Dexmedetomidine Protects Rat Liver against Ischemia-Reperfusion Injury Partly by the α2A-Adrenoceptor Subtype and the Mechanism Is Associated with the TLR4/NF-κB Pathway

Abstract

Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling plays a dominant role in the pathogenesis of liver ischemia-reperfusion (IR) injury. Dexmedetomidine (Dex) protects the liver against IR injury via α₂-adrenoceptor activation, but the contribution of TLR4 signaling remains unknown. The authors aimed to examine whether pretreatment with Dex produces hepatic protection and investigate the influence of Dex on TLR4/NF-κB signaling. Dex was given via intraperitoneal injection 30 min prior to orthotopic autologous liver transplantation (OALT) in rats, and three α₂-adrenoceptor antagonists including atipamezole (a nonselective α₂ receptor blocker), ARC-239 (a specific α2B/C blocker) and BRL-44408 (a specific α2A blocker) were injected intraperitoneally 10 min before Dex administration. Histopathologic evaluation of the liver and the measurement of serum alanine aminotransferase activity, TLR4/NF-κB expression in the liver, and pro-inflammatory factors (serum tumor necrosis factor-α, interleukin-1β and hepatic myeloperoxidase) concentrations were performed 8 h after OALT. Dex ameliorated liver injury after OALT probably by suppressing the TLR4/NF-κB pathway and decreasing inflammatory mediator levels. The protective effects of Dex were reversed by atipamezole and BRL-44408, but not by ARC-239, suggesting that these effects were mediated in part by the α2A subtype. In conclusion, Dex attenuates liver injury partly via the α2A-adrenoceptor subtype, and the mechanism is due to the suppression of the TLR4/NF-κB pathway.

Keywords: TLR4/NF-κB; dexmedetomidine; ischemia-reperfusion injury; liver transplantation; α2A-adrenoceptor subtype.

Figure 1

Histological changes in the liver of each group. Representative microphotographs taken from group S (A); group M (B); group D1 (C); group D2 (D); group B1 (E); group B2 (F); and group B3 (G). (H and E stain, 100× magnification; scale bars, 200 μm).

Figure 2

Quantification of histological scoring. The data are expressed as the means ± SD (n = 8). ** p < 0.01, vs. group S; ⁺⁺ p < 0.01, vs. group M; ^## p < 0.01, vs. group D2.

Figure 3

Serum alanine aminotransferase (sALT, U/L) level. The data are expressed as the means ± SD (n = 6–7). * p < 0.05, ** p < 0.01, vs. group S; ⁺⁺ p < 0.01, vs. group M; ^## p < 0.01, vs. group D2.

Figure 4

Expression of the Toll-Like Receptor 4 (TLR4) and NF-κB proteins in liver tissue of the different groups. (A) representative Western blotting for TLR4 in total proteins; (B) quantification analysis of TLR4 protein expressions by reference to β-actin content; (C) representative Western blotting for NF-κB p65 in nuclear proteins; and (D) quantification analysis of NF-κB p65 protein expressions by reference to Histone H3.1 content. The data are expressed as the means ± SD (n = 5–7). ** p < 0.01, vs. group S; ⁺ p < 0.05, ⁺⁺ p < 0.01, vs. group M; ^## p < 0.01, vs. group D2.

Figure 5

Expression of the phospho-NF-κB subunit p65 protein in liver tissue of the different groups as measured by immunofluorescence staining observed via laser scanning confocal microscopy (LSCM) (magnification, ×400, scale bars, 50 μm). (A) Group S; (B) group M; (C) group D1; (D) group D2; (E) group B1; (F) group B2; and (G) group B3. Positive p65 cells were stained green, and the sections were counterstained with 4,6-diamidino-2-phenylindole(DAPI) to visualize the nuclei.

Figure 6

The ratio of phospho-NF-κB subunit p65-positive cells in the liver tissue of the different groups. Cells were counted via LSCM (magnification, ×400). The data are expressed as the means ± SD (n = 8). ** p < 0.01, vs. group S; ⁺⁺ p < 0.01, vs. group M; ^## p < 0.01, vs. group D2.

Figure 7

The concentrations of plasma TNF-α (A); IL-1β (B) and activity of hepatic myeloperoxidase (MPO) (C) in the different groups. The data are expressed as the means ± SD (n = 8). * p < 0.05, ** p < 0.01, vs. group S; ⁺ p < 0.05, ⁺⁺ p < 0.01, vs. group M; ^## p < 0.01, vs. group D2.