Cardiotoxicity of Uremic Toxins: A Driver of Cardiorenal Syndrome

Clinical impact of diastolic dysfunction and atrial fibrillation before and after initiating hemodialysis in patients with end-stage kidney disease

BACKGROUND

Diastolic dysfunction with left ventricular hypertrophy and myocardial fibrosis is an important characteristic of uremic cardiomyopathy in end-stage kidney disease (ESKD). Few studies explored the relationship between changes in diastolic dysfunction and the risk of mortality or cardiovascular outcome in patients with ESKD. We investigated the clinical impact of diastolic dysfunction and atrial fibrillation (AF) on patients starting hemodialysis (HD).

METHODS

A total of 718 patients who started HD between 2010 and 2020 were included. We classified patients according to the pre- and post-HD diastolic dysfunction grades (DDG) evaluated by echocardiography. Patients with AF were classified separately. The primary outcome was a composite outcome of all-cause mortality and cardiac complication.

RESULTS

The median age was 63 years, and 61.4% were male. Patients were divided into four groups based on pre-HD echocardiography findings. After initiating HD, the patients were classified according to changes in DDG and AF. Composite outcomes were significantly higher in the pre-HD AF groups. However, after adjusting for age and history of ischemic heart disease, pre-HD AF did not affect the composite outcomes. Patients with normal post-HD diastolic function had better outcomes than those with diastolic dysfunction or AF. Furthermore, the deterioration of diastolic dysfunction after HD was associated with an increased risk of composite outcomes.

CONCLUSIONS

The deterioration of diastolic dysfunction and newly development of AF after initiating HD were identified as risk factors for mortality and cardiac complications, supporting the clinical importance of the appropriate management of diastolic dysfunction and AF in patients with ESKD.

Oxidative stress initiates hemodynamic change in CKD-induced heart disease

Chronic kidney disease (CKD) predisposes to cardiac remodeling and coronary microvascular dysfunction. Studies in swine identified changes in microvascular structure and function, as well as changes in mitochondrial structure and oxidative stress. However, CKD was combined with metabolic derangement, thereby obscuring the contribution of CKD alone. Therefore, we studied the impact of CKD on the heart and combined proteome studies with measurement of cardiac function and perfusion to identify processes involved in cardiac remodeling in CKD. CKD was induced in swine at 10-12 weeks of age while sham-operated swine served as controls. 5-6 months later, left ventricular (LV) function and coronary flow reserve were measured. LC-MS-MS-based proteomic analysis of LV tissue was performed. LV myocardium and kidneys were histologically examined for interstitial fibrosis and oxidative stress. Renal embolization resulted in mild chronic kidney injury (increased fibrosis and urinary NGAL). PV loops showed LV dilation and increased wall stress, while preload recruitable stroke work was impaired in CKD. Quantitative proteomic analysis of LV myocardium and STRING pre-ranked functional analysis showed enrichments in pathways related to contractile function, reactive oxygen species, and extracellular matrix (ECM) remodeling, which were confirmed histologically and associated with impaired total anti-oxidant capacity. H2O2 exposure of myocardial slices from CKD, but not normal swine, impaired contractile function. Furthermore, in CKD, mitochondrial proteins were downregulated suggesting mitochondrial dysfunction which was associated with higher basal coronary blood flow. Thus, mild CKD induces alterations in mitochondrial proteins along with contractile proteins, oxidative stress and ECM remodeling, that were associated with changes in cardiac function and perfusion.

Noninvasive Left Ventricular Pressure-Strain Loop for Quantitative Assessment of Early Left Ventricular Systolic Dysfunction in Patients With Chronic Kidney Disease

BACKGROUND

Patients with chronic kidney disease (CKD) possess a pronounced risk for cardiovascular events. A noninvasive left ventricular pressure-strain loop (LV-PSL) has recently been introduced to detect subtler changes in cardiac function. This study aims to investigate the value of LV-PSL for quantitative assessment of myocardial work (MW) in patients with CKD.

METHODS

Seventy-five patients with CKD were enrolled retrospectively (37 patients with CKD Stages 2-3, and 38 patients with CKD Stages 4-5), and 35 healthy volunteers were included as controls. All subjects underwent transthoracic echocardiography. LV-PSL analysis was performed to estimate LV MW and efficiency. Global work index (GWI), global constructive work (GCW), global wasted work (GWW), and global work efficiency (GWE) were obtained by echocardiography, and the differences among the groups were compared.

RESULTS

There was a significant increase in GWW and reduction in GWE in patients with CKD compared to normal controls (p < 0.05). No significant difference in GWI and GCW was observed among the three groups. Multiple linear regression revealed that increased GWW was significantly associated with age, serum creatinine, and systolic pressure, and decreased GWE was associated with age, serum creatinine, and GLS.

CONCLUSION

LV-PSL can be used for noninvasive quantitative assessment of MW in patients with CKD, providing a new sensitive approach for the clinical assessment of myocardial function.

Advances in the study of S100A9 in cardiovascular diseases

Cardiovascular disease (CVD) is a group of diseases that primarily affect the heart or blood vessels, with high disability and mortality rates, posing a serious threat to human health. The causative factors, pathogenesis, and characteristics of common CVD differ, but they all involve common pathological processes such as inflammation, oxidative stress, and fibrosis. S100A9 belongs to the S100 family of calcium-binding proteins, which are mainly secreted by myeloid cells and bind to the Toll-like receptor 4 and receptor for advanced glycation end products and is involved in regulating pathological processes such as inflammatory response, fibrosis, vascular calcification, and endothelial barrier function in CVD. The latest research has found that S100A9 is a key biomarker for diagnosing and predicting various CVD. Therefore, this article reviews the latest research progress on the diagnostic and predictive, and therapeutic value of S100A9 in inflammatory-related CVD such as atherosclerosis, myocardial infarction, and arterial aneurysm and summarizes its molecular mechanisms in the progression of CVD, aiming to explore new predictive methods and to identify potential intervention targets for CVD in clinical practice.

Accelerated idioventricular rhythm as a manifestation of chronic renocardiac syndrome: A case report

In this case report, we describe a patient who presented with chronic symptoms and signs of uremia and persistent accelerated idioventricular rhythm (AIVR) on electrocardiogram. Findings from blood tests, echocardiography, renal ultrasound, and renal scan were suggestive of heart failure with reduced ejection fraction and chronic kidney disease, and attendance of daily hemodialysis sessions led to the restoration of sinus rhythm. Typically, AIVR has a favorable prognosis and, if necessary, medical intervention focuses on addressing the underlying responsible causes. Accumulation of uremic toxins has the potential to trigger the formation of AIVR and clearance of small solutes through conventional hemodialysis may contribute to sinus rhythm restoration.

Thrombospondin-1 Drives Cardiac Remodeling in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) face a high risk of cardiovascular disease. Previous studies reported that endogenous thrombospondin 1 (TSP1) involves right ventricular remodeling and dysfunction. Here we show that a murine model of CKD increased myocardial TSP1 expression and produced left ventricular hypertrophy, fibrosis, and dysfunction. TSP1 knockout mice were protected from these features. In vitro, indoxyl sulfate is driving deleterious changes in cardiomyocyte through the TSP1. In patients with CKD, TSP1 and aryl hydrocarbon receptor were both differentially expressed in the myocardium. Our findings summon large clinical studies to confirm the translational role of TSP1 in patients with CKD.

Improvement in Echocardiographic Indexes of Systolic Heart Failure Post-Kidney Transplantation: A Retrospective Analysis

INTRODUCTION

End-stage renal disease is a major risk factor for cardiovascular morbidity and mortality, which can be partially eliminated by kidney transplantation. Systolic heart failure might be considered contraindication for kidney transplant, although some patients demonstrate myocardial recovery post-transplant. We aimed to identify and characterize the phenomenon of reverse myocardial remodeling in kidney transplanted patients.

