Antioxidant N-acetylcysteine inhibits vasoactive agents-potentiated mitogenic effect of mildly oxidized LDL on vascular smooth muscle cells.
Mildly oxidized LDL (mox-LDL) has been shown to induce monocyte-endothelial interactions and vascular smooth muscle cell (VSMC) proliferation, key events in the formation of the atherosclerotic lesion. Growth factors and vasoactive peptides are also thought to play a major role in atherogenesis. We examined the interaction between mox-LDL and well-known vasoactive agents such as serotonin (5-HT), angiotensin II (Ang-II), endothelin-1 (ET-1), or urotensin II (U-II) in inducing DNA synthesis in VSMCs. Growth-arrested VSMCs were incubated with different concentrations of native LDL, mox-LDL, or highly oxidized LDL (ox-LDL) with 5-HT, Ang-II, ET-1, or U-II in the absence or presence of N-acetylcysteine (NAC), an intracellular free radical scavenger. DNA synthesis in VSMCs was examined by [3H]thymidine incorporation into cellular DNA. Mox-LDL and ox-LDL stimulated [3H]thymidine incorporation with a maximal effect at 5 microg/ml (211%, 154%), which values were significantly greater than that for native LDL (128%). 5-HT, Ang-II, ET-1, or U-II also stimulated [3H]thymidine incorporation in a dose-dependent manner. 5-HT had a maximal stimulatory effect at a concentration of 50 micromol/l (205%), Ang-II at 1.75 micromol/l (202%), ET-1 at 0.1 micromol/l (205%), and U-II at 0.05 micromol/l (161%). When added together, mox-LDL (100 ng/ml)-induced [3H]thymidine incorporation was potentiated by low concentrations of 5-HT (1 micromol/l), Ang-II (0.5 micromol/l), ET-1 (1 nmol/l), or U-II (10 nmol/l) (114% to 330%, 325%, 338%, or 345%, respectively). Synergistic interactions of mox-LDL with 5-HT, Ang-II, ET-1, or U-II were significantly inhibited by NAC (400 micromol/l). Our results suggest that mild oxidation of LDL may enhance its atherogenic potential and exert a synergistic interaction with vasoactive agents in inducing DNA synthesis via the generation of reactive oxygen species in VSMCs.
Watanabe
Takuya
T
Third Department of Internal Medicine, Showa University School of Medicine, Tokyo, Japan.
Pakala
Rajbabu
R
Katagiri
Takashi
T
Benedict
Claude R
CR
D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002317:Cardiovascular Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D008077:Lipoproteins, LDL / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D008934:Mitogens / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits
D000975:Antioxidants; D002317:Cardiovascular Agents; D008077:Lipoproteins, LDL; D008934:Mitogens; C099252:oxidized low density lipoprotein; D004247:DNA; D000111:Acetylcysteine