Functional Evaluation of Primary Renal Cell/Biomaterial Neo-Kidney Augment Prototypes for Renal Tissue Engineering

Advances in pediatric acute kidney injury pathobiology: a report from the 26th Acute Disease Quality Initiative (ADQI) conference

BACKGROUND

In the past decade, there have been substantial advances in our understanding of the pathobiology of pediatric acute kidney injury (AKI). In particular, animal models and studies focused on the relationship between kidney development, nephron number, and kidney health have identified a number of heterogeneous pathophysiologies underlying AKI. Despite this progress, gaps remain in our understanding of the pathobiology of pediatric AKI.

METHODS

During the 26th Acute Disease Quality Initiative (ADQI) Consensus conference, a multidisciplinary group of experts discussed the evidence and used a modified Delphi process to achieve consensus on recommendations for opportunities to advance translational research in pediatric AKI. The current state of research understanding as well as gaps and opportunities for advancement in research was discussed, and recommendations were summarized.

RESULTS

Consensus was reached that to improve translational pediatric AKI advancements, diverse teams spanning pre-clinical to epidemiological scientists must work in concert together and that results must be shared with the community we serve with patient involvement. Public and private research support and meaningful partnerships with adult research efforts are required. Particular focus is warranted to investigate the pediatric nuances of AKI, including the effect of development as a biological variable on AKI incidence, severity, and outcomes.

CONCLUSIONS

Although AKI is common and associated with significant morbidity, the biologic basis of the disease spectrum throughout varying nephron developmental stages remains poorly understood. An incomplete understanding of factors contributing to kidney health, the diverse pathobiologies underlying AKI in children, and the historically siloed approach to research limit advances in the field. The recommendations outlined herein identify gaps and outline a strategic approach to advance the field of pediatric AKI via multidisciplinary translational research.

Renal tissue engineering for regenerative medicine using polymers and hydrogels

Chronic Kidney Disease (CKD) is a growing worldwide problem, leading to end-stage renal disease (ESRD). Current treatments for ESRD include haemodialysis and kidney transplantation, but both are deemed inadequate since haemodialysis does not address all other kidney functions, and there is a shortage of suitable donor organs for transplantation. Research in kidney tissue engineering has been initiated to take a regenerative medicine approach as a potential treatment alternative, either to develop effective cell therapy for reconstruction or engineer a functioning bioartificial kidney. Currently, renal tissue engineering encompasses various materials, mainly polymers and hydrogels, which have been chosen to recreate the sophisticated kidney architecture. It is essential to address the chemical and mechanical aspects of the materials to ensure they can support cell development to restore functionality and feasibility. This paper reviews the types of polymers and hydrogels that have been used in kidney tissue engineering applications, both natural and synthetic, focusing on the processing and formulation used in creating bioactive substrates and how these biomaterials affect the cell biology of the kidney cells used.

Preclinical in vitro evaluation of implantable materials: conventional approaches, new models and future directions

Nowadays, implants and prostheses are widely used to repair damaged tissues or to treat different diseases, but their use is associated with the risk of infection, inflammation and finally rejection. To address these issues, new antimicrobial and anti-inflammatory materials are being developed. Aforementioned materials require their thorough preclinical testing before clinical applications can be envisaged. Although many researchers are currently working on new in vitro tissues for drug screening and tissue replacement, in vitro models for evaluation of new biomaterials are just emerging and are extremely rare. In this context, there is an increased need for advanced in vitro models, which would best recapitulate the in vivo environment, limiting animal experimentation and adapted to the multitude of these materials. Here, we overview currently available preclinical methods and models for biological in vitro evaluation of new biomaterials. We describe several biological tests used in biocompatibility assessment, which is a primordial step in new material's development, and discuss existing challenges in this field. In the second part, the emphasis is made on the development of new 3D models and approaches for preclinical evaluation of biomaterials. The third part focuses on the main parameters to consider to achieve the optimal conditions for evaluating biocompatibility; we also overview differences in regulations across different geographical regions and regulatory systems. Finally, we discuss future directions for the development of innovative biomaterial-related assays: in silico models, dynamic testing models, complex multicellular and multiple organ systems, as well as patient-specific personalized testing approaches.

