Promotion of urinary bladder carcinogenesis in experimental animals

A study in a rat initiation-promotion bladder tumour model demonstrated no promoter/progressor potential of dapagliflozin

Dapagliflozin, a sodium-glucose co-transporter 2 (SGLT2) inhibitor, is indicated to improve glycaemic control in adults of type 2 diabetes. In nonclinical studies, dapagliflozin was neither genotoxic nor carcinogenic. However, in some clinical studies, an increased incidence of bladder cancer was observed in the dapagliflozin group vs. the placebo. Therefore, this study was undertaken to determine if dapagliflozin can act as a promoter in a 2-stage bladder cancer model in rats induced with N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN). Rats given BBN (100 or 400 mg/kg, po) twice weekly for 6 weeks in Phase 1 were assigned in Phase 2 to receive daily dose of vehicle, dapagliflozin (0.5 mg/kg, po) or uracil (positive control, 3% in diet) from weeks 8-34. All bladders were evaluated by histopathology. Verifying the validity of the model, uracil increased the incidence of bladder cancer, while dapagliflozin had no effect on the incidence or invasiveness of transitional cell carcinoma. The exposure of dapagliflozin at 0.5 mg/kg/day in rats was 7 times the clinical exposure at maximal therapeutic dose (10 mg). In conclusion, dapagliflozin does not act as promoter or progressor of bladder cancer in a validated bladder cancer model in rats.

Final Report on the Safety Assessment of Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and sodium Erythorbate

Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and Sodium Erythorbate are related ingredients that function as antioxidants in cosmetic formulations. Ascorbyl Palmitate, Ascorbyl Dipalmitate, and Ascorbyl Stearate are esters and diesters of ascorbic acid with long-chain fatty acids. Erythorbic Acid is a stereoisomer of ascorbic acid and Sodium Erythorbate is the sodium salt of Erythorbic Acid. Although all of these ingredients are used, uses of Ascorbyl Palmitate and Erythorbic Acid predominate, with combined uses in over a thousand cosmetic formulations at low concentrations. Ascorbyl Palmitate is used at concentrations between 0.01 and 0.2% , and Erythorbic Acid is used at concentrations of 0.5-1% . Ascorbyl Palmitate has vitamin C activity approximately equal to that of L-ascorbic acid, whereas Erythorbic Acid has only 5% activity. The esters are likely to penetrate the skin readily, but the acid and its salt are not likely to penetrate. These ingredients exhibit low acute oral toxicity in animals. In chronic feeding studies, decreased body weight gain, the formation of oxalate stones in the bladder, and hyperplasia were seen in rats fed high levels of Ascorbyl Palmitate. Ascorbyl Palmitate (10%) and Ascorbyl Dipalmitate (100%) were not irritating to the intact skin of albino rabbits. Ascorbic Acid (30 % ) itself caused barely perceptible erythema and Sodium Erythorbate powder caused no irritation to the intact and abraded skin of rabbits. In animal studies, Ascorbic acid was not a sensitizer, and Erythorbic Acid (10%) applied topically to porcine skin reduced ultraviolet B (UVB)-induced phototoxicity. In clinical studies, Ascorbyl Palmitate caused no dermal irritation or sensitization. These ingredients are minimally irritating to the eye. Sodium Erythorbate did not cause fetal or maternal toxicity or developmental toxicity in rats and mice fed high levels. Although these ingredients were generally negative in a wide range of genotoxicity tests, Erythorbic Acid and Sodium Erythorbate did produce isolated positive genotoxicity test results. As antioxidants, these ingredients have been studied in animals after initiation with various carcinogens. In some cases reductions in tumor incidence were seen, in others no effect was noted. In no case did treatment with these ingredients increase tumor incidence. The highest use concentrations of Erythorbic Acid and Sodium Erythorbate are in oxidative hair dyes, where they are completely consumed in the chemical reaction that takes place at mixing. The fatty acid esters of ascorbic acid are used at lower concentrations in leave-on formulations. In consideration of these uses and based on the available safety test data, Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and Sodium Erythorbate are safe for use as cosmetic ingredients in the present practices of use.

Vascular endothelial growth factor mRNA levels as a biomarker for short-term N-butyl-N-(4-hydroxybutyl) nitrosamine-induced rat bladder carcinogenesis bioassay

Generically, carcinogenic effects of chemicals in bladder carcinogenesis are judged by induction of papillary or nodular (PN) hyperplasia in rats given N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) for 4 weeks and the test chemical for 22-28 weeks. However, upregulation of vascular endothelial growth factor (VEGF) begins early in rat BBN bladder carcinogenesis. To establish a short-term rat bladder carcinogenic bioassay, we analyzed the correlations between VEGF, VEGF mRNA and bladder lesions inductions at 10 and 26 weeks after BBN treatment. Six-week-old male Wistar (slc) rats were given 0.05% BBN for 4, 10 or 26 weeks. To avoid individual rat bias, the bladders were investigated by partial cystectomy at 10 weeks and total cystectomy at 26 weeks. After induction, PN hyperplasia and carcinoma in rats increased with the length of BBN treatment and immunohistochemical VEGF expression also increased following carcinogenesis, but the immunoreactivity of individual lesions was quite variable. Moreover, induction of PN hyperplasia at 10 weeks' BBN treatment was not significantly correlated with that at 26 weeks' treatment; thus, it was not possible to predict the carcinogenic effect due to the induction of PN hyperplasia at 26 weeks' BBN treatment by that at 10 weeks' treatment. However, VEGF mRNA levels of rat bladders at 10 weeks' BBN treatment revealed a strong significant correlation with the incidence of bladder lesions at 26 weeks' treatment. Here, we suggest that quantitative VEGF mRNA levels are a good biomarker for a short-term BBN-induced bioassay for rat bladder carcinogenesis.

No Promoting Effect of Ethyl Tertiary-butyl Ether (ETBE) on Rat Urinary Bladder Carcinogenesis Initiated with N-Butyl-N-(4-hydroxybutyl)nitrosamine

The effects of ethyl tertiary-butyl ether (ETBE) on two-stage urinary bladder carcinogenesis in male F344 rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were investigated at various dose levels with regard to possible promoting activity. Groups of 30 rats were given drinking water containing 500 ppm BBN, as an initiator, for 4 weeks and starting one week thereafter received ETBE by gavage (daily, 7 days/week) at dose levels of 0 (control), 100, 300, 500 or 1000 mg/kg/day until experimental week 36. No statistically significant differences in incidences of preneoplastic lesions, papillomas, and carcinomas of the urinary bladder were evident in rats treated with 100–1000 mg/kg/day ETBE as compared with control values. Furthermore, the average numbers of preneoplastic or neoplastic lesions per unit length of basement membrane in rats given 100–1000 mg/kg/day ETBE were also comparable to control values. However, papillomatosis of the urinary bladder was found in 4 out of 30 rats (13%) in the group given 1000 mg/kg/day ETBE, and soft stones in the urinary bladder were found in 3 out of these 4 rats. The results thus demonstrated that ETBE did not exert promotional activity on urinary bladder carcinogenesis. However, papillomatosis of the urinary bladder developed in small numbers of the rats given ETBE at 1000 mg/kg/day but not in rats given 500 mg/kg/day or lower doses.

