Silver enhancement of quantum dots resulting from (1) metabolism of toxic metals in animals and humans, (2) in vivo, in vitro and immersion created zinc–sulphur/zinc–selenium nanocrystals, (3) metal ions liberated from metal implants and particles

Metallic silver fragments cause massive tissue loss in the mouse brain

Silver is a metal with well-known antibacterial effects. This makes silver an attractive coating material for medical devices for use inside the body, e.g. orthopaedic prostheses and catheters used in neurosurgery as it has been found to reduce the high risk of infections. Lately, the use of nano-silver particles in the industry, e.g. woven into fabrics and furniture has increased, and thus the exposure to silver particles in daily life increases. To study the effect of metallic silver particles on nervous tissue, we injected micron-sized silver particles into the mouse brain by stereotactic procedures. After 7, 14 days and 9 months, the silver-exposed animals had considerable brain damage seen as cavity formation and inflammation adjacent to the injected metallic silver particles. The tissue loss involved both cortical and hippocampal structures and resulted in enlargement of the lateral ventricles. Autometallographic silver enhancement showed silver uptake in lysosomes of glia cells and neurons in the ipsilateral cortex and hippocampus alongside a minor uptake on the contralateral side. Silver was also detected in ependymal cells and the choroid plexus. After 9 months, spreading of silver to the kidneys was seen. Cell counts of immunostained sections showed that metallic silver induced a statistically significant inflammatory response, i.e. increased microgliosis (7 days: p < 0.0001; 14 days: p < 0.01; 9 months: p < 0.0001) and TNF-α expression (7 and 14 days: p < 0.0001; 9 months: p = 0.91). Significant astrogliosis (7, 14 days and 9 months: p < 0.0001) and increased metallothionein (MT I + II) expression (7 and 14 days: p < 0.0001; 9 months: p < 0.001) were also seen in silver-exposed brain tissue. We conclude that metallic silver implants release silver ions causing neuroinflammation and a progressive tissue loss in the brain.

New silver-gold intensification method of diaminobenzidine for double-labeling immunoelectron microscopy

The available methods for double-labeling preembedding immunoelectron microscopy are highly limited because not only should the ultrastructure be preserved, but also the different antigens should be visualized by reaction end products that can be clearly distinguished in gray-scale images. In these procedures, one antigen is detected with 3,3'-diaminobenzidine (DAB) chromogen, resulting in a homogeneous deposit, whereas the other is labeled with either a gold-tagged immunoreagent, or DAB polymer, on the surface of which metallic silver is precipitated. The detection of the second antigen is usually impeded by the first, leading to false-negative results. The authors aimed to diminish this hindrance by a new silver intensification technique of DAB polymer, which converts the deposit from amorphous to granular. The method includes three major postdevelopmental steps: (1) treatment of nickel-enhanced DAB with sulfide, (2) silver deposition in the presence of hydroquinone under acidic conditions, and (3) precious metal replacement with gold thiocyanate. This new sulfide-silver-gold intensification of DAB (SSGI) allows a subsequent detection of other antigens using DAB. In conclusion, the new technique loads fine gold particles onto the DAB deposit at a very low background level, thereby allowing a reliable discernment between the elements stained for the two antigens at the ultrastructural level.

Zinc overload enhances APP cleavage and Aβ deposition in the Alzheimer mouse brain

Background

Abnormal zinc homeostasis is involved in β-amyloid (Aβ) plaque formation and, therefore, the zinc load is a contributing factor in Alzheimer's disease (AD). However, the involvement of zinc in amyloid precursor protein (APP) processing and Aβ deposition has not been well established in AD animal models in vivo.

Methodology/Principal Findings

In the present study, APP and presenilin 1 (PS1) double transgenic mice were treated with a high dose of zinc (20 mg/ml ZnSO4 in drinking water). This zinc treatment increased APP expression, enhanced amyloidogenic APP cleavage and Aβ deposition, and impaired spatial learning and memory in the transgenic mice. We further examined the effects of zinc overload on APP processing in SHSY-5Y cells overexpressing human APPsw. The zinc enhancement of APP expression and cleavage was further confirmed in vitro.

