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F F Kadlubar

Publications and source records attributed to F F Kadlubar.

At least 73 records · Page 4Linked to original sources
PubMed1997

Immunochemical, 32P-postlabeling, and GC/MS detection of 4-aminobiphenyl-DNA adducts in human peripheral lung in relation to metabolic activation pathways involving pulmonary N-oxidation, conjugation, and peroxidation.

4-Aminobiphenyl (ABP) is a recognized human bladder carcinogen, whose presence in cigarette smoke results in DNA adduct formation in the human urothelium. Since preliminary studies indicated that even higher levels of ABP-DNA adducts may be present in human peripheral lung, we utilized a sensitive immunochemical assay, in combination with 32P-postlabeling, to quantify the major 4-aminobiphenyl (ABP)-DNA adduct, N-(guan-8-yl)-ABP, in surgical samples of peripheral lung tissue from smokers and ex-smokers. No differences in adduct levels were detected between smokers and ex-smokers by immunoassay. In contrast, the 32P-postlabeling method showed statistically significant differences between adduct levels in smokers and ex-smokers; however, a relatively high background of smoking-related adducts chromatograph near the major ABP adducts and may compromise estimation of the level of ABP-DNA adducts in smokers. Furthermore, the levels measured by 32P-postlabeling were 20- to 60-fold lower than that measured by immunoassay. Since 32P-postlabeling may underestimate and immunochemical assays may overestimate adduct levels in the lung, selected samples were also evaluated by GC/MS. The immunochemical and GC/MS data were concordant, leading us to conclude that N-(guan-8-yl)-ABP adducts were not related to smoking status. Since ABP-DNA adduct levels in human lung did not correlate with smoking status as measured by immunoassay and GC/MS, the metabolic activation capacity of human lung microsomes and cytosols was examined to determine if another exposure (e.g., 4-nitrobiphenyl) might be responsible for the adduct. The rates of microsomal ABP N-oxidation were below the limit of detection, which was consistent with a lack of detectable cytochrome P4501A2 in human lung. N-Hydroxy-ABP O-acetyltransferase (but not sulfotransferase) activity was detected in cytosols and comparative measurements of N-acetyltransferase (NAT) using p-aminobenzoic acid and sulfamethazine indicated that NAT1 and NAT2 contributed to this activity. 4-Nitrobiphenyl reductase activity was found in lung microsomes and cytosols, with the reaction yielding ABP and N-hydroxy-ABP. Lung microsomes also demonstrated high peroxidative activation of ABP, benzidine, 4,4'-methylene-bis(2-chloroaniline), 2-aminofluorene, and 2-naphthylamine. The preferred co-oxidant was hydrogen peroxide and the reaction was strongly inhibited by sodium azide but not by indomethacin or eicosatetraynoic acid, which suggested the primary involvement of myeloperoxidase rather than prostaglandin H synthase or lipoxygenase. This was confirmed by immunoinhibition and immunoprecipitation studies using solubilized human lung microsomes and antisera specific for myeloperoxidase. These data suggest that ABP-DNA adducts in human lung result from some environmental exposure to 4-nitrobiphenyl. The bioactivation pathways appear to involve: (1) metabolic reduction to N-hydroxy-ABP and subsequent O-acetylation by NAT1 and/or NAT2; and (2) metabolic reduction to ABP and subsequent peroxidation by myeloperoxidase. The myeloperoxidase activity appears to be the highest peroxidase activity measured in mammalian tissue and is consistent with the presence of neutrophils and polymorphonuclear leukocytes surrounding particulate matter derived from cigarette smoking.

Acyltransferases↗
PubMed1997

Chemoprotection against the formation of colon DNA adducts from the food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the rat.

