Zn and Cu alteration in connection with astrocyte metallothionein I/II overexpression in the mouse brain upon physical stress

The distribution of metallothioneins I/II in the mouse brain and their specific area distribution upon physical stress were studied. To induce physical stress, groups of mice were subjected to total darkness for different periods (2 weeks, 1 month, and 2 months). The concentration of metallothioneins, evaluated by immunohistochemistry, as well as area-specific protein expression, were found in the following quantitative order: corpus striatum, cerebellum, mesencephalon, hippocampus with fornix, parts of thalamus, and pons. All other brain areas were marginally affected, or even unaffected, in terms of immunopositive metallothionein reaction. Metallothionein I/II expression was compared with the immunopositivity of glial fibrillary acidic protein (GFAP). It is noteworthy that metallothioneins and GFAP are expressed in different types of astrocytes.

Effects of lead on the human erythrocyte membrane and molecular models

Lead has no biological function; however, low, and particularly, high levels of exposure have a number of negative consequences for human health. Despite the number of reports about lead toxicity, very little information has been obtained regarding its effects on cell membranes. For this reason, the structural effects of lead on the human erythrocyte membranes were investigated. This aim was attained by making lead ions interact with intact erythrocytes, isolated unsealed erythrocyte membranes (IUM) and molecular models. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane. The results, obtained by electron microscopy, fluorescence spectroscopy and X-ray diffraction, indicated that (a) lead particles adhered to the external and internal surfaces of the human erythrocyte membrane; (b) lead ions disturbed the lamellar organization of IUM and DMPC large unilamellar vesicles (LUV) and (c) induced considerable molecular disorder in both lipid multilayers, the effects being much more pronounced in DMPC.

Melatonin prevents free radical formation due to the interaction between beta-amyloid peptides and metal ions [Al(III), Zn(II), Cu(II), Mn(II), Fe(II)]

Alzheimer's disease, among other pathological features, is characterized by an over-accumulation of amyloid-beta peptide, metal ions, and oxidative stress proteins in the brain. Amyloid-beta aggregated peptides with bound metal ions may initiate free radical generation with consequent protein and lipid oxidation, reactive oxygen species formation and eventually neuronal death. Melatonin is able to dramatically reduce the free radical formation which follows the interaction between transition metal ions and amyloid-beta. This paper reports the scavenging effect of melatonin of reactants generated by amyloid peptides in combination with some metal ions.

Binding studies on aluminum(III)-albumin interaction

The present paper reports a quantitative investigation on the binding of aluminum to human serum albumin. Equilibrium dialysis and a general thermodynamic approach have been used to determine the binding parameters. Two aluminum binding sites have been identified on the albumin molecule, involving sites with single and double occupancy modes. The binding properties of these two distinct sites appear to undergo reciprocal influences, suggesting a possible interaction between the corresponding protein moieties. Both coordination modes proceed from weak interactions, as shown by the binding energies calculated.

Some biochemical properties of melatonin and the characterization of a relevant metabolite arising from its interaction with H2O2

Melatonin is an efficient protector against hydrogen peroxide(H2O2)-induced lipid peroxidation and acts in a concentration-dependent manner. Hydrogen peroxide is rather a water stable molecule which is able to cross the cell membrane much better than some important free radicals such as superoxide anion, and consequently its local production can lead to significant spread by diffusion. In this paper we report data regarding some biochemical properties of melatonin as well as the chemical characterization of the major product formed from the interaction between melatonin and H2O2 (N1-acetyl-N2-formyl-5-methoxykynuramine) that are consistent with previous data reported by other authors. The effect of melatonin on catalase, glutathione peroxidase and superoxide dismutase in in vitro and in vivo experiments is also reported.

