The Cruciferous Nitrile, Crambene, Induces Rat Hepatic and Pancreatic GlutathioneS-Transferases

Abstract

Indoles and isothiocyanates found in cruciferous vegetables have been implicated as chemopreventive agents against carcinogenesis. The bioactivities of chemically related cruciferous nitriles, including 1-cyano-2-hydroxy-3-butene (crambene), however, have not been thoroughly evaluated. Crambene causes a prolonged elevation of rat hepatic and pancreatic glutathione and induces the GSH S-transferases (GSTs). Because elevated GST activity against the model substrate chlorodinitrobenzene does not reflect individual isoenzyme induction, quantitative HPLC evaluation of specific GST subunits is necessary to fully assess the range of GST isoenzymes induced by crambene. Accordingly, male Fischer 344 rats were given, via esophageal intubation, either 100 (Experiment 1) or 50 mg crambene/kg body wt (Experiment 2) once daily for 7 days. GSTs were extracted from hepatic cytosol by affinity chromatography, and the individual subunits that comprise the various isoenzymes were quantified by reverse-phase HPLC to gain an estimate of induction. In addition, pancreatic GST subunits were assessed in the low-dose experiment. In parallel with increased GST activity, crambene caused a generalized induction of GST subunits in both liver and pancreas, but the pattern of subunit induction was tissue dependent. In the liver, alpha subunits 1 and 2 and the mu subunit 3 were induced approximately 2-fold, while the mu subunit 4 was induced only 1.5-fold. In the pancreas, the alpha subunit 2 was induced to a much larger extent (2.6-fold) than the other subunits (from no induction to 1.6 fold). These results suggests that crambene-mediated GST induction mechanisms vary from tissue to tissue. Potential chemoprevention provided by crambene against GST-metabolized carcinogens or toxins may differ between liver and pancreas because of differences in the degree and pattern of induction.