Up-regulation of hypoxia inducible factor 1 α by isoflurane in Hep3B cells

Background: The volatile anesthetic isoflurane induces hypoxia inducible factor (HIF)-1-responsive genes heme oxygenase 1, inducible nitric oxide synthase, and vascular endothelial growth factor (VEGF) expression. Little is known about the extent to which induction of HIF-1 alpha is affected by isoflurane. Methods. Hep3B cells were exposed to isoflurane at various concentrations (0.5-4%) or for different time periods (2-8 h) at 37 degrees C. HIF-1 alpha gene expression and transcriptional activity, heme oxygenase 1, inducible nitric oxide synthase, and VEGF gene expression were quantified. Results: Isoflurane induced a time- and concentration-dependent increase in HIF-1 alpha protein but not for HIF-1 alpha messenger RNA (mRNA) in Hep3B cells. The maximal increase was induced by 2% isoflurane, and the cells incubated with 2% isoflurane for 4-8 h expressed the highest protein. Similarly, HIF-1 alpha transcriptional activity was higher in Hep3B cells exposed to 2% isoflurane for 16 h than that in control cells. The combination of 2% isoflurane and desferrioxamine, a hypoxia mimetic, caused a higher level of HIF-1 alpha protein than that induced by 2% isoflurane alone. Reoxygenation and inhibitor of proteasome pathway MG132 did not affect the isoflurane-induced HIF-1 alpha protein accumulation. Cycloheximide, an inhibitor for protein synthesis, completely abrogated the induction of HIF-1 alpha protein by isoflurane. Isoflurane stimulated heme oxygenase 1, inducible nitric oxide synthase, and VEGF mRNA expression in a concentration-dependent manner, and inactivation of HIF-1 alpha attenuated the induction of VEGF mRNA by isoflurane. Conclusion: Isoflurane can up-regulate HIF-1 alpha and enhance HIF-1-responsive genes heme oxygenase 1, inducible nitric oxide synthase, and VEGF mRNA expression in Hep3B cells. The induction of HIF-1 alpha by isoflurane does not involve protein degradation but depends on translation pathway.