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Bárta F, Dedíková A, Bebová M, Dušková Š, Mráz J, Schmeiser HH, Arlt VM, Hodek P, Stiborová M. Co-Exposure to Aristolochic Acids I and II Increases DNA Adduct Formation Responsible for Aristolochic Acid I-Mediated Carcinogenicity in Rats. Int J Mol Sci 2021; 22:ijms221910479. [PMID: 34638820 PMCID: PMC8509051 DOI: 10.3390/ijms221910479] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2021] [Revised: 09/20/2021] [Accepted: 09/23/2021] [Indexed: 11/16/2022] Open
Abstract
The plant extract aristolochic acid (AA), containing aristolochic acids I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN), unique renal diseases associated with upper urothelial cancer. Recently (Chemical Research in Toxicology 33(11), 2804–2818, 2020), we showed that the in vivo metabolism of AAI and AAII in Wistar rats is influenced by their co-exposure (i.e., AAI/AAII mixture). Using the same rat model, we investigated how exposure to the AAI/AAII mixture can influence AAI and AAII DNA adduct formation (i.e., AA-mediated genotoxicity). Using 32P-postlabelling, we found that AA-DNA adduct formation was increased in the livers and kidneys of rats treated with AAI/AAII mixture compared to rats treated with AAI or AAII alone. Measuring the activity of enzymes involved in AA metabolism, we showed that enhanced AA-DNA adduct formation might be caused partially by both decreased AAI detoxification as a result of hepatic CYP2C11 inhibition during treatment with AAI/AAII mixture and by hepatic or renal NQO1 induction, the key enzyme predominantly activating AA to DNA adducts. Moreover, our results indicate that AAII might act as an inhibitor of AAI detoxification in vivo. Consequently, higher amounts of AAI might remain in liver and kidney tissues, which can be reductively activated, resulting in enhanced AAI DNA adduct formation. Collectively, these results indicate that AAII present in the plant extract AA enhances the genotoxic properties of AAI (i.e., AAI DNA adduct formation). As patients suffering from AAN and BEN are always exposed to the plant extract (i.e., AAI/AAII mixture), our findings are crucial to better understanding host factors critical for AAN- and BEN-associated urothelial malignancy.
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Affiliation(s)
- František Bárta
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic; (F.B.); (A.D.); (M.B.); (P.H.); (M.S.)
| | - Alena Dedíková
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic; (F.B.); (A.D.); (M.B.); (P.H.); (M.S.)
| | - Michaela Bebová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic; (F.B.); (A.D.); (M.B.); (P.H.); (M.S.)
| | - Šárka Dušková
- Centre of Occupational Health, National Institute of Public Health, Šrobárova 48, 100 42 Prague 10, Czech Republic; (Š.D.); (J.M.)
| | - Jaroslav Mráz
- Centre of Occupational Health, National Institute of Public Health, Šrobárova 48, 100 42 Prague 10, Czech Republic; (Š.D.); (J.M.)
| | - Heinz H. Schmeiser
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany;
| | - Volker M. Arlt
- Department of Analytical, Environmental and Forensic Sciences Division, King’s College London, 150 Stamford Street, London SE1 9NH, UK
- Toxicology Department, GAB Consulting GmbH, Heinrich-Fuchs-Str. 96, 69126 Heidelberg, Germany
- Correspondence: ; Tel.: +49-6221-432018-0
| | - Petr Hodek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic; (F.B.); (A.D.); (M.B.); (P.H.); (M.S.)
| | - Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic; (F.B.); (A.D.); (M.B.); (P.H.); (M.S.)
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Bellamri M, Brandt K, Brown CV, Wu MT, Turesky RJ. Cytotoxicity and genotoxicity of the carcinogen aristolochic acid I (AA-I) in human bladder RT4 cells. Arch Toxicol 2021; 95:2189-2199. [PMID: 33938965 PMCID: PMC8284306 DOI: 10.1007/s00204-021-03059-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 04/21/2021] [Indexed: 11/28/2022]
Abstract
Aristolochic acid (AA-I) induces upper urothelial tract cancer (UUTC) and bladder cancer (BC) in humans. AA-I forms the 7-(2'-deoxyadenosin-N6-yl)aristolactam I (dA-AL-I) adduct, which induces multiple A:T-to-T:A transversion mutations in TP53 of AA-I exposed UTUC patients. This mutation is rarely reported in TP53 of other transitional cell carcinomas and thus recognized as an AA-I mutational signature. A:T-to-T:A transversion mutations were recently detected in bladder tumors of patients in Asia with known AA-I-exposure, implying that AA-I contributes to BC. Mechanistic studies on AA-I genotoxicity have not been reported in human bladder. In this study, we examined AA-I DNA adduct formation and mechanisms of toxicity in the human RT4 bladder cell line. The biological potencies of AA-I were compared to 4-aminobiphenyl, a recognized human bladder carcinogen, and several structurally related carcinogenic heterocyclic aromatic amines (HAA), which are present in urine of smokers and omnivores. AA-I (0.05-10 µM) induced a concentration- and time-dependent cytotoxicity. AA-I (100 nM) DNA adduct formation occurred at over a thousand higher levels than the principal DNA adducts formed with 4-ABP or HAAs (1 µM). dA-AL-I adduct formation was detected down to a 1 nM concentration. Studies with selective chemical inhibitors provided evidence that NQO1 is the major enzyme involved in AA-I bio-activation in RT4 cells, whereas CYP1A1, another enzyme implicated in AA-I toxicity, had a lesser role in bio-activation or detoxification of AA-I. AA-I DNA damage also induced genotoxic stress leading to p53-dependent apoptosis. These biochemical data support the human mutation data and a role for AA-I in BC.
