Metallothioneins and the central nervous system: from a deregulation in neurodegenerative diseases to the development of new therapeutic approaches

Metallothioneins (MT) are a family of proteins actively involved in metal detoxification and storage as well as in prevention of free-radical damage. Changes in the levels of MT have been described in a number of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, prion protein disease, Binswanger type of subcortical vascular dementia, and amyotrophic lateral sclerosis. This suggests that MT functions might be more complex and vast than what was initially thought. In this review, we summarize the current knowledge on the potential involvement of MT in the mentioned neurodegenerative diseases while also discussing the emerging evidence proposing MT modulation as a feasible therapeutic approach. Enhancing repair mechanisms after neurological damage and/or protection against oxidative stress through a proper modulation of this family of protein might indeed represent an important avenue to cope neurodegeneration.

Resveratrol and Alzheimer's disease: message in a bottle on red wine and cognition

Cognitive impairment is the final outcome of a complex network of molecular mechanisms ultimately leading to dementia. Despite major efforts aimed at unraveling the molecular determinants of dementia of Alzheimer type (DAT), effective disease-modifying approaches are still missing. An interesting and still largely unexplored avenue is offered by nutraceutical intervention. For instance, robust epidemiological data have suggested that moderate intake of red wine may protect against several age-related pathological conditions (i.e., cardiovascular diseases, diabetes, and cancer) as well as DAT-related cognitive decline. Wine is highly enriched in many polyphenols, including resveratrol. Resveratrol is a well recognized antioxidant which may modulate metal ion deregulation outcomes as well as main features of the Alzheimer’s disease (AD) brain. The review will discuss the potentiality of resveratrol as a neuroprotectant in dementia in relation to the oxidative stress produced by amyloid and metal dysmetabolism.

Effects of a copper-deficient diet on the biochemistry, neural morphology and behavior of aged mice

Copper dyshomeostasis has been suggested as an aetiological risk factor for some neurodegenerative diseases, such as Alzheimer’s disease. However, the precise mechanism at the base of this involvement is still obscure. In this work, we show the effects of a copper-deficient diet in aged CD1 mice and the influence of such a diet on: a) the concentration of various metal ions (aluminium, copper, iron, calcium, zinc) in the main organs and in different brain areas; b) the alteration of metallothioneins I-II and tyrosine hydroxylase immunopositivity in the brain; c) behavioural tests (open field, pole, predatory aggression, and habituation/dishabituation smell tests). Our data suggested that the copper-deficiency was able to produce a sort of “domino effect” which altered the concentration of the other tested metal ions in the main organs as well as in the brain, without, however, significantly affecting the animal behaviour.

Microarray analysis of gene expression profiles in human neuroblastoma cells exposed to Aβ–Zn and Aβ–Cu complexes

Aims: Abnormal metal accumulation is associated with Alzheimer’s disease and plays a relevant role in affecting amyloid-β (Aβ) peptide aggregation and neurotoxicity. Material & Methods: In the present study, employing a microarray analysis of 35,129 genes, we analyzed gene expression profile changes due to exposure to Aβ1-42 –Zn or Aβ1-42 –Cu complexes in neuronal-like cells (SH-SY5Y). Results: Microarray data indicated that Aβ–Zn or Aβ–Cu complexes selectively alter expression of genes mainly related to cell death, inflammatory responses, cytoprotective mechanisms and apoptosis. Conclusions: Taken together, these findings indicate that Aβ1–42 –Zn or Aβ1–42 –Cu show some commonalities in affecting Alzheimer’s disease-related target functions. The overall modulatory activity on these genes supports the idea of a possible net effect resulting in the activation of pathways that counteract toxic effects of Aβ–Zn or Aβ–Cu.

Resveratrol acts not through anti-aggregative pathways but mainly via its scavenging properties against Aβ and Aβ-metal complexes toxicity

It has been recently suggested that resveratrol can be effective in slowing down Alzheimer's disease (AD) development. As reported in many biochemical studies, resveratrol seems to exert its neuro-protective role through inhibition of β-amyloid aggregation (Aβ), by scavenging oxidants and exerting anti-inflammatory activities. In this paper, we demonstrate that resveratrol is cytoprotective in human neuroblastoma cells exposed to Aβ and or to Aβ-metal complex. Our findings suggest that resveratrol acts not through anti-aggregative pathways but mainly via its scavenging properties.

