Uremic toxins and oral adsorbents

Novel intestinal dialysis interventions and microbiome modulation to control uremia

PURPOSE OF REVIEW

In patients with chronic kidney disease (CKD), the gut plays a key role in the homeostasis of fluid and electrolyte balance and the production and disposal of uremic toxins. This review summarizes the current evidence on the gut-targeted interventions to control uremia, fluid overload, hyperkalemia and hyperphosphatemia in CKD.

RECENT FINDINGS

Studies have emerged that support the concept of intestinal dialysis, such as colonic perfusion with a Malone antegrade continence enema stoma or colonic irrigation with a rectal catheter, as a promising adjuvant approach to control uremia in CKD, although most findings are preliminary. The use of AST-120, an oral adsorbent, has been shown to reduce circulating levels of indoxyl sulfate and p-cresol sulfate and have potential renoprotective benefits in patients with advanced CKD. Diarrhea or inducing watery stools may modulate fluid retention and potassium and phosphorus load. Accumulating evidence indicates that plant-based diets, low-protein diets, and pre-, pro-, and synbiotic supplementation may lead to favorable alterations of the gut microbiota, contributing to reduce uremic toxin generation. The effects of these gut-targeted interventions on kidney and cardiovascular outcomes are still limited and need to be tested in future studies including clinical trials.

SUMMARY

Interventions aimed at enhancing bowel elimination of uremic toxins, fluid and electrolytes and at modulating gut microbiota may represent novel therapeutic strategies for the management of uremia in patients with CKD.

Bacterial metabolites and cardiovascular risk in children with chronic kidney disease

Cardiovascular complications are the major cause of the marked morbidity and mortality associated with chronic kidney disease (CKD). The classical cardiovascular risk factors such as diabetes and hypertension undoubtedly play a role in the development of cardiovascular disease (CVD) in adult CKD patients; however, CVD is just as prominent in children with CKD who do not have these risk factors. Hence, the CKD-specific pathophysiology of CVD remains incompletely understood. In light of this, studying children with CKD presents a unique opportunity to analyze CKD-associated mechanisms of CVD more specifically and could help to unveil novel therapeutic targets.

Here, we comprehensively review the interaction of the human gut microbiome and the microbial metabolism of nutrients with host immunity and cardiovascular end-organ damage. The human gut microbiome is evolutionary conditioned and modified throughout life by endogenous factors as well as environmental factors. Chronic diseases, such as CKD, cause significant disruption to the composition and function of the gut microbiome and lead to disease-associated dysbiosis. This dysbiosis and the accompanying loss of biochemical homeostasis in the epithelial cells of the colon can be the result of poor diet (e.g., low-fiber intake), medications, and underlying disease. As a result of dysbiosis, bacteria promoting proteolytic fermentation increase and those for saccharolytic fermentation decrease and the integrity of the gut barrier is perturbed (leaky gut). These changes disrupt local metabolite homeostasis in the gut and decrease productions of the beneficial short-chain fatty acids (SCFAs). Moreover, the enhanced proteolytic fermentation generates unhealthy levels of microbially derived toxic metabolites, which further accumulate in the systemic circulation as a consequence of impaired kidney function. We describe possible mechanisms involved in the increased systemic inflammation in CKD that is associated with the combined effect of SCFA deficiency and accumulation of uremic toxins. In the future, a more comprehensive and mechanistic understanding of the gut–kidney–heart interaction, mediated largely by immune dysregulation and inflammation, might allow us to target the gut microbiome more specifically in order to attenuate CKD-associated comorbidities.

Chronic Kidney Disease, Gut Dysbiosis, and Constipation: A Burdensome Triplet

Gut dysbiosis has been implicated in the progression of chronic kidney disease (CKD). Alterations in the gut environment induced by uremic toxins, the dietary restriction of fiber-rich foods, and multiple drugs may be involved in CKD-related gut dysbiosis. CKD-related gut dysbiosis is considered to be characterized by the expansion of bacterial species producing precursors of harmful uremic toxins, such as indoxyl sulfate and p-cresyl sulfate, and the contraction of species generating beneficial short-chain fatty acids, such as butyrate. Gut-derived uremic toxins cause oxidative stress and pro-inflammatory responses, whereas butyrate exerts anti-inflammatory effects and contributes to gut epithelial integrity. Gut dysbiosis is associated with the disruption of the gut epithelial barrier, which leads to the translocation of endotoxins. Research on CKD-related gut dysbiosis has mainly focused on chronic inflammation and consequent cardiovascular and renal damage. The pathogenic relationship between CKD-related gut dysbiosis and constipation has not yet been investigated in detail. Constipation is highly prevalent in CKD and affects the quality of life of these patients. Under the pathophysiological state of gut dysbiosis, altered bacterial fermentation products may play a prominent role in intestinal dysmotility. In this review, we outline the factors contributing to constipation, such as the gut microbiota and bacterial fermentation; introduce recent findings on the pathogenic link between CKD-related gut dysbiosis and constipation; and discuss potential interventions. This pathogenic link needs to be elucidated in more detail and may contribute to the development of novel treatment options not only for constipation, but also cardiovascular disease in CKD.

