Chronic toxicity and carcinogenicity to the urinary bladder of sodium saccharin in the in utero-exposed rat

Levels, consumption, and variations of eight artificial sweeteners in the wastewater treatment plants of Dalian city, China

Artificial sweeteners (ASs) are emerging contaminants in the environment, primarily derived from wastewater treatment plant (WWTP) effluents. In this study, the influents and effluents of three WWTPs in the Dalian urban area, China, were analyzed for the distribution of 8 typical ASs to investigate their seasonal fluctuations in the WWTPs. The results showed that acesulfame (ACE), sucralose (SUC), cyclamate (CYC), and saccharin (SAC) were both detected in the influent and effluent water samples of WWTPs, with concentrations ranging from not detected (ND) to 14.02 μg·L-1. In addition, SUC was the most abundant ASs type, accounting for 40 %-49 % and 78 %-96 % of the total ASs in the influent and effluent water, respectively. The WWTPs revealed high removal efficiencies of CYC, SAC, and ACE, while the SUC removal efficiency was poor (26 % ± 36 %). The ACE and SUC concentrations were higher in spring and summer, and all ASs showed lower levels in winter, which may be caused by the high consumption of ice-cream in warmer months. The per capita ASs loads in the WWTPs were determined in this study based on the wastewater analysis results. The calculated per capita daily mas loads for individual ASs ranged from 0.45 g·d-1·1000p-1 (ACE) to 2.04 g·d-1·1000p-1 (SUC). In addition, the relationship between per capita ASs consumption and socioeconomic status showed no significant correlation.

Non-sugar sweeteners and cancer: Toxicological and epidemiological evidence

Several toxicological and epidemiological studies were published during the last five decades on non-sugar sweeteners (NSS) and cancer. Despite the large amount of research, the issue still continues to be of interest. In this review, we provided a comprehensive quantitative review of the toxicological and epidemiological evidence on the possible relation between NSS and cancer. The toxicological section includes the evaluation of genotoxicity and carcinogenicity data for acesulfame K, advantame, aspartame, cyclamates, saccharin, steviol glycosides and sucralose. The epidemiological section includes the results of a systematic search of cohort and case-control studies. The majority of the 22 cohort studies and 46 case-control studies showed no associations. Some risks for bladder, pancreas and hematopoietic cancers found in a few studies were not confirmed in other studies. Based on the review of both the experimental data on genotoxicity or carcinogenicity of the specific NSS evaluated, and the epidemiological studies it can be concluded that there is no evidence of cancer risk associated to NSS consumption.

Association of Artificially Sweetened Beverage Consumption and Urinary Tract Cancers in the Women's Health Initiative Observational Study

Background

Insufficient data exist to conclude whether consumption of artificially sweetened beverages is associated with a higher risk of urinary tract cancers.

Objective

We sought to investigate whether urinary tract cancer incidence differed among women who consumed various amounts of artificially sweetened beverages.

Design setting and participants

This was a secondary analysis of data from the Women's Health Initiative Observational Study, a multicenter longitudinal prospective study of the health of 93 676 postmenopausal women with a mean follow-up time of 13.5 yr. Women were identified at 40 clinical centers across the USA and enrolled from 1993 to 1998. Women between the ages of 50 and 79 yr were enrolled. We included women who answered questions about artificially sweetened beverage consumption and reported no prior urinary tract cancer diagnoses. The frequency of artificially sweetened beverage consumption was categorized as follows: rare artificially sweetened beverage consumption (never to fewer than one serving per week), frequent consumption (one to six servings per week), and daily consumption (more than one servings per day).

Outcome measurements and statistical analysis

The incidence of urinary tract cancer reported during subsequent visits until February 28, 2020 was recorded. Demographic characteristics were compared between those with varying levels of artificially sweetened beverage consumption. Descriptive statistics were used to report the rates of urinary tract cancer diagnosis, and Cox regression models were constructed to determine hazard ratios and adjust for potential confounders.

Results and limitations

We identified 80 388 participants who met the inclusion criteria. Most participants (64%) were infrequent consumers of artificially sweetened beverages, with 13% (n = 10 494) consuming more than one servings per day. The incidence of urinary tract cancers was low, with only 804 cases identified. Cox regression models showed that frequent artificially sweetened beverage consumption was associated with a higher risk of kidney cancer (adjusted hazard ratio 1.34, 95% confidence interval 1.03-1.75). There was no significant association between artificially sweetened beverage intake and bladder cancer.

Conclusions

Frequent consumption of artificially sweetened beverages may be associated with a higher risk of kidney cancer among postmenopausal women.

Patient summary

A secondary analysis of the Women's Health Initiative Observational Study showed that higher consumption of artificially sweetened beverages was associated with a higher risk of kidney cancer.

Consumption of non-nutritive sweeteners during pregnancy

In an effort to reduce sugar consumption to prevent diabetes mellitus and cardiovascular diseases, "sugar-free" or "no added sugar" products that substitute sugar with non-nutritive sweeteners (NNSs) (eg, Splenda, Sweet'N Low, and Stevia) have become increasingly popular. The use of these products during pregnancy has also increased, with approximately 30% of pregnant women reporting intentional NNS consumption. In clinical studies with nonpregnant participants and animal models, NNSs were shown to alter gut hormonal secretion, glucose absorption, appetite, kidney function, in vitro insulin secretion, adipogenesis, and microbiome dysbiosis of gut bacteria. In pregnant animal models, NNS consumption has been associated with altered sweet taste preference later in life and metabolic dysregulations in the offspring (eg, elevated body mass index, increased risk of obesity, microbiome dysbiosis, and abnormal liver function tests). Despite the accumulating evidence, no specific guidelines for NNS consumption are available for pregnant women. Furthermore, there are limited clinical studies on the effects of NNS consumption during pregnancy and postpartum and long-term outcomes in the offspring.

