A review of current literature on N-nitroso compounds in foods

Volatile N-nitrosamines in processed meat products and salami from Turkey

N-nitrosamines are harmful components that can be formed in processed meat products. Due to its production technique, salami is an important meat product in terms of volatile N-nitrosamines. In this regard, the presence of volatile N-nitrosamines, which may pose a risk for human health, was investigated in salami. N-nitrosamines were extracted from the salami and determined with a validated GC-MS method. Accordingly, the analysed samples of salami contained 7.86-29.11 ppb total volatile N-nitrosamines. The salami brand affected the type and level of N-nitrosamines (P <,005).

Development of estimates of dietary nitrates, nitrites, and nitrosamines for use with the Short Willet Food Frequency Questionnaire

BACKGROUND

Studies have suggested that nitrates, nitrites, and nitrosamines have an etiologic role in adverse pregnancy outcomes and chronic diseases such as cancer. Although an extensive body of literature exists on estimates of these compounds in foods, the extant data varies in quality, quantified estimates, and relevance.

METHODS

We developed estimates of nitrates, nitrites, and nitrosamines for food items listed in the Short Willet Food Frequency Questionnaire (WFFQ) as adapted for use in the National Birth Defects Prevention Study. Multiple reference databases were searched for published literature reflecting nitrate, nitrite, and nitrosamine values in foods. Relevant published literature was reviewed; only publications reporting results for items listed on the WFFQ were selected for inclusion. The references selected were prioritized according to relevance to the U.S. population.

RESULTS

Based on our estimates, vegetable products contain the highest levels of nitrate, contributing as much as 189 mg/serving. Meat and bean products contain the highest levels of nitrites with values up to 1.84 mg/serving. Alcohol, meat and dairy products contain the highest values of nitrosamines with a maximum value of 0.531 microg/serving. The estimates of dietary nitrates, nitrites, and nitrosamines generated in this study are based on the published values currently available.

CONCLUSION

To our knowledge, these are the only estimates specifically designed for use with the adapted WFFQ and generated to represent food items available to the U.S. population. The estimates provided may be useful in other research studies, specifically in those exploring the relation between exposure to these compounds in foods and adverse health outcomes.

Epigenetic-genetic interactions in the APC/WNT, RAS/RAF, and P53 pathways in colorectal carcinoma

PURPOSE

Early events in colorectal tumorigenesis include mutation of the adenomatous polyposis coli (APC) gene and epigenetic hypermethylation with transcriptional silencing of the O(6)-methylguanine DNA methyltransferase (MGMT), human mut L homologue 1 (hMLH1), and P16/CDKN2A genes. Epigenetic alterations affect genetic events: Loss of MGMT via hypermethylation reportedly predisposes to guanine-to-adenine or cytosine-to-thymine (G:C-->A:T) transition mutations in KRAS and P53, and silencing of hMLH1 leads to high levels of microsatellite instability (MSI-H)/mutator phenotype, suggesting that epigenetic-genetic subtypes exist.

EXPERIMENTAL DESIGN

We evaluated the relationships of aberrant methylation of APC, MGMT, hMLH1, P16, N33, and five MINTs to mutations in APC, KRAS, BRAF, and P53 in 208 colorectal carcinomas.

RESULTS

We found that APC hypermethylation was age related (P = 0.04), in contrast to the other genes, and did not cluster with CpG island methylator phenotype (CIMP) markers. Hypermethylation of APC concurrently with either MGMT or hMLH1 was strongly associated with occurrence of G-to-A transitions in APC [odds ratio (OR), 26.8; P < 0.0002 from multivariable logic regression model], but C-to-T transitions had no associations. There was no relationship of hypermethylation of any gene, including MGMT, with G-to-A or C-to-T transitions in KRAS or P53, although APC hypermethylation was associated with P53 mutation (P < 0.0002). CIMP with MSI-H due to hMLH1 hypermethylation, or CIMP with loss of MGMT expression in non-MSI-H tumors, was associated with BRAF mutation (OR, 4.5; P < 0.0002). CIMP was also associated with BRAF V600E T-to-A transversion (OR, 48.5; P < 0.0002).

CONCLUSIONS

Our findings suggest that the heterogeneous epigenetic dysregulation of promoter methylation in various genes is interrelated with the occurrence of mutations, as manifested in epigenetic-genetic subgroups of tumors.

