Convenient colorimetric and fluorometric assays for S-nitrosothiols

S-nitrosothiols have been shown to affect a number of physiological functions. Several techniques have been used to detect these species in biological systems, primarily by methods utilizing chemiluminescence. Since the apparatus required for measurement of chemiluminescence are not readily available in most laboratories, methods employing more conventional techniques such as uv-vis and fluorescence spectroscopy may be of greater use. Herein, we report the development of colorimetric and fluorometric methods for the reliable quantitation of S-nitrosothiols. Solutions containing sulfanilamide/N-(1-naphthyl)- ethylenediamine dihydrochloride or 2,2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid), when exposed to S-nitrosoglutathione (GSNO), S-nitrosocysteine, or S-nitrosoacteylpenicillamine, resulted in no absorbance changes in the range of 400-800 nm. Exposure to HgCl2 or Cu(acetate)2 resulted in release of nitric oxide (NO) from the S-nitrosothiols. The liberated NO reacted subsequently with oxygen and formed a chemical species which reacted with either analysis solution, resulting in an increase in absorption between 400 and 800 nm. A plot of RSNO versus absorbance was linear for both mercury(II) and copper(II) ions where the slope in the presence of mercury ion was significantly greater than that for copper ion. The sensitivity was as low as 5 microM RSNO using HgCl2. The fluorometric method using 2, 3-diaminonaphthalene as the scavenger of the NOsolidusO2 products gave a sensitivity of 50 nM for GSNO. In addition, S-nitrosylated proteins were quantitated using the fluorometric technique. These methods provide accurate determination of low concentrations of S-nitrosothiols, utilizing conventional spectroscopic techniques available in most laboratories.

Does increased endogenous formation of N-nitroso compounds in the human colon explain the association between red meat and colon cancer?

High red meat diets have been linked with risk of sporadic colorectal cancer; but their effects on mutations which occur in this cancer are unknown. G-->A transitions in K-ras occur in colorectal cancer and are characteristic of the effects of alkylating agents such as N-nitroso compounds (NOC). We studied th effect of red meat consumption on faecal NOC levels in eight male volunteers who consumed diets low or high in meat (60 or 600 g/day), as beef, lamb or pork, whilst living in a metabolic suite. Increased intake of red meat induced a significant (P<0.024) 3-fold increase from 40 + or - 7 to ab average of 113 + or - 25 microgram/day NOC, a range of exposure in faeces similar to that from tobacco-specific NOC in cigarette smoke. THe diets were isoenergetic and contained equal amounts of fat, but concentrations of heterocyclic amines were low. Faecal excretion of the promotor ammonia was significantly increased to 6.5 + or - 1.08 mmol/day. When the high red meat diets were supplemented with 20 g phytate-free wheat bran in six volunteers there was no reduction in NOC levels (mean 138 + or - 41 microgram/day NOC), but faecal weight increased. Higher starch and non-starch polysaccharide intakes reduced intraluminal cross-linking in microcapsules (r=-0.77) and reduced faecal pH (r=-0.64). In two volunteers there was no effect of 600 g white meat and fish o faecal NOC (mean low white meat diet 68 + or - 10 microgram/day, high white meat 56 + or -6 microgram/day nor on faecal nitrate, nitrite and iron. Faecal nitrite levels increased on changing from a white to red meat diet (mean high white meat diet 46 + or - 7 mg/day, high red meat diet mean 80 + or - 7 mg/day.) Increased endogenous production of NOC and precursors from increased red meat, but not white meat and fish, consumption may be relevant to the aetiology of colorectal cancer.

