Ruptures caused by aortic aneurysms and dissections occur when the mechanical stresses in the aortic wall exceed the local aortic strength. In-vivo stresses are strongly mediated by residual stresses (RS), those existing in the absence of load. Circumferential RS can be estimated ex-vivo via the opening angle (OA), by subjecting an aortic ring to a radial cut. Although the underlying mechanism for RS remains poorly understood, our recent efforts have demonstrated strong correlations between the amounts of sulfated glycosaminoglycans (sGAG) and the OA in healthy aortas. In addition, advanced glycation end products (AGEs) are known to accumulate with age and create crosslinks within the extracellular matrix. Since ruptures are more prevalent in older tissue, the purpose of this study was to compare the effect of sGAG on the OA in intact and glycated aortic tissue.
Methods and Results
Sets of four adjacent aortic rings were excised from the upper thoracic regions of 9 porcine aortas. One ring served as a control, while a second ring underwent enzymatic sGAG depletion, a third underwent glycation, and the fourth ring underwent a combination of glycation followed by enzymatic sGAG depletion. A 100mM ammonium acetate buffer, pH 7.0 was used. Glycation and sGAG depletion were induced by incubating samples in 700mM of ribose, and 15U/mL hyaluronidase, 0.075U/mL chondroitinase ABC, 0.75U/mL heparinase for 48 hours at 37oC, respectively. The OA was then measured and the sGAG and general AGE contents were quantified. The quantification of sGAG contents in control and treated samples confirmed the successful removal of sGAG, with reductions by 94±2.5% (average ± standard deviation). In addition, a 93±27% increase in general AGEs was achieved. Statistically significant differences were found between the OAs of control and sGAG depleted, glycated, and glycated combined with sGAG depleted samples (paired sample t-test, p< 0.001). Specifically, the OA was reduced by 34±12% after sGAG depletion, 14±8% after glycation, and 45±15% after combined glycation and sGAG depletion. In addition, the OAs in sGAG depleted samples, as well as in combined glycated and sGAG depleted samples, were found to be significantly smaller than samples that underwent glycation only (paired sample t-test, p=0.002), being 22±15% and 34±18% smaller respectively.
These findings supported that sGAG depletion causes a reduction in the OA, in both intact and glycated tissue, and that AGEs may also affect the magnitude of the RS.