The findings, “The oral microbiome of early stage Parkinson’s disease and its relationship with functional measures of motor and non-motor function,” were published in PLOS One.
The specific causes of Parkinson’s, a neurodegenerative disease marked by a gradual loss of muscle control and cognitive difficulties, are still not fully understood. But scientists believe its onset and progression are dictated by a combination of genetic, epigenetic (chemical modifications in DNA that affect gene expression), and environmental and lifestyle factors.
“Over the past decade, however, it has become increasingly clear that disturbances and pathology within the upper and lower gastrointestinal (GI) system in PD [Parkinson’s disease] actually precede the pathology in the central nervous system (brain, brainstem and cerebellum, CNS),” the researchers wrote.
“Given its potential importance in understanding the complete pathophysiology [development] of PD, it is not surprising that much attention has recently focused on defining the microbiome changes in PD,” they added. “However, the vast majority of studies … have examined only lower GI or fecal samples, and examined these in subjects with well-established motor symptoms or advanced disease states.”
Researchers with SUNY Upstate Medical University and Quadrant Biosciences examined and compared the composition of the oral microbiome — the different microorganisms that live in our mouths — of people with early Parkinson’s disease and healthy individuals serving as controls.
A total of 48 people with early Parkinson’s disease (average duration of 3.4 years post-diagnosis) and 36 age- and sex-matched controls provided saliva samples that were used to isolate and analyze host and bacterial RNA (the molecule used as a template for the production of a protein).
All study participants also completed a series of assessments designed to evaluate their motor, cognitive, balance and sensory (taste and smell) skills and, in patients, determine their disease stage.
Although researchers found no differences in terms of microbe diversity between the two groups, they discovered that certain types of microbes, including bacteria, yeast and phages (a virus that infects bacteria), had an unusual pattern of distribution among people with early Parkinson’s disease.
Nearly half of these microbes had already been described in studies examining the composition of microorganisms in the feces of Parkinson’s patients and proposed as candidates to diagnose the earliest stages of the disease.
Subsequent analyses incorporating data about the distribution of 11 of these microbes found that the saliva test had an accuracy of 84.5% in identifying people with early Parkinson’s disease.
Further bioinformatic analyses on 167 different chemical signaling cascades showed alterations in pathways involved in amino-acid (the building blocks of proteins) and energy metabolism in microorganisms found in these patients.
Investigators also discovered that patients had significant alterations in the levels of nine different host RNAs, many of which were directly involved in brain function. Interestingly, these alterations were associated with changes in the composition of mouth microbes.
“Unexpectedly, we also observed robust correlations between many of the microbiota and functional measures, including those reflecting cognition, balance, and disease duration,” the researchers wrote.
And, they concluded, “the combined set of bacterial families that we observed changed in early stage PD may have broad implications for understanding the pathophysiology of the disorder.”
“I think we’ve entered a new era in terms of neurodegenerative disease research and are now starting to consider the oral microbiome and the bacteria and other biota that are there as a ripe place for discovery of potential risk factors,” Frank Middleton, an associate professor at SUNY Upstate Medical University and the study’s lead author, said in a press release.