Sarcopenia in chronic kidney disease: what have we learned so far?

The term sarcopenia was first introduced in 1988 by Irwin Rosenberg to define a condition of muscle loss that occurs in the elderly. Since then, a broader definition comprising not only loss of muscle mass, but also loss of muscle strength and low physical performance due to ageing or other conditions, was developed and published in consensus papers from geriatric societies. Sarcopenia was proposed to be diagnosed based on operational criteria using two components of muscle abnormalities, low muscle mass and low muscle function. This brought awareness of an important nutritional derangement with adverse outcomes for the overall health. In parallel, many studies in patients with chronic kidney disease (CKD) have shown that sarcopenia is a prevalent condition, mainly among patients with end stage kidney disease (ESKD) on hemodialysis (HD). In CKD, sarcopenia is not necessarily age-related as it occurs as a result of the accelerated protein catabolism from the disease and from the dialysis procedure per se combined with low energy and protein intakes. Observational studies showed that sarcopenia and especially low muscle strength is associated with worse clinical outcomes, including worse quality of life (QoL) and higher hospitalization and mortality rates. This review aims to discuss the differences in conceptual definition of sarcopenia in the elderly and in CKD, as well as to describe etiology of sarcopenia, prevalence, outcome, and interventions that attempted to reverse the loss of muscle mass, strength and mobility in CKD and ESKD patients.

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.

Plant-Based Diets, the Gut Microbiota, and Trimethylamine N-Oxide Production in Chronic Kidney Disease: Therapeutic Potential and Methodological Considerations

High circulating trimethylamine-N-oxide (TMAO) is associated with an increased risk of cardiovascular disease and mortality in people with chronic kidney disease (CKD). In individuals with CKD, reduced kidney function leads to decreased excretion of TMAO, which results in accumulation in the circulation. Higher circulating TMAO has been linked to higher intake of animal-based foods in omnivorous diets. Thus, plant-based diets have been suggested as an intervention to slow the progression of CKD and reduce cardiovascular risk, perhaps explained in part by reduced TMAO production. This article reviews the current evidence on plant-based diets as a dietary intervention to decrease gut-derived TMAO production in patients with CKD, while highlighting methodological issues that present challenges to advancing research and subsequent translation of this approach. Overall, we find that plant-based diets are promising for reducing gut-derived TMAO production in patients with CKD but that further interventional studies are warranted.

Intestinal microbiome and NAFLD: molecular insights and therapeutic perspectives

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of dysregulated lipid and glucose metabolism, which is often associated with obesity, dyslipidemia and insulin resistance. In view of the high morbidity and health risks of NAFLD, the lack of effective cure has drawn great attention. In recent years, a line of evidence has suggested a close linkage between the intestine and liver diseases such as NAFLD. We summarized the composition and characteristics of intestinal microbes and reviewed molecular insights into the intestinal microbiome in development and progression of NAFLD. Intestinal microbes mainly include bacteria, archaea, viruses and fungi, and the crosstalk between non-bacterial intestinal microbes and human liver diseases should be paid more attention. Intestinal microbiota imbalance may not only increase the intestinal permeability to gut microbes but also lead to liver exposure to harmful substances that promote hepatic lipogenesis and fibrosis. Furthermore, we focused on reviewing the latest "gut-liver axis"-targeting treatment, including the application of antibiotics, probiotics, prebiotics, synbiotics, farnesoid X receptor agonists, bile acid sequestrants, gut-derived hormones, adsorbents and fecal microbiota transplantation for NAFLD. In this review, we also discussed the potential mechanisms of "gut-liver axis" manipulation and efficacy of these therapeutic strategies for NAFLD treatment.

Artificial cell microcapsules containing live bacterial cells and activated charcoal for managing renal failure creatinine: preparation and in-vitro analysis

Activated charcoal was microencapsulated with Lactobacillus acidophilus 314 previously adapted for urea uptake. The creatinine removal capacity of this combination microcapsule was evaluated in-vitro in media simulating the small intestine. Results show that microcapsules containing both activated charcoal and L. acidophilus 314 demonstrated potential for decreasing creatinine. Interestingly, when co-encapsulating both activated charcoal and L. acidophilus 314 a smaller decrease in creatinine was observed than when encapsulating them separately. However, co-encapsulated microcapsules were more stable in various parts of the gastrointestinal system and survived longer in storage. These results suggest the feasibility of using microcapsules containing activated charcoal and probiotic bacteria as oral adjuvants for creatinine removal and provides a theoretical model for the use of these microcapsules to remove any unwanted metabolite.

