Researchers at Harvard University and the University of Pennsylvania have developed a highly accurate test to measure proteins present inside extracellular vesicles in the body, which they hope will lead to a blood test for Parkinson’s disease and other conditions in the future.
Extracellular vesicles are small lipid encapsulated particles released from most cells. They range in size, but most are smaller than 200nm. Due to the fact that they help different parts of the nervous system communicate, researchers believe they have the potential to be good biomarkers for neurodegenerative diseases such as Parkinson’s.
Measuring the contents of extracellular vesicles and also working out how much of a given protein is inside the vesicle or outside in the plasma is hard. Lead investigator David Walt, PhD, a professor at Harvard University and Brigham and Women’s Hospital, and colleagues think they have come one step closer to creating a blood test for Parkinson’s by creating a highly accurate test that can measure how much alpha-synuclein is in extracellular vesicles versus free plasma.
Alpha-synuclein is a protein mostly expressed in the neurons of the central nervous system. It has been linked to neurodegenerative disorders such as Parkinson’s disease and Dementia with Lewy bodies, although its precise function is still not totally clear.
Parkinson’s and other neurodegenerative conditions like Alzheimer’s disease can be hard to diagnose in their early stages. Although a cure is not available for these conditions, there are treatments that can help, and these are most effective at an early stage of the disease. Therefore, an effective blood test that could pick up early signs of Parkinson’s would be very helpful to both clinicians and patients.
As reported in the journal PNAS, Walt and team used a combination of high-yield size-exclusion chromatography, a protease protection assay and a Single Molecule Array (Simoa) digital enzyme-linked immunoassay (ELISA) to accurately measure proteins inside extracellular vesicles.
They used this technique to measure alpha-synuclein in these vesicles versus the plasma and found that only a small amount of this protein is found inside extracellular vesicles. They also managed to create a test that would specifically look for alpha-synuclein that is phosphorylated at the Ser129 residue, a precursor to the formation of Lewy bodies seen in Parkinson’s and similar disorders.
“Research on extracellular vesicles in our and other groups over the last few decades has steadily advanced our understanding of their complex biology and molecular composition. Yet, the isolation of pure tissue-specific extracellular vesicles from body fluids like blood or the cerebrospinal fluid surrounding the central nervous system, including the brain, and validating and quantifying their true contents with precise measurements still present formidable technical challenges,” said Walt in a press statement.
“Our recent work is providing a solution to help fill this technological gap and gets us closer to being able to obtain extracellular vesicles free from contamination in order to use them as rich sources for clinical biomarkers, as we show with the example of phosphorylated ⍺-synuclein.”
