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Perry CS, Blanchette AD, Vivanco SN, Verwiel AH, Proctor DM. Use of physiologically based pharmacokinetic modeling to support development of an acute (24-hour) health-based inhalation guideline for manganese. Regul Toxicol Pharmacol 2023; 145:105518. [PMID: 37863417 DOI: 10.1016/j.yrtph.2023.105518] [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: 04/29/2023] [Revised: 10/04/2023] [Accepted: 10/18/2023] [Indexed: 10/22/2023]
Abstract
The toxicokinetics of manganese (Mn) are controlled through homeostasis because Mn is an essential element. However, at elevated doses, Mn is also neurotoxic and has been associated with respiratory, reproductive, and developmental effects. While health-based criteria have been developed for chronic inhalation exposure to ambient Mn, guidelines for short-term (24-h) environmental exposure are also needed. We reviewed US state, federal, and international health-based inhalation toxicity criteria, and conducted a literature search of recent publications. The studies deemed most appropriate to derive a 24-h guideline have a LOAEL of 1500 μg/m3 for inflammatory airway changes and biochemical measures of oxidative stress in the brain following 90 total hours of exposure in monkeys. We applied a cumulative uncertainty factor of 300 to this point of departure, resulting in a 24-h guideline of 5 μg/m3. To address uncertainty regarding potential neurotoxicity, we used a previously published physiologically based pharmacokinetic model for Mn to predict levels of Mn in the brain target tissue (i.e., globus pallidus) for exposure at 5 μg/m3 for two short-term human exposure scenarios. The PBPK model predictions support a short-term guideline of 5 μg/m3 as protective of both respiratory effects and neurotoxicity, including exposures of infants and children.
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Affiliation(s)
- Camarie S Perry
- ToxStrategies, 9390 Research Blvd, Bldg. II, Suite 100, Austin, TX, 78759, USA.
| | | | | | - Ann H Verwiel
- ToxStrategies, 1010 B Street, Suite 208, San Rafael, CA, 94901, USA.
| | - Deborah M Proctor
- ToxStrategies, 27001 La Paz Road, Suite 260, Mission Viejo, CA, 92691, USA.
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Campbell JL, Clewell HJ, Van Landingham C, Gentry PR, Keene AM, Taylor MD, Andersen ME. Incorporation of rapid association/dissociation processes in tissues into the monkey and human physiologically based pharmacokinetic models for manganese. Toxicol Sci 2022; 191:212-226. [PMID: 36453847 PMCID: PMC9936208 DOI: 10.1093/toxsci/kfac123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
In earlier physiologically based pharmacokinetic (PBPK) models for manganese (Mn), the kinetics of transport of Mn into and out of tissues were primarily driven by slow rates of association and dissociation of Mn with tissue binding sites. However, Mn is known to show rapidly reversible binding in tissues. An updated Mn model for primates, following similar work with rats, was developed that included rapid association/dissociation processes with tissue Mn-binding sites, accumulation of free Mn in tissues after saturation of these Mn-binding sites and rapid rates of entry into tissues. This alternative structure successfully described Mn kinetics in tissues in monkeys exposed to Mn via various routes including oral, inhalation, and intraperitoneal, subcutaneous, or intravenous injection and whole-body kinetics and tissue levels in humans. An important contribution of this effort is showing that the extension of the rate constants for binding and cellular uptake established in the monkey were also able to describe kinetic data from humans. With a consistent model structure for monkeys and humans, there is less need to rely on cadaver data and whole-body tracer studies alone to calibrate a human model. The increased biological relevance of the Mn model structure and parameters provides greater confidence in applying the Mn PBPK models to risk assessment. This model is also well-suited to explicitly incorporate emerging information on the role of transporters in tissue disposition, intestinal uptake, and hepatobiliary excretion of Mn.
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Affiliation(s)
- Jerry L Campbell
- To whom correspondence should be addressed at Ramboll US Corporation, 3214 Charles B. Root Wynd, Suite 130, Raleigh, NC 27612, USA. E-mail:
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Desrosiers M, Pelletier G, Dieme D, Côté J, Jomaa M, Nong A, Bouchard M. Toxicokinetics in rats and modeling to support the interpretation of biomonitoring data for rare-earth elements. ENVIRONMENT INTERNATIONAL 2021; 155:106685. [PMID: 34134049 DOI: 10.1016/j.envint.2021.106685] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 05/25/2021] [Accepted: 06/02/2021] [Indexed: 06/12/2023]
Abstract
Toxicokinetic models are useful tools to better understand the fate of contaminants in the human body and to establish biological guidance values to interpret biomonitoring data in human populations. This research aimed to develop a biologically-based toxicokinetic model for four rare earth elements (REEs), cerium (Ce), praseodymium (Pr), neodymium (Nd) and yttrium (Y), and to establish biomonitoring equivalents (BE) serving as biological guidance values. The model was constructed using physiological data taken from the literature as well as new experimental kinetic data. These new data indicated that REEs readily disappeared from blood and accumulated mostly in the liver; excretion occurred mainly through feces although a small fraction was eliminated in urine. To properly reproduce the observed kinetics, the model was represented as 19 compartments, which include main tissues and their components (such as retention by macrophages) supplied by blood, as well as routes of excretion. The transfer coefficients between compartments were determined numerically by adjustments to experimental data. Simulations gave good fits to available experimental kinetic data and confirmed that the same model structure is applicable to the four elements. BEs of 0.3 µg/L of Pr and Nd were derived from the provisional RfD of 0.5 mg/kg bw/day established by the U.S. EPA. These BEs can be updated according to new reference dose values (RfD). Overall, the model can contribute to a better understanding of the significance of biological measurements and to the inference of exposure levels; it can also be used for the modeling of other REEs. The BEs will further allow rapid screening of different populations using biological measurements in order to guide risk assessments.
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Affiliation(s)
- Mathieu Desrosiers
- Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U424, P.O. Box 6128, Main Station, Montreal, Quebec H3C 3J7, Canada
| | - Guillaume Pelletier
- Environmental Health Science and Research Bureau, Health Canada, K1A 0K9, Ottawa, ON, Canada
| | - Denis Dieme
- Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U424, P.O. Box 6128, Main Station, Montreal, Quebec H3C 3J7, Canada
| | - Jonathan Côté
- Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U424, P.O. Box 6128, Main Station, Montreal, Quebec H3C 3J7, Canada
| | - Malek Jomaa
- Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U424, P.O. Box 6128, Main Station, Montreal, Quebec H3C 3J7, Canada
| | - Andy Nong
- Environmental Health Science and Research Bureau, Health Canada, K1A 0K9, Ottawa, ON, Canada
| | - Michèle Bouchard
- Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U424, P.O. Box 6128, Main Station, Montreal, Quebec H3C 3J7, Canada.
