Shivendra V. Singh

Specificities of murine glutathione (GSH) S-transferase (GST) isozymes mGSTA1-1, mGSTA2-2, mGSTA3-3 and mGSTA4-4 (α class), mGSTP1-1 (π class) and mGSTM1-1 (μ class) for GSH conjugation of (–)-anti- and (+)-syn-stereoisomers of benzo[g]chrysene 11,12-diol 13,14-epoxide (B[g]CDE), the activated metabolites of the environmental pollutant benzo[g]chrysene (B[g]C), have been determined. When GST activity was determined as a function of varying (–)-anti- or (+)-syn-B[g]CDE concentration (10–320 μM) at a fixed saturating concentration of GSH (2 mM), each isozyme obeyed Michaelis–Menten kinetics. mGSTA1-1 was significantly more efficient than other murine GSTs in the GSH conjugation of not only (–)-anti-stereoisomer but also (+)-syn-B[g]CDE. For example, the catalytic efficiency (k_cat/K_m) of mGSTA1-1 towards (–)-anti-B[g]CDE was ~2.3- to 16.6-fold higher compared with other murine GSTs. Likewise, mGSTA1-1 was ~2.7-, 6.7-, 4.4- and 12.4-fold more efficient than mGSTA2-2, mGSTA3-3, mGSTP1-1 and mGSTM1-1, respectively, in catalyzing the GSH conjugation of (+)-syn-B[g]CDE. Interestingly, mGSTA4-4, which also belongs to class α, was virtually inactive towards both stereoisomers of B[g]CDE. The results of the present study indicate that murine GSTs, especially α class isozymes, significantly differ in their ability to detoxify B[g]CDE stereoisomers and that mGSTA1-1 plays a major role in the detoxification of both (–)-anti- and (+)-syn-B[g]CDE, which among four B[g]CDE stereoisomers are formed from the carcinogen B[g]C as major DNA binding metabolites.

The present study reports gender related differences in ATP‐dependent transport of dinitrophenyl‐glutathione (GSH) conjugate (DNP‐SG), a model GSH xenobiotic conjugate, across murine canalicular liver plasma membrane (cLPM). ATP‐dependent transport of DNP‐SG across female A/J mouse cLPM was mediated by two components, a high‐affinity and a low‐affinity component, with corresponding K _m of 18 μM (V _max 0.02 nmol/min·mg) and 500 μM (V _max 0.23 nmol/min·mg), respectively. On the other hand, only one component for the ATP‐dependent transport of DNP‐SG was observed in male mouse cLPM (K _m 130 μM; V _max 0.18 nmol/min·mg). Moreover, the rate of ATP‐dependent transport of DNP‐SG was markedly higher in the cLPM fraction of male mouse compared with that of the female. Presence of two transport components in female mouse cLPM, but only one system in the cLPM fraction of male mouse, was confirmed by measuring DNP‐SG mediated stimulation of ATP hydrolysis (DNP‐SG ATPase activity). To the best of our knowledge, the present study is the first report on gender related differences in ATP‐dependent murine canalicular transport of GSH conjugates.

There is a growing need for short‐term and cost‐effective bioassay to assess the efficacy of potential chemo‐preventive agents. We report that the induction of glutathione (GSH) S‐transferase π (mGSTP1‐1) by a chemo‐preventive agent can be used as a reliable marker to assess its efficacy in retarding chemical carcinogenesis induced by benzo(a)pyrene (BP), which is a widespread environmental pollutant and believed to be a risk factor in human chemical carcinogenesis. This conclusion is based on 1) the relative contribution of mGSTP1‐1 of the liver and forestomach of female A/J mice in the detoxification of the ultimate carcinogenic metabolite of BP, (+)‐anti‐7,8‐dihydroxy‐9,10‐oxy‐7,8,9,10‐ tetrahydrobenzo(a)pyrene [(+)‐anti‐BPDE]; and 2) a positive correlation between the induction of hepatic and forestomach mGSTP1‐1 by 5 naturally occurring organosulfides (OSCs) from garlic (diallyl sulfide, diallyl disulfide, diallyl trisulfide, dipropyl sulfide and dipropyl disulfide) and their effectiveness in preventing BP‐induced forestomach neoplasia in mice. In the liver, the combined contribution of other GSTs in the detoxification of (+)‐anti‐BPDE was far less than the contribution of mGSTP1‐1 alone. Likewise, in the forestomach, the contribution of mGSTP1‐1 far exceeded the combined contribution of other GSTs. Studies on the effects of OSCs against BP‐induced forestomach neoplasia revealed a good correlation between their chemo‐preventive efficacy and their ability to induce mGSTP1‐1 expression in the liver (r = −0.89; p < 0.05) as well as in the forestomach (r = −0.97; p < 0.05). Our results suggest that the induction of mGSTP1‐1 may be a reliable marker for evaluating the efficacy of potential inhibitors of BP‐induced cancer in a murine model. Int. J. Cancer 73:897–902, 1997.