Angiogenesis inhibition by green propolis and the angiogenic effect of L-lysine on bladder cancer in rats

PURPOSE

To determine the effects of water-soluble derivative of green propolis in bladder cancer angiogenesis in rats given N-butyl-(-4-hydroxybutyl) nitrosamine (BBN).

METHODS

Nine groups were established, where six of them (Groups 1 to 6), the animals received 0.05% BBN in their drinking water for 14 weeks. From the 32nd to the 40th week, Groups 1, 2, 3 and 4 were treated respectively with water, L-lysine (300 mg/kg/day), celecoxib (30 mg/kg/day) and propolis (300 mg/kg/day). Groups 5 and 6 were given propolis and L-lysine from the 1st to the 40th week (150 mg/kg/day). Microvascular density was determined by histological sections stained for the marker CD-31 and analyzed with specific software.

RESULTS

The microvascular density in bladder carcinomas was lower (p<0.01) in rats receiving propolis than in controls given carcinogen only. On the other hand, the microvascular density of tumors in rats receiving carcinogen and L-lysine for 40 weeks from the beginning of carcinogen treatment was significantly higher (p<0.01) than in the corresponding controls.

CONCLUSION

Water-soluble derivative of propolis inhibits angiogenesis in BBN-induced rat bladder cancer, while L-lysine treatment stimulates angiogenesis if initiated concurrently with BBN.

Chemoprevention with green propolis green propolis extracted in L-lysine versus carcinogenesis promotion with L-lysine in N-Butyl-N-[4-hydroxybutyl] nitrosamine (BBN) induced rat bladder cancer

PURPOSE

To determine the effects of green propolis extracted in L-lysine (WSDP) and of L- lysine for 40 weeks on induced rat bladder carcinogenesis.

METHODS

The animals (groups I, II, III, IV, V and VI) received BBN during 14 weeks. Group I was treated with propolis 30 days prior received BBN, and then these animals were treated daily with propolis; Groups II and III was treated with subcutaneous and oral propolis (respectively) concurrently with BBN. The animals of Group IV were treated L-lysine; Group V received water subcutaneous; and Group VI received only to BBN. Among the animals not submitted to carcinogenesis induction, Group VII received propolis, Group VIII received L-lysine and Group IX received water.

RESULTS

The carcinoma incidence in Group I was lower than that of control (Group VI). The carcinoma multiplicity in Group IV was greater than in Group VI. All animals treated with L-lysine developed carcinomas, and they were also more invasive in Group IV than in controls. On the other hand, Group VIII showed no bladder lesions.

CONCLUSION

The WSDP is chemopreventive against rat bladder carcinogenesis, if administered 30 days prior to BBN , and that L-lysine causes promotion of bladder carcinogenesis.

Pathobiology and chemoprevention of bladder cancer

Our understanding of the pathogenesis of bladder cancer has improved considerably over the past decade. Translating these novel pathobiological discoveries into therapies, prevention, or strategies to manage patients who are suspected to have or who have been diagnosed with bladder cancer is the ultimate goal. In particular, the chemoprevention of bladder cancer development is important, since urothelial cancer frequently recurs, even if the primary cancer is completely removed. The numerous alterations of both oncogenes and tumor suppressor genes that have been implicated in bladder carcinogenesis represent novel targets for therapy and prevention. In addition, knowledge about these genetic alterations will help provide a better understanding of the biological significance of preneoplastic lesions of bladder cancer. Animal models for investigating bladder cancer development and prevention can also be developed based on these alterations. This paper summarizes the results of recent preclinical and clinical chemoprevention studies and discusses screening for bladder cancer.

Modification of N-Methyl-N-Nitrosourea initiated bladder carcinogenesis in Wistar rats by terephthalic acid

The effect of terephthalic acid (TPA) on urinary bladder carcinogenesis was examined. Male Wistar rats were initiated by injection of N-Methyl-N-Nitrosourea (MNU) (20 mg/kg b.w. ip) twice a week for 4 weeks, then given basal diet containing 5% TPA, 5% TPA plus 4% Sodium bicarbonate (NaHCO3) or 1% TPA for the next 22 weeks, and then euthanized. 5% TPA treatment induced a high incidence of urinary bladder calculi and a large amount of precipitate. Though 5% TPA plus 4% Sodium bicarbonate (NaHCO3) and 1% TPA treatment did not induce urinary bladder calculi formation, they resulted in a moderate increase in urinary precipitate. Histological examination of urinary bladder revealed that MNU-5% TPA treatment resulted in a higher incidence of simple hyperplasia, papillary or nodular hyperplasia (PN hyperplasia), papilloma and cancer than MNU control. MNU-5% TPA plus 4% Sodium bicarbonate (NaHCO3) and 1% TPA treatment increased slightly the incidence of simple hyperplasia and PN hyperplasia (not statistically significant). The major elements of the precipitate are phosphorus, potassium, sulfur, chloride, calcium and TPA. The present study indicated that the calculi induced by TPA had a strong promoting activity on urinary bladder carcinogenesis and the precipitate containing calcium terephthalate (CaTPA) may also have weak promoting activity on urinary bladder carcinogenesis.

A new method of implanting orthotopic rat bladder tumor for experimental therapies

We developed a model of orthotopic transplantation of bladder tumor cells in female Fischer rats using a new reproducible technique. After first performing the mechanical abrasion of a portion of the bladder urothelium with an Abrader inserted transurethrally via a catheter, we administered a suspension of 5-40 x 10(6) viable AY-27 tumor cells in sterile phosphate-buffered saline to the bladder cavity. This rapidly led to a tumor growth incidence of approximately 100%. The induced bladder tumors grew expansively into the bladder cavity from the surface (mucosa) and gradually invaded the submucosa, muscles, serosa and surrounding tissue (high-stage invasive transitional cell carcinoma). Size and staging were related to the quantity of tumor cells instilled into the bladder cavity. This model matches the characteristics of human bladder tumor more closely than other bladder cancer models induced with tumor cells. Moreover, it presents many advantages: the method is reproducible, tumors grow rapidly, they are directly attached to the bladder surface and they are always located on the bladder wall, in line with the urethra. This proves especially helpful for evaluating chemotherapeutic agents by different means such as in vivo fluorescence spectroscopy, a noninvasive method used in photodynamic therapy, or other methods designed to detect and treat transitional cell carcinoma.

