Role of hypoxia and metabolism in the maturation of hemodialysis arteriovenous fistulas

L’accès vasculaire pour hémodialyse est à la fois la ligne de vie et le talon d’Achille des malades souffrant d’insuffisance rénale terminale. La fistule artério-veineuse (FAV), accès vasculaire pourtant recommandé en premier intention, présente des résultats loin d’être optimaux : 50% des FAV crées présenteront une dysfonction la 1ère année. Lors de la création d’une FAV, la paroi de la veine doit s’adapter à de nouveaux paramètres. D’une part, des modifications hémodynamiques sont responsables de modifications de la matrice extracellulaire et de lésions endothéliales. D’autre part, la dissection et la manipulation de la veine par le chirurgien, impliquant la rupture des vasa vasorum, causent une ischémie de la paroi et un stress oxydatif. In fine, la migration et la prolifération des cellules vasculaires participent à l’épaississement de la paroi par une hyperplasie néointimale (HNI) excessive, entraînant une sténose et un dysfonctionnement de la FAV. Mon projet de thèse s’articulait autour de 3 objectifs: 1) Montrer que la non-dissection de la veine évite l’apparition d’HNI, 2) Cibler l’hypoxie cellulaire pour inhiber l’HNI et 3) Evaluer la régulation par l’hypoxie d’une protéine de la matrice extracellulaire, l’ostéopontine (OPN), dans l’HNI.Résultats : 1) Nous avons développé la technique RADAR (Radial Artery Deviation And Reimplantation) de création de FAV, dont le concept est d’éviter la dissection chirurgicale de la veine en détournant l’artère, et ainsi limiter l’HNI. Les résultats de la première cohorte de malades ont montré une quasi-disparition de la sténose veineuse par HNI. Afin d’étudier l’hémodynamique de RADAR, en collaboration avec l’Université Yale, nous avons créé chez le rat un modèle de FAV avec détournement de l’artère (mimant RADAR). Grâce à des mesures moléculaires, histologiques, et d’imagerie, associées aux résultats à long terme de la cohorte RADAR, nous avons confirmé que l’HNI veineuse est inhibée et montré le rôle du flux laminaire dans ce montage. 2) Nous avons cherché une substance pharmacologique qui, appliquée dès la chirurgie, ciblerait HIF pour inhiber l’INH. In vitro, nous avons étudié la réponse des différents types de cellules vasculaires (endothéliales, musculaires lisses, fibroblastes), sous l’action de l’hypoxie, de 5 médicaments (Desferrioxamine, Everolimus, Metformine, N-Acetylcystéine, Topotecan) influençant HIF et le métabolisme cellulaire, et de 3 invalidations géniques (siRNA HIF1alpha, siRNA HIF2alpha, siRNA, HIF1/2alpha). Trois de ces substances et 1 invalidation génique agissaient sur le métabolisme et la prolifération de nos cellules. Nous les avons donc testé sur un modèle murin de FAV: 2 substances et l’invalidation de HIF1/2 ont montré une inhibition significative de l’HNI. 3) Nous avons étudié l’expression d’OPN dans les cellules vasculaires sous l’effet de l’hypoxie. Si les cellules vasculaires veineuses en monoculture n’exprimaient ni ne sécrétaient d’OPN sous l’effet de l’hypoxie, la co-culture de ces trois lignées permettaient la sécrétion d’OPN induite par l’hypoxie. Nous avons ainsi montré que l’hypoxie, le métabolisme et les paramètres du flux sont impliqués dans le développement de l’HNI lors de la maturation de la FAV.For hemodialysis patients, their vascular access is both their life line and their Achille’s heel. Despite being recommended as a primary vascular access, the arteriovenous fistula (AVF) shows sub-optimal results, with about 50% of patients needing a revision during the year following creation. As the AVF is created, the venous wall must adapt to new environment. While hemodynamic changes are responsible for the adaptation of the extracellular matrix and activation of the endothelium, surgical dissection and mobilization of the vein disrupt the vasa vasorum, causing wall ischemia and oxidative stress. As a consequence, migration and proliferation of vascular cells participate in venous wall thickening by a mechanism of neointimal hyperplasia (NH). When aggressive, NH causes stenosis and AVF dysfunction. I had 3 aims during my thesis : 1) To show that minimal dissection of the vein inhibits NH, 2) to target the Hypoxia Inducible Factor (HIF) pathway to inhibit NH, and 3) to understand the hypoxic regulation of an adhesion molecule, osteopontin (OPN), in NH. Results: 1) We developed the Radial Artery Deviation And Reimplantation (RADAR) technique of AVF creation, where we avoid venous dissection to prevent NH. The first cohort of patients showed only 2% of venous stenosis. To study RADAR hemodynamics, in collaboration with Yale University, we created a rat model of artery-to-vein AVF that mimics RADAR geometry. By means of molecular, histological and imaging analysis, associated to the long-term outcome of the RADAR cohort, we confirmed that this configuration shows laminar flow and limits NH.2) We looked for a way to inhibit HIF during surgery by local delivery of a small molecule. In vitro, we analyzed the behavior of vascular cells (endothelial, smooth muscle and fibroblasts) in response to hypoxia, to 1 of 5 compounds regulating HIF or metabolism (Desferrioxamine, Everolimus, Metformine, N-Acetylcysteine, Topotecan), and to HIF silencing. Three of these compounds and HIF silencing had a significant impact on the metabolism and/or proliferation of our cells. We therefore tested them in a mouse model of AVF, to show that 2 compounds and HIF silencing inhibited NH. 3) We analyzed the expression of OPN in our cells in hypoxia. While in monoculture, they did not express or secrete OPN in response to hypoxia, co-culture of the same cell lines induced OPN secretion in hypoxia. We could show that hypoxia, metabolism and flow parameters are intricate mechanisms responsible for the development of NH during AVF maturation

