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

Current Status and Future of Artificial Kidney in Humans

The number of patients needing renal replacement therapy (RRT) is increasing rapidly with an increase in lifestyle diseases such as diabetes, hypertension, and metabolic syndrome. Kidney transplantation, whenever feasible, is the most preferred mode of RRT. However, there is a growing shortage of donor kidneys for transplantation. While dialysis is partially able to perform the filtration and excretion function of the kidneys, it is still not able to perform the other renal tubular and endocrine functions of a normal kidney and has quality-of-life issues with significant long-term morbidity. The need of the hour is to develop an ideal artificial kidney that would be wearable or implantable and would be able to perform the complete excretory, filtration, tubular, endocrine, and metabolic functions of the kidney while preserving the quality of life and minimizing complications. In this review, we discuss the characteristics of an ideal artificial kidney, the challenges of developing such a device, a brief description of the past and current work on this topic, and what the artificial kidney of the future should look like.

Novel strategies in nephrology: what to expect from the future?

Chronic kidney disease (CKD) will become the fifth global case of death by 2040. Its largest impact is on premature mortality but the number of persons with kidney failure requiring renal replacement therapy (RRT) is also increasing dramatically. Current RRT is suboptimal due to the shortage of kidney donors and dismal outcomes associated with both hemodialysis and peritoneal dialysis. Kidney care needs a revolution. In this review, we provide an update on emerging knowledge and technologies that will allow an earlier diagnosis of CKD, addressing the current so-called blind spot (e.g. imaging and biomarkers), and improve renal replacement therapies (wearable artificial kidneys, xenotransplantation, stem cell-derived therapies, bioengineered and bio-artificial kidneys).

Exogenous Biological Renal Support Improves Kidney Function in Mice With Rhabdomyolysis-Induced Acute Kidney Injury

Background: Rhabdomyolysis (RM) is a clinical syndrome characterized by breakdown of skeletal muscle fibers and release of their contents into the circulation. Myoglobin-induced acute kidney injury (AKI) is one of the most severe complications of RM. Based on our previous research, exogenous biological renal support alleviates renal ischemia–reperfusion injury in elderly mice. This study aimed to determine whether exogenous biological renal support promotes renal recovery from RM-induced AKI and to preliminarily explore the mechanisms involved.

Methods: A parabiosis animal model was established to investigate the effects of exogenous biological renal support on RM-induced AKI. Mice were divided into three groups: the control group (in which mice were injected with sterile saline), the RM group (in which mice were injected with 8 mL/kg glycerol), and the parabiosis + RM group (in which recipient mice were injected with glycerol 3 weeks after parabiosis model establishment). Blood samples and kidney tissue were collected for further processing 48 h after RM induction. Bioinformatics analysis was conducted via Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis, functional enrichment analysis, and clustering analysis.

Results: No mice died within 48 h after the procedure. Exogenous biological renal support attenuated the histological and functional deterioration in mice with RM-induced AKI. Bioinformatics analysis identified key pathways and proteins involved in this process. We further demonstrated that exogenous biological renal support ameliorated AKI through multiple mechanisms, including by suppressing the complement system; attenuating oxidative stress, inflammation, and cell death; and increasing proliferation.

Conclusions: Exogenous biological renal support provided by parabiosis can improve renal function in RM-induced AKI by suppressing the complement system; decreasing oxidative stress, inflammation, and cell death; and promoting tubular cell proliferation. Our study provides basic research evidence for the use of bioartificial kidneys to treat RM-induced AKI.

Porcine models of acute kidney injury

Pigs represent a potentially attractive model for medical research. Similar body size and physiological patterns of kidney injury that more closely mimic those described in humans make larger animals attractive for experimentation. Using larger animals, including pigs, to investigate the pathogenesis of acute kidney injury (AKI) also serves as an experimental bridge, narrowing the gap between clinical disease and preclinical discoveries. This article compares the advantages and disadvantages of large versus small AKI animal models and provides a comprehensive overview of the development and application of porcine models of AKI induced by clinically relevant insults, including ischemia-reperfusion, sepsis, and nephrotoxin exposure. The primary focus of this review is to evaluate the use of pigs for AKI studies by current investigators, including areas where more information is needed.

Exogenous biological renal support ameliorates renal pathology after ischemia reperfusion injury in elderly mice

We established an exogenous biological renal support model through the generation of parabiotic mice. At 72 hours after ischemia reperfusion injury (IRI), the aged mice that received exogenous biological renal support showed significantly higher levels of renal cell proliferation and dedifferentiation, lower levels of renal tubular injury, improved renal function, and a lower mortality than those that did not receive exogenous biological renal support. Using the Quantibody Mouse Cytokine Antibody Array, we found that aged IRI mice that received exogenous biological renal support had an up-regulation of multiple inflammatory related cytokines compared to the group that did not receive exogenous biological renal support. We suggest that the exogenous biological renal support might promote renal tubular epithelial cell proliferation and dedifferentiation and improve the prognosis of aged IRI mice. Exogenous biological renal support may play an important role in the amelioration of renal IRI by regulating the expression of multiple cytokines.

