Smart Diagnostics for Neurodegenerative Disorders: Neuro-sensors

Smart Diagnostics for Neurodegenerative Disorders: Neuro-sensors explores all available biosensor-based approaches and technologies as well as their use in the diagnosis, prognosis and therapeutic management of a variety of neurological disorders such as Alzheimer's, Parkinson's and epileptic disorders. The book also discusses contemporary and revolutionary biosensor platforms that are being used to produce a quantitative quick lab-on-a-chip point-of-care (POC) assay for several types of predictive and diagnostic biomarkers linked with neurodegenerative disorders. It offers a combinatorial strategy for learning recent advances and designing new biosensor-based technologies in the fields of medical science, engineering and biomedical technology.

Early detection of neurological conditions has the potential to treat the disease and extend the life expectancy of patients. Recent improvements in biosensor-based approaches that target specific cell surface biomarkers can be used for early detection of neurodegenerative disease.

• Provides an in-depth understanding of biomarkers associated with neurodegenerative disease to build and create a variety of biosensors
• Presents biosensor-based strategies to create and construct enhanced platforms for quick diagnosis of biomarkers linked to a variety of neurological illnesses
• Discusses the current challenges and future trends in developing diagnostic devices for early detection of neurodegenerative disorders, presenting new avenues for more sensitive and selective point-of-care devices

• Language: English
• Publisher: Academic Press
• Release date: Aug 19, 2023
• ISBN: 9780323955409

Book preview

Chapter 1

Neurobiosensors: novel approaches towards early diagnostics of neurodegenerative disorders

Arpana Parihar¹, Palak Sharma², Nishant Kumar Choudhary² and Raju Khan¹, ³,    ¹Industrial Waste Utilization, Nano and Biomaterials, CSIR-Advanced Materials and Processes Research Institute (AMPRI), Bhopal, Madhya Pradesh, India,    ²NIMS Institute of Allied Medical Science and Technology, NIMS University, Jaipur, Rajasthan, India,    ³Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India

Abstract

Protein misfolding, aggregation, and accumulation are critically important attributes resulting in cellular malfunction, synapse loss, and brain damage, which are the hallmark of neurodegenerative disorders (NDDs). Considering numerous neurological dysfunctions have a strong inverse relationship with their incidence and progression, significant characterization of the concentration profiles of selected biomarkers with their key forms and morphologies of proteins involved in these diseases, including amyloid β and α-synuclein, phosphorylated tau, dopamine, transactive response DNA-binding protein 43, and prion protein can be an effective diagnostic assay for NDDs. The potential risks associated with NDDs are rather enormous and pose a serious threat to global public health and the country’s annual budget. Conventional diagnostic techniques mainly rely on symptoms or autopsy reports, failing to address early diagnosis and treatment, the only prospect for amelioration. Thus a streamlined and sophisticated mechanism (analytical devices) to presymptomatically analyze and differentiate between these disorders is inferred in the precise detection and quantification of concentrations of biomarkers in bodily fluids, such as cerebrospinal fluid, blood, saliva, or urine. With the aid of biosensors, the detection of metabolic, proteomic, and genomic biomarkers of NDDs is swift, sensitive, cost-effective, highly reproducible, and accurate. This chapter aims to provide an overview of the classification of NDDs biomarkers and mechanistic approaches for the designing and fabrication of novel biosensors-based detection of these biomarkers with point-of-care testing along with commercialized sensor technologies and their surplus demand with future scopes.

Keywords

Neurodegenerative disorders (NDDs); biomarkers; early diagnosis; biosensors; point-of-care testing

