Manganese induced brain lesions in Macaca fascicularis as revealed by positron emission tomography and magnetic resonance imaging

Manganese and Vanadium Co-Exposure Induces Severe Neurotoxicity in the Olfactory System: Relevance to Metal-Induced Parkinsonism

Chronic environmental exposure to toxic heavy metals, which often occurs as a mixture through occupational and industrial sources, has been implicated in various neurological disorders, including Parkinsonism. Vanadium pentoxide (V2O5) typically presents along with manganese (Mn), especially in welding rods and high-capacity batteries, including electric vehicle batteries; however, the neurotoxic effects of vanadium (V) and Mn co-exposure are largely unknown. In this study, we investigated the neurotoxic impact of MnCl2, V2O5, and MnCl2-V2O5 co-exposure in an animal model. C57BL/6 mice were intranasally administered either de-ionized water (vehicle), MnCl2 (252 µg) alone, V2O5 (182 µg) alone, or a mixture of MnCl2 (252 µg) and V2O5 (182 µg) three times a week for up to one month. Following exposure, we performed behavioral, neurochemical, and histological studies. Our results revealed dramatic decreases in olfactory bulb (OB) weight and levels of tyrosine hydroxylase, dopamine, and 3,4-dihydroxyphenylacetic acid in the treatment groups compared to the control group, with the Mn/V co-treatment group producing the most significant changes. Interestingly, increased levels of α-synuclein expression were observed in the substantia nigra (SN) of treated animals. Additionally, treatment groups exhibited locomotor deficits and olfactory dysfunction, with the co-treatment group producing the most severe deficits. The treatment groups exhibited increased levels of the oxidative stress marker 4-hydroxynonenal in the striatum and SN, as well as the upregulation of the pro-apoptotic protein PKCδ and accumulation of glomerular astroglia in the OB. The co-exposure of animals to Mn/V resulted in higher levels of these metals compared to other treatment groups. Taken together, our results suggest that co-exposure to Mn/V can adversely affect the olfactory and nigral systems. These results highlight the possible role of environmental metal mixtures in the etiology of Parkinsonism.

The Role of Nonhuman Primates in Neurotoxicology Research: Preclinical Models and Experimental Methods

Although noteworthy progress has been made in developing alternatives to animal testing, nonhuman primates still play a critical role in advancing biomedical research and will likely do so for many years. Core similarities between monkeys and humans in genetics, physiology, reproduction, development, and behavior make them excellent models for translational studies relevant to human health. This unit is designed to specifically address the role of nonhuman primates in neurotoxicology research and outlines the specialized assessments that can be used to measure exposure-related changes at the structural, chemical, cellular, molecular, and functional levels. © 2023 Wiley Periodicals LLC.

Manganese Accumulation in the Brain via Various Transporters and Its Neurotoxicity Mechanisms

Manganese (Mn) is an essential trace element, serving as a cofactor for several key enzymes, such as glutamine synthetase, arginase, pyruvate decarboxylase, and mitochondrial superoxide dismutase. However, its chronic overexposure can result in a neurological disorder referred to as manganism, presenting symptoms similar to those inherent to Parkinson’s disease. The pathological symptoms of Mn-induced toxicity are well-known, but the underlying mechanisms of Mn transport to the brain and cellular toxicity leading to Mn’s neurotoxicity are not completely understood. Mn’s levels in the brain are regulated by multiple transporters responsible for its uptake and efflux, and thus, dysregulation of these transporters may result in Mn accumulation in the brain, causing neurotoxicity. Its distribution and subcellular localization in the brain and associated subcellular toxicity mechanisms have also been extensively studied. This review highlights the presently known Mn transporters and their roles in Mn-induced neurotoxicity, as well as subsequent molecular and cellular dysregulation upon its intracellular uptakes, such as oxidative stress, neuroinflammation, disruption of neurotransmission, α-synuclein aggregation, and amyloidogenesis.

Activation of protein kinase R in the manganese-induced apoptosis of PC12 cells

Manganese neurotoxicity leads to Parkinson-like symptoms associated with the apoptotic cell death of dopaminergic neurons. Protein kinase R (PKR) is a serine/threonine-specific protein kinase that has been implicated in several cellular signal transduction pathways, including the induction of apoptosis. Here, we investigated the role of PKR in the manganese-induced apoptosis of dopamine-producing pheochromocytoma PC12 cells. Manganese (0.5 mM) induced the proteolytic cleavage of PKR and caspase-3, DNA fragmentation, and cell death, which were prevented by the co-treatment of PC12 cells with a PKR specific inhibitor, C16 in a concentration-dependent manner. C16 did not affect the manganese-induced activation of the c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinase (MAPK) pathway, indicating that PKR functions downstream of JNK and p38 MAPK. In contrast, C16 triggered the activation of the p44/42 MAPK (ERK1/2) pathway and induced hemoxygenase-1, both in the absence and presence of manganese. PKR is reportedly involved in endoplasmic reticulum (ER) stress-induced apoptosis. Manganese activated all three branches of the unfolded protein response in PC12 cells; however, this effect was very weak compared with the ER stress induced by the well-known ER stress inducers thapsigargin and tunicamycin. Moreover, C16 did not affect manganese-induced ER stress at concentrations that almost prevented caspase-3 activation and DNA fragmentation. These results suggest that PKR is involved in manganese-induced apoptotic cell death and stress response, such as the activation of the p44/42 MAPK pathway and the induction of hemoxygenase-1. Although manganese induced a faint, but typical, ER stress, these events contributed little to manganese-induced apoptosis.

Manganese toxicity is targeting an early step in the dopamine signal transduction pathway that controls lateral cilia activity in the bivalve mollusc Crassostrea virginica

Manganese is a neurotoxin causing manganism, a Parkinson-like clinical disorder. Manganese has been shown to interfere with dopaminergic neurotransmission, but the neurotoxic mechanism involved is not fully resolved. In the bivalve mollusc Crassostrea virginica also known as the eastern oyster, beating rates of lateral cilia of the gill are controlled by dopaminergic-serotonergic innervation originating from their cerebral and visceral ganglia. Terminal release of dopamine activates D2-like receptors on these gill cells inhibiting adenylyl cyclase and slowing cilia beating rates. In C. virginica, manganese treatment disrupts this dopaminergic innervation of the gill, preventing the normal cilio-inhibitory response of lateral cells to dopamine. In this study an adenylyl cyclase activator (forskolin) and two different inhibitors (MDL-12,330A and SQ 22,536) were used to determine if manganese had any effects on the adenylyl cyclase step of the dopamine D2 receptor signal transduction pathway. The results showed that neither the adenylyl cyclase activator nor the inhibitors were affected by manganese in the control of lateral ciliary activity. This suggests that in C. virginica the mechanism of manganese toxicity on the dopaminergic control of lateral ciliary activity is targeting an early step in the D2R signal transduction pathway, which may involve interference with D2 receptor activation or alternatively some other downstream signaling activity that does not affect adenylyl cyclase.

