Uremic retention solute indoxyl sulfate level is associated with prolonged QTc interval in early CKD patients

Indoxyl Sulfate-Induced Macrophage Toxicity and Therapeutic Strategies in Uremic Atherosclerosis

Cardiovascular disease (CVD) frequently occurs in patients with chronic kidney disease (CKD), particularly those undergoing dialysis. The mechanisms behind this may be related to traditional risk factors and CKD-specific factors that accelerate atherosclerosis and vascular calcification in CKD patients. The accumulation of uremic toxins is a significant factor in CKD-related systemic disorders. Basic research suggests that indoxyl sulfate (IS), a small protein-bound uremic toxin, is associated with macrophage dysfunctions, including increased oxidative stress, exacerbation of chronic inflammation, and abnormalities in lipid metabolism. Strategies to mitigate the toxicity of IS include optimizing gut microbiota, intervening against the abnormality of intracellular signal transduction, and using blood purification therapy with higher efficiency. Further research is needed to examine whether lowering protein-bound uremic toxins through intervention leads to a reduction in CVD in patients with CKD.

Indoxyl sulphate-initiated activation of cardiac fibroblasts is modulated by aryl hydrocarbon receptor and nuclear factor-erythroid-2-related factor 2

In the last decade, extensive attention has been paid to the uremic toxin indoxyl sulphate (IS) as an inducer of cardiac fibroblast (cFib) activation and cardiac fibrosis in chronic kidney disease. At cellular level, IS engages aryl hydrocarbon receptor (AhR) and regulates many biological functions. We analysed how AhR inhibition by CH-223191 (CH) and overexpression of non-functional (dominant negative, DN) nuclear factor-erythroid-2-related factor 2 (NRF2), a transcription factor recruited by AhR, modulate the response of neonatal mouse (nm) cFib to IS. We also evaluated nm-cardiomyocytes after incubation with the conditioned medium (CM) of IS±CH-treated nm-cFib. IS induced activation, collagen synthesis, TLR4 and-downstream-MCP-1, and the genes encoding angiotensinogen, angiotensin-converting enzyme, angiotensin type 1 receptor (AT1r) and neprilysin (Nepr) in nm-cFib. CH antagonized IS-initiated nm-cFib activation, but did not affect or even magnified the other features. IS promoted NRF2 nuclear translocation and expression the NRF2 target Nqo1. Both pre-incubation with CH and transfection of DN-NRF2 resulted in loss of NRF2 nuclear localization. Moreover, DN-NRF2 overexpression led to greater TLR4 and MCP-1 levels following exposure to IS. The CM of IS-primed nm-cFib and to a larger extent the CM of IS+CH-treated nm-cFib upregulated AT1r, Nepr and TNFα and myostatin genes in nm-cardiomyocytes. Hence, IS triggers pro-inflammatory activation of nm-cFib partly via AhR, and AhR-NRF2 counteract it. Strategies other than AhR inhibition are needed to target IS detrimental actions on cardiac cells.

Impact of Impaired Kidney Function on Arrhythmia-Promoting Cardiac Ion Channel Regulation

Chronic kidney disease (CKD) is associated with a significantly increased risk of cardiovascular events and sudden cardiac death. Although arrhythmias are one of the most common causes of sudden cardiac death in CKD patients, the molecular mechanisms involved in the development of arrhythmias are still poorly understood. In this narrative review, therefore, we summarize the current knowledge on the regulation of cardiac ion channels that contribute to arrhythmia in CKD. We do this by first explaining the excitation-contraction coupling, outlining current translational research approaches, then explaining the main characteristics in CKD patients, such as abnormalities in electrolytes and pH, activation of the autonomic nervous system, and the renin-angiotensin-aldosterone system, as well as current evidence for proarrhythmic properties of uremic toxins. Finally, we discuss the substance class of sodium-glucose co-transporter 2 inhibitors (SGLT2i) on their potential to modify cardiac channel regulation in CKD and, therefore, as a treatment option for arrhythmias.

Pro-Arrhythmic Potential of Accumulated Uremic Toxins Is Mediated via Vulnerability of Action Potential Repolarization

Chronic kidney disease (CKD) is represented by a diminished filtration capacity of the kidneys. End-stage renal disease patients need dialysis treatment to remove waste and toxins from the circulation. However, endogenously produced uremic toxins (UTs) cannot always be filtered during dialysis. UTs are among the CKD-related factors that have been linked to maladaptive and pathophysiological remodeling of the heart. Importantly, 50% of the deaths in dialysis patients are cardiovascular related, with sudden cardiac death predominating. However, the mechanisms responsible remain poorly understood. The current study aimed to assess the vulnerability of action potential repolarization caused by exposure to pre-identified UTs at clinically relevant concentrations. We exposed human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and HEK293 chronically (48 h) to the UTs indoxyl sulfate, kynurenine, or kynurenic acid. We used optical and manual electrophysiological techniques to assess action potential duration (APD) in the hiPSC-CMs and recorded IKr currents in stably transfected HEK293 cells (HEK-hERG). Molecular analysis of KV11.1, the ion channel responsible for IKr, was performed to further understand the potential mechanism underlying the effects of the UTs. Chronic exposure to the UTs resulted in significant APD prolongation. Subsequent assessment of the repolarization current IKr, often most sensitive and responsible for APD alterations, showed decreased current densities after chronic exposure to the UTs. This outcome was supported by lowered protein levels of KV11.1. Finally, treatment with an activator of the IKr current, LUF7244, could reverse the APD prolongation, indicating the potential modulation of electrophysiological effects caused by these UTs. This study highlights the pro-arrhythmogenic potential of UTs and reveals a mode of action by which they affect cardiac repolarization.

