There has been a lot of research into the usefulness of Alzheimer¿s disease (AD)-specific biomarkers that are reflective of the central pathogenic processes of amyloid ß aggregation and hyperphosphorylation of tau protein. Although, diagnostic lumbar puncture can be done with a very low rate of clinically significant adverse events, it still represents an invasive procedure also implying direct and indirect costs. The role of neurotrophins imbalance in AD has clearly been demonstrated, but no data exists on their potential use as clinical biomarkers. Objective. To evaluate amyloid ß1¿42, total tau, phospho-tau, as well as nerve growth factor (NGF) expression and concentrations in the conjunctival epithelial cells and in the tear and aqueous samples of patients with typical AD and prodromal AD and to determine whether the levels of these markers are different compared to normal subjects. Methods. Patients and fulfilling diagnostic criteria for typical AD (n. 10), prodromal AD (n. 10) and cognitively normal age-matched controls (n. 10), all eligible for cataract surgery, will undergo conjunctival impression cytology, tear and aqueous humor samples collection. All the subjects will undergo extensive neuropsychological examination including the MMSE, the ADAS-Cog and the CDR scales, MRI of the brain, and lumbar puncture. The total mRNA will be extracted from the conjunctival epithelial cells obtained by impression cytology, thereafter APP, tau protein, NGF and NGF receptors (TrkA and p75) expression will be evaluated by Real-time PCR and related to the mRNA levels of the controls by Rest © software. NGF, TrkA, p75, APP and tau protein expression will be compared among groups. Tear and aqueous humor samples will be collected in all included subjects. Full length Amyloid Precursor Protein (APP), APP cleavage products, total and phosphorylated tau protein, NGF and pro-NGF will be evaluated by specific ELISA and Western Blot and will be compared among groups.
The goal of the project is to investigate whether the changes of amyloid ß (Aß42), total tau (t-tau), phospho-tau (p-tau), as well as nerve growth factor (NGF) expression and concentrations in the conjunctiva and in the tear and aqueous samples of patients with AD may be useful biomarker of AD.
Since APP phosphorylation occurs before and favours amyloid plaques appearance, the advantage of using APPpT668 as ocular biomarker is noteworthy, also when compared to other non-invasive tests, like the recently prospected imaging of the retinal amyloid burden.
Our study aims at identifying an early and yet unexplored biomarker of AD in the eye, as a window on the brain. Given the urgent need for an early and accurate AD diagnosis, the development of a quick, cheap, non-invasive test for AD early detection and monitoring, alone and in combination with more expensive procedures, like the positron emission tomography (PET) scans, the current clinical standard, is noteworthy. Novel biomarker discovery may both bring advance to the clinical practice and improve the efficacy assessment of AD treatments in clinical trials.