Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

Application of Nanoparticles as Novel Adsorbents in Blood Purification Strategies

BACKGROUND

Blood purification therapy for patients overloaded with metabolic toxins or drugs still needs improvement. Blood purification therapies, such as in hemodialysis or peritoneal dialysis can profit from a combined application with nanoparticles.

SUMMARY

In this review, the published literature is analyzed with respect to nanomaterials that have been customized and functionalized as nano-adsorbents during blood purification therapy. Liposomes possess a distinct combined structure composed of a hydrophobic lipid bilayer and a hydrophilic core. The liposomes which have enzymes in their aqueous core or obtain specific surface modifications of the lipid bilayer can offer appreciated advantages. Preclinical and clinical experiments with such modified liposomes show that they are highly efficient and generally safe. They may serve as indirect and direct adsorption materials both in hemodialysis and peritoneal dialysis treatment for patients with renal or hepatic failure. Apart from dialysis, nanoparticles made of specially designed metal and activated carbon have also been utilized to enhance the removal of solutes during hemoadsorption. Results are a superior adsorption capacity and good hemocompatibility shown during the treatment of patients with toxication or end-stage renal disease. In summary, nanomaterials are promising tools for improving the treatment efficacy of organ failure or toxication.

KEY MESSAGES

(i) The pH-transmembrane liposomes and enzyme-loaded liposomes are two representatives of liposomes with modified aqueous inner core which have been put into practice in dialysis. (ii) Unmodified or physiochemically modified liposomal bilayers are ideal binders for lipophilic protein-bound uremic toxins or cholestatic solutes, thus liposome-supported dialysis could become the next-generation hemodialysis treatment of artificial liver support system. (iii) Novel nano-based sorbents featuring large surface area, high adsorption capacity and decent biocompatibility have shown promise in the treatment of uremia, hyperbilirubinemia, intoxication, and sepsis. (vi) A major challenge of production lies in avoiding changes in physical and chemical properties induced by manufacturing and sterilizing procedures.

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.

Curcumenol improves renal function in 5/6 nephrectomy-induced chronic renal failure rats via the SIRT1/NF-κB pathway

The present work aimed to explore the protective effects of curcumenol and evaluate its pharmacological mechanisms in 5/6 nephrectomy-induced chronic renal failure (CRF). Rats with CRF were administrated curcumenol and the effects on renal functions were investigated. Renal function examinations were carried out, whereas serum levels of inflammatory mediators, including NF-κB, MCP-1 and IL-1β were analyzed by ELISA. The mRNA expression levels of SIRT1, p65 and IκBα were measured by qRT-PCR, and the SIRT1 protein levels were analyzed by western blot and immunohistochemistry. Our results indicated that curcumenol significantly improved the renal functions in the CRF rats. Compared to the sham group, serum levels of NF-κB, MCP-1, IL-1β, and the mRNA expression levels of p65 were significantly increased (p < 0.01), whereas the mRNA expression level of IκBα was significantly decreased (p < 0.01) and the SIRT1 levels were dramatically down-regulated (p < 0.05) in the CRF groups. Treatment with curcumenol remarkably inhibited inflammatory responses as reflected by the reduced levels of inflammatory mediators (p < 0.01) and SIRT1 up-regulation (p < 0.05). Our findings suggested that curcumenol could improve the renal function in 5/6 nephrectomy-induced CRF rats, and the mechanisms might involve suppressing the associated inflammation and modulating the SIRT1 and NF-κB signaling pathways.

Dual dialyzer hemodiafiltration: A new extracorporeal dialysis treatment modality for patients with end-stage kidney disease

BACKGROUND

The introduction of high flux (HF) hemodialyzers and their application in single dialyzer hemodiafiltration (sdHDF) for patients on extracorporeal dialysis (ECD) therapy has improved the extraction of uremic toxins, including the low molecular weight protein (LMWP) beta 2 microglobulin (β2M, 11.6 kDa). Similar increases in the extraction of protein-bound uremic toxins (PBUT) and larger LMWP (15-50 kDa) remain elusive. High concomitant losses of albumin prohibit the use of medium cutoff (MCO) or protein-losing hemodialyzers for sdHDF to increase the extraction of these molecules by convective transfer.

