Studies of the metabolic bioactivation of n-nitrosopyrrolidine in the rat

Risk assessment of N-nitrosamines in food

EFSA was asked for a scientific opinion on the risks to public health related to the presence of N-nitrosamines (N-NAs) in food. The risk assessment was confined to those 10 carcinogenic N-NAs occurring in food (TCNAs), i.e. NDMA, NMEA, NDEA, NDPA, NDBA, NMA, NSAR, NMOR, NPIP and NPYR. N-NAs are genotoxic and induce liver tumours in rodents. The in vivo data available to derive potency factors are limited, and therefore, equal potency of TCNAs was assumed. The lower confidence limit of the benchmark dose at 10% (BMDL10) was 10 μg/kg body weight (bw) per day, derived from the incidence of rat liver tumours (benign and malignant) induced by NDEA and used in a margin of exposure (MOE) approach. Analytical results on the occurrence of N-NAs were extracted from the EFSA occurrence database (n = 2,817) and the literature (n = 4,003). Occurrence data were available for five food categories across TCNAs. Dietary exposure was assessed for two scenarios, excluding (scenario 1) and including (scenario 2) cooked unprocessed meat and fish. TCNAs exposure ranged from 0 to 208.9 ng/kg bw per day across surveys, age groups and scenarios. 'Meat and meat products' is the main food category contributing to TCNA exposure. MOEs ranged from 3,337 to 48 at the P95 exposure excluding some infant surveys with P95 exposure equal to zero. Two major uncertainties were (i) the high number of left censored data and (ii) the lack of data on important food categories. The CONTAM Panel concluded that the MOE for TCNAs at the P95 exposure is highly likely (98-100% certain) to be less than 10,000 for all age groups, which raises a health concern.

Mutational specificities of environmental carcinogens in the lacl gene of Escherichia coli. III: The cyclic nitrosamine N-nitrosopyrrolidine is a complex mutagen

The mutational specificity of the cyclic nitrosamine N-nitrosopyrrolidine (NPYR) was determined through the DNA sequence characterization of 33 lacl-d mutations of Escherichia coli. Base substitution was the predominant class of mutation induced (91%). The majority of these (64%) occurred at GC base pairs, in accordance with the predicted significance of NPYR-derived guanine adducts. In addition, this nitrosamine efficiently produced other kinds of base substitution events as 11 of the 33 mutations occurred at AT base pairs. Deletion, frameshift, and duplication events were also recovered. The complexity of the NPYR mutational spectrum appears to be consistent with the suggestion that this compound acts through both direct and indirect mutational pathways.

Metabolic conversion of IQ and MeIQ to bacterial mutagens

The metabolic conversion of 2-amino-3-methyl- and 2-amino-3,4-dimethyl-imidazo[4,5-f]quinoline (IQ and MeIQ respectively) to bacterial mutagens was studied using a bacterial mutation assay. Studies were performed using S9 fractions derived from either corn oil (uninduced) or Aroclor-1254-treated Sprague-Dawley rats. Aroclor 1254 treatment lowered the S9 protein concentration required for optimum levels of mutagenesis, enhanced the numbers of mutants observed and altered the effects of metabolic inhibitors and cofactors added to the assay. Studies with uninduced preparations revealed that IQ and MeIQ exhibited similar responses to the effects of metabolic inhibitors and cofactors involved in detoxication reactions. Both IQ and MeIQ activation appeared to be inhibited by the biogenic amines tryptamine and tyramine and inactivated by conjugation with either acetyl coenzyme A or glutathione.

Effects of N-nitrosopyrrolidine and N-nitrosoproline on the incorporation of 3H-thymidine into the DNA of various organs of the mouse: tissue specificity and effects of ethanol consumption

The effects of the carcinogenic N-nitrosamine N-nitrosopyrrolidine (NPYR) and the non-carcinogenic N-nitrosamino acid N-nitrosoproline (NPRO) on 3H-thymidine incorporation into DNA were evaluated in various organs of male C57BL mice. The N-nitroso compounds were given intraperitoneally 24 hrs before sacrifice in equimolar amounts (148 mumol/kg b.wt.). Two hours before the mice were killed, they were given an intraperitoneal injection of 3H-thymidine. NPYR, but not NPRO, induced a tissue-specific inhibition of 3H-thymidine incorporation into DNA. The inhibition occurred only in organs reported to be involved in the biotransformation of NPYR, i.e., the liver, lung, and nasal mucosa. Daily oral consumption of ethanol (1.8 ml 30% ethanol for 30 days) had no effects in itself on 3H-thymidine incorporation, but resulted in an enhancement of the inhibitory action of NPYR in the lung and nasal mucosa.