VEGF and restenosis: the rest of the story

Periadventitial biomaterials to improve arteriovenous fistula and graft outcomes

Periadventitial biomaterials have been employed for nearly three decades to promote adaptive venous remodeling following hemodialysis vascular access creation in preclinical models and clinical trials. These systems are predicated on the combination of scaffolds, hydrogels, and/or particles with therapeutics (small molecules, proteins, genes, and cells) to prevent venous stenosis and subsequent maturation failure. Periadventitial biomaterial therapies have evolved from simple drug delivery vehicles for traditional drugs to more thoughtful designs tailored to the pathophysiology of access failure. The emergence of tissue engineering strategies and gene therapies are another exciting new direction. Despite favorable results in experimental and preclinical studies, no periadventitial therapy has been clinically approved to improve vascular access outcomes. After conducting an exhaustive review of the literature, we identify the seminal studies and clinical trials that utilize periadventitial biomaterials and discuss the key features of each biomaterial format and their respective shortcomings as they pertain to access maturation. This review provides a foundation from which clinicians, surgeons, biologists, and engineers can refer to and will hopefully inspire thoughtful, translatable treatments to finally address access failure.

Mechanistic exploration of Yiqi Liangxue Shengji prescription on restenosis after balloon injury by integrating metabolomics with network pharmacology

CONTEXT

Yiqi Liangxue Shengji prescription (YQLXSJ) is a traditional Chinese medicine (TCM) formula that has long been used for treatment after percutaneous coronary intervention (PCI).

OBJECTIVE

To investigate the putative pharmacological mechanism of YQLXSJ on restenosis through an integrated approach utilizing metabolomics and network pharmacology.

MATERIALS AND METHODS

Forty male Sprague-Dawley rats were divided into sham, model, YQLXSJ, and positive groups. YQLXSJ group received the treatment of YQLXSJ (6 g/kg/d, i.g.) and the positive group was treated with atorvastatin (2 mg/kg/d, i.g.). After 4 weeks, the improvement in intimal hyperplasia was evaluated by ultrasound, H&E staining, and immunofluorescence. UPLC-MS/MS technology was utilized to screen the differential metabolites. Network pharmacology was conducted using TCMSP, GeneCards, and Metascape, etc., in combination with metabolomics. Eventually, the core targets were acquired and validated.

RESULTS

Compared to models, YQLXSJ exhibited decreased intima-media thickness on ultrasound (0.23 ± 0.02 mm vs. 0.20 ± 0.01 mm, p < 0.01) and reduced intima thickness by H&E (30.12 ± 6.05 μm vs. 14.32 ± 1.37 μm, p < 0.01). We identified 18 differential metabolites and 5 core targets such as inducible nitric oxide synthase (NOS2), endothelial nitric oxide synthase (NOS3), vascular endothelial growth factor-A (VEGFA), ornithine decarboxylase-1 (ODC1) and group IIA secretory phospholipase A2 (PLA2G2A). These targets were further confirmed by molecular docking and ELISA.

DISCUSSION AND CONCLUSIONS

This study confirms the effects of YQLXSJ on restenosis and reveals some biomarkers. TCM has great potential in the prevention and treatment of restenosis by improving metabolic disorders.

Association between VEGF Gene Polymorphisms and In-Stent Restenosis after Coronary Intervention Treated with Bare Metal Stent

Background. In-stent restenosis (ISR) is the gradual narrowing of the vessel lumen after coronary stent implantation due to the increase in vascular smooth muscle cell proliferation. Vascular endothelial growth factor (VEGF) protein plays an important role in this process. Our aim was to analyze the association of single nucleotide polymorphisms of the VEGF gene (rs2010963 and rs6999447) with the occurrence of ISR after coronary artery bare metal stent (BMS) implantation. Methods. 205 patients with a history of BMS implantation and a repeated coronarography were prospectively enrolled. Patients were assigned to diffuse restenosis group (n = 105) and control group (n = 100) and VEGF genotypes were determined. Results. Diffuse ISR was significantly more frequently observed in patients with homozygous normal genotype of rs2010963 polymorphism, and this polymorphism was independently associated with diffuse ISR. Conclusions. RS2010963 is associated with higher incidence of development of diffuse coronary ISR in patients treated with BMS implantation.

