Case report: thyrotoxic periodic paralysis, an unusual cause of hypokalemia.

Introduction: Thyrotoxic periodic paralysis (TPP) is a type of hypokalemic periodic paralysis that is caused by an underlying thyrotoxicosis. It is a rare cause of hypokalemia due to intracellular potassium shift, causing acute muscle weakness.Case presentation: We present a case of a 19-year-old male of Thai descent with acute proximal symmetric lower limb weakness. The combination of these symptoms with profound hypokalemia, rapid recovery after normalization of serum potassium, and evidence of hyperthyroidism led to the diagnosis of thyrotoxic periodic paralysis, in this case due to an underlying Graves' disease.Conclusion: Clinicians should consider the diagnosis of TPP when a patient presents with the triad of acute paresis, profound hypokalemia and hyperthyroidism.

Remote sensing and signaling in kidney proximal tubules stimulates gut microbiome-derived organic anion secretion.

Membrane transporters and receptors are responsible for balancing nutrient and metabolite levels to aid body homeostasis. Here, we report that proximal tubule cells in kidneys sense elevated endogenous, gut microbiome-derived, metabolite levels through EGF receptors and downstream signaling to induce their secretion by up-regulating the organic anion transporter-1 (OAT1). Remote metabolite sensing and signaling was observed in kidneys from healthy volunteers and rats in vivo, leading to induced OAT1 expression and increased removal of indoxyl sulfate, a prototypical microbiome-derived metabolite and uremic toxin. Using 2D and 3D human proximal tubule cell models, we show that indoxyl sulfate induces OAT1 via AhR and EGFR signaling, controlled by miR-223. Concomitantly produced reactive oxygen species (ROS) control OAT1 activity and are balanced by the glutathione pathway, as confirmed by cellular metabolomic profiling. Collectively, we demonstrate remote metabolite sensing and signaling as an effective OAT1 regulation mechanism to maintain plasma metabolite levels by controlling their secretion.

A noninferiority trial comparing a heparin-grafted membrane plus citrate-containing dialysate versus regional citrate anticoagulation: results of the CiTED study.

Background: Anticoagulation is a prerequisite for successful haemodialysis. Heparin and low-molecular weight heparins are routinely used despite increased bleeding risk. Regional citrate anticoagulation (RCA) is efficacious, but is laborious and may induce metabolic disturbances. Heparin-grafted membranes are less efficacious. It is not known whether combining citrate-containing dialysate and a heparin-grafted membrane is a valid anticoagulation strategy. Methods: We performed a randomized crossover noninferiority trial, with a prespecified noninferiority threshold of 10% in maintenance dialysis patients ( n = 25). We compared the combination of citrate-containing dialysate plus a heparin-grafted membrane [CiTrate and EvoDial (CiTED) protocol] with RCA. The primary endpoint was completion of dialysis without significant clotting. Secondary endpoints included time to clotting, achieved Kt / V urea , loss of total cell volume, venous air chamber clotting score and systemic-ionized calcium concentration. Results: In total, 1284 sessions were performed according to study protocol, 636 in the CiTED arm and 648 in the RCA arm. The primary outcome of preterm interruption due to clotting occurred in 36 (5.7%) of sessions in the CiTED arm, and in 40 (6.2%) sessions in the RCA arm, thereby meeting noninferiority criteria (P < 0.0001). Most of the clotting events occurred in the fourth hour of dialysis. Repetitive clotting occurred in four patients in the CiTED arm and one patient in the RCA arm. Time to preterm interruption due to clotting and achieved Kt / V urea was not significantly different. Systemic-ionized calcium levels during treatment were significantly lower in the RCA arm and clinically relevant hypocalcaemia was noted only in the RCA arm. Conclusion: The combination of citrate-containing dialysate and a heparin-grafted membrane is a valid alternative to RCA.

The gut-kidney axis.

