Blood-based Biomarkers for Neurological Disorder Diseases: Present Status and Potential Applications in a Changing Global Healthcare Environment

Abstract

In the worldwide healthcare system, blood-based biomarkers for neurological illnesses have been recognized as important instruments for early diagnosis, disease monitoring, and individualized treatment. Currently, several research studies have reported robust assays of blood biomarkers for the identification of tau and beta-amyloid proteins for Alzheimer-type dementia. Neurofilament light polypeptide is linked to various conditions, including amyotrophic lateral sclerosis, and is used alongside inflammatory markers such as C-reactive protein and cytokines to assess neuroinflammation and underlying pathophysiologic processes. These biomarkers are intriguing, but they have issues related to standardization, sensitivity, and specificity. Blood-based biomarkers provide affordable, non-invasive diagnostic tools in the evolving healthcare landscape, particularly in resource-constrained countries where advanced imaging is less readily available. In the near future, blood-based biomarkers can be used for patient screening, tailored treatment, and remote care integration. Widespread acceptance, however, will depend on removing the present legislative and technological obstacles and guaranteeing consistent clinical utility. Blood-based biomarkers can be utilized for global management of neurological illnesses and have the potential to be used clinically. In this review, recent advancements and their fruitful implications, as discussed by neurologists, will be discussed.

INTRODUCTION

The term "neurodegeneration" refers to either the delayed process of apoptosis or immediate cell death through necrosis [1]. The primary characteristics of neurode-

generation include problems with the cytoskeleton, inflammation, aberrant protein aggregation, loss of neurons, abnormal proteostasis, and abnormalities in DNA, RNA, and mitochondrial functions [2]. Neurodegenerative disorders (NDs) can be categorized on the basis of significant genetic abnormalities, prominent clinical characteristics, or the anatomical distribution of pathological alterations [3]. Two major risk factors for neurodegenerative illness include heredity and age variables, along with gender illiteracy, metabolic state, oxidative stress, diabetes, infections, brain trauma, inflammation, and environmental variables, among others [4]. Neuroinflammation is one of the most prevalent characteristics of neurodegenerative disorders. Chronic neuroinflammation causes microglia and astrocytes to release excessive amounts of reactive oxygen species (ROS) and pro-inflammatory cytokines, which results in alterations of synapses, reduced neuronal cell growth, and neuronal cell death.

It is difficult to diagnose neurodegenerative disorders due to unusual variations or the absence of symptoms in the early stages of the disease [5]. For the diagnosis of a "neurodegenerative" disease, brain tissue analysis is the most significant but not the sole routine clinical procedure, as it demands a brain biopsy, which is intrusive and not morally feasible for a standard clinical evaluation [6]. Clinical examination serves as the foundation for most diagnostic procedures. Recent research data indicates that functional imaging may be more specific for neurodegenerative diseases and helpful in the early detection of PD and dementia. Functional imaging is frequently employed to rule out alternative diagnoses [7]. Significant advancements have been achieved in the study of protein biomarkers for neurodegenerative disorders in recent years. Biomarkers may be essential to comprehending the pathophysiology of neurodegenerative disease since they represent physiological and pathological processes that occur in the nervous system (Figs. 1 and 2). Protein biomarkers may be used as a diagnostic aid as well as for forecasting future cognitive decline in healthy persons, along with tracking of dementia progression in patients with cognitive impairments. Additionally, these biomarkers can be used as an evaluator of various stages of disease progression. Biomarkers act as therapeutic tools for the diagnosis and monitoring of disease, as their concentration changes in the brain's extracellular space, reflecting continuous metabolic changes during disease progression. The best source of biomarkers for NDs is cerebrospinal fluid (CSF) [8]. Nevertheless, the lumbar puncture method, which is used to obtain CSF, is extremely intrusive and fraught with adverse consequences such as nausea, headache, backache, and weariness. Due to the shortcomings of collecting CSF, there is an increasing requirement for collecting easily accessible diagnostic materials like blood or saliva. Assessing blood-based biomarkers is advantageous since blood collection is not overly intrusive, affordable, and easy. Various analytical methods have been developed for decades to quantify biomarkers in plasma. The enzyme-linked immunosorbent assay (ELISA) is the most common method used for the analysis of CSF. However, significant methodological issues with plasma have been observed that adversely affect the performance of ELISA. Multiple analyte profiling (xMAP) is one of the leading technologies employed as a substitute for ELISA, as it allows for the analysis of a large number of samples simultaneously with a smaller sample volume. Analysis of biological markers using Mesoscale Discovery (MSD) and Electrochemiluminescence (ECL) is progressing, as it offers better sensitivity at lower sample concentrations compared to traditional ELISA and xMAP advanced technologies. For protein analysis, immunoprecipitation and mass spectrometry (IP-MS) techniques are likewise trustworthy. Quantitation has demonstrated strong outcomes for the presence of pTau and Aß biomarkers in plasma. Research studies have revealed transcranial magnetic stimulation (TMS)-based techniques to be highly reliable and accurate for the estimation of plasma biomarkers, even though major accurate data is further required for validating the results [9]. To ascertain their diagnostic qualities, more prospective research studies are required. The recently developed technology, known as single molecule array (SIMOA), shows good diagnostic accuracy and enhanced sensitivity even when measuring at lower concentrations. The SIMOA technique depends on individual molecule arrays and the simultaneous enumeration of isolated capture microbeads.

From a therapeutic perspective, the most important methods for the quantitative estimation of blood biomarkers are completely automated processes, such as ECL and SIMOA [10]. The aim of this review is to present a summary of the latest research regarding the application of the most promising blood biomarkers in the management of common neurodegenerative diseases, including multiple sclerosis, Alzheimer's disease, Parkinson's disease, and Creutzfeldt-Jakob disease.

ALZHEIMER'S DISEASE

The most common cause of dementia is Alzheimer's disease (AD), which has significant societal and financial ramifications. According to Prince M et al., currently, there are an estimated 50 million dementia sufferers worldwide, which is expected to rise to over 80 million by 2030 [11]. Since aging is the primary risk factor for dementia, increased life expectancy contributes to the rising prevalence of the disease [12]. As a result, these disorders pose a significant and growing worldwide health burden [13]. Furthermore, accurate prognosis and illness monitoring are challenging and solely depend on gathering clinical data. Thus, the study of biomarkers will help in gathering information regarding the prevalence of disease. Biomarkers, which offer an objective measurement of pertinent pathophysiology in vivo, are now part of the diagnostic criteria for AD in current

research [14, 15]. Regulatory bodies also advise the use of biomarkers in clinical trials [16].

Moreover, if disease-modifying therapies for AD are introduced, the utilization of biomarkers will be essential in the treatment process. This will guarantee that the patients can access...