September/October 2022

Neurology: Researchers Make Progress in Early Detection of Parkinson’s Disease
By Jennifer Lutz
Today’s Geriatric Medicine
Vol. 15 No. 5 P. 28

Because Parkinson’s disease is known as a progressive neurological disease, most treatments have been aimed at slowing its progression. Therapies ranging from increased exercise to deep brain stimulation have ameliorated symptoms. Other treatments include medications, cannabis-based therapies, diet, speech therapy, and dopamine agonists, including L-DOPA.1 The commonality between these interventions is that they all begin after diagnosis. At this point, the major regulatory system indicated in Parkinson’s is irreversibly damaged. For years, researchers have been searching for a way to diagnose Parkinson’s before its clinical presentation, giving practitioners the opportunity to postpone its development rather than slow it. Now, they may have.

Gene Mapping and Bio Markers
It’s necessary to understand the hurdles to discuss different methods of early detection. In Parkinson’s disease, neurons break down and die — particularly neurons in regions of the brain called the nigrostriatal and the substantia nigra, which are responsible for dopamine production. The clinical stage of Parkinson’s disease is marked by symptoms of dopamine deficiency, including tremors, slowed movement (bradykinesia), rigid muscles, impaired posture and balance, loss of automatic movements, changes in speech, and changes in writing. Even when diagnosed early, most people with Parkinson’s disease have already lost 60% to 80% of their dopaminergic neurons. Because there are no diagnostic criteria for preclinical Parkinson’s disease, by the time a patient is diagnosed, this dopaminergic regulatory system is severely damaged, and symptoms can’t be reversed, only relieved.1

What if these dopaminergic neurons showed impairment before their breakdown and death? A group of researchers from IDIBELL and the University of Barcelona led by Antonella Consiglio, PhD, group leader at IDIBELL, ICREA Academy researcher, and a professor at the University of Barcelona’s Faculty of Medicine and Health Sciences and Institute of Biomedicine, have identified early functional deficiencies, before neuron death, in patients with genetic Parkinson’s disease.

To conduct the study, the team used induced pluripotent stem cell (iPSC) technology, which enables the creation of patient-specific, disease-relevant, cell-based experimental models of human diseases. iPSC models can produce some of the earliest signs of a disease, even at presymptomatic stages. By separating pluripotent stem cells of healthy individuals from those with genetic Parkinson’s disease, the researchers were able to observe differences at a preclinical level. The dopaminergic neurons of people with Parkinson’s disease were more spontaneously active and presented more explosive episodes than those of people without the disease. These explosive episodes could contribute to the pathogenesis of Parkinson’s.

The results of this study could initiate steps forward in the diagnosis of preclinical Parkinson’s. Consiglio explains that this research could allow the identification of key molecular events involved at the early stages of Parkinson’s disease, which could be exploited for therapeutic intervention. Moreover, the study, which was limited to patients with genetic Parkinson’s disease (about 5% of known cases), suggests the role of iPSC in the presymptomatic evaluation of neurodegenerative disorders. “Although it is unknown the cause of the disease in idiopathic patients, a relevant proportion of them have LRRK2 polymorphisms, and LRRK2 function appears dysregulated even in the absence of LRRK2 mutations/polymorphisms,” Consiglio explains. “Also, disease progression in LRRK2–G2019S carriers is clinically indistinguishable from idiopathic cases, suggesting common disease mechanisms.”

Many researchers have focused on people with a family history of Parkinson’s disease, and mutations in the LRRK2 gene are the most commonly known genetic cause. These studies implicate lysosomal and mitochondrial dysfunction and inflammation in disease pathogenesis.2

Intraneuronal accumulation of α-synuclein is the major pathological hallmark of Parkinson’s disease, but it’s not clear when these problems begin.

Other research suggests that nonmotor symptoms, such as anxiety, depression, and idiopathic anosmia, may predate motor symptoms, but these symptoms are found in many disorders and are often overlooked. Parkinson’s is known to begin long before it’s diagnosed, but the isolation of early symptoms continues to evade the medical sciences—even if the neurons themselves provide clues.

