Protein-bound uremic toxins: new culprits of cardiovascular events in chronic kidney disease patients

Advances in the mechanisms of vascular calcification in chronic kidney disease

Vascular calcification (VC) is common in patients with advanced chronic kidney disease (CKD).A series of factors, such as calcium and phosphorus metabolism disorders, uremic toxin accumulation, inflammation and oxidative stress and cellular senescence, cause osteoblast-like differentiation of vascular smooth muscle cells, secretion of extracellular vesicles, and imbalance of calcium regulatory factors, which together promote the development of VC in CKD. Recent advances in epigenetics have provided better tools for the investigation of VC etiology and new approaches for finding more accurate biomarkers. These advances have not only deepened our understanding of the pathophysiological mechanisms of VC in CKD, but also provided valuable clues for the optimization of clinical predictors and the exploration of potential therapeutic targets. The aim of this article is to provide a comprehensive overview of the pathogenesis of CKD VC, especially the new advances made in recent years, including the various key factors mentioned above. Through the comprehensive analysis, we expect to provide a solid theoretical foundation and research direction for future studies targeting the specific mechanisms of CKD VC, the establishment of clinical predictive indicators and the development of potential therapeutic strategies.

Effects of resistant starch supplementation on renal function and inflammatory markers in patients with chronic kidney disease: a meta-analysis of randomized controlled trials

BACKGROUND

Recent studies have shown that consumption of resistant starch (RS) has beneficial effects on the gut microbiota and immune function in patients with chronic kidney disease (CKD). The objective of this study was to evaluate the effects of RS on inflammation, uremic toxins, and renal function in patients with CKD through a systematic review and meta-analysis.

METHODS

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-2020. We included randomized controlled trials comparing RS supplementation to placebo. The National Library of Medicine (PubMed), Excerpta Medica Database (Embase), Cochrane Library, Web of Science, China National Knowledge Internet (CNKI) databases, and two gray literature sources - Baidu and Research Gate, were used for search, up to 28 August 2024. There was no limitation on publication date, but only manuscripts published in English and Chinese were included.

RESULTS

A total of 645 articles were retrieved. Ten articles met the inclusion criteria, and a total of 355 subjects were included. The analysis revealed that RS dietary intervention can significantly reduce indoxyl sulfate (IS) levels (SMD: -0.37, 95% confidence interval (CI): -0.70 to -0.04, p = .03) and blood urea nitrogen (BUN) levels (SMD: -0.30, 95% CI: -0.57 to -0.02, p = .03). There were no significant differences in the levels of interleukin-6 (IL-6), p-cresyl sulfate (p-CS), albumin, phosphorus, or tumor necrosis factor-α.

CONCLUSIONS

The RS diet has potential beneficial effects on uremic toxin levels and renal function indices in patients with CKD. RS supplementation can reduce uremic toxin levels and improve renal function but does not reduce the inflammatory response in patients with CKD. Nevertheless, results should be cautiously interpreted, because of the limited sample size and different treatment dosages. Further research is necessary to corroborate the beneficial effects of RS2 supplementation in this population.

Structure-based discovery of a new type of scaffold compound as binding competitors for protein-bound Uremic Toxins

Protein-bound uremic toxins (PBUTs) are the main cause of uremia, but traditional hemodialysis is ineffective in removing them because of their strong ability to bind to human serum albumin (HSA), highlighting the need for new treatments. In this study, first, structure-based docking was used to screen a diverse library of 200,376 virtual compounds against the active sites I and II. After two rounds of docking screening, 3944 candidate molecules were obtained. Second, 23 candidate molecules were obtained after ADMET prediction and toxicity analysis. Five candidate molecules were finally obtained after visual analysis and MM-PBSA calculations. We subsequently assessed their competitive displacement efficiency through a microdialysis experiment, and the results revealed that ZINC000008791789, ZINC000012297018, and ZINC000012296493 are promising binding competitors for PBUTs, as they have higher dialysis efficiency than the optimal displacer LA, approximately double the dialysis efficiency. The other two molecules, ZINC000031161007 and ZINC000004090361, although less efficient than LA, still outperformed the control group. Notably, four of them shared the same molecular scaffold, and three of them contained a flavonoid group. These findings provide a foundation for the development of more effective PBUT binding competitors, potentially benefiting uremia patients in the future.

Effects of Propolis Supplementation on Gut Microbiota and Uremic Toxin Profiles of Patients Undergoing Hemodialysis

BACKGROUND

Propolis possesses many bioactive compounds that could modulate the gut microbiota and reduce the production of uremic toxins in patients with chronic kidney disease (CKD) undergoing hemodialysis (HD). This clinical trial aimed to evaluate the effects of propolis on the gut microbiota profile and uremic toxin plasma levels in HD patients. These are secondary analyses from a previous double-blind, randomized clinical study, with 42 patients divided into two groups: the placebo and propolis group received 400 mg of green propolis extract/day for eight weeks. Indole-3 acetic acid (IAA), indoxyl sulfate (IS), and p-cresyl sulfate (p-CS) plasma levels were evaluated by reversed-phase liquid chromatography, and cytokines were investigated using the multiplex assay (Bio-Plex Magpix®). The fecal microbiota composition was analyzed in a subgroup of patients (n = 6) using a commercial kit for fecal DNA extraction. The V4 region of the 16S rRNA gene was then amplified by the polymerase chain reaction (PCR) using short-read sequencing on the Illumina NovaSeq PE250 platform in a subgroup. Forty-one patients completed the study, 20 in the placebo group and 21 in the propolis group. There was a positive correlation between IAA and TNF-α (r = 0.53, p = 0.01), IL-2 (r = 0.66, p = 0.002), and between pCS and IL-7 (r = 0.46, p = 0.04) at the baseline. No significant changes were observed in the values of uremic toxins after the intervention. Despite not being significant, microbial evenness and observed richness increased following the propolis intervention. Counts of the Fusobacteria species showed a positive correlation with IS, while counts of Firmicutes, Lentisphaerae, and Proteobacteria phyla were negatively correlated with IS. Two months of propolis supplementation did not reduce the plasma levels of uremic toxins (IAA, IS, and p-CS) or change the fecal microbiota.

Application of Nanoparticles as Novel Adsorbents in Blood Purification Strategies

BACKGROUND

Blood purification therapy for patients overloaded with metabolic toxins or drugs still needs improvement. Blood purification therapies, such as in hemodialysis or peritoneal dialysis can profit from a combined application with nanoparticles.

SUMMARY

In this review, the published literature is analyzed with respect to nanomaterials that have been customized and functionalized as nano-adsorbents during blood purification therapy. Liposomes possess a distinct combined structure composed of a hydrophobic lipid bilayer and a hydrophilic core. The liposomes which have enzymes in their aqueous core or obtain specific surface modifications of the lipid bilayer can offer appreciated advantages. Preclinical and clinical experiments with such modified liposomes show that they are highly efficient and generally safe. They may serve as indirect and direct adsorption materials both in hemodialysis and peritoneal dialysis treatment for patients with renal or hepatic failure. Apart from dialysis, nanoparticles made of specially designed metal and activated carbon have also been utilized to enhance the removal of solutes during hemoadsorption. Results are a superior adsorption capacity and good hemocompatibility shown during the treatment of patients with toxication or end-stage renal disease. In summary, nanomaterials are promising tools for improving the treatment efficacy of organ failure or toxication.

KEY MESSAGES

(i) The pH-transmembrane liposomes and enzyme-loaded liposomes are two representatives of liposomes with modified aqueous inner core which have been put into practice in dialysis. (ii) Unmodified or physiochemically modified liposomal bilayers are ideal binders for lipophilic protein-bound uremic toxins or cholestatic solutes, thus liposome-supported dialysis could become the next-generation hemodialysis treatment of artificial liver support system. (iii) Novel nano-based sorbents featuring large surface area, high adsorption capacity and decent biocompatibility have shown promise in the treatment of uremia, hyperbilirubinemia, intoxication, and sepsis. (vi) A major challenge of production lies in avoiding changes in physical and chemical properties induced by manufacturing and sterilizing procedures.

Increased levels of a mycophenolic acid metabolite in patients with kidney failure negatively affect cardiomyocyte health

Chronic kidney disease (CKD) significantly increases cardiovascular risk and mortality, and the accumulation of uremic toxins in the circulation upon kidney failure contributes to this increased risk. We thus performed a screening for potential novel mediators of reduced cardiovascular health starting from dialysate obtained after hemodialysis of patients with CKD. The dialysate was gradually fractionated to increased purity using orthogonal chromatography steps, with each fraction screened for a potential negative impact on the metabolic activity of cardiomyocytes using a high-throughput MTT-assay, until ultimately a highly purified fraction with strong effects on cardiomyocyte health was retained. Mass spectrometry and nuclear magnetic resonance identified the metabolite mycophenolic acid-β-glucuronide (MPA-G) as a responsible substance. MPA-G is the main metabolite from the immunosuppressive agent MPA that is supplied in the form of mycophenolate mofetil (MMF) to patients in preparation for and after transplantation or for treatment of autoimmune and non-transplant kidney diseases. The adverse effect of MPA-G on cardiomyocytes was confirmed in vitro, reducing the overall metabolic activity and cellular respiration while increasing mitochondrial reactive oxygen species production in cardiomyocytes at concentrations detected in MMF-treated patients with failing kidney function. This study draws attention to the potential adverse effects of long-term high MMF dosing, specifically in patients with severely reduced kidney function already displaying a highly increased cardiovascular risk.

