Evaluation of Salivary Indoxyl Sulfate with Proteinuria for Predicting Graft Deterioration in Kidney Transplant Recipients.

Acute kidney injury (AKI) is a significant risk factor for developing chronic kidney disease and progression to end-stage renal disease in elderly patients. AKI is also a relatively common complication after kidney transplantation (KTx) associated with graft failure. Since the lifespan of a transplanted kidney is limited, the risk of the loss/deterioration of graft function (DoGF) should be estimated to apply the preventive treatment. The collection of saliva and urine is more convenient than collecting blood and can be performed at home. The study aimed to verify whether non-invasive biomarkers, determined in saliva and urine, may be useful in the prediction of DoGF in kidney transplant recipients (KTRs) (n = 92). Salivary and serum toxins (p-cresol sulfate, pCS; indoxyl sulfate, IS) concentrations were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Urinary proteins, hemoglobin, and glucose were measured using a semi-quantitative strip test. Salivary IS (odds ratio (OR) = 1.19), and proteinuria (OR = 3.69) were demonstrated as independent factors for the prediction of DoGF. Satisfactory discriminatory power (area under the receiver operating characteristic curve (AUC) = 0.71 ± 0.07) and calibration of the model were obtained. The model showed that categories of the increasing probability of the risk of DoGF are associated with the decreased risk of graft survival. The non-invasive diagnostic biomarkers are a useful screening tool to identify high-risk patients for DoGF.

Protein-Bound Uremic Toxins and Immunity.

Protein-bound uremic toxins (PBUTs) are bioactive microbiota metabolites originated exclusively from protein fermentation of the bacterial community resident within the gut microbiota, whose composition and function is profoundly different in the chronic kidney disease (CKD) population. PBUTs accumulate in the later stages of CKD because they cannot be efficiently removed by conventional hemodialysis due to their high binding affinity for albumin, worsening their toxic effects, especially at the cardiovascular level. The accumulation of uremic toxins, along with oxidative stress products and pro-inflammatory cytokines, characterizes the uremic status of CKD patients which is increasingly associated to a state of immune dysfunction including both immune activation and immunodepression. Furthermore, the links between immune activation and cardiovascular disease (CVD), and between immunodepression and infection diseases, which are the two major complications of CKD, are becoming more and more evident. This review summarizes and discusses the current state of knowledge on the role of the main PBUTs, namely indoxyl sulfate and p-cresyl sulfate, as regulators of immune response in CKD, in order to understand whether a microbiota modulation may be useful in the management of its main complications, CVD, and infections. Summarizing the direct effects of PBUT on immune system we may conclude that PCS seemed to be associated to an immune deficiency status of CKD mainly related to the adaptative immune response, while IS seemed to reflect the activation of both innate and adaptative immune systems likely responsible of the CKD-associated inflammation. However, the exact role of IS and PCS on immunity modulation in physiological and pathological state still needs in-depth investigation, particularly in vivo studies.

P-cresol and Indoxyl Sulfate Impair Osteogenic Differentiation by Triggering Mesenchymal Stem Cell Senescence.

Chronic kidney disease (CKD) patients obtained high levels of uremic toxins progressively develop several complications including bone fractures. Protein-bound uremic toxins especially p-cresol and indoxyl sulfate are hardly eliminated due to their high molecular weight. Thus, the abnormality of bone in CKD patient could be potentially resulted from the accumulation of uremic toxins. To determine whether protein-bound uremic toxins have an impact on osteogenesis, mesenchymal stem cells were treated with either p-cresol or indoxyl sulfate under in vitro osteogenic differentiation. The effects of uremic toxins on MSC-osteoblastic differentiation were investigated by evaluation of bone phenotype. The results demonstrated that p-cresol and indoxyl sulfate down-regulated the transcriptional level of collagen type I, deceased alkaline phosphatase activity, and impaired mineralization of MSC-osteoblastic cells. Furthermore, p-cresol and indoxyl sulfate gradually increased senescence-associated beta-galactosidase positive cells while upregulated the expression of p21 which participate in senescent process. Our findings clearly revealed that the presence of uremic toxins dose-dependently influenced a gradual deterioration of osteogenesis. The effects partially mediate through the activation of senescence-associated gene lead to the impairment of osteogenesis. Therefore, the management of cellular senescence triggered by uremic toxins could be considered as an alternative therapeutic approach to prevent bone abnormality in CKD patients.

