Structural and functional differences in gut microbiome composition in patients undergoing haemodialysis or peritoneal dialysis

Uncovering specific taxonomic and functional alteration of gut microbiota in chronic kidney disease through 16S rRNA data

Introduction

Chronic kidney disease (CKD) is worldwide healthcare burden with growing incidence and death rate. Emerging evidence demonstrated the compositional and functional differences of gut microbiota in patients with CKD. As such, gut microbial features can be developed as diagnostic biomarkers and potential therapeutic target for CKD.

Methods

To eliminate the outcome bias arising from factors such as geographical distribution, sequencing platform, and data analysis techniques, we conducted a comprehensive analysis of the microbial differences between patients with CKD and healthy individuals based on multiple samples worldwide. A total of 980 samples from six references across three nations were incorporated from the PubMed, Web of Science, and GMrepo databases. The obtained 16S rRNA microbiome data were subjected to DADA2 processing, QIIME2 and PICRUSt2 analyses.

Results

The gut microbiota of patients with CKD differs significantly from that of healthy controls (HC), with a substantial decrease in the microbial diversity among the CKD group. Moreover, a significantly reduced abundance of bacteria Faecalibacterium prausnitzii (F. prausnitzii) was detected in the CKD group through linear discriminant analysis effect size (LEfSe) analysis, which may be associated with the alleviating effects against CKD. Notably, we identified CKD-depleted F. prausnitzii demonstrated a significant negative correlation with three pathways based on predictive functional analysis, suggesting its potential role in regulating systemic acidbase disturbance and pro-oxidant metabolism.

Discussion

Our findings demonstrated notable alterations of gut microbiota in CKD patients. Specific gut-beneficial microbiota, especially F. prausnitzii, may be developed as a preventive and therapeutic tool for CKD clinical management.

Causal relationship between gut microbiota and chronic renal failure: a two-sample Mendelian randomization study

Background

Observational studies and some experimental investigations have indicated that gut microbiota are closely associated with the incidence and progression of chronic renal failure. However, the causal relationship between gut microbiota and chronic renal failure remains unclear. The present study employs a two-sample Mendelian randomization approach to infer the causal relationship between gut microbiota and chronic renal failure at the genetic level. This research aims to determine whether there is a causal effect of gut microbiota on the risk of chronic renal failure, aiming to provide new evidence to support targeted gut therapy for the treatment of chronic renal failure.

Methods

Employing genome-wide association study (GWAS) data from the public MiBioGen and IEU OpenGWAS platform, a two-sample Mendelian randomization analysis was conducted. The causal relationship between gut microbiota and chronic renal failure was inferred using five different methods: Inverse Variance Weighted, MR-Egger, Weighted Median, Simple Mode, and Weighted Mode. The study incorporated sensitivity analyses that encompassed evaluations for pleiotropy and heterogeneity. Subsequently, the results of the Mendelian randomization analysis underwent a stringent correction for multiple testing, employing the False Discovery Rate method to enhance the validity of our findings.

Results

According to the results from the Inverse Variance Weighted method, seven bacterial genera show a significant association with the outcome variable chronic renal failure. Of these, Ruminococcus (gauvreauii group) (OR = 0.82, 95% CI = 0.71-0.94, p = 0.004) may act as a protective factor against chronic renal failure, while the genera Escherichia-Shigella (OR = 1.22, 95% CI = 1.08-1.38, p = 0.001), Lactococcus (OR = 1.1, 95% CI = 1.02-1.19, p = 0.013), Odoribacter (OR = 1.23, 95% CI = 1.03-1.49, p = 0.026), Enterorhabdus (OR = 1.14, 95% CI = 1.00-1.29, p = 0.047), Eubacterium (eligens group) (OR = 1.18, 95% CI = 1.02-1.37, p = 0.024), and Howardella (OR = 1.18, 95% CI = 1.09-1.28, p < 0.001) may be risk factors for chronic renal failure. However, after correction for multiple comparisons using False Discovery Rate, only the associations with Escherichia-Shigella and Howardella remain significant, indicating that the other genera have suggestive associations. Sensitivity analyses did not reveal any pleiotropy or heterogeneity.

Conclusion

Our two-sample Mendelian randomization study suggests that the genera Escherichia-Shigella and Howardella are risk factors for chronic renal failure, and they may serve as potential targets for future therapeutic interventions. However, the exact mechanisms of action are not yet clear, necessitating further research to elucidate their precise roles fully.

Analysis of intestinal flora and cognitive function in maintenance hemodialysis patients using combined 16S ribosome DNA and shotgun metagenome sequencing

BACKGROUND

Cognitive impairment is widely prevalent in maintenance hemodialysis (MHD) patients, and seriously affects their quality of life. The intestinal flora likely regulates cognitive function, but studies on cognitive impairment and intestinal flora in MHD patients are lacking.

METHODS

MHD patients (36) and healthy volunteers (18) were evaluated using the Montreal Cognitive Function Scale, basic clinical data, and 16S ribosome DNA (rDNA) sequencing. Twenty MHD patients and ten healthy volunteers were randomly selected for shotgun metagenomic analysis to explore potential metabolic pathways of intestinal flora. Both16S rDNA sequencing and shotgun metagenomic sequencing were conducted on fecal samples.

RESULTS

Roseburia were significantly reduced in the MHD group based on both 16S rDNA and shotgun metagenomic sequencing analyses. Faecalibacterium, Megamonas, Bifidobacterium, Parabacteroides, Collinsella, Tyzzerella, and Phascolarctobacterium were positively correlated with cognitive function or cognitive domains. Enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways included oxidative phosphorylation, photosynthesis, retrograde endocannabinoid signaling, flagellar assembly, and riboflavin metabolism.

CONCLUSION

Among the microbiota, Roseburia may be important in MHD patients. We demonstrated a correlation between bacterial genera and cognitive function, and propose possible mechanisms.

Gut Microbiota's Oxalate-Degrading Activity and Its Implications on Cardiovascular Health in Patients with Kidney Failure: A Pilot Prospective Study

Background and Objectives: The present study aims to investigate the association between gut microbiota's oxalate-degrading activity (ODA) and the risk of developing cardiovascular disease (CVD) over a three-year follow-up period in a cohort of patients undergoing kidney replacement therapy (KRT). Additionally, various factors were examined to gain insight into the potential mechanisms underlying the ODA-CVD link. Materials and Methods: A cohort of 32 KRT patients and 18 healthy volunteers was enrolled in this prospective observational pilot study. Total fecal ODA, routine clinical data, plasma oxalic acid (POx), serum indoxyl sulfate, lipid profile, oxidative stress, and proinflammatory markers were measured, and the patients were followed up for three years to assess CVD events. Results: The results revealed that patients with kidney failure exhibited significantly lower total fecal ODA levels compared to the healthy control group (p = 0.017), with a higher proportion showing negative ODA status (≤-1% per 0.01 g) (p = 0.01). Negative total fecal ODA status was associated with a significantly higher risk of CVD events during the three-year follow-up period (HR = 4.1, 95% CI 1.4-16.3, p = 0.003), even after adjusting for potential confounders. Negative total fecal ODA status was significantly associated with elevated POx and indoxyl sulfate levels and linked to dyslipidemia, increased oxidative stress, and inflammation, which are critical contributors to CVD. Conclusions: The findings contribute novel insights into the relationship between gut microbiota's ODA and cardiovascular health in patients undergoing KRT, emphasizing the need for further research to elucidate underlying mechanisms and explore potential therapeutic implications of targeting gut microbiota's ODA in this vulnerable population.

Effects of Tiaopi Xiezhuo decoction on constipation and gut dysbiosis in patients with peritoneal dialysis

CONTEXT

A Chinese herbal formula, Tiaopi Xiezhuo decoction (TXD), is developed from a classical Chinese prescription Sanhuang Xiexin decoction.

OBJECTIVE

To investigate the regulatory effect of TXD on gut dysbiosis, as a treatment of constipation in patients with peritoneal dialysis (PD).

MATERIALS AND METHODS

The chemical content of TXD was assessed by high-performance liquid chromatography. A total of 29 PD patients were enrolled and treated with TXD orally (3 g crude drug/each/twice/day) for 3 months. Blood and faecal samples were collected at the beginning and end, to determine the changes in biochemical characteristics and gut microbial composition. The stool conditions were asked to be scored. Additional 30 healthy individuals were recruited as a control for the analysis of gut microbiota.

RESULTS

Although having no significant effects on serum biochemical characteristics, 3-month TXD intervention improved constipation in PD patients: decreased 80% abdominal distention (p < 0.01), increased 2.6-fold sloppy stools (p < 0.05) and eliminated hard stool completely (p < 0.01). The analysis of gut microbiota showed that, compared to the healthy group, the microbial richness was reduced in PD patients. After a 3-month TXD treatment, this reduced richness was raised, and Paraprevotella clara, Lachnospiraceae bacterium 2-146FA, Phascolarctobaterium succinatutens, Lachnospiraceae bacterium 2-1-58FAA, Fusobacterium mortiferum, and Prevotella copri were accumulated in the intestinal flora. Furthermore, the bacterial species enriched by TXD correlated with the improvement of constipation.

DISCUSSION AND CONCLUSIONS

TXD treatment may improve constipation by modulating gut dysbiosis in PD patients. These findings provide data to support the further application of TXD in the adjuvant treatment of PD.

