Development of biomarkers for alzheimer's and parkinson's diseases

Objectives: Nowadays, Alzheimer's (AD) and Parkinson's (PD) disease are the most prevalent neurodegenerative disorders. Definitive diagnosis of these two diseases is only possible after examination of post-mortem brain tissue. There is no definitive diagnostic biomarker for these diseases. However, there are advancement in biomarker candidates such as circulating microRNAs (miRNA). microRNAs are 20-22 nucleotide long non-coding small RNA molecules which are post-transcriptional regulators of gene expression. They can be found in body fluids and also in exosomes and these features make them attractive candidate as biomarkers. In this study, we aimed to identify novel biomarker candidates and standardize the existing ones. Method: In order to validate miRNA hits from microarray study which previously done by our laboratory, we used serum and exosome samples from independent patient cohort (AD=24, FTD=17 and Control=29) and analyzed miRNAs with real time PCR. Their predicted pathway targets were analyzed with DIANA miRPath v3.0 server. Receiver Operating Characteristic (ROC) analysis was used to potential diagnostic values of validated miRNAs. Alpha-synuclein levels were measured with enzyme-linked immunosorbent assay (ELISA) following standardized protocols. Results: In our study, we found five miRNAs (miR-20b, miR-663-3, miR-762, miR-320b and miR-1915-5p) were differentially expressed in AD. The predicted targets of these miRNAs include estrogen and ras signaling, axon guidance and circadian rhythm. We found that the potential diagnostic values of miR-320b and miR-1915-5p in serum were found to be 100%. Additionally, ventricular volume is an important confounding factor for interpreting amyloid beta levels in diagnosis of AD. We showed that the alpha-synuclein ELISA kit gave similar performance in different dilutions of the samples. Conclusion: Serum miRNAs can be utilized as good biomarker candidates in discrimination of AD from control and FTD as neurological disease control group. The need for standardization between intra- and interlaboratory studies has been demonstrated before use of the alpha-synuclein ELISA kit as a biomarker.