Biliary complications in liver transplantation: role of the hepatic ischaemia-reperfusion injury

Introduction Liver transplantation is currently the only effective therapy for patients with end stage acute or chronic liver failure. The increasing request of organs has led to the more extensive use of the so-called marginal donors, in particular donors after circulatory death (DCD). Within this model of donation, a more severe degree of ischaemia-reperfusion injury (IRI) is occurring, that seems to play a role on the pathogenesis of local and remote organ complications. This research will focus on the influence of liver graft injury on the pathogenesis of local and remote organ complications, evidencing the role of IRI leading to biliary complications and development of systemic inflammatory response associated with the occurrence of acute kidney injury (AKI). Aim of the study was to assess the role of IRI in two different models of ischaemia, DCD and donation after brain death (DBD), in liver transplanted grafts, on the pathogenesis of local and remote organ complications. We evaluated the development of biliary complications and its association with the degree of donor liver graft bile duct injury after liver reperfusion. Moreover, the development of AKI after liver transplantation was considered, as consequence of IRI and systemic inflammatory response. Methods Retrospective single-centre study of adult patients who underwent liver transplantation at University Hospital Birmingham (UHB) National Health Service (NHS) Foundation Trust from January 2007 to December 2014. Characteristics of recipient at transplant, recipient renal and liver function in the immediate pre-transplant period, donor and graft variables, intra-operative parameters, indicators of initial graft function and renal function in the post-transplant period were considered. Primary end points were the occurrence of biliary complications, in particular ischaemic cholangiopathy (IC), and development of AKI. Secondary end point was the evaluation of IRI damage on the basis of transaminases, bilirubin and INR over the first week post-transplant and the appearance of bile duct retrieved after liver reperfusion on histological examination. Severity of donor bile duct injury was assessed and scored on the basis of biliary epithelial cell loss, mural stroma necrosis, inflammation, peribiliary vascular plexus (PVP) damage, arteriolonecrosis, thrombosis, periluminal and deep peribiliary glands (PBGs) damage. Cholangiocyte apoptosis in periluminal and deep PBGs was evaluated by quantitative terminal deoxy-nucleotidyl transferase dUTP-mediated nick-end labeling (TUNEL) analysis on bile duct sections. Cholangiocyte proliferation was studied in bile duct sections by PCNA immunohistochemical expression. Results One thousand and 60 liver transplant recipients (813 from DBD and 247 from DCD) were considered. Recipients from DCD had higher ALT and AST in the first 7 days after transplant, compared to DBD. The occurrence of biliary complications was higher in DCD liver transplant recipients (85/247; 34%) compared to DBD (166/813; 20%) (p<0.001), in particular IC incidence was significantly higher in DCD. The incidence of AKI was 59.3% (629/1060 recipients) and was significantly higher in DCD (160/247, 64.8%) compared to DBD (469/813, 57.7%) recipients (p=0.047). Sixty-two patients comparable with the entire cohort, had the bile duct sample available for histological evaluation. A significantly higher number of DCD patients presented necrosis >50% of the bile duct wall [DCD 14/28 (50%), DBD 9/34 (26.5%) p=0.056], PVP damage [DCD 8/28 (29%), DBD 3/34 (9%); p=0.053] and periluminal PBGs damage [DCD 20/28 (71%), DBD 14/34 (41%); p=0.016]. These features defined the occurrence of severe histological injury, that was significantly more frequent in DCD liver transplant patients [15/28 (53.6%)] compared to DBD [7/34 (20.6%)] (p=0.007). A significant increased apoptosis and decreased proliferation was evidenced in both periluminal (Tunel assay p=0.029; PCNA expression p=0.029) and deep PBGs (Tunel assay p=0.002; PCNA expression p=0.006) from bile duct sample with severe histological injury. Discussion A more severe degree of IRI is occurring within DCD, as evidenced by greater graft dysfunction and increasing peak perioperative transaminases, likely related to the added donor warm ischaemia time. The IRI seems to play a role on the pathogenesis of local and remote organ complications, evidencing the role exerted in DCD leading to biliary complications and development of systemic inflammatory response associated with the occurrence of AKI. This study also shows an early picture of microscopic damage at the level of the bile duct soon after reperfusion of liver graft during transplantation. Bile duct samples retrieved from DCD grafts expressed more severe injury at the histological level, as evidenced by the increased incidence of mural stroma necrosis, PBP damage and PBG damage, defining the new feature of severe histological injury. Bile ducts with severe histological injury showed increased apoptosis and reduced proliferation, as evaluated by Tunel assay and PCNA expression, both on periluminal and deep PBG cholangiocytes. The higher incidence of IC development in DCD strongly suggests a relation between the occurrence of severe histological injury and alteration in bile duct repair mechanisms, raising hypothesis to further evaluate those mechanisms leading to the development of bile duct non-anastomotic strictures.