Vibratome technique revealed initial carcinogenic changes that induce GST-P+ single hepatocytes and minifoci in rat liver

The drastic initial carcinogenic changes that induce single hepatocytes and minifoci positive for GST-P (a specific biomarker of foci and nodules) identified previously in rat livers (K. Satoh, Life Sci. 2018) require elucidation. Notably, after animals were administered benzyl isothiocyanate (BITC, anti-cancer phytochemical, 0.5% by wt) in their basal diet, immunocytochemical staining of vibratome-prepared liver specimens for GST-P revealed that the canalicular networks and bile ducts of the animal livers were heavily and finely stained for GST-P even though the biomarker is a cytosolic enzyme. In addition, the mean diameter of the canaliculi was greatly enlarged. The results thus indicate that GST-P was rapidly synthesized in all hepatocytes but rapidly excreted into bile. Similar results were obtained with animals administered dietary AAF carcinogen (0.04%). The biliary excretion of GST-P was detectable not only in all hepatocytes but also within minifoci, foci and nodules. A new initiation model was therefore proposed assuming that GST-P+ single hepatocytes are formed after injury to canaliculi by carcinogens to decrease the excretion of GST-P from hepatocytes. The key findings from this study and the biomarker analysis using a vibratome technique might help elucidate the ‘unknowable’ mechanism of cancer initiation in rat chemical carcinogenesis.