Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nitroso Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources
PubMed1995

Role of schistosomiasis in human bladder cancer: evidence of association, aetiological factors, and basic mechanisms of carcinogenesis.

Several epidemiological, clinical and experimental studies have been carried out to determine whether there is an aetiological role for schistosomiasis in the multi-stage process of bladder carcinogenesis. Lines of evidence supporting the association between bladder cancer and schistosomiasis include indications from the geographical correlation between the two conditions, the distinctive patterns of gender and age at diagnosis, the clinicopathological identity of schistosome-associated bladder cancer and the extensive experimental evidence in infected laboratory animals. Although the causative role of schistosomiasis is now accepted, various associated factors have been proposed in the induction of this particular type of cancer. While all may contribute to the carcinogenic process taking place in the infected bladder, none of these has yet been confirmed. Most attention has been directed at theories proposing possible roles for urinary chemical carcinogens, particularly tryptophan metabolites, N-nitroso compounds and of beta-glucuronidase, as factors that are primarily involved in the initiation of bladder carcinogenesis in areas endemic for schistosomiasis.

Adult↗
PubMed1995

The association between typhoid carriage, typhoid infection and subsequent cancer at a number of sites.

It has been demonstrated that bacteria can produce the very potent carcinogens (N-nitroso compounds), from nitrite and suitable amines. It has been hypothesized that this can happen whenever a body site which is normally sterile becomes colonized by bacteria. If this is so then such chronic infections should result in an increased incidence of local cancers and also of cancers at some distant sites. To test this we studied the risk of cancer at various sites in a cohort of chronic carriers of Salmonella typhi/paratyphi. We have observed a greatly increased risk of cancers of the biliary tract and also of cancers of the colorectum, pancreas, lung and all sites. The results are discussed in terms of the hypothesis being tested.

Adolescent↗
PubMed1999

Meat, metabolic genotypes and risk for colorectal cancer.

Persuasive data exist as to the importance of environmental factors in the pathogenesis of sporadic colorectal cancer. One possibility is that the effect of environmental factors varies between individuals, perhaps on the basis of inherited variation (polymorphism) in genes which influence the activation or inactivation of dietary carcinogens. Thus far, the focus has been on acetylator genes (NAT1, NAT2) and the activation of heterocyclic amines, carcinogens generated by cooking meat for prolonged periods at high temperature. Three case-control studies and one prospective study have shown a consistent trend towards higher risks for cancer with higher intakes of meat in rapid acetylators for NAT1, NAT2 or both genotypes. Other links between meat, cooking methods, metabolic genotypes and risk for cancer might include enhanced activation of polycyclic aromatic hydrocarbons and N-nitroso compounds by variant genotypes of CYP1A1 and CYP2E1, respectively, and modulation by meat of the protective effect of the E4 allele of apolipoprotein E on risk for cancer of the proximal colon.

Acetylation↗
PubMed2000

K-ras mutations, rectal crypt cells proliferation, and meat consumption in patients with left-sided colorectal carcinoma.

It has been suggested that N-nitroso compounds derived from meat may increase the risk of K-ras mutations in the human colon. We sought evidence of associations between red meat consumption, frequency and type of K-ras mutations in resected tumours, and the rate of crypt cell proliferation (CCP) in the normal mucosa of patients with left-sided colorectal carcinoma. Meat consumption was assessed by food frequency questionnaire, and CCP was determined in rectal biopsies obtained prior to surgery. K-ras mutations in the resected tumours were determined using a PCR-based oligonucleotide hybridization assay. Fifteen K-ras mutations were detected in tumours from 43 patients; 13/15 in codon 12, 3/15 in codon 13, and 1/15 in both codons 12 and 13. All mutations were G-->A or G-->T transitions. There was no statistically significant difference between intakes of red meat in patients with a K-ras mutation (92.4 +/- 9.7 g/day) and those without (82.3 +/- 7.7 g/day). Rectal CCP was significantly higher in patients than in healthy controls, but there was no correlation with meat consumption or K-ras mutation. These data do not support the hypothesis that meat consumption is a risk factor for acquisition of K-ras mutations during colorectal carcinogenesis.