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Edmondson DA, Ma RE, Yeh CL, Ward E, Snyder S, Azizi E, Zauber SE, Wells EM, Dydak U. Reversibility of neuroimaging markers influenced by lifetime occupational manganese exposure. Toxicol Sci 2019; 172:181-190. [PMID: 31388678 PMCID: PMC6813746 DOI: 10.1093/toxsci/kfz174] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 05/24/2019] [Accepted: 07/08/2019] [Indexed: 11/13/2022] Open
Abstract
Manganese (Mn) is a neurotoxicant that many workers are exposed to daily. There is limited knowledge about how changes in exposure levels impact measures in magnetic resonance imaging (MRI). We hypothesized that changes in Mn exposure would be reflected by changes in the MRI relaxation rate R1 and thalamic γ-aminobutyric acid (GABAThal). As part of a prospective cohort study, 17 welders were recruited and imaged on two separate occasions approximately two years apart. MRI relaxometry was used to assess changes of Mn accumulation in the brain. Additionally, GABA was measured using magnetic resonance spectroscopy (MRS) in the thalamic and striatal regions of the brain. Air Mn exposure ([Mn]Air) and cumulative exposure indexes of Mn (Mn-CEI) for the past three months (Mn-CEI3M), past year (Mn-CEI12M), and lifetime (Mn-CEILife) were calculated using personal air sampling and a comprehensive work history, while toenails were collected for analysis of internal Mn body burden. Finally, welders' motor function was examined using the Unified Parkinson's Disease Rating Scale (UPDRS). Median exposure decreased for all exposure measures between the first and second scan. ΔGABAThal was significantly correlated with ΔMn-CEI3M (ρ = 0.66, adjusted p = 0.02), ΔMn-CEI12M (ρ = 0.70, adjusted p = 0.006) , and Δ[Mn]Air (ρ = 0.77, adjusted p = 0.002). ΔGABAThal significantly decreased linearly with ΔMn-CEI3M (quantile regression, β = 15.22, p = 0.02) as well as Δ[Mn]Air (β = 1.27, p = 0.04). Finally, Mn-CEILife interacted with Δ[Mn]Air in the substantia nigra where higher Mn-CEILife lessened the ΔR1 per Δ[Mn]Air (F-test, p = 0.005). While R1 and GABA changed with Mn exposure, UPDRS was unaffected. In conclusion, our study shows that effects from changes in Mn exposure are reflected in thalamic GABA levels and brain Mn levels, as measured by R1, in most brain regions.
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Affiliation(s)
- David A Edmondson
- School of Health Sciences, Purdue University, West Lafayette, IN.,Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN
| | - Ruoyun E Ma
- School of Health Sciences, Purdue University, West Lafayette, IN.,Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN.,Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Chien-Lin Yeh
- School of Health Sciences, Purdue University, West Lafayette, IN.,Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN
| | - Eric Ward
- School of Health Sciences, Purdue University, West Lafayette, IN
| | - Sandy Snyder
- School of Health Sciences, Purdue University, West Lafayette, IN
| | - Elham Azizi
- Department of Neurology, Ochsner Medical Center, Kenner, LA
| | - S Elizabeth Zauber
- Department of Neurology, Indiana University School of Medicine, Indianapolis, IN
| | - Ellen M Wells
- School of Health Sciences, Purdue University, West Lafayette, IN.,Public Health Graduate Program, Purdue University, West Lafayette, IN
| | - Ulrike Dydak
- School of Health Sciences, Purdue University, West Lafayette, IN.,Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN
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Yoon M, Efremenko A, Van Landingham C, Gentry PR, Keene AM, Taylor MD, Clewell HJ, Andersen ME. Updating physiologically based pharmacokinetic models for manganese by incorporating rapid association/dissociation processes in tissues. Toxicol Appl Pharmacol 2019; 372:1-10. [PMID: 30978397 DOI: 10.1016/j.taap.2019.04.006] [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: 12/11/2018] [Revised: 04/02/2019] [Accepted: 04/06/2019] [Indexed: 11/30/2022]
Abstract
Previously, we developed a series of physiologically based pharmacokinetic (PBPK) models for manganese (Mn) in which saturable tissue binding and dose-dependent increases in biliary excretion captured key aspects of Mn homeostasis biology. These models reproduced the non-linear behavior of Mn kinetics in different tissues, accounting for dose-dependent changes in Mn kinetics. The original model construct had relatively slow association and dissociation rate constants for Mn binding in tissues. In this updated model, both rates of entry into tissue and the interaction of Mn with binding sites are rapid, and the step limiting Mn accumulation is the saturation of tissue binding sites. This binding reflects general cellular requirements for Mn with high affinity but rapid exchange between bound and free forms, which we captured using a dissociation constant (KD) of ~ 0.5 μM across tissues while maintaining different maximum binding capacities in each tissue. Variability in the binding capacities accounted for different background levels of Mn in particular tissues. This alternative structure successfully described Mn kinetics in tissues in adult rats exposed to Mn either in their diet or by inhalation, indicating that both the original and the present models capture the dose-dependent and tissue-specific kinetic behavior of Mn in adult rats. Although the published models that emphasize the role of smaller tissue binding rate constants in non-linear behaviors capture all relevant dose-dependent kinetic behaviors of this metal, increasing biological relevance of the model structure and parameters should provide greater confidence in applying the Mn PBPK models to risk assessment.
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Affiliation(s)
- Miyoung Yoon
- ScitoVation, LLC, RTP, Cary, NC, USA; Toxstrategies, Inc., Cary, NC, USA.
