Abstract
Lung transplantation has advanced dramatically since its inception in 1963, but still lags behind other solid organs in terms of donor organ utilization and transplant success rates. Increased use of available donor lungs, development of noninvasive techniques for early diagnosis of primary graft dysfunction (PGD), and the design of therapies to attenuate ischemia-reperfusion injury (IRI) are needed to improve the rates and outcomes of lung transplantation.
My graduate research entailed various projects that addressed three critical areas of lung transplantation. I first focused on the role of ex vivo lung perfusion (EVLP) as a platform to assess the effects of cold and warm ischemia on allograft function. High rates of lung IRI and PGD after transplantation of marginal donor lungs leads to poor outcomes and thus a reluctance among transplant centers to utilize these available organs. Using a preclinical porcine model of lung transplantation, we demonstrated that marginal donor lungs (procured after circulatory death) exposed to 6 hours of cold ischemia after EVLP can still be successfully transplanted. These findings suggest that organ allocation can be improved without compromising allograft function using a strategy that combines ex vivo assessment and rehabilitation with cold preservation. Another project that I completed explored the effect of increasing warm ischemia time (WIT) on allograft function and demonstrated that longer WIT does not predict worse lung function when lungs are assessed on EVLP. Expanding acceptable WIT after circulatory death may eventually allow for inclusion of uncontrolled donation after circulatory death (DCD) lungs (lungs procured from unplanned donors) in procurement protocols.
Considering that IRI leads to PGD and early morbidity and mortality after lung transplantation, I next explored mechanisms by which in vivo leukocyte labeling could be used to noninvasively image cell-type specific lung inflammation, thus improving and expediting diagnosis. Polymorphonuclear leukocytes (PMNs) traffic to the lungs early during acute lung injury, infiltrate in abundance, and are known to express high levels of formyl peptide receptor 1 (FPR1), which aids in chemotaxis. Thus, we established a diagnosis technique utilizing a FPR1 peptide ligand conjugated with technetium-99m (99mTc-cFLFLF) and single-photon emission computed tomography (SPECT) that enabled quantifiable, noninvasive imaging diagnosis of lung IRI and allowed for monitoring of injury resolution over time.
Finally, I turned my attention to molecular targets to attenuate lung IRI. We first demonstrated that enhanced EVLP supplemented with an adenosine A2B receptor antagonist could rehabilitate injured DCD lungs and attenuate post-transplant IRI, thus allowing for successful transplantation. Second, we identified transient receptor potential vanilloid 4 (TRPV4) cation channels as important regulators of endothelial cell permeability and epithelial cell activation during lung IRI and demonstrated that antagonism of TRPV4 may be a promising therapy to attenuate lung IRI. Finally, I focused on the role of pannexin 1 (Panx1) channels in lung IRI. We established endothelial cell Panx1 as an important mediator of vascular permeability, pulmonary edema accumulation, and leukocyte infiltration, and we demonstrated that Panx1 inhibitors attenuate IRI and edema and may be another novel therapeutic strategy to improve outcomes after lung transplantation.
Collectively, the work presented here challenges the status quo regarding lung transplantation. Utilization of EVLP to assess and rehabilitate marginal donor lungs, earlier diagnosis of lung IRI via noninvasive 99mTc-cFLFLF SPECT imaging, and the use of novel pharmacologic therapies to attenuate lung IRI may improve outcomes for lung transplant patients.