Potential effects of specific gut microbiota on periodontal disease: a two-sample bidirectional Mendelian randomization study

Introduction

Periodontal disease (PD) presents a substantial global health challenge, encompassing conditions from reversible gingivitis to irreversible periodontitis, often culminating in tooth loss. The gut-oral axis has recently emerged as a focal point, with potential gut microbiota dysbiosis exacerbating PD.

Methods

In this study, we employed a double-sample bidirectional Mendelian randomized (MR) approach to investigate the causal relationship between specific gut microbiota and periodontal disease (PD) and bleeding gum (BG) development, while exploring the interplay between periodontal health and the gut microenvironment. We performed genome-wide association studies (GWAS) with two cohorts, totalling 346,731 (PD and control) and 461,113 (BG and control) participants, along with data from 14,306 participants' intestinal flora GWAS, encompassing 148 traits (31 families and 117 genera). Three MR methods were used to assess causality, with the in-verse-variance-weighted (IVW) measure as the primary outcome. Cochrane's Q test, MR-Egger, and MR-PRESSO global tests were used to detect heterogeneity and pleiotropy. The leave-one-out method was used to test the stability of the MR results. An F-statistic greater than 10 was accepted for instrument exposure association.

Results and conclusion

Specifically, Eubacterium xylanophilum and Lachnoclostridium were associated with reduced gum bleeding risk, whereas Anaerotruncus, Eisenbergiella, and Phascolarctobacterium were linked to reduced PD risk. Conversely, Fusicatenibacter was associated with an elevated risk of PD. No significant heterogeneity or pleiotropy was detected. In conclusion, our MR analysis pinpointed specific gut flora with causal connections to PD, offering potential avenues for oral health interventions.

Intestinal homeostasis in the gut-lung-kidney axis: a prospective therapeutic target in immune-related chronic kidney diseases

In recent years, the role of intestinal homeostasis in health has received increasing interest, significantly improving our understanding of the complex pathophysiological interactions of the gut with other organs. Microbiota dysbiosis, impaired intestinal barrier, and aberrant intestinal immunity appear to contribute to the pathogenesis of immune-related chronic kidney diseases (CKD). Meanwhile, the relationship between the pathological changes in the respiratory tract (e.g., infection, fibrosis, granuloma) and immune-related CKD cannot be ignored. The present review aimed to elucidate the new underlying mechanism of immune-related CKD. The lungs may affect kidney function through intestinal mediation. Communication is believed to exist between the gut and lung microbiota across long physiological distances. Following the inhalation of various pathogenic factors (e.g., particulate matter 2.5 mum or less in diameter, pathogen) in the air through the mouth and nose, considering the anatomical connection between the nasopharynx and lungs, gut microbiome regulates oxidative stress and inflammatory states in the lungs and kidneys. Meanwhile, the intestine participates in the differentiation of T cells and promotes the migration of various immune cells to specific organs. This better explain the occurrence and progression of CKD caused by upper respiratory tract precursor infection and suggests the relationship between the lungs and kidney complications in some autoimmune diseases (e.g., anti-neutrophil cytoplasm antibodies -associated vasculitis, systemic lupus erythematosus). CKD can also affect the progression of lung diseases (e.g., acute respiratory distress syndrome and chronic obstructive pulmonary disease). We conclude that damage to the gut barrier appears to contribute to the development of immune-related CKD through gut-lung-kidney interplay, leading us to establish the gut-lung-kidney axis hypothesis. Further, we discuss possible therapeutic interventions and targets. For example, using prebiotics, probiotics, and laxatives (e.g., Rhubarb officinale) to regulate the gut ecology to alleviate oxidative stress, as well as improve the local immune system of the intestine and immune communication with the lungs and kidneys.

Association between worsening renal function severity during hospitalization and low physical function at discharge: a retrospective cohort study of older patients with heart failure and chronic kidney disease from Japan

BACKGROUND

The number of hospitalized older patients with chronic heart failure, chronic kidney disease, and worsening renal function is rising in Japan. This study aimed to clarify the impact of the severity of worsening renal function during hospitalization on low physical function at discharge of these patients.

METHODS

We included 573 consecutive heart failure patients who underwent phase I cardiac rehabilitation. Worsening renal function severity was defined according to elevation during hospitalization of baseline serum creatinine on admission: non-worsening renal function, serum creatinine < 0.2 mg/dL; worsening renal function II/I, serum creatinine ≥ 0.2 to < 0.5 mg/dL; worsening renal function III, and serum creatinine ≥ 0.5 mL/dL. Physical function was measured with the Short Performance Physical Battery. We compared background factors, clinical parameters, pre-hospitalization walking levels, Functional Independence Measure score, and physical function in the three renal function groups. Multiple regression analysis was performed with the Short Performance Physical Battery at discharge as the dependent variable.

RESULTS

The final analysis included 196 patients (mean age 82.7 years, male 51.5%) categorized into three groups based on worsening renal function: worsening renal function grade III group (n = 55), worsening renal function grade II/I group (n = 36), and non-worsening renal function group (n = 105). There is no significant difference in walking levels before hospitalization between the three groups, but physical function at discharge was significantly lower in the worsening renal function III group. Moreover, worsening renal function III was an independent factor for low physical function at discharge.

CONCLUSION

Worsening of renal function during hospitalization in older patients with heart failure and chronic kidney disease was strongly associated with low physical function at discharge, even after adjusting for other potentially confounding factors, such as pre-hospitalization walking levels, walking start day, and Geriatric Nutrition Risk Index at discharge. Notably, worsening renal function of mild or moderate severity (grade II/I) did not show a significant association with low physical function.

Effects of propolis on inflammation markers in patients undergoing hemodialysis: A randomized, double-blind controlled clinical trial

BACKGROUND AND AIMS

Several studies have been performed in vitro and in animals showing that propolis (a resin made by bees) has excellent anti-inflammatory properties, but no study has been performed in patients with chronic kidney disease (CKD) on hemodialysis (HD). The present study aimed to evaluate the effects of propolis supplementation on inflammatory markers in patients with CKD on HD.

METHODS

This is a longitudinal, double-blind, placebo-controlled trial with patients randomized into two groups: propolis (4 capsules of 100 mg/day containing concentrated and standardized dry EPP-AF® green propolis extract) or placebo (4 capsules of 100 mg/day containing microcrystalline cellulose, magnesium stearate and colloidal silicon dioxide) for two months. Routine parameters were analyzed using commercial kits. The plasma levels of inflammatory cytokines were evaluated by flow luminometry.

RESULTS

Forty-one patients completed the follow-up, 21 patients in the propolis group (45 ± 12 years, 13 women, BMI, 22.8 ± 3.7 kg/m²) and 20 in the placebo group (45.5 ± 14 years, 13 women, BMI, 24.8 ± 6.8 kg/m²). The obtained data revealed that the intervention with propolis significantly reduced the serum levels of tumour necrosis factor α (TNFα) (p = 0.009) as well as had the tendency to reduce the levels of macrophage inflammatory protein-1β (MIP-1β) (p = 0.07). There were no significant differences in the placebo group.

CONCLUSION

Short-term EPP-AF® propolis dry extract 400 mg/day supplementation seems to mitigate inflammation, reducing the plasma levels of TNFα and MIP-1β in patients with CKD on HD. This study was registered at clinicaltrials.gov (NCT04411758).

Causal Effects of Specific Gut Microbiota on Chronic Kidney Diseases and Renal Function-A Two-Sample Mendelian Randomization Study

BACKGROUND

Targeting the gut microbiota may become a new therapeutic to prevent and delay the progression of chronic kidney disease (CKD). Nonetheless, the causal relationship between specific intestinal flora and CKD is still unclear.

MATERIALS AND METHOD

To identify genetically predicted microbiota, we used summary data from genome-wide association studies on gut microbiota in 18340 participants from 24 cohorts. Furthermore, we genetically predicted the causal relationship between 211 gut microbiotas and six phenotypes (outcomes) (CKD, estimated glomerular filtration rate (eGFR), urine albumin to creatinine ratio (UACR), dialysis, rapid progress to CKD, and rapid decline of eGFR). Four Mendelian randomization (MR) methods, including inverse variance weighted (IVW), MR-Egger, weighted median, and weighted mode were used to investigate the casual relationship between gut microbiotas and various outcomes. The result of IVW was deemed as the primary result. Then, Cochrane's Q test, MR-Egger, and MR-PRESSO Global test were used to detect heterogeneity and pleiotropy. The leave-one method was used for testing the stability of MR results and Bonferroni-corrected was used to test the strength of the causal relationship between exposure and outcome.

