Detection of Aminophenylnorharman, a Possible Endogenous Mutagenic and Carcinogenic Compound, in Human Urine Samples

Metabolism and biomarkers of heterocyclic aromatic amines in humans

Heterocyclic aromatic amines (HAAs) form during the high-temperature cooking of meats, poultry, and fish. Some HAAs also arise during the combustion of tobacco. HAAs are multisite carcinogens in rodents, inducing cancer of the liver, gastrointestinal tract, pancreas, mammary, and prostate glands. HAAs undergo metabolic activation by N-hydroxylation of the exocyclic amine groups to produce the proposed reactive intermediate, the heteroaryl nitrenium ion, which is the critical metabolite implicated in DNA damage and genotoxicity. Humans efficiently convert HAAs to these reactive intermediates, resulting in HAA protein and DNA adduct formation. Some epidemiologic studies have reported an association between frequent consumption of well-done cooked meats and elevated cancer risk of the colorectum, pancreas, and prostate. However, other studies have reported no associations between cooked meat and these cancer sites. A significant limitation in epidemiology studies assessing the role of HAAs and cooked meat in cancer risk is their reliance on food frequency questionnaires (FFQ) to gauge HAA exposure. FFQs are problematic because of limitations in self-reported dietary history accuracy, and estimating HAA intake formed in cooked meats at the parts-per-billion level is challenging. There is a critical need to establish long-lived biomarkers of HAAs for implementation in molecular epidemiology studies designed to assess the role of HAAs in health risk. This review article highlights the mechanisms of HAA formation, mutagenesis and carcinogenesis, the metabolism of several prominent HAAs, and the impact of critical xenobiotic-metabolizing enzymes on biological effects. The analytical approaches that have successfully biomonitored HAAs and their biomarkers for molecular epidemiology studies are presented.

Memories of a friend and colleague - Takashi Sugimura

Takashi Sugimura, M.D., Honorary President of the National Cancer Center in Tokyo, and former President of The Japan Academy, is regarded by many as a pre-eminent contributor to the field of environmental genotoxicology. His pioneering spirit led to many key discoveries over a long and distinguished scientific career, including the first preclinical models for gastric cancer, identification of novel mutagens from cooked food, and the development of fundamental concepts in environmental chemical carcinogenesis. With his passing on September 6, 2020, many will reflect on the loss of an astute and engaging "Scientific Giant," who with warmth and good humor maintained lasting friendships both at home and abroad, beyond his many important scientific contributions.

Facile Preparation of Dual-Shell Novel Covalent-Organic Framework Functionalized Magnetic Nanospheres Used for the Simultaneous Determination of Fourteen Trace Heterocyclic Aromatic Amines in Nonsmokers and Smokers of Cigarettes with Different Tar Yields Based on UPLC-MS/MS

The facile preparation, characterization, and application of novel dual-shell TpBD (a kind of covalent-organic framework) coated magnetic nanospheres as sorbents for simple, fast, and high selectivity capture of 14 heterocyclic aromatic amines (HAAs) are reported. Quantum chemistry theory calculations were conducted to directly and quantifiably describe the multiple interactions, including π-π, hydrogen bonding, cation-π, static electricity, and ion-exchange, between TpBD and heterocyclic aromatic amines. The excellent adsorption capacity of TpBD coated magnetic nanospheres was further evaluated by extraction of 14 HAAs from nonsmokers' and smokers' urine samples. Under the optimized conditions, the magnetic solid phase extraction process can be completed with high recovery ranging from 95.4% to 129.3%. After being washed with acetonitrile and water successively, the collected sorbents can be easily recycled and reused five times without any significant difference in performance. Coupled with the ultra performance liquid chromatography-tandem mass spectrometer detection, the exposure level of HAAs in nonsmokers and smokers smoking cigarettes with different tar yields were successfully explored. And, this implied that the robust method based on the versatile TpBD coated dual-shell magnetic nanospheres sorbents represents a great potential application in the analysis of disease markers and body fluids.

