An assay for botulinum toxin types A, B and F that requires both functional binding and catalytic activities within the neurotoxin.

AIM: To develop a novel assay technique for the botulinum neurotoxin family (BoNTs) which is dependent on both the endopeptidase and receptor-binding activities of the BoNTs and which is insensitive to antigenic variation with the toxin family. METHODS AND RESULTS: An endopeptidase activity, receptor-binding assay (EARB assay) has been developed which captures biologically active toxin from media using brain synaptosomes. After capture, the bound toxin can be incubated with its substrate, and cleavage detected using serotype-specific antibodies raised against the cleaved product of each toxin serotype. The EARB assay was assessed using a range of BoNT serotypes and subtypes. For BoNT/A, detection limits for subtypes A(1), A(2) and A(3) were 0.5, 3 and 10 MLD(50) ml(-1), respectively. The limit of detection for BoNT/B(1) was 5 MLD(50) ml(-1) and a novel antibody-based endopeptidase assay for BoNT/F detected toxin at 0.5 MLD(50) ml(-1). All these BoNTs can be captured from media containing up to 10% serum without loss of sensitivity. BoNT/A(1) could also be detected in dilutions of a lactose- containing formulation similar to that used for clinical preparations of the toxin. Different serotypes were found to possess different optimal cleavage pHs (pH 6.5 for A(1), pH 7.4 for B(1)). CONCLUSIONS: The EARB assay has been shown to be able to detect a broad range of BoNT serotypes and subtypes from various media. SIGNIFICANCE AND IMPACT OF THE STUDY: The EARB assay system described is the first convenient in vitro assay system described which is requires multiple functional biological activities with the BoNTs. The assay will have applications in instances where it is essential or desirable to distinguish biologically active from inactive neurotoxin.

Relationship between environmental tobacco smoke exposure and carcinogen-hemoglobin adduct levels in nonsmokers.

BACKGROUND: A potent bladder carcinogen for workers in the dye industry, 4-aminobiphenyl (4-ABP), is present in environmental tobacco smoke and has been shown to bond covalently with hemoglobin. PURPOSE: The goal of this study was to examine the relationship between exposure to environmental tobacco smoke and levels of 4-ABP-hemoglobin adducts in nonsmoking pregnant women and to compare adduct levels in those women with levels in smoking pregnant women. METHODS: A questionnaire on smoking and exposure to environmental tobacco smoke was administered to 15 pregnant women who smoked cigarettes and 40 who did not smoke. Exposure was quantified for 1 week with a personal diary and by air sampling with a monitor worn by each woman. The monitor collected nicotine by passive diffusion to a filter treated with sodium bisulfate, and the deposit on the filter was analyzed by gas chromatography. Aliquots of maternal blood and cord blood collected during delivery were analyzed for 4-ABP-hemoglobin adducts by gas chromatography with negative ion chemical ionization mass spectrometry. RESULTS: The mean adduct level in smokers (184 pg of 4-ABP per gram of hemoglobin) was substantially higher than that in nonsmokers (22 pg/g). This difference was statistically significant. Among nonsmokers, the levels of 4-ABP adducts increased significantly with increasing environmental tobacco smoke level (P = .009). Those in the lowest exposure category (< 0.5 micrograms/m3 weekly average nicotine) had median 4-ABP-hemoglobin adduct levels of 15 pg of 4-ABP per gram of hemoglobin, while those in the highest exposure category (> or = 2.0 micrograms/m3) had median levels of 26 pg/g. Nonsmokers in this study had a median adduct level of 20 pg/g, and smokers had a median level of 143 pg/g. CONCLUSIONS: 4-ABP-hemoglobin adduct levels in nonsmokers were 14% of the levels in smokers, which is consistent with findings of 20% in two other studies. Nonsmokers may receive a nontrivial dose of carcinogens from environmental tobacco smoke proportional to their exposure to environmental tobacco smoke. IMPLICATION: The relationship between environmental tobacco smoke exposure and 4-ABP-hemoglobin adduct levels supports epidemiologic evidence that environmental tobacco smoke is carcinogenic to passive smokers.