The host-gut microbiota interaction has been the focus of increasing interest in recent years. It has been determined that this complex interaction is not only essential to many aspects of normal "mammalian" physiology but that it may also contribute to a multitude of ailments, from the obvious case of inflammatory bowel disease to (complex) diseases residing in organs outside the gut. An increasing body of evidence indicates that crosstalk between host and microbiota is pathophysiologically relevant in patients with chronic kidney disease (CKD). Interactions are bidirectional; on the one hand, uremia affects both the composition and metabolism of the gut microbiota and, on the other hand, important uremic toxins originate from microbial metabolism. In addition, gut dysbiosis may induce a disruption of the epithelial barrier, ultimately resulting in increased exposure of the host to endotoxins. Due to dietary restrictions and gastrointestinal dysfunctions, microbial metabolism shifts to a predominantly proteolytic fermentation pattern in CKD. Indoxyl sulfate and p-cresyl sulfate, both end-products of protein fermentation, and trimethylamine-N-oxide, an end-product of microbial choline and carnitine metabolism, are prototypes of uremic toxins originating from microbial metabolism. The vascular and renal toxicity of these co-metabolites has been demonstrated extensively in experimental and clinical studies. These co-metabolites are an appealing target for adjuvant therapy in CKD. Treatment options include dietary therapy, prebiotics, probiotics and host and bacterial enzyme inhibitors. Final proof of the concept should come from randomized controlled and adequately powered intervention studies.

A liquid chromatography - tandem mass spectrometry method to measure a selected panel of uremic retention solutes derived from endogenous and colonic microbial metabolism.

Chronic kidney disease (CKD) is associated with an increased risk of mortality and cardiovascular disease, which is, at least partly, mediated by the accumulation of so-called uremic retention solutes. Although there has been an increasing interest in the behavior of these solutes, derived from both the endogenous and colonic microbial metabolism, methods to simultaneously and accurately measure a broad panel of relevant uremic retention solutes remain scarce. We developed a highly sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method. A high throughput sample preparation was used with extraction of analytes from 50 µl serum using Ostro plate technology. For most solutes, stable isotopes labelled metabolites were used as internal standards. Chromatography was achieved using an Acquity UPLC CSH Fluoro Phenyl column. The total run time was 8 min, the mobile phase was a gradient of 0.1% formic acid in Milli-Q water and pure methanol at a flow rate of 0.5 ml min(-1). Detection was performed using a tandem mass spectrometer with alternated positive and negative electrospray ionization. Calibration curves were linear for all solutes. Precision was assessed according to the NCCLS EP5-T guideline, being below 15% for all metabolites. Mean recoveries were between 83 and 104% for all metabolites. The validated method was successfully applied in a cohort of 488 patients with CKD. We developed and validated a sensitive and robust UPLC-MS/MS method for quantification of 15 uremic retention solutes derived from endogenous and colonic microbial metabolism. This method allows for studying the behavior and relevance of these solutes in patients with CKD.

Microbiota-Derived Phenylacetylglutamine Associates with Overall Mortality and Cardiovascular Disease in Patients with CKD.

Colonic microbial metabolism substantially contributes to uremic solute production. p-Cresyl sulfate and indoxyl sulfate are the main representatives of solutes of microbial origin and also, protein-bound solutes, exhibiting high protein-binding affinity and dependence on tubular secretion. Phenylacetylglutamine is another microbial metabolite with high dependence on tubular secretion but low protein-binding affinity. The relevance of such solutes is unknown. Therefore, we prospectively followed 488 patients with CKD stages 1-5 and a measurement of serum phenylacetylglutamine by liquid chromatography-mass spectrometry. In a subgroup, we determined 24-hour urinary excretion as a surrogate of intestinal uptake as well as renal clearance of phenylacetylglutamine. We performed outcome analysis for mortality (51 events) and cardiovascular disease (75 events). Serum phenylacetylglutamine level correlated with 24-hour urinary excretion (rho=0.55; P<0.001) and clearance of phenylacetylglutamine (rho=-0.76; P<0.001). Phenylacetylglutamine clearance also correlated with eGFR (rho=0.84; P<0.001). Furthermore, serum phenylacetylglutamine level associated with mortality (hazard ratio per 1-SD increase, 1.77; 95% confidence interval, 1.22 to 2.57; P=0.003) and cardiovascular disease (hazard ratio, 1.79; 95% confidence interval, 1.32 to 2.41; P<0.001) after adjustment for age, sex, presence of diabetes mellitus, prior cardiovascular disease, and eGFR. Thus, serum phenylacetylglutamine level is elevated in patients with more advanced CKD and determined by intestinal uptake and renal clearance, and it is not fully accounted for by differences in eGFR. High serum phenylacetylglutamine level is a strong and independent risk factor for mortality and cardiovascular disease, suggesting the relevance of microbial metabolism and/or tubular dysfunction in CKD, irrespective of protein binding.

