Astrocytes generate isoprostanes in response to trauma or oxygen radicals

Previous studies have shown that oxygen radical scavengers prevent the reduced cerebral blood flow that occurs following experimental traumatic brain injury. The exact chemical species responsible for the posttraumatic reduction in flow is unknown. We tested whether isoprostanes, which are formed by non-cyclooxygenase-dependent free radical attack of arachidonic acid and are vasoconstrictors of the cerebral circulation, are increased in astrocytes following stretch-induced trauma or injury with a free radical generating system. Isoprostane (8-epi-prostaglandin F2alpha) was analyzed in cells and in media by immunoassay. Confluent rat cortical astrocytes in culture were injured by a hydroxyl radical generating system consisting of hydrogen peroxide and ferrous sulfate or by rapid stretch of astrocytes grown on a deformable silastic membrane. Some cells were treated with the iron chelator deferoxamine for 1 h before injury. The hydroxyl generating system caused free and cell-bound isoprostanes to increase to more than 400% of control. After trauma, free and membrane bound isoprostanes increased to 321 +/- 34% and 229 +/- 23% of control, respectively, and posttraumatic increases were prevented by deferoxamine. Since astrocytes are in close proximity to cerebral vessels, posttraumatic free radical formation may increase the formation of isoprostanes, which in turn produce vasoconstriction and decrease cerebral blood flow.