Effect of increasing dietary fiber on plasma levels of colon-derived solutes in hemodialysis patients

Probiotics, Prebiotics, and Synbiotics Improve Uremic, Inflammatory, and Gastrointestinal Symptoms in End-Stage Renal Disease With Dialysis: A Network Meta-Analysis of Randomized Controlled Trials

Background

Probiotics, prebiotics, and synbiotics are three different supplements to treat end stage renal disease (ESRD) patients by targeting gut bacteria. The comprehensive comparison of the effectiveness of different supplements are lacking.

Objectives

The purpose of this network meta-analysis (NMA) is to assess and rank the efficacy of probiotics, prebiotics, and synbiotics on inflammatory factors, uremic toxins, and gastrointestinal symptoms (GI symptoms) in ESRD patients undergoing dialysis.

Methods

Randomized clinical trials were searched from the PubMed, Embase, and Cochrane Register of Controlled Trials databases, from their inception until 4 September 2021. Random-effect model were used to obtain all estimated outcomes in network meta-analysis (NMA). Effect estimates were presented as mean differences (Mean ± SD) with 95% confidence interval (CI). The comprehensive effects of all treatments were ranked by the surface under the cumulative ranking (SUCRA) probabilities.

Results

Twenty-five studies involved 1,106 participants were included. Prebiotics were superior in decreasing Interleukin-6 (IL-6; SMD –0.74, 95% CI [–1.32, –0.16]) and tumor-necrosis factor-α (TNF-α; SMD –0.59, 95% CI [–1.09, –0.08]), synbiotics were more effective in declining C-reactive protein (CRP; SMD –0.69, 95% CI [–1.14, –0.24]) and endotoxin (SMD –0.83, 95% CI [–1.38, –0.27]). Regarding uremic toxins, prebiotics ranked highest in reducing indoxyl sulfate (IS; SMD –0.43, 95% CI [–0.81, –0.05]), blood urea nitrogen (BUN; SMD –0.42, 95% CI [–0.78, –0.06]), and malondialdehyde (MDA; SMD –1.88, 95% CI [–3.02, –0.75]). Probiotics were rated as best in alleviating GI symptoms (SMD: –0.52, 95% CI [–0.93, –0.1]).

Conclusion

Our research indicated prebiotics were more effective in declining IL-6, TNF-α, IS, MDA, and BUN, synbiotics lowering CRP and endotoxin significantly, and probiotics were beneficial for alleviating GI symptoms, which may contribute to better clinical decisions. This study was registered in PROSPERO (Number: CRD42021277056).

Systematic Review Registration

[http://www.crd.york.ac.uk/PROSPERO], identifier [CRD42021277056].

The Microbiome and Uremic Solutes

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

Acute Kidney Injury and Gut Dysbiosis: A Narrative Review Focus on Pathophysiology and Treatment

Acute kidney injury (AKI) and gut dysbiosis affect each other bidirectionally. AKI induces microbiota alteration in the gastrointestinal (GI) system, while gut dysbiosis also aggravates AKI. The interplay between AKI and gut dysbiosis is not yet well clarified but worthy of further investigation. The current review focuses on the pathophysiology of this bidirectional interplay and AKI treatment in this base. Both macrophages and neutrophils of the innate immunity and the T helper type 17 cell from the adaptive immunity are the critical players of AKI-induced gut dysbiosis. Conversely, dysbiosis-induced overproduction of gut-derived uremic toxins and insufficient generation of short-chain fatty acids are the main factors deteriorating AKI. Many novel treatments are proposed to deter AKI progression by reforming the GI microbiome and breaking this vicious cycle. Data support the benefits of probiotic treatment in AKI patients, while the results of postbiotics are mainly limited to animals. Prebiotics and synbiotics are primarily discussed in chronic kidney disease patients rather than AKI patients. The effect of adsorbent treatment seems promising, but more studies are required before the treatment can be applied to patients. Immune therapy and some repurposed drugs such as allopurinol are prospects of future treatments and are worth more discussion and survey.

Effects of an SGLT Inhibitor on the Production, Toxicity, and Elimination of Gut-Derived Uremic Toxins: A Call for Additional Evidence

Sodium–glucose cotransporter (SGLT) inhibitors are a class of oral hypoglycemic agents, which, in recent years, have been shown to improve renal and cardiovascular outcomes in patients with diabetic and non-diabetic chronic kidney disease. There remains considerable debate regarding the potential glucose-independent mechanisms by which these benefits are conferred. SGLT inhibitors, to a variable extent, impair small intestinal glucose absorption, facilitating the delivery of glucose into the colon. This suppresses protein fermentation, and thus the generation of uremic toxins such as phenols and indoles. It is acknowledged that such a shift in gut microbial metabolism yields health benefits for the host. SGLT inhibition, in addition, may be hypothesized to foster the renal clearance of protein-bound uremic toxins. Altered generation and elimination of uremic toxins may be in the causal pathway between SGLT inhibition and improved cardiometabolic health. Present review calls for additional research.

Effects of Irbesartan and Amlodipine Besylate Tablets on the Intestinal Microflora of Rats With Hypertensive Renal Damage

Objective: The present study aimed to investigate the effects of irbesartan and amlodipine besylate tablets on the intestinal microflora of rats with hypertensive renal damage.

Methods: Eighteen 12-week-old male spontaneous hypertensive rats were randomly divided into three groups. The Ai-HDG group was given irbesartan at 15 mg/kg per day by gavage, the Ci-HDG group was given amlodipine besylate tablets at 1 mg/kg per day by gavage, and the Wi-HDG group, i.e., the control, was given the same dose of distilled water per day by gavage. The treatment lasted for 6 weeks. Six 12-week-old male Wistar–Kyoto rats were used as the reference group. Bacterial DNA was extracted from the feces of all the rats for high-throughput sequencing before and after the experiment. Operational taxonomic units were used to analyze the species of the intestinal flora, and the alpha diversity index was used to analyze the diversity. The relative abundance of the intestinal microflora in each group of rats was therefore analyzed at the phylum and genus levels.

Results: Compared with the Wi-HDG group, the alpha diversity of the Ai-HDG group increased (p < 0.05), while in the Ci-HDG group, only the Shannon index increased significantly. At the phylum level, compared with the control group, in the Ai-HDG and Ci-HDG groups, Firmicutes (F) decreased, Bacteroides (B) increased, and the F/B ratio decreased (p < 0.05). At the genus level, compared with the Wi-HDG group, the Ai-HDG and Ci-HDG groups did not show a significantly delayed decline in lactic acid bacteria. However, in the Ai-HDG group, the relative abundance of Bifidobacteria increased.

Conclusion: After the administration of irbesartan and amlodipine besylate, the disorder of intestinal flora in the rats with hypertensive renal damage improved. However, irbesartan was better than amlodipine besylate at improving the diversity of the intestinal flora in these rats.

