Hypercholesterolemia Enhances 15-Lipoxygenase–Mediated Vasorelaxation and Acetylcholine-Induced Hypotension

Abstract

Objective-Arachidonic acid (AA) metabolites from 15-lipoxygenase-1 (15-LO-1), trihydroxyeicosatrienoic acid (THETA), and hydroxyepoxyeicosatrienoic acid (HEETA) relax arteries. We studied 15-LO-1 expression, THETA and HEETA synthesis, and their effect on arterial relaxations and blood pressure in hypercholesterolemic nonatherosclerotic rabbits. Methods and Results-Immunoblots, RTPCR analysis, and 14 C-AA metabolism revealed that hypercholesterolemia increased 15-LO-1 expression in the endothelium and THETA and HEETA synthesis in the arteries. Isometric tension recording, in presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors, showed greater relaxations to acetylcholine (ACH) and AA (max 76.0Ϯ4.6% and 79.5Ϯ2.4%, respectively) in aortas from hypercholesterolemic rabbits compared with normal rabbits (max 39.1Ϯ2.8% and 39.9Ϯ2.2%, respectively). AA induced greater hyperpolarization in the smooth muscle cells of hypercholesterolemic aortas (Ϫ45.85Ϯ3.0 mV) compared with normal aortas (Ϫ31.45Ϯ1.9 mV). The ACH-and AA-relaxations were inhibited by 15-LO-1 inhibitors. ACH induced hypotensive responses were greater in hypercholesterolemic rabbits in absence (Ϫ54.9Ϯ3.3%) or presence (Ϫ48.5Ϯ3.2%) of NOS and COX-inhibitors compared with control rabbits (Ϫ31.6Ϯ3.3% and Ϫ24.3Ϯ1.6%, respectively). BW755C reduced these responses in hypercholesterolemic rabbits to Ϫ29.3Ϯ2.3%. Key Words: hypercholesterolemia Ⅲ 15-lipoxygenase Ⅲ endothelium-derived hyperpolarizing factors Ⅲ blood pressure Ⅲ arachidonic acid I n presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors, agonist-induced relaxations are attributed to endothelium-derived hyperpolarizing factors (EDHFs) that regulate vascular tone. 1 Arachidonic acid (AA) metabolites from 15-lipoxygenase-1 (15-LO-1), 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA), and 11,12,15-trihydroxyeicosatrienoic acid (THETA) are EDHFs in rabbit arteries. [2][3][4] Other LO metabolites of AA, 15-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 15-hydroperoxyeicosatetraenoic acid (HpETE), are inactive in rabbit arteries. 5 15-LO-1 is important and sufficient to increase ACH-or AA-relaxations in rabbit arteries. 6,7 15-LO-1 expression increases in early atherosclerotic lesions in rabbit aorta. 8 However, progression of atherosclerosis begins with increased total plasma cholesterol levels. Hypercholesterolemia without appearance of any fatty streak lesion in the arteries alter gene expression 9 including intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule (VCAM), and P-selectin. Therefore, we hypothesized that hypercholesterolemia without atherosclerosis would effect 15-LO-1 expression. In the aortas from rabbits that were fed a 2% cholesterol diet for 2 weeks, ACH-relaxations sensitive to a LO inhibitor nordihydroguaiaretic acid (NDGA), and synthesis of AAmetabolites increased in the arteries. 10 NO-and prostaglandin (PG)-independent ACH-relaxations were also greater in the renal arteries from hypercholesterolemic rabbits. 11 ACHindu...

Role of arachidonic acid lipoxygenase metabolites in the regulation of vascular tone

“…In normotensive rats and cholesterol-fed, normotensive rabbits, inhibition of LOs with phenidone, baicalein, or BW755c did not affect basal blood pressure or heart rate (2,149). Similarly, the basal blood pressure was identical in wild-type and 12/ 15-LO knockout mice (5).…”

“…In normal rabbits, ACh decreased blood pressure in a concentration-related manner (1)(2)(3). Treatment with inhibitors of COX and NOS reduced, but did not block, the ACh-induced hypotension (1).…”

Mammalian lipoxygenases and their biological relevance

“…Although the source of these metabolites has not been identified at this stage of research [219] later expression silencing studies [220] and adenovirus mediated somatic gene transfer [221, 222] suggested the involvement of ALOX15 . Interestingly, chronic hypoxia and hypercholesterolemia enhanced ALOX15 mediated vasorelaxation in rabbit arteries [223, 224]. More direct evidence for the in vivo relevance of ALOX15 in blood pressure regulation was recently provided by experiments with ALOX15-deficient mice [225].…”

12/15-Lipoxygenase Mediates High-fat Diet-induced Endothelial Tight Junction Disruption and Monocyte Transmigration

“…Because the majority of atherogenic risk factors are associated with increased 12/15-LO expression (5)(6)(7)(8), and disruption of 12/15-LO gene-protected ApoE Ϫ/Ϫ mice from developing high-fat diet-induced atherosclerosis (24), we studied the role of 12/15-LO in EC barrier dysfunction. A quiescent monolayer of HUVECs, when treated with 5-, 12-, and 15(S)-HETE, the AA cleavage products of 5-, 12-, and 15-LO, the paracellular permeability of the monolayer, as measured by passive diffusion of FITC-conjugated dextran, significantly increased (Fig.…”