Selective D2 receptor PET in manganese-exposed workers

OBJECTIVE

To investigate the associations between manganese (Mn) exposure, D2 dopamine receptors (D2Rs), and parkinsonism using [11C](N-methyl)benperidol (NMB) PET.

METHODS

We used NMB PET to evaluate 50 workers with a range of Mn exposure: 22 Mn-exposed welders, 15 Mn-exposed workers, and 13 nonexposed workers. Cumulative Mn exposure was estimated from work histories, and movement disorder specialists examined all workers. We calculated NMB D2R nondisplaceable binding potential (BPND) for the striatum, globus pallidus, thalamus, and substantia nigra (SN). Multivariate analysis of covariance with post hoc descriptive discriminate analysis identified regional differences by exposure group. We used linear regression to examine the association among Mn exposure, Unified Parkinson's Disease Rating Scale motor subsection 3 (UPDRS3) score, and regional D2R BPND.

RESULTS

D2R BPND in the SN had the greatest discriminant power among exposure groups (p < 0.01). Age-adjusted SN D2R BPND was 0.073 (95% confidence interval [CI] 0.022-0.124) greater in Mn-exposed welders and 0.068 (95% CI 0.013-0.124) greater in Mn-exposed workers compared to nonexposed workers. After adjustment for age, SN D2R BPND was 0.0021 (95% CI 0.0005-0.0042) higher for each year of Mn exposure. Each 0.10 increase in SN D2R BPND was associated with a 2.65 (95% CI 0.56-4.75) increase in UPDRS3 score.

CONCLUSIONS AND RELEVANCE

Nigral D2R BPND increased with Mn exposure and clinical parkinsonism, indicating dose-dependent dopaminergic dysfunction of the SN in Mn neurotoxicity.

Association of MRI T1 relaxation time with neuropsychological test performance in manganese- exposed welders

This study examines the results of neuropsychological testing of 26 active welders and 17 similar controls and their relationship to welders' shortened MRI T1 relaxation time, indicative of increased brain manganese (Mn) accumulation. Welders were exposed to Mn for an average duration of 12.25 years to average levels of Mn in air of 0.11±0.05mg/m3. Welders scored significantly worse than controls on Fruit Naming and the Parallel Lines test of graphomotor tremor. Welders had shorter MRI T1 relaxation times than controls in the globus pallidus, substantia nigra, caudate nucleus, and the anterior prefrontal lobe. 63% of the variation in MRI T1 relaxation times was accounted for by exposure group. In welders, lower relaxation times in the caudate nucleus and substantia nigra were associated with lower neuropsychological test performance on tests of verbal fluency (Fruit Naming), verbal learning, memory, and perseveration (WHO-UCLA AVLT). Results indicate that verbal function may be one of the first cognitive domains affected by brain Mn deposition in welders as reflected by MRI T1 relaxation times.

Manganese exposure and neurotoxic effects in children

Manganese (Mn) is the fifth most abundant metal on earth. Although it is a well understood essential trace element, in excess, Mn is neurotoxic. Initial toxic symptoms associated with Mn are of psychiatric nature and are clinically defined as locura manganica. Neurological signs of Mn toxicity include dystonia, progressive bradykinesia, and disturbance of gait, slurring, and stuttering of speech with diminished volume. Studies indicate that children who ingested Mn in the drinking water (WMn) at or above a level of 0.241mg/L for a minimum of three years performed more poorly in school as measured by mastery of language, mathematics, and in their overall grade average. The Mn-exposed children also performed more poorly on a battery of neurobehavioral tests. It was also found a significant association between higher WMn and lower cognitive performance, verbal function, and full-scale intelligence quotient (IQ) scores. Young children appear to make up a vulnerable group in exposed populations. Toxicity of WMn is a problem particularly in areas of industrial waste or where Mn is leaching from the soil into public drinking water. Practical and cost-effective approaches are available to remove Mn from drinking water. It is crucial to protect developing brains against Mn toxicity.

A tissue dose-based comparative exposure assessment of manganese using physiologically based pharmacokinetic modeling-The importance of homeostatic control for an essential metal

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.

Parkinsonism due to Manganism in a Welder

A 33-year-old right-handed male presented complaining of a 2-year history of progressive cognitive slowing, rigidity, tremors, slowing of movements, and gait instability leading to falls. On examination, he had a Mini-Mental Status Examination (MMSE) score of 29, slowed saccadic eye pursuit, hypomimia, cogwheel rigidity, a 3- to 4-Hz tremor, and a “cock-walk” gait. His symptoms and signs were similar to idiopathic Parkinson's disease; however, he was young, inattention and forgetfulness occurred early in the course of the disorder, levodopa was unhelpful, and his gait was atypical. His work up for secondary causes of parkinsonism was negative, except for increased signal intensity on T1-weighted magnetic resonance image (MRI) in the bilateral basal ganglia. Typical etiologies for that finding were ruled-out, which led to further inquiries into the patient's lifestyle. He was a welder, and discussion with his employer revealed that he used a steel-manganese alloy, he often worked in a confined ship's hold, and he did not use a respiratory mask. Because manganese toxicity can produce increased T1-weighted signal intensities in the basal ganglia, the authors tested his serum and urine manganese, and both were elevated. This patient emphasizes the importance of a careful occupational history in persons presenting with atypical manifestations of a neurodegenerative disorder. It also lends support to the hypothesis that welding can produce enough exposure to manganese to produce neurologic impairment.

Occupational exposures and parkinsonism

In recent years, the contribution of exposure to environmental toxicants has been recognized as a significant contributor to the etiopathogenesis of parkinsonism. Of these toxicants, exposure to pesticides, metals, solvents used in manufacturing processes, as well as flame-retardant chemicals used in consumer and commercial products, has received the greatest attention as possible risk factors. Related to this, individuals who are exposed to these compounds at high concentrations or for prolonged periods of time in an occupational setting appear to be one of the more vulnerable populations to these effects. Our understanding of which compounds are involved and the potential molecular pathways that are susceptible to these chemicals and may underlie the pathogenesis has greatly improved. However, there are still hundreds of chemicals that we are exposed to in the environment for which we do not have any information on their potential neurotoxicity on the nigrostriatal dopamine system. Thus, using our past accomplishments as a blueprint, future endeavors should focus on elaborating upon these initial findings in order to identify specific and relevant chemical toxicants in our environment that can impact the risk of parkinsonism and work towards a means to attenuate or abolish their effects on the human population.

Pallidal index as biomarker of manganese brain accumulation and associated with manganese levels in blood: a meta-analysis

OBJECTIVE

The current study was designed to evaluate the sensitivity, feasibility, and effectiveness of the pallidal index (PI) serving as a biomarker of brain manganese (Mn) accumulation, which would be used as an early diagnosis criteria for Mn neurotoxicity.

METHODS

The weighted mean difference (WMD) of the PI between control and Mn-exposed groups was estimated by using a random-effects or fixed-effects meta-analysis with 95% confidence interval (CI) performed by STATA software version 12.1. Moreover, the R package "metacor" was used to estimate correlation coefficients between PI and blood Mn (MnB).

