Mutagenicity of N-nitrosomorpholine in the host-mediated assay

6 Final Report on the Safety Assessment of Morpholine

Morpholine is used in cosmetic products as a surfactant and emulsifier at concentrations up to 5%.

Morpholine is metabolized in guinea pigs but was not significantly metabolized in rats, dogs, or rabbits. Dermal LD50s in rabbits ranged between 0.3 and 1.2 g/kg. The oral LD50s in rats were between 1.1 and 1.6 g/kg; in guinea pigs the oral LD50 was 0.9 g/kg.

In studies of acute and short-term dermal toxicity Morpholine as an undiluted and unneutralized solution or as a diluted and unneutralized solution applied daily to the skin of guinea pigs and rabbits, respectively, caused the deaths of the test animals within 2 weeks. In both cases, the skin was necrotic.

Unneutralized solutions of Morpholine caused severe corneal necrosis, but upon neutralization Morpholine was not injurious to rabbit eyes.

In short-term inhalation studies (in rats) with varying concentrations of Morpholine, the effects observed included irritation of the mucous membranes and an increased respiratory rate. Chronic inhalation studies of Morpholine in rats and guinea pigs reported changes in the nervous system activity and arterial and peripheral blood pressure. At high concentrations Morpholine produced swelling of the alveolar cells and atrophy of lymphoid elements in the spleen. At lower concentrations a decrease in the size of the lymph nodules in the spleen was noted.

Morpholine was a weak positive mutagen in L5178 mouse lymphoma assay, in BALB/3T3 malignant cell transformation and fibroblast transformation assays, and in sister chromatid exchange assays, but was negative in the Ames test with and without metabolic activation. At nontoxic doses Morpholine did not increase the rate of DNA repair in rat hepatocytes. Results of other mutagenic assays varied according to the system used.

Nitrosation of Morpholine produces N-nitrosomorpholine, which has been mutagenic in a variety of test systems. Simultaneous exposure of laboratory animals to Morpholine and nitrites has caused a number of different cancers. A carcinogenic response was produced in rats in a long-term feeding study of Morpholine in which nitrites were present in the diet.

In humans, Morpholine is absorbed and is considered to be a skin and eye irritant, as well as a skin sensitizer. A formulation containing 1% Morpholine indicated that the ingredient was neither an irritant nor sensitizer.

Morpholine is not considered to be an animal carcinogen. It reacts easily with nitrosating agents, resulting in the formation of N-nitrosomorpholine. Under conditions of use, it is highly unlikely that Morpholine is totally free of carcinogenic nitrosoamines. Without quantitative data regarding the formation of N-nitrosomorpholine under conditions of use, it cannot be concluded that Morpholine is safe for use in cosmetic products.

Carcinogenic effects of N-nitroso-3-(substituted phenylimino)-indolin-2-one derivatives

AIM

A novel series of N-nitroso-3-(substituted phenylimino)-indolin-2-one 3a-h was synthesized and tested for carcinogenic effects.

MATERIALS AND METHODS

The synthesized pyrazole derivatives' chemical structures were proved by means of their infra red (IR), proton nuclear magnetic resonance ((1)H-NMR), and mass,and confirmed by elemental analyses. The carcinogenic activity was assessed by 3-(4,5dimethyl thiazole-2yl)-2,5-diphenyltetrazoliumbromide (MTT) cell-viability assay.

RESULTS

The results show that most of the synthesized compounds exhibit significant carcinogenic activities. Among the synthesized compounds, N-nitroso-3-(2,4-dinitrophenylimino)-indolin-2-one 3h exhibited the most potent carcinogenic activity.

CONCLUSION

The structure-activity relationship (SAR) studies show that the nature as well as the position of the amine are important for deciding the activity profile of the indolin-2-one derivatives, which reiterates the need for further experimental investigations.

An evaluation of the host-mediated assay and body fluid analysis. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The methodologies and status of the Host-Mediated Assay were reviewed using the published literature available up to June 1980. The Working Group reviewed 274 documents, including abstracts, research articles, review articles, and publicly available contracts and grant final reports. From this group, abstracts and reviews were rejected from critical evaluation. 77 documents were accepted and reviewed by the Working Group and the test results summarized. These selected documents yielded 208 chemicals that were evaluated in th host-mediated assay. Of these chemicals, 133 were mutagenic in this assay with one or more indicators. 76 chemicals, several of which are not considered to be carcinogenic, were not detected by any of the indicators. Of the 208 chemicals, 125 had been tested in carcinogenicity assay in rodents. 90, or 71%, of the carcinogens were detected as mutagens in the Host-Mediated Assay. In several cases, those carcinogens not detected may have been negative because of improper selection of the indicator. The Working Group concluded that the Host-Mediated Assay is an important test in mutagenicity/carcinogenicity research and that, by proper selection of protocols and indicators, valuable information can be gained that otherwise would be overlooked strict, in vitro assays.

