The induction of chromosome aberrations in Vicia faba root meristems by N-hydroxyurethane and related compounds

Mutagenicity, metabolism, and DNA interactions of urethane

Urethane, a known animal carcinogen, has been the subject of intensive research efforts spanning 40 years. Recent concerns have focused on the presence of urethane in a variety of fermented foods and alcoholic beverages, although no epidemiological studies or human case reports have been published. Much information is available about the mutagenesis, metabolism, and DNA interactions of urethane in experimental systems. Urethane is generally not mutagenic in bacteria although in some instances it acts as a weak mutagen. Urethane is not mutagenic in Nuerospora but is weakly mutagenic in Saccharomyces. Drosophila appear to be the only organisms that consistently give positive mutagenic results with urethane, but its mutagenicity is weak and in many cases shows no clear dose dependence. Urethane is a good clastogen in mammalian somatic cells in vivo, but it shows variable results with cells in vitro. It efficiently induces sister chromatid exchanges in a variety of cells. Mammalian spermatogenic cells are insensitive to the induction of specific locus and dominant lethal mutations by urethane. Mutational synergism has been reported to occur between ethyl methanesulfonate and urethane when administered two generations apart, and some investigators have suggested possible synergism for cancer-causing mutations in mice exposed to X-rays and urethane one generation apart. These studies are controversial and have not been confirmed. Studies on the induction of cancer-causing dominant mutations by urethane are at variance with results from extensive studies with the specific locus test in mice. Urethane studies with the unscheduled DNA synthesis assay in mouse spermatogenic cells and with the sperm abnormality test have given negative results. Urethane is rapidly and evenly distributed in the body. The rate of elimination of urethane from plasma is a saturable process and varies according to the strain and age of the animal. Recent studies have concentrations similar to those in wine, ethanol inhibits the tissue distribution of urethane in mice. These results are important because they suggest a lower carcinogenic/mutagenic risk than expected from exposure to urethane in alcoholic beverages. Although research on the metabolic activation of urethane has been extensive, no conclusive results have been obtained about its active metabolite, at one time thought to be N-hydroxyurethane. More recently, it has been postulated that urethane is activated to vinyl carbamate and that this metabolite is capable of reacting with DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Carcinogenic mechanisms: a critical review and a suggestion that oncogenesis may be adaptive ontogenesis

The precise mechanism(s) whereby normal cells become malignant are not known with any degree of certainty. However, many mechanisms have been proposed on the basis of available experimental evidence as interpreted by the proposer. These fall into two main groups and are based upon changes in genetic structure (somatic mutation hypotheses) or in genetic expression (epigenetic hypotheses). Yet a third group embodies elements of the first two. The more important of all these proposals are critically reviewed and yet another hypothesis is ventured. In this hypothesis, the induction of neoplasia is envisaged as embodying (a) initiation of preferentially partly-differentiated and resting stem cells and (b) promotion of the initiated cells, through mitosis and further differentiation and by adaptations of normal ontogenic mechanisms, into a variety of novel phenotypes which are malignant or potentially so. Cancer-specifying genes, altered chromosomes, de-differentiations and interrupted re-differentiations are not considered to be causally involved, although the last three of these can be present as epiphenomena. Evidence cited in support of this proposal appears to show a general absence from cancer cells of any single property, including an abnormality in genetic constitution or in cellular expression, which is specific to malignancy. Malignancy is thus envisaged as abnormal expressions of the genetic potential of the zygote. Some practical and theoretical implications of this concept are discussed.

Tumour formation in mice by urethane administered with related carbamates

A tumour initiating dose of ethyl carbamate was administered to mice by subcutaneous injection together with a dose of one of the homologous esters or an ethyl N-alkyl derivative. The homologues used were the methyl, n-propyl and n-butyl esters, and the derivatives were the N-methyl, N-ethyl and N-n-propyl ethyl esters. The mice were then given promoting treatment with croton oil for 28 weeks.Neither the homologous esters nor the N-substituted derivatives of ethyl carbamate had any influence on the yield of tumours in the skin, lung, or liver. However, increasing the dose of ethyl carbamate increased the yields of tumours.

