Indole 3-acetic acid, indoxyl sulfate and paracresyl-sulfate do not influence anemia parameters in hemodialysis patients

Iron Metabolism and Inflammatory Mediators in Patients with Renal Dysfunction

Chronic kidney disease (CKD) affects around 850 million people worldwide, posing significant challenges in healthcare due to complications like renal anemia, end-stage kidney disease, and cardiovascular diseases. This review focuses on the intricate interplay between iron metabolism, inflammation, and renal dysfunction in CKD. Renal anemia, prevalent in CKD, arises primarily from diminished erythropoietin (EPO) production and iron dysregulation, which worsens with disease progression. Functional and absolute iron deficiencies due to impaired absorption and chronic inflammation are key factors exacerbating erythropoiesis. A notable aspect of CKD is the accumulation of uremic toxins, such as indoxyl sulfate (IS), which hinder iron metabolism and worsen anemia. These toxins directly affect renal EPO synthesis and contribute to renal hypoxia, thus playing a critical role in the pathophysiology of renal anemia. Inflammatory cytokines, especially TNF-α and IL-6, further exacerbate CKD progression and disrupt iron homeostasis, thereby influencing anemia severity. Treatment approaches have evolved to address both iron and EPO deficiencies, with emerging therapies targeting hepcidin and employing hypoxia-inducible factor (HIF) stabilizers showing potential. This review underscores the importance of integrated treatment strategies in CKD, focusing on the complex relationship between iron metabolism, inflammation, and renal dysfunction to improve patient outcomes.

Saikosaponin A protects against uremic toxin indole‑3 acetic acid‑induced damage to the myocardium

Chronic kidney disease (CKD)‑associated cardiac injury is a common complication in patients with CKD. Indole‑3 acetic acid (IAA) is a uremic toxin that injures the cardiovascular system. Saikosaponin A (SSA) protects against pressure overload‑induced cardiac fibrosis. However, the role and molecular mechanisms of IAA and SSA in CKD‑associated cardiac injury remain unclear. The present study investigated the effects of IAA and SSA on CKD‑associated cardiac injury in neonatal mouse cardiomyocytes and a mouse model of CKD. The expression of tripartite motif‑containing protein 16 (Trim16), receptor interacting protein kinase 2 (RIP2) and phosphorylated‑p38 were assessed using western blotting. The ubiquitination of RIP2 was measured by coimmunoprecipitation, and mouse cardiac structure and function were evaluated using hematoxylin and eosin staining and echocardiography. The results demonstrated that, SSA inhibited IAA‑induced cardiomyocyte hypertrophy, upregulated Trim16 expression, downregulated RIP2 expression and decreased p38 phosphorylation. Furthermore, Trim16 mediated SSA‑induced degradation of RIP2 by ubiquitination. In a mouse model of IAA‑induced CKD‑associated cardiac injury, SSA upregulated the protein expression levels of Trim16 and downregulated those of RIP2. Moreover, SSA alleviated heart hypertrophy and diastolic dysfunction in IAA‑treated mice. Taken together, these results suggest that SSA is a protective agent against IAA‑induced CKD‑associated cardiac injury and that Trim16‑mediated ubiquitination‑related degradation of RIP2 and p38 phosphorylation may contribute to the development of CKD‑associated cardiac injury.

Research progress on the relationship between IS and kidney disease and its complications

Indoxyl sulphate (IS) a representative uraemic toxin in the blood of patients with chronic kidney disease (CKD). Its accumulation may be closely related to CKD and the increasing morbidity and mortality of the disease's related complications. Timely and effective detection of the IS level and efficient clearance of IS may effectively prevent the progression of CKD and its related complications. Therefore, this article summarizes the research progress of IS related, including IS in CKD and its associated complications including chronic kidney disease, chronic kidney disease with cardiovascular disease, renal anemia, bone mineral metabolic disease and neuropsychiatric disorders, looking for IS accurate rapid detection methods, and explore the efficient treatment to reduce blood levels of indole phenol sulphate.

Mechanisms of myostatin and activin A accumulation in chronic kidney disease

BACKGROUND

Myostatin and activin A induce muscle wasting by activating the ubiquitin proteasome system and inhibiting the Akt/mTOR pathway. In chronic kidney disease (CKD), myostatin and activin A plasma concentrations are increased, but it is not clear if there is an increased production or a decreased renal clearance.

