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Alzheimers disease: what is new in detection and treatmentDr. Doha Rasheedy AliLecturer of Geriatric medicineAin Shams University

backgroundHistopathology of Alzheimer s dementiaNeuronal degenerationIntracellular deposits known as neurofibrillary tangles (NFTs).Extracellular deposits known as senile plaques (SPs).

NFTs structureNeurofibrillary tangle is composed of abnormal fibrils measuring 10 nm in diameter that occur in pairs and are wound in a helical fashion with a regular periodicity of 80 nm.The primary constituent of the neurofibrillary tangle is the microtubule-associated protein tau. The tau within neurofibrillary tangles is abnormally phosphorylated.There are a number of other protein constituents associated with the neurofibrillary tangle, such as ubiquitin, cholinesterases, and beta-amyloid

Distribution of NFTsSevere involvement is seen in: the layer II neurons of the entorhinal cortex, the cornu ammonis 1 and subicular regions of the hippocampus, the amygdala, the deeper layers (layers III, V, and superficial VI) of the neocortex.The extent and distribution of neurofibrillary tangles in cases of Alzheimer's disease correlate with both the degree of dementia and the duration of illness.SPs structureExtracellular polymorphous amyloid deposits found in the brain most prominently in Alzheimer disease but also in normal aging.Their 6- to 10-nm-wide filaments consist of a 39- to 42-amino acid -amyloid protein (-AP) which is derived from proteolysis of transmembrane amyloid precursor protein (APP)A is a normal cellular product and is present in nanomolar concentrations in biological fluids, at higher concentrations, it is extremely insoluble and precipitates to form aggregatesThe most characteristic form of the amyloid plaque, is characterized by a dense core of aggregated fibrillar A, surrounded by dystrophic dendrites and axons, activated microglia, and reactive astrocytes. The diffuse plaques: diffuse deposits of A, likely representing a prefibrillary form of the aggregated peptide, are found without any surrounding dystrophic neurites, astrocytes, or microglia. These diffuse plaques can be found in limbic and association cortices, as well as in the cerebellum.Vascular Amyloid Deposition (Congophilic Angiopathy)Amyloid protein accumulates in the walls of small arteries and arterioles of the leptomeninges and within the gray matter of the cerebral cortex. These accumulations of A within the vessel walls do not appear to clog the vascular lumina or otherwise interfere with the function of these vessels.However, when the degree of vascular involvement is severe, there is a tendency for spontaneous vascular rupture leading to a focal accumulation of blood in the brain tissues. Such hemorrhages are generally not encountered in and around the lenticular nuclei and thalamus, such as is seen as a result of uncontrolled systemic hypertension. These hemorrhages tend to occur in the white matter of the frontal and/or occipital poles, are often small and multiple, and may be microscopic in size. When they are large (this is a relatively rare situation), they may be multiple and are commonly called lobar hemorrhages. Although rare, such lobar hemorrhages represent one of the few fatal intracerebral complications of Alzheimer's disease.Granulovacuolar DegenerationThis is a poorly understood lesion that consists of an intraneuronal cluster of small vacuoles measuring 2 to 4 m in diameter, each containing a small, dense basophilic granule that typically measures approximately 1 m in diameter.Little is known about the nature of these lesions or their significance. They are seen in brain specimens derived from elderly individuals with normal cognitive function.large numbers of such lesions in the boundary zone between the CA1 and CA2 regions of the caudal aspect of the hippocampus correlate well with a diagnosis of Alzheimer's diseaseEosinophilic Rodlike Inclusions (Hirano Bodies)intensely eosinophilic perineuronal lesions encountered within the CA1 region of the hippocampus.Identical inclusions in much smaller numbers are also noted in some, but not all, cases of Alzheimer's disease. Hirano bodies may also occasionally be encountered in the brains of normal aged individuals with intact cognition. Hirano bodies have a very characteristic ultrastructural appearance consisting of parallel fibers that interweave in a very regular crossing pattern reminiscent of the appearance of a tweed fabric.Synaptic LossMasliah and coworkers have shown a 45% loss of the extent of staining of presynaptic boutons in cases of Alzheimer's disease in comparison with normal controls and have argued that this loss of the critical element for neuron-to-neuron communication constitutes the major morphological counterpart to cognitive loss in Alzheimer's disease.PATHOBIOLOGY OF ALZHEIMERS DISEASEAmyloid Precursor Protein Processing and Generation of A(APP) The cleavagesAPP + - APP-CTF the cleavage A 40, A 42

Removal to Extracellular matrix oligomerization and aggregationfibrils and amyloid plaques-secretase, also called BACE1 (beta-site APP cleaving enzyme 1) -secretase, a multimeric protein complex containing presenilin, nicastrin, Aph-1, Pen-2, and CD147.Proteolysis of APP with secretase result in: a large N-terminal fragment of the protein (sAPP) that is released in the extracellular space and a small (12 kDa) membrane-anchored fragment called - APP-CTF (or C99).

