Manganese deposition in the globus pallidus in patients with biliary atresia

Brain imaging in children with neonatal cholestatic liver disease: A systematic review

AIM

To determine if children with neonatal cholestatic liver disease had concurrent and later findings on brain imaging studies that could be attributed and the cholestasis to contribute to the understanding of the impaired neuropsychological development.

METHODS

Ovid MEDLINE and EMBASE were searched on July 21, 2022, and updated on March 26, 2023. Studies with children under 18 years of age with neonatal cholestasis and a brain scan at the time of diagnosis or later in life were included. Excluded studies were non-English, non-human, reviews or conference abstracts. Data were extracted on demographics, brain imaging findings, treatment and outcome. The results were summarised by disease categories. Risk of bias was assessed using JBI critical appraisal tools.

RESULTS

The search yielded 12 011 reports, of which 1261 underwent full text review and 89 were eligible for inclusion. Haemorrhage was the most common finding, especially in children with bile duct obstruction, including biliary atresia. Some findings were resolved after liver transplantation.

CONCLUSION

Children with neonatal cholestasis had changes in brain imaging, which might play a role in impaired neuropsychological development, but longitudinal clinical research with structured assessment is needed to better qualify the aetiology of the impairment.

Intellectual development of patients with biliary atresia who underwent living donor liver transplantation in infancy

BACKGROUND

The impact of pediatric liver transplantation on intellectual development has yet to be determined. We investigated the intellectual outcomes of school-aged patients after living donor liver transplantation for biliary atresia in infancy.

METHODS

The Wechsler Intelligence Scale for Children-fourth edition test was administered to 20 patients who survived [Formula: see text] 5 years after living donor liver transplantation. Borderline full scale intelligence quotient was defined as ≤ 85. Pre-, peri-, and postoperative data were compared between patients with > 85 and ≤ 85 to identify predictive factors of borderline performance.

RESULTS

The one-sample t test demonstrated that the mean full scale intelligence quotient of patients after transplantation for biliary atresia was significantly lower than that of the general population (91.8 vs. 100.0, p = 0.026) and 7 (35%) were classified as intellectual borderline functioning. Multivariable logistic regression models were unable to identify any factors predictive of full scale intelligence quotients of ≤ 85.

CONCLUSION

This is the first study to indicate that the mean full scale intelligence quotient among school-aged patients who underwent living donor liver transplantation for biliary atresia in infancy is significantly lower than that of the general population.

Hypermanganesemia Induced Chorea and Cognitive Decline in a Tea Seller

Background

Manganese associated neurotoxicity and neurodegeneration is quite rare yet established neurological disorder. This neurotoxic element has predilection for depositing in basal ganglia structures, manifesting mainly as parkinsonian and dystonic movement disorders with behavioral abnormalities.

Case report

We report a 40-year-old man who presented with a subacute onset bilateral, asymmetric hyperkinetic movement disorder (predominantly left sided chorea) with multi-domain cognitive impairment, dysarthria, and generalized rigidity. Clinical history and examination yielded multiple differential diagnoses including deposition and metabolic disorders, autoimmune and paraneoplastic encephalitis involving basal ganglia, and neurodegenerative disorders with chorea and cognitive impairment. However, magnetic resonance imaging was suggestive of paramagnetic substance deposition, which came out to be manganese after laboratory investigations. History, clinical examinations, and investigation results pointed towards a diagnosis of acquired hypermanganesemia due to over-ingestion of manganese containing substance (i.e., black tea). He was treated symptomatically and with chelation therapy (calcium disodium edetate). At the sixth month of follow-up, complete resolution of chorea, dysarthria and partial amelioration of rigidity were observed. His cognitive decline and behavioral abnormalities improved.

Discussion

This is probably the first reported case of acquired hypermanganesemia that presented as a combination of asymmetric chorea and cognitive dysfunction with atypical imaging characteristics. The clinical picture mimicked that of Huntington's disease. We highlight the potential deleterious effects of an apparently "benign" non-alcoholic beverage (i.e., black tea) on cerebral metabolism.

ZIP14 is degraded in response to manganese exposure

Manganese (Mn) is an essential element necessary for proper development and brain function. Circulating Mn levels are regulated by hepatobiliary clearance to limit toxic levels and prevent tissue deposition. To characterize mechanisms involved in hepatocyte Mn uptake, polarized human HepaRG cells were used for this study. Western blot analysis and immunofluorescence microscopy showed the Mn transporter ZIP14 was expressed and localized to the basolateral surface of polarized HepaRG cells. HepaRG cells took up 54Mn in a time- and temperature-dependent manner but uptake was reduced after exposure to Mn. This loss in transport activity was associated with decreased ZIP14 protein levels in response to Mn exposure. Mn-induced degradation of ZIP14 was blocked by bafilomycin A1, which increased localization of the transporter in Lamp1-positive vesicles. Mn exposure also down-regulated the Golgi proteins TMEM165 and GPP130 while the ER stress marker BiP was induced. These results indicate that Mn exposure decreases ZIP14 protein levels to limit subsequent uptake of Mn as a cytoprotective response. Thus, high levels of Mn may compromise first-pass-hepatic clearance mechanisms.

