Methionine 35 oxidation reduces toxic effects of the amyloid beta-protein fragment (31-35) on human red blood cell

Delineation of the role of G6PD in Alzheimer's disease and potential enhancement through microfluidic and nanoparticle approaches

Alzheimer's disease (AD) is a neurodegenerative pathologic entity characterized by the abnormal presence of tau and macromolecular Aβ deposition that leads to the degeneration or death of neurons. In addition to that, glucose-6-phosphate dehydrogenase (G6PD) has a multifaceted role in the process of AD development, where it can be used as both a marker and a target. G6PD activity is dysregulated due to its contribution to oxidative stress, neuroinflammation, and neuronal death. In this context, the current review presents a vivid depiction of recent findings on the relationship between AD progression and changes in the expression or activity of G6PD. The efficacy of the proposed G6PD-based therapeutics has been demonstrated in multiple studies using AD mouse models as representative animal model systems for cognitive decline and neurodegeneration associated with this disease. Innovative therapeutic insights are made for the boosting of G6PD activity via novel innovative nanotechnology and microfluidics tools in drug administration technology. Such approaches provide innovative methods of surpassing the blood-brain barrier, targeting step-by-step specific neural pathways, and overcoming biochemical disturbances that accompany AD. Using different nanoparticles loaded with G6DP to target specific organs, e.g., G6DP-loaded liposomes, enhances BBB penetration and brain distribution of G6DP. Many nanoparticles, which are used for different purposes, are briefly discussed in the paper. Such methods to mimic BBB on organs on-chip offer precise disease modeling and drug testing using microfluidic chips, requiring lower sample amounts and producing faster findings compared to conventional techniques. There are other contributions to microfluid in AD that are discussed briefly. However, there are some limitations accompanying microfluidics that need to be worked on to be used for AD. This study aims to bridge the gap in understanding AD with the synergistic use of promising technologies; microfluid and nanotechnology for future advancements.

Two statins and cromolyn as possible drugs against the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides: a comparative study by advanced computer simulation methods

In this work, possible effective mechanisms of cromolyn, atorvastatin and lovastatin on the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides were investigated by classical molecular dynamics and well-tempered metadynamics simulations. The results demonstrate that all the drugs affect the behavior of the peptides, such as their ability to aggregate, and alter their secondary structures and their affinity to a particular drug. Our findings from the computed properties suggest that the best drug candidate is lovastatin. This medicine inhibits peptide aggregation, adsorbs the peptides on the surface of the drug clusters, changes the secondary structure and binds to MET₃₅, which has been seen as the reason for the toxicity of the studied peptide sequences. Moreover, lovastatin is the drug which previously has demonstrated the strongest ability to penetrate the blood-brain barrier and makes lovastatin the most promising medicine among the three investigated drugs. Atorvastatin is also seen as a potential candidate if its penetration through the blood-brain barrier could be improved. Otherwise, its properties are even better than the ones demonstrated by lovastatin. Cromolyn appears to be less interesting as an anti-aggregant from the computational data, in comparison to the two statins.

Neuroprotective Activity of Melittin-The Main Component of Bee Venom-Against Oxidative Stress Induced by Aβ25-35 in In Vitro and In Vivo Models

Melittin, a 26-amino acid peptide, is the main component of the venom of four honeybee species and exhibits neuroprotective actions. However, it is unclear how melittin ameliorates neuronal cells in oxidative stress and how it affects memory impairment in an in vivo model. We evaluated the neuroprotective effect of melittin on Aβ_25–35-induced neuro-oxidative stress in both in vitro HT22 cells and in vivo animal model. Melittin effectively protected against HT22 cell viability and significantly deregulated the Aβ_25–35-induced overproduction of intracellular reactive oxygen species. Western blot analysis showed that melittin suppressed cell apoptosis and regulated Bax/Bcl-2 ratio, as well as the expression of proapoptotic related factors: Apoptosis-inducing factor (AIF), Calpain, Cytochrome c (CytoC), Cleaved caspase-3 (Cleacas3). Additionally, melittin enhanced the antioxidant defense pathway by regulating the nuclear translocation of nuclear factor erythroid 2-like 2 (Nrf2) thus upregulated the production of the heme oxygenase-1 (HO-1), a major cellular antioxidant enzyme combating neuronal oxidative stress. Furthermore, melittin treatment activated the Tropomyosin-related kinase receptor B (TrkB)/cAMP Response Element-Binding (CREB)/Brain-derived neurotrophic factor (BDNF), contributing to neuronal neurogenesis, and regulating the normal function of synapses in the brain. In our in vivo experiment, melittin was shown to enhance the depleted learning and memory ability, a novel finding. A mouse model with cognitive deficits induced by Aβ_25–35 intracerebroventricular injection was used. Melittin had dose-dependently enhanced neural-disrupted animal behavior and enhanced neurogenesis in the dentate gyrus hippocampal region. Further analysis of mouse brain tissue and serum confirmed that melittin enhanced oxidant–antioxidant balance, cholinergic system activity, and intercellular neurotrophic factors regulation, which were all negatively altered by Aβ_25–35. Our study shows that melittin exerts antioxidant and neuroprotective actions against neural oxidative stress. Melittin can be a potential therapeutic agent for neurodegenerative disorders.

