Extracellular matrix scaffolds as a platform for kidney regeneration.

Chronic and end stage renal disease (ESRD) have reached pandemic levels and pose a substantial public health burden. Unfortunately, available therapies lack efficacy in preventing progression to its end stage phase. Regenerative medicine promises to restore function of diseased organs among which the kidney, through two possible approaches: firstly, the maximization of the innate ability of tissues to repair or regenerate following injury; secondly, the ex vivo bio-fabrication of the organ in question. When regenerative medicine is applied to the setting of chronic or ESRD, it is intuitive that endeavors to improve renal repair, promote nephrogenesis in damaged kidneys, or the de novo engineering of transplantable kidneys, could have a major impact on the current management of this pandemic. Among the different regenerative medicine technologies currently under development, cell-on-scaffold seeding technology (CSST) - involving cells seeded throughout supporting scaffold structures made from biomaterials - is the most favorable candidate in the context of realistic clinical application. In this review, we outline and describe current investigations taking place in the field of CSST as it pertains to the restoration of kidney function.

Kidney transplantation, bioengineering and regeneration: an originally immunology-based discipline destined to transition towards ad hoc organ manufacturing and repair.

Kidney transplantation (KT), as a modality of renal replacement therapy (RRT), has been shown to be both economically and functionally superior to dialysis for the treatment of end-stage renal disease (ESRD). Progress in KT is limited by two major barriers: a) a chronic and burgeoning shortage of transplantable organs and b) the need for chronic immunosuppression following transplantation. Although ground-breaking advances in transplant immunology have improved patient survival and graft durability, a new pathway of innovation is needed in order to overcome current obstacles. Regenerative medicine (RM) holds the potential to shift the paradigm in RRT, through organ bioengineering. Manufactured organs represent a potentially inexhaustible source of transplantable grafts that would bypass the need for immunosuppressive drugs by using autologous cells to repopulate extracellular matrix (ECM) scaffolds. This overview discusses the current status of renal transplantation while reviewing the most promising innovations in RM therapy as applied to RRT.

The Human Pancreas as a Source of Protolerogenic Extracellular Matrix Scaffold for a New-generation Bioartificial Endocrine Pancreas.

OBJECTIVES: Our study aims at producing acellular extracellular matrix scaffolds from the human pancreas (hpaECMs) as a first critical step toward the production of a new-generation, fully human-derived bioartificial endocrine pancreas. In this bioartificial endocrine pancreas, the hardware will be represented by hpaECMs, whereas the software will consist in the cellular compartment generated from patient's own cells. BACKGROUND: Extracellular matrix (ECM)-based scaffolds obtained through the decellularization of native organs have become the favored platform in the field of complex organ bioengineering. However, the paradigm is now switching from the porcine to the human model. METHODS: To achieve our goal, human pancreata were decellularized with Triton-based solution and thoroughly characterized. Primary endpoints were complete cell and DNA clearance, preservation of ECM components, growth factors and stiffness, ability to induce angiogenesis, conservation of the framework of the innate vasculature, and immunogenicity. Secondary endpoint was hpaECMs' ability to sustain growth and function of human islet and human primary pancreatic endothelial cells. RESULTS: Results show that hpaECMs can be successfully and consistently produced from human pancreata and maintain their innate molecular and spatial framework and stiffness, and vital growth factors. Importantly, hpaECMs inhibit human naïve CD4 T-cell expansion in response to polyclonal stimuli by inducing their apoptosis and promoting their conversion into regulatory T cells. hpaECMs are cytocompatible and supportive of representative pancreatic cell types. DISCUSSION: We, therefore, conclude that hpaECMs has the potential to become an ideal platform for investigations aiming at the manufacturing of a regenerative medicine-inspired bioartificial endocrine pancreas.

The efficacy and safety of mammalian target of rapamycin inhibitors ab initio after liver transplantation without corticosteroids or induction therapy.

BACKGROUND: Mammalian target of rapamycin inhibitors have been used along with corticosteroids and/or induction therapy immediately after liver transplantation. Our aim was to assess the safety and tolerability of everolimus ab initio after liver transplantation without corticosteroids or induction, as well as efficacy in terms of liver function, rejection and graft loss. METHODS: A retrospective observational study of 50 adult patients (86% males, median age 54 years, range 25-68) who were liver transplanted between 2009 and 2013 and followed for 12 months. All recipients received everolimus plus low doses of calcineurin inhibitors (n=38) or mycophenolate (n=12) without corticosteroids and/or induction from the day of transplant. RESULTS: The overall patient and graft survival was 80%. Liver function was stable during one year follow-up. No rejections or graft loss were observed. Only five patients (10%) required therapy for onset dyslipidemia. CONCLUSION: Everolimus-based immunosuppression regimen without corticosteroids and/or induction immediately after liver transplantation seems to be safe and effective when administered with low doses of calcineurin-inhibitor or mycophenolate; although these findings require further investigation, these regimens could avoid adverse effects of standard immunosuppression regimens with higher doses.

