Retinoids inhibit mammalian glutathione transferases

Affinity-purified cytosolic glutathione transferases from adult female rat liver, adult human liver and human term placenta were used. Of the 8 retinoids tested, all-trans retinoic acid was found to be the most potent inhibitor of placental glutathione transferase. The inhibition was non-competitive and exhibited Ki values of 20 and 41 μM for all-trans retinoic acid in the presence of varying concentrations of 1-chloro-2,4-dinitrobenzene and glutathione, respectively. Micromolar all-trans retinoic acid also caused significant (30–90%) inhibition of rat and human liver glutathione transferases. Taken together, the data suggest that inhibition of glutathione transferase(s) may represent yet another mechanism of retinoid action.