Alzheimer’s Disease: An Overview

Sneha Pandey, Vipin Kumar, Shabnam Ain*, Qurratul Ain, Babita Kumar, Nidhi Ruhela, Bhuvnesh

Sanskar College of Pharmacy and Research, Ghaziabad, Uttar Pradesh 201302, India

*Correspondence: shabnam.ain@sanskar.org; Tel.: +919310807567

DOI: https://doi.org/10.71431/IJRPAS.2025.4202

INTRODUCTION

Dementia is a neurodegenerative disease which results in the development of Alzheimer’s (It is an aggressive form of dementia. [51, 53] [47] This degeneration causes decrease cognitive abilities [48, 45], language, behaviour deficits and reduced ability to carry out daily task.[2] 44 million individuals currently live with AD, 6.2 millions are Americans and it kills more people combined breast and prostate cancer. According to the National Institute on Ageing, the rate of AD expands every five [1] years after the age of 65 [57], and as people age, so does the percentage of those affected.[1] AD will cost the US [53] over $355 billion in 2021, increasing to more than $1.5 trillion by 2050.[1]

AD has multiple aetiologies, but exact cause is not yet known. [3] According to the several hypothesis the cause of AD is the deposition of Amyloid plaques outside the neuron cell. This plaque is formed due to formation of insoluble Amyloid Precursor Protein (APP). [46, 50] A protein that present at the axon ending having some part inside the neuron and some outside. In the normal physiological conditions alpha secretase enzyme cleave the APP and result in the formation of soluble AA, responsible for the growth of neurons, in pathological condition mutation in APP occurs, particularly on chromosome number 21 region 21q11. Because of mutant APP gene it becomes more sensitive towards gamma and beta secretase enzyme and on cleavage it results in the formation of insoluble APP. [45] Increased ratio of Amyloid beta40/42 results in formation of Amyloid plaques which is the cause of cognitive disability.[57] Mutation in presenilin 1and 2 at chromosome number 14 and 1 respectively increase the ratio of Amyloid beta42/40. Another hypnosis is deposition of Neurofibirlin tangles inside the neuron. [45] These tangles formed due to Phosphorylation of the tau protein which is responsible for arrangement of microtubules in axon, Phosphorylation causes breakdown of tau into paired helical fragments that form tangles inside the neuron and causes cell death.

AD mainly occur at the age of 65 [57] or above, common in women as estrogen level decreases after menopause, estrogen binding receptors are present in brain responsible for cognitive abilities. So, decreased estrogen level will increase the chance of AD in old age. Oxidative stress, excytotoxicity, environmental factors and decreased Ach level is responsible for the disease.

Number of therapeutic measure had been taken from past decades but treatment options currently available only work to produce symptomatic relief [3], no therapies and medication present that cure AD. Because of this, attention turned towards prevention and reducing the risk of AD. [3] For the treatment of AD number of pharmacological and non- pharmacological strategies used. Currently available medication like meantime [50], Donepezil, Alantamine, Rivastigmine and Tacrine treat symptoms only.

For the treatment and maintenance of the disease, the early diagnosis is required. CSF, PET, Brain imagining, blood test etc. are available methods that helps in diagnosis. In blood plasma measurement and CSF detection, ratio of Amyloid beta 42/40 measured. In PET and Brain imagining, Amyloid plaque and NFTs are detected. These methods have disadvantages, invasiveness and high coast. Blood plasma measurement isn’t invasive but one can only identify the most vulnerable population, clinical symptoms can’t be identified. Although these methods are very helpful in management of the disease but unable to identify Alzheimer’s at early stages.

This review mainly focuses on currently available methods for the treatment and management. Future  theories  for inventing new  therapies, such  as DMT, Stem cell therapy,  mAbs [50],Gene therapy, diagnosis and etiology of the AD.

EEPIDEMIOLOGY

2023 estimate shows that approximately 55 million people suffering with the AD worldwide [4] and more than 6 million people of all the age group have Alzheimer in American alone. [5,6] 60 percent of them constitute families with low to incomes. Every year, nearly 10 million new cases. [4] About 1 in 9 people age 65 and older (10.7%) has Alzheimer’s. Two-third of American women’s are with Alzheimer’s.

According to 2020 senses, the number of AD patients (≥ 65 years) might increase greatly from 5.8 million to 13.8 million by 2050 in America [7] Particularly, age-specific global prevalence in women was 1.17 times larger than men and the age-standardized mortality rate of women also higher. Suggesting, women’s are more Vanruable. Along with the women [8] Estimates indicate that 50% or more individuals with Down syndrome construct dementia with age. The added copy of chromosome 21 contains a gene called APP, which creates a protein associated with the development of plaques in the brain. [8,9]

AD was officially listed as the 6^th prevalent reason of death in the US. As per official death certificates, 121,499 deaths from AD in 2019 recorded. In 2020 and 2021, Alzheimer’s ranked seventh among all causes of death and fifth among Americans 65 and older when COVID-19 entered the top ten reason for death . [10]

An national Institute on Aging calculated that the predominance of AD doubles like clockwork past the age of 65 and as the populace ages, a more noteworthy extent of the populace is impacted. AD will cost the US more than $355 billion out of 2021, ascending to more than $1.5 trillion by 2050 overwhelming a huge financial weight. [25]

According to the 2023 senses of Alzheimer’s association there are about more than 6 million Americans presently ordeal from Alzheimer’s disease [53], this number expected to develop as the populace beyond 65 years old keeps on developing. As indicated by the Alzheimer’s Affiliation the infection is something beyond cognitive decline, it’s lethal. On normal an individual matured 65 or more seasoned endures four to eight years after an underlying determination of the illness. As Alzheimer’s sickness builds the requirement for labourers associated with diagnosing, treating and really focusing on those with the infection additionally increments. The requirement for direct consideration labourers is supposed to develop by over 40% by 2026.