Selected renal cells harbor nephrogenic potential

Selected renal cells (SRCs), a renal epithelial cell-enriched platform, are being advanced as an autologous cell-based therapy for the treatment of chronic kidney disease. However, the mechanism underlying its renal reparative and restorative effects remains to be fully elucidated. In this study, we coupled knowledgebase data with empirical findings to demonstrate that genes differentially expressed by SRCs form interactomes within tubules and glomeruli and mediate a suite of renal developmental activities including epithelial cell differentiation, renal vasculature development, and glomerular and nephron development. In culture, SRCs form organoids which self-assemble into tubules in the presence of a scaffold. Implanted into the kidneys of subtotally nephrectomized rats, SRCs are associated with comma- and S-shaped body cell formation and glomerular development, and improvement in renal filtration indices and renal microarchitecture. These data suggest that SRCs harbor nephrogenic potential, which may explain, at least in part, their therapeutic activity.

Kidney tissue engineering in preclinical models of renal failure: a systematic review and meta-analysis

Aim: This study aims to compare the efficacy of tissue engineering for kidney reconstruction. Materials & methods: We searched MEDLINE, EMBASE (May 2021), and reference lists of review articles. Results: 19 articles matched our inclusion criteria. A range of natural, synthetic and hybrid scaffolds with or without incorporating cells/growth factors was investigated in 937 animals. More favorable results were observed with a combination of two or more biomaterials, addition of bioactive moieties, and cell seeding. Creatinine concentration, PAX2, collagen type-1, α-SMA, vimentin, IL-1, IL-6 and TNF-α gene expressions were significantly increased compared with native control. Conclusion: Tissue engineering can improve renal function and regeneration; however, further research could benefit from using hybrid scaffolds, stem cells and large animal models.

Renal Autologous Cell Therapy (REACT®) to Stabilize Function in Diabetes-Related Chronic Kidney Disease: Corroboration of Mechanistic Action with Cell Marker Analysis

Introduction

Methods

Results

Conclusion

Identification of functional pathways for regenerative bioactivity of selected renal cells

Background

Selected renal cells (SRC) are in Phase II clinical trials as a kidney-sourced, autologous, tubular epithelial cell-enriched cell-based therapy for chronic kidney disease (CKD). In preclinical studies with rodent models of CKD, SRC have been shown to positively modulate key renal biomarkers associated with development of the chronic disease condition.

Methods

A comparative bioinformatic analysis of transcripts specifically enriched or depleted in SRC component sub-populations relative to the initial, biopsy-derived cell source was conducted.

Results

Outcomes associated with therapeutically relevant bioactivity from a systematic, genome-wide transcriptomic profiling of rodent SRC are reported. Key transcriptomic networks and concomitant signaling pathways that may underlie SRC mechanism of action as manifested by reparative, restorative, and regenerative bioactivity in rodent models of chronic kidney disease are identified. These include genes and gene networks associated with cell cycle control, transcriptional control, inflammation, ECM–receptor interaction, immune response, actin polymerization, regeneration, cell adhesion, and morphogenesis.

Conclusions

These data indicate that gene networks associated with development of the kidney are also leveraged for SRC regenerative bioactivity, providing evidence of potential mechanisms of action.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02713-6.

Measurement of glomerular filtration rate reveals that subcapsular injection of shear-thinning hyaluronic acid hydrogels does not impair kidney function in mice

The continued development of minimally invasive therapeutic implants, such as injectable hydrogels, necessitates the concurrent advancement of methods to best assess their biocompatibility via functional outcomes in vivo. Biomaterial implants have been studied to treat kidney disease; however, assessment of biocompatibility has been limited to biomarker and histological assessments. Techniques now exist to measure kidney function serially in vivo in murine studies via transcutaneous measurements of glomerular filtration rate (tGFR). In this study, adult male and female wild-type BalbC mice underwent right unilateral nephrectomy. The remaining solitary left kidney was allowed 4 weeks to recover via compensatory hypertrophy, after which subcapsular injection of either saline or shear-thinning hyaluronic acid hydrogel was performed. Serial tGFR measurements before and after treatment were used to assess the effect of hydrogel injection on kidney filtration. Urine and serum biomarkers of kidney function, and kidney histology were also quantified. Hydrogel injection did not affect kidney function, as assessed by tGFR. Results were in agreement with standard metrics of serum and urine biomarkers of injury as well as histological assessment of inflammation. The model developed provides a direct functional assessment of implant compatibility for the treatment of kidney disease and impact on kidney function.