The Role of Dietary Fiber and Gut Microbiome Modulation in Progression of Chronic Kidney Disease

Nutrition is one of the fundamental approaches to promoting and preventing all kinds of diseases, especially kidney diseases. Dietary fiber forms a significant aspect of renal nutrition in treating chronic kidney disease (CKD). Dietary fiber intake influences the composition and metabolism of the gut microbiome with proven roles in reducing uremic toxin production, preserving kidney function, and retarding the progression of CKD through mechanisms of regulating metabolic, immunological, and inflammatory processes. Understanding dietary fiber’s pathogenesis and mechanistic action in modulating host and microbiome interactions provides a potential adjunct therapeutic target for preventing, controlling, and treating CKD patients. In this regard, a recommendation of adequate and appropriate dietary fiber intake to restore beneficial gut microbiota composition would reduce the risks and complications associated with CKD. This mini review summarizes current evidence of the role of dietary fiber intake in modulating the gut microbiome to improve kidney health.

Fiber intake and health in people with chronic kidney disease

Emerging evidence suggests that diet, particularly one that is rich in dietary fiber, may prevent the progression of chronic kidney disease (CKD) and its associated complications in people with established CKD. This narrative review summarizes the current evidence and discusses the opportunities for increasing fiber intake in people with CKD to improve health and reduce disease complications. A higher consumption of fiber exerts multiple health benefits, such as increasing stool output, promoting the growth of beneficial microbiota, improving the gut barrier and decreasing inflammation, as well decreasing uremic toxin production. Despite this, the majority of people with CKD consume less than the recommended dietary fiber intake, which may be due in part to the competing dietary potassium concern. Based on existing evidence, we see benefits from adopting a higher intake of fiber-rich food, and recommend cooperation with the dietitian to ensure an adequate diet plan. We also identify knowledge gaps for future research and suggest means to improve patient adherence to a high-fiber diet.

Nutrition, Immunology, and Kidney: Looking Beyond the Horizons

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is epidemic throughout the word. Despite various novel therapeutic opportunities, CKD is still associated with high morbidity and mortality. In CKD, patient's chronic inflammation is frequent and related with adverse outcomes. Both innate and adaptive immunity are dysfunctional in CKD. Therefore, it is plausible to interfere with dysfunctional immunity in these patients. In the current review, we present the updated experimental and clinical data summarizing the effects of nutritional interventions including natural products and dietary supplements on immune dysfunction in the context of CKD.

RECENT FINDINGS

Nutritional interventions including natural products and dietary supplements (e.g., curcumin, sulforaphane, resistant starch, anthocyanin, chrysin, short chain fatty acids, fish oil resistant starch) slow down the inflammation by at least 6 mechanisms: (i) decrease nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB); (ii) decrease NLR family pyrin domain containing 3 (NLRP3); (iii) decrease interleukin-1 (IL-1), decrease interleukin-6 (IL-6) secretion; (iv) decrease polymorphonuclear priming); (v) promote anti-inflammatory pathways (nuclear factor-erythroid factor 2-related factor 2 (NFR2); (vi) increase T regulatory (Tregs) cells). Natural products and dietary supplements may provide benefit in terms of kidney health. By modulation of nutritional intake, progression of CKD may be delayed.

A randomized double-blind cross-over trial to study the effects of resistant starch prebiotic in chronic kidney disease (ReSPECKD)

Background

Chronic kidney disease (CKD) is associated with a reduced quality of life and an increased risk of kidney failure, cardiovascular events, and all-cause mortality. Accumulation of nitrogen-based uremic toxins leads to worsening of symptoms in individuals with CKD. Many uremic toxins, such as indoxyl and p-cresol sulphate, are produced exclusively by the gut microbiome through the proteolytic digestion of aromatic amino acids. Strategies to reduce the production of these toxins by the gut microbiome in individuals with CKD may lessen symptom burden and delay the onset of dialysis. One such strategy is to change the overall metabolism of the gut microbiome so that less uremic toxins are produced. This can be accomplished by manipulating the energy source available to the microbiome. Fermentable carbohydrates which reach the gut microbiome, like resistant starch (RS), have been shown to inhibit or reduce bacterial amino acid metabolism. This study aims to investigate the effects of resistant potato starch (RPS) as a prebiotic in individuals with CKD before the onset of dialysis.

Methods

This is a double-blind, randomized two-period crossover trial. Thirty-six eligible participants will consent to follow a 26-week study regimen. Participants will receive 2 sachets per day containing either 15 g of RPS (MSPrebiotic, resistant potato starch treatment) or 15 g cornstarch (Amioca TF, digestible starch control). Changes in blood uremic toxins will be investigated as the primary outcome. Secondary outcomes include the effect of RPS consumption on symptoms, quality of life and abundance, and diversity and functionality of the gut microbiome.

Discussion

This randomized trial will provide further insight into whether the consumption of RPS as a prebiotic will reduce uremic toxins and symptoms in individuals who have CKD.

Trial registration

ClinicalTrials.govNCT04961164. Registered on 14 July 2021

Diagnosing metabolic acidosis in chronic kidney disease: importance of blood pH and serum anion gap

Metabolic acidosis is one of the most common complications of chronic kidney disease (CKD). It is associated with the progression of CKD, and many other functional impairments. Until recently, only serum bicarbonate levels have been used to evaluate acid-base changes in patients with reduced kidney function. However, recent emerging evidence suggests that nephrologists should reevaluate the clinical approach for diagnosing metabolic acidosis in patients with CKD based on two perspectives; pH and anion gap. Biochemistry and physiology textbooks clearly indicate that blood pH is the most important acid-base parameter for cellular function. Therefore, it is important to determine if the prognostic impact of hypobicarbonatemia varies according to pH level. A recent cohort study of CKD patients showed that venous pH modified the association between a low bicarbonate level and the progression of CKD. Furthermore, acidosis with a high anion gap has recently been recognized as an important prognostic factor, because veverimer, a nonabsorbable hydrochloride-binding polymer, has been shown to improve kidney function and decrease the anion gap. Acidosis with high anion gap frequently develops in later stages of CKD. Therefore, the anion gap is a time-varying factor and renal function (estimated glomerular filtration rate) is a time-dependent confounder for the anion gap and renal outcomes. Recent analyses using marginal structural models showed that acidosis with a high anion gap was associated with a high risk of CKD. Based on these observations, reconsideration of the clinical approach to diagnosing and treating metabolic acidosis in CKD may be warranted.

Effects of Resistant Starch on Patients with Chronic Kidney Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Chronic kidney disease (CKD) is a main health problem associated with increased risk of cardiovascular disease, morbidity, and mortality. Recent studies shown that the progression of CKD may be related to the change of intestinal flora. Resistant starch (RS) is a type of dietary fiber that can act as a substrate for microbial fermentation. Some studies have found that the supplementation of RS can improve the intestinal flora disorder in CKD patients. However, the specific effect of RS on CKD patients remains controversial.

OBJECTIVE

We designed this meta-analysis to identify and assess the effects of RS on patients with CKD.

METHODS

A comprehensive search of MEDLINE, Embase, Web of Science, and Cochrane systematic review databases was conducted in January 2020, and all new trials were updated in August 2021. Randomized trials were collected to assess the effects of RS on patients with CKD. The weighted average effect size of the net change was calculated by using the random-effects model.

