A hierarchy of manganese competition and entry in organotypic hippocampal slice cultures.

Contrast agents improve clinical and basic research MRI. The manganese ion (Mn2+ ) is an essential, endogenous metal found in cells and it enhances MRI contrast because of its paramagnetic properties. Manganese-enhanced MRI (MEMRI) has been widely used to image healthy and diseased states of the body and the brain in a variety of animal models. There has also been some work in translating the useful properties of MEMRI to humans. Mn2+ accumulates in brain regions with high neural activity and enters cells via voltage-dependent channels that flux calcium (Ca2+ ). In addition, metal transporters for zinc (Zn2+ ) and iron (Fe2+ ) can also transport Mn2+ . There is also transfer through channels specific for Mn2+ . Although Mn2+ accumulates in many tissues including brain, the mechanisms and preferences of its mode of entry into cells are not well characterized. The current study used MRI on living organotypic hippocampal slice cultures to detect which transport mechanisms are preferentially used by Mn2+ to enter cells. The use of slice culture overcomes the presence of the blood brain barrier, which limits inferences made with studies of the intact brain in vivo. A range of Mn2+ concentrations were used and their effects on neural activity were assessed to avoid using interfering doses of Mn2+ . Zn2+ and Fe2+ were the most efficient competitors for Mn2+ uptake into the cultured slices, while the presence of Ca2+ or Ca2+ channel antagonists had a more moderate effect. Reducing slice activity via excitatory receptor antagonists was also effective at lowering Mn2+ uptake. In conclusion, a hierarchy of those agents which influence Mn2+ uptake was established to enhance understanding of how Mn2+ enters cells in a cultured slice preparation.

Longitudinal MEMRI analysis of brain phenotypes in a mouse model of Niemann-Pick Type C disease.

Niemann-Pick Type C (NPC) is a rare genetic disorder characterized by progressive cell death in various tissues, particularly in the cerebellar Purkinje cells, with no known cure. Mouse models for human NPC have been generated and characterized histologically, behaviorally, and using longitudinal magnetic resonance imaging (MRI). Previous imaging studies revealed significant brain volume differences between mutant and wild-type animals, but stopped short of making volumetric comparisons of the cerebellar sub-regions. In this study, we present longitudinal manganese-enhanced MRI (MEMRI) data from cohorts of wild-type, heterozygote carrier, and homozygote mutant NPC mice, as well as deformation-based morphometry (DBM) driven brain volume comparisons across genotypes, including the cerebellar cortex, white matter, and nuclei. We also present the first comparisons of MEMRI signal intensities, reflecting brain and cerebellum sub-regional Mn2+-uptake over time and across genotypes.

Toxic levels of manganese in an acidic Cambisol alters antioxidant enzymes activity, element uptake and subcellular distribution in Triticum aestivum.

In the Montado system, in Portuguese Alentejo region, some Eutric Cambisols are known to promote manganese (Mn) toxicity in wheat. Variation on bioavailable Mn concentration depends on soil acidity, which can be increased by natural events (e.g. waterlogging) or human activity (e.g. excess use of chemical fertilizers). The effect of increasing soil Mn on crop element uptake, element distribution and oxidative stress was evaluated on winter wheat (Triticum aestivum). Plants were grown for 3 weeks in an acidic Cambisol spiked with increasing Mn concentrations (0, 45.2 and 90.4 mg MnCl2/Kg soil). Calcium (Ca), phosphorus (P), magnesium (Mg) and Mn were quantified in the soil solution, root and shoot tissues and respective subcellular fractions. The activity of the antioxidant enzymes ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), guaiacol peroxidase (GPX) and superoxide dismutase (SOD) were determined in extracts of wheat shoots and roots. Overall, increase in soil bioavailable Mn inhibited the uptake of other elements, increased the Ca proportion in the root apoplast, promoted the translocation of Mn and P to shoot tissues and increased their proportion in the shoot vacuoles. Wheat roots showed greater antioxidant enzymes activities than shoots. These activities decreased at the highest soil Mn concentration in both plant parts. Wheat roots appear to be more sensitive to oxidative stress derived from excess soil Mn and promote Mn translocation and storage in shoot vacuoles, probably in Mn and P complexes, as a detoxification strategy. Improvement in wheat production, in acidic soils, may rely on the enhancement of its Mn detoxification strategies.