Mutagenicity of several pancreatic carcinogenic derivatives of N-nitrosodipropylamine in the Ames assay

The mutagenic activity of several N-nitrosamines related to the potent hamster pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) has been investigated using the Ames Salmonella/microsomal mutagenicity test system. S9 from the livers of phenobarbital-pretreated hamsters was the source of activating enzyme, and strain TA1530 was the indicator organism. Mutagenicity assays of BOP, N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), N-nitrosobis(2-hydroxypropyl)amine (BHP), N-nitroso-2,6-dimethylmorpholine (NDMM) and N-nitrosomorpholine (NM) indicate that only HPOP was strongly mutagenic in the absence of the hamster-liver preparation. In the presence of this activation system, NDMM was the most mutagenic, and cis NDMM was 2-3 times more mutagenic than the trans isomer of this compound. BOP and BHP were considerably less mutagenic than HPOP.

Intrahepatic mutagenesis assay: a sensitive method for detecting N-nitrosomorpholine and in vivo nitrosation of morpholine

An intrahepatic host-mediated mutagenicity assay capable of detecting low levels of N-nitrosomorpholine (NMOR) is described. The indicator organism was Salmonella typhimurium TA1530 which had been injected intravenously 10 min prior to the administration of the test compound. The bacteria were subsequently recovered from the liver and scored for revertants by standard methods. The lower limit of detectibility of this system for intubated NMOR was 0.2 microgram/g body weight. This assay was then used to study the formation of NMOR in vivo from morpholine and nitrite which had been sequentially gavaged to mice. Under acidic conditions (pH 3.4) 12--19% of the administered morpholine was converted to NMOR in the presence of excess nitrite. This nitrosation, and the subsequent uptake and activation of the NMOR, took place so rapidly that most of the total mutagenic response was complete within 15 min. This response was inhibited by prior intubation of ascorbic acid, a known inhibitor of nitrosation, and enhanced by sodium thiocyanate, a nitrosation catalyst.

The effect of the mode of administration of nitrogen mustard and cytosine arabinoside on the production of chromosomal aberrations in mouse bone marrow and ascites tumour cells

The cytogenetic effects of intraperitoneally (i.p.) and subcutaneously (s.c.) administered nitrogen mustard (HN2) and cytosine arabinoside (ara-C) on bone-marrow and ascites tumour cells of mice were studied. Ehrlich ascites tumour-bearing mice were treated with the mutagens, and cytological preparations were made from ascites tumour and bone-marrow cells of the same animal. The following parameters were investigated: frequencies of mitotic and chromosomal aberrations, time of aberration maxima and aberration spectra. HN2 (0.68 mg/kg b.w.), when given i.p., induced in ascites tumour cells a strong inhibition of mitotic frequency and very high aberration rates, whereas in bone marrow no aberrant chromosomes were observed. On the other hand, after s.c. administration, the same dose induced more aberrant metaphases in bone marrow than in tumour cells. Ara-C (315 mg/kg b.w.) resulted, after s.c. administration, in higher aberration frequencies both in ascites and bone-marrow cells compared with i.p. treatment. All ascites tumour cells showed higher aberration requencies than bone-marrow cells. In bone marrow the aberration maximum occurred as soon as 6 h after treatment. Furthermore, clear differences with respect ot the types of aberration found in the two systems were evident. The differences caused by the different modes of administration in two different types of cell are discussed in terms of metabolic inactivation and differences of the two tissues with respect to karyotype, cell cycle time and repair capacity.

