Urinary Bladder Tumors In Rats Research Articles

Copper-mediated DNA damage caused by purpurin, a natural anthraquinone

BackgroundPurpurin (1,2,4-trihydroxy-9,10-anthraquinone), a natural red anthraquinone pigment, has historically been used as a textile dye. However, purpurin induced urinary bladder tumors in rats, and displayed a mutagenic activity in assay using bacteria and mammalian cells. Many carcinogenic dyes are known to induce bladder cancers via DNA adduct formation, but carcinogenic mechanisms of purpurin remain unknown. In this study, to clarify the mechanism underlying carcinogenicity of purpurin, copper-mediated DNA damage induced by purpurin was examined using 32P-labeled DNA fragments of human genes relevant to cancer. Furthermore, we also measured 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, in calf thymus DNA.ResultsPurpurin plus Cu(II) cleaved 32P-labeled DNA fragments only under piperidine treatment, indicating that purpurin caused base modification, but not breakage of the DNA backbone. In the absence of Cu(II), purpurin did not induce DNA cleavage even with piperidine treatment. Purpurin plus Cu(II) caused piperidine-labile sites predominantly at G and some T residues. Bathocuproine, a Cu(I) chelator, completely prevented the occurrence of piperidine-labile sites, indicating a critical role of Cu(I) in piperidine-labile sites induced by purpurin plus Cu(II). On the other hand, methional, a scavenger of a variety of reactive oxygen species (ROS) and catalase showed limited inhibitory effects on the induction of piperidine-labile sites, suggesting that ROS could not be major mediators of the purpurin-induced DNA damage. Considering reported DNA adduct formation by quinone metabolites of several carcinogenic agents, quinone form of purpurin, which is possibly generated via purpurin autoxidation accompanied by Cu(I)/Cu(II) redox cycle, might lead to DNA adducts and piperidine-labile sites. In addition, we measured contents of 8-oxodG. Purpurin moderately but significantly increased 8-oxodG in calf thymus DNA in the presence of Cu(II). The 8-oxodG formation was inhibited by catalase, methional and bathocuproine, suggesting that Cu(I)-hydroperoxide, which was generated via Cu(I) and H2O2, caused oxidative DNA base damage.ConclusionsWe demonstrated that purpurin induces DNA base damage possibly mediated by Cu(I)/Cu(II) redox cycle both with and without ROS generation, which are likely to play an important role in its carcinogenicity.

Human Health Effects of Biphenyl: Key Findings and Scientific Issues.

Background:In support of the Integrated Risk Information System (IRIS), the U.S. Environmental Protection Agency (EPA) has evaluated the human health hazards of biphenyl exposure.Objectives:We review key findings and scientific issues regarding expected human health effects of biphenyl.Methods:Scientific literature from 1926 through September 2012 was critically evaluated to identify potential human health hazards associated with biphenyl exposure. Key issues related to the carcinogenicity and noncancer health hazards of biphenyl were examined based on evidence from experimental animal bioassays and mechanistic studies.Discussion:Systematic consideration of experimental animal studies of oral biphenyl exposure took into account the variety of study designs (e.g., study sizes, exposure levels, and exposure durations) to reconcile differing reported results. The available mechanistic and toxicokinetic evidence supports the hypothesis that male rat urinary bladder tumors arise through urinary bladder calculi formation but is insufficient to hypothesize a mode of action for liver tumors in female mice. Biphenyl and its metabolites may induce genetic damage, but a role for genotoxicity in biphenyl-induced carcinogenicity has not been established.Conclusions:The available health effects data for biphenyl provides suggestive evidence for carcinogenicity in humans, based on increased incidences of male rat urinary bladder tumors at high exposure levels and on female mouse liver tumors. Kidney toxicity is also a potential human health hazard of biphenyl exposure.Citation:Li Z, Hogan KA, Cai C, Rieth S. 2016. Human health effects of biphenyl: key findings and scientific issues. Environ Health Perspect 124:703–712; http://dx.doi.org/10.1289/ehp.1509730

The effects of oral treatment with transfluthrin on the urothelium of rats and its metabolite, tetrafluorobenzoic acid on urothelial cells in vitro