Effects of intravascular low-level laser therapy during coronary intervention on selected growth factors levels

OBJECTIVE

The objective of this study was to evaluate the effect of intravascular low-level laser therapy (LLLT) on selected growth factor levels in subjects undergoing percutaneous coronary interventions (PCI).

BACKGROUND DATA

Restenosis remains the main problem with the long-term efficacy of PCI, and growth factors are postulated to play a crucial role in the restenosis cascade.

MATERIALS AND METHODS

In a randomized prospective study, an 808 nm LLLT (100 mW/cm2, continuous wave laser, 9 J/cm2, illuminated area 1.6-2.5 cm2) was delivered intracoronarily to patients during PCI. Fifty-two patients underwent irradiation with laser light, and 49 constituted the control group. In all individuals, serum levels of insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), transforming growth factor-β1 (TGF-β1), and fibroblast growth factor-2 (FGF-2) were measured before angioplasty, then 6 and 12 h and 1 month after the procedure. In all patients, a control angiography was performed 6 months later.

RESULTS

There were no significant differences in IGF-1 and VEGF levels between the groups. While evaluating FGF-2, we observed its significantly lower levels in the irradiated patients during each examination. There was a significant increase in TGF-β1 level in control group after 12 h of observation. In the irradiated individuals, control angiography revealed smaller late lumen loss and smaller late lumen loss index as compared with the control group. The restenosis rate was 15.0% in the treated group, and 32.4% in the control group, respectively.

CONCLUSIONS

LLLT decreases levels of TGF-β1 and FGF-2 in patients undergoing coronary intervention, which may explain smaller neointima formation.

Neuropilin 1 expression in human aortas, coronaries and the main bypass grafts

OBJECTIVES

Development of intimal hyperplasia (IH) is the main pathology underlying graft failure following coronary artery bypass graft surgeries for ischaemic heart diseases, especially for great saphenous vein grafts which have a lower patency rate than internal mammary arteries. Neuropilin 1 (NRP1), which is a co-receptor for vascular endothelial growth factor found in vascular endothelial and smooth muscle cells, affects the development of IH. We examined the difference in NRP1 expression and distribution in human coronaries, aortas, mammary arteries and saphenous veins to detect a possible relation to their susceptibility to IH.

METHODS

Ninety-five human vascular segments obtained from 40 patients were used for the comparison of NRP1 expression between different groups of blood vessels by western blot and real-time PCR. Additionally, staining scores were generated by computerized analysis of the microscopic images obtained after immunofluorescence and immunohistochemical staining to compare NRP1 expression patterns in endothelium, smooth muscles and adventitia in each vessel type.

RESULTS

NRP1 expression in the aorta (2.03 ± 1.44) was more than twice as high as mammary artery expression (0.85 ± 0.75; n = 16, P = 0.0004); NRP1 of the latter (0.99 ± 0.91) was more than 30% greater than that of the corresponding saphenous vein (0.73 ± 0.69; n = 20, P = 0.0085). In adventitia, NRP1 receptor staining of the saphenous vein was higher (22.96 ± 8.73) than in the mammary artery (15.83 ± 7.13; n = 7, P = 0.049). Variations in NRP1 protein levels were accompanied by parallel variations in its mRNA levels (n = 15, P = 0.34).

CONCLUSIONS

Autologous saphenous vein grafts, unlike internal mammary artery grafts, have lower NRP1 expression and abundant adventitial distribution of NRP1 within their walls; this may correlate with higher susceptibility to IH development.

