Salicylate Metabolites Inhibit Cyclooxygenase-2-Dependent Prostaglandin E2 Synthesis in Murine Macrophages

Abstract

The poor cyclooxygenase (COX) inhibitor and major aspirin metabolite salicylic acid is known to exert analgesic and anti-inflammatory effects by still unidentified mechanisms. In RAW 264.7 macrophages, lipopolysaccharide (LPS)-induced COX-2-dependent synthesis of prostaglandin E2 (PGE2) was suppressed by aspirin (IC50 of 5.35 μM), whereas no significant inhibition was observed in the presence of sodium salicylate and the salicylate metabolite salicyluric acid at concentrations up to 100 μM. However, the salicylate metabolite gentisic acid (2,5-dihydroxybenzoic acid; 10–100 μM) and salicyl-coenzyme A (100 μM), the intermediate product in the formation of salicyluric acid from salicylic acid, significantly suppressed LPS-induced PGE2 production. In contrast, γ-resorcylic acid (2,6-dihydroxybenzoic acid) as well as unconjugated coenzyme A failed to affect prostanoid synthesis, implying that the para-substitution of hydroxy groups and the activated coenzyme A thioester are important for COX-2 inhibition. Using real-time RT-PCR, none of the salicylate derivatives tested were found to interfere with COX-2 expression. Overall, our results suggest that certain metabolites of salicylic acid may contribute to the pharmacological action of its parent compound by inhibiting COX-2-dependent PGE2 formation at sites of inflammation.