Oxidized LDL decreases L-arginine uptake and nitric oxide synthase protein expression in human platelets: relevance of the effect of oxidized LDL on platelet function.
BACKGROUND
Oxidized LDL (ox-LDL) promotes vasoconstriction and platelet activation. The present study was undertaken to determine the involvement of the L-arginine-nitric oxide (NO) pathway in ox-LDL-mediated platelet activation.


RESULTS
Washed human platelets were incubated with native LDL or ox-LDL for 1 hour at 37 degrees C followed by measurement of platelet function and indexes of the L-arginine-NO pathway. Ox-LDL but not native LDL caused a concentration-dependent increase in thrombin-induced platelet aggregation and 14C-serotonin release. These effects of ox-LDL were inhibited by pretreatment of platelets with L-arginine, the precursor of NO. Ox-LDL also caused a concentration-dependent reduction in the uptake of 3H-L-arginine by platelets. In addition, NO synthase activity, measured as conversion of 3H-L-arginine to 3H-L-citrulline, decreased on incubation of platelet cytosol with ox-LDL. Nitrite production was also reduced by treatment of platelets with ox-LDL. These effects of ox-LDL on NO synthase activity and nitrite production were reversed by pretreatment of platelets with L-arginine. Concurrent with the decrease in NO production, cytosolic cGMP was inhibited in ox-LDL-treated platelets. The inhibitory effects of ox-LDL were dependent in part on the increase of cholesterol in the platelets. Western blot analysis demonstrated approximately 50% reduction in the expression of NO synthase protein in platelets treated with ox-LDL.


CONCLUSIONS
These observations indicate that the L-arginine-NO pathway is involved in the effects of ox-LDL on platelet function and that ox-LDL stimulates platelet function primarily by diminishing NO synthase expression as well as decreasing the uptake of L-arginine.
Chen
L Y
LY
Department of Medicine, College of Medicine, University of Florida, Gainesville, USA.
Mehta
P
P
Mehta
J L
JL
D001120:Arginine / Q000097:blood*; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D015153:Blotting, Western; D002470:Cell Survival; D002784:Cholesterol / Q000097:blood; D006152:Cyclic GMP / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D008077:Lipoproteins, LDL / Q000378:metabolism / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis*; D010084:Oxidation-Reduction
D008077:Lipoproteins, LDL; D001120:Arginine; D002784:Cholesterol; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP