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Thompson CM, Kirman C, Harris MA. Derivation of oral cancer slope factors for hexavalent chromium informed by pharmacokinetic models and in vivo genotoxicity data. Regul Toxicol Pharmacol 2023; 145:105521. [PMID: 37863416 DOI: 10.1016/j.yrtph.2023.105521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Revised: 10/01/2023] [Accepted: 10/18/2023] [Indexed: 10/22/2023]
Abstract
Hexavalent chromium [Cr(VI)] is present in drinking water from natural and anthropogenic sources at approximately 1 ppb. Several regulatory bodies have recently developed threshold-based safety criteria for Cr(VI) of 30-100 ppb based on evidence that small intestine tumors in mice following exposure to ≥20,000 ppb are the result of a non-mutagenic mode of action (MOA). In contrast, U.S. EPA has recently concluded that Cr(VI) acts through a mutagenic MOA based, in part, on scoring numerous in vivo genotoxicity studies as having low confidence; and therefore derived a cancer slope factor (CSF) of 0.5 (mg/kg-day)-1, equivalent to ∼0.07 ppb. Herein, we demonstrate how physiologically based pharmacokinetic (PBPK) models and intestinal segment-specific tumor incidence data can form a robust dataset supporting derivation of alternative CSF values that equate to Cr(VI) concentrations ranging from below background to concentrations similar to those derived using threshold approaches-depending on benchmark response level and risk tolerance. Additionally, we highlight weaknesses in the rationale EPA used to discount critical in vivo genotoxicity studies. While the data support a non-genotoxic MOA, these alternative toxicity criteria require only PBPK models, robust tumor data, and fair interpretation of published in vivo genotoxicity data for Cr(VI).
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Billmann M, Hulot C, Pauget B, Badreddine R, Papin A, Pelfrêne A. Oral bioaccessibility of PTEs in soils: A review of data, influencing factors and application in human health risk assessment. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 896:165263. [PMID: 37400023 DOI: 10.1016/j.scitotenv.2023.165263] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 06/26/2023] [Accepted: 06/30/2023] [Indexed: 07/05/2023]
Abstract
Understanding the behavior of metal(loi)ds transported from soil to humans is critical for human health risk assessment (HHRA). In the last two decades, extensive studies have been conducted to better assess human exposure to potentially toxic elements (PTEs) by estimating their oral bioaccessibility (BAc) and quantifying the influence of different factors. This study reviews the common in vitro methods used to determine the BAc of PTEs (in particular As, Cd, Cr, Ni, Pb, and Sb) under specific conditions (particularly in terms of the particle size fraction and validation status against an in vivo model). The results were compiled from soils derived from various sources and allowed the identification of the most important influencing factors of BAc (using single and multiple regression analyses), including physicochemical soil properties and the speciation of the PTEs in question. This review presents current knowledge on integrating relative bioavailability (RBA) in calculating doses from soil ingestion in the HHRA process. Depending on the jurisdiction, validated or non-validated bioaccessibility methods were used, and risks assessors applied different approaches: (i) using default assumptions (i.e., RBA of 1); (ii) considering that bioaccessibility value (BAc) accurately represents RBA (i.e., RBA equal to BAc); (iii) using regression models to convert BAc of As and Pb into RBA as proposed by the USA with the US EPA Method 1340; or (iv) applying an adjustment factor as proposed by the Netherlands and France to use BAc from UBM (Unified Barge Method) protocol. The findings from this review should help inform risk stakeholders about the uncertainties surrounding using bioaccessibility data and provide recommendations for better interpreting the results and using bioaccessibility in risk studies.
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Affiliation(s)
- Madeleine Billmann
- Univ. Lille, IMT Nord Europe, Univ. Artois, JUNIA, ULR 4515-LGCgE, Laboratoire de Génie Civil et géo-Environnement, 48 boulevard Vauban, F-59000 Lille, France; Agence de l'Environnement et de la Maîtrise de l'Énergie, 20 avenue du Grésillé BP 90406, F-49004 Angers Cedex 01, France
| | - Corinne Hulot
- Ineris, Parc technologique Alata, BP 2, F-60550 Verneuil-en-Halatte, France
| | | | - Rabia Badreddine
- Ineris, Parc technologique Alata, BP 2, F-60550 Verneuil-en-Halatte, France
| | - Arnaud Papin
- Ineris, Parc technologique Alata, BP 2, F-60550 Verneuil-en-Halatte, France
| | - Aurélie Pelfrêne
- Univ. Lille, IMT Nord Europe, Univ. Artois, JUNIA, ULR 4515-LGCgE, Laboratoire de Génie Civil et géo-Environnement, 48 boulevard Vauban, F-59000 Lille, France.
