Pathogenic factors in vascular dementia and Alzheimer's disease. Multiple actions of heparin that probably are beneficial

Methionine 35 sulphoxide reduces toxicity of Aβ in red blood cell

BACKGROUND

The oxidation of methionine residue in position 35 of Ab to sulphoxide (Ab-sulphoxide) has the ability to deeply modify wild-type Ab 1-42 (Ab) neurotoxic action. Our previous studies suggest that in nucleated cells, lower toxicity of Ab-sulphoxide might result not from structural alteration, but from elevation of methionine sulphoxide reductase A (MsrA) activity and mRNA levels.

DESIGN

On this basis, we hypothesised that red blood cell (RBC), a cell devoid almost completely of MsrA activity, shares with nucleated cells an antioxidant system induced by methionine 35 sulphoxide, responsible for the lower toxicity of Ab-sulphoxide in RBC. (Results) Supporting this hypothesis, we found that the low toxicity of Ab-sulphoxide in RBC correlated with pentose phosphate pathway (PPP) flux increase, and this event was associated with a low level of methionine oxidation in total proteins. None of these effects were observed when cells were exposed to Ab native.

DISCUSSION

These results outline the importance of the redox state of methionine 35 in the modulation of Ab-mediated events and suggest an important protective role for PPP in RBC of patients affected by Alzheimer's disease.

The participation of insulin-like growth factor-binding protein 3 released by astrocytes in the pathology of Alzheimer's disease

Background

Alzheimer’s disease (AD) is characterized by senile plaques, extracellular deposits composed primarily of amyloid–beta (Aβ), and neurofibrillary tangles, which are abnormal intracellular inclusions containing hyperphosphorylated tau.

The amyloid cascade hypothesis posits that the deposition of Aβ in the brain parenchyma initiates a sequence of events that leads to dementia. However, the molecular process by which the extracellular accumulation of Aβ peptides promotes intracellular pathologic changes in tau filaments remains unclear. To elucidate this process, we presumed that astrocytes might trigger neuronal reactions, leading to tau phosphorylation. In this study, we examined AD pathology from the perspective of the astrocyte-neuron interaction.

Results

A cytokine-array analysis revealed that Aβ stimulates astrocytes to release several chemical mediators that are primarily related to inflammation and cell adhesion. Among those mediators, insulin-like growth factor (IGF)-binding protein 3 (IGFBP-3) was highly upregulated.

In AD brains, the expression of IGFBP-3 was found to be increased by western blot analysis, and increased expression of IGFBP-3 was observed in astrocytes via fluorescence microscopy.

In addition, we reproduced the increase in IGFBP-3 after treatment with Aβ using human astrocytoma cell lines and found that IGFBP-3 was expressed via calcineurin. In AD brains, the activated forms of calcineurin were found to be increased by western blot analysis, and increased expression of calcineurin was observed in astrocytes via fluorescence microscopy.

When Ser9 of glycogen synthase kinase-3β (GSK-3β) is phosphorylated, GSK-3β is controlled and tau phosphorylation is suppressed. Aβ suppresses the phosphorylation of GSK-3β, leading to tau phosphorylation. In this study, we found that IGF-Ι suppressed tau phosphorylation induced by Aβ, although IGFBP-3 inhibited this property of IGF-Ι. As a result, IGFBP-3 contributed to tau phosphorylation and cell death induced by Aβ.

Conclusions

Our study suggested that calcineurin in astrocytes was activated by Aβ, leading to IGFBP-3 release. We further demonstrated that IGFBP-3 produced by astrocytes induced tau phosphorylation in neurons. Our study provides novel insights into the role of astrocytes in the induction of tau phosphorylation and suggests that IGFBP-3 could be an important link between Aβ and tau pathology and an important therapeutic target.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0174-2) contains supplementary material, which is available to authorized users.

