Browsing by Author "Alarcon, R"

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    Acetylcholinesterase promotes the aggregation of amyloid-beta-peptide fragments by forming a complex with the growing fibrils
    (1997) Alvarez, A; Opazo, C; Alarcon, R; Garrido, J; Inestrosa, NC
    Acetylcholinesterase (AChE), an enzyme involved in the hydrolysis of the neurotransmitter acetylcholine, consistently colocalizes with the amyloid deposits characteristic of Alzheimer's disease and may contribute to the generation of amyloid proteins and/or physically affect fibril assembly. Ln order to identify the structural domains of the amyloid-beta-peptide (A beta) involved in the aggregation induced by AChE, we have studied the effect of this cholinergic enzyme on A beta peptide fragments of different sizes. AChE enhanced the aggregation of the A beta(12-28) and A beta(25-35) peptides but not of the A beta(1-16) fragment. The inductive effect of AChE on the aggregation of A beta(12-28) was abolished by the presence of either A beta(1-16) or A beta(9-21). The effect of the enzyme was also analysed using two different mutant fragments, possessing a low and the other a high capacity for fibrillogenesis. The fragments used were A beta(12-28)(Val18-->Ala) and A beta(12-28)(Glu22-->Gln), respectively. AChE was able to promote the aggregation of these fragments in a very specific way and both mutant peptides were able to form amyloid fibrils, as revealed by negative staining under the electron microscope. Binding assays indicated that AChE was bound to A beta(12-28), as well as to the A beta(1-16) peptide. AChE was seen to form strong complexes with the A beta(12-28) fibrils as such complexes stained positively for both thioflavine-T and AChE activity, were resistant to high ionic strength treatment, and were partially sensitive to detergents, suggesting that hydrophobic interactions may play a role in the stabilization of the AChE-A beta complex. Our results suggest that such amyloid-AChE complexes are formed when AChE interacts with the growing amyloid fibrils and accelerates the assembly of A beta peptides. This is consistent with the fact that AChE is known to be present within A beta deposits including the pre-amyloid diffuse and mature senile plaques found in Alzheimer's brain. (C) 1997 Academic Press Limited.
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    Expression of scavenger receptors in glial cells - Comparing the adhesion of astrocytes and microglia from neonatal rats to surface-bound beta-amyloid
    (AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2005) Alarcon, R; Fuenzalida, C; Santibanez, M; von Bernhardi, R
    Astrocytes and microglia associate to amyloid plaques, a pathological hallmark of Alzheimer disease. Microglia are activated by and can phagocytose beta-amyloid ( A beta). Scavenger receptors ( SRs) are among the receptors mediating the uptake of fibrillar A beta in vitro. However, little is known about the function of the astrocytes surrounding the plaques or the nature of their interaction with A beta. It is unknown whether glial cells bind to nonfibrillar A beta and if binding of astrocytes to A beta depends on the same Scavenger receptors described for microglia. We determined the binding of glia to A beta by an adhesion assay and evaluated the presence of scavenger receptors in glial cells by immunocytochemistry, immunohistochemistry of brain sections, and immunoblot. We found that astrocytes and microglia from neonatal rats adhered in a concentration-dependent manner to surfaces coated with fibrillar A beta or nonfibrillar A beta. Fucoidan and poly( I), known ligands for SR-type A, inhibited adhesion of microglia and astrocytes to A beta and also inhibited A beta phagocytosis. In contrast, a ligand for SR-type B like low density lipoprotein, did not compete glial adhesion to A beta. Microglia presented immunodetectable SR-BI, SR-AI/AII, RAGE, and SR-MARCO ( macrophage receptor with collagenous structure, a member of the SR-A family). Astrocytes presented SR-BI and SR-MARCO. To our knowledge, this is the first description of the presence of SR-MARCO in astrocytes. Our results indicate that both microglia and astrocytes adhere to fibrillar and nonfibrillar A beta. Adhesion was mediated by a fucoidan-sensitive receptor. We propose that SR-MARCO could be the Scavenger receptor responsible for the adhesion of astrocytes and microglia to A beta.
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    Supplementation of female rats with alpha-linolenic acid or docosahexaenoic acid leads to the same omega-6/omega-3 LC-PUFA accretion in mother tissues and in fetal and newborn brains
    (KARGER, 2004) Valenzuela, A; von Bernhardi, R; Valenzuela, V; Ramirez, G; Alarcon, R; Sanhueza, J; Nieto, S
    Background: Maternal omega-3 fatty acid supplementation has been suggested to provide docosahexaenoic acid (DHA) for the normal brain development during gestation. DHA can be given as such ( preformed) or through the omega-3 precursor alpha-linolenic acid (LNA) which is transformed into DHA by elongation and desaturation reactions. Western diet provides low amounts of LNA and DHA; therefore, supplementation with these omega-3 fatty acids has been suggested for pregnant women. However, the bioequivalence of LNA ingestion to DHA supplementation has not been established. Methods: Recently weaning female Wistar rats were fed a diet containing a small amount of LNA and no DHA. The animals were daily supplemented 40 days before mating, during pregnancy, and until delivery with 60 mg/kg of LNA or 6 mg/kg of DHA dissolved in coconut oil. Fatty acids were given as ethyl ester derivatives. Controls received coconut oil. The fatty acid composition of blood plasma, erythrocytes, liver, visceral adipose tissue, and brain segments (frontal cortex, hippocampus, and cerebellum) was analyzed. Brain segments obtained from 16- and 19-day-old fetuses and from 2- and 21-day- old rats were also analyzed for fatty acid composition. Results: Supplementation with LNA and DHA induced a similar accretion of DHA in plasma, erythrocytes, liver, and brain segments of the mothers. The adipose tissue showed a higher DHA accretion after DHA-supplementation. The DHA accretion in frontal cortex, hippocampus, and cerebellum obtained from the fetuses and the newborn rats was similar when the mothers were supplemented with LNA and DHA. Our results show that under our experimental conditions a similar accretion of DHA in the different tissues of the mothers and in the brain segments of fetuses and newborn rats is obtained after LNA and DHA supplementation. Conclusion: LNA and DHA, at the amounts given in this study, show a similar bioequivalence for DHA accretion in different tissues of the mother and in brain segments of fetuses and newborn rats. Copyright (C) 2004 S. Karger AG, Basel.