Bioartificial kidney ameliorates gram-negative bacteria-induced septic shock in uremic animals

Feasibility of an implantable bioreactor for renal cell therapy using silicon nanopore membranes

The definitive treatment for end-stage renal disease is kidney transplantation, which remains limited by organ availability and post-transplant complications. Alternatively, an implantable bioartificial kidney could address both problems while enhancing the quality and length of patient life. An implantable bioartificial kidney requires a bioreactor containing renal cells to replicate key native cell functions, such as water and solute reabsorption, and metabolic and endocrinologic functions. Here, we report a proof-of-concept implantable bioreactor containing silicon nanopore membranes to offer a level of immunoprotection to human renal epithelial cells. After implantation into pigs without systemic anticoagulation or immunosuppression therapy for 7 days, we show that cells maintain >90% viability and functionality, with normal or elevated transporter gene expression and vitamin D activation. Despite implantation into a xenograft model, we find that cells exhibit minimal damage, and recipient cytokine levels are not suggestive of hyperacute rejection. These initial data confirm the potential feasibility of an implantable bioreactor for renal cell therapy utilizing silicon nanopore membranes.

Approaches to kidney replacement therapies—opportunities and challenges

One out of seven people develop chronic kidney disease (CKD). When kidney function continues to decline, CKD patients may develop end-stage renal disease (ESRD, or kidney failure). More than 2 out of 1,000 adults develop ESRD and these patients must live on dialysis or get a kidney transplant to survive. Each year, more than $51 billion is spent to treat patients with ESRD in the United States. In addition, ESRD greatly reduces longevity and quality of life for patients. Compared to dialysis, kidney transplant offers the best chance of survival, but few donor organs are available. Thus, there is an urgent need for innovative solutions that address the shortage of kidneys available for transplantation. Here we summarize the status of current approaches that are being developed to solve the shortage of donor kidneys. These include the bioartificial kidney approach which aims to make a portable dialysis device, the recellularization approach which utilizes native kidney scaffold to make an engineered kidney, the stem cell-based approach which aims to generate a kidney de novo by recapitulating normal kidney organogenesis, the xenotransplantation approach which has the goal to make immunocompatible pig kidneys for transplantation, and the interspecies chimera approach which has potential to generate a human kidney in a host animal. We also discuss the interconnections among the different approaches, and the remaining challenges of translating these approaches into novel therapies.

Blood purification for sepsis: an overview

Sepsis is a life-threatening organ failure exacerbated by a maladaptive infection response from the host, and is one of the major causes of mortality in the intensive care unit. In recent decades, several extracorporeal blood purification techniques have been developed to manage sepsis by acting on both the infectious agents themselves and the host immune response. This research aims to summarize recent progress on extracorporeal blood purification technologies applied for sepsis, discuss unanswered questions on renal replacement therapy for septic patients, and present a decision-making strategy for practitioners.

Safety evaluation of conditionally immortalized cells for renal replacement therapy

End-stage kidney disease represents irreversible kidney failure. Dialysis and transplantation, two main treatment options currently available, present various drawbacks and complications. Innovative cell-based therapies, such as a bioartificial kidney, have not reached the clinic yet, mostly due to safety and/or functional issues. Here, we assessed the safety of conditionally immortalized proximal tubule epithelial cells (ciPTECs) for bioartificial kidney application, by using in vitro assays and athymic nude rats. We demonstrate that these cells do not possess key properties of oncogenically transformed cells, including anchorage-independent growth, lack of contact inhibition and apoptosis-resistance. In late-passage cells we did observe complex chromosomal abnormalities favoring near-tetraploidy, indicating chromosomal instability. However, time-lapse imaging of ciPTEC-OAT1, confined to a 3D extracellular matrix (ECM)-based environment, revealed that the cells were largely non-invasive. Furthermore, we determined the viral integration sites of SV40 Large T antigen (SV40T), human telomerase (hTERT) and OAT1 (SLC22A6), the transgenes used for immortalization and cell function enhancement. All integrations sites were found to be located in the intronic regions of endogenous genes. Among these genes, early endosome antigen 1 (EEA1) involved in endocytosis, and BCL2 Like 1 (BCL2L1) known for its role in regulating apoptosis, were identified. Nevertheless, both gene products appeared to be functionally intact. Finally, after subcutaneous injection in athymic nude rats we show that ciPTEC-OAT1 lack tumorigenic and oncogenic effects in vivo, confirming the in vitro findings. Taken together, this study lays an important foundation towards bioartificial kidney (BAK) development by confirming the safety of the cell line intended for incorporation.

Role of Vitamin D in Maintaining Renal Epithelial Barrier Function in Uremic Conditions

As current kidney replacement therapies are not efficient enough for end-stage renal disease (ESRD) treatment, a bioartificial kidney (BAK) device, based on conditionally immortalized human proximal tubule epithelial cells (ciPTEC), could represent an attractive solution. The active transport activity of such a system was recently demonstrated. In addition, endocrine functions of the cells, such as vitamin D activation, are relevant. The organic anion transporter 1 (OAT-1) overexpressing ciPTEC line presented 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1) and vitamin D receptor (VDR), responsible for vitamin D activation, degradation and function, respectively. The ability to produce and secrete 1α,25-dihydroxy-vitamin D₃, was shown after incubation with the precursor, 25-hydroxy-vitamin D₃. The beneficial effect of vitamin D on cell function and behavior in uremic conditions was studied in the presence of an anionic uremic toxins mixture. Vitamin D could restore cell viability, and inflammatory and oxidative status, as shown by cell metabolic activity, interleukin-6 (IL-6) levels and reactive oxygen species (ROS) production, respectively. Finally, vitamin D restored transepithelial barrier function, as evidenced by decreased inulin-FITC leakage in biofunctionalized hollow fiber membranes (HFM) carrying ciPTEC-OAT1. In conclusion, the protective effects of vitamin D in uremic conditions and proven ciPTEC-OAT1 endocrine function encourage the use of these cells for BAK application.

