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Global Translational Medicine Elastolysis of porcine aortic adventitia

aneurysm (AAA) is a frequent occurrence. Its spontaneous Selective enzymatic digestion of the main components of
rupture is associated with high morbidity and mortality. the arterial wall (elastin, collagen) has been experimentally
Enzymatic degradation and impaired remodeling of the applied in order to assess their contributions to the
extracellular matrix are among the pathological hallmarks mechanical properties of the whole wall and to establish
of AAA [1-8] . The degenerative process is initiated through their role in the aneurysmal pathogenesis. In a recent
[22]
the activity of proteinases such as serine proteinases study , we mechanically characterized adventitial
(e.g., elastases, chymases), matrix metalloproteinases, or specimens that were subjected to in vitro collagenolysis
cysteine and aspartic proteinases (mostly cathepsins). before tensile measurements. The irradiation with UV-A
rays mechanically enhanced the degenerated tunica, while
The surgical techniques that are currently employed
to prevent the rupture of an aneurysm, or to perform an the specimens that were irradiated prior to degradation
showed the highest gain in stiffness and strength. These
emergency repair of the ruptured segment, include either findings suggested not only that irradiation is beneficial
open surgery or endovascular exclusion by means of to an already degenerated wall but also that the earlier
endograft, both aiming at the exclusion of the aneurysmal irradiation is applied, the vessel wall is more resistant to
bulge from circulation and achieving similar levels of rupture.
post-operative complications and long-term survival [9-11] .
However, the risk of serious complications remains In the present study, a similar approach was employed
present, and less invasive procedures could be beneficial. to investigate the fate of adventitial elastin after exposing
We have proposed that by mechanically strengthening the adventitia to elastase in vitro and the effect of the UV-A
aneurysmal wall, its rupture can be delayed indefinitely, irradiation. Regarding the use of elastase, we considered
and such a procedure would be associated with much less an additional aspect that was almost entirely ignored in
surgical intervention. To this end, the exposure of collagen the previous enzymolytic studies of arterial biomechanics,
to ultraviolet A (UV-A) radiation in the presence of that is, whether and to what extent collagen is degraded by
photoinitiators/photosensitizers can lead to an exogenous elastase and how the experimental results may be affected.
crosslinking process, which augments the mechanical Indeed, if the vascular collagen can be digested not only
properties (strength and stiffness) of the collagenous by collagenase but also by elastase, this may reflect on the
tissues. It should be mentioned that the endogenous interpretation of results from the previous reports.
crosslinking of native proteins, such as collagen or elastin, 2. Materials and methods
represents a natural stage within the protein turnover in
our body, over which we have little control [12,13] . In contrast, 2.1. Materials
the exogenous crosslinking of living collagen is a process Riboflavin 5’-phosphate monosodium salt (RF) was
initiated and carried out by researchers, which is aimed supplied by Cayman Chemicals (Ann Arbor, Michigan,
to be implemented in a medical application. On the other USA). Its solution in saline (0.1% w/v) was used as a
hand, a variety of crosslinking techniques (chemical, photoinitiator. Elastase from porcine pancreas (Lot No.
photochemical, thermal, or enzymatic) are extensively U1122327529), with an activity of 80 U/mg, double
employed to create protein-based scaffolds for tissue crystallized, was purchased from MP Biomedicals, LLC
engineering and biomaterials for implants [14-16] , with non- (Solon, Ohio, USA). The SuperFrost™ Plus slides for
living collagen being the commonly targeted material. histology were supplied by Menzel-Gläser, Braunschweig,
The exogenous photochemical crosslinking of corneal Germany. All other reagents or consumables were
collagen became a routine treatment for keratoconus supplied by MilliporeSigma (St Louis, Missouri, USA) and
(a condition leading to severe visual impairment) by Australian suppliers (ProSciTech, Kirwan, Queensland,
arresting its progression as a result of a crosslinking-induced POCD Scientific, North Rocks, NSW, and Australian
increase of stiffness [17,18] . More recently, photocrosslinking Biostain, Traralgon, Victoria). Water of high purity
of tarsal collagen was proposed and investigated [19,20] as a (Milli-Q or equivalent) was used in the experiments.
treatment for eyelid laxity conditions (e.g., floppy eyelid The porcine aortas were obtained from Highchester
syndrome). In a previous study , we demonstrated that Meats Pty Ltd., (Gleneagle, Queensland, Australia),
[21]
the mechanical properties of ex vivo aortic adventitial an abattoir unit operating under the Australian Code
collagen were significantly enhanced following irradiation of Practice of Animal Welfare Standards for Livestock
with UV-A rays (365-nm wavelength, 3.4 eV energy) in the Processing Establishments. Aortic segments were
presence of riboflavin as a photoinitiator. We proposed this harvested on the day of collection from the cadavers of
process as a new concept for the preventive treatment of 20-week-old pigs (the variety “beacon pigs”). The animals
AAA (and possibly other arterial aneurysms). have been sacrificed exclusively for commercial purposes,

Volume 2 Issue 2 (2023) 2 https://doi.org/10.36922/gtm.0897