Revisiting the Principles of Preservation in an Era of Pandemic Obesity.

The current obesity epidemic has caused a significant decline in the health of our donor population. Organs from obese deceased donors are more prone to ischemia reperfusion injury resulting from organ preservation. As a consequence, these donors are more likely to be discarded under the assumption that nothing can be done to make them viable for transplant. Our current methods of organ preservation-which remain relatively unchanged over the last ~40 years-were originally adopted in the context of a much healthier donor population. But methods that are suitable for healthier deceased donors are likely not optimal for organs from obese donors. Naturally occurring models of acute obesity and fasting in hibernating mammals demonstrate that obesity and resilience to cold preservation-like conditions are not mutually exclusive. Moreover, recent advances in our understanding of the metabolic dysfunction that underlies obesity suggest that it may be possible to improve the resilience of organs from obese deceased donors. In this mini-review, we explore how we might adapt our current practice of organ preservation to better suit the current reality of our deceased donor population.

A digital pathology tool for quantification of color features in histologic specimens.

In preclinical research, histological analysis of tissue samples is often limited to qualitative or semiquantitative scoring assessments. The reliability of this analysis can be impaired by the subjectivity of these approaches, even when read by experienced pathologists. Furthermore, the laborious nature of manual image assessments often leads to the analysis being restricted to a relatively small number of images that may not accurately represent the whole sample. Thus, there is a clear need for automated image analysis tools that can provide robust and rapid quantification of histologic samples from paraffin-embedded or cryopreserved tissues. To address this need, we have developed a color image analysis algorithm (DigiPath) to quantify distinct color features in histologic sections. We demonstrate the utility of this tool across multiple types of tissue samples and pathologic features, and compare results from our program to other quantitative approaches such as color thresholding and hand tracing. We believe this tool will enable more thorough and reliable characterization of histological samples to facilitate better rigor and reproducibility in tissue-based analyses.

Lysis of cold-storage-induced microvascular obstructions for ex vivo revitalization of marginal human kidneys.

Thousands of kidneys from higher-risk donors are discarded annually because of the increased likelihood of complications posttransplant. Given the severe organ shortage, there is a critical need to improve utilization of these organs. To this end, normothermic machine perfusion (NMP) has emerged as a platform for ex vivo assessment and potential repair of marginal organs. In a recent study of 8 transplant-declined human kidneys on NMP, we discovered microvascular obstructions that impaired microvascular blood flow. However, the nature and physiologic impact of these lesions were unknown. Here, in a study of 39 human kidneys, we have identified that prolonged cold storage of human kidneys induces accumulation of fibrinogen within tubular epithelium. Restoration of normoxic conditions-either ex vivo during NMP or in vivo following transplant-triggered intravascular release of fibrinogen correlating with red blood cell aggregation and microvascular plugging. Combined delivery of plasminogen and tissue plasminogen activator during NMP lysed the plugs leading to a significant reduction in markers of renal injury, improvement in indicators of renal function, and improved delivery of vascular-targeted nanoparticles. Our study suggests a new mechanism of cold storage injury in marginal organs and provides a simple treatment with immediate translational potential.

The future of marginal kidney repair in the context of normothermic machine perfusion.

Normothermic machine perfusion (NMP) is a technique that utilizes extracorporeal membrane oxygenation to recondition and repair kidneys at near body temperature prior to transplantation. The application of this new technology has been fueled by a significant increase in the use of the kidneys that were donated after cardiac death, which are more susceptible to ischemic injury. Preliminary results indicate that NMP itself may be able to repair marginal organs prior to transplantation. In addition, NMP serves as a platform for delivery of therapeutics. The isolated setting of NMP obviates problems of targeting a particular therapy to an intended organ and has the potential to reduce the harmful effects of systemic drug delivery. There are a number of emerging therapies that have shown promise in this platform. Nutrients, therapeutic gases, mesenchymal stromal cells, gene therapies, and nanoparticles, a newly explored modality, have been successfully delivered during NMP. These technologies may be effective at blocking multiple mechanisms of ischemia- reperfusion injury (IRI) and improving renal transplant outcomes. This review addresses the mechanisms of renal IRI, examines the potential for NMP as a platform for pretransplant allograft modulation, and discusses the introduction of various therapies in this setting.