Effects of glucocorticoids on generation of reactive oxygen species in platelets

Since prednisolone and dexamethasone are known as potent anti-inflammatory agents, the effects of prednisolone and dexamethasone on production of intracellular reactive oxygen species (ROS) were investigated in human platelets. Platelet ROS were measured using the intracellular fluorescent dye dichlorofluorescein diacetate after activation of protein kinase C by phorbol-12-myristate-13-acetate (PMA) or 1-oleoyl-2-acetyl-sn-glycerol (OAG). NAD(P)H oxidase activity was measured photometrically. PMA and OAG significantly increased ROS in platelets (P<0.001). Prednisolone or dexamethasone concentration-dependently reduced the PMA-induced ROS production. The PMA-induced ROS increase was significantly reduced in the presence of 10 micromol/l prednisolone to 9+/-1% (n=31; P<0.001) or in the presence of 10 micromol/l dexamethasone to 9+/-1% (n=24; P<0.001). The inhibitory effect of prednisolone or dexamethasone could also be observed in the presence of the glucocorticoid receptor inhibitor, mifepristone (RU486). Administration of testosterone or aldosterone did not significantly reduce PMA-induced ROS increase. Prednisolone had no effect on platelet NAD(P)H oxidase activity. The inhibition of oxidative phosphorylation by sodium azide reduced platelets ROS to 8+/-1% (n=35). It is concluded that glucocorticoids, prednisolone and dexamethasone, directly inhibit production of intracellular ROS. This effect may contribute to the anti-inflammatory actions of these agents.