RESULTS

A total of eight studies with 281 occupationally Mn-exposed workers met the inclusion criteria. Results were pooled and performed with the Meta-analysis. Our data indicated that the PI of the exposed group was significantly higher than that of the control (WMD: 7.76; 95% CI: 4.86, 10.65; I2 = 85.7%, p<0.0001). A random effects model was used to perform meta-analysis. These findings were remarkably robust in the sensitivity analysis, and publication bias was shown in the included studies. Seven out of the eight studies reported the Pearson correlation (r) values. Significantly positive correlation between PI and MnB was observed (r = 0.42; 95% CI, 0.31, 0.52).

CONCLUSIONS

PI can be considered as a sensitive, feasible, effective and semi-quantitative index in evaluating brain Mn accumulation. MnB can also augment the evaluation of brain Mn accumulation levels in the near future. However, the results should be interpreted with caution.

Childhood exposure to manganese and postural instability in children living near a ferromanganese refinery in Southeastern Ohio

Airborne manganese (Mn) exposure can result in neurotoxicity and postural instability in occupationally exposed workers, yet few studies have explored the association ambient exposure to Mn in children and postural stability. The goal of this study was to determine the association between Mn and lead (Pb) exposure, as measured by blood Pb, blood and hair Mn and time weighted distance (TWD) from a ferromanganese refinery, and postural stability in children. A subset of children ages 7-9 years enrolled in the Marietta Community Actively Researching Exposure Study (CARES) were invited to participate. Postural balance was conducted on 55 children residing in Marietta, Ohio and the surrounding area. Samples of blood were collected and analyzed for Mn and Pb, and samples of hair were analyzed for Mn. Neuromotor performance was assessed using postural balance testing with a computer force platform system. Pearson correlations were calculated to identify key covariates. Associations between postural balance testing conditions and Mn and Pb exposure were estimated with linear regression analyses adjusting for gender, age, parent IQ, and parent age. Mean blood Mn was 10 μg/L (SEM=0.36), mean blood Pb was 0.85 μg/dL (SEM=0.05), and mean hair Mn was 0.76 μg/g (SEM=0.16). Mean residential distance from the refinery was 11.5 km (SEM=0.46). All three measures of Mn exposure were significantly associated with poor postural balance. In addition, low-level blood Pb was also negatively associated with balance outcomes. We conclude that Mn exposure and low-level blood Pb are significantly associated with poor postural balance.

Vanadium exposure induces olfactory dysfunction in an animal model of metal neurotoxicity

Epidemiological evidence indicates chronic environmental exposure to transition metals may play a role in chronic neurodegenerative conditions such as Parkinson's disease (PD). Chronic inhalation exposure to welding fumes containing metal mixtures may be associated with development of PD. A significant amount of vanadium is present in welding fumes, as vanadium pentoxide (V2O5), and incorporation of vanadium in the production of high strength steel has become more common. Despite the increased vanadium use in recent years, the neurotoxicological effects of this metal are not well characterized. Recently, we demonstrated that V2O5 induces dopaminergic neurotoxicity via protein kinase C delta (PKCδ)-dependent oxidative signaling mechanisms in dopaminergic neuronal cells. Since anosmia (inability to perceive odors) and non-motor deficits are considered to be early symptoms of neurological diseases, in the present study, we examined the effect of V2O5 on the olfactory bulb in animal models. To mimic the inhalation exposure, we intranasally administered C57 black mice a low-dose of 182μg of V2O5 three times a week for one month, and behavioral, neurochemical and biochemical studies were performed. Our results revealed a significant decrease in olfactory bulb weights, tyrosine hydroxylase (TH) levels, levels of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and increases in astroglia of the glomerular layer of the olfactory bulb in the treatment groups relative to vehicle controls. Neurochemical changes were accompanied by impaired olfaction and locomotion. These findings suggest that nasal exposure to V2O5 adversely affects olfactory bulbs, resulting in neurobehavioral and neurochemical impairments. These results expand our understanding of vanadium neurotoxicity in environmentally-linked neurological conditions.

The neurobehavioral impact of manganese: results and challenges obtained by a meta-analysis of individual participant data

Results from a meta-analysis of aggregated data provoked a new analysis using individual data on the neuropsychological performance of occupationally exposed workers. Data from eight studies examining 579 exposed and 433 reference participants were included, 28 performance variables analyzed. The performance scores were adjusted for well-known individual-level covariates; the influence of possible, but unknown study-level covariates was attenuated by means of a z-normalization. Associations between performance and exposure were estimated by ANOVAs and ANCOVAs, the latter representing multi-level models. Four cognitive and motor performance variables each indicated significantly lower performances of exposed individuals when confounding was considered; slowed motor performances and deficits in attention and short-term memory were found. Performance on a single test was significantly related to the biomarker manganese in blood. The outcomes on susceptibility were weak. The slowing of responses was the most distinct feature of performances of exposed workers. It remains unclear, whether this result is related to the employed tests or provides important information about early stages of the neurotoxic impairment. More specific cognitive tests need to be employed to answer this question. The lack of dose-response relationships was related to features of the biomarker: it does not reflect the Mn in brain responsible for changes in performances.

Toxic encephalopathy

This article schematically reviews the clinical features, diagnostic approaches to, and toxicological implications of toxic encephalopathy. The review will focus on the most significant occupational causes of toxic encephalopathy. Chronic toxic encephalopathy, cerebellar syndrome, parkinsonism, and vascular encephalopathy are commonly encountered clinical syndromes of toxic encephalopathy. Few neurotoxins cause patients to present with pathognomonic neurological syndromes. The symptoms and signs of toxic encephalopathy may be mimicked by many psychiatric, metabolic, inflammatory, neoplastic, and degenerative diseases of the nervous system. Thus, the importance of good history-taking that considers exposure and a comprehensive neurological examination cannot be overemphasized in the diagnosis of toxic encephalopathy. Neuropsychological testing and neuroimaging typically play ancillary roles. The recognition of toxic encephalopathy is important because the correct diagnosis of occupational disease can prevent others (e.g., workers at the same worksite) from further harm by reducing their exposure to the toxin, and also often provides some indication of prognosis. Physicians must therefore be aware of the typical signs and symptoms of toxic encephalopathy, and close collaborations between neurologists and occupational physicians are needed to determine whether neurological disorders are related to occupational neurotoxin exposure.

Personalized nanomedicine advancements for stem cell tracking

Recent technological developments in biomedicine have facilitated the generation of data on the anatomical, physiological and molecular level for individual patients and thus introduces opportunity for therapy to be personalized in an unprecedented fashion. Generation of patient-specific stem cells exemplifies the efforts toward this new approach. Cell-based therapy is a highly promising treatment paradigm; however, due to the lack of consistent and unbiased data about the fate of stem cells in vivo, interpretation of therapeutic effects remains challenging hampering the progress in this field. The advent of nanotechnology with a wide palette of inorganic and organic nanostructures has expanded the arsenal of methods for tracking transplanted stem cells. The diversity of nanomaterials has revolutionized personalized nanomedicine and enables individualized tailoring of stem cell labeling materials for the specific needs of each patient. The successful implementation of stem cell tracking will likely be a significant driving force that will contribute to the further development of nanotheranostics. The purpose of this review is to emphasize the role of cell tracking using currently available nanoparticles.

