Mildly oxidized low-density lipoprotein acts synergistically with angiotensin II in inducing vascular smooth muscle cell proliferation

Objectives Considerable attention has been focused on both mildly oxidized low-density lipoprotein (mox-LDL) and highly oxidized LDL (ox-LDL) as important risk factors for cardiovascular disease. Further, angiotensin II (Ang II) appears to play a crucial role in the development of hypertension and atherosclerosis, We assessed the effect of oxidatively modified LDL and its major oxidative components, i,e,, hydrogen peroxide (H2O2), lysophosphatidylcholine (LPC), and 4-hydroxy-2-nonenal (HNE) and their interaction with Ang II on vascular smooth muscle cell (VSMC) DNA synthesis. Methods: Growth-arrested rabbit VSMCs were incubated in serum-free medium with different concentrations of native LDL, mox-LDL, ox-LDL, H2O2, LPC, or HNE with or without Ang II. DNA synthesis in VSMCs was measured by [H-3]thymidine incorporation. Results: Ang II stimulated DNA synthesis in a dose-dependent manner with a maximal effect at a concentration of 1 mu mol/l(173%). Ang II(0.5 mu mol/l) amplified the effect of native LDL at 500 ng/ml, ox-LDL at 100 ng/ml, and mox-LDL at 50 ng/ml on DNA synthesis (108 to 234%, 124 to 399%, 129 to 433%, respectively). H2O2 had a maximal effect at a concentration of 5 mu mol/l (177%), LPC at 15 mu mol/l (156%), and HNE at 0.5 mu mol/l (137%). Low concentrations of H2O2 (1 mu mol/l), LPC (5 mu mol/l), or HNE(0.1 mu mol/l) also acted synergisitically with Ang II (0.5 mu mol/l) in inducing DNA synthesis to 308, 304, or 238%, respectively. Synergistic interactions of Ang II(0.5 Icmol/l) with mox-LDL, ox-LDL (both 50 ng/ml), H2O2 (1 Icmol/l), LPC (5 mu mol/l), or HNE(0.1 mu mol/l) on DNA synthesis were completely reversed by the combined use of probucol (10 mu mol/l), a potent antioxidant and candesartan (0.1 mu mol/l), an AT(1) receptor antagonist. Conclusions Our results suggest that mox-LDL, ox-LDL, and their major components H2O2, LPC, and FINE act synergistically with Ang II in inducing VSMC DNA synthesis. A combination of antioxidants with AT1 receptor blockade may be effective in the treatment of VSMC proliferative disorders associated with hypertension and atherosclerosis.