Lysophosphatidylcholine and reactive oxygen species mediate the synergistic effect of mildly oxidized LDL with serotonin on vascular smooth muscle cell proliferation.
BACKGROUND
Mild oxidation of LDL enhances its atherogenic potential and induces a synergistic interaction with serotonin (5HT) on vascular smooth muscle cell (VSMC) proliferation. Because of its complex chemical nature, the mitogenic components of mildly oxidized LDL (moxLDL) remain unclear.


RESULTS
We examined both the effects of lysophosphatidylcholine (LPC) and hydrogen peroxide (H(2)O(2)), a donor of reactive oxygen species, as major components of moxLDL and their interactions with 5HT on VSMC proliferation. Growth-arrested VSMCs were incubated with different concentrations of moxLDL, LPC, H(2)O(2), or LPC with H(2)O(2) in the absence or presence of 5HT. DNA synthesis in VSMCs was examined by [(3)H]thymidine incorporation. MoxLDL, LPC, H(2)O(2), and 5HT stimulated DNA synthesis in a dose-dependent manner. MoxLDL had a maximal stimulatory effect at a concentration of 5 microg/mL (211%), LPC at 15 micromol/L (156%), H(2)O(2) at 5 micromol/L (179%), and 5HT at 50 micromol/L (205%). Added together, moxLDL (50 ng/mL) and 5HT (50 micromol/L) synergistically increased DNA synthesis (443%). Coincubation of LPC (1 micromol/L) with H(2)O(2) (0.5 micromol/L) and 5HT (5 micromol/L) resulted in a synergistic increase in DNA synthesis (439%), which was nearly equal to that of moxLDL with 5HT (443%). The combined effects of LPC, H(2)O(2), and 5HT on DNA synthesis were completely reversed by the combined use of an antioxidant, N:-acetylcysteine (400 micromol/L) or butylated hydroxytoluene (20 micromol/L), with a 5HT(2) receptor antagonist, LY281067 (10 microg/mL).


CONCLUSIONS
Our results suggest that both LPC and reactive oxygen species may contribute to the mitogenic effect of moxLDL on VSMCs and its synergistic effect with 5HT.
Department of Internal Medicine, Division of Cardiology, University of Texas-Houston Health Science Center, Houston, TX 77030, USA.
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Watanabe
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Pakala
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Koba
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Katagiri
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Benedict
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D004357:Drug Synergism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008237:Lysergic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D008244:Lysophosphatidylcholines / Q000494:pharmacology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology
D000975:Antioxidants; D008077:Lipoproteins, LDL; D008244:Lysophosphatidylcholines; D017382:Reactive Oxygen Species; D012702:Serotonin Antagonists; C099252:oxidized low density lipoprotein; D012701:Serotonin; D004247:DNA; D006861:Hydrogen Peroxide; D008237:Lysergic Acid; C054583:sergolexole