Human intestinal Caco-2 cell line in vitro assay to evaluate the absorption of Cd, Cu, Mn and Zn from urban environmental matrices.

The Caco-2 cell line is derived from a human colon adenocarcinoma and is generally used in toxicity assays. The ingestion of soil or dust is a significant route of human exposure to potential harmful elements (PHE), and assays of bioaccessibility or bioavailability can be used to measure the potential hazard posed by exposure to toxic substances. The in vitro digestion (UBM method) and Caco-2 cell model were used to investigate the bioaccessibility and absorption by intestinal cells of the PHE in four matrices (two urban soils and two soils with lead (Pb)-mining tailings) along with the guidance material for bioaccessibility measurements, BGS 102. The gastrointestinal (GI) compartment was simulated, and the resulting material added to Caco-2 cells. In the GI, the average bioaccessibility was 24% for cadmium (Cd), 17% for copper (Cu), 0.2% for Pb, 44% for manganese (Mn) and 6% for zinc (Zn). The poor reproducibility was attributed to the pH (6.3) and the highly complex GI fluid that formed PHE precipitates and complexes. In 2 h, Caco-2 cells absorbed 0.2 ng mg-1 of cellular protein for Cd, 13.4 ng mg-1 for Cu, 5 ng mg-1 for Mn and 31.7 µg mg-1 for Zn. Lead absorption was lower than the limit of quantification (< 2 µg L-1). Cd was presented in the cell monolayer and could interfere in the intracellular accumulation of Cu, Mn and Zn. The use of in vitro assays allowed for an estimation of the absorption of Cd, Cu, Mn and Zn from environmental matrices to be made, and except for Mn, it had a positive correlation with bioaccessible concentration, suggesting a common association of these elements in the cellular environment.

Root Engineering in Barley: Increasing Cytokinin Degradation Produces a Larger Root System, Mineral Enrichment in the Shoot and Improved Drought Tolerance.

Root size and architecture are important crop plant traits, as they determine access to water and soil nutrients. The plant hormone cytokinin is a negative regulator of root growth and branching. Here, we generated transgenic barley (Hordeum vulgare) plants with an enlarged root system by enhancing cytokinin degradation in roots to explore the potential of cytokinin modulations in improving root functions. This was achieved through root-specific expression of a CYTOKININ OXIDASE/DEHYDROGENASE gene. Enhanced biomass allocation to roots did not penalize shoot growth or seed yield, indicating that these plants were not source limited. In leaves of transgenic lines, the concentrations of several macroelements and microelements were increased, particularly those with low soil mobility (phosphorus, manganese, and zinc). Importantly, seeds contained up to 44% more zinc, which is beneficial for human nutrition. Transgenic lines also demonstrated dampened stress responses to long-term drought conditions, indicating lower drought sensitivity. Taken together, this work demonstrates that root engineering of cereals is a promising strategy to improve nutrient efficiency, biofortification, and drought tolerance.

Updating physiologically based pharmacokinetic models for manganese by incorporating rapid association/dissociation processes in tissues.

Previously, we developed a series of physiologically based pharmacokinetic (PBPK) models for manganese (Mn) in which saturable tissue binding and dose-dependent increases in biliary excretion captured key aspects of Mn homeostasis biology. These models reproduced the non-linear behavior of Mn kinetics in different tissues, accounting for dose-dependent changes in Mn kinetics. The original model construct had relatively slow association and dissociation rate constants for Mn binding in tissues. In this updated model, both rates of entry into tissue and the interaction of Mn with binding sites are rapid, and the step limiting Mn accumulation is the saturation of tissue binding sites. This binding reflects general cellular requirements for Mn with high affinity but rapid exchange between bound and free forms, which we captured using a dissociation constant (KD) of ~ 0.5 µM across tissues while maintaining different maximum binding capacities in each tissue. Variability in the binding capacities accounted for different background levels of Mn in particular tissues. This alternative structure successfully described Mn kinetics in tissues in adult rats exposed to Mn either in their diet or by inhalation, indicating that both the original and the present models capture the dose-dependent and tissue-specific kinetic behavior of Mn in adult rats. Although the published models that emphasize the role of smaller tissue binding rate constants in non-linear behaviors capture all relevant dose-dependent kinetic behaviors of this metal, increasing biological relevance of the model structure and parameters should provide greater confidence in applying the Mn PBPK models to risk assessment.