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Handa K, Jindal R. Mitigating the nephrotoxic impact of hexavalent chromium in Ctenopharyngodon idellus (grass carp) with Boerhavia diffusa (punarnava) leaf extract. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:42399-42415. [PMID: 36648730 DOI: 10.1007/s11356-022-24931-4] [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: 02/22/2022] [Accepted: 12/19/2022] [Indexed: 06/17/2023]
Abstract
In Ctenopharyngodon idellus, the ameliorative influence of rutin-containing leaf extract of Boerhavia diffusa was assessed against chronic exposure to hexavalent chromium. For this, alterations in chromium accumulation, oxidative stress, kidney function markers, histopathology (light and transmission electron microscopy), and transcriptional profiling (Nrf2 and MT2) were examined. RP-HPLC analysis confirmed the presence of rutin (90.45 ± 0.98 mg/g) in the ethanolic leaf extract of the plant. LD50 of the extract to the fish was beyond 5000 mg/kg b.w. The fish was subjected to a sublethal concentration of hexavalent chromium (5.30 mg/L) accompanied by a dose of 250 mg/kg b.w./day of extract in the diet for the experimental duration of 45 days. The extract alone did not generate any adverse consequences in the nephric tissue. Chronic exposure to hexavalent chromium damaged tissue irreparably, demonstrated by elevated levels of kidney function markers (blood urea nitrogen and creatinine) and altered histoarchitecture (DTC value of 78.02 ± 10.5). The metal exposure increased chromium accumulation and malondialdehyde (MDA) and decreased the reduced glutathione (GSH) levels, the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione-S-transferase) and gene expression in the tissue. The co-supplementation of leaf extract with metal exposure revealed a tissue architecture with normal to slight modifications, and the level of kidney markers, antioxidants, and genes expressed in a normalized range. Principal component analysis created two components with antioxidants (GSH, SOD, CAT, and GST) revealing a negative correlation with the second component comprising MDA, DTC, and chromium concentration. It can be concluded that B. diffusa leaves are safe additives in the fish diet and possess an ameliorative capacity for renal injury incurred by hexavalent chromium.
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Affiliation(s)
- Kriti Handa
- Aquatic Biology Laboratory, Department of Zoology, Panjab University, Chandigarh, 160014, India
| | - Rajinder Jindal
- Aquatic Biology Laboratory, Department of Zoology, Panjab University, Chandigarh, 160014, India.
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Assessment of intestinal injury of hexavalent chromium using a modified in vitro gastrointestinal digestion model. Toxicol Appl Pharmacol 2022; 436:115880. [PMID: 35016909 DOI: 10.1016/j.taap.2022.115880] [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: 11/14/2021] [Revised: 12/21/2021] [Accepted: 01/06/2022] [Indexed: 11/22/2022]
Abstract
Intestinal injury assessment of hexavalent chromium (Cr-VI) in humans is crucial for quantifying assessment of adverse health risk posed by the intake of Cr (VI)-contaminated water. To overcome the deficiency in simulating human gastric reduction and intestinal absorption, we modified the constituents of simulated gastric fluid in in vitro digestion method by adding reductants glutathione (18 μM) and ascorbic acid (180 μM), which incorporated with human intestinal epithelial model to construct an in vitro gastrointestinal digestion (IVGD) model for intestinal injury assessment. Cr-VI bioaccessibility results from IVGD model showed that weak gastric acidity significantly increased the intestinal accessible Cr-VI dose by 22.41-38.43 folds. The time-course intestinal absorption indicated prolongation of intestinal exposure destroyed the intestinal epithelium, and 24 h after Cr-VI treatment was a good time point to perform intestinal absorption and toxicity assessment. A series of cell-based bioassays provided initial warning of adverse effect, suggesting that epithelial integrity exhibited greatest sensitivity to Cr-VI exposure and might be used as a sensitive marker for the toxicity assessment of oral exposure to Cr-VI. Notably, this study provides a feasible strategy for delineation of Cr-VI biotransformation and intestinal injury following ingestion exposure, which contributes to address the toxicity data gap of low-dose exposure in humans and puts forward a reference for intestinal toxicity assessment of other chemicals.
