Damme, L.C.A. van

Activation of MMP8 and MMP13 by angiotensin II correlates to severe intra-plaque hemorrhages and collagen breakdown in atherosclerotic lesions with a vulnerable phenotype (Article)

2009-05-01T00:00:00Z

Angiotensin II (ATII)-mediated hypertension increases the risk for acute coronary events, which may be caused by augmented collagen degradation. Interstitial fibers of collagen type I in the plaque can be degraded by MMP8 and MMP13 specifically. Indeed high MMP8 levels have been correlated with ruptured plaques in patients. To study the contribution of ATII in plaque rupture, we evaluated its effect on MMP8 and MMP13 activity on the vulnerable lesions using an extravascular device that induces regions of pro-atherogenic shear stress in the carotid arteries of ApoE KO mice. This triggers the growth of lesions with a "vulnerable" macrophage-rich phenotype (referred to as upstream lesions) and lesions with a "stable" fibrotic phenotype (referred to as downstream lesions). ATII administration increased mean blood pressure, and increased the incidence of intra-plaque hemorrhages (IPH) from 30% to 73% of the animals in the upstream segments. The area of IPH was also increased by 5-fold. No IPHs were observed in the downstream lesions of the control group or the ATII group. In addition, ATII treatment doubled the size of upstream and downstream lesions. Upstream lesions in the ATII group were decreased in collagen content by 3-fold, contained 2-fold higher MMP8 and MMP13 levels, with a 2- and 3-fold increase in collagen type I degradation by MMP8 and MMP13 respectively compared to the upstream lesions in the control group. Gene expression analysis showed general increase in procollagens and TIMPs expression in response to ATII. However, ATII also decreased procollagen 5α3 expression in downstream lesions and decreased TIMP4 expression in upstream lesions. These data show that ATII promotes a "stable" fibrotic phenotype by inducing severe intra-plaque hemorrhages, characterized by increased degradation of interstitial collagen I via an MMP-mediated (MMP8 and MMP13) mechanism.

Donor pre-treatment with tacrolimus reduces transplant vasculopathy (Article)

2009-04-01T00:00:00Z

We tested whether transplant arteriosclerosis can be reduced by pre-treatment of the donor with immunosuppressive agents, using a rat allogeneic aorta transplantation model. Donor rats received no pre-treatment, or tacrolimus, methylprednisolone, rapamycin, or mycofenolate mofetil (MMF) 16 and 2 h before explantation of the grafts. Eight weeks after transplantation, aorta allografts were harvested. Percent intima area/intima + media area (I/I + M), inflammatory cells and in situ MMP-2 and -9 activity were determined. In pre-transplantation biopsies, MMP-2 and -9 ratio, and mRNA levels for genes of interest were determined. In pre-transplantation biopsies we found no differences in MMP-2/9 ratio, and Bcl-2, Bax, TGF-β, HO-1, p21, and HIF-1α mRNA expression between the groups. Aorta allografts, pre-treated with tacrolimus, showed significantly lower I/I + M ratio compared to untreated controls (p < 0.01). Pre-treatment with methylprednisolone, rapamycin or MMF did not significantly reduce I/I + M ratio. In situ MMP-2/MMP-9 activity was significantly reduced in grafts treated with tacrolimus and rapamycin compared to controls (p < 0.05). Immunohistochemistry revealed a high number of CD4+ cells and high CD4/CD8 ratio in grafts pre-treated with tacrolimus. Donor pre-treatment with tacrolimus significantly reduces transplant arteriosclerosis and is associated with reduced in situ MMP-2/MMP-9 activity and increased number of CD4+ cells.