Allostimulatory capacity of conditionally immortalized proximal tubule cell lines for bioartificial kidney application

Novel renal replacement therapies, such as a bioartificial kidney (BAK), are needed to improve current hemodialysis treatment of end-stage renal disease (ESRD) patients. As BAK applications may reveal safety concerns, we assessed the alloimmunization and related safety aspects of readily available conditionally immortalized human proximal tubule epithelial cell (ciPTEC) lines to be used in BAK. Two ciPTEC lines, originally derived from urine and kidney tissue, were characterized for the expression and secretion of relevant molecules involved in alloimmunization and inflammatory responses, such as HLA class-I, HLA-DR, CD40, CD80, CD86, as wells as soluble HLA class I and proinflammatory cytokines (IL-6, IL-8 and TNF-α). A lack of direct immunogenic effect of ciPTEC was shown in co-culture experiments with peripheral blood mononuclear cells (PBMC), after appropriate stimulation of ciPTEC. Tight epithelial cell monolayer formation on polyethersulfone flat membranes was confirmed by zonula occludens-1 (ZO-1) expression in the ciPTEC tight junctions, and by restricted inulin-FITC diffusion. Co-culture with (activated) PBMC did not jeopardize the transepithelial barrier function of ciPTEC. In conclusion, the absence of allostimulatory effects and the stability of ciPTEC monolayers show that these unique cells could represent a safe option for BAK engineering application.

A bio-artificial renal epithelial cell system conveys survival advantage in a porcine model of septic shock

Renal cell therapy using the hollow fiber based renal assist device (RAD) improved survival time in an animal model of septic shock (SS) through the amelioration of cardiac and vascular dysfunction. Safety and ability of the RAD to improve clinical outcomes was demonstrated in a Phase II clinical trial, in which patients had high prevalence of sepsis. Even with these promising results, clinical delivery of cell therapy is hampered by manufacturing hurdles, including cell sourcing, large-scale device manufacture, storage and delivery. To address these limitations, the bioartificial renal epithelial cell system (BRECS) was developed. The BRECS contains human renal tubule epithelial cells derived from adult progenitor cells using enhanced propagation techniques. Cells were seeded onto trabeculated disks of niobium-coated carbon, held within cryopreservable, perfusable, injection-moulded polycarbonate housing. The study objective was to evaluate the BRECS in a porcine model of SS to establish conservation of efficacy after necessary cell sourcing and design modifications; a pre-clinical requirement to move back into clinical trials. SS was incited by peritoneal injection of E. coli simultaneous to insertion of BRECS (n=10) or control (n=15), into the ultrafiltrate biofeedback component of an extracorporeal circuit. Comparable to RAD, prolonged survival of the BRECS cohort was conveyed through stabilization of cardiac output and vascular leak. In conclusion, the demonstration of conserved efficacy with BRECS therapy in a porcine SS model represents a crucial step toward returning renal cell therapy to the clinical setting, initially targeting ICU patients with acute kidney injury requiring continuous renal replacement therapy. Copyright © 2014 John Wiley & Sons, Ltd.

Stem cell-derived kidney cells and organoids: Recent breakthroughs and emerging applications

The global rise in the numbers of kidney patients and the shortage in transplantable organs have led to an increasing interest in kidney-specific regenerative therapies, renal disease modelling and bioartificial kidneys. Sources for large quantities of high-quality renal cells and tissues would be required, also for applications in in vitro platforms for compound safety and efficacy screening. Stem cell-based approaches for the generation of renal-like cells and tissues would be most attractive, but such methods were not available until recently. This situation has drastically changed since 2013, and various protocols for the generation of renal-like cells and precursors from pluripotent stem cells (PSC) have been established. The most recent breakthroughs were related to the establishment of various protocols for the generation of PSC-derived kidney organoids. In combination with recent advances in genome editing, bioprinting and the establishment of predictive renal screening platforms this results in exciting new possibilities. This review will give a comprehensive overview over current PSC-based protocols for the generation of renal-like cells, precursors and organoids, and their current and potential applications in regenerative medicine, compound screening, disease modelling and bioartificial organs.

Future Avenues to Decrease Uremic Toxin Concentration

In this article, we review approaches for decreasing uremic solute concentrations in chronic kidney disease and in particular, in end-stage renal disease (ESRD). The rationale to do so is the straightforward relation between concentration and biological (toxic) effect for most toxins. The first section is devoted to extracorporeal strategies (kidney replacement therapy). In the context of high-flux hemodialysis and hemodiafiltration, we discuss increasing dialyzer blood and dialysate flows, frequent and/or extended dialysis, adsorption, bioartificial kidney, and changing physical conditions within the dialyzer (especially for protein-bound toxins). The next section focuses on the intestinal generation of uremic toxins, which in return is stimulated by uremic conditions. Therapeutic options are probiotics, prebiotics, synbiotics, and intestinal sorbents. Current data are conflicting, and these issues need further study before useful therapeutic concepts are developed. The following section is devoted to preservation of (residual) kidney function. Although many therapeutic options may overlap with therapies provided before ESRD, we focus on specific aspects of ESRD treatment, such as the risks of too-strict blood pressure and glycemic regulation and hemodynamic changes during dialysis. Finally, some recommendations are given on how research might be organized with regard to uremic toxins and their effects, removal, and impact on outcomes of uremic patients.

