Enhanced Ultra-Sensitive Protocol Detects Parkinson’s Disease Proteins in Extracellular Vesicles in Blood

Brain disorders such as Parkinson’s Disease (PD) and Alzheimer’s Disease (AD) often begin developing well before the onset of noticeable clinical symptoms. Early intervention could potentially slow or halt disease progression, but current methods do not allow for the diagnosis of these disorders at pre-symptomatic stages. For instance, the specific brain lesions associated with PD can only be identified through brain biopsies, which are typically performed posthumously. To address this significant challenge, researchers are exploring the concept of “liquid biopsies,” which facilitate the non-invasive extraction of blood or other bodily fluids for analysis of molecules derived from the brain and other solid tissues.

One particularly promising target in body fluids is “extracellular vesicles” (EVs), which are tiny membrane-bound sacs released by brain cells and other types of cells into surrounding fluids. These vesicles contain various molecules that can be specific to the cell types that produce them, including those from the brain, potentially serving as protected biomarkers for the early detection of Parkinson’s and other neurological diseases. Despite recent advancements, experts in EV research have struggled with determining whether specific biomarker molecules measured in isolated EVs are strictly contained within these vesicles or merely bound to their surface. This uncertainty has hindered their ability to draw clear conclusions about the cargo molecules present in EVs from various tissues.

Image: Measuring the true content of extracellular vesicles in blood (Photo courtesy of Wyss Institute at Harvard University)

Now, a collaborative research team, including scientists from the Wyss Institute at Harvard University (Boston, MA, USA), has addressed this issue by incorporating a vital step into an already validated ultra-sensitive protocol. By enzymatically digesting all surface-bound proteins from a purified EV population, they successfully focused on the cargo protected inside the EVs while eliminating non-specific contaminants. Utilizing their improved protocol to measure the PD biomarker ⍺-synuclein in blood, the researchers were able to accurately differentiate the small fraction of protein contained within EVs from the total amount present in blood plasma for the first time. Notably, they combined this advancement with a newly developed ultra-sensitive detection assay for a phosphorylated form of ⍺-synuclein, which increases during the progression of PD and the related Lewy Body Dementia. After analyzing a cohort of patient samples, the researchers found an enrichment of the pathological ⍺-synuclein protein within EVs compared to total plasma. These findings have been published in Proceedings of the National Academy of Sciences (PNAS).

“Research on EVs 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 EVs 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 David Walt, Ph.D. at the Wyss Institute at Harvard University who led the research team. “Our recent work is providing a solution to help fill this technological gap, and gets us closer to being able to obtain EVs free from contamination in order to use them as rich sources for clinical biomarkers, as we show with the example of phosphorylated ⍺-synuclein.”