RESULTS

The meta-analysis included 8 studies involving 301 participants. RS intake significantly reduced serum indolephenol sulfate (IS), blood phosphorus, IL-6, and uric acid levels in dialysis patients. The mean difference (MD) of serum IS (P = 0.0002) in the dialysis subgroup was -12.57 μmol/L (95% CI: -19.28, -5.86 μmol/L). The MD of blood phosphorus (P = 0.03) was -0.39 mg/dl (95% CI: -0.78, -0.01 mg/dl). The MD of serum uric acid (P = 0.004) between the dialysis subgroup and the nondialysis subgroup was -31.58 mmol/L (95% CI: -52.99, -10.17 mmol/L). The mean difference (MD) of IL-6 (P = 0.02) in the dialysis subgroup was -1.16 μmol/L (95% CI: -2.16, -0.16 μmol/L). However, there was no significant change of RS on hs-CRP, serum creatinine, blood urea nitrogen (BUN), blood paracresol sulfate, and blood lipid.

CONCLUSIONS

The intake of RS reduced the serum IS, serum phosphorus, IL-6, and uric acid levels significantly in dialysis patients, while hs-CRP, serum creatinine, BUN, serum paracresol sulfate, and blood lipid showed no significant changes.

Indoxyl sulfate, homocysteine, and antioxidant capacities in patients at different stages of chronic kidney disease

BACKGROUND/OBJECTIVES

Increased levels of uremic toxins and decreased antioxidant capacity have a significant impact on the progression of chronic kidney disease (CKD). However, it remains unclear whether they interact with each other to mediate the damage of kidney function. The purpose of this study was to investigate whether uremic toxins (i.e., homocysteine and indoxyl sulfate [IS]), as well as glutathione-dependent antioxidant enzyme activities are dependently or independently associated with kidney function during different stages of CKD patients.

SUBJECTS/METHODS

One hundred thirty-two patients diagnosed with CKD at stages 1 to 5 participated in this cross-sectional study.

RESULTS

Patients who had reached an advanced CKD stage experienced an increase in plasma uremic toxin levels, along with decreased glutathione peroxidase (GSH-Px) activity. Plasma homocysteine, cysteine, and IS concentrations were all positively associated with each other, but negatively correlated to GSH-Px activity levels after adjusting for potential confounders in all CKD patients. Although plasma homocysteine, cysteine, IS, and GSH-Px levels were significantly associated with kidney function, only plasma IS levels still had a significant association with kidney function after these parameters were simultaneously adjusted. In addition, plasma IS could interact with GSH-Px activity to be associated with kidney function.

CONCLUSIONS

IS plays a more dominant role than homocysteine and GSH-Px activity in relation to kidney function.

Biotic Supplements in Patients With Chronic Kidney Disease: Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

Gut flora imbalance characterizes patients with chronic kidney disease (CKD). Although biotic supplementation has been proposed to lessen inflammation and oxidative stress and, thus, reduce the risk of progressive kidney damage and cardiovascular disease, the effects remain controversial. We conducted a meta-analysis to assess the therapeutic benefits of biotics in CKD.

METHODS

PubMed, Embase, and Cochrane databases were systematically searched for randomized controlled trials that evaluated any biotic (prebiotic, probiotic, synbiotics) supplements in patients with CKD (CKD, stage 3-4 to end-stage renal disease). Primary endpoints included changes in renal function, markers of inflammation, and oxidative stress. Secondary endpoints included changes in levels of uremic toxins and variations in lipid metabolism.

RESULTS

Twenty-three eligible studies included 842 participants. In a pooled-analysis, biotics did not change estimated glomerular filtration rate (mean difference [MD] = 0.08, P = .92) or serum albumin (MD = -0.01, P = .86), although prebiotics reduced serum creatinine (standardized mean difference [SMD] = -0.23, P = .009) and blood urea nitrogen (MD = -6.05, P < .00001). Biotics improved total antioxidative capacity (SMD = 0.37, P = .007) and malondialdehyde (SMD = -0.96, P = .006) and reduced the inflammatory marker interleukin-6 (SMD = -0.30, P = .01) although not C-reactive protein (SMD = -0.22, P = .20). Biotic intervention reduced some uremic toxins, including p-cresol sulfate (SMD = -2.18, P < .0001) and indoxyl sulfate (MD = -5.14, P = .0009), which decreased in dialysis-dependent patients. Another toxin, indole-3-acetic acid (MD = -0.22, P = .63), did not change. Lipids were unaffected by biotic intervention (total cholesterol: SMD = -0.01, P = .89; high-density lipoprotein: SMD = -0.08, P = .76; low-density lipoprotein: MD = 3.54, P = .28; triglyceride: MD = -2.26, P = .58).

CONCLUSION

The results highlight the favorable influence of biotics on circulating markers of creatinine, oxidant stress (malondialdehyde, total antioxidative capacity), inflammation (interleukin-6), and uremic toxins (p-cresol sulfate) in patients with CKD. Biotics did not affect estimated glomerular filtration rate, albumin, indole-3-acetic acid, or lipids in either predialysis or dialysis patients.

The Prescription of Drugs That Inhibit Organic Anion Transporters 1 or 3 Is Associated with the Plasma Accumulation of Uremic Toxins in Kidney Transplant Recipients

The renal elimination of uremic toxins (UTs) can be potentially altered by drugs that inhibit organic anion transporters 1/3 (OAT1/OAT3). The objective of the present study was to determine whether the prescription of at least one OAT1/OAT3 inhibitor was associated with the plasma accumulation of certain UTs in kidney transplant recipients. We included 403 kidney transplant recipients. For each patient, we recorded all prescription drugs known to inhibit OAT1/OAT3. Plasma levels of four UTs (trimethylamine N-oxide (TMAO), indole acetic acid (IAA), para-cresylsulfate (pCS), and indoxylsulfate (IxS) were assayed using liquid chromatography-tandem mass spectrometry. Plasma UT levels were significantly higher among patients prescribed at least one OAT inhibitor (n = 311) than among patients not prescribed any OAT inhibitors (n = 92). Multivariate analysis revealed that after adjustment for age, estimated glomerular filtration rate (eGFR), plasma level of albumin and time since transplantation, prescription of an OAT1/OAT3 inhibitor was independently associated with the plasma accumulation of pCS (adjusted odds ratio (95% confidence interval): 2.11 (1.26; 3.61]). Our results emphasize the importance of understanding the interactions between drugs and UTs and those involving UT transporters in particular.

Higher dietary fibre intake is associated with lower CVD mortality risk among maintenance haemodialysis patients: a multicentre prospective cohort study

High fibre intake is associated with reduced mortality risk in both general and chronic kidney disease populations. However, in dialysis patients, such data are limited. Therefore, the association between dietary fibre intake (DFI) and the risk of all-cause and CVD mortality was examined in this study. A total of 1044 maintenance haemodialysis (MHD) patients from eight outpatient dialysis centres in China were included in this study. Data on DFI were collected using 24-h dietary recalls for 3 d in a week and were normalised to actual dry weight. The study outcomes included all-cause and CVD mortality. Over a median of 46 months of follow-up, 354 deaths were recorded, of which 210 (59 %) were due to CVD. On assessing DFI as tertiles, the CVD mortality risk was significantly lower in patients in tertiles 2-3 (≥0·13 g/kg per d; hazard ratio (HR) 0·71; 95 % CI 0·51, 0·97) compared with those in tertile 1 (<0·13 g/kg per d). A similar but non-significant trend was found for the association between DFI (tertiles 2-3 v. tertile 1; HR 0·83; 95 % CI 0·64, 1·07) and all-cause mortality. In summary, higher DFI was associated with lower CVD mortality risk among Chinese MHD patients. This study emphasises the significance of DFI in MHD patients and provides information that is critical for the improvement of dietary guidelines for dialysis patients.

