Microbiome perturbation by oral vancomycin reduces plasma concentration of two gut-derived uremic solutes, indoxyl sulfate and p-cresyl sulfate, in end-stage renal disease

Assessment of Within- and Inter-Patient Variability of Uremic Toxin Concentrations in Children with CKD

To promote improved trial design in upcoming randomized clinical trials in childhood chronic kidney disease (CKD), insight in the within- and inter-patient variability of uremic toxins with its nutritional, treatment- and patient-related confounding factors is of utmost importance. In this study, the within- and inter-patient variability of a selection of uremic toxins in a longitudinal cohort of children diagnosed with CKD was assessed, using the intraclass correlation coefficient (ICC) and the within-patient coefficient of variation (CV). Subsequently, the contribution of anthropometry, estimated glomerular filtration rate (eGFR), dietary fiber and protein, and use of (prophylactic) antibiotics to uremic toxin variability was evaluated. Based on 403 observations from 62 children (median seven visits per patient; 9.4 ± 5.3 years; 68% males; eGFR 38.5 [23.1; 64.0] mL/min/1.73 m2) collected over a maximum of 2 years, we found that the within-patient variability is high for especially protein-bound uremic toxins (PBUTs) (ICC < 0.7; within-patient CV 37-67%). Moreover, eGFR was identified as a predominant contributor to the within- and inter-patient variability for the majority of solutes, while the impact of the child's anthropometry, fiber and protein intake, and antibiotics on the variability of uremic toxin concentrations was limited. Based on these findings, we would recommend future intervention studies that attempt to decrease uremic toxin levels to select a (non-dialysis) CKD study population with a narrow eGFR range. As the expected effect of the selected intervention should exceed the inter-patient variability of the selected uremic toxins, a narrow eGFR range might aid in improving the trial design.

A Systematic Review of Uremic Toxin Concentrations and Cardiovascular Risk Markers in Pediatric Chronic Kidney Disease

Chronic kidney disease (CKD) can lead to cardiac dysfunction in a condition known as cardiorenal syndrome (CRS). It is postulated that the accumulation of uremic toxins in the bloodstream, as a consequence of declining kidney function, may contribute to these adverse cardiac effects. While CRS in adults has been extensively studied, there is a significant knowledge gap with pediatric patients. Uremic toxin levels in children remain inadequately characterized and quantified compared to adults. This review aims to systematically evaluate the association between uremic toxin concentrations and cardiac changes in pediatric CRS and to examine the impact of different dialysis modalities, specifically hemodialysis and peritoneal dialysis, on uremic toxin clearance and cardiovascular parameters. To address this, we conducted a systematic literature search of PubMed, following PRISMA guidelines. We used the terms "uremic toxins" and "cardiorenal syndrome" with variations in syntax to search for studies discussing the relationship between uremic toxin levels in CKD, the subsequent impact on cardiac parameters, and the emergence of cardiac dysfunction. Full-text articles written in English, conducted on humans aged from birth to 18 years, and published until December 2021 were included. A comprehensive literature search yielded six studies, and their risk of bias was assessed using JBI Critical Appraisal Checklists. Our systematic review is registered on PROSPERO, number CRD42023460072. This synthesis intends to provide an understanding of the role of uremic toxins in pediatric CRS. The findings reveal that pediatric patients with end-stage CKD on dialysis exhibit elevated uremic toxin levels, which are significantly associated with cardiovascular disease parameters. Additionally, the severity of CKD correlated with higher uremic toxin levels. No conclusive evidence was found to support the superiority of either hemodialysis or peritoneal dialysis in terms of uremic toxin clearance or cardiovascular outcomes. More pediatric-specific standardized and longitudinal studies are needed to develop targeted treatments and improve clinical outcomes and the quality of life for affected children.

Dynamic gut microbiome-metabolome in cationic bovine serum albumin induced experimental immune-complex glomerulonephritis and effect of losartan and mycophenolate mofetil on microbiota modulation

Dynamic changes in gut dysbiosis and metabolomic dysregulation are associated with immune-complex glomerulonephritis (ICGN). However, an in-depth study on this topic is currently lacking. Herein, we report an ICGN model to address this gap. ICGN was induced via the intravenous injection of cationized bovine serum albumin (c-BSA) into Sprague-Dawley (SD) rats for two weeks, after which mycophenolate mofetil (MMF) and losartan were administered orally. Two and six weeks after ICGN establishment, fecal samples were collected and 16S ribosomal DNA (rDNA) sequencing and untargeted metabolomic were conducted. Fecal microbiota transplantation (FMT) was conducted to determine whether gut normalization caused by MMF and losartan contributed to their renal protective effects. A gradual decline in microbial diversity and richness was accompanied by a loss of renal function. Approximately 18 genera were found to have significantly different relative abundances between the early and later stages, and Marvinbryantia and Allobaculum were markedly upregulated in both stages. Untargeted metabolomics indicated that the tryptophan metabolism was enhanced in ICGN, characterized by the overproduction of indole and kynurenic acid, while the serotonin pathway was reduced. Administration of losartan and MMF ameliorated microbial dysbiosis and reduced the accumulation of indoxyl conjugates in feces. FMT using feces from animals administered MMF and losartan improved gut dysbiosis by decreasing the Firmicutes/Bacteroidetes (F/B) ratio but did not improve renal function. These findings indicate that ICGN induces serous gut dysbiosis, wherein an altered tryptophan metabolism may contribute to its progression. MMF and losartan significantly reversed the gut microbial and metabolomic dysbiosis, which partially contributed to their renoprotective effects.

Microbiota-mediated effects of Parkinson's disease medications on Parkinsonian non-motor symptoms in male transgenic mice

Parkinson's disease (PD) is characterized by motor symptoms and a loss of dopaminergic neurons, as well as a variety of non-motor symptoms, including constipation, depression, and anxiety. Recently, evidence has also accumulated for a link between gut microbiota and PD. Most PD patients are on dopamine replacement therapy, primarily a combination of L-DOPA and carbidopa; however, the effect of these medications on the microbiota and non-motor symptoms in PD is still unclear. In this study, we explored the effects of chronic oral treatment with L-DOPA plus carbidopa (LDCD) on the gut microbiota and non-motor symptoms in males of a transgenic mouse model of PD (dbl-PAC-Tg(SNCAA53T);Snca-/-). To further test whether the effects of these PD medications were mediated by the gut microbiota, oral antibiotic treatment (Abx; vancomycin and neomycin) was included both with and without concurrent LDCD treatment. Post-treatment, the gastrointestinal, motor, and behavioral phenotypes were profiled, and fecal, ileal, and jejunal samples were analyzed for gut microbiota composition by 16S sequencing. LDCD treatment was found to improve symptoms of constipation and depression in this model, concurrent with increases in Turicibacter abundance in the ileum. Abx treatment worsened the symptoms of constipation, possibly through decreased levels of short-chain fatty acids and disrupted gut barrier function. LDCD + Abx treatment showed an interaction effect on behavioral symptoms that was also associated with ileal Turicibacter levels. This study demonstrates that, in a mouse model, PD medications and antibiotics affect PD-related non-motor symptoms potentially via the gut microbiota.IMPORTANCEThe motor symptoms of Parkinson's disease (PD) are caused by a loss of dopamine-producing neurons and are commonly treated with dopamine replacement therapy (L-DOPA plus carbidopa). PD has also been associated with altered gut microbiota composition. However, the effects of these PD medications on PD-related non-motor symptoms and the gut microbiota have not been well characterized. This study uses a transgenic mouse model of PD to help resolve medication-induced microbiota alterations from those that are potentially disease relevant within a PD context, and explores how long-term treatment may interact with the gut microbiota to impact non-motor symptoms.

Pancreastatin deteriorates hepatic lipid metabolism via elevating fetuin B in ovariectomized rats

Hepatic steatosis is an important mstetabolic complication in women encountering postmenopausal phase of life. Pancreastatin (PST), has previously been investigated in diabetic and insulin resistant rodents. The present study highlighted the role of PST in ovariectomized rats. Female SD rats were ovariectomized and subsequently fed high fructose diet for 12 weeks. PST inhibitor peptide was intraperitoneally administered for 14 days and further examined for insulin resistance, glucose intolerance development, body mass composition, lipid profile detection and hepatic fibrosis. Gut microbial alterations has also been investigated. Results showed development of glucose intolerance in high fructose fed ovariectomized rats with reduced level of reproductive hormones including estradiol and progesterone. Enhanced lipid production was detected in these rats as they showed increased triglycerides, lipid accumulation in liver tissue (determined by HE staining, Oil Red O staining, Nile Red staining). Sirius Red and Masson's trichome analysis depicted positive results for fibrosis development. We also found gut microbiota alterations in fecal samples of these rats. Furthermore, PST inhibition decreased the expression of hepatic Fetuin B and resumed gut microbial diversity. PST deregulates hepatic lipid metabolism which leads to altered expression of Fetuin B in liver and gut dysbiosis in postmenopausal rats.

