Diet Patterns, the Gut Microbiome, and Alzheimer's Disease

The Relationship between Diet, Gut Mycobiome, and Functional Gastrointestinal Disorders: Evidence, Doubts, and Prospects

Gut fungi are important parts of intestinal microbes. Dietary ingredients have the potential to regulate the structure of gut fungi in different directions and modulate mycobiome composition by changing dietary patterns, which have been applied to neurological disorders. Emerging pieces of evidence have revealed the regulatory functions of gut mycobiome in gastrointestinal diseases, but the relationships between gut fungi and functional gastrointestinal disorders (FGIDs) are ignored in the past. This review discusses the impact of dietary nutrients and patterns on mycobiome, and the possible ways in which gut fungi are involved in the pathogenesis of FGIDs. Besides affecting host immunity, intestinal fungi can be involved in the pathogenesis of FGIDs by endosymbiosis or bidirectional regulation with gut bacteria as well. In addition, the Mediterranean diet may be the most appropriate dietary pattern for subjects with FGIDs. A full understanding of these associations may have important implications for the pathogenesis and treatment of FGIDs.

Diet patterns and cognitive performance in a UK Female Twin Registry (TwinsUK)

BACKGROUND

Plant-based diets may provide protection against cognitive decline and Alzheimer's disease, but observational data have not been consistent. Previous studies include early life confounding from socioeconomic conditions and genetics that are known to influence both cognitive performance and diet behaviour. This study investigated associations between Mediterranean (MED) diet and MIND diets and cognitive performance accounting for shared genotype and early-life environmental exposures in female twins.

METHODS

Diet scores were examined in 509 female twins enrolled in TwinsUK study. The Cambridge Neuropsychological Test Automated Battery was used to assess cognition at baseline and 10 years later (in n = 275). A co-twin case-control study for discordant monozygotic (MZ) twins examined effects of diet on cognitive performance independent of genetic factors. Differences in relative abundance of taxa at 10-year follow-up were explored in subsamples.

RESULTS

Each 1-point increase in MIND or MED diet score was associated with 1.75 (95% CI: - 2.96, - 0.54, p = 0.005 and q = 0.11) and 1.67 (95% CI: - 2.71, - 0.65, p = 0.002 and q = 0.02) fewer respective errors in paired-associates learning. Within each MZ pair, the twin with the high diet score had better preservation in spatial span especially for MED diet (p = 0.02). There were no differences between diet scores and 10-year change in the other cognitive tests. MIND diet adherence was associated with higher relative abundance of Ruminococcaceae UCG-010 (0.30% (95% CI 0.17, 0.62), q = 0.05) which was also associated with less decline in global cognition over 10 years (0.22 (95% CI 0.06, 0.39), p = 0.01).

CONCLUSIONS

MIND or MED diets could help to preserve some cognitive abilities in midlife, particularly episodic and visuospatial working memory. Effects may be mediated by high dietary fibre content and increased abundance of short-chain fatty acid producing gut bacteria. Longer follow-up with repeated measures of cognition will determine whether diet can influence changes in cognition occurring in older age.

Impact of Donepezil Supplementation on Alzheimer's Disease-like Pathology and Gut Microbiome in APP/PS1 Mice

Based on published information, the occurrence and development of Alzheimer's disease (AD) are potentially related to gut microbiota changes. Donepezil hydrochloride (DH), which enhances cholinergic activity by blocking acetylcholinesterase (AChE), is one of the first-line drugs for AD treatment approved by the Food and Drug Administration (FDA) of the USA. However, the potential link between the effects of DH on the pathophysiological processes of AD and the gut microbiota remains unclear. In this study, pathological changes in the brain and colon, the activities of superoxide dismutase (SOD) and AChE, and changes in intestinal flora were observed. The results showed that Aβ deposition in the prefrontal cortex and hippocampus of AD mice was significantly decreased, while colonic inflammation was significantly alleviated by DH treatment. Concomitantly, SOD activity was significantly improved, while AChE was significantly reduced after DH administration. In addition, the gut microbiota community composition of AD mice was significantly altered after DH treatment. The relative abundance of Akkermansia in the AD group was 54.8% higher than that in the N group. The relative abundance of Akkermansia was increased by 18.3% and 53.8% in the AD_G group and the N_G group, respectively. Interestingly, Akkermansia showed a potential predictive value and might be a biomarker for AD. Molecular docking revealed the binding mode and major forces between DH and membrane proteins of Akkermansia. The overall results suggest a novel therapeutic mechanism for treating AD and highlight the critical role of gut microbiota in AD pathology.

