Formation Of Carcinogenic Nitrosamines Research Articles

Atmospheric oxidation mechanism and kinetics of indole initiated by ●OH and ●Cl: a computational study

Abstract. The atmospheric chemistry of organic nitrogen compounds (ONCs) is of great importance for understanding the formation of carcinogenic nitrosamines, and ONC oxidation products might influence atmospheric aerosol particle formation and growth. Indole is a polyfunctional heterocyclic secondary amine with a global emission quantity almost equivalent to that of trimethylamine, the amine with the highest atmospheric emission. However, the atmospheric chemistry of indole remains unclear. Herein, the reactions of indole with ⚫OH and ⚫Cl, and subsequent reactions of resulting indole radicals with O2 under 200 ppt NO and 50 ppt HO2⚫ conditions, were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that ⚫OH addition is the dominant pathway for the reaction of ⚫OH with indole. However, both ⚫Cl addition and H abstraction are feasible for the corresponding reaction with ⚫Cl. All favorably formed indole radicals further react with O2 to produce peroxy radicals, which mainly react with NO and HO2⚫ to form organonitrates, alkoxy radicals and hydroperoxide products. Therefore, the oxidation mechanism of indole is distinct from that of previously reported amines, which primarily form highly oxidized multifunctional compounds, imines or carcinogenic nitrosamines. In addition, the peroxy radicals from the ⚫OH reaction can form N-(2-formylphenyl)formamide (C8H7NO2), for the first time providing evidence for the chemical identity of the C8H7NO2 mass peak observed in the ⚫OH + indole experiments. More importantly, this study is the first to demonstrate that despite forming radicals by abstracting an H atom at the N site, carcinogenic nitrosamines were not produced in the indole oxidation reaction.

Simultaneous preparation of N2 and CO2 from water nitrates for δ15N and δ18O analysis on the example of the Zemborzycki Reservoir studies

Nitrates are bioavailable compounds, which are necessary for every living organisms. However, their excess could be harmful, because it could lead to, i.e., methemoglobinemia, formation of carcinogenic nitrosamines and reservoir eutrophication. Isotopic analysis of δ15N and δ18O in nitrates allows to distinguish their different sources. To simplify the way of nitrate source monitoring, we developed a less complex and cheap “off-line” method for nitrate isotopic analysis, in which we obtain both gases required for isotopic analysis of NO3−, N2 for δ15N and CO2 for δ18O measurements, in one procedure. The developed method is based on simultaneous conversion of AgNO3 (mixed with C and placed into PtIr boat) to N2 and CO2 in a glass vacuum apparatus. A small amount of sample (8 mg of AgNO3) required for this procedure and a good reproducibility of the isotopic analysis (better than 0.3‰ for δ18O and 1‰ for δ15N) make this method a useful tool for environmental research.Using the developed method, we analyzed the isotopic composition of N and O in nitrates in the Zemborzycki Reservoir near Lublin (Poland), in 2015. The results indicate a large variation of δ15N (from −1.4 to +37.7‰) and δ18O (from +5.5 to +25.9‰) values in NO3− ions, while the concentration of NO3− varied from 0.2 to 15.3 mg/dm3. These preliminary results suggest that nitrate fertilizers probably are the main source of NO3− pollution. Our study points out the input of manure and/or sewage to the analyzed reservoir in the subsequent periods of sample collection.