Metallothionein I-II immunocytochemical reactivity in Binswanger's encephalopathy

Binswanger's disease is a subacute form of hypertensive encephalopathy characterized by patchy-confluent myelin loss of the deep hemispheric white matter, associated with marked regressive changes of the oligodendrocytes and variable astroglial reaction. To understand the distribution and the specificity of astrocyte pathology in Binswanger's disease we quantified reactive and degenerating astrocytes in different regions of the deep and subcortical white matter and of the cerebral cortex. Sections of frontal, temporal, parietal, and occipital lobes of 12 histologically proven cases of Binswanger's disease were immunostained with antibodies to glial fibrillary protein (GFAP) and to metallothionein I and II (MT-I-II), markers which specifically identify normal and reactive astrocytes. Control tissues were from 6 elderly patients without neurological diseases. The brains of Binswanger's disease were characterized by few and lightly immunostained astrocytes in the deep white matter, but normal and reactive astrocytes, strongly immunoreactive for GFAP and MT-I-II, were prominent in the subcortical white matter and the cerebral cortex. However, the relative distribution of GFAP positive and MT-I-II positive astrocytes was significantly different between the cerebral cortex and the subcortical white matter, the MT-I-II positive astrocytes being more frequent in the cerebral cortex, and the GFAP positive astrocytes in the subcortical white matter (p < 0.02). The GFAP and MT-I-II expressions in subsets of reactive astrocytes in the cortico-subcortical layers together with regressive astroglial changes in the deep white matter suggest that the dynamic plasticity of astroglia is topographically and biochemically differentiated in vascular dementia of Binswanger type.

In vivo and in vitro effects of aluminum on the activity of mouse brain acetylcholinesterase

Cholinesterases are a large family of enzymatic proteins widely distributed throughout both neuronal and non-neuronal tissues. In Alzheimer's disease (AD), analytical as well as epidemiological studies suggest an implication of an abnormal focal accumulation of aluminum in the brain. In this devastating disease, aluminum may interfere with various biochemical processes including acetylcholine metabolism, and can thus act as a possible etiopathogenic cofactor. Acetylcholinesterase (AChE) exists in several molecular forms that differ in solubility and mode of membrane attachment rather than in catalytic activity. Mice were treated orally with aluminum chloride or aluminum lactate (Al(lac)(3)), and AChE activity in their brain homogenates was then assayed. Results showed that this in vivo treatment augmented the activity of the enzyme. An activating effect was also observed in vitro, when the aluminum compounds were added directly to mouse brain homogenates. However, the activating effect observed in vivo was much more marked than that observed in vitro. In addition, the activation produced by Al(lac)(3) was higher than that obtained after aluminum chloride treatment. Kinetics measurements of AChE activity in the absence and presence of treatment with aluminum both in vivo and in vitro are reported. The influence of the metal speciation on enzymatic activity is discussed in relation to a possible implication of aluminum in some neurodegenerative diseases.

Astrocytosis, microgliosis, metallothionein-I-II and amyloid expression in high cholesterol-fed rabbits

Cholesterol is considered a risk factor in vascular dementia as well as in Alzheimer's disease. Several biochemical, epidemiological and genetic aspects established a correlation between cholesterol concentration and Alzheimer's disease. Microglia activation, astrocytosis with metallothionein-I-II overexpression, amyloid beta intraneuronal accumulation and a rare formation of amyloid beta extracellular positive deposits were the major immunohistochemical features observed in the brain of high cholesterol-fed animals. The relevance on the cholesterol metabolism in Alzheimer's disease pathogenesis is also discussed.

Roles of the metallothionein family of proteins in the central nervous system

Metallothioneins (MTs) constitute a family of proteins characterized by a high heavy metal [Zn(II), Cu(I)] content and also by an unusual cysteine abundance. Mammalian MTs are comprised of four major isoforms designated MT-1 trough MT-4. MT-1 and MT-2 are expressed in most tissues including the brain, whereas MT-3 (also called growth inhibitory factor) and MT-4 are expressed predominantly in the central nervous system and in keratinizing epithelia, respectively. All MT isoforms have been implicated in disparate physiological functions, such as zinc and copper metabolism, protection against reactive oxygen species, or adaptation to stress. In the case of MT-3, an additional involvement of this isoform in neuromodulatory events and in the pathogenesis of Alzheimer's disease has also been suggested. It is essential to gain insight into how MTs are regulated in the brain in order to characterize MT functions, both in normal brain physiology, as well as in pathophysiological states. The focus of this review concerns the biology of the MT family in the context of their expression and functional roles in the central nervous system.

