Important Uremic Toxins Research Articles

Indole and p-cresol in feces of healthy subjects: Concentration, kinetics, and correlation with microbiome.

Indole and p-cresol are precursors of the most important uremic toxins, generated from the fermentation of amino acids tryptophan and tyrosine by the proteolytic community of intestinal bacteria. The present study focused on the relationship between the microbiome composition, the fecal levels of indole and p-cresol, and their kinetics of generation/degradation in fecal cultures. The concentration of indole and p-cresol, the volatilome, the dry weight, and the amount of ammonium and carbohydrates were analyzed in the feces of 10 healthy adults. Indole and p-cresol widely differed among samples, laying in the range of 1.0-19.5μg/g and 1.2-173.4μg/g, respectively. Higher fecal levels of indole and p-cresol were associated with lower carbohydrates and higher ammonium levels, that are markers of a more pronounced intestinal proteolytic metabolism. Positive relationship was observed also with the dry/wet weight ratio, indicator of prolonged intestinal retention of feces. p-cresol and indole presented a statistically significant negative correlation with OTUs of uncultured Bacteroidetes and Firmicutes, the former belonging to Bacteroides and the latter to the families Butyricicoccaceae (genus Butyricicoccus), Monoglobaceae (genus Monoglobus), Lachnospiraceae (genera Faecalibacterium, Roseburia, and Eubacterium ventriosum group). The kinetics of formation and/or degradation of indole and p-cresol was investigated in fecal slurries, supplemented with the precursor amino acids tryptophan and tyrosine in strict anaerobiosis. The presence of the precursors bursted indole production but had a lower effect on the rate of p-cresol formation. On the other hand, supplementation with indole reduced the net rate of formation. The taxa that positively correlated with fecal levels of uremic toxins presented a positive correlation also with p-cresol generation rate in biotransformation experiments. Moreover other bacterial groups were positively correlated with generation rate of p-cresol and indole, further expanding the range of taxa associated to production of p-cresol (Bacteroides, Alistipes, Eubacterium xylanophylum, and Barnesiella) and indole (e.g., Bacteroides, Ruminococcus torques, Balutia, Dialister, Butyricicoccus). The information herein presented contributes to disclose the relationships between microbiota composition and the production of uremic toxins, that could provide the basis for probiotic intervention on the gut microbiota, aimed to prevent the onset, hamper the progression, and alleviate the impact of nephropaties.

The AST-120 Recovers Uremic Toxin-Induced Cognitive Deficit via NLRP3 Inflammasome Pathway in Astrocytes and Microglia.

Chronic kidney disease (CKD) is characterized by the progressive loss of renal function; moreover, CKD progression commonly leads to multiple comorbidities, including neurological dysfunction and immune disorders. CKD-triggered neuroinflammation significantly contributes to cognitive impairment. This study aimed to investigate the contribution of uremic toxins to cognitive impairment. Serum creatinine, blood urea nitrogen (BUN), indoxyl sulfate (IS), and p-cresol sulfate (PCS) levels were measured using an enzyme-linked immunosorbent assay and high-performance liquid chromatography. The creatinine, BUN, IS, and PCS levels were increased from 4 weeks after 5/6-nephrectomy in mice, which suggested that 5/6-nephrectomy could yield a CKD animal model. Further, CKD mice showed significantly increased brain and serum indoxyl sulfate levels. Immunohistochemistry analysis revealed hippocampal inflammation and NLRP3-inflammasomes in astrocytes. Further, the Y-maze and Morris water maze tests revealed learning and memory defects in CKD mice. AST-120, which is also an IS absorbent, effectively reduced serum and hippocampal IS levels as well as reversed the cognitive impairment in CKD mice. Additionally, NLRP3-knockout mice that underwent 5/6-nephrectomy showed no change in cognitive function. These findings suggested that IS is an important uremic toxin that induces NLRP3 inflammasome-mediated not only in microglia, but it also occurred in astrocytic inflammation, which subsequently causes cognitive impairment.

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.

Emodin via colonic irrigation modulates gut microbiota and reduces uremic toxins in rats with chronic kidney disease.

