Protein-bound uremic retention solutes

In vitro Removal of Protein-Bound Retention Solutes by Extracorporeal Blood Purification Procedures

INTRODUCTION

When the kidneys or liver fail, toxic metabolites accumulate in the patient's blood, causing cardiovascular and neurotoxic complications and increased mortality. Conventional membrane-based extracorporeal blood purification procedures cannot remove these toxins efficiently. The aim of this in vitro study was to determine whether commercial hemoperfusion adsorbers are suitable for removing protein-bound retention solutes from human plasma and whole blood as well as to compare the removal to conventional hemodialysis.

METHODS

For in vitro testing of the removal of protein-bound substances, whole blood and plasma were spiked with uremic retention solutes (homocysteine, hippuric acid, indoxyl sulfate, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid) and the toxins of liver failure (bilirubin, cholic acid, tryptophan, phenol). Subsequently, the protein binding of each retention solute was determined. The adsorption characteristics of the hemoperfusion adsorbers, Jafron HA and Biosky MG, both approved for the adsorption of protein-bound uremic retention solutes and Cytosorb, an adsorber recommended for adsorption of cytokines, were tested by incubating them in spiked whole blood or plasma for 1 h. Subsequently, the adsorption characteristics of the adsorbers were tested in a dynamic system. For this purpose, a 6-h in vitro hemoperfusion treatment was compared with an equally long in vitro hemodialysis treatment.

RESULTS

Hippuric acid, homocysteine, indoxyl sulfate, and tryptophan were most effectively removed by hemodialysis. Bilirubin and cholic acid were removed best by hemoperfusion with Cytosorb. A treatment with Jafron HA and Biosky MG showed similar results for the adsorption of the tested retention solutes and were best for removing phenol. 3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid could not be removed with any treatment method.

DISCUSSION/CONCLUSION

A combination of hemodialysis with hemoperfusion seems promising to improve the removal of some toxic metabolites in extracorporeal therapies. However, some very strongly protein-bound metabolites cannot be removed adequately with the adsorbers tested.

Immunosenescence and Immune Exhaustion Are Associated with Levels of Protein-Bound Uremic Toxins in Patients on Hemodialysis

BACKGROUND

The accumulation of protein-bound uremic toxins (PBUTs) in chronic kidney disease may affect patients' immune status. The aim of the study was to evaluate their potential impacts on lymphocyte alterations in patients on hemodialysis (HD).

METHODS

The plasma levels of PBUTs were assessed in 54 patients on HD and 31 healthy individuals, using ultra-performance liquid chromatography. The results correlated with the senescent and exhausted status of lymphocytes, based on certain surface molecules, analyzed by flow cytometry.

RESULTS

The plasma levels of PBUTs were significantly increased in the patients on HD compared with the healthy controls. The patients with residual kidney function had reduced hippuric acid (HA) levels, total (p = 0.03) and free (p = 0.04), and free IxS levels (p = 0.02). The total and free HA levels correlated negatively with less differentiated subpopulations, CD4+CD45RA+CD31+ (p = 0.037 and p = 0.027), CD8+CD28+CD57- (p = 0.01, p = 0.01), and naïve B cells (CD19+IgD+CD27-) (p = 0.04, p = 0.03). Both the total and the free pCS levels correlated positively with exhausted CD4 cells, p = 0.02 and p = 0.01, respectively. A multivariate analysis showed that IxS and age were the main independent parameters implicated in the reduction intotal CD4 and B lymphocytes and their naïve and early differentiated subsets.

CONCLUSIONS

Increased PBUTs levels are associated with immune disturbances of patients on HD, HA, and IxS in the immunosenescent and pCS in the immunoexhaustion alterations.