Experimental esophageal carcinogenesis: technical standardization and results

The aim of this research was to determine the occurrence of epidermoid carcinoma of the esophagus induced by diethylnitrosamine (DEN) in Wistar rats. DEN was administered (250-300 g) in drinking water (10 mg/kg body weight) to four groups of rats for 72 h/week, for a duration of 90, 120, 150, or 200 days (groups T90, T120, T150, and T200). Ten animals whose drinking water did not contain DEN constituted the control group. All rats were sacrificed and their esophaguses studied macro- and microscopically. The control group did not exhibit either carcinomas or preneoplasic lesions. The T120 and T200 groups presented, respectively, 47 and 58 in situ carcinomas; 1 and 20 submucosal carcinomas (P < 0.05); 4 and 17 microinvasive carcinomas (P < 0.05); 4 and 11 advanced carcinomas (P < 0.05); and 1 and 1 cases of benign hyperplasia. Pulmonary and liver carcinomas were also found in the T200 group. The majority of advanced macroscopic lesions in the T200 group were polypoid, exophytic, and not microscopically invasive in the esophageal wall. This research confirms the effectiveness of the DEN in bringing about carcinogenesis in the Wistar rat esophagus and also shows that the lesions are dosage dependent.

DNA alkylation and repair in the large bowel: animal and human studies

O6-methylguanine (O6-MeG), a procarcinogenic DNA adduct that arises from exposure to methylating agents, has been detected in human colorectal DNA at levels comparable to those that cause adverse effects in model systems. O6-MeG levels vary within the colon, being higher in the cancer-prone regions of the large bowel. In rats and mice, O6-MeG persistence in colon DNA is associated with the induction of colon tumors after treatment with methylating agents. These tumors frequently contain K-ras GC-->AT transition mutations, which is consistent with the mutagenic properties of O6-MeG: such mutations are also commonly found in human colorectal cancers. O6-Alkylguanine adducts are removed by the DNA repair protein, O6-alkylguanine DNA-alkyltransferase (MGMT). MGMT overexpression in transgenic mice reduces the formation of K-ras GC-->AT mutations and tumors induced by methylating agents. Interindividual variations in human colon MGMT activity are large and large bowel tumors can occur in regions of low activity. Low MGMT activity in normal mucosa has been associated with the occurrence of K-ras GC-->AT mutations, whereas reduced MGMT expression and an increased frequency of K-ras GC-->AT mutations in colorectal cancers have been linked to MGMT promoter methylation. MGMT activity is also lower in adenomas than in adjacent normal tissue but only in those adenomas with this specific mutation. These results are entirely consistent with the hypothesis that GC-->AT mutations in the K-ras oncogene result from the formation and persistence of O6-alkylguanine lesions in colorectal DNA. Human exposure to endogenous or exogenous alkylating agents may thus be an environmental determinant of colorectal cancer risk.

Applications of solid-phase microextraction in food analysis

Food analysis is important for the evaluation of the nutritional value and quality of fresh and processed products, and for monitoring food additives and other toxic contaminants. Sample preparation, such as extraction, concentration and isolation of analytes, greatly influences the reliable and accurate analysis of food. Solid-phase microextraction (SPME) is a new sample preparation technique using a fused-silica fiber that is coated on the outside with an appropriate stationary phase. Analyte in the sample is directly extracted to the fiber coating. The SPME technique can be used routinely in combination with gas chromatography (GC), GC-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC) or LC-MS. Furthermore, another SPME technique known as in-tube SPME has also been developed for combination with LC or LC-MS using an open tubular fused-silica capillary column as an SPME device instead of SPME fiber. These methods using SPME techniques save preparation time, solvent purchase and disposal costs, and can improve the detection limits. This review summarizes the SPME techniques for coupling with various analytical instruments and the applications of these techniques to food analysis.

Biogenic amines: their importance in foods

Biogenic amines are important nitrogen compounds of biological importance in vegetable, microbial and animal cells. They can be detected in both raw and processed foods. In food microbiology they have sometimes been related to spoilage and fermentation processes. Some toxicological characteristics and outbreaks of food poisoning are associated with histamine and tyramine. Secondary amines may undergo nitrosation and form nitrosamines. A better knowledge of the factors controlling their formation is necessary in order to improve the quality and safety of food.

Mean daily intake of N-nitrosodimethylamine from foods and beverages in France in 1987-1992

N-nitrosodimethylamine (NDMA) contamination was determined in 556 food samples and 75 beverages purchased in eastern France in 1987-1992. NDMA was found in 427 samples (68%). Data amassed enabled the first estimation to be made in France of the mean daily intake of NDMA from French foods and beverages in 1987-1992 (0.19 microgram/day). One-third of this daily exposure resulted from the consumption of alcoholic beverages.

