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Dey/Antonini, Manganese Health Research Program Phase 2, Core 7

Research Core Project:
Neurotoxicity after Pulmonary Exposure to Welding Fumes Containing Manganese

Core Principal Investigator (CPI): 

Richard Dey, Ph.D.,
Neurobiology and Anatomy
West Virginia University
Health Sciences Center North 4013a
Morgantown, WV 2506

Dr. Dey is officially the CPI on the contract between Vanderbilt and West Virginia University.

Key Collaborators: 
James M. Antonini, Ph.D., James P. O’Callaghan, Ph.D., Diane B. Miller, Ph.D., Krishnan Sriram, Ph.D., Stanley Benkovic, Ph.D.,
Health Effects Laboratory Division,
National Institute for Occupational Safety and Health,
1095 Willowdale Road,
Morgantown, WV 26505

Project Objectives:

1. To determine the pulmonary and neurotoxic effects of animals exposed by inhalation or intratracheal instillation to welding fumes that are comprised of varying concentrations of manganese
2. To determine the manganese content in the blood, lungs, liver, kidneys, heart, and specific brain regions from animals exposed by inhalation or intratracheal instillation to welding fumes that are comprised of varying concentrations of manganese
3. To compare the neurotoxic effects and brain concentrations of manganese after exposure to welding fumes with the same effects after intratracheal instillation of insoluble or soluble manganese

Project Description:
Serious questions have been raised regarding a possible causal association between neurological effects in welders and the presence of manganese in welding consumables. The goal of the study is to examine the potential neurotoxic effect of manganese in rats after inhalation exposure to welding fumes that contain differing levels of manganese. Neurotoxicity will be detected and quantified by measuring for increased expression of glial fibrillary acidic protein (GFAP) and using silver degeneration staining technology. Because dopaminergic systems have been implicated as targets of manganese exposure, levels of dopamine and tyrosine hydroxylase, biomarkers of dopaminergic neuronal damage, will be measured. In addition, the fate of manganese after deposition in the lungs also will be assessed following exposure to welding fumes. Manganese concentrations will be determined in other organ systems and discrete brain regions after exposure. Results from this study will significantly advance the understanding of the potential neurotoxic effects of manganese associated with welding fume exposure from a mechanistic and dosimetric perspective. Such information may assist NIOSH, OSHA, and National Toxicology Program in risk assessment and the development of prevention strategies for workers exposed to manganese-containing welding fumes.

Project Status:

Project started: February 28, 2006
Completed: December 31, 2008

Key Research Accomplishments:

• A welding fume generation and inhalation exposure system was developed to expose laboratory animals.
 
• The generated welding fume was comparable to fume generated in the workplace in terms of particle size, morphology, and metal composition.
 
• Determined the regional metal distribution in the brain following pulmonary exposure to welding fumes of varying manganese composition.
 
• Demonstrated the accumulation of manganese from welding fumes in target dopaminergic brain areas.
 
• Demonstrated that pulmonary exposure to manganese-containing welding fumes caused loss of tyrosine hydroxylase protein, a marker of dopaminergic neurons.
 
• Demonstrated that short-term inhalation exposure to manganese-containing welding fume elicited neuroinflammation and gliosis in specific brain areas, including dopaminergic targets.
 
• Demonstrated that acute inhalation exposure to manganese-containing welding fume alters the expression of divalent metal transporters in distinct brain areas.
 
• Demonstrated altered expression of Parkin (Park2), Uchl1 (Park5) and Dj1 (Park7) proteins in dopaminergic brain areas after pulmonary exposure to manganese-containing welding fumes.

 

Conclusions:

An animal model was developed that assessed the potential neurological responses associated with welding fumes that contained differing levels of manganese.  Two methods of treatment were used to expose the laboratory animals to welding fumes: intratracheal instillation and inhalation.  Intratracheal instillation is a method by which welding particles are collected onto filters during generation and directly instilled into the lungs of animals via the trachea after suspension in aqueous solution.  The welding particles are directly administered to the distal alveolar regions of the lungs bypassing upper airway deposition (e.g., nasal/olfactory).  Thus, translocation of metals after exposure from the respiratory system would be known to originate from the alveolar regions to the circulation and would not result from olfactory uptake.  The advantages of inhalation exposure are the procedure is more physiological, deposition of the particles is more evenly distributed in the lungs, and the upper airways are involved, allowing assessment of possible olfactory transport of metal particles to brain areas. Unfortunately, inhalation exposure can be technically challenging and be quite expensive.

