Pamela Zambenedetti

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

One of the neuropathological characteristics of Alzheimers 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 Alzheimers 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 Alzheimers 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 Alzheimers disease. Analysis of Alzheimers 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.

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.

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.

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

Several gene mutations are associated with an increased risk of Alzheimers disease. Previous studies reported higher transferrin C2 allele frequencies in Alzheimers 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 Alzheimers 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 Alzheimers 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 Alzheimers disease.

Activation of acetylcholinesterase by aluminium(III) : the relevance of the metal species

The present paper reports how aluminium [Al(III)] at a concentration of 3.7 microM can activate the bovine erythrocytic enzyme acetylcholinesterase (AChE) by about 38% in vitro. This same activating effect was observed on AChE form human as well as from rat erythrocyte ghosts and murine neuroblastoma cells. The interaction between Al3+ and gamma-peripheral sites of the enzyme produces AChE structural modifications as evidenced by circular dichroism measurements. This may provide a molecular explanation of the raised enzymatic activity.

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 Alzheimers disease. Several biochemical, epidemiological and genetic aspects established a correlation between cholesterol concentration and Alzheimers 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 Alzheimers disease pathogenesis is also discussed.

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.

Aluminum alters intracellular calcium homeostasis in vitro

The present paper reports data regarding the influence of aluminum, at micromolar concentrations, on intracellular calcium homeostasis. Al3+ modifies Ca2+ uptake in the endoplasmic reticulum (ER), accelerates Ca2+ release from mitochondria and strongly inhibits Ca2+-ATPase activity with a consequent high-level calcium accumulation inside the cell. These results suggest that Al3+ neurotoxicity may be related to an alteration of the intracellular calcium regulatory system.

Different effects of aluminum upon carbonic anhydrases and Na+/K+-ATPase activities in rat.

Aluminum (Al(III)) is a well established toxicant implicated as an etiological factor in several neuropathies. In this paper we report results regarding opposite effects produced by Al(III) on the activity of two enzymes utilized as models. While sodium-potassium ATP-ase (Na/K-ATPase) is strongly activated by Al(III) in a dose-effect dependent way, on the contrary, carbonic anhydrase (CA) is remarkably inhibited. The relevance of the metal speciation together with the enzymatic structural modification demonstrated by circular dichroism measurements could explain the observed modified enzymatic activities. In addition, a new experimental protocol for the preparation of Al(III) solutions at physiological pH useful in the standardization of Al(III) experimental toxicology is also proposed and discussed.

Aluminum (III) induces alterations on the physical state of the erythrocytic membrane: an ESR evaluation.

The action of aluminum [Al(III)] as Al(acac)3 on erythrocytes causes biophysical effects such as osmotic fragility and echino-acanthocytes formation. In this paper, we present these effects in terms of variation of membrane fluidity, together with findings regarding conformational modifications of membrane proteins consequent to Al(III) exposure, as well as the effects on the mobility of the membrane protein bound sialic acid. To this end, we utilized ESR measurements of rabbits and humans erythrocytic ghosts after probing or labeling with suitable stable radicals used as spin probes or labels. Our results show that the lipophilic, hydrolytically stable toxicant Al(acac)3 causes a remarkable reduction of membrane fluidity in rabbit erythrocytes, an appreciable structural compacting effect on cytoskeletal and transmembrane proteins, as well as a reduction of rotational mobility of cell-surface sialic acid of human erythrocytes.