The Effects of Indoxyl Sulfate and Oxidative Stress on the Severity of Peripheral Nerve Dysfunction in Patients with Chronic Kidney Diseases

Pieces of evidence support the view that the accumulation of uremic toxins enhances oxidative stress and downstream regulation of signaling pathways, contributing to both endothelial microangiography and cell dysfunction. This study is to address the impact of protein-binding uremic toxins on the severity of peripheral nerve function in patients with chronic kidney disease (CKD). Fifty-four patients with CKD were included in the Toronto Clinical Neuropathy Score (TCNS), nerve conduction study (NCS), and laboratory studies including protein-binding uremic toxin (indoxyl sulfate [IS] and p-cresyl sulfate [PCS]), oxidative stress (Thiol and thiobarbituric acid reacting substances [TBARS]), and endothelial dysfunction (serum intercellular adhesion molecule 1 [sICAM-1] and serum vascular adhesion molecule 1 [sVCAM-1]) at enrollment. We used composite amplitude scores (CAS) to analyze the severity of nerve conductions on peripheral nerve function. TCNS and CAS were higher in the diabetic CKD group (p = 0.02 and 0.01, respectively). The NCS revealed the compound muscle action potential of ulnar and peroneal nerves and the sensory nerve action potential of ulnar and sural nerves (p = 0.004, p = 0.004, p = 0.004, and p = 0.001, respectively), which was found to be significantly low in the diabetic group. CAS was significantly correlated with age (r = 0.27, p = 0.04), urine albumin-creatinine ratio (UACR) (r = 0.29, p = 0.046), free-form IS (r = 0.39, p = 0.009), sICAM-1 (r = 0.31, p = 0.02), sVCAM-1 (r = 0.44, p < 0.0001), TBARS (r = 0.35, p = 0.002), and thiols (r = −0.28, p = 0.045). Linear regression revealed that only TBARS and free-form IS were strongly associated with CAS. The mediation analysis shows that the sVCAM-1 level serves as the mediator between higher IS and higher CAS. IS and oxidative stress contribute to the severity of peripheral nerve dysfunction in patients with CKD, and chronic glycemic impairment can worsen the conditions.

Uremic toxins in chronic kidney disease highlight a fundamental gap in understanding their detrimental effects on cardiac electrophysiology and arrhythmogenesis

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have an estimated 700-800 and 523 million cases worldwide, respectively, with CVD being the leading cause of death in CKD patients. The pathophysiological interplay between the heart and kidneys is defined as the cardiorenal syndrome (CRS), in which worsening of kidney function is represented by increased plasma concentrations of uremic toxins (UTs), culminating in dialysis patients. As there is a high incidence of CVD in CKD patients, accompanied by arrhythmias and sudden cardiac death, knowledge on electrophysiological remodeling would be instrumental for understanding the CRS. While the interplay between both organs is clearly of importance in CRS, the involvement of UTs in pro-arrhythmic remodeling is only poorly investigated, especially regarding the mechanistic background. Currently, the clinical approach against potential arrhythmic events is mainly restricted to symptom treatment, stressing the need for fundamental research on UT in relation to electrophysiology. This review addresses the existing knowledge of UTs and cardiac electrophysiology, and the experimental research gap between fundamental research and clinical research of the CRS. Clinically, mainly absorbents like ibuprofen and AST-120 are studied, which show limited safe and efficient usability. Experimental research shows disturbances in cardiac electrical activation and conduction after inducing CKD or exposure to UTs, but are scarcely present or focus solely on already well-investigated UTs. Based on UTs data derived from CKD patient cohort studies, a clinically relevant overview of physiological and pathological UTs concentrations is created. Using this, future experimental research is stimulated to involve electrophysiologically translatable animals, such as rabbits, or in vitro engineered heart tissues.

Fibroblast growth factor 21 is associated with widening QRS complex and prolonged corrected QT interval in patients with stable angina

BACKGROUND

Fibroblast growth factor 21 (FGF21) is produced by cardiac cells, may acts in an autocrine manner, and was suggested to has a cardioprotective role in atherosclerosis. Wide QRS complex and heart rate-corrected QT interval (QTc interval) prolongation are associated to dangerous ventricular arrhythmias and cardiovascular disease mortality. Yet, the role of FGF21 in cardiac arrhythmia has never been studied. The aim of the study was to investigate the relationship between plasma FGF21 and the QRS duration and QTc interval in patients with stable angina.

METHODS

Three hundred twenty-one consecutive stable angina patients were investigated. Plasma FGF21 was measured through ELISA, and each subject underwent 12-lead electrocardiography.

RESULTS

FGF21 plasma levels were positively associated with the QRS duration (β = 0.190, P = 0.001) and QTc interval (β = 0.277, P < 0.0001). With increasing FGF21 tertiles, the patients had higher frequencies of wide QRS complex and prolonged QTc interval. After adjusting for patients' anthropometric parameters, the corresponding odd ratios (ORs) for wide QRS complex of the medium and high of FGF21 versus the low of FGF21 were 1.39 (95% CI 0.51-3.90) and 4.41 (95% CI 1.84-11.59), respectively, and p for trend was 0.001. Furthermore, multiple logistic regression analysis also showed the corresponding odd ratios (ORs) for prolonged QTc interval of the medium and high of FGF21 versus the low of FGF21 were 1.02 (95% CI 0.53-1.78) and 1.93 (95% CI 1.04-3.60) respectively with the p for trend of 0.037. In addition, age- and sex-adjusted FGF21 levels were positively associated with fasting glucose, HbA1c, creatinine, and adiponectin, but negatively associated with albumin, and the estimated glomerular filtration rate.

CONCLUSIONS

This study indicates that plasma FGF21 is associated with wide QRS complex and prolonged corrected QT interval in stable angina patients, further study is required to investigate the role of plasma FGF21 for the underlying pathogenesis.

