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The development of a rapid method for the determination of N-nitrosoamino acids is reported. Preliminary recoveries of N-nitrosoamino acids in ham fortified with 20 micrograms/kg generally ranged from 70 to 100%. The synthesis and instrumental characterization of four N-nitrosodipeptides N-terminal in proline from nitrite in aqueous acid solution are reported. Electron ionization-mass spectroscopy and infra-red spectroscopy strongly support the conclusion that only the amine nitrogen, and not the amide nitrogen at the peptide bond, is nitrosated. High-performance liquid chromatographic conditions are described for the separation of the synthesized N-nitrosodipeptides.
Chinese gooseberry juice has been found to be an efficient inhibitor of nitrosation both in vitro and in vivo. This activity appears to be due partly to high concentrations of ascorbic acid and partly to an unidentified nitrite scavenger.
Results are presented to show that N-nitrosodimethylamine demethylase is P-450 mediated and N-nitrosodimethylamine is efficiently metabolized by specific P-450 isozymes inducible by a group of new inducers. The P-450-mediated N-nitrosodimethylamine demethylase also responds differently to inhibitors when activities are compared with those of classical monooxygenase systems.
We have studied the urinary metabolites of N-nitrosopiperidine, 3- and 4-hydroxy-N-nitrosopiperidine, N-nitroso-4-piperidone, N-nitrosohexamethyleneimine and N-nitroso-heptamethyleneimine. The N-nitrosopiperidines induce primarily oesophageal tumours in rats; N-nitrosohexamethyleneimine induces oesophageal and liver tumours and N-nitrosoheptamethyleneimine induces oesophageal and lung tumours. The products were identified by gas chromatographic comparison with standards, where possible, and by gas chromatography-mass spectrometry. The percentage of the dose excreted as metabolites in the urine increased with ring size. Hydroxy and ketone derivatives of all three of the N-nitrosoalicyclic amines were found. Pimelic acid was the major metabolite (congruent to 25%) of N-nitrosoheptamethyleneimine; adipic acid was identified as a metabolite of N-nitrosohexamethyleneimine, but not glutaric acid was found from N-nitrosopiperidine.
A Weibull analysis is presented of the dose and time relationships for the effects on 4 080 inbred rats of chronic ingestion in the drinking water of 16 different doses of N-nitroso-dimethylamine (NDMA) and of N-nitrosodiethylamine (NDEA). The sites chiefly affected were the liver (by both agents) and the oesophagus (by NDEA only). Since the experiment continued into extreme old age, effects became clearly measurable even at a dose of only 0.01 mg/kg per day, which is an order of magnitude lower than previously achieved. (After only two years of treatment, however, the 'TD50' doses needed to halve the proportion of tumourless survivors would have been about 0.06 mg/kg per day of NDEA and about 0.12 mg/kg per day of NDMA.) The general pattern of response was that the log probability of remaining tumourless was given by the product of two terms, the first (the 'Weibull b-value') depending on the dose-rate but not on the duration of exposure, and the second depending not on dose at all but on (approximately the seventh power of) duration. For oesophageal tumours, the 'Weibull b-value' was approximately proportional to the cube of the dose-rate of NDEA (males 21 d3, females 11 d3, where d = dose-rate in mg/kg adult body weight/day, and the background incidence was unmeasurably low. For liver tumours induced by NDEA, the b-value was approximately proportional to the fourth power of dose-rate + 0.04 mg/kg per day (males, 19 (d + 0.04)4; females, 32 (d + 0.04)4), although the relationships were slightly different for the different subsites of liver tumour. This one formula implies both approximate linearity at low doses and an approximately cubic relationship within the higher range of doses that was studied. For liver tumours induced by NDMA, the Weibull b-value was approximately proportional to the sixth power of dose rate + 0.1 mg/kg per day (males, 37 (d + 0.1)6; females, 51 (d + 0.1)6), again with variation between liver subsites, and again implying approximate linearity at low doses. The difference between the latter two relationships may represent differences in the induction of particular DNA repair enzymes by NDMA and NDEA, or in the effects of those enzymes on methylated and on ethylated DNA. These formulae should, of course, be trusted only in the range of doses from which they were derived, and particularly not for those above it.(ABSTRACT TRUNCATED AT 400 WORDS)
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Samples of meat and meat products for the content therein of carcinogenic N-nitrose-amines were subjected to a fluorometric analysis. In case of positive results the presence of NA was confirmed by cromate-mass-spectrometric and/or mass-spectrometric methods. The mean value for the concentrations of dimethyl-nitrose-amine, diethyl-nitrose-amine and nitrose-piperidine in meat products is within the ranges of 1.5-5.4, 1.0-6.1, 0.9-23.4 gamma/kg, respectively. NA was not found in meat.
The effect of 13-cis-retinoic acid on cell proliferation in normal urothelium and during early stages in N-nitrosodibutylamine (DBN) induced malignant transformation was studied in male hairless mice. The retinoic acid was administered orally, and the parameters studied were (a) variations in total cell number, (b) labelling index (LI), (c) mitotic rate (MR), (d) the proportions of DNA-synthesizing cells in the diploid and tetraploid fractions, and (e) morphological changes. 13-cis-retinoic acid caused no effect on these parameters in normal urothelium, nor did it prevent the changes caused by DBN in the urothelium prior to malignant development.
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