Lack of enhancing effect of two Kampo medicines, Sho-saiko-to (TJ-9) and Sairei-to (TJ-114), on rat urinary bladder carcinogenesis initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine

The modifying potential of two Kampo medicines (Japanese traditional herbal medicines), Sho-saiko-to (TJ-9) and Sairei-to (TJ-114), on urinary bladder carcinogenesis in male F344 rats initiated with N-butyl-N-(4-hydroxybutyl)- nitrosamine (BBN) was evaluated. Groups of 20 animals were given 0.05% BBN in their drinking water for 4 weeks and then 0.7 or 2.8% TJ-9, 0.9 or 3.6% TJ-114, or 3.0% sodium bicarbonate (NaHCO(3)) as a positive control substance in their diet for 32 weeks. All rats were killed after 36 weeks and examined histopathologically. No adverse effects of the test compounds were found in terms of survival, clinical sign, and body weight. Administration of 0.7 and 2.8% TJ-9 and 0.9 and 3.6% TJ-114 in the diet did not affect the incidences or extent of PN hyperplasia in the BBN-treated rats. Incidences and multiplicities of papillomas were also not affected in rats fed 0.7 or 2.8% TJ-9 and 0.9% TJ-114, while they were significantly decreased in animals given 3.6% TJ-114 in the diet. The results thus demonstrated that neither of the test chemicals exerted any promotional activity on urinary bladder carcinogenesis, in clear contrast to NaHCO(3). In addition, bladder carcinogenesis was reduced by 3.6% TJ-114 in the diet, under the present experimental conditions.

Hepatocarcinogenic activity of N-butyl-N-(4-hydroxybutyl)nitrosamine in rats is not modified by sodium L-ascorbate

Male F344 and Wistar Shionogi (WS) rats were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks and then killed at week 36 (experiment 1). Although reduction of body weight increase was found, no effects on liver weights were noted. Formalin-fixed and paraffin-embedded liver tissues from rats killed terminally were cut and stained for glutathione S-transferase placental form (GST-P) immunohistochemically. Marked elevation of quantitative values of small GST-P positive (GST-P+) foci were apparent in both strains of rat administered BBN. In experiment 2, both sexes of F344 rats were given 0.05% BBN in the drinking water for 4 weeks and then fed diet containing 0 or 5.0% sodium L-ascorbate (SA) for 32 weeks. No body and liver weight changes were evident in any group. Quantitative values for small GST-P+ foci were increased in both sexes of rats exposed to BBN but were not modified by additional SA treatment. Thus, it was confirmed that the selective bladder carcinogen BBN also acts as a liver carcinogen. These results, from the quantitative analysis of small GST-P+ foci as end point marker lesions, indicate that the liver tumor modifying potential of test chemicals can be evaluated in rats by using an initiation/promotion protocol for urinary bladder carcinogenesis.

Significant overexpression of metallothionein and cyclin D1 and apoptosis in the early process of rat urinary bladder carcinogenesis induced by treatment with N-butyl-N-(4-hydroxybutyl)nitrosamine or sodium L-ascorbate

Effects of a genotoxic bladder carcinogen, N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) and a non-genotoxic bladder promoter, sodium L-ascorbate (Na-AsA), on protein expression, cell proliferation and apoptosis of the bladder epithelium with or without the influence of testicular castration were investigated. Male F344 rats were divided into six groups (groups 1-6). BBN was given with 0.05% drinking water to groups 1 and 4 for 8 weeks, groups 2 and 5 received diet with 5% Na-AsA. Then the animals were treated without any chemicals. Groups 3 and 6 were non-treated controls. Testicular castration was carried out 2 weeks before commencement of chemical treatment on groups 4-6. The total observation period was 18 weeks. Overexpression of cyclin D1 was induced by BBN but not Na-AsA and the degree of overexpression was higher in the order simple hyperplasia, papillary or nodular hyperplasia, papilloma and carcinoma. Metallothionein (MT) was also overexpressed in bladder epithelium treated with BBN but not Na-AsA, but was decreased in papillomas and never found in a carcinoma. Cyclin D1-positive cells were essentially MT-negative. Therefore, it is speculated that MT protects genes from insult by genotoxic carcinogens and its lack is associated with tumor development. Apoptotic cell death occurred during treatment with BBN and Na-AsA and after their withdrawal. Chromatin condensation of many G0/G(1) cells was particularly marked on flow cytometry analysis 1 week after cessation of treatment, this being considered as an early apoptotic change. Although testicular castration had no influence on the above events, it resulted in decreased tumor formation as compared with the case of similarly treated intact animals. Our data demonstrate that overexpression of MT and cyclin D1 is specific for treatment with a genotoxic carcinogen, and suggest that MT overexpression may play an important suppressive role in the early stages of rat urinary bladder carcinogenesis.

Calcium phosphate-containing precipitate and the carcinogenicity of sodium salts in rats

Sodium saccharin, ascorbate and other sodium salts fed at high doses to rats produce urinary bladder urothelial cytotoxicity with consequent regenerative hyperplasia. For sodium salts that have been tested, tumor activity is enhanced when administered either alone or after a brief exposure to a known genotoxic bladder carcinogen. These sodium salts alter urinary composition of rats resulting in formation of an amorphous precipitate. We examined the precipitate to ascertain its composition and further delineate the basis for its formation in rat urine. Using scanning electron microscopy with attached X-ray energy dispersive spectroscopy, the principal elements present were calcium, phosphorus, minor amounts of silicon and sulfur. Smaller elements are not detectable by this method. Infrared analyses demonstrated that calcium phosphate was in the tribasic form and silicon was most likely in the form of silica. Small amounts of saccharin were present in the precipitate from rats fed sodium saccharin (<5%), but ascorbate was not detectable in the precipitate from rats fed similar doses of sodium ascorbate. Large amounts of urea and mucopolysaccharide, apparently chondroitin sulfate, were detected in the precipitate by infrared analysis. Chemical analyses confirmed the presence of large amounts of calcium phosphate with variably small amounts of magnesium, possibly present as magnesium ammonium phosphate crystals, present in urine even in controls. Small amounts of protein, including albumin and alpha(2u)-globulin, were also detected (<5% of the precipitate). Calcium phosphate is an essential ingredient of the medium for tissue culture of epithelial cells, but when present at high concentrations (>5 mM) it precipitates and becomes cytotoxic. The nature of the precipitate reflects the unique composition of rat urine and helps to explain the basis for the species specificity of the cytotoxic and proliferative effects of high doses of these sodium salts.

Concentration dependent promoting effects of sodium L-ascorbate with the same total dose in a rat two-stage urinary bladder carcinogenesis

Sodium L-ascorbate (Na-AsA) has been demonstrated to be a strong promoter of rat urinary bladder tumor development initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). In the present study, we investigated variation in its promoting activity when the same total dose was given with different concentrations and exposure times. After 4 weeks administration of 0.05% BBN, group 1 served as a control without any post-initiation treatment. The rats in groups 2-4 received 1.25% Na-AsA diet for 36 weeks, 2.5% Na-AsA for 18 weeks and 5% Na-AsA for 8 weeks, respectively. Tumor number (papillomas and carcinomas) was greatest in group 3, and area in group 4 (P < 0.05). However, no enhancement was noted in group 2, although preneoplastic lesions were significantly increased. These results suggest that with the same total administration dose, high concentration of Na-AsA has the strongest promoting effects on tumor development in urinary bladder carcinogenesis.