Development of a living membrane comprising a functional human renal proximal tubule cell monolayer on polyethersulfone polymeric membrane

The need for improved renal replacement therapies has stimulated innovative research for the development of a cell-based renal assist device. A key requirement for such a device is the formation of a "living membrane", consisting of a tight kidney cell monolayer with preserved functional organic ion transporters on a suitable artificial membrane surface. In this work, we applied a unique conditionally immortalized proximal tubule epithelial cell (ciPTEC) line with an optimized coating strategy on polyethersulfone (PES) membranes to develop a living membrane with a functional proximal tubule epithelial cell layer. PES membranes were coated with combinations of 3,4-dihydroxy-l-phenylalanine and human collagen IV (Coll IV). The optimal coating time and concentrations were determined to achieve retention of vital blood components while preserving high water transport and optimal ciPTEC adhesion. The ciPTEC monolayers obtained were examined through immunocytochemistry to detect zona occludens 1 tight junction proteins. Reproducible monolayers were formed when using a combination of 2 mg ml(-1) 3,4-dihydroxy-l-phenylalanine (4 min coating, 1h dissolution) and 25 μg ml(-1) Coll IV (4 min coating). The successful transport of (14)C-creatinine through the developed living membrane system was used as an indication for organic cation transporter functionality. The addition of metformin or cimetidine significantly reduced the creatinine transepithelial flux, indicating active creatinine uptake in ciPTECs, most likely mediated by the organic cation transporter, OCT2 (SLC22A2). In conclusion, this study shows the successful development of a living membrane consisting of a reproducible ciPTEC monolayer on PES membranes, an important step towards the development of a bioartificial kidney.

Prospect for kidney bioengineering: shortcomings of the status quo

INTRODUCTION

Dialysis and renal transplantation are the only two therapeutic options offered to patients affected by end-stage kidney disease; however, neither treatment can be considered definitive. In fact, dialysis is able to replace only the filtration function of the kidney without substituting its endocrine and metabolic roles, and dramatically impacts on patient's quality of life. On the other hand, kidney transplantation is severely limited by the shortage of transplantable organs, the need for immunosuppressive therapies and a narrow half-life. Regenerative medicine approaches are promising tools aiming to improve this condition.

AREAS COVERED

Cell therapies, bioartificial kidney, organ bioengineering, 3D printer and kidney-on-chip represent the most appealing areas of research for the treatment of end-stage kidney failure. The scope of this review is to summarize the state of the art, limits and directions of each branch.

EXPERT OPINION

In the future, these emerging technologies could provide definitive, curative and theoretically infinite options for the treatment of end-stage kidney disease. Progress in stem cells-based therapies, decellularization techniques and the more recent scientific know-how for the use of the 3D printer and kidney-on-chip could lead to a perfect cellular-based therapy, the futuristic creation of a bioengineered kidney in the lab or to a valid bioartificial alternative.

The bioartificial kidney

Renal failure has an exceedingly high mortality rate despite advances in dialysis technology. Current renal replacement therapies (RRTs) restore only the filtration function of the kidney. Replacing the critical transport, metabolic, and endocrine functions of the kidney may provide more complete RRT, changing the natural history of these disease processes. Primary human renal epithelial cells (RECs) have been isolated and expanded under conditions that enhance propagation, resulting in maximum cell yield for use in bioengineered applications. These RECs demonstrate differentiated absorptive, metabolic, and endocrine functions of the kidney when tested under in vitro and preclinical ex vivo animal studies. When incorporated into bioengineered systems, RECs have proved to provide effective RRTs in both preclinical and clinical studies. These engineered "bioartificial kidneys" demonstrate metabolic activity with systemic effects and improvement of survival in patients with acute kidney injury and multiorgan failure. Results also indicate REC therapy influences systemic leukocyte activation and the balance of inflammatory cytokines, suggesting that this REC therapy may improve morbidity and mortality by altering the proinflammatory state of patients. This innovative approach for treating renal and inflammatory disease states may become a groundbreaking, transformative platform to current standard-of-care therapies, enabling the advancement of numerous lifesaving technologies.

The bioartificial kidney: current status and future promise

The rapid understanding of the cellular and molecular bases of organ function and disease processes will be translated in the next decade into new therapeutic approaches to a wide range of clinical disorders, including acute and chronic renal failure. Central to these new therapies are the developing technologies of cell therapy and tissue engineering, which are based on the ability to expand stem or progenitor cells in tissue culture to perform differentiated tasks and to introduce these cells into the patient either via extracorporeal circuits or as implantable constructs. Cell therapy devices are currently being developed to replace the filtrative, metabolic, and endocrinologic functions of the kidney lost in both acute and chronic renal failure. This review summarizes the current state of development of a wearable or implantable bioartificial kidney. These devices have the promise to be combined to produce a wearable or implantable bioartificial kidney for full renal replacement therapy that may significantly diminish morbidity and mortality in patients with acute or chronic kidney disease.

Therapeutic mechanisms of single Chinese medicine herb or their extracts for extrahepatic obstructive jaundice

Obstructive jaundice (OJ) is classified as extrahepatic OJ or intrahepatic OJ. Extrahepatic OJ is attributed to a variety of intricate etiological factors. Research has begun with Chinese medicine (CM), which can be used as an adjunctive therapy for extrahepatic OJ. Particular attention has been paid to the therapeutic effects and their mechanisms of single CM herb and relevant extracts. The roles of single CM or their extracts during adjunctive therapy for extrahepatic OJ have been described briefly. This review focuses on the effects and their mechanisms of relevant herbal medicines.

Developments towards an artificial kidney

This article reviews the present state of renal failure and its treatment in the industrialized world. Novel and experimental therapies for the treatment of renal failure are covered, with special emphasis on a hybrid bioartificial kidney currently undergoing clinical trials in the USA. Preclinical data, results from human trials and work on miniaturization of the bioartificial kidney for implantation are presented. Research on microfluidics and nanotechnology applied to dialysis is ongoing in many academic centers, and several promising approaches are discussed. After 10 years of incremental improvements in end-stage renal disease care, several revolutionary technologies are on the horizon and approaching the marketplace.

