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Gonzalez-Cuyar LF, Nelson G, Nielsen SS, Dlamini WW, Keyser-Gibson A, Keene CD, Paulsen M, Criswell SR, Senini N, Sheppard L, Samy S, Simpson CD, Baker MG, Racette BA. Olfactory tract/bulb metal concentration in Manganese-exposed mineworkers. Neurotoxicology 2024; 102:96-105. [PMID: 38582332 DOI: 10.1016/j.neuro.2024.04.001] [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: 09/09/2023] [Revised: 03/06/2024] [Accepted: 04/03/2024] [Indexed: 04/08/2024]
Abstract
BACKGROUND Manganese (Mn) is an essential micronutrient as well as a well-established neurotoxicant. Occupational and environmental exposures may bypass homeostatic regulation and lead to increased systemic Mn levels. Translocation of ultrafine ambient airborne particles via nasal neuronal pathway to olfactory bulb and tract may be an important pathway by which Mn enters the central nervous system. OBJECTIVE To measure olfactory tract/bulb tissue metal concentrations in Mn-exposed and non-exposed mineworkers. METHODS Using inductively coupled plasma-mass spectrometry (ICP-MS), we measured and compared tissue metal concentrations in unilateral olfactory tracts/bulbs of 24 Mn-exposed and 17 non-exposed South African mineworkers. We used linear regression to investigate the association between cumulative Mn exposures and olfactory tract/bulb Mn concentration. RESULTS The difference in mean olfactory tract/bulb Mn concentrations between Mn-exposed and non-Mn exposed mineworkers was 0.16 µg/g (95% CI -0.11, 0.42); but decreased to 0.09 µg/g (95% CI 0.004, 0.18) after exclusion of one influential observation. Olfactory tract/bulb metal concentration and cumulative Mn exposure suggested there may be a positive association; for each mg Mn/m3-year there was a 0.05 µg/g (95% CI 0.01, 0.08) greater olfactory tract/bulb Mn concentration overall, but -0.003 (95% CI -0.02, 0.02) when excluding the three influential observations. Recency of Mn exposure was not associated with olfactory tract/bulb Mn concentration. CONCLUSIONS Our findings suggest that Mn-exposed mineworkers might have higher olfactory tract/bulb tissue Mn concentrations than non-Mn exposed mineworkers, and that concentrations might depend more on cumulative dose than recency of exposure.
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Affiliation(s)
- Luis F Gonzalez-Cuyar
- University of Washington, School of Medicine and Department of Laboratory Medicine and Pathology, Division of Neuropathology, 325 9th Ave, Seattle, WA 98104, USA.
| | - Gill Nelson
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, 27 St Andrews Rd, Parktown 2193, South Africa; Department of Neurology, Barrow Neurological Institute, 240 W Thomas Rd, Phoenix, AZ 85013, USA
| | - Susan Searles Nielsen
- Department of Neurology, Washington University School of Medicine, 660 S Euclid Ave, St. Louis, MO 63110, USA
| | - Wendy W Dlamini
- Department of Neurology, Washington University School of Medicine, 660 S Euclid Ave, St. Louis, MO 63110, USA; Department of Epidemiology, School of Public Health, University of Washington, 3980 15th Ave NE, Seattle, WA 98195, USA
| | - Amelia Keyser-Gibson
- University of Washington, School of Medicine and Department of Laboratory Medicine and Pathology, Division of Neuropathology, 325 9th Ave, Seattle, WA 98104, USA
| | - C Dirk Keene
- University of Washington, School of Medicine and Department of Laboratory Medicine and Pathology, Division of Neuropathology, 325 9th Ave, Seattle, WA 98104, USA
| | - Michael Paulsen
- Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Susan R Criswell
- Department of Neurology, Barrow Neurological Institute, 240 W Thomas Rd, Phoenix, AZ 85013, USA; Department of Neurology, Washington University School of Medicine, 660 S Euclid Ave, St. Louis, MO 63110, USA
| | - Natalie Senini
- Department of Neurology, Barrow Neurological Institute, 240 W Thomas Rd, Phoenix, AZ 85013, USA
| | - Lianne Sheppard
- Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA; Department of Biostatistics, School of Public Health, University of Washington, 3980 15th Ave NE, Seattle, WA 98195, USA
| | - Shar Samy
- Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Christopher D Simpson
- Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Marissa G Baker
- Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Brad A Racette
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, 27 St Andrews Rd, Parktown 2193, South Africa; Department of Neurology, Barrow Neurological Institute, 240 W Thomas Rd, Phoenix, AZ 85013, USA; Department of Neurology, Washington University School of Medicine, 660 S Euclid Ave, St. Louis, MO 63110, USA
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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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3
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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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4
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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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5