Role of Astrocytes in Manganese Neurotoxicity Revisited

Manganese (Mn) overexposure is a public health concern due to its widespread industrial usage and the risk for environmental contamination. The clinical symptoms of Mn neurotoxicity, or manganism, share several pathological features of Parkinson's disease (PD). Biologically, Mn is an essential trace element, and Mn in the brain is preferentially localized in astrocytes. This review summarizes the role of astrocytes in Mn-induced neurotoxicity, specifically on the role of neurotransmitter recycling, neuroinflammation, and genetics. Mn overexposure can dysregulate astrocytic cycling of glutamine (Gln) and glutamate (Glu), which is the basis for Mn-induced excitotoxic neuronal injury. In addition, reactive astrocytes are important mediators of Mn-induced neuronal damage by potentiating neuroinflammation. Genetic studies, including those with Caenorhabditis elegans (C. elegans) have uncovered several genes associated with Mn neurotoxicity. Though we have yet to fully understand the role of astrocytes in the pathologic changes characteristic of manganism, significant strides have been made over the last two decades in deciphering the role of astrocytes in Mn-induced neurotoxicity and neurodegeneration.

Atypical Neuropsychiatric Presentation in a Patient Expecting Liver Transplantation

Patients presenting with acute or chronic hepatopathy can develop altered mental status with psychomotor slowing, most commonly indicating encephalopathy. We present the case of a 56-year-old patient who developed subacute atypical neuropsychiatric symptoms including cognitive and behavioural disorganization, manic-like state, and lateralized parkinsonian syndrome. The sequence of events, complete work-up, and detailed neuropsychiatric examination were not compatible with hepatic encephalopathy or delirium; therefore we extended our differential diagnosis and suggested the pathophysiological process described below.

Nutritional Needs and Support for Children with Chronic Liver Disease

Malnutrition has become a dangerously common problem in children with chronic liver disease, negatively impacting neurocognitive development and growth. Furthermore, many children with chronic liver disease will eventually require liver transplantation. Thus, this association between malnourishment and chronic liver disease in children becomes increasingly alarming as malnutrition is a predictor of poorer outcomes in liver transplantation and is often associated with increased morbidity and mortality. Malnutrition requires aggressive and appropriate management to correct nutritional deficiencies. A comprehensive review of the literature has found that infants with chronic liver disease (CLD) are particularly susceptible to malnutrition given their low reserves. Children with CLD would benefit from early intervention by a multi-disciplinary team, to try to achieve nutritional rehabilitation as well as to optimize outcomes for liver transplant. This review explains the multifactorial nature of malnutrition in children with chronic liver disease, defines the nutritional needs of these children, and discusses ways to optimize their nutritional.

Mapping the basal ganglia alterations in children chronically exposed to manganese

Chronic manganese (Mn) exposure is associated with neuromotor and neurocognitive deficits, but the exact mechanism of Mn neurotoxicity is still unclear. With the advent of magnetic resonance imaging (MRI), in-vivo analysis of brain structures has become possible. Among different sub-cortical structures, the basal ganglia (BG) has been investigated as a putative anatomical biomarker in MR-based studies of Mn toxicity. However, previous investigations have yielded inconsistent results in terms of regional MR signal intensity changes. These discrepancies may be due to the subtlety of brain alterations caused by Mn toxicity, coupled to analysis techniques that lack the requisite detection power. Here, based on brain MRI, we apply a 3D surface-based morphometry method on 3 bilateral basal ganglia structures in school-age children chronically exposed to Mn through drinking water to investigate the effect of Mn exposure on brain anatomy. Our method successfully pinpointed significant enlargement of many areas of the basal ganglia structures, preferentially affecting the putamen. Moreover, these areas showed significant correlations with fine motor performance, indicating a possible link between altered basal ganglia neurodevelopment and declined motor performance in high Mn exposed children.

