The role of cyclooxygenase-1 and cyclooxygenase-2 in lipopolysaccharide and interleukin-1 stimulated enterocyte prostanoid formation

Abstract

Lipopolysaccharide is an inflammatory agent and interleukin-1 is a cytokine. Their pro-inflammatory effects may be mediated by prostanoids produced by inducible cyclooxygenase-2. The aim of this study was to determine the prostanoids produced by lipopolysaccharide and interleukin-1 stimulated enterocytes through the cyclooxygenase-1 and 2 pathways. Cultured enterocytes were stimulated with lipopolysaccharide or interleukin-1 β with and without cyclooxygenase inhibitors. Low concentrations of indomethacin and valerylsalicylic acid (VSA) were evaluated as cyclooxygenase-1 inhibitors and their effects compared with the effects of a specific cyclooxygenase-2 inhibitor, SC-58125. Prostaglandin E2 , 6-keto prostaglandin F1α , prostaglandin D2 and leukotriene B4 levels were determined by radio immunoassay. Immunoblot analysis using isoformspecific antibodies showed that the inducible cyclooxygenase enzyme (COX-2) was expressed by 4 h in LPS and IL-1β treated cells while the constitutive COX-1 remained unaltered in its expression. Interleukin-1β and lipopolysaccharide stimulated the formation of all prostanoids compared with untreated cells, but failed to stimulate leukotriene B4. Indomethacin at 20 μ M concentration, and VSA inhibited lipopolysaccharide and interleukin 1β stimulated prostaglandin E2 , but not 6-keto prostaglandin F1α formation. SC-58125 inhibited lipopolysaccharide and interleukin-1β stimulated 6-keto prostaglandin F1α but not prostaglandin E2 release. The specific cyclooxygenase-2 inhibitor also inhibited lipopolysaccharide produced prostaglandin D2 but not interleukin-1β stimulated prostaglandin D2 While SC-58125 inhibited basal 6-keto prostaglandin-F1α formation it significantly increased basal prostaglandin E2 and prostaglandin D2 formation. As SC-58125 inhibited lipopolysaccharide and interleukin-1β induced 6-keto prostaglandin F1α production but not prostaglandin E2 production, it suggests that these agents stimulate prostacyclin production through a cyclooxygenase-2 mediated mechanism and prostaglandin E2 production occurs through a cyclooxygenase-1 mediated mechanism. Prostaglandin D2 production appeared to be variably produced by cyclooxygenase-1 or cyclooxygenase-2, depending on the stimulus.

Keywords

• Cytokines
• Eicosanoids
• Cyclooxygenase
• Inhibitors.