METHODS

The study is a retrospective cohort of patients undergoing kidney transplants between 2016 and 2019 (n = 604) at Rabin Medical Center. Patients were assessed according to availability of two echocardiographic examinations: pre- and post-kidney transplant. The change in estimated ejection fraction (EF) and possible predictors of myocardial recovery were examined.

RESULTS

Data of 293 patients was available for the final analysis. Eighty-one (28%) patients had a LVEF improvement equal to or above 5%, whereas 36 (12%) patients had a LVEF improvement of 10% or more post-transplantation. Twenty-five patients (8.5%) had moderate or severe systolic heart failure with LVEF reduced to 40% or less at baseline. 13 of them (52%) had a LVEF improvement of ≥5%, and 10 patients (40%) had an improvement of ≥10% in their EF. Cox regression analyses identified female gender as the only independent variable associated with LVEF improvement of at least 10%.

CONCLUSION

Renal transplantation might lead to improved LV systolic function in some patients.

Displacing the Burden: A Review of Protein-Bound Uremic Toxin Clearance Strategies in Chronic Kidney Disease

Uremic toxins (UTs), particularly protein-bound uremic toxins (PBUTs), accumulate in chronic kidney disease (CKD) patients, causing significant health complications like uremic syndrome, cardiovascular disease, and immune dysfunction. The binding of PBUTs to plasma proteins such as albumin presents a formidable challenge for clearance, as conventional dialysis is often insufficient. With advancements in the classification and understanding of UTs, spearheaded by the European Uremic Toxins (EUTox) working group, over 120 molecules have been identified, prompting the development of alternative therapeutic strategies. Innovations such as online hemodiafiltration aim to enhance the removal process, while novel adsorptive therapies offer a means to address the high affinity of PBUTs to plasma proteins. Furthermore, the exploration of molecular displacers, designed to increase the free fraction of PBUTs, represents a cutting-edge approach to facilitate their dialytic clearance. Despite these advancements, the clinical application of displacers requires more research to confirm their efficacy and safety. The pursuit of such innovative treatments is crucial for improving the management of uremic toxicity and the overall prognosis of CKD patients, emphasizing the need for ongoing research and clinical trials.

Cardiovascular Consequences of Uremic Metabolites: an Overview of the Involved Signaling Pathways

The crosstalk of the heart with distant organs such as the lung, liver, gut, and kidney has been intensively approached lately. The kidney is involved in (1) the production of systemic relevant products, such as renin, as part of the most essential vasoregulatory system of the human body, and (2) in the clearance of metabolites with systemic and organ effects. Metabolic residue accumulation during kidney dysfunction is known to determine cardiovascular pathologies such as endothelial activation/dysfunction, atherosclerosis, cardiomyocyte apoptosis, cardiac fibrosis, and vascular and valvular calcification, leading to hypertension, arrhythmias, myocardial infarction, and cardiomyopathies. However, this review offers an overview of the uremic metabolites and details their signaling pathways involved in cardiorenal syndrome and the development of heart failure. A holistic view of the metabolites, but more importantly, an exhaustive crosstalk of their known signaling pathways, is important for depicting new therapeutic strategies in the cardiovascular field.

Predictive value of protein-bound uremic toxins for heart failure in patients with chronic kidney disease

AIMS

This retrospective cohort study aimed to be the first to evaluate the association between plasma protein-bound uremic toxins (PBUTs) concentrations, echocardiographic parameters of heart failure (HF), and incident HF events in patients with chronic kidney disease (CKD) not on dialysis.

METHODS AND RESULTS

Retrospective, single-centre, cohort study at the Ghent University Hospital, Belgium. Adults with CKD stages G1-G5, not on dialysis, could be included. Exclusion criteria were ongoing pregnancy, age <18 years, active acute infection, active malignancy, history of transplantation, or a cardiovascular event within 3 months prior to inclusion. Free and total concentrations of five PBUTs were quantified at baseline: indoxyl sulfate (IxS), p-cresyl sulfate (pCS), p-cresyl glucuronide (pCG), indole-3 acetic acid (IAA), and hippuric acid (HA). Patients were grouped into three echocardiographic categories: normal left ventricular ejection fraction (LVEF) and normal left ventricular end-diastolic pressure (LVEDP), normal LVEF and increased LVEDP, and reduced LVEF, based on available echocardiographic data in a time interval of ±6 months around the plasma sample collection. A total of 523 patients were included between January 2011 and January 2014. Echocardiographic data within the predefined timeframe were available for 210 patients (40% of patients). Levels of pCG and pCS were significantly higher in patients with reduced (<50%) versus normal LVEF (P < 0.05). After a median follow-up 5.5 years, 43 (8.4%) patients reached the composite endpoint of hospitalization or mortality due to HF. Free fractions of IxS, pCS, and pCG showed the strongest association with clinical outcome: free IxS: HR 1.71 (95% CI 1.11-2.63; P = 0.015), free pCS: HR 1.82 (95% CI 1.11-3.01; P = 0.019), and free pCG: HR 1.67 (95% CI 1.08-2.58; P = 0.020), and these results were independent of age, gender, body mass index, diabetes, and systolic blood pressure. In models that were also adjusted for serum creatinine, the free fractions of these PBUTs remained significant.

CONCLUSIONS

Elevated free concentrations of IxS, pCG, and pCS were independently associated with an increased risk of HF events in non-dialysed CKD patients. Further research is necessary to confirm these findings and investigate the potential impact of PBUT-lowering interventions on HF events in this patient group.

Mapping cardiac remodeling in chronic kidney disease

Patients with advanced chronic kidney disease (CKD) mostly die from sudden cardiac death and recurrent heart failure. The mechanisms of cardiac remodeling are largely unclear. To dissect molecular and cellular mechanisms of cardiac remodeling in CKD in an unbiased fashion, we performed left ventricular single-nuclear RNA sequencing in two mouse models of CKD. Our data showed a hypertrophic response trajectory of cardiomyocytes with stress signaling and metabolic changes driven by soluble uremia-related factors. We mapped fibroblast to myofibroblast differentiation in this process and identified notable changes in the cardiac vasculature, suggesting inflammation and dysfunction. An integrated analysis of cardiac cellular responses to uremic toxins pointed toward endothelin-1 and methylglyoxal being involved in capillary dysfunction and TNFα driving cardiomyocyte hypertrophy in CKD, which was validated in vitro and in vivo. TNFα inhibition in vivo ameliorated the cardiac phenotype in CKD. Thus, interventional approaches directed against uremic toxins, such as TNFα, hold promise to ameliorate cardiac remodeling in CKD.

Effects of Probiotic-Enriched Minas Cheese (Lactobacillus acidophilus La-05) on Cardiovascular Parameters in 5/6 Nephrectomized Rats

Dairy foods have become an interest in chronic kidney disease (CKD) due to their nutritional profile, which makes them a good substrate for probiotics incorporation. This study evaluated the effect of probiotic-enriched Minas cheese with Lactobacillus acidophilus La-05 in an experimental rat model for CKD on cardiac, inflammatory, and oxidative stress parameters. Male Wistar rats were divided into 4 groups (n = 7/group): 5/6 nephrectomy + conventional Minas cheese (NxC); 5/6 nephrectomy + probiotic Minas cheese (NxPC); Sham + conventional Minas cheese (ShamC); Sham + probiotic Minas cheese (ShamPC). Offering 20 g/day of Minas cheese with Lact. acidophilus La-05 (108-109 log CFU/g) for 6 weeks. The cardiomyocyte diameter was determined. Superoxide dismutase (SOD) activity in plasma, heart, kidney, and colon tissue was performed. At the end of supplementation, no significant changes in lipid profile and renal parameters were found. The NxPC group showed a decrease in cardiomyocyte diameter compared to the NxC group (16.99 ± 0.85 vs. 19.05 ± 0.56 μm, p = 0.0162); also they showed reduced plasmatic SOD activity (502.8 ± 49.12 vs. 599.4 ± 94.69 U/mL, p < 0.0001). In summary, probiotic-enriched Minas cheese (Lact. acidophilus La-05) consumption suggests a promisor cardioprotective effect and was able to downregulate SOD activity in a rat model of CKD.