Bioengineering Organs for Blood Detoxification

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

Kidney-on-a-chip: untapped opportunities

The organs-on-a-chip technology has shown strong promise in mimicking the complexity of native tissues in vitro and ex vivo, and recently significant advances have been made in applying this technology to studies of the kidney and its diseases. Individual components of the nephron, including the glomerulus, proximal tubule, and distal tubule/medullary collecting duct, have been successfully mimicked using organs-on-a-chip technology and yielding strong promises in advancing the field of ex vivo drug toxicity testing and augmenting renal replacement therapies. Although these models show promise over 2-dimensional cell systems in recapitulating important nephron features in vitro, nephron functions, such as tubular secretion, intracellular metabolism, and renin and vitamin D production, as well as prostaglandin synthesis are still poorly recapitulated in on-chip models. Moreover, construction of multiple-renal-components-on-a-chip models, in which various structures and cells of the renal system interact with each other, has remained a challenge. Overall, on-chip models show promise in advancing models of normal and pathological renal physiology, in predicting nephrotoxicity, and in advancing treatment of chronic kidney diseases.

Bioengineering in renal transplantation: technological advances and novel options

End-stage kidney disease (ESKD) is one of the most prevalent diseases in the world with significant morbidity and mortality. Current modes of renal replacement therapy include dialysis and renal transplantation. Although dialysis is an acceptable mode of renal replacement therapy, it does have its shortcomings, which include poorer life expectancy compared with renal transplantation, risk of infections and vascular thrombosis, lack of vascular access and absence of biosynthetic functions of the kidney. Renal transplantation, in contrast, is the preferred option of renal replacement therapy, with improved morbidity and mortality rates and quality of life, compared with dialysis. Renal transplantation, however, may not be available to all patients with ESKD. Some of the key factors limiting the availability and efficiency of renal transplantation include shortage of donor organs and the constant risk of rejection with complications associated with over-immunosuppression respectively. This review focuses chiefly on the potential roles of bioengineering in overcoming limitations in renal transplantation via the development of cell-based bioartificial dialysis devices as bridging options before renal transplantation, and the development of new sources of organs utilizing cell and organ engineering.

From portable dialysis to a bioengineered kidney

INTRODUCTION

Since the advent of peritoneal dialysis (PD) in the 1970s, the principles of dialysis have changed little. In the coming decades, several major breakthroughs are expected.

AREAS COVERED

Novel wearable and portable dialysis devices for both hemodialysis (HD) and PD are expected first. The HD devices could facilitate more frequent and longer dialysis outside of the hospital, while improving patient's mobility and autonomy. The PD devices could enhance blood purification and increase technique survival of PD. Further away from clinical application is the bioartificial kidney, containing renal cells. Initially, the bioartificial kidney could be applied for extracorporeal treatment, to partly replace renal tubular endocrine, metabolic, immunoregulatory and secretory functions. Subsequently, intracorporeal treatment may become possible.

EXPERT COMMENTARY

Key factors for successful implementation of miniature dialysis devices are patient attitudes and cost-effectiveness. A well-functioning and safe extracorporeal blood circuit is required for HD. For PD, a double lumen PD catheter would optimize performance. Future research should focus on further miniaturization of the urea removal strategy. For the bio-artificial kidney (BAK), cost effectiveness should be determined and a general set of functional requirements should be defined for future studies. For intracorporeal application, water reabsorption will become a major challenge.

Bioengineered Renal Cell Therapy Device for Clinical Translation

The bioartificial renal epithelial cell system (BRECS) is a cell-based device to treat acute kidney injury through renal cell therapy from an extracorporeal circuit. To enable widespread implementation of cell therapy, the BRECS was designed to be cryopreserved as a complete device, cryostored, cryoshipped to an end-use site, thawed as a complete device, and employed in a therapeutic extracorporeal hemofiltration circuit. This strategy overcomes storage and distribution issues that have been previous barriers to cell therapy. Previous BRECS housings produced by computer numerical control (CNC) machining, a slow process taking hours to produce one bioreactor, was also prohibitively expensive (>$600/CNC-BRECS); major obstacles to mass production. The goal of this study was to produce a BRECS to be mass produced by injection-molded BRECS (IM-BRECS), decreasing cost (<$20/unit), and improving manufacturing speed (hundreds of units/h), while maintaining the same cell therapy function as the previous CNC-BRECS, first evaluated through prototypes produced by stereolithography BRECS (SLA-BRECS). The finalized IM-BRECS design had a significantly lower fill volume (10 ml), mass (49 g), and footprint (8.5 cm × 8.5 cm × 1.5 cm), and was demonstrated to outperform the previous BRECS designs with respect to heat transfer, significantly improving control of cooling during cryopreservation and reducing thaw times during warming. During in vitro culture, IM-BRECS performed similarly to previous CNC-BRECS with respect to cell metabolic activity (lactate production, oxygen consumption, and glutathione metabolism) and amount of cells supported.

Human proximal tubule epithelial cells cultured on hollow fibers: living membranes that actively transport organic cations

The bioartificial kidney (BAK) aims at improving dialysis by developing ‘living membranes’ for cells-aided removal of uremic metabolites. Here, unique human conditionally immortalized proximal tubule epithelial cell (ciPTEC) monolayers were cultured on biofunctionalized MicroPES (polyethersulfone) hollow fiber membranes (HFM) and functionally tested using microfluidics. Tight monolayer formation was demonstrated by abundant zonula occludens-1 (ZO-1) protein expression along the tight junctions of matured ciPTEC on HFM. A clear barrier function of the monolayer was confirmed by limited diffusion of FITC-inulin. The activity of the organic cation transporter 2 (OCT2) in ciPTEC was evaluated in real-time using a perfusion system by confocal microscopy using 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide (ASP⁺) as a fluorescent substrate. Initial ASP⁺ uptake was inhibited by a cationic uremic metabolites mixture and by the histamine H2-receptor antagonist, cimetidine. In conclusion, a ‘living membrane’ of renal epithelial cells on MicroPES HFM with demonstrated active organic cation transport was successfully established as a first step in BAK engineering.