The Influence of Prebiotic Arabinoxylan Oligosaccharides on Microbiota Derived Uremic Retention Solutes in Patients with Chronic Kidney Disease: A Randomized Controlled Trial.

UNLABELLED: The colonic microbial metabolism is a key contributor to uremic retention solutes accumulating in patients with CKD, relating to adverse outcomes and insulin resistance. Whether prebiotics can reduce intestinal generation of these microbial metabolites and improve insulin resistance in CKD patients not yet on dialysis remains unknown. We performed a randomized, placebo-controlled, double-blind, cross-over study in 40 patients with eGFR between 15 and 45 ml/min/1.73 m2. Patients were randomized to sequential treatment with prebiotic arabinoxylan oligosaccharides (AXOS) (10 g twice daily) and maltodextrin for 4 weeks, or vice versa, with a 4-week wash-out period between both intervention periods. Serum levels and 24h urinary excretion of p-cresyl sulfate, p-cresyl glucuronide, indoxyl sulfate, trimethylamine N-oxide and phenylacetylglutamine were determined at each time point using liquid chromatography-tandem mass spectrometry. In addition, insulin resistance was estimated by the homeostatic model assessment (HOMA-IR). A total of 39 patients completed the study. We observed no significant effect of AXOS on serum p-cresyl sulfate (P 0.42), p-cresyl glucuronide (P 0.59), indoxyl sulfate (P 0.70) and phenylacetylglutamine (P 0.41) and a small, albeit significant decreasing effect on serum trimethylamine N-oxide (P 0.04). There were neither effect of AXOS on 24h urinary excretion of p-cresyl sulfate (P 0.31), p-cresyl glucuronide (P 0.23), indoxyl sulfate (P 0.87) and phenylacetylglutamine (P 0.43), nor on 24h urinary excretion of trimethylamine N-oxide (P 0.97). In addition, we observed no significant change in HOMA-IR (P 0.93). In conclusion, we could not demonstrate an influence of prebiotic AXOS on microbiota derived uremic retention solutes and insulin resistance in patients with CKD not yet on dialysis. Further study is necessary to elucidate whether prebiotic therapy with other characteristics, higher cumulative exposure or in different patient populations may be of benefit. TRIAL REGISTRATION: Clinicaltrials.gov NCT02141815.

Metabolism, Protein Binding, and Renal Clearance of Microbiota-Derived p-Cresol in Patients with CKD.