The metabolomic differential plasma profile between dialysates. Pursuing to understand the mechanisms of citrate dialysate clinical benefits

Background: Currently, bicarbonate-based dialysate needs a buffer to prevent precipitation of bicarbonate salts with the bivalent cations, and acetate at 3-4 mmol/L is the most used. However, citrate is being postulated as a preferred option because of its association with better clinical results by poorly understood mechanisms. In that sense, this hypothesis-generating study aims to identify potential metabolites that could biologically explain these improvements found in patients using citrate dialysate. Methods: A unicentric, cross-over, prospective untargeted metabolomics study was designed to analyze the differences between two dialysates only differing in their buffer, one containing 4 mmol/L of acetate (AD) and the other 1 mmol/L of citrate (CD). Blood samples were collected in four moments (i.e., pre-, mid-, post-, and 30-min-post-dialysis) and analyzed in an untargeted metabolomics approach based on UPLC-Q-ToF mass spectrometry. Results: The 31 most discriminant metabolomic variables from the plasma samples of the 21 participants screened by their potential clinical implications show that, after dialysis with CD, some uremic toxins appear to be better cleared, the lysine degradation pathway is affected, and branched-chain amino acids post-dialysis levels are 9-10 times higher than with AD; and, on its part, dialysis with AD affects acylcarnitine clearance. Conclusion: Although most metabolic changes seen in this study could be attributable to the dialysis treatment itself, this study successfully identifies some metabolic variables that differ between CD and AD, which raise new hypotheses that may unveil the mechanisms involved in the clinical improvements observed with citrate in future research.

Multi metabolomics-based analysis of application of Astragalus membranaceus in the treatment of hyperuricemia

Hyperuricemia (HUA) is a common metabolic disease that is an independent risk factor for comorbidities such as hypertension, chronic kidney disease, and coronary artery disease. The prevalence of HUA has increased over the last several decades with improved living standards and increased lifespans. Metabolites are considered the most direct reflection of individual physiological and pathological conditions, and represent attractive candidates to provide deep insights into disease phenotypes. Metabolomics, a technique used to profile metabolites in biofluids and tissues, is a powerful tool for identification of novel biomarkers, and can be used to provide valuable insights into the etiopathogenesis of metabolic diseases and to evaluate the efficacy of drugs. In this study, multi metabolomics-based analysis of the blood, urine, and feces of rats with HUA showed that HUA significantly altered metabolite profiles. Astragalus membranaceus (AM) and benbromomalone significantly mitigated these changes in blood and feces, but not in urine. Some crucial metabolic pathways including lipid metabolism, lipid signaling, hormones synthesis, unsaturated fatty acid (UFAs) absorption, and tryptophan metabolism, were seriously disrupted in HUA rats. In addition, AM administration exerted better treatment effects on HUA than benbromomalone. Furthermore, additional supplementation with UFAs and tryptophan may also induce therapeutic effects against HUA.

N6-Acetyl-L-Lysine and p-Cresol as Key Metabolites in the Pathogenesis of COVID-19 in Obese Patients

Despite the growing number of the vaccinated population, COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global health burden. Obesity, a metabolic syndrome affecting one-third of the population, has proven to be a major risk factor for COVID-19 severe complications. Several studies have identified metabolic signatures and disrupted metabolic pathways associated with COVID-19, however there are no reports evaluating the role of obesity in the COVID-19 metabolic regulation. In this study we highlight the involvement of obesity metabolically in affecting SARS-CoV-2 infection and the consequent health complications, mainly cardiovascular disease. We measured one hundred and forty-four (144) metabolites using ultra high-performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC-QTOF-MS) to identify metabolic changes in response to SARS-CoV-2 infection, in lean and obese COVID-19 positive (n=82) and COVID-19 negative (n=24) patients. The identified metabolites are found to be mainly correlating with glucose, energy and steroid metabolisms. Further data analysis indicated twelve (12) significantly yet differentially abundant metabolites associated with viral infection and health complications, in COVID-19 obese patients. Two of the detected metabolites, n6-acetyl-l-lysine and p-cresol, are detected only among the COVID-19 cohort, exhibiting significantly higher levels in COVID-19 obese patients when compared to COVID-19 lean patients. These metabolites have important roles in viral entry and could explain the increased susceptibility of obese patients. On the same note, a set of six metabolites associated with antiviral and anti-inflammatory functions displayed significantly lower abundance in COVID-19 obese patients. In conclusion, this report highlights the plasma metabolome of COVID-19 obese patients as a metabolic feature and signature to help improve clinical outcomes. We propose n6-acetyl-l-lysine and p-cresol as potential metabolic markers which warrant further investigations to better understand their involvement in different metabolic pathways in COVID-19.