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Affiliation(s)
- Medjda Bellamri
- Masonic Cancer Center and Department of Medicinal Chemistry, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street, Minneapolis, MN, 55455, USA
| | - Kyle Brandt
- Masonic Cancer Center and Department of Medicinal Chemistry, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street, Minneapolis, MN, 55455, USA
| | - Christina V Brown
- Masonic Cancer Center and Department of Medicinal Chemistry, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street, Minneapolis, MN, 55455, USA
| | - Ming-Tsang Wu
- Department of Environmental and Occupational Medicine, Kaohsiung Medical University, CS Building, 100 Shih-Chuan 1st Road, Kaohsiung, Taiwan
| | - Robert J Turesky
- Masonic Cancer Center and Department of Medicinal Chemistry, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street, Minneapolis, MN, 55455, USA.
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Dedı Ková A, Bárta F, Martínek V, Kotalík K, Dušková Š, Mráz J, Arlt VM, Stiborová M, Hodek P. In Vivo Metabolism of Aristolochic Acid I and II in Rats Is Influenced by Their Coexposure. Chem Res Toxicol 2020; 33:2804-2818. [PMID: 32894017 DOI: 10.1021/acs.chemrestox.0c00198] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The plant extract aristolochic acid (AA), containing aristolochic acid I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy and Balkan endemic nephropathy, unique renal diseases associated with upper urothelial cancer. Differences in the metabolic activation and detoxification of AAI and AAII and their effects on the metabolism of AAI/AAII mixture in the plant extract might be of great importance for an individual's susceptibility in the development of AA-mediated nephropathies and malignancies. Here, we investigated in vivo metabolism of AAI and AAII after ip administration to Wistar rats as individual compounds and as AAI/AAII mixture using high performance liquid chromatography/electrospray ionization mass spectrometry. Experimental findings were supported by theoretical calculations using density functional theory. We found that exposure to AAI/AAII mixture affected the generation of their oxidative and reductive metabolites formed during Phase I biotransformation and excreted in rat urine. Several Phase II metabolites of AAI and AAII found in the urine of exposed rats were also analyzed. Our results indicate that AAI is more efficiently metabolized in rats in vivo than AAII. Whereas AAI is predominantly oxidized during in vivo metabolism, its reduction is the minor metabolic pathway. In contrast, AAII is mainly metabolized by reduction. The oxidative reaction only occurs if aristolactam II, the major reductive metabolite of AAII, is enzymatically hydroxylated, forming aristolactam Ia. In AAI/AAII mixture, the metabolism of AAI and AAII is influenced by the presence of both AAs. For instance, the reductive metabolism of AAI is increased in the presence of AAII while the presence of AAI decreased the reductive metabolism of AAII. These results suggest that increased bioactivation of AAI in the presence of AAII also leads to increased AAI genotoxicity, which may critically impact AAI-mediated carcinogenesis. Future studies are needed to explain the underlying mechanism(s) for this phenomenon.
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Affiliation(s)
- Alena Dedı Ková
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
| | - František Bárta
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
| | - Václav Martínek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
| | - Kevin Kotalík
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
| | - Šárka Dušková
- Centre of Occupational Health, National Institute of Public Health, Šrobárova 48, 100 42 Prague 10, Czech Republic
| | - Jaroslav Mráz
- Centre of Occupational Health, National Institute of Public Health, Šrobárova 48, 100 42 Prague 10, Czech Republic
| | - Volker Manfred Arlt
- Department of Analytical, Environmental and Forensic Sciences Division, King's College London, 150 Stamford Street, London SE1 9NH, United Kingdom
| | - Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
| | - Petr Hodek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 12840 Prague, Czech Republic
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Sidorenko VS. Biotransformation and Toxicities of Aristolochic Acids. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1241:139-166. [PMID: 32383120 DOI: 10.1007/978-3-030-41283-8_9] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Environmental and iatrogenic exposures contribute significantly to human diseases, including cancer. The list of known human carcinogens has recently been extended by the addition of aristolochic acids (AAs). AAs occur primarily in Aristolochia herbs, which are used extensively in folk medicines, including Traditional Chinese Medicine. Ingestion of AAs results in chronic renal disease and cancer. Despite importation bans imposed by certain countries, herbal remedies containing AAs are readily available for purchase through the internet. With recent advancements in mass spectrometry, next generation sequencing, and the development of integrated organs-on-chips, our knowledge of cancers associated with AA exposure, and of the mechanisms involved in AA toxicities, has significantly improved. DNA adduction plays a central role in AA-induced cancers; however, significant gaps remain in our knowledge as to how cellular enzymes promote activation of AAs and how the reactive species selectively bind to DNA and kidney proteins. In this review, I describe pathways for AAs biotransformation, adduction, and mutagenesis, emphasizing novel methods and ideas contributing to our present understanding of AA toxicities in humans.
