Enhanced intimal proliferation upon injury to pre-existing neointima and resistance of neointimal cells to cell death

Sialoadhesin - a macrophage-restricted marker of immunoregulation and inflammation

Sialoadhesin (Sn, also known as Siglec-1 and CD169) is a macrophage-restricted cell surface receptor that is conserved across mammals. Sn is a member of the sialic acid-binding IgG-like lectin (Siglec) family of proteins characterized by affinity to specifically sialylated ligands, and under normal conditions is expressed on subsets of macrophages in secondary lymphoid tissues, such as lymph node and spleen. However, Sn-positive macrophages can also be found in a variety of pathological conditions, including (autoimmune) inflammatory infiltrates and tumours. Sn has been shown to contribute to sialylated pathogen uptake, antigen presentation and lymphocyte proliferation, and to influence both immunity and tolerance. This review presents Sn as a macrophage-specific marker of inflammation and immunoregulation with the potential to becoming an important biomarker for immunologically active macrophages and a target for therapy.

Blockade of TGF-β by catheter-based local intravascular gene delivery does not alter the in-stent neointimal response, but enhances inflammation in pig coronary arteries

BACKGROUND

Extracellular matrix (ECM) accumulation significantly contributes to in-stent restenosis. In this regard, transforming growth factor (TGF)-β, a positive regulator of ECM deposition, may be implicated in in-stent restenosis. The goal of this study was to assess the effect of blockade of TGF-β on stent-induced restenosis in porcine coronary arteries.

METHODS

An adenovirus expressing the ectodomain of the TGF-β type II receptor (AdTβ-ExR) was applied onto a coronary arterial segment of a pig (n=10) using an Infiltrator, followed by stent deployment. Controls consisted of adenoviruses expressing β-galactosidase (AdLacZ) or phosphate-buffered saline (PBS) applied onto the other segment (n=10) of the same pig.

RESULTS

Computer-based pathological morphometric analysis of stented coronary arteries, performed 4 weeks after stenting, demonstrated no significant difference in morphometric parameters such as in-stent neointimal area and % area stenosis between the AdTβ-ExR group and control (n=7 for each). However the AdTβ-ExR group had increased neointimal cell density, infiltration of inflammatory cells mostly consisting of CD3+ T cell, accumulation of hyaluronan, cell proliferation rate, and adventitial matrix metalloproteinase-1 (MMP-1) expression compared with control. The expression of connective tissue growth factor mRNA, measured by reverse transcription PCR, in cultured rat arterial smooth muscle cells was inhibited by AdTβ-ExR at moi 60.

CONCLUSIONS

Blockade of TGF-β by catheter-based local intravascular gene delivery does not reduce stent-induced neointima formation 4 weeks after stenting in spite of modest inhibition of ECM accumulation, but it induces vascular inflammation and associated pathological changes that may potentially aggravate lesion progression.

Endothelial apoptosis and chronic transplant vasculopathy: recent results, novel mechanisms

Chronic transplant vasculopathy (CTV) is a progressive form of vascular obliteration affecting the arteries, arterioles and capillaries of solid organ transplants. It is characterized by intimal accumulation of mononuclear cells, vascular smooth muscle cells (VSMC), myofibroblasts and connective tissue. Mounting evidence, based on animal models and human biopsy results, suggests that acute and persistent rejection triggering apoptosis of endothelial cells (EC) plays a pivotal role in CTV. The precise mechanisms that underlie the induction of fibroproliferative changes in association with endothelial apoptosis have yet to be clearly delineated. Recent observations in the field of apoptosis research provide some important mechanistic clues. First, endothelial apoptosis creates a state of hyperadhesiveness for mononuclear cells, thus facilitating sustained leukocyte infiltration. Second, phosphatidylserine-dependent engulfment of apoptotic cells by infiltrating mononuclear leukocytes promotes transforming growth factor-beta1 production. Third, apoptosis of EC triggers extracellular matrix (ECM) proteolysis thus initiating the production of fibroproliferative/fibrogenic ECM fragments. The relative importance of these mechanisms in the pathophysiology of CTV will need to be addressed in vivo. Yet, these recent developments provide a new mechanistic framework that will help better define the importance of immune-mediated EC apoptosis in the regulation of vascular repair.

Impact of asymmetric stent expansion on neointimal hyperplasia following sirolimus-eluting stent implantation

To assess whether asymmetric stent expansion affects suppression of neointimal hyperplasia after sirolimus-eluting stent implantation, 64 patients in the SIRolImUS-coated Bx Velocity stent trial who underwent single 18-mm stent implantation and 3-dimensional intravascular ultrasonography at 8-month follow-up were enrolled. To assess the longitudinal stent asymmetric expansion, 2 cross sections with a maximal/minimal stent area were chosen in each patient. To assess for tomographic stent asymmetric expansion, stent eccentricity was determined by dividing the minimum stent diameter by the maximum stent diameter. At the 2 cross sections with a maximal/minimal stent area, a sirolimus-eluting stent reduced neointimal hyperplasia significantly with no interaction between the treatment and stent areas. A sirolimus-eluting stent also significantly reduced neointimal hyperplasia in the concentric and eccentric stent groups.

