Extensive oxidative DNA damageinhepatocytes oftransgenic mice withchronic active hepatitis destined todevelop hepatocellular carcinoma (1994)

Atransgenic mousestrain that expresses the hepatitis Bvirus (HBV)large envelope protein intheliver was usedtodetermine theextent ofoxidative DNA damagethat occurs during chronic HBV infection. Thismousestrain de- velops achronic necroinflammatory liver disease that mimics theinflammation, cellular hyperplasia, andincreased risk for cancer that isevident inhumanchronic active hepatitis. When perfused insitu withnitroblue tetrazolium, anindicator for superoxide formation, theliver oftransgenic micedisplayed intense formazan deposition inKupffer cells, indicating oxygen radical production, andS-phase hepatocytes werecommonly seenadjacent tothestained Kupffer cells. Similar changes were notobserved innontransgenic control livers. Todetermine whether these events wereassociated withoxidative DNA damage, genomic DNAfromthelivers oftransgenic miceand nontransgenic controls wasisolated andexamined for8-oxo- 2'-deoxyguanosine, anoxidatively modified adduct ofdeoxy- guanosine. Results showed asignificant, sustained accumula- tion insteady-state 8-oxo-2'-deoxyguanosine that started early inlife exdusively inthetransgenic miceandincreased pro- gressively withadvancing disease. Themostpronounced in- crease occurred inlivers exhibiting microscopic nodular hy- perplasia, adenomas, andhepatocellular carcinoma. Thus, HBV transgenic micewithchronic active hepatitis display greatly increased hepatic oxidative DNAdamage. Moreover, theDNA damageoccurs inthepresence ofheightened hepa- tocellular proliferation, increasing theprobability offixation of theattendant genetic andchromosomal abnormalities andthe development ofhepatocellular carcinoma. Chronic inflammatory diseases affect millions ofpeople world-wide andmaybeaprimary factor inthedevelopment ofuptoone-third ofallcancers (1). A major association between a persistent infection andcancerisevident in chronic active hepatitis Bvirus (HBV)infection (2). Epide- miological studies showthatincidence ofhepatocellular carcinoma (HCC)correlates strongly togeographical areas of endemic HBV infection (3). Furthermore, patients with chronic hepatitis havea muchhigher incidence ofliver cirrhosis andHCCthanindividuals notinfected withHBV (4). Also, HBV antigens inseraofpatients areassociated withHCC(5). Because thevirus infects >300million people throughout theworld, HBV hasbeendescribed assecond only totobacco asaknownhumancarcinogen (6). Despite theapparent epidemiological association of chronic active hepatitis infection andcancer, themechanisms involved arestill notentirely understood. Research hasbeen hampered duetothelonglatency period between theonset ofinfection andcancer development, andthelack ofsuitable animal models that mimicchronic active humanhepatitis. HBV doesnotcontain anyknownacutely transforming oncogenes, andonlyrarely dointegrated HBV sequences activate cellular protooncogenes (7-10). Incontrast, persis- tentinflammation associated withchronic active hepatitis canbeassociated withmutations intumorsuppressor genes (11)andextensive chromosomal abnormalities. Persistent HBVinfection often leads tocirrhosis that often precedes the appearance ofHCC(12). Thenecroinflammatory liver dis- easeseenduring HBVinfection isthought tobemediated by thehostimmuneresponse toviral antigens. Activated mac- rophages andother recruited leukocytes release powerful reactive oxygen species suchasHOONO(from NOandO-), HOCI,andH202atsites ofinfection, causing areas offocal necrosis andcompensatory cell division (13,14). These oxidants notonlykill target cells butmayalso overwhelm cellular antioxidant defenses ofneighboring cells, leading to damage ofimportant biomolecules, including DNA (15). We hypothesize that oxidative DNA damage maybean important underlying eventthatleads tocancerduring chronic active hepatitis andother persistent inflammatory diseases. Wetested this hypothesis using atransgenic mouse modelinwhichoverexpression oftheHBV large envelope protein causes anecroinflammatory liver disease that inex-