RESULTS

Through the MR analysis of 211 microbiotas and six clinical phenotypes, a total of 36 intestinal microflora were found to be associated with various outcomes. Among them, Class Bacteroidia (=-0.005, 95% CI: -0.001 to -0.008, p = 0.002) has a strong causality with lower eGFR after the Bonferroni-corrected test, whereas phylum Actinobacteria (OR = 1.0009, 95%CI: 1.0003-1.0015, p = 0.0024) has a strong causal relationship with dialysis. The Cochrane's Q test reveals that there is no significant heterogeneity between various single nucleotide polymorphisms. In addition, no significant level of pleiotropy was found according to MR-Egger and MR-PRESSO Global tests.

CONCLUSIONS

Through the two-sample MR analysis, we identified the specific intestinal flora that has a causal relationship with the incidence and progression of CKD at the level of gene prediction, which may provide helpful biomarkers for early disease diagnosis and potential therapeutic targets for CKD.

p-Cresyl sulfate predicts clinical outcomes in sustained peritoneal dialysis: a 5-year follow-up cohort study and meta-analysis

Background

The impact of p-cresyl sulfate (PCS) and indoxyl sulfate (IS) on the prognosis of patients with uremia remains controversial. We performed a prospective study on peritoneal dialysis (PD) to investigate the relationship between PCS or IS levels with clinical outcomes.

Methods

This prospective cohort study investigated the association of serum PCS and IS with clinical outcomes in patients undertaking PD. We performed a correlations analysis to explore the influencing factors of PCS an IS. Meta-analysis was conducted to objectively evaluate the prognostic effects of PCS and IS on different stages of CKD patients.

Results

A total of 127 patients were enrolled consecutively and followed with an average period of 51.3 months. Multivariate Cox regression showed that serum total PCS not only contributed to the occurrence of PD failure event (HR: 1.05, 95% CI = 1.02 to 1.07, p < 0.001), but also increased the risk of cardiovascular event (HR: 1.08, 95% CI = 1.04 to 1.13, p < 0.001) and PD-associated peritonitis (HR: 1.04, 95% CI = 1.02 to 1.08, p = 0.001). Dividing the total PCS level by 18.99 mg/L, which was calculated from the best cutoff value of the ROC curve, patients with total PCS higher than 18.99 mg/L had worse prognosis. Meta-analysis confirmed its value in cardiovascular event in PD.

Conclusion

The serum total PCS concentration was a detrimental factor for higher PD failure event, cardiovascular event, and PD-associated peritonitis. It could be used as an innovative marker in predicting poor clinical outcome in PD.

Assembly of chemically modified protein nanocages into 3D materials for the adsorption of uremic toxins

Hemodialysis fails to remove protein-bound uremic toxins that are attributed with high cardiovascular risk. Application of adsorption materials is a viable strategy, but suitable biocompatible adsorbents are still not available. Here, we demonstrate that adsorbents based on the bottom-up assembly of the intrinsically biocompatible protein cage ferritin are applicable for toxin adsorption. Due to the size-exclusion effect of its pores, only small molecules such as uremic toxins can enter the protein cage. Protein redesign techniques that target selectively the inner surface were used to introduce anchor sites for chemical modification. Porous crystalline adsorbents were fabricated by bottom-up assembly of the protein cage. Linkage of up to 96 phenylic or aliphatic molecules per container was verified by ESI-MS. Materials based on unmodified ferritin cages can already adsorb the uremic toxins. The adsorption capacity could be increased by about 50% through functionalization with hydrophobic molecules reaching 458 μg g^-1 for indoxyl sulfate. The biohybrid materials show no contamination with endotoxins and do not activate blood platelets. These findings demonstrate the great potential of protein-based adsorbents for the clearance of uremic toxins: modifications enhance toxin adsorption without diminishing the biocompatibility of the final protein-based material.

Effects of the uremic toxin indoxyl sulphate on human microvascular endothelial cells

Indoxyl sulphate (IS) is a uremic toxin accumulating in the plasma of chronic kidney disease (CKD) patients. IS accumulation induces side effects in the kidneys, bones and cardiovascular system. Most studies assessed IS effects on cell lines by testing higher concentrations than those measured in CKD patients. Differently, we exposed a human microvascular endothelial cell line (HMEC-1) to the IS concentrations measured in the plasma of healthy subjects (physiological) or CKD patients (pathological). Pathological concentrations reduced cell proliferation rate but did not increase long-term oxidative stress level. Indeed, total protein thiols decreased only after 24 h of exposure in parallel with an increased Nrf-2 protein expression. IS induced actin cytoskeleton rearrangement with formation of stress fibres. Proteomic analysis supported this hypothesis as many deregulated proteins are related to actin filaments organization or involved in the endothelial to mesenchymal transition. Interestingly, two proteins directly linked to cardiovascular diseases (CVD) in in vitro and in vivo studies underwent deregulation: COP9 signalosome complex subunit 9 and thrombomodulin. Future experiments will be needed to investigate the role of these proteins and the signalling pathways in which they are involved to clarify the possible link between CKD and CVD.

Metabolite profiling of human-originated Lachnospiraceae at the strain level

The human gastrointestinal (GI) tract harbors diverse microbes, and the family Lachnospiraceae is one of the most abundant and widely occurring bacterial groups in the human GI tract. Beneficial and adverse effects of the Lachnospiraceae on host health were reported, but the diversities at species/strain levels as well as their metabolites of Lachnospiraceae have been, so far, not well documented. In the present study, we report on the collection of 77 human-originated Lachnospiraceae species (please refer hLchsp, https://hgmb.nmdc.cn/subject/lachnospiraceae) and the in vitro metabolite profiles of 110 Lachnospiraceae strains (https://hgmb.nmdc.cn/subject/lachnospiraceae/metabolites). The Lachnospiraceae strains in hLchsp produced 242 metabolites of 17 categories. The larger categories were alcohols (89), ketones (35), pyrazines (29), short (C2-C5), and long (C > 5) chain acids (31), phenols (14), aldehydes (14), and other 30 compounds. Among them, 22 metabolites were aromatic compounds. The well-known beneficial gut microbial metabolite, butyric acid, was generally produced by many Lachnospiraceae strains, and Agathobacter rectalis strain Lach-101 and Coprococcus comes strain NSJ-173 were the top 2 butyric acid producers, as 331.5 and 310.9 mg/L of butyric acids were produced in vitro, respectively. Further analysis of the publicly available cohort-based volatile-metabolomic data sets of human feces revealed that over 30% of the prevailing volatile metabolites were covered by Lachnospiraceae metabolites identified in this study. This study provides Lachnospiraceae strain resources together with their metabolic profiles for future studies on host-microbe interactions and developments of novel probiotics or biotherapies.

Role of gut microbe-derived metabolites in cardiometabolic diseases: Systems based approach

BACKGROUND

The gut microbiome influences host physiology and cardiometabolic diseases by interacting directly with intestinal cells or by producing molecules that enter the host circulation. Given the large number of microbial species present in the gut and the numerous factors that influence gut bacterial composition, it has been challenging to understand the underlying biological mechanisms that modulate risk of cardiometabolic disease.

SCOPE OF THE REVIEW

Here we discuss a systems-based approach that involves simultaneously examining individuals in populations for gut microbiome composition, molecular traits using "omics" technologies, such as circulating metabolites quantified by mass spectrometry, and clinical traits. We summarize findings from landmark studies using this approach and discuss future applications.

MAJOR CONCLUSIONS

Population-based integrative approaches have identified a large number of microbe-derived or microbe-modified metabolites that are associated with cardiometabolic traits. The knowledge gained from these studies provide new opportunities for understanding the mechanisms involved in gut microbiome-host interactions and may have potentially important implications for developing novel therapeutic approaches.

Enzobiotics-A Novel Therapy for the Elimination of Uremic Toxins in Patients with CKD (EETOX Study): A Multicenter Double-Blind Randomized Controlled Trial

Design, participants, setting, and measurements: Predialysis adult participants with chronic kidney disease (CKD) and mean estimated glomerular filtration rate (eGFR) <45 mL/min per 1.73 m2) were recruited in 2019 to a multicentric double-blinded randomized controlled trial of enzobiotic therapy (synbiotics and proteolytic enzymes) conducted over 12 weeks. The primary objective was to evaluate the efficacy and safety of enzobiotics in reducing the generation of p-cresol sulfate (PCS) and indoxyl sulfate (IS), stabilizing renal function, and improving quality of life (QoL), while the secondary objective was to evaluate the feasibility of the diagnostic prediction of IS and PCS from CKD parameters. Results: Of the 85 patients randomized (age 48.76 years, mean eGFR 23.24 mL/min per 1.73 m2 in the placebo group; age 54.03 years, eGFR 28.93 mL/min per 1.73 m2 in the enzobiotic group), 50 completed the study. The absolute mean value of PCS increased by 12% from 19 µg/mL (Day 0) to 21 µg/mL (Day90) for the placebo group, whereas it decreased by 31% from 23 µg/mL (Day 0) to 16 µg/mL (Day 90) for the enzobiotic group. For IS, the enzobiotic group showed a decrease (6.7%) from 11,668 to 10,888 ng/mL, whereas the placebo group showed an increase (8.8%) from 11,462 to 12,466 ng/mL (Day 90). Each patient improvement ratio for Day 90/Day 0 analysis showed that enzobiotics reduced PCS by 23% (0.77, p = 0.01). IS levels remained unchanged. In the placebo group, PCS increased by 27% (1.27, p = 0.14) and IS increased by 20% (1.20, p = 0.14). The proportion of individuals beyond the risk threshold for PCS (>20 µg/mL) was 53% for the placebo group and 32% for the enzobiotic group. The corresponding levels for IS risk (threshold >20,000 ng/mL) were 35% and 24% for the placebo and enzobiotic groups, respectively. In the placebo group, eGFR decreased by 7% (Day 90) but remained stable (1.00) in the enzobiotic group. QoL as assessed by the adversity ratio decreased significantly (p = 0.00), highlighting an improvement in the enzobiotic group compared to the placebo group. The predictive equations were as follows: PCS (Day 0 = −5.97 + 0.0453 PC + 2.987 UA − 1.310 Creat; IS (Day 0) = 756 + 1143 Creat + 436.0 Creat2. Conclusion: Enzobiotics significantly reduced the PCS and IS, as well as improved the QoL.

