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

Neurocognitive function in adult residents of a mining district in Mexico after reducing manganese exposure: Follow-up after 11 years

BACKGROUND

Little is known about the neurotoxic effects of chronic exposure to airborne Mn once exposure has been reduced. The environmentally exposed and the reference adult populations evaluated in 2002 were followed, after an environmental management program (EMP) was implemented to reduce the exposure in a mining district in Mexico.

OBJECTIVE

The aim of this study was to compare the association between exposure to Mn and neurocognitive performance in environmentally exposed and reference groups of adults before and after EMP implementation.

METHODS

In 2013, the same battery of neurocognitive tests used in the initial study (2002) was applied to 58 adults exposed to airborne Mn and 30 adults from the reference community. A cumulative exposure index (CEI) was estimated for the study population before and after the EMP. Categorical outcomes were analyzed using logistic regression, and the resulting ORs were compared between studies. Continuous outcomes were analyzed using linear regression. All models were adjusted for age, years of education, socioeconomic status and blood lead levels.

RESULTS

Exposed adults from the post-EMP study showed an improvement in fine motor and verbal regulation of motor skills (OR < 1) compared to the exposed adults from the pre-EMP study (OR > 1). In both pre- and post-studies, the exposed adults showed a deterioration in their dynamic organization of motor activity compared to the reference group (p < 0.05); however, they showed no significant change in attention and working-memory performance.

DISCUSSION

After four years of a significant reduction in airborne Mn levels resulting from EMP implementation, chronically exposed adults showed an improvement in fine motor and verbal regulation of motor skills; however, the remaining areas of their motor and cognitive functions remained impaired.

Manganese complexes and manganese-based metal-organic frameworks as contrast agents in MRI and chemotherapeutics agents: Applications and prospects

Manganese-based Metal-organic Frameworks (Mn-MOFs) represents a unique sub-class of MOFs with low toxicity, oxidative ability, and biocompatibility, which plays vital role in the application of this class of MOFs in medical field. Mn-MOFs show great potential in biomedical applications, and has been extensively studied as compared to other MOFs in transition metal series. They are important in medical applications because Mn(II) possess large electron spin number and longer electron relaxation time. They display fast water exchange rate and could be employed as a potential MRI contrast agent because of their strong targeting ability. Manganese complexes with different ligands also display prospective applications in area such as carrier for drug targeting in anti-tumor and antimicrobial therapy. In the review presented herewith, the application of Mn-based complexes and Mn-MOFs have been emphasized in the area such as imaging viz. MRI, multimodal imaging, antitumor activities such as chemodynamic therapy, photodynamic therapy, sonodynamic therapy and antimicrobial applications. Also, how rational designing and syntheses of targeted Mn-based complexes and Mn-MOFs can engender desired applications.

Impacts of a perinatal exposure to manganese coupled with maternal stress in rats: Maternal somatic measures and the postnatal growth and development of rat offspring

Psychological stress experienced by the mother during pregnancy has been associated with emotional and cognitive disorders in children such as depression and anxiety. Socioeconomically disadvantaged populations are vulnerable to adverse life experiences and can also be disproportionally exposed to environmental contaminants. To better understand the neurodevelopmental impacts of an environmental toxicant coupled with elevated psychological stress, we exposed pregnant rats to a series of perinatal stressors. Manganese (Mn), a neurotoxicant at excessive concentrations was delivered through drinking water (0, 2, or 4 mg/mL) from gestational day (GD) 7 to postnatal day (PND) 22. A variable stress paradigm was applied to half of the animals from GD13 to PND9. Measurements of somatic development and behavior were examined in the offspring at different developmental stages. No evidence of overt maternal toxicity was observed although the 4 mg/mL Mn-exposed dams gained less body weight during gestation compared to the other dams. Stress also reduced gestational maternal weight gain. Daily fluid consumption normalized for body weight was decreased in the Mn-exposed dams in a dose-dependent manner but was not altered by the stress paradigm. Maternal stress and/or Mn exposure did not affect litter size or viability, but pup weight was significantly reduced in the 4 mg/mL Mn-exposed groups on PNDs 9 through 34 when compared to the other offspring groups. The efficacy of the manipulations to increase maternal stress levels was determined using serum corticosterone as a biomarker. The baseline concentration was established prior to treatment (GD7) and levels were low and similar in all treatment groups. Corticosterone levels were elevated in the perinatal-stress groups compared to the no-stress groups, regardless of Mn exposure, on subsequent time points (GD16, PND9), but were only significantly different on GD16. An analysis of tissue concentrations revealed Mn was elevated similarly in the brain and blood of offspring at PND2 and at PND22 in a significant dose-dependent pattern. Dams also showed a dose-dependent increase in Mn concentrations in the brain and blood; the addition of stress increased the Mn concentrations in the maternal blood but not the brain. Perinatal stress did not alter the effects of Mn on the maternal or offspring somatic endpoints described here.

YAC128 mouse model of Huntington disease is protected against subtle chronic manganese (Mn)-induced behavioral and neuropathological changes

Manganese (Mn) is an essential micronutrient but excessive levels induce neurotoxic effects. Increasing evidence suggests a deficit of bioavailable Mn in Huntington disease (HD), an inherited neurodegenerative disease characterized by motor and cognitive disturbances. Previous studies have shown rescue of some molecular HD phenotypes by acute Mn exposure. This study simultaneously examined the potential for chronic Mn exposure to attenuate HD behavioral phenotypes, and for the HD genotype to offer protection against detrimental effects of chronic Mn exposure. In two independent studies a chronic Mn exposure paradigm was implemented in the YAC128 mouse model of HD and behavior was assessed at several timepoints. Study 1 exposed WT and YAC128 mice to twice weekly subcutaneous injections of 0, 5, 15, or 50 mg/kg MnCl[2] tetrahydrate from 12 to 32 weeks of age. A promising protective effect against motor coordination decline in 5 mg/kg MnCl[2] tetrahydrate-treated YAC128 mice was detected. Study 2 thus exposed WT and YAC128 mice to either 0 or 5 mg/kg MnCl[2] tetrahydrate from 12 to 52 weeks of age (with a partial randomized treatment crossover at 31 weeks). The same protective effect was not observed under these conditions at higher statistical power. We report subtle toxicological changes in exploratory behavior and total activity induced by chronic Mn exposure in WT mice only, despite similar total increases in brain Mn in WT and YAC128 mice. Further, chronic Mn treatment resulted in a 10-12 % decrease in striatal NeuN positive cell density in WT mice but not YAC128 mice, despite vehicle cell counts already being reduced compared to WT mice as expected for the HD genotype. The subtle changes observed in specific outcome measures, but not others, following long-term low-level Mn exposure in WT mice delineate the neurobehavioral and neuropathological effects at the threshold of chronic Mn toxicity. We conclude that these chronic low-dose Mn exposures do not significantly rescue behavioral HD phenotypes, but YAC2128 mice are protected against the subtle Mn-induced behavioral changes and decreased striatal neuron density observed in Mn-exposed WT mice.