The Role of Aryl Hydrocarbon Receptor in the Endothelium: A Systematic Review

Activation of the aryl hydrocarbon receptor (AhR) has been shown to be important in physiological processes other than detoxification, including vascular homeostasis. Although AhR is highly expressed in the endothelium, its function has been poorly studied. This systematic review aims to summarise current knowledge on the AhR role in the endothelium and its cardiovascular implications. We focus on endogenous AhR agonists, such as some uremic toxins and other agonists unrelated to environmental pollutants, as well as studies using AhR knockout models. We conclude that AhR activation leads to vascular oxidative stress and endothelial dysfunction and that blocking AhR signalling could provide a new target for the treatment of vascular disorders such as cardiovascular complications in patients with chronic kidney disease or pulmonary arterial hypertension.

Gut Microbiota in Chronic Kidney Disease: From Composition to Modulation towards Better Outcomes-A Systematic Review

BACKGROUND

A bidirectional kidney-gut axis was described in patients with chronic kidney disease (CKD). On the one hand, gut dysbiosis could promote CKD progression, but on the other hand, studies reported specific gut microbiota alterations linked to CKD. Therefore, we aimed to systematically review the literature on gut microbiota composition in CKD patients, including those with advanced CKD stages and end-stage kidney disease (ESKD), possibilities to shift gut microbiota, and its impact on clinical outcomes.

MATERIALS AND METHODS

We performed a literature search in MEDLINE, Embase, Scopus, and Cochrane databases to find eligible studies using pre-specified keywords. Additionally, key inclusion and exclusion criteria were pre-defined to guide the eligibility assessment.

RESULTS

We retrieved 69 eligible studies which met all inclusion criteria and were analyzed in the present systematic review. Microbiota diversity was decreased in CKD patients as compared to healthy individuals. Ruminococcus and Roseburia had good power to discriminate between CKD patients and healthy controls (AUC = 0.771 and AUC = 0.803, respectively). Roseburia abundance was consistently decreased in CKD patients, especially in those with ESKD (p < 0.001). A model based on 25 microbiota dissimilarities had an excellent predictive power for diabetic nephropathy (AUC = 0.972). Several microbiota patterns were observed in deceased ESKD patients as compared to the survivor group (increased Lactobacillus, Yersinia, and decreased Bacteroides and Phascolarctobacterium levels). Additionally, gut dysbiosis was associated with peritonitis and enhanced inflammatory activity. In addition, some studies documented a beneficial effect on gut flora composition attributed to synbiotic and probiotic therapies. Large randomized clinical trials are required to investigate the impact of different microbiota modulation strategies on gut microflora composition and subsequent clinical outcomes.

CONCLUSIONS

Patients with CKD had an altered gut microbiome profile, even at early disease stages. Different abundance at genera and species levels could be used in clinical models to discriminate between healthy individuals and patients with CKD. ESKD patients with an increased mortality risk could be identified through gut microbiota analysis. Modulation therapy studies are warranted.

Gut microbiome studies in CKD: opportunities, pitfalls and therapeutic potential

Interest in gut microbiome dysbiosis and its potential association with the development and progression of chronic kidney disease (CKD) has increased substantially in the past 6 years. In parallel, the microbiome field has matured considerably as the importance of host-related and environmental factors is increasingly recognized. Past research output in the context of CKD insufficiently considered the myriad confounding factors that are characteristic of the disease. Gut microbiota-derived metabolites remain an interesting therapeutic target to decrease uraemic (cardio)toxicity. However, future studies on the effect of dietary and biotic interventions will require harmonization of relevant readouts to enable an in-depth understanding of the underlying beneficial mechanisms. High-quality standards throughout the entire microbiome analysis workflow are also of utmost importance to obtain reliable and reproducible results. Importantly, investigating the relative composition and abundance of gut bacteria, and their potential association with plasma uraemic toxins levels is not sufficient. As in other fields, the time has come to move towards in-depth quantitative and functional exploration of the patient's gut microbiome by relying on confounder-controlled quantitative microbial profiling, shotgun metagenomics and in vitro simulations of microorganism-microorganism and host-microorganism interactions. This step is crucial to enable the rational selection and monitoring of dietary and biotic intervention strategies that can be deployed as a personalized intervention in CKD.

Role of the Gut Microbiota in Children with Kidney Disease

Disruption of the composition and structure of the gut microbiota, namely dysbiosis, dictates the pathophysiology of kidney diseases. The bidirectional kidney-gut axis is of interest in chronic kidney disease (CKD); the uremic milieu leads to intestinal dysbiosis and gut microbial metabolites and toxins implicated in the loss of kidney function and increased comorbidity burden. Considering that kidney diseases can originate in childhood or even earlier in fetal life, identification of the pathogenetic connection between gut microbiota dysbiosis and the development of pediatric renal diseases deserves more attention. This review concentrates on the pathogenic link between dysbiotic gut microbiota and pediatric renal diseases, covering CKD, kidney transplantation, hemodialysis and peritoneal dialysis, and idiopathic nephrotic syndrome. Gut microbiota-targeted therapies including dietary intervention, probiotics, prebiotics, postbiotics and fecal microbial transplantation are discussed for their potential for the treatment of pediatric renal diseases. A deeper understanding of gut microbiota in pediatric renal diseases will aid in developing innovative gut microbiota-targeted interventions for preventing or attenuating the global burden of kidney diseases.

The Gut Microbiota (Microbiome) in Cardiovascular Disease and Its Therapeutic Regulation

In the last two decades, considerable interest has been shown in understanding the development of the gut microbiota and its internal and external effects on the intestine, as well as the risk factors for cardiovascular diseases (CVDs) such as metabolic syndrome. The intestinal microbiota plays a pivotal role in human health and disease. Recent studies revealed that the gut microbiota can affect the host body. CVDs are a leading cause of morbidity and mortality, and patients favor death over chronic kidney disease. For the function of gut microbiota in the host, molecules have to penetrate the intestinal epithelium or the surface cells of the host. Gut microbiota can utilize trimethylamine, N-oxide, short-chain fatty acids, and primary and secondary bile acid pathways. By affecting these living cells, the gut microbiota can cause heart failure, atherosclerosis, hypertension, myocardial fibrosis, myocardial infarction, and coronary artery disease. Previous studies of the gut microbiota and its relation to stroke pathogenesis and its consequences can provide new therapeutic prospects. This review highlights the interplay between the microbiota and its metabolites and addresses related interventions for the treatment of CVDs.

Intestinal microbiota dysbiosis in acute kidney injury: novel insights into mechanisms and promising therapeutic strategies

In recent years, the clinical impact of intestinal microbiota–kidney interaction has been emerging. Experimental evidence highlighted a bidirectional evolutionary correlation between intestinal microbiota and kidney diseases. Nonetheless, acute kidney injury (AKI) is still a global public health concern associated with high morbidity, mortality, healthcare costs, and limited efficient therapy. Several studies on the intestinal microbiome have improved the knowledge and treatment of AKI. Therefore, the present review outlines the concept of the gut–kidney axis and data about intestinal microbiota dysbiosis in AKI to improve the understanding of the mechanisms of the intestinal microbiome on the modification of kidney function and response to kidney injury. We also introduced the future directions and research areas, emphasizing the intervention approaches and recent research advances of intestinal microbiota dysbiosis during AKI, thereby providing a new perspective for future clinical trials.

The Microbiome and Uremic Solutes

Uremic retention solutes, especially the protein-bound compounds, are toxic metabolites, difficult to eliminate with progressive renal functional decline. They are of particular interest because these uremic solutes are responsible for the pathogenesis of cardiovascular and chronic kidney diseases. Evidence suggests that the relation between uremic toxins, the microbiome, and its host is altered in patients with chronic kidney disease, with the colon’s motility, epithelial integrity, and absorptive properties also playing an important role. Studies found an alteration of the microbiota composition with differences in species proportion, diversity, and function. Since uremic toxins precursors are generated by the microbiota, multiple therapeutic options are currently being explored to address dysbiosis. While an oral adsorbent can decrease the transport of bacterial metabolites from the intestinal lumen to the blood, dietary measures, supplements (prebiotics, probiotics, and synbiotics), and antibiotics aim to target directly the gut microbiota composition. Innovative approaches, such as the modulation of bacterial enzymes, open new perspectives to decrease the plasma level of uremic toxins.