Chronic Kidney Disease Is Associated With Increased Cardiac Corin Expression But Decreased Proatrial Natriuretic Peptide Conversion Activity

Background

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular disease. Corin converts proatrial natriuretic peptide into its active form after being activated by PCSK6 (proprotein convertase subtilisin/kexin type 6) protease. It remains unknown whether the PCSK6/corin/atrial natriuretic peptide pathway plays a role in CKD‐induced cardiomyopathy.

Methods and Results

Serum corin, left ventricular mass index, and corin–left ventricular mass index correlation were compared between outpatients with versus without CKD. Cardiac corin expression and activity as well as serum corin were compared between 5/6 nephrectomy CKD animal models and sham controls. The effects of indoxyl sulfate, a uremic toxin, on cardiomyocytes were examined in vitro in H9c2 cells. A total of 543 patients were enrolled in this study. Serum corin levels were elevated in patients with CKD compared with levels in patients without CKD. Serum corin levels correlated negatively with left ventricular mass index in participants without CKD, but not in patients with CKD. Compared with sham controls, CKD mice had higher serum corin levels and increased cardiac expression of corin but reduced cardiac corin conversion activity. Indoxyl sulfate stimulated corin expression while suppressing serine protease activity in H9c2 cardiomyoblasts. Lower PCSK6 expression in CKD mouse hearts and indoxyl sulfate–treated H9c2 cardiomyoblasts may explain, at least partly, the observed CKD‐associated reduction in corin activity.

Conclusions

In CKD, cardiac and serum levels of corin are increased, yet corin activity is suppressed. The latter may be attributable to reduced PCSK6 expression. These findings suggest that corin dysfunction may play a significant role in the pathogenesis of CKD‐associated cardiomyopathy.

Uremic Toxins and Cardiovascular Risk in Chronic Kidney Disease: What Have We Learned Recently beyond the Past Findings?

Patients with chronic kidney disease (CKD) have an elevated prevalence of atheromatous (ATH) and/or non-atheromatous (non-ATH) cardiovascular disease (CVD) due to an array of CKD-related risk factors, such as uremic toxins (UTs). Indeed, UTs have a major role in the emergence of a spectrum of CVDs, which constitute the leading cause of death in patients with end-stage renal disease. The European Uremic Toxin Work Group has identified over 100 UTs, more than 25 of which are dietary or gut-derived. Even though relationships between UTs and CVDs have been described in the literature, there are few reviews on the involvement of the most toxic compounds and the corresponding physiopathologic mechanisms. Here, we review the scientific literature on the dietary and gut-derived UTs with the greatest toxicity in vitro and in vivo. A better understanding of these toxins’ roles in the elevated prevalence of CVDs among CKD patients might facilitate the development of targeted treatments. Hence, we review (i) ATH and non-ATH CVDs and the respective levels of risk in patients with CKD and (ii) the mechanisms that underlie the influence of dietary and gut-derived UTs on CVDs.

Fibroblast Growth Factor-23-Klotho Axis in Cardiorenal Syndrome: Mediators and Potential Therapeutic Targets

Cardiorenal syndrome (CRS) is a complex disorder that refers to the category of acute or chronic kidney diseases that induce cardiovascular disease, and inversely, acute or chronic heart diseases that provoke kidney dysfunction. There is a close relationship between renal and cardiovascular disease, possibly due to the presence of common risk factors for both diseases. Thus, it is well known that renal diseases are associated with increased risk of developing cardiovascular disease, suffering cardiac events and even mortality, which is aggravated in those patients with end-stage renal disease or who are undergoing dialysis. Recent works have proposed mineral bone disorders (MBD) as the possible link between kidney dysfunction and the development of cardiovascular outcomes. Traditionally, increased serum phosphate levels have been proposed as one of the main factors responsible for cardiovascular damage in kidney patients. However, recent studies have focused on other MBD components such as the elevation of fibroblast growth factor (FGF)-23, a phosphaturic bone-derived hormone, and the decreased expression of the anti-aging factor Klotho in renal patients. It has been shown that increased FGF-23 levels induce cardiac hypertrophy and dysfunction and are associated with increased cardiovascular mortality in renal patients. Decreased Klotho expression occurs as renal function declines. Despite its expression being absent in myocardial tissue, several studies have demonstrated that this antiaging factor plays a cardioprotective role, especially under elevated FGF-23 levels. The present review aims to collect the recent knowledge about the FGF-23-Klotho axis in the connection between kidney and heart, focusing on their specific role as new therapeutic targets in CRS.

Improved cardiovascular autonomic function and decreased protein-bound uremic toxins in patients with end-stage renal disease after peritoneal dialysis

Objective

Cardiovascular autonomic neuropathy is highly prevalent in patients with end-stage renal disease (ESRD), and it has a high fatality rate. This study aimed to determine whether peritoneal dialysis (PD) improves cardiovascular autonomic function (CAF) and decreases protein-bound uremic toxin (indoxyl sulfate [IS], p-cresyl sulfate [PCS]) levels.

Methods

IS and PCS levels, and parameters of CAF (heart rate response to deep breathing [HR_DB], the Valsalva ratio, baroreflex sensitivity, and the frequency domain) were prospectively evaluated in 26 patients with ESRD undergoing PD at two time points (pre-PD and 6 months post-PD). For comparison, 19 consecutive patients with pre-dialysis chronic kidney disease and 30 age- and sex-matched healthy volunteers were included as the disease and control groups, respectively.

Results

Baroreflex sensitivity, HR_DB, and the Valsalva ratio were significantly lower in the ESRD and disease groups than in the control group. IS and PCS levels were significantly higher in the ESRD group than in the control group. Sympathetic/parasympathetic activity was improved after PD. IS levels were significantly decreased after PD and IS level changes were correlated with the frequency domain.

Conclusions

IS may play a role in cardiovascular autonomic neuropathy, and decreased IS levels after dialysis are associated with sympathetic/parasympathetic activity imbalance.

