Parkinson’s Disease
Let’s come to neurology. Preclinical models of Parkinson’s disease have shown neuroprotective activities of GLP-1. Until now, we have three randomized placebo-controlled trials with exenatide, NLY01, and lixisenatide. Two of these studies were positive, showing that the symptoms of Parkinson’s disease were stable over time and deteriorated with placebo. One study was neutral. This means we need more large-scale placebo-controlled studies in the early phases of Parkinson’s disease.
Another potential use of GIP/GLP-1 receptor agonists is in dementia. These substances, as you know, have positive effects on high blood pressure and vascular risk factors.
A working group in China analyzed 27 studies on the treatment of diabetes. A small number of randomized studies and a large number of cohort studies showed that modern antidiabetic drugs reduce the risk for dementia. The risk reduction for dementia for the GLP-1 receptor agonists was 75%. At the moment, there are only small prospective studies and they are not conclusive. Again, we need large-scale placebo-controlled studies.
The most important limitation at the moment beyond the cost is the other adverse drug reactions with the GLP-1 receptor agonists; these include nausea, vomiting, diarrhea, and constipation. There might be a slightly increased risk for pancreatitis. The US Food and Drug Administration recently reported there is no increased risk for suicide. Another potential adverse drug reaction is nonatherosclerotic anterior optic neuropathy.
These drugs, GLP-1 receptor agonists and GIP agonists, are also investigated in a variety of other non-neurologic diseases. The focus here is on metabolic liver disease, such as fatty liver and kidney diseases. Smaller, positive studies have been conducted in this area, and large placebo-controlled trials for both indications are currently underway.
If these diverse therapeutic properties would turn out to be really the case with GLP-1 receptor agonists, this would lead to a significant expansion of the range of indications. If we consider cost, this would be the end of our healthcare systems because we cannot afford this. In addition, the new antidiabetic drugs and the treatment of obesity are available only to a limited extent.
Finally, at least for neurology, it’s unclear whether the impact of these diseases is in the brain or whether it’s indirect, due to the effectiveness on vascular risk factors and concomitant diseases.
Dr. Diener is Professor in the Department of Neurology, Stroke Center-Headache Center, University Duisburg-Essen, Essen, Germany; he has disclosed conflicts of interest with numerous pharmaceutical companies.
A version of this article first appeared on Medscape.com.