Oral sorbent suppresses accumulation of albumin-bound indoxyl sulphate in serum of haemodialysis patients

Gut microbial signatures associated with uremic pruritus in hemodialysis patients

BACKGROUND

The gut microbiota influences the gut-skin-kidney axis, but its role in uremic pruritus remains poorly understood. This study aimed to explore differences in gut microbial profiles between hemodialysis (HD) patients with and without uremic pruritus and identify potential microbial signatures associated with uremic pruritus.

METHODS

We conducted a cross-sectional study of HD patients with and without uremic pruritus. Stool samples were collected from all participants, and the gut microbiota composition was analyzed using 16S rRNA gene sequencing. Alpha and beta diversity metrics were calculated to assess microbial diversity. LEfSe analysis was performed to identify differentially abundant taxa associated with uremic pruritus.

RESULTS

Among 93 HD patients (mean age: 61.9 years, 31.2 % female), uremic pruritus occurred in 61.3 % of patients, with a median visual analog scale (VAS) score of 4.0. While alpha diversity did not differ significantly between groups, beta diversity analysis revealed significant compositional differences (unweighted UniFrac metric, P = 0.004; weighted UniFrac metric, P < 0.001). LEfSe analysis revealed significant enrichment of the order Pasteurellales, family Pasteurellaceae and genus Dialister in patients with uremic pruritus, whereas the order Corynebacteriales was more abundant in patients without pruritus (P < 0.05, LDA score > 3).

CONCLUSION

In this study, we found significant differences in gut microbiota composition between HD patients with and without uremic pruritus and identified potential microbial biomarkers for uremic pruritus. Further studies are needed to elucidate the underlying mechanisms and explore microbiota-targeted therapeutic interventions.

Gut Dysbiosis and Its Role in the Anemia of Chronic Kidney Disease

The gut dysbiosis present in chronic kidney disease (CKD) has been associated with anemia. Factors such as the accumulation of gut-derived uremic toxins, increased gut barrier permeability-induced inflammation, and a reduced intestinal production of short-chain fatty acids (SCFAs), all associated with changes in the intestinal microbiota composition in CKD, may lead to the development or worsening of anemia in renal patients. Understanding and addressing these mechanisms related to gut dysbiosis in CKD patients can help to delay the development of anemia and improve its control in this population. One approach is to avoid or reduce the use of drugs linked to gut dysbiosis in CKD, such as phosphate binders, oral iron supplementation, antibiotics, and others, unless they are indispensable. Another approach involves introducing dietary changes that promote a healthier microbiota and/or using prebiotics, probiotics, or symbiotics to improve gut dysbiosis in this setting. These measures can increase the presence of SCFA-producing saccharolytic bacteria and reduce proteolytic bacteria, thereby lowering the production of gut-derived uremic toxins and inflammation. By ameliorating CKD-related gut dysbiosis, these strategies can also improve the control of renal anemia and enhance the response to erythropoiesis-stimulating agents (ESAs) in ESA-resistant patients. In this review, we have explored the relationship between gut dysbiosis in CKD and renal anemia and propose feasible solutions, both those already known and potential future treatments.

Increased Prorenin Expression in the Kidneys May Be Involved in the Abnormal Renal Function Caused by Prolonged Environmental Exposure to Microcystin-LR

Toxic algae in eutrophic lakes produce cyanotoxic microcystins. Prior research on the effect of microcystin-LR in the kidney utilized intraperitoneal injections, which did not reflect natural exposure. Oral microcystin-LR research has focused on renal function and histopathology without examining the molecular mechanisms. The present study aimed to evaluate the mechanism of microcystin-LR in the kidneys via oral administration in WKAH/HkmSlc rats over 7 weeks, alongside stimulation of the proximal tubular cells. Although there were no differences in the concentrations of plasma albumin, blood urea nitrogen, and creatinine, which are parameters of renal function, between the control and microcystin-LR-administrated rats, prorenin expression was significantly increased in the renal cortex of the rats administered microcystin-LR and the microcystin-LR-treated proximal tubular cells. The expression levels of (pro)renin receptor (PRR), transforming growth factor-β1 (TGFβ1), and α-smooth muscle actin (α-SMA) in the renal cortex did not differ significantly between the control and microcystin-LR-administered rats. However, the expression levels of prorenin were significantly positively correlated with those of PRR, TGFβ1, and α-SMA in the renal cortex of rats administered microcystin-LR. Additionally, a significant positive correlation was observed between the expression levels of TGFβ1 and α-SMA. Collectively, increased prorenin expression caused by the long-term consumption of microcystin-LR may initiate a process that influences renal fibrosis and abnormal renal function by regulating the expression levels of PRR, TGFβ1, and α-SMA.

AST-120 improved uremic pruritus by lowering indoxyl sulfate and inflammatory cytokines in hemodialysis patients

BACKGROUND AND HYPOTHESIS

Pruritus is a common and distressing symptom that affects patients with chronic kidney disease. The concentration of protein bounded uremic toxin was associated with the uremic pruritus. The aim is to assess the efficacy of AST-120 for uremic pruritus in hemodialysis patients.

MATERIALS AND METHODS

The participants were enrolled and then divided into the AST-120 treatment group and control group with a ratio of 2:1. All participants underwent pre-observation screenings two weeks before the study with three visits. In the treatment phase (week 1 to week 4), the treatment group added 6g/day of AST-120 along with routine anti-pruritic treatment. Visual analog scale (VAS) and biochemical parameters were measured.

RESULTS

The VAS score began to be lower in the AST-120 treatment group after the 5th visiting (p < 0.05). The reduction in indoxyl sulfate (IS) at 5th week along with TNF-alpha. The reduction ratio of indoxyl sulfate correlated with reduction of parathyroid hormone.

CONCLUSION

This study has demonstrated that the four-week treatment of AST-120 decreased the severity of uremic pruritus in patients with ESRD. The concentration of IS and TNF-alpha decreased in the AST-120 treatment group. The reduction of iPTH correlated with the reduction of IS in the AST-120 treatment.

