Rapid non-genomic inhibitory effects of glucocorticoids on human neutrophil degranulation

Abstract

Background: Glucocorticoids acting as anti-inflammatory or immunosuppressive drugs have been shown to exert most of their effects genomically. Recent findings suggest that non-genomic activity might be relatively more important in mediating the therapeutic effects of high-dose pulsed glucocorticoid. However, few non-genomic anti-inflammatory effects were reported, much less non-genomic mechanisms. Objective: This study was performed to investigate the nongenomic effects of glucocorticoids on human neutrophil degranulation. Methods: Purified human neutrophils were pretreated with 6α-methylprednisolone or hydrocortisone for 5 min, and then primed with N-formyl-methionyl-leucyl-phenylalanine (fMLP) (10-6 M) or phorbol myristate acetate (PMA) (50 ng/ml) in the presence of cytochalasin B. The release of two markers of neutrophil granules, lactoferrin and myeloperoxidase, was measured by ELISA and enzymology methods respectively. Results: Both 6α-methylprednisolone (10-5-10-4 M) and hydrocortisone (10-4 M) showed significant inhibitory effects on neutrophil degranulation within 5 min after fMLP administration. For PMA stimulated degranulation, 6α-methylprednisolone (10-4 M) showed significant inhibitory effects (p < 0.01), while hydrocortisone (10 -4 M) only showed an inhibitory tendency (P > 0.05). Neither RU486 (10-5 M) nor cycloheximide (10-4 M) could alter the inhibitory effects of glucocorticoids. Conclusion: Our results demonstrate that megadoses of glucocorticoids exert rapid inhibitory effects on human neutrophil degranulation at the cellular level via a new mechanism that is independent of corticosteroid type II receptor occupation or protein synthesis. We infer that these effects may be very important when glucocorticoids act as anti-inflammatory drugs during pulse therapy. © Birkhäuser Verlag, Basel, 2005.