Release of prostaglandin E2 from cells by photodynamic treatment in vitro

Photodynamic treatment in vitro, using the photosensitizer Photofrin II and light at 630 nm, was found to liberate large amounts of prostaglandin E2 (PGE2) from mouse radiation-induced fibrosarcoma tumor cells and peritoneal macrophages, but not from L929 fibroblasts. PGE2 release was dose dependent and directly related to cell membrane disruption. It occurred rapidly and was complete within 30 min of treatment. PGE2 release could be inhibited by indomethacin, meclofenamate and extended prior exposure to dexamethasone, indicating that it was due to new production involving both the phospholipase and cyclooxygenase enzyme systems. Removal of calcium ions, necessary for phospholipase activation, from the medium did not inhibit the photodynamically induced elevated PGE2 production, possibly because of Ca2+ resupply from leaking intracellular pools.