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Kazzaz SA, Giani Tagliabue S, Franks DG, Denison MS, Hahn ME, Bonati L, Powell WH. An aryl hydrocarbon receptor from the caecilian Gymnopis multiplicata suggests low dioxin affinity in the ancestor of all three amphibian orders. Gen Comp Endocrinol 2020; 299:113592. [PMID: 32858041 PMCID: PMC7771225 DOI: 10.1016/j.ygcen.2020.113592] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 07/31/2020] [Accepted: 08/18/2020] [Indexed: 11/18/2022]
Abstract
The aryl hydrocarbon receptor (AHR) plays pleiotropic roles in the development and physiology of vertebrates in conjunction with xenobiotic and endogenous ligands. It is best known for mediating the toxic effects of dioxin-like pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). While most vertebrates possess at least one AHR that binds TCDD tightly, amphibian AHRs bind TCDD with very low affinity. Previous analyses of AHRs from Xenopus laevis (a frog; order Anura) and Ambystoma mexicanum (a salamander; order Caudata) identified three amino acid residues in the ligand-binding domain (LBD) that underlie low-affinity binding. In X. laevis AHR1β, these are A354, A370, and N325. Here we extend the analysis of amphibian AHRs to the caecilian Gymnopis multiplicata, representing the remaining extant amphibian order, Gymnophiona. G. multiplicata AHR groups with the monophyletic vertebrate AHR/AHR1 clade. The LBD includes all three signature residues of low TCDD affinity, and a structural homology model suggests that its architecture closely resembles those of other amphibians. In transactivation assays, the EC50 for reporter gene induction by TCDD was 17.17 nM, comparable to X. laevis AhR1β (26.23 nM) and Ambystoma AHR (34.09 nM) and dramatically higher than mouse AhR (0.13 nM), a trend generally reflected in direct measures of TCDD binding. These shared properties distinguish amphibian AHRs from the high-affinity proteins typical of both vertebrate groups that diverged earlier (teleost fish) and those that appeared more recently (other tetrapods). These findings suggest the hypothesis that AHRs with low TCDD affinity represent a characteristic that evolved in a common ancestor of all three extant amphibian groups.
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Affiliation(s)
- Sarah A Kazzaz
- Biology Department, Kenyon College, Gambier, OH 43022, USA
| | - Sara Giani Tagliabue
- Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milan 20126, Italy
| | - Diana G Franks
- Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Michael S Denison
- Department of Environmental Toxicology, University of California-Davis, Davis, CA 95616, USA
| | - Mark E Hahn
- Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Laura Bonati
- Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milan 20126, Italy
| | - Wade H Powell
- Biology Department, Kenyon College, Gambier, OH 43022, USA.
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Martini F, Fernández C, Tarazona JV, Pablos MV. Gene expression of heat shock protein 70, interleukin-1β and tumor necrosis factor α as tools to identify immunotoxic effects on Xenopus laevis: a dose-response study with benzo[a]pyrene and its degradation products. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2012; 160:28-33. [PMID: 22035922 DOI: 10.1016/j.envpol.2011.09.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 09/06/2011] [Accepted: 09/14/2011] [Indexed: 05/31/2023]
Abstract
The exposure to benzo[a]pyrene (B[a]P) results in an alteration of immune function in mammals and fish, and the analysis of cytokine mRNA levels has been suggested for predicting the immunomodulatory potential of chemicals. To obtain evidence of the innate immune responses to B[a]P in Xenopus laevis, the present study monitored the mRNA expression of interleukin 1-β (IL-1β), tumor necrosis factor α (TNF-α) and heat shock protein 70 (HSP70) in a laboratorial exposure. Tadpoles exposed to 8.36, 14.64, 89.06 and 309.47 μg/L of B[a]P,were used for detecting hsp70, IL-1β and TNF-α mRNA induction. A dose-response increase in the expression of hsp70 and IL-1β mRNA was found. The results of this study confirmed the use of hsp70 and IL-1β, but not TNF-α, as sensitive indicators of immunotoxic effect of B[a]P in X. laevis. Further research would be required for the validation of these endpoints.
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Affiliation(s)
- Federica Martini
- Laboratory for Ecotoxicology, Department of Environment, Spanish National Institute for Agricultural and Food Research and Technology (INIA), Carretera de la Coruña, Km 7.5, 28040 Madrid, Spain.
