Dose‐dependent Immunomodulatory Effects of Acetylsalicylic Acid and Indomethacin in Human Whole Blood: Potential Role of Cyclooxygenase‐2 Inhibition

The aim of the study was to characterize the in vitro effect of non‐steroidal anti‐inflammatory drugs (NSAIDs) on the production of pro‐inflammatory cytokines in a human whole blood assay. Whole blood samples were pre‐incubated with acetylsalicylic acid, indomethacin, selective cyclooxygenase (COX)‐1 inhibitor (SC‐560), COX‐2 inhibitor (NS‐398) or prostaglandin E2 (PGE2) before stimulation with lipopolysaccharide (LPS). Pro‐inflammatory and anti‐inflammatory cytokines were determined directly at the cell level with the help of flow cytometry and/or in the plasma supernatant with the help of ELISA. High doses of acetylsalicylic acid were needed to inhibit pro‐inflammatory cytokine production. In contrast, low‐to‐moderate doses induced a modestly enhanced production of pro‐inflammatory cytokines. Moreover, indomethacin was demonstrated to increase the expression of interleukin‐6 (IL‐6) and tumour necrosis factor‐α (TNF‐α) in a dose‐dependent fashion. Upon addition of PGE2, however, LPS‐induced IL‐6 and TNF‐α production was suppressed regardless of indomethacin presence. Interestingly, selective COX‐2 inhibition (NS‐398), but not selective COX‐1 inhibition (SC‐560), exerted a stimulatory effect on the expression of pro‐inflammatory cytokines. These data emphasize that the immunomodulating effects of NSAIDs in whole blood are dose‐dependent. Furthermore, the induction of pro‐inflammatory cytokine expression by NSAIDs is potentially mediated by COX‐2 inhibition. Although NSAIDs are successfully used in clinical practice for their net anti‐inflammatory properties, our observations may contribute to the understanding of side effects induced by NSAIDs and selective COX‐2 inhibitors.