Seidel A, Friedberg T, Löllmann B, Schwierzok A, Funk M, Frank H, Holler R, Oesch F, Glatt H
Institute of Toxicology, University of Mainz, Germany.
Carcinogenesis. 1998 Nov;19(11):1975-81. doi: 10.1093/carcin/19.11.1975.
Dihydrodiol epoxides (DEs) are important carcinogenic metabolites of polycyclic aromatic hydrocarbons (PAHs). The metabolic formation of four stereoisomeric DEs (a pair of optically active diastereomers termed as syn- and anti-form) is possible. Glutathione tranferases (GSTs) have been demonstrated to catalyze the detoxification of DEs. Purified GSTs display remarkable differences in catalytic efficiencies towards bay- and fjord-region DEs along with a high degree of regio- and stereoselectivity. Here we determined to which extent heterologously expressed human GSTP1-1, a major GST isoform in lung, affects the mutagenicity of stereoisomeric bay-region DEs of benzo[a]pyrene in Chinese hamster V79 cells. To evaluate the influence of sterical crowding in the substrate on the activity of GSTP-1, the study was extended to the strongly mutagenic fjord-region (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene. GSTP1-1,reduced preferentially the mutagenicity (studied at the hprt locus) of (+)-anti and (+)-syn-DEs of benzo[a]pyrene (by 66 and 67%) as compared with the corresponding (-)-anti- and (-)-syn-enantiomers (by 15 and 13%). These results are in line with previous studies on the enantioselectivity of purified GSTP1-1 towards the DE isomers of benzo[a]pyrene and benzo[c]phenanthrene showing that enantiomers with (R)-configuration at the benzylic oxiranyl carbon are better substrates than those with (S)-configuration. Interestingly, the (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene were efficiently detoxified by GSTP-1-1 in the constructed cell line (reduction of mutagenicity by 66 and 64%). This study demonstrates that differences in the caalytic activity seen for purified GST towards individual mutagens do not necessarily reflect the detoxification of DEs by the same enzyme in a living cell and provides further evidence that specific human GSTs play a role in the detoxification of DEs of PAHs.
二氢二醇环氧化物（DEs）是多环芳烃（PAHs）重要的致癌代谢产物。四种立体异构DEs（一对旋光非对映异构体，称为顺式和反式）都有可能通过代谢形成。谷胱甘肽转移酶（GSTs）已被证明可催化DEs的解毒过程。纯化的GSTs对湾区和峡湾区DEs的催化效率存在显著差异，同时具有高度的区域选择性和立体选择性。在此，我们确定了在异源表达的人GSTP1-1（肺中的一种主要GST同工型）在多大程度上影响中国仓鼠V79细胞中苯并[a]芘立体异构湾区DEs的致突变性。为了评估底物中的空间拥挤对GSTP-1活性的影响，该研究扩展到了苯并[c]菲和二苯并[a,l]芘的强致突变峡湾区（-）-反式DEs。与相应的（-）-反式和顺式对映体（分别降低15%和13%）相比，GSTP1-1优先降低了苯并[a]芘（+）-反式和顺式DEs的致突变性（在hprt位点研究）（分别降低66%和67%）。这些结果与之前关于纯化的GSTP1-1对苯并[a]芘和苯并[c]菲的DE异构体的对映选择性研究一致，表明在苄基环氧乙烷基碳上具有（R）-构型的对映体比具有（S）-构型的对映体是更好的底物。有趣的是，在构建的细胞系中，苯并[c]菲和二苯并[a,l]芘的（-）-反式DEs被GSTP-1-1有效解毒（致突变性分别降低66%和64%）。这项研究表明，纯化的GST对单个诱变剂的催化活性差异不一定反映同一酶在活细胞中对DEs的解毒作用，并进一步证明特定的人GSTs在PAHs的DEs解毒中发挥作用。