Assessing children's exposure to manganese in drinking water using a PBPK model.

A previously published human PBPK model for manganese (Mn) in infants and children has been updated with Mn in drinking water as an additional exposure source. Built upon the ability to capture differences in Mn source-specific regulation of intestinal uptake in nursing infants who are breast-fed and formula-fed, the updated model now describes the bioavailability of Mn from drinking water in children of ages 0-18. The age-related features, including the recommended age-specific Mn dietary intake, age-specific water consumption rates, and age-specific homeostasis of Mn, are based on the available human data and knowledge of the biology of essential-metal homeostasis. Model simulations suggest that the impact of adding drinking-water exposure to daily Mn exposure via dietary intake and ambient air inhalation in children is not greater than the impacts in adults, even at a drinking-water concentration that is 2 times higher than the USEPA's lifetime health advisory value. This conclusion was also valid for formula-fed infants who are considered at the highest potential exposure to Mn from drinking water compared to all other age groups. Our multi-route, multi-source Mn PBPK model for infants and children provides insights about the potential for Mn-related health effects on growing children and will thereby improve the level of confidence in properly interpreting Mn exposure-health effects relationships in children in human epidemiological studies.

Sex differences in subacute manganese intoxication: Oxidative parameters and metal deposition in peripheral organs of adult Wistar rats.

INTRODUCTION: Manganese (Mn) is an essential element required for several biological systems. However, it is toxic in excessive accumulation. The toxic effects following Mn overexposure is well known in the CNS but other studies evaluating other target tissues remain scarce. OBJECTIVE: This study aimed to investigate sex-related differences in oxidative stress, metabolic parameters and Mn deposition in peripheral organs of Wistar rats exposed to subacute model of intoxication. METHODS: Male and female adult Wistar rats received 6 or 15 mg/kg of MnCl2, intraperitoneally, 5 days a week, for 4 consecutive weeks to mimic subacute intoxication. Control group received sterile saline 0,9% following the same protocol. After this period, the metal accumulation, oxidative stress, mitochondrial activity and histological parameters in cardiac muscle, kidney, lungs and liver were analysed. RESULTS: Increased Mn concentrations were found in all organs, especially kidneys. The cardiac muscle analysis revealed increased lipid peroxidation and decreasing of GSH levels in both doses of Mn in male and female rats. The increase of lipid peroxidation in liver was more evident in the male group, and there was a significant decrease of antioxidant capacity in males' kidney. Nevertheless, there was an increase of mitochondrial complex I activity in kidney of females and increase of mitochondrial complex II activity in male group. Histological analysis revealed morphological changes in hepatic and pulmonary tissue. CONCLUSION: Taken together, our results showed that subacute Mn exposure lead to significant metabolic, biochemical alterations especially in kidney and liver. Nevertheless, despite Mn deposition was virtually the same in the peripheral organs of male and female rats, it promotes different toxic effects between sexes.

Relative bioavailability of humate-manganese complex for broilers fed a corn-soya bean meal diet.