Relationship between gut microbiota and vascular calcification in hemodialysis patients

INTRODUCTION

Vascular calcification (VC) is an independent risk factor for cardiovascular mortality in end-stage renal disease (ESRD) patients. The pathogenesis of VC is complicated and unclear. Uremic toxins produced by gut microbiota can promote VC. This study aims to identify the differences in gut microbiota between the different VC groups and the main bacteria associated with VC in hemodialysis (HD) patients in an attempt to open up new preventive and therapeutic approaches and define the probable mechanism for VC in HD patients in the future.

METHODS

A total of 73 maintenance HD patients were enrolled in this cross-sectional study. According to the abdominal aortic calcification (AAC) scores, the participants were divided into the high AAC score group and the low AAC score group. High-throughput sequencing of the gut microbiota was performed and the results were evaluated by alpha diversity, beta diversity, species correlation, and model predictive analyses.

RESULTS

The prevalence of VC was 54.79% (40/73) in the study. The majority of phyla in the two groups were the same, including Firmicutes, Actinobacteriota, Proteobacteria, and Bacteroidota. The microbial diversity in the high AAC score group had a decreasing trend (p = 0.050), and the species abundance was significantly lower (p = 0.044) than that in the low AAC score group. The HD patients with high AAC scores showed an increased abundance of Proteobacteria and decreased abundances of Bacteroidota and Synergistota at the phylum level; increased abundances of Escherichia-Shigella, Ruminococcus_gnavus_group, and Lactobacillus; and decreased abundances of Ruminococcus and Lachnospiraceae_NK4A136_group at the genus level (p<0.05). Escherichia-Shigella and Ruminococcus_gnavus_group were positively correlated with VC, and Ruminococcus, Adlercreutzia, Alistipes, and norank_f__Ruminococcaceae were negatively correlated with VC. Escherichia-Shigella had the greatest influence on VC in HD patients, followed by Ruminococcus and Butyricimonas.

CONCLUSIONS

Our results provide clinical evidence that there was a difference in gut microbiota between the different VC groups in HD patients. Escherichia-Shigella, a lipopolysaccharide (LPS)-producing bacterium, was positively correlated with VC and had the greatest influence on VC. Ruminococcus, a short-chain fatty acid (SCFA)-producing bacterium, was negatively correlated with VC and had the second strongest influence on VC in HD patients. The underlying mechanism is worth studying. These findings hint at a new therapeutic target.

Altered gut microbiome, bile acid composition and metabolome in sarcopenia in liver cirrhosis

BACKGROUND

Sarcopenia in liver cirrhosis is associated with low quality of life and high mortality risk. The pathogenesis has yet to be fully understood. We hypothesized that gut microbiome, bile acid (BA) composition and metabolites differ between cirrhotic patients with and without sarcopenia and contribute to pathogenesis.

METHODS

Cirrhotic patients with (n = 78) and without (n = 38) sarcopenia and non-cirrhotic controls with (n = 39) and without (n = 20) sarcopenia were included in this study. Faecal microbiome composition was studied by 16S rDNA sequencing, serum and faecal BA composition by ultra-high-performance liquid chromatography-tandem mass spectrometry, and metabolite composition in serum, faeces and urine by nuclear magnetic resonance.

RESULTS

Bacteroides fragilis, Blautia marseille, Sutterella spp. and Veillonella parvula were associated with cirrhotic patients with sarcopenia, whereas Bacteroides ovatus was more abundant in cirrhotic patients without sarcopenia. We observed significantly elevated secondary BAs, deoxycholic acid (DCA; P = 0.01) and lithocholic acid (LCA; P = 0.02), and the ratios of deoxycholic acid to cholic acid (DCA:CA; P = 0.04), lithocholic acid to chenodeoxycholic acid (LCA:CDCA; P = 0.03) and 12 alpha-hydroxylated to non-12 alpha-hydroxylated BAs (12-α-OH:non-12-α-OH BAs; P = 0.04) in serum of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia, indicating an enhanced transformation of primary to secondary BAs by the gut microbiome. CA (P = 0.02) and the ratios of CA:CDCA (P = 0.03) and total ursodeoxycholic acid to total secondary BAs (T-UDCA:total-sec-BAs, P = 0.03) were significantly reduced in the stool of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia. Also, valine and acetate were significantly reduced in the serum of cirrhotic patients with sarcopenia compared with cirrhotic patients without sarcopenia (P = 0.01 and P = 0.03, respectively). Multivariate logistic regression further confirmed the association of B. ovatus (P = 0.01, odds ratio [OR]: 12.8, 95% confidence interval [CI]: 168.1; 2.2), the ratios of 12-α-OH:non-12-α-OH BAs (P = 0.03, OR: 2.54, 95% CI: 0.99; 6.55) and T-UDCA:total-sec-BAs (P = 0.04, OR: 0.25, 95% CI: 0.06; 0.98) in serum and stool CA:CDCA (P = 0.04, OR: 0.79, 95% CI: 0.62; 0.99), and serum valine (P = 0.04, OR: 1.00, 95% CI: 1.02; 1.00) with sarcopenia in cirrhosis after correcting for the severity of liver disease and sex.

CONCLUSIONS

Our study suggests a potential functional gut microbiome-host interaction linking sarcopenia with the altered gut microbiomes, BA profiles and amino acids pointing towards a potential mechanistic interplay in understanding sarcopenia pathogenesis.

Metagenome-wide analysis uncovers gut microbial signatures and implicates taxon-specific functions in end-stage renal disease

BACKGROUND

The gut microbiota plays a crucial role in regulating host metabolism and producing uremic toxins in patients with end-stage renal disease (ESRD). Our objective is to advance toward a holistic understanding of the gut ecosystem and its functional capacity in such patients, which is still lacking.

RESULTS

Herein, we explore the gut microbiome of 378 hemodialytic ESRD patients and 290 healthy volunteers from two independent cohorts via deep metagenomic sequencing and metagenome-assembled-genome-based characterization of their feces. Our findings reveal fundamental alterations in the ESRD microbiome, characterized by a panel of 348 differentially abundant species, including ESRD-elevated representatives of Blautia spp., Dorea spp., and Eggerthellaceae, and ESRD-depleted Prevotella and Roseburia species. Through functional annotation of the ESRD-associated species, we uncover various taxon-specific functions linked to the disease, such as antimicrobial resistance, aromatic compound degradation, and biosynthesis of small bioactive molecules. Additionally, we show that the gut microbial composition can be utilized to predict serum uremic toxin concentrations, and based on this, we identify the key toxin-contributing species. Furthermore, our investigation extended to 47 additional non-dialyzed chronic kidney disease (CKD) patients, revealing a significant correlation between the abundance of ESRD-associated microbial signatures and CKD progression.

CONCLUSION

This study delineates the taxonomic and functional landscapes and biomarkers of the ESRD microbiome. Understanding the role of gut microbiota in ESRD could open new avenues for therapeutic interventions and personalized treatment approaches in patients with this condition.

Autonomic Nervous System Dysfunction in Peritoneal Dialysis Patients: An Underrecognized Cardiovascular Risk Factor?

BACKGROUND

In patients with end-stage kidney disease (ESKD) receiving peritoneal dialysis (PD), cardiovascular events represent the predominant cause of morbidity and mortality, with cardiac arrhythmias and sudden death being the leading causes of death in this population. Autonomic nervous system (ANS) dysfunction is listed among the non-traditional risk factors accounting for the observed high cardiovascular burden, with a plethora of complex and not yet fully understood pathophysiologic mechanisms being involved.

SUMMARY

In recent years, preliminary studies have investigated and confirmed the presence of ANS dysfunction in PD patients, while relevant results from cohort studies have linked ANS dysfunction with adverse clinical outcomes in these patients. In light of these findings, ANS dysfunction has been recently receiving wider consideration as an independent cardiovascular risk factor in PD patients. The aim of this review was to describe the mechanisms involved in the pathogenesis of ANS dysfunction in ESKD and particularly PD patients and to summarize the existing studies evaluating ANS dysfunction in PD patients.

KEY MESSAGES

ANS dysfunction in PD patients is related to multiple complex mechanisms that impair the balance between SNS/PNS, and this disruption represents a crucial intermediator of cardiovascular morbidity and mortality in this population.

Roxadustat alleviates the inflammatory status in patients receiving maintenance hemodialysis with erythropoiesis-stimulating agent resistance by increasing the short-chain fatty acids producing gut bacteria

BACKGROUND

Hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHIs) have improved the treatment of renal anemia, especially in patients resistant to erythropoiesis-stimulating agents (ESAs). HIF facilitates maintain gut microbiota homeostasis, which plays an important role in inflammation and iron metabolism, which are in turn key factors affecting ESA resistance. The current study aimed to investigate the effects of roxadustat on inflammation and iron metabolism and on the gut microbiota in patients with ESA resistance.

METHODS

We conducted a self-controlled, single-center study including 30 patients with ESA resistance undergoing maintenance hemodialysis. All patients received roxadustat without iron agents for renal anemia. Hemoglobin and inflammatory factors were monitored. Fecal samples were collected before and after 3 months' administration and the gut microbiota were analyzed by 16S ribosomal RNA gene sequencing.

