Shen E S, Guengerich F P, Olson J R
Department of Pharmacology and Therapeutics, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.
Biochem Pharmacol. 1989 Nov 15;38(22):4075-84. doi: 10.1016/0006-2952(89)90689-8.
The induction of the murine hepatic microsomal cytochrome P-450 monooxygenase system by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was studied over a wide range of doses, including those associated with acute toxicity. Studies were conducted in two inbred strains of mice which vary at the Ah receptor and at a number of other genetic loci. C57BL/6J mice possess a high-affinity Ah receptor and are responsive to enzyme inductive effects of TCDD, whereas DBA/2J mice do not possess a high-affinity receptor and are less responsive to TCDD. In a dose-response study, 7-ethoxyresorufin O-deethylase (EROD) activity appeared to be maximally induced in C57BL/6J and DBA/2J mice at 7 days following exposure to 3 and 30 micrograms of TCDD/kg respectively. Very similar results were reported previously for the induction of aryl hydrocarbon hydroxylase activity in these strains of mice. However, at higher doses of TCDD (at least 45 micrograms/kg for C57BL/6J and 300 micrograms/kg for DBA/2J), EROD activity was further increased (2-fold) from the apparent maximal (plateau) level, resulting in an unusual biphasic log dose-response relationship. EROD activity remained at these elevated rates in both strains for doses approaching and exceeding the respective LD50 values for each strain. To further characterize this biphasic induction phenomenon, cytochrome P-450 content, benzo[a]pyrene metabolism, and EROD and NADPH-cytochrome P-450 reductase activities were measured 1, 3 and 7 days after TCDD administration to C57BL/6J (3 and 150 micrograms/kg) and DBA/2J (30 and 600 micrograms/kg) mice. Maximal responses occurred in both strains at 3 days for all doses. In both strains, TCDD produced a dose-dependent increase in cytochrome P-450 content, EROD, and benzo[a]pyrene metabolism. Furthermore, a 2-fold induction of reductase activity was observed in each strain following exposure to the respective high doses. Induction of cytochrome P1-450 and P3-450 was also measured by Western immunoblot, using antisera raised against the homologous rat isozymes. In both strains, TCDD produced a dose-related increase in two protein-staining bands recognized by anti-P-450BNF-B (P1-450) and anti-P-450BNF/ISF-G (P3-450) respectively. The extended induction of hepatic microsomal monooxygenase activities at the respective high doses of TCDD appears to be due, in part, to increases in NADPH-cytochrome P-450 reductase activity and cytochromes P1-450 and P3-450 content. Significant alterations in the expression of the cytochrome P-450 monooxygenase system following exposure to high doses of TCDD may be associated, in part, with the delayed acute toxicity reported at this level of exposure.
研究了2,3,7,8-四氯二苯并-对-二恶英（TCDD）在很宽剂量范围内对小鼠肝脏微粒体细胞色素P-450单加氧酶系统的诱导作用，包括与急性毒性相关的剂量。研究在两种近交系小鼠中进行，这两种小鼠在芳烃（Ah）受体以及其他一些基因位点上存在差异。C57BL/6J小鼠具有高亲和力的Ah受体，对TCDD的酶诱导作用有反应，而DBA/2J小鼠不具有高亲和力受体，对TCDD的反应较弱。在一项剂量反应研究中，C57BL/6J和DBA/2J小鼠分别在暴露于3和30微克TCDD/千克后7天，7-乙氧基异吩恶唑酮O-脱乙基酶（EROD）活性似乎达到最大诱导。此前报道过这些品系小鼠中芳烃羟化酶活性的诱导情况，结果非常相似。然而，在更高剂量的TCDD下（C57BL/6J至少为45微克/千克，DBA/2J为300微克/千克），EROD活性从明显的最大（平台）水平进一步增加（2倍），导致出现不寻常的双相对数剂量反应关系。在两种品系中，对于接近和超过各自半数致死剂量（LD50）值的剂量，EROD活性都保持在这些升高的水平。为了进一步表征这种双相诱导现象，在给C57BL/6J（3和150微克/千克）和DBA/2J（30和600微克/千克）小鼠施用TCDD后1、3和7天，测量了细胞色素P-450含量、苯并[a]芘代谢以及EROD和NADPH-细胞色素P-450还原酶活性。所有剂量下，两种品系在3天时都出现了最大反应。在两种品系中，TCDD均使细胞色素P-450含量、EROD和苯并[a]芘代谢呈剂量依赖性增加。此外，在暴露于各自的高剂量后，每个品系中均观察到还原酶活性诱导了2倍。还使用针对同源大鼠同工酶产生的抗血清，通过蛋白质免疫印迹法测量了细胞色素P1-450和P3-450的诱导情况。在两种品系中，TCDD分别使抗P-450BNF-B（P1-450）和抗P-450BNF/ISF-G（P3-450）识别的两条蛋白条带出现剂量相关的增加。在各自高剂量的TCDD下，肝脏微粒体单加氧酶活性的延长诱导似乎部分归因于NADPH-细胞色素P-450还原酶活性以及细胞色素P1-450和P3-450含量的增加。暴露于高剂量TCDD后细胞色素P-450单加氧酶系统表达的显著改变可能部分与该暴露水平下报道的延迟急性毒性有关。