The experiment was conducted to investigate the bioavailability of manganese (Mn) from humate-Mn complex relative to Mn sulphate for the starter broilers fed a conventional corn-soya bean meal diet. A total of 560 1-day-old Arbor Acres male broiler chicks were randomly allotted to one of eight replicate cages (10 chicks per cage) for each of seven treatments in a completely randomized design involving a 2 × 3 factorial arrangement of treatments with two Mn sources (humate-Mn and Mn sulphate) and three levels of added Mn (60, 120 or 180 mg Mn/kg) plus a Mn-unsupplemented control diet containing 27.23 mg Mn/kg by analysis. At 14 days of age, the blood, liver, heart and tibia were collected for Mn analyses, and the activity and mRNA abundance of heart manganese superoxide dismutase (MnSOD). The results showed that humate-Mn supplementation decreased feed intake from day 1 to day 14, whereas it did not influence (p > 0.20) body weight at day 14 as compared to Mn sulphate. The Mn source did not influence Mn concentration in the liver, heart and tibia, and the activity and mRNA abundance of heart MnSOD, while humate-Mn decreased plasma Mn as compared to Mn sulphate. The Mn concentration in the plasma and heart, and the activity and mRNA abundance of heart MnSOD increased linearly as dietary Mn concentration increased. Based on slope ratios from multiple linear regressions of Mn concentrations in the plasma and heart, and the activity and mRNA abundance of heart MnSOD on daily intake amount of dietary analysed Mn, the bioavailability of humate-Mn complex relative to Mn sulphate (100%) was 82.8, 90.4, 82.8 and 81.9 respectively. These results indicated that the Mn from humate-Mn complex was just as bioavailable as the Mn from Mn sulphate for the starter broilers (day 1-14).

Exploring the role of soil geochemistry on Mn and Ca uptake on 75-year-old mine spoils in western Massachusetts, USA.

Manganese pollution to plants, soils, and streams from Mn-rich mine spoils is a global and persistent issue. Some former mining sites can be revegetated readily while others struggle to support plants. We explored Mn in plants and soils following 75 years of soil development and reforestation of a pine-northern hardwood forest at the former Betts Mine in western Massachusetts, USA. We studied soils on four Mn-rich mine spoils and at two control sites: an undisturbed location adjacent to the mine and on a non-Mn mineral bearing rock formation to determine if soil conditions have influenced the uptake of Mn and Ca by vegetation. We collected mid-season foliage from five dominant canopy trees and four common understory plants and excavated three soil pits at each site during July 2018. We found that control sites had lower total Mn (980 ± 140 µg g-1) in their soils than on the mine spoil sites (5580 ± 2050 µg g-1). Our soil data indicated that < 1% of total Mn was strong acid extractable at mine spoil soils and control sites. Surprisingly, the canopy trees established on mine spoils at the Betts Mine had equal to or lower foliar Mn concentrations (840 ± 149 µg g-1) and lower Mn/Ca ratios (0.3 ± 0.1 mol mol-1) than at control sites (1667 ± 270 µg g-1; 1.1 ± 0.2 mol mol-1), refuting our hypothesis of mine spoils driving highest Mn uptake. Soil pH and physicochemical properties suggest Mn primarily exists within primary minerals or form insoluble oxides at the mine spoil sites. Our results suggest higher Ca availability and pH in soils likely reduced Mn uptake and promoted reforestation of the mine spoils.

The use of zeolite-based additives for immobilising iron during pressure filtration of coal refuse slurry.

Pressure filtration of coal refuse slurry has the potential to provide a concentrated solids stream that can be stacked, thereby offering multiple environmental benefits. However, potential leachates from the solids stream can impact the environment. In that context, this study performed preliminary investigations of the application of zeolite-based additives to adsorb metals leaching from coal refuse slurry at low pH. Additives were added to the coal refuse slurry, which was filtered using bench- and lab-scale pressure filtration units. Results indicated that the overall filtrate flux and cake moisture characteristics were not significantly affected by the addition of additives up to 20% (by weight of solids). It was shown that adsorption as high as 80% was achieved by using the additives to capture iron. It was concluded that the finer additive with less silicon content was more effective in capturing iron. The results showed that the thickener feed stream leached out less iron than the thickener underflow stream. The adsorption process was not significantly affected by slight variations in initial iron concentration in the solution. The use of lower pH water on the filter cakes treated with the additive showed minimal release of iron and manganese into the aqueous phase.