Promotion by sodium L-ascorbate in rat two-stage urinary bladder carcinogenesis is dependent on the interval of administration

In our two-stage model of rat urinary bladder carcinogenesis employing N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as the initiator, sodium L-ascorbate (Na-AsA) exhibits dose-dependent promotion. In the present study, in order to assess the possible reversibility of the promoting effects, we investigated how different administration periods of Na-AsA influence its promoting activity. In experiment 1, rats were treated with 5% Na-AsA for different administration periods with or without withdrawal and injected with 5-bromo-2'-deoxyuridine (BrdU) to allow determination of the cell proliferation status. Replicative DNA synthesis in the urinary bladder epithelium was shown to return to normal after removal of the promoting stimulus. In experiment 2, rats were initially given BBN for 4 weeks and subsequently received 16 weeks of Na-AsA, alternating with basal diet, at intervals of 4, 8 or 16 weeks, within a total 32-week period. The longer the continuous exposure to Na-AsA, the greater the yield of papillomas and carcinomas in the urinary bladder. In experiment 3, Na-AsA was given for 4 or 8 weeks after BBN initiation and the animals were killed at weeks 8 and 12. Both promotion of lesion development and increase of DNA synthesis in the urinary bladder epithelium were dependent on the length of exposure to Na-AsA and the total period of exposure. The results indicate that the promoting effects of Na-AsA in urinary bladder carcinogenesis are reversible to a certain extent after its withdrawal, and the existence of a cumulative exposure time threshold seems likely.

p16 gene overexpression in mouse bladder carcinomas

Deletion of 9p21 has frequently been observed in human bladder carcinomas. A candidate target suppressor gene, p16, was recently identified within this deleted region. In this study, we therefore investigated the loss of heterozygosity (LOH) of the p16 gene which is located on mouse chromosome 4, as well as its expression in mouse bladder carcinomas. We also studied the effects of normal cell contamination on LOH analysis using xenografts in CD-1(ICR) nude mice from B6C3F1 bladder carcinomas. We could not detect any LOH at the p16 locus in the mouse primary bladder carcinomas and xenografts. Surprisingly, overexpression of p16 was found in all primary mouse bladder carcinomas. Using microsatellite polymorphisms, a distinction could be made between PCR products derived from B6C3F1 and CD-1(ICR) nude mice. It was thereby confirmed that effects of normal cell contamination on LOH analysis are negligible when only tumor tissue is carefully sampled. The results suggest that abnormalities of p16 expression may be involved in mouse bladder carcinogenesis, but that gene deletion is not involved.

Epithelial cell proliferation in the digestive tract induced by space restriction and water-immersion stress

The effects of space restriction and water-immersion stress on epithelial cell proliferation in the digestive tract, with special attention to the esophagus, stomach and duodenum, in 8-week-old SD male rats were examined. Histological assessment revealed spotted hemorrhagic lesions in the fundus of the glandular stomach, accompanied by statistically increased 5-bromo-2'-deoxyuridine (BrdU) labeling index in the fundic and pyloric regions. Furthermore, biochemical analysis demonstrated an increased activity of ornithine decarboxylase (ODC) and spermidine/spermine N1-acetyltransferase (SAT), known as key late-limiting enzymes of the polyamine pathway, in the gastric fundus. The stress may induce a remarkable increase in expression of c-fos, c-jun and c-myc mRNAs in both fundic and pyloric regions of the glandular stomach. There were no remarkable changes in the esophagus. These results indicate that space restriction and water-immersion stress induced cell proliferation in the glandular stomach through overexpression of proto-oncogenes and increased ODC and SAT activities that might be related to the promotion of gastric carcinogenesis.

Lack of promotion of urinary bladder carcinogenesis by sodium bicarbonate and/or L-ascorbic acid in male ODS/Shi-od/od rats synthesizing alpha 2 mu-globulin but not L-ascorbic acid

The study was designed to investigate whether sodium bicarbonate (NaHCO3) and/or L-ascorbic acid (AsA) promote urinary bladder carcinogenesis in male ODS/Shi-od/od (ODS) rats, which, unlike male F344 rats, are resistant to sodium L-ascorbate (Na-AsA)-promoting effects. Whereas F344 rats can synthesize AsA and alpha 2 mu-globulin (A2 mu-G), only A2 mu-G in produced in ODS rats. The two strains were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 2 wk and then were fed basal CA-1 diet supplemented with 3% NaHCO3 plus 5% AsA (NaHCO3 + AsA), 3% NaHCO3, 5% AsA, or no chemicals for 32 wk. ODS rats given BBN-NaHCO3 or BBN-(NaHCO3 + AsA) had only a few small carcinomas in the urinary bladder, like those receiving BBN alone or BBN-AsA. In contrast, F344 rats administered BBN-NaHCO3 or BBN-(NaHCO3 + AsA) had many more, larger, carcinoma than animals of the same strain given BBN alone or BBN-AsA. AsA alone did not have any effect in either strain. Administration of NaHCO3 alone or NaHCO3 + AsA was associated with significant elevation of urinary pH and Na+ concentration to the same extent in both strains but, again, AsA alone was without effect. NaHCO3 + AsA and AsA alone increased the urinary concentration of total ascorbic acid in both strains but the observed levels wer lower in ODS rats. The results indicate that ODS rats are resistant to the modifying effects of NaHCO3 and/or AsA on two-stage urinary bladder carcinogenesis, and thus that the susceptibility to the promotional activity of sodium-salt-type compounds may be regulated by factors other than A2 mu-G-synthesizing ability and urinary levels of pH, Na+ and total ascorbic acid.

Quantitative trait loci associated with promoting effects of sodium L-ascorbate on two-stage bladder carcinogenesis in rats

In the two-stage rat bladder carcinogenesis model using N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as an initiator and sodium L-ascorbate (SA) as a promoter, we found a notable strain difference between F344/DuCrj (F344) and WS/Shi (WS) rats in susceptibility to the promoting effect of SA. Twenty each of F344, WS and reciprocal F1 hybrid rats were given 0.05% BBN in their drinking water for 4 weeks and then a basal diet with (BBN-SA group) or without (BBN group) a 5% SA supplement for 32 weeks. In F344 and also in reciprocal F1 hybrids, the number of tumors per rat was significantly higher in the BBN-SA group than in the BBN group (P < 0.0001). In contrast, WS rats were not significantly affected by either treatment (P = 0.8). These findings indicate that F344 rats are highly susceptible to the promoter effect of SA, but WS rats are not. Linkage analysis of 108 WSx (WS x F344) F1 backcrosses revealed that this difference was related to a quantitative trait locus mapped on rat Chr. 17 (maximum LOD score, 3.86) named Bladder Tumor Susceptible-1 and possibly another locus on Chr. 5 (maximum LOD score, 2.39). This study has provided the first evidence that host genes influence the risk of bladder cancer development.