From sweeteners to cell phones-Cancer myths and beliefs among journalism undergraduates

OBJECTIVE

The media are an important source of health information that can help people make their own medical decisions. However, medical news can also transmit biases produced by different factors, such as the previously held beliefs of journalists. This study identifies which cancer myths are more popular among future journalists and whether their beliefs are related to their chosen source of health information.

METHODS

A survey was conducted among journalism undergraduates (N = 249) to determine which cancer myths existed and how widespread they were. The survey included a list with different sources of health information and eight questions regarding cancer-related myths.

RESULTS

The most extensive myths among the undergraduate respondents were that sweeteners (40.2%) and cell phones (48.2%) produce cancer and that a patient's good or bad attitude can determine the outcome of such an illness (52.2%). Respondents who relied on their family and friends as a source of health information were more prone to believe in cancer myths.

CONCLUSION

This research focuses on future journalists as a group of special interest for improving knowledge about cancer. Future campaigns to debunk cancer misconceptions should pay attention to the role played by family and friends as agents of health information transmittance.

Occurrence of artificial sweeteners in human liver and paired blood and urine samples from adults in Tianjin, China and their implications for human exposure

In this study, acesulfame (ACE), saccharin (SAC) and cyclamate (CYC) were found in all paired urine and blood samples collected from healthy adults, with mean values of 4070, 918 and 628 ng mL(-1), respectively, in urine and 9.03, 20.4 and 0.72 ng mL(-1), respectively, in blood. SAC (mean: 84.4 ng g(-1)) and CYC (4.29 ng g(-1)) were detectable in all liver samples collected from liver cancer patients, while ACE was less frequently detected. Aspartame (ASP) was not found in any analyzed human sample, which can be explained by the fact that this chemical metabolized rapidly in the human body. Among all adults, significantly positive correlations between SAC and CYC levels were observed (p < 0.001), regardless of human matrices. Nevertheless, no significant correlations between concentrations of SAC (or CYC) and ACE were found in any of the human matrices. Our results suggest that human exposure to SAC and CYC is related, whereas ACE originates from a discrete source. Females (or young adults) were exposed to higher levels of SAC and CYC than males (or elderly). The mean renal clearance of SAC was 730 mL per day per kg in adults, which was significantly (p < 0.001) lower than those for CYC (10 800 mL per day per kg) and ACE (10 300 mL per day per kg). The average total daily intake of SAC and ACE was 9.27 and 33.8 μg per kg bw per day, respectively.

Systematic review of the relationship between artificial sweetener consumption and cancer in humans: analysis of 599,741 participants

BACKGROUND

The effect of artificial sweetener consumption on cancer risk has been debated in animal models for over four decades. To further investigate this relationship, this study aims to synthesise results from several of the most recent studies in humans.

METHODS

An online literature search was performed in MEDLINE from 2003 to 2014 using Ovid, PubMed, Web of Science, and Scopus using keywords 'artificial', 'sweetener' and 'cancer'. Ninety-two results were then manually assessed for eligibility. Studies were included if the relationship between artificial sweeteners and cancer was their central hypothesis, and if they adjusted for age, gender, smoking status and body mass index. Extracted data included study design, patient characteristics, outcome measure and results.

RESULTS

In the five publications that satisfied the inclusion criteria, significant direct associations with artificial consumption were found for laryngeal (odds ratio, OR 2.34, 95% CI: 1.20-4.55), urinary tract tumours (OR 2.12, 95% CI: 1.22-3.89), non-Hodgkin lymphoma in men (RR 1.31, 95% CI: 1.01-1.72), multiple myeloma in men (RR 2.02, 95% CI: 1.20-3.40) and leukaemia (RR 1.42, 95% CI: 1.00-2.02). Inverse relationships were found in breast (OR 0.70, 95% CI: 0.54-0.91, p trend = 0.015) and ovarian (OR 0.56, 95% CI: 0.38-0.81, p trend < 0.001) cancers.

CONCLUSION

The statistical value of this review is limited by the heterogeneity and observational designs of the included studies. Although there is limited evidence to suggest that heavy consumption may increase the risk of certain cancers, overall the data presented are inconclusive as to any relationship between artificial sweeteners and cancer.

The genotoxic and teratogenic effects of maltitol in rats

In the present study, the genotoxic and cytotoxic effects of the low-caloric artificial sweetener maltitol, which is a sugar alcohol (polyol), were investigated in the bone marrow cells of rats using the chromosome aberration (CA) test. In addition, the teratogenicity and embryotoxicity of maltitol was also investigated in rats. To reveal the genotoxicity and cytotoxicity of maltitol, rats were intraperitoneally administered 2.5, 5 and 10 g/kg body weight (bw) concentrations of maltitol for 6, 12 and 24 h treatment period. The pregnant females were intraperitoneally treated with 1, 2 and 4 g/kg bw/day concentrations of maltitol during the first 7 days of gestation (first trimester) to investigate the teratogenicity of maltitol. The embryos were collected after killing the dams by cervical dislocation under ether anaesthesia on gestation day 19. Maltitol did not induce the CA and did not decrease the mitotic index in bone marrow cells of rats at all concentrations and treatment periods. In addition, maltitol was not teratogenic; however, it decreased the foetuses weight and at the highest dose (4 g/kg bw) caused growth retardation.

