INTERACTIONS OF ELASTIN AND AORTA WITH SUGARS IN-VITRO AND THEIR EFFECTS ON BIOCHEMICAL AND PHYSICAL-PROPERTIES

Stiffening of blood vessel walls occurs in the early stages of atheros clerosis, and this process is known to occur earlier in diabetic subje cts. The effect could be due, in part, to glycation. Although collagen is responsible for ensuring the ultimate tensile strength of the tiss ue, elastin largely determines the compliance of the vessel wall in th e normal physiological range of pressures and this appears to be close ly matched to haemodynamic requirements. Changes in elastin are theref ore likely to affect optimal function of the tissue. We have investiga ted the susceptibility of elastin to glycation and effects of glycatio n on its mechanical and physicochemical properties. We found that puri fied elastin and a collagen-elastin preparation from the porcine thora cic aorta rapidly incorporated glucose and ribose, the extent increasi ng linearly with increasing concentration and reaching a maximum after 7 days at 37 degrees C. Biochemical analysis showed that about one of the five lysines available per elastin monomer was glycated after 12 days incubation at a sugar concentration of 250 mmol/l. In long-term i ncubations glycation was associated with the appearance of the advance d glycation end products, the fluorescent cross-link pentosidine and t he non-fluorescent putative cross-link NFC-1. In both purified elastin and the whole elastin-collagen matrix the slope of the force-extensio n curve increased significantly with glycation. The greatest increase in stiffness was observed in the elastin-collagen preparation after ri bose incubation (250 mmol/l for 1 month), where the slope, at large st rain, increased by 56 +/- 19% (mean +/- SD, n = 12). The diameter of t he tissue at 1 N force also changed: for elastin there was an increase in length of approximately 5%, but for the elastin-collagen there was a decrease of similar magnitude indicating that glycation introduces differential strains within the fibrous protein matrix. Potentiometric titration demonstrated that glycation was associated both with loss o f basic groups and shifts in pK of the acidic groups, which indicated changes in the environment of the charge groups due to conformational rearrangements. Changes in ion binding were dependent on pH, and were consistent with a reduction in effective anionic charge. Calcium bindi ng to elastin was increased at acid pH, but decreased at higher pH. We suggest that these effects are not only due to changes in the charge profile, but also in the conformation of the molecule resulting from g lycation of the charged lysine and arginine side-chain residues.