Transfluthrin, a pyrethroid insecticide, induced urinary bladder tumors in rats but not in mice in 2-year bioassays. We investigated the urothelial effects of transfluthrin in vivo in rats and the effects of its major metabolite tetrafluorobenzoic acid (TFBA) in vitro on rat (MYP3) and human (1T1) urothelial cell lines. Rats were fed diet containing 0, 2000 or 5000 (with and without 1.25% NH4Cl) ppm transfluthrin for 4weeks or 0 or 2000ppm transfluthrin for 13weeks. After 4weeks, there was no evidence of hyperplasia or increased proliferation in any treatment group. After 13weeks treatment with 2000ppm, cytotoxicity and necrosis of the rat urothelial superficial layer were detected by scanning electron microscopy. The urinary concentration of TFBA in rats fed 2000ppm transfluthrin was 2.94±0.67mM. The LC50 of TFBA was 2.25mM for MYP3 cells and 2.43mM for 1T1 cells. These studies support cytotoxicity and regenerative proliferation as the mechanism for induction of bladder tumors with high oral doses of transfluthrin due to metabolism of transfluthrin to the weakly cytotoxic TFBA which is excreted at high concentrations in the urine of rats administered high doses of transfluthrin (⩾2000ppm) for an extended period.

Urine acidification has no effect on peroxisome proliferator-activated receptor (PPAR) signaling or epidermal growth factor (EGF) expression in rat urinary bladder urothelium

We previously reported prevention of urolithiasis and associated rat urinary bladder tumors by urine acidification (via diet acidification) in male rats treated with the dual peroxisome proliferator-activated receptor (PPAR)α/γ agonist muraglitazar. Because urine acidification could potentially alter PPAR signaling and/or cellular proliferation in urothelium, we evaluated urothelial cell PPARα, PPARδ, PPARγ, and epidermal growth factor receptor (EGFR) expression, PPAR signaling, and urothelial cell proliferation in rats fed either a normal or an acidified diet for 5, 18, or 33 days. A subset of rats in the 18-day study also received 63 mg/kg of the PPARγ agonist pioglitazone daily for the final 3 days to directly assess the effects of diet acidification on responsiveness to PPARγ agonism. Urothelial cell PPARα and γ expression and signaling were evaluated in the 18- and 33-day studies by immunohistochemical assessment of PPAR protein (33-day study only) and quantitative real-time polymerase chain reaction (qRT-PCR) measurement of PPAR-regulated gene expression. In the 5-day study, EGFR expression and phosphorylation status were evaluated by immunohistochemical staining and egfr and akt2 mRNA levels were assessed by qRT-PCR. Diet acidification did not alter PPARα, δ, or γ mRNA or protein expression, PPARα- or γ-regulated gene expression, total or phosphorylated EGFR protein, egfr or akt2 gene expression, or proliferation in urothelium. Moreover, diet acidification had no effect on pioglitazone-induced changes in urothelial PPARγ-regulated gene expression. These results support the contention that urine acidification does not prevent PPARγ agonist-induced bladder tumors by altering PPARα, γ, or EGFR expression or PPAR signaling in rat bladder urothelium.

A comparative study of the sub-chronic toxic effects of three organic arsenical compounds on the urothelium in F344 rats; gender-based differences in response

Epidemiological studies indicated that human arsenic exposure can induce urinary bladder cancer. Methylation of inorganic arsenic can generate more reactive and toxic organic arsenical species. In this regard, it was recently reported that the methylated arsenical metabolite, dimethylarsinic acid [DMA(V)], induced urinary bladder tumors in rats. However, other methylated metabolites, like monomethylarsonic acid [MMA(V)] and trimethylarsine oxide (TMAO) were not carcinogenic to the urinary bladder. In order to compare the early effects of DMA(V), MMA(V), and TMAO on the urinary bladder transitional cell epithelium at the scanning electron microscope (SEM) level, we investigated the sub-chronic (13 weeks) toxicological effects of MMA(V) (187 ppm), DMA(V) (184 ppm), TMAO (182 ppm) given in the drinking water to male and female F344 rats with a focus on the urinary bladder in this study. Obvious pathological changes, including ropy microridges, pitting, increased separation of epithelial cells, exfoliation, and necrosis, were found in the urinary bladders of both sexes, but particularly in females receiving carcinogenic doses of DMA(V). Urine arsenical metabolic differences were found between males and females, with levels of MMA(III), a potential genotoxic form, higher in females treated with DMA(V) than in males. Thus, this study provides clear evidence that DMA(V) is more toxic to the female urinary bladder, in accord with sensitivity to carcinogenesis. Important gender-related metabolic differences including enhanced presentation of MMA(III) to the urothelial cells might possibly account for heightened sensitivity in females. However, the potential carcinogenic effects of MMA(III) need to be further elucidated.