The mutagenic heterocyclic aromatic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), is a pyrolysis product in cooked foods that has been shown to be a rat colon carcinogen and has been implicated in the etiology of human colon cancer. In order to identify chemoprotection strategies that could be carried out in humans, a pilot study was conducted in which PhIP-DNA-adduct levels were quantified in the colons of male F344 rats that had been subjected to 16 different putative chemoprotection regimens, followed by a gavage of PhIP (50 mg/kg) and sacrifice 24 h later. The 16 treatments (Oltipraz, benzylisothiocyanate, diallyl sulfide, garlic powder, ethoxyquin, butylated hydroxyanisole, glutathione, indole-3-carbinol, alpha-angelicalactone, kahweol/cafestol palmitates, quercetin, green tea, black tea, tannic acid, amylase-resistant starch, and physical exercise) comprised sulfur-containing compounds, antioxidants, flavonoids, diterpenes, polyphenols, high dietary fiber, etc. The strongest inhibition of PhIP-DNA adduct formation in the colon was observed upon pretreatment with black tea, benzylisothiocyanate, and a mixture (1:1) of kahweol:cafestol palmitates, which resulted in 67, 66, and 54% decreases in colon PhIP-DNA adduct levels, as compared with controls. Preliminary studies on their mechanism of action indicated that only kahweol:cafestol caused a substantial induction of glutathione S-transferase isozymes (GSTs) that are thought to be important in the detoxification of PhIP. Notably, this induction occurred in the liver rather than in the colon.

Animals↗
PubMed1997

Polymorphisms of CYP1A1 and GSTM1 influence the in vivo function of CYP1A2.

Differences in human cancer susceptibility have been attributed to polymorphisms of carcinogen metabolizing enzymes. Our efforts have focused on the systems responsible for metabolism of aromatic and heterocyclic amines found in cigarette smoke and in cooked foods. Cytochrome P4501A2 (CYP1A2), which catalyzes aromatic and heterocyclic amine N-oxidation, has been implicated as a risk factor in both urinary bladder and colorectal cancer. In the present study we used the results of caffeine phenotyping experiments to measure the effects of cigarette smoke and compounds present in meat cooked at high temperature on CYP1A2 activity. Subjects in the smoking cessation study had mean CYP1A2 activity of 17.8 (expressed as the urinary molar ratio of [17X + 17U]/137X) while smoking: however, this activity decreased to 10.9 three weeks after cessation of smoking. Subjects in the cooked meat feeding study had mean CYP1A2 activity of 9.01 after 1 week of consuming meat cooked at low temperature, but this value increased to 12.7 after 1 week of consuming meat cooked at high temperature. Because no association has been identified between differences in CYP1A2 activity and variations in the CYP1A2 structural gene, we sought to determine whether the activities of other carcinogen metabolizing enzymes are involved in the regulation of CYP1A2 activity. CYP1A2 activity was higher in individuals who express the GSTM1 null allele compared to those expressing the GSTM1*A,B allele, 10.2 vs. 8.5 for unexposed conditions and 15.0 vs. 12.3 for exposed conditions. CYP1A1 genotyping demonstrated that individuals possessing the Ile/Ile CYP1A1 genotype had greater mean CYP1A2 activity than those who had the heterozygous Ile/Val allelic variant of the CYP1A1 gene. However, upon exposure to cigarette smoke or high-temperature cooked meat, individuals possessing the heterozygous form of the CYP1A1 gene had significantly increased CYP1A2 activity (18.1) compared to those with the more common Ile/Ile CYP1A1 genotype (13.3). These results indicate that CYP1A2, CYP1A1, and GSTM1 gene-gene interactions could be important confounders in the interpretation of molecular epidemiology studies.

Arylamine N-Acetyltransferase↗
PubMed1997

Neonatal mouse assay for tumorigenicity: alternative to the chronic rodent bioassay.

