Manganese Health Research Program: Phase 1, Core 2

Research Core Projects:

(1) Biomarkers of Early Onset of Manganese Neurotoxicities among Occupationally Exposed Chinese Workers

(2) Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) in Manganese-Exposed Smelting Workers: Relationship to External and Internal Exposure Indices

Core Principal Investigator (CPI): Wei Zheng

Purdue University

550 Stadium Mall Drive, CIVL 1163

wzheng@purdue.edu

Key Collaborators: Frank Rosenthal, Purdue University, frank@purdue.edu

Ulrike Dydak, Purdue University, udydak@purdue.edu

Project Objectives – Project 1:

(1) the degree to which workers are exposed to respirable and inhalable particles containing Mn

(2) dose-response relationship of airborne Mn levels and Mn concentrations in biological matrices

(3) reliable biomarkers in serum, urine, saliva, or hair, and

(4) the no adverse effect level (NOAEL) for regulatory purposes.

Project Objectives – Project 2:

(1) to determine if the prevalence of the increased MRI signal intensity correlates with both external and internal Mn exposure indices as well as the subtle changes in neurobehavioral functions among smelting workers.

(2) to determine if Mn exposure alters the status of brain metabolites and neurotransmitters by using a non-invasive MRS technique. Neurochemicals to be determined include N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr) and myo-inositol (MI), GABA and glutamate (Glu). Changes in MRS among subjects will be correlated to their environmental, epidemiological and clinical experimental outcomes.

Project Description:

Exposure to neurotoxic metal, manganese (Mn), occurs in both civilian and military settings either in incidences of occupational exposure or more subtly in cases of environmental exposure. Currently, there is no practical method or the biomarker available for early diagnosis of Mn-induced neurodegenerative damage. Lack of such an early biomarker renders it nearly impossible to assess the human health risk and long-term social impact associated with potentially elevated Mn in environment. In project 1, the central hypothesis to be tested in this proposal is that occupational exposure to airborne Mn is associated with health disorders among exposed workers in a time-dose dependent manner. We propose a cross sectional design to evaluate the associations between airborne Mn levels and biomarkers of exposure (the concentrations of Mn, Fe, and Fe regulatory proteins) in biological matrices, and between the concentrations of biomarkers and the early signs of neurological deficits. The cohort is located in Zunyi City, “the Capital of Manganese” in Southwest of China, with industries involving Mn mining, refining, smelting, processing, and ferroalloy production and with the existing Mn intoxication cases. We propose to select 100 subjects whose exposure is expected to be high, 100 subjects whose exposure is expected to be moderate, and additional 100 subjects whose exposure is expected to be minimal. The study subjects in each group will be matched in terms of their distribution of age, sex, race and socioeconomic status. Mn exposure will be determined by personal air sampling and stationary air sampling devices. All participants will undergo physical examination. Serum, urine, saliva, and hair samples from subjects will be collected to determine concentrations of Mn in these bio-samples. The study will establish the dose-response relationship of airborne Mn levels and Mn concentrations in biological matrices, will define reliable biomarkers in serum, urine, saliva, or hair, and will determine the no adverse effect level (NOAEL) for regulatory purposes.