Role of neuroinflammation in neurodegeneration development

Studies in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and Amyotrophic lateral sclerosis, Huntington's disease, and so on, have suggested that inflammation is not only a result of neurodegeneration but also a crucial player in this process. Protein aggregates which are very common pathological phenomenon in neurodegeneration can induce neuroinflammation which further aggravates protein aggregation and neurodegeneration. Actually, inflammation even happens earlier than protein aggregation. Neuroinflammation induced by genetic variations in CNS cells or by peripheral immune cells may induce protein deposition in some susceptible population. Numerous signaling pathways and a range of CNS cells have been suggested to be involved in the pathogenesis of neurodegeneration, although they are still far from being completely understood. Due to the limited success of traditional treatment methods, blocking or enhancing inflammatory signaling pathways involved in neurodegeneration are considered to be promising strategies for the therapy of neurodegenerative diseases, and many of them have got exciting results in animal models or clinical trials. Some of them, although very few, have been approved by FDA for clinical usage. Here we comprehensively review the factors affecting neuroinflammation and the major inflammatory signaling pathways involved in the pathogenicity of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Amyotrophic lateral sclerosis. We also summarize the current strategies, both in animal models and in the clinic, for the treatment of neurodegenerative diseases.

The gut microbiome in Alzheimer's disease: what we know and what remains to be explored

Alzheimer's disease (AD), the most common cause of dementia, results in a sustained decline in cognition. There are currently few effective disease modifying therapies for AD, but insights into the mechanisms that mediate the onset and progression of disease may lead to new, effective therapeutic strategies. Amyloid beta oligomers and plaques, tau aggregates, and neuroinflammation play a critical role in neurodegeneration and impact clinical AD progression. The upstream modulators of these pathological features have not been fully clarified, but recent evidence indicates that the gut microbiome (GMB) may have an influence on these features and therefore may influence AD progression in human patients. In this review, we summarize studies that have identified alterations in the GMB that correlate with pathophysiology in AD patients and AD mouse models. Additionally, we discuss findings with GMB manipulations in AD models and potential GMB-targeted therapeutics for AD. Lastly, we discuss diet, sleep, and exercise as potential modifiers of the relationship between the GMB and AD and conclude with future directions and recommendations for further studies of this topic.

Impact of Dietary Arachidonic Acid on Gut Microbiota Composition and Gut-Brain Axis in Male BALB/C Mice

Although arachidonic acid (ARA) is the precursor of the majority of eicosanoids, its influence as a food component on health is not well known. Therefore, we investigated its impact on the gut microbiota and gut-brain axis. Groups of male BALB/c mice were fed either a standard diet containing 5% lipids (Std-ARA) or 15%-lipid diets without ARA (HL-ARA) or with 1% ARA (HL + ARA) for 9 weeks. Fatty acid profiles of all three diets were the same. The HL-ARA diet favored the growth of Bifidobacterium pseudolongum contrary to the HL + ARA diet that favored the pro-inflammatory Escherichia-Shigella genus in fecal microbiota. Dietary ARA intake induced 4- and 15-fold colic overexpression of the pro-inflammatory markers IL-1β and CD40, respectively, without affecting those of TNFα and adiponectin. In the brain, dietary ARA intake led to moderate overexpression of GFAP in the hippocampus and cortex. Both the hyperlipidic diets reduced IL-6 and IL-12 in the brain. For the first time, it was shown that dietary ARA altered the gut microbiota, led to low-grade colic inflammation, and induced astrogliosis in the brain. Further work is necessary to determine the involved mechanisms.

