Effects of Low Endothelial Shear Stress After Stent Implantation on Subsequent Neointimal Hyperplasia and Clinical Outcomes in Humans

MiR-411-5p Promotes Vascular Smooth Muscle Cell Phenotype Switch by Inhibiting Expression of Calmodulin Regulated Spectrin-Associated Protein-1

When stimulated, vascular smooth muscle cells (VSMCs) change from a differentiated to a dedifferentiated phenotype. Dedifferentiated VSMCs have a key activity in cardiovascular diseases such as in-stent restenosis. MicroRNAs (miRNAs) have crucial functions in conversion of differentiated VSMCs to a dedifferentiated phenotype. We investigated the activity of miR-411-5p in the proliferation, migration, and phenotype switch of rat VSMCs.Based on a microRNA array assay, miR-411-5p expression was found to be significantly increased in cultured VSMCs stimulated by platelet-derived growth factor-BB (PDGF-BB). A CCK-8 assay, transwell assay, and scratch test were performed to measure the effect of miR-411-5p on the proliferation and migration of PDGF-BB-treated VSMCs. MiR-411-5p promoted expression of dedifferentiated phenotype markers such as osteopontin and tropomyosin 4 in PDGF-BB-treated VSMCs. Using mimics and inhibitors, we identified the target of miR-411-5p in PDGF-BB-treated VSMCs and found that calmodulin-regulated spectrin-associated protein-1 (CAMSAP1) was involved in the phenotypic switch mediated by PDGF-BB.By inhibiting expression of CAMSAP1, miR-411-5p enhanced the proliferation, migration, and phenotype switch of VSMCs.Blockade of miR-411-5p interaction with CAMSAP1 is a promising approach to treat in-stent restenosis.

Stent underexpansion is associated with high wall shear stress: a biomechanical analysis of the shear stent study

Coronary stent underexpansion is associated with restenosis and stent thrombosis. In clinical studies of atherosclerosis, high wall shear stress (WSS) has been associated with activation of prothrombotic pathways, upregulation of matrix metalloproteinases, and future myocardial infarction. We hypothesized that stent underexpansion is predictive of high WSS. WSS distribution was investigated in patients enrolled in the prospective randomized controlled study of angulated coronary arteries randomized to undergo percutaneous coronary intervention with R-ZES or X-EES. WSS was calculated from 3D reconstructions of arteries from intravascular ultrasound (IVUS) and angiography using computational fluid dynamics. A logistic regression model investigated the relationship between WSS and underexpansion and the relationship between underexpansion and stent platform. Mean age was 63±11, 78% were male, 35% had diabetes, mean pre-stent angulation was 36.7°±14.7°. Underexpansion was assessed in 83 patients (6,181 IVUS frames). Frames with stent underexpansion were significantly more likely to exhibit high WSS (> 2.5 Pa) compared to those without underexpansion with an OR of 2.197 (95% CI = [1.233-3.913], p = 0.008). There was no significant association between underexpansion and low WSS (< 1.0 Pa) and no significant differences in underexpansion between R-ZES and X-EES. In the Shear Stent randomized controlled study, underexpanded IVUS frames were more than twice as likely to be associated with high WSS than frames without underexpansion.

Effects of different positions of intravascular stent implantation in stenosed vessels on in-stent restenosis: An experimental and numerical simulation study