Human carcinogenic risk evaluation, part IV: assessment of human risk of cancer from chemical exposure using a global weight-of-evidence approach.

In the early 1960s, the National Cancer Institute developed procedures to formalize the process for the evaluation of the human risk of cancer from chemical exposure (Boorman, 1994; Weisburger, 1983). This approach was based on decades of research that demonstrated that chemicals that were known to cause cancer in humans could be shown to induce cancer in laboratory animals as well. Despite the fact that this approach by the NCI was envisioned as an initial assessment of carcinogenic activity to identify those chemicals for which further study was needed, the use of two rodent species exposed for 2 years as the primary mechanism to identify potential human hazards was in widespread use by the early 1970s (Boorman, 1994). In 1975, this process was developed into a recommendation that has formed the basis of regulatory guidance (Sontag, 1976). This guidance represented the best thinking of the time about how to accomplish the critical but difficult task of prospectively identifying chemicals that might pose a carcinogenic risk to humans. Despite significant progress in our understanding of the biology of the carcinogenic response in animals and humans in the nearly 30 years since this guideline was published, these recommendations continue to form the foundation of how we do cancer risk assessment today. We have a large and extensive database today from which to develop a more rational, science-based approach to this process. A careful consideration of the available data suggests an alternative approach to this important task. Much of the early work done in this field that led to the use of the 2-year bioassay was done with reactive chemicals, most of which interacted with DNA (Miller, 1978). Ample evidence accumulated that compounds in classes like the polycyclic aromatic hydrocarbons that were known or suspected human carcinogens produced tumors in rodents. It was logical to assume that rodent tumor data could predict the hazard associated with human exposure. The concept of genetic versus epigenetic or alternative mechanisms of carcinogenesis originally proposed in the late 1980s is now well accepted. While much is understood about the mechanism of tumor induction by DNA-reactive carcinogens, assessment of human risk from exposure to nongenotoxic agents is more problematic. Careful and comprehensive evaluation of the modes of action of chemicals that produce tumors in rodents has led to the understanding that positive findings in long-term rodent studies do not necessarily predict human hazard. We now understand, for example, why urinary bladder tumors in rats exposed to high doses of saccharin or melamine do not imply a hazard for humans (Cohen et al., 1991; Rodent Bladder Carcinogenesis Working Group, 1995). Similarly, a broad and very comprehensive array of data on male rat kidney tumors induced by compounds like d-limonene that produce a characteristic male rat hydrocarbon nephropathy do not predict a carcinogenic hazard for humans following exposure to these chemicals (Swenberg and Lehman-McKeeman, 1999). In the pharmaceutical arena, there are numerous similar examples. Rat mammary tumors produced in response to b-adrenergic blocking agents in the 1970s caused significant disruption to drug development programs as concern was raised over the possibility of a similar tumorigenic response in humans. It is now clear that the biology surrounding the tumor promoting activity in rodents (hyperprolactinemia) is dissimilar between the two species and does not predict human hazard (Schyve et al., 1978; Welsch and Nagasawa, 1977). A similar major concern was raised over the appearance of the unusual mesovarial leiomyoma in rats exposed to b-agonists like salbutamol in this same time frame. It is now well accepted that this rodent tumorigenic response is secondary to a unique pharmacodynamic effect in this tissue in the rat and is not an indicator of human risk (Jack et al., 1983). To whom correspondence should be addressed: Schering-Plough Research Institute, 2015 Galloping Hill Rd., Kenilworth, NJ 07033. Fax: (973) 940-4159. E-mail: james.madonald@spcorp.com.

Reversibility of proliferative lesions and induction of non-papillary tumors in rat urinary bladder treated with phenylethyl isothiocyanate.