The chronic rodent bioassay for tumors has been utilized systematically for 25 years to identify chemicals with carcinogenic potential in man. In general, those chemicals exhibiting tumorigenicity at multiple sites in both mice and rats have been regarded as possessing strong carcinogenic potential in humans. In comparison, the value of data collected for those test chemicals exhibiting more sporadic tumorigenicity results (e.g., single species/single sex or dose-independent) has been questioned. As knowledge of the carcinogenic process has increased, several alternative test systems, usually faster and less expensive than the 2-year bioassay, have been suggested for identification of the strongly acting, transspecies carcinogens. The International Conference on Harmonization for Technical Requirements for the Registration of Pharmaceuticals for Human Use has proposed an international standard that allows for the use of one long-term rodent carcinogenicity study, plus one supplementary study to identify potential human pharmaceutical carcinogens. The neonatal mouse assay for tumorigenicity has been used since 1959; however, relative to other alternate tests, little has been written about this system. It is clear that this assay system successfully identifies transspecies carcinogens from numerous chemical classes, thus recommending itself as a strong candidate for a supplementary study to identify potential human carcinogens. In contrast, there are decidedly less data available from this assay in response to pharmaceuticals shown to exhibit weak and/or conflicting results in the 2-year bioassay, knowledge invaluable to the regulatory process. This paper reviews the historical development and our experience with the neonatal mouse assay and includes suggestions for a standardized protocol and strategies to document its response to "weak" and/or "nongenotoxic" carcinogens.

Animals↗
PubMed1997

Specificity of mutagenesis by 4-aminobiphenyl: mutations at G residues in bacteriophage M13 DNA and G-->C transversions at a unique dG(8-ABP) lesion in single-stranded DNA.

Mutagenesis by the human bladder carcinogen 4-aminobiphenyl (ABP) was studied in single-stranded DNA from a bacteriophage M13 cloning vector. In comparison to ABP lesions in double-stranded DNA, lesions in single-stranded DNA were approximately 70-fold more mutagenic and 50-fold more genotoxic. Sequencing analysis of ABP-induced mutations in the lacZ gene revealed exclusively base-pair substitutions, with over 80% of the mutations occurring at G sites; the G at position 6310 accounted for 25% of the observed mutations. Among the sequence changes at G sites, G-->T transversions predominated, followed by G-->C transversions and G-->A transitions. In order to further elucidate the mutagenic mechanism of ABP, an oligonucleotide containing the major DNA adduct, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG(8-ABP)), was situated within the PstI site of a single-stranded M13 genome. After in vivo replication of the adduct containing ABP-modified and control (unadducted) genomes, the mutational frequency and mutational specificity of the dG(8-ABP) lesion were determined. The targeted mutational efficiency was approximately 0.01%, and the primary mutation observed was the G-->C transversion. Thus dG(8-ABP), albeit weakly mutagenic at the PstI site, can contribute to the mutational spectrum of ABP lesions.

Amino Acid Sequence↗
PubMed1997

Metabolism of carcinogenic heterocyclic and aromatic amines by recombinant human cytochrome P450 enzymes.

The N-hydroxylation of carcinogenic arylamines represents an initial step in their metabolic activation. Animal studies have shown that this reaction is catalyzed by the cytochrome P450 (P450) enzymes P450 1A1 and P450 1A2. In this study, utilizing enzymes expressed in Escherichia coli (and purified) or in human B-lymphoblastoid cells, the catalytic activities of recombinant human P450 1A1, P450 1A2, and P450 3A4 for N-hydroxylation of several carcinogenic arylamines were determined. P450 1A2 from both expression systems catalyzed the N-hydroxylation of 4-aminobiphenyl and the heterocyclic amines, 2-amino-3-methylimidazo[4,5-f/quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Rates were similar, with values of 1.1-7.8 nmol/min/nmol P450. In contrast, P450 1A1 catalyzed N-hydroxylation of only PhIP, and no activity was observed with P450 3A4. Further kinetic analysis with purified P450 1A2 showed similar Km and Vmax values for N-hydroxylation of the arylamines. Furafylline and fluvoxamine, inhibitors of P450 1A2 activity in human liver microsomes, were found to be inhibitory of the recombinant P450 1A2 N-hydroxylation activity. Results from this study are supportive of a major role for human P450 1A2 in the metabolic activation of arylamines.