Archaea from the gut microbiota of humans: Could be linked to chronic diseases?

Archaea comprise a unique domain of organisms with distinct biochemical and genetic differences from bacteria. Methane-forming archaea, methanogens, constitute the predominant group of archaea in the human gut microbiota, with Methanobrevibacter smithii being the most prevalent. However, the effect of methanogenic archaea and their methane production on chronic disease remains controversial. As perturbation of the microbiota is a feature of chronic conditions, such as cardiovascular disease, neurodegenerative diseases and chronic kidney disease, assessing the influence of archaea could provide a new clue to mitigating adverse effects associated with dysbiosis. In this review, we will discuss the putative role of archaea in the gut microbiota in humans and the possible link to chronic diseases.

n-3 PUFA dietary lipid replacement normalizes muscle mitochondrial function and oxidative stress through enhanced tissue mitophagy and protects from muscle wasting in experimental kidney disease

INTRODUCTION AND METHODS

Skeletal muscle mitochondrial dysfunction may cause tissue oxidative stress and consequent catabolism in chronic kidney disease (CKD), contributing to patient mortality. We investigated in 5/6-nephrectomized (Nx) rats the impact of n3-polyunsaturated fatty-acids (n3-PUFA) isocaloric partial dietary replacement on gastrocnemius muscle (Gm) mitochondrial master-regulators, ATP production, ROS generation and related muscle-catabolic derangements.

RESULTS

Nx had low Gm mitochondrial nuclear respiratory factor-2 and peroxisome proliferator-activated receptor gamma coactivator-1alpha, low ATP production and higher mitochondrial fission-fusion protein ratio with ROS overproduction. n3-PUFA normalized all mitochondrial derangements and pro-oxidative tissue redox state (oxydized to total glutathione ratio). n3-PUFA also normalized Nx-induced muscle-catabolic proinflammatory cytokines, insulin resistance and low muscle weight. Human uremic serum reproduced mitochondrial derangements in C2C12 myotubes, while n3-PUFA coincubation prevented all effects. n3-PUFA also enhanced muscle mitophagy in-vivo and siRNA-mediated autophagy inhibition selectively blocked n3-PUFA-induced normalization of C2C12 mitochondrial ROS production.

CONCLUSIONS

In conclusion, dietary n3-PUFA normalize mitochondrial master-regulators, ATP production and dynamics in experimental CKD. These effects occur directly in muscle cells and they normalize ROS production through enhanced mitophagy. Dietary n3-PUFA mitochondrial effects result in normalized catabolic derangements and protection from muscle wasting, with potential positive impact on patient survival.

Serum total indoxyl sulfate levels and all-cause and cardiovascular mortality in maintenance hemodialysis patients: a prospective cohort study

BACKGROUND

The association between serum total indoxyl sulfate (tIS), and cardiovascular disease (CVD) and all-cause mortality is a matter of debate. In the current study we sought to determine the association, if any, between serum tIS, and all-cause and CVD-associated mortality in patients on maintenance hemodialysis (MHD).

METHODS

A prospective cohort study was conducted involving 500 MHD patients at Dalian Municipal Central Hospital from 31 December 2014 to 31 December 2020. Serum tIS levels were measured at baseline and classified as high (≥44.16 ng/ml) or low (< 44.16 ng/ml) according to the "X-tile" program. Besides, the associations between continuous serum tIS and outcomes were also explored. Predictors were tested for colinearity using variance inflation factor analysis. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazards regression models. Restricted cubic spline model was performed to assess dose-response relationships between tIS concentration and all-cause and CVD mortality.

RESULTS

During a 58-month median follow-up period, 224 deaths (132 CVD deaths) were documented. After adjustment for potential confounders, the serum tIS level was positively associated with all-cause mortality (HR = 1.02, 95% = 1.01-1.03); however, we did not detect a significant association when tIS was a dichotomous variable. Compared with the MHD population with a serum tIS level < 44.16 ng/ml, the adjusted HR for CVD mortality among those with a serum tIS level ≥ 44.16 ng/ml was 1.76 (95% = 1.10-2.82). Furthermore, we also noted the same association when the serum tIS level was a continuous variable.

CONCLUSION

The serum tIS level was associated with higher risk of all-cause and CVD mortality among MHD patients. Further prospective large-scale studies are required to confirm this finding.

The Interplay between Uremic Toxins and Albumin, Membrane Transporters and Drug Interaction

Uremic toxins are a heterogeneous group of molecules that accumulate in the body due to the progression of chronic kidney disease (CKD). These toxins are associated with kidney dysfunction and the development of comorbidities in patients with CKD, being only partially eliminated by dialysis therapies. Importantly, drugs used in clinical treatments may affect the levels of uremic toxins, their tissue disposition, and even their elimination through the interaction of both with proteins such as albumin and cell membrane transporters. In this context, protein-bound uremic toxins (PBUTs) are highlighted for their high affinity for albumin, the most abundant serum protein with multiple binding sites and an ability to interact with drugs. Membrane transporters mediate the cellular influx and efflux of various uremic toxins, which may also compete with drugs as substrates, and both may alter transporter activity or expression. Therefore, this review explores the interaction mechanisms between uremic toxins and albumin, as well as membrane transporters, considering their potential relationship with drugs used in clinical practice.

The Effect of ß-Glucan Prebiotic on Kidney Function, Uremic Toxins and Gut Microbiome in Stage 3 to 5 Chronic Kidney Disease (CKD) Predialysis Participants: A Randomized Controlled Trial

There is growing evidence that gut dysbiosis contributes to the progression of chronic kidney disease (CKD) owing to several mechanisms, including microbiota-derived uremic toxins, diet and immune-mediated factors. The aim of this study was to investigate the effect of a ß-glucan prebiotic on kidney function, uremic toxins and the gut microbiome in stage 3 to 5 CKD participants. Fifty-nine participants were randomized to either the ß-glucan prebiotic intervention group (n = 30) or the control group (n = 29). The primary outcomes were to assess kidney function (urea, creatinine and glomerular filtration rate), plasma levels of total and free levels of uremic toxins (p-cresyl sulfate (pCS), indoxyl-sulfate (IxS), p-cresyl glucuronide (pCG) and indoxyl 3-acetic acid (IAA) and gut microbiota using 16S rRNA sequencing at baseline, week 8 and week 14. The intervention group (age 40.6 ± 11.4 y) and the control group (age 41.3 ± 12.0 y) did not differ in age or any other socio-demographic variables at baseline. There were no significant changes in kidney function over 14 weeks. There was a significant reduction in uremic toxin levels at different time points, in free IxS at 8 weeks (p = 0.003) and 14 weeks (p < 0.001), free pCS (p = 0.006) at 14 weeks and total and free pCG (p < 0.001, p < 0.001, respectively) and at 14 weeks. There were no differences in relative abundances of genera between groups. Enterotyping revealed that the population consisted of only two of the four enterotypes: Bacteroides 2 and Prevotella. The redundancy analysis showed a few factors significantly affected the gut microbiome: these included triglyceride levels (p < 0.001), body mass index (p = 0.002), high- density lipoprotein (p < 0.001) and the prebiotic intervention (p = 0.002). The ß-glucan prebiotic significantly altered uremic toxin levels of intestinal origin and favorably affected the gut microbiome.

