Delayed Treatment with Isoflurane Attenuates Lipopolysaccharide and Interferon γ-induced Activation and Injury of Mouse Microglial Cells

Background: Isoflurane pretreatment can induce protection against lipopolysaccharide and interferon gamma (IFN gamma)-induced injury and activation of mouse microglial cells. This study's goal was to determine whether delayed isoflurane treatment is protective. Methods: Mouse microglial cells were exposed to various concentrations of isoflurane for 1 h immediately after the initiation of lipopolysaccharide (10 or 1000 ng/ml) and IFN gamma (10 U/ml) stimulation or to 2% isoflurane for 1 h at various times after initiation of the stimulation. Nitrite production, lactate dehydrogenase release, and cell viability measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay were assessed after stimulation with lipopolysaccharide and IFN gamma for 24 h. Inducible nitric oxide synthase (iNOS) protein expression was quantified by Western blotting. The iNOS expression in mouse brain was also studied. Results: Isoflurane applied 0 and 2 h after the initiation of lipopolysaccharide and IFN gamma stimulation improved cell viability. Isoflurane at 2%, but not at 1 or 3%, reduced the lipopolysaccharide and IFN gamma-induced nitrite production and decreased cell viability. Aminoguanidine, an iNOS Inhibitor, also attenuated this decreased cell viability. Chelerythrine and bisindolylmalemide IX, protein kinase C inhibitors, abolished isoflurane effects on cell viability and iNOS expression after lipopolysaccharide and IFN gamma application. Isoflurane also decreased lipopolysaccharide-induced iNOS expression in mouse brain. Late isoflurane application to microglial cells reduced lipopolysaccharide and IFN gamma-induced lactate dehydrogenase release that was not inhibited by aminoguanidine. Conclusions: These results suggest that delayed isoflurane treatment can reduce lipopolysaccharide and IFN gamma-induced activation and injury of microglial cells. These effects may be mediated by protein kinase C.