Nitrite level of pickled vegetables in Northeast China

Nitrite is commonly present in pickled vegetables. Nitrite has been proven to have adverse effects on health, including changing the normal form of hemoglobin and the formation of carcinogenic nitrosamines. The aim of our study was to determine the levels of nitrite in pickled vegetable samples consumed in Harbin, China. In this study, 218 samples of pickled turnip (PT) (n = 42, packaged (PK) = 19; unpackaged (UPK) = 23), pickled tuber mustard (PTM) (n = 44, PK = 23; UPK = 21), pickled cucumber (PCC) (n = 48, PK = 25; UPK = 23), and pickled cabbage (PCB) (n = 84, PK = 39; UPK = 45) were analyzed between October 2011 and December 2011, using colorimetric nitrite assay based on the Griess reaction. A nitrite level of <5 mg/kg was normally predominant in 147 (67%) samples of the investigated pickled vegetables, ranging from 0.01 mg/kg to 42.03 mg/kg, while a nitrite level of >20 mg/kg was detected in 9 (4%) samples. The overall nitrite content was 4.02 ± 0.62 mg/kg for PT, 4.52 ± 1.07 mg/kg for PTM, 3.91 ± 0.69 mg/kg for PCC, and 4.86 ± 0.80 mg/kg for PCB. The content of nitrite in unpackaged pickled vegetables (PT, 5.47 ± 0.89; PTM, 6.84 ± 2.02; PCC, 5.32 ± 1.27; PCB, 6.41 ± 1.28; and total, 6.08 ± 0.71 mg/kg) was significantly higher than those in packaged products (PT, 2.68 ± 0.72; PTM, 2.30 ± 0.55; PCC, 2.62 ± 0.54; PCB, 3.08 ± 0.81; and total, 2.73 ± 0.36 mg/kg) (P < 0.05). The variance in the concentration of nitrite in the pickled vegetables probably resulted from differences in quality, processing technique, and storage condition of the pickled vegetables. Our results indicated that, in China, low level nitrite is widely present in pickled vegetables. It is therefore important to assess the content of nitrite in pickled vegetables in China.

The need for reference materials when monitoring nitrate intake.

Whether dietary exposure to nitrate metabolites is detrimental or beneficial to human health has long been a matter of controversy. In spite of no consistent epidemiological evidence, nitrate metabolites are associated with the formation of carcinogenic-nitrosamines and gastric cancer. Furthermore, recent studies demonstrate that ingested nitrate plays a role in host defence against gastrointestinal pathogenic bacteria. Analytical values of nitrate content in foods are essential for estimating nitrate intake. The analytical process is of paramount importance for assessing human nitrate exposure and for establishing a link between these exposures and the current and future observed health effects. Therefore, the quality assurance of the measurement process is crucial to obtaining reliability, comparability and traceability of results. Certified Reference Materials (CRM) should play a role in the consistency of the measurement process. However, the availability of nitrate CRMs is still poor. When food monitoring is demanded, an approach could be to use In House Reference Materials (IHRM), prepared at a high metrological level, and all preparation steps should be quality driven. IHRMs were prepared, and available CRMs were used to provide traceability of the process. The homogeneity of IHRM was evaluated using an appropriate statistical design. The stability was monitored using an isochronous method. The material shelf life and storage conditions are presented. HPLC was optimised for the determination of nitrates in four vegetable categories. When a suite of IHRMs were used, the response of the HPLC system was linear over the range 1 to 8 mg L(-1). The detection limit for these compounds was 0.2 microg L(-1) and the determination limit 1.2 microg L(-1). The relationship between measurement uncertainty and critical points of the analytical process is presented. The differences in observed relative uncertainty between food categories could reflect current limitations in the food matrix reference materials.

Volatile N-nitrosamine inhibition after intake Korean green tea and Maesil ( Prunus mume SIEB. et ZACC.) extracts with an amine-rich diet in subjects ingesting nitrate

The formation of carcinogenic nitrosamines under simulated gastric conditions was studied during the incubation of amine rich food and nitrate, and its possible inhibition by adding kumquat, sweet orange, strawberry, garlic, kale juices, Maesil ( Prunus mume) and green tea extracts. The strawberry, kale juices, Maesil and green tea extracts were equally effective in reducing the formation of N-nitrosodimethylamine (NDMA). The fruits of P. mume SIEB. et ZACC. (Korean name, Maesil) have been used as a traditional drug and health food in Korea. During four weeks of test (designated EW1, EW2, EW3 and EW4; experiment week 1, 2, 3 and 4 diets) volunteers consumed a diet of low nitrate and amine (EW1) and consumed a fish meal rich in amines as nitrosatable precursors in combination with intake of nitrate-containing drinking water without (EW2) or with Maesil and green tea extracts (EW3 and EW4, respectively). The intake of nitrate-containing drinking water (340 mg nitrate/100 ml) resulted in a significant rise in mean salivary nitrate and nitrite concentrations and in mean urinary nitrate levels. Mean urinary nitrate was increased to 455.0±66.2, 334.6±67.8 and 333.4±50.7 mg/18 h after the nitrate intake of EW2, EW3 and EW4, respectively. Significant increases in urinary dimethylamine and trimethylamine levels were observed in consumption of diets (EW2, EW3, and EW4) rich in amine and nitrate. Maesil and green tea extract in EW3 and EW4 enhanced the increase of urinary dimethylamine and trimethylamine levels. Urinary excretion of N-nitrosodimethylamine in consumption of diet rich in nitrate and amine (EW2) increased to 6504.4±2638.7 ng/18 h from 257.0±112.0 ng/18 h of low nitrate and amine diet (EW1). Korean green tea and Maesil extracts in nitrate and amine rich diet reduced the excretion of N-nitrosodimethylamine to 249.7±90.6 and 752.7±595.3 ng/18 h, respectively, compared with 6504.4±2638.7 ng /18 h after ingestion of TD1 diet.

