Antithrombin III Enhances Inducible Nitric Oxide Synthase Gene Expression in Vascular Smooth Muscle Cells

Evidence suggests that antithrombin III (ATIII) exerts anti-inflammatory properties in addition to its anti-coagulative mechanisms. In animal models of sepsis, ATIII affected cytokine plasma concentrations with a decrease of pro-inflammatory cytokines. In addition to cytokines, excessive production of nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) might represent another important mediator of the cytotoxic events during sepsis. Regarding ATIII as a potential anti-inflammatory modulator, one may speculate that ATIII inhibits the synthesis of iNOS-derived NO. However, our data demonstrate that ATIII further stimulates iNOS gene expression when applied together with either interleukin-1β or the combination of lipopolysaccharide plus interferon-γ. The most prominent synergistic effects on NO synthesis were found when ATIII was given at higher concentrations (1, 5, and 10 U/ml). Although the mechanisms of ATIII signal transduction remain to be established, intensification of interleukin-1β or interferon-γ/lipopolysaccharide-induced NO synthesis by ATIII does not attribute to the anti-inflammatory properties of ATIII.