Gut microbiota plays a dual role in chronic kidney disease (CKD) and is closely linked to production of uremic toxins. Strategies of reducing uremic toxins by targeting gut microbiota are emerging. It is known that Chinese medicine rhubarb enema can reduce uremic toxins and improve renal function. However, it remains unknown which ingredient or mechanism mediates its effect. Here we utilized a rat CKD model of 5/6 nephrectomy to evaluate the effect of emodin, a main ingredient of rhubarb, on gut microbiota and uremic toxins in CKD. Emodin was administered via colonic irrigation at 5ml (1mg/day) for four weeks. We found that emodin via colonic irrigation (ECI) altered levels of two important uremic toxins, urea and indoxyl sulfate (IS), and changed gut microbiota in rats with CKD. ECI remarkably reduced urea and IS and improved renal function. Pyrosequencing and Real-Time qPCR analyses revealed that ECI resumed the microbial balance from an abnormal status in CKD. We also demonstrated that ten genera were positively correlated with Urea while four genera exhibited the negative correlation. Moreover, three genera were positively correlated with IS. Therefore, emodin altered the gut microbiota structure. It reduced the number of harmful bacteria, such as Clostridium spp. that is positively correlated with both urea and IS, but augmented the number of beneficial bacteria, including Lactobacillus spp. that is negatively correlated with urea. Thus, changes in gut microbiota induced by emodin via colonic irrigation are closely associated with reduction in uremic toxins and mitigation of renal injury.

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

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

Nitration of indoxyl sulfate facilitates its cytotoxicity in human renal proximal tubular cells via expression of heme oxygenase-1

Peroxynitrite, the reaction product of superoxide (O2−) and nitric oxide (NO), nitrates tyrosine residues, unsaturated fatty acids, cyclic guanosine monophosphate and other phenolics. We report herein that indoxyl sulfate (IS) is also nitrated by peroxynitrite in vitro and forms 2-nitro-IS, as determined from spectral characteristics and 1H-NMR. IS is one of the very important uremic toxins that accelerate the progression of chronic kidney disease via various mechanisms. However, cell viability experiments with human proximal tubular cells show that the cytotoxicity of 2-nitro-IS is several-fold higher than that of IS. The explanation for this finding seems to be that 2-nitro-IS induces a much more pronounced generation of intracellular reactive oxygen species (ROS) than IS. Results with inhibitors revealed that an organic anion transporter, several intracellular enzymes and nonprotein-bound iron ions are reasons for this finding. Most importantly, however, as detected by immunofluorescence and Western blotting, 2-nitro-IS induces the expression of heme oxygenase-1 and thereby the formation of ROS; most probably through the Fenton reaction. The final result of the increased amounts of ROS is death of the kidney cells. Thus, nitration of uremic toxins by peroxynitrite may help us to understand the initiation and progress of chronic kidney diseases.

P46 - The uremic toxin indoxyl sulfate acts as a pro- or antioxidant on LDL oxidation

Uremic toxins have been shown to play a role in chronic kidney disease (CKD) associated oxidative stress. Oxidative stress and inflammation have been associated with increased risk of cardiovascular disease in uraemia. The oxidative modification of LDL may play a role in early atherogenesis. Enhanced LDL oxidation has been found in uremic patients which may account for accelerated atherosclerosis observed in CKD. The uremic toxin indoxyl sulfate (IS) has been reported to exert oxidative and antioxidative activity. Thus, in the present study we have investigated the influence of IS on the atherogenic modifications of LDL exposed in vitro to different oxidising systems. The transition metal ion (Cu2 ) and hemin/H2O2 induced lipid oxidation reactions monitored by conjugated diene formation, were inhibited by the presence of IS, which points to possible antioxidant effects by this uremic toxin. A protective effect of IS on LDL apoprotein modification by the exposure to the product of the myeloperoxidase/H2O2/Cl- system HOCl, was also observed as estimated by protein carbonyl formation. In contrast, a marked increase in conjugated dienes and lipid hydroperoxides was observed when lipid oxidation was initiated by the free radical generator AAPH in presence of IS. The GC-MS analysis revealed the formation of indole-2,3-dione and 6,12-dihydro-6,12-dioxo-indolo[2,1–b]quinazoline (tryptanthrine) in IS/AAPH reaction. A scheme for the generation of tryptanthrine from IS via indoxyl radicals is proposed, which may facilitate LDL lipid oxidation. Our observations add further insight in the Janus-faced properties of this important uremic toxin.

