of age and/or a diet containing 1% GTN from 8 weeks of age until necropsy, i.e. for up to 78 weeks. Some animals were subjected to 2/3 partial hepatectomy (PH) at 9 weeks of age. Five sequential sacrifices (14, 32, 52, 78 and 84 weeks of age) were performed. No liver tumors developed in control rats or in rats that received GTN only by a single i.g. intubation, even when intubation was followed by PH. Preneoplastic foci, mainly of clear cell and mixed cell type (identified as positive for glutathione S-transferase placental form) were found from 14 weeks of age in rats receiving GTN in the diet. Focal eosinophilic areas (atypical foci) composed of atypical hepatocytes that often extended into the veins were observed beginning at 52 weeks of age. Some mixed hepatocholangiocellular adenomas and carcinomas arose in eosinophilic lesions. HCCs were seen beginning at 78 weeks of age, but only in rats receiving dietary GTN. Incidence of HCC in the latter animals was 50-75%. Most HCCs were well differentiated. The carcinogenic effect of GTN given in the diet was not affected by prior intubation of a large single dose followed by PH. No p53 mutations were found in 18 tumors but K-ras point mutations, all within codon 12, were found in 8/18 tumors, mostly those with cholangiocellular elements. These were first or second position G-->T transversions or second position G-->A transitions. While these mutation types have also been commonly seen in bacteria after NO-related DNA damage, the fact that tumors arose only on prolonged feeding of this potently bioactive agent at massive doses seems consistent with a more complex mechanism involving multiple (i.e. genetic and/or epigenetic) factors in carcinogenesis by GTN.