BACKGROUND AND OBJECTIVES: Colonic microbial metabolism substantially contributes to uremic retention solutes in CKD. p-Cresyl sulfate is the main representative of this group of solutes, relating to adverse outcomes. Other than sulfate conjugation, p-cresol is subjected to endogenous glucuronide conjugation. Whether the balance between sulfate and glucuronide conjugation is relevant in CKD is unexplored. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We prospectively followed 488 patients with CKD stages 1-5 (enrollment between November of 2005 and September of 2006; follow-up until December of 2010). Serum and urine levels of p-cresyl sulfate and p-cresyl glucuronide were measured using liquid chromatography-mass spectrometry. Total amount of microbial p-cresol was calculated by the sum of serum p-cresyl sulfate and p-cresyl glucuronide. Outcome analysis was performed for mortality and cardiovascular disease. RESULTS: Serum p-cresyl sulfate was a median of 193.0-fold (interquartile range, 121.1-296.6) higher than serum p-cresyl glucuronide, with a significant correlation between eGFR and proportion of serum p-cresyl sulfate to glucuronide (rho=0.23; P=0.001). There was also a significant correlation between eGFR and proportion of 24-hour urinary excretion of p-cresyl sulfate to glucuronide (rho=0.32; P<0.001). Higher serum p-cresol and lower proportion of serum p-cresyl sulfate to glucuronide were jointly and significantly associated with mortality (hazard ratio per SD higher, 1.58; 95% confidence interval, 1.10 to 2.29; P=0.01 and hazard ratio, 0.65; 95% confidence interval, 0.47 to 0.89; P<0.01, respectively) and cardiovascular disease (hazard ratio, 1.68; 95% confidence interval, 1.27 to 2.22; P<0.001 and hazard ratio, 0.55; 95% confidence interval, 0.42 to 0.72; P<0.001, respectively) after adjustment for eGFR, Framingham risk factors, mineral bone metabolism markers, C-reactive protein, and albumin. CONCLUSIONS: p-Cresol shows a preponderance of sulfate conjugation, although a relatively diminished sulfotransferase activity can be suggested in patients with advanced CKD. Along with total p-cresol burden, a relative shift from sulfate to glucuronide conjugation is independently associated with mortality and cardiovascular disease, warranting increased focus to the dynamic interplay between microbial and endogenous metabolism.

The influence of renal transplantation on retained microbial-human co-metabolites.

BACKGROUND: Colonic microbial metabolism contributes substantially to uraemic retention solutes accumulating in chronic kidney disease (CKD) and various microbial-human co-metabolites relate to adverse outcomes. The influence of renal transplantation on these solutes is largely unexplored. METHODS: We prospectively followed 51 renal transplant recipients at the time of transplantation, Day 7 and Months 3 and 12 post-transplantation. Serum levels of p-cresyl sulphate (PCS), p-cresyl glucuronide (PCG), indoxyl sulphate (IS), trimethylamine N-oxide (TMAO) and phenylacetylglutamine (PAG) were determined with liquid chromatography-tandem mass spectrometry. At each time point, transplant recipients were compared with CKD control patients matched for age, gender, diabetes mellitus and renal function. Determinants of serum levels were also compared between an unrelated cohort of 65 transplant recipients at Month 3 post-transplantation and CKD patients with 24-h urinary collection. RESULTS: Serum levels of the tested microbial-human co-metabolites significantly decreased following renal transplantation (P < 0.001). At each time point post-transplantation, serum levels of PCS, PCG, PAG and, to a lesser extent, IS, but not TMAO, were significantly lower in transplant recipients when compared with CKD control patients. Further analysis demonstrated significantly lower 24-h urinary excretion of these solutes in transplant recipients (P < 0.001). Also, renal clearances of PCG, IS, TMAO and PAG were significantly lower in transplant recipients without differences in estimated glomerular filtration rate. CONCLUSIONS: Colonic microbiota-derived uraemic retention solutes substantially decrease following renal transplantation. The 24-h urinary excretion of these microbial-human co-metabolites is lower when compared with CKD patients, suggesting an independent influence of transplantation on intestinal uptake, a composite of colonic microbial metabolism and intestinal absorption. Renal solute handling may differ between transplant recipients and CKD patients.

The Influence of CKD on Colonic Microbial Metabolism.

There is increasing interest in the colonic microbiota as a relevant source of uremic retention solutes accumulating in CKD. Renal disease can also profoundly affect the colonic microenvironment and has been associated with a distinct colonic microbial composition. However, the influence of CKD on the colonic microbial metabolism is largely unknown. Therefore, we studied fecal metabolite profiles of hemodialysis patients and healthy controls using a gas chromatography-mass spectrometry method. We observed a clear discrimination between both groups, with 81 fecal volatile organic compounds detected at significantly different levels in hemodialysis patients and healthy controls. To further explore the differential impact of renal function loss per se versus the effect of dietary and other CKD-related factors, we also compared fecal metabolite profiles between patients on hemodialysis and household contacts on the same diet, which revealed a close resemblance. In contrast, significant differences were noted between the fecal samples of rats 6 weeks after 5/6th nephrectomy and those of sham-operated rats, still suggesting an independent influence of renal function loss. Thus, CKD associates with a distinct colonic microbial metabolism, although the effect of renal function loss per se in humans may be inferior to the effects of dietary and other CKD-related factors. The potential beneficial effect of therapeutics targeting colonic microbiota in patients with CKD remains to be examined.