Aged↗
PubMed2000

Salivary excretion of N-nitrosodimethylamine in dogs.

Carcinogenic N-nitroso compounds (NOCs) are not only ingested from the environment but are also formed endogenously from precursors. It has been reported that nitrate, an NOC precursor, has an enterosalivary cycle and that the cycle increases the chance of exposure to NOCs. However, there is no information on the salivary excretion of NOCs. In the present study, the toxicokinetics of N-nitrosodimethylamine (NDMA) in dogs was evaluated, focusing on the salivary excretion. Following intravenous injection of 2 mg/kg NDMA, the plasma concentration showed a monoexponential decline, and the total body clearance and apparent distribution volume were greatly in excess of the hepatic plasma flow and total body water, respectively. A high concentration of NDMA was immediately detected in the plasma after oral administration of the same dose, and the oral bioavailability was almost 100%. NDMA was rapidly excreted into the saliva after both treatments, and the concentration in saliva was higher than that in the plasma. These results suggest that NDMA also has an enterosalivary cycle: NDMA is partially excreted from blood into saliva, delivered into the gastrointestinal tract by swallowing the saliva, and then completely reabsorbed into the systemic circulation. This concept was also supported by kinetic analysis based on a compartment model. The enterosalivary cycle of NDMA cannot be ignored in the risk assessment of carcinogenesis.

Animals↗
PubMed2000

Nitrate and nitrite concentrations in human saliva for men and women at different ages and times of the day and their consistency over time.

Salivary nitrite arises from nitrate and is the main source of gastric nitrite, a precursor of carcinogenic N-nitroso compounds. We examined nitrate and nitrite levels in unstimulated saliva from subjects consuming low-nitrate low-vitamin C diets. When saliva was collected from six men at nine times of the day (Experiment 1), night time nitrite levels were significantly higher than day time values and nitrite varied more than nitrate. When saliva was collected from 29 subjects aged 19-37 or 60-84 years at four times of the day during 1991-1993 (Experiment 2), all older subjects and older men had significantly higher nitrite levels than the corresponding younger subjects, night time nitrite levels in men were significantly raised, and nitrate and nitrite levels in the same samples were closely correlated. Saliva was collected at 6.00 a.m. on two successive days in 1997 from 16 subjects who had collected saliva in 1991-1993 (Experiment 3). Nitrate and nitrite levels on day 1 of experiment 3 were closely correlated with those on day 2. Nitrate and nitrite levels on days 1 and 2 of Experiment 3 were correlated with the corresponding parameters in Experiment 2 with P = 0.04 and 0.08 for day 1, and 0.10 and 0.28 for day 2, respectively. Hence, saliva nitrite levels rose at night and were higher in older people, especially older men, and saliva nitrate and nitrite levels varied little from day to day, but varied more after 4-6 years.

Adult↗
PubMed2000

Tobacco smoking and vitamin C concentration in gastric juice in healthy subjects and patients with Helicobacter pylori infection.