Percutaneous coronary intervention (PCI) has been widely used in the treatment of atherosclerosis, while in-stent restenosis (ISR) has not been completely resolved. Studies have shown that changes in intravascular mechanical environment are related to ISR. Hence, an in-depth understanding of the effects of stent intervention on vascular mechanics is important for clinically optimizing stent implantation and relieving ISR. Nine rabbits with stenotic carotid artery were collected by balloon injury. Intravascular stents were implanted into different longitudinal positions (proximal, middle and distal relative to the stenotic area) of the stenotic vessels for numerical simulations. Optical coherence tomography (OCT) scanning was performed to reconstruct the three-dimensional configuration of the stented carotid artery and blood flow velocity waveforms were collected by Doppler ultrasound. The numerical simulations were performed through direct solution of Naiver-Stokes equation in ANSYS. Results showed that the distributions of time-averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residual time (RRT) in near-end segment were distinctively different from other regions of the stent which considered to promote restenosis for all three models. Spearman rank-correlation analysis showed a significant correlation between hemodynamic descriptors and the stent longitudinal positions (r_TAWSS = -0.718, r_OSI = 0.898, r_RRT = 0.818, p < 0.01). Histology results of the near-end segment showed neointima thickening deepened with the longitudinal positions of stent which was consistent with the numerical simulations. The results suggest that stent implantation can promote restenosis at the near-end segment. As the stenting position moves to distal end, the impact on ISR is more significant.

Novel volumetric analysis for stent expansion after drug-eluting stent implantation: An optical coherence tomography study

OBJECTIVES

To assess the clinical significance of a novel optical coherence tomography (OCT)-derived volumetric parameter of stent expansion by comparing it with the conventional parameters in real-world practice.

BACKGROUND

The clinical significance of novel parameters in real-world practice including longer and smaller stents remains to be elucidated.

METHODS

A total of 226 de novo lesion treated with drug-eluting stents in 208 consecutive patients were enrolled. Stent expansion was retrospectively assessed on the final OCT images after stent implantation. The novel parameter was the minimum expansion index (MEI) calculated using a novel algorithm that yields the ideal lumen area in each frame by taking into account vessel tapering. The device-oriented clinical end point (DoCE) included cardiac death, target vessel-related myocardial infarction, ischemia-driven target lesion revascularization.

RESULTS

The MEI in the lesions with a DoCE (n = 22) at 2 years and cases without a DoCE (n = 204) was 64.3 ± 12.0% and 78.5 ± 14.6%, respectively (p < .001). In the receiver operating characteristic curve analyses, the areas under the curve for the MEI (0.787; p < .001) were larger than that for %stent expansion (0.718; p = .001) and minimum stent area (0.664; p = .004) in predicting the DoCE. The best cutoff of MEI for predicting the DoCE was 74.0.

CONCLUSIONS

The novel MEI was better than the conventional %stent expansion and minimum stent area for predicting DoCE.

Low shear stress damages endothelial function through STAT1 in endothelial cells (ECs)

Low shear stress (LSS) occurs in areas where atherosclerosis is prevalent. Many studies have revealed that signal transducer and activator of transcription 1 (STAT1) plays a significant role in cardiovascular disease. Nonetheless, the mechanism underlying the connection between STAT1 and LSS is not fully understood. The purpose of this study was to investigate the link between LSS and STAT1 in endothelial cells (ECs). Monolayer endothelial cells were stimulated or not stimulated by LSS. Protein expression and phosphorylation levels were determined by western blotting. Immunofluorescence was used to compare the protein expression differences in bifurcated and non-bifurcated human coronary arteries. Endothelial function was assessed by using a dihydroethidium assay, real-time PCR, western blotting and nitric oxide (NO)-sensitive fluorophore. Results showed that STAT1 played a key role in LSS-induced endothelium damage. Firstly, LSS activated STAT1, as evidenced by LSS-induced STAT1 (Tyr701) phosphorylation in ECs in vitro and the increased intimal STAT1 expression at bifurcation of human coronary arteries. Secondly, LSS-induced STAT1 phosphorylation was positively regulated by inhibitor of nuclear factor kappa-B kinase ε (IKKε). Additionally, LSS-promoted inflammatory factor expression was markedly reversed by silencing STAT1 (siSTAT1). LSS also increased reactive oxygen species (ROS) level and decreased endogenous NO release: however, siSTAT1 reversed these adverse effects through upregulating the antioxidant gene heme oxygenase-1(HO-1) and downregulating endothelial nitric oxide synthase (eNOS) Thr495 phosphorylation. According to our results, LSS-mediated EC injury may be associated with the activation of STAT1. Strategies designed to reduce STAT1 expression or inhibit STAT1 activation may be effective approaches for reducing the incidence of atherosclerosis.

