Localization of glutathione S-transferases alpha and pi in human embryonic tissues at 8 weeks gestational age.

Glutathione S-transferases (GST) are a family of enzymes involved in the detoxification of xenobiotics. In humans, GST are divided into four different classes, alpha, mu, pi and theta, with partly overlapping substrate specificity and a tissue-specific expression pattern. We studied the cellular distribution of GST alpha and pi in a variety of human embryonic organs obtained from an extra-uterine monozygotic twin pregnancy at 8 weeks' gestational age. Tissues were fixed in 4% paraformaldehyde and embedded in paraffin. Three 4 microm thick sections were used, one for routine haematein and eosin staining, the others for immunohistochemical determination using monoclonal and polyclonal antibodies against GST alpha and pi, respectively. Both GST alpha and pi were present in hepatocytes, gastrointestinal epithelium, adrenal gland medulla, and tela chorioidea in the telencephalon. GST pi, but not alpha, was found in the epithelium of pancreatic and pulmonary glands, trachea, nephrons and urinary collecting ducts, as well as in the pia mater of the telencephalon and in developing nerve tissue in the gastrointestinal muscularis mucosae. In summary, we have demonstrated that immunoreactive protein for both GST alpha and pi is expressed in the human embryo at 8 weeks' gestational age. The early expression of GST alpha and pi in the epithelia of the urinary and digestive tracts and the respiratory system supports the importance of GST in the detoxification of potentially toxic or carcinogenic compounds. Our results suggest that the embryo itself is capable of detoxifying noxious compounds that are generated intracellularly or that cross the trophoblastic tissue.