Zinc-bound metallothioneins as potential biological markers of ageing

Metallothioneins (MTs) (I+II) play pivotal roles in metal-related cell homeostasis because of their high affinity for metals forming clusters. The main functional role of MTs is to sequester and/or dispense zinc participating in zinc homeostasis. Consistent with this role, MT gene expression is transcriptionally induced by a variety of stressing agents to protect cells from reactive oxygen species. In order to accomplish this task, MTs induce the secretion of pro-inflammatory cytokines by immune and brain cells, such as astrocytes, for a prompt response against oxidative stress. These cytokines are in turn involved in new synthesis of MTs in the liver and brain. Such protective mechanism occurs in the young-adult age, when stresses are transient. Stress-like condition is instead constant in the old age, and this causes continuous stealing of intracellular zinc by MTs and consequent low bioavailability of zinc ions for immune, endocrine, and cerebral functions. Therefore, a protective role of zinc-bound MTs (I+II) during ageing can be questioned. Because free zinc ions are required for optimal efficiency of the immune-endocrine-nervous network, zinc-bound MTs (I+II) may play a different role during ageing, switching from a protective to a deleterious one in immune, endocrine, and cerebral activities. Physiological zinc supply, performed cautiously, can correct deficiencies in the immune-neuroendocrine network and can improve cognitive performances during ageing and accelerated ageing. Altogether these data indicate that zinc-bound MTs (I+II) can be considered as novel potential markers of ageing.

Effects of AlCl3 on toad skin, human erythrocytes, and model cell membranes

Aluminum, a very abundant metal, could play a toxic role in several pathological processes, including neurodegeneration. Although the effects of Al(III) on biological membranes have been extensively described, direct information concerning the molecular basis of its biological activity is rather scanty. To examine aluminum challenges on cell membranes, various concentrations of AlCl3 in aqueous solutions were incubated with human erythrocytes, isolated toad skin, and molecular models of biomembranes. The latter consisted of multilayers of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, representing phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane. These specimens were studied by scanning electron microscopy, electrophysiological measurements, and x-ray diffraction. The results indicate that Al(III) in the concentration range of 10-100 microM induced the following structural and functional effects: (i) change in the normal discoid shape of human erythrocytes to echinocytes due to the accumulation of Al(III) ions in the outer moiety of the red cell membrane; (ii) perturbation of dimyristoylphosphatidylcholine, and to a lesser extent of dimyristoylphosphatidylethanolamine bilayers, and (iii) decrease in the short-circuit current and in the potential difference of the isolated toad skin, effects that are in accordance with a time-dependent modulation of ion transport in response to changes in the molecular structure of the lipid bilayer.

Inhibitory effect of aluminum on dopamine beta-hydroxylase from bovine adrenal gland

Aluminum is a well known neurotoxic agent that is overaccumulated in the substantia nigra of patients affected by Parkinson's disease as well as in certain cerebral areas of other neurodegenerative pathologies such as Alzheimer's disease. Although the role of aluminum in neurodegenerative diseases is yet to be clearly understood, the metal ion is known to substantially alter the activity of several key enzymes in the central nervous system. The present paper reports data on the effect of aluminum on the activity of dopamine-beta-hydroxylase from bovine adrenaL gland utiLized as a model study. The metal ion inhibited the activity of this enzyme with a mixed type mechanism following the Michaelis-Menten equation. In the absence of Al, the enzyme exhibited a Km and Vmax of 2.56 mM of 4.12 pmol/min respectively, while in the presence of Al its Km and Vmax were 3.85 mM and 2.86 pmol/min respectively. The potential implications of aluminum in the etiopathogenesis of neurological disorders are discussed.