Conclusions/Significance

The present data indicate that excess zinc exposure could be a risk factor for AD pathological processes, and alteration of zinc homeostasis is a potential strategy for the prevention and treatment of AD.

The amplification of polymerized diaminobenzidine with physical developers: sensitizing effects of transition metal salts and sulphide

Amplification of metal-complexed polymerized diaminobenzidine by two light-insensitive physical developers was systematically examined in a dot blot model system following either polymerizing diaminobenzidine in the presence of transition metal salts or applying the metal salts post-diaminobenzidine polymerization. The effect of sodium sulphide treatment on subsequent amplification was also investigated. Those metal-diaminobenzidine complexes that facilitated the most powerful amplification were subsequently tested in an immunohistochemical setting. The most dramatic amplification of polymerized diaminobenzidine was observed following its post-polymerization treatment with salts of platinum alone, or gold or vanadium with subsequent sulphide treatment, and allowed previously invisible quantities of polymerized diaminobenzidine to be clearly seen. Three other transition metal salts also improved the amplification of polymerized diaminobenzidine but to a lesser degree, namely nickel alone, and silver or rhodium with subsequent sulphide treatment. Sensitivity was comparable with the colloidal gold-silver amplification system.

Clioquinol inhibits zinc-triggered caspase activation in the hippocampal CA1 region of a global ischemic gerbil model

Background

Excessive release of chelatable zinc from excitatory synaptic vesicles is involved in the pathogenesis of selective neuronal cell death following transient forebrain ischemia. The present study was designed to examine the neuroprotective effect of a membrane-permeable zinc chelator, clioquinol (CQ), in the CA1 region of the gerbil hippocampus after transient global ischemia.

Methodology/Principal Findings

The common carotid arteries were occluded bilaterally, and CQ (10 mg/kg, i.p.) was injected into gerbils once a day. The zinc chelating effect of CQ was examined with TSQ fluorescence and autometallography. Neuronal death, the expression levels of caspases and apoptosis inducing factor (AIF) were evaluated using TUNEL, in situ hybridization and Western blotting, respectively. We were able to show for the first time that CQ treatment attenuates the ischemia-induced zinc accumulation in the CA1 pyramidal neurons, accompanied by less neuronal loss in the CA1 field of the hippocampus after ischemia. Furthermore, the expression levels of caspase-3, -9, and AIF were significantly decreased in the hippocampus of CQ-treated gerbils.

Conclusions/Significance

The present study indicates that the neuroprotective effect of CQ is related to downregulation of zinc-triggered caspase activation in the hippocampal CA1 region of gerbils with global ischemia.

Chemical blocking of zinc ions in CNS increases neuronal damage following traumatic brain injury (TBI) in mice

Background

Traumatic brain injury (TBI) is one of the leading causes of disability and death among young people. Although much is already known about secondary brain damage the full range of brain tissue responses to TBI remains to be elucidated. A population of neurons located in cerebral areas associated with higher cognitive functions harbours a vesicular zinc pool co-localized with glutamate. This zinc enriched pool of synaptic vesicles has been hypothesized to take part in the injurious signalling cascade that follows pathological conditions such as seizures, ischemia and traumatic brain injury. Pathological release of excess zinc ions from pre-synaptic vesicles has been suggested to mediate cell damage/death to postsynaptic neurons.

Methodology/Principal Findings

In order to substantiate the influence of vesicular zinc ions on TBI, we designed a study in which damage and zinc movements were analysed in several different ways. Twenty-four hours after TBI ZnT3-KO mice (mice without vesicular zinc) were compared to littermate Wild Type (WT) mice (mice with vesicular zinc) with regard to histopathology. Furthermore, in order to evaluate a possible neuro-protective dimension of chemical blocking of vesicular zinc, we treated lesioned mice with either DEDTC or selenite. Our study revealed that chemical blocking of vesicular zinc ions, either by chelation with DEDTC or accumulation in zinc-selenium nanocrystals, worsened the effects on the aftermath of TBI in the WT mice by increasing the number of necrotic and apoptotic cells within the first 24 hours after TBI, when compared to those of chemically untreated WT mice.

