Comparison of studies on saccharin and sodium nitrite

A review of long term animal studies of saccharin and sodium nitrite was undertaken to assess the effect of variability of selected protocol elements on the results obtained. These elements were divided into 4 general categories: design, including selection of test animals, basal diet, dosage form and doses of test substance, route of administration, and duration of exposure; observations, including gross observations during life and at necropsy, clinical tests, and histopathology; performance, including conduct of the test and animal husbandry; and analytical procedures, including chemical and statistical analyses. Because many of the protocol elements are not fully discussed in study reports, it was often impossible to determine what actually had been done. The review of various saccharin studies suggests that bladder tumors resulted following in utero exposure. In utero exposure with sodium nitrite did not appear to cause reticuloendothelial changes. The numerous variations in protocol elements in the nitrite studies precluded identification of a prime element responsible for the variation in reticuloendothelial changes observed. It can be concluded from this review that achievement of reproducibility in long term studies requires minimal variation of protocol elements for the new study.

Chronic toxicity of sodium nitrite in mice, with reference to its tumorigenicity

Sodium nitrite has been widely used as one of the most effective food additives to tinge color on cured meat. However, it has been elucidated that this chemical is not merely a precursor of N-nitroso compounds, many of which are strongly carcinogenic, but also a mutagenic substance in biological tests. In order to ascertain the possible tumorigenicity of sodium nitrite itself, chronic toxicity of the agent in mice, by means of daily oral administration as drinking water for more than 18 months, in the concentration of 0.5 (maximum tolerated dose), 0.25, and 0.125%, was tested. As a result, development of various tumors, including thymic lymphoma, nonthymic lymphoid leukemia, pulmonary adenoma and carcinoma, and benign and malignant tumors in soft tissue, was seen in these mice. However, as to the incidence of tumors as well as the developmental time of each histologically classified tumor, no apparent difference was detected between those in the experimental groups and the control group.

Transplacental action of sodium nitrite on embryonic cells of Syrian golden hamster

Hamster embryos were treated with various doses of NaNO2 in utero, by its oral administration to the mothers, and then the embryonic cells were examined for micronucleus formation, chromosomal aberrations, morphological or malignant transformation and drug-resistant mutations. For induction of resistant mutations, the cells were cultured in normal medium for 72 h, and then selected in media containing 8-azaguanine (10 or 20 microgram/ml) or 1 mM ouabain. This treatment with NaNO2 caused marked dose-dependent induction of 8-azaguanine- and ouabain-resistant mutations. Cultured embryonic fibroblasts in the resting state also showed a marked dose-dependent increase in micronucleus formation but not an increase in chromosomal aberrations. This treatment also caused morphological and neoplastic transformation of the cells. Transplacental oral treatment with DMN, as a positive control, caused changes of similar extent in biological effects of embryonic fibroblasts, and in addition it caused chromosomal aberrations in metaphase plates. On the contrary, transplacental oral application of NaNO2 did not induce any biological change in cultured embryonic fibroblasts.

Carcinogenic effect of a quanidine pesticide administered with sodium nitrite on adult mice and on the offspring after prenatal exposure

Adult Swiss mice were treated intragastrically during the last week of pregnancy with the fungicide dodecylquanidine acetate (dodine, DGA) together with 0.05% sodium nitrite. The incidence of malignant lymphomas, lung adenomas and hepatomas was 30--70% in females. The first tumors appeared 4 months after delivery in the FO generation and at 6--7 months in the F1 generation. Among the untreated control mice the frequency of spontaneous tumors was 6%, and lymphomas developed, if at all, only after 10 months. The oncogenic activity of DGA with sodium nitrite in the offspring was dependent on the dose of DGA.A and C type RNA virus particles were demonstrated in lymphomas by electronmicroscopy. DGA alone had no effect on the cancer incidence.

[Ultrastructure of rat adenohypophysis following exposure to several amines of the polymathylene series]

Adenohypophysis ultrastructure was studied under the effect of dicyclohexylamine nitrite and oil-soluble salt of cyclohexylamine used as inhibitors of the atmospheric corrosion of metals. It is stated that even due to the early effect they cause a morphofunctional rearrangement of the organ in spite of the same reaction of the adenohypophysis cells to M-1 and dicyclohexylamine nitrite the effect of the latter causes more distinct and pronounced changes.

