Cytotoxicity and Regenerative Proliferation as the Mode of Action for Diuron-Induced Urothelial Carcinogenesis in the Rat

Author(s)

da Rocha, Mitscheli S. ^[1] ; Nascimento, Merielen G. ^[1] ; Cardoso, Ana Paula F. ^[1] ; de Lima, Patricia L. A. ^[1] ; Zelandi, Edneia A. ^[1] ; de Camargo, Joao Lauro V. ^[1] ; de Oliveira, Maria Luiza C. S. ^[1]

Affiliation

^[1] Sao Paulo State Univ UNESP, Botucatu Med Sch, Dept Pathol, Ctr Evaluat Environm Impact Human Hlth TOXICAM, BR-18618000 Sao Paulo - Brazil

• Document type: Journal article
• Source: TOXICOLOGICAL SCIENCES; v. 113, n. 1, p. 37-44, JAN 2010.
• Web of Science Citations: 11

Abstract

Diuron, a substituted urea herbicide, is carcinogenic to the urinary bladder of rats at high dietary levels. Its proposed carcinogenic mode of action (MOA) includes urothelial cytotoxicity and necrosis followed by regenerative cell proliferation and sustained urothelial hyperplasia. Cytotoxicity could be induced either by urinary solids or by chemical toxicity by diuron and/or metabolites excreted in the urine. Diuron was not genotoxic in a previous single-cell gel (comet) assay, but possible cross-linking activity remained to be evaluated. The present study explored the MOA of diuron and the effect of urinary acidification on the development of urothelial lesions. Male Wistar rats were fed diuron (2500 ppm, about 130 mg/kg of body weight) either with or without NH(4)Cl 10,000 ppm to acidify the urine. Reversibility of urothelial changes was also examined. The animals were euthanized after 15, 25, or 30 weeks. Diuron-fed rats had urinary amorphous precipitate and magnesium ammonium phosphate crystals similar to control animals. Groups treated with diuron + NH(4)Cl showed decreased urinary pH and reduced amounts of urinary crystals and precipitate. Urothelial necrosis and simple hyperplasia were observed by light microscopy and scanning electron microscopy both in diuron- and in diuron + NH(4)Cl-treated groups. Cytotoxicity and proliferative changes were mostly reversible. A modified comet assay developed in vitro with Chinese hamster ovary cells showed that diuron did not induce DNA cross-links. These data suggest that cytotoxicity with consequent regenerative cell proliferation is the predominant MOA for diuron rat urothelial carcinogenesis, the cytotoxicity being chemically induced and not due to urinary solids. (AU)

• FAPESP's process: 06/60506-1 - Agriculture pesticides as risk factor: toxicologic pathology, immunology, and molecular and analytical evaluations in experimental models of single or combined exposures
• Grantee: João Lauro Viana de Camargo
• Support Opportunities: Research Projects - Thematic Grants