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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 2018; 64:177-184. [PMID: 28676206 PMCID: PMC6664450 DOI: 10.1016/j.neuro.2017.06.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [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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6
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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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7
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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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8
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Gow AG, Frowde PE, Elwood CM, Burton CA, Powell RM, Tappin SW, Foale RD, Duncan A, Mellanby RJ. Surgical attenuation of spontaneous congenital portosystemic shunts in dogs resolves hepatic encephalopathy but not hypermanganesemia. Metab Brain Dis 2015; 30:1285-9. [PMID: 25936718 DOI: 10.1007/s11011-015-9676-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 04/23/2015] [Indexed: 12/26/2022]
Abstract
Hypermanganesemia is commonly recognized in human patients with hepatic insufficiency and portosystemic shunting. Since manganese is neurotoxic, increases in brain manganese concentrations have been implicated in the development of hepatic encephalopathy although a direct causative role has yet to be demonstrated. Evaluate manganese concentrations in dogs with a naturally occurring congenital shunt before and after attenuation as well as longitudinally following the changes in hepatic encephalopathy grade. Our study demonstrated that attenuation of the shunt resolved encephalopathy, significantly reduced postprandial bile acids, yet a hypermanganasemic state persisted. This study demonstrates that resolution of hepatic encephalopathy can occur without the correction of hypermanganesemia, indicating that increased manganese concentrations alone do not play a causative role in encephalopathy. Our study further demonstrates the value of the canine congenital portosystemic shunt as a naturally occurring spontaneous model of human hepatic encephalopathy.
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Affiliation(s)
- Adam G Gow
- Division of Veterinary Clinical Studies, Easter Bush Veterinary Centre, Royal (Dick) School of Veterinary Studies, The Roslin Institute, The University of Edinburgh, Hospital for Small Animals, Roslin, Midlothian, EH25 9RG, UK,
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9
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Respiratory manganese particle size, time-course and neurobehavioral outcomes in workers at a manganese alloy production plant. Neurotoxicology 2014; 45:276-84. [PMID: 24721790 DOI: 10.1016/j.neuro.2014.03.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Revised: 02/24/2014] [Accepted: 03/06/2014] [Indexed: 11/21/2022]
Abstract
The progression of manganism with chronic exposure to airborne manganese (Mn) is not well understood. Here, we further investigate the findings on exposure and neurobehavioral outcomes of workers from a silico- and ferromanganese production plant and non-exposed workers from the same community in 1990 and 2004, using a variety of exposure metrics that distinguish particle size and origin within the range of respirable airborne exposures. Mn exposure matrices for large respirable particulate (Mn-LRP, dust) and small respirable particulate (Mn-SRP, fume), based on process origins, were used together with detailed work histories since 1973 (plant opening), to construct exposure metrics including burdens and cumulative burdens with various clearance half-lives. For three out of eight 1990 neurobehavioral tests analyzed with linear regression models, duration of Mn exposure was the best predictor: Luria-Nebraska Neuropsychological Battery - Motor Scale, Trail-Making B and Finger Tapping. The Luria-Nebraska Motor Scale had the strongest association (t ∼ 5.0, p < 10(-6)). For outcomes on three other tests, the duration and Mn-SRP metrics were comparable: Trail Making Test A, Cancellation H and Stroop Color-Word Test (color/word subtest). Delayed Word Recall was best predicted by Mn-SRP (based on square root or truncated air-concentrations). The Word score on the Stroop Color-Word Test was the only outcome for which Mn-LRP was the leading predictor (t = -2.92, p = 0.003), while performance on the WAIS-R Digit Span Test was not significantly predicted by any metric. For outcomes evaluated in both 1990 and 2004, a mixed-effect linear regression model was used to examine estimates of within-individual trends. Duration and Mn-SRP were associated with performance on the Luria-Nebraska Motor Scale, as well as with other outcomes that appeared to have both reversible and progressive features, including Trail Making A and B, Cancellation H and Delayed Word Recall. With the mixed-effect model, Digit Span exhibited a significant irreversible association with exposure duration (t = -2.34, p = 0.021) and Mn-SRP (square root; t = -2.38, p = 0.019) metrics. The strong prediction using duration of exposure is consistent with effective homeostatic regulation of tissue-level Mn in the observed exposure range of respirable Mn (< 0.2mg/m(3)).
