Louise Normandin

Manganese deposition in basal ganglia structures results from both portal-systemic shunting and liver dysfunction

BACKGROUND & AIMS Manganese (Mn) deposition could be responsible for the T(1)-weighted magnetic resonance signal hyperintensities observed in cirrhotic patients. These experiments were designed to assess the regional specificity of the Mn increases as well as their relationship to portal-systemic shunting or hepatobiliary dysfunction. METHODS Mn concentrations were measured in (1) brain samples from basal ganglia structures (pallidum, putamen, caudate nucleus) and cerebral cortical structures (frontal, occipital cortex) obtained at autopsy from 12 cirrhotic patients who died in hepatic coma and from 12 matched controls; and from (2) brain samples (caudate/putamen, globus pallidus, frontal cortex) from groups (n = 8) of rats either with end-to-side portacaval anastomosis, with biliary cirrhosis, or with fulminant hepatic failure as well as from sham-operated and normal rats. RESULTS Mn content was significantly increased in frontal cortex (by 38%), occipital cortex (by 55%), pallidum (by 186%), putamen (by 66%), and caudate (by 54%) of cirrhotic patients compared with controls. Brain Mn content did not correlate with patient age, etiology of cirrhosis, or history of chronic hepatic encephalopathy. In cirrhotic and portacaval-shunted rats, Mn content was increased in pallidum (by 27% and 57%, respectively) and in caudate/putamen (by 57% and 67%, respectively) compared with control groups. Mn concentration in pallidum was significantly higher in portacaval-shunted rats than in cirrhotic rats. No significant changes in brain Mn concentrations were observed in rats with acute liver failure. CONCLUSIONS These findings suggest that brain Mn deposition results both from portal-systemic shunting and from liver dysfunction.

Manganese Neurotoxicity: An Update of Pathophysiologic Mechanisms

The central nervous system, and the basal ganglia in particular, is an important target in manganese neurotoxicity, a disorder producing neurological symptoms similar to that of Parkinsons disease. Increasing evidence suggests that astrocytes are a site of early dysfunction and damage; chronic exposure to manganese leads to selective dopaminergic dysfunction, neuronal loss, and gliosis in basal ganglia structures together with characteristic astrocytic changes known as Alzheimer type II astrocytosis. Astrocytes possess a high affinity, high capacity, specific transport system for manganese facilitating its uptake, and sequestration in mitochondria, leading to a disruption of oxidative phosphorylation. In addition, manganese causes a number of other functional changes in astrocytes including an impairment of glutamate transport, alterations of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, production of nitric oxide, and increased densities of binding sites for the “peripheral-type” benzodiazepine receptor (a class of receptor predominantly localized to mitochondria of astrocytes and involved in oxidative metabolism, mitochondrial proliferation, and neurosteroid synthesis). Such effects can lead to compromised energy metabolism, resulting in altered cellular morphology, production of reactive oxygen species, and increased extracellular glutamate concentration. These consequences may result in impaired astrocytic–neuronal interactions and play a major role in the pathophysiology of manganese neurotoxicity.

Role of manganese in the pathogenesis of portal-systemic encephalopathy.

Amongst the potential neurotoxins implicated in the pathogenesis of hepatic encephalopathy, manganese emerges as a new candidate. In patients with chronic liver diseases, manganese accumulates in blood and brain leading to pallidal signal hyperintensity on T1-weighted Magnetic Resonance (MR) Imaging. Direct measurements in globus pallidus obtained at autopsy from cirrhotic patients who died in hepatic coma reveal 2 to 7-fold increases of manganese concentration. The intensity of pallidal MR images correlates with blood manganese and with the presence of extrapyramidal symptoms occurring in a majority of cirrhotic patients. Liver transplantation results in normalization of pallidal MR signals and disappearance of extrapyramidal symptoms whereas transjugular intrahepatic portosystemic shunting induces an increase in pallidal hyperintensity with a concomitant deterioration of neurological dysfunction. These findings suggest that the toxic effects of manganese contribute to extrapyramidal symptoms in patients with chronic liver disease. The mechanisms of manganese neurotoxicity are still speculative, but there is evidence to suggest that manganese deposition in the pallidum may lead to dopaminergic dysfunction. Future studies should be aimed at evaluating the effects of manganese chelation and/or of treatment of the dopaminergic deficit on neurological symptomatology in these patients.

Alzheimer type II astrocytic changes following sub-acute exposure to manganese and its prevention by antioxidant treatment

Exposure to manganese in an industrial or clinical setting can lead to manganism, a neurological disorder with similarities to Parkinsons disease. Although the pathogenetic basis of this disorder is unclear, studies indicate this metal is highly accumulated in astrocytes, suggesting an involvement of these glial cells. To investigate this issue, we have used a recently characterized, sub-acute model of manganese neurotoxicity. Treatment of rats with manganese (II) chloride (50 mg/kg body weight, i.p.) once daily for 1 or 4 days led to increases in manganese levels of up to 232, 523, and 427% in the cerebral cortex, globus pallidus, and cerebellum, respectively, by instrumental neutron activation analysis. These changes were accompanied by development of pathological changes in glial morphology identified as Alzheimer type II astrocytosis in both cortical and sub-cortical structures. Co-treatment with either the antioxidant N-acetylcysteine or the manganese chelator 1,2-cyclohexylenedinitrilotetraacetic acid completely blocked this pathology, indicating the cellular transformation may be mediated by oxidative stress associated with the presence of this metal. These findings represent, to our knowledge, the first report of early induction of this pathological hallmark of manganese neurotoxicity, an event previously considered a consequence of chronic exposure to manganese in primates and in human cases of manganism. Our results also indicate that use of this rodent model may provide a novel opportunity to examine the nature and role of the Alzheimer type II astrocyte in the pathophysiology of this disorder as well as in other disease processes in which cerebral accumulation of manganese occurs.