A Manganese-based Alternative to Gadolinium: Contrast-enhanced MR Angiography, Excretion, Pharmacokinetics, and Metabolism.

Purpose To compare intravascular contrast enhancement produced by the manganese-based magnetic resonance (MR) imaging contrast agent manganese-N-picolyl-N,N',N'-trans-1,2-cyclohexenediaminetriacetate (Mn-PyC3A) to gadopentetate dimeglumine (Gd-DTPA) and to evaluate the excretion, pharmacokinetics, and metabolism of Mn-PyC3A. Materials and Methods Contrast material-enhanced MR angiography was performed in baboons (Papio anubis; n = 4) by using Mn-PyC3A and Gd-DTPA. Dynamic imaging was performed for 60 minutes following Mn-PyC3A injection to monitor distribution and elimination. Serial blood sampling was performed to quantify manganese and gadolinium plasma clearance by using inductively coupled plasma mass spectrometry and to characterize Mn-PyC3A metabolism by using high-performance liquid chromatography. Intravascular contrast enhancement in the abdominal aorta and brachiocephalic artery was quantified by measuring contrast-to-noise ratios (CNRs) versus muscle at 9 seconds following Mn-PyC3A or Gd-DTPA injection. Plasma pharmacokinetics were modeled with a biexponential function, and data were compared with a paired t test. Results Aorta versus muscle CNR (mean ± standard deviation) with Mn-PyC3A and Gd-DTPA was 476 ± 77 and 538 ± 120, respectively (P = .11). Brachiocephalic artery versus muscle CNR was 524 ± 55 versus 518 ± 140, respectively (P = .95). Mn-PyC3A was eliminated via renal and hepatobiliary excretion with similar pharmacokinetics to Gd-DTPA (area under the curve between 0 and 30 minutes, 20.2 ± 3.1 and 17.0 ± 2.4, respectively; P = .23). High-performance liquid chromatography revealed no evidence of Mn-PyC3A biotransformation. Conclusion Mn-PyC3A enables contrast-enhanced MR angiography with comparable contrast enhancement to gadolinium-based agents and may overcome concerns regarding gadolinium-associated toxicity and retention. © RSNA, 2017 Online supplemental material is available for this article.

Physiologically-based pharmacokinetic modeling suggests similar bioavailability of Mn from diet and drinking water.

Due to concerns for enhanced absorption of manganese (Mn) from drinking water compared to diet, bioavailability of Mn from drinking water remains a major data gap in understanding Mn kinetics. In this study, PBPK models for adult rats and humans were updated with a drinking water exposure route and were used to assess the homeostatic control of Mn uptake, excretion and tissue kinetics between the two different ingestion modes. Drinking water model parameters were estimated from tissue kinetic data from a drinking water study in rats. The published study included a 10 ppm-Mn diet with additional Mn added to drinking water to give a total ingested Mn dose equivalent to that from a 200 ppm diet. The 200 ppm diet and equivalent mixed drinking water/diet exposures provided Mn concentrations for brain (striatum, olfactory bulb, and cerebellum), liver and bone after 7 and 61 days of Mn exposure. Modeling of these data sets indicated that (1) the oral Mn bioavailability is similar for diet or drinking water and (2) homeostatic control of gut uptake of Mn occurs with either drinking water or dietary ingestion. This updated description for absorption and distribution of Mn from gut was added to a human Mn-PBPK model to simulate Mn exposure from multiple routes of exposure (i.e. dietary intake, drinking water, and inhalation). This increases the utility of the Mn PBPK model by allowing for the simulation of multiple Mn exposure scenarios, including variable daily food and drinking water exposures in a human population.

Single and combined effects of Zn, Mn and Fe on the Neotropical freshwater bivalve Anodontites trapesialis: Bioaccumulation and biochemical biomarkers.