RESULTS

Hemoglobin levels increased after treatment with roxadustat for 3 months (P < 0.05). Gut microbiota diversity and abundance also changed, with increases in short-chain fatty acid (SCFA)-producing bacteria (Acidaminococcaceae, Butyricicoccus, Ruminococcus bicirculans, Ruminococcus bromii, Bifidobacterium dentium, Eubacterium hallii) (P < 0.05). Serum SCFA levels also increased (P < 0.05). Inflammatory factors, including interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α, interferon-γ, and endotoxin gradually decreased (P < 0.05). Serum hepcidin, ferritin, and total and unsaturated iron-binding capacities decreased (P < 0.05), while soluble transferrin receptor levels increased at each time point (P < 0.05). There were no significant differences in serum iron and transferrin saturation at each time point. The abundance of Alistipes shahii was significantly negatively correlated with IL-6 and TNF-α (P < 0.05).

CONCLUSIONS

Roxadustat alleviated renal anemia in patients with ESA resistance by decreasing inflammatory factors and hepcidin levels and improving iron utilization. These effects were at least partly mediated by improved diversity and abundance of SCFA-producing gut bacteria, probably via activation of HIF.

The Gut-Peritoneum Axis in Peritoneal Dialysis and Peritoneal Fibrosis

Peritoneal fibrosis is an important cause of peritoneal dialysis (PD) discontinuation worldwide and is associated with high morbidity and mortality rate. Although the era of metagenomics has provided new insights into the interactions between the gut microbiota and fibrosis in various organs and tissues, its role in peritoneal fibrosis has rarely been discussed. This review provides a scientific rationale and points out the potential role of gut microbiota in peritoneal fibrosis. In addition, the interaction between the gut, circulatory, and peritoneal microbiota is highlighted, with an emphasis on the relationship to PD outcomes. More research is needed to elucidate the mechanisms underlying the role of gut microbiota in peritoneal fibrosis and potentially unveil new target options for the management of PD technique failure.

Gut Microbiota and the Ways to Correct it in Chronic Kidney Disease

Approximately 13% of the Russian population suffers from chronic kidney disease (CKD). Such a high prevalence of the disease, as well as the complexity and high cost of renal replacement therapy, explain the need for developing and implementing new approaches to treat patients at the pre-dialysis stages. The data collected in recent decades highlight the importance of gut microbiota in the progression of CKD. This review provides information about the microbiota composition in healthy individuals and patients with CKD and discusses the mechanisms of interaction in the intestine-kidney system. The article also presents the specifics of the violation of gut microbiota (GM) and correction thereof in CKD.

Gut Dysbiosis in Experimental Kidney Disease: A Meta-Analysis of Rodent Repository Data

SIGNIFICANCE STATEMENT

Alterations in gut microbiota contribute to the pathophysiology of a diverse range of diseases, leading to suggestions that chronic uremia may cause intestinal dysbiosis that contributes to the pathophysiology of CKD. Various small, single-cohort rodent studies have supported this hypothesis. In this meta-analysis of publicly available repository data from studies of models of kidney disease in rodents, cohort variation far outweighed any effect of experimental kidney disease on the gut microbiota. No reproducible changes in animals with kidney disease were seen across all cohorts, although a few trends observed in most experiments may be attributable to kidney disease. The findings suggest that rodent studies do not provide evidence for the existence of "uremic dysbiosis" and that single-cohort studies are unsuitable for producing generalizable results in microbiome research.

BACKGROUND

Rodent studies have popularized the notion that uremia may induce pathological changes in the gut microbiota that contribute to kidney disease progression. Although single-cohort rodent studies have yielded insights into host-microbiota relationships in various disease processes, their relevance is limited by cohort and other effects. We previously reported finding metabolomic evidence that batch-to-batch variations in the microbiome of experimental animals are significant confounders in an experimental study.

METHODS

To attempt to identify common microbial signatures that transcend batch variability and that may be attributed to the effect of kidney disease, we downloaded all data describing the molecular characterization of the gut microbiota in rodents with and without experimental kidney disease from two online repositories comprising 127 rodents across ten experimental cohorts. We reanalyzed these data using the DADA2 and Phyloseq packages in R, a statistical computing and graphics system, and analyzed data both in a combined dataset of all samples and at the level of individual experimental cohorts.

RESULTS

Cohort effects accounted for 69% of total sample variance ( P <0.001), substantially outweighing the effect of kidney disease (1.9% of variance, P =0.026). We found no universal trends in microbial population dynamics in animals with kidney disease, but observed some differences (increased alpha diversity, a measure of within-sample bacterial diversity; relative decreases in Lachnospiraceae and Lactobacillus ; and increases in some Clostridia and opportunistic taxa) in many cohorts that might represent effects of kidney disease on the gut microbiota .

CONCLUSIONS

These findings suggest that current evidence that kidney disease causes reproducible patterns of dysbiosis is inadequate. We advocate meta-analysis of repository data as a way of identifying broad themes that transcend experimental variation.

Abelmoschus Manihot ameliorates the levels of circulating metabolites in diabetic nephropathy by modulating gut microbiota in non-obese diabetes mice

Huangkui capsule (HKC), a traditional Chinese medicine, has been used for medication of kidney diseases, including diabetic nephropathy (DN). The current study aimed to evaluate the effects of HKC in the modulation of gut microbiota and the amelioration of metabolite levels by using non-obese diabetes (NOD) mice with DN. The microbiota from three parts of intestines (duodenum, ileum and colon) in NOD mice with and without HKC treatment were analysed using 16S rDNA sequencing techniques. Untargeted metabolomics in plasma of NOD mice were analysed with liquid mass spectrometry. Results showed that HKC administration ameliorated DN in NOD mice and the flora in duodenum were more sensitive to HKC intervention, while the flora in colon had more effects on metabolism. The bacterial genera such as Faecalitalea and Muribaculum significantly increased and negatively correlated with most of the altered metabolites after HKC treatment, while Phyllobacterium, Weissella and Akkermansia showed an opposite trend. The plasma metabolites, mainly including amino acids and fatty acids such as methionine sulfoxide, BCAAs and cis-7-Hexadecenoic acid, exhibited a distinct return to normal after HKC treatment. The current study thereby provides experimental evidence suggesting that HKC may modulate gut microbiota and subsequently ameliorate the metabolite levels in DN.

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 microbiota profile of patients on peritoneal dialysis: comparison with household contacts

BACKGROUND

Differences in patients gut microbiota composition with the potential for dysbiosis have been associated with chronic kidney disease (CKD). However, factors other than the disease itself, such as diet and cohabitation, have not been evaluated when gut microbiota of CKD patients was compared with that of healthy controls. The aim of this study was to compare the gut microbiota composition between patients on peritoneal dialysis (PD) and age-matched household contacts with normal renal function.

METHODS

Fecal samples were collected from 20 patients [men: 70%; age: 53.5 years (48.2-66; median and interquartile range); length on PD: 14 months (5.2-43.5) and 20 controls. The region V4 of the 16S ribosomal RNA gene was PCR-amplified and sequenced on Illumina MiSeq platform. Dietary intake and diet quality were assessed by a 3-day food record and a diet quality index, respectively.

RESULTS

No difference was found between the gut microbiota composition of patients and controls, assessed by alpha and beta diversities (p > 0.05) and genera differential abundance (p > 0.05). The most abundant phyla in both groups were Firmicutes (PD = 45%; Control: 47%; p = 0.65) and Bacteroidetes (PD = 41%; Control: 45%; p = 0.17). The phylum Proteobacteria, known as a potential marker of gut dysbiosis, was not different in proportions between groups (p > 0.05). No difference was observed regarding diet quality and dietary intake of fiber, protein and other nutrients (p > 0.05).

CONCLUSION

Gut microbiota of patients on PD did not differ from household contacts. This result suggests that cohabitation and dietary intake might have outweighed the disease influence on gut microbiota composition of our PD patients.

Altered gut microbiota and gut-derived p-cresyl sulfate serum levels in peritoneal dialysis patients

Peritoneal dialysis (PD) is a renal replacement therapy for end-stage renal disease. Gut microbiota-derived uremic solutes, indoxyl sulfate (IS), p-cresyl sulfate (PCS), and trimethylamine-N-oxide (TMAO) accumulate in PD patients. The objective was to explore the gut microbiota and their influence on uremic toxins in PD patients and healthy controls (HC). Fecal samples were collected from PD patients (n = 105) and HC (n = 102). 16S rRNA gene regions were sequenced for gut microbiota analysis. IS, PCS, and TMAO levels were measured using HPLC-MS. PD patients exhibited lower alpha diversity and altered gut microbiota composition compared to HC. At the genus level, PD patients showed increased abundance of opportunistic pathogenic bacteria, and decreased abundance of beneficial bacteria. Three Operational Taxonomic Units discriminated PD patients from HC. Phenylalanine metabolism increased in PD, whereas tryptophan metabolism was unaltered. Low serum PCS did not necessarily mean healthier due to the loss of alpha diversity, increased Proteobacteria and opportunistic pathogenic bacteria. High serum PCS was mainly caused by elevated p-cresol-producing bacteria, enriched amino acid related enzymes, and enhanced sulfur metabolism, rather than declined residual renal function. In patients with different urine volumes, the gut microbiota alpha diversity and composition were unaltered, but serum IS and TMAO were significantly elevated in anuric patients. In conclusion, the gut microbiota abundance, composition, and function were altered in PD patients, which increased the PCS levels. We provided a better understanding of the microbiota-metabolite-kidney axis in PD patients. Targeting certain bacteria could decrease the PCS levels, whereas preserving the residual renal function could reduce the IS and TMAO levels.