Possible roles of excess tryptophan metabolites in cancer

Tryptophan is metabolized through serotonin, indole, and kynurenine (KN) pathways. Uptake of an excess amount of tryptophan accompanied with vitamin B6 deficiency may result in the accumulation of higher concentrations of metabolites mainly from the KN pathways in the bladder. These metabolites could interact with nitrite to become mutagenic nitrosamines. They could be a promoter in the initiator-promoter model of carcinogenesis. They produced bladder cancer when implanted in the bladder. They also interact with transition metals copper or iron to form reactive radicals or reactive oxygen species (ROS). Some metabolites, 3-hydroxy-anthranilic acid, were autooxidized to mutagenic cinnabarinic and anthranilyl radical intermediates. These radical intermediates could also be ligands that interact with aryl hydrocarbon receptor (AhR) and induce xenobiotic metabolizing enzymes (XMEs) to metabolize contaminated carcinogens. When tryptophan is exposed to either visible or UV light, a photoproduct of 6-formylindolo[3,2b]-carbazole is formed, which has a very high affinity for the AhR that plays a role in carcinogenesis. This review gives an insight into various mechanisms through which tryptophan metabolites cause carcinogenesis. It could be concluded that tryptophan metabolites play a complementary role in promoting carcinogenesis along with carcinogens like aflatoxin, CCl(4) , 2-acetylaminofluorene, 4-aminobiphenyl, 2-naphthylamine, or N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide. The underlying mechanisms could be their autoxidation, exposure to either visible or UV light, interaction with nitrite or transition metals to form reactive intermediates, serving as ligands to interact with an AhR that is known to play a role in carcinogenesis through induction of XMEs. Further research is warranted.Environ.

Superficial bladder cancer: part 1. Update on etiology, classification and natural history

Superficial 'nonmuscle-invasive' bladder tumors represent a heterogeneous group of cancers, which include those that are papillary in nature and limited to the mucosa (Ta), high grade, flat and confined to the epithelium (Tis) and those that invade the submucosa or lamina propria (T1). The natural history of these bladder cancers is that of disease recurrence and progression to higher grade and stage. Furthermore, recurrence and progression rates of superficial bladder cancer vary according to several tumor characteristics. The goal in the treatment of superficial bladder cancer is twofold: reducing tumor recurrence and the subsequent need for additional therapies, such as cystoscopy, transurethral resections, intravesical therapy and the morbidity associated with these treatments; and preventing tumor progression and the subsequent need for more aggressive therapy, such as radical cystectomy. The administration of intravesical chemotherapy and immunotherapy has become an important component in accomplishing these goals. This update is the first part of two articles reviewing important contemporary concepts in the etiology, classification and natural history of superficial bladder cancer, while part II of the series will review and highlight important aspects in management of superficial bladder cancer.

The cytogenetic effects of food sweetener maltitol in human peripheral lymphocytes

The effects of the low-calorie artifical sweetener maltitol (E965), a sugar alcohol (Polyol), on sister chromatid exchange (SCE), chromosome aberration (CA), and micronucleus formation (MN) were investigated in human peripheral lymphocytes. Maltitol did not induce SCE at all concentrations (1.25, 2.5, and 5 mg/mL) and treatment periods (24 and 48 h). Maltitol induced CA, although not statistically significantly. Maltitol induced the frequency of MN at 24 and 48 h in a non-dose-dependent manner. In addition, maltitol did not decrease the replication index (RI) and the mitotic index (MI) at all concentrations and treatment periods. Maltitol did not alter the pH and osmolality of the medium. In conclusion, it can be concluded that maltitol has a weak genotoxic potential and it appears non-cytotoxic to human peripheral lymphocytes in vitro.

Enhancement of rat bladder contraction by artificial sweeteners via increased extracellular Ca2+ influx

INTRODUCTION

Consumption of carbonated soft drinks has been shown to be independently associated with the development of overactive bladder symptoms (OR 1.62, 95% CI 1.18, 2.22) [Dallosso, H.M., McGrother, C.W., Matthews, R.J., Donaldson, M.M.K., 2003. The association of diet and other lifestyle factors with overactive bladder and stress incontinence: a longitudinal study in women. BJU Int. 92, 69-77]. We evaluated the effects of three artificial sweeteners, acesulfame K, aspartame and sodium saccharin, on the contractile response of isolated rat detrusor muscle strips.

METHODS

Strips of detrusor muscle were placed in an organ bath and stimulated with electrical field stimulation (EFS) in the absence and presence of atropine, and with alpha,beta methylene ATP, potassium, calcium and carbachol.

