1.
Regulation of Neurotransmitters by the Gut Microbiota and Effects on Cognition in Neurological Disorders.
Chen, Y, Xu, J, Chen, Y
Nutrients. 2021;13(6)
-
-
-
Free full text
Plain language summary
Imbalances in the gut microbiota occur in various neurological disorders including Alzheimer’s disease (AD), Parkinson’s disease (PD), autism spectrum disorder and depression. Imbalances in key neurotransmitters are associated with the same disorders. This review focuses on the regulatory mechanisms of the intestinal microbiome and its metabolites on cognitive functions and the pathogeneses of these neurodegenerative diseases. The gut microbiota produce neurotransmitters such as glutamate, GABA, serotonin and dopamine or their precursors. These neurotransmitters are not able to cross the blood brain barrier but the precursors are, therefore the gut microbiota is indirectly involved in the regulation of the production of these key neurotransmitters and therefore neuronal activity and cognitive functions of the brain. The findings demonstrate an association between a healthy gut microbiome structure and balanced neurotransmitter levels in the host. Microbial therapy holds huge promise for the treatment of brain disorders. The development of drugs for neurological disorders must also consider effects on the physiology of the gut microbiome.
Abstract
Emerging evidence indicates that gut microbiota is important in the regulation of brain activity and cognitive functions. Microbes mediate communication among the metabolic, peripheral immune, and central nervous systems via the microbiota-gut-brain axis. However, it is not well understood how the gut microbiome and neurons in the brain mutually interact or how these interactions affect normal brain functioning and cognition. We summarize the mechanisms whereby the gut microbiota regulate the production, transportation, and functioning of neurotransmitters. We also discuss how microbiome dysbiosis affects cognitive function, especially in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease.
2.
Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease.
Dimidi, E, Cox, SR, Rossi, M, Whelan, K
Nutrients. 2019;11(8)
-
-
-
Free full text
Plain language summary
Fermented foods have grown in popularity due to their proposed health benefits but there is limited clinical evidence for the effectiveness of most fermented foods in gastrointestinal health. This review paper looks at non-dairy fermented foods which have been studied in at least one RCT: kefir, sauerkraut, natto, and sourdough bread. The health benefits are attributed to the high ratio of probiotic microorganisms, metabolites, or ability to convert compounds into active metabolites, as well as prebiotics and vitamins contained in these foods. Kimchi has the greatest evidence from epidemiological and case control studies investigating risk of gastric cancers. Different food composition of kimchi is shown to both increase and decrease risks, whilst it had no impact on H. pylori levels. There were no studies on kefir in functional bowel disorders however, it was shown to help lactose malabsorption and reduce H. pylori levels. A small RCT on Sauerkraut showed it reduced IBS severity in patients and increased in vitro activity of key liver and kidney detoxifying enzymes. There are small pockets of data that show that tempeh may influence gut microbiota in humans, and that natto may increase bifidobacterial and short-chain fatty acids in healthy volunteers. There are numerous limited cohort studies on miso and cancer risk but no studies on gastrointestinal conditions. Finally, sourdough was shown to reduce FODMAPS and be better tolerated in IBS patients, reducing bloating, nausea and discomfort. Overall, all the studies provide insufficient evidence on fermented foods and gastrointestinal health.
Abstract
Fermented foods are defined as foods or beverages produced through controlled microbial growth, and the conversion of food components through enzymatic action. In recent years, fermented foods have undergone a surge in popularity, mainly due to their proposed health benefits. The aim of this review is to define and characterise common fermented foods (kefir, kombucha, sauerkraut, tempeh, natto, miso, kimchi, sourdough bread), their mechanisms of action (including impact on the microbiota), and the evidence for effects on gastrointestinal health and disease in humans. Putative mechanisms for the impact of fermented foods on health include the potential probiotic effect of their constituent microorganisms, the fermentation-derived production of bioactive peptides, biogenic amines, and conversion of phenolic compounds to biologically active compounds, as well as the reduction of anti-nutrients. Fermented foods that have been tested in at least one randomised controlled trial (RCT) for their gastrointestinal effects were kefir, sauerkraut, natto, and sourdough bread. Despite extensive in vitro studies, there are no RCTs investigating the impact of kombucha, miso, kimchi or tempeh in gastrointestinal health. The most widely investigated fermented food is kefir, with evidence from at least one RCT suggesting beneficial effects in both lactose malabsorption and Helicobacter pylori eradication. In summary, there is very limited clinical evidence for the effectiveness of most fermented foods in gastrointestinal health and disease. Given the convincing in vitro findings, clinical high-quality trials investigating the health benefits of fermented foods are warranted.