Nitrite, N-nitroso compounds, and other analytes in physiological fluids in relation to precancerous gastric lesions

Levels of gastric juice nitrite, several urinary N-nitroso compounds, and other analytes were examined among nearly 600 residents in an area of Shandong, China, where precancerous gastric lesions are common and rates of stomach cancer are among the world's highest. Gastric juice nitrite levels were considerably higher among those with gastric juice pH values above 2.4 versus below 2.4. Nitrite was detected more often and at higher levels among persons with later stage gastric lesions, especially when gastric pH was high. Of those with intestinal metaplasia, 17.5% had detectable levels of gastric nitrite, while this analyte was detected in only 7.2% of those with less advanced lesions. Relative to those with undetectable nitrite, the odds of intestinal metaplasia increased from 1.5 (95% confidence interval = 0.6-4.1) to 4.1 (95% confidence interval = 1.8-9.3) among those with low and high nitrite concentrations, respectively. Urinary acetaldehyde and formaldehyde levels also tended to be higher among those with more advanced pathology, particularly dysplasia. However, urinary excretion levels of total N-nitroso compounds and several nitrosamino acids differed little among those with chronic atrophic gastritis and intestinal metaplasia and dysplasia, consistent with findings from recent studies in the United Kingdom, France, and Colombia. The data from this high-risk population suggest that elevated levels of gastric nitrite, especially in a high pH environment, are associated with advanced precancerous gastric lesions, although specific N-nitroso compounds were not implicated.

Characterization of nitrosation products in cosmetics raw materials by liquid chromatography/mass spectrometry techniques

Characterization of nitrosation products in cosmetics raw material samples has been accomplished by three liquid chromatography/mass spectrometry (LC/MS) techniques. Two of the techniques involved conventional methodologies of LC/MS and LC/tandem mass spectrometry, both of which can be used to detect and identify products formed under extreme-nitrosation conditions. The third technique utilized an on-line coupling of a photolysis reactor with the LC/MS, and it may be used as a rapid and specific means of screening for the presence of known and unknown N-nitrosamines, which may be carcinogenic.

Determination of extractable, apparent total N-nitroso compounds in cured-meat products

The modification of a newly developed method for determination of apparent total N-nitroso compounds by chemical denitrosation and chemiluminescence detection of nitric oxide (thermal energy analysis) is described. The minimum level of reliable measurement was 0.1 ppm, and the repeatability of the method was 0.2 ppm, based on the response of N-nitrosoproline(NPro). Seventy-three samples of cured-meat products, including frankfurters, bacon, and ham, were examined; 50 samples contained less than 1 ppm. The largest amounts, up to 24.8 ppm, were detected in canned corned beef. This method has several advantages over other methods.

Nitrosatable amines and nitrosamide formation in natural stimulants: Cola acuminata, C. nitida and Garcinia cola

Three varieties of kola nut, Cola acuminata, C. nitida and Garcinia cola, of Nigerian origin, were analysed for their content of primary and secondary amines, and assessed for their relative methylating potential due to nitrosamide formation. Primary and secondary amines were determined as benzene sulfonamides by gas chromatography/thermal energy analysis (GC/TEA). Dimethylamine, methylamine, ethylamine and isopentylamine were detected in all kola nut varieties, while pyrrolidine, piperidine and isobutylamine were detected in one or more varieties. Estimated average total daily intake of aliphatic amines by a typical kola nut chewer varied from 260 to 1040 micrograms/day for secondary amines and from 2430 to 9710 micrograms/day for primary amines. Methylating activity of the nitrosated kola nuts, expressed as N-nitroso-N-methylurea equivalents, was also determined by GC/TEA. Methylating activity was significantly higher in kola nuts (170-490 micrograms/kg) than has ever been reported for a fresh plant product. These data suggest that the possible role of kola nut chewing in human cancer aetiology should be explored in countries where kola nuts are widely consumed as stimulants.

N-nitrosodimethylamine and 7-methylguanine DNA adducts in tissues of rats fed Chinese salted fish

Previous studies have demonstrated that rats fed Chinese salted fish developed carcinomas of the nasopharynx and nasal cavity. In the present work the contents of nitrosamines in salted fish from the city of Guangzhou, southern China, and the contents of nitrosamines and possible nitrosamine-induced DNA adducts in organs of rats fed the fish were analysed. Similar levels of N-nitrosodimethylamine (NDMA) were detected in tough and soft salted fish. The NDMA content in steamed fish was higher than in raw fish. In vitro incubation of salted fish with gastric juice significantly increased the level of NDMA. NDMA was found in liver and kidney from rats fed salted fish for 2 years, but no dose-dependence was found between salted fish treatment and NDMA content. The level of 7-methylguanine in rat liver DNA was found to be slightly higher than in DNA from nasopharynx. However, there were no significant differences in the level of 7-methylguanine in DNA samples from rats fed salted fish and rats fed standard diet.