RESULTS

Sweeteners 10(-7) M to 10(-2) M enhanced the contractile response to 10 Hz EFS compared to control (p<0.01). The atropine-resistant response to EFS was marginally increased by acesulfame K 10(-6) M, aspartame 10(-7) M and sodium saccharin 10(-7) M. Acesulfame K 10(-6) M increased the maximum contractile response to alpha,beta methylene ATP by 35% (+/-9.6%) (p<0.05) and to KCl by 12% (+/-3.1%) (p<0.01). Sodium saccharin also increased the response to KCl by 37% (+/-15.2%) (p<0.05). These sweeteners shifted the calcium concentration-response curves to the left. Acesulfame K 10(-6) M increased the log EC(50) from -2.79 (+/-0.037) to -3.03 (+/-0.048, p<0.01) and sodium saccharin 10(-7) M from -2.74 (+/-0.03) to 2.86 (+/-0.031, p<0.05). The sweeteners had no significant effect on the contractile response to carbachol but they did increase the amplitude of spontaneous bladder contractions.

DISCUSSION

These results suggest that low concentrations of artificial sweeteners enhanced detrusor muscle contraction via modulation of L-type Ca(+2) channels.

Artificial sweeteners--do they bear a carcinogenic risk?

Artificial sweeteners are added to a wide variety of food, drinks, drugs and hygiene products. Since their introduction, the mass media have reported about potential cancer risks, which has contributed to undermine the public's sense of security. It can be assumed that every citizen of Western countries uses artificial sweeteners, knowingly or not. A cancer-inducing activity of one of these substances would mean a health risk to an entire population. We performed several PubMed searches of the National Library of Medicine for articles in English about artificial sweeteners. These articles included 'first generation' sweeteners such as saccharin, cyclamate and aspartame, as well as 'new generation' sweeteners such as acesulfame-K, sucralose, alitame and neotame. Epidemiological studies in humans did not find the bladder cancer-inducing effects of saccharin and cyclamate that had been reported from animal studies in rats. Despite some rather unscientific assumptions, there is no evidence that aspartame is carcinogenic. Case-control studies showed an elevated relative risk of 1.3 for heavy artificial sweetener use (no specific substances specified) of >1.7 g/day. For new generation sweeteners, it is too early to establish any epidemiological evidence about possible carcinogenic risks. As many artificial sweeteners are combined in today's products, the carcinogenic risk of a single substance is difficult to assess. However, according to the current literature, the possible risk of artificial sweeteners to induce cancer seems to be negligible.

Lifestyle issues and genitourinary tumours

A variety of lifestyle factors, including physical activity, artificial sweeteners, alcohol consumption and smoking, have been reported to contribute to the risk of developing urological malignancies. A great number of epidemiological studies suggest that sports and physical activity may have a preventive influence on genitourinary tumours, especially on the incidence of prostate cancer. Smoking appears to be the most relevant lifestyle factor significantly increasing both incidence and mortality from bladder cancer. Furthermore, there is evidence implicating an association between tobacco use and kidney cancer. In contrast, prostate and testicular cancers are unlikely to be linked to tobacco use. As far as alcohol is concerned, most studies indicate that neither amount nor type of alcohol seems to be clearly associated with a risk of developing urological malignancies. However, some more recent cohort studies suggest a moderately increased risk for prostate and bladder cancer for specific types of alcohol. On the other hand, there is evidence that moderate alcohol consumption may even protect women from developing renal cancer. Since the introduction of artificial sweeteners, reports of potential cancer risks have circulated periodically through the mass media. The wide distribution of these agents and the fact that mostly combinations of the different compounds are added to a broad variety of food, drinks, drugs, and hygiene products complicates a systematic analysis of their potential impact on the development of urological malignancies. Nevertheless, so far not a single study has convincingly demonstrated a statistically significant risk of bladder cancer due to the consumption of artificial sweeteners. This survey demonstrates that the individual assessment of lifestyle factors not only may identify groups with an increased risk for urological malignancies but also clearly displays a potential for tumour prevention.

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

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

Epigenetic carcinogens: evaluation and risk assessment

Regulatory policies in the U.S. have been developed based upon a single model of cancer causation, which assumes chemical-induced genetic alterations. Such a model predicts some degree of cancer risk even at extremely low exposure levels. Many chemicals that produce tumors in experimental animals have been shown to act by epigenetic mechanisms that do not involve an attack by the chemical on DNA leading to subsequent genetic alteration. Such indirect mechanisms require prolonged exposures to high levels of chemicals for the production of tumors. For chemicals that are carcinogenic in this manner, the cancer mechanism would not be operative at exposures below a threshold at which the relevant cellular effect does not occur. Also, in contrast to DNA-reactive mechanisms, epigenetic effects may be unique to the rodent species used for testing. Certain chemical tumorigens have been well studied and provide examples for the use of mechanistic information in risk assessment. Butylated hydroxyanisole and saccharin are nongenotoxic food additives for which no risk to humans is predicted based upon low exposure levels and the likelihood that humans are either insensitive or much less sensitive to the tumorigenic effects found in rodent test species. For another non-genotoxic food additive d-limonene, the mechanism that underlies kidney tumor development in male rats is not expected to be operative in humans at all. The pharmaceutical phenobarbital represents a large group of non-genotoxic liver microsome enzyme inducers, which produce liver cancer in mice at levels that are near to therapeutic doses in humans. Epidemiology studies have not shown phenobarbital-related tumors in humans, indicating that humans may be less sensitive to the effects of phenobarbital. The mechanistic considerations involved in the risk assessment of these agents demonstrate that humans are not at risk from current exposure levels of many epigenetic carcinogens.