Experimental Helicobacter pylori infection induces antral gastritis and gastric mucosa-associated lymphoid tissue in guinea pigs.

Humans infected with Helicobacter pylori have abnormally low levels of the antioxidant vitamin C, which protects against the formation of carcinogenic nitrosamines, in gastric juice. Guinea pigs, like humans and nonhuman primates, have a dietary requirement for vitamin C. As such, these species have gastrointestinal vitamin C transport systems not found in other animals. We have developed and characterized a guinea pig model of chronic gastric H. pylori infection with the rodent-adapted Sydney strain of H. pylori. At 4 weeks postinfection, five of six animals of the infected group and zero of two animals of the control group were positive for H. pylori as determined by culture or PCR. At 15 weeks, six of six animals of the infected group and zero of two animals of the control group were positive. H. pylori-specific seroconversion was observed among infected animals. There were no histologic abnormalities in the gastric antra or fundi of control guinea pigs. In contrast, there was multifocal, mild to moderate lymphohistiocytic antral gastritis and formation of antral lymphoid follicles in H. pylori-infected animals. The lesion distribution in the gastric antra paralleled that observed in H. pylori-infected humans. The H. pylori-infected guinea pig should prove useful in modeling the interaction of helicobacter and vitamin C in gastric carcinogenesis.

The Deteriorating Reproductive Health of the Pill Generations: A Need for Pre-conceptional Investigation and Treatment of Sexually Transmitted Infections and Exogenous Hormone-induced Changes in Nutritional Status and Immunity

In this issue, Tuula Tuormaa reviews some of the adverse effects of genito-urinary infections on fertility and neonatal health (p. 351). Clinicians may be surprised that the majority of older stable-relationship couples are harbouring a variety of undiagnosed, yet treatable, infections. Women believe that their regular cervical cancer smear check will detect infection and indeed they are frequently given a vague diagnosis of inflammatory changes, vaginosis or dysplasia. Men with pus cells in their urine are treated for the equally vague condition of non-specific urethritis. Since 1987, I have been advising prospective parents of the value of full infection screens before they attempt conception. The results obtained from screening 114 couples, most of whom had histories of recurrent miscarriage or infertility, were presented at the Buxton Clinical Ecology Conference in 1990 [I 1. One in five men and more than 50% of the women had bacterial or mycoplasmal infections with some couples having up to six different organisms. Acute Chlamydia trachomatis was uncommon both in women’s endocervical swabs and in men’s urine, prostatic secretions and semen, but 45% of the women had raised serum antibody levels to Chlamydia trachornatis. The Chlamydia trachomatis antibody immunofluorescence test reveals past infection which, if still dormant in the Fallopian tubes, can flare up and become active during pregnancy or as a result of tuba1 patency investigations [2]. The Chlamydia psittaciLGV group complement fixation test can signal active pelvic inflammatory disease. Positive results in either test indicate the need for treatment with the appropriate antibiotics for 2 weeks although the immunofluorescence test does not become negative until several years later after therapy. Cervical lesions caused by recurring viruses often form a focus for persistent cervicitis or recurrent thrush. Singer has found that one in three women has a cervical lesion caused by wart viruses. Various types of human papilloma virus (HPV) can be detected by a polymerase chain reaction test. Malignant change is nearly always associated with HPV 16 [3]. If there is secondary infection of the viral lesion, contact with semen leads to the formation of carcinogenic nitrosamines [4]. Cervical cancer tends to increase with age, sexual activity (earlier age of first sexual intercourse and number of partners), parity, social class and amount smoked [5]. An extremely important factor is exposure to exogenous sex hormones such as contraceptive pills; the net progestational effect suppresses maturation which “could make the cervical epithelium more susceptible to sexually transmitted agents” [6]. Lack of folic acid was the first nutritional deficiency to be linked with cervical cancer. Women with serum folate levels below 600 nmol - ’ are at five times the risk of cervical cancer if they have HPV infection. Folate deficiency causes chromosome breaks which may facilitate the integration of HPV into human genetic material [7].