Nitric oxide, peroxynitrite and nitroso-compounds formation by ultraviolet A (UVA) irradiated human squamous cell carcinoma: potential role of nitric oxide in cancer prognosis

Ultraviolet A (UVA) irradiated human squamous cell carcinoma (SCC-13) releases nitrogen oxides, i.e. nitric oxide (NO), peroxynitrite (ONOO-), nitrosocompounds, ammonia (NH3) and hydroxylamine (H2NOH) formed from L-arginine. Formation and/or release of these nitrogen oxides was time and concentration-dependently stimulated by UVA and decreased by N-monomethyl-L-arginine (L-NMMA), a compound that inhibits NO synthase activity. UVA irradiation of SCC-13 cells resulted in concomitant increase in soluble guanylate cyclase (sGC) which was inhibited by L-NMMA. The increased NO and ONOO- production evoked by dibutyryl cGMP and 3-isobutyl-l-methyl-xanthine (IBMX) represents an additional positive feedback mechanism that could serve to maintain NO and ONOO- release for extended periods following UVA radiation. Using an in vitro chemical model system, it was demonstrated that oxidation of NH3 to NO by hydroxyl radical (.OH) at physiological pH is chemically feasible. UVA irradiated SCC-13 cells induced a luminol-enhanced chemiluminescence signal that reaches a peak within 1 min. The modulation of this signal by ebselen is consistent with a rate-determining step corresponding to the disproportionation of a luminol-superoxide (O2-) complex. UVA irradiated SCC-13 cells promptly increased malondialdehyde (MDA) production with subsequent decrease of plasma membrane fluidity. Desferrioxamine tested in UVA irradiated SCC-13 cells showed a concentration dependent decrease in MDA production with subsequent restoration of the membrane fluidity to the normal level. Furthermore, it was shown that squamous cell carcinoma possesses higher NO synthase and sGC activity as compared to normal keratinocytes. Such an increase in NO production may be directly related to the poor prognosis of squamous cell carcinoma.

N-nitroso compounds in two nitrosated food products in southwest Korea

Gastric cancer is the commonest malignant neoplasm in Southwest Korea. The possibility of carcinogenic dietary factors led to the investigation of exposure to N-nitroso compound precursors among residents of the City of Chonju and of two outlying rural townships in North Cholla Province. Two traditional and widely consumed home-prepared food products, salted pickled cabbage (kimchi) and salted seafood sauce (chut-kal) were analysed (a) for nitrite, nitrate, total secondary amines and pH in these food products prior to nitrite incubation and (b) for volatile nitrosamines and total N-nitroso compounds before and after incubation with nitrite in simulated human stomach conditions. Nitrate levels were significantly higher in kimchi (median 1550 mg/kg) than in chut-kal (median 140 mg/kg) (P < 0.001). Secondary amine levels in non-nitrosated samples of kimchi (median 5.5 mg/kg) were significantly lower than secondary amine levels in non-nitrosated chut-kal (median 56 mg/kg) (P = < 0.001). Analyses of nitrite-incubated kimchi revealed high levels of total N-nitroso compounds (median 1173 micrograms/kg); the increase with nitrosation was significant (P = 0.001). The concentration of N-nitroso compounds in nitrite-incubated kimchi was significantly greater than that found in nitrite-incubated chut-kal (P = 0.015). The combination of high levels of nitrate in the kimchi, the demonstration of high levels of total N-nitroso compounds in this food after nitrosation, and the volume of kimchi consumed in the traditional diet suggest that salted pickled cabbage may play a role in gastric carcinogenesis in Southwest Korea.