Our research group developed an automated robotic welder to expose laboratory animals.  The fume generated by our generator was observed to be comparable to welding fume collected in the workplace.  For this study, short-term inhalation exposures to gas metal arc-mild steel welding fume, the most common in U.S. industries, were performed.  Important findings from the short-term exposures indicate that manganese can translocate from the respiratory tract to other organ systems. Importantly, manganese was observed to deposit in the olfactory bulb.  Due to the significant number of nanometer-sized particles (<0.1 mm), it is possible that intact particles are being transported along olfactory nerve processes to the brain regions, bypassing the blood brain barrier.  There was no evidence of observable changes in neuronal cell injury as assessed by histopathology.  However, subtle changes in cell markers of neuroinflammatory and gliosis were observed.  The neurofunctional significance of these findings is being investigated in longer welding fume inhalation exposure studies.

Similar observations were made after exposing animals by the intratracheal instillation method with fumes containing differing levels of manganese.  Manganese was found to translocate from the lungs via the circulation to other organs, in particular, dopaminergic brain areas.  Consistent with the observed accumulation of manganese in specific brain regions, intratracheal instillation of welding fumes with varying levels of manganese were observed to induce subtle increases in metal transporter expression and neuroinflammatory responses in the olfactory bulb, striatum, and midbrain.  These observations suggest that exposure to manganese-containing welding fumes could potentially cause dopaminergic neurotoxicity.  In addition, altered expression of Parkin (Park2), Uchl1 (Park5) and Dj1 (Park7) proteins in dopaminergic brain areas was observed.  As mutations in PARK genes have been linked to early-onset Parkinson’s disease in humans, and because welding is implicated as a risk factor for Parkinsonism, PARK genes may play a critical role in WF-mediated dopaminergic dysfunction.  Whether these molecular alterations culminate in neurobehavioral and neuropathological deficits reminiscent of Parkinson’s disease remains to be ascertained.

Publications:

1. Antonini JM, Afshari AA, Stone S, Chen B, Schwegler-Berry D, Fletcher WG, Goldsmith WT, Vandestouwe KH, McKinney W, Castranova V, and Frazer DG.  Design, Construction, and Characterization of a Novel Robotic Welding Fume Generation and Inhalation Exposure System for Laboratory Animals.  J Occup Environ Hyg 3:194-203, 2006.
2. Antonini JM, Santamaria A, Jenkins NT, Albini E, and Lucchini R.  Fate of manganese associated with the inhalation of welding fumes: Potential neurological effects.  Neurotoxicol 27:304-310, 2006.
3. 3.  Antonini JM, O’Callaghan JP, Miller DB. Development of an animal model to study the potential neurotoxic effects associated with welding fume inhalation. Neurotoxicol 27:745-751, 2006.
4. Antonini JM, Sriram K, Benkovic SA, Roberts JR, Stone S, Chen BT, Schwegler-Berry D, Jefferson AM, Billig BK, Felton CM,  Hammer MA, Ma F, Frazer DG, O’Callaghan JP, and Miller DB. Mild steel welding fume causes manganese accumulation and subtle neuroinflammatory changes but not overt neuronal damage in discrete brain regions of rats after short-term inhalation exposure; Neurotoxicol 30:915-925, 2009.
5. Sriram K, Lin, GX, Jefferson AM, Roberts JR, Chapman RS, Soukup JM, Ghio AJ, Chen BT, and Antonini JM. Dopaminergic neurotoxicity following pulmonary exposure to manganese-containing welding fumes.  Arch Toxicol 84:521-540, 2010.
6. Antonini JM, Roberts JR, Chapman R, Soukup JM, Ghio AJ, and Sriram K. Pulmonary toxicity and extrapulmonary tissue distribution of metals after repeated exposure to different welding fumes.  Inhal Toxicol 22:805-816, 2010.
7. Sriram K, Lin GX, Jefferson AM, Roberts JR, Wirth O, Hayashi Y, Krajnak KM, Soukup JM, Ghio AJ, Reynolds SH, Castranova V, Munson AE, and Antonini JM. Mitochondrial dysfunction and loss of Parkinson’s disease-linked proteins contribute to neurotoxicity of manganese-containing welding fumes.  FASEB J 24:4989-5002, 2010.

Last updated: July 15, 2011