Significance of Kidney Disease in Cardiovascular Disease Patients

Cardiorenal syndrome is a condition where is a bidirectional and mutually detrimental relationship between the heart and kidneys. The mechanisms underlying cardiorenal syndrome are multifactorial and complex. Patients with kidney disease exhibit increased cardiovascular risk, presenting as coronary and peripheral artery disease, structural heart disease, arrhythmias, heart failure, and sudden cardiac death, largely occurring because of a systemic proinflammatory state, causing myocardial and vascular remodeling, manifesting as atherosclerotic lesions, vascular and valvular calcification, and myocardial fibrosis, particularly among those with advanced disease. This review summarizes the current understanding and clinical implications of kidney disease in patients with cardiovascular disease.

Coronary Artery Disease in CKD-G5D Patients: An Update

Patients with chronic kidney disease treated by dialysis (CKD-G5D) are characterized by a high prevalence of coronary artery disease (CAD). Such patients differ from non-uremic CAD patients and have been excluded from several clinical CAD trials. CKD-G5D patients may be asymptomatic for their CAD, making their risk stratification and management challenging. This review will focus on the incidence, epidemiology, pathophysiology, screening tools, and management/treatment of CAD in CKD-G5D patients. It will also review recent studies concerning the screening tools and management strategies available for these patients. The need for improved evaluation of cardiovascular risk factors, screening and early intervention for symptomatic CAD in CKD-G5D patients will be highlighted.

Association between serum β2-microglobulin levels and the risk of all-cause and cardiovascular disease mortality in chinese patients undergoing maintenance hemodialysis

BACKGROUND

The association between serum β₂-microglobulin (β₂M) levels and the risk of all-cause and cardiovascular disease (CVD) mortality and the incidence of cardiovascular events (CVEs) in patients undergoing maintenance hemodialysis (MHD) is inconclusive. Furthermore, no study has been performed in China on the significance of serum β₂M levels in MHD patients. Therefore, this study investigated the aforementioned association in MHD patients.

METHODS

In this prospective cohort study, 521 MHD patients were followed at Dalian Municipal Central Hospital affiliated with Dalian University of Technology from December 2019 to December 2021. The serum β₂M levels were categorized into three tertiles, and the lowest tertile served as the reference group. Survival curves were calculated by the Kaplan-Meier method. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazard models. Sensitivity analysis was performed by excluding patients with CVD at baseline.

RESULTS

During the follow-up period of 21.4 ± 6.3 months, there were 106 all-cause deaths, of which 68 were caused by CVD. When excluding CVD patients at baseline, there were 66 incident CVEs. Kaplan-Meier analysis revealed that the risk of all-cause and CVD mortality in the highest tertile of serum β₂M levels was significantly higher than that in the lowest tertile (P < 0.05), but not for the CVEs (P > 0.05). After adjusting for potential confounders, serum β₂M levels were positively associated with the risk of all-cause (HR = 2.24, 95% CI = 1.21-4.17) and CVD (HR = 2.54, 95% CI = 1.19-5.43) mortality, and a linear trend was evident (P < 0.05). Besides, the results of sensitivity analysis were consistent with the main findings. However, we didn't observed the significant association between serum β₂M levels and CVEs (P > 0.05).

CONCLUSION

The serum β₂M level may be a significant predictor of the risk of all-cause and CVD mortality in MHD patients. Further studies are needed to confirm this finding.

Relationship between Excreted Uremic Toxins and Degree of Disorder of Children with ASD

Autism spectrum disorder (ASD) is a complex developmental disorder in which communication and behavior are affected. A number of studies have investigated potential biomarkers, including uremic toxins. The aim of our study was to determine uremic toxins in the urine of children with ASD (143) and compare the results with healthy children (48). Uremic toxins were determined with a validated high-performance liquid chromatography coupled to mass spectrometry (LC-MS/MS) method. We observed higher levels of p-cresyl sulphate (pCS) and indoxyl sulphate (IS) in the ASD group compared to the controls. Moreover, the toxin levels of trimethylamine N-oxide (TMAO), symmetric dimethylarginine (SDMA), and asymmetric dimethylarginine (ADMA) were lower in ASD patients. Similarly, for pCS and IS in children classified, according to the intensity of their symptoms, into mild, moderate, and severe, elevated levels of these compounds were observed. For mild severity of the disorder, elevated levels of TMAO and comparable levels of SDMA and ADMA for ASD children as compared to the controls were observed in the urine. For moderate severity of ASD, significantly elevated levels of TMAO but reduced levels of SDMA and ADMA were observed in the urine of ASD children as compared to the controls. When the results obtained for severe ASD severity were considered, reduced levels of TMAO and comparable levels of SDMA and ADMA were observed in ASD children.

Zebrafish as a Model of Cardiac Pathology and Toxicity: Spotlight on Uremic Toxins

Chronic kidney disease (CKD) is an increasing health care problem. About 10% of the general population is affected by CKD, representing the sixth cause of death in the world. Cardiovascular events are the main mortality cause in CKD, with a cardiovascular risk 10 times higher in these patients than the rate observed in healthy subjects. The gradual decline of the kidney leads to the accumulation of uremic solutes with a negative effect on every organ, especially on the cardiovascular system. Mammalian models, sharing structural and functional similarities with humans, have been widely used to study cardiovascular disease mechanisms and test new therapies, but many of them are rather expensive and difficult to manipulate. Over the last few decades, zebrafish has become a powerful non-mammalian model to study alterations associated with human disease. The high conservation of gene function, low cost, small size, rapid growth, and easiness of genetic manipulation are just some of the features of this experimental model. More specifically, embryonic cardiac development and physiological responses to exposure to numerous toxin substances are similar to those observed in mammals, making zebrafish an ideal model to study cardiac development, toxicity, and cardiovascular disease.

Effects of p-cresol, a uremic toxin, on cancer cells

Background

Though p-cresol exists at a low concentration in the blood, it accumulates in various organs of uremic patients. Previous research has shown that the p-cresol promoted bladder cancer cell invasion and migration. This study aims to see if p-cresol had similar effects on kidney cancer cells and liver cancer cells.

Methods

For 48 hours, 786-O human renal cancer cells and HepG2 human liver cancer cells were treated with p-cresol at concentrations of 0, 10, 20, 40, and 70 µM. The effects of p-cresol on cell viability, apoptosis, migration, and invasion were then analyzed using the CCK-8, TUNEL, and Transwell migration/invasion assays, respectively.

Results

P-cresol at 0 to 70 µM for 48 hours had no significant toxic effects on 786-O cells or HepG2 cells. We chose 40 µM p-cresol for 48 hours for the following experiment. The viability and proliferation of 786-O cells and HepG2 cells were unaffected after 48 hours of treatment, with 40 µM p-cresol. However, 40 µM p-cresol for 48 hours promoted HepG2 cell migration and invasion but did not have the same effect on the 786-O cell line.

Conclusions

P-cresol may be responsible for HepG2 cells' malignant biological behavior. Because the liver is the primary site of p-cresol metabolism, it is important to study the responses of cancer cells in the liver to p-cresol.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Chronic Kidney Disease as a Comorbidity in Heart Failure

Heart failure (HF) is one of the greatest problems in healthcare and it often coexists with declining renal function. The pathophysiology between the heart and the kidneys is bidirectional. Common mechanisms leading to the dysfunction of these organs result in a vicious cycle of cardiorenal deterioration. It is also associated with difficulties in the treatment of aggravating HF and chronic kidney disease (CKD) and, as a consequence, recurrent hospitalizations and death. As the worsening of renal function has an undeniably negative impact on the outcomes in patients with HF, searching for new treatment strategies and identification of biomarkers is necessary. This review is focused on the pathomechanisms in chronic kidney disease in patients with HF and therapeutic strategies for co-existing CKD and HF.