The Intestinal Microbiota and Metabolites in the Gut-Kidney-Heart Axis of Chronic Kidney Disease

Emerging evidences demonstrate the involvement of gut microbiota in the progression of chronic kidney disease (CKD) and CKD-associated complications including cardiovascular disease (CVD) and intestinal dysfunction. In this review, we discuss the interactions between the gut, kidney and heart in CKD state, and elucidate the significant role of intestinal microbiota in the gut-kidney-heart axis hypothesis for the pathophysiological mechanisms of these diseases, during which process mitochondria may serve as a potential therapeutic target. Dysregulation of this axis will lead to a vicious circle, contributing to CKD progression. Recent studies suggest novel therapies targeting gut microbiota in the gut-kidney-heart axis, including dietary intervention, probiotics, prebiotics, genetically engineered bacteria, fecal microbiota transplantation, bacterial metabolites modulation, antibiotics, conventional drugs and traditional Chinese medicine. Further, the identification of specific microbial communities and their corresponding pathophysiological metabolites and the illumination of the gut-kidney-heart axis may contribute to innovative basic research, clinical trials and therapeutic strategies against CKD progression and uremic complications in CKD patients.

Chronic Consumption of Cocoa Rich in Procyanidins Has a Marginal Impact on Gut Microbiota and on Serum and Fecal Metabolomes in Male Endurance Athletes

Cocoa is used in the sports world as a supplement, although there is no consensus on its use. We investigated the effect of cocoa intake on intestinal ischemia (intestinal fatty acid-binding protein (I-FABP)), serum lipopolysaccharide (LPS) levels, gastrointestinal symptoms, and gut microbiota in endurance athletes during their training period on an unrestricted diet. We also performed a metabolomics analysis of serum and feces after a bout of exercise before and after supplementation. Cocoa consumption had no effect on I-FABP, LPS, or gastrointestinal symptoms. Cocoa intake significantly increased the abundance of Blautia and Lachnospira genera and decreased the abundance of the Agathobacter genus, which was accompanied by elevated levels of polyphenol fecal metabolites 4-hydroxy-5-(phenyl)-valeric acid and O-methyl-epicatechin-O-glucuronide. Our untargeted approach revealed that cocoa had no significant effects on serum and fecal metabolites and that its consumption had little impact on the metabolome after a bout of physical exercise.

MicroRNA-mediated vascular intercellular communication is altered in chronic kidney disease

AIMS

Chronic kidney disease (CKD) is an independent risk factor for the development of coronary artery disease (CAD). For both, CKD and CAD, the intercellular transfer of microRNAs (miRs) through extracellular vesicles (EVs) is an important factor of disease development. Whether the combination of CAD and CKD affects endothelial function through cellular crosstalk of EV-incorporated miRs is still unknown.

METHODS AND RESULTS

Out of 172 screened CAD patients, 31 patients with CAD + CKD were identified and matched with 31 CAD patients without CKD. Additionally, 13 controls without CAD and CKD were included. Large EVs from CAD + CKD patients contained significantly lower levels of the vasculo-protective miR-130a-3p and miR-126-3p compared to CAD patients and controls. Flow cytometric analysis of plasma-derived EVs revealed significantly higher numbers of endothelial cell-derived EVs in CAD and CAD + CKD patients compared to controls. EVs from CAD + CKD patients impaired target human coronary artery endothelial cell (HCAEC) proliferation upon incubation in vitro. Consistent with the clinical data, treatment with the uraemia toxin indoxyl sulfate (IS)-reduced miR-130a-3p levels in HCAEC-derived EVs. EVs from IS-treated donor HCAECs-reduced proliferation and re-endothelialization in EV-recipient cells and induced an anti-angiogenic gene expression profile. In a mouse-experiment, intravenous treatment with EVs from IS-treated endothelial cells significantly impaired endothelial regeneration. On the molecular level, we found that IS leads to an up-regulation of the heterogenous nuclear ribonucleoprotein U (hnRNPU), which retains miR-130a-3p in the cell leading to reduced vesicular miR-130a-3p export and impaired EV-recipient cell proliferation.

CONCLUSION

Our findings suggest that EV-miR-mediated vascular intercellular communication is altered in patients with CAD and CKD, promoting CKD-induced endothelial dysfunction.

Gut microbiome in hemodialysis patients treated with calcium acetate or treated with sucroferric oxyhydroxide: a pilot study

PURPOSE

It has been proved that the gut microbiome is altered in patients with chronic kidney disease. This contributes to chronic inflammation and increases cardiovascular risk and mortality, especially in those undergoing hemodialysis. Phosphate binders may potentially induce changes in their microbiome. This trial aimed to compare the changes in the gut microbiome of hemodialysis patients treated with calcium acetate to those treated with sucroferric oxyhydroxide.

METHODS

Twelve hemodialysis patients were distributed to receive calcium acetate or sucroferric oxyhydroxide for 5 months. Blood samples (for biochemical analysis) and stool samples (for microbiome analysis) were collected at baseline, 4, 12, and 20 weeks after treatment initiation. Fecal DNA was extracted and a 16S rRNA sequencing library was constructed targeting the V3 and V4 hypervariable regions.

RESULTS

Regarding clinical variables and laboratory parameters, no statistically significant differences were observed between calcium acetate or sucroferric oxyhydroxide groups. When analyzing stool samples, we found that all patients were different (p = 0.001) among themselves and these differences were kept along the 20 weeks of treatment. The clustering analysis in microbial profiles grouped the samples of the same patient independently of the treatment followed and the stage of the treatment.

CONCLUSION

These results suggest that a 5-month treatment with either calcium acetate or sucroferric oxyhydroxide did not modify baseline diversity or baseline bacterial composition in hemodialysis patients, also about the high-variability profiles of the gut microbiome found among these patients.

Diverse roles of microbial indole compounds in eukaryotic systems

Indole and its derivatives are widespread across different life forms, functioning as signalling molecules in prokaryotes and with more diverse roles in eukaryotes. A majority of indoles found in the environment are attributed to bacterial enzymes converting tryptophan into indole and its derivatives. The involvement of indoles among lower organisms as an interspecies and intraspecies signal is well known, with many reports showing that inter‐kingdom interactions involving microbial indole compounds are equally important as they influence defence systems and even the behaviour of higher organisms. This review summarizes recent advances in our understanding of the functional properties of indole and indole derivatives in diverse eukaryotes. Furthermore, we discuss current perspectives on the role of microbial indoles in human diseases such as diabetes, obesity, atherosclerosis, and cancers. Deciphering the function of indoles as biomarkers of metabolic state will facilitate the formulation of diet‐based treatments and open unique therapeutic opportunities.

Unconjugated p-cresol activates macrophage macropinocytosis leading to increased LDL uptake

Patients with chronic kidney disease (CKD) and end-stage renal disease suffer from increased cardiovascular events and cardiac mortality. Prior studies have demonstrated that a portion of this enhanced risk can be attributed to the accumulation of microbiota-derived toxic metabolites, with most studies focusing on the sulfonated form of p-cresol (PCS). However, unconjugated p-cresol (uPC) itself was never assessed due to rapid and extensive first-pass metabolism that results in negligible serum concentrations of uPC. These reports thus failed to consider the host exposure to uPC prior to hepatic metabolism. In the current study, not only did we measure the effect of altering the intestinal microbiota on lipid accumulation in coronary arteries, but we also examined macrophage lipid uptake and handling pathways in response to uPC. We found that atherosclerosis-prone mice fed a high-fat diet exhibited significantly higher coronary artery lipid deposits upon receiving fecal material from CKD mice. Furthermore, treatment with uPC increased total cholesterol, triglycerides, and hepatic and aortic fatty deposits in non-CKD mice. Studies employing an in vitro macrophage model demonstrated that uPC exposure increased apoptosis whereas PCS did not. Additionally, uPC exhibited higher potency than PCS to stimulate LDL uptake and only uPC induced endocytosis- and pinocytosis-related genes. Pharmacological inhibition of varying cholesterol influx and efflux systems indicated that uPC increased macrophage LDL uptake by activating macropinocytosis. Overall, these findings indicate that uPC itself had a distinct effect on macrophage biology that might have contributed to increased cardiovascular risk in patients with CKD.

