Multistage carcinogenesis in the urinary bladder

Is there a promoting role for artificial sweeteners in the evolution of bladder cancer? A meta-analysis of current literature

INTRODUCTION

Urinary bladder cancer is a frequent neoplasia in the urogenital system. Ageing and smoking are the two main risk factors, however, some chemical agents such as artificial sweeteners could act as initiators or promoters.

EVIDENCE ACQUISITION

After identifying trends in scientific literature, we conducted a wide search in PubMed database and a meta-analysis was performed on extracted data to determine the role of artificial sweeteners in the development of urinary bladder cancer.

EVIDENCE SYNTHESIS

Twenty-one full reports were enrolled from screening of PubMed database into final analysis involving 116,568 subjects in comparisons. Overall, 13,682 and 102,886 cases were identified for bladder cancer patients and healthy controls, respectively. Among artificial sweetener users, 12.5% was the incidence of bladder cancer. In the control group, 11.2% of cases suffered from urothelial carcinoma of the bladder. About 40.7% of the patients suffering from urinary neoplasms and 37.8% of the healthy cases were artificial sweetener users, respectively. There were only minor differences in overall descriptive data. The incidence of urinary bladder cancer among artificial sweetener users and control cases showed no risk difference (RD: 0.00, CI: -0.06 to 0.06). The frequency of artificial sweetener use among patients suffering from urinary bladder neoplasms and healthy subjects was compared which showed equal occurrences (OR: 0.96, CI: 0.79 to 1.17).

CONCLUSIONS

According to our results, the carcinogenic risk of artificial sweeteners is not proven. Saccharin should not be kept as a promoter in urothelial malignant transformation.

Metabolic reprogramming and dysregulated metabolism: cause, consequence and/or enabler of environmental carcinogenesis?

Environmental contributions to cancer development are widely accepted, but only a fraction of all pertinent exposures have probably been identified. Traditional toxicological approaches to the problem have largely focused on the effects of individual agents at singular endpoints. As such, they have incompletely addressed both the pro-carcinogenic contributions of environmentally relevant low-dose chemical mixtures and the fact that exposures can influence multiple cancer-associated endpoints over varying timescales. Of these endpoints, dysregulated metabolism is one of the most common and recognizable features of cancer, but its specific roles in exposure-associated cancer development remain poorly understood. Most studies have focused on discrete aspects of cancer metabolism and have incompletely considered both its dynamic integrated nature and the complex controlling influences of substrate availability, external trophic signals and environmental conditions. Emerging high throughput approaches to environmental risk assessment also do not directly address the metabolic causes or consequences of changes in gene expression. As such, there is a compelling need to establish common or complementary frameworks for further exploration that experimentally and conceptually consider the gestalt of cancer metabolism and its causal relationships to both carcinogenesis and the development of other cancer hallmarks. A literature review to identify environmentally relevant exposures unambiguously linked to both cancer development and dysregulated metabolism suggests major gaps in our understanding of exposure-associated carcinogenesis and metabolic reprogramming. Although limited evidence exists to support primary causal roles for metabolism in carcinogenesis, the universality of altered cancer metabolism underscores its fundamental biological importance, and multiple pleiomorphic, even dichotomous, roles for metabolism in promoting, antagonizing or otherwise enabling the development and selection of cancer are suggested.

Experimental animal model and RNA interference: a promising association for bladder cancer research

Animal models are at the centre of laboratory bladder cancer (BC) research and at the same time, the bridge to the clinic. A new and very promising therapeutical approach is to silence abnormally up-regulated genes in cancer, through small interfering RNA (siRNA) molecules. Therapeutic use and success of siRNAs will largely depend on their efficient and safe in vivo delivery and on avoiding accidental off-target effects. Intravesical siRNA is a strategy which may be the best deliver option to surperficial BC like intravesical immunotherapy. Its direct action might allow a continuous intracellular exposure to effective siRNA concentrations. While the procedure of transurethral siRNA administration is promising for BC research allowing detection of new targets in BC therapy, the optimal intravesical carrier and the best target(s) to siRNA are to be determined.

