Detection of aflatoxins and related metabolites by radioimmunoassay.

Rabbit (outbred albino New Zealand White) antisera have been raised against aflatoxin B1 (AFB1) using as immunogen conjugates in which the hapten was coupled to bovine serum albumin (BSA) either through C1 or C8 with the oxime and the dichloride derivatives of AFB1 as intermediates. Radioimmunoassay (RIA), with [3H]AFB1 as tracer, showed that the antiserum prepared with the conjugate in which BSA was coupled to the AFB1 oxime derivative was highly specific to AFB1, whereas the antiserum raised against the conjugate in which BSA was coupled to AFB1 through the AFB1Cl2 derivative (C-antiserum) cross-reacted to a large extent with other aflatoxins, including aflatoxin M1, an important urinary metabolite of AFB1 in several species including humans. AFB1-related metabolites in the urine of inbred BD IV adult male rats given AFB1 orally at doses from 600 pmol to 385 nmol can easily be followed over 9 days by RIA in which the "cross-reactive" C-antiserum is used. This suggests that similar methodologies could be used for the monitoring of human exposure to AFB1.

Carcinogen hemoglobin adducts, urinary mutagenicity, and metabolic phenotype in active and passive cigarette smokers.

In 100 healthy volunteers, we have studied the relationship between the type (air- or flue-cured) and number of cigarettes smoked and different biomarkers relevant to the risk of bladder cancer, including the levels of 4-aminobiphenyl (ABP) hemoglobin adduct (a marker of internal dose), urinary mutagenicity in Salmonella typhimurium TA98, and the N-acetylation phenotype (a marker of susceptibility). ABP is a potent bladder carcinogen that is N-acetylated as an overall detoxification step. Levels of the ABP hemoglobin adduct were higher in smokers of black tobacco (air-cured) than in smokers of blond tobacco (flue-cured), confirming our earlier study. In addition, "slow" acetylators had higher levels of the ABP hemoglobin adduct for the same type and quantity of cigarettes smoked. Urinary mutagenicity was also associated with quantity of cigarettes but not with the acetylation phenotype. Convex dose-response relationships were found between the amount smoked and ABP hemoglobin adduct levels or urinary mutagenicity. In 15 nonsmokers who reported exposure to environmental tobacco smoke, ABP hemoglobin adduct levels, unlike urinary mutagenicity, were found to be an aspecific exposure indicator.

In vitro metabolism and microsome-mediated mutagenicity of dialkylnitrosamines in rat, hamster, and mouse tissues.

Rates of conversion of 14C-labeled dimethyl-and diethylnitrosamine by rat and hamster tissue slices to 14CO2 and/or into mutagenic reactants were measured using Salmonella typhimurium G-46 r TA 1530 and fortified tissue fractions in vitro. A correlation between the CO2 production from dimethyl- or diethylnitrosamine in liver or lung and the organ distribution of induced tumors in vivo was observed. As an exception, hamster lung, which is a major target organ in diethylnitrosamine carcinogenesis, did not convert this nitrosamine into metabolites mutagenic for S. typhimurium TA 1530 although the 14CO2 production in vitro was even higher than in hamster liver. The effect of pretreating rats, hamsters, and mice with phenobarbitone on the mutation frequency produced by dimethyl-or diethylnitrosamine in in vitro assays was determined. The relationship between the site of metabolic activation, mutagenicity, and carcinogenicity of the dialkylnitrosamines and the effect of enzyme inducers are discussed.

Mutagenicity studies in Salmonella typhimurium on some carcinogenic N-nitramines in vitro and in the host-mediated assay in rats.