Derivation and elimination of uremic toxins from kidney-gut axis

Uremic toxins are chemicals, organic or inorganic, that accumulate in the body fluids of individuals with acute or chronic kidney disease and impaired renal function. More than 130 uremic solutions are included in the most comprehensive reviews to date by the European Uremic Toxins Work Group, and novel investigations are ongoing to increase this number. Although approaches to remove uremic toxins have emerged, recalcitrant toxins that injure the human body remain a difficult problem. Herein, we review the derivation and elimination of uremic toxins, outline kidney-gut axis function and relative toxin removal methods, and elucidate promising approaches to effectively remove toxins.

The Potential Influence of Uremic Toxins on the Homeostasis of Bones and Muscles in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) often experience a high accumulation of protein-bound uremic toxins (PBUTs), specifically indoxyl sulfate (IS) and p-cresyl sulfate (pCS). In the early stages of CKD, the buildup of PBUTs inhibits bone and muscle function. As CKD progresses, elevated PBUT levels further hinder bone turnover and exacerbate muscle wasting. In the late stage of CKD, hyperparathyroidism worsens PBUT-induced muscle damage but can improve low bone turnover. PBUTs play a significant role in reducing both the quantity and quality of bone by affecting osteoblast and osteoclast lineage. IS, in particular, interferes with osteoblastogenesis by activating aryl hydrocarbon receptor (AhR) signaling, which reduces the expression of Runx2 and impedes osteoblast differentiation. High PBUT levels can also reduce calcitriol production, increase the expression of Wnt antagonists (SOST, DKK1), and decrease klotho expression, all of which contribute to low bone turnover disorders. Furthermore, PBUT accumulation leads to continuous muscle protein breakdown through the excessive production of reactive oxygen species (ROS) and inflammatory cytokines. Interactions between muscles and bones, mediated by various factors released from individual tissues, play a crucial role in the mutual modulation of bone and muscle in CKD. Exercise and nutritional therapy have the potential to yield favorable outcomes. Understanding the underlying mechanisms of bone and muscle loss in CKD can aid in developing new therapies for musculoskeletal diseases, particularly those related to bone loss and muscle wasting.

Attenuation of indoxyl sulfate-induced cell damage by cinchonidine-a Cinchona alkaloid-through the downregulation of p53 signaling pathway by promoting MDM2 cytoplasmic-nuclear shuttling in endothelial cells

Renocardiac syndromes are a critical concern among patients with chronic kidney disease (CKD). High level of indoxyl sulfate (IS), a protein-bound uremic toxin, in plasma is known to promote the pathogenesis of cardiovascular diseases by impairing endothelial function. However, the therapeutic effects of the adsorbent of indole, a precursor of IS, on renocardiac syndromes is still debated. Therefore, novel therapeutic approaches should be developed to treat IS-associated endothelial dysfunction. In the present study, we have found that cinchonidine, a major Cinchona alkaloid, exhibited superior cell-protective effects among the 131 test compounds in IS-stimulated human umbilical vein endothelial cells (HUVECs). IS-induced cell death, cellular senescence, and impairment of tube formation in HUVECs were substantially reversed after treatment with cinchonidine. Despite the cinchonidine did not alter reactive oxygen species formation, cellular uptake of IS and OAT3 activity, RNA-Seq analysis showed that the cinchonidine treatment downregulated p53-modulated gene expression and substantially reversed IS-caused G0/G1 cell cycle arrest. Although the mRNA levels of p53 were not considerably downregulated by cinchonidine in IS-treated HUVECs, the treatment of cinchonidine promoted the degradation of p53 and the cytoplasmic-nuclear shuttling of MDM2. Cinchonidine exhibited cell-protective effects against the IS-induced cell death, cellular senescence, and impairment of vasculogenic activity in HUVECs through the downregulation of p53 signaling pathway. Collectively, cinchonidine may be a potential cell-protective agent to rescue IS-induced endothelial cell damage.

Serum Level of Protein-Bound Uraemic Toxins in Haemodialysis Patients with Chronic Kidney Disease-Associated Pruritus: Myths and Facts

Recent studies place great importance on Protein-Bound Uraemic Toxins (PBUT) in the context of etiopathogenesis of chronic kidney disease-associated pruritus (CKD-aP). This study aimed to investigate the possible contribution of free and total Indoxyl Sulfate (IS) and p-Cresol Sulfate (PCS) to the cause of CKD-aP. Group A included 64 patients on maintenance haemodialysis (HD) with CKD-aP. Group B included 62 patients on maintenance HD that did not report CKD-aP, and group C included 50 healthy controls. Pruritus severity was assessed using a Numerical Rating Scale (NRS). Moreover, other tools like UP-Dial, ItchyQoL, and the 4-Item Itch Questionnaire evaluating CKD-aP were completed by the patients. The serum levels of free and total IS and PCS concentrations were measured using the Ultra Performance Liquid Chromatography System. No significant difference in the serum level of free and total IS, or PCS, was observed between the patients who reported CKD-aP and those without pruritus. Moreover, there was no correlation between serum IS or PCS levels and the severity of the itch. Our study does not support earlier findings about higher levels of IS and PCS in patients reporting CKD-aP. Further studies will be needed to investigate these discrepancies as well as to understand the cause of CKD-aP.

Uremic pruritus: pathophysiology, clinical presentation, and treatments

Uremic pruritus is one of the most common and bothersome symptoms in patients with end-stage renal disease. Most patients with uremic pruritus experience a prolonged and relapsing course and significant impairments of quality of life. The pathophysiology of uremic pruritus is not completely understood. A complex interplay among cutaneous biology and the nervous and immune systems has been implicated, with the involvement of various inflammatory mediators, neurotransmitters, and opioids. Uremic pruritus treatment outcomes are often unsatisfactory. Clinical trials have mostly been small in scale and have reported inconsistent results. Recent evidence shows that gabapentinoids, nalfurafine, and difelikefalin are effective for relieving uremic pruritus in hemodialysis patients. This review provides an overview of the epidemiology and proposed mechanisms of uremic pruritus, then highlights the manifestations of and clinical approach to uremic pruritus. Current evidence regarding treatment options, including topical treatments, treatment of underlying disease, phototherapy, and systemic treatments, is also outlined. With a better understanding of uremic pruritus, more therapeutic options can be expected in the near future.

Modulating brain function with microbiota

Microbial metabolites identified in animal models and human neurological diseases could be therapeutic targets.