Physiological cholesterol concentration is a neuroprotective factor against β-amyloid and β-amyloid-metal complexes toxicity

Alzheimer's disease is one of the most common forms of dementia in the elderly. One of its hallmarks is the abnormal aggregation and deposition of β-amyloid (Aβ). Endogenous and exogenous metal ions seem to influence β-amyloid folding process, aggregation and deposition. Besides these variables other elements appear to affect β-amyloid behavior, such as cholesterol. The physiological concentration of cholesterol in the cerebrospinal fluid (CSF) was used in order to determine the extent in which Aβ and Aβ-metal complexes in vitro aggregation and their toxicity on human neuroblastoma cell cultures is affected. Cholesterol did not appear to influence Aβ and Aβ-metal complexes aggregation, but it was effective in protecting neuroblastoma cells against Aβ complexes' toxicity. The Aβ-Al complex seemed to be the most effective in disrupting and damaging membrane external layer, and simultaneously it appears to increase its toxicity on cell cultures; both of these effects are preventable by cholesterol. The presence in physiological concentrations of cholesterol seemed to compensate membrane damage that occurred to neuroblastoma cells. These findings appear to contradict some data reported in literature. We believe that our results might shed some light on the role played by cholesterol at physiological concentrations in both cellular balance and membrane protection.

Challenges associated with metal chelation therapy in Alzheimer's disease

A close association between brain metal dishomeostasis and the onset and/or progression of Alzheimer's disease (AD) has been clearly established in a number of studies, although the underlying biochemical mechanisms remain obscure. This observation renders chelation therapy an attractive pharmacological option for the treatment of this disease. However, a number of requirements must be fulfilled in order to adapt chelation therapy to AD so that the term "metal targeted strategies" seems now more appropriate. Indeed, brain metal redistribution rather than brain metal scavenging and removal is the major goal of this type of intervention. The most recent developments in metal targeted strategies for AD will be discussed using, as useful examples, clioquinol, curcumin, and epigallocatechin, and the future perspectives will also be outlined.

Acidic vesicles of the endo-exocytic pathways as targets for some anti-monoamine oxidase drugs

Acidic vesicles are cytoplasmatic organelles delimited by a single lipoprotein membrane. They contain a large number of enzymes, mostly acidic hydrolases, catalysing various reactions at optimal acidic pH, capable of participating in intracellular digestion. In this paper, some anti-monoamine oxidase drugs (clorgyline, pargyline, amantadine and deprenyl), utilized as pharmacological treatment in some neurological disorders (e.g., Alzheimer's, Parkinson's etc. diseases), were tested for their ability to influence the pH of the acidic intracellular organelles with the aim of exploring their possible pharmacological action. Of the above mentioned drugs, clorgyline showed the most effective action in modifying the acidic vesicles' internal pH, followed by deprenyl, pargyline and amantadine. The effect was not ascribed to an increased proton conductance, but was most likely due to a weak base-like mechanism, in that they exhibit equilibria among species associated with H(+) ions and species lacking this association.

Interaction between Alzheimer's amyloid-beta and amyloid-beta-metal complexes with cell membranes

A number of observations indicate that the primary target of amyloid-beta (Abeta) peptide is the cellular membrane of neurons. In the context of these observations we investigated, using X-ray diffraction techniques, whether Abeta-metal complexes were able to affect lipid bilayers as a model of cell membranes. The binding of Al to Abeta gave particular conformational properties to the peptide that led to a marked alteration of the lipid bilayer representing phospholipids located in the outer monolayer of cell membranes. This effect was peculiar, since in our experimental conditions Abeta alone did not affect the lipid architecture, whereas the Al salt did, but only at concentrations several orders of magnitude higher than those of the Abeta-Al complex. In accordance with the effects observed with lipid bilayers, studies with human neuroblastoma cells demonstrated an impairment of cell functioning only in the presence of Abeta-Al complex. Our findings imply that Al, compared to the other Abeta-metal complexes tested, could have a specifically relevant effect in enhancing Abeta toxicity.

Role of metal ions in the abeta oligomerization in Alzheimer's disease and in other neurological disorders

Neurodegeneration is a complex and multifaceted process leading to many chronic diseased states. Neurodegenerative disorders include a number of different pathological conditions, like Alzheimer's and Parkinson's diseases, which share similar critical metabolic processes, such as protein aggregation, which could be affected by some metal ions. A huge number of reports indicate that, among putative aggravating factors, metal ions (Al, Zn, Cu, Fe) could specifically impair protein aggregation of Abeta, prion protein, ataxin, huntingtin, etc. and their oligomeric toxicity. While studying the molecular basis of these diseases, it has become clear that protein conformation plays a critical role in the pathogenic process. In this review, we will focus on Alzheimer's disease and on the role of metal ions, specifically aluminium, in affecting amyloid aggregation, oligomerization and toxicity.

Accumulation of copper and other metal ions, and metallothionein I/II expression in the bovine brain as a function of aging

Accumulation of metal ions in the brain contributes to heighten oxidative stress and neuronal damage as evidenced in aging and neurodegenerative diseases, both in humans and in animals. In the present paper we report the analysis of Cu, Zn and Mn in the brain of two series of respectively young (8-16 months) and adult (9-12 years) bovines. Our data indicate that the concentrations of Cu varied of one order of magnitude between 1.67 and 15.7microg/g wet tissue; the levels of Zn varied between 6.13 and 17.07microg/g wet tissue and the values of Mn resulted between 0.19 and 1.24microg/g wet tissue. We found relevant age-dependent differences in the distribution of Cu and Zn, whose concentrations were markedly higher in older animals. By contrast, Mn seemed to redistribute in the different cerebral areas rather than drastically change with age. Tissues from bovine brain were also analysed immunohistochemically for the presence and distribution of metallothionein I/II and also for the expression of glial fibrillary acidic protein. Metallothionein I/II immunoreactive elements included ependymal cells lining the lateral ventricles and neural cells in middle layer of the cerebellar cortex. No age differences were evident between calves and adult. The presence of liquor-contacting metallothionein I/II in cells confirms that their functions in the central nervous system are not yet completely established.