N-Nitrodimethylamine, N-nitrodiethylamine, N-nitromorpholine and their N-nitroso analogs, N-nitrosodimethylamine, N-nitrosodiethylamine, and N-nitrosomorpholine, were tested in Salmonella typhimurium strains TA100 and TA1530. The mutagenicity of all compounds, except N-nitrodiethylamine, was demonstrated in liquid incubation assays in at least one of the tester strains; it required the presence of a postmitochondrial supernatant from the liver of Aroclor-treated rats, reduced nicotinamide adenine dinucleotide phosphate-generating system, and oxygen. When compared on a molar basis with their N-nitroso analogs, N-nitromorpholine was about 10 times less mutagenic and N-nitrodimethylamine about 70 times less mutagenic. Addition of disulfiram to the assays at a final concentration of 0.1 mM efficiently inhibited mutagenesis by all nitro and nitroso compounds; ascorbic acid at a 7.4 mM concentration produced less inhibition. Mutagenic activity of the three nitramines was also determined in the host-mediated assay in rats. After p.o. administration of each of the N-nitramines, cells of S. typhimurium strains TA1530 and TA100 that had been injected i.p. were isolated from the peritoneal liquid after 1, 3, and 6 hr. All three nitramines were found to be mutagenic for strain TA1530 but not for TA100. Mutation frequencies (number of histidine revertants per 10(6) surviving cells) were in the descending order N-nitromorpholine greater than N-nitrodiemethylamine greater than N-nitrodiethylamine. After a p.o. dose of N-nitrodiethylamine to rats, bacteria were also isolated from liver, lungs, and kidneys. Mutation frequency was highest in bacteria recovered from the liver but was not increased in those obtained from lungs and kidneys. The data suggest that carcinogenic nitramines exert their mutagenic effects through the formation of alkylating intermediates.

Mutagenic and alkylating activities of 3-methyl-1-phenyltriazenes and their possible role as carcinogenic metabolites of the parent dimethyl compounds.

3-Methyl-1-phenyltriazene and a series of ring-substituted derivatives (4-methylphenyl, 4-chlorophenyl, and 2,4,6-trichlorophenyl), structurally related benzenediazonium fluoborates and phenyl azides, as well as the recently isolated [1-methyl-3-(2,4,6-trichlorophenyl)-2-triazeno]methyl-beta-D-glucopyranoside uronic acid, were studied for their mutagenic activity in Salmonella typhimurium strains. Of these compounds, the 3-methyl-1-phenyltriazene derivatives and 2,4,6-trichlorobenzenediazonium fluoborate were found to be direct-acting mutagens; the glucuronide was active in strain TA 1530 only after deconjugation with beta-glucuronidase. The half-lives of the monomethylphenyltriazenes in vitro were determined and compared with their methylating activity towards 4-(4-nitrobenzyl)pyridine and their mutagenicity. The results are discussed in relation to the possible mechanism of action of the N,N-dimethylphenyltriazenes and their monomethyl derivatives as mutagens and organ-specific carcinogens.

Carcinogenicity of chloroethylene oxide, an ultimate reactive metabolite of vinyl chloride, and bis(chloromethyl)ether after subcutaneous administration and in initiation-promotion experiments in mice.

Repeated s.c. administration of chloroethylene oxide, a reactive metabolite of the carcinogen vinyl chloride, induced local tumors in mice, with an incidence comparable to that of bis(chloromethyl)ether, a structurally related human and animal carcinogen, when both compounds were applied at maximum tolerated chronically toxic doses; no tumors distant from the injection site were produced. Bis(chloromethyl)ether, chloroethylene oxide, and its rearrangement product chloroacetaldehyde, a highly toxic compound, were further tested in an initiation-promotion experiment. Application to the skin of a single dose of either bis(chloromethyl)ether or chloroethylene oxide, followed by 3-times-weekly applications of 12-O-n-tetradecanoylphorbol-13-acetate for 42 weeks, produced skin tumors in mice; chloroacetaldehyde under comparable conditions produced no increase in benign or malignant tumors. A good correlation between the chemical reactivity, on the basis of hydrolysis constants in aqueous media, and the carcinogenicity of the three compounds was noted. Our results support the hypothesis that epoxidation of the thylenic double bond in vinyl chloride yields an ultimate carcinogenic metabolite, chloroethylene oxide, a highly reactive compound which appears also to be largely responsible for the known genetic changes caused by the parent compound.

Comparative electrophilicity, mutagenicity, DNA repair induction activity, and carcinogenicity of some N- and O-acyl derivatives of N-hydroxy-2-aminoflourene.