3.
Factors Affecting Gastrointestinal Microbiome Development in Neonates.
Chong, CYL, Bloomfield, FH, O'Sullivan, JM
Nutrients. 2018;10(3)
-
-
-
Free full text
Plain language summary
This narrative review looks at factors affecting the development of the gastrointestinal (GI) microbiome, before, during and after birth. Animal studies suggest that composition and activity of the microbiome affects the structural and functional development of the GI tract. Although evidence is still limited, it is now believed that microbial colonisation starts in utero (before birth). Mode of birth, vaginal versus caesarean section (CS), appears to play an important role in the development of the gut microbiome and can lead to long-term metabolic and immunological consequences, including a higher risk for a number of conditions in those born by CS. Likewise, breast-feeding versus formula-feeding can affect the microbiome composition. These differences are attributed to both bacteria being transferred directly through breast milk and prebiotic factors in breast milk. Maternal and infant perinatal (during birth) exposure to antibiotics has been linked to an increased risk of several conditions, including asthma, obesity, inflammatory bowel disease and other allergic and inflammatory conditions in children. Other factors that appear to affect the development of the microbiome in infants include maternal lifestyle (e.g. rural versus urban), maternal diet, and environment, in particular, staying in a Neonatal Intensive Care Unit. A limitation the authors point out in comparing study results is that different techniques, both culture based and non-culture based, are used for determining the bacterial microflora.
Abstract
The gut microbiome is established in the newborn period and is recognised to interact with the host to influence metabolism. Different environmental factors that are encountered during this critical period may influence the gut microbial composition, potentially impacting upon later disease risk, such as asthma, metabolic disorder, and inflammatory bowel disease. The sterility dogma of the foetus in utero is challenged by studies that identified bacteria, bacterial DNA, or bacterial products in meconium, amniotic fluid, and the placenta; indicating the initiation of maternal-to-offspring microbial colonisation in utero. This narrative review aims to provide a better understanding of factors that affect the development of the gastrointestinal (GI) microbiome during prenatal, perinatal to postnatal life, and their reciprocal relationship with GI tract development in neonates.
4.
Gut microbiota, cognitive frailty and dementia in older individuals: a systematic review.
Ticinesi, A, Tana, C, Nouvenne, A, Prati, B, Lauretani, F, Meschi, T
Clinical interventions in aging. 2018;13:1497-1511
-
-
-
Free full text
Plain language summary
Cognitive frailty is defined as the existence of both physical frailty and mild cognitive impairment, in the absence of a diagnosis of Alzheimer’s Disease or other form of dementia. As such, is considered to be the main pre-condition to developing dementia. Some recent studies have suggested an association between frailty and the gut microbiota, although little data exists on the links between the microbiome and cognitive health. This systematic review aimed to summarise the links made in the science between the gut microbiome and cognitive impairment and the effects of pre and pro-biotics on cognitive decline. 47 papers were identified (31 on animals and 16 on humans). Whilst a number of animal studies supported the link between cognitive impairment and the gut microbiota, there was a substantial lack of human data, preventing the researchers from formulating any clinical recommendations at this stage. Further research in human subjects is required to further our knowledge on the links between the gut microbiome and various forms of cognitive decline and dementia.