Modulation of carcinogenesis in the urinary bladder by retinoids

Bladder cancer has a 70% recurrence rate within five years and a high associated mortality. It commonly occurs in one or both of two predominant growth/behaviour patterns: either well-differentiated, relatively benign exophytic papillary lesions, or flat, poorly differentiated invasive carcinoma usually arising from carcinoma-in-situ. We have used the F344 rat treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as a model for the papillary disease, and the BBN-treated B6D2F1 mouse for flat, invasive bladder carcinoma. In the rat, carcinogenesis is a multistage process and several retinoids will delay or even halt the development of bladder cancer. Inhibition of carcinogenesis is not complete, but there is a consistent reduction in the time-related incidence of papillomas and carcinomas and a concomitant improvement in the overall differentiation of the urothelium. In the BBN/mouse model, retinoids also have anticarcinogenic activity but interpretation of the results is more complicated. Unlike the F344 rat, the B6D2F1 mouse has a non-uniform response to BBN; not all mice develop bladder cancer even after treatment with very high doses of BBN and in those that do, more than one mechanism of carcinogenesis may be involved. Individual retinoids differ markedly in their ability to modulate bladder carcinogenesis in rodents; the behaviour of one analogue cannot be predicted automatically from data obtained with another. Combined data from rodent trials in this and other laboratories have identified N-(4-hydroxyphenyl)retinamide (HPR) as the most anticarcinogenic retinoid tested so far for the rodent bladder. It is also less toxic in rodents and better tolerated in humans than either 13-cis-retinoic acid or etretinate, two retinoids currently used in dermatological practice. A prophylactic chemopreventive trial of HPR in bladder cancer patients starting in 1985 will be centered on the Middlesex Hospital, London.

Nonurothelial cancer of the bladder

In this article, we review available evidence on the treatment of patients with nonurothelial cancer of the bladder. More than 150 published works were reviewed in preparation for this summary. Squamous cell carcinoma and adenocarcinoma are ideally treated with radical cystectomy. High-risk groups for these diseases are defined. Small cell carcinoma should be treated with multimodality therapy, including chemotherapy. Other rarer tumors of the bladder are also discussed.

Effects of ginger (Zingiber officinale Roscoe) on DNA damage and development of urothelial tumors in a mouse bladder carcinogenesis model

Extracts of the spice ginger (Zingiber officinale Roscoe) are rich in gingerols and shogaols, which exhibit antioxidant, anti-inflammatory, antifungal, antimycobacterial, and anticarcinogenic proprieties. The present study evaluated the chemoprotective effects of a ginger extract on the DNA damage and the development of bladder cancer induced by N-butyl-N-(4-hydroxibutyl) nitrosamine (BBN)/N-methyl-N-nitrosourea (MNU) in male Swiss mice. Groups G1-G3 were given 0.05% BBN in drinking water for 18 weeks and four i.p. injections of 30 mg/kg body weight MNU at 1, 3, 10, and 18 weeks. Group G4 and G5 received only the BBN or MNU treatments, respectively, and groups G6 and G7 were not treated with BBN or MNU. Additionally, Groups G2, G3, and G6 were fed diets containing 1, 2, and 2% ginger extract, respectively, while Groups G1, G4, G5, and G7 were fed basal diet. Samples of peripheral blood were collected during the experiment for genotoxicity analysis; blood collected 4 hr after each MNU dose was used for the analysis of DNA damage with the Comet assay (assay performed on leukocytes from all groups), while reticulocytes collected 24 hr after the last MNU treatment of Groups G5-G7 were used for the micronucleus assay. At the end of the experiment, the urinary bladder was removed, fixed, and prepared for histopathological, cell proliferation, and apoptosis evaluations. Ginger by itself was not genotoxic, and it did not alter the DNA damage levels induced by the BBN/MNU treatment during the course of the exposure. The incidence and multiplicity of simple and nodular hyperplasia and transitional cell carcinoma (TCC) were increased by the BBN/MNU treatment, but dietary ginger had no significant effect on these responses. However, in Group G2 (BBN/MNU/2% ginger-treated group), there was an increased incidence of Grade 2 TCC. The results suggest that ginger extract does not inhibit the development of BBN-induced mouse bladder tumors.

