Gut Microbiota Altered in Mild Cognitive Impairment Compared With Normal Cognition in Sporadic Parkinson’s Disease Original paper

What was studied?

This study investigated how the gut microbiota differs between patients with sporadic Parkinson’s disease (PD) who have mild cognitive impairment, those with PD but normal cognition, and healthy controls. The central focus was to identify whether specific gut microbial changes are associated with cognitive decline in PD. Researchers collected and analyzed fecal samples from all participants, employing 16S rRNA gene sequencing to profile bacterial communities and gas chromatography–mass spectrometry to quantify short-chain fatty acids (SCFAs). The study also examined correlations between altered microbial taxa and cognitive performance, aiming to uncover distinct microbiome signatures linked to cognitive impairment in PD.

Who was studied?

The study cohort consisted of 40 individuals from Guangdong, China: 13 patients with PD-MCI, 14 patients with PD-NC, and 13 healthy spouses of PD patients serving as controls. All participants were Cantonese, omnivorous, and had no dietary restrictions. The groups were balanced for age, body mass index (BMI), education, and activities of daily living (ADL). Clinical assessments included measures of PD severity, cognitive function (using MMSE and MoCA), and non-motor symptoms. Importantly, healthy controls were spouses of PD patients, minimizing confounding due to shared environment and diet. The study controlled for potential confounders such as age, sex, BMI, education, and constipation in its statistical analyses.

Most important findings

The study found that both PD-NC and PD-MCI patients exhibited increased gut microbial alpha-diversity compared to healthy controls, but there were significant differences in microbial community structure (beta-diversity) between PD-MCI and PD-NC at the genus level. In the PD-MCI group, there was a notable enrichment of specific genera including Alistipes (Rikenellaceae family), Barnesiella, Butyricimonas, and Odoribacter (all Porphyromonadaceae family) compared to both PD-NC and controls. Conversely, the genera Blautia and Ruminococcus were significantly decreased in PD-MCI compared to PD-NC. Correlation analysis revealed that higher abundance of Alistipes, Barnesiella, Butyricimonas, Odoribacter, and Ruminococcus was associated with poorer cognitive scores (MMSE and MoCA), suggesting their negative impact on cognition. Functional prediction analysis indicated enrichment of microbial membrane transport pathways in PD-MCI, which may influence host-microbiota interactions relevant to neurodegeneration. No significant differences were found in fecal SCFA concentrations among the groups, but certain SCFA levels (isovaleric and isobutyric acids) negatively correlated with cognitive performance.

Key implications

The study provides compelling evidence that specific alterations in gut microbiota are associated with cognitive impairment in PD, particularly the enrichment of Porphyromonadaceae family genera and depletion of SCFA-producing genera such as Blautia. These microbial shifts could serve as potential biomarkers for early cognitive decline in PD and point towards novel therapeutic targets for intervention. The findings also highlight the importance of considering the gut-brain axis in PD management and the necessity for further large-scale, gender-balanced studies to validate these microbial signatures. Ultimately, understanding microbiome changes in PD-MCI may aid in predicting the progression to PD dementia (PDD) and inform the development of microbiome-based strategies for preserving cognitive function in PD.

Citation

Ren T, Gao Y, Qiu Y, Jiang S, Zhang Q, Zhang J, Wang L, Zhang Y, Wang L, Nie K. Gut Microbiota Altered in Mild Cognitive Impairment Compared With Normal Cognition in Sporadic Parkinson’s Disease. Front Neurol. 2020;11:137. doi:10.3389/fneur.2020.00137