Dose-dependent amplification by L-ascorbic acid of NaHCO3 promotion of rat urinary bladder carcinogenesis

The dose dependence of L-ascorbic acid (AsA) copromotion of urinary bladder carcinogenesis with continuous concomitant administration of NaHCO3 was investigated. In the first experiment, 83 male F344 rats were all given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 4 wk and then divided into 5 groups, which received basal diet (Oriental MF) containing AsA at 0, 1, 2, 3.5, or 5% plus 1.5% NaHCO3 for 32 wk. Relative urinary bladder weights in the 5% AsA group were significantly increased as compared to the 0 or 1% group values due to the development of tumors. Both the incidence and number of microscopic urinary bladder lesions (tumors and preneoplastic lesions) showed dose-dependent increases. Furthermore, the sizes of the urinary bladder tumors (carcinomas and papillomas) were significantly increased with the highest dose, 5-bromo-2'-deoxyuridine labeling indices showed slightly increased proliferation in preneoplastic lesions of the urinary bladder epithelium with 5% AsA treatment. In a separate experiment, scanning electron microscopic observation revealed that administration of 5% AsA plus 1.5% NaHCO3 for 8 wk, without BBN, altered the urinary bladder surface. Elevation of urinary bladder epithelium AsA content, as well as urinary AsA, was also noted. Ornithine decarboxylase (ODC) activity and ODC messenger RNA levels in urinary bladder epithelium of rats treated with 1.5% NaHCO3 plus 5% AsA for 8 wk showed no statistically significant differences as compared to the control group. The results indicate that AsA amplifies the rat urinary bladder carcinogenesis promotion activity of NaHCO3 and that its intensity of action depends on the dose, particularly at high dose.

Strain differences in sensitivity to the promoting effect of sodium L-ascorbate in a two-stage rat urinary bladder carcinogenesis model

Rat strain differences in sensitivity to the promoting effect of sodium L-ascorbate (SA) on the development of urinary bladder tumors were investigated. In experiment 1, WS/Shi (WS), ODS/Shiod/od (ODS), and LEW/Crj (LEW) rats were initiated with 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) in their drinking water and subsequently given basal Oriental MF diet (M) with or without a 5% SA supplement. In LEW rats the SA treatment increased the induction of neoplastic lesions in the urinary bladder, whereas WS and ODS animals proved unresponsive to its promoting effects. In experiment 2, WS and F344 rats were maintained on two kinds of commercial basal diets, M and CLEA CA-1 (C), during administration of SA, since dietary factors can influence promoting effects. Feeding M during the promotion period in F344 rats yielded significantly more neoplastic lesions than feeding C, but in WS rats no such dietary influence was apparent. In experiment 3, strain differences in biosynthesis of alpha-2u-globulin (alpha 1a-g) were assessed because both alpha 2a-g in the urine and administration of sodium salts of organic acids such as SA have been reported to be involved in tumor promotion. Immunohistochemical analysis of renal tubules and Western blotting analysis of urine revealed the presence of alpha 2a-g in all three strains examined. These data suggest that differences in susceptibility to promotion are due to genetic factors rather than dietary factors and the ability to synthesize alpha 2a-g.

Role of urinary physiology and chemistry in bladder carcinogenesis

Urine is a complex mixture of numerous substances, only some of which are described above. Literally thousands of substances have been identified in normal urine, including a variety of ions, non-ionic substances and macromolecules. Their presence and concentrations are highly variable, dependent on fluid intake and on nutritional, physiological and biochemical influences. Marked diurnal variations exist. Methodologies involved in the collection and analysis of these components can greatly influence the interpretation of the results. The influence of these various parameters in the urine on bladder carcinogenicity can be either direct or indirect. A major difficulty in studying this aspect of urothelial carcinogenesis is that it is essentially impossible to alter only one variable in the urine at a time. Alteration of any one variable results in physiological alteration of several other of the constituents in the urine. In addition, the processes involved in urothelial carcinogenesis frequently involve a complex interaction of multiple variables, such as volume, osmolality, cationic concentration, anionic concentration, quantitative and qualitative differences in protein, and generation of precipitate, crystals or calculi. Thus, it is likely that the actual mechanisms involved in the carcinogenic process with many of these chemicals, particularly those that are non-genotoxic, will involve a complex interaction of several constituents of the urine. Although this poses a formidable obstacle to our understanding in experimental situations as well as in extrapolating to humans, the role of specific factors appears to be discernible and should offer insight into the risk assessment process (Cohen and Ellwein, 1991 a,b and 1992).

The etiology of bladder cancer--are there any new clues or predictors of behavior?

It is well documented that the etiology of bladder cancer involves environmental factors. Most chemical carcinogens probably affect the urothelial cells via their presence in the urine. As an important cofactor, cell proliferative activity may be increased by urinary bladder infection, irritation by bladder stones or through the action of a variety of endogenously produced direct acting chemicals or agents. Among the known causative factors, avoidable major ones are occupational exposure to certain chemicals such as benzidine and 4-aminobiphenyl, cigarette smoking and bilharzial infection, which could be eradicated by a combination of praziquantel, antihelminth therapy, education and improvements in social welfare. An anticarcinogenic drug, cyclophosphamide, used as an immunosuppressive agent also seems to be associated with a high risk of idiopathic induction of bladder cancer and physicians should therefore pay particular attention to its diverse effects when considering its prescription. In contrast to the above, the consumption of coffee and tea including artificial sweeteners is now thought unlikely to be major risk. So far there is no good biochemical tool to predict individual exposure to bladder carcinogens/or relative risk of bladder cancer development. However, acetylation capacity can be applied to assess susceptibility to carcinogenic amines in people exposed in their working environment. Progress in molecular biological analysis will hopefully bring to light etiology-specific DNA damage in the bladder tumors and prove useful for prediction of tumor behavior in the near future.

Lack of promoting effects of alpha-linolenic, linoleic or palmitic acid on urinary bladder carcinogenesis in rats

Potential promoting effects of alpha-linolenic, linoleic and palmitic acids were investigated in a two-stage urinary bladder carcinogenesis model. In experiment 1, male F344 rats were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 4 weeks and then basal diet containing 10% alpha-linolenic, 10% linoleic or 10% palmitic acid along with 0.2% butylated hydroxyanisole (BHA) as an antioxidant for 24 weeks. The development of tumors in the urinary bladder was not increased by treatment with any of the fatty acids. In experiment 2, male F344 rats were given 10% alpha-linolenic, 10% linoleic or 10% palmitic acid along with 0.2% BHA in their diet for 8 weeks without prior BBN treatment. The administration of fatty acids was not associated with any increase in the 5-bromo-2'-deoxyuridine labeling index of the urinary bladder epithelium. Serum and/or urine fatty acid levels increased in the cases of alpha-linolenic and linoleic acid treatments, but not with palmitic acid. Under the present experimental conditions neither the two polyunsaturated nor the one saturated fatty acid exerted any promoting effect on urinary bladder carcinogenesis.