The uremic toxin indoxyl sulfate acts as a pro- or antioxidant on LDL oxidation

Uremic toxins have been shown to play a role in chronic kidney disease (CKD) associated oxidative stress. Oxidative stress and inflammation have been associated with increased risk of cardiovascular disease in uraemia. The oxidative modification of LDL may play a role in early atherogenesis. Enhanced LDL oxidation has been found in uremic patients which may account for accelerated atherosclerosis observed in CKD. The uremic toxin indoxyl sulfate (IS) has been reported to exert oxidative and antioxidative activity. Thus, in the present study we have investigated the influence of IS on the atherogenic modifications of LDL exposed in vitro to different oxidising systems. The transition metal ion (Cu2+) and hemin/H2O2 induced lipid oxidation reactions monitored by conjugated diene formation, were inhibited by the presence of IS, which points to possible antioxidant effects by this uremic toxin. A protective effect of IS on LDL apoprotein modification by the exposure to the product of the myeloperoxidase/H2O2/Cl− system HOCl, was also observed as estimated by protein carbonyl formation. In contrast, a marked increase in conjugated dienes and lipid hydroperoxides was observed when lipid oxidation was initiated by the free radical generator AAPH in presence of IS. The GC-MS analysis revealed the formation of indole-2,3-dione and 6,12-dihydro-6,12-dioxo-indolo[2,1-b]quinazoline (tryptanthrin) in IS/AAPH reaction. A scheme for the generation of tryptanthrin from IS via indoxyl radicals is proposed, which may facilitate LDL lipid oxidation. Our observations add further insight in the Janus-faced properties of this important uremic toxin.

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

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

The quest for a better understanding of chronic kidney disease complications: an update on uremic toxins.

Chronic kidney disease is characterized by a progressive reduction of glomerular filtration rate and/or the appearance of proteinuria, and subsequently the progressive retention of organic waste compounds called uremic toxins (UT). Over the last decades, a large number of such compounds have been identified and their effects on organs and tissues, especially the cardiovascular system, has been demonstrated. In this review, we present the current classification of UT, as proposed by the EUTox Group, and the effects of some of the probably most important UTs, such as phosphate, FGF-23, PTH, AGEs, indoxyl sulfate and para-cresyl sulfate. We provide an overview on therapeutic approaches aimed to increase their extracorporeal removal via convective and/or adsorptive strategies and to lower their intestinal production/ absorption via dietetic and pharmacological interventions. The recognition that multiple toxins contribute to the uremia supports the need for new therapeutic targets, with a potentially positive impact on CKD progression and survival.

My Addiction: The Artificial Kidney, The Rise and Fall of Dialysis

My Addiction: The Artificial Kidney, The Rise and Fall of Dialysis

P.5.035 Effects of thioperamide and raclopride on the striatal extracellular level of dopamine and histamine in Krushinsky-Molodkina and Wistar rats

Guanidinosuccinic acid (GSA), a guanidino compound found to be greatly increased in uremia, was administered by intraperitoneal (i.p.) injection to adult albino mice and to young mice 7,14 and 21 days old. Epileptogenic and toxic properties were assessed and GSA brain levels following i.p. injection were determined. In adult mice, GSA induced long-lasting generalized clonic and clonic-tonic convulsions in a dose-dependent manner with a CD50 (and 95% confidence interval) of 363 (287–458) mg/kg (n = 35), and an LD50 of 579 (445–756) mg/kg. The CD50 of GSA corresponded with a brain concentration of 56 nmol/g tissue. Electrocorticographic recording infive adult mice revealed epileptiform discharges (spikes, spike-waves, and polyspike-waves) which appeared concomitant with the convulsions. When young mice were i.p. injected with a (for adults) subconvulsive dose of GSA (250 mg/kg), an age-dependent decrease was noted in GSA-induced convulsions and in the resulting brain concentration. The presented findings suggest that GSA could be an important uremic toxin which could contribute to the epileptic symptomatology in uremia.

Dose of dialysis: Key lessons from major observational studies and clinical trials

Dose of dialysis: Key lessons from major observational studies and clinical trials

Sulfation of indoxyl by human and rat aryl (phenol) sulfotransferases to form indoxyl sulfate.

The aim of this study was to identify sulfotransferase (SULT) isoform(s) responsible for the formation of indoxyl sulfate from indoxyl (3-hydroxyindole). Indoxyl was incubated together with the co-substrate 3'-phosphoadenosine 5'-phosphosulfate (PAPS) and either human or rat liver cytosol or recombinant sulfotransferase enzymes. Formation of indoxyl sulfate from indoxyl was measured by HPLC and used for determination of sulfonation rates. Both cytosols sulfonated indoxyl with apparent Km values of 6.8 +/- 0.9 microM for human and 3.2 +/- 0.6 microM for rat cytosol. To help identify the isoform(s) of SULT responsible for indoxyl sulfate formation, indoxyl was incubated with human and rat liver cytosols and PAPS in the presence of isoform-specific SULT inhibitors. No inhibition was observed by DHEA, a specific hydroxysteroid sulfotransferase inhibitor, nor by oestrone, an inhibitor of oestrogen sulfotransferase. However, an aryl (phenol) sulfotransferase inhibitor, 2,6-dichloro-4-nitrophenol (DCNP), inhibited the formation of indoxyl sulfate with a IC50 values of 3.2 microM for human and 1.0 microM for rat cytosol indicating that human and rat aryl (phenol) sulfotransferases are responsible for the formation of indoxyl sulfate. When indoxyl was incubated with SULT1A1*2, a human recombinant aryl SULT, an apparent Km value of 5.6 +/- 1.8 microM was obtained. Kinetic studies with human and rat cytosols and human recombinant SULT1A1*2 gave similar kinetic values indicating that human and rat aryl sulfotransferases efficiently catalyze the formation of indoxyl sulfate, an important uremic toxin metabolite.

