Studies on the interaction of cholesterol with soluble and insoluble elastins

Abstract

The exchange of 3H-cholesterol in an aqueous solution of taurodeoxycholate with insoluble elastin and kappa-elastin peptides has been quantitatively studied. At higher cholesterol concentrations, and in similar experimental conditions, 0.3 μg and 0.2 μg of cholesterol could be adsorbed, respectively, on to 1 mg insoluble elastin and 1 mg kappa-elastin coacervate. Therefore, the above amounts of cholesterol fixed per mg elastin represent minimal estimates. The replacement of Na + ions by Ca 2+ ions increased the cholesterol binding both of fibrous and of soluble elastins. The binding curves tend towards a limiting value in the presence of Na +, but no saturation effect was observed in the presence of Ca 2+. The replacement of sodium ions by calcium ions in the taurodeoxycholate solutions also lowered the coacervation temperature of the kappa-elastin peptides. Fibrous elastin retained more cholesterol at 65°C than at 37°C, suggesting the importance of hydrophobic interactions in cholesterol elastin association. These results suggest that conformational changes could be induced in both soluble and insoluble forms of elastin by calcium ions increasing their affinity for cholesterol. This enhancement of cholesterol fixation by elastin in the presence of Ca 2+ ions may well have a physiopathological importance. So does also the fact that elastin-peptides exhibit a higher affinity in the presence of Ca 2+ for cholesterol than insoluble elastin, suggesting the possibility of increased cholsterol (and calcium) fixation as elastin is degraded in situ by elastases.