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6
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Leonhard MJ, Chang ET, Loccisano AE, Garry MR. A systematic literature review of epidemiologic studies of developmental manganese exposure and neurodevelopmental outcomes. Toxicology 2019; 420:46-65. [PMID: 30928475 DOI: 10.1016/j.tox.2019.03.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 03/10/2019] [Accepted: 03/19/2019] [Indexed: 12/27/2022]
Abstract
BACKGROUND Neurotoxic effects of high-level occupational exposure to manganese (Mn) are well established; however, whether lower-level environmental exposure to Mn in early life causes neurodevelopmental toxicity in children is unclear. METHODS A systematic literature review was conducted to identify and evaluate epidemiologic studies of specific Mn biomarkers assessed during gestation, childhood, or adolescence in association with neurodevelopmental outcomes, focusing on quantitative exposure-response estimates with specific endpoints that were assessed in multiple independent study populations. Study quality was evaluated using the revised RTI item bank and the Cochrane Risk of Bias tool, and the overall weight of epidemiologic evidence for causality was evaluated according to the Bradford Hill considerations. RESULTS Twenty-two epidemiologic studies were identified that estimated associations between early-life Mn biomarkers and neurodevelopmental outcomes. Seven of these studies provided adjusted estimates for the association with child intelligence assessed using versions of the Wechsler Intelligence Scales for Children; no other specific neurodevelopmental endpoints were assessed in more than three independent study populations each. Among the studies of child intelligence, five studies in four independent populations measured blood Mn, three studies measured hair Mn, and one measured dentin Mn. Overall, cross-sectional associations between Mn biomarkers and measures of child intelligence were mostly statistically nonsignificant but in a negative direction; however, the lone prospective cohort study found mostly null results, with some positive (favorable) associations between dentin Mn and child intelligence. Studies were methodologically limited by their cross-sectional design and potential for confounding and selection bias, as well as unaddressed questions on exposure assessment validity and biological plausibility. CONCLUSIONS The statistical associations reported in the few studies of specific Mn biomarkers and specific neurodevelopmental endpoints do not establish causal effects based on the Bradford Hill considerations. Additional prospective cohort studies of Mn biomarkers and validated neurodevelopmental outcomes, and a better understanding of the etiologic relevance of Mn biomarkers, are needed to shed light on whether environmental exposure to Mn causes adverse neurodevelopmental effects in children.
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Affiliation(s)
- Megan J Leonhard
- Exponent, Inc., Center for Health Sciences, 15375 SE 30th Place, Suite 250, Bellevue, WA 98007, United States.
| | - Ellen T Chang
- Exponent, Inc., Center for Health Sciences, 149 Commonwealth Drive, Menlo Park, CA 94025, United States.
| | - Anne E Loccisano
- Exponent, Inc., Center for Health Sciences, 1800 Diagonal Road, Suite 500, Alexandria, VA 22314, United States.
| | - Michael R Garry
- Exponent, Inc., Center for Health Sciences, 15375 SE 30th Place, Suite 250, Bellevue, WA 98007, United States.
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7
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Song G, Moreau M, Efremenko A, Lake BG, Wu H, Bruckner JV, White CA, Osimitz TG, Creek MR, Hinderliter PM, Clewell HJ, Yoon M. Evaluation of Age-Related Pyrethroid Pharmacokinetic Differences in Rats: Physiologically-Based Pharmacokinetic Model Development Using In Vitro Data and In Vitro to In Vivo Extrapolation. Toxicol Sci 2019; 169:365-379. [DOI: 10.1093/toxsci/kfz042] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Affiliation(s)
- Gina Song
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Marjory Moreau
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Alina Efremenko
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Brian G Lake
- Centre for Toxicology, University of Surrey, Surrey, UK
| | - Huali Wu
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
- Duke Medical Center, Durham, North Carolina 27705
| | | | | | | | - Moire R Creek
- Valent USA, LLC, Walnut Creek, California 94596
- Moire Creek Toxicology Consulting Services, Livermore, California 94550
| | | | - Harvey J Clewell
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
- Ramboll, Research Triangle Park, North Carolina 27709
| | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
- ToxStrategies, Cary, North Carolina 27511
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Physiologically-based pharmacokinetic modeling suggests similar bioavailability of Mn from diet and drinking water. Toxicol Appl Pharmacol 2018; 359:70-81. [DOI: 10.1016/j.taap.2018.09.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Revised: 09/16/2018] [Accepted: 09/17/2018] [Indexed: 12/29/2022]
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9
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Ma RE, Ward EJ, Yeh CL, Snyder S, Long Z, Gokalp Yavuz F, Zauber SE, Dydak U. Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI. Neurotoxicology 2018; 64:30-42. [PMID: 28873337 PMCID: PMC5891096 DOI: 10.1016/j.neuro.2017.08.013] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 08/30/2017] [Accepted: 08/30/2017] [Indexed: 01/08/2023]
Abstract
Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson's disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m3; High: N=13; mean air Mn=0.23±0.18mg/m3), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m3) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.
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Affiliation(s)
- Ruoyun E Ma
- School of Health Sciences, Purdue University, West Lafayette, IN, USA; Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Eric J Ward
- School of Health Sciences, Purdue University, West Lafayette, IN, USA
| | - Chien-Lin Yeh
- School of Health Sciences, Purdue University, West Lafayette, IN, USA; Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Sandy Snyder
- School of Health Sciences, Purdue University, West Lafayette, IN, USA; Department of Speech, Language and Hearing Sciences, Purdue University, West Lafayette, IN, USA
| | - Zaiyang Long
- School of Health Sciences, Purdue University, West Lafayette, IN, USA; Department of Radiology, Mayo Clinic, Rochester, MN, USA
| | - Fulya Gokalp Yavuz
- Department of Statistics, Purdue University, IN, USA; Yildiz Technical University, Istanbul, Turkey
| | - S Elizabeth Zauber
- Department of Neurology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Ulrike Dydak
- School of Health Sciences, Purdue University, West Lafayette, IN, USA; Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Speech, Language and Hearing Sciences, Purdue University, West Lafayette, IN, USA.