The Middle Molecule Hypothesis Revisited. Should Short, Three Times Weekly Hemodialysis Be Abandoned?

When the middle molecule (MM) hypothesis was formulated in 1975, no MM had yet been identified as a uremic toxin. Meanwhile, the birth and implementation of the Kt/Vurea concept gained wide acceptance and has remained the world standard for assessing dialysis adequacy. However, over the past 20 years, accumulating evidence has made it clear that MM's are important uremic toxins, and that the dose of dialysis based on removal of small molecular substances does not protect against excessive hemodialysis mortality, morbidity, or the presence of uremic signs and symptoms. These poor results are, in one way or another, linked to the accumulation of MM's and other substances behaving like MM's, such as phosphate. Dialysis schedules yielding the best clinical results, such as longer dialysis and more frequent dialysis, favor increased removal of middle molecular substances. The observation that short daily dialysis is giving results similar to long nocturnal quotidian dialysis supports early observations that the volume from which middle molecular substances are extracted mainly by hemodialysis is small (about as large as the extracellular volume), and that transfer of MM's from cells to extracellular fluid is very slow. This behavior of MM's is markedly different from that of small molecular substances, which are more rapidly transferred from intracellular to extracellular compartments and are more readily extracted from total body water during hemodialysis. In order to achieve even minimum adequate dialysis, it is now scientifically validated that toxic MM's must be removed in larger amounts than currently attained. This can only be accomplished by long dialysis sessions with a 3-times per week schedule or more frequent dialyses. Five hours 3 times per week represents the absolute minimum treatment. Dialy sis 6 to 7 times per week is the ideal schedule for patients who are willing to commit the time and effort in exchange for maximum well-being and long survival.

ARE UREA AND CREATININE UREMIC TOXINS IN THE RAT?

Urea and creatinine are not generally considered to be important uremic toxins despite evidence from dialysis experiments to the contrary, and despite striking elevations of these nitrogenous waste products in uremia. In order to study this problem in acute uremia, we used a new dietary method for prolonging the survival of bilaterally nephrectomized rats. Urea or creatinine were injected on three successive days starting one day after the inception of uremia. Urea or creatinine injections shortened the survival time of acutely uremic rats, and increased the involution of thymus and spleen. The extra urea, but not creatinine, increased the serum osmolality. These data indicate that urea and creatinine are toxic in the acutely uremic rat. Hypertonicity of the serum may contribute to the toxicity of urea. Additional mechanisms of toxicity and additional toxins are not excluded.

Kronik Böbrek Yetmezliğinde Sekonder Hiperparatiroidi Ve Depresyon

Secondary Hyperparathyroidism and Depression in Renal Failure Depression is the most commonly described psychological disorder seen in chronic renal failure (CRF) patients. Apart from different psychological theories about the pathogenesis of depression in CRF, the literature also refers to organic factors, because CRF is accompanied by various pathobiocemical changes. Parathyroid hormon is one of the most important uremic toxin in CRF. But there are few and conflicting results about the secondary hyperparathyroidism (SHP) and depression in CRF. This study was aimed at studing the relation between SHPT and depression in CRF. In this study 31 CRF patients (18 male and 13 female) were studied. The Depression Scale and the Mini Mental Test were performed. On the same day serum values of BUN, Creatinine, electrolytes and PTH were measured. Serum PTH levels were higher in the patients with depressive CRF than non-depressive CRF (p 0.05). As a result of our findings it has been concluded that high levels of PTH can play an important role in the pathogenesis of depression in CRF. We purpose keeping SHPT under control rather than giving nonspecific antidepressants in the treatment of this type of depression. Further controlled studies are indicated to enlighten the psychopathology of depression seen in CRF. Depresyon, kronik bobrek yetmezligi (KBY) olan hastalarda tanimlanan en yaygin psikiyatrik bozukluktur. Onemli bir uremik toksin olan paratiroid hormon (PTH) ile depresyon arasindaki iliskiyi gosterir cok az ve celiskili yayinlar vardir. Calismamizda KBY olan hastalarda depresyon ile sekonder hiperparatiroidi arasindaki iliskiyi arastirmayi amacladik. Calismada, yas ortalamasi 49.12+1.1 yil olan 18 erkek ve 13 kadin, toplam 31 KBY'li hasta calismaya alindi. Hastalara Hamilton Depresyon Skalasi (HAM) ve minimental test uygulandi. Depresyon tesbit edilen KBY'li hastalarda PTH duzeyleri, depresyonu olmayanlara kiyasla daha yuksek bulundu (p 0.05). Calismamizda sekonder hiperparatiroidizmin depresyonun patogenezinde onemli bir rol oynayabilecegi sonucuna varildi. KBY'de gorulen depresyon tedavisinde spesifik olmayan antidepresan ilaclar yerine, sekonder hiperparatiroidinin kontrol altinda tutulmasi onerilebilir. Ileride daha genis kontrollu calismalarla konunun fizyopatolojik olarak aydinlatilmasi yararli olabilecektir.

