Saw this being posted by science of pd on twitter. Did not come across this previously, from what I understand the natural supplement would be gromwell extract, which I did not immediately find as a dietary supplement, but rather as an ingredient for skincare products.
The paper is behind paywall so not able to see dosages applied. I did find this on toxicity, which sounds like it should be well tolerated.
Shikonin induces programmed death of fibroblast synovial cells in rheumatoid arthritis by inhibiting energy pathways 2021 ncbi.nlm.nih.gov/pmc/articl...
Shikonin is the main component of the traditional Chinese medicine comfrey, which can inhibit the activity of PKM2 by regulating glycolysis and ATP production. Rheumatoid arthritis synovial cells (RA-FLSs) have been reported to increase glycolytic activity and have other similar hallmarks of metabolic activity. In this study, we investigated the effects of shikonin on glycolysis, mitochondrial function, and cell death in RA-FLSs. The results showed that shikonin induced apoptosis and autophagy in RA-FLSs by activating the production of reactive oxygen species (ROS) and inhibiting intracellular ATP levels, glycolysis-related proteins, and the PI3K-AKT-mTOR signaling pathway. Shikonin can significantly reduce the expression of apoptosis-related proteins, paw swelling in rat arthritic tissues, and the levels of inflammatory factors in peripheral blood, such as TNF-α, IL-6, IL-8, IL-10, IL-17A, and IL-1β while showing less toxicity to the liver and kidney.
The fulltext, which is behind a paywall, reveals that the C. elegans flatworms were cultured on medium containing shikonin. That makes it a pre-treatment study, which is not a valid model of Parkinson's. The shikonin inhibited aggregation of alpha synuclein, which is nice, but does not address whether it has any effect on already aggregated alpha synuclein.
I found a mouse study of shikonin which had the same problem - simultaneous treatment with shikonin and MPTP: onlinelibrary.wiley.com/doi... Again, it was necessary to examine details behind a paywall to ascertain this.
Aggravating that so much time, effort and funding is put into invalid studies, which only serve to mislead others and thereby waste further the time and effort. Further discussion of this matter here: healthunlocked.com/cure-par...
In the past, comfrey was also used to treat stomach problems. However, it has toxic substances called pyrrolizidine alkaloids that damage the liver and can lead to death. Comfrey is no longer sold in the U.S., except in creams or ointments. The United Kingdom, Australia, Canada, and Germany also have banned the sale of oral products containing comfrey.
The dangerous substances in comfrey are also absorbed through the skin, so harmful amounts may build up in the body. Be careful if you use an ointment containing comfrey (see How to Take It section), and never use comfrey on broken skin
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Mucuna dosage question 
Our Unknowable Quest To Slow Progression...
What if we are approaching this all wrong?
Turmeric Curcumin: BCM-95 or Meriva - Maybe Neither 
