Cyclooxygenases, thromboxane, and atherosclerosis: plaque destabilization by cyclooxygenase-2 inhibition combined with thromboxane receptor antagonism.
BACKGROUND
Antagonism or deletion of the receptor (the TP) for the cyclooxygenase (COX) product thromboxane (Tx)A2, retards atherogenesis in apolipoprotein E knockout (ApoE KO) mice. Although inhibition or deletion of COX-1 retards atherogenesis in ApoE and LDL receptor (LDLR) KOs, the role of COX-2 in atherogenesis remains controversial. Other products of COX-2, such as prostaglandin (PG) I2 and PGE2, may both promote inflammation and restrain the effects of TxA2. Thus, combination with a TP antagonist might reveal an antiinflammatory effect of a COX-2 inhibitor in this disease. We addressed this issue and the role of TxA2 in the promotion and regression of diffuse, established atherosclerosis in Apobec-1/LDLR double KOs (DKOs).


RESULTS
TP antagonism with S18886, but not combined inhibition of COX-1 and COX-2 with indomethacin or selective inhibition of COX-2 with Merck Frosst (MF) tricyclic, retards significantly atherogenesis in DKOs. Although indomethacin depressed urinary excretion of major metabolites of both TxA2, 2,3-dinor TxB2 (Tx-M), and PGI2, 2,3-dinor 6-keto PGF(1alpha) (PGI-M), only PGI-M was depressed by the COX-2 inhibitor. None of the treatments modified significantly the increase in lipid peroxidation during atherogenesis, reflected by urinary 8,12-iso-iPF(2alpha)-VI. Combination with the COX-2 inhibitor failed to augment the impact of TP antagonism alone on lesion area. Rather, analysis of plaque morphology reflected changes consistent with destabilization of the lesion coincident with augmented formation of TxA2. Despite a marked effect on disease progression, TP antagonism failed to induce regression of established atherosclerotic disease in this model.


CONCLUSIONS
TP antagonism is more effective than combined inhibition of COX-1 and COX-2 in retarding atherogenesis in Apobec-1/LDLR DKO mice, which perhaps reflects activation of the receptor by multiple ligands during disease initiation and early progression. Despite early intervention, selective inhibition of COX-2, alone or in combination with a TP antagonist, failed to modify disease progression but may undermine plaque stability when combined with the antagonist. TP antagonism failed to induce regression of established atherosclerotic disease. TP ligands, including COX-1 (but not COX-2)-derived TxA2, promote initiation and early progression of atherogenesis in Apobec-1/LDLR DKOs but appear unimportant in the maintenance of established disease.
Egan
Karine M
KM
Institute for Translational Medicine and Therapeutics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Wang
Miao
M
Fries
Susanne
S
Lucitt
Margaret B
MB
Zukas
Alicia M
AM
Puré
Ellen
E
Lawson
John A
JA
FitzGerald
Garret A
GA
D000818:Animals; D001011:Aorta / Q000473:pathology; D001161:Arteriosclerosis / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004041:Dietary Fats / Q000008:administration & dosage; D004347:Drug Interactions; D005663:Furans / Q000494:pharmacology; D008565:Membrane Proteins; D051379:Mice; D009281:Naphthalenes / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D017482:Receptors, Thromboxane / Q000037:antagonists & inhibitors*; D013928:Thromboxane A2 / Q000378:metabolism
D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D004041:Dietary Fats; D005663:Furans; D008565:Membrane Proteins; D009281:Naphthalenes; D011422:Propionates; D017482:Receptors, Thromboxane; C102563:3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2(5H)-furanone; D013928:Thromboxane A2; C501362:terutroban; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse