A cell-free nutrient-supplemented perfusate allows four-day ex vivo metabolic preservation of human kidneys

Expanding the Use of Ex Situ Organ Machine Perfusion Beyond Transplantation

Machine perfusion preservation of grafts has become the gold standard organ preservation method. It has been developed to improve the quality of grafts due to the increasing gap between demand and supply of organs for transplantation. Following successful long-term machine perfusion preservation with automated commercial devices developed for preservation of organs for transplantation, there is increasing interest in utilizing perfused discarded human organs and xenografts for a variety of purposes beyond transplantation including gene therapy and modulation, drug testing, chemotherapy, ex vivo surgery, organ supporting systems, bioengineering, and surgical training and education. Here, we review all current and potential applications of machine perfusion preservation.

Endothelial dysfunction in the aging kidney

Global population aging is an escalating challenge in modern society, especially as it impairs the function of multiple organs and increases the burden of age-related diseases. The kidneys, in particular, experience function decline, reduced regenerative capacity, and increased susceptibility to injury as they age. As a result, the prevalence of chronic kidney disease (CKD) rises with aging, further contributing to the growing health burden in older populations. One of the key factors in this process is the dysfunction of specialized renal endothelial cells (RECs), which are essential for maintaining kidney health by regulating blood flow and supporting filtration, solute and water reabsorption, and vascular integrity. As the kidneys age, REC dysfunction drives vascular and microenvironmental changes, contributing to the overall decline in kidney function. In this review, we outline the structural and functional effects of aging on the kidney's macrovascular and microvascular compartments and provide a phenotypic description of the aged endothelium. We particularly focus on the molecular and metabolic rewiring driving and sustaining growth-arrested EC senescence phenotype. We finally give an overview of senotherapies acting on ECs, especially of those modulating metabolism. Given that the pathophysiological processes underlying kidney aging largely overlap with those observed in CKD, REC rejuvenation could also benefit patients with CKD. Moreover, such interventions may hold promise in improving the outcomes of aged kidney transplants. Hence, advancing our understanding of REC and kidney aging will create opportunities for innovations that could improve outcomes for both elderly individuals and patients with CKD.

Organ preservation: current limitations and optimization approaches

Despite the annual rise in patients with end-stage diseases necessitating organ transplantation, the scarcity of high-quality grafts constrains the further development of transplantation. The primary causes of the graft shortage are the scarcity of standard criteria donors, unsatisfactory organ preservation strategies, and mismatching issues. Organ preservation strategies are intimately related to pre-transplant graft viability and the incidence of adverse clinical outcomes. Static cold storage (SCS) is the current standard practice of organ preservation, characterized by its cost-effectiveness, ease of transport, and excellent clinical outcomes. However, cold-induced injury during static cold preservation, toxicity of organ preservation solution components, and post-transplantation reperfusion injury could further exacerbate graft damage. Long-term ex vivo dynamic machine perfusion (MP) preserves grafts in a near-physiological condition, evaluates graft viability, and cures damage to grafts, hence enhancing the usage and survival rates of marginal organs. With the increased use of extended criteria donors (ECD) and advancements in machine perfusion technology, static cold storage is being gradually replaced by machine perfusion. This review encapsulates the latest developments in cryopreservation, subzero non-freezing storage, static cold storage, and machine perfusion. The emphasis is on the injury mechanisms linked to static cold storage and optimization strategies, which may serve as references for the optimization of machine perfusion techniques.

Challenges in maturation and integration of kidney organoids for stem cell-based renal replacement therapy

Human pluripotent stem cell-derived kidney organoids hold promise for future applications in regenerative medicine. However, significant biological hurdles need to be overcome to enable their use as a transplantable stem cell-derived therapeutic graft. Current kidney organoid protocols do not recapitulate a complete integrated developing kidney, but embryonic kidney transplantations have provided clues for advancing maturation and functionality of kidney organoids. Transplantation, subsequent vascularization, and blood perfusion of kidney organoids improve nephron patterning and maturation, suggesting a role for angiocrine factors as well as metabolic wiring in these processes. Transplanted organoids exhibit filtration, but the resulting filtrate has no apparent exit path for excretion. Improved in vitro patterning of kidney organoids may be required such that a more structurally correct tissue is formed before transplant. Here we review current progress with transplantation of kidney organoids, as well as their engraftment and integration, and identify the key obstacles to therapeutic success and how these might be achieved.

Challenges in Spatial Metabolomics and Proteomics for Functional Tissue Unit and Single-Cell Resolution

In the last decade, advanced developments of mass spectrometry-based assays have made spatial measurements of hundreds of metabolites and thousands of proteins not only possible, but routine. The information obtained from such mass spectrometry imaging experiments traces metabolic events and helps decipher feedback loops across anatomical regions, connecting genetic and metabolic networks that define phenotypes. Herein we overview developments in the field over the past decade, highlighting several case studies demonstrating direct measurement of metabolites, proteins, and proteoforms from thinly sliced tissues at the level of functional tissue units, approaching single-cell levels. Much of this work is feasible due to multidisciplinary team science, and we offer brief perspectives on paths forward and the challenges that persist with adoption and application of these spatial omics techniques at the single-cell level on mammalian kidneys. Data analysis and reanalysis still pose issues that plague spatial omics, but many mass spectrometry imaging platforms are commercially available. With greater harmonization across platforms and rigorous quality control, greater adoption of these platforms will undoubtedly provide major insights in complex diseases.

Current Basic Research in Normothermic Machine Perfusion

BACKGROUND

Normothermic machine perfusion (NMP) is gradually being introduced into clinical transplantation to improve the quality of organs and increase utilisation. This review details current understanding of the underlying mechanistic effects of NMP in the heart, lung, liver, and kidney. It also considers recent advancements to extend the perfusion interval in these organs and the use of NMP to introduce novel therapeutic interventions, with a focus on organ modulation.

SUMMARY

The re-establishment of circulation during NMP leads to the upregulation of inflammatory and immune mediators, similar to an ischaemia-reperfusion injury response. The level of injury is determined by the condition of the organ, but inflammation may also be exacerbated by the passenger leucocytes that emerge from the organ during perfusion. There is evidence that damaged organs can recover and that prolonged NMP may be advantageous. In the liver, successful 7-day NMP has been achieved. The delivery of therapeutic agents to an organ can aid repair and be used to modify the organ to reduce immunogenicity or change the structure of the blood group antigens to create a universal donor blood group organ.

KEY MESSAGES

The application of NMP in organ transplantation is a growing area of research and is increasingly being used in the clinic. In the future, NMP may offer the opportunity to change practice. If organs can be preserved for days on an NMP system, transplantation may become an elective rather than an emergency procedure. The ability to introduce therapies during NMP is an effective way to treat an organ and avoid the complexity of treating the recipient.