Paracetamol toxicity in classic homocystinuria: Effect of N-acetylcysteine on total homocysteine

Classical homocystinuria (HCU) is caused by cystathionine β-synthase deficiency leading to impaired homocysteine transsulfuration and accumulation of homocysteine and methionine. Patients present with a wide spectrum of manifestations including ocular, skeletal, neuropsychiatric, and vascular manifestations. We report a 48-year-old female with pyridoxine-unresponsive HCU treated with betaine, cyanocobalamin, and folate. Her diet was non-restricted due to intolerance of low-methionine diet. She was admitted to hospital following a fall, with multiple fractures and subsequently developed acute liver failure with encephalopathy. Shock, sepsis, and liver ischaemia/thrombosis were excluded. In the context of glutathione depletion expected in HCU, hepatic dysfunction was presumed to be due to iatrogenic paracetamol toxicity, despite paracetamol intake at conventional therapeutic dose, with role of hypermethioninemia as a contributing factor being uncertain. Betaine was discontinued on hospital admission. N-Acetylcysteine (NAC) infusion was initiated. Plasma total homocysteine (tHcy) was 3.4 μmol/L 9 days following initiation of NAC treatment with a markedly elevated plasma methionine of 1278 μmol/L. tHcy concentration returned to pre-admission baseline after NAC was discontinued. Recovery following this episode was slow with a prolonged cholestatic phase and gradual improvement in jaundice and coagulopathy. We recommend that paracetamol should be administered cautiously in HCU patients due to underlying glutathione depletion and risk of toxicity even at therapeutic doses. NAC is clearly effective in lowering tHcy in classical HCU in the short-term however further research is required to assess clinical efficacy and use as a potential therapy in classical HCU.

Biallelic TET2 mutations confer sensitivity to 5'-azacitidine in acute myeloid leukemia

Precision medicine can significantly improve outcomes for patients with cancer, but implementation requires comprehensive characterization of tumor cells to identify therapeutically exploitable vulnerabilities. Here, we describe somatic biallelic TET2 mutations in an elderly patient with acute myeloid leukemia (AML) that was chemoresistant to anthracycline and cytarabine but acutely sensitive to 5'-azacitidine (5'-Aza) hypomethylating monotherapy, resulting in long-term morphological remission. Given the role of TET2 as a regulator of genomic methylation, we hypothesized that mutant TET2 allele dosage affects response to 5'-Aza. Using an isogenic cell model system and an orthotopic mouse xenograft, we demonstrate that biallelic TET2 mutations confer sensitivity to 5'-Aza compared with cells with monoallelic mutations. Our data argue in favor of using hypomethylating agents for chemoresistant disease or as first-line therapy in patients with biallelic TET2-mutated AML and demonstrate the importance of considering mutant allele dosage in the implementation of precision medicine for patients with cancer.

Self-Assembly and Anti-Amyloid Cytotoxicity Activity of Amyloid beta Peptide Derivatives

The self-assembly of two derivatives of KLVFF, a fragment Aβ(16-20) of the amyloid beta (Aβ) peptide, is investigated and recovery of viability of neuroblastoma cells exposed to Aβ (1-42) is observed at sub-stoichiometric peptide concentrations. Fluorescence assays show that NH2-KLVFF-CONH2 undergoes hydrophobic collapse and amyloid formation at the same critical aggregation concentration (cac). In contrast, NH2-K(Boc)LVFF-CONH2 undergoes hydrophobic collapse at a low concentration, followed by amyloid formation at a higher cac. These findings are supported by the β-sheet features observed by FTIR. Electrospray ionization mass spectrometry indicates that NH2-K(Boc)LVFF-CONH2 forms a significant population of oligomeric species above the cac. Cryo-TEM, used together with SAXS to determine fibril dimensions, shows that the length and degree of twisting of peptide fibrils seem to be influenced by the net peptide charge. Grazing incidence X-ray scattering from thin peptide films shows features of β-sheet ordering for both peptides, along with evidence for lamellar ordering of NH2-KLVFF-CONH2. This work provides a comprehensive picture of the aggregation properties of these two KLVFF derivatives and shows their utility, in unaggregated form, in restoring the viability of neuroblastoma cells against Aβ-induced toxicity.

β-Hairpin mimics containing a piperidine-pyrrolidine scaffold modulate the β-amyloid aggregation process preserving the monomer species

Alzheimer's disease is a neurodegenerative disorder linked to oligomerization and fibrillization of amyloid β peptides, with Aβ_1-42 being the most aggregative and neurotoxic one. We report herein the synthesis and conformational analysis of Aβ_1-42-amyloid related β-hairpin peptidomimetics, built on a piperidine-pyrrolidine semi rigid β-turn inducer and bearing two small recognition peptide sequences, designed on oligomeric and fibril structures of Aβ_1-42. According to these peptide sequences, a stable β-hairpin or a dynamic equilibrium between two possible architectures was observed. These original constructs are able to greatly delay the kinetics of Aβ_1-42 aggregation process as demonstrated by thioflavin-T fluorescence, and transmission electron microscopy. Capillary electrophoresis indicates their ability to preserve the monomer species, inhibiting the formation of toxic oligomers. Furthermore, compounds protect against toxic effects of Aβ on neuroblastoma cells even at substoichiometric concentrations. This study is the first example of acyclic small β-hairpin mimics possessing such a highly efficient anti-aggregation activity. The protective effect is more pronounced than that observed with molecules which have undergone clinical trials. The structural elements made in this study provide valuable insights in the understanding of the aggregation process and insights to explore the design of novel acyclic β-hairpin targeting other types of amyloid-forming proteins.

