Mildly oxidized low-density lipoprotein acts synergistically with angiotensin II in inducing vascular smooth muscle cell proliferation.
OBJECTIVE
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 [3H]thymidine incorporation.


RESULTS
Ang II stimulated DNA synthesis in a dose-dependent manner with a maximal effect at a concentration of 1 micromol/l (173%). Ang II (0.5 micromol/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 micromol/l (177%), LPC at 15 micromol/l (156%), and HNE at 0.5 micromol/l (137%). Low concentrations of H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) also acted synergisitically with Ang II (0.5 micromol/l) in inducing DNA synthesis to 308, 304, or 238%, respectively. Synergistic interactions of Ang II (0.5 micromol/l) with mox-LDL, ox-LDL (both 50 ng/ml), H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) on DNA synthesis were completely reversed by the combined use of probucol (10 micromol/l), a potent antioxidant and candesartan (0.1 micromol/l), an AT1 receptor antagonist.


CONCLUSIONS
Our results suggest that mox-LDL, ox-LDL, and their major components H2O2, LPC, and HNE 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.
Watanabe
T
T
Department of Internal Medicine, University of Texas-Houston Health Science Center, 77030, USA.
Pakala
R
R
Katagiri
T
T
Benedict
C R
CR
D000111:Acetylcysteine / Q000008:administration & dosage; D000447:Aldehydes / Q000008:administration & dosage; D000804:Angiotensin II / Q000008:administration & dosage*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage; D001562:Benzimidazoles / Q000008:administration & dosage; D001713:Biphenyl Compounds; D002318:Cardiovascular Diseases / Q000188:drug therapy; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004357:Drug Synergism; D005419:Flavonoids / Q000008:administration & dosage; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage; D008077:Lipoproteins, LDL / Q000008:administration & dosage*; D008244:Lysophosphatidylcholines / Q000008:administration & dosage; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D011341:Probucol / Q000008:administration & dosage; D011817:Rabbits; D044140:Receptor, Angiotensin, Type 1; D013777:Tetrazoles / Q000008:administration & dosage; D020032:Tyrphostins / Q000008:administration & dosage
D000447:Aldehydes; D057911:Angiotensin Receptor Antagonists; D000975:Antioxidants; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D005419:Flavonoids; D008077:Lipoproteins, LDL; D008244:Lysophosphatidylcholines; D044140:Receptor, Angiotensin, Type 1; D013777:Tetrazoles; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; C099252:oxidized low density lipoprotein; D000804:Angiotensin II; D004247:DNA; D006861:Hydrogen Peroxide; C027576:4-hydroxy-2-nonenal; D011341:Probucol; C081643:candesartan; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000111:Acetylcysteine