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.

AST-120 Treatment Alters the Gut Microbiota Composition and Suppresses Hepatic Triglyceride Levels in Obese Mice

Background: The prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing worldwide. The existence of a relationship between the microbiota and the pathology of hepatic steatosis is also becoming increasingly clear. AST-120, an oral spherical carbon adsorbent, has been shown to be useful for delaying dialysis initiation and improving uremic symptoms in patients with chronic kidney disease. However, little is known about the effect of AST-120 on fatty liver.Methods: AST-120 (5% w/w) was administrated to 6-week-old male db/db mice for 8 weeks. The body weight, blood glucose and food consumption were examined. Hepatic triglyceride (TG) levels, lipid droplets and epididymal fat cell size were measured. The gut microbiota compositions were investigated in feces and cecum.Results: Significant decreases of the hepatic weight and hepatic TG levels were observed in the AST-120-treated db/db mice. Furthermore, AST-120 treatment was also associated with a decrease of Bacteroidetes, increase of Firmicutes, and a reduced ratio of Bacteroidetes to Firmicutes (B/F ratio) in the feces in the db/db mice. The B/F ratio in the feces was correlated with the liver weight and area of the liver occupied by lipid droplets in the db/db mice.Conclusions: These data suggest that AST-120 treatment alters the composition of the fecal microbiota and suppresses hepatic TG levels in the db/db mice.

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

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

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

Intestinal microbiota and kidney diseases

Large microbial communities reside in the gut as an endogenous organ and interact with the host physiology through symbiotic relationships, affecting health. Recent advances in high-throughput sequencing techniques have made it possible to better understand these complex microbial communities and their effects on hosts. Animal and clinical studies have provided considerable evidence to show that the microbiota plays an important role in chronic kidney disease, acute kidney injury, nephrolithiasis, and kidney transplantation by altering the functions of the intestinal barrier, regulating local and systemic inflammation, controlling production of metabolic components, and affecting immune responses. Although the exact mechanism underlying the microbial shift and its impact on disease progression remains uncertain, the kidney-gut interaction clearly plays a significant role in onset and progression of kidney disease and, therefore, holds promise as a therapeutic target. Here, we review recent literature pertaining to the bidirectional relationship between microbes and humans in various kidney diseases and discuss the future direction of microbial research in nephrology.

Pharmacological Actions of Indoxyl Sulfate and AST-120 That Should Be Recognized for the Strategic Treatment of Patients with Chronic Kidney Disease

Although there are many uremic substances in the body, the most studied and well-known molecule that predominantly binds to plasma proteins is indoxyl sulfate (IS). Many research groups have reported IS to have toxic effects on the kidney and cardiovascular system. It is difficult to remove IS with regular hemodialysis or hemodiafiltration. On the other hand, AST-120 has the capacity to bind to indole, which is a precursor of IS in the intestinal tract and excrete it in feces. IS production in the liver is efficiently suppressed by AST-120 administration. However, large-scale clinical studies have not shown that AST-120 suppresses hard endpoints such as doubling serum creatinine, end-stage renal disease, and death. In patients with accelerated chronic kidney disease (CKD) progression, AST-120 is expected to suppress those hard renal endpoints, but only when compliance to treatment is high. It is necessary to validate the renal protective effect of AST-120, as expected from the basic study on IS, including more patients with slowly progressive CKD in a large-scale clinical study in the future.

Uremic Toxins Affect Erythropoiesis during the Course of Chronic Kidney Disease: A Review

Chronic kidney disease (CKD) is a global health problem characterized by progressive kidney failure due to uremic toxicity and the complications that arise from it. Anemia consecutive to CKD is one of its most common complications affecting nearly all patients with end-stage renal disease. Anemia is a potential cause of cardiovascular disease, faster deterioration of renal failure and mortality. Erythropoietin (produced by the kidney) and iron (provided from recycled senescent red cells) deficiencies are the main reasons that contribute to CKD-associated anemia. Indeed, accumulation of uremic toxins in blood impairs erythropoietin synthesis, compromising the growth and differentiation of red blood cells in the bone marrow, leading to a subsequent impairment of erythropoiesis. In this review, we mainly focus on the most representative uremic toxins and their effects on the molecular mechanisms underlying anemia of CKD that have been studied so far. Understanding molecular mechanisms leading to anemia due to uremic toxins could lead to the development of new treatments that will specifically target the pathophysiologic processes of anemia consecutive to CKD, such as the newly marketed erythropoiesis-stimulating agents.

New oral spherical carbon adsorbent effectively reduces serum indoxyl sulfate levels in moderate to advanced chronic kidney disease patients: a multicenter, prospective, open-label study

BACKGROUND

Elevated levels of serum indoxyl sulfate (IS) have been linked to cardiovascular complications in patients with chronic kidney disease (CKD). Oral sorbent therapy using spherical carbons selectively attenuates IS accumulation in CKD patients. This study aimed to investigate whether oral administration of a new oral spherical carbon adsorbent (OSCA), reduces serum IS levels in moderate to severe CKD patients.

METHODS

This prospective, multicenter, open-label study enrolled patients with CKD stages 3-5. Patients were prescribed OSCA for 8 weeks (6 g daily in 3 doses) in addition to standard management. Serum IS levels were measured at baseline and 4 and 8 weeks of treatment with OSCA.

RESULTS

A total of 118 patients were enrolled and 87 eligible patients completed 8 weeks of study. The mean age of the study subjects was 62.8 ± 13.7 years, and 80.5% were male. Baseline levels of serum IS were negatively correlated with estimated glomerular filtration rate (eGFR) (r = - 0.406, P < 0.001) and increased with increasing CKD stages (stage 3, 0.21 ± 0.21 mg/dL; stage 4, 0.54 ± 0.52 mg/dL; stage 5, 1.15 ± 054 mg/dL; P for trend = 0.001). The patients showed significant reduction in serum total IS levels as early as 4 weeks after OSCA treatment (22.5 ± 13.9% reduction from baseline, P < 0.001) and up to 8 weeks (31.9 ± 33.7% reduction from baseline, P < 0.001). This reduction effect was noted regardless of age, kidney function, or diabetes. No severe adverse effects were reported. Gastrointestinal symptoms were the most commonly reported adverse effects. In total, 21 patients withdrew from the study, with dyspepsia due to heavy pill burden as the most common reason. The medication compliance rate was 84.7 ± 21.2% (min 9%, max 101%) for 8 weeks among those who completed the study.

