Immunohistochemical detection of tumour-associated aldehyde dehydrogenase in formalin-fixed rat and mouse normal liver and hepatomas.

This communication describes a method and results for the immunohistochemical detection of a tumour-associated isoenzyme of aldehyde dehydrogenase (BALDH). The method is a substantial improvement over standard histochemical detection methods which require either frozen or mildly fixed tissues, since BALDH expression was detected in the cells of formalin-fixed paraffin-embedded liver tissues of both mice and rats. Using the immunohistochemical method, we detected BALDH expression diethylnitrosamine-induced hepatomas in the male Sprague-Dawley rat and in male B6C3F1 mouse hepatomas induced with either diethylnitrosamine, ethylnitrosourea or dichloroacetic acid. BALDH was also detected in three hepatoma cell culture lines which express different levels of BALDH. These results were compared to results with normal liver and hepatoma sections from the same animals and the three cell culture lines using a standard histochemical method to detect BALDH. In nearly all these tissue sections and cell cultures, expression of BALDH was detected in identical sites with either method. The diethylnitrosamine and dichloroacetic acid induction of the BALDH isozyme, as reported here, has not been reported previously and further substantiates the use of BALDH as a histochemical marker for mouse hepatocarcinogenesis. Given the few reliable histochemical markers for mouse hepatocarcinogenesis, the immunohistochemical method will be useful for further validation of BALDH as a histochemical marker for this species. Thus, BALDH expression could be detected in any number of carcinogen-induced lesions such as altered foci, nodule or hepatomas, from archived, formalin-fixed tissues of past mouse carcinogenesis studies which were based on a variety of mouse strains, carcinogens and induction protocols.