Manganese-induced neurotoxicity and the potential protective effects of lipoic acid and Spirulina platensis

Manganese (Mn) is essential for many physiological processes; however, its excessive accumulation in the brain causes severe dysfunctions in the nervous system. Oxidative stress is thought to be involved in Mn-induced neurotoxicity. The aim of this study was to evaluate the neurotoxic effects of Mn and the potential protective effects of alpha lipoic acid (ALA) and Spirulina platensis (SP), each alone and in combination. Sixty-four male albino rats were divided into eight equal groups: group 1 was used as control, group 2 received saline, which used as a vehicle, group 3 received ALA (50 mg/kg/day), group 4 received SP (300 mg/kg/day), group 5 received Mn (74 mg/kg, 5 days/week), group 6 received Mn + ALA, group 7 received Mn + SP, group 8 received Mn + ALA + SP. Groups 6, 7 and 8 received the same previously mentioned doses. All treatments were orally gavaged for 8 weeks. Mn administration caused neurobehavioral changes, increases of brain and serum Mn and malondialdehyde (MDA), with decreased glutathione peroxidase (GPx), dopamine and acetylcholine levels. The co-treatment with ALA and SP revealed their ability to protect against oxidative damage, neurobehavioral and biochemical changes induced by Mn.

Acute effects of methcathinone and manganese in mice: A dose response study

An intravenously injectable illicit drug made by mixing pseudoephedrine, potassium permanganate, vinegar and water, yielding methcathinone (Mcat) and manganese (Mn), induces an extrapyramidal syndrome with parkinsonism, dystonia, gait and balance disorders similar to manganism. Although the cause of the syndrome is largely attributed to Mn, the interaction of the drug's individual components is not known and the role of Mcat is possibly underestimated. Aim of the present study was to analyze dose-dependent behavioral effects of the mixture and its two main active components Mcat and Mn in an acute setting and determine the lethal doses of each substance.

Three groups of C57BL/6 mice were injected intraperitoneally with (1) the drug mixture containing 10, 25, 50, 100 or 150 mg of Mcat and respectively 1.6, 3.8, 6.9, 17.1 and 22.6 mg of Mn per kilogram of body weight; (2) 10, 25, 50, 100, 150, 200 or 300 mg of racemic Mcat/kg of body weight; (3) MnCl₂ 10, 25 or 50 mg/kg of body weight. Locomotor activity of the animals, various signs and time of death were recorded.

Lower doses (10 and 25 mg/kg) of Mcat had a clear motor activity stimulating effect and this was clearly dose-dependent. High doses of Mcat produced epileptic seizures in 74% of the animals and became lethal with the highest doses. Similarly, the mixture had a clear dose-dependent stimulating effect and the higher doses became lethal. The LD₅₀ of the pseudoephedrine mixture was 110.2 mg of Mcat/kg and for pure Mcat 201.7 mg/kg. Mn did not prove to be lethal in doses up to 50 mg/kg, but had a strong dose dependent inhibitory effect on the animals’ behavior. Our data reveal that both Mn and Mcat have a significant role in the toxicity of the mixture.

Association of exposure to manganese and iron with striatal and thalamic GABA and other neurometabolites - Neuroimaging results from the WELDOX II study

OBJECTIVE

Magnetic resonance spectroscopy (MRS) is a non-invasive method to quantify neurometabolite concentrations in the brain. Within the framework of the WELDOX II study, we investigated the association of exposure to manganese (Mn) and iron (Fe) with γ-aminobutyric acid (GABA) and other neurometabolites in the striatum and thalamus of 154 men.

MATERIAL AND METHODS

GABA-edited and short echo-time MRS at 3T was used to assess brain levels of GABA, glutamate, total creatine (tCr) and other neurometabolites. Volumes of interest (VOIs) were placed into the striatum and thalamus of both hemispheres of 47 active welders, 20 former welders, 36 men with Parkinson's disease (PD), 12 men with hemochromatosis (HC), and 39 male controls. Linear mixed models were used to estimate the influence of Mn and Fe exposure on neurometabolites while simultaneously adjusting for cerebrospinal fluid (CSF) content, age and other factors. Exposure to Mn and Fe was assessed by study group, blood concentrations, relaxation rates R1 and R2* in the globus pallidus (GP), and airborne exposure (active welders only).

RESULTS

The median shift exposure to respirable Mn and Fe in active welders was 23μg/m3 and 110μg/m3, respectively. Airborne exposure was not associated with any other neurometabolite concentration. Mn in blood and serum ferritin were highest in active and former welders. GABA concentrations were not associated with any measure of exposure to Mn or Fe. In comparison to controls, tCr in these VOIs was lower in welders and patients with PD or HC. Serum concentrations of ferritin and Fe were associated with N-acetylaspartate, but in opposed directions. Higher R1 values in the GP correlated with lower neurometabolite concentrations, in particular tCr (exp(β)=0.87, p<0.01) and choline (exp(β)=0.84, p=0.04). R2* was positively associated with glutamate-glutamine and negatively with myo-inositol.