Conclusion/Significance

ZnT3-KO mice revealed more damage after TBI compared to WT controls. Following treatment with DEDTC or selenium an increase in the number of both dead and apoptotic cells were seen in the controls within the first 24 hours after TBI while the degree of damage in the ZnT3-KO mice remained largely unchanged. Further analyses revealed that the damage development in the two mouse strains was almost identical after either zinc chelation or zinc complexion therapy.

Effects of dissolucytotic gold ions on recovering brain lesions

Recent experimental research has shown that metallic gold releases charged gold atoms when placed intracerebrally and that the liberated gold ions affect inflammation in the brain. The observations suggest that metallic gold can be used as a safe suppressor of inflammation in the central nervous system.

Biodistribution of gold nanoparticles in mouse lung following intratracheal instillation

Background

The fate of gold nanoparticles, 2, 40 and 100 nm, administered intratracheally to adult female mice was examined. The nanoparticles were traced by autometallography (AMG) at both ultrastructural and light microscopic levels. Also, the gold content was quantified by inductively coupled plasma mass spectrometry (ICP-MS) and neutron activation analysis (NAA). The liver is the major site of deposition of circulating gold nanoparticles. Therefore the degree of translocation was determined by the hepatic deposition of gold. Mice were instilled with 5 intratracheal doses of gold nanoparticles distributed over a period of 3 weeks and were killed 24 h after the last dose. One group of mice were given a single intratracheal dose and were killed after 1 h.

Results

The instilled nanoparticles were found in lung macrophages already 1 h after a single instillation. In mice instilled treated repeatedly during 3 weeks, the load was substantial. Ultrastructurally, AMG silver enhanced gold nanoparticles were found in lysosome-/endosome-like organelles of the macrophages and analysis with AMG, ICP-MS and NAA of the liver revealed an almost total lack of translocation of nanoparticles. In mice given repeated instillations of 2 nm gold nanoparticles, 1.4‰ (by ICP-MS) to 1.9‰ (by NAA) of the instilled gold was detected in the liver. With the 40 nm gold, no gold was detected in the liver (detection level 2 ng, 0.1‰) except for one mouse in which 3‰ of the instilled gold was found in the liver. No gold was detected in any liver of mice instilled with 100 nm gold (detection level 2 ng, 0.1‰) except in a single animal with 0.39‰ of the dose in the liver.

Conclusion

We found that that: (1) inert gold nanoparticles, administered intratracheally are phagocytosed by lung macrophages; (2) only a tiny fraction of the gold particles is translocated into systemic circulation. (3) The translocation rate was greatest with the 2 nm gold particles.

Unintentional silver intoxication following self-medication: an unusual case of corticobasal degeneration

Silver toxicity is a rare condition. The most notable feature is a grey-blue discoloration of the skin, argyria, although harmful effects on the liver and kidney may be seen in severe cases. Neurological symptoms are an unusual consequence of silver toxicity. So far no effective treatment has been described for this metal overdose. We report the case of a 75-year-old man who had a history of self-medication with colloidal silver and presented with myoclonic seizures.