The Influence of Dietary Protein Intake on Mammalian Tryptophan and Phenolic Metabolites.

Although there has been increasing interest in the use of high protein diets, little is known about dietary protein related changes in the mammalian metabolome. We investigated the influence of protein intake on selected tryptophan and phenolic compounds, derived from both endogenous and colonic microbial metabolism. Furthermore, potential inter-species metabolic differences were studied. For this purpose, 29 healthy subjects were allocated to a high (n = 14) or low protein diet (n = 15) for 2 weeks. In addition, 20 wild-type FVB mice were randomized to a high protein or control diet for 21 days. Plasma and urine samples were analyzed with liquid chromatography-mass spectrometry for measurement of tryptophan and phenolic metabolites. In human subjects, we observed significant changes in plasma level and urinary excretion of indoxyl sulfate (P 0.004 and P 0.001), and in urinary excretion of indoxyl glucuronide (P 0.01), kynurenic acid (P 0.006) and quinolinic acid (P 0.02). In mice, significant differences were noted in plasma tryptophan (P 0.03), indole-3-acetic acid (P 0.02), p-cresyl glucuronide (P 0.03), phenyl sulfate (P 0.004) and phenylacetic acid (P 0.01). Thus, dietary protein intake affects plasma levels and generation of various mammalian metabolites, suggesting an influence on both endogenous and colonic microbial metabolism. Metabolite changes are dissimilar between human subjects and mice, pointing to inter-species metabolic differences with respect to protein intake.

Associations of Soluble CD14 and Endotoxin with Mortality, Cardiovascular Disease, and Progression of Kidney Disease among Patients with CKD.

BACKGROUND AND OBJECTIVES: CD14 plays a key role in the innate immunity as pattern-recognition receptor of endotoxin. Higher levels of soluble CD14 (sCD14) are associated with overall mortality in hemodialysis patients. The influence of kidney function on plasma sCD14 levels and its relationship with adverse outcomes in patients with CKD not yet on dialysis is unknown. This study examines the associations between plasma levels of sCD14 and endotoxin with adverse outcomes in patients with CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We measured plasma levels of sCD14 and endotoxin in 495 Leuven Mild-to-Moderate CKD Study participants. Mild-to-moderate CKD was defined as presence of kidney damage or eGFR<60 ml/min per 1.73 m(2) for ≥3 months, with exclusion of patients on RRT. Study participants were enrolled between November 2005 and September 2006. RESULTS: Plasma sCD14 was negatively associated with eGFR (ρ=-0.34, P<0.001). During a median follow-up of 54 (interquartile range, 23-58) months, 53 patients died. Plasma sCD14 was predictive of mortality, even after adjustment for renal function, Framingham risk factors, markers of mineral bone metabolism, and nutritional and inflammatory parameters (hazard ratio [HR] per SD higher of 1.90; 95% confidence interval [95% CI],1.32 to 2.74; P<0.001). After adjustment for the same risk factors, plasma sCD14 was also a predictor of cardiovascular disease (HR, 1.30; 95% CI, 1.00 to 1.69; P=0.05). Although plasma sCD14 was associated with progression of CKD, defined as reaching ESRD or doubling of serum creatinine in models adjusted for CKD-specific risk factors (HR, 1.24; 95% CI, 1.01 to 1.52; P=0.04), significance was lost when adjusted for proteinuria (HR, 1.19; 95% CI, 0.96 to 1.48; P=0.11). There was neither correlation between plasma endotoxin and sCD14 (ρ=-0.06, P=0.20) nor was endotoxin independently associated with adverse outcome during follow-up. CONCLUSIONS: Plasma sCD14 is elevated in patients with decreased kidney function and associated with mortality and cardiovascular disease in patients with CKD not yet on dialysis.