Demonstrating the effect of forensic firearm countermeasures: Bullet characteristics generated due to barrel modifications

Forensic awareness and the declining availability of firearms have resulted in an increase in the use of modified and re-activated firearms in crime. Although some modifications are undertaken to simply acquire a functioning firearm, others are perpetrated as a direct forensic countermeasure to prevent the association between a firearm and a crime. This article describes the effects of these modifications on bullet striation patterns imparted from the barrel to a fired bullet. The key results indicated that the investigated modifications display assessable characteristics. The use of an oversized barrel imparted striations consistent with firing with the absence of typical rifling. Subsequent or consecutively fired bullets possessed striation variations, with the first showing the least evidence of striations. The application of a choke resulted in more obvious bullet elongation compared to a smoothbore barrel. The restriction caused merging of lands and groves of the imparted rifling and obscured their usual definition. Effects of breech adaption were also characterised by observing the buckling and enlargement of the cartridge case. This deformity of the cartridge case was most evident when the barrel pressure increased due to the presence of the choke. From this study it was evident that unique characteristic impressions associated with different modifications most commonly found in criminal investigations can be utilised by a forensic expert and impart significant intelligence to an investigation.

Post mortem cerebrospinal fluid α-synuclein levels are raised in multiple system atrophy and distinguish this from the other α-synucleinopathies, Parkinson's disease and Dementia with Lewy bodies

Differentiating clinically between Parkinson's disease (PD) and the atypical parkinsonian syndromes of Progressive supranuclear palsy (PSP), corticobasal syndrome (CBS) and multiple system atrophy (MSA) is challenging but crucial for patient management and recruitment into clinical trials. Because PD (and the related disorder Dementia with Lewy bodies (DLB)) and MSA are characterised by the deposition of aggregated forms of α-synuclein protein (α-syn) in the brain, whereas CBS and PSP are tauopathies, we have developed immunoassays to detect levels of total and oligomeric forms of α-syn, and phosphorylated and phosphorylated oligomeric forms of α-syn, within body fluids, in an attempt to find a biomarker that will differentiate between these disorders. Levels of these 4 different forms of α-syn were measured in post mortem samples of ventricular cerebrospinal fluid (CSF) obtained from 76 patients with PD, DLB, PSP or MSA, and in 20 healthy controls. Mean CSF levels of total and oligomeric α-syn, and phosphorylated α-syn, did not vary significantly between the diagnostic groups, whereas mean CSF levels of phosphorylated oligomeric α-syn did differ significantly (p<0.001) amongst the different diagnostic groups. Although all 4 measures of α-syn were higher in patients with MSA compared to all other diagnostic groups, these were only significantly raised (p<0.001) in MSA compared to all other diagnostic groups, for phosphorylated oligomeric forms of α-syn. This suggests that this particular assay may have utility in differentiating MSA from control subject and patients with other α-synucleinopathies. However, it does not appear to be of help in distinguishing patients with PD and DLB from those with PSP or from control subjects. Western blots show that the principal form of α-syn within CSF is phosphorylated, and the finding that the phosphorylated oligomeric α-syn immunoassay appears to be the most informative of the 4 assays would be consistent with this observation.

Protein aggregation, metals and oxidative stress in neurodegenerative diseases

There is clear evidence implicating oxidative stress in the pathology of many different neurodegenerative diseases. ROS (reactive oxygen species) are the primary mediators of oxidative stress and many of the aggregating proteins and peptides associated with neurodegenerative disease can generate hydrogen peroxide, a key ROS, apparently through interactions with redox-active metal ions. Our recent results suggest that ROS are generated during the very early stages of protein aggregation, when protofibrils or soluble oligomers are present, but in the absence of mature amyloid fibrils. The generation of ROS during early-stage protein aggregation may be a common, fundamental molecular mechanism underlying the pathogenesis of oxidative damage, neurodegeneration and cell death in several different neurodegenerative diseases. Drugs that specifically target this process could be useful in the future therapy of these diseases.

The production of hydrogen peroxide during early-stage protein aggregation: a common pathological mechanism in different neurodegenerative diseases?

By means of an ESR spin-trapping method, we have shown that Aβ (amyloid β), α-synuclein and various toxic forms of the prion protein all appear to generate H2O2in vitro. A fundamental molecular mechanism underlying the pathogenesis of cell death in several different neurodegenerative diseases could be the direct production of H2O2 during the early stages of protein aggregation.