Amines↗
PubMed1997

Metabolic activation of aromatic amines by human pancreas.

Epidemiologic studies have suggested that aromatic amines (and nitroaromatic hydrocarbons) may be carcinogenic for human pancreas. Pancreatic tissues from 29 organ donors (13 smokers, 16 non-smokers) were examined for their ability to metabolize aromatic amines and other carcinogens. Microsomes showed no activity for cytochrome P450 (P450) 1A2-dependent N-oxidation of 4-aminobiphenyl (ABP) or for the following activities (and associated P450s): aminopyrine N-demethylation and ethylmorphine N-demethylation (P450 3A4); ethoxyresorufin O-deethylation (P450 1A1) and pentoxyresorufin O-dealkylation (P450 2B6); p-nitrophenol hydroxylation and N-nitrosodimethyl-amine N-demethylation (P450 2E1); lauric acid omega-hydroxylation (P450 4A1); and 4-(methylnitrosamino)-1-(3-pyridyl-1-butanol) (NNAL) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) alpha-oxidation (P450 1A2, 2A6, 2D6). Antibodies were used to examine microsomal levels of P450 1A2, 2A6, 2C8/9/18/19, 2E1, 2D6, and 3A3/4/5/7 and epoxide hydrolase. Immunoblots detected only epoxide hydrolase at low levels; P450 levels were <1% of liver. Microsomal benzidine/prostaglandin hydroperoxidation activity was low. In pancreatic cytosols and microsomes, 4-nitrobiphenyl reductase activities were present at levels comparable to human liver. The O-acetyltransferase activity (AcCoA-dependent DNA-binding of [3H]N-hydroxy-ABP) of pancreatic cytosols was high, about twothirds the levels measured in human colon. Cytosols showed high activity for N-acetylation of p-aminobenzoic acid, but not of sulfamethazine, indicating that acetyltransferase-1 (NAT1) is predominantly expressed in this tissue. Cytosolic sulfotransferase was detected at low levels. Using 32P-post-labeling enhanced by butanol extraction, putative arylamine-DNA adducts were detected in most samples. Moreover, in eight of 29 DNA samples, a major adduct was observed that was chromatographically identical to the predominant ABP-DNA adduct, N-(deoxyguanosin-8-yl)-ABP. These results are consistent with a hypothesis that aromatic amines and nitroaromatic hydrocarbons may be involved in the etiology of human pancreatic cancer.

Acetyltransferases↗
PubMed1996

Inhibitory effect of caloric restriction on tumorigenicity induced by 4-aminobiphenyl and 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP) in the CD1 newborn mouse bioassay.

The tumorigenicity of 4-aminobiphenyl (4-ABP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were studied in combination with caloric restriction in the male neonatal CD1 mouse bioassay. 4-ABP and PhIP exhibited moderate and weak tumorigenicity, respectively, in ad libitum fed mice; however, none of the caloric restricted mice developed tumors. These results indicate that caloric restriction, even when begun 3 months after the conclusion of compound treatment, markedly inhibited 4-ABP- and PhIP-induced tumors in the CD1 mouse.

Aminobiphenyl Compounds↗
PubMed1996

Uptake of the food-derived heterocyclic amine carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and its N-hydroxy metabolite into rat pancreatic acini and hepatocytes in vitro.