Abstract
Cognitive frailty, defined as the coexistence of mild cognitive impairment symptoms and physical frailty phenotype in older persons, is increasingly considered the main geriatric condition predisposing to dementia. Recent studies have demonstrated that gut microbiota may be involved in frailty physiopathology by promoting chronic inflammation and anabolic resistance. The contribution of gut microbiota to the development of cognitive impairment and dementia is less defined, even though the concept of "gut-brain axis" has been well demonstrated for other neuropsychiatric disorders. The aim of this systematic review was to summarize the current state-of-the-art literature on the gut microbiota alterations associated with cognitive frailty, mild cognitive impairment and dementia and elucidate the effects of pre- or probiotic administration on cognitive symptom modulation in animal models of aging and human beings. We identified 47 papers with original data (31 from animal studies and 16 from human studies) suitable for inclusion according to our aims. We concluded that several observational and intervention studies performed in animal models of dementia (mainly Alzheimer's disease) support the concept of a gut-brain regulation of cognitive symptoms. Modulation of vagal activity and bacterial synthesis of substances active on host neural metabolism, inflammation and amyloid deposition are the main mechanisms involved in this physiopathologic link. Conversely, there is a substantial lack of human data, both from observational and intervention studies, preventing to formulate any clinical recommendation on this topic. Gut microbiota modulation of cognitive function represents, however, a promising area of research for identifying novel preventive and treatment strategies against dementia.
5.
Probiotic monotherapy and Helicobacter pylori eradication: A systematic review with pooled-data analysis.
Losurdo, G, Cubisino, R, Barone, M, Principi, M, Leandro, G, Ierardi, E, Di Leo, A
World journal of gastroenterology. 2018;24(1):139-149
-
-
-
Free full text
Plain language summary
Helicobacter pylori (H-pylori) is a parasite that resides in the human stomach and is associated with the development of stomach ulcers, amongst other conditions. Conventional treatment relies on a combination of antibiotics and stomach acid suppressants, however failure rates for standard treatments have been rising and alternatives are required. Probiotics (live bacteria that provide health benefits to their host) have been used alongside antibiotic treatment for H-pylori in some cases to reduce medication side effects. This systematic review of 11 studies including 517 H-pylori infected patients, aimed to assess the effects of probiotic therapy alone on H-pylori status. The study found that the eradication rate of H-pylori with a variety of probiotic strains was 12-16%, compared to a 0% success rate in the placebo groups. Clinically, this rate is low, however the authors conclude that probiotics may have a role to play in a multi-therapy approach for the eradication of H-pylori.
Abstract
AIM: To define probiotic monotherapy effect on Helicobacter pylori (H. pylori) status by performing a systematic review. METHODS Methods of analysis and inclusion criteria were based on PRISMA recommendations. Relevant publications were identified by searching PubMed, MEDLINE, Science Direct, and EMBASE. The end-point was to estimate eradication rate and urea breath test delta value before and after probiotic monotherapy across all studies and, overall, with a pooled data analysis. Adverse events of probiotic therapy were evaluated. The data were expressed as proportions/percentages, and 95%CIs were calculated. For continuous variables, we evaluated the weighted mean difference. Odd ratios (ORs) were calculated according to the Peto method for the comparison of eradication rates between probiotics and placebo. RESULTS Eleven studies were selected. Probiotics eradicated H. pylori in 50 out of 403 cases. The mean weighted eradication rate was 14% (95%CI: 2%-25%, P = 0.02). Lactobacilli eradicated the bacterium in 30 out of 235 patients, with a mean weighted rate of 16% (95%CI: 1%-31%). Saccharomyces boulardii achieved eradication in 6 out of 63 patients, with a pooled eradication rate of 12% (95%CI: 0%-29%). Multistrain combinations were effective in 14 out of 105 patients, with a pooled eradication rate of 14% (95%CI: 0%-43%). In the comparison of probiotics vs placebo, we found an OR of 7.91 in favor of probiotics (95%CI: 2.97-21.05, P < 0.001). Probiotics induced a mean reduction in delta values higher than placebo (8.61% with a 95%CI: 5.88-11.34, vs 0.19% for placebo, P < 0.001). Finally, no significant difference in adverse events was found between probiotics and placebo (OR = 1, 95%CI: 0.06-18.08). CONCLUSION Probiotics alone show a minimal effect on H. pylori clearance, thus suggesting a likely direct role.