4-Aminobiphenyl hemoglobin adducts in fetuses exposed to the tobacco smoke carcinogen in utero.

Maternal-fetal exchange of a potent tobacco-related human carcinogen, 4-aminobiphenyl, was studied in smoking (n = 14) and nonsmoking (n = 38) pregnant women. N-Hydroxy-4-aminobiphenyl, the active metabolite of 4-aminobiphenyl, forms chemical addition products (adducts) with hemoglobin. Levels of 4-aminobiphenyl hemoglobin adducts were measured in maternal-fetal paired blood samples obtained from smoking and nonsmoking women during labor and delivery. Carcinogen-hemoglobin adducts were detected in all maternal and fetal blood samples. Levels of such adducts were significantly higher (P less than .001) in maternal and fetal blood samples from smokers: the mean 4-aminobiphenyl hemoglobin adduct level was 92 +/- 54 pg/g of hemoglobin in blood samples from fetuses of smokers, and 17 +/- 13 pg/g of hemoglobin in blood samples from fetuses of nonsmokers; the mean maternal 4-aminobiphenyl hemoglobin adduct level was 183 +/- 108 pg/g of hemoglobin in smokers, and 22 +/- 8 pg/g of hemoglobin in nonsmokers. Fetal carcinogen-adduct levels were consistently lower than maternal levels: the mean maternal to fetal ratio was 2.4 +/- 1.1 in smokers and 1.9 +/- .98 in nonsmokers. Fetal 4-aminobiphenyl hemoglobin adduct levels were strongly associated (correlation coefficient [r2] = .51, P = .002) with maternal 4-aminobiphenyl hemoglobin adduct levels when paired samples from smoking mothers were analyzed. A measure of third-trimester tobacco smoke exposure based on number of cigarettes smoked per day, amount of each cigarette smoked, and depth of inhalation was associated (r2 = .59, P = .029) with maternal 4-aminobiphenyl levels but not with fetal 4-aminobiphenyl levels. This study demonstrates that a potent tobacco-related carcinogen, 4-aminobiphenyl, or its active metabolite, N-hydroxy-4-aminobiphenyl, crosses the human placenta and binds to fetal hemoglobin in concentrations that are significantly higher in smokers than in nonsmokers.

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.

Gender- and smoking-related bladder cancer risk.

BACKGROUND: There is growing evidence that, when smoking habits are comparable, women incur a higher risk of lung cancer than men. Because smokers are also at risk for bladder cancer, we investigated possible sex differences in the susceptibility to bladder cancer among smokers. METHODS: A population-based, case--control study was conducted in Los Angeles, CA, involving 1514 case patients with bladder cancer and 1514 individually matched population control subjects. Information on tobacco use was collected through in-person interviews. Peripheral blood was collected from study participants to measure 3- and 4-aminobiphenyl (ABP)-hemoglobin adducts, a marker of arylamine exposure. Data were analyzed to determine whether the risk of bladder cancer differs between male and female smokers and whether female smokers exhibit higher levels of ABP-hemoglobin adducts than male smokers with comparable smoking habits. All statistical tests were two-sided. RESULTS: Cigarette smokers had a statistically significant 2.5-fold higher risk (95% confidence interval = 2.1 to 3.0) of bladder cancer than never smokers. Use of filtered versus nonfiltered cigarettes, low-tar versus higher tar cigarettes, or the pattern of inhalation did not modify the risk. The risk of bladder cancer in women who smoked was statistically significantly higher than that in men who smoked comparable numbers of cigarettes (P =.016 for sex-lifetime smoking interaction). Consistent with the sex difference in smoking-related bladder cancer risk, the slopes of the linear regression lines of the 3- and 4-ABP--hemoglobin adducts by cigarettes per day were statistically significantly steeper in women than in men (P values for sex differences <.001 and.006, respectively). CONCLUSION: The risk of bladder cancer may be higher in women than in men who smoked comparable amounts of cigarettes.

