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F F Kadlubar

Publications and source records attributed to F F Kadlubar.

At least 145 records · Page 8Linked to original sources
PubMed1991

Aromatic and heterocyclic amine metabolism and phenotyping in humans.

Our method to evaluate acetylator phenotype and N-oxidation phenotype with a single caffeine dose and a single urine specimen collection has enabled us to examine acetylation and N-oxidation by two enzyme systems that have a known genetic polymorphism and are important in aromatic amine metabolism. Based on available data, we have hypothesized patients with urinary bladder cancer will have a higher frequency of rapid N-oxidation and slow acetylation phenotypes when compared to controls. On the other hand, patients with colorectal cancer should contain a higher proportion of both rapid N-oxidation phenotype and rapid acetylation phenotype when compared to the control group. In contrast, lung cancer patients, should contain an increased frequency of rapid arylamine N-oxidation phenotypes with the frequency of acetyltransferase phenotype being greater or perhaps the same as in the control group.

Acetyltransferases↗
PubMed1990

Aromatic amine acetyltransferase as a marker for colorectal cancer: environmental and demographic associations.

In this pilot, case-controlled investigation of 43 colorectal and 41 control male patients, we compared associations of colorectal cancer with the aromatic amine acetyltransferase polymorphism, nutritional and demographic characteristics, medical histories, industrial and occupational histories, and exposures from home environments and personal habits. Persons with the "fast" acetylator trait were at greater risk of colorectal cancer (odds ratio: 2.48; 95% confidence interval: 1.02, 6.03). Results that differed from previous reports were positive associations of colorectal cancer with agricultural and manufacturing industries and with consumption of meats prepared by smoking, curing, and barbecueing. As expected, exercise frequency, cruciferous vegetables, and dietary fiber served as protective factors.

Acetylation↗
PubMed1990

Metabolism and disposition of benzidine in the dog.

The dog is an animal model for assessing aromatic amine-induced bladder cancer. For this reason, metabolism and disposition of benzidine in dog was assessed. Dogs were administered a 1 mg/kg i.v. dose of [3H]benzidine (16.4 mCi/mmol). The plasma t1/2 of the radiolabeled material (benzidine plus metabolites) was significantly longer (approximately 3 h) than authentic benzidine (less than 30 min). During the 5 h experiment, the majority of radiolabel was associated with bile, urine and carcass. Bladder transitional epithelium exhibited a consistently higher concentration of bound radioactivity than bladder muscle. A significant amount of binding was observed in DNA from liver, kidney and bladder. DNA from bladder transitional epithelium exhibited the highest concentration of radioactivity. Approximately 30% of the radioactivity recovered following HPLC of urine or bile was identified as unmetabolized benzidine. 3-Hydroxybenzidine was a major metabolite identified in bile (8%) but not urine. Urine samples treated with acid, base or sulfatase yielded 3-hydroxybenzidine (6%) as a major hydrolysis product. Similar treatment of bile samples did not result in increased amounts of 3-hydroxybenzidine. Neither N-acetylated nor N-methylated metabolites of benzidine were observed in urine or bile. Thus, considerable metabolism of benzidine occurs in dogs by pathways that are yet to be determined.

Animals↗
PubMed1990

Detection and characterization of carcinogen-DNA adducts in exfoliated urothelial cells from 4-aminobiphenyl-treated dogs by 32P-postlabelling and subsequent thin-layer and high-pressure liquid chromatography.

