Elise A. Malecki

Manganese toxicity is associated with mitochondrial dysfunction and DNA fragmentation in rat primary striatal neurons.

Manganese (Mn) in excess is toxic to neurons of the globus pallidus, leading to a Parkinsonian-like syndrome. We used rat primary neuron cultures to examine the cellular events following manganese exposure. Following exposure to Mn(2+) for 48 h, striatal neurons showed dose-dependent losses of mitochondrial membrane potential and complex II activity. The Mn exposure effect on mitochondrial membrane potential was significant at every concentration measured (5, 50, and 500 microM), and the manganese exposure effect on complex II activity was significant at 50 and 500 microM. Exposure of striatal neurons to both Mn(2+) and the complex II inhibitor 3-nitropropionic acid resulted in additive toxicity. Striatal neurons exposed to 5 microM Mn(2+) for 48 h exhibited DNA fragmentation and decreases in the immunohistochemically detectable microtubule-associated protein MAP-2. These results indicate that manganese may trigger apoptotic-like neuronal death secondary to mitochondrial dysfunction. Rescue of neurons by apoptosis inhibitors may be helpful in treating manganese toxicity and similar neurodegenerative processes.

Existing and emerging mechanisms for transport of iron and manganese to the brain.

The metals iron (Fe) and manganese (Mn) are essential for normal functioning of the brain. This review focuses on recent developments in the literature pertaining to Fe and Mn transport. These metals are treated together because they appear to share several transport mechanisms. In addition, several neurological diseases such as Alzheimers Disease, Parkinsons Disease, and Huntingtons Disease are all associated with Fe mismanagement in the brain, particularly in the striatum and basal ganglia. Similarly, Mn accumulation in brain also appears to target the same brain regions. Therefore, stringent regulation of the concentration of these metals in the brain is essential. The homeostatic mechanisms for these metals must be understood in order to design neurotoxicity prevention strategies.

Transferrin is required for normal distribution of 59Fe and 54Mn in mouse brain

Hypotransferrinemia (hpx/hpx) is a genetic defect in mice resulting in <1% of normal plasma transferrin (Tf) concentrations; heterozygotes for this mutation (+/hpx) have low circulating Tf concentrations. These mice provide a unique opportunity to examine the role of Tf in Fe and Mn transport in the brain. Twenty weanling wild-type BALB/cJ mice, 15 +/hpx mice, and 12 hpx/hpx mice of both sexes were injected i.v. with either 54MnCl(2) or 59FeCl(3) either 1 h or 1 week before killing at 12 weeks of age. Total brain counts of 54Mn and 59Fe were measured, and regional brain distributions were assessed by autoradiography. Hypotransferrinemia did not affect total brain Mn uptake. However, 1 week after i.v. injection, hpx/hpx mice had less 54Mn in forebrain structures including cerebral cortex, corpus callosum, striatum, and substantia nigra. The +/hpx mice had the highest total brain 59Fe accumulation 1 h after i.v. injection. A striking effect of regional distribution of 59Fe was noted 1 week after injection; in hpx/hpx mice, 59Fe was located primarily in choroid plexus, whereas in +/+ and +/hpx mice 59Fe was widely distributed, with relatively high amounts in cerebral cortex and cerebellum. We interpret these data to mean that Tf is necessary for the transport of Fe but not Mn across the blood-brain barrier, and that there is a Tf-independent uptake mechanism for iron in the choroid plexus. Additionally, these data suggest that endogenous synthesis of Tf is necessary for Fe transport from the choroid plexus.

Transferrin response in normal and iron-deficient mice heterozygotic for hypotransferrinemia; effects on iron and manganese accumulation.

Hypotransferrinemia is a genetic defect in mice resultingin 1% of normal plasma transferrin (Tf) concen-trations;heterozygotes for thismutation (+/hpx) have low circulating Tf concentrations. These mice providea unique opportunity toexamine the developmental pattern and response of Tf to iron-deficient diets, andfurthermore,to address the controversial role of Tf in Mn transport. Twenty-three weanling +/hpx miceandforty-five wild-type BALB/cJ mice were either killed at weaning or fed diets containing either13 or 72 mgkg Fe, and killed after four or eight weeks. Plasma Tfconcentrations were lower in +/hpx mice, plasmaTf nearly doubled and liver Tf was only 50% of normalin response to iron deficiency. Brain iron concen-trationdid not correlate significantlywith either plasma Tf or TIBC. However, iron accumulation into braincontinued with irondeficiency whereas most other organs had less iron. These results imply that eitherthereis a selected targeting of iron to the brain by plasma Tf or there is an alternative irondelivery system tothe brain. Furthermore, we observed no differences in tissuedistribution of Mn despite the differences incirculating Tf concentrationsand body iron stores; this suggests that there are non-Tf dependent mecha-nismsfor Mntransport.