METHODS

A new extracorporeal dialysis treatment modality, dual dialyzer hemodiafiltration (ddHDF), has been designed together with a mathematical model to compare its predicted performance to that of sdHDF in the extraction of solute. The extra process that distinguishes ddHDF from sdHDF is the secondary ultrafiltration and partial reinfusion of the effluent hemodiafiltrate from the primary hemodialyzer. This allows MCO and protein-losing hemodialyzers to be used to increase the extraction of both LMWP and PBUT without excessive concomitant loss of albumin.

RESULTS

Data from the mathematical model show that ddHDF could increase the extraction of smaller and larger LMWP by an extra 102% and 220%, respectively, compared to standard HF sdHDF, while restricting the loss of albumin to 0.83 g per hour of treatment. In using albumin as a recyclable carrier molecule for the extraction of PBUT from plasma ddHDF has the potential to increase PBUT reduction ratios (RR's) to 49% by convection alone. Even higher RR's are possible if the dialysate volume flow rate can be increased beyond 600 mL/min.

CONCLUSION

ddHDF provides an opportunity for a step change increase in the level of extraction of both larger LMWP and PBUT in patients with end-stage kidney disease.

Enhancing Immune Protection in Hemodialysis Patients: Role of the Polymethyl Methacrylate Membrane

End-stage renal disease (ESRD) is characterized by deep disorders in both innate and adaptive immune systems that imply unbalance deactivation and immunosuppression. The central, widely recognized factors responsible for this immune dysregulation are uremia, uremic toxin retention, hemodialysis membrane biocompatibility, and related cardiovascular complications. Recently, several studies strengthened the concept that dialysis membranes are not considered as a simple diffusive/adsorptive device but as a platform to personalize a dialysis approach to improve the quality of life of ESRD patients. Therefore, understanding of the molecules associated with altered immune response is crucial and could lead to therapeutically intervention or adaptation of the dialysis procedure itself for the management of immunological dysfunction of ESRD patients. The polymethyl methacrylate (PMMA)-based membrane is characterized by a symmetrical structure with large-sized pores, providing a better hydrophobic and cationic adsorption capacity compared to the other synthetic membranes. Together with hydrophobic interactions, the high adsorption rate of cytokines (i.e., IL-6) can also be enhanced by the size of nano-pores placed on the membrane surface. PMMA membranes exhibit adsorptive properties for a large amount of uremic toxins including p-cresol and indoxyl sulfate, as well as β2-microglobulin characterized by higher molecular weight, maintaining the diffusive clearance of small molecules like urea with a great biocompatibility. Besides exerting a strong anti-inflammatory effects in line with the improvement of immune responses in patients undergoing dialysis, PMMA also plays a role in modulating adaptive immune response, i.e., can clear blood from soluble CD40, a natural antagonist of the CD40/CD40L signaling that acts inhibiting immunoglobulin production by B cells. This review provides an overview of the main concepts and current understanding of immune dysfunction in hemodialysis and summarizes the recent findings regarding PMMA-based dialysis as potential strategy to restore immune balance in ESRD patients.

Shenkang injection combined with alprostadil for chronic renal failure: A systematic review and meta-analysis

Objective

To systematically evaluate the clinical efficacy and safety of Shenkang injection (SKI) combined with alprostadil in the treatment of chronic renal failure (CRF).

Method

Randomized controlled trials (RCTs) of Shenkang injection combined with alprostadil in CRF treatment were investigated by retrieving a total of 7 databases including CNKI, Wanfang database, VIP, CBM, PubMed, Embase and Cochrane Library, with the search time ranging from 2012 to now. Revman 5.2 software was used for data analysis, and Cochrane bias risk tool was used to evaluate the quality of the included literature. The final results were represented by relative risk (RR), mean difference (MD) and 95% confidence interval (95% CI).

