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Bourgeois ZM, Comfort J, Schultz M, Challis JK, Cantin J, Ji X, Giesy JP, Brinkmann M. Predicting Hepatic Clearance of Psychotropic Drugs in Isolated Perfused Fish Livers Using a Combination of Two In Vitro Assays. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:15839-15847. [PMID: 36268931 DOI: 10.1021/acs.est.2c03017] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
In vitro biotransformation assays with primary trout hepatocytes (RT-HEP) or liver subcellular fractions (RT-S9) have been proposed as valuable tools to help scientists and regulators better understand the toxicokinetics of chemicals. While both assays have been applied successfully to a diversity of neutral organic chemicals, only the RT-S9 assay has been applied to a large number of ionizable organic chemicals. Here, a combination of an in vitro biotransformation assay with RT-HEP with an active transport assay based on the permanent rainbow trout liver cell line RTL-W1 was used to qualitatively predict the potential hepatic clearance of nine psychotropic drugs with various degrees of ionization. Predictions were compared with rates of clearance measured in isolated perfused rainbow trout livers, and the importance of active transport was verified in the presence of the active transport inhibitor cyclosporin A. For the first time, it was demonstrated that a combination of biotransformation and active transport assays is powerful for the prediction of rates of hepatic clearance of ionizable chemicals. Ultimately, it is expected that this approach will allow for use of fewer animals while at the same time improving our confidence in the use of data from in vitro assays in chemical risk assessment.
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Affiliation(s)
- Zoey M Bourgeois
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
| | - Jordan Comfort
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
| | - Matthew Schultz
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
| | - Jonathan K Challis
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
| | - Jenna Cantin
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
| | - Xiaowen Ji
- School of Environment and Sustainability, University of Saskatchewan, 117 Science Pl, Saskatoon, SaskatchewanS7N 5C8, Canada
| | - John P Giesy
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
- Department of Veterinary Biomedical Sciences, University of Saskatchewan, 52 Campus Dr, Saskatoon, SaskatchewanS7N 5B4, Canada
- Department of Integrative Biology and Center for Integrative Toxicology, Michigan State University, 784 Wilson Rd, East Lansing, Michigan48824, United States
- Department of Environmental Science, Baylor University, 97266 One Bear Place, Waco, Texas76798, United States
| | - Markus Brinkmann
- Toxicology Center, University of Saskatchewan, 44 Campus Dr, Saskatoon, SaskatchewanS7N 5B3, Canada
- School of Environment and Sustainability, University of Saskatchewan, 117 Science Pl, Saskatoon, SaskatchewanS7N 5C8, Canada
- Global Institute for Water Security, University of Saskatchewan, 11 Innovation Blvd, Saskatoon, SaskatchewanS7N 3H5, Canada
- Centre for Hydrology, University of Saskatchewan, 121 Research Dr, Saskatoon, SaskatchewanS7N 1K2, Canada
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2
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Schultz M, Krause S, Brinkmann M. Validation of Methods for in Vitro- in Vivo Extrapolation Using Hepatic Clearance Measurements in Isolated Perfused Fish Livers. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:12416-12423. [PMID: 35994365 DOI: 10.1021/acs.est.2c02656] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In vitro biotransformation assays using hepatocytes or liver subcellular fractions, combined with in vitro-in vivo extrapolation (IVIVE) models, have been proposed as an alternative to live fish bioconcentration studies. The uncertainty associated with IVIVE approaches to date has been attributed to assay protocols, model assumptions, or variability of in vivo data. An isolated perfused trout liver model that measures hepatic clearance has been proposed for validating IVIVE predictions in the absence of other confounding factors. Here, we investigated the hepatic clearances of five chemicals (pyrene, phenanthrene, 4-n-nonlyphenol, deltamethrin, and methoxychlor) in this model and compared measured rates to values predicted from published in vitro intrinsic clearances for validation of IVIVE models. Additionally, we varied protein concentrations in perfusates to test binding assumptions of these models. We found that measured and predicted hepatic clearances were in very good agreement (root mean squared error 16.8 mL h-1 g-1) across three levels of protein binding and across a more diverse chemical space than previously studied within this system. Our results show that current IVIVE methods can reliably predict in vivo clearance rates and indicate that discrepancies from measured bioconcentration factors might be driven by other processes, such as extrahepatic biotransformation, etc., and help streamline optimization efforts to the processes that truly matter.