Does soy-based infant formula cause ADHD? Update and public policy considerations

An earlier article hypothesized a relationship between soy-based infant formulas, manganese (Mn) neurotoxicity and symptoms of ADHD. In this update, more recent literature on ADHD, Mn and Mn neurotoxicity is reviewed, as well as the risks of Mn toxicity that may accompany ingestion of soy-based infant formula. The results of several critical studies are described, including rodent and primate models that demonstrate an association between ingestion of relatively high levels of Mn and: overactivity, disinhibition and inattention; stereotypes and disturbances of social relatedness; and alterations of dopamine D1 and D2 receptors and dopamine transporter in critical brain regions. Similar deficits have been shown in children with ADHD. In addition, ADHD-like symptoms of behavioral disinhibition were found to be correlated with Mn content in tooth enamel, apparently deposited at or before the fifth gestational month. The results are discussed in terms of their weight as a risk factor in ADHD, vis-à-vis compelling evidence of genetic, epigenetic and other environmental risk factors associated with the disorder, as well as the appropriateness of additional public policy decisions regarding the safety of soy formula.

Industrial toxicants and Parkinson's disease

The exposure of the human population to environmental contaminants is recognized as a significant contributing factor for the development of Parkinson's disease (PD) and other forms of parkinsonism. While pesticides have repeatedly been identified as risk factors for PD, these compounds represent only a subset of environmental toxicants that we are exposed to on a regular basis. Thus, non-pesticide contaminants, such as metals, solvents, and other organohalogen compounds have also been implicated in the clinical and pathological manifestations of these movement disorders and it is these non-pesticide compounds that are the subject of this review. As toxic exposures to these classes of compounds can result in a spectrum of PD or PD-related disorders, it is imperative to appreciate shared clinico-pathological characteristics or mechanisms of action of these compounds in order to further delineate the resultant disorders as well as identify improved preventive strategies or therapeutic interventions.

Manganese inhalation as a Parkinson disease model

The present study examines the effects of divalent and trivalent Manganese (Mn²⁺/Mn³⁺) mixture inhalation on mice to obtain a novel animal model of Parkinson disease (PD) inducing bilateral and progressive dopaminergic cell death, correlate those alterations with motor disturbances, and determine whether L-DOPA treatment improves the behavior, to ensure that the alterations are of dopaminergic origin. CD-1 male mice inhaled a mixture of Manganese chloride and Manganese acetate, one hour twice a week for five months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. By the end of Mn exposure, 10 mice were orally treated with 7.5 mg/kg L-DOPA. After 5 months of Mn mixture inhalation, striatal dopamine content decreased 71%, the SNc showed important reduction in the number of TH-immunopositive neurons, mice developed akinesia, postural instability, and action tremor; these motor alterations were reverted with L-DOPA treatment. Our data provide evidence that Mn²⁺/Mn³⁺ mixture inhalation produces similar morphological, neurochemical, and behavioral alterations to those observed in PD providing a useful experimental model for the study of this neurodegenerative disease.

Biomarkers of manganese intoxication

Manganese (Mn), upon absorption, is primarily sequestered in tissue and intracellular compartments. For this reason, blood Mn concentration does not always accurately reflect Mn concentration in the targeted tissue, particularly in the brain. The discrepancy between Mn concentrations in tissue or intracellular components means that blood Mn is a poor biomarker of Mn exposure or toxicity under many conditions and that other biomarkers must be established. For group comparisons of active workers, blood Mn has some utility for distinguishing exposed from unexposed subjects, although the large variability in mean values renders it insensitive for discriminating one individual from the rest of the study population. Mn exposure is known to alter iron (Fe) homeostasis. The Mn/Fe ratio (MIR) in plasma or erythrocytes reflects not only steady-state concentrations of Mn or Fe in tested individuals, but also a biological response (altered Fe homeostasis) to Mn exposure. Recent human studies support the potential value for using MIR to distinguish individuals with Mn exposure. Additionally, magnetic resonance imaging (MRI), in combination with noninvasive assessment of γ-aminobutyric acid (GABA) by magnetic resonance spectroscopy (MRS), provides convincing evidence of Mn exposure, even without clinical symptoms of Mn intoxication. For subjects with long-term, low-dose Mn exposure or for those exposed in the past but not the present, neither blood Mn nor MRI provides a confident distinction for Mn exposure or intoxication. While plasma or erythrocyte MIR is more likely a sensitive measure, the cut-off values for MIR among the general population need to be further tested and established. Considering the large accumulation of Mn in bone, developing an X-ray fluorescence spectroscopy or neutron-based spectroscopy method may create yet another novel non-invasive tool for assessing Mn exposure and toxicity.

Manganese and Parkinson's disease: a critical review and new findings

BACKGROUND

Excess accumulation of manganese (Mn) in the brain results in a neurological syndrome with cognitive, psychiatric, and movement abnormalities. The highest concentrations of Mn in the brain are achieved in the basal ganglia, which may precipitate a form of parkinsonism with some clinical features that are similar and some that are different to those in Parkinson's disease (PD). Recently, scientists have debated the possibility that Mn may have an etiological role in PD or that it may accelerate the expression of PD.

OBJECTIVE

The goal of this review was to examine whether chronic Mn exposure produces dopamine neuron degeneration and PD or whether it has a distinct neuropathology and clinical presentation.

DATA SOURCE

I reviewed available clinical, neuroimaging, and neuropathological studies in humans and nonhuman primates exposed to Mn or other human conditions that result in elevated brain Mn concentrations.

DATA EXTRACTION

Human and nonhuman primate literature was examined to compare clinical, neuroimaging, and neuropathological changes associated with Mn-induced parkinsonism.

DATA SYNTHESIS

Clinical, neuroimaging, and neuropathological evidence was used to examine whether Mn-induced parkinsonism involves degeneration of the nigrostriatal dopaminergic system as is the case in PD.

CONCLUSIONS

The overwhelming evidence shows that Mn-induced parkinsonism does not involve degeneration of midbrain dopamine neurons and that l-dopa is not an effective therapy. New evidence is presented on a putative mechanism by which Mn may produce movement abnormalities. Confirmation of this hypothesis in humans is essential to make rational decisions about treatment, devise effective therapeutic strategies, and set regulatory guidelines.

Chronic exposure to manganese alters brain responses to amphetamine: a pharmacological magnetic resonance imaging study

The parkinsonian symptoms and increased Mn accumulation in dopaminergic (DAergic) neurons of the basal ganglia implicate impaired dopamine signaling in the neurotoxic effects of chronic manganese overexposure. Using blood oxygenation level-dependent (BOLD) pharmacological magnetic resonance imaging (phMRI), we mapped brain responses to acute amphetamine (AMPH; 3 mg/kg, ip), which stimulates midbrain DAergic systems, in male Sprague-Dawley rats following 6 weeks of chronic MnCl(2) (5 mg Mn/kg, one per week, iv) or saline treatment. Plasma Mn content, measured immediately following phMRI, was elevated twofold in Mn-treated animals (p < 0.05), but the twofold increase in mean striatal Mn content did not reach significance. In saline-treated animals, AMPH stimulated robust positive BOLD responses throughout the basal ganglia and their reciprocally innervated connections. In contrast, acute AMPH stimulated a negative BOLD response in many of these structures in the Mn-treated group, resulting in significant differences between saline- and Mn-treated AMPH-evoked BOLD responses within caudate putamen, globus pallidus, substantia nigra, mediodorsal thalamic nucleus, and somatosensory cortex. These results demonstrate the utility of AMPH-evoked phMRI as readout of the DAergic signaling in vivo and confirm the vulnerability of DAergic systems to Mn.

