An electron paramagnetic resonance method for measuring the affinity of a spin-labeled analog of cholesterol for phospholipids.

Cholesterol (chol)-lipid interactions are thought to play an intrinsic role in determining lateral organization within cellular membranes. Steric compatibility of the rigid steroid moiety for ordered saturated chains contributes to the high affinity that holds chol and sphingomyelin together in lipid rafts whereas, conversely, poor affinity of the sterol for highly disordered polyunsaturated fatty acids (PUFAs) is hypothesized to drive the formation of PUFA-containing phospholipid domains depleted in chol. Here, we describe a novel method using electron paramagnetic resonance (EPR) to measure the relative affinity of chol for different phospholipids. We monitor the partitioning of 3ß-doxyl-5α-cholestane (chlstn), a spin-labeled analog of chol, between large unilamellar vesicles (LUVs) and cyclodextrin (mßCD) through analysis of EPR spectra. Because the shape of the EPR spectrum for chlstn is sensitive to the very different tumbling rates of the two environments, the ratio of the population of chlstn in LUVs and mßCD can be determined directly from spectra. Partition coefficients (K(B)(A)) between lipids derived from our results for chlstn agree with values obtained for chol and confirm that decreased affinity for the sterol accompanies increasing acyl chain unsaturation. The virtue of this EPR method is that it provides a measure of chol binding that is quick, employs a commercially available probe and avoids the necessity for physical separation of LUVs and mßCD.

Effects of local mechanical stimulation on coronary artery endothelial function and angiotensin II type 1 receptor in pressure or flow-overload.

AIMS: This study investigates the effect of local mechanical stimulation induced by pressure or flow-overload in right coronary artery (RCA) angiotensin II type 1 (AT1) receptor-mediated endothelial dysfunction in swine models of aortic or pulmonary artery banding. METHODS AND RESULTS: A total of 36 pigs (37 ± 7 kg) were studied. The RCA was exposed to pressure-overload by aortic banding (n = 6) or blood flow-overload by pulmonary artery banding (n = 6) for 4 weeks, and sham-operated animals served as controls (n = 6). The RCA of 18 pigs were exposed to acute ex-vivo pressure-overload. The effects of local mechanical stimuli on AT1 receptor were determined by external cuff. Aortic banding caused RCA pressure-overload of 118 ± 11 mmHg in comparison with 79 ± 9 mmHg for sham controls. The cross-sectional area of the RCA lumen increased 27.9% (from 8.09 ± 0.89 to 10.3 ± 0.96 mm) when the blood flow increased by 80% (from 23.8 ± 4.3 to 44.3 ± 7.2 ml/min) in the 4-week pulmonary artery banding period. Both pressure and flow-overload resulted in the up-regulation of expression and activation of AT1 receptor. An increased production of reactive oxygen species (ROS) and endothelium dysfunction were observed in the RCA. The acute inhibition of AT1 receptor and NADPH oxidase partially restored the endothelial function. The endothelial dysfunction and activation of AT1 receptor was also realized in ex-vivo pressure-overload of normal RCA. An external cuff inhibited the increase in activation of AT1 receptor and preserved endothelial function in ex-vivo pressure-overload which implicates local wall mechanical stimulation as opposed to pressure. CONCLUSION: Local mechanical stimulation activates the AT1 receptor which likely mediates ROS production and endothelial dysfunction in RCA.

Elevated oxidative stress and endothelial dysfunction in right coronary artery of right ventricular hypertrophy.

Remodeling of right coronary artery (RCA) occurs during right ventricular hypertrophy (RVH) induced by banding of the pulmonary artery (PA). The effect of RVH on RCA endothelial function and reactive oxygen species (ROS) in vessel wall remains unclear. A swine RVH model (n = 12 pigs) induced by PA banding was used to study RCA endothelial function and ROS level. To obtain longitudinal coronary hemodynamic and geometric data, digital subtraction angiography was used during the progression of RVH. Blood flow in the RCA increased by 82% and lumen diameter of RCA increased by 22% over a 4-wk period of RVH. The increase in blood flow and the commensurate increase in diameter resulted in a constant wall shear stress in RCA throughout the RVH period. ROS was elevated by ∼100% in RCA after 4 wk of PA banding. The expressions of p47(phox), NADPH oxidase (NOX1, NOX2, and NOX4) were upregulated in the range of 20-300% in RCA of RVH. The endothelial function was compromised in RCA of RVH as attributed to insufficient endothelial nitric oxide synthase cofactor tetrahydrobiopterin. In vivo angiographic analysis suggests an increased basal tone in the RCA during RVH. In conclusion, stretch due to outward remodeling of RCA during RVH (at constant wall shear stress), similar to vessel stretch in hypertension, appears to induce ROS elevation, endothelial dysfunction, and an increase in basal tone.