Diet Quality and Protein-Bound Uraemic Toxins: Investigation of Novel Risk Factors and the Role of Microbiome in Chronic Kidney Disease

OBJECTIVE

This study aims to explore the associations between diet quality, uraemic toxins, and gastrointestinal microbiota in the chronic kidney disease (CKD) population.

METHODS

This is a baseline cross-sectional study of adults with CKD participating in a randomized controlled trial of prebiotic and probiotic supplementation. Dietary intake was measured using a seven-day diet history method, administered by a specialist dietitian. Diet quality was assessed using plant-based diet index (PDI) (overall PDI, healthy PDI, and unhealthy PDI), food group analysis, protein intake, fiber intake, and dietary protein-to-fiber ratio. Serum uraemic toxins (free and total; indoxyl sulfate and p-cresyl sulfate) were determined by ultraperformance liquid chromatography. Gastrointestinal microbiota richness, diversity, composition, and functional capacity were analyzed via metagenomic sequencing.

RESULTS

Sixty-eight adults [median age: 70 (interquartile range: 58-75) years, 66% male] with an estimated glomerular filtration rate of 34 ± 11 mL/min/1.73 m² were included, with 40 participants completing the optional fecal substudy. Dietary fiber intake was associated with lower levels of total indoxyl sulfate, whereas the healthy plant-based diet index was associated with lower levels of free p-cresyl sulfate. A higher protein-to-fiber ratio was associated with an increased relative abundance of unclassified members of order Oscillospirales. Intake of vegetables and whole grains was correlated with Subdoligranulum formicile, whereas an unclassified Prevotella species was correlated with potatoes and food items considered discretionary, including sweet drinks, sweet desserts, and animal fats.

CONCLUSIONS

Diet quality may influence uraemic toxin generation and gut microbiota diversity, composition, and function in adults with CKD. Well-designed dietary intervention studies targeting the production of uraemic toxins and exploring the impact on gut microbiome are warranted in the CKD population.

Dietary strategies for gut-derived protein-bound uremic toxins and cardio-metabolic risk factors in chronic kidney disease: A focus on dietary fibers

Chronic kidney disease (CKD) is associated with altered composition and function of gut microbiota. The cause of gut dysbiosis in CKD is multifactorial and encompasses the following: uremic state, metabolic acidosis, slow colonic transit, dietary restrictions of plant-based fiber-rich foods, and pharmacological therapies. Dietary restriction of potassium-rich fruits and vegetables, which are common sources of fermentable dietary fibers, inhibits the conversion of dietary fibers to short-chain fatty acids (SCFA), which are the primary nutrient source for the symbiotic gut microbiota. Reduced consumption of fermentable dietary fibers limits the population of SCFA-forming bacteria and causes dysbiosis of gut microbiota. Gut dysbiosis induces colonic fermentation of protein and formation of gut-derived uremic toxins. In this review, we discuss the roles and benefits of dietary fiber on gut-derived protein-bound uremic toxins and plant-based dietary patterns that could be recommended to decrease uremic toxin formation in CKD patients. Recent studies have indicated that dietary fiber supplementation may be useful to decrease gut-derived uremic toxin formation and slow CKD progression. However, research on associations between adherence of healthy dietary patterns and gut-derived uremic toxins formation in patients with CKD is lacking.

A Link between Chronic Kidney Disease and Gut Microbiota in Immunological and Nutritional Aspects

Chronic kidney disease (CKD) is generally progressive and irreversible, structural or functional renal impairment for 3 or more months affecting multiple metabolic pathways. Recently, the composition, dynamics, and stability of a patient's microbiota has been noted to play a significant role during disease onset or progression. Increasing urea concentration during CKD can lead to an acceleration of the process of kidney injury leading to alterations in the intestinal microbiota that can increase the production of gut-derived toxins and alter the intestinal epithelial barrier. A detailed analysis of the relationship between the role of intestinal microbiota and the development of inflammation within the symbiotic and dysbiotic intestinal microbiota showed significant changes in kidney dysfunction. Several recent studies have determined that dietary factors can significantly influence the activation of immune cells and their mediators. Moreover, dietary changes can profoundly affect the balance of gut microbiota. The aim of this review is to present the importance and factors influencing the differentiation of the human microbiota in the progression of kidney diseases, such as CKD, IgA nephropathy, idiopatic nephropathy, and diabetic kidney disease, with particular emphasis on the role of the immune system. Moreover, the effects of nutrients, bioactive compounds on the immune system in development of chronic kidney disease were reviewed.

Effects of Probiotics, Prebiotics, and Synbiotics on Uremic Toxins, Inflammation, and Oxidative Stress in Hemodialysis Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

The dysbiosis of gut microbiota may cause many complications in patients with end-stage renal disease, which may be alleviated by probiotic, prebiotic, and synbiotic supplementation. The aim of this systematic review and meta-analysis was to assess the effects of these supplementations on circulatory uremic toxins, biomarkers of inflammation, and oxidative stress in hemodialysis patients. We searched the EMBASE, MEDLINE, Web of Science, and Cochrane Library databases until 8 August 2021. Randomized controlled trials evaluating adult patients receiving hemodialysis were included. The pooled results from 23 studies with 931 hemodialysis patients indicated that interventions significantly decreased the circulating levels of p-cresyl sulfate (standardized mean difference (SMD): 0.38; 95% CI: -0.61, -0.15; p = 0.001), endotoxins (SMD: -0.58; 95% CI: -0.99, -0.18; p = 0.005), malondialdehyde (SMD: -1.16; 95% CI: -1.81, -0.52; p = 0.0004), C-reactive proteins (CRP) (SMD: -0.61; 95% CI: -0.99, -0.23; p = 0.002), and interleukin 6 (SMD: -0.92; 95% CI: -1.51, -0.33; p = 0.002), and improved the total antioxidant capacity (SMD: 0.89; 95% CI: 0.49, 1.30; p < 0.0001) and glutathione (SMD: 0.40; 95% CI: 0.14, 0.66; p = 0.003) when compared to the placebo group. Our results suggest that treatment with probiotics, prebiotics, and synbiotics may help alleviate uremic toxin levels, oxidative stress, and the inflammatory status in hemodialysis patients.

Chronic Kidney Disease-Associated Itch (CKD-aI) in Children-A Narrative Review

Chronic kidney disease (CKD) is a condition of widespread epidemiology and serious consequences affecting all organs of the organism and associated with significant mortality. The knowledge on CKD is rapidly evolving, especially concerning adults. Recently, more data is also appearing regarding CKD in children. Chronic itch (CI) is a common symptom appearing due to various underlying dermatological and systemic conditions. CI may also appear in association with CKD and is termed chronic kidney disease-associated itch (CKD-aI). CKD-aI is relatively well-described in the literature concerning adults, yet it also affects children. Unfortunately, the data on paediatric CKD-aI is particularly scarce. This narrative review aims to describe various aspects of CKD-aI with an emphasis on children, based on the available data in this population and the data extrapolated from adults. Its pathogenesis is described in details, focusing on the growing role of uraemic toxins (UTs), as well as immune dysfunction, altered opioid transmission, infectious agents, xerosis, neuropathy and dialysis-associated aspects. Moreover, epidemiological and clinical aspects are reviewed based on the few data on CKD-aI in children, whereas treatment recommendations are proposed as well, based on the literature on CKD-aI in adults and own experience in managing CI in children.