Scavenging effects of hemoglobin and related heme containing compounds on nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke. A new method for protection against the dangerous cigarette constituents

The present study refers to the utilization of hemoglobin and related heme containing substances in scavenging noxious compounds contained in the gas phase of cigarette smoke (e.g. nitric oxide (NO), nitrogen oxides (NOx), hydrogen peroxide (H2O2), carbon monoxide (CO), aldehydes, trace elements and carcinogenic nitrosocompounds) which were up to today insufficiently retained by conventional cigarette filters. Hemoglobin impregnated conventional cigarette filters were capable of withholding the above noxious components of the cigarette smoke up to 90%. Similar results were also obtained when solid hemoglobin was sandwiched between two common filters so that all cigarette smoke drawn through the filter comes into contact with the active groups of the hemoglobin molecules (Fe3+, Fe2+, -SH, -NH2). The present study also shows that noxious oxidants contained in cigarette smoke can be retained and neutralized by appropriate scavengers like: a) substances which contain stereospecifically bound iron, b) substances which contain porphyrin ring with iron (e.g. protoporphyrin), c) substances which contain porphyrin ring that does not necessarily contain iron, d) substances which contain porphyrin ring complexed with other metals (e.g. Cu2+, Mg2+). We have also demonstrated that rat alveolar macrophages challenged by cigarette smoke release both superoxide (O2-) and NO the interaction of which resulted in the formation of peroxynitrite (ONOO-). Alveolar macrophages continue to release NO/ONOO- for 30 min following two or three puffs of smoke. Similar results were also obtained in experiments with human volunteers. It was shown that during cigarette smoking the ratio of NO/ONOO- in the inhaled smoke was 1:0.5 while in the exhaled smoke was 1:9, due to secondary redox reactions taking place in the lung resulting in the ONOO- formation. When smokers inhaled cigarette smoke passed through a conventional filter containing hemoglobin, a 70% reduction of both NO and ONOO- in their exhaled cigarette smoke was observed. All findings prove conclusively that, alveolar macrophages exposed to cigarette smoke evoke a dramatic increase of NO, NOx, ONOO- and H2O2 inside the lung. These substances stimulate by a positive feed back mechanism the alveolar macrophages and perhaps even endothelium of the alveolar vessels, to produce more oxidants resulting in lung damage.

N-nitroso compounds, nitrite and pH in human fasting gastric juice

Total N-nitroso compounds, ethyl acetate-extractable N-nitroso compounds and nitrite were measured in 146 samples of fasting gastric juice to investigate their relationship with pH. A positive correlation was found between pH and extractable N-nitroso compounds (r = 0.206, P < 0.02), whereas total N-nitroso compounds were pH-independent. It was inferred that pre-cancerous conditions associated with high gastric pH may be produced by an increase in the extractable N-nitroso compounds, which constitute only a small fraction of the total gastric N-nitroso compounds.

Spectrofluorometric method for NO determination

A spectroscopic method for the quantitative determination of NO in aqueous solution is presented. The method is based on the uv absorbance of nitrosothiols, coupled with the inner filter effect. A threshold of 5.10(-7) M with a wide dynamic range of 5.10(-7)-10(-4) M are obtained. This method enables measurements in brain homogenates. Ultimately, since this method is immune to electrical perturbances, it will be applied at the tip of an optical fiber for in situ monitoring of NO or glutathione in brain and blood vessels.

N-nitroso compounds in fresh gastric juice and their relation to intragastric pH and nitrite employing an improved analytical method

In order to examine further the relationship between intragastric N-nitrosation, gastric pH and nitrite, 457 fresh, fasting gastric juice samples were analysed for total N-nitroso compounds (NOC) and nitrite concentrations using a recently described improved assay method. Nitrite in log values was linearly related to intragastric pH (r = 0.887, P < 0.01) with a regression equation log[nitrite] (mumol/l) = 0.489 x pH - 2.209. Significantly higher NOC concentrations were found at intragastric pH ranges of 1.13-2.99 (mean +/- SE: 1.45 +/- 0.17 mumol/l, P < 0.05) and 6.00-8.42 (3.57 +/- 0.33 mumol/l, P < 0.01) compared with that at pH 3.00-5.99 (1.02 +/- 0.12 mumol/l). NOC concentration was significantly related to log nitrite concentration at both the low pH range 1.13-4.99 (r = 0.169, P < 0.01) and the high pH range 5.00-8.42 (r = 0.450, P < 0.01). The results in the present study confirm that both acid-catalysed N-nitrosation and biologically-catalysed N-nitrosation occur in the human stomach. However, great variations in nitrite and NOC concentrations were observed in both low and high pH samples, indicating that, as expected, both the acid-catalysed N-nitrosation and biologically-catalysed N-nitrosation processes are markedly affected by factors other than intragastric pH and nitrite.