Introduction to Alzheimer's disease

In 1907, Alois Alzheimer published an account (1) of a 51-year-old female patient, Auguste D., who suffered from strong feelings of jealousy towards her husband, increased memory impairment, disorientation, hallucinations, and often loud and aggressive behavior. After four and a half years of rapidly deteriorating mental illness, Auguste D died in a completely demented state. Postmortem histological analysis of her brain using the Bielschowsky silver technique revealed dense bundles of unusual fibrils within nerve cells (neurofibrillary tangles or NFTs) and numerous focal lesions within the cerebral cortex, subsequently named "senile plaques" by Simchowicz (2) Fig. 1). This combination of progressive presenile dementia with senile plaques and neurofibrillary tangles came to be known as Alzheimer's disease (AD), a term that was later broadened to include senile forms of dementia with similar neuropathological findings. It was Divry (3) who first demonstrated the presence of amyloid at the center of the senile plaque, by means of Congo red staining. All amyloid deposits were originally thought to be starch-like in nature (hence the name), but it is now apparent that they are formed from a variety of different peptides and proteins (the latest count being 18). All amyloid share the property of a characteristic birefringence under polarized light after staining with Congo red dye, which is due to the presence of well-ordered 10 nm fibrils. The underlying protein component of these fibrils invariably adopts predominantly an antiparallel β-pleated sheet configuration. Ultrastructural observations have confirmed that the core of the senile plaque consists of large numbers of closely-packed, radiating fibrils, similar in appearance to those seen in other forms of amyloidosis (4,5), and have also revealed the presence of paired helical filaments (PHFs) within the NFTs (6). However, it took more than 50 yr from Divry's original observation to determine the precise chemical nature of the senile plaque amyloid. Many neuropathologists have regarded this amyloid as a "tombstone" (an inert bystander) of AD. However, the advent of molecular genetics has finally and firmly established the central role of amyloid in the pathogenesis of the disease, although this is still disputed by some workers in the field. This introductory chapter is written in support of what has become known as the "amyloid cascade" hypothesis.

Inherited frontotemporal dementia in nine British families associated with intronic mutations in the tau gene

Genetic screening of 171 patients with frontotemporal lobar degeneration disclosed 14 patients, across nine pedigrees, with mutations in the intron to exon 10 in the tau gene, a region regulating the splicing of exon 10 via a stem loop mechanism. Thirteen of these patients had the +16 splice site mutation and one had the +13 splice site mutation. Affected members of all nine families presented with changes in behaviour and social conduct that were prototypical of frontotemporal dementia (FTD). In all patients with the +16 splice site mutation, the behavioural profile was characterized by disinhibition, restless overactivity, a fatuous affect, puerile behaviour and verbal and motor stereotypies. The single patient with the +13 mutation presented a contrasting picture of apathy and inertia. In addition, all patients had evidence of semantic loss. Pathologically, five of the six patients so far autopsied shared frontotemporal atrophy with involvement of the substantia nigra. The underlying histology was that of microvacuolar-type cortical degeneration with a few swollen cells. Tau pathology was widespread throughout the brain and present in neurones and glial cells, mostly in the frontal and temporal cortical regions. This was in the form of neurofibrillary tangles and amorphous tau deposits (pre-tangles); Pick bodies were not observed. Ultrastructurally, the tau filaments had a twisted, ribbon-like morphology distinct from the paired helical filaments of Alzheimer's disease. One patient died from an unrelated illness whilst in the early clinical stages of FTD. In this patient, cortical microvacuolar and astrocytic changes were absent, though there were scattered neurones and glial cells, immunoreactive to tau, throughout the cortical and subcortical regions. The disease process underlying the neurodegeneration within these inherited forms of FTD may therefore stem directly from early, primary alterations in the function of tau. All eight families with the +16 mutation seem to be part of a common extended pedigree, possibly originating from a founder member residing within the North Wales region of Great Britain.

Modulation of beta-amyloid production and fibrillization

Alzheimer's disease (AD) is the most common cause of dementia in old age and presently affects an estimated 4 million people in the U.S.A. and 0.75 million people in the U.K. It is a relentless, degenerative brain disease, characterized by progressive cognitive impairment. In the final stages of the disease, patients are often bedridden, doubly incontinent and unable to speak or to recognize close relatives. Pathological changes of Alzheimer's disease include extensive neuronal loss and the presence of numerous neurofibrillary tangles and senile plaques in the brain. The senile plaques contain amyloid fibrils derived from a 39-43-amino-acid peptide referred to as beta-amyloid or A beta. The basic theory of the so-called 'amyloid hypothesis' is that the deposition of aggregated forms of A beta in the brain parenchyma triggers a pathological cascade of events that leads to neurofibrillary tangle formation, neuronal loss and the associated dementia [1]. Here we discuss progress towards the identification of inhibitors of A beta production and fibrillization.

Production of reactive oxygen species from aggregating proteins implicated in Alzheimer's disease, Parkinson's disease and other neurodegenerative diseases

The deposition of abnormal protein fibrils is a prominent pathological feature of many different 'protein conformational' diseases, including some important neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), motor neurone disease and the 'prion' dementias. Some of the fibril-forming proteins or peptides associated with these diseases have been shown to be toxic to cells in culture. A clear understanding of the molecular mechanisms responsible for this toxicity should shed light on the probable link between protein deposition and cell loss in these diseases. In the case of the beta-amyloid (Abeta), which accumulates in the brain in AD, there is good evidence that the toxic mechanism involves the production of reactive oxygen species (ROS). By means of an electron spin resonance (ESR) spin-trapping method, we have shown recently that solutions of Abeta liberate readily detectable amounts of hydroxyl radicals upon incubation in vitro followed by the addition of small amounts of Fe(II). We have also obtained similar results with alpha-synuclein, which accumulates in Lewy bodies in PD. Our data suggest that hydrogen peroxide accumulates during Abeta or alpha-synuclein incubation and that this is subsequently converted to hydroxyl radicals, on addition of Fe (II), by Fenton's reaction. Consequently, we now support the idea that one of the fundamental molecular mechanisms underlying the pathogenesis of cell death in AD, PD, and possibly some other protein conformational diseases, could be the direct production of ROS during formation of the abnormal protein aggregates. This hypothesis suggests a novel approach to the therapy of this group of diseases.

