(5da) Organ Engineering

There are currently ~100,000 patients on the organ transplant waiting list in the US, a number that far exceeds the supply of available organs, and that continues to grow ~5% each year. The most promising strategies that are being explored as means for addressing this critical shortage are: 1) bioartificial tissue and organ construction (which aims to manufacture tissue and organ analogues in vitro) and 2) donor organ re-engineering methodologies (the goal of which is to recondition marginally damaged organs for transplantation). In either case, success requires the understanding of the interaction of multi-scale components (such as cell types, matrix and vascularization) of the actual tissue. Development of such a systems-level understanding of tissues and organs is limited by two main factors: i) the cell culture systems are very limited in mimicking the tissue microstructure, extracellular matrix interactions, and incorporating multiple cell types; ii) at this level of complexity, use of systems engineering approaches becomes a must in order to model and predict; metabolic engineering toolbox, such as flux analysis is ideal for this purpose, , but have not been well utilized since they have been largely focused on microorganisms - in large part due to the nonexistence of appropriate model organ systems. In this study, we describe an organ culture system development for the dual purposes of i) introducing an accessible experimental platform for development of metabolic engineering models and algorithms for tissue/biomedical engineering applications, and ii) increasing the donor organ pool by reconditioning ischemic organs through reconditioning in a model-controlled system.

In this study, we focus on the reconditioning or marginal livers for transplantation. Liver transplantation is currently the only established treatment for end-stage liver disease, but is limited by a severe shortage of viable donor organs; roughly 3,000 patients per year perish due to lack of transplantable donor organs. Livers obtained from donors after cardiac death (DCD) are currently an untapped donor source for liver transplantation and could increase the supply of donor livers by an estimated 6,000 per year. However, preservation of DCD livers by conventional methods, namely simple cold storage (SCS) in University of Wisconsin (UW) solution, is associated with a higher risk of primary non-function and delayed graft failure. Here we demonstrate a novel Normothermic Extracorporeal Liver Perfusion (NELP) system where rat livers subjected to one hour of ex-vivo warm (34°C) ischemia and preserved for 5 hours using NELP show stable metabolic parameters. Furthermore, following normothermic preservation these ischemically damaged livers could be orthotopically transplanted into syngeneic recipients with close to 100% survival (N=10) after 4 weeks, which was comparable to control animals that received healthy livers preserved by conventional SCS for 6 hours (N=6). On the other hand, animals that received ischemically damaged livers that were stored for 5 hours in UW solution all died within 12 hours post-operatively (N=6). Additionally, animals that received ischemic livers that were directly transplanted without having undergone preservation all died within 36 hours after transplantation (N=6). These results suggest that NELP has the potential to reclaim warm ischemic livers that would not be transplantable otherwise.

Further, the future impact of the organ culture platform is discussed: i) as a practical model for studying fibrosis, hepatitis as well as any other liver disease that can be induced in animal models, iii) for development and early screening of therapeutic methods for such diseases, where the delivery and dosage optimization of the therapeutic agents can be assessed prior to the involvement of the whole body, iii) as a functional liver storage technology where the donor organ can be preserved under direct model-based metabolic control, and iv) as a tool for development of multi-scale models for organs.