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Bhat VS, Cohen SM, Gordon EB, Wood CE, Cullen JM, Harris MA, Proctor DM, Thompson CM. An adverse outcome pathway for small intestinal tumors in mice involving chronic cytotoxicity and regenerative hyperplasia: a case study with hexavalent chromium, captan, and folpet. Crit Rev Toxicol 2020; 50:685-706. [PMID: 33146058 DOI: 10.1080/10408444.2020.1823934] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Small intestinal (SI) tumors are relatively uncommon outcomes in rodent cancer bioassays, and limited information regarding chemical-induced SI tumorigenesis has been reported in the published literature. Herein, we propose a cytotoxicity-mediated adverse outcome pathway (AOP) for SI tumors by leveraging extensive target species- and site-specific molecular, cellular, and histological mode of action (MOA) research for three reference chemicals, the fungicides captan and folpet and the transition metal hexavalent chromium (Cr(VI)). The gut barrier functions through highly efficient homeostatic regulation of SI epithelial cell sloughing, regenerative proliferation, and repair, which involves the replacement of up to 1011 cells per day. This dynamic turnover in the SI provides a unique local environment for a cytotoxicity mediated AOP/MOA. Upon entering the duodenum, cytotoxicity to the villous epithelium is the molecular initiating event, as indicated by crypt elongation, villous atrophy/blunting, and other morphologic changes. Over time, the regenerative capacity of the gut epithelium to compensate declines as epithelial loss accelerates, especially at higher exposures. The first key event (KE), sustained regenerative crypt proliferation/hyperplasia, requires sufficient durations, likely exceeding 6 or 12 months, due to extensive repair capacity, to create more opportunities for the second KE, spontaneous mutation/transformation, ultimately leading to proximal SI tumors. Per OECD guidance, biological plausibility, essentiality, and empirical support were assessed using modified Bradford Hill considerations. The weight-of-evidence also included a lack of induced mutations in the duodenum after up to 90 days of Cr(VI) or captan exposure. The extensive evidence for this AOP, along with the knowledge that human exposures are orders of magnitude below those associated with KEs in this AOP, supports its use for regulatory applications, including hazard identification and risk assessment.
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Affiliation(s)
| | - Samuel M Cohen
- Havlik-Wall Professor of Oncology, Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, USA
| | | | - Charles E Wood
- Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, CT, USA
| | - John M Cullen
- North Carolina State University, Raleigh, NC, USA.,EPL, Inc., Sterling, VA, USA
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Yao Y, Gao M, Zhang Y, Zheng H, Hu H, Yin H, Wang S. Nonprecious bimetallic (Mo, Fe)-N/C nanostructures loaded on PVDF membrane for toxic Cr VI reduction from water. JOURNAL OF HAZARDOUS MATERIALS 2020; 389:121844. [PMID: 31879108 DOI: 10.1016/j.jhazmat.2019.121844] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 12/06/2019] [Accepted: 12/06/2019] [Indexed: 06/10/2023]
Abstract
Nonprecious bimetallic molybdenum and iron embedded into N-doped carbon (MoFe-NC) hybrids were designed and fabricated by pyrolysis of mixed precursors and then immobilized on poly (vinylidene fluoride) (PVDF) films via a phase inversion process to obtain novel catalytic membranes (MoFe-NC@PVDF) for toxic CrVI reduction. The catalytic membranes are highly active for aqueous CrVI reduction using formic acid (FA) as a sacrificial electron donor under mild conditions. The results demonstrated that the parameters of synthesis process can efficiently adjust the morphology and textural properties of the as-synthesized MoFe-NC@PVDF membrane, and thus have a significant impact on the catalytic behavior. CrVI reduction rates significantly increased with increasing FA concentrations (0.234-0.936 M) and reaction temperature (5-35℃), but declined with the increase of CrVI concentrations (5-40 mg/L) and pH values of solution (1.87-4.62). Mo-Nx, Fe-Nx, and C-Nx are the active sites, boosting the dissociation of FA molecules into active H* species for effective catalytic reduction of CrVI. The catalytic PVDF membrane exhibited distinct porous structure and numerous interaction sites, which not only stabilized metallic nanoparticles, but also promoted mass transfer across the membrane. This cost-effective catalytic membrane provides a new approach toward the treatment of CrVI-containing water.
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Affiliation(s)
- Yunjin Yao
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China.
| | - Mengxue Gao
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China
| | - Yangyang Zhang
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China
| | - Hongda Zheng
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China
| | - Huanhuan Hu
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China
| | - Hongyu Yin
- Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, China
| | - Shaobin Wang
- School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia.
