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 hepatocell ular carcinoma (HCC) in rats after prolonged feeding, The present expe riments were undertaken to evaluate the histogenesis and molecular bio logy 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 contai ning 1% GTN from 8 weeks of age until necropsy, i.e. for up to 78 week s, Some animals were subjected to 2/3 partial hepatectomy (PH) at 9 we eks 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 int ubation was followed by PH, Preneoplastic foci, mainly of clear cell a nd mixed cell type (identified as positive for glutathione S-transfera se placental form) were found from 14 weeks of age in rats receiving G TN in the diet, Focal eosinophilic areas (atypical foci) composed of a typical hepatocytes that often extended into the veins were observed b eginning at 52 weeks of age, Some mixed hepatocholangiocellular adenom as and carcinomas arose in eosinophilic lesions, HCCs were seen beginn ing at 78 weeks of age, but only in rats receiving dietary GTN, Incide nce of HCC in the latter animals was 50-75%, Most HCCs were well diffe rentiated, The carcinogenic effect of GTN given in the diet was not af fected by prior intubation of a large single dose followed by PH, No p 53 mutations were found in 18 tumors but K-ras point mutations, all wi thin codon 12, were found in 8/18 tumors, mostly those with cholangioc ellular elements, These were first or second position G-->T transversi ons or second position G-->A transitions, While these mutation types h ave also been commonly seen in bacteria after NO-related DNA damage, t he fact that tumors arose only on prolonged feeding of this potently b ioactive agent at massive doses seems consistent with a more complex m echanism involving multiple (i.e. genetic and/or epigenetic) factors i n carcinogenesis by GTN.