Experimental models of human bladder carcinogenesis

Bladder cancer is the fifth most common cancer in the UK, yet human bladder carcinogenesis remains poorly understood and the response of bladder tumours to radio- and chemo-therapy is unpredictable. The aims of this article are to review human bladder carcinogenesis and appraise the different in vitro and in vivo approaches that have been developed to study the process. The review considers how in vitro models based on normal human urothelial (NHU) cells can be applied to human bladder cancer research. We conclude that recent advances in NHU cell culture offer novel approaches for defining urothelial tissue-specific responses to genotoxic and non-genotoxic carcinogens and elucidating the role of specific genes involved in the mechanisms of bladder carcinogenesis and malignant progression.

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.

Epidemiology of transitional cell carcinoma of the bladder: profile of an urban population in the south-west of England

OBJECTIVES

To produce an epidemiological profile of patients with transitional cell carcinoma (TCC) of the bladder living in the city of Bristol (south-west England), to determine if TCC tumorigenesis is linked to possible risk factors (occupational exposure, cigarette smoking, alcohol consumption and coffee consumption) and to assess phenotypic acetylation status and thus determine whether there may be a genetic component to tumour development.

PATIENTS AND METHODS

This cross-sectional observational epidemiological study recruited both cases and controls from one-stop haematuria clinics, providing two groups with a similar age and sex distribution. Before diagnosis, all patients were interviewed by the same researcher and results recorded on a specially designed database questionnaire, to eliminate both recall and investigator bias. Metabolic studies were also performed before diagnosis.

RESULTS

There were significant associations for occupational exposure, cigarette smoking, and beer consumption (but not wine or spirits), but no significant association with coffee consumption. Slow acetylation status also conferred an increased risk. There were linear trends in terms of dose-response for both beer and cigarette consumption, although this was significant only for cigarettes. There was no difference in risk between the use of filtered or unfiltered cigarettes.

CONCLUSION

Occupational exposure and cigarette smoking have been well documented as risk factors in the development of TCC of the bladder, as has slow acetylation status. There are very few studies linking bladder cancer with alcohol consumption. It is important to subdivide types of alcohol consumed when considering this factor in an epidemiological study. In the case of beer, methods used by different brewing processes may also contribute to differences found, were such a study to be performed on a national scale.

Chemopreventive effects of diosmin and hesperidin on N-butyl-N-(4-hydroxybutyl)nitrosamine-induced urinary-bladder carcinogenesis in male ICR mice

The chemopreventive effects of 2 flavonoids (diosmin and hesperidin) on N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced urinary-bladder carcinogenesis were examined in male ICR mice. Animals were divided into 11 groups, and groups 1 to 7 were given OH-BBN (500 ppm) in the drinking water for 6 weeks. Groups 2 to 4 were fed diets containing the test compounds (group 2, 1000 ppm diosmin; group 3, 1000 ppm hesperidin; group 4,900 ppm diosmin + 100 ppm hesperidin) for 8 weeks during the initiation phase, while groups 5 to 7 were fed these diets, respectively, for 24 weeks during the post-initiation phase. Groups 8 to 11 were controls, given only the test compounds or untreated basal diets throughout the experiment (weeks 1 to 32). The incidence of bladder lesions and cell-proliferation activity estimated by enumeration of silver-stained nucleolar-organizer-region-associated proteins (AgNORs) and by the 5-bromodeoxyuridine (BUdR)-labeling index was compared among the groups. Feeding of the test compounds, singly or in combination, during both phases caused a significant reduction in the frequency of bladder carcinoma and preneoplasia. Dietary administration of these compounds significantly decreased the AgNOR count and the BUdR-labeling index of various bladder lesions. These findings suggest that the flavonoids diosmin and hesperidin, individually and in combination, are effective in inhibiting chemical carcinogenesis of the bladder, and that such inhibition might be partly related to suppression of cell proliferation.

Lack of an antitumoral effect of immunomodulatory galactoside-specific mistletoe lectin on N-methyl-N-nitrosourea-induced urinary bladder carcinogenesis in rats