Effect of Vancomycin on the Gut Microbiome and Plasma Concentrations of Gut-Derived Uremic Solutes

Introduction

Declining renal function results in the accumulation of solutes normally excreted by healthy kidneys. Data suggest that some of the protein-bound solutes mediate accelerated cardiovascular disease. Many of the poorly dialyzable protein-bound uremic retention solutes are products of gut bacterial metabolism.

Methods

We performed a blinded-randomized controlled trial comparing the changes in plasma concentrations of a panel of protein-bound solutes and microbiome structure in response to the once-weekly oral administration of 250 mg of vancomycin or placebo over a period of 12 weeks in a cohort of stable patients with end-stage kidney disease. We also examined the pattern of recovery of the solutes and gut microbiome over 12 weeks of placebo administration following vancomycin.

Results

We enrolled 15 subjects. Ten subjects provided sufficient plasma and stool samples to permit us to examine the effect of vancomycin on plasma solute levels. We showed that a weekly dose of vancomycin resulted in a reduction in the plasma concentration of 7 colon-derived solutes. We described a significant effect of vancomycin on the microbiome structure with a decrease in alpha diversity and change in beta diversity. Multiple taxa decreased with vancomycin including genera Clostridium and Bacteroides. We demonstrated microbiome recovery after stopping vancomycin. However, recovery in the solutes was highly variable between subjects.

Conclusions

We demonstrated that microbiome suppression using vancomycin resulted in changes in multiple gut-derived uremic solutes. Future studies are needed to address whether reduction in those uremic solutes results in improvement of cardiovascular outcomes in ESKD patients.

A metabolomics approach to investigate the proceedings of mitochondrial dysfunction in rats from prediabetes to diabetes

Diabetes mellitus (DM) is a leading cause of preventable cardiovascular disease, but the metabolic changes from prediabetes to diabetes have not been fully clarified. This study implemented a metabolomics profiling platform to investigate the variations of metabolites and to elucidate their global profiling from metabolic syndrome to DM. Methods: Male Sprague-Dawley rats (n = 44) were divided into four groups. Three groups were separately fed with a normal diet, a high-fructose diet (HF), or a high-fat (HL) diet while one group was treated with streptozotocin. The HF and HL diet were meant to induce insulin resistance, obesity, and dyslipidemia, which known to induce DM. Results: The most significant metabolic variations in the DM group’s urine samples were the reduced release of citric acid cycle intermediates, the increase in acylcarnitines, and the decrease in urea excretion, all of which indicated energy metabolism abnormalities and mitochondrial dysfunction. Overall, the metabolic analysis revealed tryptophan metabolic pathway variations in the prediabetic phase, even though the mitochondrial function remains unaffected. Conclusion: This study show that widespread methylations and impaired tryptophan metabolism occur in metabolic syndrome and are then followed by a decline in citric acid cycle intermediates, indicating mitochondrial dysfunction in diabetes.

Uremic Toxins in Organ Crosstalk

Many putative uremic toxins—like indoxyl sulfate, p-cresol sulfate, kynurenic acid, uric acid, and CMPF—are organic anions. Both inter-organ and inter-organismal communication are involved. For example, the gut microbiome is the main source of indole, which, after modification by liver drug metabolizing enzymes (DMEs), becomes indoxyl sulfate. Various organic anion transporters (organic anion transporters, OATs; organic anion-transporting polypeptides, OATPs; multidrug resistance-associated proteins, MRPs, and other ABC transporters like ABCG2)—often termed “drug transporters”—mediate movement of uremic toxins through cells and organs. In the kidney proximal tubule, critical roles for OAT1 and OAT3 in regulating levels of protein-bound uremic toxins have been established using knock-out mice. OATs are important in maintaining residual tubular function in chronic kidney disease (CKD); as CKD progresses, intestinal transporters like ABCG2, which extrude urate and other organic anions into the gut lumen, seem to help restore homeostasis. Uremic toxins like indoxyl sulfate also regulate signaling and metabolism, potentially affecting gene expression in extra-renal tissues as well as the kidney. Focusing on the history and evolving story of indoxyl sulfate, we discuss how uremic toxins appear to be part of an extensive “remote sensing and signaling” network—involving so-called drug transporters and drug metabolizing enzymes which modulate metabolism and signaling. This systems biology view of uremic toxins is leading to a new appreciation of uremia as partly due to disordered remote sensing and signaling mechanisms–resulting from, and causing, aberrant inter-organ (e.g., gut-liver- kidney-CNS) and inter-organismal (e.g., gut microbiome-host) communication.

Renal Replacement Modality Affects Uremic Toxins and Oxidative Stress

Nowadays, the high prevalence of kidney diseases and their related complications, including endothelial dysfunction and cardiovascular disease, represents one of the leading causes of death in patients with chronic kidney diseases. Renal failure leads to accumulation of uremic toxins, which are the main cause of oxidative stress development. The renal replacement therapy appears to be the best way to lower uremic toxin levels in patients with end-stage renal disease and reduce oxidative stress. At this moment, despite the increasing number of recognized toxins and their mechanisms of action, it is impossible to determine which of them are the most important and which cause the greatest complications. There are many different types of renal replacement therapy, but the best treatment has not been identified yet. Patients treated with diffusion methods have satisfactory clearance of small molecules, but the clearance of medium molecules appears to be insufficient, but treatment with convection methods cleans medium molecules better than small molecules. Hence, there is an urgent need of new more validated, appropriate, and reliable information not only on toxins and their role in metabolic disorders, including oxidative stress, but also on the best artificial renal replacement therapy to reduce complications and prolong the life of patients with chronic kidney disease.

Changes in the Serum Metabolome of Patients Treated With Broad-Spectrum Antibiotics

Background:

The gut microbiome (GMB) generates numerous small chemicals that can be absorbed by the host and variously biotransformed, incorporated, or excreted. The resulting metabolome can provide information about the state of the GMB, of the host, and of their relationship. Exploiting this information in the service of biomarker development is contingent on knowing the GMB-sensitivity of the individual chemicals comprising the metabolome. In this regard, human studies have lagged far behind animal studies. Accordingly, we tested the hypothesis that serum levels of chemicals unequivocally demonstrated to be GMB-sensitive in rodent models would also be affected in a clinical patient sample treated with broad spectrum antibiotics.

Methods:

We collected serum samples from 20 hospitalized patients before, during, and after treatment with broad-spectrum antibiotics. We also collected samples from 5 control patients admitted to the hospital but not prescribed antibiotics. We submitted the samples for a non-targeted metabolomic analysis and then focused on chemicals known to be affected both by germ-free status and by antibiotic treatment in the mouse and/or rat.

Results:

Putative identification was obtained for 499 chemicals in human serum. An aggregate analysis did not show any time x treatment interactions. However, our literature search identified 10 serum chemicals affected both by germ-free status and antibiotic treatment in the mouse or rat. Six of those chemicals were measured in our patient samples and additionally met criteria for inclusion in a focused analysis. Serum levels of 5 chemicals (p-cresol sulfate, phenol sulfate, hippurate, indole propionate, and indoxyl sulfate) declined significantly in our group of antibiotic-treated patients but did not change in our patient control group.

Conclusions:

Broad-spectrum antibiotic treatment in patients lowered serum levels of selected chemicals previously demonstrated to be GMB-sensitive in rodent models. Interestingly, all those chemicals are known to be uremic solutes that can be derived from aromatic amino acids (L-phenylalanine, L-tyrosine, or L-tryptophan) by anaerobic bacteria, particularly Clostridial species. We conclude that judiciously selected serum chemicals can reliably detect antibiotic-induced suppression of the GMB in man and thus facilitate further metabolome-based biomarker development.

Randomized, Placebo-Controlled Trial of Rifaximin Therapy for Lowering Gut-Derived Cardiovascular Toxins and Inflammation in CKD

Background

Recent evidence suggests the systemic accumulation of by-products of gut microbes contributes to cardiovascular morbidity in patients with CKD. Limiting the generation of toxic bacterial by-products by manipulating the intestinal microbiota may be a novel strategy for reducing cardiovascular disease in CKD. Rifaximin is a minimally absorbed, oral antibiotic that targets intestinal pathogens and is commonly used as chronic therapy for the prevention of encephalopathy in patients with cirrhosis.