Fibrosis in tissue engineering and regenerative medicine: treat or trigger?

Fibrosis is a life-threatening pathological condition resulting from a dysfunctional tissue repair process. There is no efficient treatment and organ transplantation is in many cases the only therapeutic option. Here we review tissue engineering and regenerative medicine (TERM) approaches to address fibrosis in the cardiovascular system, the kidney, the lung and the liver. These strategies have great potential to achieve repair or replacement of diseased organs by cell- and material-based therapies. However, paradoxically, they might also trigger fibrosis. Cases of TERM interventions with adverse outcome are also included in this review. Furthermore, we emphasize the fact that, although organ engineering is still in its infancy, the advances in the field are leading to biomedically relevant in vitro models with tremendous potential for disease recapitulation and development of therapies. These human tissue models might have increased predictive power for human drug responses thereby reducing the need for animal testing.

A Bioinspired Scaffold with Anti-Inflammatory Magnesium Hydroxide and Decellularized Extracellular Matrix for Renal Tissue Regeneration

Kidney diseases are a worldwide public health issue. Renal tissue regeneration using functional scaffolds with biomaterials has attracted a great deal of attention due to limited donor organ availability. Here, we developed a bioinspired scaffold that can efficiently induce renal tissue regeneration. The bioinspired scaffold was designed with poly(lactide-co-glycolide) (PLGA), magnesium hydroxide (Mg(OH)2), and decellularized renal extracellular matrix (ECM). The Mg(OH)2 inhibited materials-induced inflammatory reactions by neutralizing the acidic microenvironment formed by degradation products of PLGA, and the acellular ECM helped restore the biological function of kidney tissues. When the PLGA/ECM/Mg(OH)2 scaffold was implanted in a partially nephrectomized mouse model, it led to the regeneration of renal glomerular tissue with a low inflammatory response. Finally, the PLGA/ECM/Mg(OH)2 scaffold was able to restore renal function more effectively than the control groups. These results suggest that the bioinspired scaffold can be used as an advanced scaffold platform for renal disease treatment.

Implantation of Autologous Selected Renal Cells in Diabetic Chronic Kidney Disease Stages 3 and 4-Clinical Experience of a "First in Human" Study

Introduction

Animal models of chronic kidney disease demonstrate that a redundant population of therapeutically bioactive selected renal cells (SRCs) can be delivered to the kidney through intraparenchymal injection and arrest disease progression. Direct injection of SRCs has been shown to attenuate nuclear factor-κB, which is known to drive tissue inflammation, as well as the transforming growth factor-β-mediated plasminogen activator inhibitor-1 response that drives tissue fibrosis.

Methods

We present experience from the first-in-human clinical study with SRCs. Seven male type 2 diabetic patients (63 ± 2 years of age) with chronic kidney disease stage 3 to 4 (estimated glomerular filtration rate 25 ± 2 ml/min) were recruited. After blood and urine sampling, iohexol clearance, magnetic resonance imaging, and renal scintigraphy, patients underwent ultrasound-guided renal biopsy. Two cores of renal tissue were shipped to the manufacturing plant for cell isolation, culture, and product preparation. Formulated SRCs were transported back to study sites (range 59-87 days after biopsy) for intracortical injection using a retroperitoneoscopic technique.

Results

Laparoscopically assisted implantation of SRCs was uneventful in all patients. However, postoperative complications were common and suggest that other techniques of SRC delivery should be used. Kidney volume, split function, and glomerular filtration rate did not change during 12 months of follow-up. An extended 24-month follow-up in 5 of the patients showed a decline in estimated glomerular filtration rate (cystatin C).