Heterogeneity of Scaffold Biomaterials in Tissue Engineering.

Tissue engineering (TE) offers a potential solution for the shortage of transplantable organs and the need for novel methods of tissue repair. Methods of TE have advanced significantly in recent years, but there are challenges to using engineered tissues and organs including but not limited to: biocompatibility, immunogenicity, biodegradation, and toxicity. Analysis of biomaterials used as scaffolds may, however, elucidate how TE can be enhanced. Ideally, biomaterials should closely mimic the characteristics of desired organ, their function and their in vivo environments. A review of biomaterials used in TE highlighted natural polymers, synthetic polymers, and decellularized organs as sources of scaffolding. Studies of discarded organs supported that decellularization offers a remedy to reducing waste of donor organs, but does not yet provide an effective solution to organ demand because it has shown varied success in vivo depending on organ complexity and physiological requirements. Review of polymer-based scaffolds revealed that a composite scaffold formed by copolymerization is more effective than single polymer scaffolds because it allows copolymers to offset disadvantages a single polymer may possess. Selection of biomaterials for use in TE is essential for transplant success. There is not, however, a singular biomaterial that is universally optimal.

Tissue-Engineering Approaches to Restore Kidney Function.

Kidney transplantation for the treatment of chronic kidney disease has established outcome and quality of life. However, its implementation is severely limited by a chronic shortage of donor organs; consequently, most candidates remain on dialysis and on the waiting list while accruing further morbidity and mortality. Furthermore, those patients that do receive kidney transplants are committed to a life-long regimen of immunosuppressive drugs that also carry significant adverse risk profiles. The disciplines of tissue engineering and regenerative medicine have the potential to produce alternative therapies which circumvent the obstacles posed by organ shortage and immunorejection. This review paper describes some of the most promising tissue-engineering solutions currently under investigation for the treatment of acute and chronic kidney diseases. The various stem cell therapies, whole embryo transplantation, and bioengineering with ECM scaffolds are outlined and summarized.

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.

Biocompatibility and characterization of a peptide amphiphile hydrogel for applications in peripheral nerve regeneration.

Peripheral nerve injury is a debilitating condition for which new bioengineering solutions are needed. Autografting, the gold standard in treatment, involves sacrifice of a healthy nerve and results in loss of sensation or function at the donor site. One alternative solution to autografting is to use a nerve guide conduit designed to physically guide the nerve as it regenerates across the injury gap. Such conduits are effective for short gap injuries, but fail to surpass autografting in long gap injuries. One strategy to enhance regeneration inside conduits in long gap injuries is to fill the guide conduits with a hydrogel to mimic the native extracellular matrix found in peripheral nerves. In this work, a peptide amphiphile (PA)-based hydrogel was optimized for peripheral nerve repair. Hydrogels consisting of the PA C16GSH were compared with a commercially available collagen gel. Schwann cells, a cell type important in the peripheral nerve regenerative cascade, were able to spread, proliferate, and migrate better on C16GSH gels in vitro when compared with cells seeded on collagen gels. Moreover, C16GSH gels were implanted subcutaneously in a murine model and were found to be biocompatible, degrade over time, and support angiogenesis without causing inflammation or a foreign body immune response. Taken together, these results help optimize and instruct the development of a new synthetic hydrogel as a luminal filler for conduit-mediated peripheral nerve repair.

Semi-xenotransplantation: the regenerative medicine-based approach to immunosuppression-free transplantation and to meet the organ demand.

Although xenografts have always held immeasurable potential as an inexhaustible source of donor organs, immunological barriers and physiological incompatibility have proved to be formidable obstacles to clinical utility. An exciting, new regenerative medicine-based approach termed "semi-xenotransplantation" (SX) seeks to overcome these obstacles by combining the availability and reproducibility of animal organs with the biocompatibility and functionality of human allografts. Compared to conventional xenotransplantation wherein the whole organ is animal-derived, SX grafts are cleansed of their antigenic cellular compartment to produce whole-organ extracellular matrix scaffolds that retain their innate structure and vascular channels. These scaffolds are then repopulated with recipient or donor human stem cells to generate biocompatible semi-xenografts with the structure and function of native human organs. While numerous hurdles must be still overcome in order for SX to become a viable treatment option for end-stage organ failure, the immense potential of SX for meeting the urgent needs for a new source of organs and immunosuppression-free transplantation justifies the interest that the transplant community is committing to the field.

