Interactions of elastin and aorta with sugars in vitro and their effects on biochemical and physical properties

Abstract

Stiffening of blood vessel walls occurs in the early stages of atherosclerosis, and this process is known to occur earlier in diabetic subjects. The effect could be due, in part, to glycation. Although collagen is responsible for ensuring the ultimate tensile strength of the tissue, elastin largely determines the compliance of the vessel wall in the normal physiological range of pressures and this appears to be closely matched to haemodynamic requirements. Changes in elastin are therefore likely to affect optimal function of the tissue. We have investigated the susceptibility of elastin to glycation and effects of glycation on its mechanical and physicochemical properties. We found that purified elastin and a collagen-elastin preparation from the porcine thoracic aorta rapidly incorporated glucose and ribose, the extent increasing 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 incubations glycation was associated with the appearance of the advanced glycation end products, the fluorescent cross-link pentosidine and the non-fluorescent putative cross-link NFC-1. In both purified elastin and the whole elastin-collagen matrix the slope of the force-extension curve increased significantly with glycation. The greatest increase in stiffness was observed in the elastin-collagen preparation after ribose incubation (250 mmol/l for 1 month), where the slope, at large strain, increased by 56 +/- 19% (mean +/- SD, n = 12). The diameter of the 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 of 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 binding 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 glycation of the charged lysine and arginine side-chain residues.

Determinants of Progression of Aortic Stiffness in Hemodialysis Patients

“…[22][23][24][25] In fact, in vitro and animal models of diabetes mellitus and hyperglycemia have shown that AGEs cross-linking with elastin and collagen increases the slop of force-extension curve significantly, and that arterial stiffness is closely correlated with arterial content of pentosidine. 9,10 Our findings show a significant association between serum pentosidine levels and progression of aortic stiffness, suggesting that AGEs could play a significant role in the progressive aortic stiffness in this population.…”

Tyrosine nitration site specificity identified by LC/MS in nitrite-modified collagen type IV

“…It is well known that the level of reactants used to study the effects of glycation on connective tissue proteins (i.e. 100-250 mM) are well above those encountered in vivo (Kohn et al, 1984;Fu et al, 1994;Winlove et al, 1996). The rationale behind the use of supraphysiologic reactant concentrations is to identify the end-products of the reaction and to simulate functional, biomechanical, and biochemical changes that could take decades to develop in vivo.…”

Morphology, mechanisms and pathology of musculoskeletal ageing

“…The cross-linking of elastin is through the same lysine-based reactions as those of collagen, but differ in that the cross-linking of elastin chains is much more extensive. Elastin can also undergo age-related stiffening as a consequence of production of AGEs [22].…”