Eric Allaire

Local overexpression of TIMP-1 prevents aortic aneurysm degeneration and rupture in a rat model.

Although matrix metalloproteinases (MMPs) are expressed in abundance in arterial aneurysms, their contribution to arterial wall degeneration, dilation, and rupture has not been determined. We investigated MMP function in a rat model of aneurysm associated with arterial dilation, elastin loss, medial invasion by mononuclear inflammatory cells, and MMP upregulation. Rupture was correlated with increased gelatinase B (MMP-9) and activated gelatinase A (MMP-2). Syngeneic rat smooth muscle cells retrovirally transfected with tissue inhibitor of matrix metalloproteinases (TIMP)-1 cDNA (LTSN) or with the vector alone as a control (LXSN) were seeded onto the luminal surface of the vessels. The seeding of LTSN cells resulted in TIMP-1 local overexpression. The seeding with LTSN cells, but not LXSN cells, decreased MMP-9, activated MMP-2 and 28-kD caseinase and elastase activity, preserved elastin in the media, and prevented aneurysmal degeneration and rupture. We conclude that MMP overexpression is responsible for aneurysmal degeneration and rupture in this rat model and that local pharmacological blockade might be a reasonable strategy for controlling the formation of aneurysms in humans.

Novel aspects of the pathogenesis of aneurysms of the abdominal aorta in humans

Aneurysm of the abdominal aorta (AAA) is a particular, specifically localized form of atherothrombosis, providing a unique human model of this disease. The pathogenesis of AAA is characterized by a breakdown of the extracellular matrix due to an excessive proteolytic activity, leading to potential arterial wall rupture. The roles of matrix metalloproteinases and plasmin generation in progression of AAA have been demonstrated both in animal models and in clinical studies. In the present review, we highlight recent studies addressing the role of the haemoglobin-rich, intraluminal thrombus and the adventitial response in the development of human AAA. The intraluminal thrombus exerts its pathogenic effect through platelet activation, fibrin formation, binding of plasminogen and its activators, and trapping of erythrocytes and neutrophils, leading to oxidative and proteolytic injury of the arterial wall. These events occur mainly at the intraluminal thrombus–circulating blood interface, and pathological mediators are conveyed outwards, where they promote matrix degradation of the arterial wall. In response, neo-angiogenesis, phagocytosis by mononuclear cells, and a shift from innate to adaptive immunity in the adventitia are observed. Abdominal aortic aneurysm thus represents an accessible spatiotemporal model of human atherothrombotic progression towards clinical events, the study of which should allow further understanding of its pathogenesis and the translation of pathogenic biological activities into diagnostic and therapeutic applications.

Cell-free arterial grafts: Morphologic characteristics of aortic isografts, allografts, and xenografts in rats

PURPOSE Chronic rejection of arterial allografts and xenografts results in arterial wall dilation and rupture, making them unsuitable for long-term arterial replacement in vascular surgery. In the arterial wall, as in other organs, the cells probably carry major antigenic determinants. Arterial wall cellular components can be removed by detergent treatment to produce a graftable matrix tube. METHODS We compared the patency and macroscopic and microscopic morphologic changes that occurred in sodium dodecyl sulfate (SDS)-treated and untreated arterial isografts, allografts, and xenografts 2 months after implantation in rats. We quantified elastin, collagen, and nuclear density in the three layers of the graft wall (intima, media, and adventitia) by morphometric methods. The SDS treatment removed endothelial and smooth muscle cells and cells in the adventitia but preserved elastin and collagen extracellular matrix. RESULTS All arterial xenografts, whether SDS treated or untreated, were aneurysmal 2 months after grafting, with loss of the medial cellular and extracellular components. In allografts, SDS treatment prevented dilation, reduced adventitial inflammatory infiltration, and preserved medial elastin. The SDS-treated allografts had an evenly distributed, noninflammatory intimal thickening that was richer in elastin fibers than that in untreated allografts. CONCLUSIONS These results suggest an interspecies, but not an intraspecies, graft antigenicity of arterial extracellular matrix. The SDS treatment prevented chronic rejection of the arterial allograft and led to the proliferation of an elastin-rich and adapted intima.

Endothelial cell injury in cardiovascular surgery : The intimal hyperplastic response

Arteries and veins respond to injury by a healing process that includes the development of a neointima. This response to injury is implicated as the primary cause of failure after arterial reconstruction. Because it is an integrator and transmitter of blood flow variations, inflammation, and growth stimuli, the endothelium is a potent regulator of long-term arterial wall mass changes. The contribution of the endothelium to intimal development depends on the type of arterial conduit. In arteries, the growth of the intima stops when the endothelium has regrown. In synthetic grafts, the endothelium stabilizes intimal growth. Hence, the mere presence of endothelial cells can influence intimal changes in arterial conduits. Understanding endothelial biology should help us define methods to prevent cell proliferation, extracellular matrix accumulation, intimal hyperplasia, and vessel narrowing.