Prophage induction in lysogenic Escherichia coli with simple hydroxylamine and hydrazine compounds

The prophage-inducing capability of hydroxylamine sulfate and 36 of its derivatives, and of hydrazine dihydrochloride and dihydrazine sulfate and 43 of their derivatives, was determined in Escherichia coli W1709 (lambda). Maximal nontoxic concentrations up to 1 mg/ml were tested. Hydroxylamine sulfate was active at 2.5 mug/ml and the following 17 derivatives were active at concentrations ranging up to 500 mug/ml: alpha-naphthylhydroxylamine, N-hydroxy-2-aminofluorene, oxamyl hydroxamic acid, O-carbamoyl hydroxylamine (isohydroxyurea), N-hydroxyurethane, N-methylhydroxylamine HCl, salicylhydroxamic acid, oxalohydroxamic acid, methoxyamine HCl, ethoxyamine HCl, N, N-diethylhydroxylamine oxalate, formaldoxime, formamidoxime, acetohydroxamic acid, acetaldoxime, acetone oxime, and hydroxyguanidine sulfate. Hydrazine dihydrochloride and dihydrazine sulfate were effective inducers at 5.0 and 2.5 mug/ml, respectively, and the following nine derivatives of them were active at concentrations ranging up to 500 mug/ml: phthalic acid hydrazide, phenylhydrazine HCl, p-nitrophenylhydrazine, p-chlorophenylhydrazine HCl, formylhydrazine, carbohydrazide, semicarbazide HCl, 1-methyl-1-phenyl-hydrazine sulfate, and acetic acid hydrazide. Nineteen hydroxylamine and 34 hydrazine derivatives were ineffective as inducers. Application of the prophage-induction system as a tool for detection of responsive hydroxylamino and hydrazino compounds which may be potential toxicological hazards in the environment is discussed.

Effects of N-hydroxyurethan on viability and metabolism of Escherichia coli

Exposure of growing cells to low levels of N-hydroxyurethan (approximately 0.05 m) resulted in loss of colony-forming ability. This was accompanied by degradation of cellular deoxyribonucleic acid. When the concentration of N-hydroxyurethan was increased to 0.2 m, bacteriostasis was the primary manifestation. The lethal action of the drug was prevented by contreatment with chloramphenicol or azauracil or by uracil-deprivation of a bacterial strain requiring this pyrimidine for growth.

Some aspects of the metabolism of urethane and N-hydroxyurethane in rodents

1. Urethane and N-hydroxyurethane are interconvertible in C(-) and C57 mice. 2. In newborn C57/DBA hybrid mice, prior treatment with 3-methylcholanthrene or urethane stimulated the N-hydroxylation of urethane; SKF 525A inhibited the N-hydroxylation at 24hr. but stimulated it at 48hr. after administration. 3. Liver homogenates of CBA and C3H mice, and of Chester Beatty and hooded rats, but not whole-body homogenates of 1-day-old C57/DBA mice or lung homogenate of 3-week-old Chester Beatty rats, metabolized urethane into N-hydroxyurethane in small but definite amounts. 4. Nitrite was detected in the bodies of newborn C57/DBA hybrid mice treated with lethal doses of urethane or N-hydroxyurethane; nitrite formation from N-hydroxyurethane was stimulated by pretreatment of the animals with 3-methylcholanthrene. 5. The rate of catabolism of N-hydroxyurethane by C57/DBA mice was faster in 8-day-old than in 1-day-old animals of the same sex, and faster in females than in males of the same age. 6. Liver slices of several species of rats and mice catabolized N-hydroxyurethane at rates that varied with the age and sex of animals of the same species; liver homogenates or microsomes were less effective than slices from the same liver. 7. The enzyme activity was destroyed by boiling or freezing the liver; it was inhibited by increasing substrate concentration and by urethane, n-butyl carbamate, cyanide, p-benzoquinone or 2,4-dinitrophenol, but not by p-chloromercuribenzoate or menadione. 8. The catabolism of N-hydroxyurethane by liver slices from adult H-strain rats was not oxygen-dependent. 9. Lung homogenates of 4-week-old female Chester Beatty rats catabolized N-hydroxyurethane at 40% of the rate of liver slices from the same source. 10. O-Acetyl- and O-ethoxycarbonyl-N-hydroxyurethane were rapidly deacylated by liver homogenates from adult hooded rats and adult C57 mice, and by human erythrocytes. 11. N-Hydroxyurethane reacted rapidly with pyridoxal phosphate at pH7.4 and 37 degrees . 12. The rate of decomposition of N-hydroxyurethane in 0.1 n-sodium hydroxide was increased by Ni(2+), Cu(2+), Mn(2+) and [Fe(CN)(6)](3-) and decreased by Cr(2+), Zn(2+), Co(2+), Mg(2+) and Fe(2+). 13. Attempts to synthesize sulphonates of N-hydroxyurethane gave ethyl hydrogen sulphate, probably via rearrangement of the unstable O-sulphonate.