Shane B S, Winston G W
Institute for Environmental Studies, Louisiana State University, Baton Rouge 70803, USA.
Environ Mol Mutagen. 1997;30(3):303-11. doi: 10.1002/(sici)1098-2280(1997)30:3<303::aid-em9>3.0.co;2-l.
1,3-, 1,6-, and 1,8-Dinitropyrene (1,3-, 1,6-, and 1,8-DNP) are direct-acting mutagens in that they do not require an exogenous source of enzymes for activation to mutagens in the Ames assay. However, the addition of mammalian S9 preparations, or the microsomal and cytosolic compartments comprising S9, modulate the mutagenic response of these DNPs. In this study, we compared the mutagenic response of these DNPs in the presence of cytosol and microsomal fractions from the liver of Aroclor-pretreated (AR) and control rats, in the Ames mutagenicity assay and umu gene induction assay. 1,3- and 1,8-DNP were deactivated to a greater extent by microsomes from AR-induced and control rats than was 1,6-DNP, in both the umu and Ames assays. In the Ames assay, S9 was more potent in deactivating the DNP than an equivalent concentration of microsomes from the same S9 preparation. Also, S9 from AR-pretreated rats deactivated the isomers to a greater extent than S9 from control rats. In contrast to the constant deactivation of all the isomers in the two assays catalyzed by microsomes and S9, the response with cytosol from AR-pretreated rats differed with respect to the three isomers in the Ames and umu assays. When cytosol from AR-treated rats was added, the mutagenicity of 1,3- and 1,6-DNP, but not 1,8-DNP, was significantly (P < 0.05) increased in the Ames assay while the mutagenicity of the three DNPs was increased in the umu assay. Also, a biphasic response was observed in the umu assay with 1,6- and 1,8-DNP, in that AR-cytosol enhanced the mutagenicity at low protein concentrations (5-50 micrograms protein/reaction) but abrogated the response at higher protein concentrations. The effect of cytosol from control rats depended on the isomer tested; 1,3-DNP was activated above the background level in both assays (nearly towfold) while 1,6-DNP and 1,8-DNP were only activated at low protein concentrations in the umu assay. In the Ames assay, cytosol from AR-pretreated rats did not alter the mutagenic response with 1,8-DNP, while control cytosol significantly (P < 0.05) deactivated 1,8-DNP at all substrate concentrations tested. In summary, this study showed that the mutagenicity of 1,3-DNP was similar in the two assays but the responses with 1,6- and 1,8-DNP differed in the two assays. These isomeric differences could be due to the varying metabolic pathways of the three DNPs as well as the detectable end points of the two assays.
1,3 - 二硝基芘、1,6 - 二硝基芘和1,8 - 二硝基芘（1,3 - DNP、1,6 - DNP和1,8 - DNP）是直接作用的诱变剂，即在艾姆斯试验中，它们不需要外源酶源来激活成为诱变剂。然而，添加哺乳动物的S9制剂，或构成S9的微粒体和胞质部分，会调节这些二硝基芘的诱变反应。在本研究中，我们在艾姆斯诱变试验和umu基因诱导试验中，比较了在来自多氯联苯预处理（AR）大鼠和对照大鼠肝脏的胞质溶胶和微粒体组分存在的情况下，这些二硝基芘的诱变反应。在umu试验和艾姆斯试验中，1,3 - DNP和1,8 - DNP被AR诱导大鼠和对照大鼠的微粒体失活的程度比1,6 - DNP更大。在艾姆斯试验中，S9比来自相同S9制剂的等量浓度微粒体更有效地使二硝基芘失活。此外，AR预处理大鼠的S9比对照大鼠的S9更能使异构体失活。与微粒体和S9在两种试验中对所有异构体的持续失活作用相反，AR预处理大鼠的胞质溶胶在艾姆斯试验和umu试验中对三种异构体的反应有所不同。当添加AR处理大鼠的胞质溶胶时，在艾姆斯试验中1,3 - DNP和1,6 - DNP的诱变性显著增加（P < 0.05），而1,8 - DNP则未增加，而在umu试验中三种二硝基芘的诱变性均增加。此外，在umu试验中观察到1,6 - DNP和1,8 - DNP有双相反应，即AR - 胞质溶胶在低蛋白浓度（5 - 50微克蛋白质/反应）下增强诱变性，但在较高蛋白浓度下消除该反应。对照大鼠胞质溶胶的作用取决于所测试的异构体；在两种试验中1,3 - DNP均在背景水平以上被激活（近两倍），而在umu试验中1,6 - DNP和1,8 - DNP仅在低蛋白浓度下被激活。在艾姆斯试验中，AR预处理大鼠的胞质溶胶未改变1,8 - DNP的诱变反应，而对照胞质溶胶在所有测试底物浓度下均显著（P < 0.05）使1,8 - DNP失活。总之，本研究表明1,3 - DNP在两种试验中的诱变性相似，但1,6 - DNP和1,8 - DNP在两种试验中的反应不同。这些异构体差异可能是由于三种二硝基芘不同的代谢途径以及两种试验可检测的终点不同所致。