Protein-bound uremic toxins (PBUTs) in chronic kidney disease (CKD) patients: Production pathway, challenges and recent advances in renal PBUTs clearance

Uremic toxins, a group of uremic retention solutes with high concentration which their accumulation on the body makes several biological problems, have recently gained a large interest. The importance of this issue more targets patients with compromised kidney function since the presence of these toxins in their bodies contributes to serious illness and death. It is reported that around 14% of people are subjected of CKD's problems. Among different classifications of uremic toxins, protein bound uremic toxins are poorly removed from the body as they tightly bind to proteins like serum albumin. A deeper and closer understanding of methods for removing protein bound uremic toxins and their efficiency is of paramount importance. This article discussed the most critical protein bound uremic toxins from different points of view including their chemistry, binding sites, interactions, and their biological impacts. Concerning the toxicity and high concentration, p-cresyl sulfate (PCS), Indoxyl sulfate (IS), 3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), and Indole- 3-acetic acid (IAA) was chosen to study in this article. Results offered that the functional groups of mentioned PBUTs and the way that they interact with the adsorbent play an important role in finding substances for removal of them. Furthermore, the development of nanoparticle (NPs) for promising biomedical purposes has been explored. However, there is still a need for further investigation to find biocompatible substances focusing on the removal of PBUTs. PBUTs are a unique class of uremic toxins whose renal clearance mechanisms and role in uremic pathophysiology are still unclear. This review outlines the biochemical aspects of PBUT/protein binding in a view to explaining their renal formation to elimination mechanisms; some examples are drawn from routes involving albumin-binding with indoxyl sulphate, p-cresyl sulfate, p-cresyl glucuronide and hippuric acid. We have also highlighted the kinetic behaviors during dialytic removal of PBUTs to address future concerns regarding dialytic therapy.

Synthesis and toxicity profile in 293 human embryonic kidney cells of the β D-glucuronide derivatives of ortho-, meta- and para-cresol

The formation of β-glucuronides is a major route by which mammals detoxify and remove breakdown products, such as l-tyrosine, as well as many xenobiotics, from their systems. In humans, dietary l-tyrosine is broken down largely by the action of the anaerobic gut bacterium C. difficile to p-cresol, providing a competitive advantage in the gut microbiota. Ortho- (o-) and meta- (m-), cresols, also present in the environment, may share a common degradative pathway. Relatively little work has been done on cresyl glucuronides. Here, a direct synthesis of o-, m-, and p-cresyl β-D-glucuronides from methyl 1,2,3,4 tetra-O-acetyl-β-d-glucuronate and the respective cresol employing trimethylsilyltriflate as promoter is presented. The protected intermediates were hydrolysed using aqueous sodium carbonate to yield the cresyl β-glucuronides. The toxicities of the o-, m- and p-cresyl β-D-glucuronides were compared. All three were less toxic to HEK293 cells than their respective cresol precursors: toxicity followed the order o < m < p for Na⁺ salts and o < p < m for Ca²⁺ salts. The m-cresyl-glucuronide Ca²⁺ salt and p-cresyl-glucuronide Na⁺ salt reduced colony formation by 11% and 9% (v. 30% reduction from the aglycone) respectively, whereas o-cresyl-glucuronide (both Na⁺ and Ca²⁺ salts), mildly stimulated HEK293 cell growth.

Exploring blood alterations in chronic kidney disease and haemodialysis using metabolomics

Chronic kidney disease (CKD) is characterized by retention of uremic solutes. Compared to patients with non-dialysis dependent CKD, those requiring haemodialysis (HD) have increased morbidity and mortality. We wished to characterise metabolic patterns in CKD compared to HD patients using metabolomics. Prevalent non-HD CKD KDIGO stage 3b-4 and stage 5 HD outpatients were screened at a single tertiary hospital. Various liquid chromatography approaches hyphenated with mass spectrometry were used to identify 278 metabolites. Unsupervised and supervised data analyses were conducted to characterize metabolic patterns. 69 patients were included in the CKD group and 35 in the HD group. Unsupervised data analysis showed clear clustering of CKD, pre-dialysis (preHD) and post-dialysis (postHD) patients. Supervised data analysis revealed qualitative as well as quantitative differences in individual metabolites profiles between CKD, preHD and postHD states. An original metabolomics framework could discriminate between CKD stages and highlight HD effect based on 278 identified metabolites. Significant differences in metabolic patterns between CKD and HD patients were found overall as well as for specific metabolites. Those findings could explain clinical discrepancies between patients requiring HD and those with earlier stage of CKD.