A novel design of bioartificial kidneys with improved cell performance and haemocompatibility

Treatment with bioartificial kidneys had beneficial effects in animal experiments and improved survival of critically ill patients with acute kidney injury in a Phase II clinical trial. However, a Phase II b clinical trial failed. This and other results suggested various problems with the current design of bioartificial kidneys. We propose a novel design to improve various properties of device, including haemocompatibility and cell performance. An important feature of the novel design is confinement of the blood to the lumina of the hollow fibre membranes. This avoids exposure of the blood to the non-haemocompatible outer surfaces of hollow fibre membranes, which usually occurs in bioartificial kidneys. We use these outer surfaces as substrate for cell growth. Our results show that commercial hollow fibre membranes can be directly applied in the bioreactor when human primary renal proximal tubular cells are grown in this configuration, and no coatings are required for the formation of robust and functional renal epithelia. Furthermore, we demonstrate that the bioreactor unit produces significant amounts of interleukins. This result helps to understand the immunomodulatory effects of bioartificial kidneys, which have been observed previously. The novel bioartificial kidney design outlined here and the results obtained would be expected to improve the safety and performance of bioartificial kidneys and to contribute to a better understanding of their effects.

Cell therapy, advanced materials, and new approaches to acute kidney injury

Acute renal failure (ARF) is a common clinical syndrome characterized by an abrupt deterioration in kidney function, resulting in abnormalities in volume-regulatory, metabolic-regulatory, excretory, and endocrine functions. Despite decades of improvements in the provision of intensive care, and specifically in the provision of renal replacement therapy, the morbidity and mortality associated with acute kidney injury (AKI) remain extremely high. This article highlights novel cell therapies, advanced materials, and approaches to AKI with the aim of illuminating a potential path for future basic, translational, and clinical research using these novel modalities.

Extracorporeal therapies in sepsis

The treatment of sepsis is an ongoing challenge for clinicians; despite the wide choice of effective antibiotics to treat infection, sepsis remains the leading cause of morbidity and mortality for patients admitted to an intensive care unit. Dysregulation of the immune response is now recognized to be a key factor in multiple organ dysfunction, yet our therapy for inflammation remains ineffective. It has been advocated for more than a decade that cytokine reduction in blood compartment could lead to a reduction in mortality in sepsis. Over the years, multiple extracorporeal techniques have evolved, with the intent of influencing the circulating levels of inflammatory mediators like cytokines and chemokines, the complement system, as well as factors of the coagulation system. These include high-volume hemofiltration, use of high cutoff membranes, and systems based on adsorption, such as coupled plasma filtration adsorption and the polymyxin-B column. In addition, new experimental systems that utilize human phagocytic cells and immobilized antibodies for targeted immunomodulation have emerged. In the context of limited resources and growing expansion in the availability of technologies, a better understanding of these therapies is required before they can be properly integrated into standard clinical practice in the hope of influencing major clinical outcomes. In this article, we will provide a concise overview of selected extracorporeal modalities currently in clinical use and briefly introduce some new promising techniques for sepsis.

The performance of primary human renal cells in hollow fiber bioreactors for bioartificial kidneys

Bioartificial kidneys (BAKs) containing human primary renal proximal tubule cells (HPTCs) have been applied in clinical trials. The results were encouraging, but also showed that more research is required. Animal cells or cell lines are not suitable for clinical applications, but have been mainly used in studies on BAK development as large numbers of such cells could be easily obtained. It is difficult to predict HPTC performance based on data obtained with other cell types. To enable more extensive studies on HPTCs, we have developed a bioreactor containing single hollow fiber membranes that requires relatively small amounts of cells. Special hollow fiber membranes with the skin layer on the outer surface and consisting of polyethersulfone/polyvinylpyrrolidone were developed. The results suggested that such hollow fiber membranes were more suitable for the bioreactor unit of BAKs than membranes with an inner skin layer. An HPTC-compatible double coating was applied to the insides of the hollow fiber membranes, which sustained the formation of functional epithelia under bioreactor conditions. Nevertheless, the state of differentiation of the primary human cells remained a critical issue and should be further addressed. The bioreactor system described here will facilitate further studies on the relevant human cell type.

Regenerative medicine of the kidney

End stage renal disease is a major health problem in this country and worldwide. Although dialysis and kidney transplantation are currently used to treat this condition, kidney regeneration resulting in complete healing would be a desirable alternative. In this review we focus our attention on current therapeutic approaches used clinically to delay the onset of kidney failure. In addition we describe novel approaches, like Tissue Engineering, Stem cell Applications, Gene Therapy, and Renal Replacement Therapy that may one day be possible alternative therapies for patients with the hope of delaying kidney failure or even stopping the progression of renal disease.

Present status and future perspectives on the development of bioartificial kidneys for the treatment of acute and chronic renal failure patients

A bioartificial renal tubule device (BTD) consisting of a hollow-fiber module and human proximal tubular epithelial cells has been completed technically by Humes and colleagues and a few other groups. Humes and colleagues developed BTD, treated acute kidney injury patients with multiorgan failure by continuous hemofiltration (CHF) in conjunction with BTD, and reported a significantly higher survival rate than that by CHF with BTD without cells in the Food and Drug Administration phase IIa trial. However, BTD has never been approved by the US Government, as the CHF+BTD treatment did not show a significant difference from the control group in the phase IIb trial. Human proximal tubular epithelial cells were confirmed to be overgrown on artificial membrane, which resulted in the inhibition of active transports and the metabolism of essential substances. Function of the BTD could be maintained in a U0126-contained medium, even if the BTD had to have been waited by a new acute kidney injury patient for several weeks. For wearable kidneys, heparin-covalently bound membrane or methacryloyloxyethyl phosphorylcholine (MPC) polymer-coated membranes are candidates for antithrombogenic hemofilters, while endothelial progenitor cells from a cord blood, CD133(+) cells-attached hemofilter in which the permeability of the cells was enhanced by the enlarged diameter of fenestrae by treating with cytochalasin B are another candidate. The MPC blend membrane containing 1% of the MPC polymer in polysulfone was developed as a BTD module. MPC was 7 times larger at the sponge layer than at the skin layer of the membrane, resulting in hemocompatibility at the sponge layer and cytocompatibility at the skin layer.

