Micronucleus tests in mice on 39 food additives and eight miscellaneous chemicals

Lack of renal tumour-initiating activity of a single dose of potassium bromate, a genotoxic renal carcinogen in male F344/NCr rats

The renal tumour-initiating activity of potassium bromate (KBrO3), a known genotoxic rat renal carcinogen, was investigated in male F344/NCr rats. 6-wk-old rats were given KBrO3 intragastrically as a single dose of 300 mg/kg body weight, which was confirmed by our preliminary toxicity study as a maximum tolerated single dose for this strain of rat. Starting 2 wk after KBrO3 treatment, groups of 39 rats received either a basal diet or a diet containing 4000 ppm barbital sodium (BBNa) as a promoting regimen and were killed at 30, 52, or 104 wk. Control rats received either dietary BBNa (4000 ppm) or the basal diet alone from wk 2 to 52 or 104 wk. Nephropathy was observed in all rats treated with KBrO3 followed by BBNa at 30 wk and in rats receiving BBNa alone, but not in rats exposed to KBrO3 alone. Dysplastic renal tubular cell foci (DTF), putative preneoplastic renal tubular cell lesions were found associated with nephropathy in rats exposed to KBrO3 followed by BBNa from 47 wk. The incidences and multiplicities of DTF and renal tubular cell tumours observed from 31 to 104 wk revealed no initiating effect of KBrO3 treatment. These results indicate that the KBrO3 dose of 300 mg/kg did not initiate renal carcinogenesis.

Relation of 8-hydroxydeoxyguanosine formation in rat kidney to lipid peroxidation, glutathione level and relative organ weight after a single administration of potassium bromate

Changes in kidney levels of 8-hydroxydeoxyguanosine (8-OH-dG), lipid peroxidation (LPO), glutathione (GSH) and relative organ weight were examined 6, 24, 48, 72 and 96 h after a single i.p. administration of potassium bromate (KBrO3) at a dose of 70 mg/kg to male F344 rats. The 8-OH-dG level was significantly increased 24 h after the treatment at this dose and thereafter gradually decreased. On the other hand, significant elevation in LPO level was observed from 6 h after the treatment with a continuous increase up to a plateau at 48 h and no subsequent drop. GSH level was significantly raised from 6 to 72 h, and relative kidney weight varied in almost the same manner as the 8-OH-dG level. Investigation of the dose-response relation revealed the 8-OH-dG and LPO levels to be significantly increased from a dose of 40 mg/kg KBrO3 in a dose-dependent manner. The results suggest that enhanced formation of 8-OH-dG in kidney DNA due to KBrO3 is closely related to the increase in LPO levels.

Chlorine dioxide gas sterilization of oxygenators in an industrial scale sterilizer: a successful model

Artificial organ oxygenators, with large surface areas and complicated structures, were sterilized using chlorine dioxide gas in an industrial scale sterilizer. Bacillus subtilis var. niger ATCC 9372 biological indicators (BI) (10(6) spores/BI) planted in the artificial organs were reproducibly sterilized in a designed cycle schedule with a 30-min dwell time with a chlorine dioxide gas concentration of approximately 30 mg/L in 80 to 85% relative humidity at 30 degrees C. The D value (time required for 90% spore inactivation under specific conditions) was estimated to be 4.4 min. Chlorine dioxide was not detected after post-sterilization aeration. The intravenous median lethal dose (LD50) of chlorine dioxide derivatives, chlorite and chlorate, in rats was found to be 112.8 and 2,228.6 mg/kg, respectively. In an immediate hypersensitivity test, chlorine dioxide gas-treated ovalbumin and bovine serum albumin, unlike ethylene oxide gas-treated proteins, did not cause sterilant-specific IgE-mediated hypersensitivity reactions in rats. Results of an Ames mutagenicity test on chlorine dioxide and on the extracts of the chlorine dioxide gas-exposed oxygenators were negative.

Toxicity and carcinogenicity of potassium bromate--a new renal carcinogen

Potassium bromate (KBrO3) is an oxidizing agent that has been used as a food additive, mainly in the bread-making process. Although adverse effects are not evident in animals fed bread-based diets made from flour treated with KBrO3, the agent is carcinogenic in rats and nephrotoxic in both man and experimental animals when given orally. It has been demonstrated that KBrO3 induces renal cell tumors, mesotheliomas of the peritoneum, and follicular cell tumors of the thyroid. In addition, experiments aimed at elucidating the mode of carcinogenic action have revealed that KBrO3 is a complete carcinogen, possessing both initiating and promoting activities for rat renal tumorigenesis. However, the potential seems to be weak in mice and hamsters. In contrast to its weak mutagenic activity in microbial assays, KBrO3 showed relatively strong potential inducing chromosome aberrations both in vitro and in vivo. Glutathione and cysteine degrade KBrO3 in vitro; in turn, the KBrO3 has inhibitory effects on inducing lipid peroxidation in the rat kidney. Active oxygen radicals generated from KBrO3 were implicated in its toxic and carcinogenic effects, especially because KBrO3 produced 8-hydroxydeoxyguanosine in the rat kidney. A wide range of data from applications of various analytical methods are now available for risk assessment purposes.

