Iatropoulos M J, Duan J-D, Schmuck G, Williams G M
New York Medical College, Valhalla, NY 10595, USA.
Bayer Schering Pharma AG, D-42096 Wuppertal, Germany.
Exp Toxicol Pathol. 2015 Sep;67(9):453-8. doi: 10.1016/j.etp.2015.06.002. Epub 2015 Jul 8.
Propoxur (PPX) is a carbamate insecticide which induced urinary bladder cancer in Wistar rats when fed at 5000ppm in Altromin 1321 diet (1321). In the present investigation, PPX was studied for induction of several key events related to modes of action (MOA) of carcinogenicity in urinary bladders (UBs). Wistar rats were administered the compound for 28 days at 8000ppm in Provini Liba SA 3883 diet, which is similar to the 1321 diet. o-Anisidine HCl (AH) was used as a genotoxic UB carcinogenic comparator, and trisodium nitrilotriacetate (NTA) as an epigenetic UB carcinogen comparator. Along with the non-dosed control and three test substance groups (PPX, AH, NTA), four more groups were additionally fed 2% ammonium chloride (AC) in the diet to acidify the urine, since 1321 was reported to increase urinary pH. AC did acidify the urine, as expected, although the 3883 diet itself did not increase pH values above 8. In the alkaline comet assay, AH produced DNA single strand breaks (SSBs) in the UB urothelium (UBU) irrespective of AC administration, whereas PPX and NTA did not. In the nucleotide (32)P-postlabeling assay (NPL), AH produced DNA adducts irrespective of AC administration, whereas PPX and NTA did not. Routine (H&E) histopathology evaluation of the UBU did not reveal any hyperplasia or evidence of luminal microprecipitates or calculi in any of the groups. Assessment of UBU proliferation as measured by immunohistochemistry of proliferating cell nuclear antigen, revealed that NTA and NTA plus AC increased the replicating fraction (RF). Also AH plus AC, but not AH alone, increased the RF of UBU, whereas PPX groups were not significantly different from controls. Thus, the results reveal no evidence for DNA SSBs, binding, or alteration of DNA synthesis in the UBU by PPX, while demonstrating UBU DNA damage by AH and showing that NTA does not damage DNA, but causes increased UBU proliferation. The findings are in accord with a genotoxic MOA for AH, and an epigenetic MOA for NTA. The MOA of PPX does not involve genotoxicity and may be specific to the 1321 diet.
残杀威（PPX）是一种氨基甲酸酯类杀虫剂，当以5000ppm的剂量添加到Altromin 1321饲料（1321）中喂给Wistar大鼠时，可诱发膀胱癌。在本研究中，对PPX诱导膀胱致癌作用的几种关键作用模式（MOA）相关事件进行了研究。将PPX以8000ppm的剂量添加到Provini Liba SA 3883饲料中，喂给Wistar大鼠28天，该饲料与1321饲料相似。邻氨基苯甲酸盐酸盐（AH）用作具有遗传毒性的膀胱致癌物对照物，次氮基三乙酸三钠（NTA）用作表观遗传膀胱致癌物对照物。除了未给药的对照组和三个受试物质组（PPX、AH、NTA）外，另外四个组在饲料中额外添加2%氯化铵（AC）以使尿液酸化，因为据报道1321会使尿液pH值升高。正如预期的那样，AC确实使尿液酸化，尽管3883饲料本身并未使pH值升高至8以上。在碱性彗星试验中，无论是否给予AC，AH都会在膀胱尿路上皮（UBU）中产生DNA单链断裂（SSB），而PPX和NTA则不会。在核苷酸（32）P后标记试验（NPL）中，无论是否给予AC，AH都会产生DNA加合物，而PPX和NTA则不会。对UBU进行常规（苏木精和伊红染色，H&E）组织病理学评估，未发现任何一组有增生或管腔微沉淀物或结石的迹象。通过增殖细胞核抗原免疫组织化学测量UBU增殖情况，结果显示NTA以及NTA加AC会增加复制分数（RF）。AH加AC也会增加UBU的RF，但单独使用AH则不会，而PPX组与对照组无显著差异。因此，结果表明没有证据显示PPX会在UBU中导致DNA SSB、结合或DNA合成改变，同时证明AH会导致UBU DNA损伤，并表明NTA不会损伤DNA，但会导致UBU增殖增加。这些发现与AH的遗传毒性作用模式以及NTA的表观遗传作用模式一致。PPX的作用模式不涉及遗传毒性，可能特定于1321饲料。