CONCLUSIONS

Our results do not provide evidence that striatal and thalamic GABA differ between Mn-exposed workers, PD or HC patients, and controls. This may be due to the low exposure levels of the Mn-exposed workers and the challenges to detect small changes in GABA. Whereas Mn in blood was not associated with any neurometabolite content in these VOIs, a higher metal accumulation in the GP assessed with R1 correlated with generally lower neurometabolite concentrations.

Manganese-Enhanced Magnetic Resonance Imaging and Studies of Rat Behavior: Transient Motor Deficit in Skilled Reaching, Rears, and Activity in Rats After a Single Dose of MnCl2

Manganese-enhanced magnetic resonance imaging (MEMRI) has been suggested to be a useful tool to visualize and map behavior-relevant neural populations at large scale in freely behaving rodents. A primary concern in MEMRI applications is Mn²⁺ toxicity. Although a few studies have specifically examined toxicity on gross motor behavior, Mn²⁺ toxicity on skilled motor behavior was not explored. Thus, the objective of this study was to combine manganese as a functional contrast agent with comprehensive behavior evaluation. We evaluated Mn²⁺ effect on skilled reach-to-eat action, locomotion, and balance using a single pellet reaching task, activity cage, and cylinder test, respectively. The tests used are sensitive to the pathophysiology of many neurological and neurodegenerative disorders of the motor system. The behavioral testing was done in combination with a moderate dose of manganese. Behavior was studied before and after a single, intravenous infusion of MnCl₂ (48 mg/kg). The rats were imaged at 1, 3, 5, 7, and 14 days following infusion. The results show that MnCl₂ infusion resulted in detectable abnormalities in skilled reaching, locomotion, and balance that recovered within 3 days compared with the infusion of saline. Because some tests and behavioral measures could not detect motor abnormalities of skilled movements, comprehensive evaluation of motor behavior is critical in assessing the effects of MnCl₂. The relaxation mapping results suggest that the transport of Mn²⁺ into the brain is through the choroid plexus-cerebrospinal fluid system with the primary entry point and highest relaxation rates found in the pituitary gland. Relaxation rates in the pituitary gland correlated with measures of motor skill, suggesting that altered motor ability is related to the level of Mn circulating in the brain. Thus, combined MEMRI and behavioral studies that both achieve adequate image enhancement and are also free of motor skills deficits are difficult to achieve using a single systemic dose of MnCl₂.

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.

Toxicology of metals and metalloids: Promising issues for future studies in environmental health and toxicology

The function and behavior of chemical elements in ecosystems and in human health probably comprise one of the most studied issues and a theme of great interest and fascination in science. Hot topics are emerging on an annual basis in this field. Bearing this in mind, some promising themes to explore in the field of metals and metalloids in the environment and in toxicology are highlighted and briefly discussed herein.

Effects of manganese exposure on visuoperception and visual memory in schoolchildren

BACKGROUND

Manganese (Mn) is an essential metal involved in multiple physiological functions. Environmental exposure to airborne Mn is associated with neurocognitive deficits in humans. Children, whose nervous system is in development, are particularly susceptible to Mn neurotoxicity.

OBJECTIVE

The objective of this study was to assess the association between Mn environmental exposure, and effects on visuoperception and visual memory in schoolchildren.

METHODS

We assessed schoolchildren between 7 and 11 years old, with similar socioeconomic status, from the mining district of Molango (n=148) and Agua Blanca (n=119, non-mining area) in Hidalgo state, Mexico. The Rey-Osterrieth Complex Figure (ROCF) test was used to assess visuoperception and short-term visual memory. Hair manganese (MnH) concentrations were determined. Linear regression models were constructed to estimate the associations between MnH and ROCF scores, adjusted for potential confounders.

RESULTS

The geometric mean MnH was nine times higher in schoolchildren from the Mn mining area (5.25μg/g) than in schoolchildren from the non-mining area (0.55μg/g). For the ROCF Copy trial, MnH was significantly associated with an increase in distortion errors (tangency, closure), angle errors, overtracing (partial overtracing). In the Immediate Recall trial, MnH was significantly associated with increased overtracing (partial overtracing) and omissions, and negatively associated with the number of perceptual drawn units, total score and percentage immediate recall.

CONCLUSIONS

MnH is associated with alterations in visuoperception and short-term visual memory in schoolchildren exposed to airborne Mn.

Review about the manganese speciation project related to neurodegeneration: An analytical chemistry approach to increase the knowledge about manganese related parkinsonian symptoms

Neurodegenerative diseases get a growing relevance for societies. But yet the complex multi-factorial mechanisms of these diseases are not fully understood, although it is well accepted that metal ions may play a crucial role. Manganese (Mn) is a transition metal which has essential biochemical functions but from occupational exposure scenarios it appeared that Mn can cause severe neurological damage. This "two-faces"-nature of manganese initiated us to start a project on Mn-speciation, since different element species are known to exhibit different impacts on health. A summary about the step-wise developments and findings from our working group was presented during the annual conference of the German trace element society in 2015. This paper summarizes now the contribution to this conference. It is intended to provide a complete picture of the so far evolved puzzle from our studies regarding manganese, manganese speciation and metabolomics as well as Mn-related mechanisms of neural damage. Doing so, the results of the single studies are now summarized in a connected way and thus their interrelationships are demonstrated. In short terms, we found that Mn-exposure leads to an increase of low molecular weight Mn compounds, above all Mn-citrate complex, which gets even enriched across neural barriers (NB). At a Mn serum concentration between 1.5 and 1.9μg/L a carrier switch from Mn-transferrin to Mn-citrate was observed. We concluded that the Mn-citrate complex is that important Mn-carrier to NB which can be found also beyond NB in human cerebrospinal fluid (CSF) or brain of exposed rats. In brain of Mn-exposed rats manganese leads to a decreased iron (Fe) concentration, to a shift from Fe(III) to Fe(II) after long term exposure and thus to a shift toward oxidative stress. This was additionally supported by an increase of markers for oxidative stress, inflammation or lipid peroxidation at increased Mn concentration in brain extracts. Furthermore, glutamate and acetylcholineesterase were elevated and many metabolite concentrations were significantly changed.