METHODS

We measured myostatin and activin A concentrations in 232 CKD patients and studied their correlation with estimated glomerular filtration rate (eGFR). We analyzed the myostatin gene (MSTN) expression in muscle biopsies of hemodialysis (HD) patients. We then measured circulating myostatin and activin A in plasma and the Mstn and Inhba expression in muscles, kidney, liver and heart of two CKD mice models (adenine and 5/6th nephrectomy models). Finally, we analyzed whether the uremic toxin indoxyl sulfate (IS) increased Mstn expression in mice and cultured muscle cells.

RESULTS

In patients, myostatin and activin A were inversely correlated with eGFR. MSTN expression was lower in HD patients' muscles (vastus lateralis) than in controls. In mice with CKD, myostatin and activin A blood concentrations were increased. Mstn was not up-regulated in CKD mice tissues. Inha was up-regulated in kidney and heart. Exposure to IS did not induce Mstn up-regulation in mice muscles and in cultured myoblasts and myocytes.

CONCLUSION

During CKD, myostatin and activin A blood concentrations are increased. Myostatin is not overproduced, suggesting only an impaired renal clearance, but activin A is over produced in kidney and heart. We propose to add myostatin and activin A to the list of uremic toxins.

Is there an association between the plasma levels of uremic toxins from gut microbiota and anemia in patients on hemodialysis?

BACKGROUND

Anemia is one of the most frequent complications in patients with chronic kidney disease (CKD). Despite being multifactorial, the relative or absolute deficiency of erythropoietin production is the leading cause. Recent studies have shown that uremic toxins produced by the gut microbiota also may play a role in the genesis of anemia in these patients.

OBJECTIVE

To evaluate the possible association between uremic toxins plasma levels and anemia in patients with CKD on hemodialysis (HD).

METHODS

This cross-sectional study evaluated one hundred fifty-four patients (53.2% men, 51.2 ± 11.2 years, hemoglobin (Hb) levels of 11.2 ± 1.6 g/dL). Biochemical variables such as urea, creatinine, hemoglobin, hematocrit, were measured according to standard methods and uremic toxins such as indoxyl sulfate (IS), indole-3-acetic acid (IAA), p-cresyl sulfate (p-CS) plasma levels were measured by reverse-phase high-performance liquid chromatography (RP-HPLC).

RESULTS

The levels of uremic toxins such as IS, IAA, p-CS were increased in all patients. However, no correlation was found between uremic toxins plasma levels and anemia parameters. Only patients with Hb < 11 g/dL presented a negative correlation between hematocrit and IAA plasma levels.

CONCLUSION

There is no strong evidence that uremic toxins produced by the gut microbiota may be associated with anemia in patients with CKD on HD.

Indolic Structure Metabolites as Potential Biomarkers of Non-infectious Diseases

Interest in indolic structure metabolites, including a number of products of microbial biotransformation of the aromatic amino acid tryptophan, is increasingly growing. The review prepared by a team of authors is based on in-depthscrutiny of data available in PubMed, Scopus, Cyberleninka, Clinical Trials, and Cochrane Library, eventually narrowing the search to a set of keywords such as tryptophan metabolites; plasma metabolomics profiling; metabolomics fingerprinting; gas-, liquid chromatography mass spectrometry; serotonin; melatonin; tryptamine; indoxyl sulfate; indole-3-acetic acid; indole-3-propionic acid; 5-hydroxyindole-3-acetic acid; gut microbiota and microbial metabolites. It provides a summary that outlines the pattern of changes in the level of indolic structure metabolites in a number of diseases and deals with the data from the field of human microbiota metabolites. In modern experimental studies, including the use of gnotobiological (germ-free) animals, it has been convincingly proved that the formation of tryptophan metabolites such as indole-3-acetic acid, indole-3-propionic acid, tryptamine, and indoxyl sulfate is associated with gut bacteria. Attention to some concentration changes of indolic compounds is due to the fact that pronounced deviations and a significant decrease of these metabolites in the blood were found in a number of serious cardiovascular, brain or gastrointestinal diseases. The literature-based analysis allowed the authors to conclude that a constant (normal) level of the main metabolites of the indolic structure in the human body is maintained by a few strict anaerobic bacteria from the gut of a healthy body belonging to the species of Clostridium, Bacteroides, Peptostreptococcus, Eubacteria, etc. The authors focus on several metabolites of the indolic structure that can be called clinically significant in certain diseases, such as schizophrenia, depression, atherosclerosis, colorectal cancer, etc. Determining the level of indole metabolites in the blood can be used to diagnose and monitor the effectiveness of a comprehensive treatment approach.

