PMC:5400024 / 22370-28503 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/5400024","sourcedb":"PMC","sourceid":"5400024","source_url":"https://www.ncbi.nlm.nih.gov/pmc/5400024","text":"DISCUSSION\nIn this proof-of-concept study, the feasibility of using inflammation and tissue injury markers in both perfusate and BALF from human donor lungs undergoing EVLP to validate the decision to use or decline them for clinical transplant was evaluated. All 16 donor lungs in this study were assessed consecutively with intent for transplant following a strict protocol with predefined criteria for EVLP and transplant suitability to reduce the risk of bias in decision making. All protein analyses were done retrospectively and had no impact on the transplant decision. Our results demonstrate a difference in protein expression in perfusate from lungs that were transplanted compared with those that were declined. This difference became more apparent for each hour of perfusion, and BALF samples showed a comparable but weaker signal from the airway compartment.\nThe difference in donor lungs was effectively demonstrated by a logistic regression model combining inflammatory cytokines IL-1β and IL-8 after 2 h of perfusion. The model revealed a clear separation of the transplanted lungs from those declined. Importantly, the model remained equally as robust when applied to perfusate samples from all time points. Furthermore, perfusate IL-1β concentrations in transplanted lungs demonstrated a clear negative correlation to early recipient oxygenation post-transplant.\nEven though our results are noteworthy, overinterpretation of this regression model should be avoided at this stage. Further investigations are required to assess its biological plausibility. A few declined lungs displayed a very low IL-1β/IL-8 signal—below that of lungs deemed reconditioned and transplanted with good outcomes after the EVLP assessment. If this finding indicates that those lungs were wrongfully declined and could safely have been transplanted, that EVLP-assessed lungs deemed suitable for transplant truly express an intermediate level of inflammation, or that this is a signal specific to this relatively small cohort needs further assessment in follow-up studies.\nThe measurement of LDH levels in perfusate had the potential to significantly predict EVLP outcome as early as 2 h into perfusion. Although real-time ligand binding assays for inflammatory cytokines and other tissue injury markers may soon become accessible [22], LDH has the benefit of being a widely recognized marker of tissue injury in serum and BALF and rapidly available as a point-of-care test [23, 24].\nThe Brisbane lung transplant group have described measures of endothelial dysfunction as potentially useful in EVLP [25, 26]. Our results strengthen that belief. Syndecan-1, released by disruption of the endothelial glycocalyx, may be a discriminatory marker in EVLP perfusate and should be further evaluated.\nIncreasing levels of inflammatory cytokines in perfusate and tissue have been shown during experimental lung perfusion in porcine models and a small preclinical human lung study, which might reflect procedure-mediated inflammation [27–29]. Our findings during full clinical EVLP support recent observations made by Machuca and colleagues [30] from Toronto and demonstrate the feasibility of identifying biomarkers that might improve EVLP assessment.\nIL-8, proposed as one of the best markers of EVLP transplant outcome in the Machuca study, has consistently shown potential in previous studies of donor lung injury from our group [12, 13]. The potential of IL-8 to discriminate successful EVLP in our study was enhanced by combining it with IL-1β.\nOur observations add significantly to previous observations because we have included an assessment of BALF inflammatory and tissue injury markers compared to EVLP perfusate measures. Even though BALF samples in this study did not add any apparent clinical value to perfusate sampling, we feel it is too early to draw any firm conclusions, and we will continue to assess a broad spectrum of markers and lung compartment samples in future studies. In addition, because protein levels are measured in a fixed volume of 2 litres of perfusate solution, we corrected protein levels for the size of lung tissue perfused. This potential confounder has been disregarded in previous studies. The pTLC of the donor lung ranged from 4.31 to 7.54 litres among the double lungs perfused, and the smallest single lung had a pTLC of only 2.70 litres. Unadjusted marker levels are therefore likely to differ widely between donor lungs regardless of the degree of lung injury present.\nA limitation of our study is its relatively small sample size, with 16 human EVLP assessments included, yet this number is sufficient to demonstrate the feasibility of using perfusate markers to discriminate successful EVLP. Outcomes were almost universally good, and this study does not identify predictors of early lung injury. Larger studies, with a cohort of patients doing less well, are needed to address that particular question. Caution is, however, required in overinterpretation of moderate to severe PGD (Grade 2–3) after transplant as a reason for donor lungs to be declined after EVLP, because many recipients with PGD 2–3 will recover and have satisfactory early outcomes.\nTruly marginal donor lungs subjected to EVLP for reconditioning purposes form by nature a subpopulation that is likely to have a higher inflammatory burden than standard donor lungs. We believe that biomarker profiles of these lungs could help support the clinical decision to use or decline the donor lungs after EVLP and allow continued safe transplant activity. Furthermore, this approach offers the potential to attenuate the inflammatory response or encourage recovery of vascular integrity in the donor lung before implantation in a stratified medicine approach, which may improve early outcomes after lung transplant and help to safely maximize lung use from the existing donor pool.\nThe results of this study need further evaluation in a larger validation cohort of lungs exposed to ex vivo perfusion but demonstrate the feasibility of identifying an early perfusate signature potentially predictive of successful EVLP 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