Metabolism of N-nitrosomorpholine by the rat in vivo and by rat liver microsomes and its oxidation by the Fenton system

N-Nitrosomorpholine is converted into N-nitroso-2-hydroxymorpholine by rat liver microsomes and by the Fenton oxidation system. The hydroxy derivative was also synthesised by the oxidation of N-nitrosodiethanolamine with permanganate and characterized as the methoxime and the 2,4-dinitrophenylhydrazone. The Fenton system also afforded products believed to be N-nitroso-2-morpholone, and the 2-hydroperoxy- and 2-peroxy-derivatives of N-nitrosomorpholine. The only urinary metabolite definitely identified was N-nitrosodiethanolamine. The significance of metabolic 2-hydroxylation in relation to the carcinogenic action of N-nitrosomorpholine is discussed.

The mutagenicity of heterocyclic N-nitrosamines for Salmonella typhimurium

14 carcinogenic and noncarcinogenic heterocyclic N-nitrosamines were evaluated for mutagenicity to Salmonella typhimurium TA-1535, which responds to mutagens inducing base-pair substitutions. Both suspension and plate tests were used, with mouse and rat liver in vitro metabolic activation systems. All carcinogenic nitrosamines showed a positive response in at least one test system, as did the noncarcinogens. In general, the mutagenic responses obtained with mouse liver were equal to, or greater than, the responses obtained with rat liver in both the suspension and plate tests. Although it is difficult to make quantitative comparisons between plate and suspension tests, both systems appeared to be responsive to the same dose ranges for the individual nitrosamines.

Chromosomal aberrations in rat lymphocytes treated in vivo with 1-phenyl-3, 3-dimethyltriazene and n-nitrosomorpholine. A further report on a possible method for carcinogenicity screening

This paper reports the results of screening two carcinogens, N-nitrosomorpholine (NM) and 1-phenyl-3, 3-dimethyltriazene (PDT), for their ability to cause an increase in chromosomal aberrations in rat lymphocytes cultured in vitro after treatment in vivo. NM is a hepatocarcinogen and PDT induces tumours mainly of the central and peripheral nervous system. Both these chemicals gave only weakly positive results in certain other established short term screening tests for carcinogenicity, despite having been shown to cause a significant increase in the number of chromosomal aberrations after a single administration of doses of 250 mg/kg and above. These aberrations were mainly of the isolocus type as opposed to the chromatid type. Significant increases in the number of aberrations of both the isolocus and chromatid types were found after single applications of PDT of 35 and 50 mg/kg. The results obtained are compared with those of other workers using the same compounds in different test systems. Modifications of the system to increase its sensitivity are suggested.

In vitro mutagenesis assays as predictors of chemical carcinogenesis in mammals

In vitro microbial mutagenesis assays coupled with mammalian activation systems offer promising technique to screen chemicals for their potential carcinogenic activity. The correlation between mutagenic and carcinogenic properties for a large array of chemicals is approximately 0.9. The best correlation exists for those carcinogens which are themselves highly electrophilic or produce electrophilic metabolites. Correlation between mutagenicity and carcinogenicity for hormonal, metallic, or physical carcinogens has been disappointing but not unexpected based on their proposed mechanisms of action. In addition to the application of in vitro mutagenesis techniques to screening chemicals for the identification of potential carcinogens, they are useful tools for investigating genetic, biochemical, and pharmacologic properties of different animal species. Studies with the chemical carcinogen dimethylnitrosamine have been conducted and show a functional relationship between mutagenesis and carcinogenesis. The assays can also be conducted using activation systems prepared from the tissues of any mammalian species. This permits a direct assessment of phylogenic extrapolation by comparing the metabolic activation capabilities of tissues from several mammalian species, including human samples. The advantages of mutagenicity testing are the short period of time required for results, the high sensitivity of the assay (microgram of nanogram quantities of chemicals can be used), and the fact that the ultimate agent can be detected biologically without first necessitating chemical identification and isolation. It appears from current studies that in vitro mutagenesis techniques may well open new avenues of investigation into some old toxicologic problems.

N-nitrosomorpholine and N-nitrosobutylamine-stimulated DNA synthesis in BHK-21/C13 cells

Non-semiconservative DNA synthesis was examined in BHK-21/C13 cells after treatment with the aliphatic N-nitrosobutylamine (NB) and the heterocyclic N-nitrosomorpholine (NM). The extent of repair synthesis after alkylation was compared quentitatively and calculations were made of the amount of DNA damage per cell and number of bases inserted per damaged site. Of the chromosome aberrations caused by NM the most predominant were dicentrics. Other aberrations included fragments, gaps, breaks and exchanges of both the chromatid and chromosome type. Unlike NM, NB elicted a higher frequency of chromatid breaks.