Fluorescence anisotropy: a method for early detection of Alzheimer beta-peptide (Abeta) aggregation

Time-resolved anisotropy measurements (TRAMS) have been used to study the aggregation of the beta-amyloid (Abeta) peptide which is suspected of playing a central role in the pathogenesis of Alzheimer's Disease (AD). The experiments, which employ small quantities of fluorescently-labelled Abeta, in addition to the untagged peptide, have shown that the sensitive TRAMS technique detects the presence of preformed "seed" particles in freshly prepared solutions of Abeta. More importantly, as 100 microM solutions of Abeta containing tagged Abeta at a concentration level of either 0.5 or 1 microM are incubated, the TRAMS prove capable of detection of the peptide aggregation process through the appearance of a continuously increasing "residual anisotropy" within the time-resolved fluorescence data. The method detects Abeta aggregation in its earliest stages, well before complexation becomes apparent in more conventional methods such as the thioflavin T fluorescence assay. The TRAMS approach promises to provide a most attractive route for establishment of a high-throughput procedure for the early detection of the presence of amyloid aggregates in the screening of biological samples.

alpha-Synuclein implicated in Parkinson's disease catalyses the formation of hydrogen peroxide in vitro

Some rare inherited forms of Parkinson's disease (PD) are due to mutations in the gene encoding a 140-amino acid presynaptic protein called alpha-synuclein. In PD, and some other related disorders such as dementia with Lewy bodies, alpha-synuclein accumulates in the brain in the form of fibrillar aggregates, which are found inside the neuronal cytoplasmic inclusions known as Lewy bodies. By means of an electron spin resonance (ESR) spin trapping method, we show here that solutions of full-length alpha-synuclein, and a synthetic peptide fragment of alpha-synuclein corresponding to residues 61-95 (the so-called non-Abeta component or NAC), both liberate hydroxyl radicals upon incubation in vitro followed by the addition of Fe(II). We did not observe this property for the related beta- and gamma-synucleins, which are not found in Lewy bodies, and are not linked genetically to any neurodegenerative disorder. There is abundant evidence for the involvement of free radicals and oxidative stress in the pathogenesis of nigral damage in PD. Our new data suggest that the fundamental molecular mechanism underlying this pathological process could be the production of hydrogen peroxide by alpha-synuclein.

New evidence that the Alzheimer beta-amyloid peptide does not spontaneously form free radicals: an ESR study using a series of spin-traps

The direct formation of free radicals from Abeta has been suggested to be a key neurotoxic mechanism in Alzheimer's disease (AD). We have explored the possibility of the spontaneous formation of peptide-derived free radicals during the incubation of Abeta 1-40 by ESR spectroscopy using N-tert-butyl-alpha-phenylnitrone (PBN), 5,5-dimethyl-1-pyrroline N-oxide (DMPO), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN), and 3,5-dibromo-4-nitrosobenzenesulfonic acid sodium salt (DBNBS) as spin traps. Employing PBN, we observed spectra during the incubation of beta-amyloid peptide, at 37 degrees C, which included adducts of 2-methyl-2-nitrosopropane (MNP), despite rigorous purification of the PBN before incubation. The formation of some of these adducts was found to be enhanced by ambient laboratory light. Our experiments have led us to propose a hypothesis that PBN undergoes hydrolysis and decomposition in the presence of oxidants, which explains the origin of all of the PBN and MNP adducts observed (even when the PBN is highly purified). Hydrogen peroxide, formed during incubation, could play a major role as an oxidant in these experiments. Of the other three spin traps, only DMPO gave (very weak) spectra, but these could be assigned to its hydroxyl radical adduct, formed as an artifact by the nucleophilic addition of water to DMPO, catalyzed by trace levels of iron ions. Thus, while spectra are observed during our experiments, none of them can be assigned to adducts of radicals derived from the peptide and, therefore, our data do not support the suggestion that radicals are spontaneously formed from beta-amyloid peptide.

3-p-Toluoyl-2-[4'-(3-diethylaminopropoxy)-phenyl]-benzofuran and 2-[4'-(3-diethylaminopropoxy)-phenyl]-benzofuran do not act as surfactants or micelles when inhibiting the aggregation of beta-amyloid peptide

The cmc and IC50 values of the beta-amyloid (Abeta) aggregation inhibitors, 3-p-toluoyl-2-[4'-(3-diethylaminopropoxy)-phenyl]-benzofuran 1, and 2-[4'-(3-diethylaminopropoxy)-phenyl]-benzofuran 2 have been determined. After comparison of the cmc data and biological data (IC50 values), we conclude that these active benzofurans do not act as surfactants or micelles at the concentration required to inhibit beta-amyloid-peptide aggregation.