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10
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Foster ML, Rao DB, Francher T, Traver S, Dorman DC. Olfactory toxicity in rats following manganese chloride nasal instillation: A pilot study. Neurotoxicology 2017; 64:284-290. [PMID: 28917718 DOI: 10.1016/j.neuro.2017.09.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Revised: 09/08/2017] [Accepted: 09/11/2017] [Indexed: 12/27/2022]
Abstract
Following inhalation, manganese travels along the olfactory nerve from the olfactory epithelium (OE) to the olfactory bulb (OB). Occupational exposure to inhaled manganese is associated with changes in olfactory function. This pilot study evaluated two related hypotheses: (a) intranasal manganese administration increases OE and OB manganese concentrations; and (b) intranasal manganese exposure impairs performance of previously trained rats on a go-no-go olfactory discrimination (OD) task. Male Fischer 344 rats were trained to either lever press ("go") in response to a positive conditioned stimulus (CS+: vanillin) or to do nothing ("no go") when a negative conditioned stimulus (CS-: amyl acetate) was present. Following odor training, rats were randomly assigned to either a manganese (200mM MnCl2) or 0.9% saline treatment group (n=4-5 rats/group). Administration of either saline or manganese was performed on isoflurane-anesthetized rats as 40μL bilateral intranasal instillations. Rats were retested 48h later using the vanillin/amyl acetate OD task, then euthanized, followed by collection of the OE and OB. Manganese concentrations in tissue samples were analyzed by ICP-MS. An additional cohort of rats (n=3-4/group) was instilled similarly with saline or manganese and nasal and OB pathology assessed 48h later. Manganese-exposed rats had increased manganese levels in both the OE and OB and decreased performance in the OD task when compared with control animals. Histopathological evaluation of the caudal nasal cavity showed moderate, acute to subacute suppurative inflammation of the olfactory epithelium and submucosa of the ethmoid turbinates and mild suppurative exudate in the nasal sinuses in animals given manganese. No histologic changes were evident in the OB. The nasal instillation and OD procedures developed in this study are useful methods to assess manganese - induced olfactory deficits.
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Affiliation(s)
- Melanie L Foster
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
| | - Deepa B Rao
- Division of Psychiatry Products, Center for Drug Evaluation and Research, Food and Drug Administration, USA.
| | - Taylor Francher
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
| | - Samantha Traver
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
| | - David C Dorman
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA.
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Smith D, Woodall GM, Jarabek AM, Boyes WK. Manganese testing under a clean air act test rule and the application of resultant data in risk assessments. Neurotoxicology 2017; 64:177-184. [PMID: 28676206 DOI: 10.1016/j.neuro.2017.06.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 06/27/2017] [Indexed: 01/19/2023]
Abstract
In the 1990's, the proposed use of methylcyclopentadienyl manganese tricarbonyl (MMT) as an octane-enhancing gasoline fuel additive led to concerns for potential public health consequences from exposure to manganese (Mn) combustion products in automotive exhaust. After a series of regulatory/legal actions and negotiations, the U.S. Environmental Protection Agency (EPA) issued under Clean Air Act (CAA) section 211(b) an Alternative Tier 2 Test Rule that required development of scientific information intended to help resolve uncertainties in exposure or health risk estimates associated with MMT use. Among the uncertainties identified were: the chemical forms of Mn emitted in automotive exhaust; the relative toxicity of different Mn species; the potential for exposure among sensitive subpopulations including females, the young and elderly; differences in sensitivity between test species and humans; differences between inhalation and oral exposures; and the influence of dose rate and exposure duration on tissue accumulation of Mn. It was anticipated that development of specific sets of pharmacokinetic (PK) information and models regarding Mn could help resolve many of the identified uncertainties and serve as the best foundation for available data integration. The results of the test program included development of several unique Mn datasets, and a series of increasingly sophisticated Mn physiologically-based pharmacokinetic (PBPK) models. These data and models have helped address each of the uncertainties originally identified in the Test Rule. The output from these PBPK models were used by the Agency for Toxic Substances and Disease Registry (ATSDR) in 2012 to inform the selection of uncertainty factors for deriving the manganese Minimum Risk Level (MRL) for chronic exposure durations. The EPA used the MRL in the Agency's 2015 evaluation of potential residual risks of airborne manganese released from ferroalloys production plants. This resultant set of scientific data and models likely would not exist without the CAA section 211(b) test rule regulatory procedure.
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Affiliation(s)
- Darcie Smith
- Office of Air Quality Planning and Standards, Office of Air and Radiation, U.S. Environmental Protection Agency, Research Triangle Park, NC, United States
| | - George M Woodall
- National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, United States
| | - Annie M Jarabek
- National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, United States
| | - William K Boyes
- Toxicity Assessment Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, United States.
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12
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Abstract
Although an essential nutrient, manganese (Mn) can be toxic at high doses. There is, however, uncertainty regarding the effects of chronic low-level Mn-exposure. This review provides an overview of Mn-related brain and functional changes based on studies of a cohort of asymptomatic welders who had lower Mn-exposure than in most previous work. In welders with low-level Mn-exposure, we found: 1) Mn may accumulate in the brain in a non-linear fashion: MRI R1 (1/T1) signals significantly increased only after a critical level of exposure was reached (e.g., ≥300 welding hours in the past 90days prior to MRI). Moreover, R1 may be a more sensitive marker to capture short-term dynamic changes in Mn accumulation than the pallidal index [T1-weighted intensity ratio of the globus pallidus vs. frontal white matter], a traditional marker for Mn accumulation; 2) Chronic Mn-exposure may lead to microstructural changes as indicated by lower diffusion tensor fractional anisotropy values in the basal ganglia (BG), especially when welding years exceeded more than 30 years; 3) Mn-related subtle motor dysfunctions can be captured sensitively by synergy metrics (indices for movement stability), whereas traditional fine motor tasks failed to detect any significant differences; and 4) Iron (Fe) also may play a role in welding-related neurotoxicity, especially at low-level Mn-exposure, evidenced by higher R2* values (an estimate for brain Fe accumulation) in the BG. Moreover, higher R2* values were associated with lower phonemic fluency performance. These findings may guide future studies and the development of occupation- and public health-related polices involving Mn-exposure.