Sinc DNA adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are formed at relatively high levels in the rat pancreas but not liver, we examined the uptake of PhIP and its N-hydroxy metabolite (N-OH-PhIP) into pancreatic acini and hepatocytes to determine if differential tissue uptake was a factor modulating the formation of PhIP-DNA adducts. In addition, since the precursors of PhIP formation are two amino acids and since various amino acid transporters have been identified in the pancreas, the possible involvement of these transporters in the uptake of PhIP and N-OH-PhIP was investigated. The uptake both heterocyclic compounds into both tissue preparations was rapid, with maximal uptake occurring with 1-2 min. However, PhIP uptake into pancreatic acini was significantly (2-way ANOVA, P < 0.05) greater than uptake of N-OH-PhIP into pancreatic acini and the uptake of both PhIP and N-OH-PhIP into hepatocytes. Although uptake was rapid, efflux of both compounds from both tissue preparations was also rapid. However, the efflux rate constant (1.86 +/- 0.6/min, mean +/- SEM) for PhIP) was significantly lower (Student's t-test, P < 0.05) than that for N-OH-PhIP (4.14 +/- 0.04/min) from pancreatic acini. This, combined with the increased uptake of PhIP into pancreatic acini , suggests that there is substantial but reversible binding of PhIP in the pancreas. The uptake of both PhIP and N-OH-PhIP into pancreatic acini and hepatocytes was not affected by the presence of various amino acids in the incubation buffer, indicating that amino acid transporters are not involved in uptake of these compounds. Furthermore, uptake of both compounds did not appear to be dependent on metabolic energy supply. The above data, together with the high octanol:buffer partition coefficients (logP = 1.322 and 1.301 for PhiP and N-OH-PhIP respectively) suggest that both uptake and efflux of PhIP and N-OH-PhIP are consistent with a process of passive diffusion. The tissue binding characteristics for PhIP in the pancreas may create conditions whereby pancreatic cytochrome P450 1A1 can catalyse the formation of N-OH-PhIP. While N-OH-PhIP is not the ultimate reactive DNA binding species, it has been shown to directly bind to and form DNA adducts. Therefore, it is possible that the apparent selective accumulation of PhIP may contribute to the high level of PhIP-DNA adducts formed in the rat pancreas.

Amino Acids↗
PubMed1996

Evidence of anti-benzo[a]pyrene diolepoxide-DNA adduct formation in human colon mucosa.

As risk factors for colorectal cancer include consumption of foods potentially contaminated with polycyclic aromatic hydrocarbons (PAHs), the level of (+)-r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE] bound to DNA of human colon mucosa samples was quantified by a sensitive and specific HPLC/fluorescence method (Alexandrov et al., Cancer Res. 51, 6248-6253, 1992). (+)-anti-BPDE-DNA adducts were detected in four out of seven colon mucosa samples but not in any of 11 human pancreas samples from smokers and non-smokers. Adduct levels in human colon varied between 0.2 and 1.0 (+)-anti-BPDE-DNA adducts/10(8) nucleotides. Our results provide evidence that: (i) the DNA in human colon cells can be damaged by benzo[a]pyrene, possibly derived from diet and/or tobacco smoke; (ii) DNA adduct formation in human colon epithelium proceeds via the diol epoxide pathway; (iii) benzo[a]pyrene and other PAHs could play a role in the etiology of human colorectal cancer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1996

Metabolism of 2-amino-alpha-carboline. A food-borne heterocyclic amine mutagen and carcinogen by human and rodent liver microsomes and by human cytochrome P4501A2.