Important concentrations of Zn, Mn and Fe were detected in a stream near a coal mining area and promoted, in field, biomarkers alterations in the bivalve Anodontites trapesialis. In order to understand the isolated and mixed effects of these metals on these Neotropical bivalves, we run short-term experiments under laboratory controlled conditions. After 96 h-exposure, tissues (gills, mantle, digestive gland, muscle, hemolymph) were removed for metal bioaccumulation analysis, oxidative stress biomarkers (reactive oxygen species (ROS), total antioxidant capacity, lipoperoxidation (LPO), proteins carbonylation (PC), metallothionein (MT), activity of superoxide dismutase and glutathione S-transferase and hemocytes DNA damage) and cholinesterase (ChE versus ASCh activity) activity evaluation. We run three independent tests. In Zn test, clams were exposed to three concentrations of Zn (0.18 mg L-1, 1.0 mg L-1, 5.0 mg L-1); in Mn test, clams were exposed to three concentrations of Mn (0.1 mg L-1, 0.5 mg L-1, 5.0 mg L-1) and in Mix test, clams were exposed to the mixture Zn (1 mg L-1) + Mn (0.5 mg L-1), with and without Fe (5.0 mg L-1). After single exposure to 5.0 mg L-1, Zn bioaccumulated in all tissues, but only in mantle and hemolymph after exposure to 1.0 mg L-1. The increased MT in gills of A. trapesialis exposed to Zn appears to be sufficient to avoid damage, since LPO occurred only in digestive glands from animals exposed to 5.0 mg L-1. We suggested that A. trapesialis had a metabolic suppression in consequence of Mn presence, based on the following results: the decrease of ROS in gills, the decrease of the Zn and Mn concentrations in tissues and the decrease of ChE versus ASCh activity in muscle. Despite this, animals exposed to Mn suffer oxidative damages (LPO and PC) in the mantle and digestive gland and MT increased in the mantle. These results showed A. trapesialis responded differently to each metal and Mn caused more damage. When exposed to Fe, gills level of ROS was increased, despite no changes in metal accumulation occurred. On the other hand, after exposure to the mixtures, tissues bioaccumulated Zn and previously observed damages caused by Mn and Fe disappeared. Consequently, biomarkers were less affected under mixture treatments, demonstrating mixtures effects or responses were not simply a combination of single exposures to Zn, Mn and Fe, but depend on metals toxicokinetics.

Mn accumulation in a submerged plant Egeria densa (Hydrocharitaceae) is mediated by epiphytic bacteria.

Many aquatic plants act as biosorbents, removing and recovering metals from the environment. To assess the biosorbent activity of Egeria densa, a submerged freshwater macrophyte, plants were collected monthly from a circular drainage area in Lake Biwa basin and the Mn concentrations of the plants were analysed. Mn concentrations in these plants were generally above those of terrestrial hyperaccumulators, and were markedly higher in spring and summer than in autumn. Mn concentrations were much lower in plants incubated in hydroponic medium at various pH levels with and without Mn supplementation than in field-collected plants. The precipitation of Mn oxides on the leaves was determined by variable pressure scanning electron microscopy-energy dispersive X-ray analysis and Leucoberbelin blue staining. Several strains of epiphytic bacteria were isolated from the field-collected E. densa plants, with many of these strains, including those of the genera Acidovorax, Comamonas, Pseudomonas and Rhizobium, found to have Mn-oxidizing activity. High Mn concentrations in E. densa were mediated by the production of biogenic Mn oxide in biofilms on leaf surfaces. These findings provide new insights into plant epidermal bacterial flora that affect metal accumulation in plants and suggest that these aquatic plants may have use in Mn phytomining.

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.

Tooth manganese as a biomarker of exposure and body burden in rats.