Effects of local hemodynamics and plaque characteristics on neointimal response following bioresorbable scaffolds implantation in coronary bifurcations

Heterogeneous neointimal response has been observed after implantation of all generations of coronary stents. Our aim was assessing local factors of shear stress (SS) and plaque characteristics in neointimal response after implantation of bioresorbable scaffolds (BRS) in bifurcations. Ten patients from the BIFSORB pilot study were analysed. Follow-up optical frequency domain imaging (OFDI) was performed at 1 month and 2 years. Coronary lumen and BRS structure were reconstructed by fusion of OFDI and angiography and were used for subsequent flow simulation. Plaque arc degree and SS were quantified using post-procedural OFDI data and were matched with follow-up OFDI using anatomical landmarks. Strut-level and segment-level analysis were performed for 1-month and 2-year follow-up respectively. A total of 444 struts (54 jailing struts) were included at 1-month follow-up. Time-average SS (TASS) was significantly lower for covered struts than for uncovered struts in non-bifurcation segments (TASS: 1.81 ± 1.87 vs. 3.88 ± 3.72 Pa, p < 0.001). The trend remained the same for jailing struts, although statistically insignificant (TASS: 10.85 ± 13.12 vs. 13.64 ± 14.48 Pa, p = 0.328). For 2-year follow-up, a total of 66 sub-regions were analysed. Neointimal hyperplasia area (NTA) was negatively correlated with TASS in core-segments (ρ = - 0.389, p = 0.037) and positively correlated with plaque arc degree in non-core segments (ρ = 0.387, p = 0.018). Slightly stronger correlations with NTA were observed when combining TASS and plaque arc degree in both core segments (ρ = - 0.412, p = 0.026) and non-core segments (ρ = - 0.395, p = 0.015). Hemodynamic microenvironment and baseline plaque characteristics may regulate neointimal response after BRS implantation in bifurcation. These findings underline the combined role of plaque characteristics and local hemodynamics in vessel healing after stent implantation.

Location-Specific Comparison Between a 3D In-Stent Restenosis Model and Micro-CT and Histology Data from Porcine In Vivo Experiments

Background

Coronary artery restenosis is an important side effect of percutaneous coronary intervention. Computational models can be used to better understand this process. We report on an approach for validation of an in silico 3D model of in-stent restenosis in porcine coronary arteries and illustrate this approach by comparing the modelling results to in vivo data for 14 and 28 days post-stenting.

Methods

This multiscale model includes single-scale models for stent deployment, blood flow and tissue growth in the stented vessel, including smooth muscle cell (SMC) proliferation and extracellular matrix (ECM) production. The validation procedure uses data from porcine in vivo experiments, by simulating stent deployment using stent geometry obtained from micro computed tomography (micro-CT) of the stented vessel and directly comparing the simulation results of neointimal growth to histological sections taken at the same locations.

Results

Metrics for comparison are per-strut neointimal thickness and per-section neointimal area. The neointimal area predicted by the model demonstrates a good agreement with the detailed experimental data. For 14 days post-stenting the relative neointimal area, averaged over all vessel sections considered, was 20 ± 3% in vivo and 22 ± 4% in silico. For 28 days, the area was 42 ± 3% in vivo and 41 ± 3% in silico.

Conclusions

The approach presented here provides a very detailed, location-specific, validation methodology for in silico restenosis models. The model was able to closely match both histology datasets with a single set of parameters. Good agreement was obtained for both the overall amount of neointima produced and the local distribution. It should be noted that including vessel curvature and ECM production in the model was paramount to obtain a good agreement with the experimental data.

Electronic supplementary material

The online version of this article (10.1007/s13239-019-00431-4) contains supplementary material, which is available to authorized users.