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.

Use of faecal volatile organic compound analysis for ante-mortem discrimination between CWD-positive, -negative exposed, and -known negative white-tailed deer (Odocoileus virginianus)

Chronic wasting disease (CWD) is a naturally occurring infectious, fatal, transmissible spongiform encephalopathy of cervids. Currently, disease confirmation relies on post-mortem detection of infectious prions in the medial retropharyngeal lymph nodes or obex in the brain via immunohistochemistry (IHC). Detection of CWD in living animals using this method is impractical, and IHC and other experimental assays are not reliable in detecting low concentrations of prion present in biofluids or faeces. Here, we evaluate the capability of faecal volatile organic compound analysis to discriminate between CWD-positive and -exposed white-tailed deer located at two positive cervid farms, and two groups of CWD-negative deer from two separate disease-free farms.

Age Drives Distortion of Brain Metabolic, Vascular and Cognitive Functions, and the Gut Microbiome

Advancing age is the top risk factor for the development of neurodegenerative disorders, including Alzheimer's disease (AD). However, the contribution of aging processes to AD etiology remains unclear. Emerging evidence shows that reduced brain metabolic and vascular functions occur decades before the onset of cognitive impairments, and these reductions are highly associated with low-grade, chronic inflammation developed in the brain over time. Interestingly, recent findings suggest that the gut microbiota may also play a critical role in modulating immune responses in the brain via the brain-gut axis. In this study, our goal was to identify associations between deleterious changes in brain metabolism, cerebral blood flow (CBF), gut microbiome and cognition in aging, and potential implications for AD development. We conducted our study with a group of young mice (5-6 months of age) and compared those to old mice (18-20 months of age) by utilizing metabolic profiling, neuroimaging, gut microbiome analysis, behavioral assessments and biochemical assays. We found that compared to young mice, old mice had significantly increased levels of numerous amino acids and fatty acids that are highly associated with inflammation and AD biomarkers. In the gut microbiome analyses, we found that old mice had increased Firmicutes/Bacteroidetes ratio and alpha diversity. We also found impaired blood-brain barrier (BBB) function and reduced CBF as well as compromised learning and memory and increased anxiety, clinical symptoms often seen in AD patients, in old mice. Our study suggests that the aging process involves deleterious changes in brain metabolic, vascular and cognitive functions, and gut microbiome structure and diversity, all which may lead to inflammation and thus increase the risk for AD. Future studies conducting comprehensive and integrative characterization of brain aging, including crosstalk with peripheral systems and factors, will be necessary to define the mechanisms underlying the shift from normal aging to pathological processes in the etiology of AD.

Discriminant biomarkers of acute respiratory distress syndrome associated to H1N1 influenza identified by metabolomics HPLC-QTOF-MS/MS platform

Acute respiratory distress syndrome (ARDS) is a serious complication of influenza A (H1N1) virus infection. Its pathogenesis is unknown and biomarkers are lacking. Untargeted metabolomics allows the analysis of the whole metabolome in a biological compartment, identifying patterns associated with specific conditions. We hypothesized that LC-MS could help identify discriminant metabolites able to define the metabolic alterations occurring in patients with influenza A (H1N1) virus infection that developed ARDS. Serum samples from patients diagnosed with 2009 influenza A (H1N1) virus infection with (n = 25) or without (n = 32) ARDS were obtained on the day of hospital admission and analyzed by LC-MS/MS. Metabolite identification was determined by MS/MS analysis and analysis of standards. The specificity of the patterns identified was confirmed in patients without 2009 influenza A(H1N1) virus pneumonia (15 without and 17 with ARDS). Twenty-three candidate biomarkers were found to be significantly different between the two groups, including lysophospholipids and sphingolipids related to inflammation; bile acids, tryptophan metabolites, and thyroxine, related to the metabolism of the gut microflora. Confirmation results demonstrated the specificity of major alterations occurring in ARDS patients with influenza A (H1N1) virus infection.