Nitrosation in vitro and in vivo by sodium nitrite, and mutagenicity of nitrogenous pesticides

37 nitrogenous pesticides, belonging to the chemical groups of amides, carbamates and ureas, were nitrosated with sodium nitrite in vitro. The nitrosated compounds were tested for mutagenic activity in the bacterial spot test with Salmonella typhimurium his G 46. Those pesticides reacting positively in this test after nitrosation were then fed to mice in combination with sodium nitrite in order to assess the formation and mutagenicity of these nitroso compounds in vivo. With the already known exception of ethylenethiourea (ETU), no pesticide produced enhanced numbers of micronuclei in mouse bone-marrow erythrocytes when fed together with nitrite. Dose-response experiments with intraperitoneal injection of N-nitroso-ETU revealed an apparent no-effect level of about 15--18 mg/kg. The findings are correlated with the pesticide residues actually present in the environment.

[Electron microscopic study of rat hepatocytes following exposure to dicyclohexylamine nitrite and an oil-soluble salt of cyclohexylamine]

Ultrastructural changes were studied in the rat liver under the effect of dicyclohexylamine nitrite and oil-soluble salt of cyclohexylamine in doses of 1/10 LD50. Both substances are stated to cause damages in the structure of hepatocytes even after three days of exposure. Dicyclohexylamine nitrite shows a more pronounced effect displayed in developed dystrophic changes of cytoplasmic organelles and in the presence of osmiophil bodies.

Effect of sodium ascorbate on tumor induction in rats treated with morpholine and sodium nitrite, and with nitrosomorpholine

Groups of male MRC Wistar rats were treated for 2 years either with morpholine (10 g/kg food) together with sodium nitrite (3 g/l drinking water) or with N-nitrosomorpholine (NM, 0.15g/l drinking water). In both cases, a group of rats was given sodium ascorbate (22.7 g/kg food) in addition to these treatments. When ascorbate was present, the liver tumors induced by morpholine and nitrite showed a 1.7-fold longer induction period, a slightly lower incidence, and an absence of metastases in the lungs, indicating that ascorbate had inhibited the in vivo formation of NM. Ascorbate did not affect liver tumor induction by the performed NM. The group treated with morpholine, nitrite, and ascorbate had a 54% incidence of forestomach tumors, including an 18% incidence of squamous cell carcinomas, possibly because ascorbate promoted NM action in this organ.

In vitro transformation of newborn hamster cells induced by sodium nitrite

The in vitro carcinogenicity of sodium nitrite was examined. Addition of a high concentration of sodium nitrite (50 mM or 100 mM) to mass cultures of newborn hamster cells for 24 hr resulted in morphological transformation of the cells. The shortest time required for morphological transformation after this treatment was 21 days. Two of 5 transformed cultures produced progressively growing tumors when injected into young adult hamsters. These tumors were diagnosed as fibrosarcomas. In two control cultures of the same experimental groups, transformed cells appeared 10 weeks or more later than those in treated cultures. The chromosomes were analysed at several stages of transformation. In the early stages of transformation, chromosome number varied widely from near diploid to tetraploid, but later they became near diploid. Morphological alteration caused by sodium nitrite was also seen in a short-term assay, in which hamster embryonic cells (1 x 10(4) cells/60 mm dish) were treated and morphology was observed 8 days after the treatment.

Large bowel carcinogenesis in mice and rats by several intrarectal doses of methylnitrosourea and negative effect of nitrite plus methylurea

The carcinogenic effect of several dose levels and regimens of an aqueous solution of N-methyl-N-nitrosourea (MNU) administered intrarectally to mice and rats is reported. In Ha/ICR Swiss mice, a single dose of 1.8 mg MNU induces mainly lymphomas and pulmonary tumors in less than 20 weeks. Repeated doses of 1.5 mg MNU induces lymphomas, pulmonary tumors, and also large bowel tumors in less than 20 weeks. Doses of 0.3 mg decreased the yield of lymphomas and increased large bowel neoplasms over a period of 40 to 60 weeks. Repeated doses of 0.06 mg also gave a low yield of lymphomas and large bowel tumors over a 60-week period. Thus, a maximal yield of lymphomas is seen with a brief regimen of high doses, whereas large bowel tumors occur with a more frequent lower dose rate. Male Fischer strain rats given 1.0 or 2.5 mg MNU 3 times a week for 10 weeks had a multiplicity of large bowel tumors, proportional to dose, in 25 to 30 weeks. In fact, the high dose level led to a 100% yield in less than 20 weeks. Lymphomas were seen only at the higher dose when the animals were were young, at the beginning of the test. In mice and rats the carcinomas were polypoid or plaque shaped and were well differentiated with extensive invasion but no metastases. The adenomas were pedunculated or sessile. Intrarectal administration of a mixture of methylurea and nitrite for 20 weeks and further observation of the rats for an additional 35 weeks yielded no colon tumors. Thus, there is indirect evidence of a lack of the in situ formation of carcinogenic MNU in the large bowel under physiological conditions.