Modeling and estimating manganese concentrations in rural households in the mining district of Molango, Mexico

Airborne manganese (Mn) is considered the most hazardous route of exposure since Mn particles can enter into the body through the lung and may access the brain directly through olfactory uptake, thereby bypassing homeostatic excretory mechanisms. Environmental indoor and outdoor manganese concentrations in PM2.5 were monitored in ten rural households from two communities of Hidalgo, Mexico, from 2006 to 2007. Indoor and outdoor air samples of PM2.5 were collected using MiniVol samplers, and Mn concentrations in the filters were measured using proton-induced X-ray emission (PIXE). An adjusted generalized linear mixed model was applied and then used for estimating indoor concentrations in non-monitored households. Our monitoring results showed a higher daily average concentration of indoor PM2.5 vs. outdoor PM2.5 (46.4 vs. 36.2 μg/m(3), respectively); however, manganese concentration in PM2.5 indoor and outdoor was 0.09 μg/m(3) in both sceneries. Predictor variables of indoor Mn concentration were outdoor Mn concentration (64.5% increase per 0.1 μg/m(3) change in Mn) and keeping the windows open (4.2% increase). Using these predictors, the average estimated indoor Mn concentration in PM2.5 was 0.07 μg/m(3) (SD = 0.05). Our results confirm the direct effect of outdoor Mn levels, opening house windows, and the distance to the mining chimney in indoor Mn levels in houses.

Manganese Toxicity Upon Overexposure: a Decade in Review

Exposure to manganese (Mn) causes clinical signs and symptoms resembling, but not identical to, Parkinson's disease. Since our last review on this subject in 2004, the past decade has been a thriving period in the history of Mn research. This report provides a comprehensive review on new knowledge gained in the Mn research field. Emerging data suggest that beyond traditionally recognized occupational manganism, Mn exposures and the ensuing toxicities occur in a variety of environmental settings, nutritional sources, contaminated foods, infant formulas, and water, soil, and air with natural or man-made contaminations. Upon fast absorption into the body via oral and inhalation exposures, Mn has a relatively short half-life in blood, yet fairly long half-lives in tissues. Recent data suggest Mn accumulates substantially in bone, with a half-life of about 8-9 years expected in human bones. Mn toxicity has been associated with dopaminergic dysfunction by recent neurochemical analyses and synchrotron X-ray fluorescent imaging studies. Evidence from humans indicates that individual factors such as age, gender, ethnicity, genetics, and pre-existing medical conditions can have profound impacts on Mn toxicities. In addition to body fluid-based biomarkers, new approaches in searching biomarkers of Mn exposure include Mn levels in toenails, non-invasive measurement of Mn in bone, and functional alteration assessments. Comments and recommendations are also provided with regard to the diagnosis of Mn intoxication and clinical intervention. Finally, several hot and promising research areas in the next decade are discussed.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

Subacute manganese exposure in rats is a neurochemical model of early manganese toxicity

Manganese (Mn) is an essential trace element, but excess exposure leads to accumulation in biological tissues, including the brain. Chronically high Mn levels in the brain are neurotoxic and can result in a progressive, irreversible neurological disorder known as manganism. Manganism has signs and symptoms similar to, but distinguishable from idiopathic Parkinson's disease, which include both psychological and motor disturbances. Evidence suggests that Mn exposure impacts neurotransmitter levels in the brain. However, it remains unclear if subacute, low-level Mn exposure resulted in alterations in neurotransmitter systems with concomitant behavioral deficits. The current study used high performance liquid chromatography to quantify neurotransmitter levels in rat striatum (STR), substantia nigra (SN), and hippocampus (HP). Subacute Mn exposure via i.p. injection of 15mg Mn/kg as MnCl2 caused significantly increased dopamine (DA) levels in the STR. The enhancement was accompanied by significantly elevated levels of the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the STR. In addition, levels of HVA were significantly increased in the SN and HP. These data indicate that subacute, low-level Mn exposure disrupts multiple neurotransmitter systems in the rat brain which may be responsible, in part, for observed locomotor deficits.

Manganese-induced atypical parkinsonism is associated with altered Basal Ganglia activity and changes in tissue levels of monoamines in the rat

Manganese neurotoxicity is associated with motor and cognitive disturbances known as Manganism. However, the mechanisms underlying these deficits remain unknown. Here we investigated the effects of manganese intoxication on motor and non-motor parkinsonian-like deficits such as locomotor activity, motor coordination, anxiety and “depressive-like” behaviors. Then, we studied the impact of this intoxication on the neuronal activity, the globus pallidus (GP) and subthalamic nucleus (STN). At the end of experiments, post-mortem tissue level of the three monoamines (dopamine, norepinephrine and serotonin) has been determined. The experiments were carried out in adult Sprague-Dawley rats, daily treated with MnCl₂ (10 mg/kg/, i.p.) for 5 weeks. We show that manganese progressively reduced locomotor activity as well as motor coordination in parallel with the manifestation of anxiety and “depressive-like” behaviors. Electrophysiological results show that, while majority of GP and STN neurons discharged regularly in controls, manganese increased the number of GP and STN neurons discharging irregularly and/or with bursts. Biochemical results show that manganese significantly decreased tissue levels of norepinephrine and serotonin with increased metabolism of dopamine in the striatum. Our data provide evidence that manganese intoxication is associated with impaired neurotransmission of monoaminergic systems, which is at the origin of changes in basal ganglia neuronal activity and the manifestation of motor and non-motor deficits similar to those observed in atypical Parkinsonism.