Methods

We conducted a randomized, double-blinded, placebo-controlled trial to determine the effect of a 10-day course of oral rifaximin 550 mg BID versus placebo on circulating concentrations of gut-derived cardiovascular toxins and proinflammatory cytokines in patients with stage 3-5 CKD (n=38). The primary clinical outcome was change in serum trimethylamine N-oxide (TMAO) concentrations from baseline to study end. Secondary outcomes included change in serum concentrations of p-cresol sulfate, indoxyl sulfate, kynurenic acid, deoxycholic acid, and inflammatory cytokines (C-reactive protein, IL-6, IL-1β), and change in composition and diversity of fecal microbiota.

Results

A total of 19 patients were randomized to each of the rifaximin and placebo arms, with n=17 and n=14 completing both study visits in these respective groups. We observed no difference in serum TMAO change (post-therapy minus baseline TMAO) between the rifaximin and placebo groups (mean TMAO change -3.9±15.4 for rifaximin versus 0.5±9.5 for placebo, P=0.49). Similarly, we found no significant change in serum concentrations for p-cresol sulfate, indoxyl sulfate, kynurenic acid, deoxycholic acid, and inflammatory cytokines. We did observe differences in colonic bacterial communities, with the rifaximin group exhibiting significant decreases in bacterial richness (Chao1, P=0.02) and diversity (Shannon H, P=0.05), along with altered abundance of several bacterial genera.

Conclusions

Short-term rifaximin treatment failed to reduce gut-derived cardiovascular toxins and inflammatory cytokines in patients with CKD.

Clinical Trial registry name and registration number

Rifaximin Therapy in Chronic Kidney Disease, NCT02342639.

Effects of Fecal Microbiota Transplantation on Composition in Mice with CKD

Background: Chronic kidney disease (CKD) is a renal disorder characterized by the accumulation of uremic toxins with limited strategies to reduce their concentrations. A large amount of data supports the pivotal role of intestinal microbiota in CKD complications and as a major source of uremic toxins production. Here, we explored whether fecal microbiota transplantation (FMT) could be attenuated in metabolic complication and uremic toxin accumulation in mice with CKD. Methods: Kidney failure was chemically induced by a diet containing 0.25% (w/w) of adenine for four weeks. Mice were randomized into three groups: control, CKD and CKD + FMT groups. After four weeks, CKD mice underwent fecal microbiota transplantation (FMT) from healthy mice or phosphate buffered saline as control. The gut microbiota structure, uremic toxins plasmatic concentrations, and metabolic profiles were explored three weeks after transplantation. Results: Associated with the increase of alpha diversity, we observed a noticeable improvement of gut microbiota disturbance, after FMT treatment. FMT further decreased p-cresyl sulfate accumulation and improved glucose tolerance. There was no change in kidney function. Conclusions: These data indicate that FMT limited the accumulation of uremic toxins issued from intestinal cresol pathway by a beneficial effect on gut microbiota diversity. Further studies are needed to investigate the FMT efficiency, the timing and feces amount for the transplantation before, to become a therapeutic option in CKD patients.

Indoxyl sulfate induces ROS production via the aryl hydrocarbon receptor-NADPH oxidase pathway and inactivates NO in vascular tissues

AIMS

The uremic toxin indoxyl sulfate (IS) was reported to be the cause of cardiovascular disease associated with chronic kidney disease. Therefore, we evaluated the direct influences of IS on vascular function, focusing on the superoxide anion (O₂^-) and nitric oxide (NO)/soluble guanylate cyclase (sGC) pathways.

MAIN METHODS

Isolated rat thoracic aortas with and without vascular endothelium were incubated with IS for 4 h in a physiological solution. In some experiments, several inhibitors were treated 30 min before the addition of IS. O₂^- production was measured by the chemiluminescence method, and the vascular reactivity to different vasorelaxants was examined using organ chamber technique.

KEY FINDINGS

1) Experiments using endothelium-intact vascular rings: IS significantly increased O₂^- production. The increase was suppressed by addition of the NADPH oxidase inhibitor apocynin, the antioxidant ascorbic acid and the aryl hydrocarbon receptor (AhR) inhibitor CH223191. Furthermore, IS attenuated the acetylcholine (ACh)-induced vasorelaxantion, which was suppressed by addition of the above drugs. 2) Experiments using endothelium-denuded vascular rings: IS significantly increased O₂^- production and also attenuated sodium nitroprusside (SNP)-induced vasorelaxation. These influences of IS were normalized only by ascorbic acid addition. On the other hand, IS did not affect the vasorelaxation by the sGC stimulator BAY 41-2272.

SIGNIFICANCE

This study suggested that IS causes O₂^- production in vascular tissues, thereby attenuating ACh- and SNP-induced vasorelaxation, probably through NO inactivation. Furthermore, it is reasonable to consider that IS-promoted O₂^- production in the presence of vascular endothelium is through binding to AhR and the activation of NADPH oxidase.

Serum indoxyl sulfate concentrations associate with progression of chronic kidney disease in children

The uremic toxins indoxyl sulfate (IS) and p-cresyl sulfate (pCS) accumulate in patients with chronic kidney disease (CKD) as a consequence of altered gut microbiota metabolism and a decline in renal excretion. Despite of solid experimental evidence for nephrotoxic effects, the impact of uremic toxins on the progression of CKD has not been investigated in representative patient cohorts. In this analysis, IS and pCS serum concentrations were measured in 604 pediatric participants (mean eGFR of 27 ± 11 ml/min/1.73m2) at enrolment into the prospective Cardiovascular Comorbidity in Children with CKD study. Associations with progression of CKD were analyzed by Kaplan-Meier analyses and Cox proportional hazard models. During a median follow up time of 2.2 years (IQR 4.3-0.8 years), the composite renal survival endpoint, defined as 50% loss of eGFR, or eGFR <10ml/min/1.73m2 or start of renal replacement therapy, was reached by 360 patients (60%). Median survival time was shorter in patients with IS and pCS levels in the highest versus lowest quartile for both IS (1.5 years, 95%CI [1.1,2.0] versus 6.0 years, 95%CI [5.0,8.4]) and pCS (1.8 years, 95%CI [1.5,2.8] versus 4.4 years, 95%CI [3.4,6.0]). Multivariable Cox regression disclosed a significant association of IS, but not pCS, with renal survival, which was independent of other risk factors including baseline eGFR, proteinuria and blood pressure. In this exploratory analysis we provide the first data showing a significant association of IS, but not pCS serum concentrations with the progression of CKD in children, independent of other known risk factors. In the absence of comorbidities, which interfere with serum levels of uremic toxins, such as diabetes, obesity and metabolic syndrome, these results highlight the important role of uremic toxins and accentuate the unmet need of effective elimination strategies to lower the uremic toxin burden and abate progression of CKD.

Associations Among Plant-Based Diet Quality, Uremic Toxins, and Gut Microbiota Profile in Adults Undergoing Hemodialysis Therapy

OBJECTIVE

The objective of the study was to evaluate associations among diet quality, serum uremic toxin concentrations, and the gut microbiota profile in adults undergoing hemodialysis therapy.

DESIGN AND METHODS

This is a cross-sectional analysis of baseline data from a clinical trial involving adults receiving hemodialysis therapy. Usual dietary intake was determined using a diet history method administered by Accredited Practising Dietitians. Two approaches were used for diet quality assessment: (1) using three a priori defined plant-based diet indices-an overall plant-based diet index (PDI), a healthy PDI, and an unhealthy PDI and (2) classification of food group intake. Serum uremic toxins (p-cresyl sulfate and indoxyl sulfate (IS); free and total) were determined by ultra-performance liquid chromatography. Gut microbiota composition was established through sequencing the 16S rRNA gene in stool samples.

RESULTS

Twenty-two adults (median age 70.5 [interquartile range: 59-76], 64% male) were included in the final analysis. Higher adherence to the PDI was associated with lower total IS levels (P = .028), independent of dialysis adequacy, urinary output, and blood albumin levels. In contrast, higher adherence to the unhealthy PDI was associated with increases in both free and total IS. Several other direct and inverse associations between diet quality with uremic toxins, microbial relative abundances, and diversity metrics were also highlighted. Diet-associated taxa showed significantly different trends of association with serum uremic toxin concentrations (P < .05). Higher adherence to the PDI was negatively associated with relative abundances of Haemophilus and Haemophilus parainfluenzae that were related to elevated total IS levels. In contrast, increased intake of food items considered unhealthy, such as animal fats, sweets and desserts, were associated with bacteria linked to higher IS and p-cresyl sulfate (total and free) concentrations.