Chronic Kidney Disease, Metabolic Syndrome and Cardiovascular Risk: Insights and Associated Mechanistic Pathways

Abstract:

This study is a narrative review that aims to address the conceptual, characteristic, pathophysiological, and mechanistic aspects that define the profile of metabolic syndrome and chronic kidney disease. The objective was to investigate current knowledge and elucidate, through discussions on the topic, the main interrelated paths. This review was carried out unsystematically, from March to May 2020, by means of a survey of the literature indexed in the PubMed, Web of Science, and Scopus (Elsevier®) databases. The scientific materials collected showed that the cross-talk between the diseases in question is mainly based on the conditions of resistance to insulin action, endothelial dysfunction, activation pathways of the Renin-Angiotensin-Aldosterone system and adipokine imbalance, also emphasizing the influence of atherosclerotic events in kidney damage. Furthermore, it was reinforced the fact that inflammatory processes play an important role in the worsening and evolution of the clinical condition of patients, especially when they have underlying pathologies chronically treated for subclinical inflammation. It is expected that a greater number of original researches will propose to investigate other possible interactions, with a view to standardized treatment of these diseases or nutritional management.

Serum indoxyl sulphate and its relation to albumin and α1-acid glycoprotein as a potential biomarkers of maternal intestinal metabolism during pregnancy and postpartum

BACKGROUND

Serum indoxyl sulfate (IS) levels depend on the production of indole in the gut. The biological effects of IS in the vascular bed could be confirmed by changes in the levels of individual serum proteins during normal pregnancy and in the postpartum period as compared with non-pregnant controls. Albumin (Alb) and α1-acid glycoprotein (AGP, orosomucoid) are the most abundant serum carrier proteins with potential interrelationships with serum levels of IS.

METHODS

Serum levels of IS, Alb and AGP were measured in 84 pregnant women in the first, second and third trimester of pregnancy and in the postpartum period, as well as in non-pregnant controls (n = 20), using ultra-performance liquid chromatography (UPLC) coupled to mass spectrometry (IS), colorimetric assay (Alb) and immunoturbidimetric assay (AGP).

RESULTS

The postpartum serum levels [mg/L] of IS were lower (p = 0.027) than in the second trimester (mean±SD: 0.85±0.39 vs 0.58±0.32). There were no differences in the IS to ALB ratio calculated in the three trimesters of pregnancy, the postpartum period, and in the non-pregnant controls. The IS/AGP ratio increased from the first to the second trimester (p = 0.039), and decreased in the postpartum period (p<0.05), when it was lower than in the second and third trimester.

CONCLUSIONS

The variability of the serum IS/AGP ratio during pregnancy and in the postpartum period may reflect shared involvement in the regulation of their intravascular relationships. The link between serum levels of IS derived from the gut and AGP could serve a potential biomarkers of maternal intestinal metabolism during pregnancy and postpartum.

Omega-3 Polyunsaturated Fatty Acid Attenuates Uremia-Induced Brain Damage in Mice

Although the cause of neurological disease in patients with chronic kidney disease (CKD) has not been completely identified yet, recent papers have identified accumulated uremic toxin as its main cause. Additionally, omega-3 polyunsaturated fatty acid (ω-3 PUFA) plays an important role in maintaining normal nerve function, but its protective effects against uremic toxin is unclear. The objective of this study was to identify brain damage caused by uremic toxicity and determine the protective effects of ω-3 PUFA against uremic toxin. We divided mice into the following groups: wild-type (wt) sham (n = 8), ω-3 PUFA sham (n = 8), Fat-1 sham (n = 8), ischemia-reperfusion (IR) (n = 20), and ω-3 PUFA+IR (n = 20) Fat-1+IR (n = 20). Brain tissue, kidney tissue, and blood were collected three days after the operation of mice (sham and IR operation). This study showed that Ki67 and neuronal nuclei (NeuN) decreased in the brain of uremic mice as compared to wt mice brain, but increased in the ω-3 PUFA-treated uremic mice and the brain of uremic Fat-1 mice as compared to the brain of uremic mice. The pro-apoptotic protein expressions were increased, whereas anti-apoptotic protein expression decreased in the brain of uremic mice as compared to wt mice brain. However, apoptotic protein expression decreased in the ω-3 PUFA-treated uremic mice and the brain of uremic Fat-1 mice as compared to the brain of uremic mice. Furthermore, the brain of ω-3 PUFA-treated uremic mice and uremic Fat-1 mice showed increased expression of p-PI3K, p-PDK1, and p-Akt as compared to the brain of uremic mice. We confirm that uremic toxin damages the brain and causes cell death. In these injuries, ω-3 PUFA plays an important role in neuroprotection through PI(3)K-Akt signaling.

Toward an individualized determination of dialysis adequacy: a narrative review with special emphasis on incremental hemodialysis

INTRODUCTION

The search for the 'perfect' renal replacement therapy has been paralleled by the search for the perfect biomarkers for assessing dialysis adequacy. Three main families of markers have been assessed: small molecules (prototype: urea); middle molecules (prototype β2-microglobulin); comprehensive and nutritional markers (prototype of the simplified assessment, albumin levels; composite indexes as malnutrition-inflammation score). After an era of standardization of dialysis treatment, personalized dialysis schedules are increasingly proposed, challenging the dogma of thrice-weekly hemodialysis.

AREAS COVERED

In this review, we describe the advantages and limitations of the approaches mentioned above, focusing on the open questions regarding personalized schedules and incremental hemodialysis.

EXPERT OPINION

In the era of personalized dialysis, the assessment of dialysis adequacy should be likewise personalized, due to the limits of 'one size fits all' approaches. We have tried to summarize some of the relevant issues regarding the determination of dialysis adequacy, attempting to adapt them to an elderly, highly comorbidity population, which would probably benefit from tailor-made dialysis prescriptions. While no single biomarker allows precisely tailoring the dialysis dose, we suggest using a combination of clinical and biological markers to prescribe dialysis according to comorbidity, life expectancy, residual kidney function, and small and medium-size molecule depuration.

Protein-Bound Uremic Toxins Induce Reactive Oxygen Species-Dependent and Inflammasome-Mediated IL-1β Production in Kidney Proximal Tubule Cells

Protein bound-uremic toxins (PBUTs) are not efficiently removed by hemodialysis in chronic kidney disease (CKD) patients and their accumulation leads to various co-morbidities via cellular dysfunction, inflammation and oxidative stress. Moreover, it has been shown that increased intrarenal expression of the NLRP3 receptor and IL-1β are associated with reduced kidney function, suggesting a critical role for the NLRP3 inflammasome in CKD progression. Here, we evaluated the effect of PBUTs on inflammasome-mediated IL-1β production in vitro and in vivo. Exposure of human conditionally immortalized proximal tubule epithelial cells to indoxyl sulfate (IS) and a mixture of anionic PBUTs (UT mix) increased expression levels of NLRP3, caspase-1 and IL-1β, accompanied by a significant increase in IL-1β secretion and caspase-1 activity. Furthermore, IS and UT mix induced the production of intracellular reactive oxygen species, and caspase-1 activity and IL-1β secretion were reduced in the presence of antioxidant N-acetylcysteine. IS and UT mix also induced NF-κB activation as evidenced by p65 nuclear translocation and IL-1β production, which was counteracted by an IKK inhibitor. In vivo, using subtotal nephrectomy CKD rats, a significant increase in total plasma levels of IS and the PBUTs, kynurenic acid and hippuric acid, was found, as well as enhanced urinary malondialdehyde levels. CKD kidney tissue showed an increasing trend in expression of NLRP3 inflammasome components, and a decreasing trend in superoxide dismutase-1 levels. In conclusion, we showed that PBUTs induce inflammasome-mediated IL-1β production in proximal tubule cells via oxidative stress and NF-κB signaling, suggesting their involvement in disease-associated inflammatory processes.

Chronic kidney disease measures for cardiovascular risk prediction

Chronic kidney disease (CKD) affects 15-20% of adults globally and causes various complications, one of the most important being cardiovascular disease (CVD). CKD has been associated with many CVD subtypes, especially severe ones like heart failure, independent of potential confounders such as diabetes and hypertension. There is no consensus in major clinical guidelines as to how to incorporate the two key measures of CKD (glomerular filtration rate and albuminuria) for CVD risk prediction. This is a critical missed opportunity to appropriately refine predicted risk and personalize prevention therapies according to CKD status, particularly since these measures are often already evaluated in clinical care. In this review, we provide an overview of CKD definition and staging, the subtypes of CVD most associated with CKD, major pathophysiological mechanisms, and the current state of CKD as a predictor of CVD in major clinical guidelines. We will introduce the novel concept of a "CKD Add-on", which allows the incorporation of CKD measures in existing risk prediction models, and the implications of taking into account CKD in the management of CVD risk.

Sponge-like Chitosan Based Porous Monolith for Uraemic Toxins Sorption

More than three million patients are treated for kidney failure world-wide. Haemodialysis, the most commonly used treatment, requires large amounts of water and generates mountains of non-recyclable plastic waste. To improve the environmental footprint, dialysis treatments need to develop absorbents to regenerate the waste dialysate. Whereas conventional dialysis clears water-soluble toxins, it is not so effective in clearing protein-bound uraemic toxins (PBUTs), such as indoxyl sulfate (IS). Thus, developing absorption devices to remove both water-soluble toxins and PBUTs would be advantageous. Vapour induced phase separation (VIPS) has been used in this work to produce polycaprolactone/chitosan (PCL/CS) composite symmetric porous monoliths with extra porous carbon additives to increase creatinine and albumin-bound IS absorption. Moreover, these easy-to-fabricate porous monoliths can be formed into the required geometry. The PCL/CS porous monoliths absorbed 436 μg/g of albumin-bound IS and 2865 μg/g of creatinine in a single-pass perfusion model within 1 h. This porous PCL/CS monolith could potentially be used to absorb uraemic toxins, including PBUTs, and thus allow the regeneration of waste dialysate and the development of a new generation of environmentally sustainable dialysis treatments, including wearable devices.