Ischémie critique du membre inférieur (résultats à moyen terme des recanalisations longues d'artère de jambe)

NICE-BU Médecine Odontologie (060882102) / SudocSudocFranceF

Role of Hypoxia and Metabolism in the Development of Neointimal Hyperplasia in Arteriovenous Fistulas

International audienceFor patients with end-stage renal disease requiring hemodialysis, their vascular access is both their lifeline and their Achilles heel. Despite being recommended as primary vascular access, the arteriovenous fistula (AVF) shows sub-optimal results, with about 50% of patients needing a revision during the year following creation. After the AVF is created, the venous wall must adapt to new environment. While hemodynamic changes are responsible for the adaptation of the extracellular matrix and activation of the endothelium, surgical dissection and mobilization of the vein disrupt the vasa vasorum, causing wall ischemia and oxidative stress. As a consequence, migration and proliferation of vascular cells participate in venous wall thickening by a mechanism of neointimal hyperplasia (NH). When aggressive, NH causes stenosis and AVF dysfunction. In this review we show how hypoxia, metabolism, and flow parameters are intricate mechanisms responsible for the development of NH and stenosis during AVF maturation

Complete traumatic aortic transection

Complete aortic transection is typically fatal and extremely rare in pediatric patients. High clinical suspicion, even in hemodynamically stable patients, is essential for timely recognition and intervention. There is scant literature on the management of complete aortic transection in pediatric patients. Retrospective chart review of an adolescent who survived a large complete thoracic aortic rupture along with systematic pediatric literature review. A 16-year old female presented with a complete thoracic aortic transection with a 5-6 cm gap after an auto-pedestrian collision. Mediastinal vascular injury was suspected based on presentation, confirmed by chest radiograph, and further delineated by computed tomography. CT angiography was critical in determining the anatomy of injury and planning repair. Repair was achieved by left heart bypass and Dacron interposition grafting. The patient survived without vascular-related complications and remains well at 3-year follow up. Literature review revealed scant data on the diagnosis and management of complete aortic transection in children. The role of selective imaging for diagnosis is warranted. The applicability of endovascular stent-grafting in pediatric patients remains uncertain.Open access journal.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]