Local inhibition of hypoxia-inducible factor reduces neointima formation after arterial injury in ApoE-/- mice

OBJECTIVE

Hypoxia plays a pivotal role in development and progression of restenosis after vascular injury. Under hypoxic conditions the hypoxia-inducible factors (HIFs) are the most important transcription factors for the adaption to reduced oxygen supply. Therefore the aim of the study was to investigate the effect of a local HIF-inhibition and overexpression on atherosclerotic plaque development in a murine vascular injury model.

METHODS AND RESULTS

After wire-induced vascular injury in ApoE-/- mice a transient, local inhibition of HIF as well as an overexpression approach of the different HIF-subunits (HIF-1α, HIF-2α) by adenoviral infection was performed. The local inhibition of the HIF-pathway using a dominant-negative mutant dramatically reduced the extent of neointima formation. The diminished plaque size was associated with decreased expression of the well-known HIF-target genes vascular endothelial growth factor-A (VEGF-A) and its receptors Flt-1 and Flk-1. In contrast, the local overexpression of HIF-1α and HIF-2α further increased the plaque size after wire-induced vascular injury.

CONCLUSIONS

Local HIF-inhibition decreases and HIF-α overexpression increases the injury induced neointima formation. These findings provide new insight into the pathogenesis of atherosclerosis and may lead to new therapeutic options for the treatment of in stent restenosis.

Ibuprofen inhibits migration and proliferation of human coronary artery smooth muscle cells by inducing a differentiated phenotype: role of peroxisome proliferator-activated receptor γ

OBJECTIVES

The search for agents that are capable of preventing restenosis and reduce the risk of late thrombosis is of utmost importance. In this study we aim to evaluate the in vitro effects of ibuprofen on proliferation and migration of human coronary artery smooth muscle cells and on endothelial cells.

METHODS

Cell proliferation was evaluated by trypan blue exclusion. Cell migration was assessed by wound-healing 'scratch' assay and time-lapse video microscopy. Protein expression was assessed by immunoblotting, and morphology by immunocytochemistry. The involvement of the PPARγ pathway was studied with the agonist troglitazone, and the use of selective antagonists such as PGF2α and GW9662.

KEY FINDINGS

We demonstrate that ibuprofen inhibits proliferation and migration of HCASMCs and induces a switch in HCASMCs towards a differentiated and contractile phenotype, and that these effects are mediated through the PPARγ pathway. Importantly we also show that the effects of ibuprofen are cell type-specific as it does not affect migration and proliferation of endothelial cells.

CONCLUSIONS

Taken together, our results suggest that ibuprofen could be an effective drug for the development of novel drug-eluting stents that could lead to reduced rates of restenosis and potentially other complications of DES implantation.

Adventitial transduction of lentivirus-shRNA-VEGF-A in arteriovenous fistula reduces venous stenosis formation

Venous neointimal hyperplasia (VNH) causes hemodialysis vascular access failure. Here we tested whether VNH formation occurs in part due to local vessel hypoxia caused by surgical trauma to the vasa vasorum of the outflow vein at the time of arteriovenous fistula placement. Selective targeting of the adventitia of the outflow vein at the time of fistula creation was performed using a lentivirus-delivered small-hairpin RNA that inhibits VEGF-A expression. This resulted in significant increase in mean lumen vessel area, decreased media/adventitia area, and decreased constrictive remodeling with a significant increase in apoptosis (increase in caspase 3 activity and TUNEL staining) accompanied with decreased cellular proliferation and hypoxia-inducible factor-1α at the outflow vein. There was significant decrease in cells staining positive for α-smooth muscle actin (a myofibroblast marker) and VEGFR-1 expression with a decrease in MMP-2 and MMP-9. These results were confirmed in animals that were treated with humanized monoclonal antibody to VEGF-A with similar results. Since hypoxia can cause fibroblast to differentiate into myofibroblasts, we silenced VEGF-A gene expression in fibroblasts and subjected them to hypoxia. This decreased myofibroblast production, cellular proliferation, cell invasion, MMP-2 activity, and increased caspase 3. Thus, VEGF-A reduction at the time of arteriovenous fistula placement results in increased positive vascular remodeling.