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.

A data-derived safety (uncertainty) factor for the intense sweetener, saccharin

An increased incidence of bladder cancer is found when male rats are fed high dietary concentrations of sodium saccharin (3% or more) from birth. This toxicity has been used as the basis for the development of a data-derived safety factor. Such an effect would attract an extra factor (10-fold) for nature of toxicity and in the absence of other data would result in a high overall safety factor. However the extensive mechanistic database on sodium saccharin allows an assessment of the potential relevance of the effect for humans. In addition the effect is only seen under specific conditions in rats, i.e. largely with the sodium salt and with a commercial rat diet. The effect is not related to the concentration of saccharin in the rat urine or bladder so that toxicokinetic considerations are simplified. The extensive animal database allows the determination of data-derived factors for inter-species differences in both toxicokinetics and toxicodynamics. Based on this analysis an overall safety factor of 50 (which includes the factor of 10 for severity of effect) would appear appropriate at the present time. This factor, and the ADI which would result from its application, are consistent with the absence of an association between the consumption of artificial sweeteners and bladder cancer in humans.

A review and biological risk assessment of sodium saccharin

Dietary sodium saccharin is associated with bladder tumors when fed at high levels to the male rat. Under these conditions urinary pH, sodium concentration, and volume are elevated and proliferative changes are present in the urothelium. Extensive epidemiological studies have shown that saccharin does not increase the risk of bladder cancer in humans and laboratory investigations have shown that sodium saccharin is not mutagenic and does not bind to DNA. Recent research indicates that the urothelium in male rats is damaged under conditions of high urinary pH and sodium levels by a mechanism that involves alpha 2u-globulin and possibly silicate crystalluria. These studies and their implications for human health risk are reviewed.

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.

Effects of in utero and postnatal sodium saccharin exposure on the nutritional status of the young rat. II. Dose response and reversibility

A previous study in our laboratory demonstrated that 30-day-old Sprague-Dawley rats exposed to 7.5% sodium saccharin (NaS) since conception differ from untreated rats in several physiological parameters. In the present study, to determine the dose response of the changes associated with NaS treatment, animals were evaluated at 30 days post-birth, after treatment with dietary levels of 0, 1, 3 or 7.5% NaS since conception. Most physiological consequences of NaS treatment in the weanling rat, including anaemia and reductions in serum folate and vitamin A concentrations, were dose dependent. Serum vitamin E, cholesterol and triglyceride concentrations were decreased at the two lower doses of NaS but were significantly increased with 7.5% NaS. The no-effect level (NOEL) was similar for physiological effects and for bladder tumour production in two-generation studies (1% NaS in the diet). The reversibility of the effects of 7.5% NaS was examined in 90-day-old rats. The increases in lipids and vitamin E were reversible. Although values for haematological parameters and serum vitamin A remained significantly reduced at 90 days, changes were less severe than at 30 days. Histological examinations revealed that the effects of 7.5% dietary NaS on the bladder were negligible, indicating that the physiological changes observed in the young rat are probably not directly related to the production of bladder tumours.

Effects of in utero and postnatal sodium saccharin exposure on the nutritional status of the young rat. I. Effects at 30 days post-birth

The incidence of sodium saccharin (NaS)-associated bladder tumours in male rats increases when exposure to high doses begins in utero or at birth compared with treatment after weaning. The present experiment evaluated the effect of NaS exposure on selected physiological parameters in young second generation rats. 6-wk-old male and female Sprague-Dawley rats were placed on either a diet supplemented with 7.5% NaS or an untreated diet, and mated 4-6 wk later. Treatment was continued through lactation and the offspring were weaned on to the same diet. Body weights were significantly depressed in NaS-treated litters by 4 days after birth, and were 35% lower than controls by 30 days when the animals were killed. NaS treatment of the offspring was associated with an increase in faecal moisture content and caecal content weight, changes in several urinary analytes, a 50% increase in serum cholesterol a 10-fold increase in serum triglycerides and decreases in serum and hepatic vitamins. In addition, NaS-treated dams and pups were anaemic. Relatively few differences between males and females were noted, but significant inter-litter differences existed. The numerous physiological changes indicate that 7.5% dietary NaS exceeds the maximum tolerated dose for weanling rats.

Lack of bladder carcinogenicity of dietary sodium saccharin in analbuminaemic rats, which are highly susceptible to N-nitroso-n-butyl-(4-hydroxybutyl)amine

A previous 1-wk study measuring the agglutinability of bladder epithelial cells by concanavalin A had suggested a high susceptibility of analbuminaemic rats to bladder carcinogenesis by sodium saccharin (Honma et al., Cancer Letters 1983, 19, 7). A long-term study was conducted to confirm the results of this short-term assay. Sodium saccharin was administered at 5% in the diet to groups of 35 male analbuminaemic rats and 36 male rats of the Sprague-Dawley strain. No bladder carcinomas nor precancerous lesions were observed in any of the rats exposed to sodium saccharin. The discrepancy between the results of the agglutination assay and the long-term experiment might be attributable to a sharp increase in urine volume in analbuminaemic rats during the first week of treatment. The resultant distension of the bladder wall might make the epithelial cells more susceptible to concanavalin A agglutination. The results indicated no demonstrable bladder carcinogenicity of sodium saccharin in analbuminaemic rats and excluded the possibility that these particular mutant rats could be useful animals for shorter-duration screening for bladder carcinogens.

