Tapuria, N.; (2010) Study of the effect of Remote Ischaemic Preconditioning (RIPC) on the early and late phase of hepatic ischaemia reperfusion injury and the role of haemoxygenase in RIPC. Doctoral thesis , UCL (University College London).

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Abstract

Reperfusion following ischaemia results in endothelial and parenchymal injury through a complex cascade of events. This often occurs in human liver transplantation as well as with major liver resections and is referred to as Ischaemia Reperfusion Injury (IRI). Ischaemic Preconditioning (IPC) is an adaptive response in which tolerance to prolonged ischaemia is induced in a target organ by prior brief periods of ischaemia. Benefits of IPC have been demonstrated in experimental models and in preliminary human clinical trials. In remote ischaemic preconditioning (RIPC) brief ischaemia involves a remote organ. RIPC has been demonstrated to reduce warm liver I/R injury in an experimental model by our research group and clinical evaluation is ongoing. The effect of RIPC on the late phase of I/R and its mechanism have not been investigated. This thesis evaluates the effect of RIPC on both the early and late phases of liver warm I/R injury with the hypothesis that beneficial effects are induced by haemoxygenase- 1(HO-1), a free radical scavenger which is involved in degradation of haem and production of the vasodilator CO. Male Sprague Dawley rats were subjected to 45 mins of partial hepatic (70 %) ischaemia followed by 3 hrs of reperfusion to investigate the early phase of hepatic IR and 24 hrs of reperfusion to study the late phase of hepatic IR. RIPC was performed with four cycles of 5 min ischaemia and 5 min reperfusion of the right hind limb before sustained ischaemia. Pyrrolidine dithiocarbamate (PDTC) and Zinc Protoporrphyrrin (ZnPP) were administered to induce and block haem oxygenase synthesis. Changes to the microcirculation, leucocyte adherence and apoptosis were assessed by intra-vital microscopy. Hepatocellular injury was assessed by standard liver function tests. HO-1 protein was demonstrated by immunohistochemistry (IHC) and measured by Western blot. RIPC improved liver sinusoid perfusion, reduced leucocyte adherence and apoptosis in both the early and late phases of IRI. Hepatocellular injury was reduced. RIPC increased HO-1 production in the liver, particularly in hepatic macrophages, as demonstrated by IHC. PDTC treatment (HO-1 inducer) reproduced the protective effect of RIPC whereas HO-1 inhibition with ZnPP abolished the protective effect. The response to HO-1 induction and inhibition indicate that HO-1 has a key role in the protective effect of RIPC. Establishing the inducing agent for HO-1 may lead to new pharmacological approaches to preconditioning and the protection of the liver from IR injury. Studies on RIPC and liver warm I/R using HO-1 knockout mice would clarify the pathways involved in RIPC.

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