The Gut as a Source of Inflammation in Chronic Kidney Disease

Organ distribution of endogenous p-cresol in hemodialysis patients

BACKGROUND

p-Cresol concentrations are high in the blood of hemodialysis (HD) patients. However, its organ distribution has not yet been investigated in detail. We herein report the distribution of p-cresolin HD patients from forensic autopsy cases.

METHODS

p-Cresol was measured in the blood, urine, lungs, liver, and kidneys from 4 HD and 4 non-HD cases. Samples were extracted with p-cresol-d8 (internal standard), derivatized,and injected on the GC-MS.

RESULTS AND DISCUSSION

The total urinary p-cresol/Cr was 79.73 ng/ml in HD cases,which was 16-fold higher than that in non-HD cases. p-Cresol in the blood and kidneys were 30-fold higher or more at 11.92 and 13.08 µg/mL(g), respectively. p-Cresol in the liver and lungs were approximately 20-fold higher at 4.82 and 9.99 µg/g, respectively. p-Cresol was markedly increased in not only the blood, but also the urine and organs of HD cases. The distribution of p-cresol in the blood, urine, and organs differed between HD and non-HD cases. In HD cases, the percentages of conjugated (C) and protein-bound conjugated (PC) urinary p-cresol were 57 and 41%, respectively. C and PC p-cresol was 66% and 25% in the kidneys, respectively, and similar results were obtained in the lungs. J. Med. Invest. 66 : 81-85, February, 2019.

Effect of Low-Protein Diet and Inulin on Microbiota and Clinical Parameters in Patients with Chronic Kidney Disease

Introduction: The gut microbiota has coevolved with humans for a mutually beneficial coexistence and plays an important role in health and disease. A dysbiotic gut microbiome may contribute to progression to chronic kidney disease (CKD) and CKD-related complications such as cardiovascular disease. Microbiota modulation through the administration of prebiotics may represent an important therapeutic target. Aim: We sought to evaluate the effects of a low-protein diet (LPD) (0.6 g/kg/day) with or without the intake of the prebiotic inulin (19 g/day) on microbiota and clinical parameters in CKD patients. Materials and Methods: We performed a longitudinal, prospective, controlled, and interventional study on 16 patients: 9 patients treated with LPD (0.6 g/kg/day) and inulin (19 g/day) and 7 patients (control group) treated only with LPD (0.6 g/kg/day). Clinical evaluations were performed and fecal samples were collected for a subsequent evaluation of the intestinal microbiota in all patients. These tests were carried out before the initiation of LPD, with or without inulin, at baseline (T0) and at 6 months (T2). The microbiota of 16 healthy control (HC) subjects was also analyzed in order to identify potential dysbiosis between patients and healthy subjects. Results: Gut microbiota of CKD patients was different from that of healthy controls. The LPD was able to significantly increase the frequencies of Akkermansiaceae and Bacteroidaceae and decrease the frequencies of Christensenellaceae, Clostridiaceae, Lactobacillaceae, and Pasteurellaceae. Only Bifidobacteriaceae were increased when the LPD was accompanied by oral inulin intake. We showed a significant reduction of serum uric acid (SUA) and C-reactive protein (CRP) in patients treated with LPD and inulin (p = 0.018 and p = 0.003, respectively), an improvement in SF-36 (physical role functioning and general health perceptions; p = 0.03 and p = 0.01, respectively), and a significant increase of serum bicarbonate both in patients treated with LPD (p = 0.026) or with LPD and inulin (p = 0.01). Moreover, in patients treated with LPD and inulin, we observed a significant reduction in circulating tumor necrosis factor alpha (TNF-α) (p = 0.041) and plasma nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX2) (p = 0.027) levels. We did not find a significant difference in the circulating levels of Interleukin (IL)-1β (p = 0.529) and IL-6 (p = 0.828) in the two groups. Conclusions: LPD, associated or not with inulin, modified gut microbiota and modulated inflammatory and metabolic parameters in patients with CKD. Our results suggest that interventions attempting to modulate the gut microbiome may represent novel strategies to improve clinical outcomes in CKD patients and may provide useful therapeutic effects.

Impaired intestinal barrier function in a mouse model of hyperuricemia

Previous studies have demonstrated the effects of hyperuricemia on the damage to target organs, including the kidneys, joints and the heart. However, it is unclear whether hyperuricemia results in damage to the intestines. The aim of the present study was to investigate intestinal barrier dysfunction in a mouse model of hyperuricemia constructed by knocking out the urate oxidase (Uox) gene. The morphology of the intestine was assessed via hematoxylin and eosin, and alcian blue staining. The serum and intestinal tissue levels of uric acid, tumor necrosis factor (TNF)‑α and interleukin (IL)‑6, in addition to the presence of uremic toxins in the serum, were assessed. The levels of diamine oxidase (DAO), D‑lactate (D‑LAC) and endotoxins in the serum, which are markers of the intestinal permeability, were measured using ELISA. The expression of the intestinal tight junction proteins zona occludens‑1 (ZO‑1) and occludin were detected by reverse transcription‑quantitative polymerase chain reaction, western blotting and immunohistochemical analysis. The Uox‑knockout mice spontaneously developed hyperuricemia. Histopathological analysis indicated notable intestinal defects including sparse villi, mucosal edema and a declining mucus layer in hyperuricemic mice. The expression levels of ZO‑1 and occludin in the intestines were downregulated, and the serum levels of DAO, D‑LAC and endotoxins were higher in the hyperuricemic mice, compared with control mice. The serum and intestinal tissue levels of IL‑6 and TNF‑α were significantly increased. Additionally, the expression levels of the serum uremic toxins, serum creatinine, blood urea nitrogen were significantly increased in hyperuricemic mice compared with the control mice, while only a marked increase in indoxyl sulfate (IS) and p‑cresol sulfate was reported. Collectively, the results of the present study suggested that intestinal barrier dysfunction and subsequent enhanced intestinal permeability may occur as a result of hyperuricemia in mice. Furthermore, we proposed that the loss of intestinal epithelium barrier function may be associated with uric acid‑induced inflammatory responses; however, further investigation is required.

Chronic kidney disease in the pathogenesis of acute ischemic stroke

Chronic kidney disease has a graded and independent inverse impact on cerebrovascular health. Both thrombotic and hemorrhagic complications are highly prevalent in chronic kidney disease patients. Growing evidence suggests that in chronic kidney disease patients, ischemic strokes are more common than hemorrhagic strokes. Chronic kidney disease is asymptomatic until an advanced stage, but mild to moderate chronic kidney disease incites various pathogenic mechanisms such as inflammation, oxidative stress, neurohormonal imbalance, formation of uremic toxins and vascular calcification which damage the endothelium and blood vessels. Cognitive dysfunction, dementia, transient infarcts, and white matter lesions are widespread in mild to moderate chronic kidney disease patients. Uremic toxins produced after chronic kidney disease can pass through the blood-brain barrier and mediate cognitive dysfunction and neurodegeneration. Furthermore, chronic kidney disease precipitates vascular risk factors that can lead to atherosclerosis, hypertension, atrial fibrillation, and diabetes. Chronic kidney disease also exacerbates stroke pathogenesis, worsens recovery outcomes, and limits the eligibility of stroke patients to receive available stroke therapeutics. This review highlights the mechanisms involved in the advancement of chronic kidney disease and its possible association with stroke.

