Polymorphism in the glutathione conjugation activity of human erythrocytes towards ethylene dibromide and 1,2-epoxy-3-( p-nitrophenoxy)-propane

Abstract

In this study a polymorphism in the conjugating activity of human erythrocyte cytosol towards the dihaloethane, ethylene dibromide (EDB; 1,2-dibromoethane) was found. Two out of 12 human erythrocyte cytosols did not catalyze the formation of glutathione (GSH) conjugates of [1,2- 14C]EDB. Ten cytosols formed the S,S′-ethylenebis(GSH) conjugate at a rate ranging from 0.5 to 3.2 (mean 1.76±0.95) pmol min −1 (mg protein) −1. The activity of the cytosols towards EDB was compared with the activity towards 1,2-epoxy-3-( p-nitrophenox3,)-propane (EPNP) and 1-chloro-2,4-dinitrobenzene (CDNB). The GSH conjugates formed from EDB, EPNP and CDNB were all quantified by HPLC. Every cytosol was active with the classical GST substrate CDNB (2.04 ± 0.74 nmol min −1 (mg protein) −1). The two samples not showing any detectable activity towards EDB were also inactive towards EPNP: The activity towards EDB correlated significantly with EPNP ( r s = 0.90, P < 0.005; Spearman's rank correlation), but not with CDNB ( r s = 0.36, P > 0.10). In the incubations with EPNP, the alpha-, mu-, and pi- class glutathione S-transferase (GST) inhibitor S-hexyl(GSH) was included, indicating that the class-theta GST is the principal GST class conjugating EDB in erythrocyte cytosol. The apparent polymorphism of GST-theta which has recently been recognized to be crucial for several mono- and dihalomethanes, will thus also have considerable implications for the risk asscssment of EDB.