Effect of uremic toxin-indoxyl sulfate on the skeletal system

Chronic kidney disease-mineral bone disorders (CKD-MBD) exhibit abnormalities in the circulating mineral levels, vitamin D metabolism, and parathyroid function that contribute to the formation of a bone lesion. The uremic toxin, indoxyl sulfate (IS), accumulates in the blood in cases of renal failure and leads to bone loss. The bone and renal responses to the action of the parathyroid hormone (PTH) are progressively decreased in CKD in spite of increasing PTH levels, a condition commonly called PTH resistance. There is a high prevalence of low bone turnover or adynamic bone disease in the early stages of CKD. This could be due to the inhibition of bone turnover, such as in PTH resistance, reduced active vitamin D levels, diabetes, aluminum, and, increased IS. With an increase in IS, there is a decrease in the osteoblast Wnt/b-catenin signaling and increase in the expression of Wnt signaling inhibitors, such as sclerostin and Dickkopf-1 (DKK1). Thus, a majority of early CKD patients exhibit deterioration of bone quality owing to the action of IS, this scenario could be termed uremic osteoporosis. However, this mechanism is complicated and not fully understood. With progressive deterioration in the renal function, IS accumulates along with persistent PTH secretion, potentially leading to high-turnover bone disease because high serum PTH levels have the ability of overriding peripheral PTH resistance and other inhibitory factors of bone formation. Finally, it leads to deterioration in bone quantity with prominent bone resorption in end stage renal disease. Uremic toxins adsorbents may decelerate oxidative stress and improve bone health in CKD patients. This review article focuses on IS and bone loss in CKD patients.

Plasma p-cresol lowering effect of sevelamer in non-dialysis CKD patients: evidence from a randomized controlled trial

BACKGROUND

The accumulation of p-cresol, a metabolic product of aromatic amino acids generated by intestinal microbiome, increases the cardiovascular risk in chronic kidney disease (CKD) patients. Therefore, therapeutic strategies to reduce plasma p-cresol levels are highly demanded. It has been reported that the phosphate binder sevelamer (SEV) sequesters p-cresol in vitro, while in vivo studies on dialysis patients showed controversial results. Aim of our study was to evaluate the effect of SEV on p-cresol levels in non-dialysis CKD patients.

METHODS

This was a single-blind, randomized placebo-controlled trial (Registration number NCT02199444) carried on 69 CKD patients (stage 3-5, not on dialysis), randomly assigned (1:1) to receive either SEV or placebo for 3 months. Total p-cresol serum levels were evaluated at baseline (T0), and 1 (T1) and 3 months (T3) after treatment start. The primary end-point was to evaluate the effect of SEV on p-cresol levels.

RESULTS

Compared to baseline (T0, 7.4 ± 2.7 mg/mL), p-cresol mean concentration was significantly reduced in SEV patients after one (- 2.06 mg/mL, 95% CI - 2.62 to - 1.50 mg/mL; p < 0.001) and 3 months of treatment (- 3.97 mg/mL, 95% CI - 4.53 to - 3.41 mg/mL; p < 0.001); no change of plasma p-cresol concentration was recorded in placebo-treated patients. Moreover, P and LDL values were reduced after 3 months of treatment by SEV but not placebo.

CONCLUSIONS

In conclusion, our study represents the first evidence that SEV is effective in reducing p-cresol levels in CKD patients in conservative treatment, and confirms its beneficial effects on inflammation and lipid pattern.

Microbiota-derived uremic retention solutes: perpetrators of altered nonrenal drug clearance in kidney disease

INTRODUCTION

Scientific interest in the gut microbiota is increasing due to improved understanding of its implications in human health and disease. In patients with kidney disease, gut microbiota-derived uremic toxins directly contribute to altered nonrenal drug clearance. Microbial imbalances, known as dysbiosis, potentially increase formation of microbiota-derived toxins, and diminished renal clearance leads to toxin accumulation. High concentrations of microbiota-derived toxins such as indoxyl sulfate and p-cresol sulfate perpetrate interactions with drug metabolizing enzymes and transporters, which provides a mechanistic link between increases in drug-related adverse events and dysbiosis in kidney disease. Areas covered: This review summarizes the effects of microbiota-derived uremic toxins on hepatic phase I and phase II drug metabolizing enzymes and drug transporters. Research articles that tested individual toxins were included. Therapeutic strategies to target microbial toxins are also discussed. Expert commentary: Large interindividual variability in toxin concentrations may explain some differences in nonrenal clearance of medications. Advances in human microbiome research provide unique opportunities to systematically evaluate the impact of individual and combined microbial toxins on drug metabolism and transport, and to explore microbiota-derived uremic toxins as potential therapeutic targets.