In vivo nitrosoproline formation and other risk factors in Costa Rican children from high- and low-risk areas for gastric cancer

The hypothesis that intragastric synthesis of N-nitroso compounds (NOC) in early life could play a role in gastric carcinogenesis was tested by applying the N-nitrosoproline (NPRO) test to about 50 children living in high- and low-risk areas for stomach cancer in Costa Rica. The median values of excretion of NPRO and the sum of three nitrosamino acids (micrograms/12 h urine) were 10-20% of those in adults from other geographical high-risk areas for stomach cancer. The urinary NPRO level after proline intake was higher in children from the high-risk area (P < 0.04) and markedly reduced after ingestion of ascorbic acid together with proline (P < 0.05). NPRO levels on the day of proline intake were highly correlated with levels of nitrate excretion (P < 0.001). Mean levels of total NOC in an aqueous (pH 2) extract of cooked beans from the high- and low-risk areas were similar. Acid-catalyzed nitrosation of the extract increased the total NOC concentration up to 1000-fold, but there was no difference between samples from the two areas. About 10% of bean extracts from both areas showed weak direct-acting genotoxicity in Escherichia coli; after acid-catalyzed nitrosation, all samples were genotoxic at similar levels. The diet of children in the low-risk area satisfied recommended levels of intake of energy and most nutrients except riboflavin and retinol equivalents. Diets from the high-risk area were deficient in energy intake and all nutrients except protein and vitamin C.(ABSTRACT TRUNCATED AT 250 WORDS)

Instability of N-nitroso compounds in gastric juice and preliminary results from analyses of fresh samples by using an improved analytical method

Using an improved method for determination of total N-nitroso compounds (NOC), we examined the stability of those compounds in fresh gastric juice samples during storage and the effects of the addition of 2% sulphamic acid on NOC concentration in 212 samples. The NOC levels in fresh samples decreased very rapidly at -20 degrees C, especially during the first 24 hours of storage (P < 0.01), and nitrite concentration also showed a decreasing trend during storage. The addition of sulphamic acid significantly reduced NOC levels from 1.97 +/- 0.21 to 1.10 +/- 0.12 mumol/l (mean +/- SE, P < 0.01), especially in samples of initially high pH. However, in some individual samples (16.5%) the NOC levels actually increased by 14.1% (P < 0.01). The results from analysis of NOC in 212 fresh samples in relation to pH demonstrated two significantly higher peaks of NOC concentrations at intragastric pH ranges 1.1 to 2.99 (P < 0.05) and 6.0 to 7.9 (P < 0.01). There was a significant relationship between nitrite level and intragastric pH (r = 0.480, P < 0.01), the nitrite concentration increasing dramatically when the pH exceeded 6.0. The present study suggest that a major proportion of the unidentified NOC formed through intragastric nitrosation is labile NOC; if the true concentration of NOC is to be determined it is therefore essential to analyse fresh gastric juice samples directly after collection and without pretreatment. It will also be necessary to characterize those labile NOC in order to study further the mechanism of endogenous N-nitrosation in man and its relation to human carcinogenesis.