Pick's disease is associated with mutations in the tau gene

Recently, mutations within the tau gene have been associated with some familial forms of frontotemporal dementia. To investigate whether tau gene mutations are also associated with Pick's disease, we analyzed the tau gene in 30 cases of pathologically confirmed Pick's disease. Two coding mutations were identified in separate cases of Pick's disease. A glycine-to-arginine mutation at codon 389 was detected in 1 case and a lysine-to-threonine mutation at codon 257 was identified in another. Analysis of dephosphorylated tau from the brain of the patient with the codon 389 mutation revealed a prominent band representing tau, with four microtubule-binding domains and no amino terminal inserts. This is in contrast to Pick's disease without any tau gene mutations, which consist of tau with mainly three microtubule-binding domains and only a trace of tau, with four microtubule-binding domains. Functional analysis of tau with these two mutations demonstrated a reduced ability of tau to promote microtubule assembly. Surprisingly, these mutations increased tau's susceptibility to calpain I digestion, suggesting that this feature may be related to the formation of a Pick type of histology. Moreover, these data suggest that Pick's disease is not a separate entity but part of the frontotemporal dementia disease spectrum.

Characterization of peptidyl boronic acid inhibitors of mammalian 20 S and 26 S proteasomes and their inhibition of proteasomes in cultured cells

Proteasomes are large multisubunit proteinases which have several distinct catalytic sites. In this study a series of di- and tri-peptidyl boronic acids have been tested on the chymotrypsin-like activity of purified mammalian 20 S and 26 S proteasomes assayed with succinyl-Leu-Leu-Val-Tyr-amidomethylcoumarin (suc-Leu-Leu-Val-Tyr-AMC) as substrate. The inhibition of 20 S proteasomes is competitive but only slowly reversible. The K(i) values for the best inhibitors were in the range 10-100 nM with suc-Leu-Leu-Val-Tyr-AMC as substrate, but the compounds tested were much less effective on other proteasome activities measured with other substrates. Free boronic acid inhibitors exhibited equivalent potency to their pinacol esters. Both benzoyl (Bz)-Phe-boroLeu and benzyloxycarbonyl (Cbz)-Leu-Leu-boroLeu pinacol ester inhibited 20 S and 26 S proteasomes with non-ideal behaviour, differences in inhibition of the two forms of proteasomes becoming apparent at high inhibitor concentrations (above 3xK(i)). Both of these compounds were also potent inhibitors of 20 S and 26 S proteasomes in cultured cells. However, gel filtration of cell extracts prepared from cells treated with radiolabelled phenacetyl-Leu-Leu-boroLeu showed that only 20 S proteasomes were strongly labelled, demonstrating differences in the characteristics of inhibition of 20 S and 26 S proteasomes. The usefulness of peptidyl boronic acid inhibitors for investigations of proteasome-mediated protein degradation was confirmed by the observation that Bz-Phe-boroLeu and Cbz-Leu-Leu-boroLeu pinacol ester inhibited NFkappaB activation with IC(50) values comparable to their K(i) values for purified proteasomes. The latter result supports the view that the chymotrypsin-like activity of proteasomes assayed with suc-Leu-Leu-Val-Tyr-AMC is a critical one for protein degradation in cells.

Alzheimer's disease: correlation of the suppression of beta-amyloid peptide secretion from cultured cells with inhibition of the chymotrypsin-like activity of the proteasome

Peptide aldehyde inhibitors of the chymotrypsin-like activity of the proteasome (CLIP) such as N-acetyl-Leu-Leu-Nle-H (or ALLN) have been shown previously to inhibit the secretion of beta-amyloid peptide (A beta) from cells. To evaluate more fully the role of the proteasome in this process, we have tested the effects on A beta formation of a much wider range of peptide-based inhibitors of CLIP than published previously. The inhibitors tested included several peptide boronates, some of which proved to be the most potent peptide-based inhibitors of beta-amyloid production reported so far. We found that the ability of the peptide aldehyde and boronate inhibitors to suppress A beta formation from cells correlated extremely well with their potency as CLIP inhibitors. Thus, we conclude that the proteasome may be involved either directly or indirectly in A beta formation.

Presenilins--in search of functionality

The discovery of the PS proteins, the complexities of their biochemistry and their potential involvement in signalling pathways and in apoptosis have galvanized research into AD. To date, the aspect of the functionality of the PSs most relevant to the pathology of AD is the effect of PS FAD mutants to increase the proportion of A beta 42 produced from cells. This, coupled to the observation that gamma-secretase cleavage is considerably reduced in neurons derived from PS-1 knockout mice, argues strongly that PS plays a very direct role in the proteolytic processing of APP.

Distinct sites of intracellular production for Alzheimer's disease A beta40/42 amyloid peptides

The Alzheimer amyloid precursor protein (APP) is cleaved by several proteases, the most studied, but still unidentified ones, are those involved in the release of a fragment of APP, the amyloidogenic beta-protein A beta. Proteolysis by gamma-secretase is the last processing step resulting in release of A beta. Cleavage occurs after residue 40 of A beta [A beta(1-40)], occasionally after residue 42 [A beta(1-42)]. Even slightly increased amounts of this A beta(1-42) might be sufficient to cause Alzheimer's disease (AD) (reviewed in ref. 1, 2). It is thus generally believed that inhibition of this enzyme could aid in prevention of AD. Unexpectedly we have identified in neurons the endoplasmic reticulum (ER) as the site for generation of A beta(1-42) and the trans-Golgi network (TGN) as the site for A beta(1-40) generation. It is interesting that intracellular generation of A beta seemed to be unique to neurons, because we found that nonneuronal cells produced significant amounts of A beta(1-40) and A beta(1-42) only at the cell surface. The specific production of the critical A beta isoform in the ER of neurons links this compartment with the generation of A beta and explains why primarily ER localized (mutant) proteins such as the presenilins could induce AD. We suggest that the earliest event taking place in AD might be the generation of A beta(1-42) in the ER.

