Effect of pentoxifylline on interferon-γ-induced nitric oxide production in L929 fibroblasts

In this study, the effect of phosphodiesterase inhibitor pentoxifylline (PTX) on nitric oxide (NO) production in IFN-gamma treated murine fibrosarcoma cell line L929 was investigated. Nitrite accumulation, a measure of NO synthesis, was determined by spectrophotometry in culture supernatants of 48 h cell cultures. Treatment of L929 cells with IFN-gamma induced NO production, dependent on protein tyrosine kinase (PTK) activity, as judged by the inhibition of NO accumulation by PTK inhibitor genistein. PTX further enhanced IFN-gamma-induced NO production,when added simultaneously with IFN-gamma. In cells in which inducible NO synthase (iNOS) had already been induced with IFN-gamma and any possible further induction was blocked by cycloheximide, PTX did not change NO production. Treatment with cAMP analogue dibutyryl-cAMP mimicked stimulatory effect of PTX on NO synthesis in L929 fibroblasts. These findings suggest that in L929 cells PTX stimulates IFN-gamma-induced iNOS expression rather than its catalytic activity, and that stimulatory action of PTX on NO synthesis could be due to the inhibition of phosphodiesterase activity and consequent rise of intracellular cAMP level.