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Diuron-induced rat bladder epithelial cytotoxicity
Mitscheli S Da Rocha1, Lora L Arnold, Karen L Pennington
1Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-3135, USA.
Abstract:
Diuron, a substituted urea herbicide, is carcinogenic to the rat urinary bladder at high dietary levels (2500 ppm). To further elucidate the mode of action, this study aimed to determine the time course and sequence of bladder cytotoxic and proliferative changes induced by diuron treatment of male Wistar rats. Rats were randomized into two groups (control and 2500 ppm diuron) and treated for 28 days. Ten rats from each group were terminated on each of study days 1, 3, 7, or 28. Scanning electron micro scopy (SEM) showed urothelial cell swelling beginning on day 1, and by day 28, showed extensive necrosis, exfoliation and piling up of cells suggestive of hyperplasia. No difference in the bromo deoxyuridine labeling index was detected. In a second experiment, rats were randomized into control and diuron-treated groups and treated for 7 days or 8 weeks. After 7 days, transmission electron microscopy showed cell degenerative changes and distention of the cytoplasm, organelles, and nuclei characteristic of cytolysis. This resulted in protrusion of the superficial cells into the lumen, corresponding to the cell swelling observed previously by SEM. After 8 weeks, bladders in the diuron-treated group showed an increased incidence of simple hyperplasia by light microscopy (6/10, p < 0.05) compared with controls (0/10) and a significantly different SEM classification. In summary, our results support the hypothesis that urothelial cytotoxicity followed by regenerative cell proliferation are the sequential key events that occur with high-dose diuron exposure in rats.
Insights
High dietary levels of the herbicide diuron cause rat urinary bladder cancer. This study reveals diuron induces urothelial cytotoxicity followed by regenerative cell proliferation, explaining its carcinogenic mode of action.
Area of Science:
- Toxicology
- Carcinogenesis
- Cell Biology
Background:
- Diuron, a substituted urea herbicide, is a known carcinogen to the rat urinary bladder at high dietary concentrations.
- Understanding the mechanism of diuron-induced bladder cancer is crucial for risk assessment.
Purpose of the Study:
- To investigate the time course and sequence of cytotoxic and proliferative changes in the rat urinary bladder following diuron exposure.
- To elucidate the mode of action of diuron as a bladder carcinogen.
Main Methods:
- Male Wistar rats were administered a high dietary level (2500 ppm) of diuron for up to 28 days or 8 weeks.
- Urinary bladders were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and light microscopy.
- Cell proliferation was assessed using the bromo deoxyuridine labeling index.
Main Results:
- SEM revealed urothelial cell swelling from day 1, progressing to necrosis and hyperplasia by day 28.
- TEM identified degenerative changes and cytolysis in urothelial cells after 7 days of treatment.
- After 8 weeks, diuron-treated rats showed a significant increase in simple hyperplasia compared to controls.
Conclusions:
- Diuron exposure initiates urothelial cytotoxicity, characterized by cell swelling and cytolysis.
- This cytotoxicity is followed by regenerative cell proliferation, leading to hyperplasia.
- These sequential events of cytotoxicity and proliferation are key mechanisms underlying diuron-induced rat urinary bladder carcinogenesis.