The Relationship between Advanced Oxidation Protein Products, Vascular Calcifications and Arterial Stiffness in Predialysis Chronic Kidney Disease Patients

Background and Objectives: Cardiovascular morbidity and mortality are increased in patients with chronic kidney disease (CKD). It is likely that the accumulation of uremic toxins resulting in increased oxidative stress (OS) is a major contributing factor, but no clear link has been identified. The purpose of this research is to establish if advanced oxidation protein product (AOPP) levels in the serum of predialysis patients are a contributing factor to vascular calcification and increased arterial stiffness. Materials and Methods: After obtaining the informed consent, 46 predialysis patients (CKD stages G3-G5) were included in the study. In order to identify vascular calcifications, hand and pelvic radiographs were performed. Valvular calcifications were identified using cardiac ultrasound. AOPP were measured using a commercially available ELISA kit. The relationships between serum AOPP values and biochemical parameters relevant in the evaluation of CKD patients were analyzed. In addition to identifying the differences in AOPP levels between patients with/without vascular or valvular calcifications, the research focused on describing the relationship between OS and arterial stiffness assessed by oscillometric pulse-wave velocity (PWV) measurement. Results: No significant relationship between serum AOPP and vascular or valvular calcifications was highlighted, but significant correlations of AOPP with C-reactive protein (p = 0.025), HDL-cholesterol levels (p = 0.04), HbA1c (p = 0.05) and PWV values (p = 0.02) were identified. Conclusions: The usefulness of (OS) measurement in clinical practice remains debatable; however, the relationship between AOPP and arterial stiffness could be valuable in improving cardiovascular risk assessment of patients with CKD.

Serum Cardiac Biomarkers in Asymptomatic Hemodialysis Patients: Role of Soluble Suppression of Tumorigenicity-2

INTRODUCTION

Cardiovascular events (CVE) remain the leading cause of mortality in hemodialysis (HD) patients. The ability to assess the risk of short-term CVE is of great importance. Soluble suppression of tumorogenicity-2 (sST2) is a novel biomarker that better stratifies risk of CVE than troponins in patients with heart failure. Few studies have investigated the role of sST2 in the HD population. The aim of this single-center study was to assess the predictive ability of sST2 on CVE in comparison to high-sensitive cardiac troponin I (hs-cTnI) and B-type natriuretic peptide (BNP) in HD patients.

METHODS

This study used a prospective, observational cohort design. We enrolled 40 chronic HD patients asymptomatic for chest pain and without recent history of acute coronary syndrome. We tested sST2 pre-/post-HD, hs-cTnI, and BNP. Demographic/dialytic/echocardiographic data were evaluated. We recorded the number of CVE for 12 months. The patients were classified into 2 groups: those who developed CVE and those who did not.

RESULTS

Ten of the 40 patients (25%) developed CVE during a 12-month follow-up. Increased sST2 levels (p < 0.0001) as well as hs-cTnI and BNP are predictive of CVE. When analyzing biomarkers as binary variables for values above or below the normal range, the correlation remained significant only for sST2 (p = 0.001). A small variation in sST2 levels before and after HD sessions was found (-2.1 ng/mL). sST2 was correlated with left ventricular (LV) echocardiographic data: LV mass index (p = 0.0001), LV ejection fraction (p = 0.01), and diastolic bulging of septum (p = 0.015). BNP and sST2 combination increased the prediction of CVE in a statistical model.

CONCLUSION

Our study confirms that sST2 is useful for stratifying CV risk in the HD population. sST2 can be evaluated simply as a dichotomous value higher or lower than the normal range, making it easily interpretable. Dialysis and residual diuresis did not affect significantly sST2. A multimarker approach that incorporates sST2 and BNP may improve the prediction of CVE.

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.

Gut Microbiota and the Quality of Oral Anticoagulation in Vitamin K Antagonists Users: A Review of Potential Implications

The efficacy and safety of vitamin K antagonists (VKAs) as oral anticoagulants (OACs) depend on the quality of anticoagulation control, as reflected by the mean time in therapeutic range (TTR). Several factors may be involved in poor TTR such as comorbidities, high inter-individual variability, interacting drugs, and non-adherence. Recent studies suggest that gut microbiota (GM) plays an important role in the pathogenesis of cardiovascular diseases, but the effect of the GM on anticoagulation control with VKAs is unknown. In the present review article, we propose different mechanisms by which the GM could have an impact on the quality of anticoagulation control in patients taking VKA therapy. We suggest that the potential effects of GM may be mediated first, by an indirect effect of metabolites produced by GM in the availability of VKAs drugs; second, by an effect of vitamin K-producing bacteria; and finally, by the structural modification of the molecules of VKAs. Future research will help confirm these hypotheses and may suggest profiles of bacterial signatures or microbial metabolites, to be used as biomarkers to predict the quality of anticoagulation. This could lead to the design of intervention strategies modulating gut microbiota, for example, by using probiotics.

Fabrication of a novel nitrogen-containing porous carbon adsorbent for protein-bound uremic toxins removal

Protein-bound uremic toxins (PBUTs), the presence of which in the blood is an important risk factor for the progression of chronic kidney disease (CKD), have not been cleared efficiently via traditional hemodialysis methods until now. In this study, biosafe and efficient nitrogen-containing porous carbon adsorbent (NPCA) beads for the clearance of PBUTs were prepared from porous acrylonitrile/divinylbenzene cross-linked copolymer beads followed by pyrolysis. The resulting NPCA beads were characterized via SEM, XPS and nitrogen adsorption/desorption tests. The results demonstrated that the NPCA beads possessed a mesoporous/microporous hierarchical structure with rich nitrogen functional groups on their surfaces and realized efficient PBUTs adsorption in human plasma. More importantly, the efficacy of PBUTs removal was substantially higher than those of commercial adsorbents that are commonly used in clinical uremia treatments. The NPCA beads also exhibited satisfactory removal efficacy towards middle-molecular-weight uremic toxins. The PBUTs removal mechanism of the NPCA beads is ascribed to effective competition between nitrogen-containing NPCA and proteins for PBUT binding. According to hemocompatibility assays, the NPCA beads possessed satisfactory in vitro hemocompatibility. This nitrogen-containing porous carbon adsorbent is an attractive and promising material for blood purification applications in the treatment of clinical uremia.

High cut-off dialysis mitigates pro-calcific effects of plasma on vascular progenitor cells

Mortality of patients with end-stage renal disease tremendously exceeds that of the general population due to excess cardiovascular morbidity. Large middle-sized molecules (LMM) including pro-inflammatory cytokines are major drivers of uremic cardiovascular toxicity and cannot be removed sufficiently by conventional high-flux (HFL) hemodialysis. We tested the ability of plasma from 19 hemodialysis patients participating in a trial comparing HFL with high cut-off (HCO) membranes facilitating removal of LMM to induce calcification in mesenchymal stromal cells (MSC) functioning as vascular progenitors. HCO dialysis favorably changed plasma composition resulting in reduced pro-calcific activity. LMM were removed more effectively by HCO dialysis including FGF23, a typical LMM we found to promote osteoblastic differentiation of MSC. Protein-bound uremic retention solutes with known cardiovascular toxicity but not LMM inhibited proliferation of MSC without direct toxicity in screening experiments. We could not attribute the effect of HCO dialysis on MSC calcification to distinct mediators. However, we found evidence of sustained reduced inflammation that might parallel other anti-calcifying mechanisms such as altered generation of extracellular vesicles. Our findings imply protection of MSC from dysfunctional differentiation by novel dialysis techniques targeted at removal of LMM. HCO dialysis might preserve their physiologic role in vascular regeneration and improve outcomes in dialysis patients.

Benefits of resistant starch type 2 for patients with end-stage renal disease under maintenance hemodialysis: a systematic review and meta-analysis

Background: Resistant starch type 2 (RS2) has been documented to regulate gut microbiota and to improve the clinical outcomes of several diseases. However, whether RS2 may benefit patients with end-stage renal disease under maintenance hemodialysis (MHD) remains unknown. Methods: We conducted a systemic review and meta-analysis of randomized controlled trials (RCTs). Adult patients receiving MHD were treated with RS2 (CRD42020160332). The primary outcomes were changes of uremic toxins, and the secondary outcomes were changes of inflammatory indicators, albumin and phosphorus. Results: After screening 65 records, five RCTs (n = 179) were included. A significant decrease of blood urea nitrogen (weighted mean difference (WMD) = -6.91, 95% CI: -11.87 to -1.95, I² = 0%, P = 0.006), serum creatinine (WMD = -1.11, 95% CI: -2.18 to -0.05, I² = 44%, P = 0.04) and interleukin (IL)-6 in blood (standard mean difference (SMD) = -1.08, 95% CI: -1.64 to -0.53, I² = 35%, P = 0.0001) was revealed in the RS2 group. Analyses of blood levels of uric acid, p-cresyl sulfate, indoxyl sulfate, high sensitive C-reaction protein, albumin and phosphorus yielded no significant difference. Conclusions: Our results suggest that RS2 may improve the residual renal function of patients under MHD and mitigate a proinflammatory response.