CONCLUSIONS

The quality of diet and food selections may influence uremic toxin production by the gut microbiota in adults receiving hemodialysis. Well-designed dietary intervention trials that adopt multi-omic technologies appropriate for the functional annotation of the gut microbiome are needed to validate our findings and establish causality.

Compositional and Functional Adaptations of Intestinal Microbiota and Related Metabolites in CKD Patients Receiving Dietary Protein Restriction

The relationship between change of gut microbiota and host serum metabolomics associated with low protein diet (LPD) has been unraveled incompletely in CKD patients. Fecal 16S rRNA gene sequencing and serum metabolomics profiling were performed. We reported significant changes in the β-diversity of gut microbiota in CKD patients having LPD (CKD-LPD, n = 16). We identified 19 genera and 12 species with significant differences in their relative abundance among CKD-LPD patients compared to patients receiving normal protein diet (CKD-NPD, n = 27) or non-CKD controls (n = 34), respectively. CKD-LPD had a significant decrease in the abundance of many butyrate-producing bacteria (family Lachnospiraceae and Bacteroidaceae) associated with enrichment of functional module of butanoate metabolism, leading to concomitant reduction in serum levels of SCFA (acetic, heptanoic and nonanoic acid). A secondary bile acid, glyco λ-muricholic acid, was significantly increased in CKD-LPD patients. Serum levels of indoxyl sulfate and p-cresyl sulfate did not differ among groups. The relationship between abundances of microbes and metabolites remained significant in subset of resampling subjects of comparable characteristics. Enrichment of bacterial gene markers related to D-alanine, ketone bodies and glutathione metabolism was noted in CKD-LPD patients. Our analyses reveal signatures and functions of gut microbiota to adapt dietary protein restriction in renal patients.

Bioavailability Based on the Gut Microbiota: a New Perspective

The substantial discrepancy between the strong effects of functional foods and various drugs, especially traditional Chinese medicines (TCMs), and the poor bioavailability of these substances remains a perplexing problem. Understanding the gut microbiota, which acts as an effective bioreactor in the human intestinal tract, provides an opportunity for the redefinition of bioavailability. Here, we discuss four different pathways associated with the role of the gut microbiota in the transformation of parent compounds to beneficial or detrimental small molecules, which can enter the body's circulatory system and be available to target cells, tissues, and organs. We further describe and propose effective strategies for improving bioavailability and alleviating side effects with the help of the gut microbiota. This review also broadens our perspectives for the discovery of new medicinal components.

Vascular Calcification: An Important Understanding in Nephrology

Vascular calcification (VC) is a life-threatening state in chronic kidney disease (CKD). High cardiovascular mortality and morbidity of CKD cases may root from medial VC promoted by hyperphosphatemia. Vascular calcification is an active, highly regulated, and complex biological process that is mediated by genetics, epigenetics, dysregulated form of matrix mineral metabolism, hormones, and the activation of cellular signaling pathways. Moreover, gut microbiome as a source of uremic toxins (eg, phosphate, advanced glycation end products and indoxyl-sulfate) can be regarded as a potential contributor to VC in CKD. Here, an update on different cellular and molecular processes involved in VC in CKD is discussed to elucidate the probable therapeutic pathways in the future.

The Controversial Role of Human Gut Lachnospiraceae

The complex polymicrobial composition of human gut microbiota plays a key role in health and disease. Lachnospiraceae belong to the core of gut microbiota, colonizing the intestinal lumen from birth and increasing, in terms of species richness and their relative abundances during the host's life. Although, members of Lachnospiraceae are among the main producers of short-chain fatty acids, different taxa of Lachnospiraceae are also associated with different intra- and extraintestinal diseases. Their impact on the host physiology is often inconsistent across different studies. Here, we discuss changes in Lachnospiraceae abundances according to health and disease. With the aim of harnessing Lachnospiraceae to promote human health, we also analyze how nutrients from the host diet can influence their growth and how their metabolites can, in turn, influence host physiology.

Gut-derived uremic toxin handling in vivo requires OAT-mediated tubular secretion in chronic kidney disease

The role of the renal organic anion transporters OAT1 (also known as SLC22A6, originally identified as NKT) and OAT3 (also known as SLC22A8) in chronic kidney disease (CKD) remains poorly understood. This is particularly so from the viewpoint of residual proximal tubular secretion, a key adaptive mechanism to deal with protein-bound uremic toxins in CKD. Using the subtotal nephrectomy (STN) model, plasma metabolites accumulating in STN rats treated with and without the OAT inhibitor, probenecid, were identified. Comparisons with metabolomics data from Oat1-KO and Oat3-KO mice support the centrality of the OATs in residual tubular secretion of uremic solutes, such as indoxyl sulfate, kynurenate, and anthranilate. Overlapping our data with those of published metabolomics data regarding gut microbiome-derived uremic solutes - which can have dual roles in signaling and toxicity - indicates that OATs play a critical role in determining their plasma levels in CKD. Thus, the OATs, along with other SLC and ABC drug transporters, are critical to the movement of uremic solutes across tissues and into various body fluids, consistent with the remote sensing and signaling theory. The data support a role for OATs in modulating remote interorganismal and interorgan communication (gut microbiota-blood-liver-kidney-urine). The results also have implications for understanding drug-metabolite interactions involving uremic toxins.

Cardiac Remodeling in Chronic Kidney Disease

Cardiac remodeling occurs frequently in chronic kidney disease patients and affects quality of life and survival. Current treatment options are highly inadequate. As kidney function declines, numerous metabolic pathways are disturbed. Kidney and heart functions are highly connected by organ crosstalk. Among others, altered volume and pressure status, ischemia, accelerated atherosclerosis and arteriosclerosis, disturbed mineral metabolism, renal anemia, activation of the renin-angiotensin system, uremic toxins, oxidative stress and upregulation of cytokines stress the sensitive interplay between different cardiac cell types. The fatal consequences are left-ventricular hypertrophy, fibrosis and capillary rarefaction, which lead to systolic and/or diastolic left-ventricular failure. Furthermore, fibrosis triggers electric instability and sudden cardiac death. This review focuses on established and potential pathophysiological cardiorenal crosstalk mechanisms that drive uremia-induced senescence and disease progression, including potential known targets and animal models that might help us to better understand the disease and to identify novel therapeutics.

Gut microbiota; an overlooked effect of phosphate binders

Hyperphosphatemia is a mineral bone-disease that increases cardiovascular complications and all-cause mortality in chronic kidney disease (CKD) patients. Oral phosphate binders absorb the dietary phosphate to prevent its high plasma levels. Moreover, they can adsorb some uremic toxins and decrease inflammation. A few recent studies highlight an ignored effect of phosphate binders on gut microbiota. Phosphorous is a major nutrient for survival and reproduction of bacteria and its intestinal concentration may impact the activity and composition of the gut microbiota. CKD is a state of an altered gut microbiome and bacterial-derived uremic toxins stimulate cardiovascular disease and systemic inflammation. The identification of the impact of phosphate binders on gut opens a new era in nephrology and fill the existing gap in interpretation of beneficial effects of phosphate binders. This review aims to highlight the impact of oral phosphate binders on the gut microbiome in CKD.

Microbiome-metabolomics reveals gut microbiota associated with glycine-conjugated metabolites and polyamine metabolism in chronic kidney disease

Dysbiosis of the gut microbiome and related metabolites in chronic kidney disease (CKD) have been intimately associated with the prevalence of cardiovascular diseases. Unfortunately, thus far, there is a paucity of sufficient knowledge of gut microbiome and related metabolites on CKD progression partly due to the severely limited investigations. Using a 5/6 nephrectomized (NX) rat model, we carried out 16S rRNA sequence and untargeted metabolomic analyses to explore the relationship between colon's microbiota and serum metabolites. Marked decline in microbial diversity and richness was accompanied by significant changes in 291 serum metabolites, which were mediated by altered enzymatic activities and dysregulations of lipids, amino acids, bile acids and polyamines metabolisms. Interestingly, CCr was directly associated with some microbial genera and polyamine metabolism. However, SBP was directly related to certain microbial genera and glycine-conjugated metabolites in CKD rats. Administration of poricoic acid A (PAA) and Poria cocos (PC) ameliorated microbial dysbiosis as well as attenuated hypertension and renal fibrosis. In addition, treatments with PAA and PC lowered serum levels of microbial-derived products including glycine-conjugated compounds and polyamine metabolites. Collectively, the present study confirmed the CKD-associated gut microbial dysbiosis and identified a novel dietary and therapeutic strategy to improve the gut microbial dysbiosis and the associated metabolomic disorders and retarded the progression of kidney disease in the rat model of CKD.