Adsorption- and Displacement-Based Approaches for the Removal of Protein-Bound Uremic Toxins

End-stage renal disease (ESRD) patients rely on renal replacement therapies to survive. Hemodialysis (HD), the most widely applied treatment, is responsible for the removal of excess fluid and uremic toxins (UTs) from blood, particularly those with low molecular weight (MW < 500 Da). The development of high-flux membranes and more efficient treatment modes, such as hemodiafiltration, have resulted in improved removal rates of UTs in the middle molecular weight range. However, the concentrations of protein-bound uremic toxins (PBUTs) remain essentially untouched. Due to the high binding affinity to large proteins, such as albumin, PBUTs form large complexes (MW > 66 kDa) which are not removed during HD and their accumulation has been strongly associated with the increased morbidity and mortality of patients with ESRD. In this review, we describe adsorption- and displacement-based approaches currently being studied to enhance the removal of PBUTs. The development of mixed matrix membranes (MMMs) with selective adsorption properties, infusion of compounds capable of displacing UTs from their binding site on albumin, and competitive binding membranes show promising results, but the road to clinical application is still long, and further investigation is required.

Salmonella pathogenicity island 1 knockdown confers protection against myocardial fibrosis and inflammation in uremic cardiomyopathy via down-regulation of S100 Calcium Binding Protein A8/A9 transcription

Background/Aim

Uremic cardiomyopathy (UCM) is a characteristic cardiac pathology that is commonly found in patients with chronic kidney disease. This study dissected the mechanism of SPI1 in myocardial fibrosis and inflammation induced by UCM through S100A8/A9.

Methods

An UCM rat model was established, followed by qRT-PCR and western blot analyses of SPI1 and S100A8/A9 expression in myocardial tissues. After alterations of SPI1 and S100A8/A9 expression in UCM rats, the blood specimens were harvested from the cardiac apex of rats. The levels of creatine phosphokinase-MB (CK-MB), blood creatinine, blood urea nitrogen (BUN), and inflammatory cytokines (interleukin [IL]-6, IL-1β, and tumor necrosis factor-α [TNF-α]) were examined in the collected blood. Collagen fibrosis was assessed by Masson staining. The expression of fibrosis markers [transforming growth factor (TGF)-β1, α-smooth muscle actin (SMA), Collagen 4a1, and Fibronectin], IL-6, IL-1β, and TNF-α was measured in myocardial tissues. Chromatin immunoprecipitation and dual-luciferase reporter gene assays were conducted to test the binding relationship between SPI1 and S100A8/A9.

Results

S100A8/A9 and SPI1 were highly expressed in the myocardial tissues of UCM rats. Mechanistically, SPI1 bound to the promoter of S100A8/A9 to facilitate S100A8/A9 transcription. S100A8/A9 or SPI1 knockdown reduced myocardial fibrosis and inflammation and the levels of CK-MB, blood creatinine, and BUN, as well as the expression of TGF-β1, α-SMA, Collagen 4a1, Fibronectin, IL-6, TNF-α, and IL-1β in UCM rats.

Conclusion

SPI1 knockdown diminished S100A8/A9 transcription, thus suppressing myocardial fibrosis and inflammation caused by UCM.

Assessment of the Influence of Asymmetric Triacetate Cellulose Membrane on the Rate of Removal of Middle Molecular Weight Uremic Toxins in Patients Treated with Postdilution Online Hemodiafiltration

BACKGROUND: Postdilution online hemodiafiltration (OL-HDF) effectively removes uremic toxins of middle molecular weight from the blood of patients with end-stage chronic kidney disease. The rate of removal of uremic toxins depends on the type of dialysis membrane, blood flow rate (Qb), net ultrafiltration flow rate (Qnuf), and total convective volume (Vconv). AIM: The aim of this study was to examine the efficacy of asymmetric triacetate cellulose dialysis membrane in patients on post-dilution OL-HDF. METHODS: Thirty-five patients treated with post-dilution OL-HDF hemodiafiltration for at least 3 months were examined. The main parameters for assessing the efficiency of removal of uremic toxins of middle molecular weight are the concentration of β2-microglobulin (β2-M) and interleukin-6 (IL-6) in serum before and after a single session of post-dilution OL-HDF. The followings were used for statistical analysis: Kolmogorov–Smirnov test, Student’s T test for bound samples and Wilcoxon test. RESULTS: The average Vconv was 20.90 ± 3.30 liters/session. The β2-M reduction index during a single session of postdilution OL-HDF was 71.10 ± 6.39%, the IL-6 reduction index was 43.75 ± 15.60%, and the albumin reduction index was 4.55 ± 2.31%. CONCLUSION: The asymmetric triacetate cellulose dialysis membrane effectively removes β2-M and IL-6 during a single session of postdilution OL-HDF. The β2-M reduction index is ∼70%, the IL-6 reduction index is ∼40%, and albumin loss is <4.0 g/4 h. The examined dialysis membrane and dialysis modality prevent the development of amyloidosis associated with dialysis, microinflammation and reduce the risk of developing atherosclerotic cardiovascular diseases in the population of patients treated with regular hemodiafiltration.

Hydrogen sulfide alleviates uremic cardiomyopathy by regulating PI3K/PKB/mTOR-mediated overactive autophagy in 5/6 nephrectomy mice

The gasotransmitter hydrogen sulfide (H₂S) plays important physiological and pathological roles in the cardiovascular system. However, the involvement of H₂S in recovery from uremic cardiomyopathy (UCM) remains unclear. This study aimed to determine the therapeutic efficacy and elucidate the underlying mechanisms of H₂S in UCM. A UCM model was established by 5/6 nephrectomy in 10-week-old C57BL/6 mice. Mice were treated with sodium hydrosulfide (NaHS, H₂S donor), L-cysteine [L-Cys, cystathionine gamma-lyase (CSE) substrate], and propargylglycine (PPG, CSE inhibitor). Treatment of H9C2 cardiomyocytes utilized different concentrations of uremic serum, NaHS, PPG, and PI3K inhibitors (LY294002). Mouse heart function was assessed by echocardiography. Pathological changes in mouse myocardial tissue were identified using hematoxylin and eosin and Masson's trichrome staining. Cell viability was assessed using the Cell Counting Kit-8. The protein expressions of CSE, p-PI3K, PI3K, p-PKB, PKB, p-mTOR, mTOR, and autophagy-related markers (Beclin-1, P62, and LC3) were detected using Western blotting. We found that NaHS and L-Cys treatment attenuated myocardial disarray, fibrosis, and left ventricular dysfunction in UCM mice. These abnormalities were further aggravated by PPG supplementation. Enhanced autophagy and decreased phosphorylation of PI3K, PKB, and mTOR protein expression by UCM were altered by NaHS and L-Cys treatment. In vitro, uremic serum increased overactive autophagy and decreased the phosphorylation levels of PI3K, PKB, and mTOR in cardiomyocytes, which was substantially exacerbated by endogenous H₂S deficiency and attenuated by pre-treatment with 100 µm NaHS. However, the protective effects of NaHS were completely inhibited by LY294002. These findings support a protective effect of H₂S exerted against UCM by reducing overactive autophagy through activation of the PI3K/PKB/mTOR pathway.

sFlt-1 in Chronic Kidney Disease: Friend or Foe?

Placental growth factor (PlGF) and its receptor, fms-like tyrosine kinase-1 (Flt-1), are important regulators involved in angiogenesis, atherogenesis, and inflammation. This review article focuses on the function of PlGF/Flt-1 signaling and its regulation by soluble Flt-1 (sFlt-1) in chronic kidney disease (CKD). Elevation of circulating sFlt-1 and downregulation of sFlt-1 in the vascular endothelium by uremic toxins and oxidative stress both exacerbate heart failure and atherosclerosis. Circulating sFlt-1 is inconsistent with sFlt-1 synthesis, because levels of matrix-bound sFlt-1 are much higher than those of circulating sFlt-1, as verified by a heparin loading test, and are drastically reduced in CKD.

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.