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Gentry PR, Van Landingham C, Fuller WG, Sulsky SI, Greene TB, Clewell HJ, Andersen ME, Roels HA, Taylor MD, Keene AM. A tissue dose-based comparative exposure assessment of manganese using physiologically based pharmacokinetic modeling-The importance of homeostatic control for an essential metal. Toxicol Appl Pharmacol 2017; 322:27-40. [PMID: 28237878 DOI: 10.1016/j.taap.2017.02.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 02/17/2017] [Accepted: 02/20/2017] [Indexed: 01/27/2023]
Abstract
A physiologically-based pharmacokinetic (PBPK) model (Schroeter et al., 2011) was applied to simulate target tissue manganese (Mn) concentrations following occupational and environmental exposures. These estimates of target tissue Mn concentrations were compared to determine margins of safety (MOS) and to evaluate the biological relevance of applying safety factors to derive acceptable Mn air concentrations. Mn blood concentrations measured in occupational studies permitted verification of the human PBPK models, increasing confidence in the resulting estimates. Mn exposure was determined based on measured ambient air Mn concentrations and dietary data in Canada and the United States (US). Incorporating dietary and inhalation exposures into the models indicated that increases in target tissue concentrations above endogenous levels only begin to occur when humans are exposed to levels of Mn in ambient air (i.e. >10μg/m3) that are far higher than those currently measured in Canada or the US. A MOS greater than three orders of magnitude was observed, indicating that current Mn air concentrations are far below concentrations that would be required to produce the target tissue Mn concentrations associated with subclinical neurological effects. This application of PBPK modeling for an essential element clearly demonstrates that the conventional application of default factors to "convert" an occupational exposure to an equivalent continuous environmental exposure, followed by the application of safety factors, is not appropriate in the case of Mn. PBPK modeling demonstrates that the relationship between ambient Mn exposures and dose-to-target tissue is not linear due to normal tissue background levels and homeostatic controls.
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Affiliation(s)
- P Robinan Gentry
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States.
| | | | - William G Fuller
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States
| | | | - Tracy B Greene
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States
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Ramoju SP, Mattison DR, Milton B, McGough D, Shilnikova N, Clewell HJ, Yoon M, Taylor MD, Krewski D, Andersen ME. The application of PBPK models in estimating human brain tissue manganese concentrations. Neurotoxicology 2017; 58:226-237. [PMID: 27989617 DOI: 10.1016/j.neuro.2016.12.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 12/01/2016] [Accepted: 12/01/2016] [Indexed: 01/16/2023]
Affiliation(s)
- Siva P Ramoju
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada.
| | - Donald R Mattison
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Brittany Milton
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada
| | - Doreen McGough
- International Manganese Institute, 17 rue Duphot, 75001 Paris, France
| | - Natalia Shilnikova
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Harvey J Clewell
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
| | - Miyoung Yoon
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
| | - Michael D Taylor
- Nickel Producers Environmental Research Association (NiPERA), 2525 Meridian Parkway, Suite 240, Durham, NC 27713, United States
| | - Daniel Krewski
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Melvin E Andersen
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
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15
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Mercadante CJ, Herrera C, Pettiglio MA, Foster ML, Johnson LC, Dorman DC, Bartnikas TB. The effect of high dose oral manganese exposure on copper, iron and zinc levels in rats. Biometals 2016; 29:417-22. [PMID: 26988220 PMCID: PMC5560020 DOI: 10.1007/s10534-016-9924-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 03/03/2016] [Indexed: 01/08/2023]
Abstract
Manganese is an essential dietary nutrient and trace element with important roles in mammalian development, metabolism, and antioxidant defense. In healthy individuals, gastrointestinal absorption and hepatobiliary excretion are tightly regulated to maintain systemic manganese concentrations at physiologic levels. Interactions of manganese with other essential metals following high dose ingestion are incompletely understood. We previously reported that gavage manganese exposure in rats resulted in higher tissue manganese concentrations when compared with equivalent dietary or drinking water manganese exposures. In this study, we performed follow-up evaluations to determine whether oral manganese exposure perturbs iron, copper, or zinc tissue concentrations. Rats were exposed to a control diet with 10 ppm manganese or dietary, drinking water, or gavage exposure to approximately 11.1 mg manganese/kg body weight/day for 7 or 61 exposure days. While manganese exposure affected levels of all metals, particularly in the frontal cortex and liver, copper levels were most prominently affected. This result suggests an under-appreciated effect of manganese exposure on copper homeostasis which may contribute to our understanding of the pathophysiology of manganese toxicity.
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Affiliation(s)
- Courtney J. Mercadante
- Department of Pathology and Laboratory Medicine, Brown University, Providence, RI 02912, USA
| | - Carolina Herrera
- Department of Pathology and Laboratory Medicine, Brown University, Providence, RI 02912, USA
| | - Michael A. Pettiglio
- Department of Pathology and Laboratory Medicine, Brown University, Providence, RI 02912, USA
| | - Melanie L. Foster
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Laura C. Johnson
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - David C. Dorman
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
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16
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Manganese-Induced Parkinsonism and Parkinson's Disease: Shared and Distinguishable Features. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2015; 12:7519-40. [PMID: 26154659 PMCID: PMC4515672 DOI: 10.3390/ijerph120707519] [Citation(s) in RCA: 216] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 12/12/2014] [Accepted: 01/06/2015] [Indexed: 11/30/2022]
Abstract
Manganese (Mn) is an essential trace element necessary for physiological processes that support development, growth and neuronal function. Secondary to elevated exposure or decreased excretion, Mn accumulates in the basal ganglia region of the brain and may cause a parkinsonian-like syndrome, referred to as manganism. The present review discusses the advances made in understanding the essentiality and neurotoxicity of Mn. We review occupational Mn-induced parkinsonism and the dynamic modes of Mn transport in biological systems, as well as the detection and pharmacokinetic modeling of Mn trafficking. In addition, we review some of the shared similarities, pathologic and clinical distinctions between Mn-induced parkinsonism and Parkinson’s disease. Where possible, we review the influence of Mn toxicity on dopamine, gamma aminobutyric acid (GABA), and glutamate neurotransmitter levels and function. We conclude with a survey of the preventive and treatment strategies for manganism and idiopathic Parkinson’s disease (PD).
