Effects of LDL Cholesterol on Vascular Function: Mechanisms of Action

[摘要] 1. Effects of native (LDL) and oxidised (ox-LDL) low density lipoproteins on cholesterol uptake have been investigated in vitro, by examination of the effects of exposure to LDL and ox-LDL on the cholesterol content of rat aortic vascular smooth muscle (VSM) cells. Hypertension and hypercholesterolemia were also examined as coexisting and interactive risk factors by comparison of effects in WKY and SHRSP VSM cells. 2. On exposure of SHRSP and WKY VSM cells to 20mug/ml LDL and ox-LDL, small increases in free membrane cholesterol content were observed. Incubation of SHRSP VSM cells with LDL and ox-LDL produced greater increases in free cholesterol content compared to the WKY normotensive reference strain. 3. Effects of the antioxidants vitamin E and N-acetyl-L-cysteine (NAC), on LDL and ox-LDL mediated cholesterol uptake were examined in WKY and SHRSP VSM cells. In the presence of vitamin E both LDL and ox-LDL mediated effects were significantly attenuated in both cell types. Vitamin E also reduced basal free membrane cholesterol levels in a concentration-dependent manner, suggesting effects in addition to antioxidant properties. NAC produced only a small attenuation of LDL and ox-LDL mediated effects on cholesterol uptake in WKY and SHRSP VSM cells, and did not alter basal free cholesterol content. 4. The effects of cell stretch on ox-LDL induced cholesterol uptake were also examined in WKY VSM cells using a novel cell stretch apparatus. Results from this preliminary study were inconclusive, but demonstrated a potential model for future investigations of hemodynamic forces on cellular function. 5. Effects of LDL and ox-LDL on vascular reactivity were characterised in vitro, in the rat aorta. Rings of rat aorta were incubated in either vehicle, LDL, or ox-LDL for 5 hours before examination of vascular reactivity using a classical organ bath setup. Exposure to LDL and ox-LDL caused an impairment of carbachol-induced endothelium dependent relaxation and L-NAME induced contraction. Ox-LDL also impaired SNP-induced endothelium independent relaxation. LDL and ox-LDL exposure augmented phenylephrine-induced contraction and showed a tendency to increase potassium chloride induced contraction, although the higher concentration of LDL (500mug/ml), caused attenuation of phenylephrine contraction and had no effect on potassium chloride induced contraction. 6. Possible mechanisms underlying LDL and ox-LDL effects on vascular ractivity in the rat aorta were examined. 7. In tissues not incubated with LDL/ox-LDL, removal of endothelium from the rings caused a significant reduction in L-NAME induced contraction by greater than 70%, demonstrating that nitric oxide assessed was mainly endothelium derived. Five hour incubation resulted in only a small induction of the L-NAME response, which was blocked in the presence of dexamethasone. Removal of the endothelium prior to incubation, caused a considerable increase in the level of induction observed. This increase was inhibited by dexamethasone. 8. The effect of LDL and ox-LDL on INOS and eNOS activity was investigated by examination of the effects of dexamethasone on the L-NAME response+/-LDL and ox-LDL. Incubation with both LDL and dexamethasone reduced L-NAME induced contraction to a similar degree as incubation with dexamethasone alone. Ox-LDL treated tissues showed a similar pattern, with a trend towards lower responses when incubation included both ox-LDL and dexamethasone. 9. Effects of vitamin E on LDL-induced alterations of vascular reactivity were examined. Vitamin E had no significant effect on LDL-induced alterations of vascular reactivity. Results suggested that only LDL-mediated attenuation of maximum carbachol induced relaxation may be altered in the presence of vitamin E (although this did not reach statistical significance). 10. Effects of superoxide dismutase (SOD) on LDL and ox-LDL induced alterations of vascular reactivity were examined. SOD alone, showed a tendency to reduce maximum phenylephrine induced contraction when compared with appropriate controls. Incubation in the presence of SOD did not significantly alter LDL and ox-LDL induced effects on vascular reactivity.

[发布机构] University:University of Glasgow

[关键词] Medicine, Physiology