Quantitative reduction in short-chain fatty acids, especially butyrate, contributes to the progression of chronic kidney disease

Chronic kidney disease (CKD) affects 10-15% of the population worldwide, results in high morbidity and mortality, and requires costly treatment and renal replacement therapy. Glomerulosclerosis, tubulointerstitial fibrosis, and persistent intestinal flora disturbance are common in CKD. Short-chain fatty acids (SCFAs), produced by the intestinal microbiota, have been previously reported to ameliorate kidney injury; however, the specific concentrations and types that are required to improve renal function remain unknown. The present study aims to evaluate the levels of SCFAs in healthy and CKD patients, and to test the hypothesis that SCFAs play a critical role in delaying CKD progression. One hundred and twenty-seven patients with CKD and 63 healthy controls from China were enrolled in the present study. Butyrate, which is considered beneficial to humans, was almost three-times higher in healthy volunteers than that in CKD5 subjects (P=0.001). Moreover, the serum SCFA levels in controls were significantly higher than that in CKD patients (P<0.05), and the butyrate level among CKD5 patients (1.48 ± 0.60 μmol/l) was less than half of that in controls (3.44 ± 2.12 μmol/l, P<0.001). In addition, we observed an inverse correlation between butyrate level and renal function (P<0.05). A CKD rat model transplanted with microbiota obtained from CKD patients exhibited accelerated CKD progression via increased production of trimethylamine N-oxide (TMAO), which was reversed by supplementation with extra butyrate. Our results showed that SCFA levels were reduced in CKD patients and that butyrate supplementation might delay CKD progression.

The gut microbiota and the brain-gut-kidney axis in hypertension and chronic kidney disease

Crosstalk between the gut microbiota and the host has attracted considerable attention owing to its involvement in diverse diseases. Chronic kidney disease (CKD) is commonly associated with hypertension and is characterized by immune dysregulation, metabolic disorder and sympathetic activation, which are all linked to gut dysbiosis and altered host-microbiota crosstalk. In this Review, we discuss the complex interplay between the brain, the gut, the microbiota and the kidney in CKD and hypertension and explain our brain-gut-kidney axis hypothesis for the pathogenesis of these diseases. Consideration of the role of the brain-gut-kidney axis in the maintenance of normal homeostasis and of dysregulation of this axis in CKD and hypertension could lead to the identification of novel therapeutic targets. In addition, the discovery of unique microbial communities and their associated metabolites and the elucidation of brain-gut-kidney signalling are likely to fill fundamental knowledge gaps leading to innovative research, clinical trials and treatments for CKD and hypertension.

Nutritional therapy reduces protein carbamylation through urea lowering in chronic kidney disease

Background

Protein carbamylation is one of the non-enzymatic reactions involved in protein molecular ageing. We sought to investigate the relationship between urea levels and protein carbamylation, and whether a Mediterranean diet (MD) and a very low protein diet (VLPD) reduce protein carbamylation through reduction in urea levels in patients with chronic kidney disease (CKD).

Methods

This is a prospective, randomized, crossover controlled trial that investigated 60 patients with CKD grades 3B-4 (46 males, mean age of 67 years). The enrolled CKD patients were randomly assigned (1:1) to two different nutritional treatment arms: (i) 3 months of free diet (FD), 6 months of VLPD, 3 months of FD and 6 months of MD; and (ii) 3 months of FD, 6 months of MD, 3 months of FD and 6 months of VLPD. Blood levels of lysine (Lys) and homocitrulline (Hcit) and their ratio were used as markers of cyanate levels. Due to a lack of pre-existing data on the potential effects of different dietary regimens and in light of the exploratory nature of the study, no formal sample size estimation was carried out.

Results

At study completion, lower diastolic blood pressure and decreased serum levels of urea, sodium, phosphorus and parathyroid hormone, but higher serum levels of bicarbonate and haemoglobin, were noted with MD and VLPD. When compared with FD, both MD and VLPD were also associated with a decrease in serum Hcit levels and Hcit/Lys ratios (P < 0.001). Notably, reductions in urea levels correlated with substantial reductions in Hcit levels (R2 = 0.16 and 0.17 for VLPD and MD, respectively).

Conclusion

In conclusion, nutritional treatments that significantly decrease serum levels of urea are associated with reduced protein carbamylation.

Specific risk factors for cerebrovascular disorders in patients with chronic kidney disease in the pre-dialysis period

Cerebral vascular disorders are one of the leading causes of disability and mortality in patients with chronic kidney disease (CKD). The article presents the currently available data on risk factors (RF) for the development of cerebrovascular disorders in pre-dialysis patients with CKD. Two groups of RF are identified: traditional and non-traditional (specific). Traditional RF, which include arterial hypertension, diabetes mellitus and hypercholesterolemia, independently affect the cerebral vascular bed and get worse against the background of CKD. Specific RF is associated with features of the CKD pathogenesis. It includes increased blood levels of homocysteine, β2-microglobulin, impaired calcium-phosphorus metabolism, accumulation of uremic toxins and toxins of intestinal bacteria, anemia and other factors. In the present review, special attention is paid to specific RF and pathogenetic mechanisms of the development of cerebrovascular disorders in predialysis patients with CKD. Timely detection of cerebral risk factors may lead to the improvement of early diagnosis and prevention of cerebral vascular disorders, optimization of therapy for patients with CKD.

Vegetable-Based Diets for Chronic Kidney Disease? It Is Time to Reconsider

Traditional dietary recommendations to renal patients limited the intake of fruits and vegetables because of their high potassium content. However, this paradigm is rapidly changing due to the multiple benefits derived from a fundamentally vegetarian diet such as, improvement in gut dysbiosis, reducing the number of pathobionts and protein-fermenting species leading to a decreased production of the most harmful uremic toxins, while the high fiber content of these diets enhances intestinal motility and short-chain fatty acid production. Metabolic acidosis in chronic kidney disease (CKD) is aggravated by the high consumption of meat and refined cereals, increasing the dietary acid load, while the intake of fruit and vegetables is able to neutralize the acidosis and its deleterious consequences. Phosphorus absorption and bioavailability is also lower in a vegetarian diet, reducing hyperphosphatemia, a known cause of cardiovascular mortality in CKD. The richness of multiple plants in magnesium and vitamin K avoids their deficiency, which is common in these patients. These beneficial effects, together with the reduction of inflammation and oxidative stress observed with these diets, may explain the reduction in renal patients' complications and mortality, and may slow CKD progression. Finally, although hyperkalemia is the main concern of these diets, the use of adequate cooking techniques can minimize the amount absorbed.