Component of Cannabis, Cannabidiol, as a Possible Drug against the Cytotoxicity of Aβ(31-35) and Aβ(25-35) Peptides: An Investigation by Molecular Dynamics and Well-Tempered Metadynamics Simulations

In this work cannabidiol (CBD) was investigated as a possible drug against the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides with the help of atomistic molecular dynamics (MD) and well-tempered metadynamics simulations. Four interrelated mechanisms of possible actions of CBD are proposed from our computations. This implies that one mechanism can be a cause or/and a consequence of another. CBD is able to decrease the aggregation of peptides at certain concentrations of compounds in water. This particular action is more prominent for Aβ(25-35), since originally Aβ(31-35) did not exhibit aggregation properties in aqueous solutions. Interactions of CBD with the peptides affect secondary structures of the latter ones. Clusters of CBD are seen as possible adsorbents of Aβ(31-35) and Aβ(25-35) since peptides are tending to aggregate around them. And last but not least, CBD exhibits binding to MET35. All four mechanisms of actions can possibly inhibit the Aβ-cytotoxicity as discussed in this paper. Moreover, the amount of water also played a role in peptide clustering: with a growing concentration of peptides in water without a drug, the aggregation of both Aβ(31-35) and Aβ(25-35) increased. The number of hydrogen bonds between peptides and water was significantly higher for simulations with Aβ(25-35) at the higher concentration of peptides, while for Aβ(31-35) that difference was rather insignificant. The presence of CBD did not substantially affect the number of hydrogen bonds in the simulated systems.

Amyloid β peptide affects erythrocyte morphology: Role of intracellular signaling pathways

BACKGROUND

Circulating red blood cells (RBCs) undergo aging, a fundamental physiological phenomenon that regulates their turnover.

OBJECTIVE

Understanding the role of Aβ in the cross talk between cell signalling pathways and modulation of the cell structural and biomechanical properties occurring in RBCs during aging.

METHODS

The morphological pattern has been monitored using Atomic Force Microscopy (AFM) imaging and measuring the RBCs' plasma membrane roughness employed as a morphological parameter capable to provide information on the structure and integrity of the membrane-skeleton.

RESULTS

We show that treatment with Aβ accelerates the occurrence of morphological and biochemical aging markers in human RBC and influences the cell metabolism. Biochemical data demonstrate that contemporaneously to morphological alterations, Aβ triggers: (i) metabolic alterations and (ii) a complex signaling pathway involving caspase 3, protein kinase C and nitric oxide derived metabolites.

CONCLUSIONS

our study provides a comprehensive picture in which Aβ treatment of RBC induces changes in specific cell signalling events and/or metabolic pathways, in turns affecting the membrane-cytoskeleton interaction and the membrane integrity.