Heparan sulfate-protein binding specificity

Heparan sulfate (HS) represents a large class of linear polysaccharides that are required for the function of all mammalian physiological systems. HS is characterized by a repeating disaccharide backbone that is subject to a wide range of modifications, making this class of macromolecules arguably the most information dense in all of biology. The majority of HS functions are associated with the ability to bind and regulate a wide range of proteins. Indeed, recent years have seen an explosion in the discovery of new activities for HS where it is now recognized that this class of glycans functions as co-receptors for growth factors and cytokines, modulates cellular uptake of lipoproteins, regulates protease activity, is critical to amyloid plaque formation, is used by opportunistic pathogens to enter cells, and may even participate in epigenetic regulation. This review will discuss the current state of understanding regarding the specificity of HS-protein binding and will describe the concept that protein binding to HS depends on the overall organization of domains within HS rather than fine structure.

Cerebrovascular reactivity to carbon dioxide in Alzheimer's disease

There is growing evidence that cerebrovascular reactivity to carbon dioxide (CVRCO2) is impaired in Alzheimer's disease (AD). Preclinical and animal studies suggest chronic hypercontractility in brain vessels in AD. We review (a) preclinical studies of mechanisms for impaired CVRCO2 in AD; (b) clinical studies of cerebrovascular function in subjects with AD dementia, mild cognitive impairment (MCI), and normal cognition. Although results of clinical studies are inconclusive, an increasing number of reports reveal an impairment of vascular reactivity to carbon dioxide in subjects with AD, and possibly also in MCI. Thus, CVRCO2 may be an attractive means to detect an early vascular dysfunction in subjects at risk.

Vascular factors and epigenetic modifications in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a debilitating illness with no known cure. Nowadays accumulating evidence suggested that the vascular endothelium and chronic hypoperfusion may play important role in pathobiology of AD. The vascular endothelium which regulates the passage of macromolecules and circulating cells from blood to tissue, is a major target of oxidative stress, playing a critical role in the pathophysiology of vascular diseases. Since the vascular endothelium, neurons and glia are all able to synthesize, store and release reactive oxygen species (ROS) and vascular active substances in response to certain stimuli, their contribution to the pathophysiology of AD can be very important. New evidence indicates that continuous formation of free ROS induces cellular damage and decreases antioxidant defenses. Specifically, oxidative stress increases vascular endothelial permeability and promotes leukocyte adhesion. We summarize the reports that sporadic, late-onset of AD results from vascular etiology. Recently an involvement of epigenetic alterations in the etiology of AD is also intensively investigated. Gaining a more complete understanding of the essential components and underlying mechanisms involved in epigenetic regulation could lead to novel treatments for a number of neurological and psychiatric conditions.

Chronic mild cerebrovascular dysfunction as a cause for Alzheimer's disease?

Alzheimer's disease (AD) is a progressive chronic disorder and is characterized by β-amyloid plaques and angiopathy, tau pathology, neuronal cell death, and inflammatory responses. The reasons for this disease are not known. This review proposes the hypothesis that a chronic mild longlasting cerebrovascular dysfunction could initiate a cascade of events leading to AD. It is suggested that (vascular) risk factors (e.g. hypercholesterolemia, type 2 diabetes, hyperhomocysteinemia) causes either damage of the cerebrovascular system including silent strokes or causes dysregulation of beta-amyloid clearance at the blood-brain barrier resulting in increased brain beta-amyloid. A cascade of subsequent downstream events may lead to disturbed metabolic changes, and neuroinflammation and tau pathology. The role of NGF on the cell death of cholinergic neurons is discussed. Additional risk factors (e.g. acidosis, metals) contribute to plaque development.

Omega-3 fatty acids: potential role in the management of early Alzheimer's disease

Omega-3 fatty acids are essential for brain growth and development. They play an important role throughout life, as critical modulators of neuronal function and regulation of oxidative stress mechanisms, in brain health and disease. Docosahexanoic acid (DHA), the major omega-3 fatty acid found in neurons, has taken on a central role as a target for therapeutic intervention in Alzheimer’s disease (AD). A plethora of in vitro, animal model, and human data, gathered over the past decade, highlight the important role DHA may play in the development of a variety of neurological and psychiatric disorders, including AD. Cross sectional and prospective cohort data have demonstrated that reduced dietary intake or low brain levels of DHA are associated with accelerated cognitive decline or the development of incipient dementia, including AD. Several clinical trials investigating the effects of omega-3 fatty acid supplementation in AD have been completed and all failed to demonstrate its efficacy in the treatment of AD. However, these trials produced intriguing data suggesting that the beneficial effects of omega-3 fatty acid supplementation may depend on the stage of disease, other dietary mediators, and apolipoprotein E status.