Uremic Toxin-Producing Bacteroides Species Prevail in the Gut Microbiota of Taiwanese CKD Patients: An Analysis Using the New Taiwan Microbiome Baseline

Rationale and Objective

Gut microbiota have been targeted by alternative therapies for non-communicable diseases. We examined the gut microbiota of a healthy Taiwanese population, identified various bacterial drivers in different demographics, and compared them with dialysis patients to associate kidney disease progression with changes in gut microbiota.

Study Design

This was a cross-sectional cohort study.

Settings and Participants

Fecal samples were obtained from 119 healthy Taiwanese volunteers, and 16S rRNA sequencing was done on the V3-V4 regions to identify the bacterial enterotypes. Twenty-six samples from the above cohort were compared with fecal samples from 22 peritoneal dialysis and 16 hemodialysis patients to identify species-level bacterial biomarkers in the dysbiotic gut of chronic kidney disease (CKD) patients.

Results

Specific bacterial species were identified pertaining to different demographics such as gender, age, BMI, physical activity, and sleeping habits. Dialysis patients had a significant difference in gut microbiome composition compared to healthy controls. The most abundant genus identified in CKD patients was Bacteroides, and at the species level hemodialysis patients showed significant abundance in B. ovatus, B. caccae, B. uniformis, and peritoneal dialysis patients showed higher abundance in Blautia producta (p ≤ 0.05) than the control group. Pathways pertaining to the production of uremic toxins were enriched in CKD patients. The abundance of the bacterial species depended on the type of dialysis treatment.

Conclusion

This study characterizes the healthy gut microbiome of a Taiwanese population in terms of various demographics. In a case-control examination, the results showed the alteration in gut microbiota in CKD patients corresponding to different dialysis treatments. Also, this study identified the bacterial species abundant in CKD patients and their possible role in complicating the patients’ condition.

Exploration of the correlation between intestinal flora and Escherichia coli peritoneal dialysis-related peritonitis

BACKGROUND

Escherichia coli peritonitis (EP) is a serious complication of peritoneal dialysis (PD). Gut microbiota alterations occur in end-stage renal disease (ESRD) patients. The relationship between the gut microbiota and PD-related peritonitis is still poorly understood. It is unclear whether the intestinal flora is involved in the pathogenesis of EP.

METHODS

We collected fecal samples from EP patients and normal group (NG) PD patients. 16S rRNA sequencing was used to analyze the gut microbiota of EP and NG patients. The demographic data and clinical indicators of all patients were collected.

RESULTS

Six EP patients and 28 NG patients were recruited for this study. The analysis of fecal community diversity with 16S rDNA sequencing showed an obvious change in the microbial structure of EP patients, where Bacteroidetes and Synergistetes were upregulated at different levels, while Bacilli and Lactobacillus were downregulated at different levels compared to the NG group. Additionally, decreased gene function associated with metabolic pathways was observed in EP patients.

CONCLUSIONS

The altered composition of the gut microbiota in EP patients provided deeper insights into the pathogenesis of EP, and these biomarkers might be established as potential therapeutic targets that deserve further exploration.

Myeloid leukocytes' diverse effects on cardiovascular and systemic inflammation in chronic kidney disease

Chronic kidney disease's prevalence rises globally. Whereas dialysis treatment replaces the kidney's filtering function and prolongs life, dreaded consequences in remote organs develop inevitably over time. Even milder reductions in kidney function not requiring replacement therapy associate with bacterial infections, cardiovascular and heart valve disease, which markedly limit prognosis in these patients. The array of complications is diverse and engages a wide gamut of cellular and molecular mechanisms. The innate immune system is profoundly and systemically altered in chronic kidney disease and, as a unifying element, partakes in many of the disease's complications. As such, a derailed immune system fuels cardiovascular disease progression but also elevates the propensity for serious bacterial infections. Recent data further point towards a role in developing calcific aortic valve stenosis. Here, we delineate the current state of knowledge on how chronic kidney disease affects innate immunity in cardiovascular organs and on a systemic level. We review the role of circulating myeloid cells, monocytes and neutrophils, resident macrophages, dendritic cells, ligands, and cellular pathways that are activated or suppressed when renal function is chronically impaired. Finally, we discuss myeloid cells' varying responses to uremia from a systems immunology perspective.

Gut Microbiome Profiling Uncovers a Lower Abundance of Butyricicoccus in Advanced Stages of Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized by the accumulation of uremic toxins which exert deleterious effects on various organ systems. Several of these uremic toxins originate from the bacterial metabolization of aromatic amino acids in the colon. This study assessed whether the gut microbial composition varies among patients in different stages of CKD. Uremic metabolites were quantified by UPLC/fluorescence detection and microbial profiling by 16S rRNA amplicon sequencing. Gut microbial profiles of CKD patients were compared among stages 1–2, stage 3 and stages 4–5. Although a substantial inter-individual difference in abundance of the top 15 genera was observed, no significant difference was observed between groups. Bristol stool scale (BSS) correlated negatively with p-cresyl sulfate and hippuric acid levels, irrespective of the intake of laxatives. Butyricicoccus, a genus with butyrate-generating properties, was decreased in abundance in advanced stages of CKD compared to the earlier stages (p = 0.043). In conclusion, in this cross-sectional study no gradual differences in the gut microbial profile over the different stages of CKD were observed. However, the decrease in the abundance of Butyricicoccus genus with loss of kidney function stresses the need for more in-depth functional exploration of the gut microbiome in CKD patients not on dialysis.

Specific alterations in gut microbiota in patients with chronic kidney disease: an updated systematic review

BACKGROUND

Emerging evidence demonstrates that gut dysbiosis is implicated in the pathogenesis of chronic kidney disease (CKD) with underlying mechanisms involving mucosal and/or systematic immunity or metabolic disorders. However, the profile of gut microbiota in patients with CKD has not been completely explored.

METHODS

Databases from their date of inception to 31 March 2020 were systematically searched for case-control or cross-sectional studies comparing the gut microbial profiles in adult patients with CKD or end-stage renal disease (ESRD) with those in healthy controls. Quantitative analysis of alterations in gut microbial profiles was conducted.

RESULTS

Twenty-five studies with a total of 1436 CKD patients and 918 healthy controls were included. The present study supports the increased abundance of, phylum Proteobacteria and Fusobacteria, genus Escherichia_Shigella, Desulfovibrio, and Streptococcus, while lower abundance of genus Roseburia, Faecalibacterium, Pyramidobacter, Prevotellaceae_UCG-001, and Prevotella_9 in patients with CKD; and increased abundance of phylum Proteobacteria, and genus Streptococcus and Fusobacterium, while lower abundance of Prevotella, Coprococcus, Megamonas, and Faecalibacterium in patients with ESRD. Moreover, higher concentrations of trimethylamine-N-oxide and p-cresyl sulfate and lower concentrations of short-chain fatty acids were observed. Gut permeability in patients with CKD was not determined due to the heterogeneity of selected parameters.

CONCLUSIONS

Specific alterations of gut microbial parameters in patients with CKD were identified. However, a full picture of the gut microbiota could not be drawn from the data due to the differences in methodology, and qualitative and incomplete reporting of different studies.

Identification of Metagenomics Structure and Function Associated With Temporal Changes in Rat (Rattus norvegicus) Skin Microbiome During Health and Cutaneous Burn

The cutaneous skin microbiome is host to a vast ensemble of resident microbes that provide essential capabilities including protection of skin barrier integrity and modulation of the host immune response. Cutaneous burn-injury promotes alteration of cutaneous and systemic immune response that can affect both commensal and pathogenic microbes. A cross-sectional study of a limited number of burn patients revealed a difference in the bacteriome of burned versus control participants. Temporal changes of the skin microbiome during health and cutaneous burn-injury remains largely unknown. Furthermore, how this microbial shift relates to community function in the collective metagenome remain elusive. Due to cost considerations and reduced healing time, rodents are frequently used in burn research, despite inherent physiological differences between rodents and human skin. Using a rat burn model, a longitudinal study was conducted to characterize the rat skin bacterial residents and associated community functions in states of health (n = 30) (sham-burned) and when compromised by burn-injury (n = 24). To address the knowledge gap, traumatic thermal injury and disruption of cutaneous surface is associated with genus-level changes in the microbiota, reduced bacterial richness, and altered representation of bacterial genes and associated predicted functions across different skin microbial communities. These findings demonstrate that, upon burn-injury, there is a shift in diversity of the skin's organismal assemblages, yielding a core microbiome that is distinct at the genome and functional level. Moreover, deviations from the core community correlate with temporal changes post-injury and community transition from the state of cutaneous health to disease (burn-injury).

