Meta-analysis of randomized controlled trials of the effects of probiotics in Parkinson's disease

Background: Patients with Parkinson's disease (PD) demonstrate intestinal dysbiosis and substantial gastrointestinal dysfunction. Preliminary evidence suggests that probiotics may have a positive effect on the motor and non-motor symptoms of PD. However, the effectiveness of probiotics in treating PD remains unclear. Therefore, a randomized controlled trial (RCT) was performed to examine the efficacy of oral probiotics in PD treatment. Methods: PubMed, Web of Science, Cochrane Library, EMBASE, Clinical Trials, and Google Scholar were searched for relevant RCTs published until January 28, 2023. Meta-analyses have examined the effects of probiotics on motor and non-motor symptom parameters in RCTs. Inverse-variance random or fixed effects were used to pool data. The Grading of Recommendations Assessment, Development, and Evaluations was used to examine the quality of evidence for outcomes of the meta-analysis. Results: Nine eligible RCTs (N = 663) were included in this meta-analysis. In the meta-analysis, probiotic treatment significantly improved motor symptoms (UPDRS-III scores: standardized mean difference [SMD] = -0.28, 95% confidence interval [CI], -0.49 to -0.07, I-2 = 7%), constipation and constipation-related quality of life (Bristol scores: SMD = 0.54; 95% CI, 0.35 to 0.73, I-2 = 0%; bowel movement scores: SMD = 0.83; 95% CI, 0.59 to 1.07, I-2 = 43%; CSBMs: SMD = 0.56; 95% CI, 0.30 to 0.82, I-2 = 0%; PAC-QCL scores: SMD = -0.84; 95% CI, -1.08 to -0.60, I-2 = 0%), and anxiety and depression parameters (HAMA scores: SMD = -0.35; 95% CI, -0.60 to -0.10, I-2 = 0%; HADM-17 scores: SMD = -0.33; 95% CI, -0.59 to -0.08, I-2 = 0%). In addition, probiotic supplements significantly reduced the use of laxatives (SMD = -0.27; 95% CI, -0.53 to -0.01, I-2 = 15%) and increased GSH levels in the serum of PD patients (SMD = 0.52; 95% CI, 0.14 to 0.90, I-2 = 0%). The certainty of evidence was graded as very low for UPDRS-III, PAC-QCL, CSBMs, HAMA, HADM-17 and Bristol scores and low for bowel movement scores. Two of the nine RCTs reported that probiotics may cause abdominal bloating at low rates on consuming probiotics, which suggests that we should pay attention to the occurrence of adverse events during the consumption of probiotics in future studies. Conclusion: Oral probiotic consumption significantly improved motor symptoms, gastrointestinal dysfunction, anxiety, and depression in patients with PD. Notably, oral probiotics also reduced the use of laxatives and increased GSH levels in the serum of patients with PD. In future studies, more high-quality evidence from large-scale RCTs is needed to determine the exact effects of probiotic treatment on PD.