Metabolomics and molecular docking to compare of the efficacies of wild-simulated and transplanted Astragali Radix based on its compatibility with Angelicae Sinensis Radix against blood deficiency

Astragali Radix (AR) has been widely used as bulk medicines in China. Currently, there are mainly two types in the market, wild-simulated AR (WAR) and transplanted AR (TAR). The present work was designed to compare their effects in treatment of blood deficiency with its compatibility with Angelicae Sinensis Radix, a classical formula Danggui Buxue decoction (DBD). UHPLC-Q-Exactive-MS-based serum metabolomics was firstly applied to compare their metabolic regulations in blood deficiency mice. Metabolic results showed that 17 metabolites were closely related to blood deficiency. WAR-DBD and TAR-DBD significantly improved 13 and 8 metabolites among them, respectively. Further, fourteen genes were selected as promising targets for treating blood deficiency by searching GeneCards and CTD database. The results of molecular docking also showed that eight components of AR and three serum metabolites had strongest correlations with blood deficiency targets. The results further revealed that WAR-DBD was better than TAR-DBD against blood deficiency. The method provided a new way to compare the hematopoietic differences of AR of different cultivation methods. In addition, molecular docking plays an irreplaceable role in explaining the molecular mechanism of biological processes.

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

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

The Influence of Inflammation on Anemia in CKD Patients

Anemia is frequently observed in the course of chronic kidney disease (CKD) and it is associated with diminishing the quality of a patient’s life. It also enhances morbidity and mortality and hastens the CKD progression rate. Patients with CKD frequently suffer from a chronic inflammatory state which is related to a vast range of underlying factors. The results of studies have demonstrated that persistent inflammation may contribute to the variability in Hb levels and hyporesponsiveness to erythropoietin stimulating agents (ESA), which are frequently observed in CKD patients. The understanding of the impact of inflammatory cytokines on erythropoietin production and hepcidin synthesis will enable one to unravel the net of interactions of multiple factors involved in the pathogenesis of the anemia of chronic disease. It seems that anti-cytokine and anti-oxidative treatment strategies may be the future of pharmacological interventions aiming at the treatment of inflammation-associated hyporesponsiveness to ESA. The discovery of new therapeutic approaches towards the treatment of anemia in CKD patients has become highly awaited. The treatment of anemia with erythropoietin (EPO) was associated with great benefits for some patients but not all.

Association between Circulation Indole-3-Acetic Acid Levels and Stem Cell Factor in Maintenance Hemodialysis Patients: A Cross-Sectional Study

Protein-bound uremic toxin is a cardiovascular (CV) risk factor for patients with end-stage renal disease. Indole-3-acetic acid (IAA) was found to be associated with CV disease but the detailed pathophysiology remains unknown. Moreover, mitogen-activated protein kinase (MAPK) signaling cascades play an important role in the pathogenesis of CV disease. Thus, we explored the association between circulating IAA levels and forty MAPK cascade associated proteins in patients undergoing hemodialysis (HD). Circulating total form IAA was quantified by mass spectrometry and forty MAPK cascade associated proteins by a proximity extension assay in 331 prevalent HD patients. Accounting for multiple testing, and in multivariable-adjusted linear regression models, circulating total form IAA levels were positively associated with stem cell factor (β coefficient 0.13, 95% confidence interval 0.04 to 0.21, p = 0.004). A bioinformatics approach using the search tool for interactions of chemicals (STITCH) tool provided information that IAA may be involved in the regulation of cell proliferation, hematopoietic cells, and the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway. The knowledge gained here can be generalized, thereby impacting the non-traditional CV risk factors in patients with kidney disease. Further in vitro work is necessary to validate the translation of the mechanistic pathways.

Inhibition of the renin-angiotensin system in the cardiorenal syndrome with anaemia: a double-edged sword

: The term 'cardiorenal syndrome' (CRS) was introduced to describe problems related to the simultaneous existence of heart and renal insufficiency. The prevalence of anaemia in CRS is high and increases the risk of hospitalizations and death. Renin-angiotensin system (RAS) inhibition is the cornerstone therapy in cardiovascular and renal medicine. As angiotensin II regulates both glomerular filtration rate (GFR) and erythropoiesis, RAS inhibition can further deteriorate renal function and lower hematocrit or cause anaemia in patients with heart failure. The aim of this review is to explore the relationship among CRS, anemia and administration of angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) and summarize the evidence suggesting that RAS inhibition may be considered an iatrogenic cause of deterioration of CRS with anemia. It should be emphasized however, that RAS inhibition reduces mortality in both groups with and without worsening of renal function, and therefore, no patient with CRS should be denied an ACEi or ARB trial without careful evaluation.