The aim of the present animal experiment was to study the effect of galactoside-specific lectin or agglutinin (VAA) from mistletoe (Viscum album L.) on chemically induced tumor development in the urinary bladder of rats. Since VAA has been shown to exert a remarkable immunomodulating effect, any change in tumor formation would indicate a lectin-triggered immune control of urothelial carcinogenesis in the used model. To produce vesical neoplasms the direct-acting urothelial carcinogen N-methyl-N-nitrosourea (MNU) was administered at a single intravesical dose (7.5 mg/kg body weight). Highly purified VAA was given subcutaneously twice a week at the immunomodulatory dose of 1 ng/kg body weight over a period of 6 months during the critical phases of tumor development. After a total experimental time of 15 months the incidence of epithelial bladder tumors was 29.3% in controls versus 27.9% in rats additionally receiving the lectin and thus not significantly different in both experimental groups. There were, moreover, no substantial differences in the histopathologic spectrum of epithelial tumors induced, their patterns of growth, grades of cellular malignancy and local extension. The frequency and histopathology of mesenchymal bladder tumors as well as the incidence and morphology of carcinomas of the ureters and renal pelves also proved to be similar in controls and in rats treated with VAA. In conclusion, the present data provide no evidence for a modifying or even inhibitory effect of the immunomodulatory galactoside-specific mistletoe lectin on experimental urothelial carcinogenesis.

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.

Urinary bladder cancer following cyclophosphamide therapy for Hodgkin's disease

Urinary bladder cancers following prolonged cyclophosphamide therapy are being increasingly reported. We report a case of transitional cell carcinoma of the urinary bladder occurring 12 years after pulse intravenous therapy with cyclophosphamide for Hodgkin's disease. The mechanism of bladder carcinogenesis and the possible role of the uroprotector MESNA in preventing cyclophosphamide induced bladder cancer are discussed.

Retinoids in cancer treatment

Since initial studies identifying the important role of vitamin A and its derivatives (retinoids) in maintaining the integrity of epithelial tissues, these compounds have served as paradigms for experimental studies exploring the pharmacologic modification of carcinogenesis. Retinoids have clearly been shown to inhibit chemically induced mammary and urothelial carcinogenesis in experimental animals. Prohibitive toxicity of the parent compound, vitamin A, led to a systematic search for synthetic derivatives with an improved therapeutic index. More than 1500 such compounds have been synthesized, many retaining chemopreventive potential, but with less toxicity. Although several anecdotal reports confirming therapeutic benefits of cis-retinoic acid in patients with acute promyelocytic leukemia and myelodysplastic syndromes appeared in the late 1970s and early 1980s, the remarkable studies of Huang and his colleagues in China in 1988 reporting complete remissions in patients with this uncommon variety of acute myelogenous leukemia with the transisomer of retinoic acid (all-trans-retinoic acid) led to a resurgence of interest in the retinoids as differentiating agents for the prevention and therapy of cancer. Furthermore, molecular studies showing DNA rearrangements of the alpha nuclear receptor for retinoic acid located on chromosome 17 in patients with acute promyelocytic leukemia, a disease invariably associated with a translocation between chromosomes 15 and 17, provided a direct connection between an altered nuclear receptor and the development of a human malignancy. The retinoids also may have important beneficial effects in prevention of recurrent malignancies once the primary tumor has been treated, such as in squamous cell carcinoma of the head and neck. Because retinoids appear to be less effective in inducing differentiation in nonpromyelocytic leukemia cells, investigators have conducted a number of studies to exploit potential synergism between retinoids and other differentiating agents or biologic effectors. Differentiation therapy and chemoprevention are attractive alternative approaches to intensive cytotoxic chemotherapy. It is now clear that retinoids represent one class of compounds with which it may be possible to reverse the progression of malignant disease and prevent carcinogenesis.

Critical review of the models to study the biologic progression of bladder cancer

For transitional cell carcinoma of the bladder, clinical data indicate that invasive, metastatic tumors can arise through at least two different progression pathways. The majority of invasive, metastatic bladder neoplasms clinically present de novo, i.e., the patients have no history of malignant bladder disease. This implies that the highly malignant tumor cells either arise de novo or have undergone a rapid progression. Alternatively, a considerable fraction of patients with superficial bladder cancer process to invasive disease after a history of relatively benign superficial TCC. The molecular and cell biological basis of tumor progression is only poorly understood. Clearly, a better understanding of this progress could have profound clinical implications, since patients with superficial TCC with a high risk for progression would have to be treated more aggressively. We discuss the problems that are associated with tumor biological studies on early steps in the progression of TCC, especially from a "model system point of view."