Manganese intoxication decreases the expression of manganoproteins in the rat basal ganglia: an immunohistochemical study

Manganese (Mn) is a cofactor for some metalloprotein enzymes, including Mn-superoxide dismutase (Mn-SOD), a mitochondrial enzyme predominantly localized in neurons, and glutamine synthetase (GS), which is selectively expressed in astroglial cells. The detoxifying effects of GS and Mn-SOD in the brain, involve catabolizing glutamate and scavenging superoxide anions, respectively. Mn intoxication is characterized by impaired function of the basal ganglia. However, it is unclear whether regional central nervous system expression of manganoproteins is also affected. Here, we use immunocytochemistry in the adult rat brain, to examine whether Mn overload selectively affects the expression of GS, Mn-SOD, Cu/Zn-SOD, another component of the SOD family, and glial fibrillary acid protein (GFAP), a specific marker of astrocytes. After chronic Mn overload in drinking water for 13 weeks, we found that the number and immunostaining intensity of GS- and Mn-SOD-positive cells was significantly decreased in the striatum and globus pallidus, but not in the cerebral frontal cortex. In addition, we found that GS enzymatic activity was decreased in the strio-pallidal regions but not in the cerebral cortex of Mn-treated animals. In contrast, Cu/Zn-SOD- and GFAP-immunoreactivity was unchanged in both the cerebral cortex and basal ganglia of Mn-treated rats. Thus, we conclude that in response to chronic Mn overload, a down-regulation of some manganoproteins occurs in neurons and astrocytes of the striatum and globus pallidus, probably reflecting the vulnerability of these regions to Mn toxicity.

Unravelling the chemical nature of copper cuprizone

During the last 50 years, formation of the highly chromogenic copper cuprizone complex has been exploited for spectrophotometric determinations of copper although the precise chemical nature of the resulting species has never been ascertained; we eventually show here, in contrast to current opinion, that copper cuprizone is a copper(III)complex.

Copper deficiency and neurological disorders in man and animals

Copper metabolism in the brain is far from being completely understood and further studies are needed on the role of copper in the CNS, starting with careful measurements, metal and biological speciation of metabolites on the molecular level, and combining copper concentration in different brain areas with morphological as well as biochemical alteration after Cu-depletion/deficiency. So far a pathological role for copper has been clearly demonstrated in some human genetic diseases (e.g., Menkes' and Wilson's diseases), but other pathological features connected with metal depletion are under investigation in several laboratories. The metabolic interaction between copper and other metal ions in some neurological disorders is also discussed in this contribution.

Comparative Effects of Aβ(1-42)-Al Complex from Rat and Human Amyloid on Rat Endothelial Cell Cultures

Metal ions are widely recognized as a key factor for the conformational changes and aggregation of the Alzheimer's disease amyloid (Abeta). So far Al(3+) has received much less attention than other biometals in terms of interaction with Abeta. Brain endothelial cells have been identified as important regulators of the neuronal microenvironment, including Abeta levels. The purpose of this study is to compare the effects of the complex amyloid (Abeta(1-42))-Al, from human and rat, with the effects produced by metal-free Abeta on rat neuroendothelial cells (NECs). To establish Abeta and Abeta-Al toxicity on NECs, survival, vitality, and angiogenesis are evaluated. Cell survival is reduced by human and rat Abeta in a time-dependent manner. This toxic effect is remarkably pronounced in the presence of human Abeta-Al. Moreover, rat Abeta has anti-angiogenic properties on NECs, and this effect is aggravated dramatically by using both human and rat Abeta-Al complexes. The data and arguments presented herein clearly demonstrate the involvement of Al(3+) in Abeta aggregation and, consequently, increasing endothelial cell toxicity.

Destabilization of non-pathological variants of ataxin-3 by metal ions results in aggregation/fibrillogenesis