The Herbal Formula Granule Prescription Mahuang Decoction Ameliorated Chronic Kidney Disease Which Was Associated with Restoration of Dysbiosis of Intestinal Microbiota in Rats

Chronic kidney disease (CKD) has become a global health issue, and there is increasing evidence showing the beneficial roles of traditional Chinese medicine (TCM) in CKD treatment. Here, we studied the renoprotective role of Mahuang decoction, a famous TCM prescription, in a rat CKD model induced with the combination of doxorubicin and adenine. Our data showed that intragastric administration of Mahuang decoction inhibited the loss of bodyweight and attenuated proteinuria, serum creatinine, and blood urea nitrogen in CKD rats. Kidney histological analysis revealed decreased tubulointerstitial injury and fibrosis in CKD rats treated with Mahuang decoction accompanied with suppressed expression of TGF-β1 and phosphorylated NF-κB/P65 (p-P65) as indicated by immunohistochemistry. ELISA analysis demonstrated reduced serum levels of proinflammatory cytokines TNFα and IL-6. Most importantly, intestinal microbiota analysis by 16s rRNA-seq showed that Mahuang decoction restored the impaired richness and diversity of intestinal microflora and recovered the disrupted microbial community through reducing the abundance of deleterious microbes and promoting the expansion of beneficial microbes in CKD rats. Collectively, our findings demonstrated that Mahuang decoction mitigated kidney functional and structural impairment in CKD rats which were associated with the restoration of dysbiosis of intestinal microbiota, implying its potential in clinical CKD treatment.

Hyaluronan reduces colitis-induced intraperitoneal inflammation during peritoneal dialysis

BACKGROUND

Peritoneal dialysis induces the inflammatory response within the peritoneal cavity, which contributes to the progressive damage of the peritoneum. Due to close contact of the peritoneal cavity and the intestines, there is the possibility that the visceral disorders can affect the intraperitoneal inflammation during peritoneal dialysis.

OBJECTIVES

Study of the effect of acute colitis on the intraperitoneal inflammation in conditions of peritoneal dialysis and evaluation of the protective effect of hyaluronan in that scenario.

METHODS

In rats with the dextran sulphate-induced colitis, 6-h peritoneal dialysis was performed with dianeal 2.5% +/- hyaluronan 10 mg/dL. In the control group, rats without colitis were studied. Peritoneal permeability and dialysate inflammation were studied at the end of the dialysate exchange.

RESULTS

In rats with colitis, intraperitoneal inflammatory reaction was increased as compared with the control group and reflected by the following studied parameters: dialysate cell count (+26%, p < 0.01), number of neutrophils (+75%, p < 0.01), generation of free radicals in the leukocytes (+70%, p < 0.05), dialysate level of elastase (+102%, p < 0.01), tumor necrosis factor α (+48%, p < 0.01) and monocyte chemoattractant protein-1 (+42%, p < 0.01). Drained dialysate volume was lower (-21%, p < 0.01) and peritoneal permeability increased in rats with colitis (+55%, p < 0.01). In animals with the hyaluronan supplemented dialysis fluids, the intensity of the intraperitoneal inflammation was reduced.

CONCLUSIONS

Visceral inflammation during colitis induces the inflammatory reaction within the peritoneal cavity that may accelerate damage to the peritoneum. Supplementation of the dialysis fluid with hyaluronan reduces the intensity of that effect.

The Effects of Hemodialysis and Peritoneal Dialysis on the Gut Microbiota of End-Stage Renal Disease Patients, and the Relationship Between Gut Microbiota and Patient Prognoses

Gut microbiota alterations occur in end-stage renal disease (ESRD) patients with or without dialysis. However, it remains unclear whether changes in gut microbiota of dialysis ESRD patients result from dialysis or ESRD, or both. Similarly, there is a dearth of information on the relationship between gut microbiota and ESRD prognoses. We collected fecal samples and tracked clinical outcomes from 73 ESRD patients, including 33 pre-dialysis ESRD patients, 19 peritoneal dialysis (PD) patients, and 21 hemodialysis (HD) patients. 16S rRNA sequencing and bioinformatics tools were used to analyze the gut microbiota of ESRD patients and healthy controls. Gut microbiota diversity was different before and after dialysis. Bacteroidetes were significantly deceased in HD patients. Twelve bacterial genera exhibited statistically significant differences, due to dialysis (all P < 0.05, FDR corrected). HD reversed abnormal changes in Oscillospira and SMB53 in pre-dialysis patients. Functional predictions of microbial communities showed that PD and HD altered signal transduction and metabolic pathways in ESRD patients. Furthermore, Bacteroides and Phascolarctobacterium were associated with cardiovascular mortality. Dorea, Clostridium, and SMB53 were related to peritonitis in PD patients. This study not only demonstrated differences in gut microbiota between pre-dialysis and dialysis ESRD patients, but also firstly proposed gut bacteria may exert an impact on patient prognosis.

Effect of Unripe Banana Flour on Gut-Derived Uremic Toxins in Individuals Undergoing Peritoneal Dialysis: A Randomized, Double-Blind, Placebo-Controlled, Crossover Trial

In chronic kidney disease (CKD), the accumulation of gut-derived metabolites, such as indoxyl sulfate (IS), p-cresyl sulfate (pCS), and indole 3-acetic acid (IAA), has been associated with the burden of the disease. In this context, prebiotics emerge as a strategy to mitigate the accumulation of such compounds, by modulating the gut microbiota and production of their metabolites. The aim of this study was to evaluate the effect of unripe banana flour (UBF-48% resistant starch, a prebiotic) on serum concentrations of IS, pCS, and IAA in individuals undergoing peritoneal dialysis (PD). A randomized, double-blind, placebo-controlled, crossover trial was conducted. Forty-three individuals on PD were randomized to sequential treatment with UBF (21 g/day) and placebo (waxy corn starch-12 g/day) for 4 weeks, or vice versa (4-week washout). The primary outcomes were total and free serum levels of IS, pCS, and IAA. Secondary outcomes were 24 h urine excretion and dialysis removal of IS, pCS, and IAA, serum inflammatory markers [high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), interleukin-10 (IL-10), and tumor necrosis factor-α (TNF-α)], serum lipopolysaccharide LPS, and dietary intake. Of the 43 individuals randomized, 26 completed the follow-up (age = 55 ± 12 years; 53.8% men). UBF did not promote changes in serum levels of IS (p = 0.70), pCS (p = 0.70), and IAA (p = 0.74). Total serum IS reduction was observed in a subgroup of participants (n = 11; placebo: median 79.5 μmol/L (31-142) versus UBF: 62.5 μmol/L (31-133), p = 0.009) who had a daily UBF intake closer to that proposed in the study. No changes were observed in other secondary outcomes. UBF did not promote changes in serum levels of IS or pCS and IAA; a decrease in IS was only found in the subgroup of participants who were able to take 21g/day of the UBF.

Distal Gastrectomy with Billroth II Reconstruction is Associated with Oralization of Gut Microbiome and Intestinal Inflammation: A Proof-of-Concept Study

BACKGROUND

Subtotal gastrectomy with Billroth II reconstruction (SGB2) results in increased gastric pH and diminished gastric barrier. Increased gastric pH following PPI therapy has an impact on the gut microbiome, intestinal inflammation, and possibly patient health. If similar changes are present after SGB2, these can be relevant for patient health and long-term outcomes after surgery. The aim of the study is to investigate whether SGB2 is associated with specific changes in gut microbiome composition and intestinal inflammation.

PATIENTS AND METHODS

This cross-sectional proof-of-concept study includes patients after SGB2 (n = 14) for early gastric cancer and their nongastrectomized in-house relatives as controls (n = 8). Fecal microbiome composition, intestinal inflammation (fecal calprotectin), gut permeability (DAO, LBP, sCD14), systemic inflammation (CRP) markers, and gastrointestinal symptoms are investigated. This study is registered at ClinicalTrials.gov (NCT03418428).

RESULTS

Microbiome oralization following SGB2 was defined by an increase in Escherichia-Shigella, Enterococcus, Streptococcus, and other typical oral cavity bacteria (Veillonella, Oribacterium, and Mogibacterium) abundance. The fecal calprotectin was increased in the SGB2 group [100.9 (52.1; 292) vs. 25.8 (17; 66.5); p = 0.014], and calprotectin levels positively correlated with the abundance of Streptococcus (rs = 0.639; padj = 0.023). Gastrointestinal symptoms in SGB2 patients were associated with distinct taxonomic changes of the gut microbiome.

CONCLUSIONS

SGB2 is associated with oralization of the gut microbiome; intestinal inflammation and microbiome changes were associated with gastrointestinal symptoms. These novel findings may open gut microbiome as a new target for therapy to improve quality of life and general patient health in long-term survivors after SGB2.

Anti-Acid Drug Treatment Induces Changes in the Gut Microbiome Composition of Hemodialysis Patients

Anti-acid drugs, proton pump inhibitor (PPI) and histamine-2 blocker (H₂-blocker), are commonly prescribed to treat gastrointestinal disorders. These anti-acid drugs alter gut microbiota in the general population, but their effects are not known in hemodialysis patients. Hence, we investigated the microbiota composition in hemodialysis patients treated with PPIs or H₂-blocker. Among 193 hemodialysis patients, we identified 32 H₂-blocker users, 23 PPI users, and 138 no anti-acid drug subjects. Fecal samples were obtained to analyze the gut microbiome using 16S RNA amplicon sequencing. Differences in the microbial composition of the H₂-blocker users, PPI users, and controls were assessed using linear discriminant analysis effect size and the random forest algorithm. The species richness or evenness (α-diversity) was similar among the three groups, whereas the inter-individual diversity (β-diversity) was different between H₂-blocker users, PPI users, and controls. Hemodialysis patients treated with H₂-blocker and PPIs had a higher microbial dysbiosis index than the controls, with a significant increase in the genera Provetella 2, Phascolarctobacterium, Christensenellaceae R-7 group, and Eubacterium oxidoreducens group in H₂-blocker users, and Streptococcus and Veillonella in PPI users. In addition, compared to the H₂-blocker users, there was a significant enrichment of the genera Streptococcus in PPI users, as confirmed by the random forest analysis and the confounder-adjusted regression model. In conclusion, PPIs significantly changed the gut microbiota composition in hemodialysis patients compared to H₂-blocker users or controls. Importantly, the Streptococcus genus was significantly increased in PPI treatment. These findings caution against the overuse of PPIs.