Safety and efficacy of using cereal food (Frugra®) to improve blood pressure and bowel health in patients undergoing chronic hemodialysis: A pilot study

Hypertension and constipation are major hemodialysis complications. Salt restriction is one of the most important nonpharmacological interventions in managing hypertension. In patients undergoing hemodialysis, nonpharmacological strategies to manage constipation are extremely difficult to develop owing to the presence of excess dietary potassium and fluids. Frugra®, which is a cereal food that has a low salt content of 0.5 g per serving, may help reduce salt intake. Additionally, Frugra is rich in dietary fiber, thereby beneficial for such patients. In this study, we evaluated the safety and efficacy of Frugra in patients undergoing hemodialysis, focusing mainly on blood pressure and bowel health by changing the usual breakfast meal to Frugra for 8 weeks. We enrolled 11 patients undergoing hemodialysis. Despite the absence of changes in the patients' dry weight levels, their systolic blood pressure levels decreased from 155.5 ± 20.9 mmHg to 137.9 ± 10.3 mmHg after 2 months (P < 0.05). All participants reported improvements in bowel movement, and the levels of indoxyl sulfate, a representative gut-derived uremic toxin, were decreased from 49.3 μg/ml to 33.4 μg/ml. Furthermore, adverse events including electrolyte abnormalities were not observed. Therefore, Frugra may be useful to manage the health of patients undergoing hemodialysis.

The value of a low-protein diet and ketoanalogues of essential amino acids in the сontrol of protein carbamylation and toxic effects of urea in chronic kidney disease

Chronic kidney disease (CKD) is characterized by high mortality from cardiovascular diseases, the development of which is facilitated by traditional risk factors (typical for the general population) and by nontraditional ones (specific to patients with CKD) as well. These factors include also uremic toxins, for which a causal relationship has been established with specific pathological processes in patients with CKD, comprising the development of vascular dysfunction and accelerated progression of atherosclerosis. Urea has long been considered not as a uremic toxin, but as a marker of metabolic imbalance or dialysis efficiency (Kt/V) in CKD patients. In recent years, more and more publications have appeared on the study of the toxic effects of urea with the development of toxic-uremic complications and the phenotype of premature aging, common in CKD. It was found that an increase in urea levels in uremic syndrome causes damage to the intestinal epithelial barrier with translocation of bacterial toxins into the bloodstream and the development of systemic inflammation, provokes apoptosis of vascular smooth muscle cells, as well as endothelial dysfunction, which directly contributes to the development of cardiovascular complications. The indirect effects of increased urea levels are associated with carbamylation reactions, when isocyanic acid (a product of urea catabolism) changes the structure and function of proteins in the body. Carbamylation of proteins in CKD patients is associated with the development of renal fibrosis, atherosclerosis and anemia. Thus, urea is now regarded as an important negative agent in the pathogenesis of complications in CKD. Studies on a low-protein diet with using ketoanalogues of essential amino acids to minimize the accumulation of urea and other uremic toxins demonstrate the clinical benefit of such an intervention in slowing the progression of CKD and the development of cardiovascular complications.

Dietary fiber intake and urinary creatinine: methodological implications for epidemiological studies

Creatinine values are used to estimate renal function and to correct for urinary dilution in exposure assessment studies. Interindividual variability in urinary creatinine (UCR) is determined positively by protein intake and negatively by age and diabetes. These factors, among others, need to be accounted for, to increase comparability throughout epidemiological studies. Recently, dietary fiber has been shown to improve renal function. This study aims to evaluate dietary fiber intake relationship with UCR and its methodological implications for studies using UCR-corrected measurements. In a cross-sectional study, we analyzed information regarding UCR, dietary fiber, age, and other UCR-related factors in 801 women residing in Northern Mexico during 2007-2009. The median fiber intake in this population was 33.14 g/day, above the adequate intake level for women > 18 years. We estimated an age-adjusted increase of 10.04 mg/dL UCR for a 10 g/day increase in dietary fiber intake. The main dietary sources of fiber in this population were corn tortillas, raw onions, flour tortillas, and beans. Our results suggest that epidemiological studies adjusting analytes by UCR should also consider controlling dietary fiber intake to improve the comparability of creatinine-corrected values and associations across different populations, such as those in Mexico and Latin America, where protein and fiber intake vary significantly.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

A Mini Review of Plant-Based Diets in Hemodialysis

BACKGROUND

Plant-based diets are defined as an eating pattern focused on the consumption of unprocessed fruits, vegetables, nuts, whole grains, oils, and beans. They can include various forms of vegetarian, vegan, DASH, and Mediterranean diets. Plant-based diets have proven useful in the prevention and treatment of several lifestyle diseases like type 2 diabetes, hypertension, and obesity. Recently, a growing body of literature has emerged regarding plant-based diets for patients with kidney failure, including those on dialysis. Although evidence is still limited, preliminary findings are encouraging.

SUMMARY

This article reviews current literature on the use of plant-based diets in the treatment of patients on dialysis.

The Impact of CKD on Uremic Toxins and Gut Microbiota

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

Medium Cut-Off Dialysis Membrane and Dietary Fiber Effects on Inflammation and Protein-Bound Uremic Toxins: A Systematic Review and Protocol for an Interventional Study

The aim of this systematic review is to investigate the effects of the use of a medium cut-off membrane (MCO) and dietary fiber on the concentration of protein-bound uremic toxins (PBUTs) and inflammatory markers in hemodialysis (HD) patients. Of 11,397 papers originally found, eight met the criteria of randomized controlled trial design. No study examined the effects of MCO membranes on PBUTs. Three studies examined the reduction in inflammatory markers with MCO membranes compared to high-flux HD membranes and showed no significant differences. Five studies of dietary fiber supplementation showed an inconclusive positive effect on PBUT levels and a significant positive effect on the reduction in inflammatory markers (interleukin-6 reduction: standardized difference in means -1.18; 95% confidence interval -1.45 to -0.9 for dietary fiber supplementation vs. control; p < 0.001). To date, no study has combined the use of an MCO membrane and fiber supplementation to reduce PBUT levels and inflammation with online hemodiafiltration as a comparator. A rationale and protocol for an interventional trial using a combination of MCO membrane dialysis and fiber supplementation to lower inflammatory markers and PBUT concentrations are presented.