Relationship between changes in brain MRI and (1)H-MRS, severity of chronic liver damage, and recovery after liver transplantation

Magnetic resonance imaging (MRI) and (1)H magnetic resonance spectroscopy ((1)H-MRS) have been used in clinics for diagnosis of chronic liver diseases. This study was designed to investigate the relationship between MRI/MRS outcomes and the severity of liver damage. Of 50 patients examined, the MRI signal intensity in the globus pallidus as determined by pallidus index (PI) increased as the disease severity (scored by Child Pugh ranking) worsened (r = 0.353, P < 0.05). The changes in PI values were also linearly associated with Mn concentrations in whole blood (MnB) (r = 0.814, P < 0.01). MRS analysis of four major brain metabolites (i.e., Cho, mI, Glx, and NAA) revealed that the ratios of Cho/Cr and mI/Cr in cirrhosis and CHE patients were significantly decreased in comparison to controls (P < 0.05), whereas the ratio of Glx/Cr was significantly increased (P < 0.05). The Child Pugh scores significantly correlated with mI/Cr (-0.484, P < 0.01) and Glx (0.369, P < 0.05), as well as MnB (0.368, P < 0.05), but not with other brain metabolites. Three patients who received a liver transplant experienced normalization of brain metabolites within 3 months of post-transplantation; the MR imaging of Mn in the globus pallidus completely disappeared 5 months after the surgery. Taken together, this clinical study, which combined MRI/MRS analysis, autopsy exam and liver transplant, clearly demonstrates that liver injury-induced brain Mn accumulation can reversibly alter the homeostasis of brain metabolites Cho, mI and Glx. Our data further suggest that liver transplantation can restore normal brain Mn levels.

Morphological changes and manganese content in the brains of rat pups subjected to subchronic poisoning with manganese chloride

Morphological changes in neurons and the distributions of nerve and glial cells were studied, the glial index was calculated, and manganese (Mn) contents were determined in the caudate nucleus, the nucleus accumbens, the dorsal and ventral septal nuclei, and the frontoparietal areas of the cerebral cortex in the 40-day-old offspring of rats given different doses (10 and 20 mg/kg) of manganese chloride (MnCl2.4H2O) 15-20 days before pregnancy, during pregnancy, and for one month after parturition with the first portion of food. Mn poisoning increased Mn contents in the brains of rat pups, damaged a small proportion of neurons, and produced marked gliosis. These changes are believed to underlie previously described impairments to learning processes and emotional state in rat pups.

Impairment of nigrostriatal dopamine neurotransmission by manganese is mediated by pre-synaptic mechanism(s): implications to manganese-induced parkinsonism

The long-term consequences of chronic manganese (Mn) exposure on neurological health is a topic of great concern to occupationally-exposed workers and in populations exposed to moderate levels of Mn. We have performed a comprehensive assessment of Mn effects on dopamine (DA) synapse markers using positron emission tomography (PET) in the non-human primate brain. Young male Cynomolgus macaques were given weekly i.v. injections of 3.3-5.0 mg Mn/kg (n = 4), 5.0-6.7 mg Mn/kg (n = 5), or 8.3-10.0 mg Mn/kg (n = 3) for 7-59 weeks and received PET studies of various DA synapse markers before (baseline) and at one or two time points during the course of Mn exposure. We report that amphetamine-induced DA release measured by PET is markedly impaired in the striatum of Mn-exposed animals. The effect of Mn on DA release was present in the absence of changes in markers of dopamine terminal integrity determined in post-mortem brain tissue from the same animals. These findings provide compelling evidence that the effects of Mn on DA synapses in the striatum are mediated by inhibition of DA neurotransmission and are responsible for the motor deficits documented in these animals.

Biomarkers of manganese exposure in a population living close to a mine and mineral processing plant in Mexico

Manganese (Mn) is considered an essential metal; nevertheless, excessive Mn exposure in humans is known to affect central nervous system. Mn access to its toxic target, the brain, is a complex phenomenon subject to physiological and physiopathological processes; in which, among others, the route of exposure plays an important role. Mn airborne exposure has gained interest both in occupational and environmental studies in order to understand the effects of low-level, long-term exposure. The objective of the present study was to describe the relationship between blood Mn and prolactin as marker of effect exposure, as well as other variables from subjects dwelling in a mining district in central Mexico environmentally exposed to the metal. This study was conducted on 230 volunteers; blood samples were obtained from cubital vein and hemoglobin, prolactin, lead (Pb), and Mn levels were measured. Non-parametrical Spearman's correlation showed statistical associations between blood and Mn levels and prolactin (rho=0.197), hemoglobin (rho= -0.213), age (rho= -0.186), and blood lead (rho= -0.167). Multiple regression analysis showed that blood Mn levels as an important factor to determine serum prolactin levels (beta=0.111, p=0.029) in a model corrected by gender and age. Results suggest that assessment of Mn exposure by biomarkers on general population is complex due to the variability and characteristics of the metal; however, specific subpopulations such as iron-deficient individuals are suspected to accumulate Mn in blood and thus they may be susceptible to the neurotoxic effects of Mn.

Basal ganglia neurotransmitter concentrations in rhesus monkeys following subchronic manganese sulfate inhalation

BACKGROUND

Manganese neurotoxicity in humans is recognized as a form of parkinsonism with lesions occurring predominantly within the globus pallidus, subthalamic nucleus, putamen, and caudate nucleus.

METHODS

This study evaluated dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin, norepinephrine, 5-hydroxyindoleacetic acid, gamma-aminobutyric acid (GABA), and glutamate concentrations in the globus pallidus, caudate, and putamen of male rhesus monkeys exposed subchronically to either air or manganese sulfate (MnSO4) at 0.06, 0.3, or 1.5 mg Mn/m3.

RESULTS

An approximate 1.5-6-fold increase (vs. air-exposed controls) in mean brain manganese concentration was observed following subchronic MnSO4 exposure. A marginally significant (P < 0.1) decrease in pallidal GABA and 5-hydroxyindoleacetic acid concentration and caudate norepinephrine concentration occurred in monkeys exposed to MnSO4 at 1.5 mg Mn/m3.

CONCLUSIONS

Despite the presence of increased tissue manganese concentrations, high-dose exposure to MnSO4 was associated with relatively few changes in basal ganglial neurotransmitter concentrations.