Golgi phosphoprotein 4 (GPP130) is a sensitive and selective cellular target of manganese exposure

Chronic elevated exposure to manganese (Mn) is associated with neurocognitive and fine motor deficits in children. However, relatively little is understood about cellular responses to Mn spanning the transition between physiologic to toxic levels of exposure. Here, we investigated the specificity, sensitivity, and time course of the Golgi Phosphoprotein 4 (GPP130) response to Mn exposure in AF5 GABAergic neuronal cells, and we determined the extent to which GPP130 degradation occurs in brain cells in vivo in rats subchronically exposed to Mn. Our results show that GPP130 degradation in AF5 cells was specific to Mn, and did not occur following exposure to cobalt, copper, iron, nickel, or zinc. GPP130 degradation occurred without measurable increases in intracellular Mn levels and at Mn exposures as low as 0.54 µM. GPP130 protein was detectable by immunofluorescence in only ∼15-30% of cells in striatal and cortical rat brain slices, and Mn-exposed animals exhibited a significant reduction in both the number of GPP130-positive cells, and the overall levels of GPP130 protein, demonstrating the in vivo relevance of this Mn-specific response within the primary target organ of Mn toxicity. These results provide insight into specific mechanism(s) of cellular Mn regulation and toxicity within the brain, including the selective susceptibility of cells to Mn cytotoxicity.

Repeated simultaneous cortical electrophysiological and behavioral recording in rats exposed to manganese-containing nanoparticles

Male Wistar rats wearing chronically implanted cortical electrodes were exposed to Mn-containing nanoparticles via the airways for 8 weeks following a 2-week pre-exposure period. The rats' cortical electrical activity and open field motility was recorded simultaneously, in weekly repetitions. It was supposed that this technique can provide better insight in the development of Mn-induced CNS damage. Decreased motility (less distance covered, longer periods of immobility) and increased total power of cortical electrical activity developed in parallel in the first 4-5 weeks of treatment but showed little change afterwards. Both the behavioral and the electrophysiological effect were in fair correlation with the rats' internal Mn exposure determined from brain samples. The results confirmed the non-linear dose- and time-dependence of Mn effects suggested by previous studies. Repeated simultaneous behavioral and electrophysiological recording during a longer treatment with neurotoxic metals (or other xenobiotics) seems to be a promising method.

Manganese mixture inhalation is a reliable Parkinson disease model in rats

Manganese (Mn) is an essential trace metal. Regardless of its essentiality, it has been reported that the overexposure causes neurotoxicity manifested as extrapyramidal symptoms similar to those observed in Parkinson disease (PD). Recently, our group reported that mice that inhaled for 5 months the mixture of manganese chloride (MnCl(2)) and manganese acetate Mn(OAc)(3) developed movement abnormalities, significant loss of substantia nigra compacta (SNc) dopaminergic neurons, dopamine depletion and improved behavior with l-DOPA treatment. However, this model has only been characterized in mice. In order to have a well-supported and generalizable model in rodents, we used male Wistar rats that inhaled a mixture of 0.04 M MnCl(2) and 0.02 M Mn(OAc)(3), 1h three times a week for 6 months. Before Mn exposure, animals were trained to perform motor tests (Beam-walking and Single-pellet reaching tasks) and were evaluated each week after the exposure. The mixture of MnCl(2)/Mn(OAc)(3) caused alterations in the motor tests, 75.95% loss of SNc dopaminergic neurons, and no cell alterations in Globus Pallidus or striatum. With these results we conclude that the inhalation of the mixture of Mn compounds is a useful model in rodents for the study of PD.

Emergency Do Not Consume/Do Not Use concentrations for potassium permanganate in drinking water

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.

Update on a Pharmacokinetic-Centric Alternative Tier II Program for MMT-Part II: Physiologically Based Pharmacokinetic Modeling and Manganese Risk Assessment

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.

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.

A pilot study with simultaneous recording of changes in motility and cortical electrical activity of rats during four weeks of oral manganese exposure

Manganese as an environmental neurotoxicant can cause oral exposure. Six rats were equipped with a connector "crown", allowing repeated recording of electrocorticogram (ECoG) with simultaneous recording of motor activity in an open field box. Weekly one 30-min recording session was held, and after two control sessions, four of the six rats had 2.5 mg/ml manganese chloride in their drinking water. The treated rats showed higher motility during the exposure period than the untreated ones; and substantially decreased total ECoG power without marked change the spectrum. The changes of both motility and ECoG were correlated to the individual brain Mn levels, and the activity decrease during a session was correlated to the total ECoG power. These effects can be likened to early adult manganism and to symptoms of children exposed to Mn via drinking water. Repeated simultaneous recording of open field motility and spontaneous cortical activity seems suitable to detect early electrophysiological and behavioral effects of an oral neurotoxic exposure.

Environmental exposure to manganese and motor function of children in Mexico

OBJECTIVES

Occupational manganese (Mn) exposure has been associated with motor deficits in adult workers, but data on the potential effects of environmental exposure to Mn on the developing motor function for a children population is scarce. The aim of this study was to evaluate the association between exposure to Mn and motor function of school aged children.

METHODS

We conducted a cross-sectional study selecting 195 children (100 exposed and 95 unexposed) between 7 and 11 years old. The following tests were used to evaluate the motor function: Grooved pegboard, finger tapping, and Santa Ana test. Mn exposure was assessed by blood (MnB) and hair concentrations (MnH). We constructed linear regression models to evaluate the association between exposure to Mn and the different test scores adjusting for age, sex, maternal education, hemoglobin and blood lead.

RESULTS

The median concentration of MnH and MnB was significantly higher in exposed (12.6 μg/g and 9.5 μg/L) compared to unexposed children (0.6 μg/g and 8.0 μg/L). The exposed children on average performed the grooved pegboard test faster, but made more errors, although these results did not reach statistical significance with neither one of the Mn exposure biomarkers. MnB showed an inverse association on the execution of the finger tapping test (average in 5 trials β -0.4, p=0.02), but no association was observed with MnH.

CONCLUSIONS

A subtle negative association of Mn exposure on motor speed and coordination was shown. In adults, the main effect of environmental Mn exposure has been associated with motor skills, but these results suggest that such alterations are not the main effect on children.