Effect of aluminium on expression and processing of amyloid precursor protein

The environmental agent aluminium has been extensively investigated for a potential role in the aetiology of Alzheimer's disease. Despite many investigations there is at present no definite proof for any involvement. If aluminium is involved it is possible that its action is mediated through interaction with the synthesis or processing of amyloid precursor protein (APP). The present study compared aluminium loaded IMR-32 neuroblastoma cells and rat brains with control cells and brains to determine if aluminium affected APP expression and/or processing. In the IMR-32 model system aluminium had no effect on steady-state APP mRNA levels or on the ratio of individual isoforms. It also had no quantitative or qualitative effect on APP-immunoreactive bands detected in protein extracts from conditioned medium of these cells. In total cell extracts, aluminium reduced the intensity of APP-immunoreactive bands between 120-105 kDa but had no effect on a 9 kDa band. In rat brains, aluminium had no effect on APP-immunoreactive bands from soluble or insoluble-membranous extracts. The results, in general, provide no evidence for any effect of aluminium on APP expression or processing.

Aggregation and metal-binding properties of mutant forms of the amyloid A beta peptide of Alzheimer's disease

The fibrillogenic properties of Alzheimer's A beta peptides corresponding to residues 1-40 of the normal human sequence and to two mutant forms containing the replacement Ala21 to Gly or Glu22 to Gln were compared. At pH 7.4 and 37 degrees C the Gln22 peptide was found to aggregate and precipitate from solution faster than the normal A beta, whereas the Gly21 peptide aggregated much more slowly. Electron microscopy showed that the aggregates all had fibrillar structures. Circular dichroism spectra of these peptides revealed that aggregation of the normal and Gln22 sequences was associated with spectral changes consistent with a transformation from random coil to beta sheet, whereas the spectrum of the Gly21 peptide remained almost unchanged during a period in which little or no aggregation occurred. When immobilised by spotting onto nitrocellulose membranes the peptides bound similar amounts of the radioisotope 65Zn2+. Of several competing metal ions, tested at 20x the concentration of Zn2+, Cu2+ displaced > 95% of the radioactivity from all three peptides and Ni2+ produced >50% displacement in each case. Some other metal ions tested caused lesser displacement, but Fe2+ and Al3+ were without effect. In a saturation binding assay, a value of 3.2 microM was obtained for the binding of Zn2+ to A beta but our data provided no evidence for a reported higher affinity site (107 nM). The results suggest that the neuropathology associated with the Gly21 mutation is not due to enhanced fibrillogenic or different metal-binding properties of the peptide and that the binding of zinc to amyloid peptides is not a specific phenomenon.

The immunoreactive profile at the N-terminal region of A beta 1-39/40 but not A beta 1-42 changes with transition from monomer/dimer to further peptide aggregates

Using site-specific antibodies, we assessed the effect of aggregation of various length forms of A beta on the immunoreactive profile of the peptides. All of the antibodies tested reacted with monomeric/dimeric forms of A beta 1-42 and its further aggregates. However, antibodies directed against the 1-24 region of A beta reacted weakly or not at all with A beta 1-39/40 monomers or dimers, but immunoreactivity was enhanced substantially following peptide incubation and aggregation. These results suggest that the conformation of the N-terminal region of monomeric and dimeric A beta 1-39/40 is different from that of aggregated forms, whereas the longer A beta 1-42 does not significantly change its N-terminal conformation during beta-sheet fibril formation. These immunochemical results are consistent with previous structural data, and help to explain the differential effects of A beta 1-39/40 and 1-42 on fibril formation in brain.

Inflammatory mechanisms in Alzheimer's disease

Alzheimer's disease is aetiologically heterogeneous, but the pathogenesis is often considered to be initiated by the deposition of amyloid fibrils, followed by neuritic tau pathology and neuronal death. A variety of inflammatory proteins has been identified in the brains of patients with Alzheimer's disease post mortem. In this article, Piet Eikelenboom and colleagues review evidence to suggest that the inflammatory processes are intimately involved in several crucial events in the pathological cascade. This suggests possibilities for the treatment of Alzheimer's disease with anti-inflammatory drugs.

Variability of beta-amyloid protein deposited lesions in Down's syndrome brains

An immunohistochemical study was carried out on the brains of 7 adult Down's syndrome cases (ages 31 to 62) using antibodies to beta-protein, beta-amyloid protein precursor and tau-protein. Variable forms of beta-protein deposited lesions (including senile plaques and cerebrovascular amyloidosis) were observed in extensive areas of the neocortex of all cases and coexistence of both beta-protein amyloid fibrils and beta-amyloid protein precursors was also seen in some of these lesions. Moreover, 3 cases at an advanced stage showed a few plaque-like lesions with beta-protein immunoreactivity in the white matter. The following temporal morphological change is suggested for the pathogenesis of Alzheimer's disease: senile plaque undergo sequential structural changes and beta-protein amyloid deposits in the form of "early plaque" precede the development of tau-immunoreactive neurofibrillary degeneration.