Continuous monitoring of N-nitroso-L-arginine using micro carbon electrode in rat brain

Constitutive brain nitric oxide (NO) synthase is described as converting L-arginine into NO. NO is thought to be the cellular messenger released by endothelial cells, and was originally termed endothelial-derived relaxing factor (EDRF). The mechanisms of its synthesis remain unclear. Using microelectrode differential pulse voltammetry in the presence of cortical constitutive rat brain NO synthase, a peak was recorded at -1.66 V with respect to a Ag/AgCl reference electrode. This voltage peak, due to the reduction of N-nitroso-L-arginine, was increased in rat brain cortex after pharmacological stimulation with L-arginine or A-23187; whereas it was abolished following application of D-arginine, N-nitro-L-arginine or pure NO. Using laser doppler measurements, the secretion of N-nitroso-L-arginine was correlated to brain blood flow. These preliminary results suggest that N-nitroso-L-arginine is synthetized by constitutive brain NO synthase of vascular endothelial cells in rat brain cortex.

[Dinitrosyl complexes of iron with thiol-containing ligands and their reverse conversion into nitrosothiols]

Bovine serum albumin (BSA) is capable of forming dinitrosyl complexes with iron (DNIC) containing one thiol and one nonthiol ligand and yielding an EPR signal at the following values of the g-factor: g1 = 2.046; g2 = 2.03; g3 = 2.012. During interaction with L-cysteine or N-acetyl-L-cysteine the complex symmetry increased due to the substitution within DNIC of the nonthiol ligand of BSA for cysteine; such DNIC was characterized by an EPR signal with an axial-symmetrical tensor of the g-factor. At high cysteine concentrations all of the Fe(NO)-groups appeared to be transferred from BSA to cysteine to form DNIC with cysteine yielding an EPR signal with a g-factor of g perpendicular = 2.037; g parallel = 2.012. The lifetime of DNIC-BSA was about 24 hrs, whereas that of DNIC-cysteine was less than 1 min due to cysteine oxidation in the air. In 0.5 M HCl DNIC-BSA and DNIC-cysteine were reversibly converted into appropriate nitrosothiols characterized by intensive adsorption at 340-360 nm. Upon subsequent neutralization of the solution and addition of the substituent (cysteine or dithionite) these nitrosothiols were converted into DNIC. In the absence of iron cysteine and dithionite caused reductive destruction of protein and low molecular weight nitrosothiols to liberate nitrogen oxide. This property of nitrosothiols makes them distinct from those DNIC, in which cysteine acts exclusively as a scavenger of Fe(NO)-groups by shifting the equilibrium between the protein and low molecular weight DNIC towards the latter.

Method for group determination of total N-nitroso compounds and nitrite in fresh gastric juice by chemical denitrosation and thermal energy analysis

A method for the determination of total N-nitroso compounds (NOC) and nitrite in fresh human gastric juice is described, which is based on earlier methods. A freshly obtained gastric juice sample is injected directly into refluxing ethyl acetate containing glacial acetic acid, HCl and HBr to determine the total concentration (A) of nitrite, total NOC and thermo- and acid-labile thermal energy analyser (TEA)-responsive compounds (TAC). Another fresh sample of the same juice (with or without the addition of sulfamic acid) is injected directly into refluxing ethyl acetate containing glacial acetic acid and HCl for determining the TAC level (B) and the total level (C) of nitrite and TAC. The NO released from nitrite, TAC and NOC is detected by TEA acting as a chemiluminescence detector. The differences between A and C and between C and B represent the concentrations of total NOC and nitrite, respectively. The method is rapid, reproducible (relative standard deviation 1-6%) and sensitive (detection limit 1.0 pmol). The behaviour of nitrite and NOC in the analytical system was studied and relevant techniques for the direct analysis of fresh gastric juice samples and for stabilization of fresh samples have been developed.

High gastric juice ascorbic acid concentrations in members of a gastric cancer family

Gastric juice ascorbic acid, total vitamin C, nitrite and N-nitroso-compound concentrations were determined in fasting gastric juice from four second generation members of a gastric cancer family, all of whom had Helicobacter pylori-associated chronic gastritis and intestinal metaplasia. Juice pH, nitrite and N-nitroso-compound concentrations were low. Juice ascorbate levels were comparable to those found in subjects with normal histology. The findings are contrary to our previous experience with juice ascorbate in H. pylori gastritis.

