750-1 Oxidized Low Density Lipoprotein Induced Activation of Smooth Muscle Cell DNA Synthesis is Mediated Through Active Oxygen Species and Lysolecithin

Abstract

It has been shown that oxidized low density lipoprotein (ox-LDL) stimulates DNA synthesis in smooth muscle cells (SMC). Due to its complex chemical structure it has been difficult to identify the active mitogenic components of ox-LDL. Within the first 48 hours of oxidation we found a 75% reduction of lecithin while lysolecithin was increased 25-fold, lipid peroxide levels increased 8-fold and aldehydes increased 20-fold as determined by the thiobarbituric reactive (TBAR) assay. To identify the components of ox-LDL responsible for stimulation of DNA synthesis, human arterial SMC were exposed to various peroxides, aldehydes, and phospholipids and DNA synthesis was analyzed by autoradiography using radioactive thymidine in corporation in nuclei. Substance % labelled nuclei ± SD p vs Ctl Control (1% serum) 23.3 3.5 LDL 5 μ g/ml 31.0 5.5 NS ox-LDL 5 μ g/ml 75.2 7.8 0.005 lysolecithin 10 μ M 75.3 4.5 0.003 LDL 5 μ g/ml + PhosholipaseA 2 41 U/ml 73.0 3.6 0.0001 H 2 O 2 2OO μ M 39.0 1.7 0.01 The DNA synthesis increased 3 fold with ox-LDL and this effect was replicated by substituting lysolecithin or LDL + Phospholipase A 2 (to generate lysolecithin) for ox-LDL. Peroxides also had a modest stimulatory effect. Malondialdehyde, oxysterols, Iysophosphatidylserine, phosphatidylserine, lecithin, sphingomyelin and sphingosine were without effect. The present results indicate that the growth stimulatory effect of oxLDL is due to the formation of lysolecithin and peroxides during the oxidation process.