Oxidized lipoproteins induce long-lasting inhibition of nitric oxide synthase from a murine endothelioma cell line (bEnd.4).
BACKGROUND
The vascular endothelium produces nitric oxide, which has vasodilatory properties. It has been postulated that some lipoproteins may increase arterial vascular tone by decreasing the availability of endothelium-derived nitric oxide. The mechanism underlying this effect, however, is still poorly understood.


METHODS
We investigated the effect of native and oxidized human low- and high-density lipoproteins on the nitric oxide synthetic activity of an endothelioma cell line (bEnd.4). Oxidized lipoproteins were obtained by incubation with CuSO4. The production of nitric oxide by the cells was monitored by quantifying the nitrite concentration in the medium using Greiss reagent.


RESULTS
The synthesis of nitric oxide by the bEnd.4 cell line was calcium-dependent and was abolished by a selective inhibitor of the constitutive nitric oxide synthase. Incubation with oxidized lipoproteins caused a time- and dose-dependent inhibition of nitric oxide synthetic activity. At a concentration of 100 micrograms/ml cholesterol, oxidized low- and high-density lipoproteins inhibited the production of nitric oxide by 27 and 51%, respectively, within 6h. The lipid fraction obtained from the native or the oxidized lipoproteins mimicked the effect of the intact lipoproteins.


CONCLUSIONS
These results support the involvement of oxidized lipoproteins in the modulation of endothelial functions relevant to the pathogenesis of cardiovascular disease.
Fogliatto
G
G
Pharmacia Farmitalia Carlo Erba Research Institute, Milan, Italy.
Musanti
R
R
Pirillo
A
A
Ghiselli
G
G
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002148:Calmodulin-Binding Proteins / Q000037:antagonists & inhibitors*; D002784:Cholesterol / Q000008:administration & dosage / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003300:Copper / Q000737:chemistry; D019327:Copper Sulfate; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D006390:Hemangioendothelioma / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D008075:Lipoproteins, HDL / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D008077:Lipoproteins, LDL / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D009252:NADPH Dehydrogenase / Q000037:antagonists & inhibitors*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism; D019001:Nitric Oxide Synthase; D009573:Nitrites / Q000037:antagonists & inhibitors / Q000378:metabolism; D010084:Oxidation-Reduction; D014407:Tumor Cells, Cultured
D002148:Calmodulin-Binding Proteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D009573:Nitrites; D009569:Nitric Oxide; D003300:Copper; D002784:Cholesterol; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D009252:NADPH Dehydrogenase; D019327:Copper Sulfate; D002118:Calcium