A neurobehavioral study of current and former welders exposed to manganese

Neurobehavioral functions were studied in 96 welders currently exposed to the geometric mean (GM) concentration of 121 microg/m(3) (range 7-2322) manganese (Mn) in welding fume (air-Mn) based on the individual mean from two successive days of sampling. They were compared to 96 age-matched referents. The arithmetic mean (AM) concentration of Mn in whole blood (B-Mn) was 8.6 microg/L versus 6.9 microg/L in the referents. Associations between the Digit Symbol and Finger Tapping test scores and B-Mn and air-Mn, respectively, were observed. The welders exposed to the highest air-Mn concentrations (GM 423 microg/m(3) range 204-2322) had statistically significantly poorer Finger Tapping test score as compared to their age-matched referents. The welders with the highest AM concentration of B-Mn (12.6 microg/L) scored statistically significantly poorer on the Digit Symbol test when compared to the age-matched referents (AM B-Mn 7.5 microg/L). The same neurobehavioral test battery was applied to 27 patients diagnosed, and financially compensated, as having welding related manganism. They were on average 44.9 (range 34-51) years old at the time of diagnosis, which on average was 5.8 years prior to this study. They had worked as welders for 23.1 years on average (range 15-30). The most affected neurobehavioral functions were associated with impaired Finger Tapping speed and Grooved Pegboard performance. The patients had no alterations in hand tremor as assessed by the CATSYS system, while a few subjects had noticeable tremor as assessed by the Static Steadiness test.

A preliminary study revealing a new association in patients undergoing maintenance hemodialysis: manganism symptoms and T1 hyperintense changes in the basal ganglia

BACKGROUND AND PURPOSE

Patients undergoing parenteral nutrition and those with portosystemic encephalopathy secondary to chronic liver disease and acquired and congenital portosystemic venous shunts frequently present manganese deposition in the basal ganglia, detected by MR imaging as hyperintense areas on T1-weighted sequences. We also observed similar abnormalities in the basal ganglia of patients with chronic renal failure undergoing maintenance hemodialysis. Our aim was to evaluate the pallidal signal intensity on T1-weighted images in a series of patients undergoing hemodialysis, with further evaluation of serum manganese levels and neurologic correlation, comparing them with patients with chronic renal failure without dialytic treatment.

MATERIALS AND METHODS

We performed MR imaging examinations in 9 patients with chronic renal failure, 5 of whom were undergoing hemodialysis. An experienced neuroradiologist scrutinized the presence of symmetric hyperintensities in the basal ganglia on T1-weighted sequences. We also determined the serum manganese levels and performed the neurologic evaluations in all patients.

RESULTS

All patients undergoing hemodialysis presented elevated serum manganese levels and symmetric hyperintensities within the globus pallidus. In this group, 4 patients presented with parkinsonian symptoms, myoclonus, and syndromes with vestibular and vestibular-auditory symptoms. The patients without dialytic treatment presented with neither bilaterally increased T1 MR imaging signal intensity within the globus pallidus nor symptoms of manganism.

CONCLUSION

Our preliminary results demonstrated the occurrence of bilateral pallidal hyperintensity on T1-weighted images in all patients undergoing hemodialysis associated with high serum manganese levels, revealing a new association.

The Neuropathology of Manganese-Induced Parkinsonism

Manganese is an essential trace metal that is widely used in industry, particularly in the manufacture of steel. Exposure to high levels of manganese can cause neurotoxicity with the development of a form of parkinsonism known as manganism. It has recently been hypothesized that manganese exposure might also cause or accelerate the development of Parkinson disease (PD). This article is a review of the pathologic studies that have been reported in patients with manganism and in primates experimentally intoxicated with manganese. They demonstrate a consistent pattern characterized by damage to the globus pallidus (particularly the internal segment) with sparing of the substantia nigra pars compacta and the absence of Lewy bodies. This finding contrasts with what is seen in PD, in which there is preferential degeneration of dopamine neurons in the substantia nigra pars compacta coupled with Lewy bodies and preservation of the pallidum. These pathologic findings do not support the notion that manganese causes PD but rather argues that manganese-induced parkinsonism and PD are distinct and separate disease entities.

Manganese: recent advances in understanding its transport and neurotoxicity

The present review is based on presentations from the meeting of the Society of Toxicology in San Diego, CA (March 2006). It addresses recent developments in the understanding of the transport of manganese (Mn) into the central nervous system (CNS), as well as brain imaging and neurocognitive studies in non-human primates aimed at improving our understanding of the mechanisms of Mn neurotoxicity. Finally, we discuss potential therapeutic modalities for treating Mn intoxication in humans.

Irreversible motor impairment in young addicts--ephedrone, manganism or both?

BACKGROUND

Parkinsonian syndrome related to intravenous use of a "designer" psychostimulant, derived from pseudoephedrine using potassium permanganate as the oxidant, has been observed in drug addicts in Estonia.

OBJECTIVE

To describe the symptomatology of four young patients, history of drug administration and chemical analysis of a drug batch.

METHODS

Mental and motor function and quality of life were scored and ephedrone was analyzed using electrospray mass spectrometry. Manganese content of the final synthetic mixture was analyzed using Inductively Coupled Plasma-Atomic Emission Spectrometry.

RESULTS

None of the four cases scored below the dementia threshold in MMSE, while other ratings (UPDRS, H&Y, PDQ-39) corresponded to disabilities seen in relatively advanced Parkinson's disease. The ephedrone yield of the reaction was approximately 44% and the mixture was found to contain 0.6 g/l of manganese.

CONCLUSIONS

The cases were exposed to extreme manganese load. Their symptomatology is probably identical to manganism. The role of ephedrone is presently unknown. Physicians must be aware of early signs of manganism in patients within social risk groups.

Parkinsonism caused by chronic usage of intravenous potassium permanganate

INTRODUCTION

Chronic overexposure to manganese (Mn) may cause neuronal degeneration. Manganese intoxication is well known to induce parkinsonism. Manganese intoxication may be associated with abnormal magnetic resonance (MR) imaging (abnormal signal hyperintensity in the globus pallidus and substantia nigra on T1-weighted images).

CASES

We report an unusual presentation of manganese intoxication due to administration of a combination of acetylsalicylic acid and ephedrine HCl, potassium permanganate, and vinegar melted in tap water and administered parenterally as a psychostimulant substance in 2 cases who developed symptoms resembling parkinsonism. Neurologic examination of both cases revealed disturbances of the extrapyramidal system and a characteristic "cock walk." Tremor was present in the first case, whereas it was lacking in the second one. Cranial MRI showed bilateral symmetric T1-weighted hyperintense patterns in the globus pallidus, probably because of manganese accumulation. Different levels of response to levodopa were reported in the literature; in our cases, there was no response to levodopa.

CONCLUSION

Chronic overexposure to manganese may cause an atypical form of parkinsonism associated with increased T1 signal in the basal ganglia on magnetic resonance imaging.