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Affiliation(s)
- Viktoriya S Sidorenko
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY, USA.
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Sborchia M, De Prez EG, Antoine MH, Bienfait L, Indra R, Valbuena G, Phillips DH, Nortier JL, Stiborová M, Keun HC, Arlt VM. The impact of p53 on aristolochic acid I-induced nephrotoxicity and DNA damage in vivo and in vitro. Arch Toxicol 2019; 93:3345-3366. [PMID: 31602497 PMCID: PMC6823306 DOI: 10.1007/s00204-019-02578-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 09/17/2019] [Indexed: 12/31/2022]
Abstract
Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. The tumour suppressor TP53 is a critical gene in carcinogenesis and frequently mutated in AA-induced urothelial tumours. We investigated the impact of p53 on AAI-induced nephrotoxicity and DNA damage in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for 2 or 6 days. Renal histopathology showed a gradient of intensity in proximal tubular injury from Trp53(+/+) to Trp53(-/-) mice, especially after 6 days. The observed renal injury was supported by nuclear magnetic resonance (NMR)-based metabonomic measurements, where a consistent Trp53 genotype-dependent trend was observed for urinary metabolites that indicate aminoaciduria (i.e. alanine), lactic aciduria (i.e. lactate) and glycosuria (i.e. glucose). However, Trp53 genotype had no impact on AAI-DNA adduct levels, as measured by 32P-postlabelling, in either target (kidney and bladder) or non-target (liver) tissues, indicating that the underlying mechanisms of p53-related AAI-induced nephrotoxicity cannot be explained by differences in AAI genotoxicity. Performing gas chromatography-mass spectrometry (GC-MS) on kidney tissues showed metabolic pathways affected by AAI treatment, but again Trp53 status did not clearly impact on such metabolic profiles. We also cultured primary mouse embryonic fibroblasts (MEFs) derived from Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice and exposed them to AAI in vitro (50 µM for up to 48 h). We found that Trp53 genotype impacted on the expression of NAD(P)H:quinone oxidoreductase (Nqo1), a key enzyme involved in AAI bioactivation. Nqo1 induction was highest in Trp53(+/+) MEFs and lowest in Trp53(-/-) MEFs; and it correlated with AAI-DNA adduct formation, with lowest adduct levels being observed in AAI-exposed Trp53(-/-) MEFs. Overall, our results clearly demonstrate that p53 status impacts on AAI-induced renal injury, but the underlying mechanism(s) involved remain to be further explored. Despite the impact of p53 on AAI bioactivation and DNA damage in vitro, such effects were not observed in vivo.
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Affiliation(s)
- Mateja Sborchia
- Department of Analytical, Environmental and Forensic Sciences, MRC-PHE Centre for Environment and Health, King's College London, London, SE1 9NH, UK
| | - Eric G De Prez
- Laboratory of Experimental Nephrology, Department of Experimental Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, 1070, Brussels, Belgium
| | - Marie-Hélène Antoine
- Laboratory of Experimental Nephrology, Department of Experimental Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, 1070, Brussels, Belgium
| | - Lucie Bienfait
- Department of Pathology, Erasme University Hospital, 1070, Brussels, Belgium
| | - Radek Indra
- Department of Biochemistry, Faculty of Science, Charles University Prague, 128 40, Prague, Czech Republic
| | - Gabriel Valbuena
- Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - David H Phillips
- Department of Analytical, Environmental and Forensic Sciences, MRC-PHE Centre for Environment and Health, King's College London, London, SE1 9NH, UK
| | - Joëlle L Nortier
- Laboratory of Experimental Nephrology, Department of Experimental Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, 1070, Brussels, Belgium
| | - Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University Prague, 128 40, Prague, Czech Republic
| | - Hector C Keun
- Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Volker M Arlt
- Department of Analytical, Environmental and Forensic Sciences, MRC-PHE Centre for Environment and Health, King's College London, London, SE1 9NH, UK.