The recent development of sensitive methods to detect carcinogen-DNA adducts offers a useful biochemical approach to human risk assessment. However, a major obstacle to developing a human biomonitoring method for carcinogen-DNA adducts has been the problem of obtaining target tissue DNA samples by non-invasive means. This work describes a method for the isolation of nanogram quantities of DNA from urothelial cells exfoliated into urine and the detection of carcinogen-DNA adducts from that DNA by 32P-postlabelling methods. Urine samples were collected on ice from dogs treated with 4-aminobiphenyl (ABP) over a 2-week period and pooled according to an experimental plan that involved analysis of cumulative 48- or 72-h samples. The pooled samples were sieved and then washed repeatedly with a sucrose buffer to dissolve contaminating triple phosphate (MgNH4PO4), calcium oxalate and uric acid crystals. DNA was isolated using an enzyme-solvent extraction method with the DNA being co-precipitated from ethanol with glycogen. The DNA was hydrolysed and postlabelled with 32P under conditions of excess ATP so that nucleotides were labelled quantitatively. Adducts observed on the resulting thin-layer chromatograms were identical to those obtained from DNA modified in vitro with N-hydroxy-4-aminobiphenyl and from dog bladder urothelial DNA isolated from the ABP-dosed animals at termination of the experiment. Furthermore, a dose-related increase in ABP-DNA adduct formation was demonstrated. Thus, it appears that the carcinogen-DNA adduct levels in the exfoliated bladder cells are reflective of the levels in the intact urothelium once steady-state levels have been achieved. To establish the identity of the major ABP-urothelial DNA adduct in chronically-treated dogs, the predominant 32P-postlabelled adduct was eluted from the thin-layer chromatograms and co-injected on an HPLC system with a synthetic [3H]N-(deoxyguanosin-8-yl)-4-aminobiphenyl-3',5'-bisphosphate standard. Dual-label analysis of 3H and 32P indicated that both eluted from the column in the same fraction, which coincided with the UV absorbance peak of the synthetic marker. Preliminary experiments with exfoliated urothelial cells from human urines indicate that these methods should have general utility for monitoring humans exposed to urinary bladder carcinogens and for investigations of the biochemical mechanisms by which such adducts are formed in the urothelium.

Aminobiphenyl Compounds↗
PubMed1990

The metabolic N-oxidation of carcinogenic arylamines in relation to nitrogen charge density and oxidation potential.

The N-oxidation of carcinogenic arylamines to form N-hydroxy arylamines has long been regarded as a necessary metabolic step for conversion to proximate carcinogenic derivatives. In contrast, arylamine ring-oxidation has been generally considered to be an important detoxification mechanism. Both enzymatic reactions are carried out in the liver and usually involve the cytochrome P-450 monooxygenases. Studies on the metabolic oxidation of certain arylamines have indicated that the relative charge density on nitrogen versus ring-carbon atoms for a nitrenium/carbenium ion-enzyme intermediate correlates with the relative proportion of N-versus ring-hydroxylated products that are formed. A further examination of this approach now shows that positive charge density on the nitrogen, as estimated by Hückel molecular orbital calculations, is consistent with the formation of N-hydroxy arylamines from aniline, 4-aminoazobenzene, 2-naphthylamine, 4-aminobiphenyl, 2-aminofluorene, and 6-aminochrysene, but not from 1-naphthylamine, 1-aminopyrene, 6-aminobenzo[a]pyrene, or 7-aminobenz[a]anthracene. Since greater positive charge on the arylamine nitrogen implies a greater charge localization during the transition state of the enzyme-substrate complex, we envisioned that higher oxidation potentials for arylamines, which might be expected to correlate inversely with the ease of total oxidation, would instead be predictive of the relative extent of N-oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amines↗
PubMed1990

Carcinogenic aromatic amine metabolism and DNA adduct detection in humans.