Decreased albumin is associated with elevated N-terminal pro-brain natriuretic peptide and poor long-term prognosis in patients with chronic heart failure

At present, the association between albumin, N-terminal pro-brain natriuretic peptide (NT-proBNP) and long-term prognosis in patients with chronic heart failure (CHF) is unclear. Therefore, the purpose of this study is to explore the relationship between albumin, NT-proBNP and all-cause mortality in CHF patients.Three hundred fifty two CHF patients were recruited in our study, and patients were divided into 2 groups according to the mean (37.16 g/L) of albumin concentration [low group (albumin < 37.16 g/L) and high group (albumin≥37.16 g/L)]. Differences between groups was compared by odds ratio (OR) and 95% confidence interval (CI).NT-proBNP in the high group was significantly lower than that in the low group at baseline [1811.50 (698.75-4037.00) vs 3479.50 (1538.50-7824.25), P < .001]. Spearman correlation analysis showed that there was a negative correlation between albumin and NT-pro BNP log10 transform (ρ= -0.217, P < .001). Furthermore, curve fitting further confirmed that albumin was negatively correlated with NT-proBNP. After a median follow-up of 1726 days, 90 patients in the high group occur all-cause mortality, and 98 patients in the low group occur all-cause mortality (46.88% vs 61.25%, OR = 0.29, 95% CI: 0.08-0.50). After adjusting for the selected confounding covariates by multivariate regression analysis, decreased albumin was still associated with increased all-cause mortality (high group vs low group: OR = 0.62, 95% CI: 0.39-0.97).Decreased albumin is associated with elevated NT-ProBNP and poor long-term prognosis in CHF patients. Clinicians need to pay enough attention to the nutritional status of CHF patients.

An LC-MS/MS analytical method for the determination of uremic toxins in patients with end-stage renal disease

End-stage renal disease (ESRD) is the last stage of chronic kidney disease, characterized by the progressive accumulation of uremic toxins (UTs). Hemodialysis is the standard approach to remove UTs from the body. Creatinine and urea levels are important indices of hemodialysis effectiveness, but the utility of those markers to estimate the removal of UTs, especially protein-binding UTs is limited. We developed an LC-MS/MS method for the quantification of UTs and to provide markers for evaluating hemodialysis effectiveness. These substances were extracted from serum samples after acetonitrile precipitation of protein and then separated on a HILIC column. The flow rate was 0.6 mL/min with a run time of 8.0 min for the negative ion mode and positive ion mode each. In this study 26 UTs were determined in normal subjects and in patients with ESRD before and after hemodialysis; serum levels were significantly higher in patients with ESRD than in subjects with normal renal function. A significant decrease in a variety of serum UTs were observed in patients after dialysis treatment, but no change in the levels of orotic acid, CMPF, kynurenic acid, p-cresol sulfate, phenyl-β-d-glucuronide, 4-ethylphenyl sulfate and 3-indolyl-β-d-glucopyranoside was found. These results show that some UTs could not be completely removed by hemodialysis. In addition, some biomarkers of different types of UTs are proposed for evaluating hemodialysis effectiveness.

Association of tubular solute clearances with the glomerular filtration rate and complications of chronic kidney disease: the Chronic Renal Insufficiency Cohort study

BACKGROUND

The secretion of organic solutes by the proximal tubules is an essential intrinsic kidney function. The degree to which secretory solute clearance corresponds with the glomerular filtration rate (GFR) and potential metabolic implications of net secretory clearance are largely unknown.

METHODS

We evaluated 1240 participants with chronic kidney disease (CKD) from the multicenter Chronic Renal Insufficiency Cohort (CRIC) Study. We used targeted mass-spectrometry to quantify candidate secretory solutes in paired 24-h urine and plasma samples. CRIC study personnel measured GFR using 125I-iothalamate clearance (iGFR). We used correlation and linear regression to determine cross-sectional associations of secretory clearances with iGFR and common metabolic complications of CKD.

RESULTS

Correlations between iGFR and secretory solute clearances ranged from ρ  = +0.30 for hippurate to ρ = +0.58 for kynurenic acid. Lower net clearances of most secretory solutes were associated with higher serum concentrations of parathyroid hormone (PTH), triglycerides and uric acid. Each 50% lower kynurenic acid clearance was associated with a 21% higher serum PTH concentration [95% confidence interval (CI) 15-26%] and a 10% higher serum triglyceride concentration (95% CI 5-16%) after adjustment for iGFR, albuminuria and other potential confounders. Secretory solute clearances were not associated with statistically or clinically meaningful differences in serum calcium, phosphate, hemoglobin or bicarbonate concentrations.

CONCLUSIONS

Tubular secretory clearances are modestly correlated with measured GFR among adult patients with CKD. Lower net secretory clearances are associated with selected metabolic complications independent of GFR and albuminuria, suggesting potential clinical and biological relevance.

Microbiome and hypertension: where are we now?

BACKGROUND

Hypertension is the leading risk factor for cardiovascular disease and accounts for approximately 9.4 million deaths globally every year. Hypertension is a complex entity, which is influenced by genetic and environmental factors, such as physical inactivity, obesity, alcohol consumption, tobacco use, stress, diet and why not the microbiome.

METHODS

We searched PubMed using the words 'microbiome', 'microbiota' and 'hypertension' until December 2018. We found information regarding the role of the brain-gut--bone marrow axis, the brain-gut--kidney axis, the high-salt diet, short-chain fatty acids (SCFAs), neurotransitters, such as serotonin, dopamine and norepinephrine, nitric oxide, endothelin and steroids in modulating gut microbiota and in contributing to the pathogenesis of hypertension. The brain--gut--bone marrow axis refers to the hypothesis that hematopoietic stem cells might migrate to the brain or to the gut, and thus, contribute to local inflammation and several immune responses. This migration may further enhance the sympathetic activity and contribute to blood pressure elevation. On the other hand, SCFAs, such as acetate and butyrate, have been shown to exert anti-inflammatory effects on myeloid and intestinal epithelial cells. Also, researchers have noted diminution in microbial richness and diversity in hypertensive patients as well as marked differences in circulating inflammatory cells in hypertensive patients, when compared with controls. In addition, activation of renal sympathetic nerve activity might directly influence renal physiology, by altering body fluid balance and plasma metabolite secretion and retention. These events culminate in the development of chronic kidney disease and hypertension.

CONCLUSION

There is a long way ahead regarding the role of gut microbiota in the pathogenesis and as an adjunctive treatment of hypertension. Treatment of dysbiosis could be a useful therapeutic approach to add to traditional antihypertensive therapy. Manipulating gut microbiota using prebiotics and probiotics might prove a valuable tool to traditional antihypertensives.

Uremic solutes of indoxyl sulfate and p-cresol enhance protease-activated receptor-2 expression in vitro and in vivo in keratinocytes

OBJECTIVES

Uremic pruritus is common in patients with chronic kidney disease (CKD). The retention of uremic solutes is thought to be associated with uremic pruritus. Meanwhile, activation of protease-activated receptor-2 (PAR-2) has been suggested to play an important role in pruritus. The present study was performed to investigate the effects of uremic solutes on the expression of PAR-2 in the skin.

METHODS

Indoxyl sulfate (IS), p-cresol (PC), and uremic sera from CKD patients were used to stimulate PAR-2 expression in normal human epidermal keratinocytes (NHEKs). Also, NHEKs were additionally pretreated with soybean trypsin inhibitor to evaluate its inhibitory effect on PAR-2 expression. Patterns of cutaneous PAR-2 expression were investigated in skin samples from five CKD patients and CKD mice.

RESULTS

In NHEKs, IS, PC, and sera from CKD patients significantly induced PAR-2 mRNA and protein expression. Soybean trypsin inhibitor significantly decreased PAR-2 mRNA and protein expression in NHEKs treated with IS, PC, and CKD sera. NHEKs treated with IS and PC exhibited significant increases in protease activity. Skin from both CKD patients and mice exhibited marked upregulation of PAR-2 expression compared to control skin.

CONCLUSIONS

Results from the present study suggest that uremic solutes either directly or indirectly affect PAR-2 expression in the skin of CKD subjects, potentially playing an important role in the pathogenesis of uremic pruritus.