The induction of bladder cancer in portally diverted rats

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A preliminary investigation of promotion of brain tumours by hexachlorophane in Sprague-Dawley rats transplacentally exposed to N-ethylnitrosourea

Two-stage carcinogenesis (initiation and promotion) has been demonstrated in various mammalian tissues, but there is no conclusive evidence that it occurs in the nervous system. The present work has investigated the possibility that it might occur in the brain of the rat. Pregnant Sprague-Dawley rats were given an initiating dose (10 mg/kg intravenously (i.v.)) of N-ethylnitrosourea (ENU), which resulted in a low but consistent yield of brain tumours in the offspring. The dose was determined in a prior dose-response investigation. The 'initiated' offspring were treated postnatally with the putative promoter, hexachlorophane, and its ability to increase tumour incidence was examined by standardized step sectioning of the brain from rats killed at 6 months. There was no evidence of promotion of ENU-induced brain neoplasms by hexachlorophane in the rat. The experimental procedure led to a reproducible incidence of glial tumours in the pups.

Chemoprevention of experimental bladder cancer

The chemopreventive efficacy of several compounds was evaluated in the N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced urinary bladder cancer model using C57BL/6 x DBA/2F1 (BDF) male mice. Compounds were administered in a defined semipurified diet (AIN-76-A) either as single agents or in combination. As single agents and at the doses employed, 2-alpha-difluoromethylornithine (DFMO), piroxicam, oltipraz, and sodium molybdate effectively inhibited the incidence of transitional cell carcinoma (TCC). 4-Hydroxyphenyl retinamide (4-HPR) was ineffective. Body weight gain and survival was not affected by the doses of agents used. Combinations of two agents which increased efficacy were 4-HPR+DFMO, DFMO+piroxicam, 4-HPR+oltipraz, and DFMO+oltipraz. Three-agent combinations which showed enhanced efficacy against TCC induction were 4-HPR+Na molybdate+DFMO, 4-HPR+DFMO+piroxicam, and 4-HPR+DFMO+oltipraz. Although the three-agent combinations were, for the most part, no more effective than the two-agent combinations at the doses employed, all combination regimens significantly reduced bladder cancer incidence even when single agent administration did not.

A comparison of spongiosis induced in the brain by hexachlorophene, cuprizone and triethyl tin in the Sprague-Dawley rat

The effect of hexachlorophene (HCP; 2,2'-methylenebis(3,4,6-trichlorophenol), cuprizone (CPZ; bicyclohexone oxaldihydrazone) and triethyl tin (TET; triethyl tin sulphate) in producing vacuoles in the brain of the Sprague-Dawley rat has been quantified by image analysis of the extent of the spongy change in the white matter. The state of the astrocytes was assessed by immunocytochemical staining for glial fibrillary acidic protein (GFAP). HCP and TET caused a dose-related spongiosis, but cuprizone had no significant effect on the brain. With chronic HCP treatment, the spongiosis was accompanied by astrocyte hypertrophy and proliferation, and the extent of the gliotic reaction was related to the dose of HCP. The results demonstrate that HCP can produce and maintain astrocyte proliferation in the rat brain. Such an agent was required for use in an investigation of a putative tumour promoter in the rat.

Environmentally related diseases of the urinary tract

Nephrotoxicity from exposure to therapeutic agents and chemicals in the environment and workplace results in a broad spectrum of clinical renal disease that may mimic disorders from other causes. Nephrotoxic agents may, in fact, be responsible for some fraction of renal disease of undetermined etiology. Specific diagnosis and treatment by removal from exposure to the toxic agent is more likely in the early phase of the disorder. Measurement and characterization of proteinuria provides the most sensitive and reliable method of early detection. Increased urinary excretion of serum proteins with molecular weight in excess of 50,000, such as albumin and transferrin, is an early indicator of glomerular injury. Low-molecular-weight proteinuria (beta 2-microglobulin or retinol-binding protein) and enzymuria, particularly excretion of NAG, are sensitive indicators of renal tubular cell injury. Tests that reflect hypersensitivity reactions are often indicative of immunologically mediated nephrotoxicity but are not specific for the kidney. Cancers of the kidney and urinary bladder appear to be increasing and are most common among the socially active and affluent. Susceptibility of the urinary tract to toxicity and carcinogenicity reflect contact of excreted toxins with the epithelial cells of nephrons and urinary bladder.