Aluminum as an inducer of the mitochondrial permeability transition

Treatment of rat liver mitochondria with aluminum in the presence of Ca2+ results in large amplitude swelling accompanied by loss of endogenous Mg2+ and K+ and oxidation of endogenous pyridine nucleotides. The presence of cyclosporin A, ADP, bongkrekic acid, N-ethylmaleimide and dithioerythritol prevent these effects, indicating that binding of aluminum to the inner mitochondrial membrane, most likely at the level of adenine nucleotide translocase, correlates with the induction of the membrane permeability transition (MPT). Indeed, aluminum binding promotes such a perturbation at the level of ubiquinol-cytochrome c reductase, which favors the production of reactive oxygen species. These metabolites generate an oxidative stress involving two previously defined sites in equilibrium with the glutathione and pyridine nucleotides pools, the levels of which correlate with the increase in MPT induction. Although the above-described phenomena are typical of MPT, they are not paralleled by other events normally observed in response to treatment with inducers of MPT (e.g., phosphate), such as the collapse of the electrochemical gradient and the release of accumulated Ca2+ and oxidized pyridine nucleotides. Biochemical and ultrastructural observations demonstrate that aluminum induces a pore opening having a conformation intermediate between fully open and closed in a subpopulation of mitochondria. While inorganic phosphate enhances the MPT induced by ruthenium red plus a deenergizing agent, aluminum instead inhibits this phenomenon. This finding suggests the presence of a distinct binding site for aluminum differing from that involved in MPT induction.

Aluminum inhibits the lysosomal proton pump from rat liver

Lysosomes are cytoplasmatic organelles, delimitated by a single lipoprotein membrane, that contain several enzymes mostly belonging to the hydrolases in that they function mainly for intracellular digestion. Lysosomal internal pH is characteristically acidic and it is maintained around pH 4.5 by a proton pump, an ATPase, that uses energy from ATP hydrolysis to translocate H+ ions into lysosomes. In the presence of Al3+ the proton pump activity is markedly reduced compromising acidic vesicles functionality. Among different species utilized, Al2(SO4)3 and AlF3 were the most effective. Aluminum effect was not observed when the delta pH was produced artificially by nigericin.

Effects of aluminum on activity of krebs cycle enzymes and glutamate dehydrogenase in rat brain homogenate

Aluminum is a neurotoxic agent for animals and humans that has been implicated as an etiological factor in several neurodegenerative diseases and as a destabilizer of cell membranes. Due to its high reactivity, Al3+ is able to interfere with several biological functions, including enzymatic activities in key metabolic pathways. In this paper we report that, among the enzymes that constitute the Krebs cycle, only two are activated by aluminum: alpha-ketoglutarate dehydrogenase and succinate dehydrogenase. In contrast, aconitase, shows decreased activity in the presence of the metal ion. Al3+ also inhibits glutamate dehydrogenase, an allosteric enzyme that is closely linked to the Krebs cycle. A possible correlation between aluminum, the Krebs cycle and aging processes is discussed.

Activation of monoamine oxidase type-B by aluminum in rat brain homogenate

Monoamine oxidase type B (MAO-B) activity is elevated in certain neurological diseases such as Alzheimer's and Parkinson's disease with respect to age-matched controls; the cause of this elevation is unknown. The documented accumulation of aluminum in certain neurodegenerative diseases prompted us to test the effect of Al3+ on the activity of MAO-B in rat brain homogenate. Results showed that the metal ion significantly increased MAO-B enzymatic activity in a dose-dependent manner, yielding a K(M) of 5.69 microM compared with 34.45 microM in the absence of the metal ion. The Vmax of 45.34 micromol/min was unchanged in the presence of the metal ion.