Welding fumes from stainless steel gas metal arc processes contain multiple manganese chemical species

Fumes from a group of gas metal arc welding (GMAW) processes used on stainless steel were generated using three different metal transfer modes and four different shield gases. The objective was to identify and measure manganese (Mn) species in the fumes, and identify processes that are minimal generators of Mn species. The robotic welding system was operated in short-circuit (SC) mode (Ar/CO2 and He/Ar), axial spray (AXS) mode (Ar/O2 and Ar/CO2), and pulsed axial-spray (PAXS) mode (Ar/O2). The fumes were analyzed for Mn by a sequential extraction process followed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis, and by X-ray diffraction (XRD). Total elemental Mn, iron (Fe), chromium (Cr) and nickel (Ni) were separately measured after aqua regia digestion and ICP-AES analysis. Soluble Mn2+, Fe2+, Fe3+, and Ni2+ in a simple biological buffer (phosphate-buffered saline) were determined at pH 7.2 and 5.0 after 2 h incubation at 37 C by ion chromatography. Results indicate that Mn was present in soluble form, acid-soluble form, and acid-soluble form after reduction by hydroxylamine, which represents soluble Mn0 and Mn2+ compounds, other Mn2+ compounds, and (Mn3+ and Mn4+) compounds, respectively. The dominant fraction was the acid-soluble Mn2+ fraction, but results varied with the process and shield gas. Soluble Mn mass percent in the fume ranged from 0.2 to 0.9%, acid-soluble Mn2+ compounds ranged from 2.6 to 9.3%, and acid plus reducing agent-soluble (Mn3+ and Mn4+) compounds ranged from 0.6 to 5.1%. Total Mn composition ranged from 7 to 15%. XRD results showed fumes had a crystalline content of 90-99% Fe3O4, and showed evidence of multiple Mn oxides, but overlaps and weak signals limited identification. Small amounts of the Mn2+ in the fume (<0.01 to ≈ 1% or <0.1 to ≈ 10 microg ml(-1)) and Ni2+ (<0.01 to ≈ 0.2% or <0.1 to ≈ 2 mg ml(-1)) ions were found in biological buffer media, but amounts were highly dependent on pH and the welding process. Mn generation rates for the fractions were tabulated, and the influence of ozone is discussed. The conclusions are that exposures to welding fumes include multiple Mn species, both soluble and insoluble, and that exposures to Mn species vary with specific processes and shield gases.

Manganese accumulation in the CNS and associated pathologies

Manganese (Mn) is an essential metal for life. It is a key constituent of clue enzymes in the central nervous system, contributing to antioxidant defenses, energetic metabolism, ammonia detoxification, among other important functions. Until now, Mn transport mechanisms are partially understood; however, it is known that it shares some mechanisms of transport with iron. CNS is susceptible to Mn toxicity because it possesses mechanisms that allow Mn entry and favor its accumulation. Cases of occupational Mn exposure have been extensively reported in the literature; however, there are other ways of exposure, such as long-term parental nutrition and liver failure. Manganism and hepatic encephalopathy are the most common pathologies associated with the effects of Mn exposure. Both pathologies are associated with motor and psychiatric disturbances, related in turn to mechanisms of damage such as oxidative stress and neurotransmitters alterations, the dopaminergic system being one of the most affected. Although manganism and Parkinson's disease share some characteristics, they differ in many aspects that are discussed here. The mechanisms for Mn transport and its participation in manganism and hepatic encephalopathy are also considered in this review. It is necessary to find an effective therapeutic strategy to decrease Mn levels in exposed individuals and to treat Mn long term effects. In the case of patients with chronic liver failure it would be worthwhile to test a low-Mn diet in order to ameliorate symptoms of hepatic encephalopathy possibly related to Mn accumulation.

Manganese-enhanced magnetic resonance imaging

Manganese-enhanced magnetic resonance imaging (MEMRI) relies on contrasts that are due to the shortening of the T (1) relaxation time of tissue water protons that become exposed to paramagnetic manganese ions. In experimental animals, the technique combines the high spatial resolution achievable by MRI with the biological information gathered by tissue-specific or functionally induced accumulations of manganese. After in vivo administration, manganese ions may enter cells via voltage-gated calcium channels. In the nervous system, manganese ions are actively transported along the axon. Based on these properties, MEMRI is increasingly used to delineate neuroanatomical structures, assess differences in functional brain activity, and unravel neuronal connectivities in both healthy animals and models of neurological disorders. Because of the cellular toxicity of manganese, a major challenge for a successful MEMRI study is to achieve the lowest possible dose for a particular biological question. Moreover, the interpretation of MEMRI findings requires a profound knowledge of the behavior of manganese in complex organ systems under physiological and pathological conditions. Starting with an overview of manganese pharmacokinetics and mechanisms of toxicity, this chapter covers experimental methods and protocols for applications in neuroscience.

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.

Intellectual function in Mexican children living in a mining area and environmentally exposed to manganese

BACKGROUND

Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children.

OBJECTIVE

This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children.

METHODS

Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure.

RESULTS

Exposed children had significantly higher median values for MnH (12.6 μg/g) and MnB (9.5 μg/L) than did nonexposed children (0.6 μg/g and 8.0 μg/L, respectively). MnH was inversely associated with Verbal IQ [β = -0.29; 95% confidence interval (CI), -0.51 to -0.08], Performance IQ (β = -0.08; 95% CI, -0.32 to 0.16), and Total Scale IQ (β = -0.20; 95% CI, -0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants.

CONCLUSIONS

The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.

Preweaning manganese exposure causes hyperactivity, disinhibition, and spatial learning and memory deficits associated with altered dopamine receptor and transporter levels

Epidemiological studies in children have reported associations between elevated dietary manganese (Mn) exposure and neurobehavioral and neurocognitive deficits. To better understand the relationship between early Mn exposure and neurobehavioral deficits, we treated neonate rats with oral Mn doses of 0, 25, or 50 mg Mn/kg/day over postnatal day (PND) 1-21, and evaluated behavioral performance using open arena (PND 23), elevated plus maze (PND 23), and 8-arm radial maze (PND 33-46) paradigms. Brain dopamine D1 and D2-like receptors, and dopamine transporter (DAT) densities were determined on PND 24, and blood and brain Mn levels were measured to coincide with behavioral testing (PND 24, PND 36). Preweaning Mn exposure caused hyperactivity and behavioral disinhibition in the open arena, but no altered behavior in the elevated plus maze. Manganese-exposed males committed significantly more reference and marginally more working errors in the radial arm maze compared to controls. Fewer Mn exposed males achieved the radial maze learning criterion, and they required more session days to reach it compared to controls. Manganese-exposed animals also exhibited a greater frequency of stereotypic response strategy in searching for the baited arms in the maze. These behavioral and learning deficits were associated with altered expression of the dopamine D1 and D2 receptors and the DAT in prefrontal cortex, nucleus accumbens, and dorsal striatum. These data corroborate epidemiological studies in children, and suggest that exposure to Mn during neurodevelopment significantly alters dopaminergic synaptic environments in brain nuclei that mediate control of executive function behaviors, such as reactivity and cognitive flexibility.