Effect of Indoxyl Sulfate on the Repair and Intactness of Intestinal Epithelial Cells: Role of Reactive Oxygen Species' Release

Chronic kidney disease (CKD) is characterized by an oxidative stress status, driving some CKD-associated complications, even at the gastrointestinal level. Indoxyl Sulfate (IS) is a protein-bound uremic toxin, poorly eliminated by dialysis. This toxin is able to affect the intestinal system, but its molecular mechanism/s in intestinal epithelial cells (IECs) remain poorly understood. This study's aim was to evaluate the effect of IS (31.2-250 µM) on oxidative stress in IEC-6 cells and on the intactness of IECs monolayers. Our results indicated that IS enhanced oxidative cell damage by inducing reactive oxygen species (ROS) release, reducing the antioxidant response and affecting Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) nuclear translocation as well its related antioxidant enzymes. In the wound healing assay model, IS reduced IEC-6 migration, slightly impaired actin cytoskeleton rearrangement; this effect was associated with connexin 43 alteration. Moreover, we reported the effect of CKD patients' sera in IEC-6 cells. Our results indicated that patient sera induced ROS release in IEC-6 cells directly related to IS sera content and this effect was reduced by AST-120 serum treatment. Results highlighted the effect of IS in inducing oxidative stress in IECs and in impairing the intactness of the IECs cell monolayer, thus significantly contributing to CKD-associated intestinal alterations.

Relationship between Gut Microbiota and Phosphorus Metabolism in Hemodialysis Patients: A Preliminary Exploration

Background

Hyperphosphatemia is a risk factor associated with mortality in patients on maintenance hemodialysis. Gut absorption of phosphate is the major source. Recent studies indicated that the intestinal flora of uremic patients changed a lot compared with the healthy population, and phosphorus is an essential element of bacterial survival and reproduction. The purpose of this study was to explore the role of intestinal microbiota in phosphorus metabolism.

Methods

A prospective self-control study was performed from October 2015 to January 2016. Microbial DNA was isolated from the stools of 20 healthy controls and 21 maintenance hemodialysis patients. Fourteen out of the 21 patients were treated with lanthanum carbonate for 12 weeks. Thus, stools were also collected before and after the treatment. The bacterial composition was analyzed based on 16S ribosomal RNA pyrosequencing. Bioinformatics tools, including sequence alignment, abundance profiling, and taxonomic diversity, were used in microbiome data analyses. Correlations between genera and the serum phosphorus were detected with Pearson's correlation. For visualization of the internal interactions and further measurement of the microbial community, SparCC was used to calculate the Spearman correlation coefficient with the corresponding P value between each two genera.

Results

Thirteen genera closely correlated with serum phosphorus and the correlation coefficient was above 0.4 (P < 0.05). We also found that 58 bacterial operational taxonomic units (OTUs) were significantly different and more decreased OTUs were identified and seven genera (P < 0.05) were obviously reduced after using the phosphate binder. Meanwhile, the microbial richness and diversity presented downward trend in hemodialysis patients compared with healthy controls and more downward trend after phosphorus reduction. The co-occurrence network of genera revealed that the network complexity of hemodialysis patients was significantly higher than that of controls, whereas treatment with lanthanum carbonate reduced the network complexity.

Conclusions

Gut flora related to phosphorus metabolism in hemodialysis patients, and improving intestinal microbiota may regulate the absorption of phosphate in the intestine. The use of phosphate binder lanthanum carbonate leads to a tendency of decreasing microbial diversity and lower network complexity.

Could resistant starch supplementation improve inflammatory and oxidative stress biomarkers and uremic toxins levels in hemodialysis patients? A pilot randomized controlled trial

An imbalance of gut microbiota is considered a new cardiovascular risk factor for chronic kidney disease (CKD) patients, since it is directly associated with increased uremic toxin production, inflammation and oxidative stress. Strategies such as prebiotic supplementation have been suggested to mitigate these complications. We hypothesized that prebiotic-resistant starch could ameliorate uremic toxins levels, oxidative stress, and inflammatory states in hemodialysis (HD) patients. This pilot study evaluated 31 HD patients assigned to either resistant starch (16 g of resistant starch Hi-Maize® 260) or placebo (manioc flour) supplementation, which they received for 4 weeks on alternate days through cookies on dialysis days and powder in a sachet on non-dialysis days. Levels of interleukin (IL)-6, high-sensitive C-reactive protein, thiobarbituric acid reactive substances plasma (TBARS), protein carbonylation, indoxyl sulfate (IS) and p-cresyl sulfate were measured. Anthropometric and biochemical parameters, as well as, food intake were also evaluated. As expected, resistant starch group increased fiber intake (p > 0.01), in addition the prebiotic supplementation reduced IL-6 (p = 0.01), TBARS (p > 0.01), and IS (p > 0.01) plasma levels. No significant differences were evident in the placebo group. Prebiotic-resistant starch supplementation seems to be a promising nutritional strategy to improve inflammation, oxidative stress and to reduce IS plasma levels in CKD patients on HD.

Hepato-splanchnic circulatory stress: An important effect of hemodialysis

The gastro-intestinal tract is being increasingly recognized as the site of key pathophysiological processes in the hemodialysis patient. Intestinal dysbiosis, increased intraluminal toxin production, and increased intestinal permeability are commonly observed processes which contribute to the pathogenesis of cardiovascular disease and thus elevated mortality. The acute circulatory effects of dialysis itself may contribute significantly to the development of gastrointestinal dysfunction as a result of both local and distant effects. Additionally, the liver, a relatively unknown entity in this process, has a substantial role as a functional barrier between the portal and systemic circulation and in the metabolism of pathogenic gut-derived uremic toxins. Here we summarize the evidence for acute gastro-intestinal and hepatic effects of hemodialysis and identify gaps in knowledge to date which require further study.

Suppression of Gut Bacterial Translocation Ameliorates Vascular Calcification through Inhibiting Toll-Like Receptor 9-Mediated BMP-2 Expression

Aims

Vascular calcification (VC) is a primary risk factor for cardiovascular mortality in chronic renal failure (CRF) patients; thus, effective therapeutic targets are urgently needed to be explored. Here, we identified the role of intestinal bacterial translocation in CRF-related VC.

Methods and Results

Antibiotic supplementation by oral gavage significantly suppressed intestinal bacterial translocation, CRF-related VC, and aortic osteogenic gene and Toll-like receptor (TLR) gene expression in CRF rats. Furthermore, TLR4 and TLR9 activation in vascular smooth muscle cells (VSMCs) aggravated inorganic phosphate- (Pi-) induced calcification. TLR9 inhibition, but not TLR4 inhibition, by both a pharmacological inhibitor and genetic methods could significantly reduce CRF rats' serum or CRF-induced VC. Interestingly, bone morphogenic protein-2 (BMP-2) levels were increased in the aorta and sera from CRF rats. Increased BMP-2 levels were also observed in VSMCs treated with TLR9 agonist, which was blocked by NF-κB inhibition. Both siRNA knockdown of BMP-2 and NF-κB inhibitor significantly blocked TLR9 agonist-induced VSMC calcification.

