A Review of Stem Cell–Based Therapies for Parkinson Disease

In assessing treatment for Parkinson disease (PD), the current standard of care involves levodopa, potentially in combination with carbidopa, to address the loss of dopamine known to occur as the condition progresses. However, several innovations in therapy for PD have occurred in recent years, particularly deep brain stimulation and the potential use of stem cells.

Discussing in a review published in International Journal of Molecular Sciences, researchers Zhaohui Liu, PhD, MSc, and Hoi-Hung Cheung, PhD, sought to discuss the development of new therapeutic strategies that have led to the initiation of exploratory clinical trials, particularly the application of stem cells for the treatment of PD.

Delving into the use of stem cell–based treatments in PD, the researchers say that several important pathways have emerged as targets for potential therapeutic intervention.

“Conventional therapeutic strategies for relieving the symptomatic stages of PD remain, but with new genetic insights, it may be possible to use preventive neuroprotective treatments for people at risk of developing PD,” they highlight. “In parallel with efforts to prevent and control symptomatic PD, researchers are also investigating stem cells as replacements for diseased neurons or degenerated tissues.”

As they note, dopaminergic (DA) cell transplantation is believed to be the most promising cell replacement therapy. Aligned with this approach, a recent novel treatment showcased the plausibility of reprogramming the skin cells of a single patient with PD to take on the characteristics of DA neurons and replace damaged brain cells. In their findings, the patient exhibited improvements in quality of life and day-to-day activities requiring motor skills. However, as this treatment was performed on only 1 person, the researchers cautioned that larger, diverse clinical studies are needed to demonstrate further efficacy and long-term results.

Other notable stem cell–based treatments include:

• Transplantation of fetal ventral mesencephalon (VM) tissue cells to the brains of patients with PD. Fetal VM tissue cells consisted of distinct neuronal populations, including DA neurons of the substantia nigra and ventral tegmental areas, oculomotor neurons, and reticular neurons.
• Transplantation of mesenchymal stem cells (MSCs), which can be isolated from various sources, including adipose tissue and peripheral blood from adult tissues. MSCs have been proven to be beneficial for treating many diseases, including PD, with clinical trials currently underway using MSCs as a therapeutic agent for the condition.

“Although we are not yet examining a disease-modifying treatment, stem cell transplantation has the potential to be at the forefront of such PD treatments in the future,” conclude the researchers. “The transplantation process and the procedures required for its optimization are still not fully understood, and further research is required to achieve treatment for PD.”

Reference

Liu Z, Cheung H-H. Stem cell-based therapies for Parkinson disease. Int J Mol Sci. Published online October 29, 2020. doi:10.3390/ijms21218060