What is the evidence for oxygenation during kidney preservation for transplantation in 2021? A scoping review

Versatile, in-line optical oxygen tension sensors for continuous monitoring during ex vivo kidney perfusion

Integration of physiological sensing modalities within tissue and organ perfusion systems is becoming a steadily expanding field of research, aimed at achieving technological breakthrough innovations that will expand the sites and clinical settings at which such systems can be used. This is becoming possible in part due to the advancement of user-friendly optical sensors in recent years, which rely both on synthetic, luminescent sensor molecules and inexpensive, low-power electronic components for device engineering. In this article we report a novel approach towards enabling automated, continuous monitoring of oxygenation during ex vivo organ perfusion, by combining versatile flow cell components and low-power, programmable electronic readout devices. The sensing element comprises a 3D printed, miniature flow cell with tubing connectors and an affixed oxygen-sensing thin film material containing in-house developed, brightly-emitting metalloporphyrin phosphor molecules embedded within a polymer matrix. Proof-of-concept validation of this technology is demonstrated through integration within the tubing circuit of a transportable medical device for hypothermic oxygenated machine perfusion of extracted kidneys as a model for organs to be preserved as transplants.

Molecular Frontiers in Transplantation-Induced Ischemia-Reperfusion Injury

This Special Issue aims to summarize the most up-to-date research on ischemia-reperfusion and organ transplantation [...].

Extracellular histone release by renal cells after warm and cold ischemic kidney injury: Studies in an ex-vivo porcine kidney perfusion model

Extracellular histones are cytotoxic molecules involved in experimental acute kidney injury. In patients receiving a renal transplant from donors after circulatory death, who suffer from additional warm ischemia, worse graft outcome is associated with higher machine perfusate extracellular histone H3 concentrations. We now investigated temperature-dependent extracellular histone release in an ex vivo porcine renal perfusion model, and subsequently studied histone release in the absence and presence of non-anticoagulant heparin. Seven pairs of ischemically damaged porcine kidneys were machine perfused at 4°C (cold ischemia) or 28°C (warm ischemia). Perfusate histone H3 concentration was higher after warm as compared to cold ischemia (median (IQR) = 0.48 (0.20-0.83) μg/mL vs. 0.02 (0.00-0.06) μg/mL; p = .045, respectively). Employing immune-electron microscopy (EM), histone containing cytoplasmic protrusions of tubular and endothelial cells were found after warm ischemic injury. Furthermore, abundant histone localization was detected in debris surrounding severely damaged glomerular cells, in a "buck shot" pattern. In vitro, histones were cytotoxic to endothelial and kidney epithelial cells in a temperature-dependent manner. In a separate ex vivo experiment, addition of heparin did not change the total histone H3 levels observed in the perfusate but revealed a continuous increase in the level of a lower molecular weight histone H3 variant. Our findings show that ischemically damaged kidneys release more extracellular histones in warm ischemia, which by EM was due to histone release by renal cells. Blocking of histone-mediated damage during transplantation may be beneficial in prevention of renal injury.

PO2 21% oxygenated hypothermic machine perfusion in kidney transplantation: Any clinical benefit?

BACKGROUND

In deceased donor kidney transplantation (KT), the use of hypothermic machine perfusion (HMP) has been acquiring the status of best practice in the pre-transplant management of kidney grafts. Two types of HMP are currently available, oxygenated HMP and non-oxygenated HMP. However, data on the real clinical impact of oxygenation on KT outcome are still heterogeneous.

METHODS

Retrospective study on a cohort of 103 patients transplanted with a single kidney graft that was managed either with end-ischemic oxygenated (O₂ group, Waves Machine, n = 51, 49.5%) or non-oxygenated HMP (no-O₂ group, Life Port Kidney Transporter Machine, n = 52, 50.5%), during the period January 2016-December 2020. Oxygenation was performed at pO₂ 21%.

RESULTS

The median cold ischemia time was 29 h:40 min [IQR 26 h:55 min-31 h:10 min] and the prevalence of grafts from extended criteria donors (ECD) was 46.7%, with a median kidney donor profile index (KDPI) of 72 [41-94]. The study groups were homogeneous in terms of recipient characteristics, ischemia times and donor characteristics. O₂ and no-O₂ groups showed comparable outcomes in terms of delayed graft function (O₂ vs no-O₂, 21.5% vs 25%, p = 0.58), vascular (0.2% vs 0.2%, p > 0.99) and urologic (13.7% vs 11.5%, p = 0.77) complications, and episodes of graft rejection (11.7% vs 7.7%, p = 0.52). At 1 year follow up, even creatinine serum levels were comparable between the groups (1.27 mg/dL [1.09 and 1.67] vs 1.4 mg/dL [1.9-1.78], p = 0.319), with similar post-transplant trend (p = 0.870). No significant benefit was either observed in ECD or KDPI > 60 subgroups, respectively.

CONCLUSIONS

Oxygenation at pO₂ 21% during HMP seems not to significantly enhance the KT outcomes in terms of postoperative complications or graft function.

Preservation of Organs to Be Transplanted: An Essential Step in the Transplant Process

Organ transplantation remains the treatment of last resort in case of failure of a vital organ (lung, liver, heart, intestine) or non-vital organ (essentially the kidney and pancreas) for which supplementary treatments exist. It remains the best alternative both in terms of quality-of-life and life expectancy for patients and of public health expenditure. Unfortunately, organ shortage remains a widespread issue, as on average only about 25% of patients waiting for an organ are transplanted each year. This situation has led to the consideration of recent donor populations (deceased by brain death with extended criteria or deceased after circulatory arrest). These organs are sensitive to the conditions of conservation during the ischemia phase, which have an impact on the graft’s short- and long-term fate. This evolution necessitates a more adapted management of organ donation and the optimization of preservation conditions. In this general review, the different aspects of preservation will be considered. Initially done by hypothermia with the help of specific solutions, preservation is evolving with oxygenated perfusion, in hypothermia or normothermia, aiming at maintaining tissue metabolism. Preservation time is also becoming a unique evaluation window to predict organ quality, allowing repair and/or optimization of recipient choice.

Adipose-Derived Stem/Stromal Cells in Kidney Transplantation: Status Quo and Future Perspectives

Kidney transplantation (KT) is the gold standard treatment of end-stage renal disease. Despite progressive advances in organ preservation, surgical technique, intensive care, and immunosuppression, long-term allograft survival has not significantly improved. Among the many peri-operative complications that can jeopardize transplant outcomes, ischemia–reperfusion injury (IRI) deserves special consideration as it is associated with delayed graft function, acute rejection, and premature transplant loss. Over the years, several strategies have been proposed to mitigate the impact of IRI and favor tolerance, with rather disappointing results. There is mounting evidence that adipose stem/stromal cells (ASCs) possess specific characteristics that could help prevent, reduce, or reverse IRI. Immunomodulating and tolerogenic properties have also been suggested, thus leading to the development of ASC-based prophylactic and therapeutic strategies in pre-clinical and clinical models of renal IRI and allograft rejection. ASCs are copious, easy to harvest, and readily expandable in culture. Furthermore, ASCs can secrete extracellular vesicles (EV) which may act as powerful mediators of tissue repair and tolerance. In the present review, we discuss the current knowledge on the mechanisms of action and therapeutic opportunities offered by ASCs and ASC-derived EVs in the KT setting. Most relevant pre-clinical and clinical studies as well as actual limitations and future perspective are highlighted.