The lipophilic iron compound TMH-ferrocene [(3,5,5-trimethylhexanoyl)ferrocene] increases iron concentrations, neuronal l-ferritin, and heme oxygenase in brains of BALB/c mice

Mismanagement of intracellular iron is a key pathological feature of many neurodegenerative diseases. Our long-term goal is to use animal models to investigate the mechanisms of iron neurotoxicity and its relationship to neurodegenerative pathologies. The immediate aim of this experiment was to determine regional distribution of iron and cellular distribution of iron storage proteins (l- and h-ferritin) and an oxidative stress marker (heme oxygenase-1) in brains of mice fed the lipophilic iron compound (3,5,5-trimethylhexanoyl) (TMH)-ferrocene. We fed male and female weanling BALB/cj mice diets either deficient in iron (0 mg Fe/kg diet), adequate in iron (35 mg Fe/kg diet; control mice), or adequate in iron and supplemented with 0.1 or 1.0 g TMH-ferrocene/kg diet for 8 wk. Iron concentrations in cerebrum were higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p<0.05). Liver iron concentrations were eightfold higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p<0.0001). l-Ferritin and heme oxygenase-1 expression were elevated in striatum in mice fed 1.0 g TMH-ferrocene/kg diet. We conculde that administration of the lipophilic iron compound TMH-ferrocene leads to subtle perturbations of cellular iron within the brain, potentially representing a model of iron accumulation similar to that seen in various neuropathological conditions.

Bone Structural and Mechanical Properties Are Affected by Hypotransferrinemia But Not by Iron Deficiency in Mice

Hypotransferrinemia is a genetic defect in mice resulting in <1% of normal plasma transferrin (Tf) concentrations; heterozygotes for this mutation (+/hpx) have low circulating Tf concentrations. We used this mutant mouse in conjunction with dietary iron deficiency to study the influence of Tf and iron on bone structural and mechanical properties. Twenty‐one weanling wild‐type BALB/cj +/+ mice and 21 weanling +/hpx mice were fed iron‐deficient or iron‐adequate diets for 8 weeks. Twelve hpx/hpx mice were fed the iron‐adequate diet. Hypotransferrinemia resulted in increased tibia iron and calcium concentrations, lower femur failure load, and extrinsic stiffness. Because the femurs of the hpx/hpx mice were disproportionately small, these bones actually had increased tissue material properties (ultimate stress [US] and modulus of elasticity) than those of wild‐type mice. This is the first report on the effect of dietary iron deficiency on bone structural and mechanical properties. Dietary iron deficiency in +/+ and +/hpx mice decreased tibia iron concentrations but had no effect on tibia calcium and phosphorus concentrations or femur structural or mechanical properties. Because the bones of the hpx/hpx mice were small, but had superior tissue mechanical properties, we conclude that Tf is important for normal bone mineralization. (J Bone Miner Res 2000; 15: 271–277)

Iron and Manganese Homeostasis in Chronic Liver Disease

The hyperintense signal in the globus pallidus of cirrhotic patients on T1-weighted magnetic resonance (MR) imaging has been postulated to arise from deposition of paramagnetic manganese2+ (Mn). Intestinal absorption of both iron and Mn are increased in iron deficiency; iron deficiency may therefore increase susceptibility to Mn neurotoxicity. To investigate the relationships between MR signal abnormalities and Mn and Fe status, 21 patients with chronic liver disease were enrolled (alcoholic liver disease, 5; primary biliary cirrhosis, 9; primary sclerosing cholangitis, 3; hepatitis B virus, 2; hepatitis C virus, 1; alpha1-antitrypsin deficiency, 1). Signal hyperintensity in the pallidum on axial T1 weighted images (repetition time/evolution time: 500 ms/15 ms) was observed in 13 of 21 subjects: four patients had mild hyperintensity, three moderate, and six exhibited marked hyperintensity. Erythrocyte Mn concentrations were positively correlated with the degree of the MR hyperintensity (Kendalls tau-b=0.52, P<0.005). The log of erythrocyte Mn concentration was also inversely correlated with all measures of iron status: hemoglobin (Pearsons R=-0.73, P<0.0005); hematocrit (R=-0.62, P<0.005); serum Fe concentrations (R=-0.65, P<0.005); and TIBC saturation (R=-0.62, P<0.005). These findings confirm the association of Mn with the development of pallidal hyperintensity in patients with liver disease. We further found that iron deficiency is an exacerbating factor, probably because of increased intestinal absorption of Mn. We therefore recommend that patients with chronic liver disease avoid Mn supplements without concurrent iron supplementation.