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Affiliation(s)
- Matthew Schultz
- Toxicology Center, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK S7N 5B3, Canada
| | - Sophia Krause
- Department of Analytical Environmental Chemistry, Helmholtz Centre for Environmental Research UFZ, Permoserstr. 15, 04318 Leipzig, Germany
| | - Markus Brinkmann
- Toxicology Center, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK S7N 5B3, Canada
- School of Environment and Sustainability, University of Saskatchewan, 117 Science Place, Saskatoon, SK S7N 5C8, Canada
- Global Institute for Water Security, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
- Centre for Hydrology, University of Saskatchewan, 121 Research Drive, Saskatoon, SK S7N 1K2, Canada
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3
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Competitive Metabolism of Polycyclic Aromatic Hydrocarbons (PAHs): An Assessment Using In Vitro Metabolism and Physiologically Based Pharmacokinetic (PBPK) Modeling. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19148266. [PMID: 35886113 PMCID: PMC9323266 DOI: 10.3390/ijerph19148266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 06/16/2022] [Accepted: 06/27/2022] [Indexed: 02/04/2023]
Abstract
Humans are routinely exposed to complex mixtures such as polycyclic aromatic hydrocarbons (PAHs) rather than to single compounds, as are often assessed for hazards. Cytochrome P450 enzymes (CYPs) metabolize PAHs, and multiple PAHs found in mixtures can compete as substrates for individual CYPs (e.g., CYP1A1, CYP1B1, etc.). The objective of this study was to assess competitive inhibition of metabolism of PAH mixtures in humans and evaluate a key assumption of the Relative Potency Factor approach that common human exposures will not cause interactions among mixture components. To test this objective, we co-incubated binary mixtures of benzo[a]pyrene (BaP) and dibenzo[def,p]chrysene (DBC) in human hepatic microsomes and measured rates of enzymatic BaP and DBC disappearance. We observed competitive inhibition of BaP and DBC metabolism and measured inhibition coefficients (Ki), observing that BaP inhibited DBC metabolism more potently than DBC inhibited BaP metabolism (0.061 vs. 0.44 µM Ki, respectively). We developed a physiologically based pharmacokinetic (PBPK) interaction model by integrating PBPK models of DBC and BaP and incorporating measured metabolism inhibition coefficients. The PBPK model predicts significant increases in BaP and DBC concentrations in blood AUCs following high oral doses of PAHs (≥100 mg), five orders of magnitude higher than typical human exposures. We also measured inhibition coefficients of Supermix-10, a mixture of the most abundant PAHs measured at the Portland Harbor Superfund Site, on BaP and DBC metabolism. We observed similar potencies of inhibition coefficients of Supermix-10 compared to BaP and DBC. Overall, results of this study demonstrate that these PAHs compete for the same enzymes and, at high doses, inhibit metabolism and alter internal dosimetry of exposed PAHs. This approach predicts that BaP and DBC exposures required to observe metabolic interaction are much higher than typical human exposures, consistent with assumptions used when applying the Relative Potency Factor approach for PAH mixture risk assessment.
