Chronic Manganese Toxicity Associated with Voltage-Gated Potassium Channel Complex Antibodies in a Relapsing Neuropsychiatric Disorder.

Heavy metal poisoning is a rare but important cause of encephalopathy. Manganese (Mn) toxicity is especially rare in the modern world, and clinicians’ lack of recognition of its neuropsychiatric manifestations can lead to misdiagnosis and mismanagement. We describe the case of a man who presented with recurrent episodes of confusion, psychosis, dystonic limb movement and cognitive impairment and was initially diagnosed with anti-voltage-gated potassium channel (VGKC) complex limbic encephalitis in view of previous positive autoantibodies. His failure to respond to immunotherapy prompted testing for heavy metal poisoning, which was positive for Mn. This is the first report to examine an association between Mn and VGKC antibodies and the effects of Mn on functional brain activity using functional near-infrared spectroscopy (fNIRS).

Inflammatory Activation of Microglia and Astrocytes in Manganese Neurotoxicity.

Neurotoxicity due to excessive exposure to manganese (Mn) has been described as early as 1837 (Couper, Br Ann Med Pharm Vital Stat Gen Sci 1:41-42, 1837). Extensive research over the past two decades has revealed that Mn-induced neurological injury involves complex pathophysiological signaling mechanisms between neurons and glial cells. Glial cells are an important target of Mn in the brain, both for sequestration of the metal, as well as for activating inflammatory signaling pathways that damage neurons through overproduction of numerous reactive oxygen and nitrogen species and inflammatory cytokines. Understanding how these pathways are regulated in glial cells during Mn exposure is critical to determining the mechanisms underlying permanent neurological dysfunction stemming from excess exposure. The subject of this review will be to delineate mechanisms by which Mn interacts with glial cells to perturb neuronal function, with a particular emphasis on neuroinflammation and neuroinflammatory signaling between distinct populations of glial cells.

Oxidative induction of pro-inflammatory cytokine formation by human monocyte-derived macrophages following exposure to manganese in vitro.

Manganese (as Mn(2+)), a superoxide dismutase mimetic, catalyzes the formation of the relatively stable membrane-permeable reactive oxygen species (ROS) hydrogen peroxide (H2O2), a mediator of intracellular redox signaling in immune and inflammatory cells. The goal of this study was to investigate the potential for Mn(2+), via its pro-oxidative properties, to activate production of pro-inflammatory cytokines/chemokines IL-1ß, IL-6, IL-8, IFNγ, TNFα, and G-CSF by human monocyte-derived macrophages in vitro. For these studies, the cells were isolated from peripheral blood mononuclear leukocytes and matured to generate a population of large CD14/CD16 co-expressing cells. The monocyte-derived macrophages were then exposed to bacterial lipopolysaccharide (LPS, 1 µg/ml) or MnCl2 (25-100 µM)-alone or in combination-for 24 h at 37 °C, after which cell-free supernatants were analyzed using a multiplex cytokine assay procedure. Exposure of the cells to LPS caused modest statistically insignificant increases in cytokine production; MnCl2 caused dose-related increases in production of all six cytokines (achieving statistical significance of p < 0.0171- < 0.0005 for IL-1ß, IL-6, IL-8, IFNγ, and TNFα). In the case of LPS and MnCl2 combinations, the observed increases in production of IL-1ß, IL-6, IL-8, IFNγ, and G-CSF were greater than those seen with cells exposed to the individual agents. The Mn(2+)-mediated induction of cytokine production was associated with increased production of H2O2 and completely attenuated by inclusion of the H2O2-scavenger dithiothreitol, and partially by inhibitors of NF-κB and p38MAP kinase. The findings from the studies here help to further characterize the pro-inflammatory mechanisms that may underpin clinical disorders associated with excess exposure to Mn(2+), particularly those disorders seen in the central nervous and respiratory systems.

Manganese promotes increased formation of hydrogen peroxide by activated human macrophages and neutrophils in vitro.