N-Myristoyloxy-N-acetyl-2-aminofluorene, N-acetoxy-N-myristoyl-2-aminofluorene, N-myristoyloxy-N-myristoyl-2-aminofluorene, and N-hydroxy-N-myristoyl-2-aminofluorene each yielded a high incidence of sarcomas in male rats within 5 to 7 months after s.c. injection of 64 micronmoles in divided doses. N-Acetoxy-N-acetyl-2-aminofluorene and N-hydroxy-2-acetylaminofluorene, although potent carcinogens at the s.c. site, were less active than the above derivatives with a myristoyl substituent. N-Sulfonoxy-N-acety--2-aminofluorene (purity larger than or equal to 70%) had little or no carcinogenic activity when administered in large amounts by s.c. injection to rats. The low incidence of tumors could have resulted from N-hydroxy-2-acetylaminofluorene or other decompostion products of the N-sulfonozy derivative. Each of the N-acetoxy and N-myristoyloxy derivatives of N-acetyl-2-aminofluorene and of N-myristoyl-2-aminofluorene showed electrophilic activity toward methionine; N-acetoxy-N-acetyl-2-aminofluorene was the most reactive and N-myristoyloxy-N-myristoyl-2-aminofluorine was the least reactive. Each of these esters also induced unscheduled tritiated thymidine incorportation in nondividing cultured human fibroblasts and thus appeared to induce lesions in DNA that lead to repair synthesis. EACH OF THE N-acetoxy derivatives was highly mutagenic for Salmonella typhimurium strains TA98 and TA1538 without tissue activation; neither N-myristoyloxy derivative was mutagenic under these conditions. While there was a qualitative correspondence between several of the above activities of these 2-aminofluorene derivatives, the quantitative differences and the lack of detectable mutagenicity of the 2N-myristoyloxy derivatives for S. typhimurium indicate the need for multiple short-term tests in the qualitative prediction of potential carcinogenic activity.

Monoclonal antibody-directed analysis of cytochrome P-450-dependent monooxygenases and mutagen activation in the livers of DBA/2 and C57BL/6 mice.

Monoclonal antibodies (MAb 1-7-1 and Mab 2-66-3) specific for cytochrome P-450 (cyt. P-450) isozymes inhibited the metabolism of carcinogens, other xenobiotics, and endogenous compounds in two strains of mice. Postmitochondrial liver supernatant (S9) was prepared from untreated, 3-methylcholanthrene-treated, phenobarbital-treated, and pregnenolone 16 alpha-carbonitrile-treated C57BL/6 (B6) and DBA/2 (D2) mice. The modifying effect of two types of MAb to a 3-methylcholanthrene-induced cyt. P-450 and a phenobarbital-induced cyt. P-450 was investigated for: (a) S9-mediated mutagenicity of aflatoxin B1, benzo(a)pyrene 7,8-dihydrodiol, 2-acetylaminofluorene, and N-nitrosomorpholine in Salmonella typhimurium strains; and (b) the activity of aryl hydrocarbon hydroxylase, ethoxycoumarin O-deethylase, ethoxyresorufin O-deethylase, aminopyrine N-demethylase, and testosterone 6 beta-, 7 alpha-, and 16 beta-hydroxylases. With certain S9s, MAb-1-7-1 inhibited only those cytochrome P-450 isozymes involved predominantly in activity of aryl hydrocarbon hydroxylase, ethoxyresorufin O-deethylase, and ethoxycoumarin O-deethylase and mutagenicity of 2-acetylaminofluorene and benzo(a)pyrene 7,8-dihydrodiol; MAb 2-66-3 inhibited only those involved in aminopyrine N-demethylase and testosterone 6 beta-, 7 alpha, and 16 beta-hydroxylase activity and aflatoxin B1 mutagenicity. Both Mab 1-7-1 and MAb 2-66-3 inhibited cytochrome P-450 isozyme(s) implicated predominantly in testosterone 7 alpha-hydroxylation in S9 from pregnenolone 16 alpha-carbonitrile-treated B6 mice. MAb 1-7-1 did not inhibit N-nitrosomorpholine mutagenicity and MAb 2-66-3 increased it by 2- to 6-fold depending on the source of S9. Using these MAbs, it is thus possible to identify the contribution of the epitope-defined single or class of cyt. P-450 to specific metabolic reactions in S9 from untreated and inducer-treated mice.