Dose heterogeneity may not affect the neointimal proliferation after gamma radiation for in-stent restenosis: a volumetric intravascular ultrasound dosimetric study

OBJECTIVES

The goal of this study was to use serial (postirradiation and follow-up) volumetric intravascular ultrasound (IVUS): 1) to evaluate the actual distribution of gamma radiation in human in-stent restenosis (ISR) lesions, and 2) to analyze the relationship between neointimal regrowth and the delivered radiation dose.

BACKGROUND

The relationship between the neointimal regrowth and delivered dose during the treatment of ISR remains unknown.

METHODS

We analyzed 20 actively (gamma emitter) treated, native artery ISR patients from the Washington Radiation for In-Stent restenosis Trial (WRIST) that met the following criteria: on both postirradiation and six-month follow-up IVUS imaging, > or =80% of the external elastic membrane circumference could be identified throughout the treated length including the lesion and proximal and distal reference segments. Intravascular ultrasound images were digitized every 1 mm. Proximal and distal reference and stented segment luminal and adventitial contours were imported and reconstructed. The source was placed circumferentially at the site of the IVUS catheter and longitudinally according to the relationship between the radioactive seeds and stent edges. Using Monte Carlo simulations, dose volume histograms for the adventitia and intima were calculated. The relationship between the neointimal regrowth and calculated doses were evaluated.

RESULTS

There was large dose heterogeneity at both the intimal and adventitial levels. Most of the sites (93%) received >4 Gy at the adventitia, and all of the sites received >4 Gy at the intima. There was no relationship between neointimal regrowth and radiation dose.

CONCLUSIONS

Although there may be large dose heterogeneity, gamma irradiation (using a fixed dose prescription) appears to deliver a sufficient dose to prevent neointimal regrowth.

Elimination of vascular fibrointimal hyperplasia by somatostatin receptor 1,4-selective agonist

The somatostatin analogs octreotide and lanreotide, selective to receptor subtypes 2 and 5, failed clinical efficacy for the prevention of restenosis after percutaneous transluminal angioplasty. These findings might have been the result of targeting a wrong subset of receptors. In rat arteries, subtypes 1 and 4 are expressed 3-4 times more prominently than 2 and 5, and subtype 1 is the nearly exclusive subtype in atherosclerotic human vessels. Here, we demonstrate that daily s.c. injections (50-500 microg/kg/d) of CH275 (DesAA1,2,5(D-W8,IAmp9)Somatostatine-14), selective to subtypes 1 and 4, dose-dependently inhibited intimal hyperplasia 14 days after rat carotid denudation injury (for intimal area P=0.0002 across the dose range). CH275 was more effective than somatostatin-14 (equal affinity to all five subtypes, P=0.03), or octreotide (selective to subtypes 2 and 5, P=0.098). When rats were given the peptides for 14 days with end-point at 28 days, CH275 still significantly inhibited intimal area expansion. Both CH275 and octreotide inhibited the outgrowth of cells from postinjury aortic tissue punch-explants and the distance migrated in vitro, but not cell replication, which indicated that the effects of somatostatin analogs were directed on the migration of intimal cell progenitors rather than on their proliferation.

Comparative efficacy of gamma-irradiation for treatment of in-stent restenosis in saphenous vein graft versus native coronary artery in-stent restenosis: An intravascular ultrasound study

BACKGROUND

We used serial volumetric (post-irradiation and follow-up) intravascular ultrasound (IVUS) to compare the effectiveness of gamma-irradiation ((192)Ir) in saphenous vein graft (SVG) versus native coronary artery in-stent restenosis (ISR).

METHODS AND RESULTS

The study population consisted of 47 patients with native coronary artery ISR from WRIST (Washington Radiation for In-Stent Restenosis Trial) and 31 patients with SVG ISR (12 from the WRIST and 19 from SVGWRIST). After irradiation and at 6-month follow-up, stent, lumen, and intimal hyperplasia (IH, stent minus lumen) areas were measured every 1 mm. ISR length was similar in the 2 groups (29+/-12 versus 29+/-14 mm, P=0.9). Post-intervention measurements of stent (280+/-154 versus 324+/-270 mm(3), P=0.4), lumen (184+/-91 versus 214+/-172 mm(3), P=0.3), and IH (96+/-77 versus 109+/-119 mm(3), P=0.5) volumes were similar in the 2 groups. The post-intervention minimum lumen cross sectional areas tended to be smaller in native artery ISR lesions (4.7+/-1.7 versus 5.4+/-1.6 mm(2), P=0.11). During follow-up, there was a slight increase in IH volume (9+/-38 mm(3)) in native artery ISR lesions and a slight decrease in IH volume in SVG ISR lesions (-9+/-32 mm(3), P=0.0463). There was also a slight decrease in minimum lumen area in the native artery ISR lesions versus a slight increase in minimum lumen area in the SVG ISR lesions (-0.8+/-1.7 versus 0.2+/-1.1, P=0.0087). As a result, the follow-up minimum lumen area in native artery lesions was smaller than in SVG ISR lesions (4.1+/-2.1 mm(2) versus 5.6+/-2.2 mm(2), P=0.0067).

CONCLUSION

gamma-Irradiation with (192)Ir brachytherapy appears to be as effective in SVGs as it is in native artery ISR lesions.