1.1 Introduction

Tens of millions of people worldwide suffer from neurodegenerative disorders (NDDs) each year, characterized by the deterioration of neuronal cells and the inevitable death of nonspecific surrounding brain cells [1]. The underlying cause of these disorders can be the progressive deposition of amyloid or aggregation of misfolded protein [2]. The mechanism of misfolded proteins, their precursors, end-products, and underlying key factors are remarkably common despite attributed to the fact that the protein aggregates are associated with various NDDs [3]. Neurological disorders account for nearly ~3.84% of the global burden of diseases measured in the disability-adjusted life years by subcategory of disease or injury and thus are increasing in prevalence. Though NDDs intensively manifest in late adulthood, the aging of the populace is closely correlated to their rising prevalence globally and thus has a significant socioeconomic impact because of their prolonged nature [4]. The precise monitoring and diagnosis for neurological-related dysfunctions continue to be challenging throughout, nevertheless on the scale of the qualified neurologists and the complexity of the assessment. Conventional diagnostics tools hold certain drawbacks in terms of costs, assay times, complex protocols, and the requirement for skilled professionals to execute procedures or interpret the results [5]. In addition, on the scale of specificity and reliability, these techniques put on the backhand and an inability to diagnose and prognosis the disease in its early stage [6]. Consequently, there is a paramount urge to identify potential biomarkers and develop diagnostic techniques that assist with early screening and thereby delay, minimize, or prevent the progression of certain disorders.

The unprecedented technological advancements and modernization of techniques centered on exploring novel biomarkers led to the development of biosensor-based point-of-care testing (POCT) in the likelihood of accurate and precise diagnosis and progression of the NDDs [7]. Intending to analyze disease incidences before any sort of dysfunctions, significant research on NDDs biomarkers (quantifiable signals indicative of injury, contamination, or illness) has been performed [8]. Furthermore, the innovations have led to the development of biosensing devices with the potential enough for real-time identification of numerous biomarkers. Biosensors are noninvasive analytical devices incorporating a biological material, or a biomimetic as the recognition molecules, which are either significantly linked to or integrated into a physicochemical transducer or transducing microsystems that convert a biological response into quantifiable and processable signals [9]. It has anticipated enabling a myriad of potential advantages, such as swift time-to-response, ease of use, efficiency, portability, and accessibility to the patient via point-of-care (POC) settings [10]. Although being employed for diagnostic purposes, biosensors now offer the opportunity to analyze tissue- and genome-based biomarkers that have the potential to portray the segments of intricate disease patterns [11]. Following the sort of signal transducer, biosensors can be classed as piezoelectric, electrochemical, or optical devices [12]. Due to their potential applications, such as nanomaterials (NMs) have recently received significant attention. NMs exhibit remarkable attributes including high conductivity, good biocompatibility, and a large surface-to-volume ratio which expands their utility as potential candidates to be utilized in the fabrication of biosensors to enhance sensitivity and lower detection limits [13]. Nanotechnology-based biosensors are anticipated to be an efficient, sensitive, economical, robust novel approach that can be versatile, automated, and miniaturized [14]. Their analytical performance governs the final prototypes of biosensors for commercial applications. With an emphasis on design methodologies and contemporary applications, we have provided a detailed overview of NDDs and their associated biomarkers in this chapter. A brief mechanistic approach for designing biosensors along with the multitude of varied sensors techniques and currently available commercialized biosensors for diagnosing NDDs are also outlined.

1.2 Overview of neurodegenerative diseases

NDD is an umbrella term for a range of conditions that primarily affect the neurons in the human brain. It usually gets worse over time and has no cure to date. It occurs mainly due to two causes: (1) loss of neurons and (2) intracellular aggregation of the protein, and these two conditions can arise due to mutation [15]. The mutation affects protein conformation and makes various other protein changes leading to the above-mentioned conditions. So far three types of intracellular aggregates (also called inclusion) have been found that are amyloid β (Aβ) inclusion (plaques), Tau (tangles), and α-synuclein (α-syn) [16]. NDDs are diverse in their pathophysiology. Examples of NDDs are as follows: (1) Alzheimer’s disease (AD) and other dementias, (2) Parkinson’s disease (PD), (3) Huntington’s disease (HD), (4) epilepsy, (5) multiple sclerosis (MS), (6) spinocerebellar ataxia, (7) spinal muscular atrophy, (8) motor neuron disease, (9) prion’s disease, and (10) corticobasal degeneration.