Lifetime toxicity/carcinogenicity studies of FD & C Blue No. 1 (brilliant blue FCF) in rats and mice

FD & C Blue No. 1 was fed to Charles River CD rats and CD-1 mice as a dietary admixture in lifetime toxicity/carcinogenicity studies. The rat study was conducted with an in utero phase in which the compound was administered to the F0 generation rats (60/sex/group) at dietary concentrations of 0.0%, 0.0%, 0.1%, 1.0% or 2.0%. After randomly selecting the F1 animals, the lifetime phase was initiated at the same levels with 70 rats/sex/group, including two control groups. The maximum exposure times were 116 and 111 wk for males and females, respectively. The no-observed-adverse-effect levels are dietary concentrations of 2.0% for males (1072 mg/kg body weight/day), and 1.0% for females (631 mg/kg/day) based on a 15.0% decrease in terminal body weight and decreased survival in the high-dose females compared with the combined control groups. Charles River CD-1 mice (60/sex/group) were fed FD & C Blue No. 1 as a dietary admixture at levels of 0.0%, 0.0%, 0.5%, 1.5% or 5.0% in a lifetime toxicity/carcinogenicity study. The maximum exposure time was 104 wk for both males and females. No consistent, significant compound-related adverse effects were noted. The no-observed-adverse-effect level established in this study is a dietary concentration of 5.0% (7354 mg/kg/day and 8966 mg/kg/day for male and female mice, respectively.

Chlorine dioxide and hemodialysis

In the United States chlorination of potable water supplies has been the standard method of disinfection for about 75 years. In recent times concern has been raised about the propensity of chlorination to introduce potentially carcinogenic trihalomethanes (THM) such as chloroform into finished water. The levels of THM introduced depend on many factors including the quality of the raw water. Numerous community water treatment facilities are experiencing difficulty in meeting current U.S. Environmental Protection Agency standards, and it is likely that the permissible levels may be lowered in the future. An alternative to chlorination which does not generate THM during disinfection is chlorine dioxide, but there are concerns about the acute and chronic toxicity of ClO2 and its disinfection by-products, chlorite and chlorate. Deleterious effects of moderately high levels of these oxychlorines have been demonstrated experimentally on red blood cells, thyroid function, and development in laboratory animals. Adverse effects in controlled prospective studies in humans and in actual use situations in community water supplies have as yet failed to reveal clear evidence of adverse health effects. Among groups who may be at special risk from this suggested alternative are patients who must undergo chronic extracorporeal hemodialysis. The special needs, precautions, and experience to date in regard to finished water are reviewed. Again, very limited human experience has failed to reveal adverse health effects. Further study, caution, and extreme vigilance are indicated, but dialysis patients in carefully controlled facilities may be at no greater risk than the general population.

Mutagenesis and micronutrients relationship

Several micronutrients have been reported to be mutagenic or co-mutagenic in certain in vitro testing systems. However, micronutrients have not been shown to be mutagenic or co-mutagenic in vivo, or at physiological concentrations in vitro. Most of the mutagenic or co-mutagenic effects of micronutrients observed in vitro can be attributed to their involvement in the generation of oxygen radicals. Many micronutrients have been shown to possess anti-mutagenic or co-antimutagenic activity in vitro and in vivo. This property of micronutrients appears to be linked to their specific and interrelated biochemical functions.

Effect of route of administration in the micronucleus test with potassium bromate

The effect of intraperitoneal injection (i.p.) versus oral gavage administration (p.o.) of potassium bromate was examined using the micronucleus test in 2 strains of male mice (MS/Ae and CD-1). First, a small acute toxicity test and a pilot micronucleus experiment were performed to determine the appropriate dose range and sampling time for the full-scale micronucleus test. The full-scale test was carried out using doses of 18.8, 37.5, 75, and 150 mg/kg in the i.p. test and of 37.5, 75, 150, and 300 mg/kg in the p.o. test. The sampling time was 24 h for both mouse strains. Potassium bromate induced micronucleated polychromatic erythrocytes (MNPCEs) dose-dependently by both routes of administration in both mouse strains. No distinct difference in route of administration was observed in the test with MS/Ae mice. In CD-1 mice more MNPCEs were induced by the i.p. route than by the p.o. route.