The molecular mechanisms underlying the toxicity of AInside the brain, A is capable of forming a high-affinity complex with the neuron-associated 7-nicotinic acetylcholine receptor, leading to its subsequent endocytosis. The resulting increase in neuronal A burden eventually causes cell lysis and ensuing extracellular accumulation of A.In addition to the nicotinic acetylcholine receptors, A binds to a variety of other receptors, including neurotransmitter receptors, toll-like receptors, NOD-like receptors, formyl peptide receptors, scavenger receptors, complement receptors, pentraxins as well as the receptor for advanced glycation products expressed on astrocytes, microglia and neurons. These interactions induce the production of proinflammatory molecules through signaling pathways, most of which involve activation of microglia, and eventually culminate in neuronal deathanother molecular mechanisms of the neurotoxicitythe C-terminal tail of APP can undergo further processing at amino acid 664 of APP695 liberating two small cytosolic fragments, Jcasp (from aa. 649 to 664 of APP695) and C31 (containing the last 31 amino acids of the C-terminus of APP, from aa. 665 to 695). Both these fragments are generated only after cleavage, require caspase-mediated processing of APP, and can activate proapoptotic pathways in a variety of cellular systems

Recent advances in diagnosisBiomarkersResearchers hope to discover an easy and accurate way to detect Alzheimer's before these devastating symptoms begin.

Brain Imaging/ neuroimaging

StructuralFunctionalMolecular A) Structural imagingstudies have shown that the brains of people with Alzheimer's shrink significantly as the disease progresses. Research has also shown that shrinkage in specific brain regions such as the hippocampus may be an early sign of Alzheimer's. However, scientists have not yet agreed upon standardized values for brain volume that would establish the significance of a specific amount of shrinkage for any individual person at a single point in time.

QUANTITATIVE MAGNETIC RESONANCE IMAGING BIOMARKERS

VOLUMETRIC MAGNETIC RESONANCE IMAGING: Medial temporal regions, such as the entorhinal cortex and hippocampus, are typically affected earliest.Later on, atrophy affects lateral temporal as well as medial and lateral parietal association cortex followed by frontal regions and, finally, primary sensorimotor cortices. So, It is not surprising that the hippocampus has been targeted as the structure most likely to provide a reliable volumetric biomarker of neurodegeneration in AD. However, hippocampal atrophy is not specific to AD, nor is all AD associated with severe hippocampal atrophy

Identifying the cut off volumeThe effects of age and intracranial volume, and possibly gender and race, must be accounted for. An individuals prior history of brain trauma, alcoholism, drug abuse, and vascular risk factors such as hypertension and smoking, would also likely influence the measure, so it is unlikely that a distinct cutoff in hippocampal volume could be identified that will reliably predict AD risk across patients.However results showed a volume loss of 20% in the hippocampus already present at a mild stage of AD dementia.(Karow DS et al. 2010)

Volumetric assessment of combined regionsThe combination of regions, naturally, improves classifier sensitivity and specificity beyond that achieved through the use of a single region.However, derivation of regional cortical volume or thickness is more challenging and computationally expensive than derivation of volumes for most subcortical structures, such as the hippocampus and ventricular subregions.Hippocampal and wider medial temporal lobe (MTL) degeneration is often associated with expansion of the temporal horn of the lateral ventricle. Therefore, temporal horn volumetry with comparison to normative values could support that the individuals hippocampus was previously larger and had undergone degeneration, as opposed to having been congenitally small.