Methodology of laboratory measurements in prospective studies on gene-environment interactions: the experience of GenAir.

Several large prospective investigations are under way or are planned in different parts of the world, aiming at the investigation of gene-environment interactions for chronic diseases. Technical, practical and ethical issues are raised by such large investigations. Here we describe how such issues were approached within a case-control study nested in EPIC, a large European cohort, and the kind of validation studies that have been set up. The GenAir investigation aimed at measuring the effects of air pollution and environmental tobacco smoke on human health in EPIC with a nested design and with biological measures. Validation studies included (a) comparisons between cotinine measurements, hemoglobin adducts and questionnaire data; (b) an analysis of the determinants of DNA adduct concentration; (c) comparison among different genotyping methods; (d) an analysis of the determinants of plasma DNA amounts. We also describe how the ethical issues were dealt with in our investigation.

Metabolic polymorphism affecting DNA binding and excretion of carcinogens in humans.

A case-control study on lung cancer patients demonstrated the pronounced effect of tobacco smoke on pulmonary carcinogen metabolism and suggested the existence of a metabolic phenotype at higher risk for tobacco-associated lung cancer. Lung cancer patients who were recent smokers showed in their lungs (i) significantly induced CYP1A1-related enzyme activity vs smoking non-lung cancer patients; (ii) increased benzo(a)pyrene (BP) tetrol formation from BP 7,8-diol by lung microsomes; and (iii) high levels of cytochrome P4501a1 by immunohistochemical staining. Levels of bulky aromatic DNA adducts (by 32P-postlabelling) and of BP-diol-epoxide (BPDE) adducts (by HPC/fluorometry) were quantified in lung parenchyma. Aryl hydrocarbon hydroxylase activity and the level of BPDE-DNA adducts (r = 0.91; p < 0.001) and to a lesser degree bulky DNA adducts were correlated. Thus pulmonary CYP1A1 expression (inducibility) controls in part polycyclic aromatic hydrocarbon-DNA adduct formation in tobacco smokers and, therefore, appears to be associated with lung cancer risk. High risk subjects for lung cancer among smokers may be identifiable through genotyping for polymorphic drug metabolizing enzymes in combination with molecular dosimetry of carcinogen-DNA adducts and mutation analysis in target (surrogate) cells. Such studies in a Finnish cohort of lung cancer patients and controls are in progress. Interim results of the effect of metabolic polymorphism on the level of PAH-DNA adducts and on the excretion of mutagens in urine are summarized.

Carcinogenic nitrosamines: free radical aspects of their action.

NDMA and other nitrosamines may be activated into DNA binding intermediates by a cytochrome P450-dependent formation of alpha-nitrosamino radicals or photochemically. Within the catalytic site of cytochrome P450, these radical intermediates either combine with HO. to form alpha-hydroxynitrosamines or decompose into nitric oxide and N-methylformaldimine. In the presence of phosphate, nutagenic alpha-phosphonooxy derivatives are formed from radicals generated chemically/photochemically. Studies on lipid peroxidation, in vivo and in vitro, have further suggested that radicals are formed as intermediates from N-nitrosodialkylamines. The level of nitrosamine-induced lipid peroxidation parallels hepatocarcinogenicity in rats. These data, although preliminary, provide further evidence that free radical damage and DNA alkylation are involved in carcinogenesis induced by nitrosamines.

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)

Detection of carcinogen-DNA adducts in exfoliated urothelial cells of cigarette smokers: association with smoking, hemoglobin adducts, and urinary mutagenicity.