High-resolution mapping of neuronal activity using the lipophilic thallium chelate complex TlDDC: protocol and validation of the method

In neurons the rate of K(+)-uptake increases with increasing activity. K(+)-analogues like the heavy metal ion thallium (Tl(+)) can be used, therefore, as tracers for imaging neuronal activity. However, when water-soluble Tl(+)-salts are injected systemically only minute amounts of the tracer enter the brain and the Tl(+)-uptake patterns are influenced by regional differences in blood-brain barrier (BBB) K(+)-permeability. We here show that the BBB-related limitations in using Tl(+) for imaging neuronal activity are no longer present when the lipophilic Tl(+) chelate complex thallium diethyldithiocarbamate (TlDDC) is applied. We systemically injected rodents with TlDDC and mapped the Tl(+)-distribution in the brain using an autometallographic (AMG) technique, a histochemical method for detecting heavy metals. We find that Tl(+)-doses for optimum AMG staining could be substantially reduced, and regional differences attributable to differences in BBB K(+)-permeability were no longer detectable, indicating that TlDDC crosses the BBB. At the cellular level, however, the Tl(+)-distribution was essentially the same as after injection of water-soluble Tl(+)-salts, indicating Tl(+)-release from TlDDC prior to neuronal or glial uptake. Upon sensory stimulation or intracortical microstimulation neuronal Tl(+)-uptake increased after TlDDC injection, upon muscimol treatment neuronal Tl(+)-uptake decreased. We present a protocol for mapping neuronal activity with cellular resolution, which is based on intravenous TlDDC injections during ongoing activity in unrestrained behaving animals and short stimulation times of 5 min.

Zinc deficiency reduces neurogenesis accompanied by neuronal apoptosis through caspase-dependent and -independent signaling pathways

Dietary zinc deficiency may affect zinc homeostasis in the brain and lead to reductions of neurogenesis and neuronal survival. However, the mechanisms responsible for the effects of zinc deficiency on hippocampal neurogenesis and neuronal death remain obscure. In the present study, young CD-1 mice were fed with zinc-deficient diet (0.85 ppm) for 5 weeks. The vesicular zinc was reduced at CA1 and CA3 regions of the hippocampus in zinc-deficient mice. The significant decreased zinc ions was associated with a reduction in proliferating cells labeled with bromo-deoxyuridine (BrdU) and immature neurons labeled with doublecortin (DCX) immunoreactivity in the dentate gyrus of the hippocampus. The processes of DCX-positive neurons were shortened, and flexuously went through into the granular cell layer in zinc-deficient hippocampus. There was also a conspicuous increase in the number of TUNEL-positive cells in the hippocampus after zinc-deficient diet treatment. Meanwhile, the apoptosis proteins, including Fas, Fas ligand (FasL), apoptosis inducing factor (AIF), and caspase-3, were significantly activated in zinc-deficient mouse hippocampus. These data suggest that chronic treatment with zinc-deficient diet results in reduction in hippocampal neurogenesis and increases neuronal apoptosis, indicating that zinc deficiency is associated with destroying structural plasticity in the hippocampus.

SLC30A3 responds to glucose- and zinc variations in beta-cells and is critical for insulin production and in vivo glucose-metabolism during beta-cell stress

BACKGROUND

Ion transporters of the Slc30A- (ZnT-) family regulate zinc fluxes into sub-cellular compartments. beta-cells depend on zinc for both insulin crystallization and regulation of cell mass.

METHODOLOGY/PRINCIPAL FINDINGS

This study examined: the effect of glucose and zinc chelation on ZnT gene and protein levels and apoptosis in beta-cells and pancreatic islets, the effects of ZnT-3 knock-down on insulin secretion in a beta-cell line and ZnT-3 knock-out on glucose metabolism in mice during streptozotocin-induced beta-cell stress. In INS-1E cells 2 mM glucose down-regulated ZnT-3 and up-regulated ZnT-5 expression relative to 5 mM. 16 mM glucose increased ZnT-3 and decreased ZnT-8 expression. Zinc chelation by DEDTC lowered INS-1E insulin content and insulin expression. Furthermore, zinc depletion increased ZnT-3- and decreased ZnT-8 gene expression whereas the amount of ZnT-3 protein in the cells was decreased. Zinc depletion and high glucose induced apoptosis and necrosis in INS-1E cells. The most responsive zinc transporter, ZnT-3, was investigated further; by immunohistochemistry and western blotting ZnT-3 was demonstrated in INS-1E cells. 44% knock-down of ZnT-3 by siRNA transfection in INS-1E cells decreased insulin expression and secretion. Streptozotocin-treated mice had higher glucose levels after ZnT-3 knock-out, particularly in overt diabetic animals.