Altered executive function in the welders: A functional magnetic resonance imaging study

Chronic exposure to manganese (Mn) can lead to impairments in motor and cognitive functions. Several recent studies reported Mn-induced executive dysfunction. The present study compared the neural correlates of ongoing executive function of welders and healthy controls. Fifty-three welders and 44 healthy controls were enrolled. Participants were given functional magnetic resonance imaging (fMRI) scans and performed two modified versions of the Wisconsin Card Sorting Task (WCST) that differed in cognitive demand, and a task that established a high-level baseline (HLB) condition. Card Sorting Test and Word-Color Test were also used to assess executive performance. Neural activation of the bilateral superior-frontal cortex, right-inferior parietal cortex, and bilateral insula cortex were greater in healthy controls than in welders when contrasting the difficult version of the WCST with the HLB. There were also correlations between executive functions by the Card Sorting Test and Word-Color Test, and brain activation in the insula cortex using the WCST. Our results indicated that welders had altered neural processing related to executive function in the prefrontal cortex under conditions of high cognitive demand. Welders also had less activation of the insula cortex, a part of a larger network comprising the lateral prefrontal cortex and parietal cortex.

Glyphosate, pathways to modern diseases III: Manganese, neurological diseases, and associated pathologies

Manganese (Mn) is an often overlooked but important nutrient, required in small amounts for multiple essential functions in the body. A recent study on cows fed genetically modified Roundup(®)-Ready feed revealed a severe depletion of serum Mn. Glyphosate, the active ingredient in Roundup(®), has also been shown to severely deplete Mn levels in plants. Here, we investigate the impact of Mn on physiology, and its association with gut dysbiosis as well as neuropathologies such as autism, Alzheimer's disease (AD), depression, anxiety syndrome, Parkinson's disease (PD), and prion diseases. Glutamate overexpression in the brain in association with autism, AD, and other neurological diseases can be explained by Mn deficiency. Mn superoxide dismutase protects mitochondria from oxidative damage, and mitochondrial dysfunction is a key feature of autism and Alzheimer's. Chondroitin sulfate synthesis depends on Mn, and its deficiency leads to osteoporosis and osteomalacia. Lactobacillus, depleted in autism, depend critically on Mn for antioxidant protection. Lactobacillus probiotics can treat anxiety, which is a comorbidity of autism and chronic fatigue syndrome. Reduced gut Lactobacillus leads to overgrowth of the pathogen, Salmonella, which is resistant to glyphosate toxicity, and Mn plays a role here as well. Sperm motility depends on Mn, and this may partially explain increased rates of infertility and birth defects. We further reason that, under conditions of adequate Mn in the diet, glyphosate, through its disruption of bile acid homeostasis, ironically promotes toxic accumulation of Mn in the brainstem, leading to conditions such as PD and prion diseases.

Genetic factors and manganese-induced neurotoxicity

Manganese (Mn), is a trace metal required for normal physiological processes in humans. Mn levels are tightly regulated, as high levels of Mn result in accumulation in the brain and cause a neurological disease known as manganism. Manganism shares many similarities with Parkinson’s disease (PD), both at the physiological level and the cellular level. Exposure to high Mn-containing environments increases the risk of developing manganism. Mn is absorbed primarily through the intestine and then released in the blood. Excessive Mn is secreted in the bile and excreted in feces. Mn enters and exits cells through a number of non-specific importers localized on the cell membrane. Mutations in one of the Mn exporters, SLC30A10 (solute carrier family 30, member 10), result in Mn induced toxicity with liver impairments and neurological dysfunction. Four PD genes have been identified in connection to regulation of Mn toxicity, shedding new light on potential links between manganism and PD.

Regional specificity of manganese accumulation and clearance in the mouse brain: implications for manganese-enhanced MRI

Manganese-enhanced MRI has recently become a valuable tool for the assessment of in vivo functional cerebral activity in animal models. As a result of the toxicity of manganese at higher dosages, fractionated application schemes have been proposed to reduce the toxic side effects by using lower concentrations per injection. Here, we present data on regional-specific manganese accumulation during a fractionated application scheme over 8 days of 30 mg/kg MnCl2 , as well as on the clearance of manganese chloride over the course of several weeks after the termination of the whole application protocol supplying an accumulative dose of 240 mg/kg MnCl2 . Our data show most rapid accumulation in the superior and inferior colliculi, amygdala, bed nucleus of the stria terminalis, cornu ammonis of the hippocampus and globus pallidus. The data suggest that no ceiling effects occur in any region using the proposed application protocol. Therefore, a comparison of basal neuronal activity differences in different animal groups based on locally specific manganese accumulation is possible using fractionated application. Half-life times of manganese clearance varied between 5 and 7 days, and were longest in the periaqueductal gray, amygdala and entorhinal cortex. As the hippocampal formation shows one of the highest T1 -weighted signal intensities after manganese application, and manganese-induced memory impairment has been suggested, we assessed hippocampus-dependent learning as well as possible manganese-induced atrophy of the hippocampal volume. No interference of manganese application on learning was detected after 4 days of Mn(2+) application or 2 weeks after the application protocol. In addition, no volumetric changes induced by manganese application were found for the hippocampus at any of the measured time points. For longitudinal measurements (i.e. repeated manganese applications), a minimum of at least 8 weeks should be considered using the proposed protocol to allow for sufficient clearance of the paramagnetic ion from cerebral tissue.