Endogenously formed N-nitroso compounds and nitrosating agents in human cancer etiology.

Humans are exposed to preformed N-nitroso compounds (NOC), but also to a wide range of precursors and nitrosating agents which can react in vivo to form potentially carcinogenic NOC and diazo compounds. Nitrite, nitrate and nitrosating agents can also be synthesized endogenously in enzymic reactions mediated by bacteria, activated macrophages and neutrophils. The latter two cell types generate, via the enzyme nitric oxide synthase, the nitric oxide radical that is involved in cytotoxicity, and is believed to be involved in formation of carcinogenic nitrosamines, DNA base deamination and oxidative damage. Thus endogenous NOC formation, DNA damage and gene mutations in humans could occur at various sites of the body such as the stomach and chronically infected or inflamed organs. Sensitive procedures to estimate the exposure of humans to NOC have been developed and applied in ecological and cross-sectional studies. These have shown that inhabitants of high-risk areas for stomach and esophageal cancer, patients with urinary tract infections (at risk for bladder cancer) and Thai subjects infected with liver fluke (at risk for cholangiocarcinoma) had significantly higher exposure to endogenous NOC. Clinical studies have examined the model of stomach carcinogenesis based on intragastric nitrosation, but the precise roles of bacterial overgrowth and of Helicobacter pylori infection in NOC synthesis and/or inducing oxidative stress in stomach mucosa remain to be clarified. Together these results support the role of NOC and other nitrite-derived mutagens in human cancer etiology, in particular when exposure starts early in life and persists over a long period.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety aspects of food preservatives.

The use of food preservatives, such as benzoic acid, nitrites, and sulphites, as antimicrobials, and butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), ascorbic acid and tocopherols, as antioxidants, has probably changed food production patterns and eating habits more than has the use of any other class of food additive. These food preservative chemicals confer substantial benefits on man, not only by the preservation and increased palatability of food, but also by affording protection against the pathological effects of reactive oxygen species (ROS) which are associated with cancer, cardiovascular disease and aging. Nevertheless, although most preservatives are now considered to be without potential adverse effects and are classified as GRAS, there have been problems concerning the safety of some of these chemicals, including the possibility of allergies from benzoic acid and sulphites, the formation of carcinogenic nitrosamines from nitrites, and the possible rodent carcinogenicity of BHA and BHT. The mechanisms of this toxicity at high dosage, the roles of the cytochromes P450, and the generation and scavenging of ROS in the toxicity of these chemicals, are reviewed and discussed.

Inhibitory effect of diet related sulphydryl compounds on the formation of carcinogenic nitrosamines