Morphological changes induced in erythrocyte by amyloid beta peptide and glucose depletion: A combined atomic force microscopy and biochemical study

Circulating red blood cells (RBCs) undergo aging, a fundamental physiological phenomenon that regulates their turnover. We show that treatment with beta amyloid peptide 1-42 (Aβ) accelerates the occurrence of morphological and biochemical aging markers in human RBCs and influences the cell metabolism leading to intracellular ATP depletion. The morphological pattern has been monitored using Atomic Force Microscopy (AFM) imaging and measuring the RBCs' plasma membrane roughness employed as a morphological parameter capable to provide information on the structure and integrity of the membrane-skeleton. Results evidence that Aβ boosts the development of crenatures and proto-spicules simultaneously to acceleration in the weakening of the cell-cytoskeleton contacts and to the induction of peculiar nanoscale features on the cell membrane. Incubation in the presence of glucose can remove all but the latter Aβ-induced effects. Biochemical data demonstrate that contemporaneously to morphological and structural alterations, Aβ and glucose depletion trigger a complex signaling pathway involving caspase 3, protein kinase C (PKC) and nitric oxide derived metabolites. As a whole, the collected data revealed that, the damaging path induced by Aβ in RBC provide a sequence of morphological and functional intermediates following one another along RBC life span, including: (i) an acceleration in the development of shape alteration typically observed along the RBC's aging; (ii) the development of characteristic membrane features on the plasma membrane and (iii) triggering a complex signaling pathway involving caspase 3, PKC and nitric oxide derived metabolites.

Glucose 6 phosphatase dehydrogenase (G6PD) and neurodegenerative disorders: Mapping diagnostic and therapeutic opportunities

Glucose 6 phosphate dehydrogenase (G6PD) is a key and rate limiting enzyme in the pentose phosphate pathway (PPP). The physiological significance of enzyme is providing reduced energy to specific cells like erythrocyte by maintaining co-enzyme nicotinamide adenine dinucleotide phosphate (NADPH). There are preponderance research findings that demonstrate the enzyme (G6PD) role in the energy balance, and it is associated with blood-related diseases and disorders, primarily the anemia resulted from G6PD deficiency. The X-linked genetic deficiency of G6PD and associated non-immune hemolytic anemia have been studied widely across the globe. Recent advancement in biology, more precisely neuroscience has revealed that G6PD is centrally involved in many neurological and neurodegenerative disorders. The neuroprotective role of the enzyme (G6PD) has also been established, as well as the potential of G6PD in oxidative damage and the Reactive Oxygen Species (ROS) produced in cerebral ischemia. Though G6PD deficiency remains a global health issue, however, a paradigm shift in research focusing the potential of the enzyme in neurological and neurodegenerative disorders will surely open a new avenue in diagnostics and enzyme therapeutics. Here, in this study, more emphasis was made on exploring the role of G6PD in neurological and inflammatory disorders as well as non-immune hemolytic anemia, thus providing diagnostic and therapeutic opportunities.

Erythrocytes as Potential Link between Diabetes and Alzheimer's Disease

Many studies support the existence of an association between type 2 diabetes (T2DM) and Alzheimer's disease (AD). In AD, in addition to brain, a number of peripheral tissues and cells are affected, including red blood cell (RBC) and because there are currently no reliable diagnostic biomarkers of AD in the blood, a gradually increasing attention has been given to the study of RBC's alterations. Recently it has been evidenced in diabetes, RBC alterations superimposable to the ones occurring in AD RBC. Furthermore, growing evidence suggests that oxidative stress plays a pivotal role in the development of RBC's alterations and vice versa. Once again this represents a further evidence of a shared pathway between AD and T2DM. The present review summarizes the two disorders, highlighting the role of RBC in the postulated common biochemical links, and suggests RBC as a possible target for clinical trials.

Purification of recombinant Aβ(1-42) and pGlu-Aβ(3-42) using preparative SDS-PAGE

Recombinant expression and purification of amyloid peptides represents a common basis for investigating the molecular mechanisms of amyloid formation and toxicity. However, the isolation of the recombinant peptides is hampered by inefficient separation from contaminants such as the fusion protein required for efficient expression in E. coli. Here, we present a new approach for the isolation of highly purified Aβ(1-42) and pGlu-Aβ(3-42), which is based on a separation using preparative SDS-PAGE. The method relies on the purification of the Aβ fusion protein by affinity chromatography followed by preparative SDS-PAGE under reducing conditions and subsequent removal of detergents by precipitation. The application of preparative SDS-PAGE represents the key step to isolate highly pure recombinant Aβ, which has been applied for characterization of aggregation and toxicity. Thereby, the yield of the purification strategy was  >60%. To the best of our knowledge, this is the first description of an electrophoresis-based method for purification of a recombinant Aβ peptide. Therefore, the method might be of interest for isolation of other amyloid peptides, which are critical for conventional purification strategies due to their aggregation propensity.