Conclusions

Gut bacterial translocation inhibited by oral antibiotic significantly reduces CRF-related VC through inhibition of TLR9/NF-κB/BMP-2 signaling.

Effects of fermentable high fiber diet supplementation on gut derived and conventional nitrogenous product in patients on maintenance hemodialysis: a randomized controlled trial

Introduction

Gut derived toxins such as p-cresol, p-cresyl sulfate (pCS) and indoxyl sulfate (IS), which belong to protein-bound uremic toxins that promote development of fibrosis inflammatory state associated with chronic kidney disease. One possible way to suppress the production of IS and pCS is to increase dietary fiber intake. The aim of the present study was to assess whether increasing dietary fiber, as high amylose diet, can affect the level of conventional and protein bound nitrogenous products.

Methods

Fifty patients with end stage renal disease (ESRD) on maintenance hemodialysis were randomly assigned to receive a diet containing resistant starch (HAM-RS2) or placebo over 8 weeks spanning February and September 2017 in the 29 Bahman hospital hemodialysis ward in Tabriz, Iran. Of these, 44 patients (23 from HAM-RS2 and 21 control) completed the study. Plasma levels of urea, creatinine, uric acid and other routine parameters were measured at the beginning and after 8 weeks of starting the supplementation. The levels of IS and p-cresol in the collected serum samples were also determined by HPLC at baseline and after intervention.

Results

There was significant reduction of creatinine and uric acid levels in HAM-RS2 supplemented patients when compared with control group (P < 0.05). Serum levels of IS was not changed significantly in both HAM-RS2 treated and control patients, whereas p-cresol level was reduced significantly during the study period in HAM-RS2 treated patients (P = 0.039). The change of other parameters including Hb, lipids, bone markers and hs-CRP were non-significant during the study in both groups.

Conclusion

Administration of fermentable high fiber diet as HAM-RS2 decreased serum levels of some nitrogenous products such as serum creatinine and p-cresol as a gut derived nitrogenous product without change in IS levels in maintenance hemodialysis patients. Due to safety, without important side effects the administration of diet enriched with fermentable fiber is suitable for patients on maintenance dialysis.

Simplified colonic dialysis with hemodialysis solutions delays the progression of chronic kidney disease

BACKGROUND

The colon plays a vital role in the disposal of nitrogenous waste products. Therefore, the colon may provide a therapeutic target for managing chronic kidney disease (CKD).

AIM

To evaluate the efficacy of a simplified model of colonic dialysis with hemodialysis solutions (SCD) to delay the progression of stages 3-5 CKD.

DESIGN

Retrospective study.

METHODS

We retrospectively analyzed 178 stages 3-5 CKD patients who did or did not receive SCD (SCD group, n = 88; control group, n = 90). The follow-up was 36 months. The outcome of CKD progression was defined as a decrease in 50% or more in estimated glomerular filtration rate, starting hemodialysis or peritoneal dialysis or undergoing transplantation. The Kaplan-Meier analysis was used to compare CKD progression between SCD and control groups as well as between subgroups at different CKD stages. Cox proportional hazard models adjusted for patients' characteristics were used to examine the association between SCD and the outcome.

RESULTS

For all patients, the outcome was significantly better in SCD group compared to control group (P < 0.05). The results were similar in the subgroups of patients at stage 4 (P = 0.001) and stage 5 (P = 0.000), but not in the subgroup of patients at stage 3 (P = 0.121). For all patients, SCD was associated with a lower risk of CKD progression after adjusted for patients' characteristics (adjusted hazard ratio, 0.373; 95% confidence interval, 0.201-0.694; P 0.002).

CONCLUSION

SCD is an effective supplementary therapy to delay the progression of stages 4-5 CKD.

Dietary Components That May Influence the Disturbed Gut Microbiota in Chronic Kidney Disease

Gut microbiota imbalance is common in patients with chronic kidney disease (CKD) and associates with factors such as increased circulating levels of gut-derived uremic toxins, inflammation, and oxidative stress, which are linked to cardiovascular disease and increased morbimortality. Different nutritional strategies have been proposed to modulate gut microbiota, and could potentially be used to reduce dysbiosis in CKD. Nutrients like proteins, fibers, probiotics, and synbiotics are important determinants of the composition of gut microbiota and specific bioactive compounds such as polyphenols present in nuts, berries. and fruits, and curcumin, may also play a key role in this regard. However, so far, there are few studies on dietary components influencing the gut microbiota in CKD, and it is therefore not possible to conclude which nutrients should be prioritized in the diet of patients with CKD. In this review, we discuss some nutrients, diet patterns and bioactive compounds that may be involved in the modulation of gut microbiota in CKD and provide the background and rationale for studies exploring whether nutritional interventions with these dietary components could be used to alleviate the gut dysbiosis in patients with CKD.

Intestinal phosphate absorption: The paracellular pathway predominates?

IMPACT STATEMENT

This review summarizes the work on transcellular intestinal phosphate absorption, arguing why this pathway is not the predominant pathway in humans consuming a "Western" diet. We then highlight the recent evidence which is strongly consistent with paracellular intestinal phosphate absorption mediating the bulk of intestinal phosphate absorption in humans.

Low-Fiber Intake Is Associated With High Production of Intraperitoneal Inflammation Biomarkers

OBJECTIVE

Fiber intake influences disturbances in the gastrointestinal tract and is associated with systemic inflammation in the general population. Systemic and intraperitoneal inflammation play an important role in defining outcomes in peritoneal dialysis (PD), but the relationship between dietary fiber intake and inflammatory biomarkers has not yet been reported in the population on PD. The objective of the present study is to analyze whether or not fiber intake in patients on PD is associated with serum and intraperitoneal levels of inflammatory biomarkers.

DESIGN AND METHODS

Adult and clinically stable PD patients were included in this observational and cross-sectional study. Fiber intake was assessed by means of a dietary survey and calculated using the DietPro program 5.6i. The population was divided into two groups according to the median fiber intake. We investigated interleukin (IL)-1β, IL-6, tumor necrosis factor-α, monocyte chemoattractant protein-1 (MCP-1), B-cell-activating factor, and plasminogen-activator inhibitor-1 in both serum and peritoneal fluid. The latter was determined after a dwell time of 4 hours.

RESULTS

Fifty-two patients (42% men; aged 53 ± 14 years, 36% diabetics) were evaluated. Low intake of dietary fiber was found in 90% of patients, with a median of 12.2 g per day (3.4-33.3). The group with the highest fiber intake presented lower intraperitoneal levels of IL-6, IL-8, and MCP-1. In contrast, only MCP-1 was lower in the serum of those who consumed more fiber. All the associations remained significant after adjustment for confounders with plasminogen-activator inhibitor-1 included.