PATHOPHYSIOLOGY

Hundreds of research are going on AD from number of years but still Alzheimer does not have full clarification about their pathogenesis and lacks treatment or therapy that induces natural healing [11, 46]  It is considered that the disease is a result of the interrelation of genetic and neurobiological processes. [12] Neuronal misfortune might be seen especially in the hippocampus, amygdala, entorhinal cortex and the cortical affiliation region of the front facing, worldly and parietal cortices, yet additionally with subcortical cores, such as the cholinergic basal core, noradrenergic locus coeruleus, and serotonergic dorsal raphe. The statement of tangles [46] follows a characterized design, beginning from the trans-entorhinal cortex; thusly the entorhinal cortex, the CA1 district of the hippocampus and afterward the cortical affiliation regions, where front facing, parietal and worldly curves are especially impacted [13] The degree and position of tangle arrangement [46] connects well with the seriousness of illness considerably more so than quantities of amyloid plaques. [13]

Aβ precursor protein

APP was the first gene having autosomal dominant mutations causing AD, as the precursor of the aggregated peptide in amyloid plaques. [14] The diffusion of Aβ42 – amyloid plaques in the brain is considered the basic pathology.  Aβ42 and Aβ40 taken from APP by the sequential action of β-secretase and γ-secretase Aβ42 and Aβ40 [16, 46] is insoluble, toxic and prone to form aggregates. [16]

In AD the genetic abnormalities occur in APP on chromosome number 21 particularly in the region 21q11, and as a result of this APP becomes more sensitive towards γ and β-secretase. These enzymes break down APP into amino acid fragments, which result in the final forms Aβ40 and Aβ42, which are amino acids 43, 45, 46, 48, 49, as well as 51. [17] As a results of this, excessive Aβ peptides are generated which diffuses into soluble oligomers and they group together to form insoluble fibril called plaques, deposited extracellularlly. [16]

These plaques generate inflammatory response that activate microglia and astrocytes, they produce chemicals such as cytokines and free radicals [16], which  causes  oxidative  damage  and  initiates  inflammatory processes leading on to neuronal death [15]

Neurofibirlin tangles (NFTs)

NFTs are aberrant fibres of hyperphosphorylated tau protein. [17, 46]  At some points, these strands may wrap around one another to form paired helical filaments (PHF), which build up in the nuclear envelope of neuralperikaryal cells, axons [17], and dendrites. [47] This results in the loss of tubulin-associated proteins and cytoskeletal micro tubules. [17] This NFTs are formed due Amyloid deposit. [17,46] Tau protein is responsible for the arrangement of microtubules in neural axon, which is responsible for information transmission.

The primary component of NFTs In the brains of AD patients is the hyperphosphorylated tau protein, and the growth of this protein can reveal the structural phase of NFTs, which consist of:

(1)     Pre-tangle stages: a form of NFT in which the somatodendritic section accumulates phosphorylated tau proteins [17, 47] lacking PHF formation

(2)      The nucleus is displaced to the margins of the soma in grow NFTs, which are distinguished by a buildup of tau protein filaments.

(3)     The stage of extracellular tangles, also known as ghost NFTs, which is brought on by a loss of neurons [47,17] as a result of high filamentous tau protein levels that partially resist proteolysis. [17]

Inflammatory mechanism and mitochondrial dysfunction

AD is closely associated with the inflammation processes. In regard, number of studies have shown that Tau protein hyper phosphorylation responsible for acute and chronic inflammatory processes [11,46] These inflammatory processes are generated or induced by [11] microglial [46] clusters around the condensed regions of Aβ plaques, by high levels of pro-inflammatory cytokines and by microglial activation that lead to the generation of NFTs. [11]

 With regard to mitochondrial dysfunction, it is hypothesized that the Aβ plaques and phosphorylated Tau protein affect mitochondrial function in brain cells, specifically causes impairment of mitochondrial oxidative metabolism. Studies related to the presence of Aβ peptides enabled to conclude, with more specificity, that these peptides can be directly toxic to neuronal mitochondria. [11]

Metal ion hypothesis

Metal dyshomeostasis is engaged with the turn of events and pathology of illnesses, including neurodegerative sicknesses and malignant growth. Ionosphere and metal chelators are notable modulators of progress metal homeostasis, and some of these particles are utilized in clinical preliminaries. Metal-restricting mixtures are by all accounts not the only fit for focusing on change metal homeostasis. Current proof shows changes in the balance of redox progress metals; chiefly copper (Cu), iron (Fe) and other follow metals. Their levels in the mind are viewed as high in Promotion. In other neurodegenerative issues, Cu, manganese, aluminum and zinc are involved. [13]