Although pro-inflammatory mechanisms have been implicated in the pathogenesis of manganese (Mn²âº)-related neurological and respiratory disorders, relatively little is known about the potential of this metal to interact pro-oxidatively with human phagocytes. The primary objective of the current study was to investigate the effects of Mn²âº as MnCl2 (0.5-100 µM) on the generation of the reactive oxygen species (ROS), superoxide, hydrogen peroxide (H2O2), and hypohalous acids by isolated human blood neutrophils and monocyte-derived macrophages following activation of these cells with the chemotactic tripeptide, FMLP (1 µM), or the phorbol ester, PMA (25 ng/mL). Generation of ROS was measured using the combination of oxygen consumption, lucigenin/luminol-enhanced chemiluminescence, spectrofluorimetric detection of oxidation of 2,7-dichlorodihydrofluorescein, radiometric assessment of myeloperoxidase (MPO)-mediated protein iodination, release of MPO by ELISA, and spectrophotometric measurement of nitrite formation. Treatment of activated neutrophils with either FMLP or PMA resulted in significantly decreased reactivity of superoxide in the setting of increased formation of H2O2 and MPO-mediated iodination, with no detectable effects on either oxygen consumption or MPO release. Similar effects of the metal with respect to superoxide reactivity and H2O2 formation were observed with activated macrophages, while generation of NO was unaffected. Taken together with the findings of experiments using cell-free ROS-generating systems, these observations are compatible with a mechanism whereby Mn²âº, by acting as a superoxide dismutase mimetic, increases the formation of H2O2 by activated phagocytes. If operative in vivo, this mechanism may contribute to the toxicity of Mn²âº.

Gene deletion of nos2 protects against manganese-induced neurological dysfunction in juvenile mice.

The mechanisms underlying cognitive and neurobehavioral abnormalities associated with childhood exposure to manganese (Mn) are not well understood but may be influenced by neuroinflammatory activation of microglia and astrocytes that results in nitrosative stress due to expression of inducible nitric oxide synthase (iNOS/NOS2). We therefore postulated that gene deletion of NOS2 would protect against the neurotoxic effects of Mn in vivo and in vitro. Juvenile NOS2 knockout (NOS2(-/-)) mice were orally exposed to 50 mg/kg of MnCl2 by intragastric gavage from days 21 to 34 postnatal. Results indicate that NOS2(-/-) mice exposed to Mn were protected against neurobehavioral alterations, despite histopathological activation of astrocytes and microglia in Mn-treated mice in both genotypes. NOS2(-/-) mice had decreased Mn-induced formation of 3-nitrotyrosine protein adducts within neurons in the basal ganglia that correlated with protection against Mn-induced neurobehavioral defects. Primary striatal astrocytes from wildtype mice caused apoptosis in cocultured striatal neurons following treatment with MnCl2 and tumor necrosis factor-α, whereas NOS2(-/-) astrocytes failed to cause any increase in markers of apoptosis in striatal neurons. Additionally, scavenging nitric oxide (NO) with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) prevented the ability of Mn- and cytokine-treated wildtype astrocytes to cause apoptosis in cocultured striatal neurons. These data demonstrate that NO plays a crucial role in Mn-induced neurological dysfunction in juvenile mice and that NOS2 expression in activated glia is an important mediator of neuroinflammatory injury during Mn exposure.

Manganese induced immune suppression of the lobster, Nephrops norvegicus.

Manganese (Mn) is one of the most abundant elements on earth, particularly in the soft bottom sediments of the oceans. As a micronutrient Mn is essential in the metabolic processes of organisms. However, at high concentrations the metal becomes a neurotoxin with well-documented effects. As a consequence of euthrophication, manganese is released from bottom sediments of coastal areas and the Norway lobsters, Nephrops norvegicus, can experience high levels of bioavailable Mn(2+). Here, we present the first report showing that Mn also affects several fundamental processes in the mobilisation and activation of immunoactive haemocytes. When N. norvegicus was exposed to a realistic [Mn(2+)] of 20 mg l(-1) for 10 days 24.1 microg ml(-1) was recorded in the haemolymph. At this concentration the total haemocyte count was reduced by ca. 60%. By using BrdU as a tracer for cell division, it was shown that the proliferation rate in the haematopoietic tissue did not increase, despite the haemocytepenia. A gene coding for a Runt-domain protein, known to be involved in maturation of immune active haemocytes in a variety of organisms, was identified also in haemocytes of N. norvegicus. The expression of this gene was >40% lower in the Mn-exposed lobsters as judged by using a cDNA probe and the in situ hybridisation technique. In response to non-self molecules, like lipopolysaccharide (LPS), the granular haemocytes of arthropods are known to degranulate and thereby release and activate the prophenoloxidase system, necessary for their immune defence. A degranulation assay, tested on isolated granular haemocytes, showed about 75% lower activity in the Mn-exposed lobsters than that for the unexposed. Furthermore, using an enzymatic assay, the activation per se of prophenoloxidase by LPS was found blocked in the Mn-exposed lobsters. Taken together, these results show that Mn exposure suppressed fundamental immune mechanisms of Norway lobsters. This identifies a potential harm that also exists for other organisms and should be considered when increasing the distribution of bioavailable Mn, as has been done through recently introduced applications of the metal.