One-shot versus multidose perioperative antibiotic prophylaxis after kidney transplantation: a randomized, controlled clinical trial.

BACKGROUND: There is no consensus on the optimal perioperative antibiotic prophylaxis regimen for renal transplant recipients. Some studies have reported that irrigation of the wound at the time of closure without systemic antibiotics may suffice to minimize the risk for surgical site infection (SSI), but many centers still use long-term, multidose regimens in which antibiotics are administered until removal of foreign bodies occur, such as the urethral catheter, drain and central line. METHODS: We designed a prospective, randomized, multicenter, controlled trial to compare a single dose versus a multidose regimen of systemic antibiotic prophylaxis in adult, nondiabetic, non-morbidly obese patients undergoing renal transplantation. The primary endpoint was the incidence of SSI; the assessment of other infection in the first postoperative month was the secondary endpoint. RESULTS: Two hundred five patients were enrolled and randomized to receive either a single (n = 103) or multidose antibiotic regimen (n = 102) for prophylaxis. The incidences of SSI and urinary tract infection were similar in both groups. CONCLUSION: As the dramatic increase in antibiotic resistance has mandated the implementation of global programs to optimize the use of antibiotic agents in humans, we believe that the single dose regimen is preferred, at least in nondiabetic, non-morbidly obese, adult renal transplant recipients.

Tissue engineering.

Ultimately much work remains to be done in the companion fields of biomaterials and stem cells. Nonetheless, the monumental progress in TE that has been reported in the studies summarized here demonstrates that regenerative approaches to problems in general surgery need to be explored in more depth. Furthermore, the surgical disciplines of reconstruction and transplantation need to recognize their research counterparts in TE, given its potential to actualize freedom from immunosuppression, one of the most elusive goals in modern surgery. The engineering and proliferation of autologous cells, tissues, and organs ex vivo before surgical operation can significantly reduce the obstacles current practitioners are intimately familiar with: donor site morbidity and immunologic rejection. Therefore, in addition to the truly exciting research and development prospects and implications for the commercial sector, patients with end-stage diseases and debilitating injury stand to gain the most from clinically adapted TE therapies.

Osseus metaplasia in kidney allografts as a paradigm of regenerative medicine principles.

We report the sixth case of osseous metaplasia that has occurred in the last 5 years, after a deceased-donor renal transplant was performed on a young man. While its clinical significance is unclear and probably irrelevant, osseous metaplasia is one of the most relevant principles of regenerative medicine, where every bodily district contains progenitor cells that can generate cells specific to the germ layer from which they come. After the Case Report, we review the literature and speculate on the underlying pathophysiology of osseous metaplasia. Available data seem to support the hypothesis that osteogenic precursor cells, inducing factors, and a suitable environment are key for osseous metaplasia.

Extracellular Matrix Scaffold Technology for Bioartificial Pancreas Engineering: State of the Art and Future Challenges.

Emergent technologies in regenerative medicine may soon overcome the limitations of conventional diabetes therapies. Collaborative efforts across the subfields of stem cell technology, islet encapsulation, and biomaterial carriers seek to produce a bioengineered pancreas capable of restoring endocrine function in patients with insulin-dependent diabetes. These technologies rely on a robust understanding of the extracellular matrix (ECM), the supportive 3-dimensional network of proteins necessary for cellular attachment, proliferation, and differentiation. Although these functions can be partially approximated by biosynthetic carriers, novel decellularization protocols have allowed researchers to discover the advantages afforded by the native pancreatic ECM. The native ECM has proven to be an optimal platform for recellularization and whole-organ pancreas bioengineering, an exciting new field with the potential to resolve the dire shortage of transplantable organs. This review seeks to contextualize recent findings, discuss current research goals, and identify future challenges of regenerative medicine as it applies to diabetes management.

Renal bioengineering with scaffolds generated from human kidneys.