2. diffusion tensor imaging (DTI)An assessment of white matter fibers using the imaging technique of DTI has revealed that the fibers connecting the hippocampus and posterior cingulate gyrus are impaired in AD).The most commonly used index is fractional anisotropy (FA) that is determined by the degree of directionality (anisotropy) of the movement of the water molecules. A reduced FA value is reflective of axonal degradation and myelin damage in the brain.However, it remains to be seen whether it can be affected in preclinical stage.B)Functional imaging functional MRI:Types: task-dependent fMRI and task-free, or resting-state, fMRI (rsfMRI). the blood oxygenation dependent (BOLD) signal is used to measure blood flow and blood oxygenation, which is believed to correlate with changes in neuronal activity at a time scale of a few secondsPOSITRON EMISSION TOMOGRAPHY (FLUORODEOXYGLUCOSE IMAGING): measures of brain glucose metabolism and cerebral blood flow are markers of synaptic dysfunction, typically obtained during resting state, but can be task dependent. A characteristic pattern of hypometabolism in the temporoparietal region of the cortex, which is involved in episodic memory function, is present at the AD dementia stagePreclinical imagingFDG-PET hypometabolism in a subset of cognitively normal subjects that carry the ApoE 4 allelle have detected changes in a subset of regions affected in AD and these changes predict progression to MCIFunctional MRI: Hyperactivation within the hippocampus memory network during memory performance occurs early in the MCI phase but reduced hippocampus activation is visible shortly before progressing to dementia, suggesting that such hippocampus hyperactivation is a transient sign impending clinical worsening.Therefore, resting state fMRI may be a more sensitive measure than FDG PET to detect early changes associated with AD pathologyC) Molecular imaging technologiesare among the most active areas of research aimed at finding new approaches to diagnose Alzheimer's in its earliest stages. Molecular strategies may detect biological clues indicating Alzheimer's is under way before the disease changes the brain's structure or function, or takes an irreversible toll on memory, thinking and reasoning. Molecular imaging also may offer a new strategy to monitor disease progression and assess the effectiveness of next-generation, disease-modifying treatments.

Several molecular imaging compounds are approved: a radioactive tracer binds to beta-amyloid in the brain. It can be visualized during a positron emission tomography (PET) brain scan, thereby revealing the presence of amyloid plaques in the brains of living patients.In 2012, the U.S. Food and Drug Administration approved the first molecular imaging tracer for (brand name Amyvid but also known as florbetapir F-18) PiB-PETA second molecular imaging tracer (brand name Vizamyl but also known as flutametamol F18) was approved in 2013. A third molecular imaging tracer (brand name Neuraceq but also known as florbetaben F18) was approved in 2014

amyloid imaging is not recommended for routine use in patients suspected of having Alzheimer's disease.A Task Force of the Society of Nuclear Medicine and Molecular Imaging (SNMMI) and the Alzheimer's Association has published criteria in which they believe the use of amyloid imaging would be appropriate

Appropriate forPatients with persistent or progressive unexplained MCI2. Patients satisfying clinical criteria for possible AD because of unclear clinical presentation, either an atypical clinical course or an etiologically mixed presentation3. Patients with progressive dementia and atypically early age of onset (usually defined as 65 years or less in age)

Not appropriate forPatients with core clinical criteria for probable AD with typical age of onset To determine dementia severityBased solely on a positive family history of dementia or presence of apolipoprotein E ( APOE ) 4 Patients with a cognitive complaint that is unconfirmed on clinical examination Instead of genotyping for suspected autosomal mutation carriers In asymptomatic individuals Nonmedical use (e.g., legal, insurance coverage, or employment screening)

Neuroimaging methods are capable of detecting substantial brain changes not only in subjects with AD dementia, but also in subjects in the mildly symptomatic MCI due to AD and even in cognitively normal subjects who may be in the preclinical stage of ADCSF markersAmyloid Beta 42 levels are decreased in cerebrospinal fluid of Alzheimers disease patient (Frosch et al., 2010). However, A-40 is unchanged. In order to find a biomarker which is more specific, Ab42/AB40 ratio was calculated and found to be useful in early and clinical phases of Alzheimers diseaseCSF-Tau:Increased CSF-tau is present during the whole course of the disease in Alzheimers disease which suggests that it may be present before the onset of clinical dementia.elevations of t-tau (total tau) and p-tau (phosphorylated tau) 181, are sensitive indicators of presymptomatic disease39Combined CSF tau, A-42 CSF ratio of phospho-tau to A-42 is more useful and can be recommended as an aid for evaluating individuals suspected of dementia due to Alzheimers diseasePre clinical stageIn MCI: Abnormal levels for A-42 (356 pg mL-1) were accompanied by increased risks for progression to Alzheimers diseaseApproximately 90 percent of patients with mild cognitive impairment and pathologic cerebrospinal fluid biomarkers will develop Alzheimers disease within 9.2 years. Therefore, these markers can identify individuals at high risk for future Alzheimers disease least five to ten years before conversion to dementia.Plasma markersA42 levels, A40 levels , A42 /40