Construction of eco-biosensor and its potential application for highly selective, sensitive and fast detection of viscumin.

Viscum album lectin 1 (Viscumin) is one of the most important plant-based protein of potential adjuvant in cancer treatment. Therefore, the use of nano-biosensor technology as a novel emerges of biosensors is crucial to detect this modal agent in pharmacological study. Molecular imprinted polymer using 9-mer peptides sequence (epitope) was applied as a template. Using ultraviolet light, hydrogen bonding attained between the functional monomer and epitope, leading to the formation of a molecularly imprinted polymer. In the following, the epitope was derived from the surface of the polymer by sodium dodecyl sulfate (SDS) 2.5% and acetic acid 0.6% w/w. Finally, the designed nano-biosensor was exposed to different concentrations of the epitope. The selectivity of the nano-biosensor was tested in complex matrices such as blood plasma and urine. The scatchard analysis was covered for a consequence of the dissociation constants and the numbers of binding sites. Based on the results, the designed nano-biosensor has a limit of detection of 0.117 ng/µl and limit of quantification of 0.517 ng/µl in PBS buffer, respectively. These amounts stood 0.5 ng/µl and 0.8 ng/µl for urine environment and 1.25 ng/µl and 5 ng/µl for human blood fresh frozen plasma in the presence of ricin as the most homologue of viscumin (ML1) in fixed concentration (12:1), respectively. The time of detection and optimum pH was 8.0 min and 7.4, respectively. Designed and synthesized nano-biosensor is adequately qualified to be used in diverse complex areas, due to good efficiency.

Microbiome modulation to correct uremic toxins and to preserve kidney functions.

PURPOSE OF REVIEW: The association between dysbiosis and CKD is well established. This review focuses on the current understanding of microbiome, in normal individuals and CKD patients, in order to hypothesize how to correct uremic toxins levels and preserve the renal function and reduce associated comorbidities. Here we discuss our current opinion on microbiome modulation in order to manage the CKD-associated dysbiosis. RECENT FINDINGS: Emerging evidence confirms the role of gut microbiome in the progression of CKD. In this scenario, the need is felt to set up multifaceted approaches for dysbiosis management. Among many strategies able to improve gut wellness, a crucial approach is represented by the functional nutrition. At the same time, drug-based treatments show significant results in microbiome modulation. Furthermore, we examine here the potentialities of fecal microbiome transplantation (FMT) in CKD, an approach currently applied in Clostridium difficile infection. SUMMARY: The gut microbiome plays a pivotal role in the pathophysiology of CKD. The vicious cycle triggered by kidney function decline leads to gut dysbiosis. Considering the gut microbiome as a therapeutic target in CKD, multiple approaches aimed at its modulation should be envisioned to preserve kidney function. Dietary interventions and pharmacological strategies are able to improve microbiome dysbiosis, oxidative stress and fibrosis. Additionally, FMT could represent a promising novel therapy in the management of CKD-associated dysbiosis.

Molecular mechanisms of protein-bound uremic toxin-mediated cardiac, renal and vascular effects: underpinning intracellular targets for cardiorenal syndrome therapy.

Cardiorenal syndrome (CRS) remains a global health burden with a lack of definitive and effective treatment. Protein-bound uremic toxin (PBUT) overload has been identified as a non-traditional risk factor for cardiac, renal and vascular dysfunction due to significant albumin-binding properties, rendering these solutes non-dialyzable upon the state of irreversible kidney dysfunction. Although limited, experimental studies have investigated possible mechanisms in PBUT-mediated cardiac, renal and vascular effects. The ultimate aim is to identify relevant and efficacious targets that may translate beneficial outcomes in disease models and eventually in the clinic. This review will expand on detailed knowledge on mechanisms involved in detrimental effects of PBUT, specifically affecting the heart, kidney and vasculature, and explore potential effective intracellular targets to abolish their effects in CRS initiation and/or progression.

In silico comparison of protein-bound uremic toxin removal by hemodialysis, hemodiafiltration, membrane adsorption, and binding competition.