The impact of antihypertensive pharmacotherapy on interplay between protein-bound uremic toxin (indoxyl sulfate) and markers of inflammation in patients with chronic kidney disease

Purpose

Indoxyl sulfate (IS) is one of the most potent uremic toxins involved in chronic kidney disease (CKD) progression, induction of inflammation, oxidative stress, and cardiovascular diseases occurrence. It is proved that hypertension is a common CVD complication and a major death risk factor as well as contributes for decline in a renal function. The aim of our study was to investigate how implementing of antihypertensive therapy impact IS concentrations and the associations between IS and markers of renal function, inflammation and oxidative stress.

Methods

Study was conducted on 50 patients diagnosed with CKD and hypertension, divided into three groups: without hypotensive therapy (CKD-NONE), hypotensive monotherapy (CKD-MONO), and hypotensive polypharmacotherapy (CKD-POLI), and 18 healthy volunteers. The markers of inflammation [interleukin-6, tumor necrosis factor-alpha (TNF-α), high-sensitive C-reactive protein (hs-CRP), neopterin, ferritin], oxidative status [superoxide dismutase (Cu/Zn-SOD), antibodies against oxidized low-density lipoprotein (oxLDL-abs)], and selectins were determinate using immunoenzymatic methods. IS levels were assayed using high-performance liquid chromatography and other parameters were analysed using routine laboratory techniques. Then cross-sectional analysis was performed.

Results

Elevated levels of IS, indicators of kidney function, markers of inflammation and blood pressure values were observed in each CKD subgroups. There was no effect of antihypertensive therapy on IS levels between studied groups, as well as there was no clear relationship between IS and blood pressure values in each studied group. The positive associations between IS and Cu/Zn SOD, neopterin, hs-CRP, creatinine and neutrophils/lymphocytes ratio were observed in CKD-NONE and CKD-POLI subgroups. Additionally, in CKD-POLI group IS positively correlated with TNF-α, ferritin and neutrophils. In CKD-MONO group, IS was positively related to oxLDL-abs, neopterin, E-selectin and creatinine, whereas it was inversely associated with hs-CRP.

Conclusions

Our study showed for the first time that the antihypertensive therapy has no impact on IS levels in CKD patients with hypertension. However, the introduction of the antihypertensive therapy modified the dependencies between IS and the studied markers of kidney function, inflammation, oxidative stress and hematological parameters that are crucial for mortality and morbidity amongst the CKD patients with hypertension.

Electronic supplementary material

The online version of this article (10.1007/s11255-018-02064-3) contains supplementary material, which is available to authorized users.

Indoxyl Sulfate, a Uremic Toxin, Stimulates Reactive Oxygen Species Production and Erythrocyte Cell Death Supposedly by an Organic Anion Transporter 2 (OAT2) and NADPH Oxidase Activity-Dependent Pathways

It is hypothesized that the uremic toxin indoxyl sulfate (IS) plays a role in the pathogenesis of renal anemia. To further explore that hypothesis, we examined the effects of IS on reactive oxygen species (ROS) production, levels of reduced glutathione (GSH), and erythrocyte death (eryptosis) in red blood cells (RBC) from healthy controls (CON-RBC) and hemodialyzed patients (HD-RBC), respectively. RBC were incubated either in either TRIS-Glc-BSA buffer or IS at concentrations of 0.01, 0.09, and 0.17 mM, respectively. We measured ROS generation (expressed as % of DCFH-DA positive RBC), eryptosis (expressed as % of annexin-V positive RBC), and GSH levels after 6, 12, and 24 h. When incubated in buffer, ROS production was approximately seven-fold higher at all time points HD-RBC when compared to CON-RBC. Incubation with IS increased ROS production in CON-RBS dose-dependently up to 10-fold. Eryptosis in buffer-incubated HD-RBC was up to seven-fold higher as compared to COB-RBC. Incubation of CON-RBC with IS increased the eryptosis rate dose-dependently up to 6-fold. Pretreatment of CON-RBC with the organic anion transporter 2 (OAT2) specific inhibitor ketoprofen or with NADPH oxidase inhibitor diphenyleneiodonium-Cl blunted the IS effect on both ROS production and eryptosis induction. While GSH levels in HD-RBC were reduced when compared to CON-RBC, they were not affected by IS incubation. In summary, IS increases ROS generation and eryptosis in CON-RBC by an activity dependent of the IS influx through OAT2, and NADPH oxidase activity-dependent, and a GSH-independent mechanism. These findings lend support to a putative role of IS in the pathogenesis of renal anemia.