Human exposure to carcinogenic aromatic amines can occur from a variety of sources, including cigarette smoke and cooked foods. Initial metabolism occurs primarily in the liver and involves N-hydroxylation by cytochrome P-450IA2 and N-acetylation by acetyltransferase, which serve as competing activation and detoxification reactions, respectively. Both enzymes are polymorphic in humans and individual phenotype can be readily assessed using caffeine ingested in coffee followed by urinary metabolite analysis. N-hydroxy arylamines can then be transported through the blood where they can form protein adducts with hemoglobin or undergo renal filtration into the urinary bladder lumen where, at acidic pH, they can react covalently with urothelial DNA. Carcinogen-DNA adduct levels in human bladder are smoking-related and the C8-deoxyguanosine derivative of 4-amino-biphenyl (ABP) is a major product. Alternatively, N-hydroxy arylamines can be conjugated in the liver by glucuronyl transferases which provides a mechanism for biliary transport to the colon lumen where beta-glucuronidases can regenerate the aglycone. In the colon mucosa, acetyltransferases can further activate the N-hydroxy metabolite by O-acetylation; and persons with the rapid acetylation phenotype are known to be at higher risk for colorectal cancer. Detection of specific arylamine-DNA adducts in human colon should provide direct evidence for the role of these carcinogens in the etiology of this disease.

Acetyltransferases↗
PubMed1989

Metabolic activation of 6-nitrochrysene in explants of human bronchus and in isolated rat hepatocytes.

It has previously been shown that 6-nitrochrysene can be activated to electrophilic species capable of reacting with DNA through metabolic pathways that form N-hydroxy-6-aminochrysene or trans-1,2-dihydroxy-1,2-dihydro-6-aminochrysene as critical intermediates. Since the lung is a known target tissue for the carcinogenic action of polycyclic nitroaromatic hydrocarbons, we investigated the metabolism and DNA binding of [3H]6-nitrochrysene in 11 specimens of human bronchus. Analysis of medium from [3H]6-nitrochrysene-treated explants indicated the presence of trans-9,10-dihydroxy-9,10-dihydro-6-nitrochrysene (0.04-330 pmol/mg epithelial DNA), trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene (12-1700 pmol/mg epithelial DNA), 6-aminochrysene (1.6-2200 pmol/mg epithelial DNA), and trans-1,2-dihydroxy-1,2-dihydro-6-aminochyrsene (3.6-610 pmol/mg epithelial DNA). Both the levels and the relative proportions of these metabolites varied widely in explants from different individuals. The amount of DNA recovered and the level of DNA modification were sufficient for adduct analysis in eight of the 11 cases for which metabolite data were obtained. Five additional bronchial specimens for which metabolite data were not obtained were also analyzed for carcinogen-DNA adducts. The levels of binding varied from 0.06 to 30.5 pmol [3H]6-nitrochrysene bound/mg DNA (two adducts per 10(8) nucleotides-10 adducts per 10(6) nucleotides). HPLC analyses of enzymatic hydrolysates of the explant DNA indicated that 11 of 13 cases contained adducts with retention times identical to those of adducts derived from trans-1,2-dihydroxy-1,2-dihydro-6-aminochrysene or N-hydroxy-6-aminochrysene. The adduct derived from trans-1,2-dihydroxy-1,2-dihydro-6-aminochrysene was the major adduct detected in eight of 13 cases. The reasons for the variation in metabolism and adduct formation observed in [3H]6-nitrochrysene-treated explants of bronchus from different donors are not known but may reflect differences in the activities of enzymes responsible for the metabolism of this compound. The influence of induction of drug metabolizing enzymes on the activation pathway of 6-nitrochrysene in an intact cell system was tested using rat hepatocytes. 6-Nitrochrysene was incubated with freshly isolated hepatocytes from rats that were either untreated or pretreated with phenobarbital, 3-methylcholanthrene or Aroclor 1254. Although the levels of adducts were similar in all cases, the pattern of DNA adducts formed in these hepatocytes was dependent on the nature of the pretreatment of the rats. As previously reported, hepatocytes from untreated rats contained adducts derived from N-hydroxy-6-aminochrysene.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Arachidonic acid-dependent peroxidative activation of carcinogenic arylamines by extrahepatic human tissue microsomes.