N-Nitroso compounds (NOCs) are known to be strong carcinogens in various animals including primates (Preussman and Stewart, (1984) N-Nitroso Compounds). Human exposure to these compounds can be by ingestion or inhalation of preformed NOCs or by endogenous nitrosation from naturally occurring precursors (Bartsch and Montesano, Carcinogenesis, 5 (1984) 1381–1393; Tannebaum (1979) Naturally Occuring Carcinogens, Mutagens and Modulators of Carcinogenesis; Shephard et al., Food Chem. Toxicol., 25 (1987) 91–108). Several factors present in the diet can modify levels of endogenously formed nitrosamines by acting as catalysts or inhibitors. Compounds in the human diet that alter nitrosamine formation would thus play an important role in carcinogenesis study. Earlier researchers have reported the nitrite scavenging nature of sulphydryl compounds (Williams, Chem. Soc. Rev., 15 (1983) 171–196). We therefore studied the modifying effect of sulphydryl compounds viz., cysteine (CE), cystine (CI), glutathione (GU), cysteamine (CEA), cystamine (CEI), cysteic acid (CIA) and thioglycolic acid (TGA) on the nitrosation of model amines viz., pyrrolidine (PYR), piperidine (NPIP) and morpholine (NMOR). Many of these compounds are present in the food we consume. The present work also describes the inhibitory effect of onion and garlic juices on the nitrosation reactions. Both onion and garlic are known to contain sulphur compounds (Block, Sci. Am., 252 (1985) 114–119). Most of these compounds behave as antinitrosating agents and their inhibitory activity towards formation of carcinogenic nitrosamines, under different conditions is described.

Chronic toxicity tests of sodium thiocyanate with sodium nitrite in F344 rats.

Sodium thiocyanate, a common environmental chemical, was found to increase the incidence of liver tumors in a group of rats treated with 0.08% in drinking water. To test the possibility that thiocyanate was catalyzing the formation of carcinogenic nitrosamines from amines and nitrite in the food, a group of 20 male and 20 female rats was given a higher dose of sodium thiocyanate (0.32%) together with sodium nitrite (0.2%) in drinking water. Similar groups of rats were given 0.32% sodium thiocyanate or 0.2% sodium nitrite in drinking water or were untreated. All treatments lasted most of the lifetime of the rats, at least 2 years. There was no difference between the groups, treated or untreated, in survival, or in the incidence of any tumor that could be related to the treatment. The results indicate that sodium thiocyanate is without carcinogenic activity in rats, alone or combined with sodium nitrite.

Inhibition of Nitrosamine Formation by Nondialyzable Melanoidins

The degradation of nitrite and the inhibition towards formation of carcinogenic nitrosamines by melanoidins, produced from the glucose-glycine system were investigated at various conditions. The degradation of nitrite was highest at pH 1.2 (29%), when the ratio of melanoidins to nitrite was 1: 3. The inhibition towards formation of nitrosamines by melanoidins had the same tendency as the degradation of nitrite, the inhibition also being highest at pH 1.2 (99%). In addition, melanoidins after nitrite treatment exhibited a little higher mutagenicity and much stronger desmutagenicity than those of the original melanoidins. The change of the structure of melanoidins after treating with nitrite was also investigated by HPLC and CP-MAS NMR.

Inhibition of nitrosamine formation by nondialyzable melanoidins.

The degradation of nitrite and the inhibition towards formation of carcinogenic nitrosamines by melanoidins, produced from the glucose-glycine system were investigated at various conditions. The degradation of nitrite was highest at pH 1.2 (29%), when the ratio of melanoidins to nitrite was 1: 3. The inhibition towards formation of nitrosamines by melanoidins had the same tendency as the degradation of nitrite, the inhibition also being highest at pH 1.2 (99%). In addition, melanoidins after nitrite treatment exhibited a little higher mutagenicity and much stronger desmutagenicity than those of the original melanoidins. The change of the structure of melanoidins after treating with nitrite was also investigated by HPLC and CP-MAS NMR.

Effects of vitamins C and E on carcinogen formation and action, and relationship to human cancer.

To introduce this subject, I will briefly review the inhibition by vitamins C and E of the formation of carcinogenic nitrosamines and nitrosamides (N-nitroso compounds), as well as effects of these vitamins on carcinogenesis and human cancer. I have previously reviewed the inhibition by vitamins C and E of N-nitroso compound formation (4, 5) and hope shortly to publish a more complete review on the subject (7).

