Image: The Schirmer’s test is an invasive filter paper strip folded over the lower lid to absorb the tear film for five minutes. The tears collected on the Schirmer’s strips can be analyzed for biomarkers (Photo courtesy of Innovative Eye Care).
Parkinson's disease is a progressive disorder that kills brain cells that produce dopamine, which is a chemical messenger important for the control of movement. The main symptoms of Parkinson's include slowness of movement, tremors, rigidity, and difficulty maintaining balance and coordination.
Tear samples from individuals with Parkinson's disease (PD) had different levels of a protein linked to the disease than those who did not have it. Such a marker could be very useful in helping to diagnose, and perhaps even treat Parkinson's because the disease can begin many years before its symptoms appear.
Scientists at the University of Southern California (Los Angeles, CA, USA) and their colleagues compared tear samples from 55 PD patients of varying severity and 27 age- and gender-matched non-PD controls were collected and pooled from both eyes for analysis of alpha synuclein, CC chemokine ligand 2 (CCL-2) and DJ-1 (Parkinson’s disease protein 7) using a Human magnetic Luminex assay kit and analysis of oligomeric alpha-synuclein using an Human alpha-synuclein oligo enzyme-linked immunosorbent assay (ELISA) kit, respectively.
The team revealed that total alpha-synuclein decreased significantly in PD patients (423.12 ± 52.6 pg/mg tear protein) relative to healthy controls (703.61 ± 136.4 pg/mg tear protein) in tears from patients acquired from Schirmer’s strips taken during an anesthetized Schirmer’s test. Oligomeric alpha-synuclein increased significantly in PD patients (1.45 ± 0.31 ng/mg tear protein) relative to controls (0.27 ± 0.07 ng/mg tear protein). While detectable in tears, neither CCL-2 nor DJ-1 varied between PD patients and non-PD controls.
While it is not yet clear how Parkinson's disease kills brain cells, scientists have discovered that toxic protein deposits known as Lewy bodies are often present in many brain cells of people with the disease. These deposits contain clusters of proteins that have not folded correctly. A major component of Lewy bodies is an oligomeric form of the protein alpha-synuclein. The oligomeric form of a protein comprises several repeats of the protein's essential amino acids, but not as many as the polymeric form. An author of a recently published study of alpha-synuclein in Parkinson's has suggested that the oligomeric protein's ability to "disrupt the integrity of the membrane" might be a key step in the process that ultimately kills the cell.
Mark F. Lew, MD, a professor of Neurology and lead investigator in the study, said, “We believe our study is the first to show that tears may be a reliable, inexpensive, and noninvasive biological marker of Parkinson's disease.” The study will be presented at the 70th annual meeting of the American Academy of Neurology, which will be held April 21-27, 2018, in Los Angeles, CA, USA.
University of Southern California