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4
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Exploring competitive inhibition of a family 10 xylanase derived from Hu sheep rumen microbiota by Oryza sativa xylanase inhibitor protein: In vitro and in silico perspectives. Enzyme Microb Technol 2022; 160:110082. [PMID: 35709658 DOI: 10.1016/j.enzmictec.2022.110082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 05/20/2022] [Accepted: 06/09/2022] [Indexed: 01/18/2023]
Abstract
The catalytic domain of family GH10 xylanase, XYN-LXY_CD derived from Hu sheep rumen microbiota was expressed in Pichia pastoris X33. The special activity of reXYN-LXY_CD in the culture supernatant was 232.56 U/mg. The optima of reXYN-LXY_CD were 53 °C and pH 7.0. Recombinant Oryza sativa xylanase inhibitor protein (rePOsXIP) competitively inhibited reXYN-LXY_CD with an inhibition constant (Ki) value of 237.37 nM. The concentration of hydrolysates released from beechwood xylan by reXYN-LXY_CD reduced when rePOsXIP was added into the hydrolytic system. Fluorescence of reXYN-LXY_CD was statically quenched by rePOsXIP in a dose-dependent manner. The details in intermolecular interaction between XYN-LXY_CD and OsXIP were investigated by using molecular dynamics (MD) simulations, binding free energy computation and non-covalent interactions (NCI) analysis. Hydrogen bonding and van der Waals played indispensable roles in the XYN-LXY_CD/OsXIP interaction. The α-7 helix of OsXIP tightly occupied the catalytic pocket of XYN-LXY_CD with hydrogen bonding such as K239OsXIP-N261/Q292/E197XYN-LXY_CD (E197, the acid-base catalytic residue), D236OsXIP-K327XYN-LXY_CD and Q242OsXIP-E211/Q212XYN-LXY_CD. Based on the quantum theory of atoms in molecules (QTAIM), the Laplacian of electron density and core-valence bifurcation index of HZ3K239-OE2E197 were 0.1025 a.u. and 0.002218, respectively. Elucidating the mechanism underlying xylanase-inhibitor interactions might help construct XYN-LXY_CD mutants that gain resistance to XIPs and high catalytic activity, which would be more efficient in feed additives in livestock.
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Ribbenstedt A, Armitage JM, Günther F, Arnot JA, Droge STJ, McLachlan MS. In Vivo Bioconcentration of 10 Anionic Surfactants in Rainbow Trout Explained by In Vitro Data on Partitioning and S9 Clearance. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:6305-6314. [PMID: 35467837 PMCID: PMC9118553 DOI: 10.1021/acs.est.1c05543] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Bioconcentration factors (BCFs) in rainbow trout were measured for 10 anionic surfactants with a range of alkyl chain lengths and different polar head groups. The BCFs ranged from 0.04 L kg-1 ww (for C10SO3) to 1370 L kg-1 ww (C16SO3). There was a strong correlation between the log BCF and log membrane lipid-water distribution ratio (DMLW, r2 = 0.96), and biotransformation was identified as the dominant elimination mechanism. The strong positive influence of DMLW on BCF was attributed to two phenomena: (i) increased partitioning from water into the epithelial membrane of the gill, leading to more rapid diffusion across this barrier and more rapid uptake, and (ii) increased sequestration of the surfactant body burden into membranes and other body tissues, resulting in lower freely dissolved concentrations available for biotransformation. Estimated whole-body in vivo biotransformation rate constants kB-BCF are within a factor three of rate constants estimated from S9 in vitro assays for six of the eight test chemicals for which kB-BCF could be determined. A model-based assessment indicated that the hepatic clearance rate of freely dissolved chemicals was similar for the studied surfactants. The dataset will be useful for evaluation of in silico and in vitro methods to assess bioaccumulation.