In project 2, we will test the central hypothesis that the external and internal manganese (Mn) exposure indices among a well-established smelter cohort are associated with changes in worker’s brain magnetic resonance imaging (MRI), and Mn-elicited neuronal damage can be mechanistically explored by magnetic resonance spectroscopy (MRS). The study will help develop a useful strategy in combining MRI and other biomarkers of Mn exposure for assessing early onset of Mn neurotoxicities. More importantly, the study, by using a novel approach of MRS, may reveal for the first time in human studies the primary brain cell type that is injured by Mn intoxication. This project was built upon the findings from the project 1. We have characterized, by exposure assessment, three unique study populations with airborne Mn levels less than 0.01 mg/m3 (control), between 0.01 and 0.1 mg/m3 (low-exposed group), or higher than 0.3 mg/m3 (high-exposed group). Among this study cohort, we have recruited a total of 328 study subjects, from whom the epidemiological questionnaires were obtained, biological samples (i.e., saliva, hair, serum, whole blood, and urine) were collected, and physical examinations, particularly neurological examination, were performed. In addition, we have conducted neurobehavioral testing among these workers by using Purdue Grooved Pegboard (for visual-motor coordination) and the Nine Hole Steadiness Tester (for intentional tremor). A well-characterized study population, plus the large quantities of original data that cover the exposure assessment, epidemiological survey, physiological examination, neurobehavioral testing, and clinical chemistry, provides a unique opportunity for further exploring an additional novel idea, i.e., using brain MRI to study the dose-dependent effect of Mn toxicity in smelters. Together with other biomarkers originally proposed to investigate, this study will help understand the potential health effects of metal fumes on exposed workers and define a better strategy for early diagnosis of Mn-induced neurotoxicity. In addition, we will use the MRS technique to investigate the damaged brain cell types among Mn-exposed smelters. Our specific aims are:

Project Status:

Project started: 1 April 2005

Scheduled completion date: 31 March 2009

Anticipated completion date: 31 Mar 2010

Key Research Accomplishments:

IRB protocol has been approved by Purdue, ZMC and DoD committees.
The ZMC was granted an Assurance number by the U.S. Department of Human Health Services, one of the six in OHPR official website.
The human study sites have been screened and selected.
A formal collaboration relationship has been established between the U.S. investigators and their Chinese counterpart.
A working site visit has been scheduled to monitor the progress and quality before the full scale of research is embarked.
Subjects have been recruited and personal air monitoring has been done.
Assays of biological examples have been accomplished.
Neurobehavioral tests have been done.
Proper statistical models have been developed and data analysis on correlations has been accomplished.
Subject recruitment for project 2 has been done.
MRI/MRS studies on subjects have been conducted in the First Affiliated Hospital of Guangxi Medical University in Nanning, China
MRI/MRS data analysis is currently in progress.

Publications Supported by MHRP

Jiang, Y-M, Zheng, W*, Long, L-L, Zhao, W-J, Li, X-G, Mo, X-A, Lu, J-P, Fu, X, Li, W-M, Liu, S-F, Long, Q-Y, Huang, J-L, and Pira, E (2007). Brain magnetic resonance imaging and manganese concentrations in red blood cells of smelting workers: Search for biomarkers of manganese exposure. NeuroToxicology 28:126-135.

Aschner, M, Nass, R, Guilarte, TR, Schneider, JS, and Zheng, W* (2007). Manganese: Recent advances in understanding its transport and neurotoxicity. Toxicol. Appl. Pharmacol. 221(2):131-147.

Jiang YM, Long LL, Zhu XY, Zheng H, Fu X, Ou SY, Wei DL, Zhou HL, and Zheng W* (2008). Evidence for altered hippocampal volume and metabolites in workers occupationally exposed to lead: A study by magnetic resonance imaging and 1H magnetic resonance spectroscopy. Toxicol Letters 181: 118-125.

Kalia K, Jiang W, and Zheng W* (2008). Manganese accumulates primarily in nuclei of cultured brain cells. NeuroToxicology 29(3):466-470.

Wang DX, Du XQ, and Zheng W* (2008). Alteration of saliva and serum concentrations of manganese, copper, zinc, cadmium and lead among career welders. Toxicol Letters 176:40-47.

Cowan DM, Fan QY, Zou Y, Shi XJ, Chen J, Rosenthal FS, Aschner M, and Zheng W* (2009). Manganese exposure among smelting workers: Blood manganese-iron ratio as a novel tool for manganese exposure assessment. Biomarkers 14(1): 3-16.

Cowan DM, Zheng W*, Zou Y, Shi XJ, Chen J, Rosenthal FS, and Fan QY (2009). Manganese exposure among smelting workers: Relationship between blood manganese-iron ratio and early onset neurobehavioral alternations. Neurotoxicology in press (doi:10.1016/j.neuro.2009.02.005)