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Fini JB, Dolo L, Cravedi JP, Demeneix B, Zalko D. Metabolism of the endocrine disruptor BPA by Xenopus laevis tadpoles. Ann N Y Acad Sci 2009; 1163:394-7. [PMID: 19456369 DOI: 10.1111/j.1749-6632.2008.03655.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Metabolism of the plasticizer bisphenol A (BPA), a thyroid function disruptor, was investigated in Xenopus laevis tadpoles. Uptake and biotransformation of [(3)H]-BPA was followed over 72 h at 1 micromol/L and 10 micromol/L +/- triiodothyronine. A rapid decrease of radioactivity in media was observed after [(3)H]-BPA was added. [(3)H]-BPA uptake reached 25% after 24 h then ranged between 6% and 15%. Metabolic profiles of water samples at 24, 48, and 72 h as well as tadpole extracts (at 72 h) were obtained using radio-HPLC. Parent (unmodified) BPA was consistently found in water samples and within tadpoles. Six peaks corresponding to BPA metabolites were detected. Based on retention time comparison with standards isolated from rat and human material, the two main metabolites were identified as BPA-glucuronide and BPA-sulfate. Thus, Xenopus laevis provides a useful model for studying BPA effects in vertebrates, as the main BPA metabolites are similar to those produced in mammals.
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Affiliation(s)
- Jean-Baptiste Fini
- UMR CNRS 5166, Evolution des Régulations Endocriniennes, Dept. Regulations, Development and Molecular Diversity, Muséum National d'Histoire Naturelle, Paris, France
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Zimmermann AL, King EA, Dengler E, Scogin SR, Powell WH. An aryl hydrocarbon receptor repressor from Xenopus laevis: function, expression, and role in dioxin responsiveness during frog development. Toxicol Sci 2008; 104:124-34. [PMID: 18385208 DOI: 10.1093/toxsci/kfn066] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Xenopus laevis and other frogs are extremely insensitive to the toxicity of xenobiotic ligands of the aryl hydrocarbon receptor (AHR), including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Premetamorphic life stages are especially insensitive, and they are reported to be refractory to induction of Cytochrome P4501As, which are readily induced in older animals. The AHR repressor (AHRR) is a member of the AHR gene family. AHRR expression is induced by TCDD; it then represses AHR in an apparent negative feedback loop. In this study, we sought to test the hypothesis that constitutive AHRR expression underlies the lack of TCDD responsiveness in frog early life stages. We determined the sequence of an AHRR complimentary DNA encoding an 85.3-kDa protein sharing 52-55% identity with the bHLH/PAS domains of other AHRRs. In transient transfection assays, X. laevis AHRR inhibited TCDD-induced reporter gene expression mediated by either X. laevis AHR paralog, AHR1alpha or AHR1beta. AHRR messenger RNA was expressed at low levels in embryos (Nieuwkoop-Faber stage 33-38; approximately 52 h.p.f.) and was induced approximately twofold following TCDD exposure (42 ng/g wet weight). In contrast, AHRR exhibited higher constitutive expression and was induced more than threefold in tadpoles at stage 52-55 (prometamorphic; approximately 4 weeks postfertilization) and in isolated viscera of stage 62 tadpoles (in the metamorphic climax; approximately 7 weeks postfertilization). Although the magnitude of induction was smaller, the temporal pattern of AHRR expression and inducibility resembled that of CYP1A6. Thus, attenuated transcriptional activation of AHR target genes and low TCDD toxicity in X. laevis embryos cannot be explained by constitutive, high-level expression of AHRR.
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Fort DJ, Rogers RL, Thomas JH, Buzzard BO, Noll AM, Spaulding CD. Comparative sensitivity of Xenopus tropicalis and Xenopus laevis as test species for the FETAX model. J Appl Toxicol 2005; 24:443-57. [PMID: 15551382 DOI: 10.1002/jat.997] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The use of Xenopus tropicalis as an alternative test species for the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) model was evaluated. Five test substances with varying developmental toxicity potential were evaluated using the traditional FETAX (X. laevis) and a modified assay to accommodate the use of X. tropicalis. Two separate definitive concentration-response tests were performed with ethanol, semicarbazide, copper, 6-aminonicotinamide (6-AN) and atrazine. In order to evaluate the impact of culture temperature on species sensitivity, tests with X. tropicalis were performed concurrently at 27 degrees C (optimum temperature) and 23 degrees C (traditional FETAX temperature). Tests with X. laevis were performed only at 23 degrees C (optimal for X. laevis). Regardless of culture temperature, tests with X. laevis and X. tropicalis indicated that each of the compounds possessed teratogenic potential: semicarbazide>6-AN>atrazine approximately copper>ethanol. Results from these studies indicated that these two species responded similarly to the test compounds. Xenopus tropicalis was somewhat less sensitive to 6-AN, semicarbizide and atrazine when tested at 27 degrees C than at 23 degrees C. Ethanol, copper and atrazine were reasonably equipotent in X. tropicalis and X. laevis in terms of teratogenic response (EC50 for malformation), whereas 6-AN and semicarbizide were less potent in X. tropicalis than in X. laevis. No substantial differences (order of magnitude) in potency were observed between X. laevis and X. tropicalis with any of the test materials evaluated. Malformation syndromes induced in both species were similar in X. tropicalis and X. laevis. These results suggested that X. tropicalis could be used effectively as a test organism for the FETAX model.
