Oct 13 2016
Blood levels of cytokines — substances associated with inflammation — are higher in people with Parkinson’s disease (PD) than in healthy individuals, according to research published in the September 26 online edition of JAMA Neurology. The results add to mounting evidence linking PD and inflammation, and point to potential biomarkers for diagnosing and monitoring PD.
Inflammation is the body’s response to injury or infection. Immune system cells secrete chemicals called cytokines that cause inflammation. Earlier studies have found signs of inflammation in the brains of people with PD, leading scientists to wonder whether it causes the disease. In addition, many studies have attempted to link inflammatory cytokines in the blood to PD, but the results have been inconsistent.
For the new research, scientists led by Yong Cheng, Ph.D., at the US National Institutes of Health (NIH) pooled data from 25 earlier studies of cytokines in blood samples from people with PD. They re-analyzed the combined data using a statistical technique called meta-analysis, and compared blood cytokine levels of 1,547 people with PD to those in 1,107 healthy study participants.
Results
- Concentrations of seven chemical markers of inflammation were higher in blood samples from people with PD compared to healthy individuals. In order of highest to lowest concentration, the seven markers are interleukin 1ß, 2, 6, and 10, C-reactive protein (CRP), and a protein called RANTES.
- Elevated levels of two of these protein, interleukin-2 and RANTES, were specific to Parkinson’s disease and have not been found in other disorders such as Alzheimer’s disease and depression.
- For three other cytokines measured, there was no difference between people with Parkinson’s disease and healthy controls.
What Does It Mean?
The new study strengthens the evidence that people with Parkinson’s disease have a heightened inflammatory response. Linking cytokines to this response raises the possibility that these substances could be monitored as biomarkers to diagnose or track the progression of Parkinson’s. In fact, other studies have suggested that cytokines may be correlated with faster disease progression.
Researchers remain unsure, however, whether inflammation increases the risk of PD or whether PD causes inflammation, i.e., which comes first. Another possibility is that the immune response may be heightened as the body’s way to protect against neurodegeneration. A limitation of this study (and the studies upon which it was based) was that it could not associate cytokines with specific Parkinson’s symptoms, length of time since a PD diagnosis or disease severity.
Further research is needed to uncover the molecular mechanisms that link PD and inflammation. The hope is that a better understanding of this connection may lead to ways to estimate the rate of PD progression and track disease severity, or lead to therapies that target the negative aspects of inflammation.
References:
Qin X-Y, Zhang S-P, Cao C, Loh YP, Cheng Y. (2016). Aberrations in Peripheral Inflammatory Cytokine Levels in Parkinson Disease: A Systematic Review and Meta-analysis. JAMA Neurology doi:10.1001/jamaneurol.2016.2742
Alcalay RN. (2016). Editorial: Cytokines as Potential Biomarkers of Parkinson Disease. JAMA Neurology, published online September 26, 2016
http://www.pdf.org/en/science_news/release/pr_1476375646?utm_source=newsletter&utm_medium=email&utm_campaign=news
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