Behavioral toxicity of guanidinosuccinic acid in adult and young mice

Guanidinosuccinic acid (GSA), a guanidino compound found to be greatly increased in uremia, was administered by intraperitoneal (i.p.) injection to adult albino mice and to young mice 7,14 and 21 days old. Epileptogenic and toxic properties were assessed and GSA brain levels following i.p. injection were determined. In adult mice, GSA induced long-lasting generalized clonic and clonic-tonic convulsions in a dose-dependent manner with a CD 50 (and 95% confidence interval) of 363 (287–458) mg/kg ( n = 35), and an LD 50 of 579 (445–756) mg/kg. The CD 50 of GSA corresponded with a brain concentration of 56 nmol/g tissue. Electrocorticographic recording infive adult mice revealed epileptiform discharges (spikes, spike-waves, and polyspike-waves) which appeared concomitant with the convulsions. When young mice were i.p. injected with a (for adults) subconvulsive dose of GSA (250 mg/kg), an age-dependent decrease was noted in GSA-induced convulsions and in the resulting brain concentration. The presented findings suggest that GSA could be an important uremic toxin which could contribute to the epileptic symptomatology in uremia.

Polyamines in the anemia of end-stage renal disease

The improvement in the anemia in patients with end-stage renal disease (ESRD) on continuous ambulatory peritoneal dialysis (CAPD) suggests that dialyzable substances present in the sera of uremic patients either inhibit erythropoiesis directly or inactivate erythropoietin (EPO). In the present study predialysis sera from patients with ESRD inhibited erythroid colony (CFU-E) (N = 10) formation to a significantly (P less than 0.01) greater degree than granulocyte-macrophage (CFU-GM) (N = 7) colony formation in mouse bone marrow (MBM) cultures. The polyamines spermine (SP) (18 to 560 nm/ml) and spermidine (SD) (4 to 648 nm/ml) exerted a more significant (P less than 0.05) inhibition of CFU-E (N greater than or equal to 5) than that of CFU-GM (N greater than or equal to 5) growth. Concentrations of 0.80, 1.0, and 1.5 nm/ml of putrescine (PU) were 92%, 85%, and 77% of erythroid colony (CFU-E) controls (N = 4) and 104%, 130%, and 127% of CFU-GM controls (N = 4). Putrescine (PU) at 1.5 nm/ml also produced a significant (P less than 0.05) inhibition of CFU-E, whereas CFU-GM were stimulated by PU. These data suggest that predialysis sera from uremic patients, as well as SP, SD, and PU, are selectively more inhibitory to CFU-E than CFU-GM growth. The immunoreactivity of EPO was not significantly changed when it was coincubated with SP, SD and PU and measured by radioimmunoassay. PU was found to inhibit noncompetitively the bioactivity of EPO in a CFU-E assay. These data support the hypothesis that polyamines may be important uremic toxins in the anemia of ESRD.

Tissue and Blood Cell Concentration of Methylguanidine in Rats and Patients with Chronic Renal Failure

Methylguanidine concentration in blood cell of nondialysed patients with chronic renal failure was quantitatively determined by the method of the present authors. We also determined tissue methylguanidine concentrations in the liver, blood cell, kidney, colon, muscle and brain of uremic rat experimentally produced by Platt's method. Methylguanidine concentrations in blood cell and tissues except the brain of the uremic rats and in blood cell of the uremic patients were 5--7 times higher than those in their serums. An increased methylguanidine concentration in the liver of the uremic rat receiving 40% protein diet was observed. These results imply that methylguanidine acts as one of the important uremic toxins in the intracellular space except for the brain, and suggest that the liver specifically affects the formation of methylguanidine.