Acute kidney injury: current perspectives

Acute kidney injury (AKI) increases morbidity and mortality, particularly for the critically ill. Recent definitions standardizing AKI to reflect graded changes in serum creatinine and urine output (per the Risk, Injury, Failure, Loss, and End-stage renal failure [RIFLE] and Acute Kidney Injury Network [AKIN] criteria) with severity of renal injury and developments in AKI pathobiology are being utilized to identify biomarkers of early kidney injury. These developments may be useful in the early intervention of preventing AKI. Although there has been progress in the management of AKI, therapeutic challenges include appropriate prophylaxis prior to contrast administration, use of diuretics, vasopressors, and the type and dose of renal replacement therapy. Future use of bioartificial dialyzers, plasma therapies, and the possibility of stem cell regeneration of injured kidney tissue are being actively investigated to provide alternative treatment options for AKI. This review aims to provide an overview of current practices, available therapies, and continued research in AKI therapy.

The bioartificial kidney in the treatment of acute kidney injury

Acute kidney injury (AKI) continues to have an exceedingly high mortality rate, despite advances in dialysis technology. Current dialysis therapies replace only the filtration function of the kidney, not the critical transport, metabolic, and endocrine functions of renal tubule cells. Replacement of these additional functions would provide more complete AKI therapy and thereby change the natural history of this disease process. A renal tubule assist device (RAD) containing living renal proximal tubule cells has been successfully engineered and has demonstrated differentiated absorptive, metabolic, and endocrine functions of normal kidney in vitro and ex vivo in animal experiments. The addition of the RAD containing human cells to conventional continuous renal replacement therapy has been shown in preclinical and clinical studies to have the potential to advance AKI treatment, from enhancing renal clearance to providing more complete renal replacement therapy. This "bioartificial kidney" demonstrates metabolic activity with systemic effects and improvement of survival in patients with AKI and multiorgan failure. It also appears to influence systemic leukocyte activation and the balance of inflammatory cytokines, suggesting that cell therapy by use of the RAD may improve morbidity and mortality by altering the proinflammatory state of patients with renal failure. In addition to providing cellular metabolic function, technologies directed toward disrupting systemic inflammatory response may well enhance the clinical outcome of critically ill patients in the future. Innovative approaches to intensive renal care such as the RAD may break the mold of current institutional dialysis therapies and provide numerous opportunities to develop lifesaving technologies.

Achievements and challenges in bioartificial kidney development

Bioartificial kidneys (BAKs) combine a conventional hemofilter in series with a bioreactor unit containing renal epithelial cells. The epithelial cells derived from the renal tubule should provide transport, metabolic, endocrinologic and immunomodulatory functions. Currently, primary human renal proximal tubule cells are most relevant for clinical applications. However, the use of human primary cells is associated with many obstacles, and the development of alternatives and an unlimited cell source is one of the most urgent challenges. BAKs have been applied in Phase I/II and Phase II clinical trials for the treatment of critically ill patients with acute renal failure. Significant effects on cytokine concentrations and long-term survival were observed. A subsequent Phase IIb clinical trial was discontinued after an interim analysis, and these results showed that further intense research on BAK-based therapies for acute renal failure was required. Development of BAK-based therapies for the treatment of patients suffering from end-stage renal disease is even more challenging, and related problems and research approaches are discussed herein, along with the development of mobile, portable, wearable and implantable devices.

Renal cell therapy and beyond

Although current dialysis techniques have transformed acute and chronic renal failure from uniformly fatal clinical disorders into treatable diseases, these therapies replace only the water and solute clearance function of the kidney and have reached a point where little further therapeutic improvement can be anticipated. In addition to their metabolic and endocrine functions, renal tubule cells presumably play an important role in the systemic inflammatory balance by participating in the complex and dynamic network of leukocyte action and pro- and anti-inflammatory cytokines. Loss of this function may result in a propensity to develop systemic inflammatory response syndrome (SIRS), multiorgan dysfunction, and a high risk of death in acute kidney injury (AKI), and may relate to chronic inflammatory state in end-stage renal disease (ESRD). A renal tubule cell assist device (RAD) containing animal or human renal tubule cells has been recently developed with the purpose of integrating the functions of tubule cells with the filtration function of current dialysis to offer a more complete renal replacement therapy. The viability and functionality of this device were confirmed in in vitro experiments and large animal studies, and recently the RAD's clinical therapeutic benefit was demonstrated with a series of FDA-approved human trials. Another novel synthetic membrane extracorporeal device that binds and inhibits circulating leukocytes has been developed with the purpose of reducing microvascular damage promoted primarily via activated circulating leukocytes in AKI and SIRS. This device, called a selective cytopheretic inhibitory device, mimics immunomodulation and duplicates RAD efficiency in preliminary studies. Both devices may become comprehensive treatments, replacing full renal function and correcting inflammatory imbalance in patients with acute and chronic renal disorders.

Continuous renal replacement therapy in sepsis and multisystem organ failure

This study reviews the role of continuous renal replacement therapy (CRRT) in sepsis with acute kidney injury (AKI) and septic shock with multiple organ failure. In addition to the conventional aim of replacing renal function in AKI, CRRT is often used with the concept of modulating immune response in sepsis. With the intention of influencing circulating levels of inflammatory mediators like cytokines and chemokines, the complement system, as well as factors of the coagulation system, several modifications of CRRT have been developed over the last years. These include high volume hemofiltration, high adsorption hemofiltration, use of high cut-off membranes, and hybrid systems like coupled plasma filtration absorbance. One of the most promising concepts may be the development of renal assist devices using renal tubular cells for implementing renal tubular function into CRRT.

Construction of bioartificial renal tubule assist device in vitro and its function of transporting sodium and glucose

To explore a new way of constructing bioartificial renal tubule assist device (RAD) in vitro and its function of transporting sodium (Na(+)) and glucose and to evaluate the application of atomic force microscope in the RAD construction, rat renal tubular epithelial cell line NRK-52E was cultured in vitro, seeded onto the outer surfaces of hollow fibers in a bioreactor, and then cultured for two weeks to construct RAD. Bioreactor hollow fibers without NRK-52E cells were used as control. The morphologies of attached cells were observed with scanning electron microscope, and the junctions of cells and polysulfone membrane were observed with atomic force microscope. Transportation of Na(+) and glucose was measured. Oubaine and phlorizin were used to inhibit the transporting property. The results showed that NRK-52E cells and polysulfone membrane were closely linked, as observed under atomic force microscope. After exposure to oubaine and phlorizin, transporting rates of Na(+) and glucose were decreased significantly in the RAD group as compared with that in the control group (P<0.01). Furthermore, when the inhibitors were removed, transportation of Na(+) and glucose was restored. It is concluded that a new RAD was constructed successfully in vitro, and it is able to selectively transport Na(+) and glucose.