Cholinergic hypothesis

Recent empirical evidence suggests that an early pathogenic event associated with mental impairment in Alzheimer’s patients is a deficiency of cholinergic innervation in the cerebral cortex. This proof prompted the plan of the “Cholinergic Speculation of Promotion” and the improvement of cholinesterase inhibitor treatments. Cholinergic neurons are distributed widely in the brain and play important role in cognition by binding with the Ach receptors. It is in charge of a person’s memory and capacity for learning. [18] The enzyme acetylcholinesterase breaks down Ach, which is found in the synaptic cleft, into acetate and choline, which are then recycled by the high-affinity choline transporter in the presynaptic nerve terminal. Due to the loss of Ach by this enzyme the level of Ach decreases at the binding site and this results in decreased cognitive abilities. [19]

Oxidative stress

Brain is an organ that has high oxygen demand as it perform activities that need more energy supply [21] This energy demand is fulfilled by mitochondrial oxidative phosphorylation. This process can generate very reactive oxygen species results in increased oxidative stress. [22] For this situation, the defensive instruments are compromised, the responsive oxygen species start to gather and the neurons become vulnerable to the excitotoxic sore. Nonetheless, this instrument relies upon Aβ sections which, when amassed, advance the decrease of iron and cerebrum copper, which are key elements to set off oxidative pressure which, under these circumstances, advances DNA harm. Cholinergic Speculation Among the systems connected with the beginning and development of AD. An incredibly concentrated on cholinergic theory, which was the principal hypothesis connected with AD pathogenesis. In general, the mind of AD transporters presents, in addition to the histopathological markers beforehand described, decay, synaptic misfortune and lack in focal. [22]

Genetic basis of Alzheimer’s disease

AD can be acquired as an autosomal predominant issue with almost complete penetrance. The autosomal prevailing type of the sickness is connected to transformations in 3 genes. [51, 23] AAP gene on chromosome 21, particularly in the region 21q21. Presenilin1 (PSEN1) on chromosome 14, in the region14q24. Presenilin 2 (PSEN2) on chromosome 1, in the region1q42. [24]

          Application changes might prompt expanded age and conglomeration of Aβ peptide. PSEN1 and PSEN2 changes lead to accumulation of Aβ by disrupting the handling of gamma-secretase [17] Changes in these 3 qualities represent around 5 % to 10 % of the multitude of cases and about most of beginning stage AD.

        Apolipoprotein E is a controller of lipid digestion [50,51] that has a proclivity for Aβ protein and is one more hereditary marker that builds the gamble of AD. [51] Isoform e4 of APOE quality (situated on chromosome 19) has been related with additional irregular and familial types of AD [50] that present after age 65. The presence of one APOEe4 allele doesn’t necessarily in every case lead to AD, however among people conveying one APOE-e4 allele around half have AD and those having two alleles, 90% foster AD. [23] Each APOE e4 allele likewise brings down the period of sickness beginning. [51] The APOE e4 allele is a major risk factor for AD transmission. Variations in the quality of the SORT1 sortilin receptor, which is fundamental for moving Application from the Golgi-endoplasmic reticulum complex to the cell surface, have been tracked down in familial and irregular types of AD. [23]

DIAGONOSIS OF ALZHEIMER’S DISEASE

           Diagnosis of AD preliminary will helps in evolving better treatment options and molding strategy to plan for the downpour of cases to come. The assessment of an individual with thought memory debilitation incorporates an exhaustive arrangement of evaluations pointed toward describing the etiology of mental deterioration and recognizing treatable pathologies. These evaluations incorporate a definite clinical background, current state of health, and mental state assessments, fundamental labs, and neuroimaging studies. Extra devices may likewise incorporate neuropsychological testing and high level cerebrum imaging procedures. When reversible causes have been precluded, signs for explicit reasons for major neurocognitive problem are looked for. A background marked by numerous strokes, for instance, may point towards a finding of vascular dementia. A background marked by head injury might propose horrible encephalopathy. A background marked by delayed liquor use confusion might uphold the conclusion of a liquor related dementia. In grown-ups north of 60, the most successive reason for moderate mental deterioration is AD. [26]

Metabolites Available for Alzheimer’s disease

Biomarkers are clinical signs of natural or pathogenic occasions which assume a urgent part in complex disorder diagnostics, progression, as well as looking at the response to treatment [30] and they help in knowing mechanism of action. As per the most recent rules of the National Institute of Ageing and Alzheimer’s Association (NIA-AA), the term AD is applied at whatever point there is biomarker evidence of presence of Aβ plaques and NFT. As of now, the amyloid-Tau-neurodegeneration (AT(N)) grouping characterize “A” biomarkers as amyloid positron emanation tomography (PET), cerebrospinal liquid (CSF) Aβ42 and CSF Aβ42/Aβ40, “T” alludes to Tau PET and CSF p-Tau, and “N” is shown by structural magnetic resonance imaging, fluorodeoxyglucose (FDG), PET, CSF complete t-Tau and neurofilament light chain protein (NFL) [29]