Modelling the effect of a functional endothelium on the development of in-stent restenosis

Treatment of stenosed coronary arteries by balloon angioplasty and stenting results in arterial injury including severe damage to the endothelium at the site of treatment and initiates a complex cascade of inflammatory processes that may lead to the development of in-stent restenosis (ISR). Many clinical and biological factors involved in the progression of restenotic lesions have been studied in detail over the past few years but the mystery behind the pathophysiological mechanisms of this disease is still unresolved. In the present work, the effects of re-endothelialization and nitric oxide release on neointimal growth are investigated in-silico using a two dimensional multi-scale model of ISR. The effect of stent deployment depths on the development of ISR is studied as a function of time after stenting. Two dimensional domains were prepared by deploying bare metal stent struts at three different deployment depths into the tissue. Shear stress distribution on endothelial cells, obtained by blood flow simulations, was translated into nitric oxide production that keeps the smooth muscle cells in quiescent state. The cellular growth trends were plotted as a function of time and the data indicate a positive correlation between the neointimal growths and strut deployment depths in the presence of a functional endothelium, in qualitative agreement with in-vivo data. Additionally, no ISR is observed if a functional endothelium appears much earlier.

Simvastatin reduces venous stenosis formation in a murine hemodialysis vascular access model

Venous neointimal hyperplasia (VNH) is responsible for hemodialysis vascular access malfunction. Here we tested whether VNH formation occurs, in part, due to vascular endothelial growth factor-A (VEGF-A) and matrix metalloproteinase (MMP)-9 gene expression causing adventitial fibroblast transdifferentiation to myofibroblasts (α-SMA-positive cells). These cells have increased proliferative and migratory capacity leading to VNH formation. Simvastatin was used to decrease VEGF-A and MMP-9 gene expression in our murine arteriovenous fistula model created by connecting the right carotid artery to the ipsilateral jugular vein. Compared to fistulae of vehicle-treated mice, the fistulae of simvastatin-treated mice had the expected decrease in VEGF-A and MMP-9 but also showed a significant reduction in MMP-2 expression with a significant decrease in VNH and a significant increase in the mean lumen vessel area. There was an increase in terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, and decreases in α-SMA density, cell proliferation, and HIF-1α and hypoxyprobe staining. This latter result prompted us to determine the effect of simvastatin on fibroblasts subjected to hypoxia in vitro. Simvastatin-treated fibroblasts had a significant decrease in myofibroblast production along with decreased cellular proliferation, migration, and MMP-9 activity but increased caspase 3 activity suggesting increased apoptosis. Thus, simvastatin results in a significant reduction in VNH, with increase in mean lumen vessel area by decreasing VEGF-A/MMP-9 pathway activity.

Neo-intimal hyperplasia, diabetes and endovascular injury

Diabetes is a significant major risk factor for peripheral arterial disease (PAD) and critical limb ischaemia (CLI), the latter which is also the most common cause of amputation in these patients. Revascularisation of the lower extremities of such patients is imperative for limb salvage and has become First-line therapy. However, the incidence of restenosis following endovascular stenting is very high and is largely due to neo-intimal hyperplasia (NIH), the regulation of which is for the greater part not understood. This article therefore reviews our understanding on the regulation of NIH following stent-induced vascular injury, and highlights the importance of future studies to investigate whether the profile of vascular progenitor cell differentiation, neo-intimal growth factors and lumen diameters predict the severity of post-stent NIH in the peripheral arteries. Results from future studies will (1) better our understanding of the regulation of NIH in general, (2) determine whether combinations of any of the vascular factors discussed are predictive of the extent of NIH postoperatively, and (3) potentially facilitate future therapeutic targets and/or change preventive strategies.

