Absence of toll-like receptor 4 (TLR4) signaling in the donor organ reduces ischemia and reperfusion injury in a murine liver transplantation model

Abstract

This study analyzes how toll-like receptor 4 (TLR4) signaling in the donor organ affects the ischemia and reperfusion injury (IRI) sequel following liver transplantation. Isogenic orthotopic liver transplantations (OLTs) with rearterialization were performed in groups of wild-type (WT) and TLR4 knockout (KO) mice after donor liver preservation in University of Wisconsin solution at 4°C for 24 hours. Unlike WT OLTs, TLR4-deficient OLTs transplanted to either WT or TLR4 KO recipients suffered significantly less hepatocellular damage, as evidenced by serum alanine aminotransferase levels, and histological Suzuki's grading of liver IRI. Disruption of TLR4 signaling in OLTs decreased local neutrophil sequestration, CD4 ϩ T cell infiltration, interferon (IFN)-␥-inducible protein 10 (CXCL10) and an intercellular adhesion molecule (ICAM-1), as well as tumor necrosis factor (TNF)-␣, interleukin (IL)-1␤, IL-2, and IFN-␥, yet increased IL-4 and IL-10 expression. The well-functioning OLTs from TLR4 KO donors revealed attenuated activity of capase-3, and enhanced heme oygenase-1 (HO-1) expression, along with decreased levels of apoptotic endothelial cells/hepatocytes, as compared with WT OLTs with intact TLR4 signaling. Thus, the functional sentinel TLR4 complex in the donor organ plays a key role in the mechanism of hepatic IRI after OLT. Disruption of TLR4 pathway downregulated the early proinflammatory responses and ameliorated hepatic IRI. These results provide the rationale to locally modify innate TLR4 signaling in the donor organ to more efficiently control the adaptive posttransplantation IRI-dependent responses. Liver Transpl 13:1435-1443, 2007. © 2007 AASLD. Received February 7, 2007 accepted May 19, 2007.The ischemia and reperfusion injury (IRI), an antigenindependent event, is an unavoidable consequence of liver transplantation. The IRI causes up to 10% of early organ failure, and can lead to a higher incidence of both acute and chronic rejection. Indeed, IRI is more frequently observed with the use of marginal donors or following prolonged cold ischemia times. 1-3 Moreover, IRI contributes to the shortage of livers available for transplantation because of the higher susceptibility of marginal organs to the ischemic insult. Thus, minimizing the impact of IRI could significantly increase the number of patients successfully undergoing liver transplantation. The mechanisms of IRI include activation of Kupffer cells with production of reactive oxygen species, upregulation of the inducible nitric oxide synthase, release of proinflammatory cytokines, increased expres-

Mechanisms of hepatic ischemia-reperfusion injury and protective effects of nitric oxide

“…HGF is produced by liver non-parenchymal cells, mainly KCs. HGF can increase hepatocyte DNA synthesis, proliferation, and glutathione expression, downregulate the expression of the oxidative stress marker ICAM-1 in sinusoidal endothelial cells, and inhibit cytokine-induced neutrophil chemotaxin and neutrophil permeability, further reducing liver damage and promoting liver cell proliferation [27] .…”

Untitled

“…Several targeted therapies have demonstrated improvements in different steps of IPRI including inhibition of Kupffer cells, neutrophil depletion, cell surface receptor blockade, antioxidant effects, delivery of exogenous or endogenous adenosine, and alteration of the endothelial nitric oxide balance. 5,15 In the pathophysiology of IPRI, intracellular energy depletion leading to activation of the innate immune system plays a central role. 2 In the absence of oxygen during preservation, ATP can only be generated through the anaerobic glycolysis.…”

“…3 In studies, therapies targeting specific aspects of IPRI have been determined to be especially effective when applied before the onset of IPRI. 4,5 The early recovery of cellular metabolism after transplant is accomplished with the prevention of IPRI. The livers are stored in preservation solutions on melting ice at 0ºC to 4ºC, allowing a safe preservation up to 12 hours; however, a cold ischemia longer than 12 hours also is associated with a greater risk of graft dysfunction.…”

TLR4 Mediates Early Graft Failure After Intraportal Islet Transplantation

“…(22). The role of TLR activation in the initiation of liver inflammatory reaction, associated with liver ischemic-reperfusion injury and in the mediation of allograft rejection have been documented (23)(24)(25) (26), heat shock proteins (HSP) (27), nucleic acids (28) and heparin sulfate (26) (32,33). Liver ischemia and reperfusion injury results in increased HMGB1 expression and can be prevented by the inhibition of HMGB1 with a neutralizing antibody (29,34 (16,19).…”