Bioaccumulation and locomotor effects of manganese phosphate/sulfate mixture in Sprague-Dawley rats following subchronic (90 days) inhalation exposure

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic manganese (Mn) compound added to unleaded gasoline in Canada. The primary combustion products of MMT are Mn phosphate, Mn sulfate, and a Mn phosphate/Mn sulfate mixture. Concerns have been raised that the combustion products of MMT containing Mn could be neurotoxic, even at low levels of exposure. The objective of this study is to investigate exposure-response relationships for bioaccumulation and locomotor effects following subchronic inhalation exposure to a mixture of manganese phosphates/sulfate mixture. A control group and three groups of 30 male Sprague-Dawley rats were exposed in inhalation chambers for a period of 13 weeks, 5 days per week, 6 h a day. Exposure concentrations were 3000, 300, and 30 microg/m(3). At the end of the exposure period, locomotor activity and resting time tests were conducted for 36 h using a computerized autotrack system. Rats were then euthanized by exsanguination and Mn concentrations in different tissues (liver, lung, testis, and kidney) and blood and brain (caudate putamen, globus pallidus, olfactory bulb, frontal cortex, and cerebellum) were determined by neutron activation analysis. Increased manganese concentrations were observed in blood, kidney, lung, testis, and in all brain sections in the highest exposure group. Mn in the lung and in the olfactory bulb were dose dependent. Our data indicate that the olfactory bulb accumulated more Mn than other brain regions following inhalation exposure. Locomotor activity was increased at 3000 microg/m(3), but no difference was observed in resting time among the exposed groups. At the end of the experiment, rats exposed to 300 and 3000 microg/m(3) exhibited significantly decreased body weight in comparison with the control group. Biochemical profiles also revealed some significant differences in certain parameters, specifically alkaline phospatase, urea, and chlorate.

Manganese neurotoxicity: behavioral, pathological, and biochemical effects following various routes of exposure.

The human central nervous system is an important target for manganese intoxication, which causes neurological symptoms similar to those of Parkinsons disease. With the increasing use of methylcyclopentadienyl manganese tricarbonyl (MMT) as an octane-improving additive to unleaded gasoline, the prospect of worldwide manganese exposure is once again attracting attention as increases in environmental manganese concentrations have been recorded relative to traffic density. One crucial question is whether a small increase of manganese contamination resulting from the widespread use of MMT could have neurotoxic effects. In this review we concentrate on central nervous system abnormalities and neurobehavioral disturbances. Most experimental animal studies on manganese neurotoxicity have been conducted in nonhuman primates and rodents. Most studies performed in rodents used oral manganese administration and did not assess bioaccumulation or central nervous system changes. The major effect found was transient modification of spontaneous motor activity. Very few inhalation toxicological studies were carried out. As manganese intoxication in humans usually occurs via inhalation, more studies are required using the respiratory route of administration. Given the proven neurotoxic effects of manganese and the prospect of worldwide MMT usage, this metal should be considered a new environmental pollutant having potentially widespread public health consequences.

Human Exposure to Respirable Manganese in Outdoor and Indoor Air in Urban and Rural Areas

Methylcyclopentadienyl manganese tricarbonyl (MMT) is used as an additive in gasoline, and its combustion leads to the emission of Mn particles, which increase atmospheric metal con-centrations. The objective of this study was to determine the level of outdoor and indoor respirable Mn (MnR) in Montreal, Canada, where MMT has been used since 1976. Ten women were involved in this study: five living in an urban area, near an expressway with high traffic density, and five residing in a rural area characterized by low traffic density. Outdoor and indoor air samples were collected each week (5 in total) during 3 consecutive days; blood sam-ples were collected at the end of the air sampling period. The average concentration of out-door MnR in the urban area was 0.025 μg/m3, which is significantly different from the average of 0.005 μg/m3 found in the rural area. The average indoor MnR concentration was also signif-icantly different between the urban area (0.017 μg/m3) and the rural area (0.007 μg/m3). The average outdoor MnR concentrations were not significantly different from the average MnR indoor concentrations within both areas. The mean blood Mn concentrations were not signifi-cantly different between the two groups. Data suggest that a high outdoor atmospheric MnR leads to a high indoor MnR, but not to an increase in blood Mn levels.