Review of the occurrence and formation of non-volatile N-nitroso compounds in foods

A review of the literature published prior to July 1991 covers the occurrence and formation of non-volatile N-nitrosamines occurring in foods and beverages. The presence of identified volatile and non-volatile N-nitrosamines accounts for less than 10% of the total apparent N-nitrosamine concentration. N-Nitrosoproline and N-nitrosothiazolidine-4-carboxylic acid are the most commonly identified non-volatile N-nitrosamines in the diet. Non-volatile N-nitrosamines account for 12 of the 21 currently identified N-nitroso compounds in foods and beverages.

Mean daily intake of primary and secondary amines from foods and beverages in West Germany in 1989-1990

264 samples of foods and beverages from the German market in 1989-1990 were analysed for primary and secondary amines. Amines were determined as benzenesulphonyl chloride derivatives by gas chromatography with chemiluminescense detection. The mean daily intake of primary amines was calculated to be 29 mg/day for women and 37 mg/day for men. For secondary amines, the mean daily intake was 6 mg/day for women and 8 mg/day for men.

Potential of endogenous formation of volatile nitrosamines from Nigerian vegetables and spices

Nitrosatability of dried Nigerian vegetables and spices was investigated under simulated gastric conditions. N-Nitroso-dimethylamine (NDMA) was the only volatile nitrosamine found above the preformed level except in ugwu where N-nitroso-piperidine (2.3 ppb) was also detected. The lowest NDMA value of 0.4 ppb was found in bitterleaf while onions had the highest level (14.7 ppb) of nitrosation. The results suggest that, under endogenous conditions, nitrosation of these foodstuffs could be an important contributory factor in cancer aetiology.

Carcinogenic N-nitrosamines in the diet: occurrence, formation, mechanisms and carcinogenic potential

Nitrosamines form a large group of genotoxic chemical carcinogens which occur in the human diet and other environmental media, and can be formed endogenously in the human body. N-Nitroso compounds can induce cancer in experimental animals. Some representative compounds of this class induce cancer in at least 40 different animal species including higher primates. Tumours induced in experimental animals resemble their human counterparts with respect to both morphological and biochemical properties. Extensive experimental, and some epidemiological data suggest that humans are susceptible to carcinogenesis by N-nitroso compounds and that the presence of these compounds in some foods may be regarded as an aetiological risk factor for certain human cancers including cancers of the oesophagus, stomach and nasopharynx.

Effect of cooking on availability and in vitro nitrosation of precursors of volatile N-nitroso compounds in seafood

Aqueous extracts of uncooked and cooked samples of squid and shrimp, characterized by their high amine content, were exposed to nitrate. The samples were cooked following traditional Italian recipes: stewing, grilling and deep-frying for squid; boiling, grilling and deep-frying for shrimp. Incubation of the aqueous extracts with nitrite in acidic medium yielded appreciable amounts of N-nitrosodimethylamine. Ascorbic acid and alpha-tocopherol were effective in preventing nitrosation of seafood amines only in the presence of molar excesses of these vitamins. An attempt at modulating nitrosation through the use of food ingredients naturally rich in vitamin C was unsuccessful.

Nitrite-cured meats as a source of endogenously and exogenously formed N-nitrosoproline in the ferret

Nitrite-cured meat containing 120 mg Na15NO2/kg was fed to male ferrets (Mustela putorius furo). During consumption of the meat, the animals were dosed orally with 0.87 mmol [2-2H]proline. All urine was collected throughout the study and analysed for total N-nitrosoproline (NPRO) and isotopic enrichment of NPRO by mass spectrometry. The cured-meat diet increased the urinary excretion of NPRO 14-fold. Isotope analyses indicated that approximately 70% of the NPRO came from the cured meat, the majority of which was analytically unavailable or 'bound' NPRO in the meat. A small portion of the excreted NPRO appeared to be formed in the stomach as a result of ingesting the cured meat. A minor amount of the excreted NPRO did not contain any isotopically labelled atoms. The administration of ascorbic acid did not significantly alter NPRO excretion. Animals dosed orally with 11.4 mumol of a peptide in which the N-terminal proline was nitrosated increased their excretion of NPRO by 385 nmol over the following 48 hr. These data indicate that nitrite-cured meat contains bound NPRO which contributes to the total amount of NPRO in the urine.