Altered white matter microstructural integrity revealed by voxel-wise analysis of diffusion tensor imaging in welders with manganese exposure

Chronic exposure to manganese (Mn), which can be an occupational hazard or can result from liver failure, is associated with adverse motor and cognitive outcomes. Evidence from previous neuroimaging and magnetic resonance spectroscopy studies suggested alteration of function in Mn-exposed brains. However, the effect of chronic exposure of the human brain to Mn on white matter (WM) structure has not yet been determined. In the present study, we used diffusion tensor imaging (DTI) to investigate whether welders exposed to Mn demonstrate differences in WM integrity, compared with control subjects. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were measured on a voxel-wise basis in 30 male welders with exposure to Mn and in 19 age- and gender-matched control subjects. Direct comparison between welders and controls using investigator-independent Statistical Parametric Mapping (SPM) voxel-wise analysis of DTI metrics revealed a reduction of FA in the corpus callosum (CC) and frontal WM in Mn-exposed welders. Further, marked increases in RD and negligible changes in AD suggested that the microstructural changes in the CC and frontal WM result from compromised radial directionality of fibers in these areas, caused primarily by demyelination. Correlation analysis with neurobehavioral performance also suggested that the microstructural abnormalities were associated with subtle motor and cognitive differences in welders.

Genetic polymorphism of CYP2D6∗2 C→T 2850, GSTM1, NQO1 genes and their correlation with biomarkers in manganese miners of Central India

Manganese (Mn) intoxication is most often regarded as an occupational manifestation and occurs in places such as manganese mines, dry cell battery plants and ceramic industries. In the present study, the influence of genetic polymorphism in cytochrome P450 2D6 (CYP2D6∗2), glutathione S-transferase M1 (GSTM1) and NAD(P)H quinone oxidoreductase 1 (NQO1) genes on blood manganese and plasma prolactin concentrations in manganese miners was investigated. Genotyping of CYP2D6∗2 C→T 2850 and NQO1 C→T 609 was carried out using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) whereas the genotyping of GSTM1 was carried out by multiplex PCR using beta globin as an internal control. Manganese miners with CYP2D6∗2 C→T 2850 variant genotype had relatively low Mn concentration [GM: 21.4±8.9 μg L(-1)] than the subjects with wild (GM: 36.3±8.5 μg L(-1)) and heterozygous (GM: 34.4±6.9 μg L(-1)) genotypes. Miners with CYP2D6∗2 variant genotypes showed low prolactin levels (GM: 13.13±1.6 ng mL(-1)) compared to the wild (GM: 16.4.4±1.5 μg L(-1)) and heterozygous (GM: 18.7±1.6 ng mL(-1)) genotypes. Gene-gene interaction studies also revealed that the subjects with CYP2D6∗2 C→T 2850 variant genotypes had low levels of Mn and prolactin. Our new findings suggest that CYP2D6∗2 C→T 2850 variant genotypes can regulate plasma prolactin levels in manganese miners of Central India and could be involved in the fast metabolism of blood manganese, compared to wild and heterozygous genotypes.