Prostaglandin H synthase (PHS), an arachidonic acid-dependent peroxidase, has been implicated in the peroxidative activation of carcinogenic aromatic amines in extrahepatic carcinogen target tissues of experimental animals. We have examined the arachidonic acid-dependent activation of [3H]benzidine to DNA-bound products by microsomal preparations from 75 normal human tissues obtained during necessary surgical procedures. For several samples of urinary bladder epithelium, prostatic epithelium, colonic mucosa, and peripheral lung tissue, an arachidonic acid-dependent, microsomal-catalyzed activation of benzidine was observed; and the activity could be inhibited appreciably by indomethacin, a known inhibitor of PHS. Little or no arachidonic acid-dependent activity was detected in human placenta, breast, or liver microsomes or the majority of colon microsomes. Substrate specificity was also examined with purified ram PHS and with human bladder and with active colon preparations. Purified PHS catalyzed the activation of benzidine much greater than 2-naphthylamine, 2-amino-6-methyldipyrido[1,2-alpha:3',2'-d]imidazole greater than 4-aminobiphenyl greater than 2-amino-3-methylimidazo[4,5-f]quinoline greater than 3-amino-1-methyl-5H-pyrido[4,3-b] indole. In comparison, human bladder and colon microsomes catalyzed the activation of benzidine greater than 4-aminobiphenyl, 2-amino-6-methyldipyrido[1,2-alpha:3',2'-d]imidazole, 2-naphthylamine greater than 2-amino-3-methylimidazo[4,5-f]quinoline, 3-amino-1-methyl-5H-pyrido[4,3-b]indole. To confirm the occurrence of PHS antigen in human extrahepatic tissues, an avidin/biotin-amplified competitive enzyme-linked immunoabsorbent assay was developed with purified ram PHS and a commercially available monoclonal antibody known to cross-react with human platelet PHS. The avidin/biotin-amplified enzyme-linked immunosorbent assay, which detected ng quantities of ram PHS, clearly established the presence of the PHS protein in human bladder, prostate, and lung microsomes. In contrast, PHS antigen was not detected in the liver or placental microsomes. The interindividual and tissue-dependent variability of PHS and its role in aromatic amine carcinogenesis are discussed.

Arachidonic Acid↗
PubMed1989

Metabolic oxidation of the carcinogens 4-aminobiphenyl and 4,4'-methylene-bis(2-chloroaniline) by human hepatic microsomes and by purified rat hepatic cytochrome P-450 monooxygenases.

Metabolic N-oxidation and ring-oxidation of carcinogenic arylamines by hepatic cytochromes P-450 are generally regarded as critical activation and detoxification pathways, respectively. Two arylamines with known human exposure, 4-aminobiphenyl (ABP) and 4,4'-methylene-bis(2-chloroaniline) (MOCA), have been examined as substrates for 10 different purified rat hepatic cytochromes P-450 and for human liver microsomal preparations from 22 individuals. Metabolites were analyzed by high-performance liquid chromatography and flow scintillation techniques. As reported for certain other carcinogenic arylamines, the isosafrole-inducible isozyme, P-450ISF-G, had the highest catalytic activity for ABP N-oxidation (13.6 nmol/min/nmol P-450), but P-450BNF-B, P-450UT-A, P-450UT-F, and P-450PB-B also showed appreciable activity. Ring-oxidation of ABP occurred only to a minor extent. In contrast, N-oxidation of MOCA was preferentially catalyzed by the phenobarbital-inducible enzymes, P-450PB-B and P-450PB-D (9.0 and 6.6 nmol/min/nmol P-450, respectively). MOCA ring-oxidation and methylene carbon oxidation showed varied cytochrome P-450 selectivity and accounted for 14 to 79% of total oxidation products. There was a 44-fold variation in rates of ABP N-oxidation in the 22 human liver microsomal preparations, while rates of N-oxidation of MOCA varied only 8-fold. Ring/methylene carbon-oxidation of MOCA accounted for 6-19% of total oxidation products in the case of the human microsomal preparations, whereas ring-oxidation of ABP accounted for less than 7% of total oxidation. In addition, there was a strong correlation (R = 0.90) between rates of ABP N-oxidation and phenacetin O-deethylation, which is considered a human genetic polymorphism. Moreover, both the ABP N-oxidation and phenacetin O-deethylation activities of human liver microsomes showed a good correlation (R = 0.72) with the levels of cytochrome P-450 immunochemically related to rat P-450ISF-G. These data indicate that specific inducible and constitutive cytochromes P-450 are involved in the metabolic activation and detoxification of the carcinogens ABP and MOCA. Therefore, individual profiles of cytochromes P-450, affected by both environmental and genetic factors, may be significant determinants of individual susceptibility to arylamine carcinogenesis.