Phenylethyl isothiocyanate (PEITC), generally thought to be a chemopreventive agent for various kinds of genotoxic carcinogens, has been found to induce rat urinary bladder carcinomas in our laboratory. To cast light on the underlying mechanisms, the reversibility of urothelial proliferative lesions and the frequencies of H-ras and p53 mutations in the induced rat urinary bladder tumors were investigated. F344 male rats were given diet containing 0.1% PEITC for 48 weeks and then killed, or for 32 weeks and then returned to normal diet without supplement for 1, 3, 7 days or 16 weeks before death. At 7 days after withdrawal of PEITC treatment, carcinomas were observed in only two of 24 rats but a high incidence of dysplasias was evident. Furthermore, 16 weeks after withdrawal, seven of 12 (58.3%) rats had carcinomas. In addition, carcinomas were induced in 11 of 12 (91.7%) rats continuously receiving PEITC for 48 weeks. Most of the carcinomas were characterized as of non-papillary transitional cell type with occasional squamous cell differentiation and/or glandular components. Bromodeoxyuridine labeling indices (LIs) were increased by PEITC administration even in normal-looking epithelium. After withdrawal of treatment, LIs in simple and papillary or nodular (PN) hyperplasias were markedly decreased and these lesions gradually disappeared, while values for dysplasias and carcinomas, which persisted, were only slightly decreased. A silent point mutation was found in H-ras in one of 12 tumor samples (8.3%), whereas seven (58.3%) had mutations in p53. These results indicate that PEITC itself is a carcinogen for the rat urinary bladder, and that while the simple and PN hyperplasia induced by PEITC are reversible, dysplasia is irreversible with the potential to give rise to non-papillary carcinomas with frequent p53 mutations.

Carcinogenicity of dimethylarsinic acid in male F344 rats and genetic alterations in induced urinary bladder tumors.

Arsenic is a well-documented human carcinogen, and contamination with this heavy metal is of global concern, presenting a major issue in environmental health. However, the mechanism by which arsenic induces cancer is unknown, in large part due to the lack of an appropriate animal model. In the present set of experiments, we focused on dimethylarsinic acid (DMA), a major metabolite of arsenic in most mammals including humans. We provide, for the first time, the full data, including detailed pathology, of the carcinogenicity of DMA in male F344 rats in a 2-year bioassay, along with the first assessment of the genetic alteration patterns in the induced rat urinary bladder tumors. Additionally, to test the hypothesis that reactive oxygen species (ROS) may play a role in DMA carcinogenesis, 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in urinary bladder was examined. In experiment 1, a total of 144 male F344 rats at 10 weeks of age were randomly divided into four groups that received DMA at concentrations of 0, 12.5, 50 and 200 p.p.m. in the drinking water, respectively, for 104 weeks. From weeks 97-104, urinary bladder tumors were observed in 8 of 31 and 12 of 31 rats in groups treated with 50 and 200 p.p.m. DMA, respectively, and the preneoplastic lesion, papillary or nodular hyperplasias (PN hyperplasia), was noted in 12 and 14 rats, respectively. DMA treatment did not cause tumors in other organs and no urinary bladder tumors or preneoplastic lesions were evident in the 0 and 12.5 p.p.m.-treated groups. Urinary levels of arsenicals increased significantly in a dose-responsive manner except for arsenobetaine (AsBe). DMA and trimethylarsine oxide (TMAO) were the major compounds detected in the urine, with small amounts of monomethylarsonic acid (MMA) and tetramethylarsonium (TeMa) also detected. Significantly increased 5-bromo-2'-deoxyuridine (BrdU) labeling indices were observed in the morphologically normal epithelium of the groups treated with 50 and 200 p.p.m. DMA. Mutation analysis showed that DMA-induced rat urinary bladder tumors had a low rate of H-ras mutations (2 of 20, 10%). No alterations of the p53, K-ras or beta-catenin genes were detected. Only one TCC (6%) demonstrated nuclear accumulation of p53 protein by immunohistochemistry. In 16 of 18 (89%) of the TTCs and 3 of 4 (75%) of the papillomas, decreased p27(kip1) expression could be demonstrated. Cyclin D1 overexpression was observed in 26 of 47 (55%) PN hyperplasias, 3 of 4 (75%) papillomas, and 10 of 18 (56%) TCCs. As a molecular marker of oxidative stress, increased COX-2 expression was noted in 17 of 18 (94%) TCCs, 4 of 4 (100%) papillomas, and 39 of 47 (83%) PN hyperplasias. In experiment 2, 8-OHdG formation in urinary bladder was significantly increased after treatment with 200 p.p.m. DMA in the drinking water for 2 weeks compared with the controls. The studies demonstrated DMA to be a carcinogen for the rat urinary bladder and suggested that DMA exposure may be relevant to the carcinogenic risk of inorganic arsenic in humans. Diverse genetic alterations observed in DMA-induced urinary bladder tumors imply that multiple genes are involved in stages of DMA-induced tumor development. Furthermore, generation of ROS is likely to play an important role in the early stages of DMA carcinogenesis.