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Gonzalez-Cuyar LF, Nelson G, Criswell SR, Ho P, Lonzanida JA, Checkoway H, Seixas N, Gelman BB, Evanoff BA, Murray J, Zhang J, Racette BA. Quantitative neuropathology associated with chronic manganese exposure in South African mine workers. Neurotoxicology 2013; 45:260-6. [PMID: 24374477 DOI: 10.1016/j.neuro.2013.12.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Revised: 12/06/2013] [Accepted: 12/19/2013] [Indexed: 11/29/2022]
Abstract
Manganese (Mn) is a common neurotoxicant associated with a clinical syndrome that includes signs and symptoms referable to the basal ganglia. Despite many advances in understanding the pathophysiology of Mn neurotoxicity in humans, with molecular and structural imaging techniques, only a few case reports describe the associated pathological findings, and all are in symptomatic subjects exposed to relatively high-level Mn. We performed an exploratory, neurohistopathological study to investigate the changes in the corpus striatum (caudate nucleus, putamen, and globus pallidus) associated with chronic low-level Mn exposure in South African Mn mine workers. Immunohistochemical techniques were used to quantify cell density of neuronal and glial components of the corpus striatum in eight South African Mn mine workers without clinical evidence of a movement disorder and eight age-race-gender matched, non-Mn mine workers. There was higher mean microglia density in Mn mine workers than non-Mn mine workers in the globus pallidus external and internal segments [GPe: 1.33 and 0.87 cells per HPF, respectively (p=0.064); GPi: 1.37 and 0.99 cells per HPF, respectively (p=0.250)]. The number of years worked in the Mn mines was significantly correlated with microglial density in the GPi (Spearman's rho 0.886; p=0.019). The ratio of astrocytes to microglia in each brain region was lower in the Mn mine workers than the non-Mn mine workers in the caudate (7.80 and 14.68; p=0.025), putamen (7.35 and 11.11; p=0.117), GPe (10.60 and 16.10; p=0.091) and GPi (9.56 and 12.42; p=0.376). Future studies incorporating more detailed occupational exposures in a larger sample of Mn mine workers will be needed to demonstrate an etiologic relationship between Mn exposure and these pathological findings.
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Affiliation(s)
- Luis F Gonzalez-Cuyar
- Department of Pathology, Division of Neuropathology, University of Washington, School of Medicine, Seattle, WA, USA
| | - Gill Nelson
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Parktown, South Africa
| | - Susan R Criswell
- Department of Neurology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Pokuan Ho
- Department of Biology, University of Washington, Seattle, WA, USA
| | | | - Harvey Checkoway
- Department of Environmental and Occupational Health, University of Washington, Seattle, WA, USA; Department of Family Medicine and Preventive Medicine, University of California, San Diego, La Jolla, CA, USA
| | - Noah Seixas
- Department of Environmental and Occupational Health, University of Washington, Seattle, WA, USA
| | - Benjamin B Gelman
- Department of Pathology, University of Texas Medical Branch, Galveston, TX, USA; Department of Neuroscience, University of Texas Medical Branch, Galveston, TX, USA; Department of Cell Biology, University of Texas Medical Branch, Galveston, TX, USA
| | - Bradley A Evanoff
- Department of Medicine, Washington University School of Medicine, Saint Louis, MO, USA
| | - Jill Murray
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Parktown, South Africa; National Institute for Occupational Health, National Health Laboratory Service, Johannesburg, South Africa
| | - Jing Zhang
- Department of Pathology, Division of Neuropathology, University of Washington, School of Medicine, Seattle, WA, USA
| | - Brad A Racette
- School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Parktown, South Africa; Department of Neurology, Washington University School of Medicine, Saint Louis, MO, USA.
