Paracetamol effectively reduces prostaglandin E2 synthesis in brain macrophages by inhibiting enzymatic activity of cyclooxygenase but not phospholipase and prostaglandin E synthase

Abstract

AbstractEpidemiological studies indicate that nonsteroidal anti‐inflammatory drugs (NSAIDs) are neuroprotective, although the mechanisms underlying their beneficial effect remain largely unknown. Given their well‐known adverse effects, which of the NSAIDs is the best for neurodegenerative disease management remains a matter of debate. Paracetamol is a widely used analgesic/antipyretic drug with low peripheral adverse effects, possibly related to its weak activity as inhibitor of peripheral cyclooxygenase (COX), the main target of NSAIDs. As microglia play an important role in CNS inflammation and pathogenesis of neurodegenerative diseases, we investigate the effect of paracetamol on rat microglial cultures. Although less potent than other NSAIDs, (indomethacin ≃ NS‐398 > flurbiprofen ≃ piroxicam > paracetamol ≃ acetylsalicylic acid), paracetamol completely inhibited the synthesis of prostaglandin E2 (PGE2) in lipopolysaccharide‐stimulated microglia, when used at concentrations comparable to therapeutic doses. The drug did not affect the expression of the enzymes involved in PGE2 synthesis, i.e., COX‐1, COX‐2, and microsomal PGE synthase, or the release of the precursor arachidonic acid (AA). Paracetamol inhibited the conversion of exogenous AA, but not PGH2, into PGE2 indicating that the target of the drug is COX activity. Consistently, paracetamol inhibited with similar IC50 the synthesis of PGF2α and thromboxane B2, two other COX metabolites. Finally, none of the NSAIDs affected the productions of nitric oxide and tumor necrosis factorα, two inflammatory mediators released by activated microglia. As paracetamol was reported to inhibit PG synthesis in peripheral macrophages with an IC50 at least three orders of magnitude higher than in microglia, we suggest that this drug represents a good tool for treating brain inflammation without compromising peripheral PG synthesis. © 2003 Wiley‐Liss, Inc.