CONCLUSIONS

OSCA effectively reduced serum IS levels in moderate to severe CKD patients. Gastrointestinal symptoms were the most commonly reported complications, but no treatment-related severe adverse effects were reported.

TRIAL REGISTRATION

Clinical Research Information Service ( KCT0001875 . 14 December 2015.).

Effects of the oral adsorbent AST-120 on fecal p-cresol and indole levels and on the gut microbiota composition

In chronic kidney disease, elevated levels of circulating uremic toxins are associated with a variety of symptoms and organ dysfunction. Indoxyl sulfate (IS) and p-cresyl sulfate (pCS) are microbiota-derived metabolites and representative uremic toxins. We have previously shown that the oral adsorbent AST-120 profoundly reduced pCS compared to IS in adenine-induced renal failure in mice. However, the mechanisms of the different attenuation effects of AST-120 between IS and pCS are unclear. To clarify the difference of AST-120 on IS and pCS, we investigated the levels of fecal indole and p-cresol, the respective precursors of IS and pCS, and examined the influence on the gut microbiota. Although fecal indole was detected in all groups analyzed, fecal p-cresol was not detected in AST-120 treatment groups. In genus level, a total of 23 organisms were significantly changed by renal failure or AST-120 treatment. Especially, AST-120 reduced the abundance of Erysipelotrichaceae uncultured and Clostridium sensu stricto 1, which have a gene involved in p-cresol production. Our findings suggest that, in addition to the adsorption of the uremic toxin precursors, AST-120 affects the abundance of some gut microbiota in normal and renal failure conditions, thereby explaining the different attenuation effects on IS and pCS.

Obesity and Cage Environment Modulate Metabolism in the Zucker Rat: A Multiple Biological Matrix Approach to Characterizing Metabolic Phenomena

Obesity and its comorbidities are increasing worldwide imposing a heavy socioeconomic burden. The effects of obesity on the metabolic profiles of tissues (liver, kidney, pancreas), urine, and the systemic circulation were investigated in the Zucker rat model using ¹H NMR spectroscopy coupled to multivariate statistical analysis. The metabolic profiles of the obese ( fa/ fa) animals were clearly differentiated from the two phenotypically lean phenotypes, ((+/+) and ( fa/+)) within each biological compartment studied, and across all matrices combined. No significant differences were observed between the metabolic profiles of the genotypically distinct lean strains. Obese Zucker rats were characterized by higher relative concentrations of blood lipid species, cross-compartmental amino acids (particularly BCAAs), urinary and liver metabolites relating to the TCA cycle and glucose metabolism; and lower amounts of urinary gut microbial-host cometabolites, and intermatrix metabolites associated with creatine metabolism. Further to this, the obese Zucker rat metabotype was defined by significant metabolic alterations relating to disruptions in the metabolism of choline across all compartments analyzed. The cage environment was found to have a significant effect on urinary metabolites related to gut-microbial metabolism, with additional cage-microenvironment trends also observed in liver, kidney, and pancreas. This study emphasizes the value in metabotyping multiple biological matrices simultaneously to gain a better understanding of systemic perturbations in metabolism, and also underscores the need for control or evaluation of cage environment when designing and interpreting data from metabonomic studies in animal models.

Measuring serum total and free indoxyl sulfate and p-cresyl sulfate in chronic kidney disease using UPLC-MS/MS

Chronic kidney disease (CKD) is a complex disorder that affects multiple organs and increases the risk of cardiovascular complications. CKD affects approximately 12% of the population in Taiwan. Loss of kidney function leads to accumulation of potentially toxic compounds such as indoxyl sulfate (IS) and p-cresyl sulfate (pCS), two protein-bound uremic solutes that can stimulate the progression of CKD. The aim of this study was to assess whether IS and pCS levels were correlated with CKD stage. We developed and validated a method for quantitating total and free IS and pCS in serum by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Serum samples were pretreated using protein precipitation with acetonitrile containing stable isotope-labeled IS and pCS as internal standards. After centrifugation, the supernatant was diluted and injected into a UPLC-MS/MS system. Analyte concentrations were calculated from the calibration curve and ion ratios between the analyte and the internal standard. The calibration curves were linear with a correlation coefficient of >0.999; the analytical measurement range was 0.05–5 mg/L. The limit of quantitation of this assay was 0.05 mg/L for both analytes. The reference interval was ≤0.05–1.15 mg/L for total-form IS, ≤0.05 −5.33 mg/L for total-form pCS, ≤0.05 mg/L for free-form IS, and ≤0.12 mg/L for free-form pCS. A positive correlation was observed between analyte concentration and CKD stage. Our sensitive UPLC-MS/MS method for quantifying total and free-form IS and pCS in serum can be used to monitor the progression of CKD in clinical settings, identify patients at risk, and facilitate development of further therapies for this devastating disease.

Non-mercaptalbumin, Oxidized Form of Serum Albumin, Significantly Associated with Renal Function and Anemia in Chronic Kidney Disease Patients

Oxidative stress plays a major role in development of cardiovascular disease in patients with chronic kidney disease (CKD). Human mercaptalbumin (HMA), a reduced form of serum albumin, and non-mercaptalbumin (HNA), an oxidized form of serum albumin, are known as indicators for evaluating oxidative stress in systemic circulation, including end-stage renal disease cases. We investigated factors associated with fraction of HNA [f(HNA)] in 112 pre-dialysis CKD patients (63.6 ± 14.0 years old; 59 males, 53 females) using a newly established anion-exchange column packed with hydrophilic polyvinyl alcohol gel as well as high performance liquid chromatography. Mean f(HNA) in our CKD patients was 30.0 ± 6.1%, higher than that previously reported for healthy subjects. In multiple regression analysis, age (β = 0.200, p = 0.014), eGFR (β = −0.238, p = 0.009), hemoglobin (β = −0.346, p < 0.001), and ferritin (β = 0.200, p = 0.019) were significantly and independently associated with f(HNA) (R² = 0.356, p < 0.001). In addition, factors related to CKD-mineral and bone disorder (CKD-MBD), including intact-PTH (β = 0.218, p = 0.049) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) (β = −0.178, p = 0.040), were significantly and independently associated with serum f(HNA) (R² = 0.339, p < 0.001), whereas fibroblast growth factor-23 was not. These findings indicate the importance of management of hemoglobin and ferritin levels, as well as appropriate control of CKD-MBD factors for a better redox state of serum albumin in CKD patients.

