Literature Review

Parkinson’s disease: Is copper culpable?



Copper modifies and accelerates alpha‑synuclein aggregation, offering potential inroads to new methods of detecting and treating Parkinson’s disease, according to investigators. The techniques used in this research also may enable rapid identification of blood-borne cofactors driving abnormal protein development in a range of other neurodegenerative diseases, reported lead author Olena Synhaivska, MSc, of the Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.

Empa researchers Peter Nirmalraj and Olena Synhaivska from the Transport at Nanoscale Interfaces lab and Silvia Campioni from the Cellulose & Wood Materials lab (from right to left) decipher important steps in the molecular disease process of Parkinson's. Empa

Empa researchers Peter Nirmalraj, Olena Synhaivska, and Silvia Campioni (from right to left) decipher important steps in the molecular disease process of Parkinson's disease.

“While alpha‑synuclein oligomers are the known neurotoxic species in Parkinson’s disease, the development of effective anti–Parkinson’s disease drugs requires targeting of specific structures arising in the early stages of alpha‑synuclein phase transitions or the nucleation-dependent elongation of oligomers into protofibrils,” the investigators wrote in ACS Chemical Neuroscience. “In parallel, advanced methods are required to routinely characterize the size and morphology of intermediary nano- and microstructures formed during self-assembly and aggregation in the presence of aqueous metal ions to track disease progression in, for example, a blood test, to provide effective personalized patient care.”

Pathologic aggregation of alpha‑synuclein

To better understand the relationship between copper and alpha‑synuclein, the investigators used liquid-based atomic force microscopy to observe the protein in solution over 10 days as it transitioned from a simple monomer to a complex, three-dimensional aggregate. Protein aggregation occurred in the absence or presence of copper; however, when incubated in solution with Cu2+ ions, alpha‑synuclein aggregated faster, predominantly forming annular (ring-shaped) structures that were not observed in the absence of copper.

Alpha-synuclein in the form of fibrils (left). When the protein is placed in a solution containing copper, ring-like structures form instead (right). Empa

Alpha-synuclein in the form of fibrils (left). When the protein is placed in a solution containing copper, ring-like structures form instead (right).

These annular oligomers are noteworthy because they are cytotoxic, and they nucleate formation of alpha‑synuclein filaments, meaning they could serve as early therapeutic targets, according to the investigators.

The above experiments were supported by Raman spectroscopy, which confirmed the various superstructures of alpha‑synuclein formed with or without copper. In addition, the investigators used molecular dynamics computer simulations to map “the dimensions, supramolecular packing interactions, and thermodynamic stabilities” involved in aggregation.

These findings “could potentially serve as guidelines for better understanding protein aggregated states in body fluids from individuals who have been exposed to environmental metals over their lifetime,” the investigators wrote. “The nanoscale imaging, chemical spectroscopy, and integrated modeling-measurement methodologies presented here may inform rapid screening of other potential blood-borne cofactors, for example, other biometals, heavy metals, physiological amino acids, and metabolites, in directing and potentially rerouting intrinsically disordered protein aggregation in the initiation and pathology of neurodegenerative diseases.”

What is copper’s role in Parkinson’s disease pathogenesis?

In a joint written comment, Vikram Khurana MD, PhD, and Richard Krolewski MD, PhD, of Brigham and Women’s Hospital and Harvard Medical School, Boston, said, “This study is important in that it demonstrates that the presence of copper can accelerate and alter the aggregation of wild type alpha‑synuclein. We know that pathologic aggregation of alpha‑synuclein is critical for diseases like Parkinson’s disease known as synucleinopathies – so any insight into how this is happening at the biophysical level has potential implications for altering that process.”

Vikram Khurana MD, PhD, of Brigham and Women's Hospital and Harvard Medical School, Boston

Dr. Vikram Khurana

While Dr. Khurana and Dr. Krolewski praised the elegance of the study, including the techniques used to observe alpha‑synuclein aggregation in near real-time, they suggested that more work is needed to determine relevance for patients with Parkinson’s disease.

Richard Krolewski MD, PhD, of Brigham and Women's Hospital and Harvard Medical School, Boston.

Dr. Richard Krolewski

“It is not clear whether this process is happening in cells, how alpha‑synuclein fibrils might be directly exposed to copper intracellularly (with most of the copper being bound to proteins), and the relevance of the copper concentrations used here are in question,” they said. “Substantially more cell biology and in vivo modeling would be needed to further evaluate the connection of copper specifically to synucleinopathy. All this notwithstanding, the findings are exciting and intriguing and definitely warrant follow-up.”

In the meantime, an increasing number of studies, including a recent preprint by Dr. Khurana and Dr. Krolewski, are strengthening the case for a link between copper exposure and Parkinson’s disease pathogenesis. This body of evidence, they noted, “now spans epidemiology, cell biology, and biophysics.”

Their study, which tested 53 pesticides associated with Parkinson’s disease in patient-derived pluripotent stem cells, found that 2 out of 10 pesticides causing cell death were copper compounds.

“Ongoing work will explore the mechanism of this cell death and investigate ways to mitigate it,” said Dr. Khurana and Dr. Krolewski. “Our hope is that this line of research will raise public awareness about these and other pesticides to reduce potential harm from their use and highlight protective approaches. The study by Dr. Synhaivska and colleagues now raises the possibility of new mechanisms.”

The study by Dr. Synhaivska and colleagues was supported by grants from the Swiss National Science Foundation and the Science Foundation Ireland. The investigators disclosed no conflicts of interest. Dr. Krolewski has been retained as an expert consultant for plaintiffs in a lawsuit on the role of pesticides in Parkinson’s disease causation.

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