BACKGROUND: In 2012, about 16,487 people received kidney transplants in the USA whereas 95,022 candidates were on the waiting list at the end of the year. Moreover, more than 2,600 kidneys procured annually for transplantation are discarded for a variety of reasons. We hypothesize that this pool of discarded kidneys could in part meet the growing, urgent need for transplantable kidneys using current methods for organ bioengineering and regeneration and surgical transplantation. The recellularization of extracellular matrix (ECM) scaffolds has the potential to meet the uniquely ambitious engineering challenges posed by complex solid organs such as the kidney. SUMMARY: Attempts to manufacture and implant simpler, hollow structures such as bladders, vessels, urethras, and segments of the upper airways have been successful in the short and mid terms. However, the bioengineering of complex solid organs such as the kidney is a more challenging task that requires a different approach. In previous studies, we showed that decellularized porcine kidneys yield renal ECM scaffolds that preserve their basic architecture and structural components, support cell growth in vivo and in vitro, and maintain a patent vasculature capable of sustaining physiological blood pressure. In a subsequent report, using the same methods, we found that detergent-based decellularization of discarded human renal kidneys preserved their innate ECM framework, biochemical properties, and angiogenic capacity and - importantly - a patent vascular network. Furthermore, the process resulted in the clearance of immunogenic antigens, which has monumental implications for clinical outcomes in the long term in terms of graft rejection. Consequently, these kidneys show promise in bioengineering and transplantation. We refer to this avenue of research and development as 'cell-scaffold technology'. KEY MESSAGES: In 2011, more than 4,700 patients died while on the waiting list for a kidney transplant. In this context, we believe that cell-scaffold technology has the potential to form a bridge between regenerative medicine and transplantation surgery. These methods, in theory, could provide a potentially inexhaustible source of transplantable organs. Unfortunately, current investigations are still in their very early stages and clinical translation is not immediately available in the short term. Thus, identifying the most important obstacles confronting cell-scaffold technology and focusing research efforts in this direction will be important for advancing the state of the art and meeting the clinical needs. We believe that cell-scaffold technology research and development would benefit greatly from a deeper understanding of the physiological mechanisms underlying the natural organogenesis, regeneration, and repair that characterize embryonic humans and simpler organisms. Furthermore, the importance of vascularization - the fundamental caveat of modern surgery - cannot be overstated, especially when discussing the implantation of de novo organs.

Tissue engineering and regenerative medicine: semantic considerations for an evolving paradigm.

Tissue engineering (TE) and regenerative medicine (RM) are rapidly evolving fields that are often obscured by a dense cloud of hype and commercialization potential. We find, in the literature and general commentary, that several of the associated terms are casually referenced in varying contexts that ultimately result in the blurring of the distinguishing boundaries which define them. "TE" and "RM" are often used interchangeably, though some experts vehemently argue that they, in fact, represent different conceptual entities. Nevertheless, contemporary scientists have a general idea of the experiments and milestones that can be classified within either or both categories. Given the groundbreaking achievements reported within the past decade and consequent watershed potential of this field, we feel that it would be useful to properly contextualize these terms semantically and historically. In this concept paper, we explore the various definitions proposed in the literature and emphasize that ambiguous terminology can lead to misplaced apprehension. We assert that the central motifs of both concepts have existed within the surgical sciences long before their appearance as terms in the scientific literature.

Regeneration and bioengineering of the kidney: current status and future challenges.

The prevalence of chronic kidney disease continues to outpace the development of effective treatment strategies. For patients with advanced disease, renal replacement therapies approximate the filtration functions of the kidney at considerable cost and inconvenience, while failing to restore the resorptive and endocrine functions. Allogeneic transplantation remains the only restorative treatment, but donor shortage, surgical morbidity and the need for lifelong immunosuppression significantly limit clinical application. Emerging technologies in the fields of regenerative medicine and tissue engineering strive to address these limitations. We review recent advances in cell-based therapies, primordial allografts, bio-artificial organs and whole-organ bioengineering as they apply to renal regeneration. Collaborative efforts across these fields aim to produce a bioengineered kidney capable of restoring renal function in patients with end-stage disease.

Considerations on the development of a model of kidney bioengineering and regeneration in rats.

Evaluation of: Song JJ, Guyette JP, Gilpin SE, Gonzalez G, Vacanti JP, Ott HC. Regeneration and experimental orthotopic transplantation of a bioengineered kidney. Nat. Med. 19(5), 646-51 (2013). Emergent technologies of regenerative medicine have shown immense potential to overcome the limitations of organ transplantation by supplying tissues and organs bioengineered ex vivo in the laboratory. So far, clinical translation has been possible for simple, hollow organs, whereas the bioengineering and regeneration of complex modular organs (namely, kidneys, hearts, livers, lungs and small bowel) remains far from our grasp. In the case of the kidney, the bioengineering and regeneration of renal organoids requires a supporting scaffold that approximates the biochemical, spatial and vascular relationships of the native kidney extracellular matrix. A recent report describes the use of rodent kidneys to generate whole organ, three-dimensional scaffolds. These scaffolds were subsequently seeded with rat neonatal kidney cells to reconstitute the parenchymal cell compartment and with human umbilical venous endothelial cells to reconstitute the endothelium and allow implantation. Once assembled and allowed to mature in bioreactors, the so-obtained constructs were able to exert some function peculiar to the kidney both in vitro and in vivo after implantation in rodents. In this invited commentary, we will address the most critical topics of organ regeneration starting from the above-mentioned experience with the kidney but eventually embracing the whole field of complex modular organs bioengineering.