Dietary Fibre Intake Is Associated with Serum Levels of Uraemic Toxins in Children with Chronic Kidney Disease

Imbalanced colonic microbial metabolism plays a pivotal role in generating protein-bound uraemic toxins (PBUTs), which accumulate with deteriorating kidney function and contribute to the uraemic burden of children with chronic kidney disease (CKD). Dietary choices impact the gut microbiome and metabolism. The aim of this study was to investigate the relation between dietary fibre and gut-derived PBUTs in paediatric CKD. Sixty-one (44 male) CKD children (9 ± 5 years) were prospectively followed for two years. Dietary fibre intake was evaluated by either 24-h recalls (73%) or 3-day food records (27%) at the same time of blood sampling for assessment of total and free serum levels of different PBUTs using liquid chromatography. We used linear mixed models to assess associations between fibre intake and PBUT levels. We found an inverse association between increase in fibre consumption (g/day) and serum concentrations of free indoxyl sulfate (−3.1% (−5.9%; −0.3%) (p = 0.035)), free p-cresyl sulfate (−2.5% (−4.7%; −0.3%) (p = 0.034)), total indole acetic acid (IAA) (−1.6% (−3.0%; −0.3%) (p = 0.020)), free IAA (−6.6% (−9.3%; −3.7%) (p < 0.001)), total serum p-cresyl glucuronide (pCG) (−3.0% (−5.6%; −0.5%) (p = 0.021)) and free pCG levels (−3.3% (−5.8%; −0.8%) (p = 0.010)). The observed associations between dietary fibre intake and the investigated PBUTs highlight potential benefits of fibre intake for the paediatric CKD population. The present observational findings should inform and guide adaptations of dietary prescriptions in children with CKD.

Challenges of reducing protein-bound uremic toxin levels in chronic kidney disease and end stage renal disease

The prevalence of chronic kidney disease (CKD) in the worldwide population is currently estimated between 11% and 13%. Adequate renal clearance is compromised in these patients and the accumulation of a large number of uremic retention solutes results in an irreversible worsening of renal function which can lead to end stage renal disease (ESRD). Approximately three million ESRD patients currently receive renal replacement therapies (RRTs), such as hemodialysis, which only partially restore kidney function, as they are only efficient in removing mainly small, unbound solutes from the circulation while leaving larger and protein-bound uremic toxins (PBUTs) untouched. The accumulation of PBUTs in patients highly increases the risk of cardiovascular events and is associated with higher mortality and morbidity in CKD and ESRD. In this review, we address several strategies currently being explored toward reducing PBUT concentrations, including clinical and medical approaches, therapeutic techniques, and recent developments in RRT technology. These include preservation of renal function, limitation of colon derived PBUTs, oral sorbents, adsorbent RRT technology, and use of albumin displacers. Despite the promising results of the different approaches to promote enhanced removal of a small percentage of the more than 30 identified PBUTs, on their own, none of them provide a treatment with the required efficiency, safety and cost-effectiveness to prevent CKD-related complications and decrease mortality and morbidity in ESRD.

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.

Protein-bound uremic toxin lowering strategies in chronic kidney disease: a systematic review and meta-analysis

INTRODUCTION

Accumulation of protein-bound uremic toxins, including indoxyl sulfate and p-cresyl sulfate, are associated with increased cardiovascular disease and mortality in chronic kidney disease (CKD). We performed a systematic review and meta-analysis to synthesize the available strategies for lowering protein-bound uremic toxin levels in CKD patients.

METHODS

We conducted a meta-analysis by searching the databases of MEDLINE, Scopus, and the Cochrane Central Register of Controlled Trials for observational studies and randomized controlled trials (RCTs) that examined the effect of dietary protein restrictions, biotic supplements (including prebiotics, probiotics, and synbiotics), AST-120, dialysis techniques, and the outcome of preservation of residual renal function (RRF) on indoxyl sulfate and p-cresyl sulfate levels. Random-effect model meta-analyses were used to compute changes in the outcomes of interest.

RESULTS

A total of 38 articles (2,492 patients), comprising 28 RCTs, 8 single-arm or prospective cohort studies, and 2 cross-sectional studies were included in this meta-analysis. When compared with placebo, prebiotics, synbiotics, and AST-120 provided significantly lower levels of both serum indoxyl sulfate and p-cresyl sulfate. There were no significant reductions in serum indoxyl sulfate and p-cresyl sulfate levels in patients receiving probiotics. Preservation of RRF in dialysis patients resulted in lower levels of both of the protein-bound uremic toxins. When compared with conventional hemodialysis, hemodiafiltration significantly decreased serum p-cresyl sulfate alone, whereas a significant change in serum indoxyl sulfate levels was observed only in studies with long-term observation periods. Very low protein diet (VLPD) and other oral medications yielded insignificant differences in protein-bound uremic toxins.

CONCLUSIONS

The present meta-analysis demonstrated that prebiotics, synbiotics, and AST-120 can effectively reduce both serum indoxyl sulfate and p-cresyl sulfate in CKD patients when compared with placebo. Preservation of RRF was associated with lower serum indoxyl sulfate and p-cresyl sulfate levels. The effect of biotic supplements was detected only in dialysis patients. For non-dialysis CKD patients, the results were limited due to the small number of studies. Further studies are needed to determine the efficacy in these populations.

Focus on the Gut-Kidney Axis in Health and Disease

The recent new developments in technology with culture-independent techniques including genome sequencing methodologies shed light on the identification of microbiota bacterial species and their role in health and disease. Microbiome is actually reported as an important predictive tool for evaluating characteristic shifts in case of disease. Our present review states the development of different renal diseases and pathologies linked to the intestinal dysbiosis, which impacts on host homeostasis. The gastrointestinal-kidney dialogue provides intriguing features in the pathogenesis of several renal diseases. Without any doubt, investigation of this interconnection consists one of the most cutting-edge areas of research with potential implications on our health.

Resistant starch type-2 enriched cookies modulate uremic toxins and inflammation in hemodialysis patients: a randomized, double-blind, crossover and placebo-controlled trial

BACKGROUND

The aim of this study was to evaluate the effect of resistant starch (RS) enriched cookies supplementation on mRNA expression of nuclear transcription factors (nuclear erythroid 2-related factor, Nrf2; nuclear factor kappa-B, NF-κB), involved with inflammation and on uremic toxins levels produced by the gut microbiota in hemodialysis (HD) patients.

METHODS

A randomized, double-blind, placebo-controlled crossover study with 26 HD patients was conducted. The patients were assigned to either resistant starch enriched cookies (16 g of RS per day) or placebo cookies supplementation during the first four weeks. After the washout period, patients were supplemented again, in the form of a crossover, for another 4 weeks. Nrf2, NF-κB, and antioxidant enzymes mRNA expression were measured by rt-PCR and protein expression by western blotting assay from isolated peripheral blood mononuclear cells (PBMC). Oxidative stress and inflammatory biomarkers, as well as uremic toxins, were evaluated. Intention-to-treat analysis was performed, using the proc mixed procedure in SAS.

RESULTS

In RS group, post-treatment mean mRNA Nrf2 expression was market increased from baseline values, associated with a high expression of NQO1 protein. Besides, IS plasma levels were reduced in the RS group. No significant difference was observed in the placebo group.

CONCLUSION

Our results suggested that resistant starch enriched cookies may be a good nutritional strategy to reduce indoxyl sulfate levels derived from the gut microbiota and also attenuate the inflammation in hemodialysis 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.