Protein-bound uremic toxins (PBUTs) are poorly removed during hemodialysis (HD) due to their low free (dialyzable) plasma concentration. We compared PBUT removal between HD, hemodiafiltration (HDF), membrane adsorption, and PBUT displacement in HD. The latter involves infusing a binding competitor pre-dialyzer, which competes with PBUTs for their albumin binding sites and increases their free fraction. We used a mathematical model of PBUT/displacer kinetics in dialysis comprising a three-compartment patient model, an arterial/venous tube segment model, and a dialyzer model. Compared to HD, improvements in removal of prototypical PBUTs indoxyl sulfate (initial concentration 100 µM, 7% free) and p-cresyl sulfate (150 µM, 5% free) were: 5.5% and 6.4%, respectively, for pre-dilution HDF with 20 L replacement fluid; 8.1% and 9.1% for post-dilution HDF 20 L; 15.6% and 18.3% for pre-dilution HDF 60 L; 19.4% and 22.2% for complete membrane adsorption; 35.0% and 41.9% for displacement with tryptophan (2000 mg in 500 mL saline); 26.7% and 32.4% for displacement with ibuprofen (800 mg in 200 mL saline). Prolonged (one-month) use of tryptophan reduces the IS and pCS time-averaged concentration by 28.1% and 29.9%, respectively, compared to conventional HD. We conclude that competitive binding can be a pragmatic approach for improving PBUT removal.

Identification of ABCG2 as an Exporter of Uremic Toxin Indoxyl Sulfate in Mice and as a Crucial Factor Influencing CKD Progression.

Chronic kidney disease (CKD) patients accumulate uremic toxins in the body, potentially require dialysis, and can eventually develop cardiovascular disease. CKD incidence has increased worldwide, and preventing CKD progression is one of the most important goals in clinical treatment. In this study, we conducted a series of in vitro and in vivo experiments and employed a metabolomics approach to investigate CKD. Our results demonstrated that ATP-binding cassette transporter subfamily G member 2 (ABCG2) is a major transporter of the uremic toxin indoxyl sulfate. ABCG2 regulates the pathophysiological excretion of indoxyl sulfate and strongly affects CKD survival rates. Our study is the first to report ABCG2 as a physiological exporter of indoxyl sulfate and identify ABCG2 as a crucial factor influencing CKD progression, consistent with the observed association between ABCG2 function and age of dialysis onset in humans. The above findings provided valuable knowledge on the complex regulatory mechanisms that regulate the transport of uremic toxins in our body and serve as a basis for preventive and individualized treatment of CKD.

Is There Enough Evidence to Prove That Hemodiafiltration Is Superior?

The evidence concerning online hemodiafiltration (HDF) includes the following: (1) the increase of removal of uremic toxin, (2) the prevention of dialysis rerated hypotension, (3) the recovery of survival, and (4) the recovery of dialysis related uncertain symptoms. Although clinical evidence has been noted, the hypothesis of the efficacy of HDF are still indefinite and require further precise research.

Generation, clearance, toxicity, and monitoring possibilities of unaccounted uremic toxins for improved dialysis prescriptions.

Current dialysis-dosing calculations provide an incomplete assessment of blood purification. They exclude clearances of protein-bound uremic toxins (PB-UTs), such as polyamines, p-cresol sulfate, and indoxyl sulfate, relying solely on the clearance of urea as a surrogate for all molecules accumulating in patients with end-stage renal disease (ESRD). PB-UTs clear differently in dialysis but also during normal renal function. The kidney clears PB toxins via the process of secretion, whereas it clears urea through filtration. Herein, we review the clearance, accumulation, and toxicity of various UTs. We also suggest possible methods for their monitoring toward the ultimate goal of a more comprehensive dialysis prescription. A more inclusive dialysis prescription would retain the kidney-filtration surrogate, urea, and consider at least one PB toxin as a surrogate for UTs cleared through cellular secretion. A more comprehensive assessment of UTs that includes both secretion and filtration is expected to result in a better understanding of ESRD toxicity and consequently, to reduce ESRD mortality.

Key Role for the Organic Anion Transporters, OAT1 and OAT3, in the in vivo Handling of Uremic Toxins and Solutes.