Human IMR-32 neuroblastoma cells as a model cell line in Alzheimer's disease research

The present study investigated expression and processing of amyloid precursor protein by neuronally differentiated IMR-32 neuroblastoma cells. APP mRNA in these cells was found to consist of approximately 58% APP695, 38% APP751, and < 4% APP770. APP-immunoreactive bands detected in western blots of cellular protein extracts were only detected by anti-APP antibodies to peptides with strong homology to APLP2, suggesting that these bands represent APP-like proteins and not APP itself. This result suggests that previous studies claiming immunodetection of cellular forms of APP may have to be re-evaluated. Four main species of C-terminal truncated, secreted APP were detected in blots of protein extracts from medium conditioned by these cells. The immunoreactive profile of these bands suggested a cleavage site N-terminal to the Lys16-Leu17 bond of alpha-secretase. This, together with differences in number and molecular mass of APP-immunoreactive bands between secreted APP from IMR-32 cells and that from the commonly used PC-12 cells, suggests differences in APP processing between these two neuronally differentiated cell lines. In theory, IMR-32 cells being of human neuronal origin may be a more appropriate cell line to study APP-processing in relation to Alzheimer's disease than the rat phaeochromocytoma PC-12 cell line. Therefore, these detected differences warrant further investigation. Additionally IMR-32 cells under certain tissue culture conditions can form intracellular fibrillary material that reacts with anti-PHF specific antibodies. Neuronally differentiated IMR-32 cells could therefore be used as a model system to investigate possible interactions between APP-processing and PHF formation.

Gerstmann-Sträussler-Scheinker disease showing beta-protein type cerebellar and cerebral amyloid angiopathy

Cerebral amyloid angiopathy is observed in several brain degenerative disorders, but this pathological condition has received little attention in Gerstmann-Sträussler-Scheinker disease (GSS). We report a 69-year-old man who showed the cardinal features of GSS together with typical and extensive congophilic angiopathy. Immunohistochemical studies revealed that the vast majority of the amyloid plaques present in the brain of this patient were consistently labeled by anti-prion protein (PrP) antibody. Double immunostaining disclosed many additional beta-protein immunoreactive plaque-like lesions, including a special type of "hybrid" plaque with colocalization of PrP and beta-protein (beta-PrP). The vascular amyloid deposits seen in both the cerebellum and cerebrum were immunoreactive only to anti-beta-protein antibody. It seems likely that the extensive deposition of beta-protein amyloid (including brain vascular amyloidosis) seen in this and other similar cases is part of pathology of GSS, although the possibility that this finding is due to ageing or concomitant Alzheimer's disease cannot be completely ruled out.

Effects of the mutations Glu22 to Gln and Ala21 to Gly on the aggregation of a synthetic fragment of the Alzheimer's amyloid beta/A4 peptide

We assessed the fibrillogenic properties of synthetic peptides corresponding to residues 13-26 of beta/A4 amyloid, containing either the normal sequence (beta 13 26) or the mutations Glu22 to Gln (beta 13-26Q22) and Ala21 to Gly (beta 13-26G21). The kinetics of aggregation were monitored at 37 degrees C and pH 7.4 by measuring the amount of peptide remaining in solution, using reverse-phase high performance liquid chromatography. Negative stain electron microscopy revealed that all of the peptides formed fibrils. However, beta 13-26Q22 showed greatly accelerated fibril formation compared to the other two. The results suggest that the Q22 mutation confers increased amyloidogenic properties on the beta/A4 peptide, whereas the G21 mutation acts by a different pathogenic mechanism.

Endopeptidase 3.4.24.11 converts N-1-(R,S)carboxy-3-phenylpropyl-Ala-Ala-Phe-p-carboxyanilide into a potent inhibitor of angiotensin-converting enzyme

It was reported recently that N-1-(R,S)carboxy-3-phenylpropyl-Ala-Ala-Phe-p-carboxyanilide (CPP-A-A-F-pAB), an inhibitor of endopeptidase 3.4.24.15 (E-24.15), also inhibits angiotensin-converting enzyme (ACE) from rabbit lung. We have found that this compound is without effect on ACE purified from pig kidney, at a concentration some 1000-fold greater than the Ki reported for inhibition of the enzyme from lung. However, preincubation of CPP-A-A-F-pAB with neutral endopeptidase 3.4.24.11 (E-24.11) does result in potent inhibitory effects on ACE. We have shown this to be due to formation of a fragment, CPP-A-A, the structure of which is closely related to ACE inhibitors such as enalaprilat. CPP-A-A was found to be a potent inhibitor of pig ACE. Under the conditions used it had an IC50 value of 1.6 x 10(-8) M, compared with the value obtained for captopril of 7.5 x 10(-10) M. These results have important implications for studies of E-24.15 when using CPP-A-A-F-pAB in vivo or in crude tissue extracts where E-24.11 might also be present.

