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<p>Objective: To investigate the effects and potential mechanisms of preconditioning of tricarbonyldichlororuthenium (III) dimer (CORM-2)-liberated CO on LPS-induced activation of endothelial cells (HUVEC).</p> <p>Methods: HUVEC were pretreated with CORM-2 at the concentration of 50 or 100&#956;M for 2 hrs, washed and stimulated with LPS (10&#956;g/ml) for additional 4 hrs. Activation (oxidative stress) of HUVEC was assessed by measuring intracellular oxidation of DHR 123 or nitration of DAF-FM, specific H₂O₂ and NO fluorochromes, respectively. The expression of HO-1, iNOS (Western blot) and ICAM-1 (cell ELISA) proteins and activation of inflammation-relevant transcription factor, NF-&#954;B (EMSA) were assessed. In addition, PMN adhesion to HUVEC was also assessed.</p> <p>Results: The obtained data indicate that pretreatment of HUVEC with CORM-2 results in: 1) decrease of LPS-induced production of ROS and NO; 2) up-regulation of HO-1 but decrease in iNOS at the protein levels; 3) inhibition of LPS-induced activation of NF-&#954;B; and 4) downregulation of expression of ICAM-1, and this was accompanied by a decrease of PMN adhesion to LPS-stimulated HUVEC.</p> <p>Conclusions: Preconditioning of CO liberated by CORM-2 elicited its anti-inflammatory effects by interfering with the induction of intracellular oxidative stress. In addition, it also supports the notion that CO is a potent inhibitor of iNOS and NF-&#954;B.</p>