Multi-dose-route, multi-species pharmacokinetic models for manganese and their use in risk assessment

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.

From manganism to manganese-induced parkinsonism: a conceptual model based on the evolution of exposure

Manganism is a distinct medical condition from Parkinson's disease. Manganese exposure scenarios in the last century generally have changed from the acute, high-level exposure conditions responsible for the occurrence of manganism to chronic exposure to much lower levels. Such chronic exposures may progressively extend the site of manganese deposition and toxicity from the globus pallidus to the entire area of the basal ganglia, including the substantia nigra pars compacta involved in Parkinson's disease. The mechanisms of manganese neurotoxicity from chronic exposure to very low levels are not well understood, but promising information is based on the concept of susceptibility that may place individuals exposed to manganese at a higher risk for developing Parkinsonian disturbances. These conditions include mutations of genes which play important pathogenetic roles in both Parkinsonism and in the regulation of manganese transport and metabolism. Liver function is also important in manganese-related neurotoxicity and sub-clinical impairment may increase the risk of Parkinsonism. The purpose and scope of this report are to explore the literature concerning manganese exposure and potential subclinical effects and biological pathways, impairment, and development of diseases such as Parkinsonism and manganism. Inhalation and ingestion of manganese will be the focus of this report.

Effect of prenatal manganese intoxication on [(3)H]glucose uptake in the brain of rats lesioned as neonates with 6-hydroxydopamine

In the present study we examined the effects of prenatal manganese (Mn) intoxication on [(3)H]glucose uptake in the brain of rats lesioned as neonates with 6-hydroxydopamine (6-OHDA). MnCl(2) . 4H(2)O (10,000 ppm) was added to the drinking water of pregnant Wistar rats for the duration of pregnancy. On the day of parturition, Mn was discontinued as an additive to the drinking water. The control group consisted of rats that consumed water without Mn. Three days after birth, rats in both groups (control and Mn) were pretreated with desipramine hydrochloride (20 mg/kg) and pargyline hydrochloride (50 mg/kg) and injected bilaterally icv with one of three doses of 6-OHDA hydrobromide (15 mug, 30 mug or 67 mug base form in saline on each side) or with saline (control). 6-[(3)H]-D-glucose (500 muCi/kg, ip) was administered to male offspring in adulthood; after 15 min, brain specimens were taken (frontal cortex, hippocampus, striatum, thalamus with hypothalamus, pons and cerebellum) for determination of radioactivity in a liquid scintillation counter. Low dose 6-OHDA (15 mug icv) increased [(3)H]glucose uptake in all brain regions (p < 0.05) in both control and Mn-intoxicated animals. In rats lesioned with a moderate dose of 6-OHDA (30 mug icv), [(3)H]glucose uptake was unaltered in both control and Mn-exposed rats. High dose 6-OHDA (67 mug icv) reduced [(3)H]glucose uptake in all brain regions of Mn-exposed rats (except for cerebellum) compared with the saline group (all, p < 0.05). There was no change in regional brain uptake of [(3)H]glucose in control rats. In conclusion, this study shows that mild neuronal insult (15 mug icv 6-OHDA) increased glucose uptake in the brain while severe damage (concomitant 60 mug icv 6-OHDA and Mn treatment) significantly diminished this process.

Inhalation of divalent and trivalent manganese mixture induces a Parkinson's disease model: immunocytochemical and behavioral evidences

The present study investigates the effects of divalent and trivalent manganese (Mn(2+)/Mn(3+)) mixture inhalation on mice to obtain a novel animal model of Parkinson disease (PD) inducing bilateral and progressive cell death in the substantia nigra compacta (SNc) and correlating these alterations with motor disturbances. CD-1 male mice inhaled a mixture of 0.04 M manganese chloride (MnCl(2)) and manganese acetate (Mn(OAc)(3)), 1 h twice a week for 5 months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. By doing this, overall behavior was assessed by ratings and by videotaped analyses; by the end of Mn exposure period, animals were killed. The mesencephalon was processed for tyrosine hydroxylase (TH) immunocytochemistry. After 5 months of Mn mixture inhalation, mice developed evident deficits in their motor performance manifested as akinesia, postural instability and action tremor. SNc of the Mn-exposed animals showed an important decrease (67.58%) in the number of TH-immunopositive neurons. Our data provide evidence that MnCl(2) and Mn(OAc)(3) mixture inhalation produces similar morphological and behavioral alterations to those observed in PD providing a useful experimental model for the study of this neurodegenerative disease.

Cerebrospinal fluid to brain transport of manganese in a non-human primate revealed by MRI

Manganese overexposure in non-human primates and humans causes a neurodegenerative disorder called manganism thought to be related to an accumulation of the metal in the basal ganglia. Here, we assess changes in the concentration of manganese in regions of the brain of a non-human primate (the common marmoset, Callithrix jacchus) following four systemic injections of 30 mg/kg MnCl2 H2O in the tail vein using T1-weighted magnetic resonance imaging (MRI) and compare these to changes in the rat following the same exposure route and dose. The doses were spaced 48 h apart and we imaged the animals 48 h after the final dose. We find that marmosets have significantly larger T1-weighted image enhancements in regions of the brain compared to rats, notably in the basal ganglia and the visual cortex. To confirm this difference across species reflects actual differences in manganese concentrations and not variations in the MRI properties of manganese, we measured the longitudinal relaxivity of manganese (chi1) in the in vivo brain and found no significant species' difference. The high manganese uptake in the marmoset basal ganglia and visual cortex can be explained by CSF-brain transport from the large lateral ventricles and we confirm this route of uptake with time-course MRI during a tail-vein infusion of manganese. There is also high uptake in the substructures of the hippocampus that are adjacent to the ventricles. The large manganese accumulation in these structures on overexposure may be common to all primates, including humans.