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6
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Chang SY, Weber EJ, Sidorenko VS, Chapron A, Yeung CK, Gao C, Mao Q, Shen D, Wang J, Rosenquist TA, Dickman KG, Neumann T, Grollman AP, Kelly EJ, Himmelfarb J, Eaton DL. Human liver-kidney model elucidates the mechanisms of aristolochic acid nephrotoxicity. JCI Insight 2017; 2:95978. [PMID: 29202460 DOI: 10.1172/jci.insight.95978] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 10/11/2017] [Indexed: 12/14/2022] Open
Abstract
Environmental exposures pose a significant threat to human health. However, it is often difficult to study toxicological mechanisms in human subjects due to ethical concerns. Plant-derived aristolochic acids are among the most potent nephrotoxins and carcinogens discovered to date, yet the mechanism of bioactivation in humans remains poorly understood. Microphysiological systems (organs-on-chips) provide an approach to examining the complex, species-specific toxicological effects of pharmaceutical and environmental chemicals using human cells. We microfluidically linked a kidney-on-a-chip with a liver-on-a-chip to determine the mechanisms of bioactivation and transport of aristolochic acid I (AA-I), an established nephrotoxin and human carcinogen. We demonstrate that human hepatocyte-specific metabolism of AA-I substantially increases its cytotoxicity toward human kidney proximal tubular epithelial cells, including formation of aristolactam adducts and release of kidney injury biomarkers. Hepatic biotransformation of AA-I to a nephrotoxic metabolite involves nitroreduction, followed by sulfate conjugation. Here, we identify, in a human tissue-based system, that the sulfate conjugate of the hepatic NQO1-generated aristolactam product of AA-I (AL-I-NOSO3) is the nephrotoxic form of AA-I. This conjugate can be transported out of liver via MRP membrane transporters and then actively transported into kidney tissue via one or more organic anionic membrane transporters. This integrated microphysiological system provides an ex vivo approach for investigating organ-organ interactions, whereby the metabolism of a drug or other xenobiotic by one tissue may influence its toxicity toward another, and represents an experimental approach for studying chemical toxicity related to environmental and other toxic exposures.
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Affiliation(s)
- Shih-Yu Chang
- Department of Environmental and Occupational Health Sciences and
| | - Elijah J Weber
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Viktoriya S Sidorenko
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York, USA
| | - Alenka Chapron
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Catherine K Yeung
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.,Department of Medicine, Division of Nephrology, Kidney Research Institute, University of Washington, Seattle, Washington, USA
| | - Chunying Gao
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Qingcheng Mao
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Danny Shen
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Joanne Wang
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Thomas A Rosenquist
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York, USA
| | - Kathleen G Dickman
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York, USA
| | | | - Arthur P Grollman
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York, USA.,Department of Medicine, Stony Brook University, Stony Brook, New York, USA
| | - Edward J Kelly
- Department of Pharmaceutics, University of Washington, Seattle, Washington, USA
| | - Jonathan Himmelfarb
- Department of Medicine, Division of Nephrology, Kidney Research Institute, University of Washington, Seattle, Washington, USA
| | - David L Eaton
- Department of Environmental and Occupational Health Sciences and
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DNA Adducts Formed by Aristolochic Acid Are Unique Biomarkers of Exposure and Explain the Initiation Phase of Upper Urothelial Cancer. Int J Mol Sci 2017; 18:ijms18102144. [PMID: 29036902 PMCID: PMC5666826 DOI: 10.3390/ijms18102144] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Revised: 09/29/2017] [Accepted: 10/11/2017] [Indexed: 02/06/2023] Open
Abstract
Aristolochic acid (AA) is a plant alkaloid that causes aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN), unique renal diseases frequently associated with upper urothelial cancer (UUC). This review summarizes the significance of AA-derived DNA adducts in the aetiology of UUC leading to specific A:T to T:A transversion mutations (mutational signature) in AAN/BEN-associated tumours, which are otherwise rare in individuals with UCC not exposed to AA. Therefore, such DNA damage produced by AA-DNA adducts is one rare example of the direct association of exposure and cancer development (UUC) in humans, confirming that the covalent binding of carcinogens to DNA is causally related to tumourigenesis. Although aristolochic acid I (AAI), the major component of the natural plant extract AA, might directly cause interstitial nephropathy, enzymatic activation of AAI to reactive intermediates capable of binding to DNA is a necessary step leading to the formation of AA-DNA adducts and subsequently AA-induced malignant transformation. Therefore, AA-DNA adducts can not only be utilized as biomarkers for the assessment of AA exposure and markers of AA-induced UUC, but also be used for the mechanistic evaluation of its enzymatic activation and detoxification. Differences in AA metabolism might be one of the reasons for an individual’s susceptibility in the multi-step process of AA carcinogenesis and studying associations between activities and/or polymorphisms of the enzymes metabolising AA is an important determinant to identify individuals having a high risk of developing AA-mediated UUC.