CONCLUSIONS

Patients on PD frequently present inadequate dietary fiber intake, which appears to have an association with the inflammatory response, particularly in the intraperitoneal component. Further prospective studies, evaluating whether or not a dietetic intervention with a focus on fiber intake affects these biomarkers and clinical outcomes, are essential to determine causality and clinical relevance.

Association of Pre-End-Stage Renal Disease Serum Albumin With Post-End-Stage Renal Disease Outcomes Among Patients Transitioning to Dialysis

OBJECTIVE

Serum albumin is a marker of malnutrition and inflammation and has been demonstrated as a strong predictor of mortality in chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. Yet, whether serum albumin levels in late-stage CKD are associated with adverse outcomes after the transition to ESRD is unknown. We hypothesize that lower levels and a decline in serum albumin in late-stage CKD are associated with higher risk of mortality and hospitalization rates 1 year after transition to ESRD.

DESIGN AND METHODS

This retrospective cohort study included 29,124 US veterans with advanced CKD transitioning to ESRD between 2007 and 2015. We evaluated the association of pre-ESRD (91 days before transition) serum albumin with 12-month post-ESRD all-cause, cardiovascular, and infection-related mortalities and hospitalization rates as well as the association of 1-year pre-ESRD albumin slope and 12-month post-ESRD mortality using hierarchical multivariable adjustments.

RESULTS

There was a negative linear association between serum albumin and all-cause mortality, such that risk doubled (hazard ratio [HR]: 2.07, 95% confidence interval [CI]: 1.87, 2.28) for patients with the lowest serum albumin <2.8 g/dL (ref: ≥4.0 g/dL) after full adjustment. A consistent relationship was observed between serum albumin and cardiovascular and infection-related mortality, and hospitalization outcomes. An increase in serum albumin of >0.25 g/dL/year was associated with reduced mortality risk (HR: 0.76, 95% CI: 0.63, 0.91) compared with a slight decline in albumin (ref: >-0.25 to 0 g/dL/year), whereas a decline more than 0.5 g/dL/year was associated with a 55% higher risk in mortality (HR: 1.55, 95% CI: 1.43, 1.68) in fully adjusted models.

CONCLUSIONS

Lower pre-ESRD serum albumin was associated with higher post-ESRD all-cause, cardiovascular, and infection-related mortalities and hospitalization rates. Declining serum albumin levels in the pre-ESRD period were also associated with worse 12-month post-ESRD mortality.

Diet, gut microbiome and indoxyl sulphate in chronic kidney disease patients

Emerging evidence suggests that intestinal dysbiosis plays an important role in host inflammation locally and systemically. Such pathological condition is even more prevailing in patients with chronic kidney disease (CKD). Of note, indoxyl sulphate (IS), a gut-derived uremic toxin, is notorious for its pro-inflammatory feature in CKD patients. IS accumulates in the body as the urinary excretion of uremic toxins is impaired, and further worsens the kidney function in a vicious cycle to CKD. Dietary restriction in vegetables, fruits and yogurt leads to the predominance of indole-producing intestinal microbial flora and further exaggerates the accumulation of IS in CKD patients. Recently, interventional studies have shown that circulating IS can be reduced by dietary prebiotic and/or probiotic supplements. However, further randomized controlled trials are warranted to examine whether such beneficial effect of dietary prebiotic/probiotic supplements could be extrapolated to better hard outcomes in CKD population. In this review, we would also like to emphasize the importance of achieving sufficient intake of dietary fibre by proper vegetable pre-treatment and accurate fruit selection, instead of directly avoiding these potassium-rich yet fibre-rich and base-producing foods.

Microbiome-metabolome reveals the contribution of gut-kidney axis on kidney disease

Dysbiosis represents changes in composition and structure of the gut microbiome community (microbiome), which may dictate the physiological phenotype (health or disease). Recent technological advances and efforts in metagenomic and metabolomic analyses have led to a dramatical growth in our understanding of microbiome, but still, the mechanisms underlying gut microbiome–host interactions in healthy or diseased state remain elusive and their elucidation is in infancy. Disruption of the normal gut microbiota may lead to intestinal dysbiosis, intestinal barrier dysfunction, and bacterial translocation. Excessive uremic toxins are produced as a result of gut microbiota alteration, including indoxyl sulphate, p-cresyl sulphate, and trimethylamine-N-oxide, all implicated in the variant processes of kidney diseases development. This review focuses on the pathogenic association between gut microbiota and kidney diseases (the gut–kidney axis), covering CKD, IgA nephropathy, nephrolithiasis, hypertension, acute kidney injury, hemodialysis and peritoneal dialysis in clinic. Targeted interventions including probiotic, prebiotic and symbiotic measures are discussed for their potential of re-establishing symbiosis, and more effective strategies for the treatment of kidney diseases patients are suggested. The novel insights into the dysbiosis of the gut microbiota in kidney diseases are helpful to develop novel therapeutic strategies for preventing or attenuating kidney diseases and complications.

Cranberries – potential benefits in patients with chronic kidney disease

Patients with chronic kidney disease (CKD) present many complications that potentially could be linked to increased cardiovascular mortality such as inflammation, oxidative stress, cellular senescence and gut dysbiosis.

Health-related quality of life in peritoneal dialysis patients: A narrative review

Health-related quality of life (HRQOL) is an important aspect of patients´ health that should be an integral part of the evaluation of patient-centered outcomes, not least because HRQOL associates with patients´ morbidity and mortality. This applies also to chronic kidney disease patients, including those dependent on renal replacement therapies, the type of which may influence patients´ perception of HRQOL. Several studies have addressed HRQOL in chronic kidney disease patients undergoing renal replacement therapies, especially transplanted patients and hemodialysis patients, while publications concerning peritoneal dialysis (PD) patients are scarcer. This review describes some of the methods used to assess HRQOL, factors influencing HRQOL in PD patients, HRQOL in PD vs hemodialysis, and the relation between HRQOL and patient outcomes. We conclude that assessment of HRQOL-often neglected at present-should be included as a standard measure of patient-centered outcomes and when monitoring the quality and effectiveness of renal care including PD treatment.

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

Background

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

Objectives

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

Animals

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

Methods

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

Results

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

Conclusions and Clinical Importance

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

Supplementation of Short-Chain Fatty Acid, Sodium Propionate, in Patients on Maintenance Hemodialysis: Beneficial Effects on Inflammatory Parameters and Gut-Derived Uremic Toxins, A Pilot Study (PLAN Study)

BACKGROUND

In end-stage renal disease (ESRD), gut-derived uremic toxins play a crucial role in the systemic inflammation and oxidative stress promoting the excess morbidity and mortality. The biochemical derangement is in part a consequence of an insufficient generation of short-chain fatty acids (SCFA) due to the dysbiosis of the gut and an insufficient consumption of the fermentable complex carbohydrates.

AIM OF THE STUDY

The primary end-point was to evaluate the potential efficacy of SCFA (specifically, sodium propionate (SP)) for patients on maintenance hemodialysis (MHD) on systemic inflammation. Secondary end-points included potential attenuation of oxidative stress markers, insulin resistance and production of gut-derived uremic toxins indoxyl sulfate and p-cresol sulfate, as well as health status after SP supplementation.