Clinical characteristics associated with the properties of gut microbiota in peritoneal dialysis patients

BACKGROUND

Gut microbiota alters in patients with end-stage renal disease, which contributes to inflammation, atherosclerosis, and results in increased incidence of cardiovascular diseases. The present study investigated the potential clinical factors, which influence the gut microbial structure and function in patients undergoing peritoneal dialysis (PD).

METHODS

This is a cross-sectional study performed in 81 prevalent PD patients. Gut microbiota was assessed by high throughput sequencing of 16S ribosomal ribonucleic acid gene in fecal samples. Gas chromatography was conducted to measure stool short-chain fat acid (SCFA) concentrations. Demographic parameters and clinical characteristics, including dialysis regimen, residual renal function, nutrition, and inflammation, were retrieved and related to the properties of gut microbiota.

RESULTS

PD duration, peritoneal glucose exposure, and estimated glomerulus filtration rate (eGFR) were identified to be associated with microbial variations. Significant separation of microbial composition was shown between patients with short or long PD duration (p = 0.015) and marginal differences were found between patients grouped by different levels of peritoneal glucose exposure (p = 0.056) or residual renal function (p = 0.063). A couple of gut bacteria showed different abundance at amplicon sequencing variant level between these patient groups (p < 0.05). In addition, stool isobutyric and isovaleric acid concentrations were significantly reduced in patients with longer dialysis duration, higher peritoneal glucose exposure, or declined eGFR (p < 0.05).

CONCLUSIONS

This pilot study demonstrated that long dialysis duration, high peritoneal glucose exposure, and loss of residual renal function were associated with gut microbiota alteration and reduced branched-chain SCFA production in PD patients.

Lipoteichoic Acid as a Potential Noninvasive Biomarker of Biofilm in Dialysis Access

Tunneled central venous catheters (TCVCs) are colonized by Gram-positive organisms and form biofilm. Lipoteichoic acid (LTA) is a Gram-positive cell wall component that can be measured in serum. The purpose of this pilot study was to characterize LTA concentrations in hemodialysis (HD) patients with TCVCs compared to other access types and to evaluate biofilm morphology and microbiology in TCVCs removed by clinical decision. The study enrolled patients with TCVCs (18), grafts (19), and fistulas (18). Blood samples were collected before HD, at 30 minutes, 2 hours, and end of HD. Catheters removed by clinical decision were evaluated by scanning electron microscopy (SEM) for biofilm morphology, and portions of the catheter were cultured. LTA was detectable in all samples and concentrations increased significantly in all access types during HD (p < 0.05 for all comparisons). Patients with TCVCs that had a >30% increase in LTA concentration from baseline also had the greatest rate of increase (slope) compared to grafts and fistulas (p = 0.03 and p = 0.04, respectively). Catheters removed by clinical decision (n = 7) and examined by SEM had deposition of fibrin. Cultures revealed polymicrobial colonization. TCVCs had the highest rate of increase of LTA during HD. Further studies to determine the source of LTA in patients with AVG and AVF are warranted.

Aortic stenosis in patients with kidney failure: Is there an advantage for a PD-first policy?

Aortic stenosis (AS) is the most common valvular disease. It is twice as prevalent in patients with kidney failure as compared to the general population. In addition, AS progresses at a faster rate and is associated with a higher risk of death and poorer quality of life in patients on dialysis. Chronic kidney disease–mineral and bone disorder (CKD-MBD), inflammation, and hemodynamic disturbances contribute to the pathophysiology and progression of AS. Whether the type of dialysis modality, that is, hemodialysis (HD) versus peritoneal dialysis (PD), has a differential impact on the development and progression of AS in patients with kidney failure remains debated. Recent data indicate that the prevalence of valvular calcifications might be lower and the development of AS delayed in PD patients, as compared to those treated with HD. This could be accounted for by several mechanisms including reduced valvular shear stress, better preservation of residual kidney function (with better removal of protein-bound uremic toxins and CKD-MBD profile), and lower levels of systemic inflammation. Given the high morbidity and mortality rates related to interventional procedures in the population with kidney failure, surgical and transcatheter aortic valve replacement should be considered in selected patients with severe AS. Strategies slowing down the progression of aortic valve remodeling should remain the cornerstone in the management of individuals with kidney failure and mild to moderate AS. This review explores the potential benefits of PD in patients with kidney failure and AS and provides some clues to help clinicians in the decision-making process when options for kidney replacement therapy are considered in patients with AS.

Changes in the Intestinal Microbiome during a Multispecies Probiotic Intervention in Compensated Cirrhosis

Probiotics have been used in trials to therapeutically modulate the gut microbiome and have shown beneficial effects in cirrhosis. However, their effect on the microbiome of cirrhosis patients is not fully understood yet. Here, we tested the effects of a multispecies probiotic on microbiome composition in compensated cirrhosis. The gut microbiome composition of 58 patients with compensated cirrhosis from a randomized controlled trial who received a daily dose of multispecies probiotics or placebo for six months was analysed by 16S rRNA gene sequencing. Microbiome composition of patients who received probiotics was enriched with probiotic strains and the abundance of Faecalibacterium prausnitzii, Syntrophococcus sucromutans, Bacteroides vulgatus, Alistipes shahii and a Prevotella species was increased in the probiotic group compared to the placebo group. Patients who had microbiome changes in response to probiotic treatment also showed a significant increase in neopterin and a significant decrease in faecal zonulin levels after intervention, which was not observed in placebo-treated patients or patients with unchanged microbiome compositions. In conclusion, multispecies probiotics may enrich the microbiome of compensated cirrhotic patients with probiotic bacteria during a six-month intervention and beneficially change the residential microbiome and gut barrier function.

The gut microbiota profile of adults with kidney disease and kidney stones: a systematic review of the literature

Background

There is mounting evidence that individuals with kidney disease and kidney stones have an abnormal gut microbiota composition. No studies to date have summarised the evidence to categorise how the gut microbiota profile of these individuals may differ from controls. Synthesis of this evidence is essential to inform future clinical trials. This systematic review aims to characterise differences of the gut microbial community in adults with kidney disease and kidney stones, as well as to describe the functional capacity of the gut microbiota and reporting of diet as a confounder in these studies.

Methods

Included studies were those that investigated the gut microbial community in adults with kidney disease or kidney stones and compared this to the profile of controls. Six scientific databases (CINHAL, Medline, PubMed, Scopus, Web of Science and Cochrane Library), as well as selected grey literature sources, were searched. Quality assessment was undertaken independently by three authors. The system of evidence level criteria was employed to quantitatively evaluate the alteration of microbiota by strictly considering the number, methodological quality and consistency of the findings. Additional findings relating to altered functions of the gut microbiota, dietary intakes and dietary methodologies used were qualitatively summarised.

Results

Twenty-five articles met the eligibility criteria and included data from a total of 892 adults with kidney disease or kidney stones and 1400 controls. Compared to controls, adults with kidney disease had increased abundances of several microbes including Enterobacteriaceae, Streptococcaceae, Streptococcus and decreased abundances of Prevotellaceae, Prevotella, Prevotella 9 and Roseburia among other taxa. Adults with kidney stones also had an altered microbial composition with variations to Bacteroides, Lachnospiraceae NK4A136 group, Ruminiclostridium 5 group, Dorea, Enterobacter, Christensenellaceae and its genus Christensenellaceae R7 group. Differences in the functional potential of the microbial community between controls and adults with kidney disease or kidney stones were also identified. Only three of the 25 articles presented dietary data, and of these studies, only two used a valid dietary assessment method.

Conclusions

The gut microbiota profile of adults with kidney disease and kidney stones differs from controls. Future study designs should include adequate reporting of important confounders such as dietary intake to assist with interpretation of findings.

Distinct Responses of Gut Microbiota to Jian-Pi-Yi-Shen Decoction Are Associated With Improved Clinical Outcomes in 5/6 Nephrectomized Rats

Gut dysbiosis contributes to the development and progression of chronic kidney disease (CKD) and its complications. However, the effect of drugs on the gut microbiota of CKD patients and its influence on treatment outcomes remains to be explored. Here, we assessed whether the response of gut microbiota to the traditional Chinese medicine Jian-Pi-Yi-Shen (JPYS) decoction differed from that to piperazine ferulate (PF), a kidney-targeted drug, by 16S rDNA sequencing, and whether the difference could be linked with drug-specific clinical outcomes. We showed that both JPYS and PF improved renal function, but only JPYS was able to restore the blood reticulocyte counting and serum calcium level in CKD rats. We also found that weighted UniFrac beta-diversity of the gut microbiome of the JPYS treated rats was significantly different from that of PF. Microbiome markers of drug-specific response were identified and subjected to correlation network analysis, together with clinical parameters and KEGG pathways. Among the microbiome markers of CKD, Corynebacterium was found to form a network hub that was closely correlated with the JPYS responder Enterococcus, suggesting a potential indirect impact of JPYS on Corynebacterium via interspecies interactions. We also identified two network hubs of the PF responder Blautia and the JPYS-only marker Coprococcus, which were connected with many genera and clinical parameters. They might serve as keystone taxa driving the response of gut microbiota to the drugs and influence host outcomes. Moreover, the JPYS-only marker Clostridium_XIVb was found to be connected to many pathways that are associated with CKD progression and might account for the improved outcomes in the JPYS treated rats. At last, the identified keystone markers of drug response were validated by qPCR for their differential abundance between CKD and the two drugs. Taken together, our study revealed that the responses of gut microbiota to JPYS were distinct from that to PF, and pinpointed drug-specific keystone microbiome markers closely correlated to clinical parameters, which could serve as candidate microbiome targets for further studies on their roles in medicating the drug efficacy of TCM in CKD.