Low gastric juice total vitamin C concentration in the presence of Helicobacter pylori infection probably plays a role in gastric carcinogenesis. Vitamin C plays a role in the neutralization of various pathogenic factors connected with H. pylori infection, including the destruction of free radicals, which damage tissues and cell DNA, and inhibition of the formation of N-nitroso compounds, which have a strong carcinogenic activity. The aim of the study was to determine whether tobacco smoking had any effect on gastric juice vitamin C concentration in healthy subjects and in patients infected with H. pylori. Eighty-six patients with dyspeptic symptoms undergoing routine endoscopy entered the study after giving informed consent. In all patients plasma and gastric juice total vitamin C levels were measured by a spectrophotometric method. They were entered into four groups: group I (controls) - H. pylori-negative non-smokers (n = 17), group II - H. pylori-negative smokers (n = 16), group III - non-smokers with H. pylori infection (n = 21), and group IV - H. pylori-infected smokers (n = 32). In the control group (I) the mean gastric juice total vitamin C concentration was 17.1 microg/ml (range 5.3-40.0 microg/ml), which was significantly higher (P < 0.05) than in group II (12.6 microg/ml, range 5.1-21.0 microg/ml), group III (5.8 microg/ml range 2.1-13.7 microg/ml) and group IV (3.9 microg/ml, range 1.1-10.6 microg/ml) (P < 0.001). Statistically significant differences also were noted between groups II and III (P < 0.01) and groups II and IV (P < 0.001) and between groups III and IV (P < 0.05). These results demonstrate that the concentration of vitamin C in gastric juice is significantly lower in smokers than in non-smokers. This was observed in healthy subjects as well as H. pylori-infected patients. This phenomenon may be one of the mechanisms whereby smoking contributes to the production of gastric lesions, impairs healing of peptic ulcers and also increases the recurrence rate of peptic ulcers in cases with H. pylori infection.

Adult↗
PubMed2001

Foods and risk of bladder cancer: a case-control study in Uruguay.

A case-control study on 144 cases of transitional cell bladder carcinoma and 576 hospitalized controls was conducted in Montevideo, Uruguay. Barbecued meat, salted meat and fried eggs were associated with significant increased risks of bladder cancer (odds ratio (OR) for high intake of salted meat 4.04, 95% confidence interval (CI) 2.24-7.27). On the other hand, all fruits, cooked vegetables, potatoes and cheese were associated with inverse associations (OR for high consumption of potatoes 0.38, 95% CI 0.23-0.64). The associations with salted and barbecued meat suggest that the way of preserving or cooking meat play a role in bladder carcinogenesis. More precisely, N-nitroso compounds and heterocyclic amines could be involved in this process.

Adult↗
PubMed2005

Drinking water and dietary sources of nitrate and nitrite and risk of glioma.

OBJECTIVE: Dietary nitrite has been associated with increased glioma risk; however, drinking water nitrate has not been extensively evaluated. METHODS: We conducted a population-based case-control study of adult glioma in Nebraska. Water utility nitrate measurements were linked to residential water source histories. We computed average nitrate exposure over a 20-year period. A food frequency questionnaire was used to assess dietary nitrate and nitrite. RESULTS: Increasing quartiles of the average nitrate level in drinking water were not significantly associated with risk (adjusted odd ratios: 1.4, 1.2, 1.3). Risk was similar among those with both higher and lower intakes of vitamin C, an inhibitor of N-nitroso compound formation. Dietary nitrite intake was not associated with risk. CONCLUSIONS: Our study does not support a role for drinking water and dietary sources of nitrate and nitrite in risk of adult glioma.

Aged↗
PubMed2002

Lack of a dose-response relationship for carcinogenicity in the rat liver with low doses of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline or N-nitrosodiethylamine.

For a long period, it has been generally considered that carcinogens, particularly genotoxic ones, have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged with regard to assessment of cancer risk to humans. Here we show that a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, forms DNA adducts at low doses, but does not induce glutathione S-transferase placental form (GST-P)-positive foci (considered to be preneoplastic lesions) or 8-hydroxy-2'-deoxyguanosine in rat liver. Moreover a N-nitroso compound, N-nitrosodiethylamine, at low doses was also found not to induce GST-P-positive foci in rat liver. These results imply that there is a no-observed effect level for hepatocarcinogenesis by these genotoxic carcinogens.

Animals↗
PubMed1990

Mechanism of stimulation of cyclic-GMP level in a neuronal cell line mediated by serotonin (5-HT3) receptors. Involvement of nitric oxide, arachidonic-acid metabolism and cytosolic Ca2+.