Ataxin-3 (AT3), a protein that causes spinocerebellar ataxia type 3, has a C-terminus containing a polyglutamine stretch, the length of which can be expanded in its pathological variants. Here, we report on the role of Cu(2+), Mn(2+), Zn(2+) and Al(3+) in the induction of defective protein structures and subsequent aggregation/fibrillogenesis of three different non-pathological forms of AT3, i.e. murine (Q6), human non-expanded (Q26) and human moderately expanded (Q36). AT3 variants showed an intrinsic propensity to misfolding/aggregation; on the other hand, Zn(2+) and Al(3+) strongly stimulated the amplitude and kinetics of these conformational conversions. While both metal ions induced a time-dependent aggregation into amyloid-like fibrillar forms, only small oligomers and/or short protofibrillar species were detected for AT3s alone. The rate and extent of the metal-induced aggregation/fibrillogenesis processes increased with the size of the polyglutamine stretch. Mn(2+) and Cu(2+) had no effect on (Q6) or actually prevented (Q26 and Q36) the AT3 structural transitions. The observation that Zn(2+) and Al(3+) promote AT3 fibrillogenesis is consistent with similar results found for other amyloidogenic molecules, such as beta-amyloid and prion proteins. Plausibly, these metal ions are a major common factor/cofactor in the etiopathogenesis of neurodegenerative diseases. Studies of liposomes as membrane models showed dramatic changes in the structural properties of the lipid bilayer in the presence of AT3, which were enhanced after supplementing the protein with Zn(2+) and Al(3+). This suggests that cell membranes could be a potential primary target in the ataxin-3 pathogenesis and metals could be a biological factor capable of modulating their interaction with AT3.

Aluminum complexing enhances amyloid β protein penetration of blood–brain barrier

A significant co-morbidity of Alzheimer's disease and cerebrovascular impairment suggests that cerebrovascular dysregulation is an important feature of dementia. Amyloid beta protein (Abeta), a relevant risk factor in Alzheimer's disease, has neurotoxic properties and is thought to play a critical role in the cognitive impairments. Previously, we demonstrated that the 42mer of Abeta (Abeta42) complexed with aluminum (Al-Abeta42) is much more cytotoxic than non-complexed Abeta42. The level of Abeta in the brain is a balance between synthesis, degradation, and fluxes across the blood-brain barrier (BBB). In the present paper, we determined whether complexing with aluminum affected the ability of radioactively iodinated Abeta to cross the in vivo BBB. We found that the rates of uptake of Al-Abeta42 and Abeta42 were similar, but that Al-Abeta42 was sequestered by brain endothelial cells much less than Abeta42 and so more readily entered the parenchymal space of the brain. Al-Abeta42 also had a longer half-life in blood and had increased permeation at the striatum and thalamus. Brain-to-blood transport was similar for Al-Abeta42 and Abeta42. In conclusion, complexing with aluminum affects some aspects of blood-to-brain permeability so that Al-Abeta42 would have more ready access to brain cells than Abeta42.

Effect of aluminum consumption on the vestibulo-ocular reflex

The effects of chronic exposure (90 days) to Aluminum chloride (AlCl(3)) were analyzed in 3, 10 and 24 month old male rats (n=270) by investigating the function of the VOR (vestibulo-ocular reflex) in correlation with Aluminum (Al) concentrations in blood and brain. The VOR was chosen and tested in basal conditions (pre-exposure measures) and during the continuous administration of three different concentrations of AlCl(3) (0.5, 1, 2 g/l in drinking solution): the control animals being exposed to NaCl (0.125, 0.25 and 5 g/l in drinking solution). Results showed that LOAEL (Lowest Observed Adverse Effect Level) was 43.1+/-11.4 mg Al/kg-day. At this concentration the Al induced significant VOR impairment in all exposed rats, regardless of animal age. Neuroanatomical analysis showed that VOR impairment was not dependent on astrocyte damage nor evidences of amyloid deposits in the exposed rats was found. Significant changes of Al concentrations were observed in nervous tissue, while its concentration in whole blood was unaffected. Furthermore, results show that it is possible to identify an individual neurotoxic threshold for each animal and therefore hypothesize the clinical use of the VOR test for the evaluation of individual risk toxicity to chronic Al exposure.

The effect of Zn(II) and streptozotocin administration in the mouse brain

Streptozotocin is a natural antibiotic produced by Streptomyces achromogenes able to induce diabetes in experimental animals. Among various toxic properties, streptozotocin is a potent source for reactive oxygen species. In this paper, we report the biological response of brain, upon treatment with streptozotocin in terms of metal ions dismetabolism and metallothionein expression. In addition, important information on the preventive effect of zinc in eliciting the pharmacological effect of the drug are reported, in relation to the effective role of the metal ions in inducing metallothionein synthesis. In the brain, streptozotocin treatment affects mostly the hippocampus and cerebellum as shown by a high GAFP and MT-I-II immunopositivity of glial cells. The Zn pre-treatment reduces significantly, as a general effect, the occurrence of hyperglycaemic status. At the brain level, the observed astrocytosis is strongly reduced. The high inducibility of MT represents a rapid and convenient response able to prevent the deleterious effects consequent to the oxidative stress. All together these results support the efficacy of the Zn treatment in order to prevent streptozotocin effects, including brain tissues.