Adsorption capacity of poly(ether imide) microparticles to uremic toxins

Uremia is a phenomenon caused by retention of uremic toxins in the plasma due to functional impairment of kidneys in the elimination of urinary waste products. Uremia is presently treated by dialysis techniques like hemofiltration, dialysis or hemodiafiltration. However, these techniques in use are more favorable towards removing hydrophilic than hydrophobic uremic toxins. Hydrophobic uremic toxins, such as hydroxy hipuric acid (OH-HPA), phenylacetic acid (PAA), indoxyl sulfate (IDS) and p-cresylsulfate (pCRS), contribute substantially to the progression of chronic kidney disease (CKD) and cardiovascular disease. Therefore, objective of the present study is to test adsorption capacity of highly porous microparticles prepared from poly(ether imide) (PEI) as an alternative technique for the removal of uremic toxins. Two types of nanoporous, spherically shaped microparticles were prepared from PEI by a spraying/coagulation process.PEI particles were packed into a preparative HPLC column to which a mixture of the four types of uremic toxins was injected and eluted with ethanol. Eluted toxins were quantified by analytical HPLC. PEI particles were able to adsorb all four toxins, with the highest affinity for PAA and pCR. IDS and OH-HPA showed a partially non-reversible binding. In summary, PEI particles are interesting candidates to be explored for future application in CKD.

[Predictors of physical incapacity degree to chronic hemodialysis patients in Kinshasa : Key role of the residual diuresis]

OBJECTIVE

Identifying predictors of physical incapacity degree in patients on chronic hemodialysis in Kinshasa.

METHODS

Bicentric analytical study, between January 2007 and July 2013. Degree of physical handicap was evaluated at 6months of hemodialysis based on the scale of Rosser. Logistic regression sought the predictors of no or light physical incapacity (Rosser<3) vs. moderate to maximum (Rosser≥3). P was set at 0.05.

RESULTS

One hundred twenty-seven patients (127) patients received at least 6months of hemodialysis (53.3±11years; 73.2 % male), 79 (62.2 %) had no or light incapacity and 48 (37.8 %) moderate to maximum. Predictors of lower physical incapacity in univaried analysis were: secured funding, high socioeconomic level, lack of diabetes mellitus, high body weight, normal systolic and diastolic blood pressure, residual diuresis 3months later, hemoglobin and hematocrit, low comorbidity, arteriovenous fistula, erythropoietin, at least 12hours of hemodialysis per week and lack of intradialytic complications. After logistic regression, a high residual diuresis 3months of hemodialysis has proved an independent predictor of lower physical Incapacity (aOR 0.998; P=0.024) next to the lack of diabetes mellitus (aOR 0.239; P=0.024), good control of systolic (aOR 0.958; P=0.013) and diastolic (aOR 1.089; P=0.003) blood pressure and the use of erythropoietin (aOR 5.687; P=0.004).

CONCLUSION

Preserving residual diuresis is associated with lower physical incapacity and must be integrated in the management in hemodialysis.

Nanosized microporous crystals: emerging applications

This review highlights recent developments in the synthesis and unconventional applications of nanosized microporous crystals including framework (zeolites) and layered (clays) type materials. Owing to their microporous nature nanosized zeolites and clays exhibit novel properties, different from those of bulk materials. The factors controlling the formation of nanosized microporous crystals are first revised. The most promising approaches from the viewpoint of large-scale production of nanosized zeolites and clays are discussed in depth. The preparation and advanced applications of nanosized zeolites and clays in free (suspension and powder forms) and fixed (films) forms are summarized. Further the review emphasises the non-conventional applications of new porous materials. A comprehensive analysis of the emerging applications of microporous nanosized crystals in the field of semiconductor industry, optical materials, chemical sensors, medicine, cosmetics, and food industry is presented. Finally, the future needs and perspectives of nanosized microporous materials (zeolites and clays) are addressed.

The association of uremic toxins and inflammation in hemodialysis patients

BACKGROUND

Cardiovascular disease is the leading cause of mortality in hemodialysis patients and is associated with chronic inflammation. Elevation of uremic toxins, particular protein-bound uremic toxins, is a possible cause of hyper-inflammation in hemodialysis patients. But the association between uremic toxins and inflammatory markers in hemodialysis is still unclear.

METHODS

We conducted a cross-sectional study to evaluate the association of the serum uremic toxins and inflammatory markers in hemodialysis patients.