The effects of high dietary concentrations of saccharin on in vitro metabolism of xenobiotics in rats

The effects of feeding male rats a diet containing 7.5% sodium saccharin on drug metabolism in vitro were studied using both one- and two-generation protocols. Saccharin administration did not affect the hepatic concentrations of total cytochrome P-450, cytochrome b5, cytochrome P-450 reductase, aryl hydrocarbon hydroxylase activity or glutathione content but caused a statistically significant increase in dimethylnitrosamine-N-demethylase activity. This increase was detectable in neonatal animals treated using a two-generation protocol. Administration of the sodium, potassium or calcium salts of saccharin or its acid form at 5% in the diet to male rats for 8 wk each caused a significant increase in dimethylnitrosamine-N-demethylase activity. Fasting control and saccharin-treated male rats for 24 hr before the dimethylnitrosamine-N-demethylase assay increased the activity of this enzyme in both groups slightly. The observed increase in dimethylnitrosamine-N-demethylase activity recorded in both male and female rats fed diets containing saccharin after 8 to 12 wk of treatment was reversed when the animals were given control diet for 4 wk.

Effect of saccharin on the ATP-induced increase in Na+ permeability in isolated chicken intestinal epithelial cells

When isolated intestinal cells from 3-wk-old chickens are treated with exogenous ATP they undergo a dramatic increase in permeability towards Na+. The increase occurs instantaneously and maximum cell loading with Na+ occurs within 2 min. The response is dose dependent (0.1-1.0 mM-ATP) and results in as much as a 10-fold increase in unidirectional influx of 22Na+ into the cells. The resting cellular Na+ gradient and membrane potential are partially dissipated and consequently Na+-dependent transport of sugars and amino acids is inhibited. Sodium saccharin (20 mM), added at the same time as ATP, completely blocks the effect of ATP on Na+ permeability and preserves the functional capacity of the cells for Na+-dependent sugar or amino acid transport. Partial protection is afforded by 10 mM-saccharin. Saccharin added 2 min after ATP will reverse the enhanced Na+ permeability that has already been induced. In cells that have not been treated with ATP, saccharin induces enhanced sugar and amino acid gradients (P less than 0.05 in paired comparisons from the same cell preparation), indicating that it may also inhibit Na+ permeability of the unperturbed membrane and allow cells to establish higher Na+ gradients and/or membrane potentials. The effect of saccharin in blocking ATP-induced Na+ permeability occurs within 10 sec and at a much lower dose than that required for blockade of facilitated diffusional sugar transfer in these cells.

Comparison of the responses of male rats to dietary sodium saccharin exposure initiated during nursing with responses to exposure initiated at weaning

In an attempt to define the role of exposure to sodium saccharin (NaS) during early life on the subsequent development of bladder tumours, we compared the responses of male rat pups to exposure to 5% dietary NaS initiated at parturition with those to exposure initiated at weaning. We also compared the effects of exposure from parturition to NaS given in a low-carbohydrate (L-CHO) diet with those of NaS in rat chow. NaS ingestion by the dam was associated with low saccharin concentrations in the pups' urine and had no effect on the caecal or bladder mass in the suckling pups. In the 10 wk after weaning, the rats ingesting NaS in chow showed decreased weight gain and increases in feed consumption, mass of caecal contents and tissue, urine output, bladder mass, relative water consumption (g water consumed/g feed consumed) and bladder hyperplasia. Except for bladder hyperplasia these effects were generally greater in the rats exposed to NaS from parturition than in those exposed only from weaning. The animals exposed to NaS in the L-CHO diet had the highest level of urinary saccharin but showed no bladder hyperplasia. The significance of these findings to the role of pre-weaning saccharin exposure in bladder tumorigenesis is discussed, and it is concluded that the effects on urinary parameters and the bladders of rats exposed to NaS during suckling and weaning may be secondary to the effects of NaS on the gastro-intestinal tract.

An hypothesis of the mechanism of urinary bladder tumorigenesis in rat ingesting sodium saccharin

An hypothesis is presented of a mechanism for the sodium saccharin (NaS)-associated tumorigenesis of the urinary bladder that occurs in male rats. The ingestion of high doses of NaS is associated with increased urine volume and bladder mass. In rats with an inherently high urine output, the diuresis associated with NaS ingestion combined with the increasing diuresis that occurs with age in male rats results in a chronic demand for a bladder-volume increase that is met by excessive cell division of the bladder epithelium. This enhanced mitosis in the bladder epithelium can result in a significant incidence of bladder tumours. Male rats exposed to NaS during early life show an exacerbation of tumour incidence, and it is proposed that this is because the exacerbation of the effects of NaS on the gastro-intestinal and urinary tracts results in increased urine output and bladder hyperplasia in these rats.

