LOCALIZATION OF NONPANCREATIC SECRETORY PHOSPHOLIPASE A(2) IN NORMAL AND ATHEROSCLEROTIC ARTERIES - ACTIVITY OF THE ISOLATED ENZYME ON LOW-DENSITY LIPOPROTEINS

Secretory nonpancreatic type II phospholipase A(2) (snpPLA(2)) hydroly zes fatty acids at the sn-2 position in phospholipids releasing free f atty acids (FFAs) and lysophospholipids. These products may act as int racellular second messengers or can be further metabolized into proinf lammatory lipid mediators. The presence of snpPLA(2) in extracellular fluids and serum during inflammation has suggested a role of the enzym e in this process. However, the presence of snpPLA(2) in a variety of normal tissues suggests that snpPLA(2) may also have physiological fun ctions. Atherosclerosis appears to have an inflammatory component. Her e we report on the snpPLA(2) localization in normal and atheroscleroti c lesions and on the properties of the isolated enzyme. A strong snpPL A(2) immunoreactivity was observed in the arterial media that was colo calized with alpha-actin-positive vascular smooth muscle cells (SMCs) in both normal and atherosclerotic vessels. In aortic atherosclerotic lesions, snpPLA(2) was observed colocalized with CD68-positive macroph ages and HHF-35-positive SMCs and extracellularly in the lipid core. s npPLA(2) was isolated from human normal arteries and from aorta with l esions. The enzyme was isolated by acid extraction of normal arterial tissues followed by immunoaffinity chromatography. The purified snpPLA (2) had an expected molecular weight of 14 kD by poly-acrylamide gel e lectrophoresis and appeared as a single band in immunoblotting. The en zymatic activity was followed by measuring release of fatty acids from phospholipid liposomes or LDL as substrates. The enzymatic activity w as inhibited with two specific inhibitors for human snpPLA(2): (1) mon oclonal antibody 187 and (2) LY311727, a synthetic selective inhibitor . The mRNA for snpPLA(2) was detected with reverse transcriptase polym erase chain reaction. These results indicate that snpPLA(2) is present in human arteries and that it is able to hydrolyze phospholipids in L DL. The results support the hypothesis that snpPLA(2) can release proi nflammatory lipids at places of LDL deposition in the arterial wall.