 Fluid (CSF) Biomarkers

Because of its close proximity to the brain’s extracellular space, the CSF may be able to capture biochemical alterations there. These factors make the CSF the best place to find AD biomarkers. [30] While some still view the necessary lumbar puncture as invasive due to the slight risk of bleeding or brainstem herniation, CSF sampling is a comparatively non-invasive technique for evaluating pathologic changes taking place within the CNS. CSF-derived biomarkers in AD have been thoroughly studied because of the CSF’s close interaction with the CNS. [29] CSF biomarkers have a higher predictive F value and a better correlation with 11C-Pittsburgh compound B (PIB) PET imaging data, they may be deemed more appealing than plasma biomarkers. Additionally, they increase the diagnostic certainty, particularly in prodromal phases or atypical presentations. Aβ42, t-Tau, and p-Tau are the three traditional CSF biomarkers used today to diagnose AD. [33] sAPPa, SAPPB, Aβ40, Aβ37, Aβ38, and AϺ42 are examples of A peptides that were the first known molecular biomarkers for AD. [4] Among the group, Aβ42 has a particular correlation with pathological and physiological symptoms; patients with cortical amyloid depositions have lower CSF levels of Aβ42 than health control. Low Aβ40 levels have been associated to AD. It might be able to distinguish AD from various closely related dementia diagnoses with the use of Aβ38 and Aβ37. Next in line for acceptance as CSF biomarkers were t-Tau and p-Tau (Thr 181). These markers are more prevalent in the CSF of AD patients and are associated with memory complaints. Mechanistically, cortical neuronal loss could be correlated with elevated t-Tau, and cortical tangle formation would be reflected by elevated p-Tau. Noteworthy is the fact that p-Tau is specific to AD and aids in differentiating AD from other types of dementia. Additionally, some research indicates that AD patients have somewhat elevated levels of alpha-synuclein. Other recent and intriguing CSF biomarkers include neurogranin and TREM-2. Research has revealed that AD patients have higher levels of the neuron-specific postsynaptic protein neurogranin. This increase appears to be unique to AD as it is not observed in other neurodegenerative diseases. In AD, there is an increase in TREM2, an innate immune receptor that is expressed on the surface of microglia, proteolytically processed, and released as a soluble fragment (STREM2). Furthermore, higher CSF t-Tau and p-Tau have been linked to elevated CSF STREM2 levels (Thr-181) (26). To date, t-Tau, p-Tau, and AϺ42 have demonstrated greater consistency and are valuable CSF biomarkers for clinical practice and research. Their accuracy ranges from 85 to 90 percent. NFL may also be added as a new biomarker, according to some suggestions. More research is required, but neurogranin seems to be a highly stating and concentrated CSF biomarker. [29]

Blood-Based Biomarkers

Research is ongoing to identify blood- based biomarkers, such as specific proteins or genetic markers. The 42-amino acid isoform of Aβ, or Aβ42, observed to be greatly aggregation-prone and to be prevalent in AD plaques that are diffuse and cored after multiple C-terminal forms of the protein were identified. A significant decrease in CSF Aβ42 was observed in AD using ELISAs specific to Aβ42; levels of Aβ42 were found to correlate inversely with cortical plaque load both in post-mortem and biopsy studies. By combining Aβ42 and Aβ40, concordance with amyloid PET is increased and inter-individual variations in amyloid beta processing as well as potential preanalytical confounders are corrected. [31]

Genetic Biomarkers

 Mutations in genes like APP, PSENI, and PSEN2 are associated with familial AD. Changes in these three genes will result in modifications to the synthesis of Aβ causes dementia and neuronal apoptosis. [32]

Inflammatory Biomarkers

Inflammation plays a role in Alzheimer’s; cytokines and markers of inflammation are studied. [33] One of the main characteristics of AD is brain inflammation. According to a recent trend, inflammatory mediators in particular, cytokines and chemokines—may be useful for the early identification of AD. Diverse investigations have documented variations in the blood concentrations of growth factors, chemokines, and cytokines among individuals suffering from AD or moderate cognitive impairment. But the evidence was sometimes contradictory, and it’s still unclear how precisely inflammation contributes to neurodegeneration. The current study, assessed the expression of 120 biomarkers in the blood of 49 patients with the following diagnostic distribution: 15 controls, 14 AD, and 20 MCI. These biomarkers belong to cytokines, chemokines, growth factors, and associated signaling proteins. Identical examination on the CSF of 20 patients, comprising 10 AD and 10 controls. 13 of the biomarkers examined had substantially altered CSF in AD patients, however none of the investigated biomarkers exhibited significant alterations in serum. It’s interesting to note that each of these indicators has been linked to the migration and development of brain stem cells or neurogenesis. Using quantitative multiplex ELISA techniques, 10 of these potential biomarkers (plus 4 more) were assessed in the blood serum and CSF of an expanded cohort made up of 24 control patients and 31 AD patients in the study’s second section. Findings support the diagnostic use of previously identified blood biomarkers and suggest a few more (TNFR-I and IL-8). [41]

Metabolic Markers

Changes in the brain’s metabolism of glucose can be assessed using PET scans. [38] As Amyloid plaques formation start it activate our immune cells that clear the plaques during this process energy requirement of the brain cells increase to fulfil this energy requirement glucose metabolism takes place. [34]

MicroRNA Profiles

Ongoing progress in the non-coding RNA field complement that microRNAs are strong biomarkers in human disease. Facilitating corroboration highlight that spreading miRNAs in the CSF and blood serum have trademark changes in AD patients. In any case, miRNAs can be utilized in AD conclusion, unaccompanied or in mix with other AD biomarkers (e.g., Aβ and tau), is elusive. AD can likewise be analyzed in view of the degree of somewhere around one miRNA in the example among the biomarkers, for example, miR-191, miR-15b, miR-142-3p, Let-7g, Let-7d, miR-301a and miR-545. A unit intended for diagnosing AD, has a specialist that explicitly faculties the presence of something like one miRNA in an example containing coursing miRNAs from the accompanying miR-191, miR-15b, miR-142-3p, Let-7g, Let-7d, or their blends.