2-Amino-alpha-carboline (A alpha C) is a mutagenic and carcinogenic heterocyclic amine that is formed as a pyrolysis product during the high temperature cooking of food and the burning of tobacco. Human, rat, and mouse hepatic microsomes each catalyzed the NADPH-dependent oxidation of A alpha C to form six products separable by HPLC. The two major metabolites, which together accounted for approximately 85% of the total metabolism, were characterized by UV, fluorescence, proton magnetic resonance, and mass spectral analyses as 3-hydroxy-A alpha C and 6-hydroxy-A alpha C. The remaining 15% were judged to be N-hydroxy-A alpha C and its oxidation products, based on chromatographic and spectral comparisons with a standard, whose synthesis and characterization are also described. Although the proportions of each metabolite were similar across species and individuals, the overall rate of metabolism of A alpha C by human hepatic microsomes showed a wide interindividual variation (37-fold), with a mean activity that was comparable with that observed with rat or mouse liver microsomes. alpha-Naphthoflavone, a selective inhibitor for cytochromes P4501A1 and P4501A2, strongly inhibited formation of both ring-hydroxylation and N-oxidation products by human, rat, or mouse liver hepatic microsomes. In addition, A alpha C oxidation was strongly correlated (r = 0.98; p < 0.001) with the oxidation of 4-aminobiphenyl, a known selective substrate for human and rodent cytochromes P4501A2. Immunoblot analyses confirmed the presence of cytochromes P4501A2, and not P4501A1, in human liver microsomes. Additional studies using recombinant human cytochromes P450 show that high catalytic activity for A alpha C metabolism was associated with human cytochrome P4501A2. Lower, but significant activity was also noted for P4501A1 and P4502C10, which could have important implications for the metabolic activation of A alpha C extrahepatic tissues. Neither A alpha C metabolism nor immunoreactive cytochrome P4501A2 (or P4501A1) was detected in human pancreatic microsomes. Although further carcinogenicity and biomarker studies for A alpha C are needed, the high rate of A alpha C metabolism by human liver cytochrome P4501A2 suggests that humans with the rapid P4501A2 phenotype with may be more susceptible than rodents to this heterocyclic amine carcinogen.

Animals↗
PubMed1996

Mouse liver microsomal metabolism of chloral hydrate, trichloroacetic acid, and trichloroethanol leading to induction of lipid peroxidation via a free radical mechanism.

Metabolism of chloral hydrate (CH) by male B6C3F1 mouse liver microsomes (control-microsomes) generated free radical intermediates that resulted in endogenous lipid peroxidation, forming malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT), acetone, and propionaldehyde. Because MDA, FA, and ACT are tumorigens, endogenous formation of lipid peroxidation products via a free radical mechanism may be responsible for hepatocellular tumorigenicity of CH to the B6C3F1 mice. Trichloroacetic acid (TCA) and trichloroethanol (TCE), the primary metabolites of CH, also generated free radicals and induced lipid peroxidation. Lipid peroxidation from TCA equaled that induced by CH, whereas that from TCE was 3- to 4-fold lower, suggesting that metabolism of CH to TCA may be the predominant pathway leading to lipid peroxidation. Metabolism of CH, TCA, and TCE by liver microsomes of mice pretreated with pyrazole (pyrazole-microsomes) yielded lipid peroxidation products at a level 2- to 3-fold higher than those from liver microsomes of untreated mice. In addition, CH-induced lipid peroxidation catalyzed by control-microsomes and pyrazole-microsomes was reduced significantly by 2,4-dichloro-6-phenylphenoxyethylamine, a general cytochrome P450 inhibitor. Thus, our study suggests that cytochrome P450 is the enzyme catalyzing the metabolic activation of CH and its metabolites (TCA and TCE) leading to lipid peroxidation, and that CYP2E1 may be the major isozyme responsible. This latter conclusion was supported by results using human lymphoblastoid cells expressing cytochrome P4502E1, which metabolized CH to reactants inducing mutations, whereas the parental cell line was inactive.

Allopurinol↗
PubMed1996

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.

Age Factors↗
PubMed1996

Cytochrome P-450 and acetyltransferase expression as biomarkers of carcinogen-DNA adduct levels and human cancer susceptibility.