How can science untangle preclinical symptoms from those that occur after a significant loss of dopaminergic function? Researchers in Russia have been examining exactly that. The goal is to identify biomarkers in body fluids that could signal the development of the disease. Discovering those biomarkers is a multistep process.

“The most important takeaway is that neurodegenerative diseases like Parkinson’s and Alzheimer’s begin 20 to 30 years before we see symptoms; at this point, the regulatory systems are already almost completely destroyed. The only conclusion is that it’s absolutely necessary to develop preclinical diagnostic criteria so we can apply neuroprotective therapies in the early stages of the disease,” says Michael V. Ugrumov, MD, PhD, head of the Laboratory of Neural and Neuroendocrine Regulations Koltzov at the Institute of Developmental Biology RAS. Ugrumov explains the importance of Parkinson’s being a systematic disease; it means other clinical signs—premotor symptoms and biomarkers in body fluids—precede the death of dopaminergic neurons, and it’s why previous research has focused on uncovering such biomarkers.

To differentiate clinical indicators from preclinical indicators, Ugrumov and colleagues compared biomarkers of clinical Parkinson’s disease in human models to biomarkers of preclinical Parkinson’s in mice models.3 “The idea is to research Parkinson’s in humans in tandem with animal models. We focus on select markers from the clinical stage of Parkinson’s in humans that we also observed in the preclinical stage of animal models,” Ugrumov says. The researchers discovered that 25% of all markers found in patients with clinical Parkinson’s were also found in the preclinical animal models. “It is believed that only these markers can be used to diagnose Parkinson’s at the preclinical stage,” he adds.

The researchers understood the importance of producing the same metabolic pathogenesis of Parkinson’s that’s been identified in humans in the mice model. To achieve this, the researchers reproduced Parkinson’s in mice by administering a toxin of dopaminergic neurons. The hypothetical preclinical biomarkers of Parkinson’s disease were represented by a reduced concentration of L-DOPA and DOPAC in plasma and a change in the gene expression of a dopamine receptor (D3) in lymphocytes.

The comparison of clinical Parkinson’s in humans with preclinical Parkinson’s in animals was just the first step—the results aren’t conclusive enough to design diagnostic protocol. The next step was to find these clinical markers in people at risk for Parkinson’s—selected by premotor symptoms, PET scans, and known biomarkers.

Provocative Tests — Applying Internal Medicine to Neurological Diagnostic
A provocative test predicts a person’s risk for developing a disease by deliberately provoking characteristic aspects of the disease. For example, an oral glucose tolerance test is widely used to detect the abnormal regulation of glucose metabolism in diabetics. Provocative tests are common in internal medicine but, according to Ugrumov, haven’t been applied to testing chronic brain diseases at the preclinical stage. “The provocative allows us to make a specific test for a chronic disease,” he says. The researchers based their study on the knowledge that in Parkinson’s motor symptoms appear at the threshold of degradation of the nigrostriatal dopaminergic system, with a loss of 70% dopamine in the striatum and 50% to 60% dopaminergic neurons in the substantia nigra. They used α-methyl-p-tyrosine (αMpT) as a provocative agent, which has a dose-dependent reversible short-term inhibitory effect on tyrosine hydroxylase, inhibiting dopamine synthesis.

Ugrumov and colleagues first found the dose that would surpass the threshold for dopamine loss and cause motor symptoms in the mice without preclinical Parkinson’s symptoms—170 mg/kg. Next, they confirmed that a lower dose of 125 mg/kg did not cross that threshold or initiate motor symptoms in mice exhibiting biomarkers of preclinical Parkinson’s. Then, the team administered a 125 mg/kg dose to mice that exhibited the preclinical signs of Parkinson’s disease as predicted from their previous study. Having received this 125 mg/kg dose, the mice displayed symptoms of clinical Parkinson’s disease. The results confirmed these preclinical signs as potential biomarkers for early diagnosis.

