Effect of Guanosine-5`-monophosphate on Nitric Oxide Synthesis in SW982 cells

Abstract

The purpose of this study was to identify the role of guanosine-5`-monophosphate (5`GMP) in interleukin (IL)-1β-induced nitric oxide (NO) synthesis and inducible NO synthase (iNOS) expression, and the effect of sildenafil citrate, phosphodiesterase(PDE)5 inhibitor, on the activation of IL-1β in human synovial sarcoma SW982 cells. IL-1β activated SW982 cells to generate NO in a both dose- and time-dependent manners, and the guanylate cyclase (GC) inibitor LY83583 dose-dependently inhibited IL-1β-induced NO production. The effect of GC inibition was consistent with increase in cGMP level by IL-1β, which reached maximal levels after 30 min. When the cells were treated with 8-bromo-cGMP, a hydrolyzable analog of cGMP, NO synthesis was increased without IL-1β stimulation, and sildenafil citrate suppressed IL-1β-induced NO synthesis and iNOS expression. In order to examine the effect of sildenafil citrate on the IL-1β activation, SW982 cells were pretreated with 30uM sildenafil citrate for 1h, and then treated with 10ng/ml IL-1β for 48h. Sildenafil citrate significantly inhibited IL-1β-induced NO synthesis. Treatment of 5`-GMP also increasd NO synthesis dose-dependently in SW982 cels with 5`GMP induced iNOS mRNA and peotein expression. Several studies have shown that the levels of expression of soluble guanylyl cyclase(sGC) or cGMP-dependent protein kinase (PKG) are activated in cytokine stimulated cell lines. However, in SW982 cells, PKG inhibitor KT5823 was not decreased IL-1β induced NO synthesis. These results indicate that 5`GMP may play an important role in activating iNOS expression to increase NO release, and sildenafil citrate can suppress the IL-1β-induced NO release and iNOS expression in SW982 cells by inhibition of conversion of cGMP to 5`GMP.