Abstract 19092: Cyclooxygenase 2 Mediates Increased Endothelium-Dependent Vascular Contraction in Hyperhomocysteinemia and Hyperlipidemia

Abstract

Objectives: We recently reported that elevation of plasma homocysteine level_hyperhomocysteinemia (HHcy) accelerates atherosclerosis and vascular inflammation in hyperlipidemia (HLP). In this study, we examined the role of cyclooxygenase 2 (COX2)[[Unable to Display Character: —]]an inducible isoform of COX in responsible to inflammation, in HHcy/HPL-induced endothelial dysfunction (ED). Methods: Endothelial function was assessed in the thoracic aorta of a novel severe HHcy (plasma Hcy=221 μM) mouse model: human cystathionine β-synthase (CBS) transgenic, mouse CBS and apolipoprotine E gene deficient mouse fed with a high fat diet for 8 weeks (HHcy/HLP Cbs-/-¬ mice). Results: Endothelium-dependent relaxation to acetylcholine (ACh) was significantly impaired in HHcy/HLP Cbs-/- mice compared to HHcy/HLP Cbs+/+ mice. In the presence of eNOS inhibitor N(G)-nitro-L-Arg-methyl ester (L-NAME), ACh induced endothelium-dependent contraction in HHcy/HLP Cbs-/- but not in HHcy/HLP Cbs+/+ mice. L-NAME plus COX1/2 inhibitor indomethacin (INDO) completely blocked the HHcy/HLP-induced endothelium-dependent contraction. Moreover, INDO, COX2 inhibitor nimesulide, and thromboxane A2/prostaglandin H2 receptor antagonist SQ29548, but not COX1 inhibitor SC560, improved vascular relaxation to ACh in HHcy/HLP Cbs-/-¬ mice, indicating that COX2 plays a major role. Preincubation the aorta with antioxidants Tempol, polyethylene glycol superoxide dismutase and apocynin also improved endothelial function in HHcy/HLP Cbs-/- mice. Expression of COX2 and 3-nitrotyrosin (3-NT), but not COX1, was markedly increased in the endothelium of aorta of HHcy/HLP Cbs-/- mice. ICAM-1, VCAM-1, and TNFα were markedly increased in the aorta of HHcy/HLP Cbs-/- mice. Moreover, COX2 and 3-NT, but not COX1, was significantly increased in cultured human aortic endothelial cells treated with a combination of DL-Hcy (500 μM) and oxidized-LDL (200 μg/ml) for 48 hrs. Furthermore, DL-Hcy/oxidized-LDL-induced COX2 was prevented by PEG-SOD. Finally, HHcy markedly accelerated urinary 2,3-dinor TXB2, TXB2, 8-isoprostan and 6-keto prostaglandin F1α levels in HPL. Conclusions: COX2 mediates HHcy-induced endothelium-dependent vascular contraction in HPL via oxidative stress-dependent pathway.