Efficacy and safety of renal tubule cell therapy for acute renal failure

The mortality rate for patients with acute renal failure (ARF) remains unacceptably high. Although dialysis removes waste products and corrects fluid imbalance, it does not perform the absorptive, metabolic, endocrine, and immunologic functions of normal renal tubule cells. The renal tubule assist device (RAD) is composed of a conventional hemofilter lined by monolayers of renal cells. For testing whether short-term (up to 72 h) treatment with the RAD would improve survival in patients with ARF compared with conventional continuous renal replacement therapy (CRRT), a Phase II, multicenter, randomized, controlled, open-label trial involving 58 patients who had ARF and required CRRT was performed. Forty patients received continuous venovenous hemofiltration + RAD, and 18 received CRRT alone. The primary efficacy end point was all-cause mortality at 28 d; additional end points included all-cause mortality at 90 and 180 d, time to recovery of renal function, time to intensive care unit and hospital discharge, and safety. At day 28, the mortality rate was 33% in the RAD group and 61% in the CRRT group. Kaplan-Meier analysis revealed that survival through day 180 was significantly improved in the RAD group, and Cox proportional hazards models suggested that the risk for death was approximately 50% of that observed in the CRRT-alone group. RAD therapy was also associated with more rapid recovery of kidney function, was well tolerated, and had the expected adverse event profile for critically ill patients with ARF.

The future of renal replacement therapy

The worldwide epidemic of chronic kidney disease shows no signs of abating in the near future. Current dialytic forms of renal replacement therapy (RRT), even though successful in sustaining life and improving quality of life somewhat for patients with end-stage renal disease, have many limitations that result in still unacceptably high morbidity and mortality. Transplantation is an excellent option but is limited by the scarcity of organs. An ideal form of RRT would mimic the functions of natural kidneys and be implantable, safe, and cost-effective. Until recently, these goals would have been hard to achieve, but with the application of nanotechnology and microfluidics to RRT, they appear closer than ever before. Newer approaches include the human nephron filter (HNF), a novel form of RRT consisting of 2 membranes in series. The first membrane mimics the function of the glomerulus, and the other membrane mimics the function of the tubule. Investigators have proposed the synthesis of a silicone membrane that more closely resembles the glomerular filtration membrane and the use of a membrane with implanted renal tubular cells to provide tubular and other kidney functions. Membraneless dialysis that utilizes the principle of microfluidics has been proposed. Application of microelectromechanical systems (MEMS) technology will provide the ideal miniature detection system for future implantable dialysis devices. Finally, stem cells hold much promise, both for kidney disease and as a source of tissues and organs. In summary, nephrology is at an exciting crossroad with the application of innovative and novel technologies to RRT that hold considerable promise for the near future.

Effect of continuous bioartificial kidney therapy on porcine multiple organ dysfunction syndrome with acute renal failure

The bioartificial kidney (BK) was fabricated with primary culture of human proximal tubular cells growing in a hemofilter. A porcine model with multiple organ dysfunction syndrome, including acute renal failure, was induced by cecal ligation and puncture and bilateral ureteral ligation. The models were treated with BK (group A) or sham BK (group B) or without treatment (group C). Mean arterial pressure (mm Hg) was higher in group A (88.13 +/- 7.62) than in groups B and C (63.50 +/- 11.82, 53.50 +/- 2.52) at 24 hours (p < 0.01). Serum blood urea nitrogen, Cr, K, Pao2, and HCO3 were similar during the treatment periods between groups A and B, which were better than those in group C. In group A, tumor necrosis factor (TNF)-alpha (pg/mL) was 394.42 +/- 35.62 at 24 hours, lower than that of groups B and C (531.76 +/- 30.23, 552.89 +/- 27.81) (p < 0.05). Peak level of interleukin (IL)-10 (pg/mL) was higher in group A (272.36 +/- 48.89) than in groups B and C (106.30 +/- 29.69, 102.59 +/- 10.21) (p < 0.01). There was no difference of serum IL-6 between pretreatment and post-treatment in groups A and B, but serum IL-6 gradually increased in group C. The survival time (hours) was longer in group A than in other groups, which was prolonged by 46.20% and 58.39%. Results indicate that BK can ameliorate mean arterial pressure, decrease serum TNF-alpha, increase serum IL-10, and prolong survival time of pigs with multiple organ dysfunction syndrome and acute renal failure.

Bioartificial kidney in the treatment of acute renal failure associated with sepsis

Acute renal failure (ARF) associated with sepsis has a high rate of mortality. It is not merely a surrogate marker for severity of disease but also an independent predictor of mortality and a separate pathogenic entity, even when nearly physiological doses of fluid and small-molecule clearance are maintained with currently available renal replacement therapies (RRT). The techniques to remove cytokines, including high-volume haemofiltration, haemodialysis using high-cut-off haemofilters, and absorptive techniques, lead to some improvement in outcome but are still insufficient to reverse the complicated biological dysregulation resulting from ARF associated with sepsis. The novel and exciting technique of cell therapy, which is based on the principle of using functional cells to replace a greater range of renal functions, may add significant benefit to current RRT in dealing with this disease process. Because renal tubule cells appear to play critical roles in immunoregulation, renal tubule cell therapy during ARF associated with sepsis should alter the detrimental multiple-organ consequences of sepsis. The development of a bioartificial kidney consisting of a conventional haemofiltration cartridge in series with a renal tubule assist device containing renal proximal tubule cells represents a new therapeutic approach to this clinical disorder. The results to date of large animal studies and recent Phase I/II and Phase II clinical trials show that such a device replaces multiple kidney functions and modifies the sepsis condition to improve survival in ARF.