Cardiorenal syndrome: Pathophysiology as a key to the therapeutic approach in an under-diagnosed disease

Cardiorenal syndrome is a clinical condition that impacts both the heart and the kidneys. One organ's chronic or acute impairment can lead to the other's chronic or acute dysregulation. The cardiorenal syndrome has been grouped into five subcategories that describe the etiology, pathophysiology, duration, and pattern of cardiac and renal dysfunction. This classification reflects the large spectrum of interrelated dysfunctions and underlines the bidirectional nature of heart-kidney interactions. However, more evidence is needed to apply these early findings in medical practice. Understanding the relationship between these two organs during each organ's impairment has significant clinical implications that are relevant for therapy in both chronic and acute conditions. The epidemiology, definition, classification, pathophysiology, therapy, and outcome of each form of cardiorenal syndrome are all examined in this review.

Serum total indoxyl sulfate levels and all-cause and cardiovascular mortality in maintenance hemodialysis patients: a prospective cohort study

BACKGROUND

The association between serum total indoxyl sulfate (tIS), and cardiovascular disease (CVD) and all-cause mortality is a matter of debate. In the current study we sought to determine the association, if any, between serum tIS, and all-cause and CVD-associated mortality in patients on maintenance hemodialysis (MHD).

METHODS

A prospective cohort study was conducted involving 500 MHD patients at Dalian Municipal Central Hospital from 31 December 2014 to 31 December 2020. Serum tIS levels were measured at baseline and classified as high (≥44.16 ng/ml) or low (< 44.16 ng/ml) according to the "X-tile" program. Besides, the associations between continuous serum tIS and outcomes were also explored. Predictors were tested for colinearity using variance inflation factor analysis. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazards regression models. Restricted cubic spline model was performed to assess dose-response relationships between tIS concentration and all-cause and CVD mortality.

RESULTS

During a 58-month median follow-up period, 224 deaths (132 CVD deaths) were documented. After adjustment for potential confounders, the serum tIS level was positively associated with all-cause mortality (HR = 1.02, 95% = 1.01-1.03); however, we did not detect a significant association when tIS was a dichotomous variable. Compared with the MHD population with a serum tIS level < 44.16 ng/ml, the adjusted HR for CVD mortality among those with a serum tIS level ≥ 44.16 ng/ml was 1.76 (95% = 1.10-2.82). Furthermore, we also noted the same association when the serum tIS level was a continuous variable.

CONCLUSION

The serum tIS level was associated with higher risk of all-cause and CVD mortality among MHD patients. Further prospective large-scale studies are required to confirm this finding.

Characterization of metal(loid)s and antibiotic resistance in bacteria of human gut microbiota from chronic kidney disease subjects

BACKGROUND

Human Gut Microbiota (HGM) is composed of more than one thousand species, playing an important role in the health status of individuals. Dysbiosis (an HGM imbalance) is augmented as chronic kidney disease (CKD) progresses, as loss of kidney function accelerates. Increased antibiotic use in CKD subjects and consumption of nephrotoxic heavy metals and metalloids such as lead, cadmium, arsenic, and mercury in tap water increases the dysbiosis state. Studies in people with stage 3 CKD are complex to carry out, mainly because patients are self-reliant who rarely consult a specialist. The current work focused on this type of patient.

RESULTS

Lead and arsenic-resistant bacteria were obtained from self-reliant (that stands on its own) stage 3 CKD subjects. Pathogen-related Firmicutes and Proteobacteria genus bacteria were observed. Resistance and potentiation of antibiotic effects in the presence of metal(loid)s in vitro were found. Furthermore, the presence of the following genes markers for antibiotic and metal(loid) resistance were identified by qPCR: oxa10, qnrB1, mphB, ermB, mefE1, arr2, sulll, tetA, floR, strB, dhfr1, acrB, cadA2k, cadA3k, arsC, pbrA. We observed a decrease in the number of metal resistance markers.

CONCLUSIONS

The presence of cadA and arsC genetic markers of antibiotics and metal(loid)s resistance were detected in samples from stage 3 CKD subjects. Lower gene amplification in advanced stages of CKD were also observed, possibly associated with a decrease in resident HGM during kidney disease progression.

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.

Chronic Renal Failure and Cardiovascular Disease: A Comprehensive Appraisal

Coronary artery disease is highly prevalent in patients with chronic kidney disease. The concomitant renal disease often poses a major challenge in decision making as symptoms, cardiac biomarkers and noninvasive studies for evaluation of myocardial ischemia have different sensitivity and specificity thresholds in this specific population. Moreover, the effectiveness and safety of intervention and medical treatment in those patients is of great doubt as most clinical studies exclude patients with advance CKD. In the present paper, we discuss and review the literature in the diagnosis, treatment and prevention of CAD in the acute and chronic setting, in patients with CKD.

The Interplay between Uremic Toxins and Albumin, Membrane Transporters and Drug Interaction

Uremic toxins are a heterogeneous group of molecules that accumulate in the body due to the progression of chronic kidney disease (CKD). These toxins are associated with kidney dysfunction and the development of comorbidities in patients with CKD, being only partially eliminated by dialysis therapies. Importantly, drugs used in clinical treatments may affect the levels of uremic toxins, their tissue disposition, and even their elimination through the interaction of both with proteins such as albumin and cell membrane transporters. In this context, protein-bound uremic toxins (PBUTs) are highlighted for their high affinity for albumin, the most abundant serum protein with multiple binding sites and an ability to interact with drugs. Membrane transporters mediate the cellular influx and efflux of various uremic toxins, which may also compete with drugs as substrates, and both may alter transporter activity or expression. Therefore, this review explores the interaction mechanisms between uremic toxins and albumin, as well as membrane transporters, considering their potential relationship with drugs used in clinical practice.

Effects of Expanded Hemodialysis with Medium Cut-Off Membranes on Maintenance Hemodialysis Patients: A Review

Kidney failure is associated with high morbidity and mortality. Hemodialysis, the most prevalent modality of renal replacement therapy, uses the principle of semipermeable membranes to remove solutes and water in the plasma of patients with kidney failure. With the evolution of hemodialysis technology over the last half century, the clearance of small water-soluble molecules in such patients is adequate. However, middle molecules uremic toxins are still retained in the plasma and cause cardiovascular events, anemia, and malnutrition, which significantly contribute to poor quality of life and high mortality in maintenance hemodialysis patients. A new class of membrane, defined as a medium cut-off (MCO) membrane, has emerged in recent years. Expanded hemodialysis with MCO membranes is now recognized as the artificial kidney model closest to natural kidney physiology. This review summarizes the unique morphological characteristics and internal filtration–backfiltration mechanism of MCO membranes, and describes their effects on removing uremic toxins, alleviating inflammation and cardiovascular risk, and improving quality of life in maintenance hemodialysis patients.

Serum concentrations of free indoxyl and p-cresyl sulfate are associated with mineral metabolism variables and cardiovascular risk in hemodialysis patients

BACKGROUND

Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are uremic toxins associated with cardiovascular outcome in CKD patients. The present work is an analysis of the association of serum free, total IS and PCS with cardiovascular events and calcium-phosphate metabolism variables in hemodialysis patients.

METHODS

Serum levels of total and free IS and PCS were measured in 139 hemodialysis patients. Their relationship with calcium-phosphate metabolism variables were tested in an observational cohort study. In addition, their association with cardiovascular events was investigated during a 4-year follow-up.

RESULTS

Patients in the highest tertile (T3) of serum free IS showed lower serum 1,25(OH)₂D compared to patients in the middle (T2) and lowest tertile (T1); in addition to this, T3 patients showed lower serum irisin than T1 patients and lower serum PTH than all the other subjects (T1 + T2) combined. Serum PTH was also measured during the two years after the baseline measurement and was higher in patients in the T1 than in those in the T3 of serum free IS. Cox regression analysis showed that cardiovascular risk was lower in T1 patients than in those in the T3 of serum free PCS, both using a univariate (OR 2.55, 95% CI 1.2-5.43; p = 0.015) or multivariate model (OR 2.48, 95% CI 1.12-5.51; p = 0.003).