Indoxyl sulfate promotes the atherosclerosis through up-regulating the miR-34a expression in endothelial cells and vascular smooth muscle cells in vitro

Atherosclerosis (AS) is one of the most common cardiovascular events in patients with chronic renal insufficiency (CRI). During the development of CRI, uremic toxins, including indoxyl sulfate (IS), are pivotal risk factors for AS. However, the underlying mechanism between AS and IS has not been fully elucidated. The present study was designed to test our hypothesis that IS promotes the AS by regulating viability, proliferation, migration and apoptosis of endothelial cells and vascular smooth muscle cells. In this present study, our date showed that IS inhibited the cell viability of human umbilical vein endothelial cells (HUVECs) and human aortic vascular smooth muscle cells (HA-VSMCs) in a dose-dependent manner (P < .05). Moreover, IS inhibited the proliferation, migration and induced apoptosis of HUVECs and HA-VSMCs significantly (P < .05). However, inhibition of the miR-34a abolished these effects of IS in vitro, indicating that miR-34a is involved in the development of AS induced by IS. In addition, the luciferase reporter gene assay showed that up-regulating of miR-34a inhibited the Notch1 transcriptional activity remarkably (P < .05). The expression of Notch1 decreased after IS treatment, while miR-34a inhibitor attenuated this effect. Moreover, the expression of miR-34a-related proteins Wnt-1, Jag1, E2F1 and SIRT1 decreased, while the expression of p53 increased in HUVECs and HA-VSMCs after IS treatment. Consistently, blockage of miR-34a abolished the remarkable effects on protein expressions induced by IS. Taken together, this study showed that IS can inhibit the proliferation, migration and promote apoptosis of HUVECs and HA-VSMCs through the Notch1 signal and miR-34a-related proteins by up-regulating miR-34a. These findings may provide new insights into the underlying mechanism of AS in CRI.

Drugs Commonly Applied to Kidney Patients May Compromise Renal Tubular Uremic Toxins Excretion

In chronic kidney disease (CKD), the secretion of uremic toxins is compromised leading to their accumulation in blood, which contributes to uremic complications, in particular cardiovascular disease. Organic anion transporters (OATs) are involved in the tubular secretion of protein-bound uremic toxins (PBUTs). However, OATs also handle a wide range of drugs, including those used for treatment of cardiovascular complications and their interaction with PBUTs is unknown. The aim of this study was to investigate the interaction between commonly prescribed drugs in CKD and endogenous PBUTs with respect to OAT1-mediated uptake. We exposed a unique conditionally immortalized proximal tubule cell line (ciPTEC) equipped with OAT1 to a panel of selected drugs, including angiotensin-converting enzyme inhibitors (ACEIs: captopril, enalaprilate, lisinopril), angiotensin receptor blockers (ARBs: losartan and valsartan), furosemide and statins (pravastatin and simvastatin), and evaluated the drug-interactions using an OAT1-mediated fluorescein assay. We show that selected ARBs and furosemide significantly reduced fluorescein uptake, with the highest potency for ARBs. This was exaggerated in presence of some PBUTs. Selected ACEIs and statins had either no or a slight effect at supratherapeutic concentrations on OAT1-mediated fluorescein uptake. In conclusion, we demonstrate that PBUTs may compete with co-administrated drugs commonly used in CKD management for renal OAT1 mediated secretion, thus potentially compromising the residual renal function.

Hypoalbuminemia: a price worth paying for improved dialytic removal of middle-molecular-weight uremic toxins?

Hemodiafiltration (HDF) increases the removal of middle-molecular-weight uremic toxins and may improve outcomes in patients with end-stage kidney disease (ESKD), but it requires complex equipment and comes with risks associated with infusion of large volumes of substitution solution. New high-flux hemodialysis membranes with improved diffusive permeability profiles do not have these limitations and offer an attractive alternative to HDF. However, both strategies are associated with increased albumin loss into the dialysate, raising concerns about the potential for decreased serum albumin concentrations that have been associated with poor outcomes in ESKD. Many factors can contribute to hypoalbuminemia in ESKD, including protein energy wasting, inflammation, volume expansion, renal loss and loss into the dialysate; of these factors, loss into the dialysate is not necessarily the most important. Furthermore, recent studies suggest that mild hypoalbuminemia per se is not an independent predictor of increased mortality in dialysis patients, but in combination with inflammation it is a poor prognostic sign. Thus, whether hypoalbuminemia predisposes to increased morbidity and mortality may depend on the presence or absence of inflammation. In this review we summarize recent findings on the role of dialysate losses in hypoalbuminemia and the importance of concomitant inflammation on outcomes in patients with ESKD. Based on these findings, we discuss whether hypoalbuminemia may be a price worth paying for increased dialytic removal of middle-molecular-weight uremic toxins.

Endothelial cells exposed to phosphate and indoxyl sulphate promote vascular calcification through interleukin-8 secretion

BACKGROUND

Vascular calcification (VC) is amplified during chronic kidney disease, partly due to uraemic toxins such as inorganic phosphate (Pi) and indoxyl sulphate (IS) that trigger osteogenic differentiation of vascular smooth muscle cells (VSMCs). These toxins also alter endothelial cell (EC) functions but whether this contributes to VC is unknown. Here, we hypothesized that ECs exposed to Pi and IS promote VSMC calcification.

METHODS

Human umbilical vein ECs were treated with Pi, IS or both, and then the conditioned media [endothelial cell conditioned medium (EC-CM)] was collected. Human aortic SMCs (HASMCs) were exposed to the same toxins, with or without EC-CM, and then calcification and osteogenic differentiation were evaluated. Procalcifying factors secreted from ECs in response to Pi and IS were screened. Rat aortic rings were isolated to assess Pi+IS-induced calcification at the tissue level.

RESULTS

Pi and Pi+IS induced HASMCs calcification, which was significantly exacerbated by EC-CM. Pi+IS induced the expression and secretion of interleukin-8 (IL-8) from ECs. While IL-8 treatment of HASMCs stimulated the Pi+IS-induced calcification in a concentration-dependent manner, IL-8 neutralizing antibody, IL-8 receptors antagonist or silencing IL-8 gene expression in ECs before collecting EC-CM significantly prevented the EC-CM procalcifying effect. IL-8 did not promote the Pi+IS-induced osteogenic differentiation of HASMCs but prevented the induction of osteopontin (OPN), a potent calcification inhibitor. In rat aortic rings, IS also promoted Pi-induced calcification and stimulated the expression of IL-8 homologues. Interestingly, in the Pi+IS condition, IL-8 receptor antagonist lifted the inhibition of OPN expression and partially prevented aortic calcification.

CONCLUSION

These results highlight a novel role of IL-8, whose contribution to VC in the uraemic state results at least from interaction between ECs and VSMCs.

Cardiovascular Calcification in Chronic Kidney Disease-Therapeutic Opportunities

Patients with chronic kidney disease (CKD) are highly susceptible to cardiovascular (CV) complications, thus suffering from clinical manifestations such as heart failure and stroke. CV calcification greatly contributes to the increased CV risk in CKD patients. However, no clinically viable therapies towards treatment and prevention of CV calcification or early biomarkers have been approved to date, which is largely attributed to the asymptomatic progression of calcification and the dearth of high-resolution imaging techniques to detect early calcification prior to the 'point of no return'. Clearly, new intervention and management strategies are essential to reduce CV risk factors in CKD patients. In experimental rodent models, novel promising therapeutic interventions demonstrate decreased CKD-induced calcification and prevent CV complications. Potential diagnostic markers such as the serum T50 assay, which demonstrates an association of serum calcification propensity with all-cause mortality and CV death in CKD patients, have been developed. This review provides an overview of the latest observations and evaluates the potential of these new interventions in relation to CV calcification in CKD patients. To this end, potential therapeutics have been analyzed, and their properties compared via experimental rodent models, human clinical trials, and meta-analyses.

Structural and metabolic performance of p-cresol producing microbiota in different carbon sources

p-Cresol (PC) is a potential off-flavor and carcinogenic compound that affects food flavor and safety. However, controlling the production of PC when making fermented food is hindered by a lack of knowledge of the microbial diversity and the growth requirements of the microbiota that produce PC. To address this, the present study used three media with selected carbon sources (glucose, ethanol and lactic acid) to explore the microbial origin of PC and to determine the preferred carbon source for the PC-producing microbiota in the pit mud of the strong-aroma type Baijiu. The results showed that the different carbon sources affected the microbial structure, especially of the PC-producing microbiota. Glucose led to the highest production of PC and lactic acid to the lowest. The production of PC was significantly correlated (p < 0.05, |ρ| > 0.6) with Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella Soehngenia, Clostridium and Sedimentibacter in the glucose medium; with Proteiniborus, Ruminococcus and Sporanaerobacter in the ethanol medium; and with Lutispora and Tepidimicrobium in the lactic acid medium. Multiphasic metabolite target analysis further indicated that the PC-producing microbiota could also metabolize flavor compounds. Lactic acid could inhibit the production of PC and ensure that the microbiota produced the appropriate flavor compounds during culture. Collectively, Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella_Soehngenia, Clostridium, Sedimentibacter, Proteiniborus, Ruminococcus and Lutispora were identified as potential PC producers in three media with glucose preferred as the carbon source. These findings provide a perspective on the microbiota and carbon source preference for ultimately improving the quality of distilled alcoholic beverage.