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Affiliation(s)
- Anton Ribbenstedt
- Department
of Environmental Science, Stockholm University, 106 91 Stockholm, Sweden
| | - James M. Armitage
- AES
Armitage Environmental Sciences, Inc., Ottawa, Ontario K1L 8C3, Canada
| | - Felix Günther
- Department
of Mathematics, Stockholm University, 106 91 Stockholm, Sweden
| | - Jon A. Arnot
- ARC
Arnot Research and Consulting Inc., Toronto, Ontario M4M 1W4, Canada
- Department
of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Ontario M1C 1A4, Canada
| | - Steven T. J. Droge
- Institute
for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, 1090 GE Amsterdam, The Netherlands
| | - Michael S. McLachlan
- Department
of Environmental Science, Stockholm University, 106 91 Stockholm, Sweden
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6
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Franco ME, Johanning K, Matson CW, Lavado R. Reduced biotransformation of polycyclic aromatic hydrocarbons (PAHs) in pollution-adapted Gulf killifish (Fundulus grandis). THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 806:150854. [PMID: 34655636 DOI: 10.1016/j.scitotenv.2021.150854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 07/22/2021] [Accepted: 10/03/2021] [Indexed: 06/13/2023]
Abstract
Anthropogenic pollution represents a significant source of selection, potentially leading to the emergence of evolutionary adaptations in chronically exposed organisms. A recent example of this scenario corresponds to Gulf killifish (Fundulus grandis) populations inhabiting the Houston Ship Channel (HSC), Texas, USA, which have been documented to have adapted to this heavily contaminated environment. Although not fully elucidated, one particularly important aspect of their adaptation involves the reduced inducibility of the aryl hydrocarbon receptor (AhR) and, potentially, the alteration of major biotransformation pathways. In the present study, we employed a modified Organization for Economic Cooperation and Development (OECD) 319-B test guideline to explore population and sex-related differences in the hepatic biotransformation of six polycyclic aromatic hydrocarbons (PAHs) in F. grandis populations with different exposure histories. Pollution-adapted F. grandis showed significantly lower hepatic clearance of PAHs than non-adapted fish, especially for high molecular weight PAHs (chrysene, benzo[k]fluoranthene, and benzo[a]pyrene), with pollution-adapted females presenting the lowest clearance. The characterization of different phase I biotransformation enzymes revealed that the basal activity of CYP1A, fundamental in the biotransformation of PAHs, was significantly lower in pollution-adapted fish, especially in females, which showed the lowest activity. Contrarily, basal CYP2C9-like activity was significantly higher in pollution-adapted fish. These results demonstrate the importance of exposure and evolutionary histories in shaping organisms' responses to pollution and provide significant evidence of sex-specific biotransformation differences in F. grandis populations.
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Affiliation(s)
- Marco E Franco
- Department of Environmental Science, Baylor University, Waco, TX 76798, United States of America
| | - Karla Johanning
- KJ Scientific, LLC, Georgetown, TX 78626, United States of America
| | - Cole W Matson
- Department of Environmental Science, Baylor University, Waco, TX 76798, United States of America; Center for Reservoir and Aquatic Systems Research, Baylor University, Waco, TX 76798, United States of America
| | - Ramon Lavado
- Department of Environmental Science, Baylor University, Waco, TX 76798, United States of America.
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7
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Aguilar L, Lara-Flores M, Rendón-von Osten J, Kurczyn JA, Vilela B, da Cruz AL. Effects of polycyclic aromatic hydrocarbons on biomarker responses in Gambusia yucatana, an endemic fish from Yucatán Peninsula, Mexico. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2021; 28:47262-47274. [PMID: 33891236 DOI: 10.1007/s11356-021-13952-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 04/12/2021] [Indexed: 06/12/2023]
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are petroleum components that, when dissolved in the aquatic environment, can disrupt normal animal physiological functions and negatively affect species populations. Gambusia yucatana is an endemic fish of the Yucatán Peninsula that seems to be particularly sensitive to the presence of PAHs dissolved in the water. Here, we examined PAH effects on gene expressions linked to endocrine disruption and biotransformation in this species. Specifically, we examined the expression of vitellogenin I (vtg1), vitellogenin II (vtg2), oestrogen receptor α (esr1), oestrogen receptor β (esr2), aryl hydrocarbon receptor (AhR) and the cytochrome P4503A (CYP3A) genes. We exposed G. yucatana to different concentrations of PAHs (3.89, 9.27, 19.51 μg/L) over a period of 72 h and found changes associated with reproduction, such as increases in hepatic expression of vtg, esr, AhR and CYP3A, mainly at concentrations of 9.27 and 19.51 μg/L. Our results also indicate that benzo[a]pyrene was probably the main PAH responsible for the observed effects. The genes examined here can be used as molecular markers of endocrine-disrupting compounds, as the PAHs, present in the environment, as gene expression increases could be observed as early as after 24 h. These biomarkers can help researchers and conservationists rapidly identify the impacts of oil spills and improve mitigation before the detrimental effects of environmental stressors become irreversible.