CONCLUSIONS

Serum free IS may be associated with PTH and 1,25(OH)₂D secretion, whereas free PCS may predict cardiovascular risk in hemodialysis patients.

Cardiorenal syndrome: long road between kidney and heart

Almost 200 years ago, the first evidence described by Robert Bright (1836) showed the strong interaction between the kidneys and heart and, since then, the scientific community has dedicated itself to better understanding the mechanisms involved in the kidney-heart relationship, known in recent decades as cardiorenal syndrome (CRS). This syndrome includes a wide clinical variety that affects the kidneys and heart, in an acute or chronic manner. Moreover, it is well established in the literature that the immune system, the sympathetic nervous system, the renin-angiotensin-aldosterone, and the oxidative stress actively play a strong role in the cellular and molecular processes present in CRS. More recently, uremic molecules and epigenetic factors have been also shown to be key mediators in the development of syndrome. The present review intends to present the state of the art regarding CRS and to show the paths known, until now, in the long road between the kidneys and heart.

Role and Mechanism of the Renin-Angiotensin-Aldosterone System in the Onset and Development of Cardiorenal Syndrome

Cardiorenal syndrome (CRS), a clinical syndrome involving multiple pathological mechanisms, exhibits high morbidity and mortality. According to the primary activity of the disease, CRS can be divided into cardiorenal syndrome (type I and type II), renal heart syndrome (type III and type IV), and secondary heart and kidney disease (type V). The renin-angiotensin-aldosterone system (RAAS) is an important humoral regulatory system of the body that exists widely in various tissues and organs. As a compensatory mechanism, the RAAS is typically activated to participate in the regulation of target organ function. RAAS activation plays a key role in the pathogenesis of CRS. The RAAS induces the onset and development of CRS by mediating oxidative stress, uremic toxin overload, and asymmetric dimethylarginine production. Research on the mechanism of RAAS-induced CRS can provide multiple intervention methods that are of great significance for reducing end-stage organ damage and further improving the quality of life of patients with CRS.

Blood-incompatibility in haemodialysis: alleviating inflammation and effects of coagulation

Blood-incompatibility is an inevitability of all blood-contacting device applications and therapies, including haemodialysis (HD). Blood leaving the environment of blood vessels and the protection of the endothelium is confronted with several stimuli of the extracorporeal circuit (ECC), triggering the activation of blood cells and various biochemical pathways of plasma. Prevention of blood coagulation, a major obstacle that needed to be overcome to make HD possible, remains an issue to contend with. While anticoagulation (mainly with heparin) successfully prevents clotting within the ECC to allow removal of uraemic toxins across the dialysis membrane wall, it is far from ideal, triggering heparin-induced thrombocytopenia in some instances. Soluble fibrin can form even in the presence of heparin and depending on the constitution of the patient and activation of platelets, could result in physical clots within the ECC (e.g. bubble trap chamber) and, together with other plasma and coagulation proteins, result in increased adsorption of proteins on the membrane surface. The buildup of this secondary membrane layer impairs the transport properties of the membrane to reduce the clearance of uraemic toxins. Activation of complement system-dependent immune response pathways leads to leukopenia, formation of platelet–neutrophil complexes and expression of tissue factor contributing to thrombotic processes and a procoagulant state, respectively. Complement activation also promotes recruitment and activation of leukocytes resulting in oxidative burst and release of pro-inflammatory cytokines and chemokines, thereby worsening the elevated underlying inflammation and oxidative stress condition of chronic kidney disease patients. Restricting all forms of blood-incompatibility, including potential contamination of dialysis fluid with endotoxins leading to inflammation, during HD therapies is thus still a major target towards more blood-compatible and safer dialysis to improve patient outcomes. We describe the mechanisms of various activation pathways during the interaction between blood and components of the ECC and describe approaches to mitigate the effects of these adverse interactions. The opportunities to develop improved dialysis membranes as well as implementation strategies with less potential for undesired biological reactions are discussed.

The membrane perspective of uraemic toxins: which ones should, or can, be removed?

Informed decision-making is paramount to the improvement of dialysis therapies and patient outcomes. A cornerstone of delivery of optimal dialysis therapy is to delineate which substances (uraemic retention solutes or 'uraemic toxins') contribute to the condition of uraemia in terms of deleterious biochemical effects they may exert. Thereafter, decisions can be made as to which of the accumulated compounds need to be targeted for removal and by which strategies. For haemodialysis (HD), the non-selectivity of membranes is sometimes considered a limitation. Yet, considering that dozens of substances with potential toxicity need to be eliminated, and targeting removal of individual toxins explicitly is not recommended, current dialysis membranes enable elimination of several molecules of a broad size range within a single therapy session. However, because HD solute removal is based on size-exclusion principles, i.e. the size of the substances to be removed relative to the mean size of the 'pores' of the membrane, only a limited degree of selectivity of removal is possible. Removal of unwanted substances during HD needs to be weighed against the unavoidable loss of substances that are recognized to be necessary for bodily functions and physiology. In striving to improve the efficiency of HD by increasing the porosity of membranes, there is a greater potential for the loss of substances that are of benefit. Based on this elementary trade-off and availability of recent guidance on the relative toxicity of substances retained in uraemia, we propose a new evidence-linked uraemic toxin elimination (ELUTE) approach whereby only those clusters of substances for which there is a sufficient body of evidence linking them to deleterious biological effects need to be targeted for removal. Our approach involves correlating the physical properties of retention solutes (deemed to express toxicity) with key determinants of membranes and separation processes. Our analysis revealed that in attempting to remove the relatively small number of 'larger' substances graded as having only moderate toxicity, uncontrolled (and efficient) removal of several useful compounds would take place simultaneously and may compromise the well-being or outcomes of patients. The bulk of the uraemic toxin load comprises uraemic toxins below <30 000 Da and are adequately removed by standard membranes. Further, removal of a few difficult-to-remove-by-dialysis (protein-bound) compounds that express toxicity cannot be achieved by manipulation of pore size alone. The trade-off between the benefits of effective removal of the bulk of the uraemic toxin load and risks (increased loss of useful substances) associated with targeting the removal of a few larger substances in 'high-efficiency' HD treatment strategies needs to be recognized and better understood. The removability during HD of substances, be they toxic, inert or beneficial, needs be revised to establish the pros and cons of current dialytic elimination strategies.  .

Clinical relevance of abstruse transport phenomena in haemodialysis

Haemodialysis (HD) utilizes the bidirectional properties of semipermeable membranes to remove uraemic toxins from blood while simultaneously replenishing electrolytes and buffers to correct metabolic acidosis. However, the nonspecific size-dependent transport across membranes also means that certain useful plasma constituents may be removed from the patient (together with uraemic toxins), or toxic compounds, e.g. endotoxin fragments, may accompany electrolytes and buffers of the dialysis fluids into blood and elicit severe biological reactions. We describe the mechanisms and implications of these undesirable transport processes that are inherent to all HD therapies and propose approaches to mitigate the effects of such transport. We focus particularly on two undesirable events that are considered to adversely affect HD therapy and possibly impact patient outcomes. Firstly, we describe how loss of albumin (and other essential substances) can occur while striving to eliminate larger uraemic toxins during HD and why hypoalbuminemia is a clinical condition to contend with. Secondly, we describe the origins and mode of transport of biologically active substances (from dialysis fluids with bacterial contamination) into the blood compartment and biological reactions they elicit. Endotoxin fragments activate various proinflammatory pathways to increase the underlying inflammation associated with chronic kidney disease. Both phenomena involve the physical as well as chemical properties of membranes that must be selected judiciously to balance the benefits with potential risks patients may encounter, in both the short and long term.