The role of AMP-activated protein kinase α1-mediated endoplasmic reticulum stress in alleviating the toxic effect of uremic toxin indoxyl sulfate on vascular endothelial cells by Klotho

Recently, the Klotho protein (Klotho) has received substantial attention as protective factor against cardiovascular complications of chronic kidney disease (CKD). However, the direct effect and mechanism of Klotho on endothelial cells injury are not well-known. In this study, we incubated human vein umbilical endothelial cells (HUVECs) with uremic toxin indoxyl sulfate (IS) to mimic CKD internal environment and investigated the direct effect of Klotho on the HUVECs injury induced by IS and to explore the mechanism in this process. We found IS inhibited cell viability, increased endoplasmic reticulum stress, and mediated apoptosis of HUVECs. Treatment with Klotho significantly attenuated IS-induced above effects. Furthermore, Klotho alleviated the IS toxic effect on HUVECs via promoting AMP-activated protein kinase (AMPK) α1 phosphorylation instead of directly upregulating AMPKα1, which could be partly blocked by AMPK pathway inhibitor-Compound C. In addition, Klotho also inhibited intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression induced by IS. Altogether, these results indicated that Klotho can protect HUVECs from IS-induced injury by alleviating AMPKα1-mediated endoplasmic reticulum stress.

Proarrhythmic Effects of Electrolyte Imbalance in Virtual Human Atrial and Ventricular Cardiomyocytes

Dialysis is prescribed to renal failure patients as a long-term chronic treatment. Whereas dialysis therapeutically normalizes serum electrolytes and removes small toxin molecules, it fails to alleviate fibroblast induced structural fibrosis, and unresponsive uremia. The simultaneous presence of altered electrolytes and fibrosis or uremia is thought to be pro-arrhythmogenic. This study explored potential arrhythmogenesis under pre-dialysis (high electrolyte levels) and post-dialysis (low physiological electrolyte levels) in the presence of fibrosis and uremia in human atrial and ventricular model cardiomyocytes.Two validated human cardiomyocyte models were used in this study that permitted simulation of cardiac atrial and ventricular detailed electrophysiology. Pathological conditions simulating active fibrosis and uremia were implemented in both models. Pre- and post-dialysis conditions were simulated using high and low electrolyte levels respectively. Arrythmogenesis was quantified by computing restitution curves that permitted identification of action potential duration and calcium transient alternans instabilities.In comparison to control conditions, fibrosis abbreviated action potential durations while uremia prolonged the same. Under pre-dialysis conditions, an elevation of serum electrolyte levels caused action potential durations to be abbreviated under both fibrosis and uremia. Alternans instability was observed in the ventricular cardiomyocyte model. Under post-dialysis conditions, lower levels of serum electrolytes promoted an abbreviated action potential duration under fibrosis but caused a large increase of the control and uremic action potential durations. Alternans instabilities were observed in the atrial cardiomyocyte model under post-dialysis conditions at physiological heart rates. The calcium transient restitution showed similar alternans instabilities.Co-existing conditions such as fibrosis and uremia in the presence of unphysiological electrolyte levels promote arrhythmogenesis and may require additional treatment to improve dialysis outcomes.Clinical Relevance. Knowledge of model response to clinically relevant conditions permits use of in silico modeling to better understand and dissect underlying arrhythmia mechanisms.

Gut-Derived Protein-Bound Uremic Toxins

Chronic kidney disease (CKD) afflicts more than 500 million people worldwide and is one of the fastest growing global causes of mortality. When glomerular filtration rate begins to fall, uremic toxins accumulate in the serum and significantly increase the risk of death from cardiovascular disease and other causes. Several of the most harmful uremic toxins are produced by the gut microbiota. Furthermore, many such toxins are protein-bound and are therefore recalcitrant to removal by dialysis. We review the derivation and pathological mechanisms of gut-derived, protein-bound uremic toxins (PBUTs). We further outline the emerging relationship between kidney disease and gut dysbiosis, including the bacterial taxa altered, the regulation of microbial uremic toxin-producing genes, and their downstream physiological and neurological consequences. Finally, we discuss gut-targeted therapeutic strategies employed to reduce PBUTs. We conclude that targeting the gut microbiota is a promising approach for the treatment of CKD by blocking the serum accumulation of PBUTs that cannot be eliminated by dialysis.

The Arrhythmogenic Effect of Protein-Bound Uremic Toxin p-Cresylsulfate: An In Vitro Study

BACKGROUND

p-Cresylsulfate (PCS) is a protein-bound uremic toxin that accumulates in patients with chronic kidney disease. Previous studies have indicated that serum total PCS levels are significantly increased in the presence of abnormal corrected QT (QTc) intervals, and that they are associated with QTc prolongation. However, the QTc prolongation effect of PCS remains unclear. The current study aimed to investigate the arrhythmogenic effect of PCS using in vitro experiments and computer simulation.

METHODS

The arrhythmogenic effect of PCS was evaluated by incubating H9c2 rat ventricular cardiomyocytes in vitro with increasing concentrations of PCS. Electrophysiological studies and mathematical computer simulations were performed.

RESULTS

in vitro, the delayed rectifier potassium current (I_K ) was significantly decreased in a dose-dependent manner after treatment with PCS. The modulation of PCS on I_K was through regulation of the phosphorylation of the major potassium ion channel protein Kv2.1. In computer simulations, the decrease in I_K induced by PCS prolonged the action potential duration (APD) and sped up the re-entrant wave, which is known to be a trigger mechanism for lethal ventricular arrhythmias.

CONCLUSIONS

PCS significantly downregulated the phosphorylation of the I_K channel protein Kv2.1 and I_K current activity, which increased the cardiomyocyte APD. This was observed both in vitro and in the computer O'Hara-Rudy dynamic human ventricular model. These findings suggest that PCS may play a key role in the development of cardiac arrhythmias.