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Stiborová M, Arlt VM, Schmeiser HH. Balkan endemic nephropathy: an update on its aetiology. Arch Toxicol 2016; 90:2595-2615. [PMID: 27538407 PMCID: PMC5065591 DOI: 10.1007/s00204-016-1819-3] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 08/04/2016] [Indexed: 02/02/2023]
Abstract
Balkan endemic nephropathy (BEN) is a unique, chronic renal disease frequently associated with upper urothelial cancer (UUC). It only affects residents of specific farming villages located along tributaries of the Danube River in Bosnia-Herzegovina, Croatia, Macedonia, Serbia, Bulgaria, and Romania where it is estimated that ~100,000 individuals are at risk of BEN, while ~25,000 have the disease. This review summarises current findings on the aetiology of BEN. Over the last 50 years, several hypotheses on the cause of BEN have been formulated, including mycotoxins, heavy metals, viruses, and trace-element insufficiencies. However, recent molecular epidemiological studies provide a strong case that chronic dietary exposure to aristolochic acid (AA) a principal component of Aristolochia clematitis which grows as a weed in the wheat fields of the endemic regions is the cause of BEN and associated UUC. One of the still enigmatic features of BEN that need to be resolved is why the prevalence of BEN is only 3-7 %. This suggests that individual genetic susceptibilities to AA exist in humans. In fact dietary ingestion of AA along with individual genetic susceptibility provides a scenario that plausibly can explain all the peculiarities of BEN such as geographical distribution and high risk of urothelial cancer. For the countries harbouring BEN implementing public health measures to avoid AA exposure is of the utmost importance because this seems to be the best way to eradicate this once mysterious disease to which the residents of BEN villages have been completely and utterly at mercy for so long.
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Affiliation(s)
- Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40, Prague 2, Czech Republic.
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environmental and Health, King's College London, 150 Stamford Street, London, SE1 9NH, UK
- NIHR Health Protection Research Unit in Health Impact of Environmental Hazards at King's College London in partnership with Public Health England, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry (E030), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
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9
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Hashimoto K, Zaitseva IN, Bonala R, Attaluri S, Ozga K, Iden CR, Johnson F, Moriya M, Grollman AP, Sidorenko VS. Sulfotransferase-1A1-dependent bioactivation of aristolochic acid I and N-hydroxyaristolactam I in human cells. Carcinogenesis 2016; 37:647-655. [PMID: 27207664 DOI: 10.1093/carcin/bgw045] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 04/12/2016] [Indexed: 11/14/2022] Open
Abstract
Aristolochic acids (AA) are implicated in the development of chronic renal disease and upper urinary tract carcinoma in humans. Using in vitro approaches, we demonstrated that N-hydroxyaristolactams, metabolites derived from partial nitroreduction of AA, require sulfotransferase (SULT)-catalyzed conjugation with a sulfonyl group to form aristolactam-DNA adducts. Following up on this observation, bioactivation of AA-I and N-hydroxyaristolactam I (AL-I-NOH) was studied in human kidney (HK-2) and skin fibroblast (GM00637) cell lines. Pentachlorophenol, a known SULT inhibitor, significantly reduced cell death and aristolactam-DNA adduct levels in HK-2 cells following exposure to AA-I and AL-I-NOH, suggesting a role for Phase II metabolism in AA activation. A gene knockdown, siRNA approach was employed to establish the involvement of selected SULTs and nitroreductases in AA-I bioactivation. Silencing of SULT1A1 and PAPSS2 led to a significant decrease in aristolactam-DNA levels in both cell lines following exposure to AA-I, indicating the critical role for sulfonation in the activation of AA-I in vivo Since HK-2 cells proved relatively resistant to knockdown with siRNAs, gene silencing of xanthine oxidoreductase, cytochrome P450 oxidoreductase and NADPH:quinone oxidoreductase was conducted in GM00637 cells, showing a significant increase, decrease and no effect on aristolactam-DNA levels, respectively. In GM00637 cells exposed to AL-I-NOH, suppressing the SULT pathway led to a significant decrease in aristolactam-DNA formation, mirroring data obtained for AA-I. We conclude from these studies that SULT1A1 is involved in the bioactivation of AA-I through the sulfonation of AL-I-NOH, contributing significantly to the toxicities of AA observed in vivo.