Secretory form of Alzheimer amyloid precursor protein 695 in human brain lacks beta/A4 amyloid immunoreactivity

It is not clear how Alzheimer amyloid precursor proteins (APP) are metabolized in the brain itself. Secretory forms of APP in a phosphate buffer-soluble fraction were purified from post-mortem human brain by heparin-affinity and ion-exchange chromatography and analyzed by N-terminal amino acid sequencing and SDS polyacrylamide gel electrophoresis/immunoblotting. We found apparently similar multi-isoforms of secretory APP (at 93-97, 105-112 and 123 KDa) to those that we have described recently in cerebrospinal fluid. Antisera to the initial part of the beta/A4 sequence labelled only those bands that were found to react with antiserum to the Kunitz-type inhibitor insert of APP, suggesting that beta/A4 amyloid may be generated specifically from APP-695.

Quantification of beta A4 protein deposition in the medial temporal lobe: a comparison of Alzheimer's disease and senile dementia of the Lewy body type

The distribution of beta-amyloid protein (beta A4) was examined in the medial temporal lobes from cases of Alzheimer's disease (AD) (n = 13), senile dementia of Lewy body type (SDLT) (n = 12) and age matched controls (n = 9). Using a previously described image analysis technique the extent of beta A4 pathology was determined in ten distinct anatomical sites within the medial temporal lobe. AD and SDLT cases contained very similar amounts of beta A4 in the areas sampled and both contained significantly more beta A4 than the age matched controls, particularly in the dentate and parahippocampal gyri. The similarity of the beta A4 load in the two conditions is in contrast to reported differences in the number of neurofibrillary tangles which can be observed. It is suggested that AD and SDLT represent a spectrum of pathology which centres around the aberrant processing of the beta A4 precursor protein.

Quantitative differences in the deposition of beta A4 protein in the sulci and gyri of frontal and temporal isocortex in Alzheimer's disease

The distribution of beta-amyloid protein (beta A4) in the frontal and temporal isocortex of 14 Alzheimer's disease brains was examined using a combination of immunohistochemistry and computer image analysis. The area of cortex covered by beta A4 deposits was determined and expressed as a percentage of the total cortical grey matter area in each field of interest. Significantly more beta A4 was found in the grey matter of the sulci as compared to that of the gyral crests in both the frontal and the temporal lobes (P less than 0.05). Furthermore, in each case, greater quantities of beta A4 were observed in the frontal rather than the temporal lobes. This apparent differential vulnerability is likely to reflect underlying anatomical connections or perhaps differences in cell packing density and appears to strengthen the case for an anatomical basis for the spread of the disease pathology.

Amyloid deposition as the central event in the aetiology of Alzheimer's disease

While there may be many causes of Alzheimer's disease (AD), the same pathological sequence of events, described here by John Hardy and David Allsop, is likely to occur in all cases. The recent discovery of a pathogenic mutation in the beta-amyloid precursor protein (APP) gene on chromosome 21 suggests that APP Mismetabolism and beta-amyloid deposition are the primary events in the disease process. The occurrence of AD in Down syndrome is consistent with this hypothesis. The pathological cascade for the disease process is most likely to be: beta-amyloid deposition----tau phosphorylation and tangle formation----neuronal death. The development of a biochemical understanding of this pathological cascade will facilitate rational design of drugs to intervene in this process.

Alzheimer amyloid beta/A4 peptide binding sites and a possible 'APP-secretase' activity associated with rat brain cortical membranes

We carried out ligand binding experiments on membranes from rat brain cortical grey matter using radioiodinated beta/A4 8-17, with non-specific binding determined by the addition of 10 microM unlabelled peptide. Specific, reversible binding amounted to 60-75% of total binding and showed a clear dependence on time, temperature, pH and membrane concentration. Kinetic analyses indicated a high-affinity binding site with an apparent KD of 440 pM. However, the ligand was partly degraded with loss of the Ser8, Lys16 and Leu17 residues. Excision of the two C-terminal amino acids was inhibited by EDTA, EGTA, dithiothreitol or Zn2+ but was stimulated by Ca2+ or Mn2+. These studies demonstrate high-affinity binding sites for beta/A4 8-17 (or its derivatives) in rat brain, suggesting that this region may contain a physiologically important amino acid sequence and identify a potential membrane-associated amyloid precursor protein (APP) secretase activity.

Immunohistochemical and immunoelectron microscopical characterization of cerebrovascular and senile plaque amyloid in aged dogs' brains

Immunohistochemical and immunoelectron microscopical studies were carried out on 28 aged dogs' brains. Amyloid deposits were seen in the arteries and capillaries in the leptomeninges and in superficial areas of the cortices in 19 (67.9%) of the 28 dogs (10-22 years of age). Immunohistochemically, these amyloid deposits were reactive for anti-beta/A4 antibody. Additionally, a variable number of parenchymal deposits with diffuse beta/A4-immunoreactivity (diffuse plaques) was also noted throughout the cerebral cortex in 24/28 dogs (85.7%). However, these plaque lesions were undetectable in Congo red staining. Electron microscopically, amyloid fibrils, measuring 10 nm in width, were located mainly in the tunica media of the arteries, and in less involved vessels they tended to be present among collagen fibres in the adventitia and smooth muscle cells in the outer layer of the media. The plaque lesions appeared to contain sparse aggregations of amyloid fibrils. In immunoelectron microscopical examinations, all amyloid fibrils in both blood vessels and plaques were selectively labelled by gold particles. These findings indicate that aged dogs can provide a useful experimental model for research into the beta/A4-type of cerebral amyloidosis commonly seen in Alzheimer's disease.