Inhibition by Cholesterol Oxides of NO Release From Human Vascular Endothelial Cells

Abstract

Abstract-Recent studies have demonstrated that, unlike cholesterol, cholesterol oxidized at position 7 can reduce the maximal endothelium-dependent relaxation of isolated rabbit aortas (Circulation. 1997;95:723-731). The aim of the current study was to determine whether cholesterol oxides reduce the release of nitric oxide (NO) from human umbilical vein endothelial cells (HUVECs). The amount of NO released by histamine-stimulated HUVECs was determined by differential pulse amperometry using a nickel porphyrin-and Nafion-coated carbon microfiber electrode. The effects of cholesterol (preserved from oxidation by butylated hydroxytoluene), 7-ketocholesterol, 7␤-hydroxycholesterol, 5␣,6␣-epoxycholesterol, 19-hydroxycholesterol (60 g/mL), and ␣-lysophosphatidylcholine (10 g/mL) were compared. Pretreatment of HUVECs with cholesterol, 5␣,6␣-epoxycholesterol, or 19-hydroxycholesterol did not alter histamineactivated NO production. In contrast, pretreatment with 7-ketocholesterol or 7␤-hydroxycholesterol significantly decreased NO release. The inhibitory effect of 7-ketocholesterol was time and dose dependent and was maintained in the presence of L-arginine. In the absence of serum, lysophosphatidylcholine also reduced NO production. In ionomycin-stimulated cells, pretreatment with 7-ketocholesterol did not inhibit NO release. These results demonstrate that cholesterol derivatives oxidized at the 7 position, the main products of low density lipoprotein oxidation, reduce histamine-activated NO release in HUVECs. Such an inhibitory effect of cholesterol oxides may account, at least in part, for the ability of oxidized low density lipoprotein to reduce the endothelium-dependent relaxation of arteries. Key Words: human endothelial cells Ⅲ cholesterol oxides Ⅲ histamine Ⅲ NO production T he endothelium of blood vessels regulates vascular tone by releasing endothelium-derived relaxing and contracting factors.1-3 In particular, it has now been clearly established that the endothelium-dependent relaxation of arteries induced by acetylcholine or histamine involves the release of endothelium-derived relaxing factor, 1,4 identified as NO. 5,6 Recent studies have demonstrated that alterations in vascular reactivity can be associated with cardiovascular disorders [7][8][9][10] and that arteries from hypercholesterolemic and atherosclerotic patients exhibit marked attenuation of endothelium-dependent relaxation. 7,11,12 Although the impairment of arterial relaxation at an early stage of the atherosclerotic process may constitute a crucial step in disease progression, the related molecular mechanisms remain unclear. Several studies have demonstrated that LDLs, rather than native LDLs, can mimic the impairment of arterial relaxation observed in hyperlipidemia. [13][14][15][16] Whereas in some previous studies the inhibition of endothelium-dependent relaxation was attributed to LPC, 14,15,17 other studies did not support this view. 16,18 In particular, no significant relationship between the LPC content of LDLs and their ability to reduc...

HDL particles from type 1 diabetic patients are unable to reverse the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

“…This defect consists of loss of the ability to protect arteries from ox-LDL-induced inhibition of endothelium-dependent relaxation. The inhibitory effect of ox-LDL and of some of their specific compounds, such as derivatives of cholesterol oxidised in position 7, on endothelium-dependent vasorelaxation is mainly related to decreased bioavailability of nitric oxide (NO) [9].…”

Inability of HDL from type 2 diabetic patients to counteract the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

“…In contrast, no significant correlation was observed between the HDL fructosamine:total protein ratio or PON activity and Emax (ox-LDL+HDL) in type 2 diabetic patients or control subjects. The inhibitory effect of ox-LDL and some of their specific compounds such as derivatives of cholesterol oxidised in position 7 or lysophophatidylcholine on endothelium-dependent vasorelaxation is mainly related to a decreased bioavailability of NO [13][14][15][16][17]. HDL are likely to counteract the inhibitory effect of ox-LDL on endotheliumdependent vasorelaxation both by a direct and an indirect way.…”

Probucol Reduces Oxysterol Formation in Hypertensive Rabbits

“…21 Cholesterol oxidation products may be one of the agents responsible not only for vascular injury as discussed above but may also be responsible for the inhibition of NO production by the vascular endothelium. 38 There is evidence that the lipoxygenase pathway is a mediator of angiotensin II, implicating a role for humoral factors such as angiotensin II in mediating oxidative stress responses in the vessel wall. 39 Thus, activation of lipoxygenase may be a possible mechanism contributing to formation of lipid peroxides and oxysterols.…”