The presence of covalent modifications in DNA obtained from exfoliated urothelial cells of smokers and nonsmokers was determined using 32P postlabeling methods. Urine and blood samples were procured from 73 persons. Cells were removed from the urine by filtration. DNA was isolated using an enzyme-solvent extraction method and then coprecipitated with glycogen. Sufficient DNA to detect 1 carcinogen-DNA adduct/10(9) normal nucleotides was obtained from 40 of the 73 samples. DNA was hydrolyzed to 3'-phosphodeoxynucleotides and then 32P postlabeled under conditions of excess [32P]ATP. Carcinogen-DNA adducts were resolved using anion-exchange thin-layer chromatography and visualized by autoradiography; film exposures lasted as long as 7 days. Twelve different carcinogen-DNA adducts and a diagonal zone of radioactivity could be found, but no sample contained all adducts. At least four adducts appeared to be cigarette smoking related. These adducts were from 2 to 20 times higher in the smokers than the nonsmokers. Two carcinogen-DNA adducts were qualitatively very similar to adducts described earlier in a study of human bladder biopsies. One of these corresponded to N-(deoxyguanosin-8-yl)-4-aminobiphenyl. Adducts were correlated significantly with the levels of 4-aminobiphenyl hemoglobin adducts and number of cigarettes smoked. In addition, levels of the putative N-(deoxyguanosin-8-yl)-4-aminobiphenyl adduct and a measure of total adducts were correlated with the mutagenic activity of the individual's urine. These data suggest that noninvasive, biological monitoring techniques can be applied to the study of carcinogen-DNA adducts in humans at high risk for bladder cancer.

White blood cell DNA adducts, smoking, and NAT2 and GSTM1 genotypes in bladder cancer: a case-control study.

We conducted a case-control study on 114 bladder cancer patients and 46 hospital controls. DNA adducts were measured in WBCs by 32P postlabeling and showed no association with smoking habits and the glutathione-S-transferase M1 genotype. A strong association between adduct levels and the N-acetyltransferase (NAT2) genotype was found (P = 0.0002). The NAT2 genotype was associated in a nonstatistically significant way to the case-control status (odds ratio, 1.6; 95% confidence interval, 0.8-3.2). In a logistic regression model, the log of DNA adduct levels was associated in a highly significant way to the risk of bladder cancer (regression coefficient, 0.75; P = 0.0006), independently of smoking habits. Using the median of DNA adducts (RAL, 0.3) as a cutoff point, the odds ratio for the risk of bladder cancer was 4.1 (age-adjusted; 95% confidence interval, 1.9-9.0). Our study suggests that sources other than tobacco smoke contribute to the formation of aromatic DNA adducts in WBCs. The role of WBC-DNA adducts in predicting bladder cancer is still to be clarified.

Cytochrome P4501A2: enzyme induction and genetic control in determining 4-aminobiphenyl-hemoglobin adduct levels.

Cytochrome P4501A2 (CYP1A2) activity may be related to bladder cancer risk through metabolic activation of aromatic amines, such as 4-aminobiphenyl (ABP), to reactive intermediates that can form DNA and hemoglobin (Hb) adducts. In the context of a study on smoking and bladder cancer risk, 97 healthy male volunteers were investigated. CYP1A2-dependent N-oxidation activity was measured using a molar ratio of urinary caffeine metabolites [(paraxanthine + 1,7-dimethyluric acid)/caffeine] obtained between the fourth and fifth h after drinking a standardized cup of coffee. N-Oxidation activity was induced by blond tobacco smoke, meat consumption the dinner before the test, or more than four cups of coffee a day. The regular use of medication appeared associated with a decrease in N-oxidation levels. Age and alcohol consumption were not related with CYP1A2 activity. A polymorphic distribution of the CYP1A2 and N-acetyltransferase-2 (determined by the caffeine metabolite ratio 5-acetylamino-6-formylamino-3-methyluracil:1-methylxanthine) phenotypes was examined in relation to susceptibility to ABP-Hb adduct formation. Rapid oxidizers and subjects with the combined slow acetylator-rapid oxidizer phenotype showed the highest ABP-Hb adduct levels at a low smoking dose. Blond tobacco smokers exhibited higher adduct levels compared with black tobacco smokers, after adjustment for the quantity of cigarettes smoked. At the highest levels of smoking exposure, no major difference in ABP-Hb adduct levels was found among the different combinations of CYP1A2 and N-acetyltransferase-2 phenotypes. In a subset of only 45 available samples, no association was seen between the ABP-Hb adduct levels and the glutathione S-transferase M1 genotype.

Black (air-cured) and blond (flue-cured) tobacco cancer risk. IV: Molecular dosimetry studies implicate aromatic amines as bladder carcinogens.