Direct effects of manganese compounds on dopamine and its metabolite Dopac: an in vitro study

Following combustion of fuel containing the additive methylcyclopentadienyl-manganese-tricarbonyl (MMT), manganese phosphate (MnPO(4)) and manganese sulfate (MnSO(4)) are emitted in the atmosphere. Manganese chloride (MnCl(2)), another Mn(2+) species, is widely used experimentally. Using rat striatal slices, we found that MnPO(4) decreased tissue and media dopamine (DA) and media Dopac (a DA metabolite) levels substantially more than either MnCl(2) or MnSO(4); antioxidants were partially protective. Also, both MnCl(2) and MnPO(4) (more potently) oxidized DA and Dopac even in the absence of tissue in the media, suggesting a direct interaction between Mn and DA/Dopac. Because aminochrome is a major oxidation product of DA, we next determined whether MnPO(4) will be more potent in forming aminochrome than MnCl(2) or MnSO(4) which, indeed, was the case. Thus, a potential additional mechanism for the neurotoxic effects of environmentally-relevant forms of Mn, MnPO(4) in particular, is the generation of reactive DA intermediates.

Adequacy and consistency of animal studies to evaluate the neurotoxicity of chronic low-level manganese exposure in humans

The adequacy of existing animal studies to understand the effects of chronic low-level manganese exposures in humans is unclear. Here, a collection of subchronic to chronic rodent and nonhuman primate studies was evaluated to determine whether there is a consistent dose-response relationship among studies, whether there is a progression of effects with increasing dose, and whether these studies are adequate for evaluating the neurotoxicity of chronic low-level manganese exposures in humans. Neurochemical and behavioral effects were compared along the axis of estimated internal cumulative manganese dose, independent of the route of exposure. In rodents, motor effects emerged at cumulative doses below those where occupationally exposed humans start to show motor deficits. The main neurochemical effects in rodents were an increase in striatal gamma-aminobutyric acid (GABA) concentration throughout the internal cumulative dose range of 18 to 5300 mg Mn/kg but a variable effect on striatal dopamine concentration emerging at internal cumulative doses above approximately 200 mg Mn/kg. Monkey studies showed motor deficits and effects on the globus pallidus at relatively low doses and consistent harmful effects on both the globus pallidus and the caudate and putamen at higher doses (> 260 mg Mn/kg). Internal cumulative manganese doses of animal studies extend more than two orders of magnitude (< 1 to 5300 mg Mn/kg) above the doses at which occupationally exposed humans show neurological dysfunction (10-15 mg Mn/kg). Since the animal data indicate that manganese neurotoxicity may be different at low compared to elevated exposures, most existing animal model studies might be of limited relevance for the risk assessment of chronic low-level manganese exposure to humans.

Effects of chronic manganese exposure on cognitive and motor functioning in non-human primates

Acute exposure to manganese is associated with complex behavioral/psychiatric signs that may include Parkinsonian motor features. However, little is known about the behavioral consequences of chronic manganese exposures. In this study, cynomolgus macaque monkeys were exposed to manganese sulfate (10-15 mg/kg/week) over an exposure period lasting 272+/-17 days. Prior to manganese exposure, animals were trained to perform tests of cognitive and motor functioning and overall behavior was assessed by ratings and by videotaped analyses. By the end of the manganese exposure period, animals developed subtle deficits in spatial working memory and had modest decreases in spontaneous activity and manual dexterity. In addition, stereotypic or compulsive-like behaviors such as compulsive grooming increased in frequency by the end of the manganese exposure period. Blood manganese levels measured at the end of the manganese exposure period ranged from 29.4 to 73.7 micro g/l (mean=55.7+/-10.8 (compared to levels of 5.1-14.2 micro g/l at baseline (mean=9.2+/-2.7)), placing them within the upper range of levels reported for human environmental, medical or occupational exposures. These results suggest that chronic exposure to levels of manganese achieved in this study may have detrimental effects on behavior, cognition and motor functioning.

Metals in motor neuron diseases

Degenerative processes within the nervous system are common features in disease entities such as dementia of Alzheimer type (DAT), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS). ALS is a neurodegenerative disease with unknown etiology; widespread muscle wasting and respiratory failure lead to death within a few years. Denervation can be detected with electromyography and axonal deterioration monitored by motor unit number estimates. Several suggestions about the cause of ALS have emerged but no solid theory has yet precipitated. Lead or mercury exposure has been suggested. Exposure data alone cannot support this connection. Alterations in metal kinetics may underlie the deterioration of motor function observed in patients with ALS. In this review the role of metals in motor neuron disease is discussed. Both classic studies on exposure and recent understanding of metal binding proteins are considered. Aspects of peak exposure and excretion are merged toward an understanding of metal dynamics in ALS. An overview of chemical and electrophysiological investigations is given in the context of neurodegeneration.

Is electric arc welding linked to manganism or Parkinson's disease?

Manganese and its inorganic compounds are widely used in many industries and have been accepted as occupational neurotoxins that have caused a distinct and disabling clinical entity, manganism, in several types of work, notably where exposure is by way of dust. There is inconclusive and inconsistent evidence that, in these occupations, subclinical neurological effects, detectable only by neurobehavioural studies, may be caused by low doses. This has prompted a re-evaluation of occupational exposure limits. Some countries, including the UK, already demand much higher levels of protection against exposure than 5 years ago. Welding is the most common source of occupational exposure as manganese is an essential component of steel and so its compounds are inevitable components of fume emitted from steel welding processes. There it is found in respirable particles, often as complex oxides (spinels), sometimes within a core protected by a silicon oxide shell - as distinct from the much simpler form of particle formed by disintegration in processes such as mining and ore milling where manganism has been diagnosed convincingly. Millions of workers are at risk of exposure to manganese-containing compounds in fumes from electric arc welding of steel. In recent years it has been asserted that neurological and neurobehavioural disorders may develop consequent to exposure to steel welding fumes and that employment as a welder is associated with the unusually early onset of Parkinson's disease. Causal relationships have been postulated. Welders have been recorded as having been exposed to high levels of manganese-containing fume, especially where they have worked in confined, unventilated spaces, although this appears from limited data to be the exception rather than the rule. Even then the dose received is generally less than in mining or ore crushing. When care is taken to exclude exposures from hardfacing and burning and cutting arc processes, where manganese may form a high percentage of the fume, manganese compounds usually form a relatively low percentage of the composition of welding fume particles, <2.0%, much outweighed by iron. Although these manganese-compound-containing welding fume particles are insoluble in water, the manganese compounds in particles that are retained in the alveoli may be absorbed, at least in part. Manganese concentrations in biological material samples in some exposed groups reflect this relative to unexposed workers. Some of the transfer systems for absorption and transport, including across the blood-brain barrier, are used in competition with iron which is present in abundance in welding fume. This may reduce absorption of manganese in welders and thus reduce the opportunity for sufficient doses to cause neurotoxicological consequences. Scrutiny of the literature covering the last 40 years has revealed only five cases that meet sufficient criteria for manganism to just cross the diagnostic threshold, and even then they carry a degree of doubt with them. This low incidence alone gives notice that welders have not been and are not at high risk of clinically apparent damage from exposure to manganese. If this needs to be further emphasised, there is the fact that the literature contains no confirmed cases of manganism in welders. Assertions of abnormal results in neurobehavioural studies of welders have raised the possibility of there being a subclinical form of manganism with loss of fine motor control as one of its features. While observations of such changes in workers in other industries have caused regulators in some countries to apply more stringent controls of exposure, as yet the results lack convincing consistency and there is no indication of any dose-effect relationship. If welding fume can have these motor effects it would be a heavy and perhaps career-ending blow to those affected. It would not be prudent to dismiss the warnings sounded by the results of studies of welders, no matter how flawed these investigations are, but wiser and better to act with vigour to reduce exposure and monitor the effectiveness of this additional protection whilst conducting high quality research to allow sound conclusions to be drawn as to whether there actually is a subclinical disorder. Idiopathic Parkinson's disease is a common disorder affecting 1-2% of those in the general population aged >65 years. It has been suggested, on flawed and contested evidence, not that welding causes the disease but rather that employment as a welder carries with it the risk of developing this disease at a younger age than if that trade had not been followed. Manganese in welding fume has been nominated as the neurotoxin. This may be biologically feasible if manganese destroys insufficient receptor cells to produce clinical manganism but sufficient to enhance the effects of a reduced supply of dopamine to give the manifestations of already developing idiopathic Parkinson's disease earlier in the course of destruction of the substantia nigra than if all receptors were intact.