Establishment of a Drug Screening Model for Cardiac Complications of Acute Renal Failure

Acute renal failure (ARF) is a clinical critical syndrome with rapid and severe decline of renal function. Complications of ARF, especially its cardiac complications (cardiorenal syndrome type 3, CRS-3), are the main causes of death in patients with ARF. However, the shortage and limited efficacy of therapeutic drugs make it significant to establish new large-scale drug screening models. Based on the Nitroreductase/Metronidazole (NTR/MTZ) cell ablation system, we constructed a Tg(cdh17:Dendra2-NTR) transgenic zebrafish line, which can specifically ablate renal tubular epithelial cells. The absence of renal tubular epithelial cells can lead to ARF in zebrafish larvae. The ARF symptoms, such as heart enlargement, slow heart rate and blood stasis, are similar to the clinical manifestations of human CRS-3. Furthermore, two therapeutic drugs (digoxin and enalapril) commonly used in the clinical treatment of heart failure were also effective in alleviating the symptoms of CRS-3 in zebrafish, which proved the effectiveness of this model. Drug screening further discovered a potential drug candidate, α-lipoic acid, which can effectively alleviate the symptoms of CRS-3 through its antioxidant function. Accordingly, we established a new ARF model of zebrafish, which laid a foundation for large-scale screening of new therapeutic drugs for its complications.

Platelet Function in CKD: A Systematic Review and Meta-Analysis

BACKGROUND

Patients with CKD are at high risk for thrombotic and hemorrhagic complications. Abnormalities in platelet function are central to these complications, but reports on platelet function in relation to CKD are conflicting, and vary from decreased platelet reactivity to normal or increased platelet responsiveness. The direct effects of uremic toxins on platelet function have been described, with variable findings.

METHODS

To help clarify how CKD affects platelet function, we conducted a systematic review and meta-analysis of platelet activity in CKD, with a focus on nondialysis-induced effects. We also performed an extensive literature search for the effects of individual uremic toxins on platelet function.

RESULTS

We included 73 studies in the systematic review to assess CKD's overall effect on platelet function in patients; 11 of them described CKD's effect on ex vivo platelet aggregation and were included in the meta-analysis. Although findings on platelet abnormalities in CKD are inconsistent, bleeding time was mostly prolonged and platelet adhesion mainly reduced. Also, the meta-analysis revealed maximal platelet aggregation was significantly reduced in patients with CKD upon collagen stimulation. We also found that relatively few uremic toxins have been examined for direct effects on platelets ex vivo; ex vivo analyses had varying methods and results, revealing both platelet-stimulatory and inhibitory effects. However, eight of the 12 uremic toxins tested in animal models mostly induced prothrombotic effects.

CONCLUSIONS

Overall, most studies report impaired function of platelets from patients with CKD. Still, a substantial number of studies find platelet function to be unchanged or even enhanced. Further investigation of platelet reactivity in CKD, especially during different CKD stages, is warranted.

Uremic Toxins and Their Relation with Oxidative Stress Induced in Patients with CKD

The presence of toxins is believed to be a major factor in the development of uremia in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD). Uremic toxins have been divided into 3 groups: small substances dissolved in water, medium molecules: peptides and low molecular weight proteins, and protein-bound toxins. One of the earliest known toxins is urea, the concentration of which was considered negligible in CKD patients. However, subsequent studies have shown that it can lead to increased production of reactive oxygen species (ROS), and induce insulin resistance in vitro and in vivo, as well as cause carbamylation of proteins, peptides, and amino acids. Other uremic toxins and their participation in the damage caused by oxidative stress to biological material are also presented. Macromolecules and molecules modified as a result of carbamylation, oxidative stress, and their adducts with uremic toxins, may lead to cardiovascular diseases, and increased risk of mortality in patients with CKD.

Hemodialysis exacerbates proteolytic imbalance and pro-fibrotic platelet dysfunction

Multi-organ fibrosis among end stage renal disease (ESRD) patients cannot be explained by uremia alone. Despite mitigation of thrombosis during hemodialysis (HD), subsequent platelet dysfunction and tissue dysregulation are less understood. We comprehensively profiled plasma and platelets from ESRD patients before and after HD to examine HD-modulation of platelets beyond thrombotic activation. Basal plasma levels of proteolytic regulators and fibrotic factors were elevated in ESRD patients compared to healthy controls, with isoform-specific changes during HD. Platelet lysate (PL) RNA transcripts for growth and coagulative factors were elevated post-HD, with upregulation correlated to HD vintage. Platelet secretome correlations to plasma factors reveal acutely induced pro-fibrotic platelet phenotypes in ESRD patients during HD characterized by preferentially enhanced proteolytic enzyme translation and secretion, platelet contribution to inflammatory response, and increasing platelet dysfunction with blood flow rate (BFR) and Vintage. Compensatory mechanisms of increased platelet growth factor synthesis with acute plasma matrix metalloproteinase (MMP) and tissue inhibitor of MMPs (TIMP) increases show short-term mode-switching between dialysis sessions leading to long-term pro-fibrotic bias. Chronic pro-fibrotic adaptation of platelet synthesis were observed through changes in differential secretory kinetics of heterogenous granule subtypes. We conclude that chronic and acute platelet responses to HD contribute to a pro-fibrotic milieu in ESRD.

Computational Models Used to Predict Cardiovascular Complications in Chronic Kidney Disease Patients: A Systematic Review

Background and objectives: cardiovascular complications (CVC) are the leading cause of death in patients with chronic kidney disease (CKD). Standard cardiovascular disease risk prediction models used in the general population are not validated in patients with CKD. We aim to systematically review the up-to-date literature on reported outcomes of computational methods such as artificial intelligence (AI) or regression-based models to predict CVC in CKD patients. Materials and methods: the electronic databases of MEDLINE/PubMed, EMBASE, and ScienceDirect were systematically searched. The risk of bias and reporting quality for each study were assessed against transparent reporting of a multivariable prediction model for individual prognosis or diagnosis (TRIPOD) and the prediction model risk of bias assessment tool (PROBAST). Results: sixteen papers were included in the present systematic review: 15 non-randomized studies and 1 ongoing clinical trial. Twelve studies were found to perform AI or regression-based predictions of CVC in CKD, either through single or composite endpoints. Four studies have come up with computational solutions for other CV-related predictions in the CKD population. Conclusions: the identified studies represent palpable trends in areas of clinical promise with an encouraging present-day performance. However, there is a clear need for more extensive application of rigorous methodologies. Following the future prospective, randomized clinical trials, and thorough external validations, computational solutions will fill the gap in cardiovascular predictive tools for chronic kidney disease.

The Complexity of FGF23 Effects on Cardiomyocytes in Normal and Uremic Milieu

Fibroblast growth factor-23 (FGF23) appears to be one of the most promising biomarkers and predictors of cardiovascular risk in patients with heart disease and normal kidney function, but moreover in those with chronic kidney disease (CKD). This review summarizes the current knowledge of FGF23 mechanisms of action in the myocardium in the physiological and pathophysiological state of CKD, as well as its cross-talk to other important signaling pathways in cardiomyocytes. In this regard, current therapeutic possibilities and future perspectives are also discussed.

Involvement of chronic inflammation via monocyte chemoattractant protein-1 in uraemic cardiomyopathy: a human biopsy study

Aims

Patients undergoing dialysis, even those without coronary artery disease or valvular abnormalities, sometimes present with reduced heart function, which resembles dilated cardiomyopathy (DCM). This condition is known as uraemic cardiomyopathy (UCM). The mechanisms of UCM development are not fully understood. Previous studies demonstrated that the balance between placental growth factor (PlGF) and fms‐like tyrosine kinase‐1 (Flt‐1) is correlated with renal function, and PlGF/Flt‐1 signalling is involved in the development of cardiovascular diseases in patients with chronic kidney disease. This study was conducted to evaluate the pathogenesis of UCM and clarify the differences in the mechanisms of UCM and DCM by using human endomyocardial biopsy and blood samples.