BACKGROUND: Neonates and children are particularly vulnerable to the toxic effects of excess manganese (Mn), but studies of Mn exposure during these developmental periods are hampered by a lack of validated biomarkers. Deciduous teeth may be used to assess Mn exposure during these developmental periods but require further validation to determine the relationship between tooth Mn, Mn in target tissues, and exposure. OBJECTIVES: To determine the relationship of tooth Mn concentrations with: (i) exposure dose, (ii) the timing/duration of exposure, and (iii) with Mn concentrations in blood, brain and bone. METHODS: Rats in different treatment groups were orally exposed to 0, 25 or 50µg/g/day Mn either from postnatal day (PND) 1 - 21 and culled at PND 24, from PND 1 - 21 and culled as adults (>PND 290), or from PND 1 - throughout life and culled at >290 PND. Mn was measured in second molars, femurs, brain and blood by ICP-MS. RESULTS: Tooth Mn increased significantly with dose in rats exposed for 21 PND and culled at 24 PND (p<0.001). In rats culled at >290 PND, tooth Mn increased with exposure duration (p<0.001) and reflected exposure duration. A significant, positive association between tooth Mn and Mn levels in blood (Spearman's rho 0.69, p<0.01) brain (rho 0.59, p<0.05) and bone (rho 0.69, p<0.01) was observed in animals with lifelong exposure. Tooth Mn and Mn levels in bone were also significantly positively associated in animals exposed only early in life (rho 0.76, p<0.001). CONCLUSIONS: Teeth are a sensitive biomarker of active and past Mn exposure and Mn burden in tissues. Unlike blood, teeth retain information on exposure history over the short and long-term.

Interplay between lysosomal, mitochondrial and death receptor pathways during manganese-induced apoptosis in glial cells.

Manganese (Mn) is an essential trace metal which plays a critical role in brain physiology by acting as a cofactor for several enzymes. However, upon overexposure, Mn preferentially accumulates within the basal ganglia leading to the development of a Parkinsonism known as Manganism. Data from our group have proved that Mn induces oxidative stress-mediated apoptosis in astrocytoma C6 cells. In the present study we described how cathepsins impact on different steps of each apoptotic cascade. Evidence obtained demonstrated that Mn generates lysosomal membrane permeabilization (LMP) and cathepsin release. Both cathepsins B (Ca-074 Me) and D (Pepstatin A) inhibitors as well as Bafilomycin A1 prevented caspases-3, -7, -8 and -9 activation, FasL upregulation, Bid cleavage, Δφm disruption and cytochrome c release. Results from in vivo studies showed that intrastriatal Mn injection increased cathepsin D levels from corpus striatum and substantia nigra pars compacta. Our results point to LMP and lysosomal cathepsins as key mediators in the apoptotic process triggered by Mn. These findings highlight the relevance of targeting the lysosomal pathway for Manganism therapy.

Nanodiamond-Manganese dual mode MRI contrast agents for enhanced liver tumor detection.

Contrast agent-enhanced magnetic resonance (MR) imaging is critical for the diagnosis and monitoring of a number of diseases, including cancer. Certain clinical applications, including the detection of liver tumors, rely on both T1 and T2-weighted images even though contrast agent-enhanced MR imaging is not always reliable. Thus, there is a need for improved dual mode contrast agents with enhanced sensitivity. We report the development of a nanodiamond-manganese dual mode contrast agent that enhanced both T1 and T2-weighted MR imaging. Conjugation of manganese to nanodiamonds resulted in improved longitudinal and transverse relaxivity efficacy over unmodified MnCl2 as well as clinical contrast agents. Following intravenous administration, nanodiamond-manganese complexes outperformed current clinical contrast agents in an orthotopic liver cancer mouse model while also reducing blood serum concentration of toxic free Mn2+ ions. Thus, nanodiamond-manganese complexes may serve as more effective dual mode MRI contrast agent, particularly in cancer.

Functional magnetic resonance microscopy at single-cell resolution in Aplysia californica.

In this work, we show the feasibility of performing functional MRI studies with single-cell resolution. At ultrahigh magnetic field, manganese-enhanced magnetic resonance microscopy allows the identification of most motor neurons in the buccal network of Aplysia at low, nontoxic Mn(2+) concentrations. We establish that Mn(2+) accumulates intracellularly on injection into the living Aplysia and that its concentration increases when the animals are presented with a sensory stimulus. We also show that we can distinguish between neuronal activities elicited by different types of stimuli. This method opens up a new avenue into probing the functional organization and plasticity of neuronal networks involved in goal-directed behaviors with single-cell resolution.