Disposition and clinical implications of protein-bound uremic toxins

In patients with chronic kidney disease (CKD), adequate renal clearance is compromised, resulting in the accumulation of a plethora of uremic solutes. These uremic retention solutes, also named uremic toxins, are a heterogeneous group of organic compounds with intrinsic biological activities, many of which are too large to be filtered and/or are protein bound. The renal excretion of protein-bound toxins depends largely on active tubular secretion, which shifts the binding and allows for active secretion of the free fraction. To facilitate this process, renal proximal tubule cells are equipped with a range of transporters that co-operate in basolateral uptake and luminal excretion. Many of these transporters have been characterized as mediators of drug disposition, but have recently been recognized for their importance in the proximal renal tubular transport of uremic toxins as well. This also indicates that during uremia, drug disposition may be severely affected as a result of drug–uremic toxin interaction. In addition, CKD patients receive various drugs to treat their complications potentially resulting in drug–drug interactions (DDIs), also for drugs that are non-renally excreted. This review discusses the current knowledge on formation, disposition and removal of protein-bound uremic toxins. Furthermore, implications associated with drug treatment in kidney failure, as well as innovative renal replacement therapies targetting the protein-bound uremic toxins are being discussed. It will become clear that the complex problems associated with uremia warrant a transdisciplinary approach that unites research experts in the area of fundamental biomedical research with their colleagues in clinical nephrology.

Effects of Uremic Toxins from the Gut Microbiota on Bone: A Brief Look at Chronic Kidney Disease

Patients with chronic kidney disease (CKD) frequently have mineral and bone disorders (CKD-MBD) that are caused by several mechanisms. Recent research has suggested that uremic toxins from the gut such as p-cresyl sulfate (PCS) and indoxyl sulfate (IS) could also be involved in the development of bone disease in patients with CKD. IS and PCS are produced by microbiota in the gut, carried into the plasma bound to serum albumin, and are normally excreted into the urine. However, in patients with CKD, there is an accumulation of high levels of these uremic toxins. The exact mechanisms of action of uremic toxins in bone disease remain unclear. The purpose of this brief review is to discuss the link between uremic toxins (IS and PCS) and bone mineral disease in chronic kidney disease.

Altered intestinal microbial flora and impaired epithelial barrier structure and function in CKD: the nature, mechanisms, consequences and potential treatment

Chronic kidney disease (CKD) results in systemic inflammation and oxidative stress which play a central role in CKD progression and its adverse consequences. Although many of the causes and consequences of oxidative stress and inflammation in CKD have been extensively explored, little attention had been paid to the intestine and its microbial flora as a potential source of these problems. Our recent studies have revealed significant disruption of the colonic, ileal, jejunal and gastric epithelial tight junction in different models of CKD in rats. Moreover, the disruption of the epithelial barrier structure and function found in uremic animals was replicated in cultured human colonocytes exposed to uremic human plasma in vitro We have further found significant changes in the composition and function of colonic bacterial flora in humans and animals with advanced CKD. Together, uremia-induced impairment of the intestinal epithelial barrier structure and function and changes in composition of the gut microbiome contribute to the systemic inflammation and uremic toxicity by accommodating the translocation of endotoxin, microbial fragments and other noxious luminal products in the circulation. In addition, colonic bacteria are the main source of several well-known pro-inflammatory uremic toxins such as indoxyl sulfate, p-cresol sulfate, trimethylamine-N-oxide and many as-yet unidentified retained compounds in end-stage renal disease patients. This review is intended to provide an overview of the effects of CKD on the gut microbiome and intestinal epithelial barrier structure and their role in the pathogenesis of systemic inflammation and uremic toxicity. In addition, potential interventions aimed at mitigating these abnormalities are briefly discussed.

