Oana Sorop

Small Artery Remodeling Depends on Tissue-Type Transglutaminase

Remodeling of small arteries is essential in the long-term regulation of blood pressure and blood flow to specific organs or tissues. A large part of the change in vessel diameter may occur through non–growth-related reorganization of vessel wall components. The hypothesis was tested that tissue-type transglutaminase (tTG), a cross-linking enzyme, contributes to the inward remodeling of small arteries. The in vivo inward remodeling of rat mesenteric arteries, induced by low blood flow, was attenuated by inhibition of tTG. Rat skeletal muscle arteries expressed tTG, as identified by Western blot and immunostaining. In vitro, activation of these arteries with endothelin-1 resulted in inward remodeling, which was blocked by tTG inhibitors. Small arteries obtained from rats and pigs both showed inward remodeling after exposure to exogenous transglutaminase, which was inhibited by addition of a nitric oxide donor. Enhanced expression of tTG, induced by retinoic acid, increased inward remodeling of porcine coronary arteries kept in organ culture for 3 days. The activity of tTG was dependent on pressure. Inhibition of tTG reversed remodeling, causing a substantial increase in vessel diameter. In a collagen gel contraction assay, tTG determined the compaction of collagen by smooth muscle cells. Collectively, these data show that small artery remodeling associated with chronic vasoconstriction depends on tissue-type transglutaminase. This mechanism may reveal a novel therapeutic target for pathologies associated with inward remodeling of the resistance arteries.

The genous™ endothelial progenitor cell capture stent accelerates stent re‐endothelialization but does not affect intimal hyperplasia in porcine coronary arteries

Objectives: To study the effect of endothelial progenitor cell (EPC) capture on the vascular response to coronary stenting. Background: The introduction of drug‐eluting stents has reduced the need for target lesion revascularization, but their effect on delayed healing, inflammation, and vascular dysfunction has emphasized the need to design strategies that improve current DES. One such strategy is to improve endothelialization by capturing CD34‐positive cells (EPC) by the stent surface. The first human clinical trial using coronary EPC capture stents showed stent safety but neointimal thickness (NIT) was not reduced compared to bare metal stents (BMS). To understand these responses we studied the coronary response to the EPC capture stent in swine. Methods and Results: The stent, coated with murine antihuman monoclonal CD34 antibodies, was assessed with QCA guided stent implantation in normal swine coronary arteries for early endothelialization at 2 and 5 days, and NIT at 28 and 90 days in comparison to control stents carrying a non‐specific murine antibody or to BMS. The main finding was that while the EPC capture stent significantly improved early endothelialization it did not reduce NIT at 28 and 90 days. Conclusions: The EPC capture stent improves early endothelialization in swine but this does not affect neointimal thickness as compared to control stents at 28 and 90 days.

Functional and Structural Adaptations of Coronary Microvessels Distal to a Chronic Coronary Artery Stenosis

Distal to a chronic coronary artery stenosis, structural remodeling of the microvasculature occurs. The microvascular functional changes distal to the stenosis have not been studied in detail. We tested the hypothesis that microvascular structural remodeling is accompanied by altered regulation of coronary vasomotor tone with increased responsiveness to endothelin-1. Vasomotor tone was studied in coronary microvessels from healthy control swine and from swine 3 to 4 months after implantation of an occluder that causes a progressive coronary narrowing, resulting in regional left ventricular dysfunction and blunted myocardial vasodilator reserve. Arterioles (≈200-&mgr;m passive inner diameter at 60 mm Hg) were isolated from regions perfused by the stenotic left anterior descending and normal left circumflex coronary arteries and studied in vitro. Passive pressure–diameter curves demonstrated reduced distensibility of subendocardial left anterior descending compared with subendocardial left circumflex or control arterioles, suggestive of structural remodeling. Myogenic responses were blunted in subendocardial left anterior descending compared with left circumflex arterioles, reflecting altered smooth muscle function. However, vasodilator responses to nitroprusside and bradykinin were not different in the endocardium, suggesting preserved endothelium and smooth muscle responsiveness. Finally, vasoconstrictor responses to endothelin-1 were enhanced in left anterior descending arterioles compared with left circumflex or control arterioles. Regional myocardial vascular conductance responses to bradykinin and endothelin in vivo confirmed the in vitro observations. In conclusion, inward remodeling of coronary microvessels distal to a stenosis is accompanied by exaggerated vasoconstrictor responses to endothelin-1. These structural and functional alterations may aggravate flow abnormalities distal to a chronic coronary artery stenosis.