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Affiliation(s)
| | | | | | | | | | | | - Francis Johnson
- Department of Pharmacological Sciences.,Department of Chemistry and
| | | | - Arthur P Grollman
- Department of Pharmacological Sciences.,Department of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
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10
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Dračínská H, Bárta F, Levová K, Hudecová A, Moserová M, Schmeiser HH, Kopka K, Frei E, Arlt VM, Stiborová M. Induction of cytochromes P450 1A1 and 1A2 suppresses formation of DNA adducts by carcinogenic aristolochic acid I in rats in vivo. Toxicology 2016; 344-346:7-18. [PMID: 26845733 PMCID: PMC4804751 DOI: 10.1016/j.tox.2016.01.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 01/21/2016] [Accepted: 01/29/2016] [Indexed: 02/05/2023]
Abstract
Aristolochic acid I (AAI) is a natural plant alkaloid causing aristolochic acid nephropathy, Balkan endemic nephropathy and their associated urothelial malignancies. One of the most efficient enzymes reductively activating AAI to species forming AAI-DNA adducts is cytosolic NAD(P)H quinone oxidoreductase 1. AAI is also either reductively activated or oxidatively detoxified to 8-hydroxyaristolochic acid (AAIa) by microsomal cytochrome P450 (CYP) 1A1 and 1A2. Here, we investigated which of these two opposing CYP1A1/2-catalyzed reactions prevails in AAI metabolism in vivo. The formation of AAI-DNA adducts was analyzed in liver, kidney and lung of rats treated with AAI, Sudan I, a potent inducer of CYP1A1/2, or AAI after pretreatment with Sudan I. Compared to rats treated with AAI alone, levels of AAI-DNA adducts determined by the (32)P-postlabeling method were lower in liver, kidney and lung of rats treated with AAI after Sudan I. The induction of CYP1A1/2 by Sudan I increased AAI detoxification to its O-demethylated metabolite AAIa, thereby reducing the actual amount of AAI available for reductive activation. This subsequently resulted in lower AAI-DNA adduct levels in the rat in vivo. Our results demonstrate that CYP1A1/2-mediated oxidative detoxification of AAI is the predominant role of these enzymes in rats in vivo, thereby suppressing levels of AAI-DNA adducts.
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Affiliation(s)
- Helena Dračínská
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - František Bárta
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Kateřina Levová
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Alena Hudecová
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Michaela Moserová
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Klaus Kopka
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Heidelberg, Germany; German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Eva Frei
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment & Health, King's College London, London, United Kingdom
| | - Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
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11
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Milichovský J, Bárta F, Schmeiser HH, Arlt VM, Frei E, Stiborová M, Martínek V. Active Site Mutations as a Suitable Tool Contributing to Explain a Mechanism of Aristolochic Acid I Nitroreduction by Cytochromes P450 1A1, 1A2 and 1B1. Int J Mol Sci 2016; 17:213. [PMID: 26861298 PMCID: PMC4783945 DOI: 10.3390/ijms17020213] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Revised: 01/13/2016] [Accepted: 01/21/2016] [Indexed: 12/21/2022] Open
Abstract
Aristolochic acid I (AAI) is a plant drug found in Aristolochia species that causes aristolochic acid nephropathy, Balkan endemic nephropathy and their associated urothelial malignancies. AAI is activated via nitroreduction producing genotoxic N-hydroxyaristolactam, which forms DNA adducts. The major enzymes responsible for the reductive bioactivation of AAI are NAD(P)H quinone oxidoreductase and cytochromes P450 (CYP) 1A1 and 1A2. Using site-directed mutagenesis we investigated the possible mechanisms of CYP1A1/1A2/1B1-catalyzed AAI nitroreduction. Molecular modelling predicted that the hydroxyl groups of serine122/threonine124 (Ser122/Thr124) amino acids in the CYP1A1/1A2-AAI binary complexes located near to the nitro group of AAI, are mechanistically important as they provide the proton required for the stepwise reduction reaction. In contrast, the closely related CYP1B1 with no hydroxyl group containing residues in its active site is ineffective in catalyzing AAI nitroreduction. In order to construct an experimental model, mutant forms of CYP1A1 and 1A2 were prepared, where Ser122 and Thr124 were replaced by Ala (CYP1A1-S122A) and Val (CYP1A2-T124V), respectively. Similarly, a CYP1B1 mutant was prepared in which Ala133 was replaced by Ser (CYP1B1-A133S). Site-directed mutagenesis was performed using a quickchange approach. Wild and mutated forms of these enzymes were heterologously expressed in Escherichia coli and isolated enzymes characterized using UV-vis spectroscopy to verify correct protein folding. Their catalytic activity was confirmed with CYP1A1, 1A2 and 1B1 marker substrates. Using (32)P-postlabelling we determined the efficiency of wild-type and mutant forms of CYP1A1, 1A2, and 1B1 reconstituted with NADPH:CYP oxidoreductase to bioactivate AAI to reactive intermediates forming covalent DNA adducts. The S122A and T124V mutations in CYP1A1 and 1A2, respectively, abolished the efficiency of CYP1A1 and 1A2 enzymes to generate AAI-DNA adducts. In contrast, the formation of AAI-DNA adducts was catalyzed by CYP1B1 with the A133S mutation. Our experimental model confirms the importance of the hydroxyl group possessing amino acids in the active center of CYP1A1 and 1A2 for AAI nitroreduction.
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Affiliation(s)
- Jan Milichovský
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-12843 Prague 2, Czech Republic.
| | - František Bárta
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-12843 Prague 2, Czech Republic.
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King's College London, London SE1 9NH, UK.
| | - Eva Frei
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-12843 Prague 2, Czech Republic.
| | - Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-12843 Prague 2, Czech Republic.
| | - Václav Martínek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, CZ-12843 Prague 2, Czech Republic.