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17
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Behera SN, Betha R, Huang X, Balasubramanian R. Characterization and estimation of human airway deposition of size-resolved particulate-bound trace elements during a recent haze episode in Southeast Asia. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2015; 22:4265-4280. [PMID: 25292299 DOI: 10.1007/s11356-014-3645-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Accepted: 09/22/2014] [Indexed: 06/03/2023]
Abstract
Toxic elements present in airborne particulate matter (PM) are associated with human health effects; however, their toxic characteristics depend on the source of their origins and their concentrations in ambient air. Twenty four elements (Al, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Na, Ni, Pb, Se, Sr, Te, Tl, and Zn) in 12 different size fractions of PM ranging from 10 nm to 10 μm were characterized in Singapore during two different atmospheric conditions (smoke haze and non-haze periods) in 2012 for the first time. In addition, their possible sources were identified based on backward air trajectory analysis and principal component analysis (PCA). The health implications of inhalable particles were assessed using a human airway deposition model, the Multiple-Path Particle Dosimetry model (MPPD). The results concerning particle-bound trace elements are interpreted in terms of coarse (PM2.5-10), fine (PM2.5), ultrafine (PM0.01-0.1, 0.01 μm < Dp < 0.10 μm), and nano (PM0.01-0.056, 0.01 μm < Dp < 0.056 μm) particles. The ratios of elemental concentrations measured between the smoke haze episode and the non-haze period in coarse, fine, ultrafine, and nano particles varied from 1.2 (Bi) to 6.6 (Co). Both the PCA and backward trajectory analysis revealed that trans-boundary biomass-burning emissions from Indonesia were primarily responsible for enhanced concentrations of particulate-bound elements during the smoke haze episode. The particle depositions in the respiratory system were higher during the smoke haze episode compared to the non-haze period. The study finds that ultrafine and nano particles present in the atmosphere have higher tendencies to be deposited into the deeper parts of the respiratory system, compared to coarse and fine particles.
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Affiliation(s)
- Sailesh N Behera
- Department of Civil and Environmental Engineering, National University of Singapore, Singapore, 117576, Republic of Singapore
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18
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Hoet P, Roels HA. Significance and Usefulness of Biomarkers of Exposure to Manganese. MANGANESE IN HEALTH AND DISEASE 2014. [DOI: 10.1039/9781782622383-00355] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Manganese (Mn) accomplishes functions essential to maintaining human health, but at the same time this trace element can be toxic at low levels of exposure and accurate estimation of internal exposure is needed. A biomarker of exposure to Mn is meaningful only if there is sufficient knowledge of the toxicokinetics determining its presence in a biological medium (e.g. whole blood, plasma, urine, hair, nail). Moreover, biological monitoring of exposure to Mn is useful only when the biomarker is sufficiently specific and sensitive to distinguish exposed from non-exposed subjects, when it is dose-related to the external exposure (current, recent, or time-integrated), and when it displays reasonable dose–effect/response relationships with the occurrence of adverse effects on the central nervous system, the critical target for Mn exposure. Human investigations in which biomarkers of Mn exposure meet all these criteria are hard to locate. Overall, the available studies report poor or no associations on an individual basis between external (Mn in air or drinking water) and internal (Mn in blood, urine, hair, or nail) Mn exposure indices. This may be to some extent explained by features inherent of the Mn metabolism (homeostatic control), the Mn biomarker's half-life with respect to the exposure window, and the variable nature of external exposure scenarios. Studies particularly dealing with Mn inhalation exposure, different or poorly described methodological approaches, or air sampling strategies may render direct comparison and interpretation of results a tedious task. Nevertheless, several studies report significant dose–effect associations between biomarkers of Mn exposure and subclinical deficits of psychomotor or neuropsychological test performances. Because directly associated with the site of toxic action and providing the magnetic resonance imaging is done no later than three months after Mn exposure ceased, the Mn T1 relaxation time is potentially the better biomarker of Mn exposure in a clinical context (e.g. after long-term parenteral nutrition, chronic liver failure, methcathinone drug abuse). Magnetic resonance imaging is, however, unpractical as a tool for biological monitoring of exposure to Mn in the occupational setting (inhalation) and in the general population (air, drinking water). In conclusion, it would be inappropriate to recommend, on the basis of the currently available evidence, a reliable well-validated biomarker of exposure to Mn, or to establish a health-based threshold value for subclinical neurotoxic effects.
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Affiliation(s)
- Perrine Hoet
- Université catholique de Louvain (UCL), Institut de Recherche Expérimentale et Clinique (IREC), Louvain Centre for Toxicology and Applied Pharmacology (LTAP) Bruxelles Belgium
| | - Harry A. Roels
- Université catholique de Louvain (UCL), Institut de Recherche Expérimentale et Clinique (IREC), Louvain Centre for Toxicology and Applied Pharmacology (LTAP) Bruxelles Belgium
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19
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Grünecker B, Kaltwasser SF, Zappe AC, Bedenk BT, Bicker Y, Spoormaker VI, Wotjak CT, Czisch M. Regional specificity of manganese accumulation and clearance in the mouse brain: implications for manganese-enhanced MRI. NMR IN BIOMEDICINE 2013; 26:542-556. [PMID: 23168745 DOI: 10.1002/nbm.2891] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 10/17/2012] [Accepted: 10/21/2012] [Indexed: 06/01/2023]
Abstract
Manganese-enhanced MRI has recently become a valuable tool for the assessment of in vivo functional cerebral activity in animal models. As a result of the toxicity of manganese at higher dosages, fractionated application schemes have been proposed to reduce the toxic side effects by using lower concentrations per injection. Here, we present data on regional-specific manganese accumulation during a fractionated application scheme over 8 days of 30 mg/kg MnCl2 , as well as on the clearance of manganese chloride over the course of several weeks after the termination of the whole application protocol supplying an accumulative dose of 240 mg/kg MnCl2 . Our data show most rapid accumulation in the superior and inferior colliculi, amygdala, bed nucleus of the stria terminalis, cornu ammonis of the hippocampus and globus pallidus. The data suggest that no ceiling effects occur in any region using the proposed application protocol. Therefore, a comparison of basal neuronal activity differences in different animal groups based on locally specific manganese accumulation is possible using fractionated application. Half-life times of manganese clearance varied between 5 and 7 days, and were longest in the periaqueductal gray, amygdala and entorhinal cortex. As the hippocampal formation shows one of the highest T1 -weighted signal intensities after manganese application, and manganese-induced memory impairment has been suggested, we assessed hippocampus-dependent learning as well as possible manganese-induced atrophy of the hippocampal volume. No interference of manganese application on learning was detected after 4 days of Mn(2+) application or 2 weeks after the application protocol. In addition, no volumetric changes induced by manganese application were found for the hippocampus at any of the measured time points. For longitudinal measurements (i.e. repeated manganese applications), a minimum of at least 8 weeks should be considered using the proposed protocol to allow for sufficient clearance of the paramagnetic ion from cerebral tissue.