Isolation and Quantification of Uremic Toxin Precursor-Generating Gut Bacteria in Chronic Kidney Disease Patients

In chronic kidney disease (CKD), impaired kidney function results in accumulation of uremic toxins, which exert deleterious biological effects and contribute to inflammation and cardiovascular morbidity and mortality. Protein-bound uremic toxins (PBUTs), such as p-cresyl sulfate, indoxyl sulfate and indole-3-acetic acid, originate from phenolic and indolic compounds, which are end products of gut bacterial metabolization of aromatic amino acids (AAA). This study investigates gut microbial composition at different CKD stages by isolating, identifying and quantifying PBUT precursor-generating bacteria. Fecal DNA extracts from 14 controls and 138 CKD patients were used to quantify total bacterial number and 11 bacterial taxa with qPCR. Moreover, isolated bacteria from CKD 1 and CKD 5 fecal samples were cultured in broth medium supplemented with AAA under aerobic and anaerobic conditions, and classified as PBUT precursor-generators based on their generation capacity of phenolic and indolic compounds, measured with U(H)PLC. In total, 148 different fecal bacterial species were isolated, of which 92 were PBUT precursor-generators. These bacterial species can be a potential target for reducing PBUT plasma levels in CKD. qPCR indicated lower abundance of short chain fatty acid-generating bacteria, Bifidobacterium spp. and Streptococcus spp., and higher Enterobacteriaceae and E. coli with impaired kidney function, confirming an altered gut microbial composition in CKD.

The effects of a multispecies synbiotic on microbiome-related side effects of long-term proton pump inhibitor use: A pilot study

Side effects of proton pump inhibitors (PPI) can be linked to the changes in the intestinal microbiome that occur during therapy, especially in long-term users. Therefore, the microbiome might also be a key player in the reduction of PPI side effects. We tested the effects of a three-month intervention with a multispecies synbiotic on intestinal inflammation, gut barrier function, microbiome composition, routine laboratory parameters and quality of life in patients with long-term PPI therapy. Thirty-six patients received a daily dose of a multispecies synbiotic for three months and were clinically observed without intervention for another three months. After intervention 17% of patients reached normal calprotectin levels; the overall reduction did not reach statistical significance (−18.8 ng/mg; 95%CI: −50.5; 12.9, p = 0.2). Elevated zonulin levels could be significantly reduced (−46.3 ng/mg; 95%CI: −71.4; −21.2; p < 0.001). The abundance of Stomatobaculum in the microbiome was reduced and Bacillus increased during the intervention. Furthermore, albumin, alkaline phosphatase and thrombocyte count were significantly increased and aspartate transaminase was significantly decreased during intervention. Gastrointestinal quality of life showed significant improvements. In conclusion, microbiome-related side effects of long-term PPI use can be substantially reduced by synbiotic intervention. Further studies are warranted to optimize dosage and duration of the intervention.

Peritoneal Microbiome in End-Stage Renal Disease Patients and the Impact of Peritoneal Dialysis Therapy

Factors influencing the occurrence of peritoneal dialysis (PD)-related infections are still far from fully understood. Recent studies described the existence of specific microbiomes in body sites previously considered microbiome-free, unravelling new microbial pathways in the human body. In the present study, we analyzed the peritoneum of end-stage kidney disease (ESKD) patients to determine if they harbored a specific microbiome and if it is altered in patients on PD therapy. We conducted a cross-sectional study where the peritoneal microbiomes from ESKD patients with intact peritoneal cavities (ESKD non-PD, n = 11) and ESKD patients undergoing PD therapy (ESKD PD, n = 9) were analyzed with a 16S rRNA approach. Peritoneal tissue of ESKD patients contained characteristically low-abundance microbiomes dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. Patients undergoing PD therapy presented lower species richness, with dominance by the Pseudomonadaceae and Prevotelaceae families. This study provides the first characterization of the peritoneal microbiome in ESKD patients, bringing new insight to the human microbiome. Additionally, PD therapy may induce changes in this unique microbiome. The clinical relevance of these observations should be further explored to uncover the role of the peritoneal microbiome as a key element in the onset or aggravation of infection in ESKD patients, especially those undergoing PD.

High-throughput sequencing analysis of intestinal flora changes in ESRD and CKD patients

BACKGROUND

Chronic kidney disease (CKD) disease affects gut flora by causing dysbiosis and lead to systemic inflammatory conditions. Here, we provide intestinal flora changes of CKD patients undertook different hemodialysis therapy.

METHODS

From 2017 to 2019, a total of 166 patients from Guangzhou Red Cross Hospital were recruited and divided into four groups with 17 cases in healthy control group, 47 cases in CKD non-dialysis group, 49 cases in HD group, and 53 cases in PD group. Intestinal flora genome 16S rDNA sequencing and further bio-informatic analysis were performed.

RESULTS

Decreased diversity and altered communities of intestinal flora in PD patients, in which microbial diversity was positive correlated with the albumin level were observed. A total of 20 intestinal flora phyla were detected in 166 fecal samples, divided into 3 dominant intestinal types including Bacteroides-dominant gut type, Firmicutes-dominant type and Proteobacteria-dominant gut type. Further analyses found 198 genera, the abundance of 86 genera were significantly different. Butyrate-producing taxa as Faecalibacterium in genera level and Bifidobacteriaceae and Prevotellaceae in family level were dominant genus in CT, CKD, and HD groups, while urease containing-, indole- and p-cresol-forming taxa as Escherichia in genera and Enterobacteriaceae, Enterococcaceae in family level was dominated genus in PD group. Number of differential expressed genes in KEGG enrichment pathways were significantly different in PD group in carbohydrate metabolism, amino acid metabolism, energy metabolism, translation, and membrane transport.

CONCLUSION

Our results suggest peritoneal dialysis therapy could result in reduced diversity and altered microbial communities, with reduced probiotic butyrate-producing taxa and increased urease containing-, indole- and p-cresol-forming taxa. The disordered intestinal flora can seriously affect the nutrition level in CKD patients with PD therapy.

Effects of a multispecies synbiotic on glucose metabolism, lipid marker, gut microbiome composition, gut permeability, and quality of life in diabesity: a randomized, double-blind, placebo-controlled pilot study

Purpose

Diabesity, the combination of obesity and type 2 diabetes, is an ever-growing global health burden. Diabesity-associated dysbiosis of the intestinal microbiome has gained attention as a potential driver of disease and, therefore, a possible therapeutic target by means of pro- or prebiotic supplementation. This study tested the effects of a multispecies synbiotic (i.e. a combination of probiotics and prebiotics) on glucose metabolism, gut microbiota, gut permeability, neutrophil function and quality of life in treatment-experienced diabesity patients.

Methods

A randomized, double-blind, placebo-controlled pilot study with 26 diabesity patients was conducted in which patients received a daily dose of a multispecies probiotic and a prebiotic (or a placebo) for 6 months.

Results

There were no changes in glucose metabolism or mixed meal tolerance test responses throughout the study. The analysis of secondary outcomes revealed beneficial effects on hip circumference [− 1 (95% CI − 4; 3) vs +3 (− 1; 8) cm, synbiotics vs. placebo, respectively, p = 0.04], serum zonulin [− 0.04 (− 0.2; 0.1) vs +0.3 (− 0.05; 0.6) ng/ml, p = 0.004)] and the physical role item of the SF36 quality of life assessment [+ 5.4 (− 1.7; 12.5) vs − 5.0 (− 10.1; 0.2) points, p = 0.02] after 3 months of intervention, and lipoprotein (a) [− 2.1 (− 5.7; 1.6) vs +3.4 (− 0.9; 7.9) mg/dl, p = 0.02] after 6 months. There were no significant differences in alpha or beta diversity of the microbiome between groups or time points.

Conclusions

Glucose metabolism as the primary outcome was unchanged during the intervention with a multispecies synbiotic in patients with diabesity. Nevertheless, synbiotics improved some symptoms and biomarkers of type 2 diabetes and aspects of quality of life suggesting a potential role as adjuvant tool in the management of diabesity.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s00394-019-02135-w) contains supplementary material, which is available to authorized users.