The mechanism by which serotonin (5-HT3) receptors mediate a rise in cyclic-GMP level was investigated in a neuronal cell line. Inhibitors of phospholipase A2 (mepacrine) and of lipoxygenase (eicosatetraynoic acid or nordihydroguaiaretic acid) suppressed the action of serotonin. On the other hand, inhibition by hemoglobin indicates a role for nitric oxide which could be in part responsible for the cyclic-GMP effect as an intercellular stimulant. The suppression of the serotonin effect by the arginine analogues N omega-methyl-L-arginine and canavanine is consistent with the notion that nitric oxide could be released from arginine. The serotonin-induced rise of cyclic-GMP level depends on the presence of extracellular Ca2+ with half-maximal stimulation at 0.3 mM Ca2+. The serotonin-stimulated rise of cyclic GMP was inhibited by (a) addition of inorganic blockers of Ca2(+)-permeable channels (La3+, half-maximal inhibitory concentration (IC50) 0.04 mM; Mn2+, IC50, 0.4 mM; Co2+, IC50, 0.9 mM; Ni2+, IC50, 1.2 mM) and (b) of organic blockers (diltiazem: IC50, 6 microM, methoxyverapamil: IC50, 3 microM and (c) intracellular application of the Ca2+ chelator bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (IC50, 2 microM). Thus, two pathways for the activation of soluble guanylate cyclase by serotonin are possible: (a) via lipoxygenase products of arachidonic acid and/or (b) via nitric oxide or a related nitroso compound. Serotonin mediates a rise of cytosolic Ca2+ activity due to entry of extracellular Ca2+. It still has to be investigated which step depends on a rise of cytosolic Ca2+ activity that appears to be a prerequisite for activation of guanylate cyclase.

Animals↗
PubMed1991

The role of the L-arginine-nitric oxide pathway in relaxation of the opossum lower oesophageal sphincter.

1. The role of the L-arginine-nitric oxide pathway in lower oesophageal sphincter (LOS) relaxation and oesophageal peristalsis was investigated. 2. Twenty four adult opossums were anaesthetized and the right vagus nerve was isolated in the neck and sectioned. Electrical stimulation, applied to the peripheral end of the nerve, resulted in a frequency-dependent relaxation of the LOS, and peristaltic and non-peristaltic contractions in the oesophageal body. 3. N omega-nitro-L-arginine (L-NNA, 10(-8)-10(-5) mol kg-1), an inhibitor of the L-arginine-nitric oxide pathway, inhibited LOS relaxation in a dose-dependent manner, but did not affect resting LOS pressure. At the highest dose of L-NNA no relaxation of the LOS was elicited in response to vagal stimulation. The effect of L-NNA, (10(-5) mol kg-1) was fully reversed by infusion of 10(-4) mol kg-1 L-arginine. Peristaltic velocity and amplitude of contractions in the oesophageal body were unaffected by L-NNA. 4. Infusion of sodium nitroprusside reduced LOS pressure to zero, and the drug was equally potent in control animals (-log ED50:8.1 +/- 0.2 mol kg-1) and in animals pretreated with L-NNA (-log ED50:8.2 +/- 0.3 mol kg-1). This suggests that the effect of L-NNA was not directly on guanylate cyclase. 5. A significant elevation of blood pressure was recorded after administration of L-NNA (10(-5) mol kg-1). 6. It is suggested that the L-arginine-nitric oxide pathway plays an important functional role for relaxation of the LOS, but not for oesophageal peristalsis. Whether the active substance is nitric oxide or a related nitroso-compound remains to be settled.

Animals↗
PubMed1986

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.

Animals↗
PubMed1995

An experimental study of gastric stump carcinoma in Wistar rats.