Effects and Safety of an Oral Adsorbent on Chronic Kidney Disease Progression: A Systematic Review and Meta-Analysis

Background: AST-120 (Kremezin), which is an oral spherical carbon adsorbent, has been reported to have the potential for retarding disease progression in patients with chronic kidney disease. We aimed to evaluate its efficacy and safety in this study. Methods: We systematically searched for randomized controlled trials published in PubMed, Embase, and Cochrane databases. The primary outcomes were the renal outcome and all-cause mortality, and the change in serum indoxyl sulfate (IS) levels. The safety outcome was also evaluated in terms of reported major adverse events. A random-effects model was used when heterogeneity was expected. Results: Eight studies providing data for 3349 patients were included in the meta-analysis. The risk ratio of renal outcome and all-cause mortality were 0.97 (95% CI: 0.88–1.07; 6 trials) and 0.94 (0.73–1.20; 5 trials), respectively. Furthermore, the weighted mean change in IS levels from baseline to the end of the study was −0.28 mg/dL (95% CI: −0.46 to −0.11; 4 trials). Conclusions: This study provides evidence that AST-120 can effectively lower IS levels but still controversial in terms of slowing disease progression and all-cause mortality. Except for dermatological events, the incidence of adverse events did not differ significantly between the AST-120 and placebo groups.

Effect of Bone Marrow-Derived Mesenchymal Stem Cells on Ischaemic-Reperfused Hearts in Adult Rats with Established Chronic Kidney Disease

Background and Objectives

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are adult multipotent non-haematopoietic stem cells that have regeneration potential. The current study aimed to detect the ability of BM-MSCs to improve kidney and cardiac functions in adult rats with established chronic kidney disease.

Methods

Rats were divided into sham-operated control, untreated sub totally nephrectomised and treated sub totally nephrectomised groups. Body weight, kidney and cardiac tissue weights, plasma creatinine and urea levels and arterial blood pressure were measured. ECG was recorded, and an in vitro isolated heart study was performed.

Results

Stem cell treatment decreased the elevated plasma creatinine and urea levels and decreased systolic, diastolic and mean arterial blood pressure values. These changes were accompanied by a decrease in glomerular hypertrophy with apparent normal renal parenchyma. Additionally, BM-MSCs shortened Q-To and Q-Tc intervals, all time to peak tension values, the half relaxation value at 30 min of reperfusion and the contraction time at 15 and 30 min of reperfusion. Moreover, stem cell treatment significantly increased the heart rate, QRS voltage, the peak tension at the 15- and 30-min reperfusion time points and the peak tension per left ventricle at the 30-min reperfusion time point compared to the pre-ischaemia baseline. BM-MSCs resolve inter muscular oedema and lead to the re-appearance of normal cardiomyocytes. This improvement occurs with the observations of BM-MSCs in renal and heart tissues.

Conclusions

BM-MSCs can attenuate chronic kidney disease progression and the associated cardiac electrophysiological and inotropic dysfunction.

Heart-kidney interactions: mechanistic insights from animal models

Pathological changes in the heart or kidney can instigate the release of a cascade of cardiorenal mediators that promote injury in the other organ. Combined dysfunction of heart and kidney is referred to as cardiorenal syndrome (CRS) and has gained considerable attention. CRS has been classified into five distinct entities, each with different major pathophysiological changes. Despite the magnitude of the public health problem of CRS, the underlying mechanisms are incompletely understood, and effective intervention is unavailable. Animal models have allowed us to discover pathogenic molecular changes to clarify the pathophysiological mechanisms responsible for heart-kidney interactions and to enable more accurate risk stratification and effective intervention. Here, this article focuses on the use of currently available animal models to elucidate mechanistic insights in the clinical cardiorenal phenotype arising from primary cardiac injury, primary renal disease with special emphasis of chronic kidney disease-specific risk factors, and simultaneous cardiorenal/renocardiac dysfunction. The development of novel animal models that recapitulate more closely the cardiorenal phenotype in a clinical scenario and discover the molecular basis of this condition will be of great benefit.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

The regulation of NLRP3 inflammasome expression during the development of cardiac contractile dysfunction in chronic kidney disease

Chronic inflammation plays a crucial role in the long-term complications in patients with chronic kidney disease (CKD). This study aimed to assess the role of NLR pyrin domain-containing protein (NLRP3) inflammasome in cardiac contractile dysfunctions in CKD. The cardiac contractile function was evaluated and the expression of NLRP3 inflammasome and related cytokines in the heart was assessed in a murine sham-operated and 5/6 nephrectomy CKD model in vivo. In vitro, H9c2 cells were treated with uremic toxin indoxyl sulfate (IS), with or without NLRP3 inflammasome inhibition, which was achieved by using small interfering RNA (siRNA)-mediated knockdown of the NLRP3 gene. Moreover, the activation of nuclear factor κB (NF-κB) signaling and apoptosis marker levels were assessed in the IS-treated H9c2 cells. The results demonstrated that CKD can lead to the development of cardiac contractile dysfunction in vivo associated with the upregulation of NLRP3 inflammasome, IL-1β, IL-18, and contribute to the myocardial apoptosis. In vitro experiments showed the upregulation of inflammasome, IL-1β, and IL-18 levels, and cell apoptosis in the IS-treated H9c2 cells through the activation of NF-κB signaling pathway. The transfection of cells with si-NLRP3 was shown to alleviate IL-1β, IL-18, and cell apoptosis. Moreover, decreased cell viability induced by IS was shown to be attenuated by IL-1β or IL-18-neutralizing antibody. In summary, CKD can result in the development of cardiac contractile dysfunction associated with the upregulation of NLRP3 inflammasome/IL-1β/IL-18 axis induced by the uremic toxins.

