In vitro modulation of inducible nitric oxide synthase gene expression andnitric oxide synthesis by procalcitonin

Objective: Serum procalcitonin (PGT) concentration was recently introduced as valuable diagnostic marker for systemic bacterial infection and sepsis. At present, the cellular sources and biological properties of PCT are uncle ar. During sepsis and septic shock, inducible nitric oxide synthase (iNOS) gene expression is stimulated followed by the release of large amounts of n itric oxide (NO). We investigated the possible association between PGT and iNOS gene expression in an in vitro cell culture model. Design: Prospective, controlled in vitro cell culture study. Setting: University research laboratories. Interventions: Confluent rat vascular smooth muscle cells (VSMC) were incub ated for 24 hrs and 48 hrs with PGT (1 ng/mL, 10 ng/mL, 100 ng/mL, 1000 ng/ mL, 5000 ng/mL) alone or with the combination of tumor necrosis factor-alph a (TNF-alpha, 500 U/mL) plus interferon-gamma (IFN-gamma, 100 U/mL). iNOS g ene expression was measured by qualitative as well as quantitative polymera se chain reaction analysis, NO release was estimated by the modified Griess method. Measurements and Main Results: PGT in increasing concentrations had no effe ct on iNOS gene expression and nitrite/nitrate release for 24 hrs and 48 hr s, respectively. However, PCT ameliorated TNF-alpha /IFN-gamma -induced iNO S gene expression in a dose-dependent manner (maximal inhibition at PCT 100 ng/mL by -66% for 24 hrs and -80% for 48 hrs). This was accompanied by a s ignificantly reduced release of nitrite/nitrate into the cell culture super natant (maximal reduction at PCT 100 ng/mL by -56% and -45% for 24 hrs and 48 hrs, respectively). Conclusions: We conclude that recombinant PCT inhibits the iNOS-inducing ef fects of the proinflammatory cytokines TNF-alpha /IFN-gamma in a dose-depen dent manner. This might be a counterregulatory mechanism directed against t he large production of NO and the concomitant systemic hypotension in sever e sepsis and septic shock.