Oral adsorbent AST-120 ameliorates gut environment and protects against the progression of renal impairment in CKD rats

Background

Oral charcoal adsorbent AST-120 (AST) is reported to ameliorate renal dysfunction by the absorption of toxic substance in the gut. Recent study revealed that, in CKD, gut environment is disturbed including the decrease in tight junctions and Lactobacillus (Lact). In this study, we examined whether AST improves the renal dysfunction through gut environment.

Method

Six-week-old spontaneously hypertensive rats (SHR) were rendered CKD by 5/6th nephrectomy (Nx). SHRs were divided into SHR (Sham), SHR with Nx (Nx), and Nx given AST (Nx + AST) (n = 10, each). After 12 weeks, rats were killed and biochemical parameters were explored. The gut flora was analyzed. Furthermore, gut molecular changes in tight junctions and toll-like receptors were examined. We also investigated the effects of the combination therapy with AST and Lact.

Results

The increase in serum urea nitrogen and urinary protein excretion in Nx was restored in Nx + AST. The increased renal glomerulosclerosis in Nx was ameliorated in Nx + AST. Increases in serum uremic toxins and IL-6 in Nx were ameliorated in Nx + AST. The gut flora analysis revealed that the decrease in Lact in Nx was restored in Nx + AST. The downregulation in the tight junction and TLR2 in Nx was mitigated by AST. However, combination therapy failed to exhibit additional effects.

Conclusion

AST ameliorated renal function with the restoration of Lact and tight junction through TLR pathway, which would mitigate systemic inflammation and contributed to their renoprotective effects. Our study provides a novel mechanism of the renoprotective effects by AST.

Gut microbiota, hypertension and chronic kidney disease: Recent advances

A large number of different microbial species populates intestine. Extensive research has studied the entire microbial population and their genes (microbiome) by using metagenomics, metatranscriptomics and metabolomic analysis. Studies suggest that the imbalances of the microbial community causes alterations in the intestinal homeostasis, leading to repercussions on other systems: metabolic, nervous, cardiovascular, immune. These studies have also shown that alterations in the structure and function of the gut microbiota play a key role in the pathogenesis and complications of Hypertension (HTN) and Chronic Kidney Disease (CKD). Increased blood pressure (BP) and CKD are two leading risk factors for cardiovascular disease and their treatment represents a challenge for the clinicians. In this Review, we discuss mechanisms whereby gut microbiota (GM) and its metabolites act on downstream cellular targets to contribute to the pathogenesis of HTN and CKD, and potential therapeutic implications.

Impact of the Oral Adsorbent AST-120 on Organ-Specific Accumulation of Uremic Toxins: LC-MS/MS and MS Imaging Techniques

Elevated circulating uremic toxins are associated with a variety of symptoms and organ dysfunction observed in patients with chronic kidney disease (CKD). Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are representative uremic toxins that exert various harmful effects. We recently showed that IS induces metabolic alteration in skeletal muscle and causes sarcopenia in mice. However, whether organ-specific accumulation of IS and PCS is associated with tissue dysfunction is still unclear. We investigated the accumulation of IS and PCS using liquid chromatography/tandem mass spectrometry in various tissues from mice with adenine-induced CKD. IS and PCS accumulated in all 15 organs analyzed, including kidney, skeletal muscle, and brain. We also visualized the tissue accumulation of IS and PCS with immunohistochemistry and mass spectrometry imaging techniques. The oral adsorbent AST-120 prevented some tissue accumulation of IS and PCS. In skeletal muscle, reduced accumulation following AST-120 treatment resulted in the amelioration of renal failure-associated muscle atrophy. We conclude that uremic toxins can accumulate in various organs and that AST-120 may be useful in treating or preventing organ dysfunction in CKD, possibly by reducing tissue accumulation of uremic toxins.

Gut microbiome and kidney disease: a bidirectional relationship

Recent technological advances and efforts, including powerful metagenomic and metatranscriptomic analyses, have led to a tremendous growth in our understanding of microbial communities. Changes in microbial abundance or composition of human microbial communities impact human health or disease state. However, explorations into the mechanisms underlying host-microbe interactions in health and disease are still in their infancy. Although changes in the gut microbiota have been described in patients with kidney disease, the relationships between pathogenesis, mechanisms of disease progression, and the gut microbiome are still evolving. Here, we review changes in the host-microbiome symbiotic relationship in an attempt to explore the bidirectional relationship in which alterations in the microbiome affect kidney disease progression and how kidney disease may disrupt a balanced microbiome. We also discuss potential targeted interventions that may help re-establish this symbiosis and propose more effective ways to deploy traditional treatments in patients with kidney disease.

Indoxyl Sulfate-Review of Toxicity and Therapeutic Strategies

Indoxyl sulfate is an extensively studied uremic solute. It is a small molecule that is more than 90% bound to plasma proteins. Indoxyl sulfate is derived from the breakdown of tryptophan by colon microbes. The kidneys achieve high clearances of indoxyl sulfate by tubular secretion, a function not replicated by hemodialysis. Clearance by hemodialysis is limited by protein binding since only the free, unbound solute can diffuse across the membrane. Since the dialytic clearance is much lower than the kidney clearance, indoxyl sulfate accumulates to relatively high plasma levels in hemodialysis patients. Indoxyl sulfate has been most frequently implicated as a contributor to renal disease progression and vascular disease. Studies have suggested that indoxyl sulfate also has adverse effects on bones and the central nervous system. The majority of studies have assessed toxicity in cultured cells and animal models. The toxicity in humans has not yet been proven, as most data have been from association studies. Such toxicity data, albeit inconclusive, have prompted efforts to lower the plasma levels of indoxyl sulfate through dialytic and non-dialytic means. The largest randomized trial showed no benefit in renal disease progression with AST-120. No trials have yet tested cardiovascular or mortality benefit. Without such trials, the toxicity of indoxyl sulfate cannot be firmly established.

