Attenuation of diet‐induced atherosclerosis in rabbits with a highly selective 15‐lipoxygenase inhibitor lacking significant antioxidant properties

Abstract

. Louis MO 63110; {Departments of Artherosclerosis Therapeutics, }Biochemistry and }Chemistry Parke-Davis, Ann Arbor MI 48105 and #Department of Pharmacology, Columbia University, New York, NY 10032, U.S.A.1 15-Lipoxygenase (15-LO) has been implicated in the pathogenesis of atherosclerosis because of its localization in lesions and the many biological activities exhibited by its products. To provide further evidence for a role of 15-LO, the e ects of PD 146176 on the development of atherosclerosis in cholesterol-fed rabbits were assessed. This novel drug is a speci®c inhibitor of the enzyme in vitro and lacks signi®cant non speci®c antioxidant properties. 2 PD 146176 inhibited rabbit reticulocyte 15-LO through a mixed noncompetitive mode with a K i of 197 nM. The drug had minimal e ects on either copper or 2,2'-azobis(2-amidinopropane)hydrochloride (ABAP) induced oxidation of LDL except at concentrations 2 orders higher than the K i . 3 Control New Zealand rabbits were fed a high-fat diet containing 0.25% wt./wt. cholesterol; treated animals received inhibitor in this diet (175 mg kg 71 , b.i.d.). Plasma concentrations of inhibitor were similar to the estimated K i (197 nM). During the 12 week study, there were no signi®cant di erences in weight gain, haematocrit, plasma total cholesterol concentrations, or distribution of lipoprotein cholesterol. 4 The drug plasma concentrations achieved in vivo did not inhibit low-density lipoprotein (LDL) oxidation in vitro. Furthermore, LDL isolated from PD 146176-treated animals was as susceptible as that from controls to oxidation ex vivo by either copper or ABAP. 5 PD 146176 was very e ective in suppressing atherogenesis, especially in the aortic arch where lesion coverage diminished from 15+4 to 0% (P50.02); esteri®ed cholesterol content was reduced from 2.1+0.7 to 0 mg mg 71 (P50.02) in this region. Immunostainable lipid-laden macrophages present in aortic intima of control animals were totally absent in the drug-treated group. 6 Results of these studies are consistent with a role for 15-LO in atherogenesis.

12/15-Lipoxygenase Translocation Enhances Site-specific Actin Polymerization in Macrophages Phagocytosing Apoptotic Cells

“…Both human and rabbit atherosclerotic lesions express 15-LO mRNA, protein, and enzymatic activity (7, 24 -26). Importantly, inhibitors of 15-LO decreased atherogenesis in rabbits (18,19), and deleting 12/15-LO activity in apo E Ϫ/Ϫ mice dramatically decreased atherogenesis (8). These data support an important pathophysiological role for 12/15-LO in atherogenesis.…”

“…1b). This ability of the 12/15-LO-positive cells to bind apoptotic cells was significantly reduced when the elicited macrophages were pretreated with the specific 12/15-LO inhibitor PD 146176 (18). The effect of PD 146176 was dosedependent.…”

“…Representative spectra and time courses from three experiments are shown. 18,19,[23][24][25][26]. Inhibitors of 12/15-LO decrease the ability of murine macrophages to oxidize LDL (14,23), and murine fibroblasts transfected with human 15-LO have a greatly enhanced ability to initiate oxidation of LDL (12).…”

Critical Role of Macrophage 12/15-Lipoxygenase for Atherosclerosis in Apolipoprotein E–Deficient Mice

“…3,7 Pharmacological inhibition of 15-LO in hypercholesterolemic rabbits resulted in attenuation of atherosclerosis. 8,9 In the apoE Ϫ/Ϫ , LDLR Ϫ/Ϫ , and apobec-1 Ϫ/Ϫ /LDL-R Ϫ/Ϫ mouse models of atherosclerosis, disruption of the 12/ 15-LO gene significantly retarded the initiation and progression of atherosclerosis. 10 -12 A variety of vascular cells are able to express 12/15-LO, including endothelial cells, 13,14 smooth muscle cells, 13,14 and monocytes/macrophages.…”

Catalytic consumption of nitric oxide by 12/15- lipoxygenase: Inhibition of monocyte soluble guanylate cyclase activation

“…15-and 12͞15-LOXs play a central role in vascular disease, because (i) 15-LOX mRNA, protein, and lipid products are found in atheroma, (ii) inhibition of 15-LOX prevents atherosclerosis in rabbits, and (iii) functional inactivation of the 12͞15-LOX gene slows down aortic lipid deposition in apo E-deficient mice, and inhibits streptozotocin-induced diabetes (19)(20)(21)(22)(23)(24)(25). Furthermore, in vivo, 12͞15-LOX expression is required for neointimal thickening in ballooninjured rat aortae (26,27).…”