A concise review of the toxicity and carcinogenicity of dimethylarsinic acid

Dimethylarsinic acid (DMA) has been used as a herbicide (cacodylic acid) and is the major metabolite formed after exposure to tri- (arsenite) or pentavalent (arsenate) inorganic arsenic (iAs) via ingestion or inhalation in both humans and rodents. Once viewed simply as a detoxification product of iAs, evidence has accumulated in recent years indicating that DMA itself has unique toxic properties. DMA induces an organ-specific lesion — single strand breaks in DNA — in the lungs of both mice and rats and in human lung cells in vitro. Mechanistic studies have suggested that this damage is due mainly to the peroxyl radical of DMA and production of active oxygen species by pulmonary tissues. Multi-organ initiation-promotion studies have demonstrated that DMA acts as a promotor of urinary bladder, kidney, liver and thyroid gland cancers in rats and as a promotor of lung tumors in mice. Lifetime exposure to DMA in diet or drinking water also causes a dose-dependent increase in urinary bladder tumors in rats, indicating that DMA is a complete carcinogen. These data collectively suggest that DMA plays a role in the carcinogenesis of inorganic arsenic.

Inhibitory effect of peptide vilon on the development of induced rat urinary bladder tumors in rats.

The effect of peptide vilon (Lys-Glu) on urinary bladder carcinogenesis in rats was studied. Urinary bladder tumors were induced with a selective carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine. The tumors developed in 56% vilon-treated animals and in 75.5% controls. Vilon 2-fold decreased the incidence of preneoplastic and early neoplastic changes in urinary bladder mucosa and significantly inhibited carcinogenesis.

Urothelial Cytotoxicity and Regeneration Induced by Dimethylarsinic Acid in Rats

Inorganic arsenic is a known human carcinogen of the skin and respiratory tract. Epidemiologic evidence indicates that it is also carcinogenic to the urinary bladder and other internal organs. Lack of an animal model has limited progress on understanding the mechanism of arsenic carcinogenesis. It was recently reported that high doses of an organic arsenical, dimethylarsinic acid (DMA), increased urinary bladder tumors in rats when administered in the diet or in the drinking water for 2 years, with the female being more sensitive than the male. We previously showed that high doses of DMA (40 or 100 ppm of the diet) fed for 10 weeks increased urothelial cell proliferation in the rat. Treatment with DMA also increased renal calcification and increased urinary calcium concentration. In 2 experiments, we examined the urothelial proliferative effects of treatment with 100 ppm DMA in the diet in female F344 rats for 2 and 10 weeks and for 6 and 24 h, and 3, 7, and 14 days. Cytotoxic changes in the urothelium were evident by SEM as early as 6 h after treatment was begun. Foci of cellular necrosis were detected after 3 days of treatment, followed by widespread necrosis of the urothelium after 7 days of treatment. The bromodeoxyuridine (BrdU) labeling index was not increased until after 7 days of treatment, suggesting that administration of DMA results in cytotoxicity with necrosis, followed by regenerative hyperplasia of the bladder epithelium. Although the rat provides an animal model to study the urothelial effects of DMA, the relevance of this finding to inorganic arsenic carcinogenesis in humans must be extrapolated cautiously, due to the high doses of DMA necessary to produce these changes in the rat and the differences in metabolism of arsenicals in rodents, especially rats, compared to humans.