Indoxyl Sulfate Induces Mesangial Cell Proliferation via the Induction of COX-2

Indoxyl sulfate (IS) is one of important uremic toxins and is markedly accumulated in the circulation of end stage renal disease (ESRD) patients, which might contribute to the damage of residual nephrons and progressive loss of residual renal function (RRF). Thus this study was undertaken to investigate the role of IS in modulating mesangial cell (MC) proliferation and the underlying mechanism. The proliferation of MCs induced by IS was determined by cell number counting, DNA synthase rate, and cell cycle phase analysis. COX-2 expression was examined by Western blotting and qRT-PCR, and a specific COX-2 inhibitor NS398 was applied to define its role in IS-induced MC proliferation. Following IS treatment, MCs exhibited increased total cell number, DNA synthesis rate, and number of cells in S and G2 phases paralleled with the upregulation of cyclin A2 and cyclin D1. Next, we found an inducible inflammation-related enzyme COX-2 was remarkably enhanced by IS, and the inhibition of COX-2 by NS398 significantly blocked IS-induced MC proliferation in line with a blockade of PGE2 production. These findings indicated that IS could induce MC proliferation via a COX-2-mediated mechanism, providing new insights into the understanding and therapies of progressive loss of RRF in ESRD.

Effect of a sustained difference in hemodialytic clearance on the plasma levels of p-cresol sulfate and indoxyl sulfate

BACKGROUND

The protein-bound solutes p-cresol sulfate (PCS) and indoxyl sulfate (IS) accumulate to high plasma levels in renal failure and have been associated with adverse events. The clearance of these bound solutes can be altered independently of the urea clearance by changing the dialysate flow and dialyzer size. This study tested whether a sustained difference in clearance would change the plasma levels of PCS and IS.

METHODS

Fourteen patients on thrice-weekly nocturnal hemodialysis completed a crossover study of two periods designed to achieve widely different bound solute clearances. We compared the changes in pre-dialysis plasma PCS and IS levels from baseline over the course of the two periods.

RESULTS

The high-clearance period provided much higher PCS and IS clearances than the low-clearance period (PCS: 23 ± 4 mL/min versus 12 ± 3 mL/min, P < 0.001; IS: 30 ± 5 mL/min versus 17 ± 4 mL/min, P < 0.001). Despite the large difference in clearance, the high-clearance period did not have a different effect on PCS levels than the low-clearance period [from baseline, high: +11% (-5, +37) versus low: -8% (-18, +32), (median, 25th, 75th percentile), P = 0.50]. In contrast, the high-clearance period significantly lowered IS levels compared with the low-clearance period [from baseline, high: -4% (-17, +1) versus low: +22% (+14, +31), P < 0.001). The amount of PCS removed in the dialysate was significantly greater at the end of the high-clearance period [269 (206, 312) versus 199 (111, 232) mg per treatment, P < 0.001], while the amount of IS removed was not different [140 (87, 196) versus 116 (89, 170) mg per treatment, P = 0.15].

CONCLUSIONS

These findings suggest that an increase in PCS generation prevents plasma levels from falling when the dialytic clearance is increased. Suppression of solute generation may be required to reduce plasma PCS levels in dialysis patients.

Increased Levels of Total p-Cresylsulfate Are Associated with Pruritus in Patients with Chronic Kidney Disease

BACKGROUND

Pruritus is a common and distressing symptom that affects patients with chronic kidney disease (CKD). Indoxyl sulfate (IS) and p-cresylsulfate (PCS) are uremic toxins with similar protein binding, dialytic clearance, and proinflammatory features. Pruritus in CKD may correlate better with uremic toxins than the glomerular filtration rate (GFR), suggesting that uremic toxins either in the central nervous system or peripherally may play an important role in the pathophysiology.

OBJECTIVE

We sought to investigate the potential contribution of serum total IS and PCS to the pathogenesis of pruritus.

METHODS

The serum levels of total IS and PCS concentrations were measured in all patients by using the Ultra Performance LC System. The characteristics of pruritus were assessed using a visual analog scale score and an interview questionnaire.

RESULTS

Among the 320 CKD patients, 35% had pruritus. The patients with pruritus were older and had a higher frequency of diabetes mellitus, higher uric acid, calcium, phosphorus, creatinine, high-sensitivity C-reactive protein, and total IS and PCS levels, and lower albumin concentrations and estimated GFR (eGFR) than those without pruritus. Increasing concentrations of total PCS were independently and significantly associated with pruritus. Multiple logistic regression analysis revealed total PCS as an independent association factor for pruritus, even after full adjustment of known biomarkers. Furthermore, serum total PCS levels were positively associated with calcium, phosphorus, blood urea nitrogen, creatinine, and white blood cell count, and negatively associated with eGFR, hemoglobin, and hematocrit.

CONCLUSION

Our results indicate that total PCS may play a role in the pathogenesis of pruritus.

The intestine and the kidneys: a bad marriage can be hazardous

The concept that the intestine and chronic kidney disease influence each other, emerged only recently. The problem is multifaceted and bidirectional. On one hand, the composition of the intestinal microbiota impacts uraemic retention solute production, resulting in the generation of essentially protein-bound uraemic toxins with strong biological impact such as vascular damage and progression of kidney failure. On the other hand, the uraemic status affects the composition of intestinal microbiota, the generation of uraemic retention solutes and their precursors and causes disturbances in the protective epithelial barrier of the intestine and the translocation of intestinal microbiota into the body. All these elements together contribute to the disruption of the metabolic equilibrium and homeostasis typical to uraemia. Several measures with putative impact on intestinal status have recently been tested for their influence on the generation or concentration of uraemic toxins. These include dietary measures, prebiotics, probiotics, synbiotics and intestinal sorbents. Unfortunately, the quality and the evidence base of many of these studies are debatable, especially in uraemia, and often results within one study or among studies are contradictory. Nevertheless, intestinal uraemic metabolite generation remains an interesting target to obtain in the future as an alternative or additive to dialysis to decrease uraemic toxin generation. In the present review, we aim to summarize (i) the role of the intestine in uraemia by producing uraemic toxins and by generating pathophysiologically relevant changes, (ii) the role of uraemia in modifying intestinal physiology and (iii) the therapeutic options that could help to modify these effects and the studies that have assessed the impact of these therapies.

