Interactions between cultured bovine arterial endothelial and smooth muscle cells; effects of modulated low density lipoproteins on cell proliferation and prostacyclin release

We exposed bovine aortic endothelial cells in culture to native LDL (n-LDL) and LDL modulated by dimethylsulfoxide (DMSO-LDL), dimethylsulfoxide-soluble particles from cigarette smoke (DSP-LDL) or Cu2+ (Cu(2+)-LDL) to explore the hypothesis that these LDL-forms might influence interactions between endothelial and smooth muscle cells. It was shown that 3H-thymidine incorporation into endothelial cells was decreased by DMSO-LDL, DSP-LDL and Cu(2+)-LDL compared to n-LDL, while it was higher by DSP-LDL compared to its control i.e. DMSO-LDL. These effects could be transferred by conditioned medium to smooth muscle cell cultures. DSP-LDL or Cu(2+)-LDL decreased total cellular protein of endothelial cells. Initial (15 min) prostacyclin release from endothelial cells was increased by all LDL preparations compared to medium without LDL, most pronounced for Cu(2+)-LDL. If n-LDL was control, only Cu(2+)-LDL significantly increased the release of prostacyclin during 15 min and during 24 h. The release of prostacyclin assayed after 24 h was depressed by DSP-LDL compared to DMSO-LDL. This study demonstrated that interactions between endothelial and smooth muscle cells could be influenced by LDL treated by dimethylsulfoxide-soluble particles from cigarette smoke or by Cu2+, and their effects were not similar. DSP-LDL, in contrast to Cu(2+)-LDL, significantly decreased the release of prostacyclin by endothelial cells after 24 h incubations and via endothelial cell conditioned medium stimulated smooth muscle cell proliferation judged by increased 3H-thymidine incorporation. The results might be of relevance for atherogenesis.

Influence of lipoproteins on endothelial function

The endothelium is a physical barrier between the blood and vascular smooth muscle, a source of enzymes activating and deactivating cardiovascular hormones and a site of production of relaxing and contracting factors. Nitric oxide is a potent vasodilator and inhibitor of platelet function which under most circumstances is released together with prostacyclin which exerts similar effects. Both substances play an important protective role in the coronary circulation in that they cause continuous vasodilation and inhibition of platelet function. In addition, the endothelium is a source of contracting factors such as endothelin-1, thromboxane A2 and endoperoxides. Due to its strategic anatomic position, the endothelium is a primary target of injuries and cardiovascular risk factors. Besides other risk factors such as hypertension and diabetes, low density lipoproteins alter endothelial function. A reduced release of endothelium-derived relaxing factors and an enhanced liberation of endothelium-derived contracting factors are common in the presence of lipoproteins. These alterations in endothelial function are likely to contribute to the pathogenesis as well as progression and complications of coronary artery disease such as vasospasm and thrombus formation. This review will focus on the influence of lipoproteins on endothelial function.

Interactions between cultured bovine arterial endothelial and smooth muscle cells: studies on uptake and degradation of low density lipoproteins by smooth muscle cells

This study was designed to investigate the effects of substances released from non-injured and injured bovine arterial endothelial cells on 125I-low density lipoprotein uptake and degradation by smooth muscle cells in culture. It was demonstrated that endothelial cell-released non-dialysable (molecular weight cut off 12-14000) substances significantly stimulated 125I-low density lipoprotein uptake and degradation by smooth muscle cells. Endothelial cell-released dialysable substances and endothelin-1 did not cause this stimulation. The increase in 125I-low density lipoprotein uptake and degradation by smooth muscle cells could be dissociated from cell proliferation. However, in endothelial cell-smooth muscle cell co-culture 125I-low density lipoprotein uptake and degradation by smooth muscle cells were not stimulated. Injury to endothelial cells by lipid-soluble smoke particles or ultraviolet light, which reduced total cellular protein by 15-25%, enhanced the endothelial cell release of the substances stimulating 125I-low density lipoprotein uptake. The results are discussed in relation to atherogenesis.

Progression of aortic stenosis. Role of age and concomitant coronary artery disease

To determine the spontaneous progression of valvular aortic stenosis and to delineate clinical factors related to progression, a longitudinal study, including 49 patients (aged 16 to 81 years), was performed. All patients had auscultatory findings of aortic stenosis and multiple Doppler echocardiograms separated by at least 11 months. Rapid progression of aortic stenosis was defined as an increase of maximal instantaneous pressure gradient by > or = 10 mm Hg per year. During a mean follow-up period of 32 months (11 to 66 months), maximal pressure gradient rose from 38 +/- 15 to 60 +/- 20 mm Hg in the entire study population, resulting in a median increase of 7.2 mm Hg per year. In 21 patients (43 percent), an increase of > or = 10 mm Hg per year was found; in this subgroup with rapid progression, patients were older (64 vs 53 years, p < 0.01) and coronary artery disease was more prevalent (38 percent vs 7 percent, p = 0.01). We conclude that nearly half the patients with initially mild to moderate valvular aortic stenosis reveal a progression of > or = 10 mm Hg per year.