Neuronal exosomes in saliva of Parkinson's disease patients: A pilot study

Parkinson's disease (PD) is the most common neuro-degenerative movement disorder of old age affecting about 2–3% of population ≥ 65yrs of age worldwide [ [1] Poewe W. Seppi K. Tanner C.M. et al. Parkinson disease. Nat. Rev. Dis. Prim. 2017; 3: 17013 Crossref PubMed Scopus (718) Google Scholar ]. But, there are still no reliable biomarkers as the molecular pathology markers like plasma or cerebrospinal fluid (CSF) α-synuclein has its oligomeric variants. These are based on the currently understood pathophysiology, individually neither correlate well with the disease severity nor discriminate between different PD with the sufficient confidence [ [2] Wang Y. Shi M. Chung K.A. et al. Phosphorylated α-synuclein in Parkinson's disease. Sci. Transl. Med. 2012; 4: 121ra20 Crossref PubMed Scopus (170) Google Scholar ]. Recent findings of α-synuclein efflux and other proteins from CSF to peripheral blood incorporated into exosomes is a growing focus on exosomes as having important role in PD pathophysiology [ [3] Shi M. Liu C. Cook T.J. et al. Plasma exosomal α-synuclein is likely CNS-derived and increased in Parkinson's disease. Acta Neuropathol. 2014; 128: 639-650 Crossref PubMed Scopus (281) Google Scholar ]. Furthermore, exosomes from PD patients have been shown to induce α-synuclein oligomerization, suggesting that pathogenic α-synuclein oligomers may be preferentially sorted into exosomes and act as a seed for fibril growth. Salivary glands release α-synuclein into the saliva, the mechanism yet-to-be defined, a fraction of this secreted protein may be linked to exosomes [ [4] Devic I. Hwang H. Edgar J.S. et al. Salivary α-synuclein and DJ-1: potential biomarkers for Parkinson's disease. Brain. 2011; 134: e178 Crossref PubMed Scopus (149) Google Scholar ]. In our study, we have observed for the first time that there is increased level of neuronal salivary exosomes in PD patients than the healthy control. Further, we demonstrated a new method to correlate the concentration of total salivary exosomes with the PD patients.