In vivo kinetics of the uremic toxin p-cresyl sulfate in mice with variable renal function

Uremic toxins such as p-cresyl sulfate (PCS) are associated with increased mortality for chronic kidney disease (CKD) patients, but in vivo PCS toxicity studies are limited due to the lack of a standard animal model. To establish such a model, we measured the pharmacokinetics of PCS in mice with variable renal function. Male Balb/c mice subjected to 5/6 nephrectomy (CRF), unilateral nephrectomy (UNX), or no surgery (controls) were given PCS (po, 50 mg/kg). Blood samples were collected over time and plasma PCS concentrations were measured. Over 4 h, PCS was significantly higher in the plasma of CRF mice (63.28 ± 2.76 mg/L), compared to UNX mice (3.11 ± 0.64 mg/L) and controls (0.39 ± 0.12 mg/L). The PCS half-life was greatest in CRF mice (12.07 ± 0.12 h), compared to 0.79 ± 0.04 h in UNX mice and 0.48 ± 0.02 h in control mice. However, the potential presence of additional uremic toxins along with PCS in CRF mice and rapid PCS clearance in control mice suggest that the UNX mouse would be a better PCS model to study toxicity.

Alterations of intestinal barrier and microbiota in chronic kidney disease

Recent studies have highlighted the close relationship between the kidney and the gastrointestinal (GI) tract--frequently referred to as the kidney--gut axis--in patients with chronic kidney disease (CKD). In this regard, two important pathophysiological concepts have evolved: (i) production and accumulation of toxic end-products derived from increased bacterial fermentation of protein and other nitrogen-containing substances in the GI tract, (ii) translocation of endotoxins and live bacteria from gut lumen into the bloodstream, due to damage of the intestinal epithelial barrier and quantitative/qualitative alterations of the intestinal microbiota associated with the uraemic milieu. In both cases, these gut-centred alterations may have relevant systemic consequences in CKD patients, since they are able to trigger chronic inflammation, increase cardiovascular risk and worsen uraemic toxicity. The present review is thus focused on the kidney-gut axis in CKD, with special attention to the alterations of the intestinal barrier and the local microbiota (i.e. the collection of microorganisms living in a symbiotic coexistence with their host in the intestinal lumen) and their relationships to inflammation and uraemic toxicity in CKD. Moreover, we will summarize the most important clinical data suggesting the potential for nutritional modulation of gut-related inflammation and intestinal production of noxious by-products contributing to uraemic toxicity in CKD patients.

Uremic toxicity and sclerostin in chronic kidney disease patients

BACKGROUND AND AIMS

Sclerostin is a circulating inhibitor of the Wnt/β-catenin pathway and may have a role in chronic kidney disease (CKD)-mineral and bone disorder. Blood sclerostin levels are known to be elevated in patients undergoing maintenance dialysis. The aims of the present study were to evaluate sclerostin levels in patients at different CKD stages and study potential associations between sclerostin levels and (i) biochemical parameters that are disturbed in CKD, (ii) markers of vascular disease and (iii) mortality.

METHODS

One hundred and forty patients at CKD stages 2-5D were included in the present study. Routine clinical biochemistry tests and assays for sclerostin, protein-bound uremic toxins (indoxylsulphate [IS] and p-cresyl sulphate [PCS]) and the toxin β2 microglobulin (β2M) were performed. Aortic and coronary calcification and arterial stiffness were assessed by multislice spiral computed tomography and pulse wave velocity measurements. The enrolled patients were prospectively monitored for mortality.

RESULTS

Sclerostin levels were found to be elevated in CKD patients (especially those on hemodialysis). Furthermore, sclerostin levels were positively correlated with inflammation markers, phosphate, fibroblast growth factor 23, IS, PCS, β2M and arterial stiffness. A multivariate linear regression analysis indicated that sclerostin levels were independently associated with IS, PCS and β2M levels. Elevated serum sclerostin appeared to be associated with mortality (independently of age and inflammation). However, this association disappeared after adjustment for a propensity score including age, phosphate, interleukin-6, CKD stage and PCS.

CONCLUSION

Our results indicate that sclerostin levels are elevated in CKD patients and are associated with inflammation, vascular lesions, uremia and (potentially) mortality.

[Pleiotropic effects of sevelamer: a model of intestinal tract chelating agent]

The number of patients with chronic kidney disease (CKD) with its associated complications has increased dramatically worldwide in recent years. Therefore, many experimental and clinical studies have examined over the last decade the mechanisms involved, in order to explain the sharp increase in cardiovascular mortality. Hyperphosphatemia is a major problem in these patients especially at advanced stages of CKD, and it is associated with cardiovascular and mineral complications in these patients. Sevelamer is a phosphate binder that allows a better control of hyperphosphatemia, like other phosphate binder agents, but it has additional pleiotropic effects such as correcting certain abnormalities of lipid metabolism and clearance of several uremic toxins. These effects of sevelamer, restricted to the intestinal lumen, underline the importance of intestinal pathway in CKD and open the way to new therapeutic strategies for the management of the CKD and its complications.

