AbstractBackground and objective
According to the response-to-injury hypothesis, endothelial dysfunction is the first step in atherogenesis. The objective of the current study was to challenge this hypothesis by dissociating endothelial (dys)function and atherosclerosis initiation and progression using selective lowering of plasma homocysteine, plasma cholesterol, or both.Methods
A hyperhomocysteinemic and atherogenic diet was started at the age of 12 weeks in C57BL/6 homozygous low density lipoprotein receptor (LDLr) deficient/heterozygous cystathionine-β-synthase (CBS) deficient mice. Three weeks later, gene transfer was performed with E1E3E4-deleted adenoviral vectors for hepatocyte-restricted overexpression of CBS (AdCBS) or of the LDLr (AdLDLr), or with the control vector Adnull. In a fourth group, AdCBS and AdLDLr were co-administered.Results
Compared to the homocysteine plasma level at the day of gene transfer (88 ± 5.0 µM), AdCBS gene transfer resulted in a 5.6-fold (p < 0.0001) decrease of plasma homocysteine at day 14 (16 ± 1.1 µM) after gene transfer. This effect was stable for the entire duration of the experiment and was similar in the combined gene transfer group. AdLDLr gene transfer did not affect homocysteine levels. Plasma cholesterol levels were similar before (680 ± 39 mg/dl) and after AdCBS gene transfer (710 ± 28 mg/dl) whereas AdLDLr transfer and the combination of both vectors induced 6.2-fold (p < 0.0001) lower cholesterol levels in the period of 13 weeks after gene transfer compared to control mice. This major reduction of cholesterol occurred predominantly in VLDL, IDL, and LDL. Selective homocysteine lowering but not selective cholesterol lowering restored endothelium-dependent vasodilatation to normal at 6 weeks after gene transfer. Intimal area in the aortic root and in the brachiocephalic artery at 13 weeks was more than 100-fold (p < 0.001) smaller in AdLDLr and AdCBS/AdLDLr mice than in control mice and AdCBS mice. No differences in intimal area were observed between control mice and AdCBS mice. Oxidative stress was significantly reduced by selective homocysteine lowering but not by selective cholesterol lowering. In a model of carotid artery thrombosis, the average time to first occlusion and to stable occlusion were 1.9-fold (p < 0.01) and 2.1-fold longer (p < 0.01), respectively, in AdCBS treated mice than in control mice,Conclusion
Endothelial dysfunction is neither necessary nor sufficient to induce atherosclerosis. Selective homocysteine lowering has anti-thrombotic but no anti-atherogenic effects.