Acetylator phenotype, aminobiphenyl-hemoglobin adduct levels, and bladder cancer risk in white, black, and Asian men in Los Angeles, California.

BACKGROUND: There is a large body of epidemiologic and experimental data that have identified a number of arylamines as human bladder carcinogens. Metabolic activation is required to biotransform these arylamines into their carcinogenic forms, and N-hydroxylation, which is catalyzed by the hepatic cytochrome P4501A2 isoenzyme, is generally viewed as the first critical step. On the other hand, the N-acetylation reaction, catalyzed by the hepatic N-acetyltransferase enzyme, represents a detoxification pathway for such compounds. The N-acetyltransferase enzyme is coded by a single gene displaying two phenotypes, slow and rapid acetylators. In the United States, cigarette smoking is a major cause of bladder cancer in men, and carcinogenic arylamines present in cigarette smoke are believed to be responsible for inducing bladder cancer in smokers. PURPOSE: Our purpose was to test the differences in three ethnic/racial groups for the prevalence of acetylator phenotypes and to ascertain whether slow acetylators actually have higher levels of activated arylamines in comparison with rapid acetylators. METHODS: One hundred thirty-three male residents of Los Angeles County who were either white, black, or Asian (Chinese or Japanese) and over the age of 35 years were assessed for their acetylator phenotype and levels of 3- and 4-aminobiphenyl (ABP) hemoglobin adducts. Subjects were either lifetime nonsmokers (n = 72) or current cigarette smokers of varying intensity (n = 61). RESULTS: The proportion of slow acetylators was highest among whites (54%), intermediate among blacks (34%), and lowest among Asians (14%). Similarly, geometric mean levels of both 3- and 4-ABP-hemoglobin adducts were highest in whites (1.80 and 49.2 pg/g hemoglobin [Hb], respectively), intermediate in blacks (1.54 and 38.5 pg/g Hb), and lowest in Asians (0.73 and 36.0 pg/g Hb). As expected, cigarette smokers had significantly higher mean levels of both 3- and 4-ABP-hemoglobin adducts relative to nonsmokers, and the levels increased with the number of cigarettes smoked per day (P < .0005 for both adducts). Slow acetylators consistently exhibited higher mean levels of ABP-hemoglobin adducts relative to rapid acetylators, independent of race and level of smoking. CONCLUSION: The present cross-sectional survey supports acetylation phenotype as an important determinant of bladder cancer risk and a possible major factor in the varying bladder cancer risk among whites, blacks, and Asians.

In vivo metabolism and whole-blood clearance of n-nitrosomethylbenzylamine in the rat.

The pharmacokinetics and metabolism of N-nitrosomethyl-benzylamine, N-nitroso[methyl-14C]benzylamine, and N-nitrosomethyl[benzyl-7-14C]amine were studied in male Sprague-Dawley rats, and a major urinary metabolite was identified. N-Nitrosomethylbenzylamine (4.7 mg/kg body weight i.p.) was distributed throughout extracellular water and cleared from the whole blood by metabolism with a half-life of 66 min. Less than 1% of the administered dose of N-nitrosomethylbenzylamine (4.7 mg/kg i.p. or 3.3 mg/kg intragastric intubation) was excreted and expired as the parent compound. In the 24-hr period following injection of N-nitroso[methyl-14C1benzylamine (3.4 mg, 1 mCi/kg i.p.), 46% of the radioactivity administered was expired with a half-life of 2.1 hr. In contrast, 81% of the radioactivity from a dose of N-nitrosomethyl[benzyl-7-14C1amine (2.4 mg, 1 mCi/kg i.p.) was excreted in the urine with a half-life of 4.2 hr. Hippuric acid accounted for 80% of the radioactivity recovered in the urine.

Hemoglobin adducts of 4-aminobiphenyl in smokers and nonsmokers.

