The temporal relationship of cytokine‐induced expression of genes involved in the metabolism of L‐arginine in bovine pulmonary artery endothelial cells

Abstract

Inflammatory stimuli have been shown to increase both iNOS and arginase expression and activity. We hypothesized that inflammatory stimuli would result in a transient induction of iNOS and prolonged induction of arginase, thereby representing a mechanism whereby host defense functions predominate early and host repair functions predominate later in the course. To investigate this hypothesis, we studied bovine pulmonary artery endothelial cells (bPAEC) stimulated with lipopolysaccharide (LPS) and tumor necrosis factor–α (TNF‐α) or treated with vehicle. Cells were harvested at 0, 1, 2, 4, 8, 24, 48, 72 and 96 hours after stimulation. We examined expression levels of mRNA for iNOS, arginase II, ornithine decarboxylase (ODC) and ornithine aminotransferase (OAT). Expression levels of iNOS mRNA in LPS/TNF‐α treated cells were increased at 2 hours and peaked by 24 hours with a return to baseline expression between 48 and 72 hours. Conversely, arginase II mRNA expression was increased at 4 hours and remained elevated throughout the experimental period. The mRNA levels of ODC and OAT were relatively high in control cells; although, LPS/TNF‐α stimulation did increase expression. These data are consistent with our hypothesis that inflammatory stimuli result in an early, transient NOS response followed by a sustained arginase response. Taken together, the observed pattern of expression of these enzymes would result in L‐arginine metabolism to NO early in the inflammatory response, followed at 48 to 72 hours by a shift to an arginase‐mediated metabolism of L‐arginine to ornithine and subsequent polyamine and L‐proline production.