The effect of saccharin ingestion on the excretion of microbial amino acid metabolites in rat and man

Low dietary levels of sodium saccharin (0-2%) fed to male rats for 6 weeks produced a dose-related increase in the urinary excretion of p-cresol, a major microbial metabolite of tyrosine. Some animals fed higher levels of saccharin (5-7.5%) for 6 weeks excreted increased amounts of p-cresol, but many excreted negligible amounts so that the overall dose-response relationship was bell shaped. After 20 weeks of exposure, all rats in the higher dose groups showed increased p-cresol excretion and by 26 weeks the 7.5% saccharin group showed a 36-fold increase over animals fed the 0% saccharin diet. The urinary excretion of phenol, another microbial amino acid metabolite, was constant in animals fed dietary levels of saccharin below 2% for 6 weeks, but was virtually abolished at higher levels. The excretion of indican (formed from indole, a microbial metabolite of tryptophan) was increased by saccharin in a dose-related fashion at all time points, but showed only a 3-fold increase at 7.5% compared with the 0% group. p-Cresol may therefore prove more sensitive than indican as an indicator of altered microbial metabolism due to saccharin. In a separate study the effect of 7.5% saccharin on p-cresol and indican excretion was shown to be largely reversible and the excretion of phenol increased rapidly when saccharin was withdrawn from the diet. Chronic saccharin administration to man at high doses (1 g/day for 4 weeks) had no perceptible effect on the excretion of these three metabolites.

The metabolism of intense sweeteners

Three organic acids (saccharin, acesulfame-K and cyclamate) are used or have been used extensively as intense sweeteners. Once absorbed from the gut they are eliminated, largely in the urine, without undergoing metabolism. Early studies using radiolabelled saccharin indicated the existence of limited metabolism, but this was not confirmed by later more extensive studies using highly purified compound. Metabolism could not be induced by a variety of pretreatments. Following an initial report of the presence of traces of cyclohexylamine in the urines of subjects given cyclamate, it was shown that chronic administration of the sweetener caused the induction of extensive metabolism. The metabolism, which showed wide inter- and intra-individual variability was performed the gut microflora. The peptide sweeteners (aspartame and thaumatin) are metabolized to their constituent amino acids in the gastro intestinal tract, prior to absorption. As such they are incorporated into normal intermediary metabolism and their low-calorie applications derive from their intense sweetness.

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.

Morphologic changes in the urinary bladder and stomach after long-term administration of sodium saccharin in F344 rats

The effects of long-term administration of sodium saccharin on the urinary bladder and stomach of F344 rats were investigated. Sixty-eight male F344 rats, aged 7 weeks at the beginning of the experiment, were maintained on diet supplemented with 5% sodium saccharin for 112 weeks. Animals were killed periodically and investigated for gross and microscopic lesions in the urinary bladder and stomach. Papillary or nodular hyperplasia was evident in the urinary bladder epithelium from 8 weeks onwards although no papillomas or transitional cell carcinomas developed. Lesions observed in the bladders of control animals fed the basal diet without the saccharin supplement were limited throughout the experiment to a few areas of simple hyperplasia. While no changes were apparent in the stomach of control animals, a 100% incidence of hyperkeratosis at the limiting ridge of the forestomach was observed after 80 weeks administration of saccharin, 5 of 20 animals also having papillomas. Furthermore, erosion was pronounced in the glandular stomach of saccharin-treated animals with 4 cases of atypical gland being observed. No histopathological lesions were apparent in the liver, kidneys or spleen of either control or experimental groups.

The microbial metabolism of tryptophan in rats fed a diet containing 7.5% saccharin in a two-generation protocol

Sodium saccharin was fed at 7.5% in the diet to rats in a two-generation protocol. Saccharin-treated animals in both generations showed increased urinary excretion of indican. During lactation, the pups of saccharin-fed dams were exposed to elevated levels of indican via the milk. Establishment of the gut flora in pups at weaning in the presence of saccharin was associated with increased caecal size and caecal protein, decreased caecal tryptophanase activity, and increased urine volume and urinary indican excretion. Pups from dams fed saccharin from birth only, showed more-variable responses during the first weeks of life than pups from dams fed saccharin from before conception, due to variations in tryptophanase activity. The various biochemical and physiological changes were detected soon after the pups were weaned, and were found equally in both males and females. After adjustment for body weight, the changes detected were greatest during the first month after weaning.

The effect of saccharin on the microbial metabolism of tryptophan in man

The microbial catabolism of tryptophan to indole has been studied in 15 human subjects by analysis of the daily urinary excretion of indican (potassium indoxylsulphate) before, during and after chronic saccharin ingestion. The daily excretion of indican during a 3-wk control period showed marked inter- and intra-subject variability. Analysis of the urinary excretion of saccharin during chronic administration demonstrated good compliance for both saccharin ingestion and urine collection. The urinary excretion of indican was not increased significantly by the ingestion of saccharin (1 g/day as divided doses with meals) for one month. These findings are consistent with epidemiology studies which show the absence of a consistent excess risk of cancer of the urinary bladder in humans ingesting saccharin as a food additive.

