Heme oxygenase-1 mediates the anti-inflammatory effect of isoflurane preconditioning in LPS-stimulated macrophages

Aim: The aim of this study was to investigate the anti-inflammatory action of isoflurane preconditioning in a model of lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophages and examine the role of heme oxygenase (HO)-1 in this process. Methods: Murine 264.7 macrophages were pretreated with or without 1%-3% isoflurane for 1 h. Thirty minutes later, the cells were incubated with or without LPS for 24 h. Cell viability was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell injury was assessed by measuring the release of lactate dehydrogenase (LDH). HO-1 and inducible nitric oxide synthase (iNOS) protein expression was analyzed by Western blotting. Tumor necrosis factor (TNF)-alpha levels, nitrite production and HO activity were also determined. Results: Pretreatment with the nontoxic and clinically approved anesthetic isoflurane potently attenuated the cell injury and the decrease in cell viability that was induced by LPS. Treatment or pretreatment with 2% isoflurane induced HO-1 protein expression and caused an induction of HO activity. This result correlated with a decrease in iNOS expression, a decrease in the production of nitric oxide (NO) and impaired release of TNF-alpha in LPS-stimulated macrophages. Blockade of HO activity with tin protoporphyrin (SnPP) reversed these effects. Conclusion: Isoflurane preconditioning exerts its anti-inflammatory activity through the HO-1 pathway in an in vitro inflammation model.