Animal models of BMAA neurotoxicity: a critical review

Of all the molecules reported to have toxicological effects, BMAA (beta-methylamino alanine) stands out as having the most checkered past. In the late 1960's it was reported to be a toxic component of the cycad flour consumed by Chamorros on Guam which caused the high incidence of amyotrophic lateral sclerosis (ALS) in Guam, that was associated with a Parkinson's disease-like dementia complex (ALS-PDC). However, because ALS-PDC is a slow onset disease, manifesting itself as long as 30 years following exposure to the putative neurotoxin, and only acute toxic effects of BMAA were observed in animal studies, interest in BMAA waned. A seminal study by Spencer et al., in 1987 showing neurological impairments with long-term BMAA-fed monkeys revived the hypothesis that BMAA could cause ALS-PDC. However, the amounts of BMAA used in that study were viewed as being the equivalent of a person consuming their body weight of cycad flour every day. Again, the BMAA hypothesis was discarded. Recently a third iteration of the BMAA hypothesis has been proposed. It is based on the discovery of a novel dietary source of BMAA via biomagnification of BMAA in flying foxes, once consumed in great amounts by Chamorros. Also, reports that BMAA can be incorporated into plant and animal proteins, a heretofore unrecognized dietary source of BMAA, further solidified this new hypothesis. However, once again this hypothesis has its detractors and it remains controversial. This manuscript critically evaluates in vivo studies directed at establishing an animal model of BMAA-induced ALS-PDC and their implications for this hypothesis.

Biomarkers of Mn exposure in humans

BACKGROUND

Studies have reported associations between manganese (Mn) exposures and Mn levels in blood and urine, though the suitability of these biological measures as biomarkers of exposure is not well known.

METHODS

We evaluated whether whole blood, plasma, and urine Mn levels reflect exposures in occupationally exposed humans.

RESULTS

In active ferroalloy workers, blood Mn was associated with total air Mn levels in subjects currently exposed to low (median = 0.42 microg/m(3), P = 0.009) and moderate (median = 4.2 microg/m(3), P = 0.007) air Mn levels, but not in workers exposed to the highest Mn levels (median = 292 microg/m(3), P = 0.31). In bridge welders blood Mn (P < 0.01), but not plasma or urine Mn was significantly associated with their cumulative respiratory exposure index. In welders, approximately 6% (range approximately 3-9%) of whole blood Mn was contained in the plasma fraction, though there was no association between whole blood and plasma Mn levels (Pearson's R = 0.258, P = 0.12). In contrast, in fresh whole blood samples spiked with Mn ex vivo approximately 80% or more of added Mn partitioned in the plasma, while only approximately 20% or less partitioned in the cellular fraction.

CONCLUSIONS

These data suggest a complex and limited relationship between exposure and blood Mn levels that may depend upon exposure attributes and the latency of blood sampling relative to exposure; plasma and urine Mn appear to be of little utility as exposure biomarkers. This underscores the need to fully characterize and validate these or other biomarkers for use in constructing appropriate exposure metrics and determining exposure-effect relationships.

From lead to manganese through mercury: mythology, science, and lessons for prevention

BACKGROUND

Lead (Pb), mercury (Hg), and manganese (Mn) are well-known neurotoxic metals. The knowledge of toxicity was developed through an extensive amount of research, starting with lead and mercury and proceeding today with manganese. Unfortunately, the consequent implementation of preventive measures was generally delayed, causing important negative effects to the exposed populations.

METHODS

A review and historical reconstruction of the research development that yielded modern understanding of lead and mercury neurotoxicity was conducted to derive useful lessons for the prevention of manganese neurotoxicity.

RESULTS

Medieval alchemists named planets and metals from gods since they were already aware of the toxicity and the adverse effects caused by lead and mercury. Historical lessons learned from these two metals may help to avoid the repetition of further mistakes regarding other neurotoxic metals like manganese. The knowledge and experience on the toxicokinetics and toxicodynamics of lead and mercury is useful and valuable to identify a proper approach to "safe" exposure levels for manganese.

CONCLUSIONS

Further information is still needed on the early neurotoxic and neurobehavioral effects after prolonged exposure to very low doses of lead, mercury, and manganese. Nevertheless, according to the precautionary principle, effective preventive measures should be already undertaken to prevent the onset of more severe health effects in the population. This is the most important lesson to be learned and applied from more than 30 years of occupational and environmental neurotoxicology of metals.

Low-level manganese exposure alters glutamate metabolism in GABAergic AF5 cells

Recent studies have suggested that the globus pallidus may be a particularly sensitive target of manganese (Mn), however, in vitro studies of the effects of Mn on GABAergic neurons have been restricted by the lack of a cell model expressing GABAergic properties. Here, we investigated the effects of low-level Mn treatment on cellular GABA and glutamate metabolism using the newly characterized AF5 rat neural-derived cell line, which displays GABAergic properties during culture in vitro. Intracellular GABA and glutamate levels were measured along with measurement of the release of GABA and glutamate into the culture medium, glutamine uptake from the culture medium, and the specific effects of Mn on the enzymes directly responsible for the synthesis and degradation of GABA, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T). Our results demonstrate that Mn had no effect on the activities of GAD or GABA-T. Similarly, low-level Mn treatment of AF5 cultures had only a small effect on intracellular GABA levels (114% of control) and no effect on the release of GABA. In contrast, intracellular and extracellular glutamate levels were enhanced to 170 and 198% of control during Mn treatment, respectively, while extracellular glutamine decreased to 73% of controls. Together, these results suggest that glutamate homeostasis may be preferentially affected over GABA in AF5 cells during low-level Mn treatment, suggesting a novel mechanism by which Mn-induced excitotoxicity might arise.