1.2.1 Alzheimer’s disease

Dementia, a degenerative neurological condition that affects people, is primarily brought on by AD. It can be divided into two groups: sporadic and familial. The phrase sporadic Alzheimer’s refers to the disease's late-onset type, whose precise causes are unknown but undoubtedly include a wide variety of inherited and environmental risk factors [17]. It accounts for 90%–95% of cases. AD that develops sporadically affects between 1% of persons between the ages of 60 and 65 and 50% of those over the age of 85 [18]. A gene that has been implicated in the pathogenesis of AD is the e4 allele of the apolipoprotein E gene (ApoE-e4) [19]. The patients that inherit one e4 allele elevate the likelihood of developing AD and two e4 alleles (one from each parent) increase the probability even further. ApoE aids in the breakdown of β-amyloid, however, the ApoE-e4 allele appears to be significantly less potent than the ApoE-e2 variant [20]. Just as ApoE-e4 increases the risk of sporadic AD, on the contrary, ApoE-e2 is protective against Alzheimer’s. In contrast, familial Alzheimer’s refers to the early onset of the disease where an inherited dominant gene potentially accelerates the progression of the disease [21]. About 5%–10% of instances are familial, and multiple gene alterations are the root cause. Early-onset Alzheimer's has been associated with the first mutation in the PSEN-1 or -2 genes on chromosome 14 or 1. These genes encode presenilin-1 and -2, both protein subunits of γ-secretase. Mutations in PSEN-1 and -2 genes alter the site where γ-secretases cuts amyloid precursor protein (APP), resulting in variable lengths of β-amyloid molecules that manifest to be superior at aggregating and forming plaques. Another known hereditary etiology of Alzheimer’s is Trisomy-21 (Down’s syndrome) which consists of an extra copy of chromosome 21. The APP gene is located on chromosome 21, which implies that patients with Down's syndrome have an additional copy of the gene resulting in increased APP expressions and probably more amyloid plaque. Because of this, familial AD frequently progresses by the age of 40.

Pathophysiology: Though the exact course of AD is uncertain, the two main reasons that are frequently cited in its progression are plaques and tangles. The brain neuron’s cell membrane consists of APP of which one end of the APP is in the cell, and the other end is outside. After damage, APP aids the neuron’s growth and repair. Because APP is a protein, it is utilized, degrades over time, and is eventually recycled. Normally, APP gets broken down by enzymes known as α- and γ-secretase and becomes a soluble peptide [22]. But if another enzyme, β-secretase teams up with γ-secretase instead, then the leftover fragment of chopped APP is not soluble, and create a monomer called amyloid β. These monomers tend to be chemically sticky and bond together just outside the neurons and form β-amyloid plaques [23]. These plaques may encroach upon neurons, interfere with neuronal signaling, and thus alter brain functions. On the other hand, tangles are found inside the cell (neuron), as opposed to the β-amyloid plaques. The cytoskeleton of the neurons is partly made up of microtubules that transport nutrients and molecules along the length of the cell. A special protein called tau makes sure that these microtubules do not break apart. If neuronal dysfunction activates the kinase enzyme, which adds a phosphate group to the tau protein. The tau protein subsequently undergoes a shapeshift, ceases to stabilize the microtubules, aggregates with other tau proteins, or becomes tangled, which results in the development of neurofibrillary tangles. Tangled and dysfunctional microtubules prevent signaling and undergo apoptosis. As neurons die, the brain atrophy shrinks, and the Gyrus (gyri) gets narrower, which are characteristic brain ridges. Additionally, Sulci, the grooves between the gyri, widen. The brain’s ventricles, which are chambers filled with fluid, enlarge with atrophy [20,21,24]. Fig. 1.1 summarizes the entire pathophysiology of AD disease.

Figure 1.1 A schematic illustration of the pathophysiology of Alzheimer’s disease.

1.2.2 Parkinson’s disease

PD is a movement disorder where motor function is affected due to the degeneration of dopamine (DA)-producing neurons in the substantia nigra of the brain. Parkinson’s is one of the most common neurological disorders. It is a progressive adult-onset disease and it gets more common with age. It was first described as Shaking palsy by James Parkinson in 1817, and later Jean-Martin Charot proposed its current name to honor James Parkinson [25]. The basal ganglia of the brain, which include the substantia nigra, serve primarily to restrain undesirable motor behaviors. When a person intends to move, this inhibition is removed by the action of DA [26]. Lower levels of DA make it more difficult to initiate voluntary movements in PD patients as dopaminergic neurons are gradually destroyed in these individuals as demonstrated in Fig. 1.2. There is a dearth of knowledge of the mechanisms underlying neuronal cell death however the existence of so-called Lewy bodies in the neurons before their demise might offer logical insights and is currently the focus of significant research [27–29]. Most of the time there is no known cause of this disease but in a few cases, there might be an environmental and genetic cause like mutations in the PINK 1, PARK 2, or α-syn gene, protein aggregation, autophagy destruction, neuroinflammation, changes in cell metabolism or mitochondrial function, blood–brain barrier (BBB) breakdown and, exposure to herbicides and pesticides [30].