Structural Alteration of Gut Microbiota During the Amelioration of Chronic Psychological Stress-Aggravated Diabetes-Associated Cognitive Decline by a Traditional Chinese Herbal Formula, ZiBu PiYin Recipe

BACKGROUND

Chronic psychological stress (PS) hinders the treatment of diabetes-associated cognitive decline (DACD). However, the impact of chronic PS on the risk of developing DACD remains unclear. There is growing evidence that gut flora interventions are promising targets for treating stress-related diseases.

OBJECTIVE

We examined whether chronic PS triggers or exacerbates the onset of DACD in rats and aimed to elucidate whether ZiBuPiYin recipe (ZBPYR) prevents and treats chronic PS-aggravated DACD by dynamically maintaining the components of the gut microbiota.

METHODS

We performed chronic PS (restraint, rotation, and congestion) on ZDF rats to establish a model. Cognitive function was evaluated by behavioral experiments, and activation of the hypothalamic-pituitary-adrenal axis was detected by ELISA. Weekly feces from rats were collected for 16 S RNA sequencing.

RESULTS

We found that chronic PS promoted cognitive abnormalities and exacerbated DACD phenotypes. Additionally, chronic PS altered intestinal flora diversity, dynamically elevating the abundance of Alistipes and Coprococcus; enriching Module 1 (Dorea, Blautia, Ruminococcus) and Module 48 (Blautia); and inhibiting Module 20 (Lactobacillus, SMB53), and Module 42 (Akkermansia). ZBPYR significantly alleviated hyperglycemia and cognitive impairment in chronic PS-aggravated DACD rats and dynamically reduced the abundance of Alistipes and Coprococcus; significantly enriched Module 3 (Ruminococcus) and Module 45 (Lactobacillus, Coprococcus, SMB53); and suppressed Module 2 (Lactobacillus), Module 16 (Turicibacter, Trichococcus, Lactobacillus, 02d06, Clostridium), Module 23 (Bifidobacterium), and Module 43 (Clostridium).

CONCLUSION

ZBPYR might prevent and treat chronic PS-aggravated DACD by dynamically regulating Lactobacillus, Alistipes, and Coprococcus.

Flavonoids bridging the gut and the brain: intestinal metabolic fate, and direct or indirect effects of natural supporters against neuroinflammation and neurodegeneration

In recent years, experimental evidence suggested a possible role of the gut microbiota in the onset and development of several neurodegenerative disorders, such as AD and PD, MS and pain. Flavonoids, including anthocyanins, EGCG, the flavonol quercetin, and isoflavones, are plant polyphenolic secondary metabolites that have shown therapeutic potential for the treatment of various pathological conditions, including neurodegenerative diseases. This is due to their antioxidant and anti-inflammatory properties, despite their low bioavailability which often limits their use in clinical practice. In more recent years it has been demonstrated that flavonoids are metabolized by specific bacterial strains in the gut to produce their active metabolites. On the other way round, both naturally-occurring flavonoids and their metabolites promote or limit the proliferation of specific bacterial strains, thus profoundly affecting the composition of the gut microbiota which in turn modifies its ability to further metabolize flavonoids. Thus, understanding the best way of acting on this virtuous circle is of utmost importance to develop innovative approaches to many brain disorders. In this review, we summarize some of the most recent advances in preclinical and clinical research on the neuroinflammatory and neuroprotective effects of flavonoids on AD, PD, MS and pain, with a specific focus on their mechanisms of action including possible interactions with the gut microbiota, to emphasize the potential exploitation of dietary flavonoids as adjuvants in the treatment of these pathological conditions.