Mutagens, N-nitroso compounds and their precursors in gastric juice from patients with and without precancerous lesions of the stomach

This study examined whether elevated risk of gastric cancer is associated with high levels of total N-nitroso compounds (NOC), their precursors and nitrosation-dependent genotoxins in gastric juice (GJ). An improved method for quantifying total NOC was used and genotoxicity was assayed in E. coli. Results from patients (n = 210) with or without precancerous lesions of the stomach and living in three areas with up to 8-fold variations in gastric cancer risk (U.K., France, Colombia) were compared. The level of nitrite (range < 1-472 mumol/l) was found to increase with the pH of GJ from the three countries and was dependent on country of collection. The levels of NOC (range: < or = 0.01-8.0 mumol/l) in GJ were not affected by stomach histology and country of collection. NOC levels increased linearly with nitrite concentrations, but the slope of the regression line was greater for acidic GJ (pH < or = 4). These data together suggest that chemical nitrosation contributes at least as much as other nitrosation pathways to the intragastric formation of NOC. Acid-catalysed nitrosation of GJ in vitro increased the NOC concentration (range: 7-1332 mumol/l) up to several 1000-fold but this increase was not predictive of gastric cancer risk either by country or by stomach histology. After acid-catalysed nitrosation, direct genotoxicity (SOS-inducing potency) was significantly higher in GJ with original pH > 4 and highest in samples from Colombia. The results (a) provide no support that intragastric total NOC levels are elevated in subjects with precancerous stomach lesions or living in a high risk area for stomach cancer; (b) confirm that a high nitrite level and elevated pH in GJ are strongly associated, the level of nitrite being associated with precancerous stomach conditions only in Colombia; (c) reveal the presence of precursor compounds in GJ, that after nitrosation yield direct mutagens that probably contain NOC and other substances. As their concentrations were significantly higher in achlorhydric subjects and highest in Colombian patients, these data together provide support for a role of intragastrically formed nitrite-derived direct mutagens in gastric cancer aetiology.

Colloidal gold ultraimmunocytochemical localization of DNA and RNA adducts in rat hepatocytes

The localization of DNA and RNA adducts was studied at the ultrastructural level using antibodies directed against O6-methylguanine (O6-metG) and the protein A-gold technique. Primary rat hepatocyte cultures were exposed for 2 h to 5 mM N-nitrosodimethylamine (NDMA). In NDMA-treated cells, the O6-metG-induced immunoreactive sites do not appear at random but seem to be concentrated in the nucleus, and in the cytoplasm, in areas rich in rough endoplasmic reticulum (RER) elements. Mitochondria were not significantly labelled. Untreated control preparations showed no specific immunogold labelling. After RNase digestion of ultrathin sections obtained from cells exposed to NDMA and subsequent immunogold labelling, most of the immunolabelling in the cytoplasm had disappeared, and that over the nucleus had only been slightly reduced, as compared to undigested specimens from NDMA-treated cultures. After similar digestion with DNase, a strong reduction of the labelling of the nucleus was observed, but labelling of the cytoplasm was practically unaffected by this enzymatic treatment, as compared to what was observed in undigested preparations of NDMA-treated hepatocytes. The results provide evidence of preferential formation of O6-metG at the DNA and RNA levels, in the nucleus and cytoplasm RER, respectively. Furthermore, this study demonstrates the applicability of the high-resolution protein A-gold technique for ultrastructural detection of nucleic acid adducts in NDMA-treated hepatocytes using affinity-purified anti-O6-metG polyclonal antibodies.

The metabolism of 1,3-dinitrobenzene by rat testicular subcellular fractions

The metabolism of 1,3-dinitrobenzene by rat testicular subcellular fractions (microsomes, cytosol or 9000 x g supernatant (S-9)) was studied. The effects of NADPH, oxygen, glutathione (GSH) and carbon monoxide upon the rate of metabolism were determined. Three metabolites were identified, and characterised as 3-nitrosonitrobenzene, 3-nitrophenylhydroxylamine and 3-nitroaniline by co-chromatography with authentic standards. These findings indicate the presence of an inherent enzyme system capable of facilitating nitro-reduction in the testes. The implications of these findings to the mechanism of 1,3-DNB-induced testicular toxicity are discussed.