Measurement of serum interleukin-10 in the dog

The objective was to evaluate independently the reliability of a commercially available canine serum interleukin-10 (IL-10) enzyme-linked immunoassay (ELISA) and to investigate canine serum IL-10 concentrations in healthy dogs, in dogs with a naturally-occurring acute phase reaction and in dogs following surgical stimulus by assessing intra- and interassay imprecision, inaccuracy and detection limits. Median (and range) serum IL-10 concentrations (ng/L) in the various groups were as follows: healthy dogs (n=15), 18.9 (11.2-71.5); dogs with pyometra (n=9), 37.9 (12.4-201.8); dogs with angiostrongylosis (n=8), 20.29 (14.3-108.7) and values in dogs following surgical stimulus (n=15), 14.8 (10.7-65.8). The assay measured canine serum IL-10 reliably (intra- and interassay imprecision 4.9-8.3% and 9.9-10.9%, respectively; detection limit 10.7 ng/L with no significant inaccuracy). No significant increases in IL-10 were observed following surgical stimulus and no difference in IL-10 was observed between the diagnostic groups. IL-10 values showed a higher degree of variation in dogs with an inflammatory response, i.e. those with elevated serum C-reactive protein (CRP) concentrations, compared to healthy dogs. As anticipated, healthy dogs had low levels of both analytes, whereas dogs with an acute phase response had IL-10 levels with no clear relationship to CRP concentrations, with observed low IL-10 values even when there was a marked inflammatory response.

Present status and perspectives of bioartificial kidneys

Currently, hemodialysis is not adequate as a renal replacement therapy because it provides intermittent treatment and does not provide the metabolic function of renal tubules. The next generation of artificial kidney should replace intermittent hemodialysis with continuous hemofiltration and provide the full metabolic function of renal tubules. The current decade has witnessed the development of bioartificial kidneys using artificial membranes and renal tubular epithelial cells. Active transport and metabolic functions were confirmed in the confluent monolayers of tubular cells on artificial membranes. Bioartificial kidneys have succeeded in improving the prognosis of patients with multiple organ dysfunction, presumably by lowering plasma cytokine levels in patients. For successful treatment of chronic renal failure using bioartificial kidneys, it is necessary to overcome some technical hurdles such as improving the antithrombogenic properties of the surface of artificial membranes and prolonging the function of renal tubule cells on an artificial membrane. Transfection of functional protein genes into renal tubule cells enables bioartificial tubule devices to increase their transport capacity and metabolic functions such as digoxin secretion and water transport. The development of wearable roller pumps is also essential for the clinical application of a continuous treatment system.

The future of hemodialysis membranes

Hemodialytic treatment of patients with either acute or chronic renal failure has had a dramatic impact on the mortality rates of these patients. Unfortunately, this membrane-based therapy is still incomplete renal replacement, as the mortality and morbidity of these patients remain unacceptably high. Much progress must be made to improve the biocompatibility of hemodialysis membranes as well as their hydraulic and permselective properties to remove small solutes and 'middle molecules' in compact cartridges. The next directions of development will leverage materials and mechanical engineering technology, including microfluidics and nanofabrication, to further improve the clearance functions of the kidney to replicate glomerular permselectivity while retaining high rates of hydraulic permeability. The extension of membrane technology to biohybrid devices utilizing progenitor/stem cells will be another substantive advance for renal replacement therapy. The ability to not only replace solute and water clearance but also active reabsorptive transport and metabolic activity will add additional benefit to the therapy of patients suffering from renal failure. This area of translational research is rich in creative opportunities to improve the unmet medical needs of patients with either chronic or acute renal failure.

Differentiated Growth of Human Renal Tubule Cells on Thin-Film and Nanostructured Materials

Over 300,000 Americans are dependent on hemodialysis as treatment for renal failure, and kidney transplantation is limited by scarcity of donor organs. This shortage has prompted research into tissue engineering of renal replacement therapy. Existing bioartificial kidneys are large and their use labor intensive, but they have shown improved survival compared to conventional therapy in preclinical studies and an US Food and Drug Administration-approved phase 2 clinical trial. This hybrid technology will require miniaturization of hemofilters, cell culture substrates, sensors, and integration of control electronics. Using the same harvesting and isolation techniques used in preparing bioartificial kidneys for clinical use, we characterized human renal tubule cell growth on a variety of silicon and related thin-film material substrates commonly used in the construction of microelectromechanical systems (MEMS), as well as novel silicon nanopore membranes (SNMs). Human cortical tubular epithelial cells (HCTC) were seeded onto samples of single-crystal silicon, polycrystalline silicon, silicon dioxide, silicon nitride, SU-8 photoresist, SNMs, and polyester tissue culture inserts, and grown to confluence. The cells formed confluent monolayers with tight junctions and central cilia. Transepithelial resistances were similar between SNMs and polyester membranes. The differentiated growth of human tubular epithelial cells on MEMS materials strongly suggests that miniaturization of the existing bioartificial kidney will be feasible, paving the way for widespread application of this novel technology.

Stem cell approaches for the treatment of renal failure

The inadequacy of current treatment modalities and insufficiency of donor organs for cadaveric transplantation have driven a search for improved methods of dealing with renal failure. The rising concept of cell-based therapeutics has provided a framework around which new approaches are being generated, and its combination with advances in stem cell research stands to bring both fields to clinical fruition. This budding partnership is presently in its very early stages, but an examination of the cell-based therapies currently under development clearly shows the magnitude of the role that stem cells will ultimately play. The issue over reports of unexpected plasticity in adult stem cell differentiation remains a focus of debate, and evidence for bone marrow-derived stem cell contributions to renal repair has been challenged. The search for adult renal stem cells, which could have a considerable impact on much of the work discussed here, appears to be narrowing. The use of embryonic tissue in research continues to provide valuable insights but will be the subject of intense societal scrutiny and debate before it reaches the stage of clinical application. Embryonic stem (ES) cells, with their ability to generate all, or nearly all, of the cell types in the adult body and a possible source of cells genetically identical to the donor, hold great promise but face ethical and political hurdles for human use. Immunoisolation of heterologous cells by encapsulation creates opportunities for their safe use as a component of implanted or ex vivo devices.