Overexpression of Transforming Growth Factor-β1 Stabilizes Already-Formed Aortic Aneurysms A First Approach to Induction of Functional Healing by Endovascular Gene Therapy

Background—The cell response to transforming growth factor-&bgr;1 (TGF-&bgr;1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-&bgr;1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis. Methods and Results—Active TGF-&bgr;1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-&bgr;1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-&bgr;1. Transient exogenous TGF-&bgr;1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-&bgr;1. Overexpression of active TGF-&bgr;1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-&bgr;1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell–, collagen-, and elastin-rich intima. Conclusions—Local TGF-&bgr;1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

Endothelial cell injury in cardiovascular surgery: atherosclerosis.

Most of the indications for cardiovascular operation and many of its complications are in large part due to advanced atherosclerosis. The pathogenesis of atherosclerosis involves inflammatory infiltration of the vessel wall, cellular proliferation, fibrous plaque formation, and ultimately plaque rupture and occlusive thrombosis. Many of these events are linked, at least initially, to chronic injury of the vascular endothelium. Endothelial cell injury from hypertension, diabetes mellitus, hyperlipidemia, fluctuating shear stress, smoking, or transplant rejection disrupts normal endothelial cell function. This results in the loss of the constitutive protective mechanisms and an increase in inflammatory, procoagulant, vasoactive, and fibroproliferative responses to injury. These changes promote vasospasm, intimal proliferation, and thrombus formation, all of which play a significant role in the initiation, progression, and clinical manifestations of atherosclerosis. Understanding the role of the chronically injured endothelium and its interactions with circulating immune cells and the underlying smooth muscle cells may lead to novel therapeutic interventions for the prevention and treatment of atherosclerosis.

Colon ischemia following abdominal aortic aneurysm repair in the era of endovascular abdominal aortic repair

OBJECTIVE To review, in the era of endovascular abdominal aortic repair (EVAR), the clinical spectrum of colonic ischemia (CI) following abdominal aortic aneurysm (AAA) repair and to assess the rate, overall mortality, and associated factors of occurrence. METHODS Between 1995 and 2005, 1174 patients with infrarenal AAA were treated either by open surgery (n = 682) or by EVAR (n = 492). Preoperative risk factors, clinical presentation, intraoperative data, and early postoperative outcomes were prospectively assessed. Overt colonic ischemia as proven by colonoscopy and/or by operation was considered as a validating event and was correlated to collected variables. RESULTS CI occurred in 34 patients (2.9%). Eighteen out of 34 (53%) patients died within 1 month. At 2 years, the survival rate was 35% in the CI group vs 86% in the non-CI group. Associated factors of occurrence of CI were: type of operation (open group = 27/682 [4%] vs EVAR = 7/492 [1.4%] [P = .01]), aneurysm rupture (11/88 [12.5%] vs 23/1086 [2.1%], P < .001), preoperative renal insufficiency (4/30 [13.3%] vs 29/1133 [3.1%], P = .01), preoperative respiratory insufficiency (8/157 [7%] vs 23/1005 [2%], P = .01), duration of operation (<2 hours [518] = 1.7%, between 2 to 4 hours [558] 2.9%, more than 4 hours [66] 13.6%, P = .001). Mean blood loss was greater in patients with CI (CI = 2000 ml [650-3350] than in those without CI = 1000 ml [500-1800] P = .008). Logistic regression analysis showed that rupture (OR 6.03 [interval of confidence (IC) 95% 2.68-13.5] P = .0001), duration of operation (OR 5.73 [IC 95% 2.06-15.9] P = .001) and creatinin > 200 mol/l (OR 4.67 [IC 95% 1.39-15.7] P = .028) were independent factors of CI. The mortality due to colonic ischemia was not statistically different between open surgery 14/27 (52%) and EVAR 4/7 (57%). CONCLUSION CI remains a serious complication following AAA repair. In the univariate analysis, EVAR was associated with a lower rate of colonic ischemia. However, the logistic regression analysis showed that only rupture, long duration of operation, and prior renal disease were independently associated with CI. Within the two treatment modalities, the mortality rate remained identical.