Aminobiphenyl Compounds↗
PubMed1989

The formation of 2-aminofluorene-DNA adducts in vivo: evidence for peroxidase-mediated activation.

Formation of DNA adducts in various tissues of dogs fed a single dose of the carcinogen 2-aminofluorene was investigated. Adduct analysis was performed using a technique that allows measurement of both N-(deoxyguanosin-8-yl)-2-amino-2-aminofluorene-DNA adduct formed by reaction of N-hydroxy-2-aminofluorene with DNA, as well as the polar 2-aminofluorene-DNA adducts formed when 2-aminofluorene is activated by prostaglandin H synthase-peroxidase in vitro. Two male beagle (A and B) dogs were examined and a different DNA adduct profile was observed with each dog. For the dog A, N-(deoxyguanosin-8-yl)-2-aminofluorene was the major adduct found in hepatic DNA; no peroxidase-derived adducts were detected in this tissue. In contrast, adducts eluting similarly to peroxidase-derived adducts were found in urinary tract tissues of this dog with the relative abundance of these adducts in the order urothelium greater than renal medulla greater than renal cortex, which correlates with the respective tissues' prostaglandin H synthase activity. N-(Deoxyguanosin-8-yl)-2-aminofluorene was detected in the renal tissues, but not in urothelium. For dog B, only the N-(deoxyguanosin-8-yl)-2-aminofluorene adduct was observed in all tissues examined, including the urothelium. However, total binding to liver, kidney, and bladder were two-, two-, and four-fold lower, respectively, than dog A. These data indicate that both prostaglandin H synthase-mediated activation and N-hydroxylation of 2-aminofluorene occur in vivo and may be subjected to pharmacodynamic considerations. Furthermore, the tissue distribution of the peroxidase-mediated 2-aminofluorene adducts suggests this process may also be of importance in the bladder-specific carcinogenicity of aromatic amines.

Animals↗
PubMed1989

The effect of lifetime sodium saccharin dosing on mice initiated with the carcinogen 2-acetylaminofluorene.

Sodium saccharin has been reported to promote the development of urinary bladder tumors in rats following low doses of several carcinogens. To evaluate the generality of this effect between species, an initiation-promotion study was conducted in mice. Weanling female BALB/c mice were initiated with 200 ppm dietary 2-acetylaminofluorene for 90 days. Following a 2-week period of control diet, saccharin was administered at 0, 0.1, 0.5, 1.0, and 5.0% in the diet for the remainder of the 132-week study. An elevated incidence of persistent bladder transitional cell hyperplasia and a low incidence of urothelial and hepatocellular tumors indicated that these organs achieved an adequate dose of the initiator. However, sodium saccharin dosing did not result in an increased incidence of tumors in either the bladder or liver and is therefore not considered to be a promoter of carcinogenesis at these sites in the mouse. Furthermore, sodium saccharin exhibited a modest inhibitory effect on the rate of development of lymphomas in both initiated and noninitiated animals. Interspecies differences in the bladder tumorigenic effect of sodium saccharin and their association with differences in urinary tract physiology are discussed.

2-Acetylaminofluorene↗
PubMed1989

Human cytochrome P-450PA (P-450IA2), the phenacetin O-deethylase, is primarily responsible for the hepatic 3-demethylation of caffeine and N-oxidation of carcinogenic arylamines.