Soluble urokinase receptor is a biomarker of cardiovascular disease in chronic kidney disease.

Soluble urokinase-type plasminogen activator receptor (suPAR) accumulates in patients with chronic kidney disease (CKD). In various non-CKD populations, suPAR has been proposed as a prognostic marker for mortality and cardiovascular disease. However, it is not known whether suPAR holds prognostic information in patients with mild-to-moderate CKD. In a prospective observational study of 476 patients with mild-to-moderate kidney disease, we examined multivariate associations between suPAR, overall mortality, and cardiovascular events. After a mean follow-up of 57 months, 52 patients died and 76 patients had at least one fatal or nonfatal cardiovascular event. Higher suPAR was directly and significantly associated with both overall mortality (univariate hazard ratio 5.35) and cardiovascular events (univariate hazard ratio 5.06). In multivariate analysis, suPAR remained significantly associated with cardiovascular events (full model, hazard ratio 3.05). Thus, in patients with mild-to-moderate CKD, suPAR concentrations show a clear, direct, and graded association with a higher risk for new-onset cardiovascular disease.

Heparin-coated dialyzer membranes: is non-inferiority good enough?

Evidence on the optimal anticoagulation regimen for hemodialysis in patients at high bleeding risk is scarce. The HepZero study is the first large multinational study comparing two different anticoagulation strategies to avoid systemic heparinization. The use of a heparin-coated dialysis membrane proved to be non-inferior to saline infusion. Superiority of either treatment, however, could not be demonstrated. These findings challenge current guidelines but equally raise questions on the choice of either strategy as compared with regional citrate anticoagulation.

Cardiovascular disease relates to intestinal uptake of p-cresol in patients with chronic kidney disease.

BACKGROUND: Serum p-cresyl sulfate (PCS) associates with cardiovascular disease in patients with chronic kidney disease. PCS concentrations are determined by intestinal uptake of p-cresol, human metabolism to PCS and renal clearance. Whether intestinal uptake of p-cresol itself is directly associated with cardiovascular disease in patients with renal dysfunction has not been studied to date. METHODS: We performed a prospective study in patients with chronic kidney disease stage 1 - 5 (NCT00441623). Intestinal uptake of p-cresol, under steady state conditions, was estimated from 24 h urinary excretion of PCS. Primary endpoint was time to first cardiovascular event, i.e., cardiac death, myocardial infarction/ischemia, ventricular arrhythmia, cardiovascular surgery, ischemic stroke or symptomatic peripheral arterial disease. Statistical analysis was done using Kaplan-Meier estimates and Cox proportional hazard analyses. RESULTS: In a cohort of 200 patients, median 24 h urinary excretion of PCS amounted to 457.47 µmol (IQR 252.68 - 697.17). After a median follow-up of 52 months, 25 patients reached the primary endpoint (tertile 1/2/3: 5/6/14 events, log rank P 0.037). Higher urinary excretion of PCS was directly associated with cardiovascular events (univariate hazard ratio per 100 µmol increase: 1.112, P 0.002). In multivariate analysis, urinary excretion of PCS remained a predictor of cardiovascular events, independent of eGFR (hazard ratio 1.120, P 0.002). CONCLUSIONS: In patients with chronic kidney disease, intestinal uptake of p-cresol associates with cardiovascular disease independent of renal function. The intestinal generation and absorption of p-cresol may be therapeutic targets to reduce cardiovascular disease risk in patients with renal dysfunction.

Nonextracorporeal methods for decreasing uremic solute concentration: a future way to go?