STUDY DESIGN

We performed a single-center non-randomized pilot study in 20 MHD patients. They received the food additive SP with a daily intake of 2 × 500 mg in the form of capsules for 12 weeks. Pre-dialysis blood samples were taken at the beginning, after six weeks and at the end of the administration period, as well as four weeks after withdrawal of the treatment.

RESULTS

The subjects revealed a significant decline of inflammatory parameters C-reactive protein (-46%), interleukin IL-2 (-27%) and IL-17 (-15%). The inflammatory parameters IL-6 and IFN-gamma showed a mild non-significant reduction and the anti-inflammatory cytokine IL-10 increased significantly (+71%). While the concentration of bacterial endotoxins and TNF-α remained unchanged, the gut-derived uremic toxins, indoxyl sulfate (-30%) and p-cresyl sulfate (-50%), revealed a significant decline. The SP supplementation reduced the parameters of oxidative stress malondialdehyde (-32%) and glutathione peroxidase activity (-28%). The serum insulin levels dropped by 30% and the HOMA-index by 32%. The reduction of inflammatory parameters was associated with a lowering of ferritin and a significant increase in transferrin saturation (TSAT). Four weeks after the end of the treatment phase, all improved parameters deteriorated again. Evaluation of the psycho-physical performance with the short form 36 (SF-36) questionnaire showed an enhancement in the self-reported physical functioning, general health, vitality and mental health. The SP supplementation was well tolerated and without important side effects. No patient had left the study due to intolerance to the medication. The SP supplementation in MHD patients reduced pro-inflammatory parameters and oxidative stress and improved insulin resistance and iron metabolism. Furthermore, SP effectively lowered the important gut-derived uremic toxins indoxyl and p-cresol sulfate. These improvements were associated with a better quality of life. Further controlled studies are required in a larger cohort to evaluate the clinical outcome.

Association between fibre intake and indoxyl sulphate/P-cresyl sulphate in patients with chronic kidney disease: Meta-analysis and systematic review of experimental studies

BACKGROUND AND OBJECTIVE

Indoxyl sulphate (IS) and p-cresyl sulphate (PCS), which are difficult to excrete adequately out of the body, are closely related to the progression of chronic kidney disease (CKD) and various deuteropathy. Better than peritoneal dialysis (PD) and haemodialysis (HD), dietary fibre has been considered to reduce IS and PCS levels. In view of the absence of formal recommendations on fibre intake in CKD nutritional guidelines, we conducted this meta-analysis to assess the effects of dietary fibre on IS and PCS for CKD patients.

METHODS

The effects were pooled and expressed in terms of weighted mean difference (WMD) with 95% confidence interval (95% CI). Q test and I² statistics were used to assess the heterogeneity.

RESULTS

A total of 12 relevant estimates from 7 reports, including 203 CKD patients, showed that dietary fibre significantly reduced their PCS level (WMD = -16.160, 95% CI: -23.824, -8.495).

CONCLUSIONS

The meta-analysis produced a strong corroboration that dietary fibre intake does have a good therapeutic effect on patients with CKD. The conclusions need to be validated by randomised controlled experiments (RCT) with better design, larger samples, longer course of treatment and higher quality.

Inflammation-Related Mechanisms in Chronic Kidney Disease Prediction, Progression, and Outcome

Persistent, low-grade inflammation is now considered a hallmark feature of chronic kidney disease (CKD), being involved in the development of all-cause mortality of these patients. Although substantial improvements have been made in clinical care, CKD remains a major public health burden, affecting 10–15% of the population, and its prevalence is constantly growing. Due to its insidious nature, CKD is rarely diagnosed in early stages, and once developed, its progression is unfortunately irreversible. There are many factors that contribute to the setting of the inflammatory status in CKD, including increased production of proinflammatory cytokines, oxidative stress and acidosis, chronic and recurrent infections, altered metabolism of adipose tissue, and last but not least, gut microbiota dysbiosis, an underestimated source of microinflammation. In this scenario, a huge step forward was made by the increasing progression of omics approaches, specially designed for identification of biomarkers useful for early diagnostic and follow-up. Recent omics advances could provide novel insights in deciphering the disease pathophysiology; thus, identification of circulating biomarker panels using state-of-the-art proteomic technologies could improve CKD early diagnosis, monitoring, and prognostics. This review aims to summarize the recent knowledge regarding the relationship between inflammation and CKD, highlighting the current proteomic approaches, as well as the inflammasomes and gut microbiota dysbiosis involvement in the setting of CKD, culminating with the troubling bidirectional connection between CKD and renal malignancy, raised on the background of an inflammatory condition.

Effects of Prebiotic Fiber Xylooligosaccharide in Adenine-Induced Nephropathy in Mice

SCOPE

This study evaluates the effect of the prebiotic fiber xylooligosaccharide (XOS) on kidney function and gut microbiome in mice with adenine-induced chronic kidney disease (CKD).

METHOD AND RESULTS

Mice are fed the control diet containing adenine for 3 weeks to induce CKD and are switched to XOS supplemented (2 or 7%) or control diets for another 3 weeks. Mice with CKD exhibit increased blood urea nitrogen (BUN), creatinine, and kidney histopathology. XOS significantly reverses kidney injuries in CKD mice. Analysis of cecum microbiota reveales that adenine-induced CKD does not change alpha diversity, and XOS induces a decrease of alpha diversity in control mice and mice with CKD. Beta diversity analysis shows significant clustering according to experimental groups. Six out of the nine bacterial genera enriched in CKD are significantly reduced with XOS intervention. Furthermore, XOS increases cecal short-chain fatty acid (SCFA) production in both control and CKD mice. Cecal SCFAs and blood propionate are negatively correlated with BUN. XOS also decreases blood p-cresol sulfate in CKD mice, likely resulting from altered microbial tyrosine metabolism.

CONCLUSION

These results show that XOS intervention improves kidney function in mice with CKD, and is associated with profound changes in microbial composition and metabolism.

Probiotic supplementation in trained trotter horses: effect on blood clinical pathology data and urine metabolomic assessed in field

The attention of sports community toward probiotic supplementation as a way to promote exercise and training performance, together with good health, has increased in recent years. This has applied also to horses, with promising results. Here, for the first time, we tested a probiotic mix of several strains of live bacteria typically employed for humans to improve the training performance of Standardbred horses in athletic activity. To evaluate its effects on the horse performance, we measured lactate concentration in blood, a translational outcome largely employed for the purpose, combined with the study of hematological and biochemical parameters, together with urine from a metabolomics perspective. The results showed that the probiotic supplementation significantly reduced postexercise blood lactate concentration. The hematological and biochemical parameters, together with urine molecular profile, suggested that a likely mechanism underlying this positive effect was connected to a switch of energy source in muscle from carbohydrates to short-chain fatty acids. Three sulfur-containing molecules differently concentrated in urines in connection to probiotics administration suggested that such switch was linked to sulfur metabolism. NEW & NOTEWORTHY Probiotic supplementation could reduce postexercise blood lactate concentration in Standardbred horses in athletic activity. Blood parameters, together with urine molecular profile, suggest the mechanism underlying this positive effect is connected to a switch of energy source in muscle from carbohydrates to short-chain fatty acids. Sulfur-containing molecules found in urines in connection to probiotics administration suggested that such switch was linked to sulfur metabolism.