On the generation of OH(·) radical species from H2O2 by Cu(I) amyloid beta peptide model complexes: a DFT investigation

According to different studies, the interaction between amyloid β-peptide (Aβ) and copper ions could yield radical oxygen species production, in particular the highly toxic hydroxyl radical OH(·) that is suspected to contribute to Alzheimer's disease pathogenesis. Despite intensive experimental and computational studies, the nature of the interaction between copper and Aβ peptide, as well as the redox reactivity of the system, are still matter of debate. It was proposed that in Cu(II) → Cu(I) reduction the complex Cu(II)-Aβ could follow a multi-step conformational change with redox active intermediates that may be responsible for OH(·) radical production from H2O2 through a Fenton-like process. The purpose of this work is to evaluate, using ab initio Density Functional Theory computations, the reactivity of different Cu(I)-Aβ coordination modes proposed in the literature, in terms of OH(·) production. For each coordination model, we considered the corresponding H2O2 adduct and performed a potential energy surface scan along the reaction coordinate of O-O bond dissociation of the peroxide, resulting in the production of OH(·) radical, obtaining reaction profiles for the evaluation of the energetic of the process. This procedure allowed us to confirm the hypothesis according to which the most populated Cu(I)-Aβ two-histidine coordination is not able to perform efficiently H2O2 reduction, while a less populated three-coordinated form would be responsible for the OH(·) production. We show that coordination modes featuring a third nitrogen containing electron-donor ligand (an imidazole ring of an histidine residue is slightly favored over the N-terminal amine group) are more active towards H2O2 reduction.

Influence of the Side Chain in the Structure and Fragmentation of Amino Acids Radical Cations

The conformational properties of ionized amino acids (Gly, Ala, Ser, Cys, Asp, Gln, Phe, Tyr, and His) have been theoretically analyzed using the hybrid B3LYP and the hybrid-meta MPWB1K functionals as well as with the post-Hartree Fock CCSD(T) level of theory. As a general trend, ionization is mainly localized at the -NH2 group, which becomes more planar and acidic, the intramolecular hydrogen bond in which -NH2 acts as proton donor being strengthened upon ionization. For this reason, the so-called conformer IV(+) becomes the most stable for nonaromatic amino acid radical cations. Aromatic amino acids do not follow this trend because ionization takes place mainly at the side chain. For these amino acids for which ionization of the side chain prevails over the -NH2 group, structures III(+) and II(+) become competitive. The Cα-X fragmentations of the ionized systems have also been studied. Among the different decompositions considered, the one that leads to the loss of COOH(•) is the most favorable one. Nevertheless, for aromatic amino acids fragmentations leading to R(•) or R(+) start being competitive. In fact, for His and Tyr, results indicate that the fragmentation leading to R(+) is the most favorable process.

Amyloid beta peptide (1-42)-mediated antioxidant imbalance is associated with activation of protein kinase C in red blood cells

Glycolysis and pentose phosphate pathway (PPP) in red blood cell (RBC) are modulated by the cell oxygenation state. This metabolic modulation is connected to variations in intracellular nicotinamide adenine dinucleotide phosphate-reduced form (NADPH) and adenosine triphosphate (ATP) levels as a function of the oxygenation state of the cell, and, consequently, it should have physiologic relevance. In the present study, we analysed the effects of amyloid beta peptide (1-42) (Abeta) on RBC metabolism and its relationship with the activity of protein kinase C (PKC). Our results showed that metabolic response to Abeta depended on the degree of cell oxygenation. In particular, under high O2 pressure, in Abeta-treated RBC, glucose metabolized through PPP approached that metabolized by RBC under low O2 pressure, differently to that observed in untreated cells. The effect of Abeta on RBC metabolism was paralleled by increase in PKC enzyme activity, but cytosolic Ca2+ concentration does not seem to be involved in this mechanism. Incubation of Abeta-treated RBC with a specific inhibitor of PKC partially restores PPP flux. A possible rationalization of the different metabolic behaviours shown by RBC following Abeta treatment is proposed. It takes into account the known post-translational modifications to cytoskeleton proteins induced by PKC. The reduction in PPP flux may lead to a weakened defence system of antioxidant reserve in RBC, becoming a source of reactive species, and, consequently, its typical, structural and functional features are lost. Therefore, oxidative stress may outflow from the RBC and trigger damage events in adjacent cells and tissue, thus contributing to vascular damage.