Interactions of Al(acac)3 with cell membranes and model phospholipid bilayers

Aluminum is a neurotoxic agent; however, little information has been obtained regarding its molecular cytotoxicity and the effects on the stability of biological membranes. This is mainly due to the ill-defined chemical speciation of the metal compounds. For this reason, the present study used aluminum acetylacetonate, (Al(acac)3), a neutral, chemically well-defined, hydrolytically stable and lipophilic compound. To understand the molecular mechanism of its interaction with cell membranes, Al(acac)3 was incubated with human erythrocytes, isolated toad skin and molecular models of biomembranes. The latter consisted of multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoyphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. The results showed that Al(acac)3 interacted with the erythrocyte membrane modifying its normal discoid morphology to both echinocytic and stomatocytic shapes. This finding indicates that the Al complex was inserted in both the outer and inner layers of the red cell membrane, a conclusion supported by X-ray diffraction analyses of DMPC and DMPE bilayers. Electrophysiological measurements performed on toad skin revealed a significant decrease in the potential difference and short-circuit current responses after application of Al(acac)3, effects interpreted to reflect inhibition of the active transport of ions. Al(acac)3 was active on both surfaces of the skin suggesting that the membrane was permeated by the metal complex. It is concluded that Al(acac)3 both alters the molecular structure of the lipid bilayer, thereby modifying the biophysical properties of the cell membrane, and changes its physiological properties.

Formation of titanium(IV) transferrin by reaction of human serum apotransferrin with titanium complexes

The reaction of human serum apotransferrin with titanium(IV) citrate under physiological conditions results in the formation of a specific bis-titanium(IV) transferrin adduct (Ti2Tf hereafter) with two titanium(IV) ions loaded at the iron binding sites. The same specific Ti2Tf complex is formed by reacting apotransferrin with titanium(III) chloride and exposing the sample to air. The derivative thus obtained was characterized by spectroscopic techniques, including absorption, UV difference, circular dichroism and 13C NMR spectroscopies, and shown to be stable within the pH range 5.5-9.0. Surprisingly, the reaction of apoTf with titanium(IV) nitrilotriacetate (NTA) does not lead to formation of appreciable amounts of Ti2Tf, even after long incubation times, although some weak interactions of Ti(IV)-NTA with apoTf are spectroscopically detected. Implications of the present results for a role of transferrin in the uptake, transport and delivery of soluble titanium(IV) compounds under physiological conditions are discussed.

Histochemical localization of glycoconjugates on microglial cells in Alzheimer's disease brain samples by using Abrus precatorius, Maackia amurensis, Momordica charantia, and Sambucus nigra lectins

Four lectins (Abrus precatorius (APA), Maackia amurensis (MAA), Momordica charantia (MCA) and Sambucus nigra (SNA)) have been used to identify glycohistochemically the microglial cells (MGC) activation in autoptic brain samples from Alzheimer's disease (AD) subjects. Three of these lectins (APA, MAA and MCA) have utilized as microglial cell markers for the first time. The identification of new markers for the study of MGC is very important to better understand the role of these type of cells in the metabolic/dismetabolic control of betaA4 in AD which still represents a vexata questio.

Metallothioneins are highly expressed in astrocytes and microcapillaries in Alzheimer's disease

One of the neuropathological characteristics of Alzheimer's disease is the presence of a large number of reactive astrocytes, often, but not always, associated with senile plaques. The factors responsible for such an activation are as yet totally unknown. Other characteristic features of this disease such as betaA4 amyloid accumulation, senile plaques and neurofibrillary tangles represent well known pathological phenomena. Some studies suggest that betaA4 plays a major role in the reactive astrocytosis characteristic of Alzheimer's disease. In the normal human brain, metallothionein isoforms I and II are expressed in astrocytes but not in neurons. In the present study, we used anti-metallothionein antibodies to detect cells expressing metallothioneins isoforms I and II in normal and Alzheimer's disease (AD) brain sections. Results showed that expression of these proteins in the cortex, cerebral white matter and cerebellum is a relevant anatomopathological characteristic of Alzheimer's disease. Analysis of Alzheimer's disease brain sections revealed high expression of metallothioneins I/II in astrocytes and microcapillaries, and in the granular but not the molecular layer of the cerebellum. Furthermore, metallothionein expression can be used as a marker to identify subtypes of astrocytes.