Figure 1.2 Comparison between healthy and Parkinson’s disease substantia nigra of the brain.

1.2.3 Huntington’s disease

HD was likely first described in the late 1300s as the dancing mania. A few of the reports over the next century were noted but it was George Huntington’s eloquent description of this hereditary chorea that led to the designation of this condition as HD [31]. Interestingly it was published in the year 1872, as a paper titled On Chorea. HD is an autosomal dominant, progressive NDD, with a distinct phenotype [32]. The mutant protein in HD is Huntington, based on chromosome four which results from an expanded CAG repeat leading to a polyglutamine strand of variable length (with more than 35 CAG repeat) at the N-terminus [33]. How the CAG repeats affect Huntington’s gene is debated. Evidence suggests that this tail confers a toxic gain of function. However, the precise path of the physiological mechanism of Huntington’s is poorly understood. What is known is the affected Huntington protein leads to inclusions within the nucleus cytoplasm, leading to the destruction of the cortex, but mainly a very selective area of the brain called the striatum which is composed of caudate and putamen, Fig. 1.3 shows the effects of Mutant huntingtin only in the cytoplasm for simplicity [34,35]. Specific neurons in these areas being most damaged include striatal and nigral medium-size spiny neurons and large striatal interneurons. HD can have an adult onset (between ages 35 and 45) and a juvenile onset (<15 years of age) [36]. The triad of symptoms of chorea (meaning dance in Greek), behavioral changes, and dementia are the three most characteristic findings seen in most Huntington’s patients. These findings can occur together or precede each other for many years. The diagnosis of HD in the past has been purely clinical based on the patient’s history, especially family history, along with physical examination. Since the onset of genetic testing, this has become increasingly important in confirming the diagnosis. Genetic testing evaluates the CAG repeats on chromosome four; patients with 40 or more repeats have a fully penetrant disease, 36–39 CAG repeats state a reduced penetrance, and the patient may develop the disease. Another method that can help in diagnosis is imaging [37,38].

Figure 1.3 Cellular pathogenesis of Huntington’s disease [34]. Reproduced with permission from C.A. Ross, Huntington’s disease: New paths to pathogenesis. Cell 2004;118:4–7. https://doi.org/10.1016/j.cell.2004.06.022.

1.2.4 Epilepsy

Patients with epilepsy experience recurrent and unpredictable seizures because the word epilepsy implies seizure disorder. A seizure is a disorder where the brain's neurons are simultaneously active when they are not supposed to be. When a neuron is active the electrical signal passes through the in and out flow of ions from protein channels [39]. This flow of ions is controlled through neurotransmitters. Some neurotransmitters bind to the receptors and trigger neurons for opening the ion channels and convey electrical signals are known as excitatory neurotransmitters; on the other hand, some neurotransmitters that close the ion channels are known as inhibitory neurotransmitters. Clusters of neurons in the brain temporarily lose their function during seizures, triggering them to deliver a surge of excitatory signals that are frequently referred to as paroxysmal seizures [40]. These paroxysmal electrical discharges are presumed to arise from either excessive excitation or insufficient inhibition. The principal excitatory neurotransmitter receptor in the brain is called NMDA, and it responds to glutamate by opening ion channels that let Ca²+ in, which directs the cell to send signals. Some epilepsy patients appear to have persistent activation of these receptors [41]. On the contrary hand, GABA, which binds to GABA receptors and directs cells to block signals by opening channels that let in Cl− ions, is the primary inhibitory neurotransmitter in the brain. Some epileptic patients appear to have genetic mutations that cause their GABA receptors to be dysfunctional and unable to inhibit signals as shown in Fig. 1.4. Although these receptors and ion channels might share a primary genetic cause, they might also be affected by other conditions including brain tumors, injury, or infections. When clusters of neurons fire repeatedly and simultaneously, because of a loss in inhibition or an increase in activation, external symptoms including jerking, moving, and losing consciousness are observed. Partial or focal seizures come from this aberrant electrical surge occurring just in a small portion of the brain; generalized seizures occur when the entire brain is affected. Partial seizures are further divided into simple and complex partial seizures depending on the damaged brain regions. Simple partial seizures cause patients to have odd feelings, bizarre sensations, or involuntary jerky movements, but they nevertheless retain consciousness and awareness of their environment, whereas complex partial seizures involve loss of consciousness, awareness, and responsiveness. Generalized seizures are further subdivided into absence, tonic, atonic, clonic, myoclonic, and convulsive seizures. The electroencephalogram (EEG), which scans unusual brain waves, is employed to diagnose epilepsy in addition to symptom observation, medical history, and other factors [40,42,43].

