Abstract
BackgroundAlzheimer's disease (AD) and Parkinson's disease (PD) are two of the most common neurodegenerative diseases, and mild cognitive impairment (MCI) is considered a prodromal stage of clinical AD. Animal studies have shown that probiotics can improve cognitive function and mitigate inflammatory response, however, results from randomized controlled trials in humans are still unclear.ObjectivesA systematic review and meta-analysis was conducted to evaluate the efficacy and safety of probiotic therapy on cognitive function, oxidative stress, and gastrointestinal function in patients with AD, MCI, and PD.MethodsWe searched the electronic databases such as PubMed, EMBASE, Cochrane Library until October 2020 for the eligible randomized controlled trials, as well as the unpublished and ongoing trials. Our primary endpoints were cognitive function, inflammatory and oxidative stress biomarkers, gastrointestinal function, and adverse events.ResultsAfter screening 2,459 titles and abstracts about AD or MCI, we selected 6 eligible studies (n = 499 patients). After screening 1,923 titles and abstracts about PD, we selected 5 eligible studies (n = 342 patients). Compared with the control group, treatment with probiotics improved the cognitive function of patients with AD in the intervention group (P = 0.023). Cognitive function also improved in MCI patients (P = 0.000). Inflammation-related indicators: Malondialdehyde (MDA) was significantly reduced (P = 0.000); and hs-CRP decreased (P = 0.003). Lipid-related indicators: VLDL decreased (P = 0.026); triglyceride decreased (P = 0.009); and insulin resistance level improved: decreased Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (P = 0.019).ConclusionOur analyses suggest that probiotics can improve cognitive and gastrointestinal symptoms in patients with AD, MCI, and PD, which is possibly through reducing inflammatory response and improving lipid metabolism. The safety has also been proven. However, more RCTs with rigorous study design are needed to support our findings.Systematic Review RegistrationPROSPERO, Identifier: CRD42021231502.
Highlights
Neurodegenerative diseases are a heterogeneous of disorders characterized by the progressive degeneration of the structure and function of the central nervous system (CNS) or peripheral nervous system (PNS)
Clinical studies have shown a significant reduction in cellulose-degrading bacteria and a significant increase in hypothetical pathogens such as Escherichia coli, Streptococcus, Proteus and Enterococcus in fecal samples from Parkinson’s disease (PD) patients compared to healthy controls (Cirstea et al, 2020)
For PD, 1,920 articles were obtained after the initial search of the electronic databases and 3 studies were identified through a manual search of the reference lists of relevant published reviews
Summary
Neurodegenerative diseases are a heterogeneous of disorders characterized by the progressive degeneration of the structure and function of the central nervous system (CNS) or peripheral nervous system (PNS) These age-related diseases are becoming more common, partly because the elderly population has grown in recent years (Heemels, 2016). MCI is considered a prodromal stage of clinical AD (Petersen, 2004) These diseases mainly affect aging individuals and progress steadily due to increased loss of specific neurons in the brain. The gut-brain axis (GBA) is a bidirectional link between the CNS and the enteric nervous system (ENS) (Skonieczna-Zydecka et al, 2018) It involves direct and indirect pathways connecting cognitive and affective centers in the brain with peripheral intestinal function. Animal studies have shown that probiotics can improve cognitive function and mitigate inflammatory response, results from randomized controlled trials in humans are still unclear
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