Metabolomics for Investigating Physiological and Pathophysiological Processes

Metabolomics uses advanced analytical chemistry techniques to enable the high-throughput characterization of metabolites from cells, organs, tissues, or biofluids. The rapid growth in metabolomics is leading to a renewed interest in metabolism and the role that small molecule metabolites play in many biological processes. As a result, traditional views of metabolites as being simply the "bricks and mortar" of cells or just the fuel for cellular energetics are being upended. Indeed, metabolites appear to have much more varied and far more important roles as signaling molecules, immune modulators, endogenous toxins, and environmental sensors. This review explores how metabolomics is yielding important new insights into a number of important biological and physiological processes. In particular, a major focus is on illustrating how metabolomics and discoveries made through metabolomics are improving our understanding of both normal physiology and the pathophysiology of many diseases. These discoveries are yielding new insights into how metabolites influence organ function, immune function, nutrient sensing, and gut physiology. Collectively, this work is leading to a much more unified and system-wide perspective of biology wherein metabolites, proteins, and genes are understood to interact synergistically to modify the actions and functions of organelles, organs, and organisms.

Alleviating chronic kidney disease progression through modulating the critical genus of gut microbiota in a cisplatin-induced Lanyu pig model

In the present study, we investigated the effects of Probiotic mix 1 (Pm1) with Lactobacillus plantarum subsp. plantarum, Lactobacillusparacasei subsp. paracasei, and Streptococcus salivarius subsp. thermophilus on preventing renal injury using a chronic kidney disease (CKD) minipig model previously developed in our lab using cisplatin-induced CKD in Lanyu pigs. The results indicated that the high dosage Pm1 (H.Pm1) group demonstrated lower incidence of lesions, including atrophy, mononuclear inflammation, cell infiltration, and interstitial fibrosis in renal tubules in hematoxylin and eosin (H&E) and Masson's trichrome stain. We further systematically investigated the preventing effect of Pm1. The H.Pm1 group decreased inflammatory cytokines production and increased the level of superoxide dismutase activity in plasma. The pigs fed with high dosage of Pm1 group also showed reduced both creatinine and blood urea nitrogen (BUN) when compared with the cisplatin group. Microbiota results indicated that Pm1-intervention not only reduced the abundance of Gram-negative bacteria but also affected the abundance of specific genera biomarkers, Anaerovibrio, possible_genus_SK018, Holdemanella, and Lachnospiraceae_UCG_010 in gut microbiota, leading to decreased inflammation and apoptosis in the kidney and further prevention/alleviation of the symptoms of CKD.

Transplant associated infections-The role of the gastrointestinal microbiota and potential therapeutic options

Infectious complications are common following kidney transplantation and rank in the top five causes of death in patients with allograft function. Over the last 5 years, there has been emerging evidence that changes in the gastrointestinal microbiota following kidney transplantation may play a key role in the pathogenesis of transplant-associated infections. Different factors have emerged which may disrupt the interaction between the gastrointestinal microbiota and the immune system, which may lead to infective complications in kidney transplant recipients. Over the last 5 years, there has been emerging evidence that changes in the gastrointestinal microbiota following kidney transplantation may play a key role in the pathogenesis of transplant-associated infections. This review will discuss the structure and function of the gastrointestinal microbiota, the changes that occur in the gastrointestinal microbiota following kidney transplantation and the factors underpinning these changes, how these changes may lead to transplant-associated infectious complications and potential treatments which may be instituted to mitigate this risk.

Biomarkers for oralization during long-term proton pump inhibitor therapy predict survival in cirrhosis

Proton pump inhibitors (PPI) are an invaluable therapy option for acid related diseases; however, PPI therapy is also linked to a series of side effects in cirrhosis, such as microbiome alterations, spontaneous bacterial peritonitis and hepatic encephalopathy. Decision tools to balance benefits and risks of PPI therapy are largely missing. In this study, we tested gut-derived biomarkers to identify PPI-associated dysbiosis, its association with gut barrier function and liver-related mortality. In this observational study, faecal microbiome composition data obtained from 16S rDNA sequencing of 90 cirrhotic patients with and without long-term PPI use and additional potential biomarkers identified from the literature were evaluated for their predictive value regarding PPI-associated dysbiosis and liver-related three-year mortality. In addition, faecal calprotectin, faecal zonulin and serum lipopolysaccharides were assessed as markers for intestinal inflammation, gut permeability and bacterial translocation. Streptococcus salivarius, Veillonella parvula and the genus Streptococcus were significantly increased in patients with long-term PPI therapy and performed well as biomarkers for PPI-associated dysbiosis (accuracy: 74%, 72% and 74%, respectively). The abundance of Streptococcus salivarius was linked to intestinal inflammation and gut barrier dysfunction, whereas the abundance of Veillonella parvula showed associations with liver disease severity; both were independent predictors for liver-related three-year mortality. Gut-derived biomarkers of PPI-associated dysbiosis are linked to worse outcome and a potential option to evaluate the risks of adverse events during long-term PPI therapy.

Modulation of the Gut Microbiota by Resistant Starch as a Treatment of Chronic Kidney Diseases: Evidence of Efficacy and Mechanistic Insights

Chronic kidney disease (CKD) has been associated with changes in gut microbial ecology, or "dysbiosis," which may contribute to disease progression. Recent studies have focused on dietary approaches to favorably alter the composition of the gut microbial communities as a treatment method in CKD. Resistant starch (RS), a prebiotic that promotes proliferation of gut bacteria such as Bifidobacteria and Lactobacilli, increases the production of metabolites including short-chain fatty acids, which confer a number of health-promoting benefits. However, there is a lack of mechanistic insight into how these metabolites can positively influence renal health. Emerging evidence shows that microbiota-derived metabolites can regulate the incretin axis and mitigate inflammation via expansion of regulatory T cells. Studies from animal models and patients with CKD show that RS supplementation attenuates the concentrations of uremic retention solutes, including indoxyl sulfate and p-cresyl sulfate. Here, we present the current state of knowledge linking the microbiome to CKD, we explore the efficacy of RS in animal models of CKD and in humans with the condition, and we discuss how RS supplementation could be a promising dietary approach for slowing CKD progression.

Contributory Role of Gut Microbiota and Their Metabolites Toward Cardiovascular Complications in Chronic Kidney Disease. Semin Nephrol. 2018;38:193-205. [PMID: 29602401 DOI: 10.1016/j.semnephrol.2018.01.008]

The gut microbiome recently has emerged as a novel risk factor that impacts health and disease. Our gut microbiota can function as an endocrine organ through its unique ability to metabolize various dietary precursors, and can fuel the systemic inflammation observed in chronic disease. This is especially important in the setting of chronic kidney disease, in which microbial metabolism can contribute directly to accumulation of circulating toxins that then can alter and shift the balance of microbiota composition and downstream functions. To study this process, advances in -omics technologies are providing opportunities to understand not only the taxonomy, but also the functional diversity of our microbiome. We also reliably can quantify en masse a wide range of uremic byproducts of microbial metabolism. Herein, we examine the bidirectional relationship between the gut microbiome and the failing kidneys. We describe potential approaches targeting gut microbiota for cardiovascular risk reduction in chronic kidney disease using an illustrative example of a novel gut-generated metabolite, trimethylamine N-oxide.

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.

Dysregulated Handling of Dietary Protein and Muscle Protein Synthesis After Mixed-Meal Ingestion in Maintenance Hemodialysis Patients

Introduction

Skeletal muscle loss is common in patients with renal failure who receive maintenance hemodialysis (MHD) therapy. Regular ingestion of protein-rich meals are recommended to help offset muscle protein loss in MHD patients, but little is known about the anabolic potential of this strategy.

Methods

Eight MHD patients (age: 56 ± 5 years; body mass index [BMI]: 32 ± 2 kg/m²) and 8 nonuremic control subjects (age: 50 ± 2 years: BMI: 31 ± 1 kg/m²) received primed continuous L-[ring-²H₅]phenylalanine and L-[1-¹³C]leucine infusions with blood and muscle biopsy sampling on a nondialysis day. Participants consumed a mixed meal (546 kcal; 20-g protein, 59-g carbohydrates, 26-g fat) with protein provided as L-[5,5,5-²H₃]leucine-labeled eggs.

Results

Circulating dietary amino acid availability was reduced in MHD patients (41 ± 5%) versus control subjects (61 ± 4%; P = 0.03). Basal muscle caspase-3 protein content was elevated (P = 0.03) and large neutral amino acid transporter 1 (LAT1) protein content was reduced (P = 0.02) in MHD patients versus control subjects. Basal muscle protein synthesis (MPS) was ∼2-fold higher in MHD patients (0.030 ± 0.005%/h) versus control subjects (0.014 ± 0.003%/h) (P = 0.01). Meal ingestion failed to increase MPS in MHD patients (absolute change from basal: 0.0003 ± 0.007%/h), but stimulated MPS in control subjects (0.009 ± 0.002%/h; P = 0.004).

Conclusions

MHD patients demonstrated muscle anabolic resistance to meal ingestion. This blunted postprandial MPS response in MHD patients might be related to high basal MPS, which results in a stimulatory ceiling effect and/or reduced plasma dietary amino acid availability after mixed-meal ingestion.

The Gut-Kidney Axis: Putative Interconnections Between Gastrointestinal and Renal Disorders

Diabetic kidney disease (DKD) is a devastating condition associated with increased morbidity and premature mortality. The etiology of DKD is still largely unknown. However, the risk of DKD development and progression is most likely modulated by a combination of genetic and environmental factors. Patients with autoimmune diseases, like type 1 diabetes, inflammatory bowel disease, and celiac disease, share some genetic background. Furthermore, gastrointestinal disorders are associated with an increased risk of kidney disease, although the true mechanisms have still to be elucidated. Therefore, the principal aim of this review is to evaluate the impact of disturbances in the gastrointestinal tract on the development of renal disorders.