Risk assessment of an essential element: manganese

Manganese (Mn) is an essential element for humans, animals, and plants and is required for growth, development, and maintenance of health. Mn is present in most tissues of all living organisms and is present naturally in rocks, soil, water, and food. High-dose oral, parenteral, or inhalation exposures are associated with increased tissue Mn levels that may lead to development of adverse neurological, reproductive, or respiratory effects. Manganese-induced clinical neurotoxicity is associated with a motor dysfunction syndrome commonly referred to as manganism. Because Mn is an essential element and absorption and excretion are homeostatically regulated, a reasonable hypothesis is that there should be no adverse effects at low exposures. Therefore, there should be a threshold for exposure, below which adverse effects may occur only rarely, if at all, and the frequency of occurrence of adverse effects may increase with higher exposures above that threshold. Lowest-observed-adverse-effect levels (LOAELs), no-observed-adverse-effect levels (NOAELs), and benchmark dose levels (BMDs) have been derived from studies that were conducted to evaluate subclinical neurotoxicity in human occupational cohorts exposed to Mn. Although there is some uncertainty about the predictive value of the subclinical neuromotor or neurobehavioral effects that were observed in these occupational cohort studies, results of the neurological tests were used in risk assessments to establish guidelines and regulations for ambient air levels of Mn in the environment. A discussion of the uncertainties associated with these tests is provided in this review. The application of safety and uncertainty factors result in guidelines for ambient air levels that are lower than the LOAELs, NOAELs, or BMDs from occupational exposure studies by an order of magnitude, or more. Specific early biomarkers of effect, such as subclinical neurobehavioral or neurological changes or magnetic resonance imaging (MRI) changes, have not been established or validated for Mn, although some studies attempted to correlate certain biomarkers with neurological effects. Pharmacokinetic studies with rodents and monkeys provide valuable information about the absorption, bioavailability, and tissue distribution of various Mn compounds with different solubilities and oxidation states in different age groups. These pharmacokinetic studies showed that rodents and primates maintain stable tissue Mn levels as a result of homeostatic mechanisms that tightly regulate absorption and excretion of ingested Mn and limit tissue uptake at low to moderate levels of inhalation exposure. In addition, physiologically based pharmacokinetic (PBPK) models are being developed to provide for the ability to conduct route-to-route extrapolations, evaluate nasal uptake to the central nervous system (CNS), and determine life-stage differences in Mn pharmacokinetics. Such models will facilitate more rigorous quantitative analysis of the available human pharmacokinetic data for Mn and will be used to identify situations that may lead to increased brain accumulation related to altered Mn kinetics in different human populations, and to develop quantitatively accurate predictions of elevated Mn levels that may serve as a basis of dosimetry-based risk assessments. Such dosimetry-based risk assessments will permit for the development of more scientifically refined and robust recommendations, guidelines, and regulations for Mn levels in the ambient environment and occupational settings.

Optimizing nutritional management in children with chronic liver disease

Malnutrition is common in infants and children with chronic liver disease (CLD) and may easily be underestimated by clinical appearance alone. The cause of malnutrition in CLD is multifactorial, although insufficient dietary intake is probably the most important factor and is correctable. Fat malabsorption occurs in cholestatic disorders, and one must also consider any accompanying fat-soluble vitamin and essential fatty acid deficiencies. The clinician should proactively evaluate, treat, and re-evaluate response to treatment of nutritional deficiencies. Because a better nutritional state is associated with better survival before and after liver transplantation, aggressive nutritional management is an important part of the care of these children.

[Brain MRI associated with chronic hepatic failure and hypermanganism]

INTRODUCTION

Hypermanganism is primarily linked to inhalation exposure. Several observations of exogenous manganese poisoning have been reported associating neuropsychiatric symptoms, parkinsonian syndrome and hyperintensities of the two pallida on T1 weighted sequences on brain MRI. Recently, similar neurological and radiological signs have been described without exogenous exposure to manganese but in the framework of endogenous poisoning particularly in chronic hepatic failure.

CASE REPORT

We report the case of a 41-year-old HIV-positive and HVC-positive man who presented psychomotor impairment associated with bipallidal T1 hyperintensities on the brain MRI. The diagnosis of a hypermanganesemia was made on blood samples. We present a literature review on exogenous and endogenous hypermanganesemia and discuss differential diagnosis in the radiological setting of bipallidal T1 hyperintensities.

CONCLUSION

Bipallidal T1 hyperintensities on brain MRI may suggest hypermanganism even in the clinical setting of a non-specific neurological disorder such as psychomotor impairment.

Acquired hepatocerebral degeneration

Cirrhosis and its co-morbidities may cause a variety of neurological complications, the most common being bouts of toxic metabolic encephalopathy. A proportion of patients with chronic liver disease develop acquired hepatocerebral degeneration (AHD), a chronic progressive neurological syndrome characterized by parkinsonism, ataxia and other movement disorders. This article reviews the clinical spectrum, pathophysiology, neuroimaging features and differential diagnosis of AHD along with emerging treatment options.

State-of-the-science review: Does manganese exposure during welding pose a neurological risk?

Recent studies report that exposure to manganese (Mn), an essential component of welding electrodes and some steels, results in neurotoxicity and/or Parkinson's disease (PD) in welders. This "state-of-the-science" review presents a critical analysis of the published studies that were conducted on a variety of Mn-exposed occupational cohorts during the last 100 yr, as well as the regulatory history of Mn and welding fumes. Welders often perform a variety of different tasks with varying degrees of duration and ventilation, and hence, to accurately assess Mn exposures that occurred in occupational settings, some specific information on the historical work patterns of welders is desirable. This review includes a discussion of the types of exposures that occur during the welding process--for which limited information relating airborne Mn levels with specific welding activities exists--and the human health studies evaluating neurological effects in welders and other Mn-exposed cohorts, including miners, millers, and battery workers. Findings and implications of studies specifically conducted to evaluate neurobehavioral effects and the prevalence of PD in welders are also discussed. Existing exposure data indicate that, in general, Mn exposures in welders are less than those associated with the reports of clinical neurotoxicity (e.g., "manganism") in miners and smelter workers. It was also found that although manganism was observed in highly exposed workers, the scant exposure-response data available for welders do not support a conclusion that welding is associated with clinical neurotoxicity. The available data might support the development of reasonable "worst-case" exposure estimates for most welding activities, and suggest that exposure simulation studies would significantly refine such estimates. Our review ends with a discussion of the data gaps and areas for future research.