Gelatinolytic activity in atherosclerotic plaques is highly localized and is associated with both macrophages and smooth muscle cells in vivo (Article)

2007-02-01T00:00:00Z

BACKGROUND - Atherosclerosis is considered an inflammatory disease. Recent studies provided evidence for a predominant upstream location of plaque inflammation. The present study introduces a novel technique that evaluates the underlying mechanism of this spatial organization. METHODS AND RESULTS - In hypercholesterolemic rabbits, atherosclerosis of the infrarenal aorta was induced by a combination of endothelial denudation and a high-cholesterol diet (2% cholesterol for 2 months). At the time of death, aortic vessel segments were dissected and reconstructed with a new technique that preserved the original intravascular ultrasound-derived lumen geometry. This enabled us to study the spatial relation of histological markers like macrophages, smooth muscle cells, lipids, gelatinolytic activity, and oxidized low-density lipoprotein. Results showed a predominant upstream localization of macrophages and gelatinase activity. Colocalization studies indicated that gelatinase activity was associated with macrophages and smooth muscle cells. Further analysis revealed that this was caused by subsets of smooth muscle cells and macrophages, which were associated with oxidized low-density lipoprotein accumulation. CONCLUSIONS - Upstream localization of a vulnerable plaque phenotype is probably due to an accumulation of oxidized low-density lipoprotein, which activates/induces subsets of smooth muscle cells and macrophages to gelatinase production.

In vivo temperature heterogeneity is associated with plaque regions of increased MMP-9 activity. (Article)

2005-10-01T00:00:00Z

AIMS: Plaque rupture has been associated with a high matrix metalloproteinase (MMP) activity. Recently, regional temperature variations have been observed in atherosclerotic plaques in vivo and ascribed to the presence of macrophages. As macrophages are a major source of MMPs, we examined whether regional temperature changes are related to local MMP activity and macrophage accumulation. METHODS AND RESULTS: Plaques were experimentally induced in rabbit (n=11) aortas, and at the day of sacrifice, a pull-back was performed with a thermography catheter. Hot (n=10), cold (n=10), and reference (n=11) regions were dissected and analysed for smooth muscle cell (SMC), lipids (L), collagen (COL), and macrophage (MPhi) cell densities (%); a vulnerability index (VI) was calculated as VI=MPhi+L/(SMC+COL). In addition, accumulation and activity of MMP-2 and MMP-9 were determined with zymography. Ten hot regions were identified with an average temperature of 0.40+/-0.03 degrees C (P<0.05 vs. reference) and 10 cold regions with 0.07+/-0.03 degrees C (P<0.05 vs. hot). In the hot regions, a higher macrophage density (173%), less SMC density (77%), and a higher VI (100%) were identified. In addition, MMP-9 (673%) activity was increased. A detailed regression analysis revealed that MMP-9 predicted hot regions better than macrophage accumulation alone. CONCLUSION: In vivo temperature measurements enable to detect plaques that contain more macrophages, less SMCs, and a higher MMP-9 activity.

Intravascular thermography: Immediate functional and morphological vascular findings (Article)

2004-01-01T00:00:00Z

AIMS: To investigate safety, feasibility, and injurious effect on endothelial cells of a thermography catheter as well as effect of flow on measured temperature in non-obstructive arteries. METHODS AND RESULTS: Safety and feasibility were tested in both rabbit aortas and pig coronary arteries. Evaluation of endothelial damage by the catheter (acute, 7 and 14 days) was performed in pig coronaries using Evans Blue, scanning electron microscopy (SEM) and Factor-VIII antibody and compared with normal arteries and arteries that underwent intravascular ultrasound (IVUS). The effect of flow on temperature heterogeneity was analysed both in vitro and in vivo conditions. All procedures were successful without any adverse events; intra- and inter-operator variability was low. Intracoronary use of the catheter was associated with acute but reversible de-endothelialization, paralleling the findings associated with IVUS use. Changes in flow velocities under physiologic flow conditions did not significantly influence the temperature differences measured both in vitro and in vivo; temperature heterogeneity was more pronounced in absence of flow. CONCLUSIONS: Intracoronary thermography using a dedicated catheter is safe and feasible with a similar degree of de-endothelialization as IVUS. Temperature heterogeneity remained unchanged under normal physiologic flow conditions allowing clinical use of thermography.

