Clonidine-Induce dEnhancemen to fiNO SExpressio nInvolve sNF-B

Background. Up-regulation of inducible nitric oxide synthase (iNOS) plays a crucial role in initiating sys- temic inflammatory response during sepsis. Clonidine, a widely used anti-hypertension agent and an effective adjunct to anesthesia/sedation and pain management, has been shown to enhance iNOS expression, but the mechanisms underlying its action remain unstudied. Among the possible mechanisms, enzyme induction and enzyme stability are two most likely ones. Endotoxin-induced iNOS induction is regulated by nu- clear factor-B (NF-B). Stability of iNOS mRNA is regulated by RNA stabilizing factor, e.g., Hu antigen R (HuR), and RNA destabilizing factors, e.g., AU-rich element/poly(U) binding factor-1 (AUF-1) and tristet- raprolin (TTP). We sought to elucidate which of these enzymes is involved in the clonidine-induced enhance- ment of iNOS expression. Materials and methods. Confluent murine macro- phages were randomized to receive 1 phosphated buffer saline, clonidine (100 M), lipopolysaccharide (LPS, 100 ng/mL), or LPS plus clonidine (100 M). Ex- pression of iNOS and stability of iNOS mRNA were then measured. Expression of the aforementioned rel- evant enzymes in each group was also analyzed. Results. Clonidine significantly enhanced LPS- induced iNOS expression. Clonidine also significantly enhanced LPS-induced NF-B activation by enhanc- ing the nuclear translocation of NF-B as well as in- creasing the NF-B-DNA binding activity. However, clonidine did not affect iNOS mRNA stability. The LPS-induced expression of AUF-1 and TTP but not HuR was significantly enhanced by clonidine.