Absence of promoting potential of bracken fern (Pteridium aquilinum) in rat urinary bladder carcinogenesis induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine and uracil

Conventional studies on bracken fern (Pteridium aquilinum; PA) carcinogenicity have used high dietary concentrations (around 30%) and long-term exposure (up to 52-70 weeks) without consideration of the multistep character of the chemical carcinogenesis process. The present study evaluated specifically the promoting potential of 3-5% dietary crude PA in the rat urinary bladder mucosa in a 32-week-long initiation-promotion assay for chemical carcinogenesis. Initiation of urothelial carcinogenesis was accomplished with N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN). Uracil (U) was provided through the diet in order to expand the population of initiated cells. Seven groups (G) of male Wistar rats were submitted to the following treatments: G1 = BBN (n = 8); G2 = U (n = 10); G3 = BBN-U (n = 9); G4 = BBN-PA-U-PA (n = 16); G5 = PA (n = 8); G6 = BBN-PA (n = 10); G7 = PA-U-PA (n = 12). At the end of the experiment rats presenting epithelial papillary or nodular hyperplasia (PNH), papillomas (PAP), or simultaneous PNH plus PAP numbered, respectively G1: 2-0-1; G2: 0-0-0; G3: 3-0-2; G4: 4-3-2; G5: 1-0-1; G6: 8-0-0; and G7: 0-0-0, with no significant differences in the incidence of lesions among the groups. More frequent and more severe lesions occurred in BBN-initiated animals, predominantly in those also exposed to uracil (G3 and G4). Low-dose crude bracken fern in the diet does not promote rat urinary bladder carcinogenesis after a 32-week period of exposure, even when the initiated urothelial cell population has been expanded through a mechanical stimulus.

Prohibitin gene is overexpressed but not mutated in rat bladder carcinomas and cell lines

Prohibitin was isolated as a candidate antiproliferating gene in rat liver cells, and it has been suggested as a tumor suppressor gene in human breast cancer. We investigated the steady state level of prohibitin mRNA in rat bladder cell lines and in rat bladder carcinoma induced by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) and sodium saccharin, as well as the protein level in rat bladder epithelial cells. We also examined the prohibitin gene for mutations using the polymerase chain reaction (PCR) single strand conformation polymorphism (SSCP) and direct sequencing methods. All rat bladder tumors investigated and several cell lines had unexpectedly increased steady state levels of prohibitin mRNA compared with that of normal rat bladder or liver. The prohibitin protein was easily detected by Western blotting in all cell lines regardless of their malignant status or growth rate. However, PCR-SSCP and direct sequencing analysis showed no mutations in the prohibitin gene. These results These results indicate that prohibitin overexpression, but not mutations, may be involved in the early stage of rat bladder carcinogenesis.

Modification of N-butyl-N-(4-hydroxybutyl)nitrosamine-initiated urinary bladder carcinogenesis in rats by phytic acid and its salts

The effects of dietary phytic acid and its salts on the promotion stage of two-stage urinary bladder carcinogenesis were examined. Male F344 rats were initiated by exposure to 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine in the drinking water for 4 wk, and then treated with basal diet containing a 2% supplement of phytic acid (PA), phytic acid dodecasodium salt (Na-PA), phytic acid dodecapotassium salt (K-PA), phytic acid hexamagnesium salt n-hydrate (Mg-PA) or no added chemical for 32 wk. Na-PA significantly increased the development of preneoplastic and neoplastic lesions of the urinary bladder. K-PA also brought about a tendency for increase in papillomas, whereas Mg-PA and PA were without effect. Both Na-PA and K-PA caused elevation of urinary pH, and Na+ or K+ concentration, respectively. These results confirm the promoting activity of the sodium salt of phytic acid for urinary bladder carcinogenesis and indicate modulation by urinary components, as demonstrated by increases in urinary pH, and Na+ concentration.

Mutations and expression of the p53 gene in rat bladder carcinomas and cell lines

Abnormalities of the p53 gene are frequently observed in human tumors, including urinary bladder carcinoma, suggesting that p53 plays an important role in human carcinogenesis. However, its role in rat bladder carcinogenesis is unclear. We investigated p53 gene mutations and expression in rat urinary bladder carcinogenesis in vivo and in vitro. Fifteen urothelial cell lines, including six untransformed (nontumorigenic) ones, six transformed (tumorigenic) in vitro, and three derived from tumors induced in vivo, were examined for p53 expression by immunochemical analysis and for p53 mutations; in addition, 81 rat bladders were analyzed immunohistochemically for p53 expression, and 23 rat bladder tumors were analyzed for p53 mutations. Four cell lines had mutations in the p53 gene. Two of these were missense point mutations, and the other two were splicing mutations. On the other hand, no mutations were found in the bladder tumors induced in rats. By immunoprecipitation with PAb240, which is supposed to be specific for mutant p53, we detected mutations in three of the cell lines; PAb240 did not react with wild-type p53. However, in all cell lines and in growing populations of primary cultured bladder urothelial cells, p53 expression was detected immunohistochemically or by western blotting using PAb240 or PAb 421 monoclonal antibodies. In a high percentage of transitional cell carcinomas, wild-type p53 expression was detected by immunohistochemical analysis with PAb240. These results suggest that p53 gene mutations may not occur frequently in rat bladder carcinogenesis in vivo but may occur in vitro and that p53 overexpression detected immunohistochemically is common and may be related to cell proliferation rather than to the presence of mutations in rat bladder carcinogenesis.

Toxicokinetic and mechanistic considerations in the interpretation of the rodent bioassay

When chemicals that are nongenotoxic in conventional assays produce increases in tumor incidence in rodents in chronic bioassays, the determination of the significance of these data for human safety is a challenging task. An important first step in this process is consideration of available data on the mechanism of action and biological properties of the chemical as well as pharmacokinetic and metabolism data in the species showing the response. In recent years, there has been an increase in the understanding of so-called "secondary mechanisms" of carcinogenesis (e.g., thyroid tumors in rats following exposure to enzyme inducers). Application of these data may assist in determination of human risk. There are 2 important questions that will be explored and developed: Are there biological effects produced in the test species that could explain the increase in tumor incidence, and will these effects be reproduced in humans? What is the exposure to the chemical that is associated with the increase in tumors, and how does this relate to exposure in humans?

Chemoprevention by indomethacin of tumor promotion in a rat urinary bladder carcinogenesis model

The chemopreventive effects of indomethacin (IM) on the enhancement of bladder carcinogenesis and transitional-epithelial-cell proliferation by butylated hydroxyanisole (BHA) or sodium L-ascorbate (Na-AsA) were investigated. All animals were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 4 weeks. They then received 2% BHA or 5% Na-AsA for 20 weeks, followed by 20 ppm IM in the drinking water or normal tap water without supplement for a further 20 weeks, or BHA or Na-AsA alone or concomitantly with IM for 40 weeks. No differences in bladder-tumor development were found when IM was administered after cessation of BHA or Na-AsA exposure. However, IM in combination with either BHA or Na-AsA significantly reduced both the incidence and the multiplicity of papillomas and carcinomas as compared with the values of groups receiving BHA or Na-AsA alone. This was associated with decreased DNA synthesis and prostaglandin (PG) E2 levels in the existing bladder tumors. Combined treatment with IM did not exert any effects on BHA forestomach carcinogenesis. A separate 8-week combination study demonstrated that IM diminished the increase in expression of proliferation nuclear-cell antigen (PCNA) induced by BHA or Na-AsA alone. The present results suggest that PGE2 may be involved in promotion of rat bladder carcinogenesis and that the PG synthesis blocker IM might exert preventive effects on the development of bladder cancer in humans.