Histological changes in the urinary bladder secondary to urethral catheterisation

The macroscopic and microscopic features of the urothelial response of the human urinary bladder to urethral catherisation are described. The catheter reaction is characterised by a predominantly eosinophilic inflammatory response producing, macroscopically, a papillary mucosal appearance termed polypoid cystitis. The severity of the epithelial inflammatory response correlates significantly with the duration of catheterisation. Urothelial dysplasia confined to the catheter reaction site was noted in 6% of cases. The possible implications of these findings are discussed.

The Copenhagen case-control study of bladder cancer. V. Review of the role of urinary-tract infection

During the years 1979-1981, a population-based study of 388 patients with bladder cancer, including papilloma, and of 790 controls was conducted in Greater Copenhagen. No pronounced difference between cases and controls of either sex was observed for bladder infection, kidney infection or bladder stones. Women with kidney stones had a significantly elevated relative bladder cancer risk (RR = 3.7; 95% CI = 1.2-12.1); the risk for bladder cancer was also increased (RR = 1.5), although not significantly so, in women who had ever had a 'kidney disease'. A review of the existing studies in humans and in animals of the association between bladder infection and cancer reveals a need for studies to determine whether urinary-tract infections increase either the true risk for bladder tumours or only complications of early bladder cancer before a clinical diagnosis has been made.

Inactivation of antiadherence effect of bladder surface glycosaminoglycans as possible mechanism for carcinogenesis

We have shown that the urinary bladder secretes and binds to its surface a glycosaminoglycan layer whose nonspecific antiadherence effect protects the bladder from infection and perhaps from stone formation. If bladder cancer is caused by agents present in the urine, as is widely believed, this mechanism may also protect against carcinogenesis. We performed the current study to determine whether suspected carcinogens or cocarcinogens in the urine gain access to the transitional cells by impairing or inactivating the surface antiadherence effect. Using an in vivo method to quantitate bacterial adherence to the rabbit bladder, we compared adherence in control and glycosaminoglycan-deficient bladders to adherence in bladders treated with one of several suspected urinary carcinogens. There were statistically significant differences between adherence in control bladders and adherence in bladders treated with the tryptophan metabolites 3-hydroxykynurenine and 3-hydroxyanthranilic acid, sodium cyclamate, and sodium saccharin. These data indicate that perhaps certain suspected urinary bladder carcinogens inactivate the anti-adherence effect of the glycosaminoglycan layer at the bladder surface and thereby penetrate to the transitional cells to exert their tumorigenic effects; or they may serve as cocarcinogens that inactivate the glycosaminoglycan barrier and permit other urinary carcinogens to transform the transitional cells.

Chemoprevention of bladder cancer

There is a growing body of basic science and epidemiologic evidence to support a research thrust to determine whether several natural or synthetic agents, given alone or together, can lower cancer incidence. Candidate agents include analogs of vitamin A and the vitamin A precursor, beta-carotene, vitamins C and E, and the trace metal selenium. Other agents now being studied in the laboratory include phenolic antioxidants, protease inhibitors, prostaglandin synthesis inhibitors, and indoles. Research in chemoprevention involves identifying and characterizing agents with reported activity, efficacy and toxicologic testing to select the most promising agents, and clinical trials to test those with the most potential in humans. Activities are underway in all the above areas, including 24 clinical trials, to evaluate selected compounds in preventing cancer at various cancer sites. Included are studies of individuals at high risk, individuals with precancerous lesions and individuals free of cancer but at risk to second cancers. A number of agents have shown activity in reducing bladder cancer incidence in animal models. The potential applicability of these agents for studies in human cancer risk reduction intervention studies is discussed. Cancer induction is postulated to be a multistage process involving initiation and promotion. Progress in cancer prevention may result from not only reducing exposures to initiators, but also suppressing promotional activity in initiated cells. Newly developed research technologies including cellular, animal, and epidemiologic procedures are being used for identifying, refining, and testing cancer prevention strategies.

Differential induction of transcription of c-myc and c-fos proto-oncogenes by 12-O-tetradecanoylphorbol-13-acetate in mortal and immortal human urothelial cells

The effect of the skin tumor-promoter TPA (12-O-tetradecanoylphorbol-13-acetate) on expression of cellular proto-oncogenes has been examined in cell lines derived from human urothelium. A single treatment with TPA (1 microgram/ml) increased the transcription of c-fos and c-myc proto-oncogenes at least 20-fold in the mortal cell line HU 1752. The induction was transient and was accompanied by a rapid but transient change in cell morphology. When immortalized cell lines were treated with TPA a similar rapid and transient morphological response was observed, but the TPA treatment only increased the level of c-fos mRNA, suggesting that the normal regulation of c-myc transcription is altered in immortalized cells irrespective of their tumorigenic properties. The levels of c-Ha-ras and c-Ki-ras mRNAs were unaffected by TPA treatment in all cell lines.

