November 13, 2024 | Researchers in Israel recently showcased a novel platform that can be used in the future for the early diagnosis of Parkinson’s disease (PD) by quantifying the distribution of alpha-synuclein (α-syn) in skin biopsies. A proof-of-concept study in humans, supported in part by the Michael J. Fox Foundation, suggests the single-molecule-level detection method might enable the disease to be detected up to 20 years before the first motor symptoms appear.
The small-sized α-syn aggregates, known as oligomers, are the toxic ones believed to be the primary cause of damage to dopamine-producing neurons in the brain—not the much larger, more stable Lewy bodies that are hallmarks of the disease—and could be spotted with a super-resolution microscope used in the study, published in Frontiers in Molecular Neuroscience (DOI: 10.3389/fnmol.2024.1431549).
The analysis found a higher number of these aggregates in seven PD patients than in a matched set of healthy controls as well as differences in aggregate size, density, and number of molecules per aggregate, reports Uri Ashery, Ph.D., a neurobiology professor at Tel Aviv University. Damage to nerve cells was also seen in areas of the skin having a large concentration of the pathological-type α-syn protein.
Images produced by direct stochastic optical reconstruction microscopy (dSTORM) were coupled with computational tools and highlighted the potential of the approach as a quantitative assay for the small α-syn oligomers, Ashery says. If optimized for high throughput, it theoretically could also function as a companion diagnostic for PD therapies being investigated in a clinical trial.
Many other neurological disorders, including Alzheimer’s disease as well as amyotrophic lateral sclerosis and Huntington’s disease, are likewise associated with a protein that pathologically aggregates, he adds. The platform therefore might be used more broadly to quantify and analyze those aggregates.
Parkinson’s disease is currently diagnosed based primarily on clinical symptoms such as tremors or gait dysfunctions, alongside relevant questionnaires, says Ashery, rather than any sort of quantitative, non-biased assessment of patient status or biological biomarker. It can't be definitively diagnosed before motor symptoms appear, since the α-syn aggregates in the nuclei of brain cannot be detected by current methods. And by that time, between 50% to 80% of the brain’s dopaminergic neurons are already dead.
While scientists have been looking for these aggregates in skin biopsies for more than 10 years now, the methods have yet to prove good enough for clinical adoption based on their ability to accurately identify people who do and don’t have the disease, he adds. One of the main obstacles has been capturing small aggregates below the resolution of conventional light microscopy, which was overcome using the dSTORM method.
The analyzed skin biopsy images in the latest study were composed of many points that each represented a normal or abnormal (phosphorylated) α-syn molecule to define both the number of aggregated regions and the molecules therein, says Ashery. This effectively enabled the differentiation and characterization of the small toxic aggregates and thus their potential role as a new molecular biomarker for PD.
If the super-resolution microscopy platform performs well in larger clinical studies, it might be used in the future to identify patients for alpha-synuclein targeting therapies, several of which are now under development.
In a previous preclinical study using mice with a truncated form of alpha-synuclein that creates PD-like symptoms, Ashery and his colleagues used the same technique to find an increase in the pathological oligomers at several time points as the disease progressed. They also showed that a drug—known as anle138b, developed by the German biotech company MODAG—relieved some of the motor symptoms and small α-syn aggregates in the brain. Teva Pharmaceutical and MODAG subsequently announced a strategic collaboration on clinical development of the compound.
The dSTORM method is now widely deployed, primarily in basic research, he says. Several big-pharma companies are applying the method to understanding the mechanism of action of α-syn aggregation inhibitors. But the platform is increasingly being used by research groups for clinical analysis in human patients.
Next steps include a new study enrolling 45 patients and 45 healthy controls, Ashery says, and funding is being raised for another follow-up study with family members in their 30s, 40s, and 50s who are at risk for Parkinson’s disease. The targets are family members of PD patients who carry two mutations widespread among Ashkenazi Jews that increase the risk for the disease.
PD patients in the initial study were being treated at a trio of locations—Tel Aviv Sourasky Medical Center, Meir Medical Center, and Sheba Medical Center—each having a specialist in Parkinsonian motor dysfunction, he adds. People genetically at risk for PD are also routinely assessed there.
The 90-subject study seeks to pinpoint the exact juncture at which a normal quantity of alpha-synuclein turns into a pathological aggregate, says Ashery. A machine learning algorithm will also be developed to identify correlations between the results of motor and cognitive tests and molecular findings under the microscope.
Alpha-synuclein is a necessary protein found in essentially every nerve cell in the brain and allows them to communicate via the release of neurotransmitters including dopamine, the most important neurotransmitter in PD, as well as other chemicals such as serotonin and norepinephrine, he says. It’s a problem only when it aggregates into toxic oligomers, contributing to development of the devastating neurodegenerative brain disorder.
Groups around the world are trying to develop methods and means to diagnose PD, which might provide additional barometers for quantifying development of the disease and more effective therapies for treating it, Ashery points out. A clinical trial is already underway testing a drug’s ability to hinder formation of the aggregates causing the disease.
A handful of medicines are also on the market with more on the way to address some of the non-motor symptoms of PD, he adds. Emerging analysis methods, including the new super-resolution microscopy platform, could aid in personalizing those therapies to individuals and tracking their response—and, ultimately, perhaps prevent the disease entirely.