Coronary microvascular dysfunction in a porcine model of early atherosclerosis and diabetes

Detailed evaluation of coronary function early in diabetes mellitus (DM)-associated coronary artery disease (CAD) development is difficult in patients. Therefore, we investigated coronary conduit and small artery function in a preatherosclerotic DM porcine model with type 2 characteristics. Streptozotocin-induced DM pigs on a saturated fat/cholesterol (SFC) diet (SFC + DM) were compared with control pigs on SFC and standard (control) diets. SFC + DM pigs showed DM-associated metabolic alterations and early atherosclerosis development in the aorta. Endothelium-dependent vasodilation to bradykinin (BK), with or without blockade of nitric oxide (NO) synthase, endothelium-independent vasodilation to an exogenous NO-donor (S-nitroso-N-acetylpenicillamine), and vasoconstriction to endothelin (ET)-1 with blockade of receptor subtypes, were assessed in vitro. Small coronary arteries, but not conduit vessels, showed functional alterations including impaired BK-induced vasodilatation due to loss of NO (P < 0.01 vs. SFC and control) and reduced vasoconstriction to ET-1 (P < 0.01 vs. SFC and control), due to a decreased ET(A) receptor dominance. Other vasomotor responses were unaltered. In conclusion, this model demonstrates specific coronary microvascular alterations with regard to NO and ET-1 systems in the process of early atherosclerosis in DM. In particular, the altered ET-1 system correlated with hyperglycemia in atherogenic conditions, emphasizing the importance of this system in DM-associated CAD development.

Lowering the Dose of Sirolimus, Released From a Nonpolymeric Hydroxyapatite Coated Coronary Stent, Reduces Signs of Delayed Healing

OBJECTIVES The aim of this study was to compare efficacy of low- and high-dose sirolimus release (25, 40, or 100 microg) from hydroxyapatite (HAp) with Cypher (Cordis, Johnson & Johnson, Warren, New Jersey) (111 microg sirolimus) in porcine coronary arteries. BACKGROUND Polymer-based sirolimus-eluting stents such as Cypher interfere with vascular healing, probably due to the permanent presence of the polymer coating and the high sirolimus dose. The use of low-dose sirolimus and inert nonpolymeric but biodegradable coatings such as HAp might be more appropriate. METHODS Stents (n = 68) were implanted, guided by quantitative coronary angiography. All swine received clopidogrel and acetylsalicylic acid during 28 days follow-up. Safety of the coating in absence of drugs was studied by comparing HAp with and without a lipid-based release regulating layer (HApR) with bare-metal stents. Efficacy was studied by comparing the release of 25, 40, and 100 microg sirolimus with Cypher. RESULTS The safety study (without drug) revealed no differences in neointimal thickening in response to HAp and HApR with complete healing in all groups. Dose response analysis showed that neointimal thickening was similar in all groups regardless of sirolimus dose, with a normal appearance of the endothelium. There was, however, a dose-dependent increase in fibrinoid (p = 0.028), considered to be a marker of delayed healing. The Cypher stent induced the highest amount of fibrinoid. CONCLUSIONS Reducing the dose of sirolimus eluting from a biocompatible HAp coated stent reduces signs of delayed vascular healing, without affecting neointimal hyperplasia.

The microcirculation: a key player in obesity-associated cardiovascular disease

It is increasingly recognized that obesity is a risk factor for microvascular disease, involving both structural and functional changes in the microvasculature. This review aims to describe how obesity impacts the microvasculature of a variety of tissues, including visceral adipose tissue, skeletal muscle, heart, brain, kidneys, and lungs. These changes involve endothelial dysfunction, which in turn (i) impacts control of vascular tone, (ii) contributes to development of microvascular insulin resistance, (iii) alters secretion of paracrine factors like nitric oxide and endothelin, but (iv) also influences vascular structure and perivascular inflammation. In concert, these changes impair organ perfusion and organ function thereby contributing to altered release and clearance of neurohumoral factors, such as adipokines and inflammatory cytokines. Global microvascular dysfunction in obese subjects is therefore a common pathway that not only explains exercise-intolerance but also predisposes to development of chronic kidney disease, microvascular dementia, coronary microvascular angina, heart failure with preserved ejection fraction, chronic obstructive pulmonary disease, and pulmonary hypertension.

Endothelial function rather than endothelial restoration is altered in paclitaxel- as compared to bare metal-, sirolimusand tacrolimus-eluting stents.

textabstractAims: Drug eluting stents (DES) are under scrutiny for late stent thrombosis. Impaired re-endothelialisation is proposed as an explanation but coronary and peripheral-artery models disagree. We assessed physical and functional endothelial restoration within bare (BMS), paclitaxel, sirolimus and tacrolimus eluting stents and the distal microvasculature in porcine coronary arteries. Methods and results: Endothelium within and distal to DES and BMS was assessed for stent-strut endothelial-restoration (five days) and endothelial-function (five, 28 days, by eNOS and vWF expression) and by in vitro microvascular function. There were no significant differences (P=0.3) in stent strut endothelial-restoration at five days between DES (76-90%) and BMS (95%). However, the microvasculature distal to PES showed a decreased NO bioavailability at five days, which improved at 28 days. Within the stent, however, PES still showed a reduced eNOS expression at 28 days (P≤0.002). Conclusions: DES in porcine coronary arteries show no significant early differences in re-endothelialisation as compared to BMS. However, PES did affect endothelial function both within and distal to stents. These results extend the concept of delayed healing in DES to include delayed restoration of function rather than endothelial presence as a possible explanation for late unwanted sequelae. Microvascular dysfunction does not predict in-stent delayed endothelialisation in this model.