Mutagenicity in Surface Waters: Synergistic Effects of Carboline Alkaloids and Aromatic Amines

For decades, mutagenicity has been observed in many surface waters with a possible link to the presence of aromatic amines. River Rhine is a well-known example of this phenomenon but responsible compound(s) are still unknown. To identify the mutagenic compounds, we applied effect-directed analysis (EDA) utilizing novel analytical and biological approaches to a water sample extract from the lower Rhine. We could identify 21 environmental contaminants including two weakly mutagenic aromatic amines, and the known alkaloid comutagen norharman along with two related β-carboline alkaloids, carboline, and 5-carboline, which were reported the first time in surface waters. Results of mixture tests showed a strong synergism of the identified aromatic amines not only with norharman, but also with carboline and 5-carboline. Additionally, other nitrogen-containing compounds also contributed to the mutagenicity when aromatic amines were present. Thus, comutagenicity of β-carboline alkaloids with aromatic amines is shown to occur in surface waters. These results strongly suggest that surface water mutagenicity is highly complex and driven by synergistic mechanisms of a complex compound mixture (of which many are yet unidentified) rather than by single compounds. Therefore, mixture effects should be considered not only from mutagens alone, but also including possible comutagens and nonmutagenic compounds.

Role of human sulfotransferase 1A1 and N-acetyltransferase 2 in the metabolic activation of 16 heterocyclic amines and related heterocyclics to genotoxicants in recombinant V79 cells

Heterocyclic aromatic amines (HAAs) are primarily produced during the heating of meat or fish. HAAs are mutagenic and carcinogenic, and their toxicity in model systems depend on metabolic activation. This activation is mediated by cytochrome P450 (CYP) enzymes, in particular CYP1A2. Some studies have indicated a role of human sulfotransferase (SULT) 1A1 and N-acetyltransferase (NAT) 2 in the terminal activation of HAAs. In this study, we conducted a metabolism/genotoxicity relationship analysis for 16 HAAs and related heterocyclics. We used the γH2AX genotoxicity assay in V79 cells (deficient in CYP, SULT and NAT) and V79-derived cell lines genetically engineered to express human CYP1A2 alone or in combination with human SULT1A1 or NAT2. Our data demonstrated genotoxic properties for 13 out of the 16 compounds tested. A clear relationship between metabolic bioactivation and genotoxicity allowed to distinguish four groups: (1) Trp-P-1 genotoxicity was linked to CYP1A2 bioactivation only-with negligible effects of phase II enzymes; (2) Glu-P-2, Glu-P-1, Trp-P-2, APNH, MeAαC and AαC were bioactivated by CYP1A2 in combination with either phase II enzyme tested (NAT2 or SULT1A1); (3) IQ, 4-MeIQ, IQx, 8-MeIQx, and 4,8-DiMeIQx required CYP1A2 in combination with NAT2 to be genotoxic, whereas SULT1A1 did not enhance their genotoxicity; (4) PhIP became genotoxic after CYP1A2 and SULT1A1 bioactivation-NAT2 had not effect. Our results corroborate some previous data regarding the genotoxic potency of seven HAAs and established the genotoxicity mechanism for five others HAAs. This study also permits to compare efficiently the genotoxic potential of these 13 HAAs.

Metabolism and biomarkers of heterocyclic aromatic amines in molecular epidemiology studies: lessons learned from aromatic amines