Functional expression of endothelial nitric oxide synthase fused to green fluorescent protein in transgenic mice (Article)

2003-01-01T00:00:00Z

The activity of endothelial nitric oxide synthase (eNOS) is subject to complex transcriptional and post-translational regulation including the association with several proteins and variations in subcellular distribution. In the present study we describe a transgenic mouse model expressing eNOS fused to green fluorescent protein (GFP), which allows the study of localization and regulation of eNOS expression. We tested the functionality of eNOS in the eNOS-GFP mice. Expression of eNOS was restricted to the endothelial lining of blood vessels in various tissues tested, without appreciable expression in non-endothelial cells. Activity of the enzyme was confirmed by assaying the conversion of L-arginine to L-citrulline. NO production in isolated vessels was increased in transgenic mice when compared to non-transgenic control animals (4.88 +/- 0.59 and 2.48 +/- 0.47 micro mol/L NO, respectively, P < 0.005). Both the mean aortic pressure and the pulmonary artery pressure were reduced in eNOS-GFP mice (both approximately 30%, P < 0.05). Plasma cholesterol levels were also slightly reduced ( approximately 20%, P < 0.05). In conclusion, eNOS-GFP mice express functional eNOS and provide a unique model to study regulation of eNOS activity or eNOS-mediated vascular events, including response to ischemia, response to differences in shear stress, angiogenesis and vasculogenesis, and to study the subcellular distribution in relation with functional responses to these events.

Augmentation of wall shear stress inhibits neointimal hyperplasia after stent implantation: inhibition through reduction of inflammation? (Article)

2003-01-01T00:00:00Z

BACKGROUND: Low wall shear stress (WSS) increases neointimal hyperplasia (NH) in vein grafts and stents. We studied the causal relationship between WSS and NH formation in stents by locally increasing WSS with a flow divider (Anti-Restenotic Diffuser, Endoart SA) placed in the center of the stent. METHODS AND RESULTS: In 9 rabbits fed a high-cholesterol diet for 2 months to induce endothelial dysfunction, 18 stents were implanted in the right and left external iliac arteries (1 stent per vessel). Lumen diameters were measured by quantitative angiography before and after implantation and at 4-week follow-up, at which time, macrophage accumulation and interruption of the internal elastic lamina was determined. Cross sections of stent segments within the ARED (S+ARED), outside the ARED (S[minus]ARED), and in corresponding segments of the contralateral control stent (SCTRL) were analyzed. Changes in WSS induced by the ARED placement were derived by computational fluid dynamics. Computational fluid dynamics analysis demonstrated that WSS increased from 0.38 to 0.82 N/m2 in the S+ARED immediately after ARED placement. This augmentation of shear stress was accompanied by (1) lower mean late luminal loss by quantitative angiography ([minus]0.23+/-0.22 versus [minus]0.58+/-0.30 mm, P=0.02), (2) reduction in NH (1.48+/-0.58, 2.46+/-1.25, and 2.36+/-1.13 mm2, P<0.01, respectively, for S+ARED, S[minus]ARED, and SCTRL), and (3) a reduced inflammation score and a reduced injury score. Increments in shear stress did not change the relationship between injury score and NH or between inflammation score and NH. CONCLUSIONS: The newly developed ARED flow divider significantly increases WSS, and this local increment in WSS is accompanied by a local reduction in NH and a local reduction in inflammation and injury. The present study is therefore the first to provide direct evidence for an important modulating role of shear stress in in-stent neointimal hyperplasia.

Inflammation and atherosclerosis: mechanisms underlying vulnerable plaque. (Article)

2003-01-01T00:00:00Z

Introduction Atherosclerosis belongs to the chronic diseases with the highest mortality in the Western world. While the disease has traditionally been explained by risk factors like high cholesterol and hypertension, evidence is now accumulating for a role of the immune system in the progression of atherosclerosis. This article will explore the role of innate and adaptive immunity in atherosclerosis only. It does not aim at describing all facets of the immune system. In order to facilitate the reading of the article the pathophysiology of the immune system in atherosclerosis is preceded by the relevant physiology.