Objective:To determine whether probiotics are effective for constipation, a common and often difficult-to-treat problem, in Parkinson’s disease (PD).Methods:In this double-blind, randomized placebo-controlled single-centre trial, 280 PD patients were screened and 72 eligible patients were block-randomized (1:1) to receive either multi-strain probiotics capsules (n=34), or identical-appearing placebo (n=38), for four weeks. The primary endpoint was the change in the average number of spontaneous bowel movements (SBM) per week during the last two weeks of intervention, compared with the two-week pre-intervention phase, recorded by daily stool diary. Secondary outcome measures included changes in stool consistency, constipation severity score, and quality of life related to constipation. Satisfaction with intervention received was assessed. Change in levels of fecal calprotectin, a marker of intestinal inflammation, was an exploratory outcome.Results:SBM increased by 1.0±1.2/week after treatment with probiotics, and decreased by 0.3±1.0/week in the placebo group (mean difference 1.3, 95%CI: 0.8-1.8, P<0.001). Significant improvements were also seen for secondary outcomes after correction for multiple comparisons, including stool consistency (P=0.009) and quality of life related to constipation (P=0.001). In the treatment group, 65.6% reported satisfaction with the intervention, vs. only 21.6% in the placebo group (P<0.001). One patient (2.9%) in the treatment group withdrew due to a non-serious adverse event. Fecal calprotectin did not change significantly during the study.Conclusions:Multi-strain probiotics treatment was effective for constipation in PD. Further studies are needed to investigate the long-term efficacy and safety of probiotics in PD, as well as their mechanisms of action.Classification of evidence:This study provides Class I evidence that for people with PD, multi-strain probiotics significantly increased the average number of spontaneous bowel movements per week.Clinicaltrials.gov identifier:NCT03377322

The gut–brain axis is a hot topic in Parkinson's disease (PD). It has been postulated that gut pathogens and dysbiosis can contribute to peripheral inflammatory states or trigger downstream metabolic effects that exacerbate the neurodegenerative process in PD. Several preclinical and clinical studies have demonstrated disrupted intestinal permeability, intestinal inflammation, altered gut microbiome, and reduced fecal short‐chain fatty acids in PD. In this regard, microbial‐directed therapies such as probiotics are emerging as potential therapeutic options. Probiotic supplementation is postulated to confer a variety of health benefits due to the diverse functions of these live microorganisms, including inhibition of pathogen colonization, modulation/“normalization” of the microbiome and/or its function, immunomodulatory effects (e.g. reducing inflammation), and improved host epithelial barrier function. Interestingly, several PD animal model studies have demonstrated the potential neuroprotective effects of probiotics in reducing dopaminergic neuronal degeneration. Notably, two randomized placebo‐controlled trials have provided class I evidence for probiotics as a treatment for constipation in PD. However, the effects of probiotics on other PD aspects, such as motor disability and cognitive function, and its long‐term efficacy (including effects on PD drug absorption in the gut) have not been investigated adequately. Further targeted animal and human studies are also warranted to understand the mechanisms of actions of probiotics in PD and to tailor probiotic therapy based on individual host profiles to improve patient outcomes in this disabling disorder.

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