Study of Liver Ischaemia-reperfusion Injury and Its Modulation by N-acetylcysteine

Liver ischaemia-reperfusion (I/R) injury occurs in a number o f clinical settings, including liver surgery, transplantation and haemorrhagic shock with subsequent fluid resuscitation. It is well recognised as a significant cause o f morbidity and mortality and characterised by oxidative stress accompanied with depletion o f antioxidants. Its pathophysiology is complex. This thesis investigates the effect o f lobar liver I/R injury on liver microcirculation, hepatic oxygenation, cellular energetics and nitric oxide (N O ) metabolism. It evaluates also the hypothesis that the antioxidant N-acetylcysteine (NAC) ameliorates liver I/R injury. Initially an experimental rabbit model was established where both phases (early and late) o f liver I/R injury could be studied. New Zealand white rabbits underwent 60 min of lobar ischaemia followed by 7 h of reperfusion. It was found that cannulation of the femoral artery, for monitoring of the arterial blood pressure, induced remote liver injury, which could be avoided by use of the ear artery. Lobar liver I/R caused significant decrease in hepatic microcirculation, liver tissue oxygenation and cellular energetics. It also caused significant alterations in NO metabolism during the late phase (increase in plasma nitrites and plasma S-nitrosothiols, decrease in liver tissue nitrotyrosine) and significant oxidative stress. Intravenous administration o f NAC (150 mg/Kg/h over the 15 min before reperfusion and maintenance at 10 mg /Kg/h during the 7 h reperfusion period) had a clear protective effect during the late phase of reperfusion injury in rabbits with normal and steatotic liver. This effect was associated with improved cellular energy metabolism (maintenance o f cytochrome oxidase activity, increased acetates and decreased lactates in bile) and altered NO metabolism (reduced plasma nitrites, S-nitrosothiols and reactive nitrogen species). In conclusion, this thesis has shown that lobar hepatic I/R induces significant alterations on cellular energetics and NO metabolism. It provides also significant new information about the timing and the possible mechanism of the protective effect o f NAC. It could form the basis for the performance of large scale prospective randomised clinical trials where the effect o f thiols in clinical settings o f liver I/R injury will be investigated.