Effects in the mammalian spot test: cyclamate versus saccharin

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 genetic toxicology of putative nongenotoxic carcinogens

This report examines a group of putative nongenotoxic carcinogens that have been cited in the published literature. Using short-term test data from the U.S. Environmental Protection Agency/International Agency for Research on Cancer genetic activity profile (EPA/IARC GAP) database we have classified these agents on the basis of their mutagenicity emphasizing three genetic endpoints: gene mutation, chromosomal aberration and aneuploidy. On the basis of results of short-term tests for these effects, we have defined criteria for evidence of mutagenicity (and nonmutagenicity) and have applied these criteria in classifying the group of putative nongenotoxic carcinogens. The results from this evaluation based on the EPA/IARC GAP database are presented along with a summary of the short-term test data for each chemical and the relevant carcinogenicity results from the NTP, Gene-Tox and IARC databases. The data clearly demonstrate that many of the putative nongenotoxic carcinogens that have been adequately tested in short-term bioassays induce gene or chromosomal mutations or aneuploidy.

Assessment of the carcinogenicity of the nonnutritive sweetener cyclamate

The weight of the evidence from metabolic studies, short-term tests, animal bioassays, and epidemiological studies indicates that cyclamate (CHS) is not carcinogenic by itself; however, there is evidence from in vitro and in vivo studies in animals that implies it may have cancer-promoting or cocarcinogenic activity. Epidemiological studies indicate that the use of nonnutritive sweeteners (CHS and saccharin) has not resulted in a measurable overall increase in the risk of bladder cancer in individuals who have ever used these products. No epidemiological information exists on the possible associations of these sweeteners and cancers other than those of the urinary tract. It is recommended that (1) no further studies on the metabolism of CHS to evaluate its carcinogenicity are required since no potentially hazardous metabolites have been appreciably detected in humans; (2) no further animal bioassays to test for the carcinogenicity of CHS by itself are necessary; (3) the studies in rodents that suggest a promotional or cocarcinogenic effect of CHS should be repeated because they cannot be ruled out; (4) because the significance to human health of a positive outcome of such studies is uncertain, additional research aimed at understanding the predictive value for human health of such results and more generic studies to develop well-validated systems that can be relied on in the assessment of cancer-promoting agents are recommended; (5) in populations where CHS continues to be used, epidemiological monitoring should be continued to determine whether there is an increased risk of cancer in humans who are heavy or long-term users or for those observed long after first exposure. In such monitoring, other cancer sites--in addition to the bladder--should be considered.

The present lack of evidence for unique rodent germ-cell mutagens

Six chemicals, diethylhexyl phthalate (DEHP), ethanol, cyclohexylamine (CHA), sodium saccharin (NaS), cadmium chloride (CdCl2) and triflupromazine (TFP), were suggested to be unique germ-cell mutagens (Auletta and Ashby, 1988) by the GeneTox Workgroups of the U.S. Environmental Protection Agency (EPA). If this is a correct classification it would have major consequences when screening for mutagenicity and when labelling genotoxic substances. However, our re-evaluation of the GeneTox literature, including some more recent publications, has failed to find substantive evidence that any of these chemicals have been unequivocally established as having unique mutagenic activity in germ cells. For DEHP, NaS and TFP the evidence for genotoxic/mutagenic effects is questionable, in both germinal and somatic cells. Ethanol and CdCl2 showed clastogenic activity, but it was not restricted to germ cells. Both, ethanol and cadmium salts, appear to induce aneuploidy. The unconfirmed clastogenic effect of CHA was restricted to rats, but it occurred in both bone marrow and spermatogonia. Therefore, the general observation that rodent germ-cell mutagens are also genotoxic in somatic cells in vivo (Brusick, 1980; Holden, 1982) remains valid.

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.

The mouse spot test. Evaluation of its performance in identifying chemical mutagens and carcinogens

The published results on 60 chemicals and X-rays investigated in the mouse spot test were compared with data on the same chemicals tested in the bacterial mutation assay (Ames test) and lifetime rodent bioassays. The performance of the spot test as an in vivo complementary assay to the in vitro bacterial mutagenesis test reveals that of 60 agents, 38 were positive in both systems, 6 were positive only in the spot test, 10 were positive only in the bacterial test and 6 were negative in both assays. The spot test was also considered as a predictor of carcinogenesis; 45 chemicals were carcinogenic of which 35 were detected as positive by the spot test and 3 out of 6 non-carcinogens were correctly identified as negative. If the results are regarded in sequence, i.e. that a positive result in a bacterial mutagenicity test reveals potential that may or may not be realized in vivo, then 48 chemicals were mutagenic in the bacterial mutation assay of which 38 were active in the spot test and 31 were confirmed as carcinogens in bioassays. 12 chemicals were non-mutagenic to bacteria of which 6 gave positive responses in the spot test and 5 were confirmed as carcinogens. These results provide strong evidence that the mouse coat spot test is an effective complementary test to the bacterial mutagenesis assay for the detection of genotoxic chemicals and as a confirmatory test for the identification of carcinogens. The main deficiency at present is the paucity of data from the testing of non-carcinogens. With further development and improvement of the test it is probable that the predictive performance of the assay in identifying carcinogens should improve, since many of the false negative responses may be due to inadequate testing.

The genotoxicity of sodium saccharin and sodium chloride in relation to their cancer-promoting properties

The literature indicates that sodium saccharin is non-reactive to DNA and inactive as a gene mutagen in vitro. At elevated dose levels it is capable of producing structural disturbances in eukaryotic chromosomes in vitro, and it shows intermittent activity as a very weak germ-cell and somatic-cell mutagen in vivo. Its possible mode of action in these respects is speculated on and related to its ability to promote bladder tumours in rats at elevated dose levels. A review of the toxicology of sodium chloride reveals a profile of genotoxic activities almost identical to that of sodium saccharin. It is suggested that the recorded genotoxic and cancer-promoting activities of these chemicals will only become apparent at elevated dose levels that define them as significant contributors to the biological medium (solvent) rather than as trace xenobiotic toxins (solutes). The possible activity of acid saccharin, or of its potassium, calcium and ammonium salts, as ionic genotoxins requires urgent evaluation.

Effect of saccharin on the induction of chromosomal translocations in male mice and their F1 offspring

The dose-dependent effects of sodium saccharin on the fertility and the induction of chromosomal translocations in treated mice and their F1 males were examined. C3H X 101 mice were treated with saccharin for 2 successive weeks at doses of 200 and 500 mg/kg of body wt. Data from the fertility study showed that saccharin did not induce any significant effect on fertility. Cytological analysis of meiotic cells showed no chromosomal rearrangements. Semisterility and sterility were noted in F1 males of saccharin-treated animals. In semi-sterile and sterile F1 males of saccharin-treated animals chromosomal translocations were not found.