2,2,2-Trifluoroethanol toxicity in hamsters (Mesocricetus auratus)

As part of an effort to further elucidate the mechanism whereby fluorinated ether anesthetics express their various toxic effects, Golden Syrian hamsters were utilized to determine acute and subchronic toxicities of the anesthetic metabolite 2,2,2-trifluoroethanol (TFE). The major lesion observed with the TFE (0.25 g/kg ip) was coagulation necrosis characterized by nuclear pyknosis in epithelial cells of intestinal villi, the deeper portion of gastric mucosae, lymphoid organs such as thymus, spleen and mesenteric lymph nodules and brain. Hepatocyte hypertrophy with diffuse vacuolar degeneration was also found. Lungs had a characteristic focal terminal bronchiolar epithelial hyperplasia with discrete mucous metaplasia in the terminal bronchioles. In subchronic studies, hamsters were injected with sublethal doses of TFE (0.20 g/kg once per week for 5 weeks). The major lesions observed were severe hepatocyte hyperplasia and hypertrophy with fatty degeneration, necrosis of hair germinal matrix, urinary bladder transitional epithelial cellular hypertrophy, and hyperplasia with vacuolar degeneration and submucosal edema. Ultrastructural studies of acutely treated animals indicate that fat vacuoles formed within the hepatic endoplasmic reticulum characterized by lamellar bodies forming multiple myelin figures within the fat vacuoles. Hepatic cytochrome P-450 concentrations measured as a possible index of endoplasmic reticulum damage, failed to reveal any significant differences between the treated and non-treated hamsters.

Modification of N-methyl-N-nitrosourea-induced urinary bladder carcinogenesis in rats following stimulation of urothelial proliferation by a partial cystectomy

The present experiments are concerned with the question whether stimulation of urothelial proliferation modifies tumor development in the urinary bladder. To induce proliferative activity of the urothelium a partial cystectomy (one-third resection of the bladder) was performed in female Wistar rats. N-Methyl-N-nitrosourea (MNU) was used as a carcinogen which acts directly on the urothelium without requiring metabolic activation. MNU was given as a single intravesicular dose of 5 mg/kg body weight via a urethral catheter. After an experimental period of 15 months rats with an intact quiescent bladder showed a tumor incidence of 32.6%. Rats having received MNU 45 h following partial cystectomy - when proliferative activity reached its peak - had developed bladder tumors with a frequency of 17.9%. Initial administration of MNU followed 24 h later by a one-third resection of the bladder resulted in a tumor incidence of only 8.8%. The histologic types of tumors induced proved to be similar to those found with other carcinogens. However, by contrast the majority of urothelial tumors were characterized by a squamous metaplasia. There was no substantial difference between the various histologic tumor types found in the resting and regenerating bladder. The mechanisms responsible for the observed inhibition of tumor development in the regenerating bladder are unknown. It is assumed that an increased capacity of the proliferating urothelial cells to repair carcinogen-induced DNA damage may play an important role.

Toxicological aspects of cyclamate and cyclohexylamine

In the late 1960s the artificial sweetener cyclamate was implicated as a bladder carcinogen in rats. This finding and other concerns about its safety ultimately led to a ban on cyclamate in the U.S. and restrictions on its use in many other countries. Since that time, the carcinogenic potential of cyclamate and cyclohexylamine, its principal metabolite, has been reevaluated in a group of well-controlled, well-designed bioassays that have failed to substantiate the earlier findings. This review of the published and unpublished literature on cyclamate attempts to evaluate the carcinogenicity question and other important aspects of the toxicity of cyclamate and cyclohexylamine, including their effects on various organ systems, their genotoxic potential, and their effects on reproduction. In addition, the physiological disposition of cyclamate is reviewed, with particular attention directed toward the site and extent of its conversion to cyclohexylamine.

