Composite Vascularized Allograft Machine Preservation: State of the Art

Design of a Multiparametric Perfusion Bioreactor System for Evaluating Sub-Normothermic Preservation of Rat Abdominal Wall Vascularized Composite Allografts

Static cold storage (SCS), the current clinical gold standard for organ preservation, provides surgeons with a limited window of time between procurement and transplantation. In vascularized composite allotransplantation (VCA), this time limitation prevents many viable allografts from being designated to the best-matched recipients. Machine perfusion (MP) systems hold significant promise for extending and improving organ preservation. Most of the prior MP systems for VCA have been built and tested for large animal models. However, small animal models are beneficial for high-throughput biomolecular investigations. This study describes the design and development of a multiparametric bioreactor with a circuit customized to perfuse rat abdominal wall VCAs. To demonstrate its concept and functionality, this bioreactor system was employed in a small-scale demonstrative study in which biomolecular metrics pertaining to graft viability were evaluated non-invasively and in real time. We additionally report a low incidence of cell death from ischemic necrosis as well as minimal interstitial edema in machine perfused grafts. After up to 12 h of continuous perfusion, grafts were shown to survive transplantation and reperfusion, successfully integrating with recipient tissues and vasculature. Our multiparametric bioreactor system for rat abdominal wall VCA provides an advanced framework to test novel techniques to enhance normothermic and sub-normothermic VCA preservations in small animal models.

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.

Ex vivo normothermic preservation of amputated limbs with a hemoglobin-based oxygen carrier perfusate

BACKGROUND

Ex vivo normothermic limb perfusion (EVNLP) preserves amputated limbs under near-physiologic conditions. Perfusates containing red blood cells (RBCs) have shown to improve outcomes during ex vivo normothermic organ perfusion, when compared with acellular perfusates. To avoid limitations associated with the use of blood-based products, we evaluated the feasibility of EVNLP using a polymerized hemoglobin-based oxygen carrier-201 (HBOC-201).

METHODS

Twenty-four porcine forelimbs were procured from Yorkshire pigs. Six forelimbs underwent EVNLP with an HBOC-201-based perfusate, six with an RBC-based perfusate, and 12 served as static cold storage (SCS) controls. Ex vivo normothermic limb perfusion was terminated in the presence of systolic arterial pressure of 115 mm Hg or greater, fullness of compartments, or drop of tissue oxygen saturation by 20%. Limb contractility, weight change, compartment pressure, tissue oxygen saturation, oxygen uptake rates (OURs) were assessed. Perfusate fluid-dynamics, gases, electrolytes, metabolites, methemoglobin, creatine kinase, and myoglobin concentration were measured. Uniformity of skin perfusion was assessed with indocyanine green angiography and infrared thermography.

RESULTS

Warm ischemia time before EVNLP was 35.50 ± 8.62 minutes (HBOC-201), 30.17 ± 8.03 minutes (RBC) and 37.82 ± 10.45 (SCS) (p = 0.09). Ex vivo normothermic limb perfusion duration was 22.5 ± 1.7 hours (HBOC-201) and 28.2 ± 7.3 hours (RBC) (p = 0.04). Vascular flow (325 ± 25 mL·min-1 vs. 444.7 ± 50.6 mL·min-1; p = 0.39), OUR (2.0 ± 1.45 mL O2·min-1·g-1 vs. 1.3 ± 0.92 mL O2·min-1·g-1 of tissue; p = 0.80), lactate (14.66 ± 4.26 mmol·L-1 vs. 13.11 ± 6.68 mmol·L-1; p = 0.32), perfusate pH (7.53 ± 0.25 HBOC-201; 7.50 ± 0.23 RBC; p = 0.82), flexor (28.3 ± 22.0 vs. 27.5 ± 10.6; p = 0.99), and extensor (31.5 ± 22.9 vs. 28.8 ± 14.5; p = 0.82) compartment pressures, and weight changes (23.1 ± 3.0% vs. 13.2 ± 22.7; p = 0.07) were not significantly different between HBOC-201 and RBC groups, respectively. In HBOC-201 perfused limbs, methemoglobin levels increased, reaching 47.8 ± 12.1% at endpoint. Methemoglobin saturation did not affect OUR (ρ = -0.15, r2 = 0.022; p = 0.45). A significantly greater number of necrotic myocytes was found in the SCS group at endpoint (SCS, 127 ± 17 cells; HBOC-201, 72 ± 30 cells; RBC-based, 56 ± 40 cells; vs. p = 0.003).

CONCLUSION

HBOC-201- and RBC-based perfusates similarly support isolated limb physiology, metabolism, and function.

Preservation solutions for attenuation of ischemia-reperfusion injury in vascularized composite allotransplantation

Vascularized composite allotransplantation represents the final level of the reconstructive ladder, offering treatment options for severe tissue loss and functional deficiencies. Vascularized composite allotransplantation is particularly susceptible to ischemia–reperfusion injury and requires preservation techniques when subjected to extended storage times prior to transplantation. While static cold storage functions to reduce ischemic damage and is widely employed in clinical settings, there exists no consensus on the ideal preservation solution for vascularized composite allotransplantation. This review aims to highlight current clinical and experimental advances in preservation solution development and their critical role in attenuating ischemia–reperfusion injury in the context of vascularized composite allotransplantation.