Increased expression of cyclooxygenase-2 protein in rat urinary bladder tumors induced by N -butyl- N -(4-hydroxybutyl) nitrosamine

The anti-inflammatory drugs, aspirin and piroxicam, are known to possess chemopreventive potential against rat superficial urinary bladder carcinogenesis induced by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). Recently, we found similar inhibitory effects with a selective cyclooxygenase (COX)-2 inhibitor, nimesulide. In order to clarify the inhibitory mechanisms, we have further studied the expression of COX-2 protein in urinary bladder tumors induced by BBN in Fischer 344 male rats. For comparison, papillomatosis caused by uracil-induced urolithiasis, and normal epithelial cells, were also investigated. Western blot analysis revealed COX-2 protein to be barely expressed in the normal epithelial cells, whereas it was increased 13-22-fold in varying sizes of urinary bladder tumors and 7-fold in papillomatosis. Immunohistochemically, COX-2 protein was diffusely expressed in transitional cell carcinomas and nodulo-papillary hyperplasia but weakly expressed only in basal cells in simple hyperplasia and normal-looking surrounding epithelia. In papillomatosis, it was moderately expressed only in endothelial cells in stroma. These results indicate that COX-2 plays important roles in the development of preneoplastic and neoplastic lesions in the rat urinary bladder, and therefore could be a good target for chemoprevention of superficial lesions.

Loss of heterozygosity in (LewisxF344)F1 rat urinary bladder tumors induced with N-butyl-N-(4-hydroxybutyl)nitrosamine followed by dimethylarsinic acid or sodium L-ascorbate.

Dimethylarsinic acid (DMA), a main metabolite of arsenicals which are carcinogenic in man, exerts tumor‐promoting activity on rat urinary bladder carcinogenesis initiated with N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine (BBN). Sodium L‐ascorbate (Na‐AsA) is also a strong tumor promoter in this animal model. In this study, we used (Lewis×F344)F1 rats to compare molecular alterations in urinary bladder tumors caused by BBN followed by DMA or Na‐AsA. Male, 6‐week‐old rats were given 0.05% BBN in their drinking water for 4 weeks, and then the rats in group 1 were maintained with no further treatment for 40 weeks. The animals of groups 2 and 3 were administered 0.01% DMA in their drinking water (group 2) or 5% Na‐AsA in the powder diet (group 3) after the BBN treatment. Group 4 rats were given 0.05% BBN continuously for 36 weeks. At weeks 12, 20, 36 and 44, subgroups of rats were killed. Histopathological examination revealed promoting activity for DMA and, to a greater extent, Na‐AsA on urinary bladder carcinogenesis. Loss of heterozygosity (LOH), detected with the polymerase chain reaction using 36 microsatellite markers, was found to be present in 2 of 9 (22%) urinary bladder tumors after treatment with DMA and 3 of 22 (14%) induced by continuous administration with BBN. No LOH was, however, detected in urinary bladder tumors after treatment with Na‐AsA. The results thus suggest that the mechanisms of action of these two promoters, DMA and Na‐AsA, may differ in rat urinary bladder carcinogenesis.

Progressive growth of rat bladder carcinomas after exposure to prolonged uracil‐induced urolithiasis

Dietary uracil at the 3% level induces urinary bladder tumors in rats through urolithiasis-dependent mechanical irritation. In the present study, comparison of lesions induced by uracil administration over the different periods of 36 weeks (middle-term) and up to 103 weeks (long-term) revealed significant elevation of both incidences and multiplicity of transitional cell carcinomas (TCCs) in the long-term group. Histopathological assessment in terms of tumor biology further demonstrated significantly higher grading on the basis of the degree of cellular and structural atypia, and greater depth of invasion in the long-term group. Application of markers for cell proliferation activities including proliferating cell nuclear antigen (PCNA) and silver-binding nucleolar organizer regions (AgNORs) also revealed significantly elevated AgNOR counts in the long-term group TCC. AgNOR counts and PCNA rates in TCCs showed relation to the histological grades. Thus the present study demonstrated that prolonged uracil-induced urolithiasis causes more biologically aggressive bladder carcinomas with invasive potential. Continuous stimulation of cell proliferation presumably has the potential to facilitate multiple genetic alterations leading to development of more malignant carcinomas. However, it should be borne in mind that the difference in bladder cancer development might also be related to the fact that the animals survived longer and that the early lesions therefore had more time to progress to more advanced stages.