Effects of ionizing radiation on biological molecules--mechanisms of damage and emerging methods of detection

SIGNIFICANCE

The detrimental effects of ionizing radiation (IR) involve a highly orchestrated series of events that are amplified by endogenous signaling and culminating in oxidative damage to DNA, lipids, proteins, and many metabolites. Despite the global impact of IR, the molecular mechanisms underlying tissue damage reveal that many biomolecules are chemoselectively modified by IR.

RECENT ADVANCES

The development of high-throughput "omics" technologies for mapping DNA and protein modifications have revolutionized the study of IR effects on biological systems. Studies in cells, tissues, and biological fluids are used to identify molecular features or biomarkers of IR exposure and response and the molecular mechanisms that regulate their expression or synthesis.

CRITICAL ISSUES

In this review, chemical mechanisms are described for IR-induced modifications of biomolecules along with methods for their detection. Included with the detection methods are crucial experimental considerations and caveats for their use. Additional factors critical to the cellular response to radiation, including alterations in protein expression, metabolomics, and epigenetic factors, are also discussed.

FUTURE DIRECTIONS

Throughout the review, the synergy of combined "omics" technologies such as genomics and epigenomics, proteomics, and metabolomics is highlighted. These are anticipated to lead to new hypotheses to understand IR effects on biological systems and improve IR-based therapies.

Benzothiazole aniline tetra(ethylene glycol) and 3-amino-1,2,4-triazole inhibit neuroprotection against amyloid peptides by catalase overexpression in vitro

Alzheimer's disease, Familial British dementia, Familial Danish dementia, Type 2 diabetes mellitus, plus Creutzfeldt-Jakob disease are associated with amyloid fibril deposition and oxidative stress. The antioxidant enzyme catalase is a neuroprotective amyloid binding protein. Herein the effects of catalase overexpression in SH-SY5Y neuronal cells on the toxicity of amyloid-β (Aβ), amyloid-Bri (ABri), amyloid-Dan (ADan), amylin (IAPP), and prion protein (PrP) peptides were determined. Results showed catalase overexpression was neuroprotective against Aβ, ABri, ADan, IAPP, and PrP peptides. The catalase inhibitor 3-amino-1,2,4-triazole (3-AT) and catalase-amyloid interaction inhibitor benzothiazole aniline tetra(ethylene glycol) (BTA-EG4) significantly enhanced neurotoxicity of amyloid peptides in catalase overexpressing neuronal cells. This suggests catalase neuroprotection involves breakdown of hydrogen peroxide (H2O2) plus a direct binding interaction between catalase and the Aβ, ABri, ADan, IAPP, and PrP peptides. Kisspeptin 45-50 had additive neuroprotective actions against the Aβ peptide in catalase overexpressing cells. The effects of 3-AT had an intracellular site of action, while catalase-amyloid interactions had an extracellular component. These results suggest that the 3-AT and BTA-EG4 compounds may be able to inhibit endogenous catalase mediated neuroprotection. Use of BTA-EG4, or compounds that inhibit catalase binding to amyloid peptides, as potential therapeutics for Neurodegenerative diseases may therefore result in unwanted effects.

Fragmentation chemistry of [Met-Gly]•+, [Gly-Met]•+, and [Met-Met]•+ radical cations

Radical cations [Met-Gly](•+), [Gly-Met](•+), and [Met-Met](•+) have been generated through collision-induced dissociation (CID) of [Cu(II)(CH3CN)2(peptide)](•2+) complexes. Their fragmentation patterns and dissociation mechanisms have been studied both experimentally and theoretically using density functional theory at the UB3LYP/6-311++G(d,p) level. The captodative structure, in which the radical is located at the α-carbon of the N-terminal residue and the proton is on the amide oxygen, is the lowest energy structure on each potential energy surface. The canonical structure, with the charge and spin both located on the sulfur, and the distonic ion with the proton on the terminal amino group, and the radical on the α-carbon of the C-terminal residue have similar energies. Interconversion between the canonical structures and the captodative isomers is facile and occurs prior to fragmentation. However, isomerization to produce the distonic structure is energetically less favorable and cannot compete with dissociation except in the case of [Gly-Met](•+). Charge-driven dissociations result in formation of [b(n) - H](•+) and a(1) ions. Radical-driven dissociation leads to the loss of the side chain of methionine as CH3-S-CH=CH2 producing α-glycyl radicals from both [Gly-Met](•+) and [Met-Met](•+). For [Met-Met](•+), loss of the side chain occurs at the C-terminal as shown by both labeling experiments and computations. The product, the distonic ion of [Met-Gly](•+), NH3 (+)CH(CH2CH2SCH3)CONHCH(•)COOH dissociates by loss of CH3S(•). The isomeric distonic ion NH3 (+)CH2CONHC(•)(CH2CH2SCH3)COOH is accessible directly from the canonical [Gly-Met](•+) ion. A fragmentation pathway that characterizes this ion (and the distonic ion of [Met-Met](•+)) is homolytic fission of the Cβ-Cγ bond to lose CH3SCH2(•).