A quantitative method has been developed for the analysis of 4-aminobiphenyl (4-ABP) covalently bound as the sulfinic acid amide to the 93 beta cysteine of human hemoglobin. The method uses mild basic hydrolysis of hemoglobin to release the parent amine, derivatization to form the pentafluoropropionamide, and capillary gas chromatography with detection by negative-ion chemical ionization mass spectrometry. The method is precise and gives reproducible results on multiple blood samples taken from individuals over 48 h. Application of this method to blood samples from cigarette smokers and nonsmokers revealed consistently higher adduct levels in smokers. The mean value for smokers was 154 pg 4-ABP per g Hb compared to 28 pg/g Hb for nonsmokers, with no overlap of adduct levels between the two groups. Studies on quitting smokers revealed that adduct levels declined over a period of 6-8 weeks to nonsmoker levels. The finding of 4-ABP adducts in all nonsmokers was not anticipated but is consistent with low-level ubiquitous contamination of air, food, or water. In other animals sampled, rats and dogs had measurable adduct levels, but monkeys and fish did not. The hemoglobin adduct of 4-ABP is the product of a series of reactions between the hemoprotein and N-hydroxy-4-ABP. The formation of hydroxylamines from carcinogenic aromatic amines and their subsequent reactions with DNA are generally thought to be critical events in the initiation of bladder tumors. We suggest that the observed hemoglobin adduct levels formed by this proximate carcinogen will reflect the extent to which these steps have occurred. This is the first report of 4-ABP adducts in human blood.

Isolation and characterization of the major fluoranthene-hemoglobin adducts formed in vivo in the rat.

The binding of fluoranthene (FA) to hemoglobin was studied both in vitro and in vivo in the rat. The in vitro binding of microsomally activated FA to rat hemoglobin appeared to involve the fluoranthene 2,3-dihydrodiol-1,10b-epoxides. Three classes of hemoglobin adducts were observed in rats chronically administered FA in the diet. Based on high pressure liquid chromatography retention times, UV and mass spectral evidence, and behavior upon cis-diol affinity chromatography, the major class of globin adducts formed in vivo was demonstrated to result from binding of syn and anti isomers of FA 2,3-dihydrodiol-1,10b-epoxides to beta-cysteine-125 of rat hemoglobin. These adducts represented at least 41% of the total binding to globin. A minor class of adducts (12% of the total binding) appeared to involve the binding of an unidentified FA metabolite to the same cysteine residue of the protein. A substantial portion of FA binding to rat hemoglobin in vivo (29%) involved metabolic pathways which were not duplicated by simple in vitro systems. That portion of the binding to globin has not been characterized.

Decline of the hemoglobin adduct of 4-aminobiphenyl during withdrawal from smoking.

The hemoglobin adduct of the human bladder carcinogen 4-aminobiphenyl (4ABP-Hb) declined in the blood of 34 smokers enrolled in a withdrawal program, from a mean of 120 +/- 7 (SE) pg/g of hemoglobin at the start to a mean of 82 +/- 6 pg/g after 3 weeks and a mean of 34 +/- 5 pg/g among the 15 exsmokers who had not resumed smoking after 2 months. Although 4ABP-Hb declined faster than expected under the assumption that the human erythrocyte has a life span of 120 days, it persisted much longer than cotinine. Therefore, 4ABP-Hb may complement the use of cotinine as a marker of exposure to tobacco smoke. The strength of the within-person association of 4ABP-Hb with smoking, coupled with the weakness of the between-person association (correlation coefficient, 0.33), is evidence that between-person variation in modifying factors is substantial. Study of the modifiers of 4ABP-Hb levels may help elucidate the etiology of human susceptibility to aromatic amine-induced bladder cancer.

Pharmacokinetic model for N-nitrosodimethylamine based on Michaelis-Menten constants determined with the isolated perfused rat liver.

A pharmacokinetic model was constructed to describe the absorption, distribution, and metabolic clearance of N-nitrosodimethylamine. The model is composed of two compartments, total body water and the liver, which are linked by blood flow. Metabolic clearance is presumed to occur only in the liver. Liver clearance kinetics was determined with isolated perfused livers. Clearance appeared to obey Michaelis-Menten kinetics with Km = 8.3 +/- 4.8 microM and Vmax = 0.15 +/- 0.02 mumol/min . liver. The observed value for Km is about 1 order of magnitude lower than any observed when clearance is determined using liver microsome preparations. The model is used to calculate whole-body clearance of N-nitrosodimethylamine and relative tissue exposure as a function of the route of administration. The calculations are compared with previously published experimental data, and it is shown that the accuracy of the model for low doses is a result of the novel value observed for Km in the perfused liver.