Tobacco smoking causes a major fraction of male urinary bladder cancers and the relative risk of bladder cancer is reported to be two to three times higher for smoking of black (air-cured) than for smoking of blond (flue-cured) tobacco. In molecular dosimetry studies to examine the hypothesis that aromatic amines in tobacco smoke are primarily responsible for bladder cancer, the higher bladder cancer risk in smokers of black tobacco was correlated with two to five times higher exposure to carcinogenic aromatic amines present in black tobacco smoke, notably 4-aminobiphenyl (ABP). For the same amount of smoking, black tobacco smokers had levels of ABP-haemoglobin (Hb) adducts 1.5 times higher and excreted a 1.8-fold higher level of urinary mutagens. These mutagens were characterised as aromatic amines, and included the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a known mutagen and multiorgan/species carcinogen. In smoking volunteers, the ABP-Hb adduct level depended significantly on the acetylator and P-450IA2 phenotypes, being 1.3- to 1.5-fold lower in fast acetylators, slow/intermediate P-450IA2 individuals. The N-(deoxyguanosine-8-yl)-ABP adduct was a major smoking-related DNA adduct in bladder biopsies from surgical patients. It was also tentatively identified in exfoliated urothelial cells of smoking volunteers, who showed a significant and linear correlation between adduct levels of ABP with Hb and with deoxyguanosine in urothelial DNA; both were related to number of cigarettes smoked per day. Levels of several smoking-related DNA adducts in urothelial cells were 2-20 times elevated in smokers. Similar convex dose-response relationships have been found between the number of cigarettes smoked and the relative risk for bladder cancer and between the levels of ABP-Hb adducts and markers of recent smoking. A possible explanation is that fast and slow acetylators have different susceptibility to aromatic amine carcinogens. Case-control studies have consistently revealed an excess of variable magnitude of slow acetylators in subgroups exposed occupationally to carcinogenic aromatic amines. Altogether, results from these studies reinforce the association between cigarette smoking, carcinogen-DNA adducts in urothelial cells, and implicate primary aromatic and possibly heterocyclic amines as bladder carcinogens.

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.

Preparation of aflatoxin B1-BSA conjugate with high hapten/carrier molar ratio.

We reported previously on the properties of an anti-aflatoxin B1 (AFB) antiserum raised with a conjugate in which AFB is coupled at the C8 position to bovine serum albumin (BSA). The hapten/carrier protein molar ratio of the conjugate was 14. We have since been able to optimize the coupling conditions, resulting in the preparation of another conjugate, with a molar ratio of 45. Comparison of the 2 conjugates by double-gel immunodiffusion analysis shows that little BSA 'activity' remains on the conjugate with a high molar ratio; on the other hand, its capacity to precipitate in the presence of anti-AFB antibodies is increased.

Urinary excretion of S-benzylmercapturic acid as an indicator of N-nitroso-N-methylbenzylamine exposure.

The excretion of S-benzylmercapturic acid (SBzMA) in the urine of rats treated with N-nitroso-N-methylbenzylamine (NMBzA) was determined by gas chromatography-mass spectrometry (GC-MS). The identity of SBzMA in the urine was confirmed by full scan GC-MS. The amount of urinary SBzMA varied with the dose of NMBzA (up to 5 mg/kg) and with rat strain. For the three strains investigated, most of a 2.5 mg/kg dose of SBzMA was excreted within 24 h. Comparison of the levels of this SBzMA excreted by rats treated with equivalent doses of either NMBzA or benzaldehyde indicates that urinary SBzMA is derived mainly from benzylating species resulting from the hydroxylation of the methyl group of NMBzA.

Mutagenicity and metabolism of vinyl chloride and related compounds.

The various adverse biological effects of vinyl chloride appear to be dependent upon the metabolic conversion of this compound into chemically reactive metabolites. The metabolism of vinyl chloride in mammals and in man, including the formation of monochloroacetic acid and some identified sulfur conjugates is reviewed. Hepatic microsomal mixed function oxidases from rats, mice, and humans were equally effective in transforming vinyl chloride into alkylating agents in vitro. Two of the enzyme reaction products, i.e., chloroethylene oxide and 2-chloroacetaldehyde, showed potent genetic activity in microorganisms and Chinese hamster V79 cells. The role of liver microsomal enzymes in the generation of electrophilic mutagenic vinyl chloride metabolites is discussed.