Effects of glutathione transferase activity on benzo[a]pyrene 7,8-dihydrodiol metabolism and mutagenesis studied in a mammalian cell co-cultivation assay

Abstract

This study deals with the role of glutathione transferase (GST)-mediated conjugation of (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-oxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE) in two mammalian cell lines, human mammary carcinoma cells (MCF-7) and rat hepatoma cells (H4IIE), in relation to their capacity to metabolize (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene [(-)-BP-7,8-diol] to products that induce mutations in co-cultivated V79 cells. Both MCF-7 and H4IIE cells metabolized (-)-BP-7,8-diol to BPDE, but mutations in co-cultivated V79 cells were only detected with MCF-7 cells. However, depletion of glutathione (GSH) in H4IIE cells increased the mutagenicity of (-)-BP-7,8-diol to a similar level to that found with MCF-7 cells. Measurements of GST activity using GSH and post-microsomal supernatants from H4IIE, V79 and MCF-7 cells indicated a substantial difference in conjugation capacity. Although preparations from all three cell-lines showed GST activity with 1-chloro-2,4-dinitrobenzene as the substrate, GST activity towards BPDE could only be detected in supernatants from H4IIE cells. This is consistent with the presence of GST 7-7 an isoenzyme highly efficient in catalysing BPDE-GSH conjugation. The difference in GSH-conjugation activity towards BPDE was confirmed using intact H4IIE and MCF-7 cells in culture. These results indicate that GSH-conjugation plays a pivotal role in mutagenesis induced by polycyclic aromatic hydrocarbons (PAH). Accordingly, a deficiency in GSH-conjugation capacity may be regarded as one important factor in defining a target cell population with an increased risk for tumour initiation following exposure to PAH.

Preferential Glutathione Conjugation of a Reverse Diol Epoxide Compared with a Bay Region Diol Epoxide of Benzo[a]pyrene in Human Hepatocytes

“…These studies demonstrated that bay region and fjord region diol epoxides can be converted to GSH conjugates by GST M1, GST P1, and GST A1, and that such conjugation was in most cases protective against DNA damage and mutagenicity. However, in one study using unadulterated MCF-7 human breast carcinoma cells incubated with BPDE, no activity was found (Romert et al, 1989). Another notable study found that only approximately 1 to 2% of the rate expected for GSH conjugation of BPDE was actually observed in cells, which indicated the importance of competing reactions of BPDE (Sundberg et al, 2002).…”

“…Taken together, these results were quite surprising because they seemed to contradict the hypothesis that carcinogenic bay region diol epoxides, such as Phe-1,2-D-3,4-E and BPDE, were detoxified by GST-catalyzed conjugation. Many studies have investigated the conjugation of BPDE with GSH, catalyzed by GST-M1-1, GST-P1-1, and GST-A1-1, either as purified or expressed enzymes or in cellular systems engineered to overexpress these enzymes (Robertson et al, 1986;Jernström et al, 1989Jernström et al, , 1996Romert et al, 1989;Sundberg et al, 1997Sundberg et al, , 2001Sundberg et al, , 2002Fields et al, 1998;Seidel et al, 1998;Hu et al, 1999;Srivastava et al, 1999;Kushman et al, 2007a,b). All of these studies demonstrate GSH conjugation of BPDE, and most show a decrease in BPDE-DNA binding and mutagenesis in tandem with the conjugation.…”

Transcriptional regulation of fosl-1 by licorice in rat Clone 9 cells

“…It is believed that antioxidants like flavonoids in licorice not only play a role in combating reactive oxygen species directly but also have a functional role in unlocking other detoxifying enzymes. GSTs detoxify electrophilic xenobiotics and their metabolites such as antibenzo(a)pyrene-7,8-dihydrodiol 9,10-epoxide in human and rat (Romert et al, 1989) whereas DTdiaphorase could reduce quinones, quinone epoxides and quinoneimines from forming reactive oxygen species (Cadenas et al, 1992). Both xenobiotics-initiated electrophiles and quinone-generated free radicals could be efficiently removed and thus it reduces the chance of cancer development.…”

Reprint of “In utero exposure to benzo[a]pyrene increases adiposity and causes hepatic steatosis in female mice, and glutathione deficiency is protective”

“…BaP-7,8-dione is an arylhydrocarbon receptor (AHR) ligand, enabling it to be shuttled to the nucleus, where it undergoes redox cycling, generating reactive oxygen species (ROS) and oxidative DNA lesions, such as 8-oxo-7,8-dihydro-2 -deoxyguanosine (8-OHdG) (Park et al, 2009). Glutathione transferase-mediated conjugation with glutathione (GSH) is a major Phase II biotransformation/detoxification pathway for BPDE and BaP-7,8-dione metabolites of BaP (Jernström et al, 1996;Romert et al, 1989;Xue and Warshawsky, 2005). As a major cellular antioxidant, GSH also detoxifies ROS that are produced as a result of BaP metabolism.…”