Molecular mechanisms of propofol-involved suppression of no biosynthesis and inducible inos gene expression in lps-stimulated macrophage-like raw 264.7 cells

Propofol (PPF), a widely used intravenous anesthetic agent, has been reported to have immunosuppressive and antioxidative effects. NO plays crucial roles in mediating inflammatory reactions. This study was designed to evaluate the effects of PPF on regulation of iNOS and its possible signal-transducing mechanisms in LPS-activated macrophage-like Raw 264.7 cells. Exposure of Raw 264.7 cells to LPS significantly increased nitrite production, but PPF reduced such enhancement in concentration- and time-dependent manners. In parallel, treatment of Raw 264.7 cells with a clinically relevant concentration of PPF (50 μM) significantly inhibited iNOS mRNA and protein production in LPS-activated Raw 264.7 cells. Propofol at 50 μM decreased the LPS-caused augmentation in nuclear c-Jun levels. An electrophoretic mobility shift assay revealed that PPF significantly decreased the binding affinity of the nuclear extracts from LPS-treated Raw 264.7 cells to activator protein 1 (AP-1) consensus DNA elements. A reporter gene assay further showed that PPF ameliorated the transactivated activity of AP-1 in LPS-stimulated Raw 264.7 cells. LPS sequentially increased phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) 4 and c-Jun N-terminal kinase (JNK) 1/JNK-2. Meanwhile, a therapeutic concentration of PPF significantly decreased the activation of these two protein kinases. Application of Toll-like receptor 4 (TLR-4) siRNA to Raw 264.7 cells decreased cellular TLR-4 levels and LPS-caused activation of MEK-4. Cotreatment with PPF and TLR-4 siRNA synergistically lowered the LPS-induced increased biosynthesis of iNOS mRNA and nitrite. Therefore, a clinically relevant concentration of PPF can inhibit NO production and iNOS gene expression in LPS-activated Raw 264.7 cells. The suppressive mechanisms may occur through sequential down-regulation of TLR-4/MEK-4/JNK-1/JNK-2/AP-1 activation.