Microbial Contribution to the Human Metabolome: Implications for Health and Disease

The human gastrointestinal tract is home to an incredibly dense population of microbes. These microbes employ unique strategies to capture energy in this largely anaerobic environment. In the process of breaking down dietary- and host-derived substrates, the gut microbiota produce a broad range of metabolic products that accumulate to high levels in the gut. Increasingly, studies are revealing that these chemicals impact host biology, either by acting on cells within the gastrointestinal tract or entering circulation and exerting their effects at distal sites within the body. Given the high level of functional diversity in the gut microbiome and the varied diets that we consume, the repertoire of microbiota-derived molecules within our bodies varies dramatically across individuals. Thus, the microbes in our gut and the metabolic end products they produce represent a phenotypic lever that we can potentially control to develop new therapeutics for personalized medicine. Here, we review current understanding of how microbes in the gastrointestinal tract contribute to the molecules within our gut and those that circulate within our bodies. We also highlight examples of how these molecules affect host physiology and discuss potential strategies for controlling their production to promote human health and to treat disease.

Gastrointestinal Microbiota in Patients with Chronic Kidney Disease: A Systematic Review

Emerging evidence suggests that gastrointestinal (GI) microbiota dysbiosis is associated with chronic kidney disease (CKD) and metabolite concentrations. The purpose of this systematic review was to evaluate and contextualize the research characterizing GI microbiota in patients with CKD. We searched for full-text, peer-reviewed, English studies in PubMed, Cumulative Index to Nursing and Allied Health Literature, Web of Science, and Google Scholar using a combination of MeSH terms and keywords. Eleven of the 20 studies examined GI microbiota in patients with CKD, and 9 studies focused on the effect of interventions on GI microbiota or metabolites. Available data characterizing GI microbiota in patients with CKD suggest a decline in saccharolytic bacteria and an increase in fermenters of nitrogen-containing compounds, serving as a source for circulating uremic toxins. However, studies examined limited sets of predetermined microbes, which do not reflect the entire GI microbial community and its influence on host physiology. We recommend further studies examining the entire microbial community and the potential role in regulating host physiology in CKD.

A swan song for Kt/Vurea

Dialyzer clearance of urea multiplied by dialysis time and normalized for urea distribution volume (Kt/V_urea or simply Kt/V) has been used as an index of dialysis adequacy since more than 30 years. This article reviews the flaws of Kt/V, starting with a lack of proof of concept in three randomized controlled hard outcome trials (RCTs), and continuing with a long list of conditions where the concept of Kt/V was shown to be flawed. This information leaves little room for any conclusion other than that Kt/V, as an indicator of dialysis adequacy, is obsolete. The dialysis patient might benefit more if, instead, the nephrology community concentrates in the future on pursuing the optimal dialysis dose that conforms with adequate quality of life and on factors that are likely to affect outcomes more than Kt/V. These include residual renal function, volume status, dialysis length, ultrafiltration rate, the number of intra-dialytic hypotensive episodes, interdialytic blood pressure, serum potassium and phosphate, serum albumin, and C reactive protein.

The role of chronic kidney disease-associated dysbiosis in cardiovascular disease

IMPACT STATEMENT

Negative alterations, or dysbiosis, in the intestinal microbial community balance in response to chronic kidney disease is emerging as a substantial and important factor in inducing and exacerbating multiple comorbid conditions. Patients with renal insufficiency experience a substantial increase in cardiovascular risk, and recent evidence is shedding light on the close interaction between microbiome dysbiosis and increased cardiovascular events in this population. Previous association and recent causality studies utilizing experimental animal models have enriched our understanding and confirmed the impact of microbial community imbalance on cardiac health in both the general population and in patients with renal impairment.

Unilateral ureteral obstruction causes gut microbial dysbiosis and metabolome disorders contributing to tubulointerstitial fibrosis

Chronic kidney disease (CKD) increases the risk and prevalence of cardiovascular disease (CVD) morbidity and mortality. Recent studies have revealed marked changes in the composition of the microbiome and the metabolome and their potential influence in renal disease and CVD via the accumulation of microbial-derived uremic toxins. However, the effect of unilateral ureteral obstruction (UUO) on the gut microbiome and circulating metabolites is unknown. Male Sprague-Dawley rats were randomized to UUO and sham-operated control groups. Renal histology, colonic microbiota, and plasma metabolites were examined two weeks later. We employed 16S rRNA sequence and untargeted metabolomic analyses to explore the changes in colonic microbiota and plasma metabolites and their relationship with tubulointerstitial fibrosis (TIF). The UUO rats exhibited tubular atrophy and dilatation, interstitial fibrosis and inflammatory cell infiltration in the obstructed kidney. UUO rats showed significant colonic enrichment and depletion of genera. Significant differences were identified in 219 plasma metabolites involved in lipid, amino acid, and bile acid metabolism, which were consistent with gut microbiota-related metabolism. Interestingly, tryptophan and its metabolites kynurenine, 5-hydroxytryptophan and 5-hydroxytryptamine levels, which were linked with TIF, correlated with nine specific genera. Plasma tryptophan level was positively correlated with Clostridium IV, Turicibacter, Pseudomonas and Lactobacillales, and negatively correlated with Oscillibacter, Blautia, and Intestinimonas, which possess the genes encoding tryptophan synthase (K16187), indoleamine 2,3-dioxygenase (K00463) and tryptophan 2,3-dioxygenase (K00453) and their corresponding enzymes (EC:1.13.11.52 and EC:1.13.11.11) that exacerbate TIF. In conclusion, UUO results in profound changes in the gut microbiome and circulating metabolites, events that contribute to the pathogenesis of inflammation and TIF.

Evolution of protein-bound uremic toxins indoxyl sulphate and p-cresyl sulphate in acute kidney injury

BACKGROUND

There is a gradual increase in serum concentrations of protein-bound colon-derived uremic toxins indoxyl sulphate (IxS) and p-cresyl sulphate (pCS) as chronic kidney disease (CKD) progresses. In acute kidney injury (AKI), up till now, the retention pattern has not been studied.

METHODS

In this study, 194 adult patients admitted with sepsis to the intensive care unit were included. IxS, pCS and serum creatinine (sCrea) were quantified at inclusion (D0) and at day 4, unless follow-up ended earlier (D_end).

RESULTS

Serum levels of sCrea (P < 0.001), IxS (P < 0.001) and pCS (P < 0.05) were higher in patients with AKI according to RIFLE classification at D0. In contrast with sCrea, IxS and pCS levels only increased from stage I (IxS) and F (pCS) on. When grouped according to evolution in RIFLE class from D0 to D_end, all solute concentrations were higher (P < 0.001) in the group with unfavourable evolution. In this group, there was a marked rise in sCrea (P < 0.001), a moderate one for pCS (P < 0.05), but no change for IxS (P = 0.112). There was a decrease (P < 0.001) of all solute concentrations in the group with favourable evolution. Comparing AKI with CKD patients matched for sCrea, total levels of both IxS and pCS were higher (P < 0.01) in patients with CKD.

CONCLUSIONS

Although concentrations of IxS and pCS both tend to rise in sepsis patients with AKI, their evolution does not conform with that of sCrea. For the same level of sCrea, IxS and pCS concentrations are lower in AKI compared with CKD.

The fecal microbiome and serum concentrations of indoxyl sulfate and p-cresol sulfate in cats with chronic kidney disease

Background

Intestinal dysbiosis has been documented in humans with chronic kidney disease (CKD) and is thought to contribute to production of the uremic toxins indoxyl sulfate (IS) and p‐cresol sulfate (pCS). Characteristics of the fecal microbiome in cats with CKD and correlation to serum concentrations of uremic toxins are unknown.

Objectives

To characterize the fecal microbiome and measure serum IS and pCS concentrations of cats with CKD in comparison to healthy older cats.

Animals

Thirty client‐owned cats with CKD (International Renal Interest Society stages 2‐4) and 11 older (≥8 years) healthy control cats.

Methods

Prospective, cross‐sectional study. Fecal samples were analyzed by sequencing of 16S rRNA genes and Escherichia coli quantitative PCR (qPCR). Serum concentrations of IS and pCS measured using liquid chromatography tandem mass spectrometry.