Manganese accumulation in the brain: MR imaging

Manganese (Mn) accumulation in the brain is detected as symmetrical high signal intensity in the globus pallidi on T1-weighted MR images without an abnormal signal on T2-weighted images. In this review, we present several cases of Mn accumulation in the brain due to acquired or congenital diseases of the abdomen including hepatic cirrhosis with a portosystemic shunt, congenital biliary atresia, primary biliary cirrhosis, congenital intrahepatic portosystemic shunt without liver dysfunction, Rendu-Osler-Weber syndrome with a diffuse intrahepatic portosystemic shunt, and patent ductus venosus. Other causes of Mn accumulation in the brain are Mn overload from total parenteral nutrition and welding-related Mn intoxication.

Application of pharmacokinetic data to the risk assessment of inhaled manganese

There is increased interest within the scientific community concerning the neurotoxicity of manganese owing in part to the use of methylcyclopentadienyl manganese tricarbonyl (MMT) as a gasoline fuel additive and an enhanced awareness that this essential metal may play a role in hepatic encephalopathy and other neurologic diseases. Neurotoxicity generally arises over a prolonged period of time and results when manganese intake exceeds its elimination leading to increases in brain manganese concentration. Neurotoxicity can occur following high dose oral, inhalation, or parenteral exposure or when hepatobiliary clearance of this metal is impaired. Studies completed during the past several years have substantially improved our understanding of the health risks posed by inhaled manganese by determining exposure conditions that lead to increased concentrations of manganese within the central nervous system and other target organs. Many of these studies focused on phosphates, sulfates, and oxides of manganese since these are formed and emitted following MMT combustion by an automobile. These studies have evaluated the role of direct nose-to-brain transport of inhaled manganese and have examined differences in manganese toxicokinetics in potentially sensitive subpopulations (e.g., fetuses, neonates, individuals with compromised hepatic function or sub-optimal manganese intake, and the aged). This manuscript reviews the U.S. Environmental Protection Agency's current risk assessment for inhaled manganese, summarizes these contemporary pharmacokinetic studies, and considers how these data could inform future risk assessments of this metal following inhalation.

Improving predictive modeling in pediatric drug development: pharmacokinetics, pharmacodynamics, and mechanistic modeling

A workshop was conducted on November 18-19, 2004, to address the issue of improving predictive models for drug delivery to developing humans. Although considerable progress has been made for adult humans, large gaps remain for predicting pharmacokinetic/pharmacodynamic (PK/PD) outcome in children because most adult models have not been tested during development. The goals of the meeting included a description of when, during development, infants/children become adult-like in handling drugs. The issue of incorporating the most recent advances into the predictive models was also addressed: both the use of imaging approaches and genomic information were considered. Disease state, as exemplified by obesity, was addressed as a modifier of drug pharmacokinetics and pharmacodynamics during development. Issues addressed in this workshop should be considered in the development of new predictive and mechanistic models of drug kinetics and dynamics in the developing human.

The emergence of manganese-related health problems in Quebec: An integrated approach to evaluation, diagnosis, management and control

This paper describes the strategy developed in Quebec to deal with an emerging problem: manganism in welders. Only two cases of manganism had been reported to the Commission de la santé et de la sécurité du travail (CSST, Workers Compensation Board in Quebec) before 2000. In the fall of 2001, the CSST was informed of a possible cluster of manganism and received 20 compensation claims from one plant. Action was rapidly taken to understand and tackle this emerging problem. Under the leadership of the CSST, a coordinating working group implemented medical and environmental subcommittees involving representatives of the different partners of the prevention network. After a literature review to document the health risks associated with manganese and the lack of some important information, a panel of international experts was formed to try to reach agreement on the parameters to consider in the diagnosis and management of manganism. The CSST compensation management policies would be adjusted accordingly. Simultaneously, all the available industrial hygiene data were analyzed to estimate where and at what levels workers were exposed to manganese. To complete these data, the exposure of workers in more than 50 industrial plants was evaluated and existing control measures were documented. All these data have been presented for a revision of the Quebec permissible exposure limit (PEL). In this integrated approach, the next step targets the formation of neurologists and neuropsychologists for a standardized medical evaluation, to complete workplace evaluation in the high risk sectors, inform workers and employers and recommend control measures where required, based on a revised PEL. Many strategies will be used to inform the prevention network (about 1000 people), employers and employees of the risks of overexposure to manganese and of the measures to control exposure in all the plants where workers are susceptible to be exposed to manganese.

