Conference Coverage

Biomarkers in tears may help identify patients with Parkinson’s disease



Oligomeric alpha synuclein levels in tears can help clinicians distinguish between patients with Parkinson’s disease and healthy controls, according to research presented at the annual meeting of the American Academy of Neurology. Chemokine (C-C motif) ligand 2 (CCL2), a cytokine, may be used for the same purpose, according to researchers.

Dr. Mark Lew, professor of neurology, the vice chair of the department of neurology, and the director of the division of movement disorders at the University of Southern California

Dr. Mark Lew

Lacrimal glands have high numbers of cholinergic and other neurons. Parasympathetic and sympathetic neural pathways stimulate the tears that lacrimal grands secrete. It is possible that the production, packaging, and secretion of proteins into tears may alter when nerve function in the lacrimal glands and cornea changes. This idea may be tested by collecting reflex tears (i.e., stimulated tears provoked by an unanesthetized Schirmer’s test).

Mark Lew, MD, professor of clinical neurology at University of Southern California, Los Angeles, and colleagues previously studied patients using basal tears collected from an anesthetized Schirmer’s test. To examine whether the protein composition of reflex tears differs in patients with Parkinson’s disease, compared with healthy controls, they collected reflex tears from 85 patients with Parkinson’s disease and 80 age- and sex-matched healthy controls using an unanesthetized Schirmer’s test. The researchers pooled samples from both eyes to analyze alpha synuclein, CCL2, and total protein using enzyme-linked immunosorbent assays or multiplex ELISA.

Eligible participants were aged 30-85 years and had a Montreal Cognitive Assessment (MoCA) score of 21 or higher. Patients with Parkinson’s disease had a lower MoCA score than controls did, although it was still in the normal range. Tear flow was significantly decreased in patients with Parkinson’s disease, compared with controls.

Dr. Lew and colleagues found that the amount of oligomeric alpha synuclein was increased nearly 400% in the tears of patients with Parkinson’s disease, compared with those of healthy controls (4.21 ng/mg tear protein vs. 0.90 ng/mg tear protein). This difference was statistically significant. Similarly, CCL2 was significantly increased in the tears of patients with Parkinson’s disease, compared with those of healthy controls (165.8 pg/mg tear protein vs. 116.3 pg/mg tear protein). Among men, Parkinson’s disease was associated with greater rises in oligomeric alpha synuclein (4.95 ng/mg tear protein vs. 0.89 ng/mg tear protein in healthy controls) and CCL2 (201.5 pg/mg tear protein vs. 117.9 pg/mg tear protein in healthy controls) than in women. The origin of sex differences in these biomarker values requires further study, the investigators said.

Dr. Lew reported receiving research support from the Parkinson’s Study Group, the Michael J. Fox Foundation, Biotie Therapies, NeuroDerm, Enterin, Pharm2B Fellowship Grants, Allergan, and Medtronic.

SOURCE: Lew M et al. AAN 2019, Abstract S10.001

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