CONCLUSION/SIGNIFICANCE

Zinc transporting proteins in beta-cells respond to variations in glucose and zinc levels. ZnT-3, which is pivotal in the development of cellular changes as also seen in type 2 diabetes (e.g. amyloidosis in Alzheimer's disease) but not previously described in beta-cells, is present in this cell type, up-regulated by glucose in a concentration dependent manner and up-regulated by zinc depletion which by contrast decreased ZnT-3 protein levels. Knock-down of the ZnT-3 gene lowers insulin secretion in vitro and affects in vivo glucose metabolism after streptozotocin treatment.

Protracted elimination of gold nanoparticles from mouse liver

The present study aims at revealing the fate of 40-nm gold nanoparticles after intravenous injections. The gold nanoparticles were traced histochemically with light and transmission electron microscopy using autometallographic (AMG) staining, and the gold content in the liver was determined with inductively coupled plasma mass spectrometry (ICP-MS). Gold nanoparticles were identified in almost all Kupffer cells one day after the injection, but the fraction of gold-loaded cells gradually decreased to about one fifth after 6 months. Transmission electron microscopic analysis showed that the gold nanoparticles had accumulated inside the vesicular lysosome/endosome-like structures of the macrophages. At day 1, about 4.5 per thousand of the area of the liver sections was AMG-stained, after 1 month it had decreased to 0.7 per thousand, and thereafter no further significant reduction was recorded. Because ICP-MS only showed a 9% fall in the gold content over the observed 6 months, the AMG finding of a significant reduction in the stained area of the liver sections and number of macrophages loaded with gold nanoparticles reveals that over time an increasing part of the total amount of gold nanoparticles in the liver is contained in fewer macrophages accumulated in growing clusters.

Physicochemical mechanisms of histological silver staining and their utilization for rendering individual silver methods selective and reliable

Staining morphological or chemical constituents of biological tissues, cells and microorganisms with silver proceeds via different reaction routes. In this paper, I put their physicochemical mechanisms into a coherent system and discuss how these can be controlled and separated from each other, thereby permitting selective, sensitive and reliable demonstration of individual tissue constituents.

Can silver nanoparticles be useful as potential biological labels?

Silver (Ag) nanoparticles have unique plasmon-resonant optical scattering properties that are finding use in nanomedical applications such as signal enhancers, optical sensors, and biomarkers. In this study, we examined the chemical and biological properties of Ag nanoparticles of similar sizes, but that differed primarily in their surface chemistry (hydrocarbon versus polysaccharide), in neuroblastoma cells for their potential use as biological labels. We observed strong optical labeling of the cells in a high illumination light microscopy system after 24 h of incubation due to the excitation of plasmon resonance by both types of Ag nanoparticle. Surface binding of both types of Ag nanoparticle to the plasma membrane of the cells was verified with scanning electron microscopy as well as the internalization and localization of the Ag nanoparticles into intracellular vacuoles in thin cell sections with transmission electron microscopy. However, the induction of reactive oxygen species (ROS), degradation of mitochondrial membrane integrity, disruption of the actin cytoskeleton, and reduction in proliferation after stimulation with nerve growth factor were found after incubation with Ag nanoparticles at concentrations of 25 µg ml(-1) or greater, with a more pronounced effect produced by the hydrocarbon-based Ag nanoparticles in most cases. Therefore, the use of Ag nanoparticles as potential biological labels, even if the surface is chemically modified with a biocompatible material, should be approached with caution.