Figure 1.4 Dysfunctional neurotransmitters lead to uncontrolled flow of ions and cause epilepsy (seizure) [44]. Reproduced with permission from E. Akyuz, A.K. Polat, E. Eroglu, I. Kullu, E. Angelopoulou, Y.N. Paudel, Revisiting the role of neurotransmitters in epilepsy: An updated review. Life Sciences 2021;265:118826. https://doi.org/10.1016/J.LFS.2020.118826.

1.2.5 Multiple sclerosis

The brain and spinal cord are both portions of the central nervous system, which is affected by the demyelinating disease MS. Neurons' axons are protected by a myelin sheath, which enables them to rapidly send electrical impulses [45]. The group of cells known as oligodendrocytes, which provide support for neurons, produces myelin. Demyelination in MS occurs when the body's immune system mistakenly assaults and damages the myelin, which impairs neuronal communication and eventually resulted in a wide range of sensory, motor, and cognitive issues [46]. Only specific molecules and cells can pass across the BBB, shielding the brain from the blood. The BBB expresses additional receptors when immune cells, such as T cells, enter the brain and are reactivated by CNS-resident antigen-presenting cells that present myelin. This makes it easier for immune cells to adhere and enter, which causes demyelination. As a type-IV hypersensitivity reaction or cell-mediated delayed reaction, MS is characterized by the secretion of cytokines by myelin-specific T cells, including interleukin (IL)-1, -6, tumor necrosis factor (TNF)-γ, and interferon. These cytokines dilate blood vessels, allowing more immune cells to enter the body, and directly damage oligodendrocytes [47]. In addition, these cytokines drive macrophages and B-cells as a result of the inflammatory response. These B-cells start producing antibodies that identify the proteins found in the myelin sheath, and macrophages subsequently employ this antibody marker to engulf and kill the oligodendrocytes [47,48]. This process has been demonstrated in Fig. 1.5. The absence of oligodendrocytes results in the area of scar tissue, commonly known as plaques or sclera because there is no myelin to protect the neurons. Regulatory T cells block the activity of the other immune cells, which reduces inflammation in MS because these autoimmune attacks frequently emerge in bouts. This process helps oligodendrocytes heal and extends new myelin to encase the neurons and is known as remyelination [49]. Remyelination gradually stops when the oligodendrocytes disappear, and the loss of axons causes irreparable damage. Similar to other autoimmune disorders, the precise etiology of multiple sclerosis is unknown, however, it is associated with both hereditary and environmental factors [49]. There are four main types of MS based on the pattern of symptoms over time. First is relapsing-remitting multiple sclerosis (RRMS) in which autoimmune attacks occur at intervals of months or years and result in a greater degree of disability. The second kind is secondary progressive multiple sclerosis, which is akin to RRMS in which the immunological onslaught gradually becomes persistent and results in a steady progression of disability. Primary progressive multiple sclerosis, the third form, is characterized by a single ongoing attack on myelin that results in a gradual escalation of disability over the course of a person's lifetime. The last type is progressive relapsing multiple sclerosis, which is similarly a continuous attack but this time has multiple bouts during which impairment worsens much more instantly. The diagnosis of MS is supported by some conventional methods like MRI which exhibits multiple central nervous system lesions, called white matter plaques. Also, a high level of antibodies in cerebrospinal fluid (CSF) can indicate an autoimmune process. Finally, a visual evoked potential/response tool gauges the neural system's reaction to visual