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Affiliation(s)
- Douglas J Fort
- Fort Environmental Laboratories, 1414 South Sangre, Stillwater, OK 74074, USA.
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Song MO, Fort DJ, McLaughlin DL, Rogers RL, Thomas JH, Buzzard BO, Noll AM, Myers NK. Evaluation of Xenopus tropicalis as an alternative test organism for frog embryo teratogenesis assay--Xenopus (FETAX). Drug Chem Toxicol 2003; 26:177-89. [PMID: 12953658 DOI: 10.1081/dct-120022647] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
As a formal recommendation from an Interagency Coordinating Committee for the Validation of Alternative Methods (ICCVAM) workshop review of the Frog Embryo Teratogenesis Assay--Xenopus (FETAX) developmental toxicity model, the use of Xenopus tropicalis as an alternative test species for this model was evaluated. Three test substances with varying developmental toxicity potentials were evaluated using FETAX modified to accommodate the use of X. tropicalis. Two separate definitive concentration-response tests were performed with isoniazid, methotrexate, and 6-aminonicotinamide. Historical FETAX results with X. laevis were compared to the results from FETAX assays with X. tropicalis. Test with X. tropicalis indicated that each of the compounds possessed teratogenic potential with varying degrees of potency: 6-aminonicotinamide > methotrexate > isoniazid. Based on overt teratogenicity, but not embryo-lethality, results from these studies indicated that these two species responded similarly to the test compounds. Malformation syndromes induced in both species were similar in X. tropicalis and X. laevis. These results suggested that X. tropicalis should be further evaluated as an alternative test organism for the FETAX model.
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Affiliation(s)
- Min Ok Song
- National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
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Fort DJ, Paul RR. Enhancing the predictive validity of Frog Embryo Teratogenesis Assay--Xenopus (FETAX). J Appl Toxicol 2002; 22:185-91. [PMID: 12015799 DOI: 10.1002/jat.848] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a 4-day, alternative developmental toxicity assay designed to pre-screen chemicals and environmental mixtures. An approach used in the scoring of FETAX results, which focuses on the determination of characteristic abnormalities induced by a given test material, was used to evaluate results from previous validation efforts. Characteristic abnormalities are induced specifically by exposure to a given test material and are determined by the relationship between concentration and the response induced and the change in severity of response. Use of this approach eliminates non-specific effects that alter numerical endpoints, reduces intralaboratory variability, reduces the number of equivocal test results (gray area), helps to determine specific syndromes associated with teratogen exposure and, in some instances, increases the predictability of FETAX. In an effort to evaluate this approach, a 12-compound validation study that produced a relatively high degree of equivocal FETAX results was re-evaluated using the characteristic malformation criteria. Data were evaluated for repeatability, predictability and variability. Results from this study indicated that this scoring approach increased repeatability, test endpoint precision and predictability.
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Affiliation(s)
- Douglas J Fort
- Fort Environmental Laboratories, Inc., 1414 S. Sangre Road, Stillwater, OK 74074, USA.
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Fort DJ, Rogers RL, Stover EL, Finch RA. Optimization of an exogenous metabolic activation system for FETAX. I. Post-isolation rat liver microsome mixtures. Drug Chem Toxicol 2001; 24:103-15. [PMID: 11360429 DOI: 10.1081/dct-100102604] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The developmental toxicity of cyclophosphamide, coumarin, 2-acetyl-aminofluorine (2-AAF), and trichloroethylene (TCE) was assessed with Frog Embryo Teratogenesis Assay: Xenopus (FETAX). Late Xenopus laevis blastulae were exposed to each test material for 96-h in two separate static-renewal tests with and without the presence of five differently induced exogenous metabolic activation systems (MAS). The MAS consisted of Aroclor 1254- (Aroclor 1254 MAS), isoniazid- (INH MAS), phenobarbital- (PB MAS), or beta-naphthoflavone- (beta-NF MAS), or a post-isolation mixture (mixed MAS) of INH-, PB-, and beta-NF-induced rat liver microsomes. Addition of the Aroclor 1254 MAS bioactivated cyclophosphamide, coumarin, 2-AAF, but not TCE. Addition of the PB MAS bioactivated cyclophosphamide, weakly bioactivated coumarin and 2-AAF, but had no effect on TCE developmental toxicity. The beta-NF MAS bioactivated coumarin and 2-AAF, weakly bioactivated cyclophosphamide, but did not alter the developmental toxicity of TCE. Addition of the INH-induced MAS only bioactivated TCE, whereas the post-isolation mixed MAS bioactivated each test material. Based on LC50 and EC50 (malformation) values, embryo growth, and types and severity of induced malformations, each test material was developmentally toxic. Use of post-microsome isolation mixtures from differentially induced rat livers increased the efficacy of the exogenous MAS routinely used by FETAX.