Approaches to uremia

The development of dialysis was a dramatic step forward in medicine, allowing people who would soon have died because of lack of kidney function to remain alive for years. We have since found, however, that the "artificial kidney" does not live up fully to its name. Dialysis keeps patients alive but not well. Part of the residual illness that dialysis patients experience is caused by retained waste solutes that dialysis does not remove as well as native kidney function does. New means are available to identify these toxic solutes, about which we currently know remarkably little, and knowledge of these solutes would help us to improve therapy. This review summarizes our current knowledge of toxic solutes and highlights methods being explored to identify additional toxic solutes and to enhance the clearance of these solutes to improve patient outcomes.

Effects of AST-120 on blood concentrations of protein-bound uremic toxins and biomarkers of cardiovascular risk in chronic dialysis patients

BACKGROUND

Removal of protein-bound uremic toxins by dialysis therapy is limited. The effect of oral adsorbent AST-120 in chronic dialysis patients has rarely been investigated.

METHODS

AST-120 was administered 6.0 g/day for 3 months in 69 chronic dialysis patients. The blood concentrations of indoxyl sulfate, p-cresol sulfate and biomarkers of cardiovascular risk were determined before and after AST-120 treatment.

RESULTS

AST-120 significantly decreased both the total and free forms of indoxyl sulfate and p-cresol sulfate ranging from 21.9 to 58.3%. There were significant simultaneous changes of the soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK, 24% increase), malondialdehyde (14% decrease) and interleukin-6 (19% decrease). A significant association between the decrease of indoxyl sulfate and changes of sTWEAK and interleukin-6 was noted.

CONCLUSIONS

AST-120 effectively decreased indoxyl sulfate and p-cresol sulfate levels in both total and free forms. AST-120 also improved the profile of cardiovascular biomarkers.

Protein-bound molecules: a large family with a bad character

Many small solutes excreted by the kidney are bound to plasma proteins, chiefly albumin, in the circulation. The combination of protein binding and tubular secretion allows the kidney to reduce the free, unbound concentrations of such solutes to lower levels than could be obtained by tubular secretion alone. Protein-bound solutes accumulate in the plasma when the kidneys fail, and the free, unbound levels of these solutes increase more than their total plasma levels owing to competition for binding sites on plasma proteins. Given the efficiency by which the kidney can clear protein-bound solutes, it is tempting to speculate that some compounds in this class are important uremic toxins. Studies to date have focused largely on two specific protein-bound solutes: indoxyl sulfate and p-cresyl sulfate. The largest body of evidence suggests that both of these compounds contribute to cardiovascular disease, and that indoxyl sulfate contributes to the progression of chronic kidney disease. Other protein-bound solutes have been investigated to a much lesser extent, and could in the future prove to be even more important uremic toxins.

AST-120 for the management of progression of chronic kidney disease

Uremic toxins such as indoxyl sulfate contribute to the pathogenesis of chronic kidney disease (CKD) by promoting glomerulosclerosis and interstitial fibrosis with loss of nephrons and vascular damage. AST-120, an orally administered intestinal sorbent, adsorbs indole, a precursor of indoxyl sulfate, thereby reducing serum and urinary concentrations of indoxyl sulfate. AST-120 has been available in Japan since 1991, and subsequently Korea (2005), and the Philippines (2010) as an agent to prolong the time to initiation of hemodialysis and for improvement of uremic symptoms in patients with CKD. A Medline search was performed to identify data supporting clinical experience with AST-120 for managing CKD. Prospective open-label and double-blind trials as well as retrospective analyses were included. In prospective trials and retrospective analyses, AST-120 has been shown to prolong the time to initiation of hemodialysis, and slow decline in glomerular filtration rate and the increase serum creatinine. In an initial randomized, double-blind, placebo-controlled trial in the United States, AST-120 was associated with a significant dose-dependent reduction in serum indoxyl sulfate levels and a decrease in uremia-related malaise. The Evaluating Prevention of Progression in CKD (EPPIC) trials, two double-blind, placebo-controlled trials undertaken in North America/Latin America and Europe, are evaluating the efficacy of AST-120 for preventing the progression of CKD. The results of the EPPIC trials will further define the role of AST-120 in this debilitating condition.

The gut microbiome, kidney disease, and targeted interventions

The human gut harbors >100 trillion microbial cells, which influence the nutrition, metabolism, physiology, and immune function of the host. Here, we review the quantitative and qualitative changes in gut microbiota of patients with CKD that lead to disturbance of this symbiotic relationship, how this may contribute to the progression of CKD, and targeted interventions to re-establish symbiosis. Endotoxin derived from gut bacteria incites a powerful inflammatory response in the host organism. Furthermore, protein fermentation by gut microbiota generates myriad toxic metabolites, including p-cresol and indoxyl sulfate. Disruption of gut barrier function in CKD allows translocation of endotoxin and bacterial metabolites to the systemic circulation, which contributes to uremic toxicity, inflammation, progression of CKD, and associated cardiovascular disease. Several targeted interventions that aim to re-establish intestinal symbiosis, neutralize bacterial endotoxins, or adsorb gut-derived uremic toxins have been developed. Indeed, animal and human studies suggest that prebiotics and probiotics may have therapeutic roles in maintaining a metabolically-balanced gut microbiota and reducing progression of CKD and uremia-associated complications. We propose that further research should focus on using this highly efficient metabolic machinery to alleviate uremic symptoms.

Targeting protein-bound uremic toxins in chronic kidney disease

INTRODUCTION

Protein-bound uremic toxins such as indoxyl sulfate cannot be removed efficiently by hemodialysis. These protein-bound uremic toxins have emerged as important risk factors for the progression of chronic kidney disease (CKD) as well as cardiovascular disease (CVD).