Aggregation/fibrillogenesis of recombinant human prion protein and Gerstmann-Sträussler-Scheinker disease peptides in the presence of metal ions

In this study we investigated the role of Cu(2+), Mn(2+), Zn(2+), and Al(3+) in inducing defective conformational rearrangements of the recombinant human prion protein (hPrP), which trigger aggregation and fibrillogenesis. The research was extended to the fragment of hPrP spanning residues 82-146, which was identified as a major component of the amyloid deposits in the brain of patients affected by Gerstmann-Sträussler-Scheinker (GSS) disease. Variants of the 82-146 wild-type subunit [PrP-(82-146)(wt)] were also examined, including entirely, [PrP-(82-146)(scr)], and partially scrambled, [PrP-(82-146)(106)(-)(126scr)] and [PrP-(82-146)(127)(-)(146scr)], peptides. Al(3+) strongly stimulated the conversion of native hPrP into the altered conformation, and its potency in inducing aggregation was very high. Despite a lower rate and extent of prion protein conversion into altered isoforms, however, Zn(2+) was more efficient than Al(3+) in promoting organization of hPrP aggregates into well-structured, amyloid-like fibrillar filaments, whereas Mn(2+) delayed and Cu(2+) prevented the process. GSS peptides underwent the fibrillogenesis process much faster than the full-length protein. The intrinsic ability of PrP-(82-146)(wt) to form fibrillar aggregates was exalted in the presence of Zn(2+) and, to a lesser extent, of Al(3+), whereas Cu(2+) and Mn(2+) inhibited the conversion of the peptide into amyloid fibrils. Amino acid substitution in the neurotoxic core (sequence 106-126) of the 82-146 fragment reduced its amyloidogenic potential. In this case, the stimulatory effect of Zn(2+) was lower as compared to the wild-type peptide; on the contrary Al(3+) and Mn(2+) induced a higher propensity to fibrillation, which was ascribed to different binding modalities to GSS peptides. In all cases, alteration of the 127-146 sequence strongly inhibited the fibrillogenesis process, thus suggesting that integrity of the C-terminal region was essential both to confer amyloidogenic properties on GSS peptides and to activate the stimulatory potential of the metal ions.

Metallothionein-I-II and GFAP positivity in the brains from frontotemporal dementia patients

Frontotemporal dementia regards a group of presenile progressive neurodegenerative form of dementias which includes Pick's disease, corticobasal degeneration, frontotemporal dementia with motor neuron disease, frontal lobe degeneration, dementia-parkinsonism-amyotrophy complex, familial non-specific dementia mapping to chromosome 3, non-Alzheimer degenerative dementia lacking distinctive histological features as well as a number other infrequent syndromes with dementia and focal neurological signs. The aim of this study was to investigate the regional distribution of metallothionein-I-II, an ubiquitary group of buffering proteins, in cases of frontotemporal dementia. The aim of the present study was to study the metallothionein-I-II expression in relationship to the expression in astrocytes of glial fibrillary acidic protein (GFAP) as we have already done in previous studies of Alzheimer's and Binswanger's diseases [31,32]. Our findings indicate that metallothionein-I-II expression in the most affected areas is likely to be regionally distinct and layer-dependent, in that it is highest in the deep layers of the frontotemporal cortex and the allocortex (hippocampus) while insignificantly immunopositive in the occipital cortex. In addition, the potential use of metallothionein-I-II as a new pharmacological approach to contrast some deleterious aspects of this disease has been also discussed.

Metallothionein-I–II expression in young and adult bovine pineal gland

Aging is characterized, among other features, by an increased concentration of metal ions in the brain that may contribute to a greater increase in free radicals production. The present paper reports data regarding the concentration of some relevant metal ions (Cu, Fe, Mn, Zn), as well as the immunopositivity of metallothionein-I-II and GFAP in the bovine pineal gland with respect to animal aging. The pineal gland of young bovines displays several immunoreactive metallothionein-I-II positive elements in the parenchyma, whose number decreases with age. We also report that a well defined group of neurons bordering the third ventricle and located close to the subcommissural organ shows an intense metallothionein-I-II immunopositivity. The presence of metallothionein-I-II was confirmed by means of liquid chromatography coupled to tandem mass spectrometry. In particular, it proved possible to identify the amino acid sequences of the unique tryptic peptide not containing cysteine and two pepsin fragments containing cysteines. In conclusion, our data suggest the presence of a metallothionein-I-II expressing system in the pineal gland and ventricle-adjacent areas of the bovine epithalamus might possibly be related to the anti-aging effects of melatonin.

Ceruloplasmin in neurodegenerative diseases

For decades, abnormalities in ceruloplasmin (Cp) synthesis have been associated with neurodegenerative disease. From the early observation that low circulating serum ceruloplasmin levels served as a marker for Wilson's disease to the recent characterization of a neurodegenerative disorder associated with a complete lack of serum ceruloplasmin, the link between Cp and neuropathology has strengthened. The mechanisms associated with these different central nervous system abnormalities are very distinct. In Wilson's disease, a defect in the P-type ATPase results in abnormal hepatic copper accumulation that eventually leaks into the circulation and is abnormally deposited in the brain. In this case, copper deposition results in the neurodegenerative phenotype observed. Patients with autosomal recessive condition, aceruloplasminemia, lack the ferroxidase activity inherent to the multi-copper oxidase ceruloplasmin and develop abnormal iron accumulation within the central nervous system. In the following review ceruloplasmin gene expression, structure and function will be presented and the role of ceruloplasmin in iron metabolism will be discussed. The molecular events underlying the different forms of neurodegeneration observed will be presented. Understanding the role of ceruloplasmin within the central nervous system is fundamental to further our understanding of the pathology observed. Is the ferroxidase function more essential than the antioxidant role? Does Cp help maintain nitrosothiol stores or does it oxidize critical brain substrates? The answers to these questions hold the promise for the treatment of devastating neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. It is essential to further elucidate the mechanism of the neuronal injury associated with these disorders.