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11
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Willhite CC, Bhat VS, Ball GL, McLellan CJ. Emergency Do Not Consume/Do Not Use concentrations for potassium permanganate in drinking water. Hum Exp Toxicol 2012; 32:275-98. [DOI: 10.1177/0960327112456316] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Over the past decade, regulatory authorities and water purveyors have become increasingly concerned with accidental or intentional adulteration of municipal drinking water. Emergency response guidelines, such as the ‘Do Not Consume’ or use concentration limits derived herein, can be used to notify the public in such cases. Potassium permanganate (KMnO4) is used to control iron concentrations and to reduce the levels of nuisance materials that affect odor or taste of finished drinking water. Manganese (Mn) is recognized an essential nutrient, permanganate (MnO4−) and manganous (Mn+2) ions are caustic, and the acute toxicity of KMnO4 is defined by its oxidant/irritant properties and by the toxicity of Mn. Ingestion of small amounts (4–20 mg/kg) of aqueous KMnO4 solutions that are above 200 mg/L causes gastrointestinal distress, while bolus ingestion has caused respiratory arrest following coagulative necrosis and hemorrhage in the esophagus, stomach, or liver. Dilute KMnO4 solutions (1–100 mg/L) are used as a topical antiseptics and astringents, but >1:5000 (200 mg/L) dilutions can irritate or discolor sensitive mucous membranes and direct skin or ocular contact with concentrated KMnO4 can perforate tissues. Based on clinical experience with 200 mg/L KMnO4, a Do Not Consume concentration of 7 mg/L KMnO4 (equivalent to 2 mg Mn/L) is recommended. Recognizing limited empirical data from which to calculate an ocular reference value, a skin contact ‘Do Not Use’ concentration of 30 mg Mn/L is recommended based on the skin irritation in some patients after a 10-min contact with 100 mg KMnO4/L.
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Affiliation(s)
| | | | | | - CJ McLellan
- NSF International, Dixboro Road, Ann Arbor, Michigan, USA
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12
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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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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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14
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Boyes WK. Essentiality, toxicity, and uncertainty in the risk assessment of manganese. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2010; 73:159-65. [PMID: 20077286 DOI: 10.1080/15287390903340419] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Risk assessments of manganese by inhalation or oral routes of exposure typically acknowledge the duality of manganese as an essential element at low doses and a toxic metal at high doses. Previously, however, risk assessors were unable to describe manganese pharmacokinetics quantitatively across dose levels and routes of exposure, to account for mass balance, and to incorporate this information into a quantitative risk assessment. In addition, the prior risk assessment of inhaled manganese conducted by the U.S. Environmental Protection Agency (EPA) identified a number of specific factors that contributed to uncertainty in the risk assessment. In response to a petition regarding the use of a fuel additive containing manganese, methylcyclopentadienyl manganese tricarbonyl (MMT), the U.S. EPA developed a test rule under the U.S. Clean Air Act that required, among other things, the generation of pharmacokinetic information. This information was intended not only to aid in the design of health outcome studies, but also to help address uncertainties in the risk assessment of manganese. To date, the work conducted in response to the test rule has yielded substantial pharmacokinetic data. This information will enable the generation of physiologically based pharmacokinetic (PBPK) models capable of making quantitative predictions of tissue manganese concentrations following inhalation and oral exposure, across dose levels, and accounting for factors such as duration of exposure, different species of manganese, and changes of age, gender, and reproductive status. The work accomplished in response to the test rule, in combination with other scientific evidence, will enable future manganese risk assessments to consider tissue dosimetry more comprehensively than was previously possible.
