Understanding how gut flora influences gut-brain communications has been the subject of significant research over the past decade. The broadening of the term “microbiota-gut-brain axis” from “gut-brain axis” underscores a bidirectional communication system between the gut and the brain. The microbiota-gut-brain axis involves metabolic, endocrine, neural, and immune pathways which are crucial for the maintenance of brain homeostasis. Alterations in the composition of gut microbiota are associated with multiple neuropsychiatric disorders. Although a causal relationship between gut dysbiosis and neural dysfunction remains elusive, emerging evidence indicates that gut dysbiosis may promote amyloid-beta aggregation, neuroinflammation, oxidative stress, and insulin resistance in the pathogenesis of Alzheimer’s disease (AD). Illustration of the mechanisms underlying the regulation by gut microbiota may pave the way for developing novel therapeutic strategies for AD. In this narrative review, we provide an overview of gut microbiota and their dysregulation in the pathogenesis of AD. Novel insights into the modification of gut microbiota composition as a preventive or therapeutic approach for AD are highlighted.

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Gut Microbiota and Dysbiosis in Alzheimer's Disease: Implications for Pathogenesis and Treatment.

Type 2 diabetes is the fastest-growing metabolic disease in the world. Many clinical studies have found that type 2 diabetes patients have metabolic disorders and chronic inflammatory states accompanied by disturbances in the gut microbiota. The gut microbiota plays an important role in body metabolism and immune regulation, and disturbances in the gut microbiota in conjunction with destruction of the intestinal barrier in type 2 diabetes patients causes damage to multiple organs. Therefore, the gut microbiota may be a new therapeutic target for treating type 2 diabetes and related diseases. In this review, we introduce the characteristics of the gut microbiota in type 2 diabetes and related diseases, as well as highlight the potential molecular mechanisms of their effects on intestinal barrier disruption, metabolic disorders, and chronic inflammation. Finally, we summarize an intestinal microecological therapeutic strategy, with a focus on shaping the intestinal bacteria, to improve the malignant progress of type 2 diabetes and related diseases. AUTHOR SUMMARY: Type 2 diabetes (T2D) is the fastest-growing metabolic disease in the world. Many clinical studies have found that T2D patients have metabolic disorders and chronic inflammatory states, accompanied by disturbances of the gut microbiota and increased intestinal permeability. The number of human gut microbiota is more than 10 times of human cells, and they play an important role in the body's metabolism and immune regulation. The abnormal intestinal metabolites and intestinal barrier disruption caused by the gut microbiota dysbiosis in the T2D facilitate intestinal bacteria and their harmful metabolites entering the circulatory system. The abnormal entering will cause the damage to multiple organs through disturbing insulin sensitivity, glucose metabolism, and immune homeostasis. Therefore, the gut microbiota may be a new therapeutic target for improving T2D and its related diseases. In this review, we introduce the compositional characteristics of the gut microbiota in T2D, and highlight some new molecular mechanisms of their effects on intestinal barrier disruption, metabolic disorders and chronic inflammation in T2D and its related diseases. Finally, we summarize an intestinal microecological therapeutic strategy, with a focus on shaping the intestinal bacteria, to improve the malignant progress of T2D and related diseases.

Role of the gut microbiota in type 2 diabetes and related diseases.

Numerous studies have indicated that the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD) is strictly associated with the accumulation of toxic metabolites in blood and other metabolic compartments. This accumulation was suggested to be related to enhanced generation of toxins from the dysbiotic microbiome accompanied by their reduced elimination by impaired kidneys. Intestinal microbiota play a key role in the accumulation of uremic toxins due to the fact that numerous uremic solutes are generated in the process of protein fermentation by colonic microbiota. Some disease states, including CKD, are associated with the presence of dysbiosis, which can be defined as an “imbalanced intestinal microbial community with quantitative and qualitative changes in the composition and metabolic activities of the gut microbiota”. The results of studies have confirmed the altered composition and functions of gut microbial community in chronic kidney disease. In the course of CKD protein-bound uremic toxins, including indoxyl sulfate, p-cresyl glucuronide, p-cresyl sulfate and indole-3-acetic acid are progressively accumulated. The presence of chronic kidney disease may be accompanied by the development of intestinal inflammation and epithelial barrier impairment leading to hastened systemic translocation of bacterial-derived uremic toxins and consequent oxidative stress injury to the kidney, cardiovascular and endocrine systems. These findings offer new therapeutic possibilities for the management of uremia, inflammation and kidney disease progression and the prevention of adverse outcomes in CKD patients. It seems that dietary interventions comprising prebiotics, probiotics, and synbiotics could pose a promising strategy in the management of uremic toxins in CKD.

The Impact of CKD on Uremic Toxins and Gut Microbiota.

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Immune Dysfunction in Uremia 2020

The probiotic L. casei Zhang slows the progression of acute and chronic kidney disease