The effect of gonadal ablation on transplacentally induced neurogenic tumors in hamsters

The effects of gonadectomy on tumors induced transplancentally by the ethylnitrosourea precursors, ethylurea and sodium nitrite, were investigated in hamsters. The pregnant hamsters were exposed to four daily doses of ethylurea (100 mg/kg) and sodium nitrite (50 mg/kg) administered from Day 12 to 15 of pregnancy. Weaned offspring were gonadectomized when they reached the age of 5 weeks. Orchiectomized male progeny showed a multiplicity and greater frequency of peripheral nervous system tumors and of any other tumor types than did intact males or their ovariectomized and intact female siblings. The possible inhibitory effects of endogenous androgens on the development and growth of neurogenic tumors in the peripheral nervous system and the influence of an induced endocrinal imbalance on prenatally induced neoplasms are discussed.

Toxicology of some inorganic antihypertensive anions

Sodium nitroprusside reacts with hemoglobin in vitro and in vivo to cause the formation of cyanmethemoglobin and the liberation of excess free cyanide. The latter is responsible for the typical signs of acute cyanide poisoning in mice after lethal doses of nitroprusside. Differences in the reactivity of the red cells of various species toward nitroprusside are due to differences in the permeability of the red cell membranes to nitropruside. In vivo thiocyanate results in the formation of methemoglobin in an elevation of blood cyanide levels in mice. The latter, however, does not result in cyanide poisoning since it is bound in the biologically inert form of cyanmethemoglobin. Thus, both nitroprusside and thiocyanate generate their own antidote in mice, but an excess of cyanide is released in the case of nitroprusside whereas excess methemoglobin is generated in the case of thiocyanate. Acute poisoning with thiocyanate salts apparently involves direct excitatory effects on the central nervous system. In vitro the reaction between thiocyanate and hemoglobin proceeds only in the presence of hydrogen peroxide. Chronic administration of nitroprusside results in the elevation of blood thiocyanate levels presumably because of continuous, endogenous cyanide metabolism via rhodanese (thiosulfate sulfurtransferase). When one includes these previously unrecognized effects of nitroprusside and thiocyanate, there appears to be some correlation between the ability of a chemical to oxidize hemoglobin and its ability to activate nonadrenergic receptors for the relaxation of vascular smooth muscle.

Induction of mouse lung adenomas by amines or ureas plus nitrite and by N-nitroso compounds: effect of ascorbate, gallic acid, thiocyanate, and caffeine

Lung adenomas were induced in strain A mice by chronic treatment with N-nitroso compounds (given in drinking water) and with amines or ureas in food plus NaNO2 in drinking water. We studied the effects of varying the concentrations of three N-nitroso compounds and NaNO2 concentration in the morpholine plus NaNO2 and methylurea plus NaNO2 systems. Sodium ascorbate (NaASC) at the highest level tested (11.5 or 23 g/kg food) gave 89-98% inhibition of adenoma induction by the NaNO2 plus piperazine, morpholine, and methylurea systems. In 7 groups, NaASC produced increases of 15-59% in adenoma induction by nitrosomorpholine (NM) and mononitrosopiperazine (MNP), possibly because the mice consumed more of the nitrosamine solution. Adenoma induction by morpholine plus NaNO2 was strongly inhibited by gallic acid, moderately inhibited by caffeine, and unaffected by thiocyanate (all added to the food). Gallic acid inhibited or had no effect on the action of NM and MNP. We discussed the proposal that NaASC (or perhaps gallic acid) be administered with readily nitrosatable drugs.

Tumor induction in rats by feeding heptamethyleneimine and nitrite in water

Groups of 15 males and 15 females Sprague-Dawley rats were given 20 ml of drinking water solution containing either 0.2% heptamethyleneimine hydrochloride or this salt together with 0.2% sodium nitrite, 5 days a week for 28 weeks. Another group of 17 male and 30 female rats was given 0.2% sodium nitrite solution for 104 weeks. Most of the animals given heptamethyleneimine hydrochloride or sodium nitrite alone survived 2 years or more after the beginning of the treatment, and no tumors attributable to the treatment were seen at death; tumors appearing were those of endocrine origin found commonly in untreated controls. In the group receiving the combined treatment, most females were dead at 50 weeks and most males were dead at 80 weeks, 27 of 30 having tumors not seen in either control group. A total of 16 had squamous carcinomas in the lung; 25 had tumors of the oropharynx, tongue, esophagus, and forestomach; and there were a few animals with tumors in the nasal cavity and trachea. The expericment showed that squamous tumors of the lung could be induced by ingestion an amine and sodium nitrite.