RESULTS

The uremic toxins were not associated with inflammatory markers--including high sensitivity C-reactive protein, IL(Interleukin) -1β, IL-6, tumor necrosis factor-α. In multiple linear regression, serum levels of total p-cresol sulfate (PCS) were independently significantly associated with serum total indoxyl sulfate (IS) (standardized coefficient: 0.274, p<0.001), and co-morbidity of diabetes mellitus (DM) (standardized coefficient: 0.342, p<0.001) and coronary artery disease (CAD) (standardized coefficient: 0.128, p = 0.043). The serum total PCS levels in hemodialysis with co-morbidity of DM and CAD were significantly higher than those without co-morbidity of DM and CAD (34.10±23.44 vs. 16.36±13.06 mg/L, p<0.001). Serum levels of total IS was independently significantly associated with serum creatinine (standardized coefficient: 0.285, p<0.001), total PCS (standardized coefficient: 0.239, p = 0.001), and synthetic membrane dialysis (standardized coefficient: 0.139, p = 0.046).

CONCLUSION

The study showed that serum levels of total PCS and IS were not associated with pro-inflammatory markers in hemodialysis patients. Besides, serum levels of total PCS were independently positively significantly associated with co-morbidity of CAD and DM.

Effect of uremic serum and uremic toxins on drug metabolism in human microsomes

There is increasing evidence that renal impairment modifies nonrenal drug clearance through drug metabolizing cytochrome P450 (CYP) enzymes. In this study, the direct inhibitory effect of serum from chronic renal failure (CRF) patients receiving dialysis was evaluated in CYP3A4 (testosterone) and CYP2B6 (bupropion) metabolism assays. Human liver microsomes were incubated with ultrafiltered serum collected pre- and post-hemodialysis from ten CRF patients. Additionally, several uremic toxins were evaluated in the CYP3A4 assay. In only three patients was there a significant decrease or increase in testosterone or bupropion metabolism post-dialysis. Urea, mannitol, guanidine, homocysteine, uridine and creatinine had no effect on CYP3A4 metabolism. CMPF, hippuric acid and p-cresol had IC50 values that fell within CRF patient plasma concentrations. The IC50 values for indoxyl sulfate and indole-3-acetic acid were greater than CRF plasma concentrations. The lack of a consistent effect on CYP3A4 or CYP2B6 metabolism by uremic serum may be due in part to the frequency of hemodialysis in these patients which reduced the accumulation of uremic toxins. CMPF, hippuric acid and p-cresol have the ability to inhibit CYP3A4 metabolism at clinical concentrations which may correspond to reports of changes in hepatic metabolism in some CRF patients.

ROS and PDFG-β receptors are critically involved in indoxyl sulfate actions that promote vascular smooth muscle cell proliferation and migration

Patients with chronic renal failure are at greater risk of developing atherosclerosis than healthy individuals, and recent data suggest that the putative uremic toxin indoxyl sulfate (IS) promotes the pathogenesis of atherosclerosis. The present study examined the effects of IS on vascular smooth muscle cells (VSMCs) with respect to reactive oxygen species (ROS), platelet-derived growth factor (PDGF) receptors, and mitogen-activated protein kinases (MAPKs). IS induced the migration and proliferation of VSMCs and synergistically enhanced their PDGF-induced migration as well as proliferation. The effects of PDGF were promoted after a 24-h incubation with IS despite the absence of IS during PDGF stimulation. Intracellular ROS levels were increased in the presence of IS, and PDGF-dependent ROS production was augmented by a prior 24-h incubation with IS even in the absence of IS during PDGF stimulation. These data suggest that IS increases the sensitivity of VSMCs to PDGF. IS also phosphorylated PDGF-β-receptors and upregulated PDGF-β receptor but not α-receptor protein expression in the absence of exogenous PDGF. The NADPH oxidase inhibitor diphenylene iodonium blocked IS-dependent increase in receptor expression. Administration of IS to nephrectomized rats also elevated receptor protein expression in arterial VSMCs. Inhibitors of NADPH oxidase, PDGF-β receptors, extracellular-regulated protein kinase (ERK), and p38 MAPK all inhibited IS-induced VSMCs migration and proliferation. Taken together, these findings indicate that IS induces the migration as well as proliferation of VSMCs through PDGF-β receptors and that ROS generation is critically involved in this process, which promotes the development of atherosclerosis.