From bench to the hemodialysis clinic: protein-bound uremic toxins modulate NF-κB/Nrf2 expression

PURPOSE

Uremic toxins produced by gut microbiota (indoxyl sulfate-IS, p-cresyl sulfate-p-CS, and indole-3-acetic acid-IAA) accumulate in hemodialysis (HD) patients and exhibit potent inflammatory effects. However, the impact of these toxins on nuclear E2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-κB) expression in HD patients remains poorly defined. The aim of this study was to evaluate the association between uremic toxins and Nrf2/NF-κB expression in vitro (RAW 264.7 macrophage-like cells) and in peripheral blood mononuclear cells from HD patients.

METHODS

Uremic toxins, C-reactive protein (CRP), interleukin-6 (IL-6) and malondialdehyde (MDA) levels were measured in fifteen HD patients and nine healthy individuals. RAW 264.7 macrophage-like cells were incubated with IS, as a prototype of protein-bound uremic toxin. Nrf2 and NF-κB expressions were analyzed by RT-qPCR.

RESULTS

HD patients presented high levels of inflammatory markers, MDA and uremic toxins. In addition, they presented high NF-κB and low Nrf2 expression. Uremic toxins were positively correlated with NF-κB expression (IS, ρ = 0.58, p < 0.003; p-CS, ρ = 0.71, p < 0.001; IAA, ρ = 0.62, p < 0.001) and negatively with Nrf2 (IS, ρ = - 0.48, p = 0.01; p-CS, ρ = - 0.46, p < 0.02). Uremic toxins also exhibited positive correlations with CRP and MDA levels. Multivariate analysis revealed that p-CS is a determinant factor of NF-κB expression. In RAW 264.7 culture, NF-κB mRNA expression was stimulated by IS, while Nrf2 was downregulated.

CONCLUSIONS

Thus, uremic toxins may stimulate NF-κB mRNA and decrease Nrf2 expression in HD patients and, consequently, trigger inflammation and oxidative stress.

Association of QT interval with mortality by kidney function: results from the National Health and Nutrition Examination Survey (NHANES)

Objective

Prolonged QT interval predisposes to ventricular arrhythmias and sudden cardiac death. However, the association between QT interval and mortality by the level of pre-existing kidney function has not been investigated.

Methods

We followed 6565 participants from the National Health and Nutrition Examination Survey III for a median of 13.3 years. Sample divided according to corrected QT (QTc) interval was as follows: normal (QTc <450 ms for men and <460 ms for women) or prolonged. It was further categorised as follows: (1) no chronic kidney disease (CKD), that is, albumin to creatinine ratio (ACR) <30 mg/g and estimated glomerular filtration rate (eGFR) > 60 mL/min/1.73 m²; (2) CKD by eGFR only (eGFR <60 mL/min/1.73 m², ACR <30 mg/g); (3) CKD by ACR only (ACR >30 mg/g, eGFR >60 mL/min/1.73 m²) and (4) CKD by both. Cox proportional hazards models were used.

Results

CKD group had prolonged QTc than those without CKD (20.5%vs12.9%, p<0.0001). Both prolonged QTc and CKD are independently associated with increased risk of mortality. When combined, risk of mortality is higher in those with CKD by eGFR with prolonged QTc than normal QTc (HR 2.6 (1.7-3.9) and 3.1 (1.7-5.4) vs 1.4 (1.1-1.7) and 1.7 (1.3-2.1) for all-cause and CV mortality). There is no significant difference in risk in those with CKD by ACR when QTc is prolonged. There is significant improvement in risk prediction for all-cause and CV mortality when QTc is added to CKD beyond established CV risk factors (net reclassification index p<0.00001).

Conclusion

A screening ECG in those with CKD may help in finer risk stratification and may be considered.

Role of uremic toxin indoxyl sulfate in the progression of cardiovascular disease

The prevalence of cardiovascular disease (CVD) among patients with chronic kidney disease (CKD) is relatively high. Deterioration of renal function in CKD leads to accumulation of indoxyl sulfate, a tryptophan metabolite produced by gut microbiota. It is acknowledged that indoxyl sulfate is capable to stimulate oxidative stress, which in turn contributes to the progression of vascular disorders and its resultant coronary artery disease. Recent research have demonstrated the adverse effects of indoxyl sulfate on the heart, together with the acceleration of vascular dysfunction, suggesting that indoxyl sulfate might contribute to high prevalence of CVD in CKD. The present mini review has focused on the potential mechanisms by which indoxyl sulfate exerts this pro-oxidant effects on the cardiovascular system. The action of indoxyl sulfate are related to multiple NADPH oxidase-mediated redox signaling pathways, which have been implicated in the pathophysiology of different forms of CVD, including chronic heart failure, arrhythmia, atherosclerotic vascular disease and coronary calcification. Future therapeutic options are discussed, including modulating gut microbial flora and blocking responsible pathophysiologic pathways.

Indoxyl sulfate - the uremic toxin linking hemostatic system disturbances with the prevalence of cardiovascular disease in patients with chronic kidney disease

Background

During chronic kidney disease progression, kidney-specific risk factors for cardiovascular disease come into play. The present study investigated the impact of indoxyl sulfate, dietary tryptophan-derived uremic toxin, accumulated in the blood of patients with chronic kidney disease on hemostatic parameters, markers of inflammation, oxidative stress and monocyte to macrophage transition.

Methods

Fifty-one CKD patients not undergoing hemodialysis were enrolled in the study. Coagulation factors, fibrinolytic parameters, adhesion molecules, endothelial dysfunction markers, oxidative stress as well as inflammation markers were examined using immune-enzymatic method. Indoxyl sulfate levels were assessed using high-performance liquid chromatography. Biochemical parameters were determined by routine laboratory techniques using an automated analyzers. All assessed parameters were compared with controls and subjected to cross-sectional statistical analysis.

