Authors: Sarah Hamm-Alvarez (Keck School of Medicine, CA, USA)
Take a look behind the scenes of a recent research article published in Biomarkers in Medicine entitled, ‘Oligomeric α-synuclein is increased in basal tears of Parkinson’s patients‘, as we ask first author Sarah Hamm-Alvarez (Keck School of Medicine, CA, USA) about what inspired her group to carry out this work into basal tear proteins, including the potential of translating oligomeric α-synuclein in basal tears into the clinic as a biomarker for Parkinson’s disease (PD).
What inspired you to carry out this work into basal tear proteins in Parkinson’s?
My group has traditionally studied the changes in the tear film associated with the autoimmune disease, Sjögren’s syndrome. This is a disease associated in part with inflammation and loss of function of the lacrimal gland, an exocrine gland that is the main producer of aqueous tears, and which is associated with severe dry eye disease. The lacrimal gland is extensively innervated by parasympathetic and sympathetic neurons, and changes in innervation of the lacrimal gland are thought to be related to changes in tear composition.
We happened to see a call for proposals in the area of novel biomarker development for PD from the Michael J Fox Foundation (NY, USA). In a brainstorming meeting with my colleagues, we reasoned that some of the same changes in neural innervation associated with autoimmune inflammation of the lacrimal gland in Sjögren’s syndrome might occur with PD and in fact, other neurological disorders. In particular, the lacrimal gland is extensively responsive to cholinergic stimulation, which is known to be dysregulated in PD.
We speculated that we might be able to detect differences in the protein composition in tears of PD patients associated with early changes in the activity of neurons innervating the gland. We submitted a grant proposal for biomarker discovery utilizing non-invasive approaches to the Michael J Fox Foundation, which was, luckily, funded, and proceeded to test this hypothesis. While the mechanisms underlying the observed changes are still unresolved, we were excited to be able to detect changes in oligomeric α-synuclein and α-synuclein in basal tears as reported here.
At present, what are the main issues with biomarkers used for PD?
There is considerable interest in identification of biomarkers for earlier diagnosis of PD. The disease is typically diagnosed in patients manifesting significant motor symptoms, and by the time this occurs it is thought that irreversible neurological damage has already occurred. The defining clinical feature of PD is the accumulation of Lewy bodies in the brain, while the major protein constituent of the Lewy body is aggregated α-synuclein. As a result, changes in the protein composition of different biofluids have been explored as an earlier diagnostic strategy, focusing primarily on α-synuclein and its oligomers but also on other proteins including some explored here like CCL-2 and DJ-1.
The biofluids that have been explored most extensively so far have been blood/serum and CSF, although there has also been interest in saliva. Some of the challenges in biomarker identification in these fluids has been the complex composition of blood/serum and the invasiveness of isolation of CSF. As well, α-synuclein content seems to be fairly low in these biofluids and has been below the limits of detection in some assays.
How does your research help overcome these issues?
First, isolation of tears is non-invasive and low risk, unlike isolation of blood or certainly, CSF. Second, tears are highly concentrated in proteins, with basal tears reaching 6–10 mg/ml in protein, which is higher than in saliva. We have found, either because of the higher protein abundance in tears, and/or the active secretion of oligomeric α-synuclein into tears, that the tears seem to be a good source for detection of α-synuclein and its aggregates.
How long do you expect to see oligomeric α-synuclein in basal tears translated to the clinic as biomarkers for PD?
We are optimistic about the potential for its translation to the clinic. We believe a tear-based assay could have tremendous benefits for patients. We are currently engaged in a follow-up study, which is measuring whether oligomeric α-synuclein in tears of patients at different times from diagnosis increases either with disease severity or with increasing time from diagnosis, an additional valuable property of a biomarker. We would also like to test the levels of oligomeric α-synuclein in patients with atypical Parkinsonism to see if it could be beneficial with this patient population. We are eager to identify a partner that can develop a more customized ELISA assay specifically for clinical use. And we are very eager to test our assay across multiple sites, perhaps participating as part of a consortium, to reinforce our findings in a bigger population and to determine how the assay can be scaled across multiple sites.
What next steps are required to get there?
More grant funding would definitely aid us in pursuing each of these goals, as well as identification of additional clinical sites that are willing to partner with us in expanding the use of this assay and demonstrating its utility and scalability.
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