The uremic milieu is consequential to a disrupted balance between availability of retention solutes and the excretory capacity of the kidneys. Although metabolism is the prime contributor to the internal milieu, a significant fraction of uremic retention solutes originates from other sources. The main route of entrance is via the intestinal tract, directly from the diet and indirectly from commensal microbial metabolism. This latter dynamic interplay between the intestines and kidney has been coined the gut-kidney axis. This review summarizes current understanding of the gut-kidney axis and explores the impact of dietary and other nonextracorporeal therapeutic interventions in patients with chronic kidney disease.

The soluble urokinase receptor is not a clinical marker for focal segmental glomerulosclerosis.

The soluble urokinase receptor (suPAR) promotes proteinuria and induces focal segmental glomerulosclerosis (FSGS)-like lesions in mice. A serum suPAR concentration cutoff of 3000 pg/ml has been proposed as a clinical biomarker for patients with FSGS. Interestingly, several studies in patients with glomerulopathy found an inverse correlation between the estimated glomerular filtration rate (eGFR) and suPAR. As patients with FSGS present at different eGFRs, we studied the relationship between eGFR and suPAR in a cohort of 476 non-FSGS patients and 54 patients with biopsy-proven idiopathic FSGS. In the non-FSGS patients, eGFR was the strongest significant determinant of suPAR. The proposed cutoff for suPAR in FSGS patients was exceeded in 17%, 39%, and 88% in patients with eGFRs of more than 60, 45-60, and 30-45 ml/min per 1.73 m(2), respectively. In patients with eGFR of <30 ml/min per 1.73 m(2), suPAR exceeded the cutoff in 95% of patients. Levels of suPAR in patients with idiopathic FSGS overlapped with non-FSGS controls and for any given eGFR did not discriminate FSGS cases from non-FSGS controls. In the overall cohort, there was a negative association between idiopathic FSGS and suPAR, and idiopathic FSGS was not an independent predictor of FSGS concentration over 3000 pg/ml. Thus, this study does not support an absolute, eGFR-independent, suPAR concentration cutoff as a biomarker for underlying FSGS pathology and questions the validity of relative, eGFR-dependent suPAR cutoff values.

Renal clearance and intestinal generation of p-cresyl sulfate and indoxyl sulfate in CKD.

BACKGROUND AND OBJECTIVES: p-Cresyl sulfate and indoxyl sulfate contribute to cardiovascular disease and progression of renal disease. Renal clearance of both solutes mainly depends on tubular secretion, and serum concentrations are widely dispersed for any given stage of CKD. From this information, it is inferred that estimated GFR is not a suitable proxy of the clearance of these solutes. Formal clearance studies have, however, not been performed to date. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This study analyzed renal clearances of p-cresyl sulfate and indoxyl sulfate in the Leuven CKD cohort (NCT00441623; inclusion between November of 2005 and September of 2006) and explored their relationship with estimated GFR. Multivariate linear regression models were built to evaluate contributions of estimated GFR, demographics, and generation rates to p-cresyl sulfate and indoxyl sulfate serum concentrations. RESULTS: Renal clearances were analyzed in 203 patients with CKD stages 1-5. Indoxyl sulfate clearances (median=17.7, interquartile range=9.4-33.2 ml/min) exceeded p-cresyl sulfate clearances (median=6.8, interquartile range=3.4-12.0 ml/min) by about threefold. A linear relationship was observed between estimated GFR and clearances of p-cresyl sulfate (R(2)=0.50, P<0.001) and indoxyl sulfate (R(2)=0.55, P<0.001). In multivariate regression, p-cresyl sulfate concentrations were associated (R(2)=0.75) with estimated GFR and generation rate (both P<0.001). Indoxyl sulfate concentrations were associated (R(2)=0.74) with estimated GFR, generation rate (both P<0.001), age (P<0.05), and sex (P<0.05). CONCLUSIONS: Estimated GFR provides an acceptable estimate of renal clearance of p-cresyl sulfate and indoxyl sulfate. Remarkably, clearances of indoxyl sulfate exceed clearances of p-cresyl sulfate by approximately threefold, suggesting substantial differences between tubular transporter affinities and/or involvement of separate transporter systems for p-cresyl sulfate and indoxyl sulfate.