Influence of erythrocyte glutathione S-transferase T1 on sister chromatid exchanges induced by diepoxybutane in cultured human lymphocytes.

Humans can be classified as either DEB-sensitive or DEB-resistant on the basis of the frequency of sister chromatid exchanges (SCEs) induced in whole-blood lymphocyte cultures by 1,2,3,4-diepoxybutane (DEB), an epoxide metabolite of 1,3-butadiene. Sensitivity to in vitro SCE induction by DEB has been explained by a deletion of the glutathione S-transferase T1 gene (GSTT1), resulting in a deficiency of erythrocytic GSTT1 activity among GSTT1 null homozygotes. To verify that the GSTT1 activity of erythrocytes is responsible for differential SCE induction by DEB, SCEs induced by a 48-h exposure to DEB (2 or 5 microM) were analyzed in whole-blood and isolated lymphocyte cultures of four GSTT1 positive and four GSTT1 null individuals. The mean frequency of SCEs/cell was about twice as high among the GSTT1 null donors as compared with the GSTT1 positive donors, at both 2 microM DEB (mean 53.1 versus 25.8) and 5 microM DEB (mean 74.4 versus 38.4) in whole-blood lymphocyte cultures. In isolated lymphocyte cultures, DEB induced higher SCE frequencies than in whole-blood cultures and there was essentially no difference between the response of the two GSTT1 genotypes (mean 68.3 for GSTT1+ and mean 69.2 for GSTT1- at 2 microM DEB and 85.0 and 92.7, respectively, at 5 microM DEB). The isolated lymphocyte cultures were also much more sensitive to the cytotoxic effect of DEB, observed as significantly decreased replication indices at both DEB concentrations and genotypes. The whole-blood lymphocyte cultures showed lower replication indices for the GSTT1 null subjects than for those having the GSTT1 gene at both concentrations of DEB. These results support the role of GSTT1 activity in erythrocytes as a major detoxification pathway for DEB.