Aromatic amines are well known as occupational carcinogens and are found in cooked foods, tobacco smoke, synthetic fuels, and agricultural chemicals. For the primary arylamines, metabolic N-oxidation by hepatic cytochromes P-450 is generally regarded as an initial activation step leading to carcinogenesis. The metabolic activation of 4-aminobiphenyl, 2-naphthylamine, and several heterocyclic amines has been shown recently to be catalyzed by rat cytochrome P-450ISF-G and by its human ortholog, cytochrome P-450PA. We now report that human hepatic microsomal caffeine 3-demethylation, the initial major step in caffeine biotransformation in humans, is selectively catalyzed by cytochrome P-450PA. Caffeine 3-demethylation was highly correlated with 4-aminobiphenyl N-oxidation (r = 0.99; P less than 0.0005) in hepatic microsomal preparations obtained from 22 human organ donors, and both activities were similarly decreased by the selective inhibitor, 7,8-benzoflavone. The rates of microsomal caffeine 3-demethylation, 4-aminobiphenyl N-oxidation, and phenacetin O-deethylation were also significantly correlated with each other and with the levels of immunoreactive human cytochrome P-450PA. Moreover, a rabbit polyclonal antibody raised to human cytochrome P-450PA was shown to inhibit strongly all three of these activities and to inhibit the N-oxidation of the carcinogen 2-naphthylamine and the heterocyclic amines, 2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole and 2-amino-3-methylimidazo[4,5-f]-quinoline. Human liver cytochrome P-450PA was also shown to catalyze caffeine 3-demethylation, 4-aminobiphenyl N-oxidation, and phenacetin O-deethylation. Thus, estimation of caffeine 3-demethylation activity in humans may be useful in the characterization of arylamine N-oxidation phenotypes and in the assessment of whether or not the hepatic levels of cytochrome P-450PA, as affected by environmental or genetic factors, contribute to interindividual differences in susceptibility to arylamine-induced cancers.

Amines↗
PubMed1989

Alkyl and aryl carcinogen adducts detected in human peripheral lung.

Human peripheral lung tissue samples were obtained at autopsy from 17 individuals of known occupational and smoking histories. A spectrum of different carcinogen-DNA adducts was detected using a variety of sensitive techniques. High-pressure liquid chromatography-linked synchronous fluorescent spectrophotometry and an ultrasensitive enzyme radioimmunoassay detected adducts derived from benzo[a]pyrene diol epoxide and other apparent polycyclic aromatic hydrocarbons. An amplified enzyme-linked immunosorbent assay demonstrated the presence of 4-aminobiphenyl-DNA adducts in many of these samples. A number of these specimens also contained O6-alkyldeoxyguanosine as measured by 32P-postlabeling techniques. Thus this pilot study indicates not only that human lung contains a spectrum of carcinogen-DNA adducts, but also that a full scale molecular dosimetry study of human exposure to both aryl and alkyl chemical carcinogens is warranted.

Adolescent↗
PubMed1988

Immunochemical quantitation of DNA adducts derived from the human bladder carcinogen 4-aminobiphenyl.

To assess target-tissue exposure to the human urinary bladder carcinogen 4-aminobiphenyl (ABP), we have developed a sensitive immunochemical method for measuring the major arylamine-DNA adduct formed, N-(guan-8-yl)-ABP (Gua-C8-ABP). High-affinity polyclonal antisera from rabbits immunized with N-(guanosin-8-yl)-ABP coupled to keyhole limpet hemocyanin were characterized and shown to have high specificity for antigenic determinants on the purine and biphenyl rings of Gua-C8-ABP and minimal cross-reactivity with ABP, deoxyguanosine, or hydrolyzed DNA. Assay standards containing ABP-modified DNA were prepared by reacting [3H]N-hydroxy-ABP with calf thymus DNA. DNA samples were hydrolyzed with trifluoroacetic acid and dried under vacuum, and the residues were dissolved in dimethyl sulfoxide under argon. Using a streptavidin-biotin amplified enzyme-linked immunosorbent assay, DNA hydrolysates competed at 25 micrograms DNA/microtiter well for a limiting amount of anti-keyhole limpet hemocyanin-(Gua-C8-ABP) in the presence of excess solid-phase bovine serum albumin-(Gua-C8-ABP) coating antigen. The limit of sensitivity for this assay using 25 micrograms DNA was 2 adducts/10(8) nucleotides. Gua-C8-ABP adducts in liver and bladder epithelial DNAs were readily quantified after p.o. administration of 5 mg/kg ABP to dogs. This methodology is capable of detecting adducts at levels of biological significance and should be applicable to human target-tissue dosimetry.