The C2 variant of human serum transferrin retains the iron binding properties of the native protein

The tryptic digests of blood samples obtained from transferrin C1 and C2 (TfC 1 and TfC2 hereafter) genotypes were analysed by Liquid Chromatography coupled to Electrospray Mass Spectrometry (LC/ESI--MS/MS). The analytical results confirmed the single base change in exon 15 of the Tf gene. The solution behaviour and the iron binding properties of the two Tf variants were studied by UV-visible spectrophotometry and by circular dichroism. It appears that TfC2 globally manifests the same spectral features as the native protein. The local conformation of the two iron binding sites is conserved in the two Tf variants as evidenced by the visible absorption and CD spectra. Also, the iron binding capacities and their pH-dependent profiles are essentially the same. Overall, our investigation points out that the single amino acid substitution in TfC2 (Pro 570 Ser) does not affect the general conformation of the protein nor the local structure of the iron binding sites. The implications of these results for the etiopathogenesis of Alzheimer's disease are discussed.

Copper and zinc dismetabolism in the mouse brain upon chronic cuprizone treatment

Recent reports describe successful treatment using copper chelation therapy in neurodegenerative animal models. However, the success claimed for chelation therapy in neurodegenerative diseases is still rather controversial. To acquire new information on copper metabolism/homeostasis, we utilized cuprizone, a very sensitive and selective copper-chelating agent with well-known neurotoxic properties, as a relevant chemical model in mice. Upon cuprizone treatment, mice developed a pronounced astrocytosis, with brain oedema and spongiosis characterised by vacuolisations of the neuropil predominantly in the white matter. In addition, cuprizone treatment severely altered copper and zinc homeostasis in the central nervous system (CNS) as well as in all other tissues examined, with increasing metal ion concentrations particularly in the CNS. Concomitant with this increase in the Cu and Zn concentration in the brain, metallothionein-I and -II were also highly immunoreactive in astrocyte, consistent with the astrocytosis and demyelination observed in our and other laboratories.

Aluminum-triggered structural modifications and aggregation of β-amyloids

We investigated the structural effects induced by Al3+ on different beta-amyloid (Abeta) fragments at pH 7.4 and T=25 degrees C, with particular attention given to the sequences 1-40 and 1-42. Al3+ caused peptide enrichment in beta sheet structure and formation of solvent-exposed hydrophobic clusters. These intermediates evolved to polymeric aggregates which organized in fibrillar forms in the case of the Al3+-Abeta(1-42) complex. Comparative studies showed that Zn2+ and Cu2+ were much less efficient than Al3+ in stimulating the spontaneous aggregation/fibrillogenesis of Abetas. Studies with liposomes as membrane models showed dramatic changes in the structural properties of the lipid bilayer in the presence of Al3+-Abeta complexes, suggesting a major role of Al3+ in Abeta-induced cell dysfunction. Al3+ effects were abolished by desferrioxamine mesylate (DFO) only in solution. We concluded that, in vivo, DFO may act as a protective agent by preventing or reverting Abeta aggregation in the extracellular spaces.

Structural effects of titanium citrate on the human erythrocyte membrane

The structural effects of titanium citrate on the human erythrocyte membrane were studied through its interaction with intact erythrocytes and isolated unsealed human erythrocyte membranes (IUM). The studies were carried out by scanning electron microscopy and fluorescence spectroscopy, respectively. Titanium citrate induced shape changes in erythrocytes, which were damaged and ruptured leaving empty and retracted membranes. Fluorescence spectroscopy measurements in IUM indicated a disordering effect at both the polar head group and the acyl chain packing arrangements of the membrane phospholipid bilayer. Titanium citrate also interacted with molecular models of the erythrocyte membrane consisting in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing classes of phospholipids located in the outer and inner monolayers of the erythrocyte membrane, respectively. X-ray diffraction indicated that titanium citrate induced structural perturbation of the polar head group and of the hydrophobic acyl regions of DMPC, while the effects on DMPE bilayers were negligible. This conclusion is supported by fluorescence spectroscopy measurements on DMPC large unilamellar vesicles. All these findings indicate that the structural perturbations induced by titanium to human erythrocytes can be extended to other cells, thereby affecting their functions.