Uremic Vascular Calcification: The Pathogenic Roles and Gastrointestinal Decontamination of Uremic Toxins

Uremic vascular calcification (VC) commonly occurs during advanced chronic kidney disease (CKD) and significantly increases cardiovascular morbidity and mortality. Uremic toxins are integral within VC pathogenesis, as they exhibit adverse vascular influences ranging from atherosclerosis, vascular inflammation, to VC. Experimental removal of these toxins, including small molecular (phosphate, trimethylamine-N-oxide), large molecular (fibroblast growth factor-23, cytokines), and protein-bound ones (indoxyl sulfate, p-cresyl sulfate), ameliorates VC. As most uremic toxins share a gut origin, interventions through gastrointestinal tract are expected to demonstrate particular efficacy. The “gastrointestinal decontamination” through the removal of toxin in situ or impediment of toxin absorption within the gastrointestinal tract is a practical and potential strategy to reduce uremic toxins. First and foremost, the modulation of gut microbiota through optimizing dietary composition, the use of prebiotics or probiotics, can be implemented. Other promising strategies such as reducing calcium load, minimizing intestinal phosphate absorption through the optimization of phosphate binders and the inhibition of gut luminal phosphate transporters, the administration of magnesium, and the use of oral toxin adsorbent for protein-bound uremic toxins may potentially counteract uremic VC. Novel agents such as tenapanor have been actively tested in clinical trials for their potential vascular benefits. Further advanced studies are still warranted to validate the beneficial effects of gastrointestinal decontamination in the retardation and treatment of uremic VC.

Source and Composition in Amino Acid of Dietary Proteins in the Primary Prevention and Treatment of CKD

Nutrition is a cornerstone in the management of chronic kidney disease (CKD). To limit urea generation and accumulation, a global reduction in protein intake is routinely proposed. However, recent evidence has accumulated on the benefits of plant-based diets and plant-derived proteins without a clear understanding of underlying mechanisms. Particularly the roles of some amino acids (AAs) appear to be either deleterious or beneficial on the progression of CKD and its complications. This review outlines recent data on the role of a low protein intake, the plant nature of proteins, and some specific AAs actions on kidney function and metabolic disorders. We will focus on renal hemodynamics, intestinal microbiota, and the production of uremic toxins. Overall, these mechanistic effects are still poorly understood but deserve special attention to understand why low-protein diets provide clinical benefits and to find potential new therapeutic targets in CKD.

Effects of dietary fiber on vascular calcification by repetitive diet-induced fluctuations in plasma phosphorus in early-stage chronic kidney disease rats

Vascular calcification progresses under hyperphosphatemia, and represents a risk factor for cardiovascular disease in chronic kidney disease (CKD) patients. We recently indicated that phosphorus (P) fluctuations also exacerbated vascular calcification in early-stage CKD rats. Dietary fiber intake is reportedly associated with cardiovascular risk. This study investigated the effects of dietary fiber on vascular calcification by repeated P fluctuations in early-stage CKD rats. Unilateral nephrectomy rats were used as an early-stage CKD model. For 36 days, a P fluctuation (LH) group was fed low-P (0.02% P) and high-P (1.2% P) diets alternating every 2 days, and a P fluctuation with dietary fiber intake (LH + F) group was fed low-P and high-P diets containing dietary fiber alternating every 2 days. The effect on vascular calcification was measured calcium content. Effects on uremic toxin were measured levels of indoxyl sulfate (IS) and investigated gut microbiota. The LH + F group showed significantly reduced vessel calcium content compared to the LH group. Further, dietary fiber inhibited increases in blood levels of IS after intake of high-P diet, and decreased uremic toxin-producing intestinal bacteria. Dietary fiber may help suppress progression of vascular calcification due to repeated P fluctuations in early-stage CKD rats by decreasing uremic toxin-producing intestinal bacteria.

The effects of 16-weeks of prebiotic supplementation and aerobic exercise training on inflammatory markers, oxidative stress, uremic toxins, and the microbiota in pre-dialysis kidney patients: a randomized controlled trial-protocol paper

BACKGROUND

Chronic kidney disease (CKD) is characterized by dysbiosis, elevated levels of uremic toxins, systemic inflammation, and increased markers of oxidative stress. These factors lead to an increased risk of cardiovascular disease (CVD) which is common among CKD patients. Supplementation with high amylose maize resistant starch type 2 (RS-2) can change the composition of the gut microbiota, and reduce markers of inflammation and oxidative stress in patients with end-stage renal disease. However, the impact of RS-2 supplementation has not been extensively studied in CKD patients not on dialysis. Aerobic exercise training lowers certain markers of inflammation in CKD patients. Whether combining aerobic training along with RS-2 supplementation has an additive effect on the aforementioned biomarkers in predialysis CKD patients has not been previously investigated.

METHODS

The study is being conducted as a 16-week, double-blind, placebo controlled, parallel arm, randomized controlled trial. Sixty stage 3-4 CKD patients (ages of 30-75 years) are being randomized to one of four groups: RS-2 & usual care, RS-2 & aerobic exercise, placebo (cornstarch) & usual care and placebo & exercise. Patients attend four testing sessions: Two baseline (BL) sessions with follow up visits 8 (wk8) and 16 weeks (wk16) later. Fasting blood samples, resting brachial and central blood pressures, and arterial stiffness are collected at BL, wk8 and wk16. A stool sample is collected for analysis of microbial composition and peak oxygen uptake is assessed at BL and wk16. Blood samples will be assayed for p-cresyl sulphate and indoxyl sulphate, c-reactive protein, tumor necrosis factor α, interleukin 6, interleukin 10, monocyte chemoattractant protein 1, malondialdehyde, 8-isoprostanes F2a, endothelin-1 and nitrate/nitrite. Following BL, subjects are randomized to their group. Individuals randomized to conditions involving exercise will attend three supervised moderate intensity (55-65% peak oxygen uptake) aerobic training sessions (treadmills, bikes or elliptical machine) per week for 16 weeks.

DISCUSSION

This study has the potential to yield information about the effect of RS-2 supplementation on key biomarkers believed to impact upon the development of CVD in patients with CKD. We are examining whether there is an additive effect of exercise training and RS-2 supplementation on these key variables.

TRIAL REGISTRATION

Clinicaltrials.gov Trial registration# NCT03689569 . 9/28/2018, retrospectively registered.

Kidney-gut crosstalk in renal disease

INTRODUCTION

The colon has an important role in managing nitrogenous waste products, electrolytes, and mineral balance during kidney diseases. However, colonic microbiota produces uremic toxins, such as indoxyl sulfate and p-cresyl sulfate, in chronic kidney disease (CKD) patients, which due to their proinflammatory properties contribute to CKD progression. Conversely, in acute renal injury patients, intestinal microbiota could reduce inflammation by secreting short-chain fatty acids and inducing a renal protective immune response. However, since the intestines are the most frequently affected organ in advanced sepsis, colonic microbiota can also represent a negative factor for kidney health in this scenario.

CONCLUSION

In the present review, the main characteristics of kidney-gut crosstalk are described.

Pilot Randomized Controlled Trial of a Standard Versus a Modified Low-Phosphorus Diet in Hemodialysis Patients

INTRODUCTION

The standard low-phosphorus diet restricts pulses, nuts, and whole grains and other high phosphorus foods to control hyperphosphatemia. We conducted a randomized controlled trial to evaluate the effectiveness, safety, and tolerability of the modified diet, which introduced some pulses and nuts, increased the use of whole grains, increased focus on the avoidance of phosphate additives, and introduced the prescription of low-biological-value protein such as bread.