Objective Patients with renal failure suffer from symptoms caused by uraemic toxins, possibly of gut microbial origin, as deduced from studies in animals. The aim of the study is to characterise relationships between the intestinal microbiome composition, uraemic toxins and renal failure symptoms in human end-stage renal disease (ESRD). Design Characterisation of gut microbiome, serum and faecal metabolome and human phenotypes in a cohort of 223 patients with ESRD and 69 healthy controls. Multidimensional data integration to reveal links between these datasets and the use of chronic kidney disease (CKD) rodent models to test the effects of intestinal microbiome on toxin accumulation and disease severity. Results A group of microbial species enriched in ESRD correlates tightly to patient clinical variables and encode functions involved in toxin and secondary bile acids synthesis; the relative abundance of the microbial functions correlates with the serum or faecal concentrations of these metabolites. Microbiota from patients transplanted to renal injured germ-free mice or antibiotic-treated rats induce higher production of serum uraemic toxins and aggravated renal fibrosis and oxidative stress more than microbiota from controls. Two of the species, Eggerthella lenta and Fusobacterium nucleatum, increase uraemic toxins production and promote renal disease development in a CKD rat model. A probiotic Bifidobacterium animalis decreases abundance of these species, reduces levels of toxins and the severity of the disease in rats. Conclusion Aberrant gut microbiota in patients with ESRD sculpts a detrimental metabolome aggravating clinical outcomes, suggesting that the gut microbiota will be a promising target for diminishing uraemic toxicity in those patients. Trial registration number This study was registered at ClinicalTrials.gov (NCT03010696).

https://gut.bmj.com/content/gutjnl/69/12/2131.full.pdf

Aberrant gut microbiota alters host metabolome and impacts renal failure in humans and rodents.

Renal insufficiency (RI) is a frequent comorbidity among patients with acute coronary syndrome (ACS). We aimed to evaluate the attributable risk associated with mild RI for the in-hospital outcomes in patients with ACS.The Improving Care for Cardiovascular Disease in China-ACS (CCC-ACS) Project was a collaborative study of the American Heart Association and the Chinese Society of Cardiology. A total of 92,509 inpatients with a discharge diagnosis of ACS were included. The attributable risk was calculated to investigate the effect of mild RI (eGFR 60-89 ml / min · 1.73 m2) on major adverse cardiovascular events (MACEs) during hospitalization.The average age of these ACS patients was 63 years, and 73.9% were men. The proportion of patients with mild RI was 36.17%. After adjusting for other possible risk factors, mild RI was still an independent risk factor for MACEs in ACS patients. In the ACS patients, the attributable risk of eGFR 60-89ml/min·1.73m2 to MACEs was 7.78%, 4.69% of eGFR 45-59 ml/min·1.73m2, 4.46% of eGFR 30-44 ml/min·1.73m2, and 3.36% of eGFR<30 ml/min·1.73m2.Compared with moderate to severe RI, mild RI has higher attributable risk to MACEs during hospitalization in Chinese ACS population. 

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Mild renal insufficiency and attributable risk of adverse In-hospital outcomes in patients with Acute Coronary Syndrome from the improving care for Cardiovascular Disease in China (CCC) project

Objective: To investigate the effects of different types of heart failure on long-term renal prognosis in patients with renal insufficiency and heart failure. Methods: The patients with renal insufficiency [baseline estimated glomerular filtration rate < 60 ml·min-1·(1.73 m2)-1] and heart failure followed-up for more than 2 years and hospitalized in Beijing Anzhen Hospital, Capital Medical University from January 1, 2018 to June 30, 2019 were enrolled in this retrospective cohort study. The patients were divided into three groups based on the baseline left ventricular ejection fraction (LVEF): heart failure with reduced ejection fraction (HFrEF, LVEF < 40%) group, heart failure with mildly reduced ejection fraction (HFmrEF, 40% ≤ LVEF < 50%) group, and heart failure with preserved ejection fraction (HFpEF, LVEF ≥ 50%) group. Clinical data were collected and endpoint events (adverse renal outcome: the composite outcome of all-cause death or worsening renal function) were recorded through the electronic medical record system. Kaplan-Meier survival curve was used to analyze the incidence of endpoint events of different heart failure subgroups. Cox regression model was performed to analyze the risk factors of endpoint events. Results: A total of 228 patients with renal insufficiency complicated with heart failure were included, with age of (68.14±14.21) years old and 138 males (60.5%). There were 85 patients (37.3%) in the HFrEF group, 40 patients (17.5%) in the HFmrEF group, and 103 patients (45.2%) in the HFpEF group. There were statistically significant differences in age, proportion of age > 65 years old, sex distribution, systolic blood pressure, pulmonary artery pressure, serum sodium, serum calcium, hemoglobin, serum cholesterol, low-density lipoprotein cholesterol, serum uric acid, troponin I, hypersensitive C-reactive protein, LVEF, ventricular septal thickness, left ventricular end-diastolic diameter, B-type natriuretic peptide, estimated glomerular filtration rate, and proportions of using beta blockers, using spirolactone, myocardial infarction, hypertension, cardiomyopathy and atrial fibrillation (all P < 0.05). During the median follow-up of 36.0 (28.0, 46.0) months, 73 patients (32.0%) had adverse renal outcomes. The total incidences of adverse renal outcomes were 32.9% (28/85) in the HFrEF group, 35.0% (14/40) in the HFmrEF group, and 30.1% (31/103) in the HFpEF group. Kaplan-Meier survival curve showed that there was no significant difference in the incidence of endpoint events among the three groups (log-rank test χ2=0.17, P=0.680). Multivariate Cox regression analysis showed that HFpEF (HFrEF as reference, HR=2.430, 95% CI 1.055-5.596, P=0.037) was an independent influencing factor of endpoint events. Conclusions: The long-term renal prognosis of patients with renal insufficiency and heart failure is poor. Compared with HFrEF, HFpEF is an independent risk factor of poor long-term renal prognosis in renal insufficiency patients with heart failure.

Weijing Bian

Papers

Aberrant gut microbiota alters host metabolome and impacts renal failure in humans and rodents.

Mild renal insufficiency and attributable risk of adverse In-hospital outcomes in patients with Acute Coronary Syndrome from the improving care for Cardiovascular Disease in China (CCC) project

[Impact of different types of heart failure on long-term renal prognosis in patients with renal insufficiency and heart failure].