BACKGROUND: Toll-like receptor 4 (TLR4) is involved in innate immunity by recognizing endotoxin resulting in a burst of inflammatory cascade. We investigated the relation between activation of TLR4 and liver injury in partial hepatic ischemia/reperfusion (I/R) injury in mice.
METHODS: TLR4-deficient mice (C3H/Hej) and wild type mice (WT, C3H/Heouj) were used in the model of I/R injury. Partial hepatic ischemia was produced by occlusion of inflow to the median and left lobes for 45 minutes. Blood was drawn at 1 and 3 hours after reperfusion. The blood was analyzed for aspartate aminotransferase (AST) and tumor necrosis factor alpha (TNF-α). TNF-α mRNA expression and myeloperoxidase (MPO) level in the ischemic lobes were examined by northern blot and myeloperoxidase assay respectively.
RESULTS: AST levels were significantly decreased in TLR4deficient mice compared with WT mice at both time points (WT: 1215.5±174.03, 2958.17±186.81 IU/L at 1 and 3 hours respectively vs TLR4def: 661.83±106.09, 1145.17±132.43 IU/L at 1 and 3 hours, mean±SD, 6 mice/group, t=-6.65 and -5.57, P<0.001). Consistent with the role of TNF-α in hepatic I/R, serum TNF-α was decreased in TLR4 deficient mice at 3 hours after reperfusion compared with WT (152.39±43.3 vs 249.12±51.89, n=6, t=-3.13, P<0.05). MPO level in the ischemic lobes in TLR4 deficient mice at 3 hours after reperfusion was significantly lower than that in WT mice (0.059 ±0.004 vs 0.173±0.025, n=6, F=33.49, P<0.001). This difference appears to be mediated at the gene level since TLR4 deficient mice had decreased TNF-α mRNA expression at 1 hour after reperfusion compared with WT mice (80.3±28.8 vs 189.4±24.6, t=-3.25, P<0.05).
CONCLUSIONS: Compared with WT mice, TLR4-deficient mice appear to have a mild I/R injury. Regulation of TNF-α at mRNA level seems to have a critical effect. These suggest TLR4 be involved in the mechanism of hepatic I/R injury in mice.