METHODS

We conducted a multicenter, pragmatic, parallel-arm, open-label, randomized controlled trial of modified versus standard diet in 74 adults on hemodialysis with hyperphosphatemia over 1 month. Biochemistry was assessed using monthly laboratory tests. Dietary intake was assessed using a 2-day record of weighed intake of food, and tolerability was assessed using a patient questionnaire.

RESULTS

There was no significant difference in the change in serum phosphate between the standard and modified diets. Although total dietary phosphorus intake was similar, phytate-bound phosphorus, found in pulses, nuts, and whole grains, was significantly higher in the modified diet (P < 0.001). Dietary fiber intake was also significantly higher (P < 0.003), as was the percentage of patients reporting an increase in bowel movements while following the modified diet (P = 0.008). There was no significant difference in the change in serum potassium or in reported protein intake between the 2 diets. Both diets were similarly well tolerated.

CONCLUSION

The modified low phosphorus diet was well tolerated and was associated with similar phosphate and potassium control but with a wider food choice and greater fiber intake than the standard diet.

Gut-Derived Protein-Bound Uremic Toxins

Chronic kidney disease (CKD) afflicts more than 500 million people worldwide and is one of the fastest growing global causes of mortality. When glomerular filtration rate begins to fall, uremic toxins accumulate in the serum and significantly increase the risk of death from cardiovascular disease and other causes. Several of the most harmful uremic toxins are produced by the gut microbiota. Furthermore, many such toxins are protein-bound and are therefore recalcitrant to removal by dialysis. We review the derivation and pathological mechanisms of gut-derived, protein-bound uremic toxins (PBUTs). We further outline the emerging relationship between kidney disease and gut dysbiosis, including the bacterial taxa altered, the regulation of microbial uremic toxin-producing genes, and their downstream physiological and neurological consequences. Finally, we discuss gut-targeted therapeutic strategies employed to reduce PBUTs. We conclude that targeting the gut microbiota is a promising approach for the treatment of CKD by blocking the serum accumulation of PBUTs that cannot be eliminated by dialysis.

The Efficacy of Lactobacillus-Containing Probiotic Supplementation in Hemodialysis Patients: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVES

This study was performed to determine the effects of probiotic supplementation on cholesterol-triglyceride ratio, an indirect marker of insulin resistance, protein-bound uremic toxins, biomarkers of inflammation, and microbial translocation in end-stage renal disease patients on hemodialysis.

METHODS

Fifty-six patients aged 39-75 years were assigned into two groups to receive either probiotic sachets (n = 28) or a placebo (n = 28) in a randomized double-blinded placebo-controlled clinical trial. The patients in the probiotic group received twice daily sachets that contained a mixture of three viable and freeze-dried strains: Lactococcus lactis subsp. Lactis LL358, Lactobaccillus salivarius LS159, and Lactobaccillus pentosus LPE588 at high dose (100 billion; 1 × 10¹¹ cfu/day) for 6 months.

RESULTS

A total of 50 patients were available for final analysis. Probiotic supplementation did not have a significant influence on cholesterol-triglyceride ratio. Probiotic supplementation for 6 months caused a significant decrease in serum levels of indoxyl sulfate. Compared with the placebo, probiotic supplementation did not result in significant changes in hemoglobin levels, blood urea nitrogen, blood glucose, serum p-cresyl sulfate, inflammatory, and microbial translocation markers. No clinically significant changes in body composition were observed between the two groups during the study period. The probiotic supplementation was well tolerated by all subjects with minimal adverse effects during the 6-month-long study.

CONCLUSION

Our results suggest that high-dose multistrain lactobaccillus probiotic supplementation over 6 months as a monotherapy did not significantly decrease markers of insulin resistance, cholesterol-triglyceride ratio, and most of the studied markers, with the exception of levels of indoxyl sulfate in patients on HD.

Impaired Tubular Secretion of Organic Solutes in Acute Kidney Injury

BACKGROUND

Impairment of kidney function is routinely assessed by measuring the accumulation of creatinine, an organic solute cleared largely by glomerular filtration. We tested whether the clearance of solutes that undergo tubular secretion is reduced in proportion to the clearance of creatinine in humans with AKI.

METHODS

Four endogenously produced organic solutes (phenylacetylglutamine [PAG], hippurate [HIPP], indoxyl sulfate [IS], and p-cresol sulfate [PCS]) were measured in spot urine and plasma samples from ten patients with AKI and 17 controls. Fractional clearance relative to creatinine was calculated to assess tubular secretion. Fractional clearance values were calculated in terms of the free, unbound levels of HIPP, IS, and PCS that bind to plasma proteins.

RESULTS

Fractional clearance values for PAG, HIPP, IS, and PCS were >1.0 in patients with AKI as well as controls, indicating that these solutes were still secreted by the tubules of the injured kidneys. Fractional clearance values were, however, significantly lower in patients with AKI than controls, indicating that kidney injury reduced tubular secretion more than glomerular filtration (AKI versus control: PAG, 2.1±0.7 versus 4.6±1.4, P<0.001; HIPP, 10±5 versus 15±7, P=0.02; IS, 10±6 versus 28±7, P<0.001; PCS, 3.3±1.8 versus 10±3, P<0.001). Free plasma levels rose out of proportion to total plasma levels for each of the bound solutes in AKI, so that calculating their fractional clearance in terms of their total plasma levels failed to reveal their impaired secretion.

CONCLUSIONS

Tubular secretion of organic solutes can be reduced out of proportion to glomerular filtration in AKI. Impaired secretion of protein-bound solutes may be more reliably detected when clearances are expressed in terms of their free, unbound levels in the plasma.

Pilot Study of Probiotic Supplementation on Uremic Toxicity and Inflammatory Cytokines in Chronic Kidney Patients

Background:

Bacterial metabolism contributes to the generation of uremic toxins in patients with chronic kidney disease (CKD). It has been investigated the use of probiotics in the reduction of uremic toxins intestinal production.

Objective:

The aim of this pilot study was to evaluate the effect of probiotic supplementation on reducing the production of uremic toxins and the inflammatory profile of CKD patients.

Methods:

We performed a randomized, blind, placebo-controlled, crossover study on patients with CKD stages 3 and 4. The intervention was a probiotic formulation composed of Lactobacillus acidophilus strains given orally three times a day for 3 months. Changes in uremic toxins (p-Cresylsulfate and Indoxyl Sulfate) and serum inflammatory cytokines were the primary endpoints.

Results:

Of the 44 patients randomized, 25 completed the study (mean age 51 ± 9.34, 64% female, mean eGFR 36 ± 14.26 mL/min/1.73m², mean BMI 28.5 ± 5.75 kg/m²). At 3 months, there were no significant changes in any of the studied biomarkers including p-cresylsulfate (p = 0.57), Indoxyl sulfate (p = 0.08) and interleukin-6 (p = 0.55).

Conclusion:

Lactobacillus acidophilus strains given as probiotic were not able to reduce serum levels of uremic toxins and biomarkers of inflammation in CKD patients in stage 3 and 4.