Objective: We measured alpha-synuclein total (a-syn_total) and alpha-synuclein oligomers (a-syn_olig) concentration in 70 healthy subjects, of different ages (from 18 to 88 years old) to detect if salivary a-syn concentration is influenced by aging.

Background: The pathological hallmark of PD is a-syn deposition leading to the formation of Lewy bodies. A-syn can be detected in biological fluids including saliva. A-syn_olig exerts a crucial neurotoxic effect in PD. In PD patients we detected lower salivary a-syn_total and higher a-syn_olig than healthy subjects. Previous studies have shown that a-syn neuronal aggregates increase during aging.

Methods: Subjects have been divided into 5 groups of 14 subjects each one. The I group includes subjects from 18 to 26 years old (YO), the II group includes subjects from 30 to 36 YO, the III subjects from 40 to 46 YO, the IV subjects from 50 to 65 YO and the V includes subjects from 70 to 88 YO. Samples of saliva were collected following the protocol reported in previous study (Vivacqua et al., 2016). ELISA analysis was performed using two specific ELISA kits: SensoLyte 55550 for a-syn_total and MyBioSource MBS043824 for a-syn_olig. Statistical significance was evaluated by Mann-Whitney U test.

Results: No significative differences have been found in the concentration of a-syn_tot and a-syn_olig between the first four groups (p>0,05). The mean concentration of a-syn_olig is respectively: 0,10±0,081 ng/ml in the I group, 0,17±0,13 ng/ml in the II group, 0,19±0,16 ng/ml in the III group and 0,14±0,14 ng/ml in the IV group. Salivary a-syn_total was significantly lower, whereas a-syn_olig was significantly higher in the subjects of the V group confronting with the others (p<0,05). A-syn_olig concentration in the V group was 0,96±0,15 ng/ml. No significative correlations have been detected between a-syn concentration and age in the five groups.

Conclusions: In the subjects of the V group, decreased salivary concentration of a-syn_total may reflect the reduction of a-syn monomers (a-syn_mon), leading to the formation of insoluble intracellular inclusions during aging process. This is supported by the increased concentration of a-syn_olig in the same group. Moreover, the similar concentration of a-syn_olig in PD patients and in aging healthy subjects  suggests that measurement of a-syn in saliva might be a useful method  for help the diagnosis of PD especially in the early stages of the disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/salivary-alpha-synuclein-in-aging/