β-amyloid decreases detectable endothelial nitric oxide synthase in human erythrocytes: a role for membrane acetylcholinesterase

Until few years ago, many studies of Alzheimer's disease investigated the effects of this syndrome in the central nervous system. Only recently, the detection of amyloid beta peptide (Aβ) in the blood has evidenced the necessity to extend studies on extraneuronal cells, particularly on erythrocytes. Aβ is also present in brain capillaries, where it interacts with the erythrocytes, inducing several metabolic and functional alterations. Recently, functionally active endothelial type nitric oxide synthase (eNOS) was discovered in human erythrocytes. The goal of the present study was to evidence the effect of Aβ on erythrocyte eNOS. We found that Aβ following to 24-h exposure causes a decrease in the immune staining of erythrocyte eNOS. Concurrently, Aβ alters erythrocyte cell morphology, decreases nitrites and nitrates levels, and affects membrane acetylcholinesterase activity. Propidium, an acetylcholinesterase inhibitor, was able to reverse the effects elicited by Aβ. These events could contribute to the vascular alterations associated with Alzheimer's disease disease.

Methionine-35 of aβ(1-42): importance for oxidative stress in Alzheimer disease

Alzheimer disease (AD) is an age-related progressive neurodegenerative disorder. This devastating disease is characterized by the presence of senile plaques (SP), neurofibrillary tangles (NFTs), and loss of synapses. Amyloid beta-peptide 1-42 (Aβ(1-42)) is the main component of SP and is pivotal to AD pathogenesis. Brain of subjects with AD and arguably its earliest manifestation, mild cognitive impairment (MCI), demonstrate increased levels of oxidative stress markers. Our laboratory combined these two aspects of AD and MCI and proposed the Aβ(1-42)-associated free radical oxidative stress hypothesis to explain oxidative stress under which the MCI and AD brain exist and the loss of synapses in both disorders. A large number of in vitro and in vivo studies showed that Aβ causes protein oxidation, lipid peroxidation, reactive oxygen species formation, and cell death in neuronal and synaptosomal systems. Methionine located at residue 35 of Aβ(1-42) is an important contributor to the oxidative stress associated with this neurotoxic peptide. In this paper, we summarize studies involving Met-35 of Aβ(1-42). Understanding the role of the single methionine residue of Aβ(1-42) may help in understanding underlying disease mechanisms in AD and MCI.

Amyloid peptide inhibits ATP release from human erythrocytes

The oxygen required to meet metabolic needs of all tissues is delivered by the erythrocyte, a small, flexible cell, which, in mammals, is devoid of a nucleus and mitochondria. Despite its simple appearance, this cell has an important role in its own distribution, enabling the delivery of oxygen to precisely meet localized metabolic need. When an erythrocyte enters in a hypoxic area, a signalling pathway is activated within the cell resulting in the release of ATP in amounts adequate to activate purinergic receptors on vascular endothelium, which trigger secretion of nitric oxide and other factors resulting in vasodilatation. Among other mechanisms, binding of deoxyhemoglobin to the cytoplasmic domain of the anion-exchange protein band 3 is probably involved in this pathway. The present study investigates the effect of amyloid beta peptide exposure on this molecular mechanism. We report that deoxygenated human erythrocytes fail to release ATP following 24 h exposure to amyloid beta peptide. Concurrently, amyloid beta peptide induces caspase 3 activation. Preincubation of amyloid beta peptide treated erythrocytes with a specific inhibitor of caspase 3 prevents amyloid-induced caspase 3 activation and restores the erythrocyte's ability to release ATP under deoxygenated conditions. Since the activity of red cell phosphofructokinase, a key step in glycolytic flux, is not modified within the red cell following amyloid peptide exposure, it is likely that ATP release reduction is not dependent on glycolytic flux alterations. It has also been suggested that the heterotrimeric G protein, Gi, and adenylyl cyclase are downstream critical components of the pathway responsible for ATP release. We show that cAMP synthesis and ATP release are not failed in amyloid-peptide-treated erythrocytes in response to incubation with mastoparan 7 or forskolin plus 3-isobutyl-1-methyl xanthine, agents that stimulate cAMP synthesis. In conclusion, these results indicate that amyloid beta peptide inhibits ATP release from deoxygenated erythrocytes by activating red cell caspase 3, suggesting a pathophysiologic role for vascular amyloid peptide 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.

