Role of GSTT1and GSTM1genotypes in determining individual sensitivity to sister chromatid exchange induction by diepoxybutane in cultured human lymphocytes

Abstract

The individual genotoxic response of cultured human lymphocytes to diepoxybutane (DEB), an epoxide metabolite of 1,3-butadiene, shows a bimodal distribution. Blood donors can be classified as either DEB-sensitive or DEB-resistant on the basis of the frequency of sister chromatid exchanges (SCEs) induced by DEB in whole-blood lymphocyte cultures. The genetic basis of this phenomenon has thusfar been unknown. To investigate if differences in the ability of individuals to detoxify DEB could explain the bimodal response, sister chromatid exchanges (SCEs) induced by a 48-h treatment with DEB (2 and 5 microM) were analyzed in whole-blood lymphocyte cultures of 20 human donors with known genotypes of two polymorphic glutathione S-transferases (GSTs), GSTT1 and GSTM1. Both polymorphisms include a homozygous null genotype lacking the respective GST gene and isozyme. The mean frequency of SCEs/cell was 1.6 times higher among GSTT1 null donors (n = 8) than GSTT1 positive donors (n = 12) at both 2 microM DEB (mean 67.3 versus 40.9) and 5 microM DEB (mean 123.2 versus 77.5), with no overlapping in DEB-induced individual SCE frequencies between the two genotypes. Thus, all DEB-sensitive individuals were of the GSTT1 null genotype, while all DEB-resistant persons had a detectable GSTT1 gene. A significant (P < 0.05) negative correlation (r = -0.65 at 5 microM, r = -0.56 at 2 microM) was obtained in the GSTT1 positive donors between DEB-induced individual SCE frequency and RBC GSTT1 activity, measured by formaldehyde formation from dichloromethane; the GSTT1 null individuals showed no GSTT1 activity. At 5 microM DEB, the lymphocyte cultures of the GSTT1 null donors also had a significantly decreased replication index, indicating an impact of GSTT1 genotype on the cytotoxicity of DEB. No influence on DEB-induced SCEs or cytotoxic effects was observed for GSTM1 genotype. It is concluded that sensitivity to in vitro SCE induction by DEB is explained by the lack of GSTT1.

Prognostic significance of the null genotype of glutathione S-transferase-T1 in patients with acute myeloid leukemia: increased early death after chemotherapy

“…26,27 Lymphocytes with the GSTT1 − genotype acquire chromosomal aberrations more sensitively than the GSTT1 + genotype when exposed to specific mutagenic substrates. 18,[28][29][30][31] Importantly, the increased expression of GST has been shown to be associated with resistance to a range of cytotoxic drugs, including alkylating agents, 32 anthracyclines, 33 and nitrosoureas. 34 Glutathione (GSH)-related enzymes and the GSH-conjugate export pump are associated with cellular resistance to anti-cancer drugs.…”

Sister chromatid exchanges and micronuclei in peripheral lymphocytes of shoe factory workers exposed to solvents.

“…In contrast, there is some evidence that the GSTT1 null genotype is associated with an increased baseline frequency of SCEs (61)(62)(63)(64) and possibly also CA (54,65). This finding does not appear to be explained by smoking or other known exposures.…”

The role of individual susceptibility in cancer burden related to environmental exposure.

“…Recently, a close correlation has been observed between aliphatic epoxide-induced sister chromatid exchanges (SCEs) in cultured human lymphocytes and GSTT1 polymorphism. The null genotype had higher induced, as well as background, frequencies of SCEs (25,26). Because mutagenic epoxides produced from lipid peroxidation products could be substrates for GSTTI (27), but this discovery was challenged later (28).…”