Mutagenicity of hydroxamic acids and the probable involvement of carbamoylation.

A series of hydroxamic acids (aceto-, propiono-, benzo-, and p-nitrobenzo-) and seven derivatives of these were examined for biological activity using Salmonella typhimurium. Acylation to yield O-acetyl and O-benzoyl derivatives markedly enhanced toxic properties and was necessary for mutagenic activity for all but p-nitrobenzohydroxamic acid. The dose necessary to produce a minimum significant mutagenic response varied from 21 microM for O-benzoyl benzohydroxamate to 430 microM for O-acetyl acetohydroxamate. These two compounds were also tested with human lymphoblasts to which they were toxic at 100 microM but not mutagenic. O-Acetyl benzohydroxamate, a mutagen, was prepared wih a 14C label in the carbonyl carbon atom of the benzoyl group and was shown to form an adduct in vitro with DNA and polyguanylic acid. The level of binding was 1 mol of 14C per 5 X 10(4) mol of DNA phosphate and 1 mol of 14C per 10(5) mol of polyguanylic acid phosphate.

Conservation of histone carcinogen adducts during replication: implications for long-term molecular dosimetry.

The effect of cell replication on histone-carcinogen adducts was investigated by determining the specific adduct levels as a function of time following carcinogen treatment of human TK6 cells grown in culture. Core histones isolated from cells treated with aflatoxin B1 or r-7,t-8 dihydroxy-t-9,t-10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene exhibited a decrease over five generations in specific adduct level that did not exceed the decrease expected as a result of dilution with newly synthesized protein except during the early phase (< 1 generation) of the experiment when loss of chemically unstable adducts might occur. Similar kinetics without the initial, more rapid phase was observed when cells were treated with N-nitroso-N-methylurea. Multigeneration stability of aflatoxin B1 and N-nitroso-N-methylurea adducts that formed on histone H1 was also observed; in these experiments it was not possible to determine if there was an initial phase in the kinetics. These experiments indicate that cell replication does not result in the repair or removal of adducted histones, establishing the feasibility of using histone-carcinogen adducts for molecular dosimetry purposes.

In vivo dosimetry of 4-aminobiphenyl in rats via a cysteine adduct in hemoglobin.

The feasibility of monitoring doses of 4-aminobiphenyl (ABP) via adduction to hemoglobin was investigated. Rats dosed with ABP (from 0.5 micrograms/kg to 5 mg/kg) formed a stable covalent hemoglobin:ABP adduct. Approximately 5% of a single dose was bound as hemoglobin:ABP; chronic dosing led to an accumulation of the adduct to a level 30 times greater than that found after a single dose. Facile in vitro hydrolysis of the adduct regenerated ABP, allowing detection at the sub-ng level. Human hemoglobin was also readily adducted, using N-hydroxy-ABP in vitro. The predominant site of adduction appeared to be the cysteine residue in hemoglobin. The use of such adducts as dosimeters for arylamine exposures in humans is discussed.

Measurement of 4-aminobiphenyl-hemoglobin adducts in lung cancer cases and controls.

Hemoglobin adducts of the activated carcinogenic aromatic amine 4-aminobiphenyl have been measured in a case-control study of lung cancer. Data obtained for lung cancer cases are compared to those obtained for controls that consisted of patients with either chronic obstructive pulmonary disease or non-pulmonary cancers. Both simple and multivariate analysis found a positive association of 4-aminobiphenyl-hemoglobin adducts with the quantity of tobacco smoked as determined by either urine cotinine or questionnaire data. No association was found between 4-aminobiphenyl-hemoglobin adducts and cancer diagnosis, and adduct levels were not related to remote tobacco use, i.e., total pack years of smoking. There was no association between the levels of adducts detected and the ability of an individual to metabolize debrisoquine (debrisoquine metabolic phenotype, CYP2D6). Whereas 4-aminobiphenyl-hemoglobin adduct levels reflected recent tobacco smoking, they were not correlated with lung cancer risk.

