Ultraviolet-induced mechanical augmentation of the degraded porcine aortic adventitia: Its significance for preventing aneurysmal rupture

In the previous studies, we have shown that the tunica adventitia of porcine abdominal aorta could be mechanically reinforced by irradiating it with ultraviolet A (UV-A) rays to promote the photocrosslinking of constitutive collagen, and we have proposed the method as a procedure to prevent or delay abdominal aortic aneurysm (AAA) ruptures. We have also demonstrated that UV irradiation-induced mechanical augmentation despite the degradation of the adventitia through collagenolysis in vitro. Considering that elastolysis is equally a relevant event in the pathogenesis of AAA, the degradation of elastin was also investigated in the present study. A total of 50 porcine aortas were used in the study. All processed samples were evaluated in a mechanical tester before and after degradation and/or irradiation. The adventitial layer was isolated and subjected to elastase for either 1 – 48 h. We found that both elastin and collagen were digested by elastase, with the former being completely digested after 48 h. The samples degraded for 1 h were subsequently irradiated with UV-A (365 nm) in the presence of riboflavin as a photoinitiator, a process that induced an enhancement of the strength and stiffness of the tissue. This is an indication that a partly degenerated aortic wall, like that in an aneurysmal region, can be reinforced mechanically by UV irradiation, possibly to the extent of delaying, or preventing altogether, the wall’s rupture. It appears important to irradiate the wall as early as possible.