Amyloid induced suicidal erythrocyte death

Amyloid peptides are known to induce apoptosis in a wide variety of cells. Erythrocytes may similarly undergo suicidal death or eryptosis, which is characterized by scrambling of the cell membrane with subsequent exposure of phosphatidylserine (PS) at the cell surface. Eryptosis is triggered by increase of cytosolic Ca(2+) activity and by activation of acid sphingomyelinase with subsequent formation of ceramide. Triggers of eryptosis include energy depletion and isosmotic cell shrinkage (replacement of extracellular Cl(-) by impermeable gluconate for 24 h). The present study explored whether amyloid peptide Abeta (1-42) could trigger eryptosis and to possibly identify underlying mechanisms. Erythrocytes from healthy volunteers were exposed to amyloid and PS-exposure (annexin V binding), cell volume (forward scatter), cytosolic Ca(2+) activity (Fluo3 fluorescence) and ceramide formation (anti-ceramide antibody) were determined by FACS analysis. Exposure of erythrocytes to the amyloid peptide Abeta (1-42) (> or = 0.5 microM) for 24 h significantly triggered annexin V binding, an effect mimicked to a lesser extent by the amyloid peptide Abeta (1-40) (1 microM). Abeta (1-42) (> or = 1.0 microM) further significantly decreased forward scatter of erythrocytes. The effect of Abeta (1-42) (> or = 0.5 microM) on erythrocyte annexin V binding was paralleled by formation of ceramide but not by significant increase of cytosolic Ca(2+) activity. The presence of Abeta (1-42) further significantly enhanced the eryptosis following Cl(-) depletion but not of glucose depletion for 24 hours. The present observations disclose a novel action of Abeta (1-42), which may well contribute to the pathophysiological effects of amyloid peptides, such as vascular complications in Alzheimer's disease.

High sensitivity analysis of amyloid-beta peptide composition in amyloid deposits from human and PS2APP mouse brain

Cortical amyloid-beta (Abeta) deposition is considered essential in Alzheimer's disease (AD) and is also detectable in nondemented individuals with pathologic aging (PA). The present work presents a detailed analysis of the Abeta composition in various plaque types from human AD and PA cases, compared with plaque Abeta isolated from PS2APP mice. To determine minute amounts of Abeta from 30 to 50 laser-dissected amyloid deposits, we used a highly sensitive mass spectrometry procedure after restriction protease lysyl endopeptidase (Lys-C) digestion. This approach allowed the analysis of the amino-terminus and, including a novel ionization modifier, for the first time the carboxy-terminus of Abeta at a detection limit of approximately 200 fmol. In addition, full length Abeta 40/42 and pyroglutamate 3-42 were analyzed using a highly sensitive urea-based Western blot procedure. Generally, Abeta fragments were less accessible in human deposits, indicative of more posttranslational modifications. Thioflavine S positive cored plaques in AD were found to contain predominantly Abeta 42, whereas thioflavine S positive compact plaques and vascular amyloid consist mostly of Abeta 40. Diffuse plaques from AD and PA, as well as from PS2APP mice are composed predominantly of Abeta 1-42. Despite biochemical similarities in human and PS2APP mice, immuno-electron microscopy revealed an extensive extracellular matrix associated with Abeta fibrils in AD, specifically in diffuse plaques. Amino-terminal truncations of Abeta, especially pyroglutamate 3-40/42, are more frequently found in human plaques. In cored plaques we measured an increase of N-terminal truncations of approximately 20% between Braak stages IV to VI. In contrast, diffuse plaques of AD and PA cases, show consistently only low levels of amino-terminal truncations. Our data support the concept that diffuse plaques represent initial Abeta deposits but indicate a structural difference for Abeta depositions in human AD compared with PS2APP mice already at the stage of diffuse plaque formation.