Aromatic amines and heterocyclic aromatic amines (HAAs) are structurally related classes of carcinogens that are formed during the combustion of tobacco or during the high-temperature cooking of meats. Both classes of procarcinogens undergo metabolic activation by N-hydroxylation of the exocyclic amine group to produce a common proposed intermediate, the arylnitrenium ion, which is the critical metabolite implicated in toxicity and DNA damage. However, the biochemistry and chemical properties of these compounds are distinct, and different biomarkers of aromatic amines and HAAs have been developed for human biomonitoring studies. Hemoglobin adducts have been extensively used as biomarkers to monitor occupational and environmental exposures to a number of aromatic amines; however, HAAs do not form hemoglobin adducts at appreciable levels, and other biomarkers have been sought. A number of epidemiologic studies that have investigated dietary consumption of well-done meat in relation to various tumor sites reported a positive association between cancer risk and well-done meat consumption, although some studies have shown no associations between well-done meat and cancer risk. A major limiting factor in most epidemiological studies is the uncertainty in quantitative estimates of chronic exposure to HAAs, and thus, the association of HAAs formed in cooked meat and cancer risk has been difficult to establish. There is a critical need to establish long-term biomarkers of HAAs that can be implemented in molecular epidemioIogy studies. In this review, we highlight and contrast the biochemistry of several prototypical carcinogenic aromatic amines and HAAs to which humans are chronically exposed. The biochemical properties and the impact of polymorphisms of the major xenobiotic-metabolizing enzymes on the biological effects of these chemicals are examined. Lastly, the analytical approaches that have been successfully employed to biomonitor aromatic amines and HAAs, and emerging biomarkers of HAAs that may be implemented in molecular epidemiology studies are discussed.

Aniline in hydrolyzed urine and plasma--possible biomarkers for phenylisocyanate exposure

There are few studies on phenylisocyanate (PhI) exposure, although there are studies indicating that PhI is a very potent chemical sensitizer. The aim of this study was to evaluate aniline in urine and plasma as possible biomarkers of exposure to PhI. Occupational airborne exposure to PhI was measured during one day for 11 workers exposed to thermal degradation products from polyurethane with filters impregnated with 2-methoxyphenyl piperazine. A urine sample was collected from each worker on measurement day, and plasma samples were collected within the following 2 weeks. Urine and plasma samples also were collected from four unexposed subjects. The biological samples were hydrolyzed and analyzed with gas chromatography mass spectrometry. The time-weighted averages (TWA) for the workers were between 0.1 and 1.6 microg/m3. Aniline levels in urine were in the same range for the exposed and unexposed workers, but there was a significant correlation between air and urinary levels (Pearson's correlation coefficient r = 0.518; p = 0.05). All exposed workers had higher levels in the plasma samples than the highest control, and there was a significant correlation between the plasma levels and measured air levels (r = 0.675; p = 0.008). The conclusion is that aniline in hydrolyzed urine and plasma are possible biomarkers of exposure to PhI, and that the plasma biomarker is more sensitive, at least at this rather low exposure.

Tumor-initiating potency of a novel heterocyclic amine, aminophenylnorharman in mouse colonic carcinogenesis model

A novel heterocyclic amine, 9-(4'-aminophenyl)-9H-pyrido[3,4-b]indole (aminophenylnorharman, APNH), which is formed from nonmutagenic 9H-pyrido[3,4-b]indole (norharman) and aniline, is mutagenic to bacteria and mammalian cells and potently carcinogenic in rats. APNH is detected in human urine samples, suggesting that humans are continuously exposed to APNH. In the present study, (32)P-postlabelin analysis revealed that the levels of APNH-DNA adduct 24 hr after the treatment with APNH (1, 5 and 20 mg/kg body weight) in male ICR mice were increased in a dose-dependent manner in the colon and liver. Based on these findings, we determined the tumor-initiating potency of APNH in an inflammation-related and two-stage mouse colon carcinogenesis model. Male Crj: CD-1 (ICR) mice were given a single intragastric administration (1, 2, 5 or 10 mg/kg body weight) of APNH and subsequent 1-week oral exposure to dextran sodium sulfate (DSS, 2% in drinking water). Treatment with APNH and DSS resulted in numerous colon tumor development: the incidence and multiplicity of the tumors were the highest in the mice received 10 mg/kg body weight of APNH and followed by DSS. Development of colon tumors was dose-dependent of APNH. Seven of 9 (77.8%) colonic adenocarcinomas developed in mice treated with APNH (10 mg/kg body weight) and DSS had beta-catenin gene mutations at codons 32 and 37, being predominantly transversion. These findings indicate that APNH has an initiating activity in inflamed mouse colon and the APNH-DNA adduct formation correlates with its tumorigenic potential.