Endothelial Glycocalyx Shedding Occurs during Ex Vivo Lung Perfusion: A Pilot Study.

BACKGROUND: Damage to the endothelium has been established as a key pathological process in lung transplantation and ex vivo lung perfusion (EVLP), a new technology that provides a platform for the assessment of injured donor lungs. Damage to the lung endothelial glycocalyx, a structure that lines the endothelium and is integral to vascular barrier function, has been associated with lung dysfunction. We hypothesised that endothelial glycocalyx shedding occurs during EVLP and aimed to establish a porcine model to investigate the mechanism underlying glycocalyx breakdown during EVLP. METHODS: Concentrations of endothelial glycocalyx breakdown products, syndecan-1, hyaluronan, heparan sulphate, and CD44, were measured using the ELISA and matrix metalloproteinase (MMP) activity by zymography in the perfusate of both human (n = 9) and porcine (n = 4) lungs undergoing EVLP. Porcine lungs underwent prolonged EVLP (up to 12 hours) with perfusion and ventilation parameters recorded hourly. RESULTS: During human EVLP, endothelial glycocalyx breakdown products in the perfusate increased over time. Increasing MMP-2 activity over time was positively correlated with levels of syndecan-1 (r = 0.886; p=0.03) and hyaluronan (r = 0.943; p=0.02). In the porcine EVLP model, hyaluronan was the only glycocalyx product detectable during EVLP (1 hr: 19 (13-84) vs 12 hr: 143 (109-264) ng/ml; p=0.13). Porcine hyaluronan was associated with MMP-9 activity (r = 0.83; p=0.02) and also with dynamic compliance (r = 0.57; p=0.03). CONCLUSION: Endothelial glycocalyx products accumulate during both porcine and human EVLP, and this accumulation parallels an accumulation of matrix-degrading enzyme activity. Preliminary evidence in our porcine EVLP model suggests that shedding may be related to organ function, thus warranting additional study.

Endothelial Glycocalyx Shedding Predicts Donor Organ Acceptability and Is Associated With Primary Graft Dysfunction in Lung Transplant Recipients.

BACKGROUND: The endothelial glycocalyx, a sieve-like structure located on the luminal surface of all blood vessels, has been found to be integral to regulation of capillary permeability and mechanotransduction. Given this, we investigated the role of endothelial glycocalyx breakdown products in organ donors and recipients in terms of acceptability for transplant and risk of primary graft dysfunction (PGD). METHODS: Endothelial glycocalyx breakdown products were measured in the peripheral blood of 135 intended and actual organ donors. Breakdown product levels were tested for association with donor demographic and clinical data, organ acceptability for transplant along with lung recipient outcomes (n = 35). Liquid chromatography mass spectrometry analysis was performed to confirm glycosaminoglycan levels and sulfation patterns on donor samples (n = 15). In transplant recipients (n = 50), levels were measured pretransplant and daily for 4 days posttransplant. Levels were correlated with PGD severity and intubation time. RESULTS: Decreased hyaluronan levels in peripheral blood independently predicted organ acceptability in intended and actual donors (odds ratio, 0.96; [95% confidence interval, 0.93-0.99] P = 0.026). Furthermore, high donor syndecan-1 levels were associated with PGD in recipients (3142 [1575-4829] versus 6229 [4009-8093] pg/mL; P = 0.045). In recipient blood, levels of syndecan-1 were correlated with severe (grades 2-3) PGD at 72 hours posttransplant (5982 [3016-17191] versus 3060 [2005-4824] pg/mL; P = 0.01). CONCLUSIONS: Endothelial glycocalyx breakdown occurs in lung transplant donors and recipients and predicts organ acceptability and development of PGD. Glycocalyx breakdown products may be useful biomarkers in transplantation, and interventions to protect the glycocalyx could improve transplant outcomes.

Erratic tacrolimus exposure, assessed using the standard deviation of trough blood levels, predicts chronic lung allograft dysfunction and survival.

BACKGROUND: Erratic tacrolimus blood levels are associated with liver and kidney graft failure. We hypothesized that erratic tacrolimus exposure would similarly compromise lung transplant outcomes. This study assessed the effect of tacrolimus mean and standard deviation (SD) levels on the risk of chronic lung allograft dysfunction (CLAD) and death after lung transplantation. METHODS: We retrospectively reviewed 110 lung transplant recipients who received tacrolimus-based immunosuppression. Cox proportional hazard modeling was used to investigate the effect of tacrolimus mean and SD levels on survival and CLAD. At census, 48 patients (44%) had developed CLAD and 37 (34%) had died. RESULTS: Tacrolimus SD was highest for the first 6 post-transplant months (median, 4.01; interquartile range [IQR], 3.04-4.98 months) before stabilizing at 2.84 µg/liter (IQR, 2.16-4.13 µg/liter) between 6 and 12 months. The SD then remained the same (median, 2.85; IQR, 2.00-3.77 µg/liter) between 12 and 24 months. A high mean tacrolimus level 6 to 12 months post-transplant independently reduced the risk of CLAD (hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.63-0.86; p < 0.001) but not death (HR, 0.96; 95% CI, 0.83-1.12; p = 0.65). In contrast, a high tacrolimus SD between 6 and 12 months independently increased the risk of CLAD (HR, 1.46; 95% CI, 1.23-1.73; p < 0.001) and death (HR, 1.27; 95% CI, 1.08-1.51; p = 0.005). CONCLUSIONS: Erratic tacrolimus levels are a risk factor for poor lung transplant outcomes. Identifying and modifying factors that contribute to this variability may significantly improve outcomes.