No enhancing effects of calcium/magnesium salts of L-glutamate and L-ascorbate on tumor development in a rat medium-term multiorgan carcinogenesis bioassay

Calcium/magnesium salts of L-glutamate and L-ascorbate were tested for modification potential using a rat multiorgan carcinogenesis bioassay. Following sequential treatment with three different carcinogens (diethylnitrosamine, N-methylnitrosourea, and dihydroxydi-N-propylnitrosamine) over a 4-wk period, rats were given diet containing 5% monocalcium di-L-glutamate tetrahydrate (Ca-glutamate), 2.5% monomagnesium di-L-glutamate tetrahydrate (Mg-glutamate), 5% L-glutamic acid, 5% monocalcium di-L-ascorbate dihydrate (Ca-ascorbate), 2.5% monomagnesium di-L-ascorbate dihydrate (Mg-ascorbate), or 5% L-ascorbic acid for 16 wk. Body weight increase was slightly suppressed in the groups receiving Ca-ascorbate, Mg-ascorbate, and ascorbic acid supplementation after the carcinogen treatments. While administration of Ca-glutamate or Ca-ascorbate raised urinary pH, ascorbic acid values were decreased. Concentrations of calcium and magnesium ions in the urine increased after ingestion of Ca-glutamate or Ca-ascorbate, and Mg-glutamate or Mg-ascorbate, respectively, but phosphorus levels decreased in all groups given calcium and magnesium salts. No consistent treatment-related changes in the concentrations of sodium or potassium ions in the urine were detected. Histopathological investigation at wk 20 did not demonstrate any modification of tumorigenesis with regard to the incidence of frequency of lesions developing in the various target organs/tissues. The present results thus revealed no apparent enhancement of carcinogenesis at any site, including the urinary system, by calcium or magnesium salts using the present rat multiorgan carcinogenesis bioassay.

Lack of promotion of N-butyl-N-(4-hydroxybutyl)nitrosamine-initiated urinary bladder carcinogenesis in mice by rat cancer promoters

The effects of dietary exposure to sodium L-ascorbate (Na-AsA), butylated hydroxyanisole (BHA), and diphenyl on the development of urinary bladder tumors in a mouse two-stage carcinogenesis model were examined. Male B6C3F1 mice received 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in the drinking water for 4 weeks and were then treated with 5% Na-AsA, 1% BHA, or 1% diphenyl for 32 weeks. None of these chemicals enhanced the development of either preneoplastic or neoplastic lesions in the urinary bladder. Furthermore, DNA synthesis levels of urinary bladder epithelium in mice treated with each substance alone for 8 weeks were not elevated significantly, although Na-AsA was associated with a significant increase in the urinary pH value and Na+ concentration. The results indicate that Na-AsA, BHA, and diphenyl do not exert an enhancing influence on mouse bladder carcinogenesis, in clear contrast to the case in the rat.

Transitional cell carcinoma of the ureteral stump 23 years after radical nephrectomy for adenocarcinoma

We report a case of simultaneous invasive transitional cell carcinoma in a ureteral stump and superficial bladder tumor occurring 23 years after ipsilateral radical nephrectomy for adenocarcinoma of the kidney. We review the literature on similar cases and discuss potential etiologies of tumor formation in the ureteral stump.

Inhibition of two-step urinary bladder carcinogenesis by the somatostatin analogue RC-160

Fisher 344 female rats were exposed for 4 weeks to the initiator carcinogen N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) 0.05% in the drinking water and thereafter to the promoter carcinogen mitomycin C (0.08 mg per animal per week) intravesically for 12 weeks. High incidence of urinary bladder transitional cell cancers was observed (17 in situ and 17 invasive carcinomas among 40 rats). When the somatostatin analogue RC-160 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2) was administered s.c. at the dose of 50 micrograms per animal per day during 6-week period of promotion with mitomycin C, the incidence of urinary bladder cancer was dramatically reduced. Only 1 in situ carcinoma was observed among 20 rats and only preblastomatous lesions (dysplasias and papillomas) occurred. This effect could indicate that RC-160 interferes with the process of promotion by induction of enhanced apoptosis (programmed cell death) of the dysplastic urothelial cells. RC-160 could be tried therapeutically for the hormonal prevention of malignant transformation of preneoplastic lesions in the urinary bladder.

Synergism of environmental carcinogens and promoters on bladder cancer development initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine in F344 rats

Synergistic or additive effects of combined treatments with carcinogens or promoters on N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-initiated rat bladder carcinogenesis were examined. Male F344 rats were given BBN as an initiator followed by low doses of 3 sodium salts (sodium bicarbonate, sodium L-ascorbate and sodium citrate) and/or 3 antioxidants (butylated hydroxyanisole, butylated hydroxytoluene and tertiary butylhydroxyquinone). Combined treatments with 3 sodium salts or 3 antioxidants, and especially all 6 chemicals together promoted bladder carcinogenesis. In addition, these combined treatments were associated with increased DNA synthesis of the bladder epithelium. Combined administration of the carcinogens, o-anisidine, p-cresidine, and 4-chloro-o-phenylenediamine at low doses also enhanced BBN-initiated bladder carcinogenesis. These results indicate that environmental carcinogens or promoters can exert synergistic or additive actions on bladder cancer induction.

Chemical carcinogenesis of the urinary bladder--a status report

Cigarette smoking and certain types of occupational exposure to arylamines appear to be the main cause of human urinary bladder cancer. Little is known of the promotion of bladder cancer in humans, although this stage has been demonstrated in rodents. Perhaps as a consequence of initiation, multifactorial alterations of cellular genes occur. These genes include the epidermal growth factor receptor gene, erbB-2, int-2, hst, and H-ras, which exert positive control over cell growth, as well as the suppressor genes Rb-1, and the gene coding for p53. Chromosomal changes such as deletions, translocations and/or amplifications related to these genes may be of significance for prognosis of this disease.