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Suh M, Wikoff D, Lipworth L, Goodman M, Fitch S, Mittal L, Ring C, Proctor D. Hexavalent chromium and stomach cancer: a systematic review and meta-analysis. Crit Rev Toxicol 2019; 49:140-159. [DOI: 10.1080/10408444.2019.1578730] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Mina Suh
- ToxStrategies, Inc, Mission Viejo, CA, USA
| | | | - Loren Lipworth
- Vanderbilt University Medical Center, Nashville, TN, USA
| | - Michael Goodman
- Emory University Rollins School of Public Health, Atlanta, GA, USA
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Moffat I, Martinova N, Seidel C, Thompson CM. Hexavalent Chromium in Drinking Water. ACTA ACUST UNITED AC 2018. [DOI: 10.1002/awwa.1044] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Ivy Moffat
- Water and Air Quality Bureau; Health Canada; Ottawa Ont. Canada
| | - Nadia Martinova
- Water and Air Quality Bureau; Health Canada; Ottawa Ont. Canada
| | - Chad Seidel
- Corona Environmental Consulting; Louisville Colo
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Spatial Distribution and Mobility Assessment of Carcinogenic Heavy Metals in Soil Profiles Using Geostatistics and Random Forest, Boruta Algorithm. SUSTAINABILITY 2018. [DOI: 10.3390/su10030799] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Thompson CM, Kirman CR, Hays SM, Suh M, Harvey SE, Proctor DM, Rager JE, Haws LC, Harris MA. Integration of mechanistic and pharmacokinetic information to derive oral reference dose and margin-of-exposure values for hexavalent chromium. J Appl Toxicol 2018; 38:351-365. [PMID: 29064106 PMCID: PMC5813206 DOI: 10.1002/jat.3545] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Revised: 08/28/2017] [Accepted: 09/05/2017] [Indexed: 01/18/2023]
Abstract
The current US Environmental Protection Agency (EPA) reference dose (RfD) for oral exposure to chromium, 0.003 mg kg-1 day-1 , is based on a no-observable-adverse-effect-level from a 1958 bioassay of rats exposed to ≤25 ppm hexavalent chromium [Cr(VI)] in drinking water. EPA characterizes the confidence in this RfD as "low." A more recent cancer bioassay indicates that Cr(VI) in drinking water is carcinogenic to mice at ≥30 ppm. To assess whether the existing RfD is health protective, neoplastic and non-neoplastic lesions from the 2 year cancer bioassay were modeled in a three-step process. First, a rodent physiological-based pharmacokinetic (PBPK) model was used to estimate internal dose metrics relevant to each lesion. Second, benchmark dose modeling was conducted on each lesion using the internal dose metrics. Third, a human PBPK model was used to estimate the daily mg kg-1 dose that would produce the same internal dose metric in both normal and susceptible humans. Mechanistic research into the mode of action for Cr(VI)-induced intestinal tumors in mice supports a threshold mechanism involving intestinal wounding and chronic regenerative hyperplasia. As such, an RfD was developed using incidence data for the precursor lesion diffuse epithelial hyperplasia. This RfD was compared to RfDs for other non-cancer endpoints; all RfD values ranged 0.003-0.02 mg kg-1 day-1 . The lowest of these values is identical to EPA's existing RfD value. Although the RfD value remains 0.003 mg kg-1 day-1 , the confidence is greatly improved due to the use of a 2-year bioassay, mechanistic data, PBPK models and benchmark dose modeling.
