Investigations of rodent urinary bladder carcinogens: collection, processing, and evaluation of urine and bladders

Strain-related Differences in Urine Composition of Male Rats of Potential Relevance to Urolithiasis

In carcinogenicity studies with PPAR γ and α/γ agonists, urinary bladder tumors have been reported in Harlan Sprague-Dawley (HSD) and Charles River Sprague-Dawley (SD) but not Wistar (WI) rats, with urolithiasis purported to be the inciting event. In two 3-month studies, the authors investigated strain-related differences in urine composition by sampling urine multiple times daily. Urine pH, electrolytes, creatinine, protein, citrate and oxalate levels, and serum citrate were assessed; urine sediment was analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. HSD rats had significantly higher urine calcium than SD or WI rats, primarily as calcium phosphate-containing precipitate. When compared to SD rats, HSD rats had lower urine volume, higher urine protein, and a comparable (week 4) to lower (week 13) burden of MgNH4PO4 aggregates. Relative to WI rats, HSD rats had higher urine protein and magnesium and lower serum and urine citrate. Overall, the susceptibility to urolithiasis in male rats was HSD > SD > WI; this was likely due to strain-related differences in the amount of urine protein (a nidus for crystal formation), lithogenic ions, citrate (an inhibitor of lithogenesis), and/or volume. Strain-related differences in urine composition need to be considered when interpreting the outcome of studies with compounds that alter urine composition.

Urinary retention and cystitis associated with subcutaneous estradiol pellets in female nude mice

Unexpected deaths occurred in studies involving a nude mouse model of mammary cancer that required subcutaneous implantation of 0.5 mg twenty-one-day release estrogen pellets for growth of the estrogen-dependent mammary tumor xenograft BT474c. Early deaths occurred in female nude mice and were associated with urinary retention, frequently with cystitis. Drug treatment had no effect on the incidence or severity of cystitis. Histological findings did not alter significantly over various time points following pellet implantation. Changes were not seen in males or in females receiving lower doses of estradiol even when the duration of administration was prolonged, suggesting that a threshold level was required for the onset of urinary retention. Because of the influence of estrogen on micturition, immunohistochemistry for estrogen receptor alpha (ERalpha) in the urinary bladder was carried out, which did not demonstrate any differences between females implanted with 0.5 mg twenty-one-day release estrogen pellets and nonimplanted females. Although previous publications have concentrated on possible mechanisms of action, this paper describes the histopathological changes seen in the urinary bladder of female nude mice resulting from exposure to high levels of estradiol.

Urothelial carcinogenesis in the urinary bladder of rats treated with naveglitazar, a gamma-dominant PPAR alpha/gamma agonist: lack of evidence for urolithiasis as an inciting event

Naveglitazar, a gamma-dominant peroxisome proliferator-activated receptor (PPAR) alpha/gamma dual agonist, was tested for carcinogenicity in F344 rats in a 2-year study. Changes in urine composition and urothelial morphology were characterized in a companion 18-month investigative study. A significant increase in neoplasms of the bladder occurred only in females of the high-dose group (14/60) in the carcinogenicity study. Trends toward increased cell proliferation in the urothelium were noted in both sexes at all time points evaluated in the 18-month study. Group means for urothelial mitogenesis were increased statistically significantly only in high-dose females at 12 and 18 months. Urothelial hyperplasia occurred in high-dose females at 18 months. Morphologic changes in the urothelium at earlier time points were limited to hypertrophy and decreased immunolabeling of the superficial cells for cytokeratin 20 (a marker of terminal differentiation in urothelial cells) in both males and females. No treatment-related changes in urinary parameters, including urinary sediments, were associated with the occurrence of urothelial proliferation. Urinary pH was unaffected by treatment in both males and females, but expected diurnal changes were demonstrated. Collectively, these data indicate that naveglitazar was associated with hypertrophic and proliferative effects on the urothelium, but a link with changes in urinary parameters was not demonstrated.

Inhalation of tobacco smoke induces increased proliferation of urinary bladder epithelium and endothelium in female C57BL/6 mice

Cigarette smoking is the major environmental risk factor for bladder cancer in humans. Aromatic amines, potent DNA-reactive bladder carcinogens present in cigarette smoke, contribute significantly. However, increased cell proliferation, caused by direct mitogenesis or in response to cytotoxicity, may also play a role since urothelial hyperplasia has been observed in human cigarette smokers. We examined the urothelial effects of cigarette smoke (whole body inhalation exposure (Teague) system) in female C57BL/6 mice at various times in two studies, including reversibility evaluations. In both studies, no urothelial hyperplasia was observed by light microscopy in any group. However, in study 1, the Ki-67 labeling index (LI) of the urothelium was significantly increased in the smoke exposed group compared to controls through 3 months, but was not present at 6, 9 or 12 months even with continued exposures. In the groups that discontinued smoke exposure, it returned to the same levels as controls or lower. In study 2, the bromodeoxyuridine LI was similar to controls on day 1 but significantly increased at 5 days in the smoke exposed group. In the group that discontinued smoke exposure for 2 days, the LI was increased compared to controls but not significantly. Superficial urothelial cell cytotoxicity and necrosis were detectable by scanning electron microscopy at 5 days. Changes in LI of submucosal endothelial cells generally followed those of the urothelium and effects were reversible upon cessation of exposure. The increased urothelial proliferation appeared to be due to superficial cell cytotoxicity with consequent regeneration.