DOSING-INDUCED STRESS CAUSES HEPATOCYTE APOPTOSIS IN RATS PRIMED BY THE RODENT NONGENOTOXIC HEPATOCARCINOGEN CYPROTERONE-ACETATE

It has been proposed that several nongenotorric compounds act as hepat ocarcinogens by suppressing the apoptosis that would normally act to r emove damaged or potentially initiated cells from the liver. During ou r investigations of this hypothesis using a widely applied protocol, w e have found that the stress induced by the process of gavage dosing c an induce massive apoptosis in livers uniquely primed by withdrawal of the hepatomitogen cyproterone acetate from the hyperplastic rat liver . This effect of gavage dosing was not seen in livers of naive animals . Apoptosis was measured by both in situ end labeling (ISEL) of the DN A damage associated with programmed cell death and conventional hemato xylin and eosin (H&E) staining of apoptotic morphology. Apoptotic rate s measured by H&E increased significantly from 0.005 +/- 0.010% on Day 11 to 0.657 +/- 0.315% of hepatocytes on Day 15, 4 days after cessati on of 10 days dosing with CPA (120 mg/kg). The readministration of CPA suppressed >89% of this Day 15 apoptosis. However, the readministrati on of vehicle alone (corn oil) caused a 390% increase in apoptosis to 2.56 +/- 1.31% of hepatocytes. Similar results were obtained using ISE L. Measurements of liver to body weight ratios and total DNA per liver reflected these changes in cell loss by apoptosis. In a second experi ment, CPA was administered for 10 days as before then animals were sub jected to readministration of CPA in corn oil, CPA in saline, corn oil , saline, or sham dosed. Again, apoptosis was dramatically suppressed by the readministration of CPA in either vehicle but was dramatically increased to around 2% of hepatocytes in all other groups, including t he sham dosed group. Data on food consumption provided no evidence for a reduction in food intake as a causative agent but rather pointed to a less efficient usage of food in the stressed animals, The ability o f stress to induce liver apoptosis should be borne in mind in the desi gn and interpretation of future toxicological studies aimed at underst anding the putative suppression of apoptosis by liver nongenotoxic car cinogens and other toxicants. (C) 1995 Academic Press, Inc.