Journal Article•
Stress-strain characteristics and collagen-elastin content of abdominal aortic aneurysms.
About: This article is published in Surgery gynecology & obstetrics.The article was published on 1970-03-01 and is currently open access. It has received 176 citations till now. The article focuses on the topics: Elasticity (economics) & Elastin.
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TL;DR: The recruitment of inflammatory cells into the adventitia, with subsequent elaboration of metalloproteinases, including gelatinase B, may contribute to the rapid growth and rupture of larger aneurysms.
Abstract: The risk of rupture of an abdominal aortic aneurysm increases with aortic diameter. To obtain insight into the pathological processes associated with the vascular remodeling that accompanies aortic dilatation, we compared the histological features and the activity of matrix metalloproteinases (MMPs) in biopsies from 21 small (4.0 to 5.5 cm in diameter) and 45 larger abdominal aortic aneurysms. The histological feature most clearly associated with enlarging aneurysm diameter was a higher density of inflammatory cells in the adventitia, P = .018. This inflammation was nonspecific, principally macrophages and B lymphocytes. Fibrosis of the adventitia provided compensatory thickening of the aortic wall as the aneurysm diameter increased. A combination of zymography and immunoblotting identified gelatinase A (MMP-2) as the principal metallogelatinase in small aneurysms, whereas zymography indicated an increasing activity of gelatinase B (MMP-9) in large aneurysms. Homogenates prepared from both small and large aneurysms had similar total activity against gelatin or type IV collagen. However, the concentration of gelatinase A, determined by immunoassay, was highest for small aneurysms: median concentrations, 385, 244, and 166 ng/mg protein for small aneurysms, large aneurysms, and atherosclerotic aorta, respectively. Immunolocalization studies indicated that gelatinase A was concentrated along fibrous tissue of both the acellular media and the atherosclerotic plaque. The recruitment of inflammatory cells into the adventitia, with subsequent elaboration of metalloproteinases, including gelatinase B, may contribute to the rapid growth and rupture of larger aneurysms.
659 citations
TL;DR: Finite element simulations showed that the computed AAA wall stresses changed by only 4% or less when both the parameters were varied within the 95% confidence intervals for the patient population studied, indicating that in lieu of the patient-specific material parameters, which are difficult to determine, the model to be reasonably employed in a clinical setting is sufficiently accurate.
575 citations
Journal Article•
TL;DR: It is demonstrated that medial SMC density is significantly decreased in human AAA tissues associated with evidence of SMC apoptosis and increased production of p53, a potential mediator of cell cycle arrest and programmed cell death.
Abstract: Abdominal aortic aneurysms (AAAs) are characterized by structural deterioration of the aortic wall leading to progressive aortic dilatation and eventual rupture. The histopathological changes in AAAs are particularly evident within the elastic media, which is normally dominated by vascular smooth muscle cells (SMCs). To determine whether a decrease in vascular SMCs contributes to medial degeneration, we measured SMC density in 21 normal and pathological human abdominal aortic tissue specimens using immunohistochemistry for alpha-SMC actin and direct cell counts (medial SMCs per high-power field (HPF)). Medial SMC density was not significantly different between normal aorta (n = 5; 199.5 +/- 14.9 SMCs/HPF) and atherosclerotic occlusive disease (n = 6; 176.4 +/- 13.9 SMCs/HPF), but it was reduced by 74% in AAA (n = 10; 50.9 +/- 6.1 SMCs/HPF; P < 0.01 versus normal aorta). Light and electron microscopy revealed no evidence of overt cellular necrosis, but SMCs in AAAs exhibited ultrastructural changes consistent with apoptosis. Using in situ end-labeling (ISEL) of fragmented DNA to detect apoptotic cells, up to 30% of aortic wall cells were ISEL positive in AAAs. By double-labeling techniques, many of these cells were alpha-actin-positive SMCs distributed throughout the degenerative media. In contrast, ISEL-positive cells were observed only within the intimal plaque in atherosclerotic occlusive disease. The amount of p53 protein detected by immunoblotting was increased nearly fourfold in AAA compared with normal aorta and atherosclerotic occlusive disease (P < 0.01), and immunoreactive p53 was localized to lymphocytes and residual SMCs in the aneurysm wall. Using reverse transcription polymerase chain reaction assays a substantial amount of p53 mRNA expression was observed in AAAs. These results demonstrate that medial SMC density is significantly decreased in human AAA tissues associated with evidence of SMC apoptosis and increased production of p53, a potential mediator of cell cycle arrest and programmed cell death. Given the role that SMCs normally play in maintaining medial architecture and in arterial wall matrix remodeling, the induction of SMC apoptosis likely makes an important contribution to the evolution of aneurysm degeneration.
478 citations
TL;DR: The history and state-of-the-art of this field is reviewed--including investigations into the biomechanical behavior of AAA tissues, modeling AAA wall stress and factors which influence it, and the potential clinical utility of these estimates in predicting AAA rupture.
471 citations
TL;DR: The results suggest that the presence of elastase within the aortic media leads to aneurysm formation and that plasmin may enhanceElastase activity and aggravate the aneurYSmal lesion.
Abstract: An experimental in vivo model of aortic aneurysm was established by perfusing an isolated segment of rat abdominal aorta with pancreatic elastase. Ten rats were used in each protocol. Saline-perfused aortas developed no aneurysmal dilations. Elastase-perfused aortas contained aneurysms in the perfused area and a total loss of elastic tissue. Control aortas contained no elastic tissue lesions. There was a quantitative relation between the amount of elastase perfused and aneurysm formation: 1-2 units induced neither macroscopic nor microscopic lesions; 3-6 units induced microscopic elastic tissue damage without macroscopic aneurysm; and more than 6 units produced aneurysmal dilation in all cases. In situ elastase secretion by macrophages was induced by perfusing rat aortas with thioglycollate-activated macrophages or with thioglycollate alone. There was aortitis without true aneurysm and a total loss of elastic tissue in the vicinity of activated macrophages within the aortic media. Perfusion of infra-aneurysmal amount of elastase (1 or 2 units) or thioglycollate plus plasmin (2 units) always induced a large aneurysm, whereas plasmin alone induced neither macroscopic nor microscopic lesions. These morphological results were supported by the significantly elevated elastolytic activity within the aortic wall of animals perfused with thioglycollate plus plasmin 9 days, after perfusion (207.6 +/- 54.8 micrograms elastin-rhodamine lysed/18 hr; control rats, 25.43 +/- 11.13). The results suggest that the presence of elastase within the aortic media leads to aneurysm formation. Activated macrophages within the aortic media may be responsible for elastase secretion and elastic tissue destruction. Plasmin may enhance elastase activity and aggravate the aneurysmal lesion.
443 citations