Invasive coronary imaging in animal models of atherosclerosis

Experimental disease models have enhanced our understanding of the pathogenesis of atherosclerosis development. For example, insight has been gained into the role of the endothelium, lipids, platelets and inflammation, as well as into potential diagnostic and therapeutic interventions. Moreover, transgenic and knock-out technologies have become a widespread approach and this is a growing field to assess the role of individual genes in vascular biology and pathology. However, atherosclerosis is most of all a multifactorial disease, influenced by a multitude of environmental factors. Therefore, it is important to also study non-transgenic animal models that closely resemble the human situation with atherosclerotic lesions at anatomical locations that mimic the clinical manifestation of the disease, e.g. coronary artery disease (CAD). Although no model completely mimics human atherosclerosis, much can be learned from existing models in the study of this disease, also with respect to the development of new interventions. Here, we describe the most relevant animal models of atherosclerosis, while focusing on CAD development and the use of coronary diagnostic and therapeutic interventions. In addition, we show examples of features of a large animal model of CAD including pictures of invasive coronary imaging.

Specific coronary drug-eluting stents interfere with distal microvascular function after single stent implantation in pigs.

OBJECTIVES The aim of this study was to compare the effects of single drug-eluting stents (DES) on porcine coronary function distal to the stent in vivo and in vitro. BACKGROUND The mechanism of endothelial dysfunction occurring in human coronary conduit arteries up to 9 months after DES implantation is unknown. METHODS A sirolimus-eluting stent (SES), paclitaxel-eluting stent (PES), and a bare-metal stent (BMS) were implanted in the 3 coronary arteries of 11 pigs. After 5 weeks, in vivo responses in distal coronary flow to different doses of bradykinin (BK) and nitrates were measured. In vitro, vasodilation to BK and nitrates, as well as vasoconstriction to endothelin (ET)-1 were assessed in both distal coronary conduit and small arteries. In addition, contributions of nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHFs) and cyclic guanosine monophosphate (cGMP) responses to BK-stimulation were determined in vitro. RESULTS Both DES did not alter in vivo distal vasomotion. In vitro distal conduit and small arterial responses to BK were also unaltered; DES did not alter the BK-induced increase in cGMP. However, after NO synthase blockade, PES showed a reduced BK-response in distal small arteries as compared with BMS and SES (p < 0.05). The ET-1-induced vasoconstriction and vascular smooth muscle cell function were unaltered. CONCLUSIONS In this study of single stenting in healthy porcine coronaries for 5 weeks, SES did not affect distal coronary vascular function, whereas PES altered distal endothelial function of small arteries under conditions of reduced NO bioavailability. Therefore, specifically the EDHF component of microvascular function seems affected by PES.

Integrative control of coronary resistance vessel tone by endothelin and angiotensin II is altered in swine with a recent myocardial infarction

Several studies have indicated an interaction between the renin-angiotensin (ANG II) system and endothelin (ET) in the regulation of vascular tone. Previously, we have shown that both ET and ANG II exert a vasoconstrictor influence on the coronary resistance vessels of awake normal swine. Here, we investigated whether the interaction between ANG II and ET exists in the control of coronary resistance vessel tone at rest and during exercise using single and combined blockade of angiotensin type 1 (AT(1)) and ET(A)/ET(B) receptors. Since both circulating ANG II and ET levels are increased after myocardial infarction (MI), we investigated if the interaction between these systems is altered after MI. In awake healthy swine, coronary vasodilation in response to ET(A)/ET(B) receptor blockade in the presence of AT(1) blockade was similar to vasodilation produced by ET(A)/ET(B) blockade under control conditions. In awake swine with a 2- to 3-wk-old MI, coronary vasodilator responses to individual AT(1) and ET(A)/ET(B) receptor blockade were virtually abolished, despite similar coronary arteriolar AT(1) and ET(A) receptor expression compared with normal swine. Unexpectedly, in the presence of AT(1) blockade (which had no effect on circulating ET levels), ET(A)/ET(B) receptor blockade elicited a coronary vasodilator response. These findings suggest that in normal healthy swine the two vasoconstrictor systems contribute to coronary resistance vessel control in a linear additive manner, i.e., with negligible cross-talk. In contrast, in the remodeled myocardium, cross-talk between ANG II and ET emerges, resulting in nonlinear redundant control of coronary resistance vessel tone.