Discussion

Postoperative complications following retroperitoneoscopic implantation of SRC in the kidney cortex seem to be related to the surgical procedure rather than to injection of the cell product. No changes in renal function were observed during the original 12-month protocol. Beyond the first 12 months after cell implantation, individual renal function began to deteriorate during further follow-up.

Selected renal cells modulate disease progression in rodent models of chronic kidney disease via NF-κB and TGF-β1 pathways

AIM

Identification of mechanistic pathways for selected renal cell (SRC) therapeutic bioactivity in rodent models of chronic kidney disease.

MATERIALS & METHODS

In vivo and in vitro functional bioassays applied to investigate regenerative outcomes associated with delivery of SRC to diseased rodent kidney.

RESULTS

In vivo, SRC reduces chronic infiltration by monocytes/macrophages. SRC attenuates NF-κB and PAI-1 responses while simultaneously promoting host tubular cell expansion through trophic cues. In vitro, SRC-derived conditioned media attenuates TNF-α-induced NF-κB response, TGF-β-mediated PAI-1 response and increases expression of transcripts associated with cell cycle regulation. Observed bioactive responses were from vesicle and nonvesicle-associated factors, including specific miRNAs.

CONCLUSION

We identify a paracrine mechanism for SRC immunomodulatory and trophic cues on host renal tissues, catalyzing long-term functional benefits in vivo.

Cell-based therapeutic products: potency assay development and application

Potency is a critical quality attribute of biological products, defined by the US FDA as the specific ability or capacity of the product, as indicated by appropriate laboratory tests or by adequately controlled clinical data obtained through the administration of the product in the manner intended, to effect a given result. Ideally, a potency assay will leverage the product's mechanism of action. Alternatively, the assay may focus on a therapeutically relevant biological activity. The absence of rigorous mechanistic data for the majority of cell-based therapeutics currently in the process research pipeline has impeded efforts to design and validate indices of product potency. Development of a systematic battery of parallel functional assays that, taken together, can address all potential mechanisms of action believed to be relevant for the product platform is recommended. Such an approach is especially important during preclinical development. Here, we summarize the principal and unique challenges facing the development of functionally relevant and rigorous potency assays for cell-based therapeutics. We present perspectives regarding potency assay development for these products as illustrated by our experiences in process R&D of cryopreserved hepatocytes (Incara Pharmaceuticals) and selected renal cells (Tengion).

Cell-based therapy approaches: the hope for incurable diseases

Cell therapies aim to repair the mechanisms underlying disease initiation and progression, achieved through trophic effect or by cell replacement. Multiple cell types can be utilized in such therapies, including stem, progenitor or primary cells. This review covers the current state of cell therapies designed for the prominent disorders, including cardiovascular, neurological (Parkinson's disease, amyotrophic lateral sclerosis, stroke, spinal cord injury), autoimmune (Type 1 diabetes, multiple sclerosis, Crohn's disease), ophthalmologic, renal, liver and skeletal (osteoarthritis) diseases. Various cell therapies have reached advanced clinical trial phases with potential marketing approvals in the near future, many of which are based on mesenchymal stem cells. Advances in pluripotent stem cell research hold great promise for regenerative medicine. The information presented in this review is based on the analysis of the cell therapy collection detailed in LifeMap Discovery(®) (LifeMap Sciences Inc., USA) the database of embryonic development, stem cell research and regenerative medicine.