Results

Cats with CKD had significantly decreased fecal bacterial diversity and richness. Escherichia coli qPCR showed no significant difference in bacteria count between control and CKD cats. Cats with stage 2 (P = .01) and stages 3 and 4 (P = .0006) CKD had significantly higher serum IS concentrations compared to control cats. No significant difference found between stage 2 and stages 3 and 4 CKD. The pCS concentrations were not significantly different between CKD cats and control cats.

Conclusions and Clinical Importance

Decreased fecal microbiome diversity and richness is associated with CKD in cats. Indoxyl sulfate concentration is significantly increased with CKD, and cats with stage 2 CKD may suffer from a similar uremic toxin burden as do cats with later stage disease.

Action Mechanisms and Therapeutic Targets of Renal Fibrosis

Renal fibrosis was a chronic and progressive process affecting kidneys in chronic kidney disease (CKD), regardless of cause. Although no effective targeted therapy yet existed to retard renal fibrosis, a number of important recent advances have highlighted the cellular and molecular mechanisms underlying the renal fibrosis. The advances including TGF-β/Smad pathway, oxidative stress and inflammation, hypoxia and gut microbiota-derived from uremic solutes were highlighted that could provide therapeutic targets. New therapeutic targets and strategies that are particularly promising for development of new treatments for patients with CKD were also highlighted.

Microbiome and Cardiovascular Disease in CKD

Patients with CKD exhibit a disproportionate burden of cardiovascular mortality, which likely stems from the presence of unique, nontraditional risk factors that accompany deteriorating kidney function. Mounting evidence suggests that alterations to the intestinal microbiome in CKD may serve as one such risk factor. The human intestinal tract is home to >100 trillion micro-organisms made up of a collection of commensal, symbiotic, and pathogenic species. These species along with their local environment constitute the intestinal microbiome. Patients with CKD show intestinal dysbiosis, an alteration of the gut micro-organism composition and function. Recent evidence links byproducts of intestinal dysbiosis to vascular calcification, atherosclerosis formation, and adverse cardiovascular outcomes in CKD. CKD-associated intestinal dysbiosis may also be accompanied by defects in intestinal barrier function, which could further enhance the negative effects of pathogenic intestinal bacteria in the human host. Thus, intestinal dysbiosis, defective intestinal barrier function, and a reduced capacity for clearance by the kidney of absorbed bacterial byproducts may all potentiate the development of cardiovascular disease in CKD. This narrative review focuses on microbiome-mediated mechanisms associated with CKD that may promote atherosclerosis formation and cardiovascular disease. It includes (1) new data supporting the hypothesis that intestinal barrier dysfunction leads to bacterial translocation and endotoxemia that potentiate systemic inflammation, (2) information on the accumulation of dietary-derived bacterial byproducts that stimulate pathways promoting atheromatous changes in arteries and cardiovascular disease, and (3) potential interventions. Despite great scientific interest in and a rapidly growing body of literature on the relationship between the microbiome and cardiovascular disease in CKD, many important questions remain unanswered.

Characteristics of Colon-Derived Uremic Solutes

BACKGROUND AND OBJECTIVES

Colon microbial metabolism produces solutes that are normally excreted in the urine and accumulate in the plasma when the kidneys fail. This study sought to further identify and characterize human colon-derived uremic solutes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Colon-derived solutes normally excreted in the urine were identified by comparing urine from controls (n=17) and patients with total colectomies (n=12), using an established metabolomic platform. Colon-derived solutes that accumulate in kidney failure were then identified by comparing the plasma of the control patients with that of patients on dialysis (n=14).

RESULTS

Ninety-one urinary solutes were classified as colon-derived on the basis of the finding of a urine excretion rate at least four-fold higher in control patients than in patients with total colectomies. Forty-six were solutes with known chemical structure, 35 of which had not previously been identified as colon-derived. Sixty of the colon-derived solutes accumulated in the plasma of patients with ESKD to a degree greater than urea and were therefore classified as uremic. The estimated urinary clearance for 27 out of the 32 colon-derived solutes for which clearance could be calculated exceeded that of creatinine, consistent with tubular secretion. Sulfatase treatment revealed that 42 out of the 91 colon-derived solutes detected were likely conjugates.

CONCLUSIONS

Metabolomic analysis identified numerous colon-derived solutes that are normally excreted in human urine. Clearance by tubular secretion limits plasma levels of many colon-derived solutes.

The effect of isohydric hemodialysis on the binding and removal of uremic retention solutes

Background

There is growing evidence that the accumulation of protein- bound uremic retention solutes, such as indoxyl sulfate, p-cresyl sulfate and kynurenic acid, play a role in the accelerated cardiovascular disease seen in patients undergoing chronic hemodialysis. Protein-binding, presumably to albumin, renders these solutes poor-dialyzable.

We previously observed that the free fraction of indoxyl sulfate was markedly reduced at the end of hemodialysis. We hypothesized that solute binding might be pH-dependent and attributed the changes in free solute concentration to the higher serum pH observed at the end of standard hemodialysis with dialysis buffer bicarbonate concentration greater than 35 mmol/L. We observed that acidification of uremic plasma to pH 6 in vitro greatly increased the proportion of freeIS.

Methods

We tested our hypothesis by reducing the dialysate bicarbonate buffer concentration to 25 mmol/L for the initial half of the hemodialysis treatment (“isohydric dialysis”). Eight stable hemodialysis patients underwent “isohydric dialysis” for 90 minutes and then were switched to standard buffer (bicarbonate = 37mmol/L). A second dialysis, 2 days later, employed standard buffer throughout.

Results

We found a clearcut separation of blood pH and bicarbonate concentrations after 90 minutes of “isohydric dialysis” (pH = 7.37, bicarbonate = 22.4 mmol/L) and standard dialysis (pH = 7.49, bicarbonate = 29.0 mmol/L). Binding affinity varied widely among the 10 uremic retention solutes analyzed. Kynurenic acid (0.05 free), p-cresyl sulfate (0.12 free) and indoxyl sulfate (0.13 free) demonstrated the greatest degree of binding. Three solutes (indoxyl glucuronide, p-cresyl glucuronide, and phenyl glucuronide) were virtually unbound. Analysis of free and bound concentrations of uremic retention solutes confirmed our prediction that binding of solute is affected by pH. However, in a mixed models analysis, we found that the reduction in total uremic solute concentration during dialysis accounted for a greater proportion of the variation in free concentration, presumably an effect of saturation binding to albumin, than did the relatively small change in pH produced by isohydric dialysis. The effect of pH on binding appeared to be restricted to those solutes most highly protein-bound.

The solutes most tightly bound exhibited the lowest dialyzer clearances. An increase in dialyzer clearance during isohydric and standard dialyses was statistically significant only for kynurenic acid.

Conclusion

These findings provide evidence that the binding of uremic retention solutes is influenced by pH. The effect of reducing buffer bicarbonate concentration (“isohydric dialysis:”), though significant, was small but may be taken to suggest that further modification of dialysis technique that would expose blood to a greater decrease in pH would lead to a greater increase the free fraction of solute and enhance the efficacy of hemodialysis in the removal of highly protein-bound uremic retention solutes.

Enalapril decreases rat plasma concentration of TMAO, a gut bacteria-derived cardiovascular marker

INTRODUCTION

Increased plasma level of trimethylamine N-oxide (TMAO), a bacterial metabolite of choline, is associated with an increased cardiovascular risk. Indoxyl sulfate, a bacterial metabolite of tryptophan, is thought to be associated with higher mortality in cardiorenal syndrome. We hypothesized that enalapril, a well-established drug reducing cardiovascular mortality, may affect the plasma level of gut bacteria-derived metabolites and gut bacteria composition.

MATERIALS AND METHODS

14-16-week-old Wistar rats were maintained either on water (controls) or water solution of enalapril for two weeks (5.3 or 12.6 mg/kg b.w.). Blood plasma and urine were analyzed for the concentration of TMAO and indoxyl sulfate using liquid chromatography coupled with triple-quadrupole mass spectrometry. Gut bacteria composition was analyzed with 16S rRNA gene sequence analysis.

RESULTS

Rats treated with enalapril showed a significantly lower plasma TMAO level and a trend towards higher 24 h urine excretion of TMA and TMAO. Plasma indoxyl level was similar between the groups. There was no significant difference between the groups in gut bacteria composition.

CONCLUSIONS

Enalapril decreases rat plasma TMAO, but does not affect the plasma level of indoxyl sulfate and gut bacteria composition. The enalapril-induced decrease in plasma TMAO level may be of therapeutic and diagnostic importance.