Summation effects of uracil and other promoters on epithelial lesion development in the F344 rat urinary bladder initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine

Five non-genotoxic chemicals previously demonstrated to be bladder cancer promoters in 36-week in vivo assays for carcinogenesis were reevaluated in a 20-week experiment in order to assess the summation influence of dietary uracil, a component of RNA, on the development of (pre)neoplastic lesions. The test chemicals, sodium bicarbonate, sodium L-ascorbate, sodium citrate, butylated hydroxytoluene and ethoxyquin, were mixed into the diet at concentrations of 3%, 5%, 5%, 1% and 0.8%, respectively, and administered to male F344 rats after initiation with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 4 weeks. The test chemicals were given from the 4th to the 8th and the 11th to 20th experimental weeks, uracil being administered at the level of 3% in the diet during the intervening period. Rats in the control group received only BBN and uracil. All animals were killed at week 20 and the bladders were evaluated for the occurrence of putative preneoplastic papillary or nodular (PN) hyperplasia and tumors. Significant increase in the occurrence of PN hyperplasia was observed in all groups initiated with BBN and fed uracil and test chemicals. Quantitative values for papillomas were also significantly increased except in the ethoxyquin-treated group. The results confirm that uracil given in the middle of the post-initiation stage enhances the promoting activity of chemicals and suggest that the use of this chemical might be useful to reduce the duration of current bioassays for bladder chemical carcinogens.

Early indicators of bladder carcinogenesis produced by non-genotoxic agents

There are several early indicators of non-genotoxic bladder tumorigenicity. The non-invasive indications are polydipsia, diuresis, changes in urine pH and urinary cation concentrations, especially Na and Ca. The indicators requiring invasive techniques are increased bladder weight and increased cell replication assessed by DNA labeling or histologically as epithelial hyperplasia. SEM has been used to characterize bladder surface changes, and a reduction of bladder tissue Ca has been implicated in one mechanism leading to bladder cancer. Wherever multiple species have been tested, the non-genotoxic bladder carcinogens have induced bladder responses only in rats. This is true whether the criterion was complete carcinogenesis, promotion or short-term indicators. It is also evident that the response can vary greatly within rat strains and is dependent upon the diet being fed. These variables make the relevance of the results obtained in the rat bladder of questionable significance to man. In relation to chronic studies it is clear that as the male rat ages it loses the capacity to concentrate urine, probably because of the endemic, age-progressive loss of functional renal tissue. It is also clear that the bladder grows to accommodate the increase in urine output. Thus it is likely that any agent or treatment that causes bladder damage may be associated with increased neoplasia expression in aged male rats. No other species shows the degree of spontaneous nephrosis seen in the male rat, a condition which is both rat strain- and diet-dependent. Finally, it should be recognized that while there are some early indicators of bladder tumorigenesis that can be useful as warning signs, each compound is likely to yield unique responses when its mechanism is studied in detail. To facilitate discussion of the parameters that have been identified as early indicators of bladder tumorigenesis associated with non-genotoxic agents, the proposed mechanisms of cancer development, the information which led to these proposals and a critique of the mechanisms have been presented.

Comparative promoting activities of phosphate salts on rat two-stage bladder carcinogenesis under conditions of equivalent urinary Na+ or K+ levels

Promoting effects of Na or K phosphate salts on rat two-stage bladder carcinogenesis were compared. Animals were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 4 weeks and thereafter received 1.4% Na3PO4, 2.0% NaH2PO4, 1.0% K3PO4, or 2.5% KH2PO4, these dietary concentrations being selected because they result in approximately equal levels of Na+ and K+ in the urine, equivalent to moderate natriuresis or kaluresis in comparison with our previous data. Treatment with Na3PO4 or K3PO4 induced significant increase in urinary pH compared with control values, whereas urinary pH in the NaH2PO4 and KH2PO4 groups was comparable to control values. With regard to preneoplastic lesion development, both incidences and multiplicity were significantly increased in the groups given Na3PO4 or K3PO4 compared with both controls and NaH2PO4 or KH2PO4 groups, respectively. Furthermore, treatment with Na3PO4 significantly increased multiplicity of papillomas, accompanied by a tendency to increased incidence. No statistically significant difference in promoting potential between Na3PO4 and K3PO4 groups was evident. The present results thus suggest that tumor promotion under conditions of moderate natriuresis or kaluresis depends primarily on high urinary pH.

Histochemical and stereological analysis of putative preneoplastic hepatic lesions

Histochemistry is a valuable tool in the analysis of altered hepatic foci. These lesions contain alterations in the activities of certain enzymes, including gamma-glutamyl transpeptidase (GGT), placental glutathione-S-transferase (PGST), glucose-6-phosphatase (G6Pase), and ATPase, or in certain cellular functions, such as the ability to store iron. The appearance of altered hepatic foci has been found to correlate with the later appearance of hepatocellular carcinomas in rodents. The markers PGST and GGT are the most sensitive at detecting altered hepatic foci induced by most chemicals, but are unable to detect altered hepatic foci induced by some agents, such as peroxisome proliferators. Other markers, such as ATPase or G6Pase, should therefore be used in combination with PGST or GGT in identifying altered hepatic foci. The strain of rat used and the type of diet fed also influence the number of altered hepatic foci induced and the enzyme markers seen. The number of foci per cm2 and the diameters of altered hepatic foci in histochemically-stained tissue sections can easily be quantified. The number of foci per cm2, however, does not give a reliable estimate of the number of altered hepatic foci induced because larger altered hepatic foci are more likely to be transected. The equations of quantitative stereology therefore should be used to transform the data to obtain the number of foci induced per cm3 or per liver, the average volume of individual foci, and the percent of the liver volume occupied by altered hepatic foci. In conclusion, the use of histochemistry to identify preneoplastic lesions and the use of quantitative stereology to estimate their number and volume allow accurate and sensitive quantitation of altered hepatic foci.

Promoting effect of the peroxisome proliferator, clofibrate, but not di(2-ethylhexyl)phthalate, on urinary bladder carcinogenesis in F344 rats initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine

The modifying potential of clofibrate and di(2-ethylhexyl)phthalate (DEHP) on second stage, N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-initiated urinary bladder carcinogenesis was investigated in male F344 rats, using a uracil-accelerated transitional cell proliferation model. Six-week-old animals received 0.05% BBN in their drinking water for 4 weeks and then clofibrate (1.0, 0.5, and 0.25%) and DEHP (1.2, 0.6, and 0.3%) were given during experimental weeks 5-8 and weeks 12-20. Uracil was administered during weeks 9-11 at a dietary level of 3.0%. Control rats were treated with BBN and uracil without peroxisome proliferator. Surviving animals were killed at the end of week 20 of the experiment, when the densities of putative preneoplastic, papillary or nodular (PN) hyperplasias (numbers per 10 cm of basement membrane) were significantly increased in all clofibrate-treated, but not the DEHP groups. The incidences of PN hyperplasia were similar in both treated animals and controls. In a second experiment, rats fed diets containing 1.0% clofibrate or 1.2% DEHP were assessed for levels of DNA synthesis in urinary bladder epithelium by 5-bromo-2-deoxyuridine immunohistochemistry. Numbers of labeled nuclei remained within normal levels, and no proliferative changes were evident. Thus, the present experiments indicated that while clofibrate, but not DEHP, exerts weak enhancing effects on BBN-initiated urinary bladder carcinogenesis in rats this is not associated with increased levels of DNA synthesis in the affected epithelium.