The renin angiotensin system in bypass graft surgery

Vascular grafts

Autogenous vein is the conduit of choice in the surgical creation of bypasses of small-to-medium-caliber vessels in patients with peripheral occlusive arterial disease and will remain so for the near future. The success rate of bypasses using conduits of diameters greater than 6 mm has been excellent, whereas the majority of bypasses using smaller conduits fail within 5 years. In addition, due to a steep increase in rates of diabetes and decreasing cardiovascular mortality rates, increasing challenges are presented by this population. These facts have motivated much of the research in the cardiovascular arena over the past four decades, with improved techniques and new materials. Strategies to improve outcomes include the use of alternative materials including autologous, nonautologous and prosthetic grafts, utilizing different methods for their harvesting and preservation; tissue engineering, using either polymer- or biological-based scaffolds for cell seeding; endovascular methodologies; and gene therapy. This report presents an overview of the several options currently available in the management of patients with peripheral arterial occlusive disease, as well as the ongoing research directed towards the creation of an artificial engineered vessel, discussing experimental work in which endothelial cells have been seeded on different scaffolds and finally the potential application of gene therapy in the field of vascular reconstruction.

Mineralocorticoid receptor expression in human venous smooth muscle cells: a potential role for aldosterone signaling in vein graft arterialization

Experimental studies have suggested a role for the local renin-angiotensin-aldosterone system in the response to vascular injury. Clinical data support that aldosterone, via activation of the mineralocorticoid receptor (MR), is an important mediator of vascular damage in humans with cardiovascular disease. In mineralocorticoid-sensitive target tissue, aldosterone specificity for MR is conferred enzymatically by the cortisol-inactivating enzyme 11β-hydroxysteroid-dehydrogenase-2 (11βHSD2). However, the role of MR/aldosterone signaling in the venous system has not been explored. We hypothesized that MR expression and signaling in venous smooth muscle cells contributes to the arterialization of venous conduits and the injury response in vein bypass grafts. MR immunostaining was observed in all samples of excised human peripheral vein graft lesions and in explanted experimental rabbit carotid interposition vein grafts, with minimal staining in control greater saphenous vein. We also found upregulated transcriptional expression of both MR and 11βHSD2 in human vein graft and rabbit vein graft, whereas control greater saphenous vein expressed minimal MR and no detectable 11βHSD2. The expression of MR and 11βHSD2 was confirmed in cultured human saphenous venous smooth muscle cells (hSVSMCs). Using an adenovirus containing a MR response element-driven reporter gene, we demonstrate that MR in hSVSMCs is capable of mediating aldosterone-induced gene activation. The functional significance for MR signaling in hSVSMCs is supported by the aldosterone-induced increase of angiotensin II type-1 receptor gene expression that was inhibited by the MR antagonist spironolactone. The upregulation of MR and 11βHSD2 suggests that aldosterone-mediated tissue injury plays a role in vein graft arterialization.

Distinct role of nox1, nox2, and p47phox in unstimulated versus angiotensin II-induced NADPH oxidase activity in human venous smooth muscle cells

Human saphenous veins (SV) are used for coronary bypass surgery despite the higher rate of graft failure observed as compared to arteries. A higher production of reactive oxygen species (ROS) in SV than in internal mammary artery (IMA) has been incriminated as possibly implicated in graft failure. NADPH oxidase, involved in vascular ROS production, was therefore characterized in human smooth muscle cells from SV. ROS production was confirmed to be essentially NADPH oxidase dependent in cultured smooth muscle cells (SMC) from human SV and increased in comparison with IMA. To investigate the role of NADPH oxidase subunits, siRNA for nox1, nox2, or p47 mRNA were studied. In cultured venous SMC under unstimulated conditions, inhibition of nox1 or nox2 mRNA decreased ROS production, whereas p47 silencing increased it. During angiotensin II (AngII) activation, nox2 or p47 mRNA silencing decreased ROS production, while nox1 inhibition had no effect. Venous SMC express functional nox1 and nox2. Only nox2 is implicated in response to AngII whilst nox1 is involved in unstimulated ROS production. p47 negatively regulates ROS generation under basal conditions, whereas it enhances AngII increased ROS production. Thus, nox1, nox2, and p47 have distinct roles in NADPH oxidase activity in human veins.

Present status of outcome prediction of invasive coronary treatment by using genetic markers

A growing number of studies suggest that the outcome after invasive coronary treatment may be in part genetically determined. Here, we review the present status of outcome prediction of invasive coronary treatments by using genetic markers. Although some studies found an association between one or another genetic marker with one or another clinical endpoint, many other studies found no such relations; to date, none of the genetic markers that have been investigated in association studies are used in routine clinical practice to prospectively assess the prognosis following invasive coronary treatment or to decide upon therapeutic strategies. Many associations between genetic markers and certain clinical endpoints were initially reported in small studies but could not be confirmed in larger ones. Some of these discrepancies may be explained by publication bias. Some genetic variants may have true effects on clinical endpoints, which, albeit biologically interesting, do not bear much clinical relevance. On the other hand, many-if not most-studies that have been published to date are more or less grossly underpowered and very rarely report on the results of an a priori power analysis. Thus, there is still a need for further high-quality studies designed to investigate the specific contribution of genetic factors to the outcome after invasive coronary interventions.

Angiotensin and cytoskeletal proteins: role in vascular remodeling

Vascular remodeling occurs during normal development and is involved in various physiologic events. However, the adaptive structural changes of the vasculature can also be pathologic, leading to vascular disease such as hypertension, atherosclerosis, and vein graft disease. Pre-eclampsia may develop as a consequence of inappropriate vascular remodeling during pregnancy. Angiotensin II contributes to vascular remodeling by activating signal transduction cascades that promote vasoconstriction, growth, and inflammation. The cytoskeleton also participates in structural adaptation responses of the vasculature; cytoskeletal filaments may mediate vasoactive responses, transduce mechanical stimuli, and are involved in pharmacologic signal transduction. It has become clear that many of the cytoskeletal changes during vascular remodeling can be induced by angiotensin II. Recently, the small G-protein Rho has attracted much attention. The Rho/Rho-kinase system is activated by angiotensin II, is a prominent regulator of the cytoskeleton, and is involved in pathologic vascular remodeling.