Renal replacement therapy and acute renal failure

PURPOSE OF REVIEW

Acute renal failure (ARF) is a syndrome that occurs when there is a sudden decline in the glomerular filtration rate. The purpose of this review is to examine new developments and clinical applications of renal replacement therapies including hemodialysis, continuous renal replacement therapy, the bioartificial kidney, and peritoneal dialysis in the management of this complicated syndrome.

RECENT FINDINGS

New developments in hemodialysis include in-line hematocrit monitoring and improved biocompatible dialyzer membranes. While recent studies indicate that increased delivery of dialysis improves the outcome of patients with ARF, the optimal regimen of intermittent dialysis or continuous renal replacement therapy remains to be determined. The bioartificial kidney, combining hemofiltration with a device containing human tubular cells, is currently in clinical trials and represents another alternative in the management of ARF. In peritoneal dialysis, new solutions using icodextrin may improve fluid removal and blood pressure.

SUMMARY

The optimal choice of renal replacement therapy depends on many factors. Use of new options in renal replacement therapy and early initiation of dialysis may help to improve survival and outcome of patients with ARF.

The Future of Renal Support: High-Flux Dialysis to Bioartificial Kidneys

Renal failure continues to cause a major burden of morbidity and mortality in both its acute and chronic forms, regardless of advances in current renal replacement therapies. A bioartificial kidney that includes a conventional dialysis filter and a renal tubule assist device containing approximately 10(8) renal proximal tubule cells was recently successfully engineered. This therapeutic modality may decrease the survival gap between current renal replacement therapies and healthy kidney functions and may lessen the heavy burden of morbidity and mortality associated with renal failure, both acute and chronic, in the near future.

Sepsis and the Kidney

Acute renal failure (ARF) secondary to sepsis is a highly prevalent diagnosis in the ICU setting and continues to be associated with a high rate of morbidity and mortality. The pathophysiology of sepsis-induced acute renal failure involves ischemic or toxic injury to the renal tubular epithelia, resulting in necrosis or apoptosis, and clinically is characterized as acute tubular necrosis. The management of sepsis-induced ARF includes both conventional intermittent hemodialysis and continuous renal replacement therapies. Experimental therapies to improve outcomes in sepsis-associated ARF include the provision of plasmapheresis and adsorption therapies, and the recent development and deployment of a renal tubule assist device.

Initial clinical results of the bioartificial kidney containing human cells in ICU patients with acute renal failure

BACKGROUND

Acute renal failure (ARF) in intensive care unit patients continues to have mortality rates exceeding 70%, despite hemodialysis or continuous renal replacement therapy (CRRT). The delivery of cellular metabolic function to CRRT may provide more complete renal replacement therapy, thereby changing the natural history of this disease process. An FDA-approved Phase I/II clinical trial on 10 patients has been completed, and demonstrated that this experimental treatment can be delivered safely for up to 24 hours.

METHODS

The bioartificial kidney is a synthetic hemofilter connected in series with a bioreactor cartridge containing approximately 10(9) human proximal tubule cells, as a renal tubule assist device (RAD), within an extracorporeal perfusion circuit utilizing standard hemofiltration pump systems. All 10 patients had ARF and multiorgan failure (MOF), with predicted hospital mortality rates averaging above 85%.

RESULTS

Data indicate that the RAD maintains viability, durability, and functionality in this ex vivo clinical setting. The device also demonstrated differentiated metabolic and endocrinologic activity, with glutathione degradation and endocrinologic conversion of 25-OH-D(3) to 1,25-(OH)(2)-D(3). All but one treated patient with more than a 3-day follow-up in the intensive care unit showed improvement as assessed by acute physiologic scores 1 to 7 days following therapy. Six of the 10 treated patients survived past 30 days. One patient expired within 12 hours after RAD treatment due to his family's request to withdraw ventilatory life support. Three other patients died due to complications from acute or chronic comorbidities unrelated to ARF or RAD therapy. Plasma cytokine levels suggest that RAD therapy produced dynamic and individualized responses in patients. For the subset of patients who had excessive proinflammatory levels, RAD treatment resulted in significant declines in granulocyte colony stimulating factor (G-CSF), interleukin (IL)-6, IL-10, and IL-6/IL-10 ratios.

CONCLUSION

The addition of human renal tubule cell therapy to CRRT has been accomplished and demonstrates metabolic activity with systemic effects in patients with ARF and MOF. These initial clinical results are encouraging, so that a randomized, controlled Phase II clinical trial is underway to further assess the clinical safety and efficacy of this new therapeutic approach.

N-acetylcysteine in the prevention of radiocontrast-induced nephropathy: clinical trials and end points

N-acetylcysteine (NAC) has been suggested to prevent radiocontrast-induced nephropathy (RCIN) in patients with a reduced renal function. However, clinical studies have not been demonstrating this effect consistently. Also, reviews and meta-analyses dealing with the question of prevention of RCIN by NAC have been controversial. Nearly all investigators used serum creatinine as surrogate end point of their trials, and changes in serum creatinine concentrations are thought to reflect the extent of renal injury as primary outcome. In a recent study, an effect of NAC on creatinine values and estimated glomerular filtration rate without any effect on cystatin C levels has been shown in volunteers with a normal renal function. Therefore, before renal protective effects of NAC in RCIN are proposed, any direct effects of NAC on creatinine, urea, and estimated glomerular filtration rate should be addressed. In future trials, the glomerular filtration rate should preferentially be measured directly, or at least additional markers of the renal function (e.g., serum cystatin C) have to be assessed. Furthermore, additional 'hard' end points, i.e., hospital morbidity, mortality, or dialysis dependency, should be considered in the design of future studies of RCIN.