The Effects of COX-Metabolites on Cyclooxygenase-2 Induction in LPS-treated Endothelial Cells
PRA VIT AKARASEREENONT, M.D., Ph.D.*, SIRIKUL CHOTEWUTTAKORN, M.Sc. *, KITIRA T TECHATRAISAK, M.D., Ph.D.**, ATHIWAT THAWORN, Cert., M.S.T.*
Affiliation : * Department of Pharmacology, ** Department of Obstetrics and Gynecology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
Cyclooxygenase (COX) is the first enzyme in the pathway in which arachidonic acid is converted to PGs, also called COX-metabolites. COX exists as COX-I and COX-2 isoforms. Each COX-metabolite has different characters and functions. The amounts of each COX-metabolite pro- duced in cells are also different depending on cell type and mitogen stimulated cells. These were thought to be autoregulation among COX-metabolites. Here, we have investigated the effects of COX-metabolites, such as PGI2, PGE2, PGF2a and U44069, on the induction of COX-2 in human umbilical vein endothelial ~ells (HUVEC) treated with LPS (1 jlg/ml). COX activity was measured by the production of 6-keto-PGF1a' PGE2, PGF2a and TXB2 in the presence of exogenous arachidonic acids (10 jlM for 10 min) using enzyme immunoassay (EIA). COX-I and COX-2 protein was mea- sured by immunoblotting using specific antibody. PGI2, PGE2, PGF2a or U44069, did not affect on basal COX activity in untreated HUVEC (24 h incubation). Untreated HUVEC contained COX-I protein but not COX-2 protein. When HUVEC were treated with LPS (1 jlg/ml for 24 h), COX activity and COX-2 protein was increased in a dose dependent manner. The increased COX activity in LPS (1 jlg/ml) treated HUVEC was inhibited with PGE2 (0.03, 0.3 or 3 jlM), but not PGI2, PGF2a or U44069, in a dose dependent manner. Similary, COX-2 protein expression in LPS treated HUVEC was also inhibited with PGE2, but not PGI2, PGF2a or U44069, in a dose dependent manner. These results suggested that PGE2, but not PGI2, PGF2a or TXA2 is a key in feedback regulation of COX- metabolites produced in HUVEC.
Keywords : COX-2, Prostaglandins, Endotoxin, Endothelium