Methods and results

The clinical and pathological features of 30 patients on dialysis with reduced cardiac function [left ventricular ejection fraction (LVEF) ≤50%] (UCM group; mean age: 58.5 ± 9.4 years and LVEF: 39.1 ± 7.2%), 196 DCM patients (DCM group; mean age: 62.7 ± 14.0 years and LVEF: 33.5 ± 8.8%) as controls with reduced cardiac function (LVEF ≤ 45%), and 21 patients as controls with normal cardiac function (control group; mean age: 56.2 ± 19.3 years and LVEF: 67.5 ± 6.7%) were analysed. The percentage of the interstitial fibrosis area in the UCM group was greater than that in the DCM group (P = 0.045). In UCM patients, the percentage of the interstitial fibrosis area was positively correlated with the duration of renal replacement therapy (P < 0.001). The number of infiltrated CD68‐positive macrophages in the myocardium and expression of monocyte chemoattractant protein‐1 (MCP‐1) in cardiomyocytes were significantly greater in the UCM group than in the other groups (P < 0.001, respectively). Furthermore, while the serum level of soluble form of Flt‐1, an endogenous inhibitor of PlGF, in the UCM group was lower compared with that in the DCM group (P < 0.001), the serum levels of PlGF and PlGF/soluble form of Flt‐1 ratio and plasma level of MCP‐1 in the UCM group were higher than those in the DCM group (P < 0.001, respectively).

Conclusions

These results suggest that activated PlGF/Flt‐1 signalling and subsequent macrophage‐mediated chronic non‐infectious inflammation via MCP‐1 in the myocardium are involved in the pathogenesis of UCM.

Uremic Toxins: An Alarming Danger Concerning the Cardiovascular System

The kidneys and heart share functions with the common goal of maintaining homeostasis. When kidney injury occurs, many compounds, the so-called "uremic retention solutes" or "uremic toxins," accumulate in the circulation targeting other tissues. The accumulation of uremic toxins such as p-cresyl sulfate, indoxyl sulfate and inorganic phosphate leads to a loss of a substantial number of body functions. Although the concept of uremic toxins is dated to the 1960s, the molecular mechanisms capable of leading to renal and cardiovascular injuries are not yet known. Besides, the greatest toxic effects appear to be induced by compounds that are difficult to remove by dialysis. Considering the close relationship between renal and cardiovascular functions, an understanding of the mechanisms involved in the production, clearance and overall impact of uremic toxins is extremely relevant for the understanding of pathologies of the cardiovascular system. Thus, the present study has as main focus to present an extensive review on the impact of uremic toxins in the cardiovascular system, bringing the state of the art on the subject as well as clinical implications related to patient's therapy affected by chronic kidney disease, which represents high mortality of patients with cardiac comorbidities.

Reversing endothelial dysfunction with empagliflozin to improve cardiomyocyte function in cardiorenal syndrome

Sodium-glucose cotransporter 2 inhibitors offer cardiovascular and renal benefits in patients with chronic kidney disease through not yet clearly defined mechanisms. Juni et al. showed that sodium-glucose cotransporter 2 inhibitor empagliflozin exposure in vitro can restore cardiomyocyte function by counteracting harmful effects of uremic serum on the endothelium-cardiomyocyte crosstalk between endothelial cells and cardiomyocytes. The author's findings improved our understanding of cardiovascular impairment in chronic kidney disease and provided new perspectives for the beneficial effects of sodium-glucose cotransporter 2 inhibitor therapy.

Toxin Removal and Inflammatory State Modulation during Online Hemodiafiltration Using Two Different Dialyzers (TRIAD2 Study)

Uremic toxins play a pathological role in atherosclerosis and represent an important risk factor in dialysis patients. Online hemodiafiltration (HDF) has been introduced to improve the clearance of middle- and large-molecular-weight solutes (>500 Da) and has been associated with reduced cardiovascular mortality compared to standard hemodialysis. This non-randomized, open-label observational study will explore the efficacy of two dialyzers currently used for online HDF, a polysulfone-based high-flux membrane, and a cellulose triacetate membrane, in hemodialysis patients with signs of middle-molecule intoxication or intradialytic hypotension. In particular, the two filters will be evaluated for their ability in uremic toxin removal and modulation of inflammatory status. Sixteen subjects in standard chronic bicarbonate hemodialysis requiring a switch to online HDF in view of their clinical status will be enrolled and divided into two treatment arms, according to the previous history of hypersensitivity to polysulfone/polyethersulfone dialysis filters and hypersensitivity to drugs or other allergens. Group A will consist of 16 patients without a previous history of hypersensitivity and will be treated with a polysulfone filter (Helixone FX100), and group B, also consisting of 16 patients, with a previous history of hypersensitivity and will be treated with asymmetric triacetate (ATA; SOLACEA 21-H) dialyzer. Each patient will be followed for a period of 24 months, with monthly assessments of circulating middle-weight toxins and protein-bound toxins, markers of inflammation and oxidative stress, lymphocyte subsets, activated lymphocytes, and monocytes, cell apoptosis, the accumulation of advanced glycation end-products (AGEs), variations in arterial stiffens measured by pulse wave velocity (PWV), and mortality rate. The in vitro effect on endothelial cells of uremic serum collected from patients treated with the two different dialyzers will also be investigated to examine the changes in angiogenesis, cell migration, differentiation, apoptosis and proliferative potential, and gene and protein expression profile. The expected results will be a better awareness of the different effects of polysulfone gold-standard membrane for online HDF and the new ATA membrane on the removal of uremic toxins removal and inflammation due to blood-membrane interaction.

The association of secondary hyperparathyroidism and myocardial damages in hemodialysis end-stage renal disease patients: assessed by cardiovascular magnetic resonance native T1 mapping

BACKGROUND

Secondary hyperparathyroidism is a common complication of end-stage renal disease (ESRD), which may be associated with cardiovascular diseases. Thus, this study aimed to explore myocardial damage using non-contrast cardiovascular magnetic resonance (CMR) in ESRD patients undergoing hemodialysis and further investigate its relationship with parathyroid hormone (PTH) toxicity.

METHODS

Seventy-two adult ESRD patients receiving regular hemodialysis and 30 healthy subjects underwent CMR examination. Continuous CMR cine sections from the mitral valve level to the left ventricular (LV) apex in the short-axis plane, cine series of vertical two-chamber long-axis plane, and horizontal four-chamber plane were acquired. Native T1 mapping was obtained using modified Look-Locker inversion recovery (MOLLI) sequences. Native T1 values and myocardial strain were analyzed.  Immunoreactive parathyroid hormone (iPTH) was obtained from all enrolled patients.

RESULTS

Forty (55.6%) hemodialysis ESRD patients were found to have increased iPTH levels. LV ejection fraction (LVEF) of both ESRD patients with targeted and increased iPTH levels was decreased compared with healthy subjects (55.9 ± 12.0% vs. 65.0 ± 4.5%; 51.7 ± 12.8 vs. 65.0 ± 4.5%, both P < 0.05). The mean peak radial strain (PRS), peak circumferential strain (PCS), and peak longitudinal strain (PLS) were lowest in ESRD patients with increased iPTH; however, no significant difference was observed among these three groups. Segmentally, from base to apex, the native T1 of ESRD patients with increased iPTH levels tended to be higher than those with targeted iPTH and healthy subjects (all P < 0.05). In ESRD patients with targeted iPTH, both native T1 of basal and middle segments were significantly higher than normal subjects (basal, 1304 ± 41 ms vs. 1238 ± 36 ms, P = 0.001; middle, 1300 ± 43 ms vs. 1242 ± 50 ms, P < 0.001). Comparing global native T1 values in the three groups, ESRD patients with targeted and increased iPTH level showed increased native T1 (1305 ± 41 ms vs. 1251 ± 49 ms, P = 0.001; 1334 ± 40 ms vs. 1251 ± 49 ms, P < 0.001, respectively). Native T1 values of the basal segment and global native T1 were moderately associated with iPTH (r = 0.4, P < 0.001; r = 0.5, P < 0.001). Multiple linear regression analysis showed that global native T1 values (beta = 1.0, P = 0.01) were independently associated with iPTH.

CONCLUSIONS

Elevated iPTH level was associated with and was an independent risk factor for myocardial damage in ESRD patients undergoing maintenance hemodialysis.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ( http://www.chictr.org.cn/index.aspx ) ChiCTR-DND-17012976, 13/12/2017, retrospectively registered.