Anticarcinogenic effects of retinoids in animals

Retinoids are effective inhibitors of chemical carcinogenesis in the skin, mammary gland, esophagus, respiratory tract, pancreas, and urinary bladder of experimental animals. Modification of the basic retinoid structure has produced retinoids with enhanced target organ specificity, resulting in increased anticancer activity with reduced systemic toxicity. Newer retinoidal benzoic acid derivatives are even more active. Combining retinoid treatment with other modulators of carcinogenesis results in a synergistic inhibition of tumor development. Retinoids in combination with hormonal manipulation are much more effective in inhibiting mammary carcinogenesis than is either treatment alone; this combination approach also inhibits mammary tumor recurrence following surgical removal of the first tumor. Retinoids are most effective when administered shortly after the carcinogenic insult. However, even when retinoid treatment is delayed, the compounds are still effective cancer chemopreventive agents for the mammary gland and urinary bladder. The time that retinoid exposure can be delayed and retain an anticancer effect is directly related to tumor latency, with a longer delay permissible against tumors with long latent periods. The mechanism(s) by which retinoids inhibit carcinogenesis is unknown; however, in the mammary gland, retinoids inhibit differentiation and proliferation, DNA synthesis, and RNA polymerase activity. Cytosolic retinoid-retinoid receptor complexing is apparently a prerequisite for the nuclear interaction of retinoids, at least in mammary cells.

Induction of urinary bladder hyperplasia in Sprague-Dawley rats orally administered tri-n-butyl phosphate

The effects of tri-n-butyl phosphate (TBP) were investigated in the Sprague-Dawley rat over an 18-wk period. Groups of randomized female (average weight [AW] = 206 +/- 10 g) and male (AW = 294 +/- 13 g) rats were divided into low-dose, high-dose, and control groups (12 rats/sex X group). Tri-n-butyl phosphate was administered by gavage once a day for 5 days/wk over an 18-wk period. Low-dose animals received 0.20 g/kg X day throughout the experiment and high-dose animals received 0.30 g/kg X day for the first 6 wk. For the remaining 12 wk, the high-dose level was increased to 0.35 g/kg X day. Histopathological examination of tissues revealed that all test rats examined developed diffuse hyperplasia of the urinary bladder epithelium. Similar changes were not found in the control animals.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Schistosome related cancers: a possible role for genotoxins

Schistosomiasis has long been associated with cancer. This association is most prevalent between Schistosoma hematobium and bladder cancer. Numerous theories have been proposed to explain the causal link between the parasite infestation and the ensuing neoplasia. One theory that has not received as much attention as others, however, is the role of genotoxins in the neoplastic process. Considering the substantial amount of supportive evidence for the cocarcinogenic effects of schistosomes, concern for the health effects resulting from exposure of infested individuals to either exogenous or endogenous genotoxins is certainly warranted.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Cultures of normal human urothelial cells from ureters of perfused cadaver transplant kidneys

In this comparative study, we report that urothelial cultures initiated from ureters of mechanically perfused cadaver-obtained transplant kidneys display characteristics of explant attachment, explant viability, cellular morphology and area of outgrowth essentially indistinguishable from cultures established from ureters of living donor kidneys. We conclude that ureter specimens from cadaver kidneys are a suitable, routinely available source of tissue from which cultures of normal human urothelial cells can be propagated.

The induction of urothelial hyperplasia by methyl methanesulphonate and ethyl methanesulphonate

The early and late morphological changes induced in rat bladder urothelium by intravesicular administration of the alkylating agents methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS) are described. In the short-term, both compounds produced dose-related toxic damage followed by a regenerative hyperplasia of the urothelium. At any given dose-level, the effects of MMS were more severe than those of EMS. Two years after administration of multiple doses of 2.5 mg MMS or 7.5 mg EMS the majority of animals had dose-related simple urothelial hyperplasias with occasional mild dysplasia. However, in three MMS-treated animals the hyperplasias had progressed to well-differentiated transitional-cell carcinomas. No bladder neoplasms were seen in EMS-treated animals. The urothelial response of the rat to MMS and EMS is discussed with reference to the known chemical reactivity of these compounds. It is concluded that EMS is a mitogen for the urothelium and that the few carcinomas which develop following topical exposure of the bladder to MMS do not necessarily reflect any initiating potential in this compound. Rather it is argued that the results are consistent with MMS acting as a promoter in cells which have either been previously initiated or which carry a latent oncogene.