“For the development of any technology, we must first prove it’s not toxic by testing it in animal models. Next, we move to clinical trials in humans,” Ugrumov says. Proving safety was the main goal of the study. “Because we used an inhibitor that is reversible and cannot be metabolized by the body, it provokes the loss of dopamine for only a short time; it is then eliminated from the body.” In the mice models, the dopamine content in the striatum returned to a normal level, followed by normalization of motor behavior within 24 hours of administering the inhibitor. There were also no structural or functional changes in the nigrostriatal dopaminergic system one week later. However, the researchers did note that intranasal administration of the inhibitor (αMpT) is important to avoid decreased content of catecholamines in the brain and peripheral nervous system, which is an effect of systematic administration.

Early Diagnosis to Early Treatment
Without early treatments, patients are unlikely to benefit greatly from early diagnosis. “I always say, show me the situation in which we developed a treatment before a diagnosis,” Ugrumov says. “Also, we already know various neuroprotectors, so if we can diagnose early, we’d be able to select neuroprotectors that are most precise—we could also potentially combine therapies,” he says. Indeed, many studies are testing the potential of neuroprotective agents—none have shown great success, but there have been some promising results. Among the agents being studied are antidiabetics, such as exenatide. Anticancer drugs such as nilotinib are also being studied, along with glutamate receptor agonists. Another future treatment option could be neurotrophic factors.

The accumulation of α-syn is an example of a targeted biomarker. As researchers learn more about early biomarkers, research can continue to become more specific and targeted.

The Beginning of Novel Treatments in Neurodegenerative Disease?
Parkinson’s is the second most common neurodegenerative disease in the United States; Alzheimer’s is the first. Both are systemic diseases. Many researchers, including Ugrumov, believe that developing a method for early diagnosis of one neurological disease could be universally applied to others. Because neurodegenerative diseases are systemic, the key is finding the earliest pathologies—sort of like finding the first knot in your tangled headphones. For example, tau proteins are indicated in the pathologies of both Alzheimer’s and Parkinson’s, but tau is one of many pathologies. By the time patients are in the clinical stage of disease progression, multiple biomarkers are already present. This is evident when we hear researchers debate whether tau proteins or amyloid proteins are the initiating factor in Alzheimer’s. Knowing what comes first could mean a breakthrough in treatment, but once a certain amount of damage is done, neurodegenerative diseases cascade, and providers are left to treat the symptoms. The recent progress in the early diagnosis of Parkinson’s is no small feat—it could be the model for early diagnosis of neurodegenerative disease.

— Jennifer Lutz is a freelance journalist who covers health, politics, and travel. She’s written for both consumer and professional medical magazines as well as popular newspapers. Her writing can be found in Practical Pain Management, Endocrine Web, Psycom Pro, The Guardian, New York Daily News, Thrive Global, BuzzFeed, and The Local Spain. In addition to journalism, Lutz works as a strategies and communication consultant for nonprofits focused on improving community health.

References
1. Parkinson's disease: challenges, progress, and promise. National Institute of Neurological Disorders and Stroke website. https://www.ninds.nih.gov/health-information/patient-caregiver-education/hope-through-research/parkinsons-disease/parkinsons-disease-challenges-progress-and-promise. Accessed July 4, 2022.

2. Ntetsika T, Papathoma PE, Markaki I. Novel targeted therapies for Parkinson’s disease. Mol Med. 2021;27(1):17.

3. Ugrumov M. Development of early diagnosis of Parkinson's disease: illusion or reality? CNS Neurosci Ther. 2020;26(10):997-1009.

4. Salamon A, Zádori D, Szpisjak L, et al. Neuroprotection in Parkinson’s disease: facts and hopes. J Neural Transm. 2020;127:821-829.

5. Henderson MX, Sengupta M, Trojanowski JQ, et al. Alzheimer’s disease tau is a prominent pathology in LRRK2 Parkinson’s disease. Acta Neuropathol Commun. 2019;7(1):183.