8-OHDG AND A CARCINOGENIC CHOLINE-DEFICIENT DIET

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We have used a model of liver carcinogenesis based on feeding rats a choline deficient (CD) diet, either as an initiator or as a promoter. The method causes the appearance of cirrhosis, and since in humans 60-90% of hepatocarcinomas develop in cirrhotic livers, it may allow is to scrutinize whether there are common mechanism(s) involved in both processes. Consistent with the long-term goal of our investigations, i.e., to elucidate the mechanism(s) of liver carcinogenesis under conditions in which there is concomitant fibrosis, what have found that F344 rats given a CD diet for 24 wks show the expected formation of preneoplastic foci and in addition, an accumulation of 8- hydroxydeoxyguanosine (8-OHdG). This DNA adduct, generated by reactive oxygen species, is normally low in the liver of rats given sufficient choline. The appropriate treatment time at which it should be measured in treated animals, however, is not known. Hence, it will become imperative to evaluate the 8-OHdG content at various time of feeding the CD diet. We have fond also the F344 and both sexes of the PVG strain of rats are resistant to the development of preneoplastic markers, to cirrhosis and to changes in the values of 8-OHdG. our hypothesis is that the CD diet induces increased levels of oxygen free radical and oxidative damage, with accumulation of 8-OHdG. This, if not repaired, prompts DNA mutations and/or deletions. Along with the DNA alterations, oxidative changes result in cellular toxicity and necrosis, followed by cell proliferation and fibrosis. To support this thesis, the effect of antioxidants on 8-OhdG will be determined together with number and size of foci and of the liver fibrosis. We will measure, as well, the values of serum alanine aminotransferase and the existence of PCNA/Cycline in rat liver tissues. By estimating toxicity and cell replication in this manner, and in conjunction with the preceding variables, we will attempt to explain if toxicity and levels of 8-OHdG are coupled or separable. The identification of CD resistant strain of rats will provide the opportunity to investigate if there is a genetic basis for the phenomena observed. Consequently, we propose to do a genetic analysis in crosses of susceptible (F344) and resistant (PVG) strains. The identification of specific loci for preneoplasia will be don using the amounts of 8-OHdG and positive foci. Future experiments, if our assumptions are correct, will strive to map the change, most likely utilizing molecular biology techniques. These studies will furnish new evidence for the participation of reactive oxygen free radicals in the process of cirrhosis and initiation/promotion during rat liver hepatocarcinogenesis.