Evaluation of the dose response and in utero exposure to saccharin in the rat

A two-generation bioassay on sodium saccharin (NaS), involving 2500 second-generation male rats, was designed to determine the dose response for urinary bladder tumours in male rats and to evaluate other changes possibly related to the occurrence of the tumours. Six treatment groups (125-700 rats/group) were fed dietary levels of NaS ranging from 1.0 to 7.5%. To evaluate the role of in utero exposure, two additional groups were exposed to NaS either only during gestation via dams fed diet containing 5.0% NaS or for a single generation beginning at birth. In the latter group, the nursing dams were placed on an NaS diet immediately after giving birth and their offspring were weaned onto diets containing 5.0% NaS. A third additional group, included to evaluate the specificity of NaS and the role of excess sodium in the occurrence of urinary bladder tumours, was fed diet containing sodium hippurate (NaH) for two generations--5.0% NaH to the first generation and to the second until 8 wk old, and subsequently 3.0% because of unexpected toxicity. A clear dose response for urinary bladder tumours was observed in the second-generation NaS-treated male rats. The steep slope of the dose-response curve indicated a rapid decline in tumour incidence with decreasing dose. The 1.0% dietary level (fed to 700 rats) was considered to be a no-effect level for bladder tumours. The only other treatment-related pathological changes were an increase in urinary bladder weight in rats fed greater than or equal to 3.0% and an increase in mineralization of the kidneys with greater than or equal to 1.0%. Several physiological effects were seen in the NaS-treated groups showing an increase in bladder tumours (i.e. those fed greater than or equal to 3.0%). Some changes, e.g. depressed growth and increased water consumption, were indicative of a general disturbance of these rats, but analysis of body-weight, food-consumption, compound-consumption and water-consumption data revealed no correlations within any dose group between these quantitative data and the occurrence of bladder tumours. Other changes indicative of the compromised situations of the rats fed high dietary levels of NaS were anaemia in weanling rats fed 5.0 or 7.5% and a reduction in litter size at dietary levels greater than or equal to 3.0%. Changes in urine volume and urine osmolality were highly correlated with the occurrence of the urinary bladder tumours.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of high dietary levels of sodium saccharin on mineral and water balance and related parameters in rats

The effects of sodium saccharin (NaS) treatment on mineral and water balance and a number of related parameters were studied over a 10-day period in 7-month-old Charles River CD rats. Eight groups of 10 male and 10 female rats were studied. In four of the groups the rats were the F1 offspring of rats that had been exposed to NaS at 1, 3, 5 or 7.5% in the diet and the offspring were treated with the same dietary levels of NaS as their parents. Prior treatment in two other groups was modified in order to evaluate the role of in utero exposure to NaS on the study parameters: rats in one group were only exposed in utero via dams fed diets containing 5% NaS while treatment in the other group did not include in utero exposure, but was started at birth via dams fed diets containing NaS and continued at a dietary concentration of 5% NaS. Second-generation rats in another group were fed diets containing 5% sodium hippurate (NaH), a compound with a number of physical and chemical properties similar to those of NaS; this group was included in order to evaluate the specificity of NaS and/or the effect of sodium on the study parameters. A group of untreated rats served as controls. Treatment-related effects were observed in most study parameters. In addition, a number of differences between male and female rats in baseline values and/or in response to NaS administration were observed. With increasing dietary levels of NaS body weights decreased, but there were increases in water consumption, faecal water content, and caecal weights. NaS treatment resulted in increased urine volume and decreased urine osmolality, changes in urine mineral concentrations (increased sodium, decreased potassium and zinc) and increases in fresh and dry bladder weights, bladder-tissue hydration, and mineral concentrations (sodium, potassium, magnesium and zinc) in bladder tissue. The parameters in which clear sex-related differences in baseline values were observed were body weight, food and water consumption, urine volume, urine osmolality, fresh bladder mass, bladder-tissue hydration and the concentrations of sodium, potassium, magnesium and zinc in the bladder tissue. With the exception of urine osmolality, the values were higher in females. Differences between males and females in response to treatment were observed for NaS consumption (increased in females), caecal weight (increased in females), NaS concentration in the urine (increased in males), and the concentration of sodium, potassium, magnesium and zinc in the bladder tissue (increased in males).(ABSTRACT TRUNCATED AT 400 WORDS)

Highlights in the history of saccharin toxicology

Saccharin has successfully survived a half century of scrutiny of its safety. Experience during almost 60 years of common use in foods, as well as several rat feeding studies including that conducted by the FDA, established its GRAS status under the 1958 Food Additives Amendment. Many chronic one-generation and three (unvalidated) two-generation rat studies subsequently conducted by regulatory and independent agencies in the USA and elsewhere have been interpreted by expert committees, especially those of the National Academy of Sciences/National Research Council, as supportive of saccharin's non-carcinogenicity under possible conditions of use. Not convinced of saccharin's safety, because of the (inconsistent) evidence of bladder tumours in saccharin-treated F1 male rats, the FDA proposed a ban on its use as a food additive. This ban has been temporarily postponed by Congressional moratoria, while better designed and executed studies into the mode of action of this unmetabolized non-genotoxic substance are in progress.

Some changes in gastro-intestinal metabolism and in the urine and bladders of rats in response to sodium saccharin ingestion

In rats fed sodium saccharin in the diet changes in urine composition, increased bladder-tissue mass and, in males only, an accumulation of minerals in the bladder tissue have been observed. In this report evidence is presented that indicates that these changes are a consequence of the effects of sodium saccharin in the gastro-intestinal tract and are not due to systemic sodium saccharin. Sodium saccharin has been shown to inhibit gastro-intestinal enzymes that digest carbohydrates and proteins and to increase caecal absorption of mineral ions. The significance of these findings to saccharin-associated bladder tumorigenesis is discussed.