Selective induction of rat urinary bladder tumors by simultaneous administration of 3,2'-dimethyl-4-aminobiphenyl (DMAB) and butylated hydroxyanisole or butylated hydroxytoluene is associated with increased DMAB-DNA adduct formation

Modification of 3,2'-dimethyl-4-aminobiphenyl (DMAB) multi-organ carcinogenesis by simultaneous treatment with butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT) was studied using young and old male F344 rats. Animals, 4 or 54 weeks old, were given DMAB (s.c. injection of 50 mg/kg body wt once a week for 10 weeks) along with BHA (2.0% in diet for 11 weeks) or BHT (1.0% in diet for 11 weeks). The experiments were terminated 55 weeks after the commencement. Combined administration of BHA or BHT with the carcinogen resulted in development of urinary bladder tumors in greater than 90% of both young and old rats thus treated, whereas no tumors were induced in animals given DMAB alone. In contrast, the appearance of preneoplastic lesions in the liver and pancreas was reduced by BHA or BHT treatment. Tumor development (less than 30% incidence) was also evident in the small and large intestines, prostate, preputial glands, skin/subcutis and ear duct, with no modification by BHA or BHT. No ageing effects were evident. The formations of DMAB-DNA adducts, evaluated by the enzyme-linked immunosorbent assay and immunohistochemical staining, correlated well with tumorigenesis in the urinary bladder, liver and pancreas. The selective enhancement of urinary bladder tumor induction by BHA and BHT appeared to be due to both increased DMAB-DNA adduct formation caused by metabolic alteration of DMAB in the liver and increased DNA synthesis in the urothelial cells.

Nucleolar organizer regions in rat urinary bladder tumors induced by N-butyl-N-(4-hydroxybutyl)nitrosamine

The number of nucleolar organizer regions (NORs) stained by the one-step silver colloid method was measured in preneoplastic and neoplastic bladder lesions induced by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in rats. Male ACI/N rats, 6 weeks of age, were given 0.05% BBN in drinking water for 5, 8, 12, 18 and 30 weeks to induce preneoplastic and neoplastic transitional cell lesions. The mean numbers of silver-stained NORs (AgNORs) in such lesions were as follows: untreated transitional epithelium (n = 6), 1.26 +/- 0.09; transitional cell epithelium outside focal lesions (n = 10), 1.75 +/- 0.10; simple hyperplasia (n = 10), 2.01 +/- 0.15; papillary or nodular (PN) hyperplasia (n = 10), 2.15 +/- 0.19; transitional cell papilloma (n = 5), 2.37 +/- 0.12; transitional cell carcinoma (n = 5), 3.52 +/- 0.23. Thus, the mean number of AgNORs showed a step-wise increase from untreated and treated, histologically normal transitional epithelium through simple hyperplasia and PN hyperplasia to transitional cell papilloma and carcinoma. These results suggest that the mean number of AgNORs may reflect the proliferative nature of bladder lesions induced by BBN, as reported in preneoplastic and neoplastic lesions in other organs. PN hyperplasias were classified into two types based upon the mean number of AgNORs, indicating that they include reversible and irreversible changes in contrast with simple hyperplasia which is reversible change.

The effect of lifetime sodium saccharin dosing on mice initiated with the carcinogen 2-acetylaminofluorene

Sodium saccharin has been reported to promote the development of urinary bladder tumors in rats following low doses of several carcinogens. To evaluate the generality of this effect between species, an initiation-promotion study was conducted in mice. Weanling female BALB/c mice were initiated with 200 ppm dietary 2-acetylaminofluorene for 90 days. Following a 2-week period of control diet, saccharin was administered at 0, 0.1, 0.5, 1.0, and 5.0% in the diet for the remainder of the 132-week study. An elevated incidence of persistent bladder transitional cell hyperplasia and a low incidence of urothelial and hepatocellular tumors indicated that these organs achieved an adequate dose of the initiator. However, sodium saccharin dosing did not result in an increased incidence of tumors in either the bladder or liver and is therefore not considered to be a promoter of carcinogenesis at these sites in the mouse. Furthermore, sodium saccharin exhibited a modest inhibitory effect on the rate of development of lymphomas in both initiated and noninitiated animals. Interspecies differences in the bladder tumorigenic effect of sodium saccharin and their association with differences in urinary tract physiology are discussed.