Immunotherapy with injectable hydrogels to treat obstructive nephropathy

Hydrogels are gaining attention as injectable vehicles for delivery of therapeutics for a range of applications. We describe self-assembling and injectable Dock-and-Lock hydrogels for local delivery of interleukin-10 (IL-10) to abate the progression of inflammation and fibrosis that leads to chronic kidney disease. As monitored with a fluorescent tag, hydrogels degraded within a few days in vitro and matched IL-10 release profiles; however, hydrogels remained in the kidney for up to 30 days in vivo. A unilateral ureteral obstruction (UUO) mouse model was used to investigate in vivo outcomes after hydrogel injection and IL-10 delivery. Eight groups were investigated (7, 21, 35 days, n = 4): healthy, sham, healthy injected with mouse serum albumin (MSA), healthy + hydrogel, UUO, UUO + IL-10, UUO + hydrogel, UUO + hydrogel/IL-10. 15 μL of IL-10, hydrogel, or hydrogel/IL-10 was injected under the renal capsule 3 days after the UUO. Immunohistochemistry (IHC) was performed on paraffin sections to identify macrophages and apoptotic cells and trichrome staining was used to evaluate fibrosis. There were no significant differences in inflammatory markers between all control groups. With hydrogel delivery, macrophage infiltration and apoptosis were significantly reduced at days 21 and 35 compared to untreated animals. By day 35, IL-10 delivery via hydrogel reduced macrophage infiltration and apoptosis more than IL-10 injection alone. Fibrosis was decreased by day 35 in all treatment groups. This work supports the use of hydrogel delivery of IL-10 to treat chronic kidney disease.

Care of rodent models used for preclinical evaluation of tissue-engineered/regenerative medicine product candidates

The pre-, peri-, and postoperative care of animal surgical models used for testing tissue engineering/regenerative medicine product candidates includes the thoughtful consideration of several important factors. It must ensure the health and comfort of the animals and the success and reproducibility of the model. In order to reduce the number of animals needed in creating the model and to reduce costs, a preliminary evaluation of surgical procedures and instruments should be performed on cadavers. Once a minimal level of proficiency has been acquired, non-survival surgeries should be executed successfully before attempting survival surgeries. Planning ahead is crucial and will involve all aspects of the animal's care such as allowing the animal to become accustomed to soft foods (as in the case of gastrointestinal surgeries), planning appropriate pain management, and the use of positive reinforcement. We present specific examples of pre-, peri- and post-operative care of rodents using our experiences in developing tissue engineering products for kidney, esophagus, small intestine and lung.

Formulation of selected renal cells for implantation into a kidney

Delivery of cells to organs has primarily relied on formulating the cells in a nonviscous liquid carrier. We have developed a methodology to isolate selected renal cells (SRC) that have provided functional stability to damaged kidneys in preclinical models (Kelley et al. Poster presentation at 71st scientific sessions of American diabetes association , 2011; Kelley et al. Oral presentation given at Tissue Engineering and Regenerative Medicine International Society (TERMIS)-North America annual conference, 2010; Presnell et al. Tissue Eng Part C Methods 17:261-273, 2011; Kelley et al. Am J Physiol Renal Physiol 299:F1026-F1039, 2010). In order to facilitate SRC injection into the kidney of patients who have chronic kidney disease, we have developed a strategy to immobilize the cells in a hydrogel matrix. This hydrogel (gelatin) supports cells by maintaining them in a three-dimensional state during storage and shipment (both at cold temperatures) while facilitating the delivery of cells by liquefying when engrafting into the kidney. This chapter will define a method for the formulation of the kidney epithelial cells within a hydrogel.

Preparation and evaluation of natural scaffold materials for kidney regenerative applications

Tissue engineering involves the concerted action of biomaterials, cells, and growth factors. Kidney -regeneration relies on the same combination of ingredients. Here, we describe an example of gelatin-based biomaterial preparation and its evaluation in the context of kidney biocompatibility and integration. This biomaterial manufacturing technique is simple, cost-effective, highly reproducible and the in vivo evaluation procedure highly informative on the biocompatibility and regenerative potential of the tested construct.

Phenotypic analysis of bioactive cells for application in regenerative medicine

The following chapter outlines methodologies to phenotypically characterize primary cells for the use in tissue-engineered and regenerative medicine applications. Methods covered include analyzing cells using immunocytochemistry, fluorescence-activated cell sorting, and confocal microscopy of adherent and suspended cells, as well as combinations of formulated cell-biomaterial constructs.