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Affiliation(s)
- Letícia Aguilar
- Institute of Biology, Laboratory of Animal Physiology, Federal University of Bahia, Rua Barão de Jeremoabo 147, Salvador, Bahia, CEP 40.170-115, Brazil
| | - Maurílio Lara-Flores
- Institute of Ecology, Fisheries and Oceanography of the Gulf of Mexico, Laboratory of Ecotoxicology, Autonomous University of Campeche, Av. Héroe de Nacozari 480, C.P. 24029, San Francisco de Campeche, Campeche, Mexico
| | - Jaime Rendón-von Osten
- Institute of Ecology, Fisheries and Oceanography of the Gulf of Mexico, Laboratory of Ecotoxicology, Autonomous University of Campeche, Av. Héroe de Nacozari 480, C.P. 24029, San Francisco de Campeche, Campeche, Mexico
| | - Jorge A Kurczyn
- Institute of Engineering, Coastal Engineering and Processes Laboratory, National Autonomous University of Mexico, Puerto de Abrigo s/n, 97356, Sisal, Yucatán, Mexico
| | - Bruno Vilela
- Institute of Biology, Spatial Ecology Laboratory, Federal University of Bahia, Rua Barão de Jeremoabo 147, Salvador, Bahia, CEP 40.170-115, Brazil
| | - André Luis da Cruz
- Institute of Biology, Laboratory of Animal Physiology, Federal University of Bahia, Rua Barão de Jeremoabo 147, Salvador, Bahia, CEP 40.170-115, Brazil.
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8
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Armitage JM, Toose L, Camenzuli L, Redman AD, Parkerton TF, Saunders D, Wheeler J, Martin A, Vaiopoulou E, Arnot JA. Acritical review and weight of evidence approach for assessing the bioaccumulation of phenanthrene in aquatic environments. INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT 2021; 17:911-925. [PMID: 33620129 PMCID: PMC8451923 DOI: 10.1002/ieam.4401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 10/01/2020] [Accepted: 02/17/2021] [Indexed: 05/31/2023]
Abstract
Bioaccumulation (B) assessment is challenging because there are various B-metrics from laboratory and field studies, multiple criteria and thresholds for classifying bioaccumulative (B), very bioaccumulative (vB), and not bioaccumulative (nB) chemicals, as well as inherent variability and uncertainty in the data. These challenges can be met using a weight of evidence (WoE) approach. The Bioaccumulation Assessment Tool (BAT) provides a transparent WoE assessment framework that follows Organisation for Economic Co-operation and Development (OECD) principles for performing a WoE analysis. The BAT guides an evaluator through the process of data collection, generation, evaluation, and integration of various lines of evidence (LoE) (i.e., B-metrics) to inform decision-making. Phenanthrene (PHE) is a naturally occurring chemical for which extensive B and toxicokinetics data are available. A B assessment for PHE using the BAT is described that includes a critical evaluation of 74 measured in vivo LoE for fish and invertebrate species from laboratory and field studies. The number of LoE are reasonably well balanced across taxa (i.e., fish and invertebrates) and the different B-metrics. Additionally, in silico and in vitro biotransformation rate estimates and corresponding model-predicted B-metrics are included as corroborating evidence. Application of the BAT provides a consistent, coherent, and scientifically defensible WoE evaluation to conclude that PHE is not bioaccumulative (nB) because the overwhelming majority of the bioconcentration, bioaccumulation, and biomagnification metrics for both fish and invertebrates are below regulatory thresholds. An analysis of the relevant data using fugacity ratios is also provided, showing that PHE does not biomagnify in aquatic food webs. The critical review identifies recommendations to increase the consistency of B assessments, such as improved standardization of B testing guidelines, data reporting requirements for invertebrate studies, and consideration of temperature and salinity effects on certain B-metrics. Integr Environ Assess Manag 2021;17:911-925. © 2021 Concawe. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).
