Neurodegenerative diseases of aging like Parkinson's disease or Alzheimer's disease are usually not diagnosed until the disease has progressed significantly, and symptoms are present. Right not, there is no way to diagnose these disorders before things like brain lesions have occurred, in the case of Parkinsons; or memory loss is happening to Alzheimer's patients. Brain samples can only be analyzed after patients have died. When a diagnosis is made at a late stage, it is harder to apply effective treatments.
Researchers have long been searching for ways to identify these diseases earlier, when treatments might be more effective. Little sacs that cells release and use for signaling, called extracellular vesicles (EVs), may present a diagnostic option for neurodegenerative diseases. Since EVs are present in blood, they could be a noninvasive way to identify people who are at risk of developing brain disorders like Parkinson's. Though much more research will be needed, scientists are making progress in developing an ultra-sensitive assay for this purpose.
One important step will be differentiating between biomarkers that are found inside of EVs, and those that are on the surface of EVs. Researchers have now found a way to do that, with an enzymatic digestion that removes proteins from EV surfaces. After that is performed, the scientists were able to assess the stuff that was only found inside of EVs. The study was reported in the Proceedings of the National Academy of Sciences (PNAS).
In this work, the investigators measured a biomarker of Parkinson's called α-synuclein in blood, and the levels of this protein in EVs. This assay was combined with a very sensitive test to detect a modified type of α-synuclein, which has higher levels of a chemical modification known as phosphorylation during the progression of Parkinson's and Lewy Body Dementia.
The researchers were able to measure higher levels of aberrant α-synuclein protein inside of EVs relative to total plasma. The quantification test the team created utilizes a technique that can separate molecules of different sizes, called size exclusion chromatography (SEC). These hghly sensitive assays can count individual proteins, and have been made for different biomarkers found on EVs.
The scientists also created a test that could detect α-synuclein that is modified or phosphorylated at a particular site called pSer129 as Parkinson's progresses.
This study showed that the majority of α-synuclein that is found in EVs is less than five percent of the α-synuclein that is found freely in blood. The researchers want to eventually measure the α-synuclein in EVs that come from neurons, relative to EVs from blood cells.
"When we applied our advanced methodology to a cohort of blood samples obtained from patients with [Parkinson's] and Lewy Body Dementia as well as healthy control donors, we found that the ratio of phosphorylated α-synuclein relative to total α-synuclein was two to three-fold higher inside EVs relative to outside of EVs," noted co-first study author Tal Gilboa, PhD, a Postdoctoral Fellow at the Wyss Institute.
"This was extremely exciting because it suggests that EVs may protect the phosphorylation state of proteins from circulating phosphatases that would otherwise erase this highly informative mark."
Now, more research will be needed to confirm that this approach can be used to diagnose Parkinson's or other neurodegenerative disorders.
Sources: Harvard University, Proceedings of the National Academy of Sciences (PNAS)