Aminobiphenyl Compounds↗
PubMed1988

Specificity of mutagenesis by 4-aminobiphenyl. A possible role for N-(deoxyadenosin-8-yl)-4-aminobiphenyl as a premutational lesion.

Mutagenesis by N-acetoxy-N-trifluoroacetyl-4-aminobiphenyl, a reactive form of the human bladder carcinogen 4-aminobiphenyl (ABP), was studied in Escherichia coli virus M13mp10. N-acetoxy-N-trifluoroacetyl-4-ABP-treated DNA containing 140 lesions/duplex genome, when introduced into excision repair-competent cells induced for SOS mutagenic processing, resulted in a 40-fold increase in mutation frequency over background in the lacZ alpha gene fragment. DNA sequence changes were determined for 20 independent mutants. G-C base pairs were the major targets for base pair substitution mutations, although significant mutagenic activity was also observed at certain A-T base pairs. Deletion and frameshift mutations also were found in this sample. The salient feature of this partial "mutational spectrum" was a hotspot that occurred at position 6357 (amino acid 30 of the beta-galactosidase fragment encoded by M13mp10); this A-T to T-A transversion appeared in 6 of the 20 mutants. The property of ABP to mutate A-T base pairs was consistent with the result that N-hydroxy-ABP reverted Salmonella typhimurium strain TA104, which is presumed to revert primarily due to mutations at these sites. The ability of the major carcinogen-DNA adduct formed by ABP in vivo and in vitro, N-(deoxyguanosin-8-yl)-4-aminobiphenyl, to cause base pair substitution mutations was also investigated. This adduct was positioned specifically in the minus strand at position 6270 in duplex M13mp10 DNA. In the presence of the mutagenesis-enhancing plasmid pGW16 and UV induction of SOS mutagenic processing, it was shown that fewer than 0.02% of the adducts resulted in transition or transversion mutations following transfection of DNA into excision-repair competent cells. Similar results were obtained in uvrA and uvrC backgrounds. Although the major adduct did not cause base substitution mutations under these experimental conditions, the contribution of this lesion to the entire spectrum of mutations in the lacZ alpha fragment seems likely.

Amino Acid Sequence↗
PubMed1988

Estimates of the risk of bladder tumor promotion by saccharin in rats.

Tumor data from an initiation-promotion bioassay in rats are used to illustrate how urinary bladder tumor risk estimates can be modified to reflect tumor promotion by saccharin. Assuming equal carcinogenic potency in humans and rats, the estimated human risk is equal to the probability of tumors in rats due to saccharin promotion following administration of an initiator times the ratio of the proportion of humans that are initiated to the proportion of initiated rats. The proportion of initiated humans may be somewhere between the proportion of deaths due to bladder cancer in the U.S. population, 0.005, and 1.0. The proportion of initiated animals in the bioassay may be somewhere between the proportion of animals with bladder tumors, 0.41, as observed in an initiated group, and 1.0. Hence, the ratio of the proportion of initiated humans to animals may be between 0.005 and 2.4. Then, the risk of bladder tumors is estimated to be between 0.005 and 2.4 times the estimated risk of tumors in rats promoted by saccharin following administration of an initiator. An upper limit on bladder tumor risk is estimated to be between 0.00038 and 0.18 times the percentage of saccharin in the diet. If a threshold dose exists for saccharin bladder tumor promotion which is above the saccharin consumption level of all humans, then the risk is zero.

Animals↗