In vitro data indicates that the kidney proximal tubule (PT) transporters of uremic toxins and solutes (e.g., indoxyl sulfate, p-cresol sulfate, kynurenine, creatinine, urate) include two "drug" transporters of the organic anion transporter (OAT) family: OAT1 (SLC22A6, originally NKT) and OAT3 (SLC22A8). Here, we have examined new and prior metabolomics data from the Oat1KO and Oat3KO, as well as newly obtained metabolomics data from a "chemical double" knockout (Oat3KO plus probenecid). This gives a picture of the in vivo roles of OAT1 and OAT3 in the regulation of the uremic solutes and supports the centrality of these "drug" transporters in independently and synergistically regulating uremic metabolism. We demonstrate a key in vivo role for OAT1 and/or OAT3 in the handling of over 35 uremic toxins and solutes, including those derived from the gut microbiome (e.g., CMPF, phenylsulfate, indole-3-acetic acid). Although it is not clear whether trimethylamine-N-oxide (TMAO) is directly transported, the Oat3KO had elevated plasma levels of TMAO, which is associated with cardiovascular morbidity in chronic kidney disease (CKD). As described in the Remote Sensing and Signaling (RSS) Hypothesis, many of these molecules are involved in interorgan and interorganismal communication, suggesting that uremia is, at least in part, a disorder of RSS.

Evaluation of the impact of gut microbiota on uremic solute accumulation by a CE-TOFMS-based metabolomics approach.

Gut microbiota is involved in the metabolism of uremic solutes. However, the precise influence of microbiota to the retention of uremic solutes in CKD is obscure. To clarify this, we compared adenine-induced renal failure and control mice under germ-free or specific pathogen-free (SPF) conditions, examining the metabolite profiles of plasma, feces, and urine using a capillary electrophoresis time-of-flight mass spectrometry-based approach. Mice with renal failure under germ-free conditions demonstrated significant changes in plasma metabolites. Among 183 detected solutes, plasma levels of 11 solutes, including major uremic toxins, were significantly lower in germ-free mice than in SPF mice with renal failure. These 11 solutes were considered microbiota-derived uremic solutes and included indoxyl sulfate, p-cresyl sulfate, phenyl sulfate, cholate, hippurate, dimethylglycine, γ-guanidinobutyrate, glutarate, 2-hydroxypentanoate, trimethylamine N-oxide, and phenaceturate. Metabolome profiling showed that these solutes were classified into three groups depending on their origins: completely derived from microbiota (indoxyl sulfate, p-cresyl sulfate), derived from both host and microbiota (dimethylglycine), and derived from both microbiota and dietary components (trimethylamine N-oxide). Additionally, germ-free renal failure conditions resulted in the disappearance of colonic short-chain fatty acids, decreased utilization of intestinal amino acids, and more severe renal damage compared with SPF mice with renal failure. Microbiota-derived short-chain fatty acids and efficient amino acid utilization may have a renoprotective effect, and loss of these factors may exacerbate renal damage in germ-free mice with renal failure. Thus, microbiota contributes substantially to the production of harmful uremic solutes, but conversely, growth without microbiota has harmful effects on CKD progression.

Effects of nonsteroidal anti-inflammatory drugs on the renal excretion of indoxyl sulfate, a nephro-cardiovascular toxin, in rats.

Chronic kidney disease (CKD) is a health problem worldwide. Indoxyl sulfate (IS) is a nephro-cardiovascular toxin accumulated in CKD patients and cannot be removed through hemodialysis. The renal excretion of IS was mediated by organic anion transporters (OATs) OAT 1 and OAT 3. Because a number of nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to inhibit OATs, we hypothesize that NSAIDs might inhibit the renal excretion of IS. Rats were intravenously injected IS with and without diclofenac, ketoprofen or salicylic acid, individually. Blood samples were collected at predetermined time points and the concentrations of IS were determined by HPLC method. The results showed that diclofenac and ketoprofen at 10.0mg/kg significantly decreased the systemic clearance of IS by 71% and 82%, and increased the MRT of IS by 106% and 105%, respectively, whereas salicylic acid did not exhibit significant effects. Cell studies indicated that diclofenac and ketoprofen inhibited the uptake of IS mediated by OAT 1 and OAT 3. In conclusion, diclofenac and ketoprofen inhibited the excretion of IS through inhibition on OAT 1 and OAT 3.

Uremic Toxin-Producing Gut Microbiota in Rats with Chronic Kidney Disease.