about 26 investigations have been performed to evaluate both A40 and A42 as useful diagnostic markers. However, the results of these studies were contradictory because some report an association between a decline in plasma A40 and A42 levels as well as in the A42/A40 ratio with development of AD, while other studies found no correlation between plasma A and AD.factors associated with A plasma levels are age, creatinine levels, high density lipoproteins, body mass index, race and sex. Like CSF levels, plasma levels show a circadian fluctuation. Therefore, standardization of sampling time is important.further clinical research and assay development are needed before measures of plasma A can be interpreted as biomarkers for AD.PLASMA TAU FORMSusing classic systems tau is virtually undetectable in MCI and/or AD.Recently, an ultra-sensitive immunoassay for quantification of tau protein in serum samples was published and is based on antibodies reacting with all tau isoforms, both normal and phosphorylated tau.Preliminary data also show increased serum tau levels in AD patients, with about twice as high levels as in cognitively normal elderly. These data suggest that serum tau may have a potential as a screening tool for the identification of ADPLASMA PROTEOMICS18-plasma protein profile, consisting of endocrine and hormone-like proteins, which identified AD patients from controls with a high specificity. But clinically significant protein markers of AD did not replicate across cohorts.NT-proBNP, CRP, pancreatic polypeptide, fatty acid binding protein, etc.plasma Beta-site APP Cleaving Enzyme (BACE-1), and soluble forms of Amyloid Precursor Protein were found to significantly elevated in plasma from AD patients, which may offer diagnostic value in AD.cystatin C, A1AcidG, ICAM1, CC4, pigment epithelium-derived factor [PEDF], A1AT, RANTES, ApoC3) were strongly associated with disease severity and disease progressionThese markers were characterized by a good diagnostic value in correctly classifying AD patients and HCs that may in addition entail a value in progression from MCI to AD.complement factor H [CFH] and alpha-2-macroglobulin [A2M]) serum amyloid P (SAP), complement C4 (CC4), and ceruloplasmin, all of which have been implicated in AD pathogenesis.Clusterin, also known as apolipoprotein J, is a heterodimeric glycoprotein expressed in the majority of mammalian tissues is associated with hippocampal atrophy and clinical progression.Transthyretin (TTR) and apolipoprotein A1 (ApoA1) to be associated with faster declining AD subjects

Neuronal and glial derived proteins (such as S100B have also been studied in this regard. Glial derived protein S100B (S100 calcium binding protein B) is responsible for, proliferation of melanoma cells, neurite extension stimulation of Ca2+fluxes, astrocytosis and axonal proliferation, inhibition of PKC-mediated phosphorylation and inhibition of microtubule assembly. In a developing brain it functions as a neurotrophic factor and neuronal survival protein. Hence, serum levels of S100B are studied as a marker for brain functional condition reflect morphological status in AD. serum levels of S100B are significantly reduced with a positive correlation between S100B levels and AD severity.48Individual blood biomarkers have been unsuccessful in defining the disease pathology, progression and thus diagnosis. This directs to the need for discovering a multiplex panel of blood biomarkers as a promising approach with high sensitivity and specificity for early diagnosisBiomarkers associated with vascular risk, metabolic and inflammation statesTotal cholesterol:Evidence from cell culture and animal studies demonstrate that the production, aggregation, deposition and recycling of cerebral A as well as its neurotoxicity may be modulated by cholesterol.However, we still do not have a complete understanding of how cholesterol levels can influence AD pathogenesis, and despite early evidence from observational studies that cholesterol lowering by statins might reduce the risk of dementia.