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Affiliation(s)
- B Grünecker
- Max Planck Institute of Psychiatry, Munich, Germany
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20
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Schroeter JD, Dorman DC, Yoon M, Nong A, Taylor MD, Andersen ME, Clewell HJ. Application of a Multi-Route Physiologically Based Pharmacokinetic Model for Manganese to Evaluate Dose-Dependent Neurological Effects in Monkeys. Toxicol Sci 2012; 129:432-46. [DOI: 10.1093/toxsci/kfs212] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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21
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Wanger T, Scheich H, Ohl FW, Goldschmidt J. The use of thallium diethyldithiocarbamate for mapping CNS potassium metabolism and neuronal activity: Tl+-redistribution, Tl+-kinetics and Tl+-equilibrium distribution. J Neurochem 2012; 122:106-14. [DOI: 10.1111/j.1471-4159.2012.07757.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Taylor MD, Clewell HJ, Andersen ME, Schroeter JD, Yoon M, Keene AM, Dorman DC. Update on a Pharmacokinetic-Centric Alternative Tier II Program for MMT-Part II: Physiologically Based Pharmacokinetic Modeling and Manganese Risk Assessment. J Toxicol 2012; 2012:791431. [PMID: 22645610 PMCID: PMC3356703 DOI: 10.1155/2012/791431] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2011] [Accepted: 01/25/2012] [Indexed: 01/24/2023] Open
Abstract
Recently, a variety of physiologically based pharmacokinetic (PBPK) models have been developed for the essential element manganese. This paper reviews the development of PBPK models (e.g., adult, pregnant, lactating, and neonatal rats, nonhuman primates, and adult, pregnant, lactating, and neonatal humans) and relevant risk assessment applications. Each PBPK model incorporates critical features including dose-dependent saturable tissue capacities and asymmetrical diffusional flux of manganese into brain and other tissues. Varied influx and efflux diffusion rate and binding constants for different brain regions account for the differential increases in regional brain manganese concentrations observed experimentally. We also present novel PBPK simulations to predict manganese tissue concentrations in fetal, neonatal, pregnant, or aged individuals, as well as individuals with liver disease or chronic manganese inhalation. The results of these simulations could help guide risk assessors in the application of uncertainty factors as they establish exposure guidelines for the general public or workers.
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Affiliation(s)
- Michael D. Taylor
- Health, Safety, Environment, and Security, Afton Chemical Corp., Richmond, VA 23219, USA
| | - Harvey J. Clewell
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
| | - Melvin E. Andersen
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
| | - Jeffry D. Schroeter
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
| | - Miyoung Yoon
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA
| | - Athena M. Keene
- Health, Safety, Environment, and Security, Afton Chemical Corp., Richmond, VA 23219, USA
| | - David C. Dorman
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA
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23
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Yoon M, Schroeter JD, Nong A, Taylor MD, Dorman DC, Andersen ME, Clewell HJ. Physiologically based pharmacokinetic modeling of fetal and neonatal manganese exposure in humans: describing manganese homeostasis during development. Toxicol Sci 2011; 122:297-316. [PMID: 21622944 DOI: 10.1093/toxsci/kfr141] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Concerns for potential vulnerability to manganese (Mn) neurotoxicity during fetal and neonatal development have been raised due to increased needs for Mn for normal growth, different sources of exposure to Mn, and pharmacokinetic differences between the young and adults. A physiologically based pharmacokinetic (PBPK) model for Mn during human gestation and lactation was developed to predict Mn in fetal and neonatal brain using a parallelogram approach based upon extrapolation across life stages in rats and cross-species extrapolation to humans. Based on the rodent modeling, key physiological processes controlling Mn kinetics during gestation and lactation were incorporated, including alterations in Mn uptake, excretion, tissue-specific distributions, and placental and lactational transfer of Mn. Parameters for Mn kinetics were estimated based on human Mn data for milk, placenta, and fetal/neonatal tissues, along with allometric scaling from the human adult model. The model was evaluated by comparison with published Mn levels in cord blood, milk, and infant blood. Maternal Mn homeostasis during pregnancy and lactation, placenta and milk Mn, and fetal/neonatal tissue Mn were simulated for normal dietary intake and with inhalation exposure to environmental Mn. Model predictions indicate similar or lower internal exposures to Mn in the brains of fetus/neonate compared with the adult at or above typical environmental air Mn concentrations. This PBPK approach can assess expected Mn tissue concentration during early life and compares contributions of different Mn sources, such as breast or cow milk, formula, food, drinking water, and inhalation, with tissue concentration.
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Affiliation(s)
- Miyoung Yoon
- Center for Human Health Assessment, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709, USA.
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24
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Schroeter JD, Nong A, Yoon M, Taylor MD, Dorman DC, Andersen ME, Clewell HJ. Analysis of manganese tracer kinetics and target tissue dosimetry in monkeys and humans with multi-route physiologically based pharmacokinetic models. Toxicol Sci 2010; 120:481-98. [PMID: 21205636 DOI: 10.1093/toxsci/kfq389] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Manganese (Mn) is an essential nutrient with the capacity for toxicity from excessive exposure. Accumulation of Mn in the striatum, globus pallidus, and other midbrain regions is associated with neurotoxicity following high-dose Mn inhalation. Physiologically based pharmacokinetic (PBPK) models for ingested and inhaled Mn in rats and nonhuman primates were previously developed. The models contained saturable Mn tissue-binding capacities, preferential fluxes of Mn in specific tissues, and homeostatic control processes such as inducible biliary excretion of Mn. In this study, a nonhuman primate model was scaled to humans and was further extended to include iv, ip, and sc exposure routes so that past studies regarding radiolabeled carrier-free (54)MnCl(2) tracer kinetics could be evaluated. Simulation results accurately recapitulated the biphasic elimination behavior for all exposure routes. The PBPK models also provided consistent cross-species descriptions of Mn tracer kinetics across multiple exposure routes. These results indicate that PBPK models can accurately simulate the overall kinetic behavior of Mn and predict conditions where exposures will increase free Mn in various tissues throughout the body. Simulations with the human model indicate that globus pallidus Mn concentrations are unaffected by air concentrations < 10 μg/m(3) Mn. The use of this human Mn PBPK model can become a key component of future human health risk assessment of Mn, allowing the consideration of various exposure routes, natural tissue background levels, and homeostatic controls to explore exposure conditions that lead to increased target tissue levels resulting from Mn overexposure.