Accumulated uremic toxins attenuate bone mechanical properties in rats with chronic kidney disease

The prevalence of hip fracture is very high among patients with chronic kidney disease (CKD); however, the reason for this is unclear. We examined the effects of accumulated uremic toxins on bone chemical composition and elastic mechanical properties. Rats underwent thyroparathyroidectomy and progressive partial nephrectomy (TPTx-Nx), and were administered with vehicle or AST-120 to reduce serum indoxyl sulfate (IS) levels. Bone mechanical properties, bone mineral density (BMD), cortical bone chemical composition, and histomorphometry were determined. Storage modulus was reduced in TPTx-Nx rats compared with rats that underwent TPTx alone. BMD and histomorphometric parameters did not differ between the groups. In terms of cortical bone chemical composition, the mineral/matrix ratio and carbonate substitution was increased, whereas crystallinity was decreased in TPTx-Nx rats. The enzymatic crosslink ratio and pentosidine:matrix ratio were increased in TPTx-Nx rats. AST-120 abolished the effects of TPTx-Nx and decreased the serum IS concentration. Stepwise multiple regression analysis revealed that the pentosidine:matrix and mineral:matrix ratios were independent contributors to the storage modulus. In conclusion, the accumulated uremic toxins, including IS, seem to play an important role in deteriorating bone mechanical properties by altering the chemical composition of bone. This mechanism may account for the increased prevalence of hip fracture among patients with CKD.

Plasma p-cresol lowering effect of sevelamer in peritoneal dialysis patients: evidence from a Cross-Sectional Observational Study

p-Cresol is a by-product of the metabolism of aromatic aminoacid operated by resident intestinal bacteria. In patients with chronic kidney disease, the accumulation of p-cresol and of its metabolite p-cresyl-sulphate causes endothelial dysfunction and ultimately increases the cardiovascular risk of these patients. Therapeutic strategies to reduce plasma p-cresol levels are highly demanded but not available yet. Because it has been reported that the phosphate binder sevelamer sequesters p-cresol in vitro we hypothesized that it could do so also in peritoneal dialysis patients. To explore this hypothesis we measured total cresol plasma concentrations in 57 patients with end-stage renal disease on peritoneal dialysis, 29 receiving sevelamer for the treatment of hyperphosphatemia and 28 patients not assuming this drug. Among the patients not assuming sevelamer, 16 were treated with lanthanum whereas the remaining 12 received no drug because they were not hyperphosphatemic. Patients receiving sevelamer had plasma p-cresol and serum high sensitivity C-reactive protein concentrations significantly lower than those receiving lanthanum or no drug. Conversely, no difference was observed among the different groups either in residual glomerular filtration rate, total weekly dialysis dose, total clearance, urine volume, protein catabolic rate, serum albumin or serum phosphate levels. Multiple linear regression analysis showed that none of these variables predicted plasma p-cresol concentrations that, instead, negatively correlated with the use of sevelamer. These results suggest that sevelamer could be an effective strategy to lower p-cresol circulating levels in peritoneal dialysis patients in which it could also favorably affect cardiovascular risk because of its anti-inflammatory effect.

Protein-bound uremic toxins…new targets to prevent insulin resistance and dysmetabolism in patients with chronic kidney disease

The retention of p-cresyl sulfate (PCS), the prototype of protein-bound uremic toxins that is produced by the gut microbiota and normally excreted by the kidney, may contribute to the development of insulin resistance in patients with chronic kidney disease. In a recent study, we demonstrated in mice, as in cultured muscle cells, that PCS interferes with intracellular insulin signaling pathways and triggers insulin resistance. The treatment of CKD mice with a prebiotic that reduces the intestinal production and decreases blood levels of PCS prevented insulin resistance and lipid abnormalities, suggesting new opportunities to prevent metabolic disturbances in patients with CKD. This study highlights the uremic toxins as new actors in metabolic alterations associated with CKD and allows for the consideration of new therapeutic approaches (e.g., prebiotics, probiotics, adsorbents) to better prevent them.

Oral activated charcoal adsorbent (AST-120) ameliorates chronic kidney disease-induced intestinal epithelial barrier disruption

BACKGROUND

Chronic kidney disease (CKD) impairs intestinal barrier function which by allowing influx of noxious products causes systemic inflammation. We have recently shown that intestinal barrier dysfunction in CKD is due to degradation of epithelial tight junction (TJ) which is, in part, mediated by influx of urea and its conversion to ammonia by microbial urease. We hypothesized that by adsorbing urea and urea-derived ammonia, oral activated charcoal (AST-120) may ameliorate CKD-induced intestinal epithelial barrier disruption and systemic inflammation.