Results

Elevated concentrations of indoxyl sulfate, the vast majority of parameters affecting hemostasis, and markers of renal insufficiency conditions were observed. Part of hemostatic factors, namely tissue factor, von Willebrand factor, thrombomodulin, soluble urokinase-type plasminogen activator receptor, soluble intercellular adhesion molecule-1, soluble vascular cell adhesion protein were correlated with the fraction of indoxyl sulfate. A significant quantity of assessed parameters showed strong correlations with superoxide-dismutase, renal insufficiency rate, C-reactive protein, and neopterin. Levels of indoxyl sulfate were independently associated with markers of impaired endothelial function (thrombomodulin, adhesion molecules), oxidative stress (superoxide-dismutase) and monocytes activation determinant (neopterin), which indicate unconventional links between these systems and the role of indoxyl sulfate. Furthermore, parameters that correlated with the levels of indoxyl sulfate (von Willebrand factor, soluble urokinase-type plasminogen activator receptor, soluble intercellular adhesion molecule-1) were positively associated with the prevalence of cardiovascular disease in a CKD patients.

Conclusions

The study demonstrated that in conditions of chronic exposure to uremic toxins, indoxyl sulfate seems to be one of the “missing links” between impaired renal function and prevalence of cardiovascular events, especially hemostatic disorders. The main functions of the action appear to be altered monocytes activation, intensified inflammatory process, and augmented oxidative stress by this uremic toxin.

Electronegative LDL-mediated cardiac electrical remodeling in a rat model of chronic kidney disease

The mechanisms underlying chronic kidney disease (CKD)–associated higher risks for life-threatening ventricular tachyarrhythmias remain poorly understood. In rats subjected to unilateral nephrectomy (UNx), we examined cardiac electrophysiological remodeling and relevant mechanisms predisposing to ventricular arrhythmias. Adult male Sprague-Dawley rats underwent UNx (n = 6) or sham (n = 6) operations. Eight weeks later, the UNx group had higher serum blood urea nitrogen and creatinine levels and a longer electrocardiographic QTc interval than did the sham group. Patch-clamp studies revealed epicardial (EPI)-predominant prolongation of the action potential duration (APD) at 50% and 90% repolarization in UNx EPI cardiomyocytes compared to sham EPI cardiomyocytes. A significant reduction of the transient outward potassium current (I_to) in EPI but not in endocardial (ENDO) cardiomyocytes of UNx rats led to a decreased transmural gradient of I_to. The reduction of I_to currents in UNx EPI cardiomyocytes was secondary to downregulation of KChIP2 but not Kv4.2, Kv4.3, and Kv1.4 protein expression. Incubation of plasma electronegative low-density lipoprotein (LDL) from UNx rats with normal EPI and ENDO cardiomyocytes recapitulated the electrophysiological phenotype of UNx rats. In conclusion, CKD disrupts the physiological transmural gradient of I_to via downregulation of KChIP2 proteins in the EPI region, which may promote susceptibility to ventricular tachyarrhythmias. Electronegative LDL may underlie downregulation of KChIP2 in CKD.

The burden of major adverse cardiac events in patients with coronary artery disease

Background

Patients with a history of cardiovascular disease are at high risk of developing secondary major adverse cardiac events (MACE). This study aimed to identify independent predictors of MACE after hospital admission which could be used to identify of high-risk patients who may benefit from preventive strategies.

Methods

This study included 1,520 consecutive patients with coronary artery disease (CAD) (654 with acute coronary syndrome (ACS) and 866 with elective percutaneous coronary intervention (PCI) patients) who received PCI and/or stenting. MACE was defined as all-cause mortality or rehospitalization for a cardiovascular- related illness. Cardiovascular-related illnesses included heart failure, reinfarction (nonfatal), recurrence of angina pectoris and repeat PCI or coronary artery bypass graft.

Results

During a mean follow-up period of 32 months, 558 of the 1,520 patients developed at least one MACE. Cox regression analysis showed that the baseline clinical and biochemical variables which associated with MACE were age, being illiterate, a widow or widower, and/or economically dependent, having triple vessel disease, stent implantation, anemia, and/or diabetes mellitus, waist to hip ratio (WHR), diastolic blood pressure, fasting glucose, total cholesterol, high-density lipoprotein cholesterol (HDL-C), creatinine, estimated glomerular filtration rate (eGFR), red blood cell count, hemoglobin, hematocrit, and mean corpuscular-hemoglobin concentration (MCHC) in ACS patients, and age, malnourished, and/or economically dependent, taking hypoglycemic medication, having triple vessel disease, stent implantation, anemia, diabetes mellitus, and/or hypertension, WHR, fasting glucose, HDL-C, uric acid, creatinine, eGFR, high-sensitivity C-reactive protein, mean corpuscular volume, and MCHC in elective PCI patients. Using multivariate Cox regression analysis, we found the MACE’s independent factors are triple vessel disease, stent implantation, hypertension, and eGFR in ACS patients, and having triple vessel disease, stent implantation, hypertension, and uric acid in elective PCI patients.

Conclusions

Having triple vessel disease, stent implantation, hypertension, and eGFR or uric acid independently predicted MACE in patients with CAD after long-term follow-up. Fortunately, these factors are modifiable and should be identified and monitored early.

Hemodialysis-induced repolarization abnormalities on ECG are influenced by serum calcium levels and ultrafiltration volumes

PURPOSE

Hemodialysis (HD) patients are known to have high cardiovascular mortality rate. Sudden cardiac death (SCD) due to arrhythmias causes most of the cardiac deaths. HD per se may lead to ECG abnormalities and ventricular arrhythmias. Monitoring ECG parameters such as corrected QT interval, QT dispersion (QTd), Tpe interval may be useful to stratify the patients with high risk of arrhythmia and SCD. Herein we aimed to investigate the effects of changes in serum electrolyte levels and pH on ECG parameters before and after the HD.