Delivery of EPC embedded in HA-hydrogels for treatment of acute kidney injury

Adoptive transfer of stem cells has shown potential as an effective treatment for acute kidney injury (AKI). The current strategy for adoptive transfer of stem cells is by intravenous injection. However, this conventional method of stem cell delivery is riddled with problems causing reduced efficacy of the therapeutic potential of delivered stem cells. This review summarizes the recent advancements in an alternative method of stem cell delivery for treatment of AKI, embedding stem cells in hyaluronic acid (HA-) based hydrogels followed by their implantation. Furthermore, one stem cell type in particular, endothelial progenitor cells (EPC), have shown remarkable therapeutic benefits for treatment of AKI when delivered by HA-hydrogels. The review also summarizes the delivery of EPC by HA-hydrogels in the setting of AKI.

A population of selected renal cells augments renal function and extends survival in the ZSF1 model of progressive diabetic nephropathy

New treatment paradigms that slow or reverse progression of chronic kidney disease (CKD) are needed to relieve significant patient and healthcare burdens. We have shown that a population of selected renal cells (SRCs) stabilized disease progression in a mass reduction model of CKD. Here, we further define the cellular composition of SRCs and apply this novel therapeutic approach to the ZSF1 rat, a model of severe progressive nephropathy secondary to diabetes, obesity, dyslipidemia, and hypertension. Injection of syngeneic SRCs into the ZSF1 renal cortex elicited a regenerative response that significantly improved survival and stabilized disease progression to renal structure and function beyond 1 year posttreatment. Functional improvements included normalization of multiple nephron structures and functions including glomerular filtration, tubular protein handling, electrolyte balance, and the ability to concentrate urine. Improvements to blood pressure, including reduced levels of circulating renin, were also observed. These functional improvements following SRC treatment were accompanied by significant reductions in glomerular sclerosis, tubular degeneration, and interstitial inflammation and fibrosis. Collectively, these data support the utility of a novel renal cell-based approach for slowing renal disease progression associated with diabetic nephropathy in the setting of metabolic syndrome, one of the most common causes of end-stage renal disease.

Developmental engineering the kidney: leveraging principles of morphogenesis for renal regeneration

Multiple methodological approaches are currently under active development for application in tissue engineering and regenerative medicine of tubular and solid organs. Most recently, developmental engineering (TE/RM), or the leveraging of embryonic and morphological paradigms to recapitulate aspects of organ development, has been proposed as a strategy for the sequential, iterative de novo assembly of tissues and organs as discrete developmental modules ex vivo, prior to implantation in vivo. In this article, we focus on the kidney to highlight in detail how principles of developmental biology are impacting approaches to TE of this complex solid organ. Ultimately, such methodologies may facilitate the establishment of clinically relevant therapeutic strategies for regeneration of renal structure and function, greatly impacting treatment regimens for chronic kidney disease.

Organ specific regenerative markers in peri-organ adipose: kidney

Background

Therapeutically bioactive cell populations are currently understood to promote regenerative outcomes in vivo by leveraging mechanisms of action including secretion of growth factors, site specific engraftment and directed differentiation. Constitutive cellular populations undoubtedly participate in the regenerative process. Adipose tissue represents a source of therapeutically bioactive cell populations. The potential of these cells to participate in various aspects of the regenerative process has been demonstrated broadly. However, organ association of secretory and developmental markers to specific peri-organ adipose depots has not been investigated. To characterize this topographical association, we explored the potential of cells isolated from the stromal vascular fraction (SVF) of kidney sourced adipose to express key renal associated factors.

Results

We report that renal adipose tissue is a novel reservoir for EPO expressing cells. Kidney sourced adipose stromal cells demonstrate hypoxia regulated expression of EPO and VEGF transcripts. Using iso-electric focusing, we demonstrate that kidney and non-kidney sourced adipose stromal cells present unique patterns of EPO post-translational modification, consistent with the idea that renal and non-renal sources are functionally distinct adipose depots. In addition, kidney sourced adipose stromal cells specifically express the key renal developmental transcription factor WT1.

Conclusions

Taken together, these data are consistent with the notion that kidney sourced adipose stromal (KiSAS) cells may be primed to recreate a regenerative micro-environment within the kidney. These findings open the possibility of isolating solid-organ associated adipose derived cell populations for therapeutic applications in organ-specific regenerative medicine products.