Oxidation of methionine 35 reduces toxicity of the amyloid beta-peptide(1-42) in neuroblastoma cells (IMR-32) via enzyme methionine sulfoxide reductase A expression and function

The beta amyloid peptide (Abeta), the major protein component of brain senile plaques in Alzheimer's disease, is known to be directly responsible for the production of free radicals that may lead to neurodegeneration. Our recent evidence suggest that the redox state of methionine residue in position 35 (Met-35) of Abeta has the ability to deeply modify peptide's neurotoxic actions. Reversible oxidation of methionine in proteins involving the enzyme methionine sulfoxide reductase type A (MsrA) is postulated to serve a general antioxidant role and a decrease in MsrA has been implicated in Alzheimer's disease. In rat neuroblastoma cells (IMR-32), we used Abeta(1-42), in which the Met-35 is present in the reduced state, with a modified peptide with oxidized Met-35 (Abeta(1-42)Met35(OX)), as well as an Abeta-derivative in which Met-35 is substituted with norleucine (Abeta(1-42)Nle35) to investigate the relationship between Met-35 redox state, expression and function of MsrA and reactive oxygen species (ROS) generation. The obtained results shown that MsrA activity, as well as mRNA levels, increase in IMR-32 cells treated with Abeta(1-42)Met35(OX), differently to that shown by the reduced derivative. The increase in MsrA function and expression was associated with a decline of ROS levels. None of these effects were observed when cells were exposed to Abeta containing oxidized Met35 (Abeta1-42)Met35(OX). Taken together, the results of the present study indicate that the differential toxicity of Abeta peptides containing reduced or oxidised Met-35 depends on the ability of the latter form to reduce ROS generation by enhancing MsrA gene expression and function and suggests the therapeutic potential of MsrA in Alzheimer's disease.

Methionine does not reduce Cu(II)-beta-amyloid!--rectification of the roles of methionine-35 and reducing agents in metal-centered oxidation chemistry of Cu(II)-beta-amyloid

The potential risk of metal-centered oxidative catalysis has been overlooked in the research of the copper complexes of the Alzheimer's disease-related beta-amyloid (Abeta) peptides. Cu(2+) complexes of Abeta(1-40) and its 1-16 and 1-20 fragments have recently been shown to exhibit significant metal-centered oxidative activities toward several catecholamine neurotransmitters with and without H(2)O(2) around neutral pH [G.F.Z. da Silva, L.-J. Ming, "Metallo-ROS" in Alzheimer's disease: metal-centered oxidation of neurotransmitters by Cu(II)-beta-amyloid and neuropathology of Alzheimer's disease, Angew. Chem. Int. Ed. 46 (2007) 3337-3341]. The results further support the metallo-Abeta-associated oxidative stress theory often considered to be connected to the neuropathology of the disease. The metal-centered oxidative catalysis of CuAbeta(1-16/20) challenges the long-standing proposed redox role of Met35 in Abeta because Abeta(1-16/20) do not contain a Met. External Met has been determined by kinetic, optical, and electron paramagnetic resonance methods to bind directly to the Cu(2+) center of CuAbeta(1-40) and CuAbeta(1-20) with K(d)=2.8 mM and 11.3 microM, respectively, which reflects less accessibility of the metal center in the full-length CuAbeta(1-40). However, Met does not serve as a reducing agent for the Cu(II) which thus must amplify the observed oxidative catalysis of CuAbeta(1-20)through a non-redox mechanism. Conversely, the CuAbeta-catalyzed oxidation reaction of dopamine is inhibited by bio-available reducing agents such as ascorbate (competitive K(ic)=66 microM) and glutathione (non-competitive, K(inc)=53 microM). These data indicate that the oxidation chemistry of metallo-Abeta is not initiated by Met35. The results yield further molecular and mechanistic insights into the roles of metallo-Abeta in this disease.