Carcinogen-DNA adducts are generally regarded as relevant biomarkers of carcinogen exposure and their levels in target tissues have often been predictive of tumor incidence in experimental animals. Thus, human risk assessment procedures have utilized dose-response models that assume proportional relationships between carcinogen exposure and cancer susceptibility, even though wide inter-individual variations in human metabolic activating enzymes have now been clearly established. To evaluate these approaches, we have examined the relationship between carcinogen exposure, DNA adduct levels, metabolic activation phenotypes, and cancers of the larynx, urinary bladder, and colon. Cigarette smoking is a strong risk factor for cancers of the larynx and urinary bladder. In the larynx, the DNA adducts appear to be derived predominantly from polycyclic aromatic hydrocarbons (PAHs) and are evident only in tissue from smokers. However, adduct levels appear to be determined primarily by expression of cytochrome P450 (CYP) 2C9/10, which varies > 10-fold in different individuals. This CYP catalyzes the metabolic activation of benzo (alpha) pyrene (BP) to a 9-hydroxy-BP-DNA adduct that accounts for up to 25% of the putative PAH adducts formed in vivo. For the urinary bladder, putative aromatic amine (AA)-DNA adducts are predominant and are significantly elevated in current smokers. Rapid CYP1A2 and slow acetyltransferase (NAT2) phenotypes have been previously implicated in the activation (N-oxidation) and detoxification (N-acetylation) of AAs for human bladder carcinogenesis. Data now indicate that NAT1, which is expressed in human urothelium and catalyzes the O-acetylation of N-hydroxy arylamines, is significantly correlated with DNA adduct levels and is bimodally distributed in this tissue. Colo-rectal cancer risk, which has been associated with exposure to heterocyclic amines (HAs) in cooked foods, is strongly elevated in individuals with the combined rapid phenotypes for CYP1A2 and NAT2. These enzymes are uniquely responsible for HA N-oxidation and subsequent O-acetylation, forming DNA adducts that are found in human colon. These studies indicate that cancer risk assessment procedures should be redesigned to include biomarkers of susceptibility, especially those involved in carcinogen bioactivation.

Acetyltransferases↗
PubMed1995

Formation of malondialdehyde-modified 2'-deoxyguanosinyl adduct from metabolism of chloral hydrate by mouse liver microsomes.

We previously reported that metabolism of chloral hydrate (CH), a widely used sedative and hypnotic, by male B6C3F1 mouse liver microsomes resulted in lipid peroxidation, producing the tumorigen malondialdehyde (MDA). Now we have found that incubation of CH in the presence of calf thymus DNA resulted in the formation of an MDA-modified DNA adduct as detected by 32P-postlabeling analysis. Similar results were obtained from incubation of trichloroacetic acid and trichloroethanol, both metabolites of CH.

Animals↗
PubMed1995

Polymorphism in the N-acetyltransferase 1 (NAT1) polyadenylation signal: association of NAT1*10 allele with higher N-acetylation activity in bladder and colon tissue.

Exposures to carcinogens present in the diet, in cigarette smoke, or in the environment have been associated with increased risk of bladder and colorectal cancer. The aromatic amines and their metabolites, a class of carcinogen implicated in these exposures, can be N- or O-acetylated by the NAT1 and NAT2 enzymes. Acetylation may result in activation to DNA-reactive metabolites or, in some cases, detoxification. Many studies have focused on genetic variation in NAT2 and its potential as a risk factor in bladder and colorectal cancer; however, NAT1 activity is higher in bladder and colonic mucosa than NAT2, and the NAT1 enzyme also exhibits phenotypic variation among human tissue samples. We hypothesized that specific genetic variants in the polyadenylation signal of the NAT1 gene would alter tissue levels of NAT1 enzyme activity and used a PCR-based method to distinguish polymorphic NAT1 alleles in samples obtained from 45 individuals. When the NAT1 genotype was compared with the NAT1 phenotype in bladder and colon tissue samples (p-aminobenzoic acid activity), we observed a approximately 2-fold higher NAT1 enzyme activity in samples from individuals who inherited a variant polyadenylation signal (NAT1*10 allele). This is the first observation relating a genetic polymorphism in NAT1 to a rapid/slow NAT1 phenotype in humans.

Acetylation↗