Effects of chronic treatment with sodium tetrachloroaurate(III) in mice and membrane models

Gold is a nonessential element with a variety of applications in medicine. A few gold(I) compounds are used in the clinics for treatment of rheumatoid arthritis and of discoid lupus. Some novel gold(III) compounds are under evaluation as anticancer agents. It is known that gold compounds generally produce toxic effects on the kidneys and characteristic lesions in the brain. However, information concerning the neurotoxicity of gold derivatives in humans as well as in experimental toxicology is rather scarce. For this reason we tried to shed some further light on this aspect of gold neurotoxicity by chronic treatment of mice with sodium tetrachloroaurate(III) in order to observe possible biophysical and morphological alterations that may occur in the brain. Chronic gold treatment resulted in a markedly decreased expression of metallothioneins and of glial fibrillary acidic protein in astrocytes of different brain areas. To examine its effects on cell membranes, interactions of sodium tetrachloroaurate(III) with molecular models were also evaluated. The models consisted in bilayers built-up of classes of phospholipids located in the outer and inner monolayers of biological membranes. Structural perturbation of cell membrane models was observed only at concentrations 10(5) times higher than those detected in the brains of animals after three months' treatment. These results show that toxic effects on animal brain upon treatment with sodium tetrachloroaurate develop with difficulty and may be observed only at high doses.

Effects of steroid hormones on the Zn, Cu and MTI/II levels in the mouse brain

The effects of some steroid hormones (corticosterone, hydrocortisone, testosterone and estrone) on the Zn, Cu metabolism and metallothioneins levels in the mouse brain were studied. To administrate the hormones, aqueous suspensions and olive oil solutions injected subcutaneously were used alternatively. The quantification of metals and metallothioneins concentrations in brain homogenates revealed significant alterations of both metal ions and protein expression levels, yet the subcutaneous oil injection increased per se the tissue metallothionein expression and metal content. We have also defined by immunohistochemistry the area-specific distribution of metallothioneins isoforms-I/II and of glial fibrillar acid protein. Upon treatment, corpus callosum, mesencephalon, pons, hippocampus and cerebellum were found to be the areas that increase the protein expression levels, whereas all other brain areas were marginally affected or were unaffected in terms of immunopositive metallothionein reaction. The metallothionein-I/II expression was compared with the immunopositivity of glial fibrillar acid protein and the results are discussed within the framework of the physiological role of corticosteroids and the potential therapeutical importance of sexual hormones.

Chronic Aluminum Administration to Old Rats Results in Increased Levels of Brain Metal Ions and Enlarged Hippocampal Mossy Fibers

The effect of chronic aluminium administration (2 g/L/6 months) was investigated in the central nervous system (CNS) of old rats. The content of Al(3+), Cu(2+), Zn(2+), and Mn(2+) was measured in prosencephalon + mesencephalon, pons-medulla, and cerebellum. The area occupied by the mossy fibers in the hippocampal CA3 zone was also measured. In Al-treated rats the contents of Al(3+), Cu(2+), Zn(2+), and Mn(2+) were significantly increased in prosencephalon + mesencephalon and pons-medulla, while no change was observed in the cerebellum except a Cu(2+) decrease. The area occupied by the mossy fibers in the CA3 field was significantly increased (+32%) in Al-treated rats. Taken together, the present findings document that the aging CNS is particularly susceptible to aluminum toxic effects that may be responsible for a consistent rise in the cell load of oxidative stress. This may contribute, as an aggravating factor, to the development of neurodegenerative events, as observed in Alzheimer disease.

Clioquinol, a Drug for Alzheimer's Disease Specifically Interfering with Brain Metal Metabolism: Structural Characterization of Its Zinc(II) and Copper(II) Complexes

Clioquinol, a 8-hydroxyquinoline derivative, is producing very encouraging results in the treatment of Alzheimer's disease (AD). Its biological effects are most likely ascribed to complexation of specific metal ions, such as copper(II) and zinc(II), critically associated with protein aggregation and degeneration processes in the brain. We report here, for the first time, a structural characterization of the zinc(II) and copper(II) complexes of clioquinol. A ligand to metal stoichiometry of 2:1 is found in both cases, though in the presence of quite different coordination polyhedra. The present findings are discussed in the frame of modern approaches to AD treatment.

Aluminum fluoride affects the structure and functions of cell membranes

No useful biological function for aluminum has been found. To the contrary, it might play an important role in several pathologies, which could be related to its interactions with cell membranes. On the other hand, fluoride is a normal component of body fluids, soft tissues, bones and teeth. Its sodium salt is frequently added to drinking water to prevent dental caries. However, large doses cause severe pathological alterations. In view of the toxicity of Al(3+) and F(-) ions, it was thought of interest to explore the damaging effects that AlF(3) might induce in cell membranes. With this aim, it was incubated with human erythrocytes, which were examined by phase contrast and scanning electron microscopy, and molecular models of biomembranes. The latter consisted of large unilamellar vesicles (LUV) of dimyristoylphosphatidylcholine (DMPC) and bilayers of DMPC and dimyristoylphosphatidylethanolamine (DMPE) which were studied by fluorescence spectroscopy and X-ray diffraction, respectively. In order to understand the effects of AlF(3) on ion transport (principally sodium and chloride) we used the isolated toad skin to which electrophysiological measurements were applied. It was found that AlF(3) altered the shape of erythrocytes inducing the formation of echinocytes. This effect was explained by X-ray diffraction which revealed that AlF(3) perturbed the structure of DMPC, class of lipids located in the outer monolayer of the erythrocyte membrane. This result was confirmed by fluorescence spectroscopy on DMPC LUV. The biphasic (stimulatory followed by inhibitory) effects on the isolated skin suggested changes in apical Cl(-) secretion and moderate ATPase inactivation.