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Affiliation(s)
- D J Fort
- Fort Environmental Laboratories, Inc., Stillwater, OK, USA.
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Fort DJ, Stover EL, Bantle JA, Finch RA. Evaluation of the developmental toxicity of thalidomide using frog embryo teratogenesis assay-xenopus (FETAX): biotransformation and detoxification. TERATOGENESIS, CARCINOGENESIS, AND MUTAGENESIS 1999; 20:35-47. [PMID: 10607376 DOI: 10.1002/(sici)1520-6866(2000)20:1<35::aid-tcm4>3.0.co;2-i] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The developmental toxicity of thalidomide was evaluated using FETAX (Frog Embryo Teratogenesis Assay - Xenopus). Young X. Laevis embryos were exposed to this compound in each of two concentration-response experiments with and without differently induced exogenous metabolic activation systems (MASs) and/or inhibited MASs. Young male Sprague-Dawley rats were treated with either isoniazid or Aroclor 1254 to induce cytochrome P-450. Several of the rats were subsequently treated with diethyl maleate (DM) to deplete glutathione reserves. Specific aliquots of rat liver microsomes were treated with 3-amino-1,2,4-triazole (ATZ) or alpha-napthoflavone (alpha-N) to selectively inhibit P-450 activity. Bioactivation was indicated by increased developmental toxicity observed in MAS tests. Results obtained indicated that thalidomide was predominantly activated by P-450 isozyne CYP2E1, although weak cross-specificity between CYP1A1/A2 may have existed. Detoxification pathways for thalidomide were investigated by treatment of the MAS with cyclohexene oxide (CHO) and DM to inhibit the epoxide hydrolase and glutathione conjugation pathways, respectively. Results indicated that epoxide hydrolase was primarily responsible for the detoxification of bioactivated thalidomide. Teratogenesis Carcinog. Mutagen. 20:35-47, 2000.
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Affiliation(s)
- D J Fort
- The Stover Group, Laboratory Services Division, Stillwater, Oklahoma 74074, USA.
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Camatini M, Bonfanti P, Colombo A, Urani C, Crippa S. Cellular and Molecular Targets of Benzo[a]pyrene and Metal Toxicity in Xenopus laevis Embryos and in Hep G2 Cells. Altern Lab Anim 1999; 27:325-37. [PMID: 25470671 DOI: 10.1177/026119299902700321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This paper describes the use of two in vitro systems (stage 35 Xenopus laevis embryos and the human hepatoblastoma cell line, Hep G2) to study effects of some environmental contaminants (benzo[a]pyrene, copper and zinc), which are representative of chemicals with different cell targets and mechanisms of action. The ability to activate benzo[a[pyrene and to metabolise it with the cytochrome P4501A isozyme were demonstrated in both in vitro systems by assessing the formation of water-soluble and protein-bound benzo[a]pyrene metabolites and by immunochemical analysis. In X. laevis embryos, the formation of DNA adducts demonstrated the ability to produce benzo[a]pyrene reactive metabolites. Moreover, in Hep G2 cells, the cytoskeletal protein, tubulin, and the reduced form of glutathione proved to be the cellular targets of copper and zinc toxicity. In response to metal-induced stress in Hep G2 cells, there was a cytoplasmic reorganisation of heat shock protein, Hsp 70. In conclusion, the in vitro systems provide for a rapid evaluation of heterogeneous compounds such as benzo[a]pyrene and heavy metals that differ in toxic potency and mechanisms of action. They could also be used to study the mechanisms of toxic action and to identify specific cellular and molecular targets.
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Affiliation(s)
- M Camatini
- Department of Environmental Sciences, University of Milan, Via Emanueli 15, 20126 Milan, Italy
| | - P Bonfanti
- Department of Environmental Sciences, University of Milan, Via Emanueli 15, 20126 Milan, Italy
| | - A Colombo
- Department of Environmental Sciences, University of Milan, Via Emanueli 15, 20126 Milan, Italy
| | - C Urani
- Department of Environmental Sciences, University of Milan, Via Emanueli 15, 20126 Milan, Italy
| | - S Crippa
- Department of Environmental Sciences, University of Milan, Via Emanueli 15, 20126 Milan, Italy
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