Removal of the protein-bound solutes indican and p-cresol sulfate by peritoneal dialysis

BACKGROUND AND OBJECTIVES

Protein-bound solutes are poorly cleared by peritoneal dialysis. We examined the hypothesis that plasma concentrations of bound solutes would therefore rise as residual renal function is lost.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Clearances of urea indican and p-cresol sulfate were measured in peritoneal dialysis patients with and without residual function.

RESULTS

In patients with residual function, protein binding restricted the peritoneal indican and p-cresol sulfate clearances to 0.3 +/- 0.1 ml/min, as compared to the peritoneal urea clearance of 5.5 +/- 1.1 ml/min. The urinary indican and p-cresol sulfate clearances of 2.7 +/- 2.5 and 1.3 +/- 1.0 ml/min were closer to the urinary urea clearance of 3.9 +/- 2.2 ml/min, reflecting the superior ability of native kidney function to clear bound solutes. Urinary clearance thus provided the majority of the total indican and p-cresol sulfate clearances of 3.0 +/- 2.5 and 1.6 +/- 1.0 ml/min in patients with residual function but the minority of total urea clearance of 9.4 +/- 2.2 ml/min. Loss of residual function lowered the total clearances for indican and p-cresol sulfate to 0.5 +/- 0.2 and 0.4 +/- 0.2 ml/min, whereas the urea clearance fell only slightly. However there was only a modest increase in the plasma indican level and no increase in the plasma p-cresol sulfate level in patients with no residual function because reduction in the daily removal of these solutes accompanied the reduction in their total clearance rates.

CONCLUSIONS

Reduction in the removal of indican and p-cresol sulfate kept plasma levels from rising markedly when residual function was lost.

Mass spectrometry analysis of urine and catheter of a patient with purple urinary bag syndrome

INTRODUCTION

Purple urinary bag syndrome (PUBS) is considered to be a benign condition observed in the urinary catheter and bag in some catheterized patients with urinary tract infections. This syndrome is usually reported to occur in alkaline urine.

CASE REPORT

We report of a catheterized patient with PUBS and slightly acidic urine (pH 6-6.5). A novel analysis method was developed using high pressure liquid chromatography and mass spectrometry (HPLC/MS) to detect compounds that are thought to be associated with PUBS. Urine, urinary sediment, and the plastic collection system were assayed and quantitated using these methods. The potential toxicity of one of these compounds, indoxyl sulfate, is discussed.

CONCLUSIONS

The presence of PUBS in a catheterized patient with slightly acidic urine is reported. A novel method for the analysis of chemical components of PUBS and the first direct confirmation of the presence of indigo in the urine sediment and collecting system are described.

Increasing the Clearance of Protein-Bound Solutes by Addition of a Sorbent to the Dialysate

The capacity of sorbent systems to increase solute clearances above the levels that are provided by hemodialysis has not been well defined. This study assessed the extent to which solute clearances can be increased by addition of a sorbent to the dialysate. Attention was focused on the clearance of protein-bound solutes, which are cleared poorly by conventional hemodialysis. A reservoir that contained test solutes and artificial plasma was dialyzed first with the plasma flow set at 46 +/- 3 ml/min and the dialysate flow (Q(d)) set at 42 +/- 3 ml/min using a hollow fiber kidney with mass transfer area coefficients greater than Q(d) for each of the solutes. Under these conditions, the clearance of urea (Cl(urea)) was 34 +/- 1 ml/min, whereas the clearances of the protein-bound solutes indican (Cl(ind)), p-cresol sulfate (Cl(pcs)), and p-cresol (Cl(pc)) averaged only 5 +/- 1, 4 +/- 1, and 14 +/- 1 ml/min, respectively The effect of addition of activated charcoal to the dialysate then was compared with the effect of increasing Q(d) without addition of any sorbent. Addition of charcoal increased Cl(ind), Cl(pcs), and Cl(pc) to 12 +/- 1, 9 +/- 2, and 35 +/- 4 ml/min without changing Cl(urea). Increasing Q(d) without the addition of sorbent had a similar effect on the clearance of the protein-bound solutes. Mathematical modeling predicted these changes and showed that the maximal effect of addition of a sorbent to the dialysate is equivalent to that of an unlimited increase in Q(d). These results suggest that as an adjunct to conventional hemodialysis, addition of sorbents to the dialysate could increase the clearance of protein-bound solutes without greatly altering the clearance of unbound solutes.