Results

A total of 20 RCTs and 1,573 patients were included in this study. Meta-analysis showed that the overall response rate (ORR) of the treatment group was superior to the control group [RR = 0.20, 95% CI (0.16, 0.25), P &lt; 0.00001]. Compared with the control group, the treatment group achieved favorable improvement in terms of the creatinine clearance rate (Ccr) [MD = 9.48, 95% CI (8.73, 10.24), P &lt; 0.00001], serum creatinine (Scr) [MD = −55.12, 95% CI (−63.42, −46.82), P &lt; 0.00001], quantitative urine protein (Upro) [MD = −0.48, 95% CI (−0.53, −0.43), P &lt; 0.00001], and blood urea nitrogen (BUN) [MD=-3.73, 95% CI (−4.08, −3.3) 7, P &lt; 0.00001]. There was no statistical difference in the incidence of adverse reactions in each group.

Conclusion

Currently, Shenkang injection combined with alprostadil has been widely used in clinical treatment of CRF due to the certain effect superior to other methods. However, its specific efficacy and safety need to be further verified through numerous large-scale clinical trials.

Systematic Comparison of Uremic Toxin Removal Using Different Hemodialysis Modes: A Single-Center Crossover Prospective Observational Study

Many hypotheses could explain the mortality decrease observed using hemodiafiltration, such as reduction of intradialytic hypotension and more efficient toxin removal. We led a systematic analysis of representative uremic toxin removal with hemodialysis (HD), online postdilution hemodiafiltration (postHDF) and online predilution hemodiafiltration (preHDF), in a single-center crossover and prospective observational study. The primary outcome was the reduction ratio of uremic toxins of the three categories defined by the Eutox group. Twenty-six patients were treated by those three techniques of extra renal epuration. Mean Kt/Vurea was not different between the treatment methods. Mean reduction ratio of beta2microglobulin was significantly higher for both HDF treatments than for HD (p < 0.001). Myoglobin, kappa, and lambda free light chain reduction ratio was significantly different between the modes: 37.75 ± 11.95%, 45.31 ± 11% and 61.22 ± 10.56%/57.21 ± 12.5%, 63.53 ± 7.93%, and 68.40 ± 11.79%/29.12 ± 8.44%, 34.73 ± 9.01%, and 45.55 ± 12.31% HD, preHDF, and postHDF, respectively (p < 0.001). Mean protein-bound solutes reduction ratio was not different between the different treatments except for PCS with a higher reduction ratio during HDF treatments. Mean albumin loss was always less than 2 g. HDF improved removal of middle molecules but had no effect on indoles concentration without any difference between synthetic dialysis membranes.

Assembly of chemically modified protein nanocages into 3D materials for the adsorption of uremic toxins

Hemodialysis fails to remove protein-bound uremic toxins that are attributed with high cardiovascular risk. Application of adsorption materials is a viable strategy, but suitable biocompatible adsorbents are still not available. Here, we demonstrate that adsorbents based on the bottom-up assembly of the intrinsically biocompatible protein cage ferritin are applicable for toxin adsorption. Due to the size-exclusion effect of its pores, only small molecules such as uremic toxins can enter the protein cage. Protein redesign techniques that target selectively the inner surface were used to introduce anchor sites for chemical modification. Porous crystalline adsorbents were fabricated by bottom-up assembly of the protein cage. Linkage of up to 96 phenylic or aliphatic molecules per container was verified by ESI-MS. Materials based on unmodified ferritin cages can already adsorb the uremic toxins. The adsorption capacity could be increased by about 50% through functionalization with hydrophobic molecules reaching 458 μg g^-1 for indoxyl sulfate. The biohybrid materials show no contamination with endotoxins and do not activate blood platelets. These findings demonstrate the great potential of protein-based adsorbents for the clearance of uremic toxins: modifications enhance toxin adsorption without diminishing the biocompatibility of the final protein-based material.

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.