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Affiliation(s)
- Jeffry D Schroeter
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709-2137, USA.
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25
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Sasso AF, Isukapalli SS, Georgopoulos PG. A generalized physiologically-based toxicokinetic modeling system for chemical mixtures containing metals. Theor Biol Med Model 2010; 7:17. [PMID: 20525215 PMCID: PMC2903511 DOI: 10.1186/1742-4682-7-17] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Accepted: 06/02/2010] [Indexed: 12/30/2022] Open
Abstract
Background Humans are routinely and concurrently exposed to multiple toxic chemicals, including various metals and organics, often at levels that can cause adverse and potentially synergistic effects. However, toxicokinetic modeling studies of exposures to these chemicals are typically performed on a single chemical basis. Furthermore, the attributes of available models for individual chemicals are commonly estimated specifically for the compound studied. As a result, the available models usually have parameters and even structures that are not consistent or compatible across the range of chemicals of concern. This fact precludes the systematic consideration of synergistic effects, and may also lead to inconsistencies in calculations of co-occurring exposures and corresponding risks. There is a need, therefore, for a consistent modeling framework that would allow the systematic study of cumulative risks from complex mixtures of contaminants. Methods A Generalized Toxicokinetic Modeling system for Mixtures (GTMM) was developed and evaluated with case studies. The GTMM is physiologically-based and uses a consistent, chemical-independent physiological description for integrating widely varying toxicokinetic models. It is modular and can be directly "mapped" to individual toxicokinetic models, while maintaining physiological consistency across different chemicals. Interaction effects of complex mixtures can be directly incorporated into the GTMM. Conclusions The application of GTMM to different individual metals and metal compounds showed that it explains available observational data as well as replicates the results from models that have been optimized for individual chemicals. The GTMM also made it feasible to model toxicokinetics of complex, interacting mixtures of multiple metals and nonmetals in humans, based on available literature information. The GTMM provides a central component in the development of a "source-to-dose-to-effect" framework for modeling population health risks from environmental contaminants. As new data become available on interactions of multiple chemicals, the GTMM can be iteratively parameterized to improve mechanistic understanding of human health risks from exposures to complex mixtures of chemicals.
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Affiliation(s)
- Alan F Sasso
- Environmental and Occupational Health Sciences Institute, A joint institute of UMDNJ-Robert Wood Johnson Medical School and Rutgers University, Piscataway, New Jersey, USA
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26
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Yoon M, Nong A, Clewell HJ, Taylor MD, Dorman DC, Andersen ME. Lactational Transfer of Manganese in Rats: Predicting Manganese Tissue Concentration in the Dam and Pups from Inhalation Exposure with a Pharmacokinetic Model. Toxicol Sci 2009; 112:23-43. [DOI: 10.1093/toxsci/kfp197] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Yoon M, Nong A, Clewell HJ, Taylor MD, Dorman DC, Andersen ME. Evaluating placental transfer and tissue concentrations of manganese in the pregnant rat and fetuses after inhalation exposures with a PBPK model. Toxicol Sci 2009; 112:44-58. [PMID: 19726578 DOI: 10.1093/toxsci/kfp198] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A Physiologically Based Pharmaco Kinetic (PBPK) model, based on a published description of manganese (Mn) kinetics in adult rats, has been developed to describe Mn uptake and tissue distribution in the pregnant dam and fetus during dietary and inhalation exposures. This extension incorporated key physiological processes controlling Mn pharmacokinetics during pregnancy and fetal development. After calibration against tissue Mn concentrations observed during late gestation, the model accurately simulated Mn tissue distribution in the dam and fetus following both diet and inhalation exposures to the pregnant rat. Maternal to fetal transfer of Mn through placenta was described using two pathways: a saturable active transport with high affinity and a simple diffusion. The active transport dominates at basal and lower Mn exposure, whereas at higher Mn exposure, the relative contribution of the diffusion pathway increases. To simulate fetal tissue Mn, tissue-binding parameters and preferential influx/efflux rates in fetal brain were adjusted from the adult model based on differential developmental processes and varying tissue demands for Mn in early life. Model simulations were consistent with observed tissue Mn concentrations in fetal tissues, including brain for diet alone and for combined diet and inhalation. Simulations of Mn in placenta and other maternal tissues in late gestation correlated well with measured tissue concentrations. This model, together with our published models for Mn kinetics during lactation and postnatal development, will help to address concerns about Mn neurotoxicity in potentially sensitive human subpopulation, such as infants and children by providing an estimate of Mn exposure in the population of interest.
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Affiliation(s)
- Miyoung Yoon
- The Hamner Institutes for Health Sciences, 6 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
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28
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Proposal for a revised Reference Concentration (RfC) for manganese based on recent epidemiological studies. Regul Toxicol Pharmacol 2009; 55:330-9. [PMID: 19686793 DOI: 10.1016/j.yrtph.2009.08.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 08/11/2009] [Accepted: 08/11/2009] [Indexed: 11/21/2022]
Abstract
In 1993, based on observations of subclinical neurological effects in workers, the United States Environmental Protection Agency (US EPA) published a Reference Concentration (RfC) of 0.05 microg/m(3) for manganese (Mn). The geometric mean exposure concentration, 150 microg/m(3) respirable Mn, was considered the lowest observable adverse effect level (LOAEL), and uncertainty factors (UFs) were applied to account for sensitive populations, database limitations, a LOAEL, subchronic exposure, and potential differences in toxicity of different forms of Mn. Based on a review of more recent literature, we propose two alternate Mn RfCs. Of 12 more recent occupational studies of eight cohorts with chronic exposure durations, examining subclinical neurobehavioral effects, predominantly on the motor system, three were considered appropriate for development of an RfC. All three studies yielded no observable adverse effect levels (NOAELs) of approximately 60 microg/m(3) respirable Mn. Converting the occupational NOAEL to a human equivalent concentration (HEC) of 21microg/m(3) (for continuous exposure) and applying a UF of 10 to account for intraspecies variability yielded an RfC of 2microg/m(3). We also derived a similar RfC (7 microg/m(3)) using an Mn benchmark dose (BMD) as the point of departure. Overall confidence in both RfCs is medium.
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