Exosomes derived from M1 macrophages aggravate neointimal hyperplasia following carotid artery injuries in mice through miR-222/CDKN1B/CDKN1C pathway

The role of M1 macrophages (M1M)-derived exosomes in the progression of neointimal hyperplasia remains unclear now. Using a transwell co-culture system, we demonstrated that M1M contributed to functional change of vascular smooth muscle cell (VSMC). We further stimulated VSMCs with exosomes isolated from M1M. Our results demonstrated that these exosomes could be taken up by VSMCs through macropinocytosis. Using a microRNA array assay, we identified that miR-222 originated from M1M-derived exosomes triggered the functional changes of VSMCs. In addition, we confirmed that miR-222 played a key role in promoting VSMCs proliferation and migration by targeting Cyclin Dependent Kinase Inhibitor 1B (CDKN1B) and Cyclin Dependent Kinase Inhibitor 1C (CDKN1C) in vitro. In vivo, M1M-derived exosomes significantly aggravated neointima formation following carotid artery ligation injury and wire injury and these effects were partly abolished by miR-222 inhibitor 2′OMe-miR-222. Our findings thus suggest that exosomes derived from M1M could aggravate neointimal hyperplasia through delivering miR-222 into VSMCs. Future studies are warranted to validate if the post-injury vascular neointimal hyperplasia and restenosis could be attenuated by inhibiting miR-222.

Post-implantation shear stress assessment: an emerging tool for differentiation of bioresorbable scaffolds

Optical coherence tomography based computational flow dynamic (CFD) modeling provides detailed information about the local flow behavior in stented/scaffolded vessel segments. Our aim is to investigate the in-vivo effect of strut thickness and strut protrusion on endothelial wall shear stress (ESS) distribution in ArterioSorb Absorbable Drug-Eluting Scaffold (ArterioSorb) and Absorb everolimus-eluting Bioresorbable Vascular Scaffold (Absorb) devices that struts with similar morphology (quadratic structure) but different thickness. In three animals, six coronary arteries were treated with ArterioSorb. At different six animals, six coronary arteries were treated with Absorb. Following three-dimensional(3D) reconstruction of the coronary arteries, Newtonian steady flow simulation was performed and the ESS were estimated. Mixed effects models were used to compare ESS distribution in the two devices. There were 4591 struts in the analyzed 477 cross-sections in Absorb (strut thickness = 157 µm) and 3105 struts in 429 cross-sections in ArterioSorb (strut thickness = 95 µm) for the protrusion analysis. In cross-section level analysis, there was significant difference between the scaffolds in the protrusion distances. The protrusion was higher in Absorb (97% of the strut thickness) than in ArterioSorb (88% of the strut thickness). ESS was significantly higher in ArterioSorb (1.52 ± 0.34 Pa) than in Absorb (0.73 ± 2.19 Pa) (p = 0.001). Low- and very-low ESS data were seen more often in Absorb than in ArterioSorb. ArterioSorb is associated with a more favorable ESS distribution compared to the Absorb. These differences should be attributed to different strut thickness/strut protrusion that has significant effect on shear stress distribution.

Local delivery of thalidomide to inhibit neointima formation in rat model with artery injury

OBJECTIVE

To observe the effect of local administration of thalidomide on neointimal formation after balloon-induced carotid artery injury in rats.

METHODS

Forty-eight male Sprague-Dawley rats were randomly divided into 3 groups (n = 16): Sham operation group (group A), alone operation group (group B) and Thalidomide group (group C). The carotid arteries of group B and group C were injured by a conventional percutaneous transluminal coronary angioplasty (PTCA) balloon catheter. Group C was treated by local delivery of thalidomide, and group B did not receive thalidomide. The arteries of group A were not injured. Seven and 14 days after balloon injury, rats were sacrificed. Serum concentrations of vascular endothelial growth factor (VEGF) and tumor necrosis factor-α (TNF-α) were measured using enzyme-linked immunosorbent assay (ELISA). Neointima area, lumen area, macrophage infiltration and local expression of VEGF were measured using morphometric and immunohistochemical analyses. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) was used to examine VEGF mRNA expression.