BIOACCUMULATION AND LOCOMOTOR EFFECT OF MANGANESE DUST IN RATS

The primary goal of this study is to determine the effects of Mn exposure via inhalation. The bioaccumulation of Mn in different organs and tissues, the alteration of biochemical parameters, and the locomotor activity were assessed. A group of 26 male Sprague-Dawley rats (E) were exposed to 3750 µg/m3 of Mn dust for 6 h/day, 5 days/wk for 13 consecutive weeks and compared to a control group of 12 rats (C) exposed to 4 µg/m3. After exposure, neurological evaluation was carried out for 36 h (a night-day-night cycle) using a computerized autotrack system. Rats were then sacrificed by exsanguination, and Mn content in organs and tissues was determined by neutron activation analysis. Mn concentrations in lung, putamen, and cerebellum were significantly higher in E than in C (0.30 vs. 0.17, 0.89 vs. 0.44, 0.63 vs. 0.48 ppm; p < .01), as well as in the kidney, frontal cortex, and globus pallidus (1.15 vs. 0.96, 0.84 vs. 0.47, 1.28 vs. 0.55 ppm; p < .05). Potassium concentration was significantly lower in E than in C (5.11 vs. 5.79 mmol/L; p < .05), as was alkaline phosphatase (106.9 vs. 129.6 U/L; p < .01). Locomotor activity indicated higher distance covered in the first 12-h period for E (45 383 vs. 36 098 cm; p < .05) and lower resting time in the last 12-h period for E (36 326 vs. 37 393 s; p < .05). This study is the first of several ongoing studies in our laboratory that address health concerns associated with inhalation exposure to different Mn species and to different levels of exposure.

Potential of dandelion (Taraxacum officinale) as a bioindicator of manganese arising from the use of methylcyclopentadienyl manganese tricarbonyl in unleaded gasoline.

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic manganese (Mn) compound currently added to unleaded gasoline in Canada. It has been suggested that the combustion of MMT containing Mn could cause various deleterious health effects in animals and humans at very high concentrations. This study evaluates the potential of dandelions (Taraxacum officinale) as bioindicators of Mn environmental contamination. Samples were picked at three different distances from a highway: a highly exposed site (E++), a lightly exposed site (E+) and a control site (E), located respectively at 10, 50 and 100 m. The total Mn, Mg, Ca, Al, Fe and Zn concentrations were measured in the soils and in the plants (flower, stem, leaves and root) by neutron activation analysis. Exchangeable Mn was measured in soils by atomic absorption spectrophotometry. Mn concentrations of the different parts of the plant and exchangeable Mn in soils were not correlated with distance from the roadway and, thus, do not seem to be a sensitive indicator of Mn contamination. Soil Mn concentrations were correlated with distance from the roadway. This suggests the hypothesis that the environmental fate of Mn from MMT sources could be associated with an increased total Mn in soil but does not lead to an increase in exchangeable Mn.

Repeated measures of validated and novel biomarkers of exposure to polycyclic aromatic hydrocarbons in individuals living near an aluminum plant in Quebec, Canada.

A longitudinal biomonitoring study was conducted to assess exposure to polycyclic aromatic hydrocarbons (PAH) in non-occupationally exposed nonsmoking adults living in the vicinity of an aluminum plant. Metabolites of several PAH (pyrene, naphthalene, chrysene, fluoranthene, benz[a]anthracene) were measured in the urine of the participants, including 1-hydroxypyrene (1-OHP) as a validated biomarker and pyrene diones as novel biomarkers. In total, 73 individuals living about 1 km away from the plant (taken as the exposed group) were compared repeatedly with 71 individuals living at least 11 km from the smelter (used as the control group). Complete first morning voids were collected twice, at a 2-wk interval, in the fall of 2005 and twice weekly for 2 consecutive weeks in the spring of 2006. Urinary biomarker concentrations were then measured by an ultra-performance liquid chromatography (UPLC) method with time-of-flight mass spectrometry detection (MS-TOF) (UPLC-MS-TOF). For most sampling days, individuals living near the plant showed significantly higher excretion values of both 1-OHP and pyrene diones (mean ratio up to 2- and 2.4-fold, respectively) than individuals living further from the plant. In the group living near the plant, geometric mean concentrations of 1-OHP varied from 0.047 to 0.058 μmol/mol creatinine, depending on the sampling day, as compared to 0.025 to 0.04 μmol/mol creatinine in the reference group. Corresponding mean values for pyrene diones were 0.017–0.056 μmol/mol creatinine and 0.014–0.039 μmol/mol creatinine, respectively. Urinary 1- and 2-naphthols were also measured as a reference and showed no significant differences between the two groups for most sampling days; metabolite concentrations of the other monitored PAH (chrysene, fluoranthene, benz[a]anthracene) were mostly below the analytical limit of detection of 0.005 to 0.01 μg/L, depending on the metabolite, with a detection rate varying from 0 to at most 21%. Individuals living near the aluminum plant thus appeared to be repeatedly exposed to higher pyrene levels than the control group, on the basis of both 1-OHP and pyrene dione excretions. However, 1-OHP concentrations observed in this first group were similar to those of other reference populations of nonsmokers studied in the past. Uptake of the other PAH associated with plant emissions was too small to significantly increase the excretion of their metabolites.