BACKGROUND: In patients with chronic kidney disease (CKD), many metabolites of gut microbiota retain in the body as uremic toxins (UTs). However, the kinds of bacteria producing UTs are rarely discussed. METHODS: We analyzed UT production and the composition of gut microbiota in CKD rats and cecectomized rats. AST-120, a spherical carbon adsorbent, was administrated to evaluate how the precursors of UT affect gut microbiota. Serum and urine levels of UTs were quantified by liquid chromatography/electrospray ionization-tandem mass spectrometry. Gut microbiota were analyzed using 454-pyrosequencing of the 16S rRNA gene. Operational taxonomic unit (OTU) clustering and UniFrac analysis were performed to compare gut microbiota among the groups. RESULTS: Serum and urine levels of indoxyl sulfate and phenyl sulfate were higher in CKD versus control rats (p < 0.05). AST-120 administration decreased UT production (p < 0.01) and changed overall gut microbiota composition in CKD rats. UT urinary excretion and gut microbiota composition changed in cecectomized rats, with the relative abundance of Clostridia- and Bacteroidia-affiliated species being significantly reduced (p < 0.01). We identified candidate indole- and phenol-producing intestinal microbiota, 3 Clostridia, and 2 Bacteroidia. These OTUs have a tryptophanase/tyrosine phenol-lyase gene in the closest sequenced genome out of the OTUs declined following cecectomy. CONCLUSION: Our data suggest that UT production is correlated with a subset of indigenous gut microbiota. However, UT may be induced by other non-symbiotic microbiota that are influenced by factors other than microbiota populations. The relationship between specific microbiota and UTs in patients requires further clarification.

Modulation of a Circulating Uremic Solute via Rational Genetic Manipulation of the Gut Microbiota.

Renal disease is growing in prevalence and has striking co-morbidities with metabolic and cardiovascular disease. Indoxyl sulfate (IS) is a toxin that accumulates in plasma when kidney function declines and contributes to the progression of chronic kidney disease. IS derives exclusively from the gut microbiota. Bacterial tryptophanases convert tryptophan to indole, which is absorbed and modified by the host to produce IS. Here, we identify a widely distributed family of tryptophanases in the gut commensal Bacteroides and find that deleting this gene eliminates the production of indole in vitro. By altering the status or abundance of the Bacteroides tryptophanase, we can modulate IS levels in gnotobiotic mice and in the background of a conventional murine gut community. Our results demonstrate that it is possible to control host IS levels by targeting the microbiota and suggest a possible strategy for treating renal disease.

Clinical Significance of Human Papillomavirus Type 16 for Breast Cancer & Adenocarcinomas of Various Internal Organs and Alzheimer's Brain with Increased ß-amyloid (1-42); Combined Use of Optimal Doses of Vitamin D3 and Taurine 3 times/day Has Significant Beneficial Effects of Anti-Cancer, Anti-Ischemic Heart, and Memory & Other Brain Problems By Significant Urinary Excretion of Viruses, Bacteria, and Toxic Metals & Substances.

Human Papillomavirus type 16 (HPV-16) has a significant role in various cancers and Alzheimer's disease. 500 breast cancer mammograms as well as 3 cases of adenocarcinomas of esophagus, stomach, colon, prostate gland, uterus, ovary that was examined had significant infection of HPV- 16 with significantly increased ß- amyloid (1-42). When a strong HPV-16 infection is found in the oral cavity, repeated exposure to the infected individual's coughing can infect others easily through saliva. Just like all of above cancer tissues, all 20 Alzheimer's cases that were examined had significantly increased HPV-16 of 1500-3000ng with markedly reduced Acetylcholine of 0.5~1.5ng and significantly increased 3- amyloid (1-42) of 7.5ng or higher. Since every cancer and Alzheimer's patient examined had significantly reduced amounts of Vitamin D3 and Taurine, the author examined the effects of Vitamin D3 and Taurine independently, or by combination. Each of optimal doses of Vitamin D3 and Taurine had significant beneficial effects that were anti-cancer, anti-cardiac ischemia, and memory loss & other brain problems, with significant excretion of HPV- 16 and bacteria such as Borrelia Burgdorferi, if it exists, through the urine, without using any anti-viral or anti-bacterial agents. However, when optimal doses of Taurine and Vitamin D3 were used together, 3 times/day, there was reduction of cancer-associated Oncogene CfosAB-2 or Integrin a5p1 with significantly high values of 200-500ng which were reduced to 0.001-0.004ng. Memory and brain function improved by increasing markedly reduced abnormal Acetylcholine of 1.5ng or less to a few hundred-2500ng with increase in DHEA. Abnormally increased P-amyloid (1-42) is markedly reduced. Ischemic heart, where there is abnormally increased Cardiac Troponin I, reduced significantly. In addition, abnormally reduced DHEA levels often increase. HPV- 16 in urine increased from an average of 100~15ng to an average of 4000ng and cancer related parameters in the urine significantly increased. Thus, the author found combined use of optimal dose of Vitamin D3 400 I.U. and optimal dose of Taurine 175mg, 3/day, was found to be one of the safest, most effective treatments for cancer, memory problems & other brain abnormality, and Ischemic heart problems, and this combination seems to improve any part of the body. One should try this method before using any other treatment, which has a potential side effect.