METHODS

A total of 50 chronic HD patients (mean age 58 ± 19; male 27) were enrolled. Patients with unmeasurable T waves; atrial fibrillation; bundle branch block; use of class I or class III antiarrhythmic drugs were excluded. Serum potassium, magnesium, calcium, urea, creatinine and pH were measured before and after HD treatment. Standard surface 12-lead ECGs were recorded before and after HD. QTc, QTd, Tpe, JT interval, P-wave-duration, P-wave dispersion were determined.

RESULTS

Serum potassium and magnesium decreased, and calcium, pH and bicarbonate levels increased; QRS and Tpe interval were increased after HD. Basal Tpe was correlated with urea (r = 0.31, p = 0.02). Tpe interval was higher in hypocalcemic compared to normocalcemic patients (77 ± 11 vs 70 ± 9 ms, p = 0.02). ∆Tpe was correlated with ∆calcium (r = -0.32, p = 0.02). Basal QTc was correlated with calcium (r = -0.62, p < 0.001). ∆QTc was correlated with basal calcium (r = 0.39, p = 0.005) and ∆calcium (r = -0.46, p < 0.001). Basal JT was correlated with calcium (r = -0.55, p < 0.001). ∆JT was correlated with pH (r = 0.35, p = 0.01), ∆calcium (r = -0.53, p < 0.001) and ∆magnesium (r = -0.30, p = 0.03). Before HD, 12 patients (12%) were hypermagnesemic of whom JT intervals were lower (314 ± 20 vs 332 ± 23 ms, p = 0.02). Ultrafiltration per body weight was associated with ∆QTc (r = -0.40, p = 0.007) and ∆JT (r = -0.36, p = 0.01).

CONCLUSION

QRS and Tpe intervals were increased after HD. Tpe interval was longer in hypocalcemic patients. Change in Tpe was negatively associated with the change in calcium. Ultrafiltration was associated with ∆QTc and ∆JT. Calcium and ultrafiltration seem to be the most important determinants of ECG parameters of HD-induced repolarization abnormalities.

Increased Levels of Total p-Cresylsulfate Are Associated with Pruritus in Patients with Chronic Kidney Disease

BACKGROUND

Pruritus is a common and distressing symptom that affects patients with chronic kidney disease (CKD). Indoxyl sulfate (IS) and p-cresylsulfate (PCS) are uremic toxins with similar protein binding, dialytic clearance, and proinflammatory features. Pruritus in CKD may correlate better with uremic toxins than the glomerular filtration rate (GFR), suggesting that uremic toxins either in the central nervous system or peripherally may play an important role in the pathophysiology.

OBJECTIVE

We sought to investigate the potential contribution of serum total IS and PCS to the pathogenesis of pruritus.

METHODS

The serum levels of total IS and PCS concentrations were measured in all patients by using the Ultra Performance LC System. The characteristics of pruritus were assessed using a visual analog scale score and an interview questionnaire.

RESULTS

Among the 320 CKD patients, 35% had pruritus. The patients with pruritus were older and had a higher frequency of diabetes mellitus, higher uric acid, calcium, phosphorus, creatinine, high-sensitivity C-reactive protein, and total IS and PCS levels, and lower albumin concentrations and estimated GFR (eGFR) than those without pruritus. Increasing concentrations of total PCS were independently and significantly associated with pruritus. Multiple logistic regression analysis revealed total PCS as an independent association factor for pruritus, even after full adjustment of known biomarkers. Furthermore, serum total PCS levels were positively associated with calcium, phosphorus, blood urea nitrogen, creatinine, and white blood cell count, and negatively associated with eGFR, hemoglobin, and hematocrit.

CONCLUSION

Our results indicate that total PCS may play a role in the pathogenesis of pruritus.

Moderate Increase of Indoxyl Sulfate Promotes Monocyte Transition into Profibrotic Macrophages

OBJECTIVE

The uremic toxin Indoxyl-3-sulphate (IS), a ligand of Aryl hydrocarbon Receptor (AhR), raises in blood during early renal dysfunction as a consequence of tubular damage, which may be present even when eGFR is normal or only moderately reduced, and promotes cardiovascular damage and monocyte-macrophage activation. We previously found that patients with abdominal aortic aneurysms (AAAs) have higher CD14+CD16+ monocyte frequency and prevalence of moderate chronic kidney disease (CKD) than age-matched control subjects. Here we aimed to evaluate the IS levels in plasma from AAA patients and to investigate in vitro the effects of IS concentrations corresponding to mild-to-moderate CKD on monocyte polarization and macrophage differentiation.

METHODS

Free IS plasma levels, monocyte subsets and laboratory parameters were evaluated on blood from AAA patients and eGFR-matched controls. THP-1 monocytes, treated with IS 1, 10, 20 μM were evaluated for CD163 expression, AhR signaling and then induced to differentiate into macrophages by PMA. Their phenotype was evaluated both at the stage of semi-differentiated and fully differentiated macrophages. AAA and control sera were similarly used to treat THP-1 monocytes and the resulting macrophage phenotype was analyzed.

RESULTS

IS plasma concentration correlated positively with CD14+CD16+ monocytes and was increased in AAA patients. In THP-1 cells, IS promoted CD163 expression and transition to macrophages with hallmarks of classical (IL-6, CCL2, COX2) and alternative phenotype (IL-10, PPARγ, TGF-β, TIMP-1), via AhR/Nrf2 activation. Analogously, AAA sera induced differentiation of macrophages with enhanced IL-6, MCP1, TGF-β, PPARγ and TIMP-1 expression.

CONCLUSION

IS skews monocyte differentiation toward low-inflammatory, profibrotic macrophages and may contribute to sustain chronic inflammation and maladaptive vascular remodeling.