OBJECTIVE: To investigate the protective mechanism of TAK242, a specific inhibitor of Toll-like receptor 4 (TLR4), on the liver of septic rats.
METHODS: Eighteen male Sprague-Dawley (SD) rats were randomly divided into three groups (n = 6 in each group). The septic model was established by intraperitoneal injection of lipopolysaccharide (LPS) 15 mg/kg. The rats in the TAK242 intervention group received intraperitoneal injection of TAK242 (5 mg/kg) before modeling, while the rats in the septic model group and the control group were injected with the same amount of solvent [10% dimethyl sulfoxide (DMSO)+90% corn oil]. Six hours later, the blood of abdominal aorta was collected and the levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured by enzyme linked immunosorbent assay (ELISA). The rats were sacrificed to obtain liver, the expression levels of TLR4, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), cysteinyl aspartate-specific proteinase-3 (caspase-3), nuclear factor-κB p65 (NF-κB p65) and phosphorylated NF-κB p65 (p-NF-κB p65) were detected by Western blotting. Immunohistochemical staining was used to observe NF-κB p65 protein expression in liver, and hepatocyte injury was assessed by hematoxylin-eosin (HE) staining.
RESULTS: Serum ALT and AST levels in the septic model group were significantly higher than those in the control group [ALT (μg/L): 26.639±7.814 vs. 2.847±2.150, AST (μg/L): 28.442±8.417 vs. 5.779±3.019, both P < 0.01]. The ALT and AST levels in the TAK242 intervention group were significantly lower than those in septic model group [ALT (μg/L): 7.269±3.398 vs. 26.639±7.814, AST (μg/L): 3.580±3.115 vs. 28.442±8.417, both P < 0.01]. Light microscopy showed that the hepatocytes in the septic model group were disordered, with obvious cell edema and increased inflammatory cells infiltration; the hepatocytes in the TAK242 intervention group were more neatly arranged, with significantly reduced hepatocyte edema and reduced inflammatory cells infiltration. Western blotting results showed that caspase-3 protein expression in hepatic tissue of septic model group was significantly higher than that in the control group (caspase-3/GAPDH: 0.794±0.164 vs. 0.482±0.055, P < 0.05), and caspase-3 protein expression in the TAK242 intervention group significantly decreased than that in the septic model group (caspase-3/GAPDH: 0.482±0.056 vs. 0.794±0.164, P < 0.05), which indicated that TAK242 could attenuate hepatocytes apoptosis of septic rats. The expression of IL-6, TNF-α and TLR4 protein and the ratio of p-NF-κB p65/NF-κB p65 in hepatic tissue of septic model group were significantly higher than those in control group (IL-6/GAPDH: 1.442±0.204 vs. 1.019±0.024, TNF-α/GAPDH: 1.089±0.098 vs. 0.806±0.005, TLR4/GAPDH: 1.292±0.085 vs. 0.941±0.087, p-NF-κB p65/NF-κB p65 ratio: 1.936±0.081 vs. 1.579±0.183, all P < 0.05), IL-6, TNF-α and TLR4 protein expression and p-NF-κB p65/NF-κB p65 ratio in the TAK242 intervention group were significantly lower than those in septic model group (IL-6/GAPDH: 1.035±0.042 vs. 1.442±0.204, TNF-α/GAPDH: 0.572±0.096 vs. 1.089±0.098, TLR4/GAPDH: 0.984±0.078 vs. 1.292±0.085, p-NF-κB p65/NF-κB p65 ratio: 1.484±0.255 vs. 1.936±0.081, all P < 0.05), it is suggested that LPS-induced sepsis could activate the inflammatory response mediated by TLR4/NF-κB pathway in liver, and the activation of TLR4/NF-κB pathway was inhibited by TAK242 through the TLR4 pathway, therefore, the inflammation of liver in septic rats was reduced. Immunohistochemical staining showed that the positive expression of NF-κB p65 in liver was significantly increased in the septic model group compared with the control group; the positive expression of NF-κB p65 was significantly reduced in the TAK242 intervention group compared with the septic model group, and there was almost no positive expression in the nucleus.
CONCLUSIONS: TAK242 could reduce liver function injury and protect the liver by inhibition TLR4/NF-κB pathway in septic rats.
