Treatment with the antioxidant metal-alloy nanozyme reduced the build-up (aggregation) and transmission of disease-causing alpha-synuclein protein in the nerve cells and brains of a Parkinson’s disease mouse model, a study reported.
Investigators believe these findings support further research to evaluate nanozymes as a Parkinson’s treatment.
The study, “Nanozyme scavenging ROS for prevention of pathologic α-synuclein transmission in Parkinson’s disease,” was published in the journal Nano Today.
Parkinson’s disease is characterized by the build-up of alpha-synuclein protein fibers (aggregates) called Lewy bodies in the nervous system, particularly in neurons producing dopamine in the brain. Dopamine is a key chemical messenger that carries signals between brain cells.
Recent evidence suggests that alpha-synuclein aggregates first form in the enteric nervous system (ENS) — the nervous system of the gut — then spread along the vagus nerve that connects the stomach and small intestine to the brain.
It is thought that these aggregates spread by triggering the misfolding of normal alpha-synuclein. That in turn leads to more aggregation, thus spreading from one area to another, and driving disease development (pathology).
One known driver of aggregate spreading is oxidative stress, which is an imbalance in the production of reactive oxygen species (ROS) — natural byproducts of metabolism. This imbalance becomes more pronounced with age, and such oxidative stress can lead to cell and tissue damage.
“Oxidative stress caused by reactive oxygen species is inescapable, and increases with age due to mechanistic slowdowns in processes such as protein degradation,” Xiaobo Mao, PhD, assistant professor of neurology at Johns Hopkins University School of Medicine and the study’s senior author, said in a press release.
“This indicates the importance of antioxidants, because in Parkinson’s disease, roaming reactive oxygen species promote the spread of misfolded alpha-synuclein, leading to worse symptoms,” Mao said.
In an attempt to block aggregate spreading, Mao and his team, together with colleagues based in China, developed the antioxidant nanozyme, a metal alloy made of platinum and copper called PtCu bimetallic nanoalloy (NA).
Now, the researchers tested its ability to reduce ROS production and prevent the spread of alpha-synuclein aggregates in cells and in a Parkinson’s animal model.
The alpha-synuclein preformed fibrils (PFF) model was used — a lab-made form of alpha-synuclein protein that, when injected into mice, leads to aggregate formation and spreading. That causes neurotoxicity and motor and non-motor symptoms that mimic sporadic Parkinson’s disease.
After generating PtCu-NAs, tests confirmed their antioxidant properties by showing they behave like two enzymes found in the body, known as catalase and superoxide dismutase, that break down ROSs.
Next, neurons from mice were administered alpha-synuclein fibrils, which increased ROS levels compared with control cells that did not receive these fibrils. Treatment with PtCuNAs significantly decreased the ROS production in these cells.
Exposing cells to alpha-synuclein preformed fibrils led to the accumulation of aggregated alpha-synuclein. Meanwhile, cells treated with the fibrils and PtCu-NA showed a significant decrease in aggregated protein in comparison, as measured by the levels of a Parkinson’s disease marker called pS129, used to assess the levels of alpha-synuclein pathology and transmission.
Because alpha-synuclein aggregation can cause neurotoxicity, neurons were administered preformed fibrils, which induced substantial neurotoxicity. In contrast, PtCu-NA significantly suppressed neurotoxicity in fibril-treated neurons by about 50%. Notably, there also was no significant difference in neurotoxicity between vehicle-treated controls and PtCu-treated neurons.
“These data show that PtCu NAs significantly inhibited the neurotoxicity induced by PFF, and PtCuNAs alone did not exhibit any appreciable neurotoxicity,” the researchers wrote.
To test the ability of PtCu-NAs to block the spreading of aggregates, alpha-synuclein fibril-exposed neurons were grown in a chamber that was connected to another chamber containing neurons treated with PtCu-NAs or vehicle control. Substantial aggregation was seen in vehicle-treated neurons, whereas a significant reduction of the amount of aggression was found in PtCu-treated neurons. Those findings showed PtCu-NAs prevented cell-to-cell transmission.
Finally, to confirm these results in vivo, or in the body, alpha-synuclein fibrils were injected into two-month-old mice in an area of the brain called the striatum. PtCu-NA, meanwhile, was injected into the region of the brain known as the substantia nigra, where dopamine-producing neurons are most affected in Parkinson’s patients.
After two months, an examination of brain tissue found a substantial amount of alpha-synuclein aggregation (by increased pS129 levels) in the substantia nigra of alpha-synuclein-injected mice treated with a control vehicle. In contrast, PtCu-NAs significantly reduced the amount of substantia nigra aggregates.
To assess the impact of PtCu-NAs on aggregate spreading, striatum and substantia nigra tissue were examined in detail, and the levels of soluble, non-aggregated alpha-synuclein and insoluble, aggregated protein were measured.
While there were no differences in the amount of soluble alpha-synuclein following either vehicle or PtCu-NA treatment, PtCu-NA exposure significantly reduced the amount of insoluble alpha-synuclein (which increased in the substantia nigra following fibril injection). That showed that “treatment with PtCu NAs significantly reduced [alpha-syn] transmission induced by PFF in vivo,” the researchers wrote.
“In summary, the PtCu nanozyme exhibits significant efficacy in preventing [alpha-syn aggregation] spreading in sporadic [Parkinson’s disease] models,” they concluded. “These data taken together provide a concept of proof that the redox nanozyme can be considered to be developed as a therapeutic strategy against pathologic [alpha-syn] spreading in [Parkinson’s disease].”
Mao hopes that further research may lead to a Parkinson’s disease therapy that targets the gut.
“We know that the nanoenzymes work when injected directly into the brain,” Mao said. “Now, we’d like to see if the nanoenzymes can block the disease progression induced by pathogenic alpha-synuclein traveling from the gut, across the blood-brain barrier and into the brain.”