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Affiliation(s)
- James M. Armitage
- ARC Arnot Research and Consulting Inc.TorontoOntarioCanada
- AES Armitage Environmental Science Inc.OttawaOntarioCanada
| | - Liisa Toose
- ARC Arnot Research and Consulting Inc.TorontoOntarioCanada
| | - Louise Camenzuli
- ExxonMobil Petroleum & Chemical B.V.MachelenBelgium
- Member of ConcaweBrusselsBelgium
| | - Aaron D. Redman
- ExxonMobil Petroleum & Chemical B.V.MachelenBelgium
- Member of ConcaweBrusselsBelgium
| | - Tom F. Parkerton
- ExxonMobil Biomedical Sciences Inc.SpringTexasUSA
- Member of ConcaweBrusselsBelgium
| | - David Saunders
- Shell Health, Shell International B.V.The Haguethe Netherlands
- Member of ConcaweBrusselsBelgium
| | - James Wheeler
- Shell Health, Shell International B.V.The Haguethe Netherlands
- Member of ConcaweBrusselsBelgium
| | | | | | - Jon A. Arnot
- ARC Arnot Research and Consulting Inc.TorontoOntarioCanada
- Department of Physical and Environmental SciencesUniversity of Toronto ScarboroughTorontoOntarioCanada
- Department of Pharmacology and ToxicologyUniversity of TorontoTorontoOntarioCanada
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9
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Nichols JW, Hoffman AD, Swintek JA, Droge ST, Fitzsimmons PN. Addition of Phenylmethylsulfonyl Fluoride Increases the Working Lifetime of the Trout Liver S9 Substrate Depletion Assay, Resulting in Improved Detection of Low Intrinsic Clearance Rates. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2021; 40:148-161. [PMID: 33045099 PMCID: PMC7901806 DOI: 10.1002/etc.4901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 07/14/2020] [Accepted: 10/07/2020] [Indexed: 05/11/2023]
Abstract
The activity of a trout liver S9 substrate depletion assay has been shown to decline over time, presumably due to proteolytic degradation of biotransformation enzymes. To address this problem, assay performance was evaluated following the addition of phenylmethylsulfonyl fluoride (PMSF) or a general-purpose protease inhibitor cocktail to liver homogenization buffers and/or S9 reaction mixtures. Addition of PMSF to liver homogenization buffers and/or S9 reaction mixtures had little or no effect on clearance of phenanthrene, a model cytochrome P450 substrate, in short-term (25 or 30 min) depletion experiments but resulted in significant improvements in retention of this initial activity over time. The protease inhibitor cocktail strongly inhibited initial activity when added to homogenization buffers or reaction mixtures. Taking into consideration potential effects on liver carboxylesterases, the treatment approach determined to be optimal was addition of 10 µM PMSF to the S9 reaction mixture. Addition of 10 µM PMSF to the mixture resulted in significantly higher rates of phenanthrene clearance in 2-h incubations relative to those obtained in the absence of PMSF and a 6-fold increase in the working lifetime of the preparation. The results of a statistical power analysis suggest that by increasing the working lifetime of the assay, addition of PMSF to the reaction mixture could result in substantially improved detection of low in vitro clearance rates when compared to current practice. These findings demonstrate the value of adding PMSF to the trout S9 preparation and may have broad implications for use of this assay to support chemical bioaccumulation assessments for fish. Environ Toxicol Chem 2021;40:148-161. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
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Affiliation(s)
- John W. Nichols
- US Environmental Protection Agency, Office of Research and Development, Center for Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division, Duluth, Minnesota, USA
- Address correspondence to
| | - Alex D. Hoffman
- US Environmental Protection Agency, Office of Research and Development, Center for Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division, Duluth, Minnesota, USA
| | | | - Steven T.J. Droge
- Department of Freshwater and Marine Ecology, Institute for Biodiversity and Ecosystem Dynamics, Universiteit van Amsterdam, Amsterdam, NL
| | - Patrick N. Fitzsimmons
- US Environmental Protection Agency, Office of Research and Development, Center for Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division, Duluth, Minnesota, USA
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