Glutathione S-transferases in human and rodent skin: multiple forms and species-specific expression

The glutathione S-transferases (GST) are a family of widely distributed multifunctional detoxification enzymes that catalyze the reaction between reduced glutathione and a variety of electrophiles. Of interest is the fact that several extracutaneous tissues exhibit a distinct spectrum of isozymes that are expressed in a highly controlled fashion. Despite the fact that the skin is continuously exposed to numerous injurious agents, little is known about the expression of GST isozymes and their role in metabolism of physiologic and xenobiotic substrates in cutaneous tissue. Using specific polyclonal antibodies to the Alpha, Mu, and Pi classes of GST, we identified their expression in rat, mouse, and human skin cytosol. In each species, GST isozymes expressed activities towards 1-chloro-2,4-dinitrobenzene, benzo(a)pyrene 4,5-oxide, styrene 7,8-oxide, leukotriene A₄, and ethacrynic acid, but not towards bromosulfophthalein and cumene hydroperoxide. Western blot analysis indicated the predominant expression of Pi isozyme in all three species. Alpha class of isozyme(s) was present only in human skin, whereas Mu class of isozyme(s) was detected only in rat and mouse skin. Similarly, in normal and transformed cultured human keratinocytes Pi was the predominant isozyme. In situ localization studies using immunohistochemical techniques confirmed the observations of Western blotting. In mouse skin, Pi and Mu isozyme(s) were found to be predominantly localized in sebaceous glands, whereas no reactivity was observed with the Alpha class of isozymes. Our data show that multiple forms of GST exist in rodent and human skin and that GST Pi is the predominant isozyme in each species. Furthermore, cutaneous GST can metabolize both endogenous substrates and foreign compounds.