Serial magnetic resonance imaging (MRI) was used to evaluate the influences of dietary
deoxycholic acid (DCA) on the rate of progression of chemically induced hepatocellular
neoplasms in rats. Male Fischer-344 rats with established persistent hepatocellular nodules generated by the Solt-Farber protocol were exposed to dietary DCA (0.3%) between 6 and 12 mo of age. Growth of nodules and
carcinomas in vivo was measured by morphometric quantification of
tumor images obtained every 6 wk. The final stages of neoplastic progression were determined by terminal histopathological examination and by expression and functional evaluation of
glutathione S-transferase (GST)
isoenzyme phenotypes. Dietary DCA increased the number of hepatocellular
neoplasms per rat, accelerated the rate of growth of persistent nodules, and increased the histological progression of liver
tumors. Expression of immunoreactive GST subunits Yf, Ya, and Yb1 was induced in early persistent nodules, a pattern that was maintained throughout the study in both basal diet and DCA-fed groups. However, 5% of early nodules and about 75% of advanced
neoplasms were partially or completely deficient in GST Yb2 expression in both groups. DCA did not alter the cytosolic activity for the GST substrates
1-chloro-2,4-dinitrobenzene (CDNB) or
trans-4-phenyl-3-buten-2-one (tPBO) in
tumors or surrounding liver. However, in both groups, CDNB activity was increased in the
tumors relative to the surrounding nonneoplastic tissue, whereas activity for tPBO, a substrate more specific for the Yb2 subunit, was reduced in the
tumors. All advanced
neoplasms were similarly more resistant than surrounding liver to
DNA-binding metabolites of
aflatoxin B1 or
benzo[a]pyrene. These data demonstrate that DCA can increase the progression of established hepatocellular nodules to larger, more advanced
neoplasms but does not preferentially select for a specific GST phenotype. Preferential loss of constitutively expressed GST Yb2 in both basal diet and DCA-fed groups may be an important aspect of progression from resistant nodules to advanced
cancers in this model. These studies also demonstrate that serial MRI is a useful tool for measuring the rates of enlargement and patterns of growth in established hepatocellular
neoplasms.