Impact of Altered Intestinal Microbiota on Chronic Kidney Disease Progression

In chronic kidney disease (CKD), accumulation of uremic toxins is associated with an increased risk of CKD progression. Some uremic toxins result from nutrient processing by gut microbiota, yielding precursors of uremic toxins or uremic toxins themselves, such as trimethylamine N-Oxide (TMAO), p-cresyl sulphate, indoxyl sulphate and indole-3 acetic acid. Increased intake of some nutrients may modify the gut microbiota, increasing the number of bacteria that process them to yield uremic toxins. Circulating levels of nutrient-derived uremic toxins are associated to increased risk of CKD progression. This offers the opportunity for therapeutic intervention by either modifying the diet, modifying the microbiota, decreasing uremic toxin production by microbiota, increasing toxin excretion or targeting specific uremic toxins. We now review the link between nutrients, microbiota and uremic toxin with CKD progression. Specific focus will be placed on the generation specific uremic toxins with nephrotoxic potential, the decreased availability of bacteria-derived metabolites with nephroprotective potential, such as vitamin K and butyrate and the cellular and molecular mechanisms linking these toxins and protective factors to kidney diseases. This information provides a conceptual framework that allows the development of novel therapeutic approaches.

Does inflammation affect outcomes in dialysis patients?

Chronic, low-grade inflammation is a common comorbid condition in chronic kidney disease (CKD), and particularly in chronic dialysis patients. In this review, we consider the question of whether inflammation affects outcomes in dialysis patients. Levels of proinflammatory cytokines, as well as C-reactive protein, are elevated in chronic dialysis patients. Multiple factors likely contribute to chronic inflammatory activation in kidney disease patients including the uremic milieu, lifestyle and epigenetic influences, infectious and thrombotic events, the dialysis process, and dysbiosis. Increased inflammatory markers in both CKD and chronic dialysis patients are associated with adverse clinical outcomes including all-cause mortality, cardiovascular events, kidney disease progression, protein energy wasting and diminished motor function, cognitive impairment, as well as other adverse consequences including CKD-mineral and bone disorder, anemia, and insulin resistance. Strategies that have been shown to reduce chronic systemic inflammation in CKD and chronic dialysis patients include both pharmacological and nonpharmacological interventions. However, despite evidence that systemic inflammatory markers can be lowered in kidney disease patients treated with various strategies, evidence that this improves clinical outcomes is largely unavailable and represents an important future research direction. Overall, there is strong observational evidence that inflammation is high in chronic dialysis patients and that this is independently associated with numerous adverse clinical outcomes. Targeting inflammation represents a potentially novel and attractive strategy if it can indeed improve adverse outcomes common in this population.

Biochemical transformation of calciprotein particles in uraemia

Calciprotein particles (CPP) have emerged as nanoscale mediators of phosphate-induced toxicity in Chronic Kidney Disease (CKD). Uraemia favors ripening of the particle mineral content from the amorphous (CPP-I) to the crystalline state (CPP-II) but the pathophysiological significance of this transformation is uncertain. Clinical studies suggest an association between CPP ripening and inflammation, vascular dysfunction and mortality. Although ripening has been modelled in vitro, it is unknown whether particles synthesised in serum resemble their in vivo counterparts. Here we show that in vitro formation and ripening of CPP in uraemic serum is characterised by extensive physiochemical rearrangements involving the accretion of mineral, loss of surface charge and transformation of the mineral phase from a spherical arrangement of diffuse domains of amorphous calcium phosphate to densely-packed lamellar aggregates of crystalline hydroxyapatite. These physiochemical changes were paralleled by enrichment with small soluble apolipoproteins, complement factors and the binding of fatty acids. In comparison, endogenous CPP represent a highly heterogeneous mixture of particles with characteristics mostly intermediate to synthetic CPP-I and CPP-II, but are also uniquely enriched for carbonate-substituted apatite, DNA fragments, small RNA and microbe-derived components. Pathway analysis of protein enrichment predicted the activation of cell death and pro-inflammatory processes by endogenous CPP and synthetic CPP-II alike. This comprehensive characterisation validates the use of CPP-II generated in uraemic serum as in vitro equivalents of their endogenous counterparts and provides insight into the nature and pathological significance of CPP in CKD, which may act as vehicles for various bioactive ligands.

Dietary tetrahydrocurcumin reduces renal fibrosis and cardiac hypertrophy in 5/6 nephrectomized rats

Tetrahydrocurcumin (THC) is the principal metabolite of curcumin and has antioxidant properties. In the present investigation, the effect of THC on renal and cardiovascular outcomes was studied in rats with chronic kidney disease (CKD). CKD rats were randomized following 5/6 nephrectomy to a special diet for 9 weeks which contained 1% THC (CKD+THC group). Low-dose polyenylphosphatidylcholine was used as a lipid carrier to increase bioavailability. Endpoints included tail blood pressure, normalized heart weight, plasma and urine biochemical data, and kidney tissue analyses. CKD animals demonstrated increased proteinuria, decreased creatinine clearance, hypertension, and cardiac hypertrophy. The antioxidant proteins CuZn SOD and glutathione peroxidase were decreased in the remnant kidney, while apoptosis (caspase-3) and fibrosis (alpha-SM actin) were increased. Renal fibrosis was confirmed histologically on trichrome staining. These pathologic changes were ameliorated in the CKD+THC group with significant decrease in proteinuria, hypertension, and kidney fibrosis. THC therapy restored levels of CuZn SOD and glutathione peroxidase. Consistent with prior reports, dietary THC did not improve nuclear Nrf2 levels. In summary, dietary THC therapy improved expression of antioxidant proteins in the remnant kidney, decreased renal fibrosis and proteinuria, and ameliorated hypertension in 5/6 nephrectomized rats.