           It has been detailed that miRNAs can help as strong biomarkers in human disease. AD patients have been found to have essentially modified circling miRNAs in the CSF and blood serum. Nonetheless, miRNAs alone act as devices in AD diagnosis or they require a mix with other AD biomarkers (e.g., amyloid and tau) is still elusive. Studies have shown that microRNA that objectives a courier of apoptosis (e.g., Bc12, and so on.), synaptosis pathway (e.g., PS1, Onecut2, and so forth.), homeobox pathway (Onecut 2, and so on.), can be utilized as potential biomarker for Promotion. These microRNAs are distinguished by hybridization. The hybridization is accomplished with a help, for example, a strong help, include test bound to a surface, e.g., to catch the microRNA by hybridization to the test. Regular backings for immobilization of the test involve controlled pore glass, glass plates, polystyrene, avidin-covered polystyrene dabs, cellulose, nylon, acrylamide gel and actuated dextran. From there on, microRNAs can be quantitatively estimated utilizing the procedures like Northern smear strategy, continuous PCR, confocal laser – initiated fluorescence location, oligo-exhibit based technologies. [35]

Visualizing modes

To find the signals that are leading to more precise AD detection, various improved imaging techniques are being applied. [27,1] A more thorough use of the quantitative analysis of brain degeneration identification is being made. To generate a more definitive prediction, various neuroimaging-based signals such as CT scan, PET, sMRI, fMRI, and DTI are used. [27]

Computerized Tomography Scan

A cross-sectional image of the brain region is created using a computerized tomography (CT) scan [45,3], which uses an x-ray machine that is continuously exposed to radioactive particles. Compared to standard x-rays, these pictures are 100% more translucent. Since more sophisticated techniques are yielding more accurate and exact results, CT scans cannot be used as a standard for the early identification of AD. A few studies aimed to demonstrate its coherence and efficacy in detecting AD in order to cost-effectiveness when compared to alternative methods such as PET or MRI. It is reasonable to say that it has no significant impact on AD early detection. [3]

Magnetic Resonance Image

This imaging method creates high-quality, high-resolution 2D and 3D images of brain structures by combining radio waves and magnetic fields. [28,48] No radioactive tracers or harmful X-ray radiation is produced. [28] Structural MRI, which measures brain volumes in vivo to detect brain degeneration (loss of tissue, cells, neurons, etc.), is the most frequently used MRI for cases of AD. [45] A progressive and inevitable aspect of AD is brain degeneration. Alternatively, brain topography can be found and the human primary visual cortex measured using functional magnetic resonance imaging (fMRI), a commonly used technique. fMRI offers important data and information about the activity of the human brain. Brain imaging based on arterial Blood Oxygenation Level Dependent contrasts and spin labelling is one example of fMRI technique that is sensitive to cerebral oxygen consumption rate and cerebral metabolic rate of oxygen consumption. [28]

Positron Emission Tomography (PET)

Radiation signals are used in PET to produce a three-dimensional, colour image of the human body. A radiotracer, which is a radioactive medication attached to a naturally occurring chemical, is injected into the patient. A chemical that is frequently used in AD research is glucose. The organs that utilise that particular molecule as an energy source are reached by the radio tracer. [45] Positron emissions occur during the compound’s metabolism. The energy from these positrons is detected by the PET scan, which converts the input into an image on the output screen. The number of colors and intensities produced as a result of the amount of positron energy released correspond to the level of brain activity. A PET scan is able to identify alterations in the brain’s blood flow, metabolism, cellular communication, and other internal processes. A study that was published in the Journal of Clinical Psychiatry in 1996 explained how a PET scan can be used to identify alterations in a patient’s brain’s glucose metabolism. An abnormally low glucose metabolic rate is observed in the parietal, temporal, and posterior cortices. Individuals with advanced disease stages and more affected brain regions experienced a further decline in the rate. Long before symptoms manifest clinically, alterations in glucose metabolism could be identified with a PET scan. A PET scan also use to assess how well AD treatments are working. [45,3]

CSF and Blood Tests

The brain is surrounded by CSF, which is accessible via lumbar puncture. [1,26] Variations in the CSF levels of the proteins tau and Aβ decades before the onset of clinically relevant AD develop. CSF tests developed in recent decades, the most well-known ones are the phosphorylated tau at threonine 181 in the CSF (P-tau181) and the CSF Aβ 42: Aβ 40 ratio. It is hoped that CSF P-tau217, which is detectable in peripheral circulation, will offer a biomarker with extremely high sensitivity and specificity. AD, was created by C2N Diagnostics in St. Louis, Missouri, because blood is more accessible than CSF. The test looks for certain species of Aβ in serum that are less common in AD using mass spectrometry. The test is currently not covered by insurance, making it a substantial expense that qualified individuals may be able to offset with the help of a financial assistance programme. A probability score is the test’s outcome, and they should be interpreted in conjunction with other testing methods; it is not meant to be used as a stand-alone diagnostic tool. Studies on P-tau181 and the plasma AϺ<Aβ42: Aβ40 ratio point to possible value. [1, 26]

