Many studies suggest diabetes does increase the risk of Parkinson’s disease; however, there is no absolute proof. A lot more people live with Parkinson’s disease and no diabetes compared to those with both conditions. (1) We know that both Parkinson’s disease and type 2 diabetes are more likely as we grow older. Both conditions are due to a progressive loss of hormone production. Parkinson’s disease is a loss of dopamine-producing cells, and diabetes is a loss of insulin production and beta cells in the pancreas, in addition to insulin resistance.

Diabetes can have effects on the brain. High glucose levels can damage blood vessels in the brain and thereby increase the risk of stroke. Increased glucose levels and insulin resistance affect contribute to inflammation in the brain. Type 2 diabetes increases the risk of Alzheimer’s and other dementias. (2)

Parkinson’s disease is an inflammatory, progressive condition in the brain. When type 2 diabetes and Parkinson’s disease coexist, they may create a destructive environment in the brain. (3)

Diabetes medications and Parkinson’s

Because of the common cellular changes that happen between both conditions, medications for diabetes may reduce the impact of Parkinson’s disease. Insulin actively crosses the blood-brain barrier and is produced in small quantities within the brain. Insulin is a neuroprotective hormone in the brain. Parkinson’s disease reduces the actions of insulin. With this information, it follows that some medications used for the treatment of type 2 diabetes may have beneficial effects with Parkinson’s disease.

A group of medications used in type 2 diabetes, GLP-1 agonists, may improve cognition and motor function in Parkinson’s disease.  GLP-1 is a naturally occurring hormone produced by cells lining our gut which is released when we eat. This natural hormone slows the gut motion and helps the pancreas release extra insulin. In type 2 diabetes, this hormone, also called an incretin hormone, does not work as efficiently as a person without diabetes. This group of injectable medications for type 2 diabetes produces the same and more potent response. (4)

In human clinical trials, Exenatide had positive effects on practically defined off-medication motor scores in Parkinson’s disease, which were sustained beyond the period of the trial. The longevity of these effects is uncertain. (5) In mouse models, Liraglutide and Lixisenatide protected mice from the toxicity of induced Parkinson’s disease. (6) In the REWIND study of people living with type 2 diabetes, the risk of considerable cognitive impairment was reduced by 14% in those assigned Dulaglutide. (7)

Much more research is needed to determine if GLP-1 agonists may be introduced to people living with diabetes and Parkinson’s disease with dual benefits. Further research could determine if people with a significant risk of Parkinson’s disease or cognitive decline may reduce the risk of onset.

 Donna Itzstein   Pharmacist, CDE

References

1. Gilbert, Dr Rebecca. The link between Parkinson’s disease and diabetes. American Parkinson Disease Association. [Online] June 26th, 2018. https://www.apdaparkinson.org/article/link-between-diabetes-and-parkinsons/.
2. Diabetes Mellitus and Parkinson’s Disease: Shared Pathophysiological Links and Possible Therapeutic Implications. Hassan A, Sharma Kandel R, Mishra R, Gautam J, Alaref A, Jahan N. 8, s.l. : Cureus, August 18th, 2020, Vol. 12.
3. Type 2 diabetes and Parkinson’s disease. Shaw, K. 4, August 22nd, 2019, Practical Diabetes, Vol. 36, pp. 115-116a.
4. Glucagon peptide-1 agonists as treatment for Parkinson’s. Golfelty, E J, et al. 6, May 15th, 2020, Expert Opinion, Vol. 20.
5. Exenatide once weekly versus placebo in Parkinson’s disease: a randomised, double-blind, placebo-controlled trial. Athauda, Dilan, et al. 10103, October 7th, 2017, The Lancet (British edition), , Vol. 390, pp. 1664-1675.
6. Neuroprotective effects of lixisenatide and liraglutide in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson’s disease. W. Liu, J. Jalewa, M. Sharma, G. Li, L. Li, C. Hölscher,. 2015, Neuroscience, Vol. 303, pp. 42-50.
7. Effect of dulaglutide on cognitive impairment in type 2 diabetes: an exploratory analysis of the REWIND trial. Cukierman-Yaffe, T, et al. 7, July 2020, Lancet neurology, Vol. 19, pp. 582-590.