Mass spectrometry imaging (MSI) enables the detection of neuroactive compounds and metabolites within a single tissue section and has firmly established its value as a powerful tool in advancing research into neurological disease. Parkinson's disease is a chronic, progressive neurological disorder that affects movement in the body in more than 1.1 million people in the United States alone, with 90,000 new diagnoses annually.1
Chronic diseases are the leading drivers of healthcare costs in the USA and account for 90 percent of the nation's $5.3 trillion in annual health care expenditure.2 As healthcare costs spiral, building our understanding of Parkinson’s disease helps guide research, improve use of resources and develop better treatment. Growing our knowledge of its causes, as well as the conflicting side effects of a therapeutic drug used to alleviate its symptoms, levodopa (L-DOPA), is key in managing its diagnosis, progression, and care.
The Spatial Mass Spectrometry group at Uppsala University in Sweden is conducting ground-breaking Parkinson’s disease. The group focuses on a specific stage of the disease called L-DOPA-induced dyskinesia (LID), which develops in approximately 40 percent of patients after five to six years of treatment with the L-DOPA therapy.3
What are the characteristics of Parkinson’s disease?
Parkinson’s disease is a progressive and incurable neurodegenerative disease characterized by motor dysfunction, resting tremor, bradykinesia (slowness of movement), muscle rigidity, and postural instability.
These symptoms result primarily from the loss of dopamine-producing neurons in the substantia nigra pars compacta of the brain, leading to reduced dopamine levels in the striatum, a brain region essential for movement control. The primary treatment for Parkinson’s is L-3,4-dihydroxyphenylalanine (levodopa, or L-DOPA), a precursor to dopamine that crosses the blood-brain barrier and is converted into dopamine in the brain. L-DOPA therefore restores dopamine levels and improves motor symptoms, but it neither replaces the lost dopaminergic neurons nor halts disease progression.
While L-DOPA is highly effective during the early stages of Parkinson’s disease, long-term treatment is often complicated by LID, a treatment-limiting complication characterized by involuntary, erratic, and uncontrollable movements that can severely compromise an individual’s quality of life.
The pathophysiology of LID is poorly understood. A key unanswered question is why only certain individuals are susceptible. The research group in the Department of Pharmaceutical Biosciences at Uppsala University is using MSI to investigate brain neurochemical alterations that are linked with LID, working with animal models and human blood–cerebrospinal fluid (CSF) biobank samples supplied by collaborators at the Karolinska Institute, Stockholm, Bordeaux University, and King’s College London.
MS imaging: supporting advances in Parkinson’s disease understanding
MSI is a label-free mass spectrometry tool that can be used to map the spatial distribution of molecules such as neurotransmitters, lipids, neuropeptides, proteins and metabolites directly within thin tissue sections. Unlike traditional MS, it provides an additional identification parameter by enabling the accurate simultaneous determination of multiple compounds in tissues and their distributions. This quantitative regional mapping and high-resolution visualization of molecular change supports research into neurodegenerative disease.
The research group at Uppsala University is focused on imaging the spatial distribution of the neurotransmitters (the brain’s signaling molecules) that are known to be affected by Parkinson’s disease. A groundbreaking new method that images neurotransmitters in a specific brain region has been developed that provides a different view of the brain and the transmitters involved. This method uses matrix-assisted laser desorption/ionization (MALDI)-MSI to facilitate the simultaneous measurement and quantification of different neurotransmitters and their metabolites and precursors.4, 5
MSI reveals elevated L-DOPA levels throughout the brain
A study6 used ultrahigh mass resolution Fourier transform ion cyclotron resonance (FTICR) MALDI-MSI (7T solariX XR, Bruker Daltonics) to map the spatial distribution of L-DOPA and metabolites associated with monoaminergic pathways in the brains of dyskinetic and non-dyskinetic animal models. This approach enabled the simultaneous imaging and identification of numerous neurotransmitters and metabolites.
Compared with non-dyskinetic animals, dyskinetic animals exhibited elevated levels of L-DOPA and its metabolite 3-O-methyldopa in all brain regions examined. Increases in dopamine and metabolites were noted in all regions analyzed, except the striatum.
These findings suggest that dopamine formation from exogenous L-DOPA is not tightly regulated in extrastriatal brain regions, raising the possibility that dopamine, and perhaps L-DOPA itself, could modulate neuronal signaling across widespread brain areas and contribute to adverse effects of L-DOPA therapy.
MALDI-MSI reveals altered neuropeptide signaling and processing
MALDI-MSI using FTICR was also used to map and compare neuropeptides in brain samples from the same cohort of animals from the previously described model of Parkinson’s disease.7 Dyskinesia severity was associated with higher levels of several abnormally processed neuropeptide fragments in multiple brain regions. Such processing can alter how these molecules interact with their receptors and, consequently, how they affect neuronal signaling.
At the same time, levels of several biologically active neuropeptides in basal ganglia regions involved in movement control correlated with L-DOPA concentrations in the putamen, but not with dopamine concentrations. This suggests that these neuropeptide systems are sensitive to the availability of L-DOPA itself. Overall, LID was associated with both increased neuropeptide levels and abnormal neuropeptide processing throughout the basal ganglia. These changes may represent a compensatory response to elevated L-DOPA levels, although their precise biological consequences remain to be determined.
Linking spatial lipidomics and neurotransmitter dysregulation in LID
Spatial lipidomics using MALDI-MSI has emerged as an important area of metabolomics research, particularly in the study of neurodegenerative diseases. Lipids are implicated in numerous aspects of Parkinson’s disease pathophysiology; however, their role in the development and progression of LID is still insufficiently understood.
High resolution FTICR MALDI-MSI was used in a study8 to map brain region-specific alterations of glycerophospholipids and sphingolipids in the same animal model cohort of Parkinson’s with and without LID following long term L-DOPA treatment. Spatial lipidomic analysis identified region-specific lipid dysregulation as a novel aspect of LID pathology, highlighting lipid pathways as potential targets for future research. Because lipid alterations correlated strongly with dyskinesia severity, dopamine and L-DOPA concentrations, this supports a mechanistic link between lipid metabolism, neurotransmitter dysregulation and LID.
Building a better understanding of LID
MSI will continue to play a critical role in advancing our understanding of the molecular mechanisms underlying Parkinson’s disease. Adopting an integrated approach facilitates precise measurements of metabolites across brain tissue regions for a deeper understanding of the disease, its progression pathways, and its treatment.
About the authors
Dr. Per Andrén originally earned his MSc in Pharmacy and his PhD in Medical Sciences (Psychiatry) at Uppsala University, Sweden. Following his doctoral studies, he served as a postdoc in Professor Richard Caprioli's group during the early days of electrospray development, emerging as a veteran in the field of mass spectrometry. He later returned to Uppsala University, where he was appointed as the world’s first Professor of Mass Spectrometry Imaging in the Department of Pharmaceutical Biosciences. Today, Dr. Andrén directs his research toward advancing MSI methods for biological systems. His work focuses heavily on the brain and neurodegenerative disorders, with a specialized emphasis on Parkinson’s disease.
Dr. Michael Easterling is Vice President of MALDI Imaging at Bruker Daltonics. Following his PhD in Chemistry from The University of Georgia, Dr. Easterling has worked at Bruker Daltonics for almost 25 years, specializing in MALDI mass spectrometry. Dr. Easterling focuses on multimodal spatial analysis, more recently integrating mass spectrometry imaging with transcriptomics and proteomics to advance understanding of complex biological systems, including neurodegenerative disease.