Adsorption of the uremic toxin p-cresol onto hemodialysis membranes and microporous adsorbent zeolite silicalite

Para-cresol CH3C6H4OH is a protein-bound solute which is not eliminated efficiently by hemodialysis systems. In this study, we present adsorption of p-cresol as a complementary process to hemodialysis. The kinetics and isotherms of adsorption onto cellulose-based membranes (cellulose diacetate and triacetate), synthetic membranes (polyamide, polysulfone, polyacrylonitrile and polymethylmethacrylate) and microporous zeolite silicalite (MFI), have been evaluated in static conditions. The results indicate that p-cresol has a low affinity to all membranes but polysulfone and polyamide and that the times to reach equilibrium conditions are slow. In contrast, equilibration time on silicalite is fast (2 min to eliminate 90%) while adsorption levels are high (maximum adsorption about 106 mg g(-1)). Adsorption onto microporous adsorbents could be a novel way to eliminate uremic toxins from blood.

Purple urine bag syndrome in a hemodialysis patient

Purple urine bag syndrome (PUBS) is an uncommon disorder, in which the plastic disposable urinary catheter bag turns purple or blue following hours or days of urinary catheterization. The purple discoloration results from indirubin dissolved in the plastic mixing with indigo in the urine. Bacteria possessing indoxyl sulfatase degrade indoxyl sulfate into indirubin and indigo. Indoxyl sulfate is derived from the metabolism of tryptophan. PUBS usually occurs in chronic catheterized elderly women who are constipated and poorly ambulant. The clinical course is benign and rarely causes sepsis. This investigation reports a 61-year-old female diabetic patient with end-stage renal disease on maintenance hemodialysis, who had two episodes of blue or purple urine bag discoloration. The urine culture of the first episode yielded Klebsiella pneumoniae, whereas that of the second episode yielded Escherichia coli, Enterococcus faecalis, and Proteus vulgaris. Both episodes resolved following oral antibiotics treatment and placement of new foley catheters. To our knowledge, this is the first recorded case of PUBS in a dialysis patient.

The clearance of protein-bound solutes by hemofiltration and hemodiafiltration

BACKGROUND

Hemofiltration in the form of continuous venovenous hemofiltration (CVVH) is increasingly used to treat acute renal failure. Compared to hemodialysis, hemofiltration provides high clearances for large solutes but its effect on protein-bound solutes has been largely ignored.

METHODS

Standard clinical systems were used to remove test solutes from a reservoir containing artificial plasma. Clearances of the protein-bound solutes phenol red (C(PR)) and indican (C(IN)) were compared to clearances of urea (C(UREA)) during hemofiltration and hemodiafiltration. A mathematical model was developed to predict clearances from values for plasma flow Q(p), dialysate flow Q(d), ultrafiltration rate Q(f), filter size and the extent of solute binding to albumin.

RESULTS

When hemofiltration was performed with Q(p) 150 mL/min and Q(f) 17 mL/min, clearance values were C(PR) 1.0 +/- 0.1 mL/min; C(IN) 3.7 +/- 0.5 mL/min; and C(UREA) 14 +/- 1 mL/min. The clearance of the protein-bound solutes was approximately equal to the solute-free fraction multiplied by the ultrafiltration rate corrected for the effect of predilution. Addition of Q(d) 42 mL/min to provide HDF while Q(p) remained 150 mL/min resulted in proportional increases in the clearance of protein-bound solutes and urea. In contrast, the clearance of protein-bound solutes relative to urea increased when hemodiafiltration was performed using a larger filter and increasing Q(d) to 300 mL/min while Q(p) was lowered to 50 mL/min. The pattern of observed results was accurately predicted by mathematical modeling.

CONCLUSION

In vitro measurements and mathematical modeling indicate that CVVH provides very limited clearance of protein-bound solutes. Continuous venous hemodiafiltration (CVVHDF) increases the clearance of protein-bound solutes relative to urea only when dialysate flow rate and filter size are increased above values now commonly employed.