Recovery of porcine aortic endothelial cell prostaglandin synthesis following inhibition by sublethal concentrations of hydrogen peroxide

Abstract

Confluent monolayers of porcine aortic endothelial cells exposed for 10 min to 100 μM H 2O 2 lose their capacity to produce prostaglandins in response to addition of saturating exogenous arachidonic acid. Significant recovery of prostaglandin I 2 and E 2 synthesis occurred within 3 h and full enzymatic capacity returned by 6 h. Reducing the injury by exposure to half the amount of H 2O 2 allowed prostaglandin I 2 production to recover to a greater extent in 3 h, while cells exposed for 60 min to either 0.5 or 1.0 mM H 2O 2 demonstrated no recovery. Pre-treatment with either actinomycin D or cycloheximide also prevented recovery following exposure to 100 μM peroxide. Injured cells did not recover when incubated with balanced salts after removal of peroxide, while incubation with medium 199 allowed for the complete return of synthetic capacity. Addition of 1% fetal calf serum in medium 199 did not facilitate recovery. Production of prostaglandins from endogenous arachidonic acid, released by either bradykinin or the ionophore A23187, was also inhibited by H 2O 2 exposure, however, full recovery of this stimulated synthesis occurred within 3 h. Cycloheximide pre-treatment completely inhibited recovery of bradykinin-induced prostaglandin I 2 synthesis. These data demonstrate that sublethal concentrations of H 2O 2 irreversibly inactivate fatty acid cyclooxygenase and that synthesis of new enzyme is required for recovery. This return of activity occurs more rapidly for production of prostaglandins from endogenous arachidonic acid compared with production following addition of exogenous substrate.