## 5 Microbiome Modification as a Therapeutic Target for Neurodegenerative Diseases
### Probiotics  
Probiotics are live microorganisms that have a profitable effect on the body when consumed in adequate abundance [54; 55]. These microorganisms cannot colonize the gut permanently and must survive through the digestive system. Probiotics modulate the constitution of the gut microbiota and the production of healthful products that derive from fermentation [56]. The main probiotic genera are _Bifidobacterium_ and _Lactobacillus_[54]. Examples of probiotic bacteria, mainly included in dairy products, are _Lactobacillus acidophilus_, _Lactobacillus casei_, and _Bifidobacterium_. Antagonistic attachment to epithelium and mucosa by pro-inflammatory microbes ameliorates the intestinal barrier's integrity and activity via SCFA production [54; 55]. Effects of Probiotics  
In a 12-week multicenter, parallel, randomized, double-blind, and placebo-controlled clinical trial, the impact of probiotic supplementation was investigated on the cognitive situation of 90 older adults aged 50-90 years suffering from AD. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Study Type** & **Study Sample/Duration** & **Participants** & **Protocol** & **Summary of Results** & **Study Reference** \\ \hline \multirow{9}{*}{Cross-sectional study.} & \multirow{4}{*}{41 adult patients/12 days.} & \multirow{4}{*}{25 males and 16 females.} & 25 patients consumed & FOS/-fiber-enriched formulae, and 16 patients consumed standard formulae. The standard formulae included & \multirow{4}{*}{Fecal butyrate concentrations were higher in patients consuming the FOS/fiber-enriched formula in comparison to the standard formula.} \\  & & & & &  
Probiotic consumption, compared with taking a placebo, had a positive impact on the anxiety, cognitive status, and instrumental daily functions of patients suffering from AD [57]. In another randomized, double-blind, placebo-controlled clinical trial, the aim was to examine the impact of the consumption of probiotics and vitamin D on the inflammatory features of PD and its complications. The Gastrointestinal Symptom Rating Scale (GSRS), Beck Anxiety Inventory (BAI), and Unified Parkinson's Disease Rating Scale (UPDRS) were estimated at the beginning and the end of the trial. The supplementation of probiotics and vitamin D induced the reduction in inflammatory cytokines TNF-\(\alpha\), IFN-\(\gamma\), and IL-1\(\beta\) and increased anti-inflammatory cytokines such as IL-10. BAI, GSRS, and UPDRS determined that the supplementation of probiotics and vitamin D significantly diminished the variables compared to the placebo group [58]. In the following animal study, the aim was to observe the anti-Alzheimer impact of acetylcholine-producing _L. plantarum_ MTCC1325 against D-galactose-provoked AD in albino rats via its antioxidant features and GBA. _L. plantarum_ MTCC1325 has the capacity to produce acetylcholine neurotransmitters. During the AD induction period, the body weight of rats progressively diminished when compared to the control group. The protective group exhibited elevated body weight when compared with the AD-model group. AD-model rats exhibited significantly diminished activity in comparison to the control group. _L. plantarum_ MTCC 1325-treated groups showed amelioration in the activity of rats. The ACh load was diminished in the cortex and hippocampus of the AD-model group rat brain. Treatment with _L. plantarum_ MTCC 1325 exhibited an important augmentation of ACh in both the cerebral cortex and hippocampus [59]. In another animal study, a genetic MitoPark PD mouse model was used. The MitoPark PD mouse has characteristics of PD, such as degeneration in dopaminergic neurons at an older age and the evolving impairment of motor activity, GI impairment, and gut microbiome modification. The aim of this study was to examine whether the daily consumption of probiotics can reduce motor impairment in a PD mouse model. This study showed that the daily consumption of probiotics for 16 weeks has a neuroprotective impact and mitigates the progressive impairment of motor activity in MitoPark PD mice.