偶氮甲烷是一种结肠致癌物，会导致 DNA 加合物的形成。
Azoxymethane is a colon carcinogen which leads to the formation of DNA adducts.
Azoxymethane is a colon carcinogen which leads to the formation of DNA adducts. On an equal protein basis, hepatic microsomes are much more active than SI and colon microsomes in NADPH-dependent Azoxymethane bioactivation and N7-mG adduct formation. Hepatic microsomes show the highest activity in the hydroxylation of Azoxymethane, followed by SI and colon microsomes[1].
Regardless of the strain, the amounts of O6-mG and N7-mG produced by Azoxymethane are highest in the liver, followed by proximal and distal colons, which have similar levels, and then by duodenum, jejunum and ileum. Results indicate that the Azoxymethane-induced DNA adduct formation in the SI and colon does not depend on bioactivation by hepatic P450 enzymes. Irrespective of the mouse strain, no aberrant crypt foci (ACF) is detected in the colons of saline-treated mice; in contrast, colonic ACF is detected in all three strains of Azoxymethane-treated mice[1]. The Azoxymethane-treated athymic mice have approximately an 11-fold lower tumor incidence than similarly treated WT animals[2].
联苯甲酸甲酯是一种大肠癌致癌物，会导致DNA加合物的形成。在相同的蛋白质基础上，肝微粒体比小肠和结肠微粒体在NADPH依赖的联苯甲酸甲酯活化和N7-mG加合物形成方面更加活跃。肝微粒体在联苯甲酸甲酯的加氢作用中显示出最高活性，其次是小肠和结肠微粒体[1]。
无论鼠种如何，联苯甲酸甲酯引起的O6-mG和N7-mG的量在肝脏最高，其次是近端和远端结肠，这两者的水平相似，然后是十二指肠、空肠和回肠。结果表明，小肠和结肠中的联苯甲酸甲酯诱导的DNA加合物形成不依赖于肝脏P450酶的生物活化。无论鼠种如何，对照组小鼠的结肠中都没有检测到畸变隐窝；相比之下，联苯甲酸甲酯处理的三种鼠种中的结肠都检测到了畸变隐窝[1]。裸鼠中的联苯甲酸甲酯处理小鼠患肿瘤的发病率比同样处理的野生型动物低约11倍[2]。
[1]. Megaraj V, et al. Role of hepatic and intestinal p450 enzymes in the metabolic activation of the colon carcinogen azoxymethane in mice. Chem Res Toxicol. 2014 Apr 21;27(4):656-62. [2]. Whetstone RD, et al. Colon carcinogenesis in wild type and immune compromised mice after treatment with azoxymethane, and azoxymethane with dextran sodium sulfate. Mol Carcinog. 2016 Jul;55(7):1187-95.
|
Kinase experiment: |
The assay for Azoxymethane-induced in vitro DNA adduct formation is performed. Briefly, microsomes (0.5 to 2.0 mg/mL) are incubated with calf thymus DNA (1 mg/mL) and Azoxymethane (200 μM) in a total volume of 1.0 mL. The assay buffer consists of 0.1 M Tris-HCl (pH 7.4), 1 mM EDTA, 20 mM MgCl2, 0.3 M KCl, and 1.5 mM NADPH. Incubations are carried out at 37°C for 60 min in a shaking water bath. An additional 30 nM of NADPH is added after the first 30 min. The reaction is stopped by the addition of 0.5 mL of ice-cold 7.5 M ammonium acetate. DNA is then extracted for tissue homogenates. Control incubations are performed without NADPH[1]. |
|
Animal experiment: |
Male, 8 to 10 week old, WT-A/J, IECN-A/J, and LCN-A/J mice (8 per group) are treated with either saline or Azoxymethane (7.5 mg/kg BW, s.c.), once weekly for 3 weeks. Mice are sacrificed 6 weeks post-treatment for aberrant crypt foci (ACF) detection. The entire colon is excised. A longitudinal incision is made along the entire length of the colon, which is further cut into two equal-length segments, representing proximal and distal portions of the colon. The segments are dipped in PBS to remove fecal pellets and then kept flat between filter papers in 10% buffered formalin for at least 24 h. Subsequently, the colons are immersed in freshly prepared 0.1% methylene blue for 10 min and rinsed briefly in deionized H2O to remove excess dye. The colon is mounted carefully on a microscope slide with the mucosal surface side up and viewed under a light microscope. The ACF in the entire mucosal surface of the colon are counted blindly and independently by two investigators and recorded[1]. |
|
参考文献: [1]. Megaraj V, et al. Role of hepatic and intestinal p450 enzymes in the metabolic activation of the colon carcinogen azoxymethane in mice. Chem Res Toxicol. 2014 Apr 21;27(4):656-62. |
|
动态评分
0.0