The risk of gastric stump carcinoma is increased 15-20 years after gastric resection for benign disease. Reflux of duodenal juice, bacterial overgrowth and formation of N-nitroso compounds are possible etiological factors. There is a geographical variation in the incidence of gastric cancer, possibly explained by differences in food intake. Experimentally it is possible to induce gastric stump carcinoma in rats without the addition of exogenous carcinogens. The aim of this study was: 1) to find the incidence of gastric carcinoma in rats subjected to BII resection and followed for 10 months, and 2) to examine if acetic acid, a common dietary factor, could influence the development of gastric carcinoma. Amongst BII-operated male Wistar rats, infiltrating carcinoma was found in 5/20 on a normal diet and in 5/24 exposed to acetic acid (NS). Benign mucosal changes were seen in 12/20 and 16/24 respectively (NS). With the exception of a profound inflammation in one sham-operated animal, no mucosal pathological changes were found in 24 sham-operated and 24 control animals where no operation was performed.

Acetates↗
PubMed1993

Intragastric nitrosation of nicotine is not a significant contributor to nitrosamine exposure.

To determine the potential for intragastric nicotine nitrosation, we carried out a kinetic study of the reaction of nicotine with nitrous acid in aqueous solution. The reaction of nicotine with nitrous acid resulted in the formation of three products, NNA, NNN, and NNK. The three parallel reactions were first order of 10-6 L/mol/s. The optimum pH range for formation of NNA, NNN, and NNK was 2.4 to 3.1. Thiocyanate (100 mM) slightly increased the rate of formation of NNN and NNK but tripled the rate of formation of NNA at pH 3.5 at 37 degrees C. We have also studied the nitrosation of pseudooxynicotine, a bacterial and fungal metabolite of nicotine. This secondary amine nitrosated rapidly to produce NNK. Our proposed mechanism for the conversion of nicotine to NNK includes nine kinetically distinct steps and is in agreement with our experimental results. The rate limiting step involves the formation of nicotine-1',2'-iminium ion. This ion hydrolyzes to form pseudooxynicotine which undergoes rapid, irreversible nitrosation to NNK. Given the very slow rate of nicotine nitrosation, it is unlikely that nicotine itself contributes to exposure to nitroso compounds due to chemically mediated intragastric nitrosation.

Butanones↗
PubMed1976

The microsomal N-oxidation of phentermine.

The microsomal N-oxidation of phentermine (Ia) to N-hydroxyphentermine (Ib) and to alpha,alpha-dimethyl-alpha-nitroso-beta-phenylethane (Ic was investigated. Maximum activities were obtained with microsomal (9000 g supernatant and microsomes) fractions of rabbit liver in the presence of an NADPH generating system. Incubation of Ia with hepatic washed microsomes from a phenobarbitone pretreated rabbit increased the formation of Ib and decreased that of Ic but the total amount of N-oxidized metabolites (i.e. Ib + Ic) was not affected. The ratio of the metabolically produced Ic to Ib but not the total amount of N-oxygenated metabolites varied greatly depending of the liver microsomal fractions used in the incubation mixtures of Ia; more Ib was produced from Ia using 9000 g supernatant and conversely, more Ic was formed using the washed microsomes of the same liver. The nitroso compound (Ic) was metabolically reduced to Ib and Ib to Ia by the hepatic 9000 g supernatant and soluble fraction; under the same conditions, washed microsomes had only limited reductive properties towards Ic and Ib. N-Hydroxyphentermine (Ib) was not metabolically oxidized to Ic when incubated with washed microsomes from rabbit liver. The use of known carbon-oxidation inhibitors showed that cytochrome P-450 is not involved in the incorporation of oxygen at the nitrogen centre of Ia. The metabolic characteristics and kinetic behavior of the microsomal N-oxidation of Ia supported a recently proposed mechanism explaining the independent formation of Ib and Ic from a common precursor resulting from metabolic N-oxidation of Ia.

Animals↗
PubMed1973

N-nitrosation by nitrite ion in neutral and basic medium.

Formaldehyde catalyzed the conversion of various secondary amines to nitrosamines in the pH range 6.4 to 11.0. Chloral was also an effective catalyst. The reaction proceeds easily enough to have potential synthetic applications; the proposed mechanism could explain some reported anomalies regarding the synthesis of carcinogenic N-nitroso compounds in vivo and in vitro.

Amines↗