Cyclooxygenase-2 inhibitors attenuate the severity of galactosamine-lipopolysaccharide induced acute liver injury in mice

Abstract

Background and Aims: Cyclooxygenase (COX) is a key enzyme that converts arachidonic acid to PGH2, which is then converted to a series of end products such as PGE2 and thromboxanes. COX has two isoforms; COX- I (constitutively expressed) and COX-2 (inducible form). We investigated the role of COX inhibitors on the lethality, hepatic injury and inflammatory mediators induced by LPS in Galactosamine-sensitized mice. Methods: Adult male ICR mice were given a single i.p. injection of 600mg/kg of Galactosamine (Gal) and 20~g/kg of LPS. COX-2 inhibitors (indomethacin, 3 mg/kg or Nimesulide, 30 mgikg) were given 30 minutes before Gal/LPS injection. Corresponding negative (vehicle only) and positive control (Gal-LPS only) groups were also included. Sixteen hours after injection, the mice were killed. Liver tissue and blood were obtained. Histology (H&E staining), serum ALT, TBARS, RT-PCR, immunohistochemistry and Western Blotting for TNF-a, COX-1, COX-2, iNOS, nitrotyrosine and CIEBP-a and gel shift analysis for NF-KB were performed. Results: There was a marked reduction in the degree of hepatic necrosis in the indomethacin and (INDO) and Nimesulide-pretreated (NIM) mice when compared with the positive controls. Histological changes were confirmed by serum ALT levels. A significant reduction (p i 0.05) in hepatic oxidative and nitrosative stress [TBARS, iNOS mRNA and protein and nitrotyrosine protein] was observed in mice pre-treated with either INDO or NIM when compared with positive controls. There was an inverse relationship between COX-1 and COX-2 mRNAs and protein as well as between COX-2 and C/EBP-a protein expression in both the COX-2 inhibitor-pretreated mice and controls. TNF-a mRNA and NF-KB expression were also markedly higher in the positive controls when compared with the COX-2 inhibitor-pretreated mice. Conclusion: COX-2 inhibitors protected the liver from Gal-LPS induced hepatotoxicity as shown by a significant reduction in hepatic necrosis and serum ALT and oxidative stress. A marked reduction of iNOS, nitrotyrosine, TBARS, TNF-a and NF-KB expression was also observed, suggesting the use of COX inhibitors as therapeutic agents in preventing acute liver injury.