OxysterolsThe brain eliminates excess cholesterol by excreting two oxidized oxysterols into the circulation: 24Shydroxycholesterol and 27-hydroxycholesterolLevels of 24S-hydroxycholesterol appear to reflect brain production (and number of neurons) as well as hepatic elimination. Although evidence suggests that oxysterols play a role in AD pathogenesis by interacting with A and regulating astrocytic production of APOE, the precise mechanisms are not clear. data on the association of circulating oxysterols with incident dementia are scarce.Homocysteine, vitamins B12 and folate, and related metabolites:Plasma homocysteine and methylmalonic acid, and more recently holotranscobalamin, have been shown to be better indicators of vitamin B12 status and associated with risk of incident dementia and AD.Considerable evidence suggests that an elevation of total plasma homocysteine (tHcy) is associated with a subsequent higher risk of AD. The mechanisms underlying this association remain uncertain and it is not clear whether tHcy is an AD risk factor or merely a risk marker.

Possible mechanisms: Homocysteine promotes calcium influx and generation of toxic free oxygen radicals, thus accelerating DNA damage within hippocampal neuronsA metabolite of homocysteine, homocysteic acid, activates excitotoxic glutamatergic N-methyl-D-aspartate receptors Elevated tHcy levels promote the homocysteinylation of proteins, thus altering protein functioninhibit Na+/K+-ATPase activityHomocysteine increases presenilin-mediated A generation and potentiates the neurotoxicity of insoluble A depositspromotes tau hyperphosphorylationHomocysteine could increase dementia risk via its vasculotoxic effects on large arteriesInsulin and amylinDiabetes is associated with a higher risk of dementia, possibly due to dysfunction in insulin signaling pathways in the brain since peripheral and perhaps central insulin resistance is a defining characteristic of type 2 diabetes.The mechanisms underlying the insulindementia association are not clear, and may include decreased clearance of A by the insulin-degrading enzyme (which preferentially binds insulin but has a physiological role in A clearance), increased tau hyperphosphorylation, or an indirect effect such as potentiating vascular injury or the adverse effects of inflammation.Amylin, or islet amyloid polypeptide, an amyloidogenic peptide hormone produced by the pancreas along with insulin, was recently shown to be present in the brains of persons with AD but a prospective association of circulating amylin levels and risk of AD has not been demonstrated.

platelet membrane proteome as a source of peripheral biomarkersfor Alzheimers diseaseplatelets share many similarities with synaptic terminals in neurons and have been used as a model for studying synaptic vesicle metabolism.both platelets and neurons secrete and respond to neurotransmitters and share many of the same secretory pathways and transporters for neurotransmitter uptake and packaging.Platelets also contain a high concentration of amyloid precursor protein (APP) and possess , , and secretases.Increased levels of activated platelets have been reported in patients with early AD compared to healthy, age-matched controls, and the platelet activation state has been positively correlated with the rate of cognitive decline measured by the mini mental status exam (MMSE). However, some studies [JAREMO et al., 2012] reported a decrease in platelet activity in AD. studies have reported that patients with amnestic mild cognitive impairment (MCI) with elevated levels of activated platelets were at an increased risk of progression to AD within 3 yearWhole platelet proteome and subproteomes have been profiled using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)144 proteins were determined significantly altered in the platelet membrane proteome in patients with probable AD.In particular, proteins encompassing the -secretory granule pathway including , , and -chains of fibrinogen, thrombospondin-1 (THBS1), von Willebrand factor and fibronectin were dramatically reduced in AD.Lymphoblast Calmodulin in lymphoblastThere is a functional relationship between Ca2+/calmodulin (CaM) and the main signaling pathways controlling cell survival or death depending upon growth factor availability. current evidence relates the process of neuronal apoptosis occurring in AD to the aberrant re-entry of differentiated neurons into the cell cycleResearches detected significantly increased levels of CaM in AD lymphoblasts.CaM level was higher in AD > MCI> controls. Thus it is considered a useful biomarker to help in early diagnosis of AD, enabling one to discriminate AD from other dementias with high levels of sensitivity and specificity.

Buccal cells associated alzheimer markersBuccal micronucleus cytome biomarkersFrequencies of basal cells (P < 0.0001), condensed chromatin cells (P < 0.0001) and karyorrhectic cells (P < 0.0001) were found to be significantly lower in Alzheimers patients. These changes may reflect alterations in the cellular kinetics or structural profile of the buccal mucosa, and may be useful as potential biomarkers in identifying individuals with a high risk of developing AD

Altered Cytological Parameters in Buccal Cells(Francois et al.,2014)An automated buccal cell assay was developed using laser scanning cytometry (LSC) to measure buccal cell type ratios, nuclear DNA content and shape, and neutral lipid content of buccal cells.DNA content was significantly higher in all cell types in both MCI (P