METHODS

Rats were randomized to the CKD or control groups. The CKD group was fed a chow containing 0.7% adenine for 2 weeks. They were then randomized to receive a chow with or without AST-120 (4 g/kg/day) for 2 weeks. Rats consuming regular diet served as controls. Animals were then euthanized, colons were removed and processed for Western blot and immunohistology, and plasma was used to measure endotoxin and oxidative and inflammatory markers.

RESULTS

Compared with the controls, the untreated CKD rats showed elevated plasma endotoxin, IL-6, TNF-α, MCP-1, CINC-3, L-selectin, ICAM-1, and malondialdehyde, and depletions of colonic epithelial TJ proteins, claudin-1, occludin, and ZO1. Administration of AST-120 resulted in partial restoration of the epithelial TJ proteins and reduction in plasma endotoxin and markers of oxidative stress and inflammation.

CONCLUSIONS

CKD animals exhibited depletion of the key protein constituents of the colonic epithelial TJ which was associated with systemic inflammation, oxidative stress and endotoxemia. Administration of AST-120 attenuated uremia-induced disruption of colonic epithelial TJ and the associated endotoxemia, oxidative stress and inflammation.

Emerging effects of sevelamer in chronic kidney disease

Sevelamer, a non-absorbable anion exchange resin, is used to control hyperphosphatemia in chronic kidney disease (CKD) by binding to dietary phosphate in the gastrointestinal tract. Lipid-lowering effect is a widely recognized pleiotropic effect of sevelamer. In addition, many studies have reported that sevelamer leads to reduced vascular calcification compared with calcium-containing phosphate binders, which is attributed to the improved lipid profiles and decreased calcium load. In addition, recent studies have suggested novel pleiotropic effects on bone structure, inflammation, oxidative stress, anemia, fetuin-A, and trace element metabolism in CKD patients. All of these effects have the potential to suppress the development/progression of cardiovascular lesions and reduce mortality. This review summarizes novel findings from recent studies and discusses the potential pleiotropic effects of sevelamer on non-traditional cardiovascular risk factors in CKD patients.

A metabolomic approach to clarifying the effect of AST-120 on 5/6 nephrectomized rats by capillary electrophoresis with mass spectrometry (CE-MS)

The oral adsorbent AST-120 is composed of spherical carbon particles and has an adsorption ability for certain small-molecular-weight compounds that accumulate in patients with chronic kidney disease (CKD). So far, very few compounds are known to be adsorbed by AST-120 in vivo. To examine the effect of AST-120 in vivo, we comprehensively evaluated the plasma concentrations of 146 compounds (61 anions and 85 cations) in CKD model rats, with or without four weeks of treatment with AST-120. By capillary electrophoresis with mass spectrometry, we identified 6 anions and 17 cations that were significantly decreased by AST-120 treatment. In contrast, we also identified 2 cations that were significantly increased by AST-120. Among them, 4 anions, apart from indoxyl sulfate and hippurate, and 19 cations were newly identified in this study. The plasma levels of N-acetyl-neuraminate, 4-pyridoxate, 4-oxopentanoate, glycine, γ-guanidinobutyrate, N-γ-ethylglutamine, allantoin, cytosine, 5-methylcytosine and imidazole-4-acetate were significantly increased in the CKD model compared with the sham-operated group, and were significantly decreased by AST-120 treatment. Therefore, these 10 compounds could be added as uremic compounds that indicate the effect of AST-120 treatment. This study provides useful information not only for identifying the indicators of AST-120, but also for clarifying changes in the metabolic profile by AST-120 treatment in the clinical setting.

Role of uremic toxins and oxidative stress in the development of chronic kidney disease-mineral and bone disorder

The kidney plays an important role in the regulation of mineral metabolism. As kidney function declines, there is a progressive deterioration in mineral homeostasis, along with various abnormalities, including bone disease and vascular calcification, which has recently been named as "Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD)." Although the precise mechanisms of this systemic disorder remain to be elucidated, accumulating evidence suggest that uremic toxins contribute substantially to the development of CKD-MBD, partly through evoking oxidative stress in the bone and cardiovascular systems. This brief review summarizes recent work on the role of uremic toxins and oxidative stress in the development of CKD-MBD.