Brain magnetic resonance imaging and manganese concentrations in red blood cells of smelting workers: search for biomarkers of manganese exposure

The MRI technique has been used in diagnosis of manganism in humans and non-human primates. This cross-sectional study was designed to explore whether the pallidal signal intensity in T1-weighted MRI correlated with Mn levels in the blood compartment among Mn-exposed workers and to understand to what extent the MRI signal could reflect Mn exposure. A group of 18 randomly selected male Mn-exposed workers of which 13 were smelting workers with high exposure (mean of airborne Mn in work place: 1.26 mg/m3; range: 0.31-2.93 mg/m3), and 5 power distribution control workers with low exposure (0.66 mg/m3 and 0.23-0.77 mg/m3) from a ferroalloy factory, and another group of 9 male subjects as controls from a non-smelting factory who were office or cafeteria workers (0.01 mg/m3 and 0-0.03 mg/m3) were recruited for neurological tests, MRI examination, and analysis of Mn in whole blood (MnB), plasma (MnP) or red blood cells (MnRBC). No clinical symptoms and signs of manganism were observed among these workers. MRI data showed average increases of 7.4% (p<0.05) and 16.1% (p<0.01) in pallidal index (PI) among low- and high-exposed workers, respectively, as compared to controls. Fourteen out of 18 Mn-exposed workers (78%) had intensified PI values, while this proportion was even higher (85%) among the high Mn-exposed workers. Among exposed workers, the PI values were significantly associated with MnRBC (r=0.55, p=0.02). Our data suggest that the workers exposed to airborne Mn, but without clinical symptoms, display an exposure-related, intensified MRI signal. The MRI, as well as MnRBC, may be useful in early diagnosis of Mn exposure.

The diagnosis of manganese-induced parkinsonism

Parkinsonism is a clinical syndrome consisting of tremor, bradykinesia, rigidity, gait, balance problems, in addition to various non-motor symptoms. There are many causes of parkinsonism such as neurodegenerative disease, drugs, vascular causes, structural lesions, infections, and toxicants. Parkinson's disease, or idiopathic parkinsonism, is the most common form of parkinsonism observed in the clinic. There is degeneration of the substantia nigra, pars compacta, which results in loss of striatal dopamine. Parkinson's disease is a slowly progressive condition in which there is a dramatic and sustained responsiveness to levodopa therapy. Manganese is an essential trace element that can be associated with neurotoxicity. Hypermanganism can occur in a variety of clinical settings. The clinical symptoms of manganese intoxication include non-specific complaints, neurobehavioral changes, parkinsonism, and dystonia. Although the globus pallidus is the main structure of damage, other basal ganglia areas can also be involved. MRI scans may show globus pallidus changes during (and for a short period after) exposure. Fluorodopa PET scans that assess the integrity of the substantia nigra dopaminergic system are abnormal in Parkinson's disease. However, these scans re-reported to be normal in a few cases studied with manganese-induced parkinsonism. The parkinsonism due to manganese may have some clinical features that occur less commonly in Parkinson's disease, such as kinetic tremor, dystonia, specific gait disturbances, and early mental, balance and speech changes. The clinical signs tend to be bilateral whereas Parkinson's disease begins on one side of the body. Patients with manganese-induced parkinsonism may be younger at the onset of the disease than with Parkinson's disease. Lastly, there appears to be a lack of response to levodopa therapy in manganese-induced parkinsonism. In summary it may be possible to differentiate manganese-induced parkinsonism from Parkinson's disease using clinical and imaging studies.

Neuroimaging in manganism

Neuroimaging such as magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) have been used in the last decade for investigating the neurotoxicolgy of manganese (Mn). Increased signal intensities on a T1-weighted image may reflect increased Mn deposits (e.g., due to exposure to Mn) but not necessarily manganism. In a biologically based dose-response model, our recent results strongly suggest that signal intensities in T1-weighted MRI reflect a target site dose. However, the threshold of signal intensity associated with clinical symptoms of manganism remains to be solved. Functional neuroimaging such as PET or SPECT examines the integrity of the nigrostriatal dopaminergic system, and thus is very important for the differential diagnosis of manganism. However, neuroimaging research should also aim at developing specific and sensitive parameters for manganism in Mn-exposed individuals.

Correlation of brain magnetic resonance imaging changes with pallidal manganese concentrations in rhesus monkeys following subchronic manganese inhalation

High-dose manganese exposure is associated with parkinsonism. Because manganese is paramagnetic, its relative distribution within the brain can be examined using magnetic resonance imaging (MRI). Herein, we present the first comprehensive study to use MRI, pallidal index (PI), and T(1) relaxation rate (R1) in concert with chemical analysis to establish a direct association between MRI changes and pallidal manganese concentration in rhesus monkeys following subchronic inhalation of manganese sulfate (MnSO(4)). Monkeys exposed to MnSO(4) at > or = 0.06 mg Mn/m(3) developed increased manganese concentrations in the globus pallidus, putamen, olfactory epithelium, olfactory bulb, and cerebellum. Manganese concentrations within the olfactory system of the MnSO(4)-exposed monkeys demonstrated a decreasing rostral-caudal concentration gradient, a finding consistent with olfactory transport of inhaled manganese. Marked MRI signal hyperintensities were seen within the olfactory bulb and the globus pallidus; however, comparable changes could not be discerned in the intervening tissue. The R1 and PI were correlated with the pallidal manganese concentration. However, increases in white matter manganese concentrations in MnSO(4)-exposed monkeys confounded the PI measurement and may lead to underestimation of pallidal manganese accumulation. Our results indicate that the R1 can be used to estimate regional brain manganese concentrations and may be a reliable biomarker of occupational manganese exposure. To our knowledge, this study is the first to provide evidence of direct olfactory transport of an inhaled metal in a nonhuman primate. Pallidal delivery of manganese, however, likely arises primarily from systemic delivery and not directly from olfactory transport.