Nrf2 Activation in Chronic Kidney Disease: Promises and Pitfalls

The nuclear factor erythroid 2-related factor 2 (Nrf2) protects the cell against oxidative damage. The Nrf2 system comprises a complex network that functions to ensure adequate responses to redox perturbations, but also metabolic demands and cellular stresses. It must be kept within a physiologic activity range. Oxidative stress and alterations in Nrf2-system activity are central for chronic-kidney-disease (CKD) progression and CKD-related morbidity. Activation of the Nrf2 system in CKD is in multiple ways related to inflammation, kidney fibrosis, and mitochondrial and metabolic effects. In human CKD, both endogenous Nrf2 activation and repression exist. The state of the Nrf2 system varies with the cause of kidney disease, comorbidities, stage of CKD, and severity of uremic toxin accumulation and inflammation. An earlier CKD stage, rapid progression of kidney disease, and inflammatory processes are associated with more robust Nrf2-system activation. Advanced CKD is associated with stronger Nrf2-system repression. Nrf2 activation is related to oxidative stress and moderate uremic toxin and nuclear factor kappa B (NF-κB) elevations. Nrf2 repression relates to high uremic toxin and NF-κB concentrations, and may be related to Kelch-like ECH-associated protein 1 (Keap1)-independent Nrf2 degradation. Furthermore, we review the effects of pharmacological Nrf2 activation by bardoxolone methyl, curcumin, and resveratrol in human CKD and outline strategies for how to adapt future Nrf2-targeted therapies to the requirements of patients with CKD.

Impact of Uremic Toxins on Endothelial Dysfunction in Chronic Kidney Disease: A Systematic Review

Patients with chronic kidney disease (CKD) are at a highly increased risk of cardiovascular complications, with increased vascular inflammation, accelerated atherogenesis and enhanced thrombotic risk. Considering the central role of the endothelium in protecting from atherogenesis and thrombosis, as well as its cardioprotective role in regulating vasorelaxation, this study aimed to systematically integrate literature on CKD-associated endothelial dysfunction, including the underlying molecular mechanisms, into a comprehensive overview. Therefore, we conducted a systematic review of literature describing uremic serum or uremic toxin-induced vascular dysfunction with a special focus on the endothelium. This revealed 39 studies analyzing the effects of uremic serum or the uremic toxins indoxyl sulfate, cyanate, modified LDL, the advanced glycation end products N-carboxymethyl-lysine and N-carboxyethyl-lysine, p-cresol and p-cresyl sulfate, phosphate, uric acid and asymmetric dimethylarginine. Most studies described an increase in inflammation, oxidative stress, leukocyte migration and adhesion, cell death and a thrombotic phenotype upon uremic conditions or uremic toxin treatment of endothelial cells. Cellular signaling pathways that were frequently activated included the ROS, MAPK/NF-κB, the Aryl-Hydrocarbon-Receptor and RAGE pathways. Overall, this review provides detailed insights into pathophysiological and molecular mechanisms underlying endothelial dysfunction in CKD. Targeting these pathways may provide new therapeutic strategies reducing increased the cardiovascular risk in CKD.

Chronic Kidney Disease-Associated Itch (CKD-aI) in Children-A Narrative Review

Chronic kidney disease (CKD) is a condition of widespread epidemiology and serious consequences affecting all organs of the organism and associated with significant mortality. The knowledge on CKD is rapidly evolving, especially concerning adults. Recently, more data is also appearing regarding CKD in children. Chronic itch (CI) is a common symptom appearing due to various underlying dermatological and systemic conditions. CI may also appear in association with CKD and is termed chronic kidney disease-associated itch (CKD-aI). CKD-aI is relatively well-described in the literature concerning adults, yet it also affects children. Unfortunately, the data on paediatric CKD-aI is particularly scarce. This narrative review aims to describe various aspects of CKD-aI with an emphasis on children, based on the available data in this population and the data extrapolated from adults. Its pathogenesis is described in details, focusing on the growing role of uraemic toxins (UTs), as well as immune dysfunction, altered opioid transmission, infectious agents, xerosis, neuropathy and dialysis-associated aspects. Moreover, epidemiological and clinical aspects are reviewed based on the few data on CKD-aI in children, whereas treatment recommendations are proposed as well, based on the literature on CKD-aI in adults and own experience in managing CI in children.