Diffusion Tensor Imaging (DTI)

 DTI is a sophisticated neuroimaging modality that produces magnetic resonance images corresponding to modifications in microscopic axons organization by utilizing the diffusion properties of water molecules. [1,26] This methodology can be applied to assess the topology of vertical cellular microcircuits, also known as “minicolumns.” Minicolumns are known to change during ageing, MCI, and AD in a little bit predictably and progressively, as previous research has shown. Additionally, a Cognitive decline and increased plaque load are related to pathologic alterations in the cortex columnar architecture. It is possible to measure DTI and use it as a neurodegenerative marker with the help of proprietary software. [1, 26]

TREATMENT AND MANAGEMENT OF ALZHEIMER’S DISEASE

A few FDA-approved treatments exist for AD [36], slowing down the disease’s progression despite the fact that it is a public health concern. Antagonist to N-methyl D-aspartate. [40, 56] Cholinesterase inhibitors [40, 36, 45, 56] and antibodies against amyloid plaques are among them. Prompt medical intervention can enhance patients’ quality of life.

Cholinesterase Enzymes Inhibitor

AD causes the death of Ach-producing cells, which lessens the brain’s cholinergic transmission. [37] The messenger function of acetylcholine is carried out by nerve cells. [40] Currently, donepezil, rivastigmine, and galantamine/tacrine are the three Cls that are used as the first-line therapy for harmless to moderately severe AD. [39,45] The action of The three types of inhibitors of Ace are irreversible, pseudo-reversible, and reversible is to increase the amount of Ach in the synaptic cleft by preventing the breakdown of Ach by cholinesterase enzymes (AChE and butyrylcholinesterase). [38] Ach and butyrylcholinesterase are both inhibited by galantamine [38 45] while donepezil and rivastigmine are selective inhibitors. [38,45,58]  ADL and behaviour did not improve, according to a meta-analysis involving 13 randomized, double-blind trials intended to assess the effectiveness and security of Cls. Additionally, there was no discernible difference between the effects of rivastigmine and donepezil on behaviour, ADLs, or cognitive abilities. Overall, all three medications showed comparable advantages. Although Cls have demonstrated impact for a considerable amount of time, it is known that they cannot stop the progression of the disease. A randomly assigned, double-blind study found that those on donepezil for a long time weren’t experiencing any positive effects for a maximum of two years. Increasing the dosages of Cls administered might have some additional advantages. In a 48-week, randomized, double-blind, parallel-group study, patients treated with higher doses of rivastigmine showed improvements in the AD Assessment Scale-cognitive subscale and significantly less decline in activities of daily living. Cls side effects are rare and typically restricted to gastrointestinal complaints like nausea, vomiting, and diarrhoea. Guidelines for the use of these medications have been released by the National Institute for Health and Care Excellence (NICE). [40, 45]

NMDA Receptor Blockers

Increased calcium ion inflow brought on by overactivation of NMD receptors encourages cell death and brain dysfunction. [38] Memantine is an NMDA antagonist that is non-competitive. [45,59] In addition to being an agonist of the AMPA receptor, it blocks the calcium channels of this particular receptor, preventing calcium from entering neurons and the toxicity it causes. Studies using double blinds have shown improvements in behaviour and cognition. In the US, phase III studies are currently underway. Vomits, restlessness, vertigo, fatigue, and dizziness are some of the adverse effects. There is a 15–20 mg dose every day. [39]

Antidepressants and Antipsychotic

A common occurrence in AD, BPSD significantly increases the burden on carers. To some extent, memantine and Cls help to control these symptoms, but as patients’ conditions worsen, these medications are unable to keep the symptoms under control. Depression is widespread, particularly in the early and late stages of the illness. To combat this, antidepressants such as tricyclic agents, combined serotonergic and noradrenergic inhibitors, and selective serotonin reuptake inhibitors  (citalopram, fluoxetine, paroxetine, sertraline, trazodone) used. In a double blinded, randomised, parallel-group placebo controlled trial, patients with depression who stopped taking antidepressants experienced significantly higher levels of depression compared to those who continued treatment. These findings demonstrate the positive effects of antidepressants. Olanzapine, quetiapine, and risperidone are common antipsychotics used in AD treatment for agitation and psychosis. The use of these medications seems to be debatable because, when compared to patients given a placebo, patients receiving antipsychotic medication showed appreciable declines in cognitive function. [40]