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.

The use of magnetic resonance imaging (MRI) in the study of manganese neurotoxicity

Manganese (Mn), an element found in many foods, is an important and essential nutrient for proper health and maintenance. It is toxic in high doses, however, and exposure to excessive levels can result in the onset of a neurological disorder similar to, but distinct from, Parkinson's disease. Historically, Mn neurotoxicity was most commonly associated with various occupations, such as Mn mining, welding and steel production. More recently, increases in both blood and brain Mn levels have been observed in persons with liver disease or those receiving prolonged parenteral nutrition. Additionally, rodent data suggest that iron deficiency and anemia may be risk factors for Mn neurotoxicity. Clinically, brain Mn accumulation can be monitored in vivo using non-invasive magnetic resonance imaging (MRI) due to the paramagnetic nature of this element. Indeed, MRI has been used in a variety of settings to evaluate the brain Mn deposition in various populations. This review focuses on the use of MRI technology in studies related specifically to Mn neurotoxicity. Thus, we will examine reports using MRI to confirm brain Mn accumulation in human populations, and conclude with data from non-human primate and rodent models of Mn neurotoxicity.

Manganese

Manganese is an essential mineral that is found at low levels in virtually all diets. Manganese ingestion represents the principal route of human exposure, although inhalation also occurs, predominantly in occupational cohorts. Regardless of intake, animals generally maintain stable tissue manganese levels as a result of homeostatic mechanisms that tightly regulate the absorption and excretion of this metal. However, high-dose exposures are associated with increased tissue manganese levels, causing adverse neurological, reproductive and respiratory effects. In humans, manganese-induced neurotoxicity is associated with a motor dysfunction syndrome, commonly referred to as manganism or Parkinsonism, which is of paramount concern and is considered to be one of the most sensitive endpoints. This article focuses on the dosimetry of manganese with special focus on transport mechanisms of manganese into the CNS. It is not intended to be an exhaustive review of the manganese literature; rather it aims to provide a useful synopsis of contemporary studies from which the reader may progress to other research citations as desired. Specific emphasis is directed towards recent published literature on manganese transporters' systemic distribution of manganese upon inhalation exposure as well as the utility of magnetic resonance imaging in quantifying brain manganese distribution.

Nutritional aspects of manganese homeostasis

Manganese (Mn) is an essential mineral. It is present in virtually all diets at low concentrations. The principal route of intake for Mn is via food consumption, but in occupational cohorts, inhalation exposure may also occur (this subject will not be dealt with in this review). Humans maintain stable tissue levels of Mn. This is achieved via tight homeostatic control of both absorption and excretion. Nevertheless, it is well established that exposure to high oral, parenteral or ambient air concentrations of Mn can result in elevations in tissue Mn levels. Excessive Mn accumulation in the central nervous system (CNS) is an established clinical entity, referred to as manganism. It resembles idiopathic Parkinson's disease (IPD) in its clinical features, resulting in adverse neurological effects both in laboratory animals and humans. This review focuses on an area that to date has received little consideration, namely the potential exposure of parenterally fed neonates to exceedingly high Mn concentrations in parenteral nutrition solutions, potentially increasing their risk for Mn-induced adverse health sequelae. The review will consider (1) the essentiality of Mn; (2) the concentration ranges, means and variation of Mn in various foods and infant formulas; (3) the absorption, distribution, and elimination of Mn after oral exposure and (4) the factors that raise a theoretical concern that neonates receiving total parenteral nutrition (TPN) are exposed to excessive dietary Mn.