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Affiliation(s)
| | | | - Sean M Hays
- Summit Toxicology, LLP, Bozeman, MT, 59722, USA
| | - Mina Suh
- ToxStrategies, Inc., Mission Viejo, CA, 92692, USA
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Thompson CM, Suh M, Proctor DM, Haws LC, Harris MA. Ten factors for considering the mode of action of Cr(VI)-induced gastrointestinal tumors in rodents. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2017; 823:45-57. [DOI: 10.1016/j.mrgentox.2017.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 08/26/2017] [Accepted: 08/28/2017] [Indexed: 12/28/2022]
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Shil K, Pal S. Metabolic adaptability in hexavalent chromium-treated renal tissue: an in vivo study. Clin Kidney J 2017; 11:222-229. [PMID: 29644063 PMCID: PMC5887570 DOI: 10.1093/ckj/sfx069] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Accepted: 05/30/2017] [Indexed: 12/17/2022] Open
Abstract
Background Hexavalent chromium [Cr(VI)], an environmental pollutant that originates mostly from anthropogenic sources, is a serious threat to human health. After entering into cells, Cr(VI) is capable of producing excessive free radicals and causing tissue damage. The present study aims to reveal the toxic manifestation of Cr(VI) on the metabolic activity of renal tissue. Methods Male Swiss albino mice were treated orally with potassium dichromate (K2Cr2O7) at a dose of 10 mg/kg body weight for a period of 30 days. Important tricarboxylic acid (TCA) cycle enzyme activities like isocitrate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, as well as the activities of enzymes involved in oxidative phosphorylation such as Nicotinamide adenine dinucleotide (NADH) dehydrogenase, were measured. Additionally, transaminase and protease (pronase, cathepsin and trypsin) activities, tissue protein and free amino nitrogen were estimated in renal tissue. Glucose-6-phosphatase, glucose-6-phosphate dehydrogenase and alkaline phosphatase activities, as well as lactic acid, pyruvic acid and chromium contents, of kidneys were determined following standard protocols. Kidney histology was performed by hematoxylin and eosin staining. Results Cr(VI) suppresses the rate-limiting enzymes of the TCA cycle and oxidative phosphorylation indicating an inhibition of renal ATP production. It decreases protease activity by eliminating the protein substrates and alters the gluconeogenic pathway. Cr(VI) worsens the normophysiological attributes of renal tissue by enhancing the activity of alkaline phosphatase, pointing towards kidney disease. Histopathological observations confirmed these biochemical results through the presence of chronic tubular nephritis and altered glomerular structure. Cr(VI) retention occurs to a greater extent in renal tissue, which intensifies the toxic manifestation of this pollutant in the kidney. Conclusions Cr(VI) disrupts the metabolic interaction between carbohydrates and proteins in mammalian renal tissue.
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Affiliation(s)
- Kanu Shil
- Nutritional Biochemistry and Toxicology Laboratory, Department of Human Physiology, Tripura University, Suryamaninagar, West Tripura, India
| | - Sudipta Pal
- Nutritional Biochemistry and Toxicology Laboratory, Department of Human Physiology, Tripura University, Suryamaninagar, West Tripura, India
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Kirman C, Suh M, Proctor D, Hays S. Improved physiologically based pharmacokinetic model for oral exposures to chromium in mice, rats, and humans to address temporal variation and sensitive populations. Toxicol Appl Pharmacol 2017; 325:9-17. [DOI: 10.1016/j.taap.2017.03.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 03/26/2017] [Accepted: 03/29/2017] [Indexed: 10/19/2022]
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Thompson CM, Rager JE, Suh M, Ring CL, Proctor DM, Haws LC, Fry RC, Harris MA. Transcriptomic responses in the oral cavity of F344 rats and B6C3F1 mice following exposure to Cr(VI): Implications for risk assessment. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2016; 57:706-716. [PMID: 27859739 PMCID: PMC5215477 DOI: 10.1002/em.22064] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 10/27/2016] [Indexed: 05/13/2023]
Abstract
Exposure to hexavalent chromium [Cr(VI)] in drinking water was previously reported to increase oral tumor incidence in F344 rats. To investigate the mode of action for these tumors, transcriptomic profiles in oral mucosa samples of F344 rats and B6C3F1 mice were analyzed following exposure to 0.1-180 ppm Cr(VI) for 7 or 90 days. In rats, genome-wide microarray analyses identified no significantly differentially expressed genes (DEGs) at either time point. In mice, 14 and 1 DEGs were respectively identified after 7 and 90 days of exposure. Therefore, relaxed statistical criteria were employed to identify potential DEGs (pDEGs), followed by high-throughput benchmark dose modeling to identify responsive pDEGs for pathway enrichment analysis. This identified 288 and 168 pDEGs in the rat oral mucosa, of which only 20 and 7 showed evidence of dose-response. No significant pathway enrichment was obtained with either pDEG or dose-responsive pDEG lists. Similar results were obtained in mice. These analyses indicate a negligible transcriptional response in the oral mucosa of both species. Comparison of the total number of gene changes in the oral mucosa of rats and mice with responses in the duodenum of animals from the same study demonstrated remarkable dose-response concordance across tissues and species as a function of tissue chromium concentration. The low chromium levels in the oral mucosa and negligible transcript response are consistent with an absence of tissue lesions. These findings are used to compare the merits of linear and nonlinear approaches for deriving toxicity criteria based on the oral tumors in rats. Environ. Mol. Mutagen. 57:706-716, 2016. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc.
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Affiliation(s)
| | | | - Mina Suh
- ToxStrategies, IncMission ViejoCalifornia
| | | | | | | | - Rebecca C. Fry
- Department of Environmental Sciences and EngineeringGillings School of Global Public HealthChapel HillNorth Carolina
- Curriculum in Toxicology, University of North Carolina at Chapel HillChapel HillNorth Carolina
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