Adventitial gene transfer of VEGFR-2 specific VEGF-E chimera induces MCP-1 expression in vascular smooth muscle cells and enhances neointimal formation

BACKGROUND

The role of vascular endothelial growth factors (VEGFs) in neointimal formation has been controversial. VEGF receptor (R)-2 signaling pathway is crucial in bringing about the effects of VEGFs including vasodilatation, endothelial cell migration and proliferation. In this study we have used an established adventitial gene transfer technique, in vitro studies and a novel VEGF-E/PlGF chimera that binds specifically to VEGFR-2, to investigate the role of VEGFR-2 in neointimal formation.

METHODS

Intimal hyperplasia was induced in the carotid arteries of cholesterol fed male New Zealand White rabbits using a silastic collar. Adenoviral vectors encoding VEGF-E chimera (1×10(9) pfu/ml) were transferred to the adventitia of the carotid arteries either alone or together with adenoviruses encoding soluble VEGFR-2 (sVEGFR-2). Adenoviruses encoding LacZ were used as controls. All animals were sacrificed 7 days after the gene transfer.

RESULTS

Significant increases in neointimal formation, proliferating cells, inflammatory responses and adventitial angiogenesis were observed in the VEGF-E chimera transduced arteries. The number of medial smooth muscle cells expressing VEGFR-2 was significantly (p<0.001) higher. MCP-1 mRNA levels were significantly (p<0.01) increased in the VEGF-E chimera transduced arteries and transduced rabbit aortic smooth muscle cells (p<0.05). Soluble VEGFR-2 (sVEGFR-2) significantly inhibited VEGF-E chimera induced neointimal formation (p<0.01), cellular proliferation (p<0.01), inflammatory responses (p<0.01) and adventitial angiogenesis (p<0.01).

CONCLUSIONS

The results indicate that VEGFR-2 mediated signaling could aggravate neointimal formation and suggest a potential therapeutic role of sVEGFR-2 in inhibiting neointimal formation and adventitial angiogenesis.

Protein kinase C delta mediates arterial injury responses through regulation of vascular smooth muscle cell apoptosis

AIMS

A balance between apoptosis and proliferation of vascular smooth muscle cells (VSMC) influences the development of intimal hyperplasia. We have previously demonstrated that protein kinase C delta (PKCdelta) regulates both apoptosis and proliferation of VSMC in vitro. Here we investigate the role of PKCdelta in intimal hyperplasia through gene deletion or overexpression in rodent models of arterial injury.

METHODS AND RESULTS

Arterial injury was induced in mice and rats by means of carotid ligation or balloon angioplasty, respectively. Overexpression of PKCdelta was achieved by adenovirus-mediated gene transfer immediately after balloon injury in rat carotid arteries. Levels of PKCdelta protein were profoundly increased in the carotid wall 3-7 days after balloon injury, co-localizing to TUNEL-positive medial cells. When subjected to arterial injury, PKCdelta gene-deficient mice responded with an enhanced intimal hyperplasia accompanied by an 80% reduction in the number of TUNEL-positive cells detected in the injured arteries as compared with their wild-type littermates. Conversely, arterial gene transfer of PKCdelta further increased the arterial expression of PKCdelta, which was associated with a marked increase in apoptosis and reduction of intimal hyperplasia. Neither manipulation led to significant alteration in cell proliferation, suggesting that the function of PKCdelta after arterial injury is predominantly pro-apoptotic. This notion is further supported by our observation of high PKCdelta expression in human restenotic lesions that also co-localized with apoptosis.

CONCLUSION

The expression of PKCdelta is upregulated in the arterial wall in response to injury. This induction appears to be a mechanism of arterial response that negatively influences the degree of intimal hyperplasia by stimulating VSMC apoptosis.