Non-nutritive sweeteners and bladder cancer

Saccharin mechanistic data and risk assessment: urine composition, enhanced cell proliferation, and tumor promotion

Sodium saccharin (NaSac) produces bladder tumors consistently in male rats only after lifetime exposure that begins at birth. NaSac is not metabolized and is negative in most genotoxicity tests. NaSac-induced cell damage and proliferation have been proposed as important factors in tumor promotion, and dose-response information demonstrating a threshold for these parameters is available. One theory proposes that high levels of NaSac, combined with protein in a high Na+, high pH environment found only in the male rat, form toxic microscopic crystals; therefore, NaSac-induced tumors may not be relevant to human carcinogenesis.

The health risks of saccharin revisited

Almost from its discovery in 1879, the use of saccharin as an artificial, non-nutritive sweetener has been the center of several controversies regarding potential toxic effects, most recently focusing on the urinary bladder carcinogenicity of sodium saccharin in rats when fed at high doses in two-generation studies. No carcinogenic effect has been observed in mice, hamsters, or monkeys, and numerous epidemiological studies provide no clear or consistent evidence to support the assertion that sodium saccharin increases the risk of bladder cancer in the human population. Mechanism of action studies in the one susceptible species, the rat, continue to provide information useful in assessing potential risk to the human from saccharin consumption. Unlike typical carcinogens which interact with DNA, sodium saccharin is not genotoxic, but leads to an increase in cell proliferation of the urothelium, the only target tissue. It also appears that the effect of saccharin is modified by the salt form in which it is administered, despite equivalent concentrations of saccharin in the urine. The chemical form of saccharin in the urine is unaffected, and there is no evidence for a specific cell receptor for the saccharin molecule. Changes in several urinary parameters, such as pH, sodium, protein, silicates, volume, and others, appear to influence the reaction of the urothelium to sodium saccharin administration. Silicon-containing precipitate and/or crystals appear to be generated in the urine under specific circumstances, acting as microabrasive, cytotoxic material. Using a mathematical model of carcinogenesis, which encompasses the temporal dynamics and complexity of the process at a cellular level, including spontaneous genetic transitions, it has been shown that the effects of sodium saccharin can be explained entirely in terms of its non-genotoxic influence on cell proliferation. In interpreting these analytical studies in the human context, particularly as they pertain to the urinary milieu which appears to be pivotal in the effect of sodium saccharin, we are led to the conclusion that there is a threshold effect in male rats and that an effect on the human urothelium is unlikely at even the highest levels of human consumption.

Tobacco smoking, coffee, cocoa and tea consumption in relation to mortality from urinary bladder cancer in Italy

This paper examines changes in mortality from urinary bladder cancer in Italy during the years 1950-81 in relation to changes in smoking habits and in coffee, cocoa and tea consumption. The authors found that, in both sexes and for all ages, mortality has been increasing throughout this period, although the rates and relative increase have consistently been much lower and more gradual for women than for men. From the analysis of age-cohort-period variation it seems that bladder cancer mortality can also be influenced by changes in smoking habit patterns and by variation in the quality of diagnoses. The increase in death risk for both sexes in Italy up to cohorts born around 1905-10 can be related to occupational exposures and to high-tar-content tobacco smoking, whereas the tendency for mortality rates to stabilize and decline in cohorts born after 1910 were influenced by changes from high-tar-content and no-filter cigarettes to low-tar-content and filter cigarettes and by prevention measures taken in at-risk working environments. The consumption of coffee, cocoa and tea does not seem to be related to the increase in bladder cancer risk in Italy.

Cell growth dynamics in long-term bladder carcinogenesis

A biologically based probabilistic model of the carcinogenic process has been developed based on a two-stage theory of carcinogenesis. The model has been validated utilizing experimental urinary bladder carcinogenesis studies in the rat, with an emphasis on quantification of cell dynamics. Critical parameters tracked through this process include mitotic rates, cell loss and birth rates, and irreversible cellular transitions from normal to initiated to transformed states. Analyses demonstrate the sensitivity of tumor incidence to the timing and magnitude of changes to these cellular variables. Modeling has been applied to genotoxic compounds, such as N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide, and non-genotoxic compounds, such as sodium saccharin. For the latter compounds, complex administration regimens have been studied, including two-generation experiments, initiation-promotion experiments, and sodium saccharin administration following ulceration and regenerative hyperplasia. Modeling indicates that the effects of such compounds can be explained entirely on the basis of cytotoxicity and consequent hyperplasia. Quantitative modeling based on biological processes has the potential for direct application to carcinogenic risk assessment.

Workshop on guidelines to the epidemiology of weak associations. Confounding

The magnitude of confounding is examined in nine case studies of two "weak" relationships: between artificial sweeteners and bladder cancer, and between oral contraceptives and cervical dysplasia. Confounding had little or no influence on the results of any published study. The responsible epidemiologist must always consider the possibility of confounding, no less when associations are weak than when they are strong. Identification of potentially confounding variables is an integral part of good epidemiologic practice. Rarely, however, does confounding itself, especially from unidentified sources, live up to its reputation for introducing seriously spurious associations. An investigator is more likely to be led astray by undetected biases than by pure confounding.

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.

A review of epidemiological studies on artificial sweeteners and bladder cancer

Next to tobacco, saccharin may be the substance that has been most studied epidemiologically. Over 5000 patients with bladder cancer have participated in case-control studies; over 27,000 diabetics have been observed for 234,000 person-years. The summary relative risk from combining all case-control studies is less than 0.98, the standardized mortality ratio for bladder cancer in diabetics is only 70. Analysis of these studies leads to the conclusion that saccharin is not related to human bladder cancer.