Abnormal Salivary Total and Oligomeric Alpha-Synuclein in Parkinson’s Disease

In Parkinson’s disease (PD), alpha-synuclein (a-syn) can be detected in biological fluids including saliva. Although previous studies found reduced a-syn total (a-syn(total)) concentration in saliva of PD patients, no studies have previously examined salivary a-syn oligomers (a-syn(olig)) concentrations or assessed the correlation between salivary a-syn(total), a-syn(olig) and clinical features in a large cohort of PD patients. Is well known that a-syn(olig) exerts a crucial neurotoxic effect in PD. We collected salivary samples from 60 PD patients and 40 age- and sex-comparable healthy subjects. PD was diagnosed according to the United Kingdom Brain Bank Criteria. Samples of saliva were analyzed by specific anti-a-syn and anti-oligomeric a-syn ELISA kits. A complete clinical evaluation of each patient was performed using MDS-Unified Parkinson's Disease Rating Scale, Beck Depression Inventory, Montreal Cognitive Assessment and Frontal Assessment Battery. Salivary a-syn(total) was lower, whereas a-syn(olig) was higher in PD patients than healthy subjects. The a-syn(olig)/a-syn(total) ratio was also higher in patients than in healthy subjects. Salivary a-syn(total) concentration negatively correlated with that of a-syn(olig) and correlated with several patients’ clinical features. In PD, decreased salivary concentration of a-syn(total) may reflect the reduction of a-syn monomers (a-syn(mon)), as well as the formation of insoluble intracellular inclusions and soluble oligomers. The combined detection of a-syn(total) and a-syn(olig) in the saliva might help the early diagnosis of PD.