Chemical stabilization of the extracellular matrix attenuates growth of experimentally induced abdominal aorta aneurysms in a large animal model

Abstract

Objective The goal of the present study was to test the safety and efficacy of chemical stabilization of the arterial extracellular matrix as a novel nonoperative treatment of abdominal aortic aneurysms (AAAs) in a clinically relevant large animal model. Methods To achieve matrix stabilization, we used 1,2,3,4,6-pentagalloylglucose (PGG), a noncytotoxic polyphenolic agent capable of binding to and stabilizing elastin and collagen against the action of degrading enzymes. We first optimized the therapeutic PGG formulation and time of exposure by in vitro testing on porcine aortas using phenol histologic staining with iron chloride, elastic recoil assays, and PGG quantification as a function of tissue thickness. We then induced AAAs in 16 swine using sequential balloon angioplasty and elastase/collagenase and calcium chloride treatment of the infrarenal segment. We monitored AAA induction and development using digital subtraction angiography. At 2 weeks after induction, after the AAAs had reached ∼66% arterial expansion, the swine were randomly assigned to 2 groups. In the treatment group, we delivered PGG to the aneurysmal aorta endoluminally using a weeping balloon and evaluated the AAA diameters using digital subtraction angiography for another 10 weeks. The control swine did not receive any treatment. For the safety evaluation, we collected blood and performed comprehensive metabolic panels and complete blood counts every 2 to 3 weeks for all the animals. The swine were routinely monitored for neurologic and physical attributes such as behavior, inactivity, alertness, appetite, discomfort, and weight gain. After euthanasia and full necropsy, we analyzed the AAA tissue samples for PGG content, elastic recoil, and histologic features. Results In vitro, a single 2.5-minute intraluminal delivery of 0.3% PGG to the swine aorta was sufficient for PGG to diffuse through the entire thickness of the porcine arterial tissues and to bind with high affinity to the elastic lamellae, as seen by positive iron chloride staining, a reduction of elastic recoil, and an increase in PGG content. In vivo, the control swine AAA tissues were thickened and showed the typical aspects of AAA, including chronic inflammation, adventitial reactivity, smooth muscle cell proliferation, elastic lamellae degradation, and medial and adventitial calcification. Similar aspects were noted in the PGG-treated arteries, except for the lack of calcification and an apparent diminished hyperplasia. PGG treatment was effective in reducing AAA expansion and reversing the process of AAA dilation by reducing the aortic diameters to ≤30% by week 12 ( P < .05). PGG was specifically localized to the aneurysmal segments as seen by histologic examination, the reduction of elastic recoil, and an increase in PGG content. PGG treatment did not affect the swine's neurologic or physical attributes, weight, blood chemistry, blood cells, or functionality of remote orga...

Animal Model Dependent Response to Pentagalloyl Glucose in Murine Abdominal Aortic Injury

“…However, direct periadventitial application would be technically difficult for patients not undergoing an open laparotomy and nearly impossible for patients treated with EVAR. Nonetheless, others have demonstrated PGG’s efficacy using nanoparticle-based approaches in rats [ 11 , 12 ] and surgical intraluminal pressure infusion in pigs and rats [ 15 , 16 , 18 ]. It is difficult to compare the different approaches to PGG delivery, as each method has its own merits and shortcomings.…”

“…This cross-linking of extracellular matrix (ECM) proteins has led to a stabilized arterial microstructure of the abdominal aorta [ 8 ] and partial prevention of mechanical degradation in enzyme-treated arterial tissues [ 9 , 10 ]. Specifically, PGG has been utilized in rat [ 8 , 11 , 12 , 13 ], mice [ 14 ], and porcine [ 15 , 16 ] models of AAA to suppress the pathological expansion. Isenburg et al [ 8 , 17 ] first reported on the periadventitial application of PGG in a rat CaCl 2 model of AAA, which resulted in an overall reduction of arterial dilation.…”

“…In terms of large animal models, porcine animals have been utilized to understand the effect of PGG on the elastase aneurysmal model [ 15 ] and a combined elastase/collagenase/periadventitial CaCl 2 model [ 16 ]. Both methods utilize a balloon catheter for expansion of the abdominal aorta and for the intraluminal delivery of PGG.…”

“…Kloster et al [ 15 ] found that PGG-treated pigs experienced a reduction in the external anterior–posterior diameter to typical physiological values, demonstrating this polyphenol’s ability to inhibit early AAA development. Simionescu et al [ 16 ] suggest that intraluminal PGG delivery to medium-size aneurysms attenuated AAA diameter expansion. Although this combined chemical approach of porcine AAA model development for evaluating PGG shows promise, it is difficult to elucidate which biochemical pathways are suppressed or promoted by PGG application.…”

Repositioning Natural Antioxidants for Therapeutic Applications in Tissue Engineering

“…Moreover, elastin is not stabilised by glutaraldehyde; therefore, other molecules such as some phytochemicals can similarly or even better improve the physical integrity of protein and polymeric biomaterial. Notably, a large number of polyphenols (e.g., pentagalloyl glucose) are able to enhance the stability as well as the strength of collagen or elastin fibres with different mechanisms [ 87 ]. The tannins, in particular the class of PA, are flavonoids with a great influence on biomechanical properties of both collagen and elastin.…”