Inhibitory Effect of Betel Nut Extracts on Endogenous Nitrosation in Humans&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;&lt;xref ref-type="fn" rid="FN3"&gt;3&lt;/xref&gt;

Extracts of betel nut (Areca catechu) were tested for their capacity to inhibit the endogenous formation of nitrosamines by measurement of the amount of urinary N-nitroso-L-proline (NPRO) following ingestion of sodium nitrate (300 mg) and L-proline (300 mg) by 2 volunteers. A water extract of the dried nuts, an ether extract containing mainly (+)-catechin and (-)-epicatechin, and a caffeine-precipitated n-butyl alcohol extract containing primarily proanthocyanidins (tannins) strongly reduced the endogenous formation of NPRO. An average of 14.7 and 10.9 micrograms NPRO (8 expts per individual) was excreted in the urine of the 2 volunteers over a 24-hour period following the intake of sodium nitrate and L-proline. The water extract and the proanthocyanidin (tannin)-containing extract, both of which contain the dose equivalent of one-quarter of a nut, reduced the excreted NPRO to background levels, which varied from 0.5 to 3.6 micrograms and from 0.6 to 2.1 micrograms (6 expts) in 24-hour urine samples from the 2 volunteers. These results may exemplify the way in which naturally occurring phenolics, which are ingested daily in relatively large quantities, could affect the endogenous formation of carcinogenic nitrosamines.

Nitrite, nitrite alternatives, and the control of Clostridium botulinum in cured meats.

Historically, nitrite has been a component of meat-curing additives for several centuries. In recent years the safety of nitrite as an additive in cured meats has been questioned mainly because of the possible formation of carcinogenic nitrosamines. Nitrite has many important functions in meat curing including its role in color development, flavor, antioxidant properties, and antimicrobial activity. The inhibition of Clostridium botulinum growth and toxin production is an especially important antimicrobial property of nitrite. This review discusses the effects of processing, curing ingredients (especially nitrite), and storage of cured meats in relation to the control of C. botulinum. If nitrite is eliminated from cured meats or the level of usage decreased, then alternatives for the antibotulinal function of nitrite need to be considered. Several potential alternatives including sorbates, parabens, and biological acidulants are discussed.

Formation of carcinogenic nitrosamines in soils

The possible formation of carcinogenic nitrosamines in soils was examined. Soil samples amended with NO 2 −-N and dimethylamine incubated for 30 days and analysed every 3 days, showed increasing amounts of dimethylnitrosamine up to 12–15 days. The concentration reached as high as 6.5 parts/10 6, thereafter, a decline was noted. Most of the nitrosamines disappeared in soils after 30 days. Addition of inorganic N reduced the decomposition of dimethylamine. Soil incubation studies with NO 2 − and trimethylamine showed about 80% reduction in the amount of nitrosamines formed as compared to dimethylamine. Analysis of soil samples from fertilized and polluted areas showed significant amounts of NO − 3-N but no nitrosamines. Application of 10 parts/10 6 of dimethylamine to these soil samples resulted in the formation of 0.10 to 0.50 parts/10 6 of nitrosamines. Autoclaved soil samples incubated with NO 2 − and dimethylamine for 12–15 days produced small amounts of nitrosamines. Addition of glucose to soil samples increased the amounts of nitrosamines formed.

Nitrosamine Studies: Induction of Lung Adenomas by Concurrent Administration of Sodium Nitrite and Secondary Amines in Swiss Mice&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;

Piperazine (6.25 g/kg of food), morpholine (6.33 g/kg of food), and N-methylaniline (1.95 g/kg of food) given together with sodium nitrite (1.0 g/liter of drinking water) to Swiss mice resulted in a highly significant increase in lung adenoma incidence. This increase was more pronounced in males than in females. Dimethylamine hydrochloride (5.9 g/kg of food) was ineffective when given with nitrite, probably because of the strong basicity of the amine. Dinitrosopiperazine given as a 40 mg/liter solution in the drinking water, nitrosomorpholine (80 mg/liter), dimethylnitrosamine (10 mg/liter), and N-nitroso-N-methylaniline (70 mg/liter) increased the number of lung adenomas per mouse tenfold to thirtyfold over control untreated mice. Treatment with sodium nitrite alone or with the secondary amines alone produced no effect. The data strongly suggest that the induction of lung adenomas in animals treated with these secondary amines and nitrite is due to in vivo nitrosation (presumably in the stomach) with the formation of carcinogenic nitrosamines.