Abundant expression of zinc transporters in the amyloid plaques of Alzheimer's disease brain

The pathological key features of Alzheimer's disease (AD) are beta-amyloid peptide (Abeta)-containing senile plaques (SP) and neurofibrillary tangles. Previous studies have suggested that an extracellular elevation of the zinc concentration can initiate the deposition of Abeta and lead to the formation of SP. In the present study, we present data showing a correlation between zinc ions, zinc transporters (ZNTs) and AD, using immersion autometallography (AMG) and double immunofluorescence for the ZNTs and Abeta. We found that all the ZNTs tested (ZNT1, 3, 4, 5, 6, 7) were extensively present in the Abeta-positive plaques in the cortex of human AD brains, and the density of autometallographic silver enhanced zinc-sulphur nanoparticles were much higher in the plaques than in the surrounding zinc enriched (ZEN) terminals. Moreover, we found an abundant expression of ZNT3 and autometallographic grains in the amyloid angiopathic vessels. The subcellular localization of ZNTs and zinc ions were not detected, due to the limited tissue preservation in the present study. In conclusion, our data provided significant morphological evidence of zinc ions and ZNTs being actively involved in the pathological processes that lead to plaque formation.

Selenium-mercury interactions in man and animals

Selenium-mercury interactions were most extensively studied in relation to alleviation of Hg toxicity by added selenium. This presentation considers the influence of mercury on endogenous selenium, on its tissue and cellular "status" after lifelong or acute exposure to mercury vapor (Hg o). Discussed are data obtained from (1) humans living near or working in a mercury mine, and (2) rats experimentally exposed in the mine. Mercury vapor is unique--or similar to methylmercury--because of its ability to penetrate cell membranes and so invade all cells, where it is oxidized in the biologically active form (Hg++) by catalase. Such in situ-generated ions can react with endogenously generated highly reactive Se metabolites, like HSe-, and render a part of the selenium unavailable for selenoprotein synthesis. Data on human populations indicate that in moderate Hg exposure combined with an adequate selenium supply through diet, Se bioavailability can be preserved. On the other hand, the results of an acute exposure study emphasize the dual role of selenium in mercury detoxification. Besides the well-known Se coaccumulation through formation of nontoxic Hg-Se complexes, we observed noticeable Se (co)excretion, at least at the beginning of exposure. The higher Hg accumulation rate in the group of animals with lower basal selenium levels can also point to selenium involvement in mercury excretion. In such conditions there is a higher probability for decreased selenoprotein levels (synthesis) in some tissues or organs, depending on the synthesis hierarchy.

Kupffer cells are central in the removal of nanoparticles from the organism

Background

The study aims at revealing the fate of nanoparticles administered intravenously and intraperitoneally to adult female mice, some of which were pregnant. Gold nanoparticles were chosen as a model because these particles have been found to be chemically inert and at the same time are easily traced by autometallography (AMG) at both ultrastructural and light microscopic levels.

Results

Gold nanoparticles were injected intravenously (IV) or intraperitoneally (IP) and traced after 1, 4 or 24 hours. For IV injections 2 and 40 nm particles were used; for IP injections 40 nm particles only. The injected nanoparticles were found in macrophages only, and at moderate exposure primarily in the Kupffer cells in the liver. IV injections resulted in a rapid accumulation/clustering of nanoparticles in these liver macrophages, while the uptake in spleen macrophages was moderate. IP injections were followed by a delayed uptake in the liver and included a moderate uptake in macrophages located in mesenteric lymph nodes, spleen and small intestine. Ultrastructurally, the AMG silver enhanced nanocrystals were found in lysosome-like organelles of the Kupffer cells and other macrophages wherever located.

Accumulations of gold nanoparticles were not found in any other organs analysed, i.e. kidneys, brain, lungs, adrenals, ovaries, placenta, and fetal liver, and the control animals were all void of AMG staining.