Development of an ELISA microarray assay for the sensitive and simultaneous detection of ten biodefense toxins.

Plant and microbial toxins are considered bioterrorism threat agents because of their extreme toxicity and/or ease of availability. Additionally, some of these toxins are increasingly responsible for accidental food poisonings. The current study utilized an ELISA-based protein antibody microarray for the multiplexed detection of ten biothreat toxins, botulinum neurotoxins (BoNT) A, B, C, D, E, F, ricin, shiga toxins 1 and 2 (Stx), and staphylococcus enterotoxin B (SEB), in buffer and complex biological matrices. The multiplexed assay displayed a sensitivity of 1.3 pg mL(-1) (BoNT/A, BoNT/B, SEB, Stx-1 and Stx-2), 3.3 pg mL(-1) (BoNT/C, BoNT/E, BoNT/F) and 8.2 pg mL(-1) (BoNT/D, ricin). All assays demonstrated high accuracy (75-120 percent recovery) and reproducibility (most coefficients of variation <20%). Quantification curves for the ten toxins were also evaluated in clinical samples (serum, plasma, nasal fluid, saliva, stool, and urine) and environmental samples (apple juice, milk and baby food) with overall minimal matrix effects. The multiplex assays were highly specific, with little cross-reactivity observed between the selected toxin antibodies. The results demonstrate a multiplex microarray that improves current immunoassay sensitivity for biological warfare agents in buffer, clinical, and environmental samples.

Investigation of basic mobile phases with positive ESI LC-MS for metabonomics studies.

BACKGROUND: Accurate mass based LC-MS combined with statistical analysis is established as a core analytical technology for metabonomic studies. This is primarily due to the specificity, sensitivity and structural elucidation capabilities of the technology. The vast majority of these studies are performed using acidic-based mobile phases in combination with positive ESI mode LC-MS. Recent studies have investigated the use of highly basic pH mobile phases (>10 pH units) in bioanalytical studies that utilize positive ESI mode LC-MS. This non-traditional combination has been shown to improve analyte retention, chromatographic peak shape, and S/N for a variety of probe pharmaceutical compounds in biofluid samples. RESULTS: The incorporation of basic pH mobile phases resulted in increased retention for analytes that where comparatively weakly retained by a traditional acidic-modified mobile phase. Increased resolution of isomers, which otherwise co-eluted under acidic conditions, was observed. Moreover, the implementation of basic pH mobile phases further allowed for the detection of complementary marker ions. CONCLUSION: Basic pH mobile phases utilized with positive ESI mode LC-MS have the potential for producing increased information from metabonomic studies and could lead to the detection of analytes that may prove to be valid biomarkers.

Cardiorenal syndrome: the emerging role of protein-bound uremic toxins.

Cardiorenal syndrome is a condition in which a complex interrelationship between cardiac dysfunction and renal dysfunction exists. Despite advances in treatment of both cardiovascular and kidney disease, cardiorenal syndrome remains a major global health problem. Characteristic of the pathophysiology of cardiorenal syndrome is bidirectional cross-talk; mediators/substances activated by the disease state of 1 organ can play a role in worsening dysfunction of the other by exerting their biologically harmful effects, leading to the progression of the syndrome. Accumulation of uremic toxins is a hallmark of renal excretory dysfunction. Removal of some toxins by conventional dialysis is particularly problematic because of their high protein binding. In this review, we demonstrate that protein-bound uremic toxins may play an important role in progression of cardiovascular disease in the setting of chronic kidney disease. The highly protein-bound uremic toxin indoxyl sulfate has emerged as a potent toxin adversely affecting both the kidney and heart. Direct cardiac effects of this toxin have been recently demonstrated both in vitro and in vivo. Specifically, potent fibrogenic and prohypertrophic effects, as well as oxidative stress-inducing effects, appear to play a central role in both renal and cardiac pathology. Many of these adverse effects can be suppressed by use of a gut adsorbent, AST-120. Potential mechanisms underlying indoxyl sulfate-induced cardiorenal fibrosis are discussed. Future research and clinical implications conclude this review.