Efficacy of Nutritional Interventions on Inflammatory Markers in Haemodialysis Patients: A Systematic Review and Limited Meta-Analysis

Low-grade chronic inflammation is prevalent in patients undergoing haemodialysis (HD) treatment and is linked to the development of premature atherosclerosis and mortality. The non-pharmacological approach to treat inflammation in HD patients through nutritional intervention is well cited. We aimed to assess the efficacy of different nutritional interventions at improving inflammatory outcomes in HD patients, based on markers such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α). We searched PubMed, Cochrane Library, and Embase for randomized controlled trials (RCT) published before June 2017. Inclusion criteria included RCTs on adult patients on maintenance HD treatment with duration of nutritional interventions for a minimum 4 weeks. Risk of bias was assessed using the Jadad score. In total, 46 RCTs experimenting different nutritional interventions were included in the review and categorized into polyphenols rich foods, omega-3 fatty acids, antioxidants, vitamin D, fibres, and probiotics. Meta-analyses indicated significant reduction in CRP levels by omega-3 fatty acids (Random model effect: -0.667 mg/L, p < 0.001) and vitamin E (fixed model effect: -0.257 mg/L, p = 0.005). Evidence for other groups of nutritional interventions was inconclusive. In conclusion, our meta-analysis provided evidence that omega-3 fatty acids and vitamin E could improve inflammatory outcomes in HD patients.

Altered microbiome in chronic kidney disease: systemic effects of gut-derived uremic toxins

In chronic kidney disease (CKD), influx of urea and other retained toxins exerts a change in the gut microbiome. There is decreased number of beneficial bacteria that produce short-chain fatty acids, an essential nutrient for the colonic epithelium, concurrent with an increase in bacteria that produce uremic toxins such as indoxyl sulphate, p-cresyl sulphate, and trimethylamine-N-oxide (TMAO). Due to intestinal wall inflammation and degradation of intercellular tight junctions, gut-derived uremic toxins translocate into the bloodstream and exert systemic effects. In this review, we discuss the evidence supporting a role for gut-derived uremic toxins in promoting multiorgan dysfunction via inflammatory, oxidative stress, and apoptosis pathways. End-organ effects include vascular calcification, kidney fibrosis, anemia, impaired immune system, adipocyte dysfunction with insulin resistance, and low turnover bone disease. Higher blood levels of gut-derived uremic toxins are associated with increased cardiovascular events and mortality in the CKD population. Clinical trials that have examined interventions to trap toxic products or reverse gut microbial dysbiosis via oral activated charcoal AST-120, prebiotics and probiotics have not shown impact on cardiovascular or survival outcomes but were limited by sample size and short trials. In summary, the gut microbiome is a major contributor to adverse cardiovascular outcomes and progression of CKD.

Fluid Overload and Inflammation Axis

Extracellular fluid overload (FO), which is assessed using bioimpedance technologies, is an important predictor of outcome in dialysis patients and in patients with early stages of chronic kidney disease. While traditional cardiovascular abnormalities are assumed to mediate this risk, recently also, the importance of noncardiovascular factors, such as systemic inflammation and malnutrition has been shown. While both FO and inflammation are independent risk factors for mortality, recent studies have shown that their combined presence can lead to a cumulative risk profile. From a pathophysiologic viewpoint, FO and inflammation can also be mutually reinforcing. Inflammation could contribute to FO by hypoalbuminemia, capillary leakage, and a (unnoticed) decline in lean and/or fat tissue mass resulting in incorrect estimation of dry weight. Reciprocally, FO could lead to inflammation by the translocation of endotoxins through a congested bowel wall or by a proinflammatory effect of tissue sodium. The relative importance of these putative factors is, however, not clear yet and epidemiological studies have shown no clear temporal direction regarding the relationship between FO and inflammation. FO and inflammation appear to be part of (dynamic) clusters of risk factors, including malnutrition and hyponatremia. Technology-guided fluid management of the often vulnerable dialysis patient with FO and inflammation cannot yet be based on evidence from randomized controlled trials, in which these specific patients were in general not included. In the absence of those trials, treatment should be based on identifying actionable causes of inflammation and on the judicious removal of excess volume based on frequent clinical reassessment.

Spleen contributes significantly to increased circulating levels of fibroblast growth factor 23 in response to lipopolysaccharide-induced inflammation

Background

Circulating levels of fibroblast growth factor 23 (FGF23) increase progressively and correlate with systemic inflammation in chronic kidney disease (CKD). The aim of this study was to identify and characterize the causal relationship between FGF23 and inflammation in CKD.

Methods

Circulating FGF23 and inflammatory cytokines were correlated in healthy subjects and patients with varying levels of CKD. In addition, FGF23 expression in blood and solid organs was measured in normal mice that were exposed acutely (one time) or chronically (2-week) to low-dose lipopolysaccharide (LPS); chronic exposure being either sustained (subcutaneous pellets), intermittent (daily injections) or combined sustained plus acute (subcutaneous pellets plus acute injection on the day of sacrifice). Blood was analyzed for both terminal (cFGF23) and intact (iFGF23) FGF23 levels. Solid tissues were investigated with immunohistochemistry, enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction.

Results

FGF23 levels correlated significantly with neutrophil gelatinase-associated lipocalin ( r = 0.72, P < 0.001), C-reactive protein ( r = 0.38, P < 0.001), tumor necrosis factor-α ( r = 0.32, P = 0.001) and interleukin-6 ( r = 0.48, P < 0.001). Acute LPS administration increased tissue FGF23 mRNA and plasma levels of cFGF23 but not iFGF23. Neither chronic sustained nor chronic pulsatile LPS increased the tissue or circulating levels of FGF23. However, acute on chronic LPS raised tissue FGF23 mRNA and both circulating cFG23 and iFGF23. Interestingly, the spleen was the major source of FGF23.

Conclusion

Acute on chronic exposure to LPS stimulates FGF23 production in a normal mouse model of inflammation. We provide the first evidence that the spleen, under these conditions, contributes substantially to elevated circulating FGF23 levels.

Inflammation and Peritoneal Dialysis

Inflammation is one of the well-recognized nontraditional risk factors that contributes to the excessive cardiovascular mortality in peritoneal dialysis (PD) patients. Serum C-reactive protein and interleukin-6 levels are common surrogate markers used to measure inflammatory burden and predict adverse clinical outcomes in PD patients. Causes of inflammation are complex and can be categorized into factors related to a decrease in renal function and factors related to dialysis. They interact with each other and finally result in systemic and intraperitoneal inflammation. This review discusses the various causes and clinical implications of inflammation in PD patients. More importantly, potential therapeutic options that target the underlying pathogenic mechanisms are explored.

[Micro-inflammation and digestive bacterial translocation in chronic kidney disease]

Micro-inflammation has been recognized as a major factor associated with the poor prognosis of patients with chronic kidney disease. Those patients have an increased rate of pro-inflammatory markers like interleukin 6, C-Reactive protein, Tumor Necrosis Factor α and fibrinogen. Among multiple and complex causes of micro-inflammation the gut microbiota could be an important actor considering the dysbiosis in chronic kidney disease which would enhance the synthesis of uremic toxins with cardiovascular toxicity and the bacterial translocation. This review details the role of the gut microbiota in human pathology and in chronic kidney disease focusing on the bacterial translocation that could occur because of an impaired digestive permeability. This bacterial translocation could induce a chronic immune response and could take part in the raise of pro-inflammatory markers in chronic kidney disease. New therapeutic strategies aiming at preventing metabolic and cardiovascular complications could emerge from the understanding of the relationships between gut microbiota and host in this particular pathology.