Molecular dosimetry of polycyclic aromatic hydrocarbon epoxides and diol epoxides via hemoglobin adducts.

Ten reactive metabolites of five polycyclic aromatic hydrocarbons and styrene were investigated to determine the generality of ester adduct formation with human hemoglobin in the form of RBC and hydrolysis to the corresponding tetrahydrotetrols or dihydrodiols. No exceptions were noted among the compounds tested, which included the anti-diol epoxides of benzo[a]pyrene (BaP), chrysene, and benz[a]anthracene; the syn-diol epoxide of BaP; a mixture of syn- and anti-diol epoxides of benzo[e]pyrene; and epoxides of styrene, benzo[e]pyrene, BaP, and cyclopenta[c,d]pyrene. A test of the propensity of the simplest benzylic epoxide, styrene oxide, to form esters that hydrolyze via a BAL1 mechanism was performed. Hydrolysis of styrene oxide-adducted hemoglobin in H2(18)O at neutral pH yielded 18O incorporation results that suggest this mechanism of hydrolysis is operant to a minor degree in styrene oxide-hemoglobin ester adducts. A method was developed for the isolation and quantification of the polycyclic aromatic alcohols, which consists of enzymatic proteolysis, immunoaffinity chromatography, and gas chromatography-mass spectrometry or fluorimetry. The method allows for routine analysis of hemoglobin from individual samples as small as 1 ml of whole blood. Analysis of blood from different human populations revealed that hemoglobin adducts of the anti-diol epoxide of BaP dominated the spectrum of adducts formed by the selected metabolites.

Acetylation phenotype, carcinogen-hemoglobin adducts, and cigarette smoking.

Levels of 4-aminobiphenyl-hemoglobin adducts in smokers of blonde (flue-cured) and black (air-cured) tobacco have been found to be proportional to bladder cancer risk. In addition, risk of bladder cancer due to exposure to occupational carcinogens is elevated in genetically determined slow acetylators. In this study of normal male volunteers, 4-aminobiphenyl-hemoglobin adducts were found to be related to both the quantity and the type of tobacco smoked, as well as to the acetylator phenotype (independently of smoking habits). The demonstration that both the genetically determined slow acetylator phenotype and tobacco smoking are independently associated with levels of the carcinogen 4-aminobiphenyl in adducted hemoglobin suggests a single mechanism to explain the contribution of genetic susceptibility and environmental exposure in bladder carcinogenesis.

Identification of the major serum albumin adduct formed by 4-aminobiphenyl in vivo in rats.

Serum albumin was isolated from rats at 27 h after administration of the carcinogen [2,2'-3H]-4-aminobiphenyl. Pronase digestion of the purified albumin yielded a mixture of radiolabeled materials which was resolved into 5 major components by reverse-phase liquid chromatography. From detailed UV, 1H-NMR, and mass spectral analyses, four of these were determined to be 4-aminobiphenyl, 4'-hydroxy-4-acetylaminobiphenyl, and two other metabolites, all of which are presumed to be non-covalently associated with the serum albumin. The fifth component, however, resulted from covalent bond formation and was identified as a tetrapeptide containing 3-tryptophanyl-4-acetylaminobiphenyl, the amino acid sequence of which was H2N-ala-trp-ala-val. Since rat serum albumin contains only a single tryptophan residue in a hydrophobic drug binding site, its high selectivity for carcinogen binding suggests a unique role for this protein in the detoxification and/or transport of ultimate carcinogenic metabolites.

Frequency of urination and its effects on metabolism, pharmacokinetics, blood hemoglobin adduct formation, and liver and urinary bladder DNA adduct levels in beagle dogs given the carcinogen 4-aminobiphenyl.