The uremic toxin indoxyl sulfate reflects cardio-renal risk and intestinal-renal relationship

Uremic syndrome and condition is primarily a result of kidney failure in which uremic toxins are accumulated. More and more attention is paid to possibilities for removal of uremic toxins, which not only means dialysis, but also takes into account special dietary considerations and treatments, which aim to absorb the toxins or reduce their production. These uremic toxins, which also increase the cardiovascular risks, play a major part in morbidity and mortality of patients suffering from chronic renal failure and those receiving renal replacement therapy. One of them is a member of the indol group, the indoxyl sulfate. This toxin is difficult to remove with dialysis and is an endogenous protein-bound uremic toxin. Today we know that indoxyl sulfate is a vascular-nephrotoxic agent, which is able to enhance progression of cardiovascular and renal diseases. It is of particular importance that because of its redox potency, this toxin causes oxidative stress and antioxidant effects at the same time and, on top of that, it is formed in the intestinal system. Its serum concentration depends on the nutrition and the tubular function and, therefore, it can also signal the progression of chronic renal failure independently of glomerular filtration rate. Successful removal of indoxyl sulfate reduces the morbidity and mortality and improves survival. Therefore, it could be a possible target or area to facilitate the reduction of uremia in chronic renal failure. The use of probiotics and prebiotics with oral adsorbents may prove to be a promising opportunity to reduce indoxyl sulfate accumulation. Orv. Hetil., 2011, 152, 1724–1730.

Renovascular protective effects of erythropoietin in patients with chronic kidney disease

BACKGROUND/AIMS

Erythropoietin (EPO) has been widely used for the treatment of anemia in chronic kidney disease (CKD). A growing body of evidence indicates that the therapeutic benefits of EPO could extend beyond the improvement of anemia. The aim of the present study was to determine whether EPO affects renovascular and oxidative stress biomarkers in pre-dialysis CKD patients with anemia.

METHODS

The study was a single-arm prospective study. Fifteen CKD patients (9 males and 6 females, mean age 63 years) with anemia (mean Hb: 8.1 g/dL) were treated with recombinant human EPO; 12,000 U administered subcutaneously once every 2 weeks. Various parameters were measured before and 6 months after treatment. These included serum hemoglobin (Hb), creatinine, estimated glomerular filtration rate (eGFR), proteinuria, urinary liver-type fatty acid binding protein (L-FABP--a biomarker of renal injury), urinary 8-hydroxydeoxyguanosine (8-OHdG--a marker of oxidative stress), serum asymmetrical dimethylarginine (ADMA), carotid artery intima-media thickness (IMT) and brachial-ankle pulse wave velocity (baPWV) as vascular markers and plasma brain natriuretic peptide (BNP) levels and left ventricular ejection fraction (LVEF) as cardiac function markers and cardio-thoracic ratio (CTR) and inferior vena cava dimension (IVCS) as extra fluid retention markers.

RESULTS

After 6 months, serum Hb was significantly increased (p<0.001) and urinary levels of protein, L-FABP and 8-OHdG, carotid IMT, baPWV, plasma BNP and serum ADMA levels were significantly decreased (p<0.001). Serum creatinine, eGFR, LVEF, CTR and IVCS showed little difference throughout the experimental period.

CONCLUSION

These data suggest that recombinant human EPO may ameliorate renal injury, oxidative stress and progression of atherosclerosis in addition to improving anemia in CKD patients.

Developmental and regional patterns of GAP-43 immunoreactivity in a metamorphosing brain

Growth-associated protein-43 is typically expressed at high levels in the nervous system during development. In adult animals, its expression is lower, but still observable in brain areas showing structural or functional plasticity. We examined patterns of GAP-43 immunoreactivity in the brain of the bullfrog, an animal whose nervous system undergoes considerable reorganization across metamorphic development and retains a strong capacity for plasticity in adulthood. Immunolabeling was mostly diffuse in hatchling tadpoles, but became progressively more discrete as larval development proceeded. In many brain areas, intensity of immunolabel peaked at metamorphic climax, the time of final transition from aquatic to semi-terrestrial life. Changes in intensity of GAP-43 expression in the medial vestibular nucleus, superior olivary nucleus, and torus semicircularis appeared correlated with stage-dependent functional changes in processing auditory stimuli. Immunolabeling in the Purkinje cell layer of the cerebellum and in the cerebellar nucleus was detectable at most developmental time points. Heavy immunolabel was present from early larval stages through the end of climax in the thalamus (ventromedial, anterior, posterior, central nuclei). Immunolabel in the tadpole telencephalon was observed around the lateral ventricles, and in the medial septum and ventral striatum. In postmetamorphic animals, immunoreactivity was confined mainly to the ventricular zones and immediately adjacent cell layers. GAP-43 expression was present in olfactory, auditory and optic cranial nerves throughout larval and postmetamorphic life. The continued expression of GAP-43 in brain nuclei and in cranial nerves throughout development and into adulthood reflects the high regenerative potential of the bullfrog's central nervous system.