AREAS COVERED

Indoxyl sulfate shows toxic effects on a variety of cells such as renal proximal tubular cells, glomerular mesangial cells, vascular smooth muscle cells, vascular endothelial cells, cardiomyocytes, cardiac fibroblasts, monocytes, osteoblasts and osteoclasts. This review overviews the cellular toxicity of indoxyl sulfate, its molecular mechanism and its role in the progression of CKD and CVD. Further, this review summarizes the clinical effects of AST-120 and the other strategies to reduce serum levels of indoxyl sulfate.

EXPERT OPINION

Protein-bound uremic toxins such as indoxyl sulfate have emerged as target molecules for therapeutic intervention of not only CKD but also CVD. An oral sorbent AST-120 reduces serum level of indoxyl sulfate by adsorbing indole in the intestine. The modulation of intestinal bacteria by prebiotics/probiotics might be effective in reducing the production of indole in the intestine followed by reduced serum levels of indoxyl sulfate. An alternative approach might be antagonist which can counteract indoxyl sulfate-induced cellular effects and signaling pathways.

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.

In vitro study of removal of protein-bound toxins

Protein-bound toxins are not efficiently removed by conventional hemodialysis techniques. In order to improve the removal of protein-bound toxins, we performed an in vitro study to evaluate the effects of dilution and pH change on the dissociation of protein-bound toxins from albumin. Human plasma harvested by therapeutic apheresis treatment was diluted with saline or isotonic NaHCO3 solution, and the amounts of the free fractions of indoxyl sulfate (IS) and homocysteine were determined. The results suggested that IS was dissociated easily from albumin by dilution and pH change; higher dilution was associated with more effective removal and a greater increase of the free fraction of IS. However, these methods did not facilitate dissociation of homocysteine from albumin. Effective removal of some protein-bound toxins may be achieved by applying dilution and pH change methods to blood purification techniques, such as pre-dilution on-line hemodiafiltration.

Association between AST-120 and abdominal aortic calcification in predialysis patients with chronic kidney disease

BACKGROUND

Vascular calcification is associated with mortality and cardiovascular events in patients with chronic kidney disease. AST-120, which adsorbs uremic toxins, is reported to reduce the risk of cardiovascular disease and death in chronic kidney disease patients. The aim of the current study was to investigate the association between abdominal aortic calcification and the use of AST-120 in predialysis chronic kidney disease patients.

METHODS

A retrospective analysis was conducted including 199 predialysis chronic kidney disease patients (stages 4 and 5) who underwent abdominal plain computed tomography in our institution between 2005 and 2010. Abdominal aortic calcification was assessed by aortic calcification index (ACI). Patients were divided into two groups based on whether or not AST-120 was administered for at least six months, and ACI was compared between the two groups.

RESULTS

The aortic calcification index was significantly lower in patients taking AST-120 [12.2 (2.5-30.3) vs. 25.7 (13.4-45.3) %, P < 0.001]. According to multivariate linear regression analysis, the use of AST-120 was independently and significantly correlated with ACI after adjusting for confounding factors.

CONCLUSIONS

The use of AST-120 was independently associated with less aortic calcification in predialysis chronic kidney disease patients.

Dysregulated oxygen metabolism of the kidney by uremic toxins: review

Because kidneys consume a large amount of oxygen and are relatively inefficient in oxygen uptake, they are susceptible to hypoxia, especially in patients with advanced chronic kidney disease accompanied by loss of peritubular capillaries. Accumulating evidence suggests that chronic tubulointerstitial hypoxia acts as a final common pathway leading to end-stage renal disease. Some biologically active uremic retention molecules, considered as uremic toxins, accumulate as the renal function declines, and at this moment, more than 90 bioactive uremic toxins have been identified. Uremic toxins per se have been proven to accelerate the progression of renal failure. However, the causal relationship between uremic toxin and tubulointerstitial hypoxia remains unclear. Our studies provided direct evidence that uremic toxin dysregulates oxygen metabolism in the kidney. Indoxyl sulfate (IS), a representative protein-bound uremic toxin, increased oxygen consumption in proximal renal tubules, decreased renal oxygenation, and consequently aggravated hypoxia in the remnant rat kidneys. The increase in tubular oxygen consumption by IS was dependent on sodium-potassium adenosine triphosphatase and oxidative stress. Our work also indicated a possible connection between IS and the desensitization of the oxygen-sensing mechanism in erythropoietin-producing cells, which may partly explain inadequate erythropoietin production in hypoxic kidneys of end-stage renal disease patients. Studies of uremic toxins will open a new avenue in development of novel therapeutic approaches of kidney disease.

Indoxyl sulfate induces nephrovascular senescence

Indoxyl sulfate is markedly accumulated in the serum of chronic kidney disease (CKD) patients. The oral sorbent AST-120 reduces serum levels of indoxyl sulfate in CKD patients by adsorbing indole, a precursor of indoxyl sulfate, in the intestine. Indoxyl sulfate is taken up by proximal tubular cells through organic anion transporters (OAT1, OAT3), and it induces reactive oxygen species (ROS) with impairment of cellular antioxidative system. Indoxyl sulfate stimulates progression of CKD by increasing renal expression of profibrotic cytokines such as transforming growth factor beta 1. Further, it promotes the expression of p53 by ROS-induced activation of nuclear factor kappa B, thereby accelerating senescence of proximal tubular cells with progression of CKD. Administration of indoxyl sulfate to hypertensive rats reduces renal expression of Klotho and promotes cell senescence, with expression of senescence-associated beta-galactosidase, p53, p21, p16, and retinoblastoma protein, accompanied by kidney fibrosis. Indoxyl sulfate downregulates Klotho expression in the kidneys through production of ROS and activation of nuclear factor kappa B in proximal tubular cells. It promotes cell senescence, with expression of senescence-associated beta-galactosidase, p53, p21, p16, and retinoblastoma protein, in the aorta of hypertensive rats. It also promotes aortic calcification and aortic wall thickening in hypertensive rats with expression of osteoblast-specific proteins, induces ROS in vascular smooth muscle cells and vascular endothelial cells, stimulates proliferation and osteoblastic transdifferentiation of vascular smooth muscle cells, and inhibits viability and nitric oxide production of vascular endothelial cells. Thus, indoxyl sulfate accelerates the progression of not only CKD but also of cardiovascular disease by inducing nephrovascular cell senescence.