Targeting Alpha-Synuclein in the Gut May Slow Down Parkinson's Disease

Scientists are testing the hypothesis that by targeting the gut with a compound that can inhibit the aggregation of alpha-synuclein, they may be able to slow the progression of Parkinson's disease

Amsterdam, NL – Aggregates of the protein alpha-synuclein arising in the gut may play a key role in the development of Parkinson's disease (PD). Investigators are testing the hypothesis that by targeting the enteric nervous system with a compound that can inhibit the intracellular aggregation of alpha-synuclein, they can restore enteric functioning in the short term, and possibly slow the progressive deterioration of the central nervous system in the long term. They review results to date in the Journal of Parkinson's Disease.

"There is growing evidence that PD may start off in the gut, explained senior author Michael Zasloff, MD, PhD, Enterin Inc., Philadelphia, PA, and MedStar Georgetown Transplant Institute, Georgetown University Medical Center, Washington, DC. "The concept is that aggregates of the protein alpha-synuclein, thought to play a key role in the disease, arise within the enteric nervous system (ENS) and travel up the peripheral nerves to the central nervous system (CNS) where they ultimately cause inflammation and destruction of parts of the brain. Targeting the formation of alpha-synuclein aggregates in the ENS may therefore slow the progression of the disease."

Alpha-synuclein is one of the defensive proteins produced by enteric nerves when they encounter infections. In children with acute bacterial gastrointestinal (GI) infections, for example, intestinal nerves produce alpha-synuclein. In children who have undergone intestinal transplants and who are prone to GI infections, investigators have shown that enteric neurons start making alpha-synuclein at the time of acute viral infections, and this outlasts the infection by many months, protecting nerve cells for prolonged periods of time. Within a nerve cell, alpha-synuclein could envelop invading viruses and disrupt their replication. It could also attach itself to small vesicles containing neurotransmitters and be released from the nerve cell hitching a ride with them. Once on the outside, it can attract protective immune cells from surrounding tissues.

Graphic representation of the proposed immune roles of alpha-synuclein within the ENS

"Recent data from our laboratory and others demonstrate that alpha-synuclein is induced in the setting of viral and bacterial infection and serves an immune function by protecting the ENS, by alerting the adaptive immune system and through pre-emptive defense of the CNS in advance of the infectious agent," noted first author Denise Barbut, MD, FRCP, Enterin Inc., Philadelphia, PA. "In the setting of chronic GI infections or impaired intestinal barrier function, when the expression of alpha-synuclein exceeds its clearance, neurotoxic aggregates of alpha-synuclein form damaging aggregates in the ENS and traffic to the CNS."

To determine whether targeting alpha-synuclein within enteric neurons might help patients with PD, Dr. Barbut, Dr. Zasloff and colleagues are currently conducting clinical trials with a compound called ENT-01 (Enterin Inc.). ENT-01 is a synthetic derivative of squalamine, a compound originally isolated from dogfish bile by Dr. Zasloff. It displaces alpha-synuclein from nerve cell membranes and restores the normal electrical activity of enteric neurons. Investigators completed a 50-patient Phase 2a study (RASMET) in patients with PD in 2018, which corrected constipation in more than 80% of participants, with the dose titrated up for each patient until a response was obtained. Constipation is a common symptom of PD.

According to Dr. Barbut, "The RASMET study demonstrated that the ENS is not irreversibly damaged in patients with PD, despite the longstanding constipation that might suggest otherwise. We believe that this is the first demonstration of the reversal of a neurodegenerative process in humans." Beyond the bowel symptoms, possible benefits were also observed in motor and non-motor symptoms such as hallucinations, depression and cognitive function.

A 110-patient double-blind, placebo-controlled Phase 2b trial (KARMET) evaluating the effect of oral ENT-01 tablets on constipation and neurologic symptoms is currently being conducted.

PD is a slowly progressive disorder that affects movement, muscle control and balance. It is the second most common age-related neurodegenerative disorder affecting about 3% of the population by the age of 65 and up to 5% of individuals over 85 years of age.


Full open access study: "Gastrointestinal Immunity and Alpha-Synuclein" by Denise Barbut, Ethan Stolzenberg and Michael Zasloff (DOI: 10.3233/JPD-191702). The article is published in the Journal of Parkinson's Disease, Volume 9, Supplement 2 entitled "The Gut-Brain Axis in Parkinson's Disease Revisited," Guest Editor Teus van Laar, MD, PhD, Director, Parkinson Expertise Center Groningen, Department of Neurology, University Medical Center Groningen, University of Groningen, The Netherlands. It is openly available at:

For additional information and requests for interviews contact Diana Murray, IOS Press (+1 718-640-5678 or To reach the authors, contact Denise Barbut (+1 917 975-1377 or or Michael Zasloff (+1 484-433-7807 or

About this Supplement to JPD: The Gut-Brain Axis in Parkinson's Disease
This special supplement to the Journal of Parkinson's Disease reveals the enormous complexity of the gut-brain axis and demonstrates that there are still unanswered questions. Does PD start in the gut in all patients, or is this potential trigger site relevant only in a small subgroup of patients? What is the role of constipation, and what distinguishes those patients who are not constipated in terms of underlying disease mechanisms? What is the effect of constipation on the microbiome? Does constipation lead to a different subtype of PD? The supplement explores a variety of topics and hopefully will contribute to an improved understanding of the role of the gut in PD, and ultimately stimulate the development of new therapies that improve the lives of patients with PD. This supplement to is openly available at or via the short link

About Journal of Parkinson's Disease
Launched in 2011, the Journal of Parkinson's Disease (JPD) is dedicated to providing an open forum for original research in basic science, translational research and clinical medicine that will expedite our fundamental understanding and improve treatment of Parkinson's disease. The journal is international and multidisciplinary and aims to promote progress in the epidemiology, etiology, genetics, molecular correlates, pathogenesis, pharmacology, psychology, diagnosis and treatment of Parkinson's disease. JPD publishes research reports, reviews, short communications, and letters-to-the-editor and offers very rapid publication and an affordable open access option.

About IOS Press
IOS Press is headquartered in Amsterdam with satellite offices in the USA, Germany, India and China and serves the information needs of scientific and medical communities worldwide. IOS Press now publishes more than 80 international peer-reviewed journals and about 75 book titles each year on subjects ranging from computer science, artificial intelligence, and engineering to medicine, neuroscience, and cancer research.