Amyloid-beta peptide affects the oxygen dependence of erythrocyte metabolism: a role for caspase 3

Human erythrocyte metabolism is modulated by the cell oxygenation state. Among other mechanisms, competition of deoxyhemoglobin and some glycolytic enzymes for the cytoplasmic domain of band 3 is probably involved in modulation. This metabolic modulation is connected to variations in intracellular NADPH and ATP levels as a function of the oxygenation state of the cell, and, consequently, it should have physiologic relevance. The present study investigates the effect of amyloid-beta peptide exposure on this metabolic modulation and its relationship with the activity of erythrocyte caspase 3. Metabolic differences between erythrocytes incubated at high and low oxygen saturation disappear following to 24 h exposure to amyloid-beta peptide. Western blotting analysis shows that caspase 3 is concurrently activated. Pre-incubation of amyloid-beta peptide-treated erythrocytes with a specific inhibitor of caspase 3, partially restores the oxygen-dependent modulation. This finding suggests that human erythrocytes following to exposure to amyloid-beta peptide show a complete loss of the oxygen-dependent metabolic modulation, which is partially restored by caspase 3 inhibitor-treatment.

Methionine Radical Cation: Structural Studies as a Function of pH Using X- and Q-Band Time-Resolved Electron Paramagnetic Resonance Spectroscopy

A comprehensive high resolution electron paramagnetic resonance (EPR) characterization of the l-methionine radical cation and its N-acetyl derivative in liquid solution at room temperature is presented. The cations were generated photochemically in high yield by excimer laser excitation of a water soluble dye, anthraquinone sulfonate sodium salt, the excited triplet state of which is quenched by electron transfer from the side chain sulfur atom of methionine or N-acetylmethionine. The radicals were detected by continuous wave (CW) time-resolved electron paramagnetic resonance (TREPR) spectroscopy at X-band (9.5 GHz) and Q-band (35 GHz) microwave frequencies. At pH values well below the pK(a) of the protonated amine nitrogen, the cation forms a dimer with another ground-state methionine molecule through a S-S three-electron bond. In basic solution, the lone pair on the nitrogen of the amino acid is available to make an intramolecular S-N three-electron bond with the side chain sulfur atom, leading to a five-membered ring structure for the cation. When the amino acid nitrogen is unsubstituted (methionine itself), rapid deprotonation to an aminyl radical takes place at high pH values. If the nitrogen is substituted (N-acetylmethionine), the cyclic structure is observed within its electron spin relaxation time at about 1 micros. Spectral simulation provides chemical shifts (g-factors) and hyperfine coupling constants for all structures, and isotopic labeling experiments strongly support the assignments.

Aβ(31-35) and Aβ(25-35) fragments of amyloid beta-protein induce cellular death through apoptotic signals: Role of the redox state of methionine-35

In order to clarify the basis of neuronal toxicity exerted by the shortest active peptides of amyloid beta-protein (Abeta), the toxic effects of Abeta(31-35) and Abeta(25-35) peptides on isolated rat brain mitochondria were investigated. The results show that exposure of isolated rat brain mitochondria to Abeta(31-35) and Abeta(25-35) peptides determines: (i) release of cytochrome c; (ii) mitochondrial swelling and (iii) a significant reduction in mitochondrial oxygen consumption. In contrast, the amplitude of these events resulted attenuated in isolated brain mitochondria exposed to the Abeta(31-35)Met35(OX) in which methionine-35 was oxidized to methionine sulfoxide. The Abeta peptide derivative with norleucine substituting Met-35, i.e., Abeta(31-35)Nle-35, had not effect on any of the biochemical parameters tested. We have further characterized the action of Abeta(31-35) and Abeta(25-35) peptides on neuronal cells. Taken together our result indicate that Abeta(31-35) and Abeta(25-35) peptides in non-aggregated form, i.e., predominantly monomeric, are strongly neurotoxic, having the ability to enter within the cells, determining mitochondrial damage with an evident trigger of apoptotic signals. Such a mechanism of toxicity seems to be dependent by the redox state of methionine-35.