Carcinogenic N-nitroso compounds and their environmental significance

A short review is given on the potent and organ-specific carcinogenic effects of N-nitroso compounds. Like many other chemical carcinogens, nitrosamino compounds require activation in vivo via enzymatic alpha-hydroxylation to form alkylating agents as ultimate carcinogens. Since no epidemiological data in man are available, extrapolation of animal data to man are important as well as dose-response studies in risk evaluations. Important aspects of these problems are presented. Finally the environmental impact of N-nitroso compounds is summarized.

Reductive metabolism of N-nitrosodiphenylamine to the corresponding hydrazine derivative

The first evidence for the reductive metabolism of a noncyclic nitrosamine to the corresponding hydrazine derivative in vivo and in vitro is provided. Under anaerobic conditions, N-nitrosodiphenylamine was reduced by guinea pig liver 9000g supernatant to 1,1-diphenylhydrazine in the presence of 2-hydroxypyrimidine or to acetaldehyde diphenylhydrazone in the presence of acetaldehyde. These metabolites were identified unequivocally by comparative study with authentic samples. In addition, the study shows that such reductive reactions of the nitrosamine can be catalyzed by guinea pig and rabbit liver aldehyde oxidase in the presence of its electron donors. When the nitrosamine was given orally to acetaldehyde-treated guinea pigs, a metabolite was detected from plasma and identified as acetaldehyde diphenylhydrazone by comparison with the authentic sample.

The role of nicotinamide and of certain other modifying factors in diethylnitrosamine carcinogenesis: fusaria mycotoxins and "spontaneous" tumors in animals and man

Pretreatment of rats with large doses of nicotinamide, which has been shown to increase the incidence of pancreatic islet-cell tumors after streptozotocin and after heliotrine, appears to promote the development of kidney neoplasias in rats given several doses of diethylnitrosamine. Nicotinamide, one of the B vitamins, and a constituent of NAD coenzymes, will prevent the depletion of NAD coenzymes by alkylating agents. It may protect the animal to some extent from the acute effects of hepatocarcinogens but not from the induction of tumors, although it may change the localization of the latter. The possible mechanisms involved in the action of nicotinamide and of certain other modifying agents are discussed. Attention is drawn to the possibility that pituitary, mammary and certain other tumors that sometimes occur among the controls, as well as among experimental animals, may be due to the occasional presence in laboratory animal diets of estrogenic and/or toxic secondary metabolites of the field fungi, Fusaria. Mycotoxins, such as zearalenone and the trichothecenes, are also likely to contaminate human foods; this could explain why multiple tumors in man occur mainly in the sex organs and in the digestive tract.

Direct alkyl chain cleavage after C-hydroxylation of dialkylnitrosamines in rats. A new pathway of the oxidative biotransformation

Comparative in vivo investigations on the biotransformation of di-n-butylnitrosamine (DBNA) and (2-hydroxybutyl)-n-butylnitrosamine (HBBNA) showed the known omega-oxidation. However, a new metabolic mechanism of direct oxidative alkyl chain cleavage in the vicinity of the hydroxy group of HBBNA could be demonstrated.