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Roberts DJ, McKeon M, Xu Y, Stankowski LF. Comparison of integrated genotoxicity endpoints in rats after acute and subchronic oral doses of 4-nitroquinoline-1-oxide. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2016; 57:17-27. [PMID: 26407646 PMCID: PMC7362388 DOI: 10.1002/em.21981] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 08/17/2015] [Indexed: 05/16/2023]
Abstract
During interlaboratory validation trials for the Pig-a gene mutation assay we assessed the genotoxicity of 4-nitroquinoline-1-oxide (4NQO) across endpoints in multiple tissues: induction of Pig-a mutant red blood cells (RBCs) and reticulocytes (RETs); micronucleated RETs (MN RETs); and DNA damage in blood and liver via the alkaline Comet assay (%tail intensity [TI]). In a previous subchronic toxicity study with 28 daily doses, biologically meaningful increases were observed only for Pig-a mutant RBCs/RETs while marginal increases in the frequency of MN RET were observed, and other clastogenic endpoints were negative. Follow up acute studies were performed using the same cumulative doses (0, 35, 70, 105, and 140 mg/kg) administered in a bolus, or split over three equal daily doses, with samples collected up to 1 month after the last dose. Both of the acute dosing regimens produced similar results, in that endpoints were either positive or negative, regardless of 1 or 3 daily doses, but the three consecutive daily dose regimen yielded more potent responses in TI (in liver and blood) and Pig-a mutant frequencies. In these acute studies the same cumulative doses of 4NQO induced positive responses in clastogenic endpoints that were negative or inconclusive using a subchronic study design. Additionally, a positive control group using combination doses of cyclophosphamide and ethyl methanesulfonate was employed to assess assay validity and potentially identify a future positive control treatment for integrated genetic toxicity studies.
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Affiliation(s)
- Daniel J Roberts
- Bristol-Myers Squibb, New Brunswick, NJ, USA
- Joint Graduate Program of Toxicology, Rutgers, NJ, USA
| | | | - Yong Xu
- BioReliance Corporation, Rockville, MD, USA
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13
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Stiborová M, Bárta F, Levová K, Hodek P, Schmeiser HH, Arlt VM, Martínek V. A Mechanism of O-Demethylation of Aristolochic Acid I by Cytochromes P450 and Their Contributions to This Reaction in Human and Rat Livers: Experimental and Theoretical Approaches. Int J Mol Sci 2015; 16:27561-75. [PMID: 26593908 PMCID: PMC4661905 DOI: 10.3390/ijms161126047] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Revised: 10/30/2015] [Accepted: 11/05/2015] [Indexed: 01/30/2023] Open
Abstract
Aristolochic acid I (AAI) is a plant alkaloid causing aristolochic acid nephropathy, Balkan endemic nephropathy and their associated urothelial malignancies. AAI is detoxified by cytochrome P450 (CYP)-mediated O-demethylation to 8-hydroxyaristolochic acid I (aristolochic acid Ia, AAIa). We previously investigated the efficiencies of human and rat CYPs in the presence of two other components of the mixed-functions-oxidase system, NADPH:CYP oxidoreductase and cytochrome b₅, to oxidize AAI. Human and rat CYP1A are the major enzymes oxidizing AAI. Other CYPs such as CYP2C, 3A4, 2D6, 2E1, and 1B1, also form AAIa, but with much lower efficiency than CYP1A. Based on velocities of AAIa formation by examined CYPs and their expression levels in human and rat livers, here we determined the contributions of individual CYPs to AAI oxidation in these organs. Human CYP1A2 followed by CYP2C9, 3A4 and 1A1 were the major enzymes contributing to AAI oxidation in human liver, while CYP2C and 1A were most important in rat liver. We employed flexible in silico docking methods to explain the differences in AAI oxidation in the liver by human CYP1A1, 1A2, 2C9, and 3A4, the enzymes that all O-demethylate AAI, but with different effectiveness. We found that the binding orientations of the methoxy group of AAI in binding centers of the CYP enzymes and the energies of AAI binding to the CYP active sites dictate the efficiency of AAI oxidation. Our results indicate that utilization of experimental and theoretical methods is an appropriate study design to examine the CYP-catalyzed reaction mechanisms of AAI oxidation and contributions of human hepatic CYPs to this metabolism.
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Affiliation(s)
- Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, Prague 2 CZ-12843, Czech Republic.
| | - František Bárta
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, Prague 2 CZ-12843, Czech Republic.
| | - Kateřina Levová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, Prague 2 CZ-12843, Czech Republic.
| | - Petr Hodek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, Prague 2 CZ-12843, Czech Republic.
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King's College London, London SE1 9NH, UK.
| | - Václav Martínek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, Prague 2 CZ-12843, Czech Republic.