Transferrin C2 variant does confer a risk for Alzheimer's disease in caucasians

Several gene mutations are associated with an increased risk of Alzheimer's disease. Previous studies reported higher transferrin C2 allele frequencies in Alzheimer's disease compared with normal controls. However, potential interactions between transferrin C2 and APOE (epsilon 4), have not been extensively investigated and have been the subject of controversial reports from several laboratories. We have carried out a case-control study on the association between Alzheimer's disease and transferrin C2 and APOE epsilon 4 alleles. epsilon 4 allele was associated with a four fold increase in the risk of disease, and transferrin C2 allele was significantly associated with Alzheimer's disease only in epsilon 4 negative subjects. These results suggest that apoE and transferrin may be part of a complex mechanism in the pathogenesis of Alzheimer's disease.

The effect of chronic aluminum(III) administration on the nervous system of aged rats: Clues to understand its suggested role in Alzheimer's disease

The effect of chronic aluminum intake has been investigated in the brain of aged male Wistar rats to assess the potential role of the accumulation of this metal ion on the development of neurodegenerative features observed in Alzheimer's disease. AlCl3 x 6 H2O (2g/L) was administered to experimental animals for 6 months in the drinking water. The total content of Al (microg/g fresh tissue) was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), while the content of Cu, Zn and Mn was determined by flame AAS in the prosencephalon + mesencephalon, pons-medulla and cerebellum of control and Al(III)-treated animals. The area occupied by mossy fibres in the CA3 field of the hippocampus was estimated by a computer-assisted morphometric method following Timm's preferential staining. In Al(III)-treated rats the concentration of Cu, Zn and Mn did not increase significantly (p < 0.5) in prosencephalon + mesencephalon, nor in pons-medulla (p < 0.5) except for Cu (p < 0.05) in pons-medulla. In the cerebellum the only significant increase was seen for Zn (p < 0.01) while no change was observed for Cu and Mn. The area occupied by the mossy fibres in the hippocampal CA3 field was significantly increased (+32%) in aged Al(III)-treated rats. Since Cu, Zn and Mn are essential components of the cytosolic and mitochondrial superoxide dismutases, it is possible that the increased content of these ions in aged Al(III)-treated rats represents an increased amount of genetic expression of these antioxidant enzymes. Considering that the positivity to Timm's reaction is based on the presence of free or loosely bound Zn2+ ions within synaptic terminals and that Zn2+ ions are reported to be accumulated by hippocampal neurons when tissue injury occurs, the increased area of the mossy fibres in CA3 field of Al(III)-treated rats could indicate increased hippocampal damage in these animals. Taken together, the present findings indicate that the aging CNS is particularly susceptible to Al(III) toxic effects which may increase the cell load of oxidative stress and may contribute, as an aggravating factor, to the development of neurodegenerative events as observed in Alzheimer's disease.

The role of metals in neurodegenerative processes: aluminum, manganese, and zinc

Until the last decade, little attention was given by the neuroscience community to the neurometabolism of metals. However, the neurobiology of heavy metals is now receiving growing interest, since it has been linked to major neurodegenerative diseases. In the present review some metals that could possibly be involved in neurodegeneration are discussed. Two of them, manganese and zinc, are essential metals while aluminum is non-essential. Aluminum has long been known as a neurotoxic agent. It is an etiopathogenic factor in diseases related to long-term dialysis treatment, and it has been controversially invoked as an aggravating factor or cofactor in Alzheimer's disease as well as in other neurodegenerative diseases. Manganese exposure can play an important role in causing Parkinsonian disturbances, possibly enhancing physiological aging of the brain in conjunction with genetic predisposition. An increased environmental burden of manganese may have deleterious effects on more sensitive subgroups of the population, with sub-threshold neurodegeneration in the basal ganglia, generating a pre-Parkinsonian condition. In the case of zinc, there has as yet been no evidence that it is involved in the etiology of neurodegenerative diseases in humans. Zinc is redox-inactive and, as a result of efficient homeostatic control, does not accumulate in excess. However, adverse symptoms in humans are observed on inhalation of zinc fumes, or accidental ingestion of unusually large amounts of zinc. Also, high concentrations of zinc have been found to kill bacteria, viruses, and cultured cells. Some of the possible mechanisms for cell death are reviewed.