Manganese dosimetry: species differences and implications for neurotoxicity

Manganese (Mn) is an essential mineral that is found at low levels in food, water, and the air. Under certain high-dose exposure conditions, elevations in tissue manganese levels can occur. Excessive manganese accumulation can result in adverse neurological, reproductive, and respiratory effects in both laboratory animals and humans. In humans, manganese-induced neurotoxicity (manganism) is the overriding concern since affected individuals develop a motor dysfunction syndrome that is recognized as a form of parkinsonism. This review primarily focuses on the essentiality and toxicity of manganese and considers contemporary studies evaluating manganese dosimetry and its transport across the blood-brain barrier, and its distribution within the central nervous system (CNS). These studies have dramatically improved our understanding of the health risks posed by manganese by determining exposure conditions that lead to increased concentrations of this metal within the CNS and other target organs. Most individuals are exposed to manganese by the oral and inhalation routes of exposure; however, parenteral injection and other routes of exposure are important. Interactions between manganese and iron and other divalent elements occur and impact the toxicokinetics of manganese, especially following oral exposure. The oxidation state and solubility of manganese also influence the absorption, distribution, metabolism, and elimination of manganese. Manganese disposition is influenced by the route of exposure. Rodent inhalation studies have shown that manganese deposited within the nose can undergo direct transport to the brain along the olfactory nerve. Species differences in manganese toxicokinetics and response are recognized with nonhuman primates replicating CNS effects observed in humans while rodents do not. Potentially susceptible populations, such as fetuses, neonates, individuals with compromised hepatic function, individuals with suboptimal manganese or iron intake, and those with other medical states (e.g., pre-parkinsonian state, aging), may have altered manganese metabolism and could be at greater risk for manganese toxicity.

Manganese neurotoxicity and glutamate-GABA interaction

Brain extracellular concentrations of amino acids (e.g. aspartate, glutamate, taurine) and divalent metals (e.g. zinc, copper, manganese) are primarily regulated by astrocytes. Adequate glutamate homeostasis is essential for the normal functioning of the central nervous system (CNS). Glutamate is of central importance for nitrogen metabolism and, along with aspartate, is the primary mediator of the excitatory pathways in the brain. Similarly, the maintenance of proper manganese levels is important for normal brain functioning. Several in vivo and in vitro studies have linked increased manganese concentrations with alterations in the content and metabolism of neurotransmitters, namely dopamine, gamma-aminobutyric acid, and glutamate. It has been reported by our laboratory and others, that cultured rat primary astrocytes exposed to manganese displayed decreased glutamate uptake, thereby increasing the excitotoxic potential of glutamate. Furthermore, decreased uptake of glutamate has been associated with decreased gene expression of glutamate:aspartate transporter (GLAST) in manganese-exposed astroctyes. Additional studies have suggested that attenuation of astrocytic glutamate uptake by manganese may be a consequence of reactive oxygen species (ROS) generation. Collectively, these data suggest that excitotoxicity may occur due to manganese-induced altered glutamate metabolism, representing a proximate mechanism for manganese-induced neurotoxicity.

Myoclonic involuntary movement associated with chronic manganese poisoning

We report a 17-year-old man showing myoclonic involuntary movement (IVM) associated with chronic manganese (Mn) poisoning. The patient, a welder, showed myoclonic IVM mainly in the right upper and lower extremities, elevated levels of Mn in the blood and hair and high-intensity signals in the globus pallidus on T1-weighted MR images. Chelation therapy resulted in improvement of the myoclonic IVM and MRI abnormalities. This is the first report of Mn poisoning characterized by myoclonic IVM without parkinsonism.

Persistence of mild parkinsonism 4 months after liver transplantation in patients with preoperative minimal hepatic encephalopathy: a study on neuroradiological and blood manganese changes

Pallidal hyperintensity at magnetic resonance imaging (MRI) correlates to blood manganese (Mn) levels and parkinsonian signs in patients with cirrhosis. Similarly, metabolite changes in the basal ganglia (BG) at proton spectroscopy are related to these neurological signs. The evolution of these abnormalities after liver transplantation (OLT) is incompletely described. We evaluated 14 unselected consecutive patients with cirrhosis (minimal hepatic encephalopathy [HE] n=8, no HE n=6) before and 4 months after successful OLT for the evolution of parkinsonism using a validated scale (the United Parkinson's Disease Rating Scale, or UPDRS). Pallidal intensity at MRI, spectroscopic changes in the BG at magnetic resonance spectroscopy (MRS), and whole blood manganese concentrations were measured. After OLT in patients with preoperative minimal HE, the UPDRS scores improved, but mild parkinsonism persisted (16.1+/-3.6 to 6.2+/-4.8, P<0.05). Pallidal hyperintensity remained abnormal in 5/8 of cases, but spectroscopic changes normalized in all patients. Blood Mn remained elevated in 4/6 patients. In patients without HE, UPDRS values remained negligible (2.42+/-1.5 to 2.5+/-1.4). Pallidal hyperintensity normalized in 7/8 patients and spectroscopic changes normalized in all patients. Blood Mn remained elevated in 5/6 patients. Four months after successful OLT, patients with preoperative minimal HE and severe pallidal hyperintensity showed persistent mild parkinsonism. The role of blood manganese determination appears limited in the monitoring of MRI and parkinsonian signs changes after OLT.