Age and apoE associations with complex pathologic features in Alzheimer's disease

The risk for Alzheimer's disease (AD) is influenced by both age and ApoE status. The present study addresses the associations of age and ApoE status on complex pathologic features in AD (n=81) including coexistent cerebrovascular disease (CVD), argyrophilic grain disease (AGD), and Lewy body disease (LBD). The frequency of coexistent cerebrovascular disease increased with increasing age. Age and ApoE status were differentially associated with atherosclerosis, lacunar infarctions, and microvascular pathology. Coexistent Lewy body pathology was negatively associated with age, dropping off abruptly after age 90. The presence of an ApoE epsilon4 allele was associated with an increased frequency of coexistent LBD. Logistic regression analyses demonstrated both dependent and independent effects of age and ApoE status on the presence of coexistent Lewy body pathology in AD. While the decreasing frequency of LBD in AD after age 90 could be partly accounted for by a lower probability of an ApoE epsilon4 allele, the independent association with age suggests either 1) a survival effect, 2) decreased incidence with advancing age, or 3) both.

Soluble adhesion molecules and angiotensin-converting enzyme in dementia

We aimed to determine plasma and cerebrospinal fluid (CSF) levels of angiotensin-converting enzyme (ACE) and the soluble forms of intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1) and platelet endothelial cell adhesion molecule-1 (sPECAM-1) as surrogate markers for endothelial cell activation in clinically diagnosed patients with Alzheimer's disease (AD, n=260), dementia with Lewy bodies (DLB, n=39) and non-demented controls (n=34). Plasma sICAM-1 and sPECAM-1 were higher and CSF sVCAM-1 were lower in AD and DLB patients than in controls (p<0.001). DLB patients had higher CSF sICAM-1, but lower CSF sVCAM-1 (p<0.001). No difference in ACE levels was found between the dementia groups and controls. In controls and AD patients CSF sICAM and sVCAM-1 strongly correlated with each other and with blood barrier permeability whereas in DLB group these correlations were weaker. The observed patterns in adhesion molecules may reflect distinctions in the pathophysiological basis of their generation in dementia patients.

Relationship Between Serum Insulin-Like Growth Factor-1 Levels and Alzheimer's Disease and Vascular Dementia

OBJECTIVES

To determine whether decreased serum insulin-like growth factor-1 (IGF-1) levels could be a risk factor for dementia in older people.

DESIGN

Case control study.

SETTING

Showa University Karasuyama Hospital, Tokyo, Japan.

PARTICIPANTS

A total of 436 Japanese elderly subjects: 106 patients with Alzheimer's disease (AD), 103 patients with vascular dementia (VaD), and 227 age-matched controls without dementia.

MEASUREMENTS

Serum concentrations of IGF-1 and atherogenic lipoproteins, carotid artery intima-media thickness (IMT), and plaques were determined.

RESULTS

Mini-Mental State Examination (MMSE) scores were positively correlated with serum IGF-1 concentrations as well as mean blood pressure or body mass index and were negatively correlated with age, serum low-density lipoprotein cholesterol and lipoprotein(a) concentrations, and carotid IMT. Serum IGF-1 concentrations had a significant inverse correlation with carotid IMT. Analysis across the IGF-1 quartiles revealed a threshold effect of low IGF-1 on MMSE score in subjects with the IGF-1 levels of 140 ng/mL or less (50% percentile) versus those with IGF-1 levels greater than 140 ng/mL. Multiple logistic regression concerning AD and VaD retained serum IGF-1 concentrations of 140 ng/mL or less and carotid IMT of 0.9 mm or more. Patients with AD and VaD had significantly lower IGF-1 concentrations and greater mean IMT than nondemented controls.

CONCLUSION

These results suggest that decreased serum IGF-1 level and the progression of carotid atherosclerosis could play a role as independent risk factors for dementia.