Non Steroid Anti-inflammatory Drugs

In patients, AD incidence is comparatively low. Administered anti-inflammatory medications in the same manner as the cognitive impairment. [35, 62] Studies indicate that long-term NSAID use offer protection against AD, particularly for patients who have one or more apolipoprotein E epsilon 4 alleles. The similar nature of the biological defense is unknown; however it might entail COX activity inhibition. Suppression of beta secretase activity, inhibition of beta amyloid (1-42) (Aβ42) synthesis, activation of PPAR-Gamma, or stimulation of neutrophin synthesis. Regrettably, long-term placebo control trials involving non-selective and COX-2 selective NSAIDs in patients with AD unfortunately yield negative outcomes. Negative results were also found in a primary prevention study using Naproxen and Celecoxib in elderly subjects with a family history of AD in addition to in a second prevention study using Rofecoxib in individuals with modest cognitive decline. Chronic NSAID use is thought to only have positive effects in the normal brain if it prevents the production of Aβ42. Since they inhibit the activity of activated microglia in the AD brain, which mediate Aβ clearance and trigger compensatory hippocampal neurogenesis, NSAIDs become ineffective and even harmful once the Aβ deposition process has begins. [39, 61]

Monoclonal Antibodies

Monoclonal antibodies, which are chosen for their long-lasting effects, potency, specificity, and ease of administration [56], are used to treat AD. [58] These antibodies target molecules like tau or amyloid beta that are vital to the beginnings and course of the illness. They may be injected, which makes them more convenient to use for those who have difficulty taking other medications. The safety and effectiveness of mAbs have also been proven in clinical trials; aducanumab [49], for instance, has an FDA license to treat early-stage AD.

      To treat AD, several mAb subtypes are being investigated:

1.      Anti-Aβ mAbs: These mAbs specifically target Aβ plaques by either preventing the formation of Aβ plaques or making it easier to remove them. [58]

2.      Anti-tau mAbs: These mAbs aim to disassemble any pre-existing tau tangles and prevent tau from aggregating.

3.      Using mAbs were with double aimed mAbs may have a synergistic effect on the removal of both types of degenerative lesions because these mAbs bind to tau and Aβ simultaneously.

Aducanumab

Aducanumab’s biological effect on Aβ [58] in a phase II study, removal using PET and an amyloid tracer was investigated. [44] Subsequent phase III research commenced, but they were discontinued in March 2019 because the interim analysis was unsuccessful. [43] Biogen stated on October 22, 2019 that EMERGE had achieved its primary endpoint for the high dose, but not the low dose, and that interim periods analysis of futility was flawed. [44] This was based on a more thorough examination of a bigger body of data. Adecanumab was therefore approved by FDI in 2021 to treat mild MCI. [43,56,57,58] According to phase 3 trials [44], the medication successfully reduces amyloid [59] PET signals in many early-onset AD patients to a level that is under control. Aducanumab can also cause radiographic abnormalities with edema or hemorrhage, which are referred to as AD-related imaging abnormalities (ARIA-E and ARIA-H), just like other mAbs can. As a result, the most recent Aducanumab use guidelines stress the significance of identifying prior medical conditions that may increase the patient’s risk of developing ARIA complications or predispose them to ARIA. Open-label multicenter extension studies using Aducanumab are being conducted post-approval to assess long-term safety and tolerability; the study concluded in October 2023 [43].

Donanemab

A humanized mAb derived from mouse mE8-IgG2a is called donanemab (N3pG). This mAb is specific for the N-terminally modified Aβ proteins present in amyloid plaques and facilitates the phagocytosis of plaque by microglia. [44] Donanemab is not intended to stop deposition; rather, it is intended to target deposited plaques. [58] There are currently three trials (NCT04437511, NCT05026866, and NCT05508789) testing donanemab. [58] Phase III, double-blind, placebo-controlled TRAILBLAZER-ALZ2 (NCT04437511) study aims to assess the safety and effectiveness of donanemab in individuals 60-85 years of age with early symptomatic AD in the presence of validated AD biomarkers [43,44].

Lecanemab

Lecanemab (BAN2401, NCT03887455) [43] is a humanized monoclonal antibody that exhibits preference for soluble aggregated Aβ. [44,51,58] Its efficacy is being evaluated on individuals with early-stage AD [43], and it is active against oligomers, protofibrils, and insoluble fibrils. [51] lecanemab work by neutralization and Removal of potentially toxic amyloid-beta aggregates found in the brain in AD. [59] Eisai/Biogen applied for and was granted a marketing [43] license by the FDA [56] in January 2023.[57] The company’s phase 2b data, which demonstrates a sharp decline in plaques, provided approval. The study’s conclusion demonstrated that more extensive testing is still required to ascertain lecanemab’s safety and effectiveness in early AD. [43]

Non -Pharmacological Treatment

Cognitive stimulation therapy, physical exercise [52], and carer support programmes are examples of non-pharmacological AD treatment options. [56] Music therapy [44,55], art therapy, and aromatherapy are three non-drug therapies that have some hope for enhancing life quality and symptoms. In addition to medication and non-pharmacological approaches [55], research on potential disease-modifying treatments is being conducted.

          Living with Alzheimer’s symptoms can be made easier in a variety of simple ways they include:

1.      Using a calendar, diary, or calendar clock to remind a person of important dates, appointments, and events.

2.      Labelling cabinets to show what’s inside.

3.      Setting reminders for chores or appointments on a tablet or smartphone.

Assistant

1.      Using rhymes and mental pictures to help recall new information.

2.      Utilising technology, such as voice-activated virtual assistants.

Diets Mediterranean diet: A nutrient-dense diet high in veggies, fruit, grain products, and healthy fats is the Mediterranean diet. It has been shown to improve cognitive function and mood. [44]

           The ancient Mediterranean meals of Greece, Italy, and Spain provide the basis of the Mediterranean diet [54, 62] which is a diet based on plants. It contains a lot of fruits and vegetables, whole grains, legumes, nuts, and seeds, as well as some fish, poultry, and low-fat dairy products. Red meat and processed meats are consumed in moderation. The diet has been shown to reduce the risk of heart disease, stroke, type 2 diabetes, and certain types of cancer, as well as to improve cognitive function and protect against AD. [52]

           Fruits and vegetables, whole grains, legumes, nuts, seeds, fish, poultry, and low-fat dairy products are all important.