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14
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Stiborová M, Bárta F, Levová K, Hodek P, Frei E, Arlt VM, Schmeiser HH. The influence of ochratoxin A on DNA adduct formation by the carcinogen aristolochic acid in rats. Arch Toxicol 2014; 89:2141-58. [PMID: 25209566 DOI: 10.1007/s00204-014-1360-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 08/28/2014] [Indexed: 11/28/2022]
Abstract
UNLABELLED Exposure to the plant nephrotoxin and carcinogen aristolochic acid (AA) leads to the development of AA nephropathy, Balkan endemic nephropathy (BEN) and upper urothelial carcinoma (UUC) in humans. Beside AA, exposure to ochratoxin A (OTA) was linked to BEN. Although OTA was rejected as a factor for BEN/UUC, there is still no information whether the development of AA-induced BEN/UUC is influenced by OTA exposure. Therefore, we studied the influence of OTA on the genotoxicity of AA (AA-DNA adduct formation) in vivo. AA-DNA adducts were formed in liver and kidney of rats treated with AA or AA combined with OTA, but no OTA-related DNA adducts were detectable in rats treated with OTA alone or OTA combined with AA. Compared to rats treated with AA alone, AA-DNA adduct levels were 5.4- and 1.6-fold higher in liver and kidney, respectively, of rats treated with AA combined with OTA. Although AA and OTA induced NAD(P)H quinone oxidoreductase (NQO1) activating AA to DNA adducts, their combined treatment did not lead to either higher NQO1 enzyme activity or higher AA-DNA adduct levels in ex vivo incubations. Oxidation of AA I (8-methoxy-6-nitrophenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid) to its detoxification metabolite, 8-hydroxyaristolochic acid, was lower in microsomes from rats treated with AA and OTA, and this was paralleled by lower activities of cytochromes P450 1A1/2 and/or 2C11 in these microsomes. Our results indicate that a decrease in AA detoxification after combined exposure to AA and OTA leads to an increase in AA-DNA adduct formation in liver and kidney of rats.
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Affiliation(s)
- Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40, Prague 2, Czech Republic.
| | - František Bárta
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40, Prague 2, Czech Republic
| | - Kateřina Levová
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40, Prague 2, Czech Republic
| | - Petr Hodek
- Department of Biochemistry, Faculty of Science, Charles University, Albertov 2030, 128 40, Prague 2, Czech Republic
| | - Eva Frei
- Division of Preventive Oncology, National Center for Tumor Diseases, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environmental and Health, King's College London, 150 Stamford Street, London, SE1 9NH, UK
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry (E030), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
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15
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Stiborová M, Frei E, Schmeiser HH, Arlt VM, Martínek V. Mechanisms of enzyme-catalyzed reduction of two carcinogenic nitro-aromatics, 3-nitrobenzanthrone and aristolochic acid I: Experimental and theoretical approaches. Int J Mol Sci 2014; 15:10271-95. [PMID: 24918288 PMCID: PMC4100152 DOI: 10.3390/ijms150610271] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 05/30/2014] [Accepted: 05/30/2014] [Indexed: 01/14/2023] Open
Abstract
This review summarizes the results found in studies investigating the enzymatic activation of two genotoxic nitro-aromatics, an environmental pollutant and carcinogen 3-nitrobenzanthrone (3-NBA) and a natural plant nephrotoxin and carcinogen aristolochic acid I (AAI), to reactive species forming covalent DNA adducts. Experimental and theoretical approaches determined the reasons why human NAD(P)H quinone oxidoreductase (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 have the potential to reductively activate both nitro-aromatics. The results also contributed to the elucidation of the molecular mechanisms of these reactions. The contribution of conjugation enzymes such as N,O-acetyltransferases (NATs) and sulfotransferases (SULTs) to the activation of 3-NBA and AAI was also examined. The results indicated differences in the abilities of 3-NBA and AAI metabolites to be further activated by these conjugation enzymes. The formation of DNA adducts generated by both carcinogens during their reductive activation by the NOQ1 and CYP1A1/2 enzymes was investigated with pure enzymes, enzymes present in subcellular cytosolic and microsomal fractions, selective inhibitors, and animal models (including knock-out and humanized animals). For the theoretical approaches, flexible in silico docking methods as well as ab initio calculations were employed. The results summarized in this review demonstrate that a combination of experimental and theoretical approaches is a useful tool to study the enzyme-mediated reaction mechanisms of 3-NBA and AAI reduction.
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Affiliation(s)
- Marie Stiborová
- Department of Biochemistry, Faculty of Science, Charles University, Hlavova 2030, CZ-12843, Prague 2, Czech Republic.
| | - Eva Frei
- Division of Preventive Oncology, National Center for Tumor Diseases, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
| | - Heinz H Schmeiser
- Radiopharmaceutical Chemistry E030, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environmental & Health, King's College London, 150 Stamford Street, London SE1 9NH, UK.
| | - Václav Martínek
- Department of Biochemistry, Faculty of Science, Charles University, Hlavova 2030, CZ-12843, Prague 2, Czech Republic.
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