RESULTS

The VEGF levels were significantly increased in group B than in group C at 7 days (4.82 ± 0.17 pg/mL vs 0.98 ± 0.1 pg/mL, P < 0.01) and 14 days (6.3 ± 0.16 pg/mL vs 1.03 ± 0.09 pg/mL, P < 0.01). The TNF-α levels were also significantly increased in group B than in group C at 7 days (83 ± 1.01 pg/mL vs 76.37 ± 0.75 pg/mL, P < 0.01) and 14 days (84.06 ± 1.11 pg/mL vs 78.46 ± 0.94 pg/mL, P < 0.01). However, the area of neointimal formation was significantly reduced in group C than in group B at 14 days (0.07± 0.01 mm² vs 0.12± 0.04 mm², P < 0.01). Macrophage infiltration and local expression of VEGF in the injured arteries were significantly reduced in group C than in group B at 14 days. VEGF mRNA expression was significantly reduced in Group C than in group B at 14 days (6.3 ± 0.16 vs 1.02 ± 0.1, P < 0.01).

CONCLUSIONS

Thalidomide, which is a specific VEGF inhibitor, significantly inhibited neointimal hyperplasia and vascular restenosis after balloon injury to the carotid artery in rats, thus potentially providing a novel method for the prevention and treatment of restenosis, especially in-stent restenosis.

Implications of the local hemodynamic forces on the formation and destabilization of neoatherosclerotic lesions

OBJECTIVE

To examine the implications of endothelial shear stress (ESS) distribution in the formation of neoatherosclerotic lesions.

METHODS

Thirty six patients with neoatherosclerotic lesions on optical coherence tomography (OCT) were included in this study. The OCT data were used to reconstruct coronary anatomy. Blood flow simulation was performed in the models reconstructed from the stent borders which it was assumed that represented the lumen surface at baseline, immediate after stent implantation, and the estimated ESS was associated with the neointima burden, neoatherosclerotic burden and neointima characteristics. In segments with neointima rupture blood flow simulation was also performed in the model representing the lumen surface before rupture and the ESS was estimated at the ruptured site.

RESULTS

An inverse association was noted between baseline ESS and the incidence and the burden of neoatherosclerotic (β = -0.60, P < 0.001, and β = -4.05, P < 0.001, respectively) and lipid-rich neoatherosclerotic tissue (β = -0.54, P < 0.001, and β = -3.60, P < 0.001, respectively). Segments exposed to low ESS (<1 Pa) were more likely to exhibit macrophages accumulation (28.2% vs 10.9%, P < 0.001), thrombus (11.0% vs 2.6%, P < 0.001) and evidence of neointima discontinuities (8.1% vs 0.9%, P < 0.001) compared to those exposed to normal or high ESS. In segments with neointima rupture the ESS was high at the rupture site compared to the average ESS over the culprit lesion (4.00 ± 3.65 Pa vs 3.14 ± 2.90 Pa, P < 0.001).

CONCLUSIONS

Local EES is associated with neoatherosclerotic lesion characteristics, which suggests involvement of ESS in the formation of vulnerable plaques in stented segments.

Local Hemodynamic Forces After Stenting: Implications on Restenosis and Thrombosis

Local hemodynamic forces are well-known to modulate atherosclerotic evolution, which remains one of the largest cause of death worldwide. Percutaneous coronary interventions with stent implantation restores blood flow to the downstream myocardium and is only limited by stent failure caused by restenosis, stent thrombosis, or neoatherosclerosis. Cumulative evidence has shown that local hemodynamic forces affect restenosis and the platelet activation process, modulating the pathophysiological mechanisms that lead to stent failure. This article first covers the pathophysiological mechanisms through which wall shear stress regulates arterial disease formation/neointima proliferation and the role of shear rate on stent thrombosis. Subsequently, the article reviews the current evidence on (1) the implications of stent design on the local hemodynamic forces, and (2) how stent/scaffold expansion can influence local flow, thereby affecting the risk of adverse events.