MIND diet: The MIND diet is a hybrid of the Mediterranean and DASH diets. [54]  It is specifically intended to improve brain health. Fruits, vegetables, whole grains, and healthy fats are abundant in the MIND diet. It also has low levels of saturated and trans fats, as well as red meat and processed foods.

DISCUSSION

Alzheimer’s disease (AD) remains a significant challenge in healthcare, with its etiological pathologies of neurofibrillary tangles (p-tau) and senile plaques (Aβ) being primary targets for research into potential treatments. Various strategies have been devised to tackle these pathologies, including targeting Aβ plaques with monoclonal antibodies and inhibiting enzymes involved in Aβ peptide production. However, the effectiveness of these treatments remains a subject of debate, especially concerning the optimal timing of intervention.

One of the central debates in AD research revolves around the timing of treatment initiation. There is uncertainty regarding whether early intervention in the preclinical period or treatment in later stages of the disease is more effective in delaying or stopping neurological deterioration. Early identification of individuals at risk for AD is crucial, as evidenced by ongoing clinical trials targeting asymptomatic individuals with genetic predispositions or biomarkers indicating a higher risk of developing AD. These trials highlight the potential benefits of early therapeutic interventions in mitigating the progression of the disease.

However, conducting clinical trials for AD treatments poses significant challenges. Recruitment issues, difficulties in predicting success based on existing research, and high overall costs are some of the obstacles faced in these endeavors. Collaboration between researchers, corporate and governmental financing, and targeted screening of at-risk groups are essential for overcoming these challenges and improving the efficiency of clinical trials.

Recent research has focused on anti-amyloid and anti-tau therapies, with monoclonal antibodies targeting Aβ plaques and drugs inhibiting enzymes involved in Aβ peptide production showing promise. However, findings regarding their efficacy in improving cognitive outcomes in individuals with AD have been mixed. While some studies have shown positive results, others have failed to demonstrate significant benefits, particularly in individuals with mild to moderate illness.

Looking ahead, future directions in AD research include the development of novel therapeutic approaches targeting tau protein, which is believed to be the direct source of symptoms in AD. Ongoing efforts to enhance our understanding of the disease mechanisms will be critical in identifying new treatment targets and improving patient outcomes. Ultimately, addressing the unmet medical needs in AD treatment requires continued collaboration, innovation, and investment in research efforts aimed at developing effective therapies for this debilitating disease.

CONCLUSION

To improve outcomes for people with AD, early detection and treatments are essential. This enables the use of a variety of therapeutic strategies, including medication and non-pharmacological therapies, to control symptoms and reduce disease development. Biomarkers are clinical signs of natural or pathogenic events that play a vital role in complex disorder diagnostics, progression, and treatment response. The AT(N) grouping classifies “A” biomarkers as amyloid PET, CSF Aβ42 and CSF Aβ42/Aβ40, “T” Tau PET and CSF p-Tau, and “N” by structural magnetic resonance imaging, fluorodeoxyglucose, PET, CSF complete t-Tau, and NFL. Key biomarkers used in Alzheimer’s include CT scans, PET, sMRI, fMRI, and DTI. By utilizing these techniques, researchers can better understand the mechanisms of action and improve Alzheimer’s detection. Researchers are also working on creating disease-modifying medications that target the underlying pathology of AD, such as amyloid-beta plaques and tau tangles. Lifestyle adjustments such as a healthy diet, consistent exercise, enough sleep, and social interactions have been demonstrated to improve symptom management and may reduce the likelihood of acquiring the illness. As research progresses, it is critical for individuals and carers to keep current on the changing landscape of treatment choices and support techniques. Despite current therapy, which focuses on treating symptoms and halting disease progression.

Alzheimer’s is a brain disease that worsens over time and affects cholinergic impulse transmission. It’s a complex and multifaceted condition that requires various treatments and therapies. Treatments include donepezil, rivastigmine, galantamine/tacrine, AChEIs, NMDA receptor blockers, antidepressants, antipsychotics, NSAIDs, and mAbs. Aducanumab, donanemab, and lecanemab are being investigated for AD therapy. Aducanumab is approved for mild MCI, while donanemab targets N-terminally modified Aβ proteins in amyloid plaques. However, Additional investigation is required to ascertain the safety and effectiveness of these treatments. Long-term NSAID use may offer protection against AD, but long-term placebo control trials have yielded negative outcomes.

While some medications have shown promise in treating the disease, further research is needed to determine the safety and effectiveness of these treatments.

CONFLICT OF INTEREST

None

ACKNOWLEDGEMENT

I sincerely thank Sanskar College of Pharmacy and Research for their constant support and encouragement. I am grateful to my faculty and mentors for their valuable guidance, which has been instrumental in shaping this work.

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