Vascular Smooth Muscle Cell Endovascular Therapy Stabilizes Already Developed Aneurysms in a Model of Aortic Injury Elicited by Inflammation and Proteolysis

Objective:To investigate the efficiency of endovascular smooth muscle cell (VSMC) seeding in promoting healing and stability in already-developed aneurysms obtained by matrix metalloproteases (MMPs)-driven injury. Summary Background Data:VSMCs are instrumental in arterial healing after injury and are in decreased number in arterial aneurysms. This cellular deficiency may account for poor healing capabilities and ongoing expansion of aneurysms. Methods:Aneurysmal aortic xenografts in rats displaying extracellular matrix injury by inflammation and proteolysis were seeded endoluminally with syngeneic VSMCs, with controls receiving culture medium only. Diameter, structure, and the destruction/reconstruction balance were assessed. Results:Eight weeks after endovascular infusion, aneurysmal diameter had increased further, from 3.0 ± 0.3 mm to 10.9 ± 6.5 mm (P = 0.009), and medial elastin content had decreased from 36.5 ± 8.5 to 5.2 ± 5.5 surface-percent (S%; P = 0.009) in controls, whereas these parameters remained stable in the seeded group (3.0 ± 0.3 to 2.7 ± 0.2 mm, P = 0.08; 36.5 ± 8.4 to 31.6 ± 9.7 S%, P = 0.22). VSMC seeding was followed by a decrease in mononuclear infiltration. MMP-1, -3, -7, -9, and -12 mRNA contents were sharply decreased in the diseased wall in response to seeding. Tissue inhibitor of metalloproteinase-1, -2, and -3 mRNAs in the intima were increased in a 2 to 10 magnitude in comparison with controls. Gelatin zymography showed the disappearance of MMP-9 activity and reverse zymography a strong increase in tissue inhibitor of metalloproteinase-3 activity in the seeded group. VSMC-seeded aneurysms were rich in collagen and lined with an endothelium instead of a thrombus in controls. Conclusions:VSMCs endovascular seeding restores the healing capabilities of proteolytically injured extracellular matrix in aneurysmal aortas, and stops expansion.

Measuring the maximum diameter of native abdominal aortic aneurysms: review and critical analysis.

OBJECTIVES Maximum diameter is a determinant parameter for the clinical management of asymptomatic abdominal aortic aneurysm (AAA). However, its measurement is not standardised. We review the different methods used to measure AAA maximum diameter, with ultrasound (US) or computed tomography (CT). METHODS A review of maximum diameter measurement methods with US and CT was performed, focussing on screening, surveillance before repair and decision for intervention. Diameter measurement methodology was described according to four parameters: plane of acquisition, axis of measurement, position of callipers and selected diameter. A quality score to evaluate methodology descriptions was defined (plane, axis, callipers placement and selected diameter), ranging from 0 (worst) to 4 (best). RESULTS Review showed a wide range of definitions and practices. The mean value of the quality score was 2.52 in screening studies, 1.66 in guidelines for screening, 2.81 in follow-up studies and 1.63 in studies describing decision for intervention. CONCLUSION To improve the efficiency of AAA management (in screening programmes, follow-up and decision for intervention), and enable comparison between future studies, a standardised methodology for AAA maximum diameter measurement is necessary. Until such a consensus is reached, publications should at least clearly report the method of measurement.

Metalloproteinase Blockade by Local Overexpression of TIMP-1 Increases Elastin Accumulation in Rat Carotid Artery Intima

We have recently demonstrated that the blockade of matrix metalloproteinases by local overexpression of the intrinsic inhibitor tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) reduces intimal hyperplasia. We now report a major change in the elastin content of the intima of rat carotid arteries seeded with TIMP-1-overexpressing smooth muscle cells. To understand the mechanism responsible for elastin accumulation, synthesis and degradation of elastin in TIMP-1 and control cell-seeded rats were measured. There were no differences in elastin mRNA or elastin synthesis, as documented by 14[C]proline incorporation between TIMP-1 and control cell-seeded arteries. In contrast, there was an increase in cross-linked elastin in the TIMP-1 group. In addition, in TIMP-1 and control rats, an elastase activity of approximately 28 kD was detected by elastin zymography and was decreased in TIMP-1 cell-seeded vessels. The 28 kD elastolytic activity was inhibited by exogenously added TIMP-1 and EDTA but not by PMSF, suggesting that it was a metalloelastase. Therefore, we have demonstrated that a shift of the proteolytic balance toward protease inhibition by TIMP-1 overexpression does not change elastin synthesis but rather changes posttranslational processing, resulting in increased elastin accumulation.