Pretreatment of dexamethasone before cardiopulmonary bypass upregulates intrahepatic synthesis of IL-10 via the transcription factors Sp1 and Sp3 and CCAAT/enhancer-binding protein

Background and aim

IL-10 is an anti-inflammatory cytokine produced by a variety of cell types including Kuffper cells and hepatocytes. A recent study showed that IL-10 gene expression induced by endotoxin (LPS) in mouse macrophages is controlled by the cooperation of the promoter-selective transcription factors (Sp)1 and Sp-3 as well as by CCAAT/enhancer-binding protein β (C/EBPβ). Dexamethasone (Dex) has been recommended during cardiac surgery since it increases blood IL-10 levels during cardiopulmonary bypass (CPB) and reduces the release of proinflammatory mediators including tumor necrosis factor alpha. In an experimental model of cardiac surgery, it reduces the production of iNOS and COX-2.

This study was designed to identify the signaling pathways involved in intrahepatic overexpression of IL-10 induced by pretreatement by Dex before CPB.

Methods

Animals were treated with Dex (1 mg/kg) (n = 9) or with saline (n = 6) given intervenously before normothermic CPB. Samples of liver tissue were taken before and 6 hours after CPB. IL-10 mRNA was assessed by competitive RT-PCR. Protein levels of IL-10, iNOS and COX-2 were assessed by western blot. Phosphorylation of extracellular regulating kinase (ERK1/2) and of the inhibitory protein of NF-κB (IkB) as well as nuclear protein levels of C/EBPβ were also detected by western blot. Activation of Sp1 and Sp3, C/EBPβ, NF-κB, and AP-1 were assessed by electrophoretic mobility shift assay with supershift. Liver tissue damage score was assessed by standard histology.

Results

Pigs treated with Dex showed significantly higher intrahepatic concentration of IL-10 and lower concentrations of iNOS and COX-2 than the others. The former also showed lower tissue damage score. This upregulation of IL-10 and down-regulation of iNOS and COX-2 observed in the treated group was associated with a higher activation of Sp1 and Sp3 as well as C/EBPβ. Moreover, levels of phospho-ERK1/2 and of C/EBPβ in nuclear extract were significantly higher 6 hours after CPB in pigs treated with Dex than in the others. Activation of NF-κB and of activator protein-1 was not significantly different between both groups.

Conclusion

Our results show for the first time that Dex administration prior to CPB upregulates IL-10 via Sp1 and Sp3 as well as throughout C/EBPβ activation. This leads to attenuation of expression of iNOS and COX-2 and to hepatic protection.