Relation of cyclooxygenase isoenzyme expression and coronary artery remodeling

Abstract

Inflammation plays a key role in coronary atherosclerosis. Increased markers of inflammation have been consistently associated with a worse outcome in patients with clinical or subclinical coronary artery disease. 1 Cyclooxygenase (COX) or prostaglandin synthase G/H are key enzymes responsible for the metabolism of arachidonic acid, and they exist in 2 isoforms—COX-1 and COX-2. COX activity has been described in both healthy human coronary arteries and in association with atherosclerosis and transplant vasculopathy. 2,3 Coronary arteries undergo changes in lumen size in response to coronary atherosclerosis; a phenomenon described as coronary remodeling. 4,5 Coronary remodeling encompasses outward expansion or positive remodeling, and conversely, narrowing or negative remodeling. Positive remodeling, although serving to maintain luminal size and thus possibly maintaining adequate coronary flow, is associated with a higher incidence of unstable coronary syndromes. 6 Although a previous studies 7 has suggested a relation between inflammation and coronary remodeling, the role of the COX pathway has not been explored. We sought to determine the relation between the localization of COX isoenzymes and coronary artery remodeling in patients who underwent directional coronary atherectomy (DCA). ••• The study population consisted of 21 patients who had DCA performed for a single epicardial lesion in a native coronary artery. Clinical presentation was defined as stable or unstable using standard clinical criteria. 8 Intravascular ultrasound imaging was performed using standard techniques as previously reported. 9 All images were obtained using a 30-MHz 3.5Fr monorail ultrasound catheter (Boston Scientific, Watertown, Massachusetts) interfaced with a scanner (Hewlett-Packard, Andover, Massachusetts). After coronary angiography, intravenous heparin and intracoronary nitroglycerin were administered, and the ultrasound catheter was inserted over a guide wire distal to the target lesion site. The ultrasound catheter was then withdrawn manually during continuous imaging, and images were recorded on 1/2-in SuperVHS videotape. The lesion site was identified using cine angiography and verbal annotation. Each piece of tissue was fixed for 8 hours in Histochoice (Amresco, Solon, Ohio). The tissue was then processed and paraffin was embedded according to standard laboratory procedures. Sections were cut from each block at 4 m, collected onto electrostatically charged slides, and baked at 60°C for 60 minutes. Two sections were collected and immunostained for each antibody. The antibodies used in this study were anti-HAM56 (Dako, Carpinteria California), anti-COX-1 (Cayman Chemical, Ann Arbor, Michigan), anti-COX-2 (Cayman Chemical), and anti--actin (Dako). The paraffin was removed from the baked tissue sections in 3 changes of xylene, and the tissue was hydrated through graded alcohols before rinsing them in phosphate-buffered saline (PBS). Immunohistochemical staining was performed using a Jung Histostainer (Leica, Illinois), with processing occurring at 30°C. The first stage of the procedure involved the application of a 1% hydrogen peroxide solution in methanol for 5 minutes to remove any endogenous peroxidase present in the tissue section. A blocking solution comprising a 1:10 dilution of normal rabbit serum (Dako) in PBS was added for 10 minutes before application of the primary antibody. The required dilutions of antibody were prepared using 1% bovine serum albumin in PBS. Incubation occurred at 30°C for 60 minutes, and a 1:200 dilution of biotinylated rabbit anti-mouse polyclonal antibody (Dako) was added for an additional 30 minutes. The antibodies were labeled using an Elite avidin/biotin/peroxidase complex (Vector Laboratories, Burlingame, California) applied for 30 minutes. The final stage comprised the addition of 3,3diaminobenzidine as a chromogen (DAB Kit, Vector