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Affiliation(s)
- 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, North Carolina 27711, USA.
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Andersen ME, Dorman DC, Clewell HJ, Taylor MD, Nong A. Multi-dose-route, multi-species pharmacokinetic models for manganese and their use in risk assessment. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2010; 73:217-234. [PMID: 20077292 DOI: 10.1080/15287390903340849] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Manganese (Mn) is an essential element that may be toxic in conditions of overexposure. Nearly 10 years ago, some of the authors of this article published a proposed methodology to perform a tissue-dose-based risk assessment and a detailed list of data needs necessary to perform the assessment. Since that time, a substantial body of Mn pharmacokinetic (PK) data has been generated in rats and nonhuman primates, allowing for the construction of physiologically based pharmacokinetic (PBPK) models for Mn. This study reviews the development of the Mn PBPK models, reassesses the previously identified data needs, and details potential uses of these models in risk assessment of Mn. Based upon numerous animal experiments, pharmacokinetic (PK) models have effectively simulated tissue kinetics of Mn from both inhaled and oral Mn intake. PK models achieve this by incorporating homeostatic control processes, saturable tissue binding capacities, and preferential fluxes in various tissue regions. While minor data gaps still exist, the models captured the main dose-dependent characteristics of Mn disposition in rodents and monkeys and provide a structure to parameterize an equivalent PK description in humans. These models are organized to contribute to a tissue-dose based risk assessment of Mn that simultaneously considers ingestion and inhalation kinetics of Mn along with homeostatic control of Mn.
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Affiliation(s)
- Melvin E Andersen
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709-2137, USA
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16
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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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Nong A, Taylor MD, Clewell HJ, Dorman DC, Andersen ME. Manganese Tissue Dosimetry in Rats and Monkeys: Accounting for Dietary and Inhaled Mn with Physiologically based Pharmacokinetic Modeling. Toxicol Sci 2008; 108:22-34. [DOI: 10.1093/toxsci/kfn264] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Nong A, Teeguarden JG, Clewell HJ, Dorman DC, Andersen ME. Pharmacokinetic modeling of manganese in the rat IV: Assessing factors that contribute to brain accumulation during inhalation exposure. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2008; 71:413-426. [PMID: 18306088 DOI: 10.1080/15287390701838697] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A recently published physiologically based pharmacokinetic (PBPK) model successfully accounted for steady-state tissue manganese (Mn) concentration seen with normal dietary intakes and for biphasic, whole-body time-course profiles observed with tracer (54Mn) dosing. In this present study, PBPK modeling was used to evaluate Mn kinetics and brain concentrations in rats exposed to Mn both in their diet and by inhalation. Three published studies were used: (1) rats fed on diets ranging from 2 to 100 ppm, (2) rats on 125 ppm in diet and exposed via inhalation at 0.0 to 3.00 mg Mn/m3 each day for 14 d, and (3) rats to 0.1 or 0.5 mg Mn/m3 for 6 h/d, 5 d/wk over a 90-d period. The original model structure with well-mixed and "deep" compartments for each tissue could not describe rapid increases in tissue concentrations and rapid declines seen in high concentration inhalation studies. A second structure was developed that included (1) saturable, high-affinity binding of Mn in all tissues and (2) asymmetric diffusion from blood into brain (i.e., transport into and out of specific brain regions such as the striatum was described with different diffusion constants). This second model was consistent with liver and striatum experimental data. Preferential increases in some brain regions were predicted for exposures above 0.2 mg/m3 and had a rapid (i.e., 1 or 2 wk) return to steady-state levels. Multi-dose-route PBPK models for Mn based on this alternative model structure can be readily scaled to evaluate tissue Mn kinetics in other species and for human populations. Once validated across test animals, these PBPK models will be useful in tissue-dose based risk assessment with manganese.
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Affiliation(s)
- Andy Nong
- Division of Computational Biology Division, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709-2137, USA.
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