Conclusion

Our results suggest that: (1) inert gold nanoparticles do not penetrate cell membranes by non-endocytotic mechanisms, but are rather taken up by endocytosis; (2) gold nanoparticles, independent of size, are taken up primarily by Kupffer cells in the liver and secondarily by macrophages in other places; (3) gold nanoparticles do not seem to penetrate the placenta barrier; (4) the blood-brain barrier seems to protect the central nervous system from gold nanoparticles; (5) 2 nanometer gold particles seem to be removed not only by endocytosis by macrophages, and we hypothesize that part of these tiny nanoparticles are released into the urine as a result of simple filtration in the renal glomeruli.

Autometallographic tracing of Hg-S quantum dots in frogs exposed to inorganic mercury

The histochemical distribution of mercury in the kidneys and gut of frogs (Rana ridibunda) exposed to inorganic mercury was analyzed with autometallography (AMG). It was found that most mercury in the kidneys accumulated in the proximal convoluted tubules as Hg-S nanocrystal, while control animals were totally void of AMG grains. In the gut the highest concentration of mercury was observed in the large intestine. The AMG grains were primarily located in the apical part of the absorptive cells, although rather high concentrations of silver enhanced mercury quantum dots were also detected in a special cell type of gut epithelium and the glycocalyx. A certain amount of AMG grains were detected in the lumen of the gut. We hypothesize that this pool of quantum dots results from sloughed off epithelial cells and macrophages. Such still intact cells and red blood cells containing AMG grains were also found in the lumen of the gut.

Amyloid plaques arise from zinc-enriched cortical layers in APP/PS1 transgenic mice and are paradoxically enlarged with dietary zinc deficiency

The ZnT3 zinc transporter is uniquely expressed in cortical glutamatergic synapses where it organizes zinc release into the synaptic cleft and mediates beta-amyloid deposition in transgenic mice. We studied the association of zinc in plaques in relation to cytoarchitectural zinc localization in the APP/PS1 transgenic mouse model of Alzheimer's disease. The effects of low dietary zinc for 3 months upon brain pathology were also studied. We determined that synaptic zinc distribution within cortical layers is paralleled by amyloid burden, which is heaviest for both in layers 2-3 and 5. ZnT3 immunoreactivity is prominent in dystrophic neurites within amyloid plaques. Low dietary zinc caused a significant 25% increase in total plaque volume in Alzheimer's mice using stereological measures. The level of oxidized proteins in brain tissue did not changed in animals on a zinc-deficient diet compared with controls. No obvious changes were observed in the autometallographic pattern of zinc-enriched terminals in the neocortex or in the expression levels of zinc transporters, zinc importers or metallothioneins. A small decrease in plasma zinc induced by the low-zinc diet was consistent with the subclinical zinc deficiency that is common in older human populations. While the mechanism remains uncertain, our findings indicate that subclinical zinc deficiency may be a risk factor for Alzheimer's pathology.

In vitro liberation of charged gold atoms: autometallographic tracing of gold ions released by macrophages grown on metallic gold surfaces

The present study demonstrates that cultured macrophages are able to liberate gold ions from metallic gold surfaces, a process suggested to be called "dissolucytosis", in a way analogous to the release taking place when metallic implants are placed in a body. Using the ultra-sensitive autometallographic (AMG) technique, we demonstrate that murine macrophages grown on a surface of metallic gold liberate gold ions. Ultra-structural AMG reveals that the gold ions are located in an ultra-thin membrane-like structure, "the dissolution membrane", intervened between the macrophages and the metal surface. The presence of AMG silver enhanced gold nanoparticles in the dissolution membrane proves that the release of charged gold atoms takes place extracellularly. The dissolution membrane is most likely secreted and chemically controlled by the "dissolucytes", here macrophages, and the membrane is essential for the dissolution of metal implants and particles, which cannot be phagocytosed. Our findings support the notion that whenever a metallic gold surface is attacked by dissolucytes, gold ions are liberated and taken up by surrounding cells. As gold ions can suppress the inflammatory process, it is reasonable to expect that when dissolucytosis takes place in the living organism the liberated gold ions will cause local immunosuppression.