Prostaglandin E2 Inhibit Cyclooxygenase-2 Induction In lps-treated Endothelial Cells Through Camp

Abstract

Cyclooxygenase (COX), which exists as COX-1 and COX-2 isoforms, is the

first enzyme in the pathway in which arachidonic acid is converted to prostaglandins

(PGs). PGE₂ is one of the PGs which have numerous cardiovascular and

inflammatory effects. PGE₂ also exerts a variety of biological activities for the

maintenance of local homeostasis in the body. Elucidation of PGE₂ involvement in

the signalling molecules such as COX could lead to potential therapeutic

interventions. Here, we have investigated the effects of PGE₂ on the induction of

COX-2 in human umbilical vein endothelial cells (HUVEC) treated with

lipopolysaccharide (LPS; 1 μg/ml). COX activity was measured by the production of

6-keto-PGF_1α, PGE₂, PGF_2α and TXB₂ in the presence of exogenous arachidonic

acids (10 μM for 10 min) using enzyme immunoassay (EIA). COX-1 and COX-2

protein was measured by immunoblotting using specific antibody. Untreated HUVEC

contained only COX-1 protein while LPS treated HUVEC contained COX-1 and

COX-2 protein. PGE₂ (3 μM for 24 h) did not affect on COX activity and protein in

untreated HUVEC. Interestingly, PGE₂ (0.003, 0.03 and 3 μM for 24h) can inhibit

COX-2 protein, but not COX-1 protein, expressed in HUVEC treated with LPS

(1 μg/ml) in a dose dependent manner. Moreover, this inhibition was reversed by

coincubation with foskolin ( cAMP activator; 100 μM). The increased COX activity in

HUVEC treated with LPS was also inhibited by PGE₂ (0.03, 0.3 and 3 μM for 24h) in

a dose dependent manner. Similarly, foskolin (10, 50 or 100 mM) can also reverse the

inhibition of PGE₂ on increased COX activity in LPS treated HUVEC. The results

suggested that i) PGE₂ can be negative feedback regulation in the induction of COX-2

elicited by LPS in endothelial cells, ii) the inhibition of PGE₂ on COX-2 protein and

activity in LPS treated HUVEC was mediated through cAMP and iii) the therapeutic

uses of PGE₂ in the pathological conditions which COX-2 has been involved may

have roles.