The human urinary bladder carcinogen, 4-aminobiphenyl (ABP), is known to undergo hepatic metabolism to an N-hydroxy arylamine and its corresponding N-glucuronide. It has been proposed that these metabolites are both transported through the blood via renal filtration to the urinary bladder lumen where acidic pH can facilitate the hydrolysis of the N-glucuronide and enhance the conversion of N-hydroxy-4-aminobiphenyl (N-OH-ABP) to a reactive electrophile that will form covalent adducts with urothelial DNA. Blood ABP-hemoglobin adducts, which have been used to monitor human exposure to ABP, are believed to be formed by reactions within the erythrocyte involving N-OH-ABP that has entered the circulation from the liver or from reabsorption across the urothelium. To test these hypotheses directly, experimental data were obtained from female beagles given [3H]ABP (p.o., i.v., or intraurethrally). [3H]N-OH-ABP (i.v. or intraurethrally), or [3H]N-OH-ABP N-glucuronide (i.v.). Analyses included determinations of total ABP in whole blood and plasma, ABP-hemoglobin adducts in blood erythrocytes, ABP and N-OH-ABP levels (free and N-glucuronide) in urine, urine pH, frequency of urination (controlled by urethral catheter), rates of reabsorption of ABP and N-OH-ABP across the urothelium, and apparent volumes of distribution in the blood/tissue compartment. The major ABP-DNA adduct, N-(guan-8-yl)-4-aminobiphenyl, was also measured in urothelial and liver DNA using a sensitive immunochemical method. An analog/digital hybrid computer was then utilized to construct a multicompartmental pharmacokinetic model for ABP and its metabolites that separates: (a) absorption; (b) hepatic metabolism and distribution in blood and tissues; (c) ABP-hemoglobin adduct formation; (d) hydrolysis and reabsorption in the urinary bladder lumen; and (e) excretion. Using this model, cumulative exposure of the urothelium to free N-OH-ABP was simulated from the experimental data and used to predict ABP-DNA adduct formation in the urothelium. The results indicated that exposure to N-OH-ABP and subsequent ABP-DNA adduct formation are directly dependent on voiding frequency and to a lesser extent on urine pH. This was primarily due to the finding that, after p.o. dosing of ABP to dogs, the major portion of the total N-OH-ABP entering the bladder lumen was free N-OH-ABP (0.7% of the dose), with much lower amounts as the acid-labile N-glucuronide (0.3% of the dose).(ABSTRACT TRUNCATED AT 400 WORDS)

Altered aromatic amine metabolism in epileptic patients treated with phenobarbital.

The fate of carcinogens differs among individuals who have different activities of drug-metabolizing enzymes that are important in activating and detoxifying carcinogens. A drug that profoundly alters the metabolism of the drugs and carcinogens is the anticonvulsive agent phenobarbital. To investigate why epileptic patients appear to have a low risk of cancer of the urinary bladder, and on the basis of the observation that levels of aromatic amine-hemoglobin adducts are strongly associated with various risk factors for cancer at that site, we determined aromatic amine-hemoglobin adducts in 62 epileptic patients as a surrogate measure of the reaction of carcinogenic metabolites with DNA in target tissue. Although adducts were detected in all subjects, the levels were proportional to daily tobacco consumption. When the subjects were stratified into groups smoking 20 g tobacco/day or more, smoking <20 g/day, and not smoking, an effect of medication was detected. Epileptic patients treated chronically with phenobarbital or primidone, which is effectively metabolized to phenobarbital, were found to have lower levels of 4-aminobiphenyl adducts than patients on the other treatment (P = 0.02; ANOVA). In nonsmokers, no effect of medication could be demonstrated above background variation; however, an increasing effect was seen with tobacco consumption with only one-half the increase in adducts per g of tobacco smoked as epileptic patients on other treatment. The difference in the increases (slopes of regression lines) was highly significant statistically. This reduction in the level of hemoglobin-aromatic amine adducts is probably due to induction of detoxification enzymes in the patients treated with phenobarbital.