In situ freezing of the urinary bladder: a trigger of rapid development of sodium o-phenylphenate-induced urinary bladder tumors in the rat.

The effect of in situ freezing of the urinary bladder on sodium o-phenylphenate (OPP-Na)-induced urinary bladder tumor development was investigated in male F344 rats. Freezing was performed at the start of the experiment by touching the serosal surface of the bladder with a frozen steel rod. As a result, three out of 27 rats (11%) developed bladder tumors within 78 weeks when 0.5% OPP-Na feeding was started 2 weeks after freezing and one out of 27 rats (4%) when the feeding was started 12 weeks after freezing. 0.5% OPP-Na alone did not induce any bladder lesions. In a second experiment, 19 out of 25 rats (76%) developed bladder tumors (carcinomas in 12 rats and papillomas in seven rats) when 2% OPP-Na was administered from 6 weeks after freezing, whereas only one rat (5%) demonstrated a bladder carcinoma in the group given 2% OPP-Na without prior freezing. In neither experiment were tumors induced by freezing alone. Enzyme histochemistry revealed no remarkable changes in enzyme activities of regenerative hyperplasia induced by freezing. The results indicate that in situ freezing of the urinary bladder acts as a trigger of rapid development of OPP-Na-induced rat urinary bladder tumors.

Evaluation of the Effects of Cotinine and Nicotine-<italic>N</italic>′-oxides on the Development of Tumors in Rats Initiated With <italic>N</italic>-[4-(5-Nitro-2-furyl)-2-thiazolyl]formamide<xref ref-type="fn" rid="FN2">2</xref><xref ref-type="fn" rid="FN3">3</xref>

The effects of cotinine and nicotine-N'-oxides on tumor development in F344 rats initiated with N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide [(FANFT) CAS: 24554-26-5] were evaluated. When rats were 6 weeks old, FANFT in an agar diet was administered for a 6-week period. Subsequently, cotinine, trans-nicotine-N'-oxide, and a mixture of cis-nicotine-N'-oxide and trans-nicotine-N'-oxide in drinking water were given as promoters in concentrations of 0.1, 0.02, and 0.02%, respectively. These nicotine metabolites were offered ad libitum for 78 weeks. Control groups consisted of rats that received tap water with or without prior administration of FANFT. Cotinine, trans-nicotine-N'-oxide, and the mixture of cis- and trans-nicotine-N'-oxides were neither carcinogens nor promoters of urinary bladder tumors in rats initiated with FANFT. A reduced incidence of urinary bladder tumors was observed in FANFT-pretreated animals that also received a mixture of cis- and trans-nicotine-N'-oxides. FANFT administration increased the incidences of mesothelioma of the peritoneum and thyroid tumors. Tumor formation in the tongue and palate observed in FANFT-treated rats was not affected by administration of these nicotine metabolites. There was, however, a significant increase in the incidence of forestomach tumors in rats that were initiated with FANFT and subsequently received either trans-nicotine-N'-oxide or a mixture of cis- and trans-nicotine-N'-oxides.

Trisodium Nitriloacetate Monohydrate: Promoting Effect in Urinary Bladder Carcinogenesis in Rats Treated With <italic>N</italic>-Buty1-<italic>N</italic>-(4-hydroxybutyl)nitrosamine<xref ref-type="fn" rid="FN2">2</xref>

The effect of trisodium nitrilotriacetate monohydrate [(Na3NTA X H2O) CAS: 18662-53-8] on development of urinary bladder tumors in rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine [(BBN) CAS: 3817-11-6] was studied. Twenty-one male inbred W rats 6 weeks of age were given drinking water containing 500 ppm of BBN for 4 weeks and then put on diet containing 10,000 ppm of Na3NTA X H2O for 28 weeks. Na3NTA X H2O promoted the development of urinary bladder tumors in rats treated with BBN. The incidences of papilloma and transitional cell carcinomas in the urinary bladder were 90% (18/20) and 25% (4/20), respectively, in rats treated with BBN and then Na3NTA X H2O and 0 in those treated with BBN or Na3NTA X H2O alone. The incidence of papillary or nodular hyperplasia in week 32 was 100% (20/20) in rats treated with BBN and then Na3NTA X H2O and 61% (13/21) in rats treated with BBN only.