Biomarkers of Alzheimer's Disease: A Review

Abstract

Mohapatra D, Jena S, Prusty S K, Sahu P K

Alzheimer’s disease (AD) is a progressive and irreversible neurodegenerative disease. Neuropathological hallmarks of AD are amyloid plaques and neurofibrillary tangles. The biomarkers used in the diagnosis of AD are mostly invasive. Established methods are available to identify biomarkers in cerebrospinal fluid (CSF) and plasma. β-amyloid (1-42) [Aβ (1-42)], total tau (T-tau) and phosphorylated tau (P-tau) are the three biomarkers present in CSF as well as plasma. Increased level of these three biomarkers is associated with AD. These biomarkers in CSF can be measured by enzyme linked immunosorbent assay (ELISA), but measuring these biomarkers in blood need more sensitive and specific assays. Dendritic proteins like neurogranin, synaptosomal associated protein 25 (SNAP-25) and synaptotagmin-1 (SYT1) in CSF can also be used as biomarkers as their level is decreased in AD. Neurofilament light (NFL) level (increased) in both CSF and plasma can serve as a biomarker for AD. Collection of CSF by lumbar puncture is a measure drawback which limits its use as a diagnostic tool. Biomarkers in non-invasive samples such as urine, saliva, hair and nail are under development and can be used in near future. Level of 8-hydroxy-2-deoxyguanosine (8-OHdG) and isoprostane in urine, cortisol level in saliva, concentration of trace elements in hair and nail can be used as biomarkers in AD.